Download synthesis and reactions of tris dialkyl dithiocarbamates of group 15

SYNTHESIS AND REACTIONS OF TRIS DIALKYL
DITHIOCARBAMATES OF GROUP 15 WITH THE
HALIDES OF GROUP 12
Thesis submitted
By
Mohamed Elnaiem Mohamed Abdelbagi
B.Sc. Honours U. of K.
For the degree of M.Sc. in Chemistry
Department of Chemistry
Faculty of Science
University of Khartoum
September, 2006
LIST OF CONTENTS
Item
Page
Contents…………………………………………………………….
I
Acknowledgment …………………………………………………..
IV
Dedication ………………………………………………………….
V
Abstract ………………………………………………………….....
VI
Abstract (Arabic) …………………………………………………...
VII
CHAPTER ONE
Introduction…………………………………………………………. 1
CHAPTER TWO
EPERIMENTAL
2.1 General Techniques……………………………………………..
20
2.2 Melting point……………………………………………………. 20
2.3 Elemental Analysis……………………………………………...
20
2.4 NMR spectra……………………………………………………. 20
2.5 Purification of chemicals………………………………………..
21
2.6 Preparation of starting materials………………………………... 22
2.6.1 Preparation of phosphorus(III) tris (N,N-dimethyl amide)…… 22
2.6.2 Preparation of phosphorus(III) tris (N,N-dimethyl
dithiocarbamate)……………………………………………….........
22
2.6.3 Preparation of phosphorus(III) tris diethyl amide…………….. 23
2.6.4 Preparation of phosphorus(III) tris (N,N-diethyl
dithiocarbamate)………………………………………………….....
24
2.6.5 Preparation of arsenic(III) tris (N,N-diethyl dithiocarbamate).. 25
2.6.6 Preparation of antimony(III) tris (N,N-diethyl
dithiocarbamate)…………………………………………………….. 26
2.6.7 Preparation of lithium diethyl amide………………………….
27
2.6.8 Preparation of antimony(III) tris (N,N-diethyl amide)……….. 27
2.6.9 Preparation of copper(I) iodide……………………………….. 28
2.6.10 Preparation of silver(I) iodide……………………………….. 29
2.7 Reactions………………………………………………………... 29
2.7.1 Reaction of phosphorus(III) tris (N,N-diethyl dithio
carbamate) [1] with group 12 metals halides……………………….. 29
2.7.1.1 Reaction of compound [1] with zinc(II) iodide……………..
29
2.7.1.2 Reaction of compound [1] with cadmium(II) iodide……….. 30
2.7.1.3 Reaction of compound [1] with mercury(II) iodide
31
2.7.1.4 Reaction of compound [1] with zinc(II) chloride…………... 32
2.7.1.5 Reaction of compound [1] with cadmium(II) bromide……... 32
2.7.1.6 Reaction of compound [1] with mercury(II) bromide………
33
2.7.2 Reaction of arsenic(III) tris (N,N-diethyl dithiocarbamate) [2]
with group 12 metals halides………………………………………..
34
2.7.2.1 Reaction of compound [2] with zinc(II) iodide……………..
34
2.7.2.2 Reaction of compound [2] with cadmium(II) iodide……….. 34
2.7.2.3 Reaction of compound [2] with mercury (II) iodide………... 35
2.7.2.4 Reaction of compound [2] with cadmium(II) bromide……... 36
2.7.3 Reaction of antimony(III) tris (N,N-diethyl dithiocarbamate)
[3] with group 12 metals halides……………………………………. 36
2.7.3.1 Reaction of compound [3] with zinc(II) iodide……………..
36
2.7.3.2 Reaction of compound [3] with cadmium(II) iodide……….. 37
2.7.3.3 Reaction of compound [3] with mercury(II) iodide………… 37
2.7.3.4 Reaction of compound [3] with cadmium(II) bromide……... 38
2.7.4 Reactions of phosphorus(III) tris (N,N-dimethyl dithio
carbamate) [4] with ZnI2, CdI2 and HgI2……………………………
38
2.7.5 Reaction of antimony(III) tris (N,N-diethyl amide) with
copper(I) iodide in 1:1 molar ratio………………………………….. 39
2.7.6 Reaction of antimony(III) tris (N,N-diethyl amide) with
silver(I) iodide in 1:1 molar ratio…………………………………… 40
CHAPTER THREE
RESULTS AND DISCUSSION
3.1 Preparation of phosphorus(III), arsenic(III), and antimony(III)
tris (N,N-dialkyl dithiocarbamate)………………………………….. 41
3.2 Reactions of tris dialkyl dithiocarbamates of phosphorus(III),
arsenic(III), and antimony(III) with the dihalides of group 12 (Zn,
Cd and Hg).......................................................................................... 43
3.3 Reaction of antimony(III) tris (N,N–diethyl amine) with copper
(I) and silver(I) halides……………………………………………… 51
3.4 31P, 1H NMR spectra…………………………………………...
54
3.5 Conclusion……………………………………………………… 67
REFERENCES……………………………………………………...
68
ACKNOWLEDGMENT
I wish to express my sincere thanks and gratitude to my supervisor
professor El-Nigumi, Y. O. for his helpful supervision, suggestions and
continued support throughout the course of this work.
I am greatly indebted to prof. Kempe, R. of the Institute of Inorganic
Chemistry, University of Bayreuth, Germany for his generous invitation and
permission to use the research facilities of his research group at the
University of Bayreuth.
My appreciations are due to Dr. Awal Noor, University of Bayreuth
for his assistance on NMR spectroscopy and x-ray diffraction studies.
I wish to extend my thanks to my colleagues working in uni-bayreuth
and U of K for a friendly atmosphere.
Finally the financial support of the DAAD during the tenure of this
study is certainly acknowledged.
DEDICATION
To my beloved Family &
Friends
With my love
ABSTRACT
The present work is directed towards the study of the reactions of the
dimethyl and diethyl dithiocarbamates of group 15 elements (P, As, and Sb)
with the halides of group 12 metals MX2 (where M is Zn, Cd and Hg; X= Cl,
Br and I).
The reactions were conducted in dry conditions using a two-manifold
vacuum line or glove box by transferring ligand solution to stirred solution of
the metal halide in the appropriate organic solvent, under an atmosphere of
dry oxygen-free argon.
The results of the reactions of dialkyl dithiocarbamates of group 15
elements (P, As, Sb) with ZnX2, CdX2, and HgX2 is the isolation of ligand
exchange complexes which have the general empirical formula:
M(CS2NR2)2 or MX(CS2NR2) depending upon reaction molar ratio. (Where
M= Zn, Cd, Hg; X= Cl, Br, I; R= Me or Et).
The isolated ligand exchange-complexes were identified by the
following methods:
1- Elemental analysis for carbon, hydrogen and nitrogen.
2- Determination of the meting points.
3- 1H and 31P-NMR spectroscopy.
4- Studying the full crystal structure, by x-ray diffractometer, for
representative compounds; zinc (II) bis(diethyl dithiocarbamate) and
cadmium (II) bis (diethyl dithiocarbamate).
‫اﻟﺨﻼﺻﺔ‬
‫اﺷﺘﻤﻠﺖ هﺬﻩ اﻟﺪراﺳﺔ ﻋﻠﻰ ﺗﻔﺎﻋﻼت ﻣﺮآﺒﺎت ﺛﻨﺎﺋﻲ ﻣﻴﺜﻴﻞ و ﺛﻨﺎﺋﻲ إﻳﺜﻴﻞ داﻳﺜﻴﻮآﺎرﺑﺎﻣﻴﺖ ﻋﻨﺎﺻﺮ‬
‫اﻟﻤﺠﻤﻮﻋﺔ ‪ ) 15‬اﻟﻔﺴﻔﻮر‪ ,‬اﻟﺰرﻧﻴﺦ و اﻷﻧﺘﻤﻮن( ﻣﻊ ﺛﻨﺎﺋﻲ هﺎﻟﻴﺪات ﻋﻨﺎﺻﺮ اﻟﻤﺠﻤﻮﻋﺔ ‪) 12‬اﻟﺨﺎرﺻﻴﻦ‪,‬‬
‫اﻟﻜﺎدﻣﻴﻮم و اﻟﺰﺋﺒﻖ(‪.‬‬
‫أُﺟﺮﻳﺖ هﺬﻩ اﻟﺘﻔﺎﻋﻼت ﻓﻲ ﺟﻮ ﺧﺎﻣﻞ ﻣﻦ ﻏﺎز اﻻرﺟﻮن اﻟﺠﺎف و اﻟﺨﺎﻟﻲ ﻣﻦ اﻷوآﺴﺠﻴﻦ ﺑﺎﺳﺘﺨﺪام‬
‫‪Vacuum line‬و‪ Glove box‬و ذﻟﻚ ﻋﻦ ﻃﺮﻳﻖ إﺿﺎﻓﺔ ﻣﺤﻠﻮل اﻟﻠﻴﻘﺎﻧﺪ إﻟﻰ ﻣﺤﻠﻮل هﺎ ﻟﻴﺪ اﻟﻤﻌﺪن‬
‫ﻓﻲ اﻟﻤﺬﻳﺐ اﻟﻌﻀﻮي اﻟﻤﻨﺎﺳﺐ‪.‬‬
‫ﻧﺘﺞ ﻋﻦ ﺗﻔﺎﻋﻼت ﻣﺮآﺒﺎت ﺛﻨﺎﺋﻲ اﻟﻜﻴﻞ داﻳﺜﻴﻮآﺎرﺑﻤﻴﺖ ﻋﻨﺎﺻﺮ اﻟﻤﺠﻤﻮﻋﺔ ‪ 15‬ﻣﻊ ﺛﻨﺎﺋﻲ هﺎﻟﻴﺪات ﻓﻠﺰات‬
‫اﻟﻤﺠﻤﻮﻋﺔ ‪ 12‬ﻣﻌﻘﺪات ﻟﻬﺎ اﻟﺼﻴﻎ اﻟﻜﻴﻤﻴﺎﺋﻴﺔ‪:‬‬
‫)‪ MX(CS2NR2‬أو ‪M (CS2NR2)2‬‬
‫اﻋﺘﻤﺎدا ﻋﻠﻰ اﻟﻨﺴﺒﺔ اﻟﻤﻮﻟﻴﺔ ﻟﻠﺘﻔﺎﻋﻞ‪ ,‬واﻳﻀﺎ ﻣﺮآﺒﺎت ﺑﺎﻟﺼﻴﻐﺔ‪:‬‬
‫‪X- Y (CS2NR2)2‬‬
‫ﺣﻴﺚ‪:‬‬
‫)‪( M= Zn, Cd and Hg; Y= P,As and Sb; R= Me or Et; X= Cl, Br and I‬‬
‫أﻣﻜﻦ اﻟﺘﻌﺮف ﻋﻠﻲ اﻟﻤﺮآﺒﺎت اﻟﺘﻲ ﺗﻢ ﻓﺼﻠﻬﺎ ﻋﻦ ﻃﺮﻳﻖ‪:‬‬
‫‪ -1‬اﻟﺘﺤﻠﻴﻞ اﻟﻌﻨﺼﺮي ﻟﻜﻞ ﻣﻦ اﻟﻜﺮﺑﻮن‪ ,‬اﻟﻬﻴﺪروﺟﻴﻦ و اﻟﻨﻴﺘﺮوﺟﻴﻦ‪.‬‬
‫‪ -2‬ﻗﻴﺎس ﻧﻘﻂ اﻻﻧﺼﻬﺎر‪.‬‬
‫‪ -3‬اﻟﺮﻧﻴﻦ اﻟﻨﻮوي اﻟﻤﻐﻨﻄﻴﺴﻲ ﻟﻠﺒﺮوﺗﻮن و اﻟﻔﺴﻔﻮر ‪.31‬‬
‫‪ -4‬دراﺳﺔ اﻟﺘﺮآﻴﺐ اﻟﺒﻠﻮري ﻋﻦ ﻃﺮﻳﻖ ﺗﺸﺘﺖ اﻷﺷﻌﺔ اﻟﺴﻴﻨﻴﺔ ﻟﺒﻌﺾ اﻟﻤﻌﻘﺪات ﻣﺜﻞ اﻟﺨﺎرﺻﻴﻦ )‪(II‬‬
‫ﺛﻨﺎﺋﻲ )ﺛﻨﺎﺋﻲ اﻳﺜﻴﻞ داﻳﺜﻴﻮآﺎرﺑﺎﻣﻴﺖ( و اﻟﻜﺎدﻣﻴﻮم )‪ (II‬ﺛﻨﺎﺋﻲ )ﺛﻨﺎﺋﻲ اﻳﺜﻴﻞ داﻳﺜﻴﻮآﺎرﺑﺎﻣﻴﺖ(‪.‬‬
CHAPTER ONE
INTRODUCTION
Tertiary phosphines, arsines and stibines as unidentate ligands are
known to form a wide variety of Lewis acid–base complexes with transition
metals. These complexes exhibit a rich and interesting area of chemistry that
has been extensively studied.
Complexes of tertiary phosphines , arsines and stibines with group 12
(zinc, cadmium, mercury) divalent metals halides were first prepared by
Evans R. et al(1), and this was the start of a chemistry which has since
expanded enormously.
During the last few decades numerous papers have reported the
spectroscopic behavior, synthetic strategies, structural studies and other
physical properties of these complex systems and have shed much light on
coordination modes, stereochemistry, steric and electronic factors and other
trends.
The study of these complexes has blossomed because of their potential
catalytic activity, medical and biological importance and practical
applications in different fields. For instance, triphenyl phosphine-Zn(П)
systems [CoI2 (pph3)n]–ZnX2 exhibit high catalytic activity for the homo–
Diels–Alder cycloaddition of norbornadiene with various terminal and
internal acetylenes.(2) Bis 2,6–diflouro phenoxide zinc and cadmium tertiary
phosphine adducts were used as catalysts for the coupling reaction of carbon
dioxide and epoxides, cyclohexene oxide, to afford high molecular–weight
poly carbonates or cyclic carbonates.(3)
Some tertiary phosphines adducts of Zn(П) halides, ZnX2L2 (X= CL,
Br, I;
L = PMe2ph, PEt3, PBu3, pph3, PCy3) have shown recently (4) a high
catalytic activity for the coupling reaction of CO2 and ethylene oxide to
produce five–membered cyclic ethylene carbonate:
O
O
+
CO2
catalyst
O
O
R
Zn(П) tertiary phosphine–catalyzed coupling reactions are attracting
increasing interest because of the enlarged applications of cyclic carbonates
and the growing concern about the utilization of carbon dioxide.(4)
Low coordinate Zn(П) complexes supported by sterically demanding
phosphine ligands showed remarkably catalytic activity for polymerization
of lactide and copolymerization of epoxides and CO2.(5,6)
Likewise, complexes of group 12 and group 11 metals (Cu, Ag and
Au) with monodentate phosphines are of great interest in catalysis. For
instance Cu Cl (pph3)2 is used in the cyclization of acetylene.(7) Aryl
phosphine based complexes of copper(1) halides act as sensitizers(8) for some
organic systems. Also some gold(1) phosphines, AuX(PEt3)n, find clinical
importance and are used currently in treatment of arthritis.(9)
In contrast to that of divalent cadmium and mercury, relatively little
work has been done on the coordination chemistry of Zn(П) with group 15
donors. In the case of zinc(П) halides and tertiary phosphines, two structural
types have been identified, bis phosphine complexes of the general formula
ZnX2L2, and mono-phosphine complexes (ZnX2L). It has been believed that
the steric demands of the tertiary phosphine ligand may be fundamental in
determining which structure is adopted, i.e. with less sterically demanding
phosphine ligands; the bis-phosphine complexes would be favoured, whereas
bulky tertiary phosphines would prefer the mono-ligand complexes. Such a
theory seems reasonable and is in agreement with the cone angle theory first
reported by Tolman.(10)
Zn(П) halides complexes of the type ZnX2 (R3P)2 (where R= Et or
Et2Ph; X=Cl, Br, I) were prepared by reaction of ZnX2 and the stoichiometric
amount of tertiary phophine in methanol. These complexes were
spectroscopically characterized as monomeric tetrahedral species, however
Zn I2 (PEt3)2 was structurally identified by single – crystal x-ray diffraction
and found to has a mixed ligands, Zn I2 (Et3P) (Et3PO).(11)
Cotton and Schmidt(12) made crystallographic studies on the previously
prepared ZnCl2 (Me3P)2 and found that the corresponding complex has a
monomeric tetrahedral geometry. In further investigation the same workers
have also identified Zn2Cl4(Me3P)3, with unusual stoichiometry, in which a
cationic (Me3P)3Zn+2 moiety is linked via a chlorine bridge to an anionic
ZnCl3– moiety.
A convenient synthetic method has been applied to the preparation of
1:1 Zn(П) complexes of tertiary phosphines, of low steric requirements, and
can be summarized in reacting di–iodophosphorane compound (R3PI2) with
an inactivated zinc powder in ether. This method has led to the formation of
variety unexpected 1:1 phosphine complexes.(13)
R3PI2 + Zn
Et2O,N2
[ZnI2(R3P)]2
(R= Me, Et, Prn, Bun)
[Zn (PEt3) I2]2 was the first simple Zn(П) phosphine to be
crystallographically characterized as dimeric with two iodine bridges, as
shown below:
I
Et3P
Zn
I
I
Zn
I
Et3P
Few years later,(14) the same synthetic route was employed in the
preparation of several 1:2 Zn(П) iodide tertiary phosphine complexes ZnI2
(PR3)2 according to the following equation:
2R3PI2 + 2Zn
Et2O,N2
ZnI2(R3P)2 + ZnI2
R3 = ph3 , ph2Et, ph2Me
The formation of the unusual 1:2 complexes is surprising and assumed
to be due to favourable π-π interactions on the ligands and crystal packing
forces other than steric factors. The related complexes were characterized by
1
H, and
31
P NMR spectroscopy. However, the x-ray crystal structure of
monomeric ZnI2 (PPh2Me) 2 was described.
Zn(П) halides, along with Cd(П) and Hg(П), afford a variety of
complexes with tricyclohexyl phosphine ligands. Zinc (П) halides form only
isolable 1:1 complexes; on the other hand, cadmium(П) and mercury(П)
halides form 1:1 as well as 1:2 complexes with PCy3
(where Cy =
cyclohexyl group). Molecular weight data showed that the 1:1 complexes of
all three metals exist in solution as dimeric molecular species, M2X4
[P(Cy)3]2.(15)
Vibrational spectra of the CdX2 [P (Cy)3]2 complexes in solid state, are
consistent with a pseudo tetrahedral structure. The 1:2 adducts of zinc(П)
halides do not exist as these complexes, according to
31
P NMR
measurements, dissociate extensively in solution to give the 1:1 complexes
and free phosphine which is readily oxidized to the phosphine oxide;
subsequent reaction of the oxide with 1:1 complexes results in the formation
of ZnX2 P(Cy)3 [OP(Cy)3].(16)
The very bulky phosphines, such as P(But)3, form dimeric 1:1 adduct
with zinc(П) halides and also with cadmium and mercury dihalides.(17)
Zinc(П) halides tend to form both 1:1 and 1:2 complexes with
triphenyl phosphine.(18) Tri p–chloro phenyl phosphine was found, according
to a recent report,(19) to give only a 1:1 adduct whereas bulkier tri–( ortho–
substituted phenyl) phosphines don't react with ZnX2.
Complexes of divalent zinc halides with tertiary arsines can be
prepared by methods similar to the phosphine analogues. For instance, Et3As
I2 reacts with zinc metal powder to produce the dimeric complex
[ZnI2(AsE3t)]2, whereas Me3AsI2 gave [ ZnI2(AsMe3)2] and ZnI2. In both
complexes the zinc atom is in essentially tetrahedral geometry but significant
distortion is noted for [ZnI2(AsMe3)2].(20)
Although no zinc(П) complexes of tertiary stibines are known, 2:1
isostructural complexes of trimethyl stibine sulphide (TMSS) with Zn(П),
Cd(П), and Hg(П), were obtained.(21) Based on infra-red spectra, it was found
that (TMSS) coordinates to the metal through the sulfur atom.
In further investigation, reactions of (TMSS) in methanol solution with
zinc(П) and cadmium(П) nitrates resulted in the formation of the 4:1
complexes formulated as [(TMSS)4M](NO3)2(22) with uncoordinated nitrate
anions. Unlikely, tri phenyl phosphine oxide with Zn(NO3)2 and Cd(NO3)2
formed 2:1 complexes alone. This difference may be due to the more basic
character of the sulfur atom in Sb–S than that of the oxygen in P–O bond.(22)
The complexes [Zn(Me2N)3PS)4](ClO4)2, [Cd(Me2N)3PS)4](CLO4)2
and ZnCl2(Ph3PO)2 were prepared similarly and some 31P NMR data of these
complexes were reported. (23)
Mercury(П) halides HgX2 (X= Cl, Br or I) form a wide variety of
complexes with tertiary phosphines. The most common stoichiometries are
the 2:1 and 1:1, viz (R3P)n HgX2 (n=1 or 2). The former complexes have
monomeric tetrahedral arrangements with varying degrees of distortion
depending on the δ–donor ability and the steric effect of the phosphine
ligands(24); whereas the later 1:1 adducts show much greater structural
variations ranging from monomeric units, weakly linked infinite polymeric
chains and halo–bridged dimers. (25)
The dimeric complexes [L2Hg2X4] can adopt symmetrical (A) or
unsymmetrical (B) structures depending on the nature of the ligand (L).
L
X
X
X
L
Hg
Hg
X
X
Hg
Hg
L
L
(A)
X
X
X
(B)
Of these the most commonly observed is the symmetrical structure
(A). The unsymmetric structure occurs with ligands having bulky alkyl
groups such as PPr3 and PBut,(26) the chain polymer structure is mainly
adopted by the more basic and sterically less demanding ligands such as
PMe3 and PEt3.(27)
The mercury(П) phosphine complexes of the general formula
(R3P)3HgX2 (where R = Ph, Et, 1–phenyl dibenzo phosphole (DBP), 1–
phenyl 3,4 – dimethyl phosphole (DMPP); X= Cl, Br or I and PBu3; X= Cl)
have been prepared and their solution and solid state structures were
determined and found to be distorted tetrahedra.(28)
The structural chemistry of 1:1 complexes is more diverse. For
instance the crystal structures of HgCl2(PMe3) and HgCl2(PEt3) have been
completely established and showed that both complexes are polymeric with
mercury atoms in distorted trigonal bipyramidal environments.(28) In
comparison 1:1 adducts of HgCl2 with triphenyl phosphine and 1,2,5–
triphenyl
phosphole are discrete centro–symmetric chlorine–bridged
dimers.(29)
According to a recent report the crystal structure of [Ph3P.HgI2]2 was
found to be, similarly, a halogen–bridged dimer with phosphine ligands
attached trans to the two mercury atoms.(30) However the double halogen
bridge is very asymmetric, the greater donor ability of iodide compared to
chloride does not appear to have a major effect on the adopted structure.
The 1:1 complex HgCl2(PBut3) exists in two forms known as ∝– and
β–forms. The β–forms contains discrete centrosymmetric dimers, while the
∝–form consists of a tetrameric unit in which [(PBu3)2 Hg2Cl4] dimers are
linked together via additional weaker Hg….Cl contacts.(31)
On the basis of multiplicity of γ (Hg–Cl) terminal bands in the far–
infrared and Raman spectra of the 1: 1 adduct HgCl2 (PCy3) (where Cy =
Cyclohexyl) the asymmetrically chlorine–bridged dimeric structure was
proposed.(32) However, a study based on single crystal x–ray diffraction
analysis for the complex demonstrated that the unit cell contains two
independent centrosymmetric dimers.(33)
HgX2–phosphine complexes with unusual stoichiometry have been
described. For example, (Me2EtP)3 (HgCl2)2 was found to have a chain – like
structure with the unusual feature of mercury atoms having alternating
coordination numbers of four and five. The structure is consisting of
[(Me2EtP)2 HgCl]+ cations and [ (Me2EtP) HgCl3 ]– anions linked via
chlorine bridges.(34) Other complexes formulated as (Me3P)2 (HgI2)3 and
(R3As)2 (HgI2)3 (where R=Et
or Pr) have also been prepared and
crystallographically identified.(35)
A large number of complexes of the formula HgX2(PPh3) X = Cl, Br
or I; HgX2 (1,2,5– tri phenyl phosphole) X = Cl or Br; HgCl2(PR3) (R= Me,
Et, Bun and Cy) were extensively investigated(36) by far– infrared and Raman
spectroscopies. Although the known structures of these complexes are
apparently quite varied, their spectra can be explained in terms of a common
centrosymmetric halogen–bridged dimer. This demonstrates obviously the
risk of structural elucidation from spectroscopic data alone.
Correlations between solid state structure and vibrational spectra have
been applied to novel 1:1 adducts like HgX2(PR3) (where R3 = ph2Me,
phMe2, Et3, Me3 and But3; X = Cl, Br, or I); the bromide complexes in this
series were found to be isostructural with their chloride analogues. However
interpretation of the spectra of these complexes is much more problematic as
the spectra are clearly not characteristic. This was obviously noted for the
tetramer HgBr2(PBu3).(37) A further problem exists with HgBr2(PPr3) as there
is clearly a strong single γ (Hg–Br) band at 144 cm-1 for bridging halogen
and no other bands at lower wave numbers for the terminal modes.(37)
Marked structural variations have been noted(38) in the series
Pr3P.HgX2 (X= Cl, Br, or I). The chloride and bromide complexes are
halogen–bridged dimers with increasing asymmetry in the (HgX2Hg) bridge
from chloride to bromide; whereas the α–form of the iodide complex
HgI2PPr3, was found to adopt the unsymmetric dimeric arrangement. Thus
the complex can be formulated as I2Hg (µ-I)2Hg(PPr3)2. Coordination about
the mercury atom to which both phosphines are attached is considerably
distorted (P-Hg-P angle = 149.1o)(39) and this is attributed to the strong бdonating ability of the PPr3 ligands.
In contrast, the β–form of [HgI2 PPr3] consists of approximately
trigonal planer (PHgI2) monomeric units in which coordination of mercury is
increased to five by association via very long (Hg…I) interactions with two
neighboring molecules.
Reactions of the very basic and sterically demanding (cone angle 184°)
tris (2,4,6–tri methoxy phenyl) phosphine (TMPP) were found to afford
complexes of stoichiometry (TMPP)x (HgX2)y having x : y ratios of 1:1, 2:1,
2:3 and 1:2. The structure of the 1:1 bromide and iodide are discrete
monomers unlike most other tertiary phosphine analogous. The
31
P–NMR
spectra of acetonitrile solutions of the 1:1 (TMPP)HgX2 revealed the
presence of the ionic complexes [HgX (TMPP)]+ and [ Hg (TMPP)2 ]+2.(40)
The 1:2
complex of the formula TMPP(HgI2)2
has been structurally
characterized as (TMPP) HgI (µ-I) HgI (µ -I)2 HgI (µ -I) HgI (TMPP).(41)
I
I
Hg
I
TMPP
I
Hg
Hg
I
TMPP
I
Hg
I
I
Similarly tris (2,4,6–trimethoxy phenyl ) phosphine (TMPP) has been
reacted with Ag(I) halides AgX (X= Cl, Br or I ) and found to afford the 1:1
adducts [(TMPP) AgX ]. The structures of these complexes were best
described as monomers with approximately linear two– coordination about
the silver atom, the P–Ag– X angles being ≈ 175°.(42)
Reactions of divalent mercury halides in ethanol with bulky tris (2,6–
dimethoxy phenyl) phosphine (DMPP) resulted in the isolation of only 1:1
adducts, the (DMPP) mercury(П) chloride and bromide complexes are
weakly linked dimers, while the iodide is the first example of an HgI2–
phosphine complex with a monomeric distorted trigonal planer arrangement
around mercury.(43)
In order to examine the importance of the electronic nature of the
substituents attached to phosphorus, a study carried out by Norman A. Bell
et al(44) showed that tris (2–cyanoethyl) phosphine forms readily isolable
crystalline adducts with HgX2 in different ratios. In accordance to far infra–
red spectra of the related complexes, tris (2–cyanoethyl ) phosphine was
found to be
a strong sigma donor, despite the electron– withdrawing
property of the cyano group, and comparable with P(Et3) in its interaction
with HgX2.(45)
Tertiary phosphine–based complexes of Hg(П) have been extensively
investigated by both 31P– and
199
Hg–NMR spectroscopies. For instance 31P–
NMR and x–rays data of the complex HgX2(PPh3)2 (where X = Cl, Br, I,
NO3, SCN and CN) have shown that larger J(199Hg, 31P) coupling constants
and (P–Hg–P) bond angles are found for the harder X ligands than for the
softer ones; the nature of X ligands and P–Hg–P angle make important
contributions to the changes in the coupling constant of the corresponding
complexes.(46)
In further studies,
31
P–NMR data were reported for L2HgX2 and
L2Hg2X4 (where L = Bu2PhP, BuPh2P and Et2PhP; X = Cl, Br or I). The
coupling constants J(31P–199Hg) were found to increase with the
electronegativity of the halogen and in the order of the basicity of the
phosphine i.e. Bu3P > Bu2PhP > BuPh2P. It was also well established that
J(P–Hg) is considerably larger in the halogen–bridged dimer L2Hg2X4 than in
the corresponding monomeric L2HgX2.(47)
Spectroscopic studies based on
31
P–NMR were presented(48) for a
series of complexes of the general formula HgX2 (PR3)n (where for n = 1 R is
o–tolyl, But, Cy and Ph. And for n = 2; R is Cy and Ph; X = Cl, Br, I, SCN,
CH3COO and NO3). Factors including the electronegativity of X, basicity
and bulkiness of the phosphine and geometry at the mercury atom were
found to affect substantially the coupling constants and the chemical shifts.
Generally, the ongoing NMR study of Hg–phosphine complexes has
resulted in the accumulation of many data, which have been interpreted in
terms of several empirical trends. The following trends for the complexes of
the type HgX2P2 (P= tri–organo phosphine; X = anionic ligand) have been
found:
• For a given coordinated X, 'J (Hg–P) increases with increasing
phosphine basicity. But if X is non coordinating 'J(Hg–P)
decreases.
• For a given phosphine, 'J (Hg–P) decreases with increasing
Lewis basicity of the coordinated anion, X.
• J(Hg–P) often varies in direct proportion to the coordinating
chemical shits (∆).
∆ = δ (complexed phosphine)–δ (free phosphine).(49)
The nature of anion (X) in the complexes HgX2 (PR3) was found to
have a significant role in the distortion from regular tetrahedral geometry.(50)
This is attributed to the competition between the lone pair of the phosphorus
atom in the phosphine ligand (:PR3) and those of the atom X for б – bonding
to mercury. It was thus confirmed that:
• The greater the donor strength of the phosphine the more the P–
Hg bonding dominates over X–Hg with larger P–Hg–P angles
and longer Hg–X bond lengths.
• The greater Hg–X interaction, the less significant is the Hg–P
bonding, with smaller P–Hg–P angles and longer Hg–P bonds.
When the ligand (X) in the metal coordination sphere is a soft (halide,
SCN–, CN–), it can satisfy the Lewis acidity of mercury and prevent the
formation of a complex with a ligand to metal ratio greater than two.
However, when (X) is ClO4–, whose hardness and poor basicity are known, a
1:3 complex formulated as [Hg(TMPP)3]2+(CLO4)2 (where TMPP is tri p–
methoxy phenyl phosphine) was isolated.(51) The structure of the complex
cation [Hg(TMPP)3]+2 was described as distorted trigonal planer.(52) Other
cationic
complexes
of
substituted
tertiary
aryl
phosphine
[Hg(phosphine)n](CLO4)2 (n= 2 or 3), have been reported and studied by
vibrational spectroscopies.(53)
Crystal and molecular structures of the dimers bis–(acetato) (tri–
cyclohexyl phosphine)(54), bis–(acetato) (tri o–tolyl phosphine) and dinitrato
(tri cyclohexyl phosphine) mercury(П) were reported.(55) The three
complexes are isostructural and found to be centrosymmetric dimeric
molecules with acetato or nitrato bridging modes. In contrast, crystal
structure determinations(56) and NMR studies(57) showed that mercury(П)
acetate and flouroacetate complexes of the formula Ph3P Hg(O2CR)2 and
But3PHg(O2CR)2 where R is CH3 or CF3, have monomeric penta-coordinate
structures in which the acetate groups are bonded to the mercury atom in an
assymmetrically bidentate manner giving rise to a distorted trigonal
bipyramidal arrangement.
Dithiocyanato mercury(II) complexes of the type [Hg(SCN)2(PPh3)](58)
and [Hg(SCN)2(AsPh3)](59) were found to be three–coordinated monomeric
molecules with a distorted trigonal bipyramidal geometry around mercury.
This is attributed to further two Hg–NCS intramolecular interactions;
although previous infra-red spectral data were interpreted in favour of a
dimeric SCN– bridged structure.(60) On the other hand, Hg(SCN)2 complex of
the bulky PCy3, [Hg(SCN)2(P(Cy)3], was described as a distorted trigonal –
pyramidal with one Hg–NCS inter–molecular interaction from a neighboring
molecule. The crystal structure thus contains infinite chains of mercury
atoms linked by bridging thiocyanato groups. (61)
As the 1:2 complexes of mercury(II) thiocyanate with the ligands
P(C6H11)3, PPh3 and P(o–MeC6H4) are well established(62), reactions of
cadmium(II) thiocyanate with these ligands resulted in the formation of only
1:1 complexes. Single crystal x–rays diffraction study and vibrational spectra
of the complexes are consistent with a polymeric structure involving bridging
SCN and five–coordinated cadmium atoms.(63)
Differences in the coordination behavior of Hg(SCN)2 and Cd(SCN)2
towards phosphine Ligands are best explained in terms of the different
preferences of the two metals for the hard N and the soft P or S donors.
Cadmium(II), unlike mercury(II), prefers the hard N donor site to the soft S
or P donor sites, whereas the opposite is true for mercury(II) which is
undoubtedly a soft acid.(63)
Cadmium(II) salts are known to form complexes with tertiary
phosphines with different stoichiometries. For instance, the 1:2 complex
CdX2 [P(p–yC6H4)3]2 (where X = Cl, Br or I and Y= H, CH3, CH3O, or
Me2N-) can be readily obtained from the reactions of CdX2 with the
stoichiometric amounts of the appropriate phosphines in refluxing ethanol.
The vibrational spectral data of these complexes are in accord with a
monomeric pseudo tetrahedral structure.(64) The 1:1 complexes of
cadmium(II) salts with substituted triaryl phosphines were found to be
isostructural
with
the
corresponding
dimeric
bridged
mercury(II)
complexes.(65)
In a systematic study of novel cadmium(II) complexes of the formula
CdA2(Phosphine)n, the dependence of the coordination number of cadmium
atom on the nature of phosphine and the anion (A) is well established.(66) As
an example cadmium(II) halides form both 1:1
and 1:2 adducts with
P(C6H11)3 formulated as [CdX2P(C6H11)3]2 and CdX2[P(C6H11)3]2. These
adducts are reported(66) as being halogen–bridged and tetrahedral monomers
respectively with four–coordinated cadmium atoms in both cases. On the
other hand, Raman and infra–red spectra of Cd(ClO4)2[P(C6H11)3]2 suggest
that the involvement of perchlorate in coordination to cadmium is minimum
and that the cadmium species may be best regarded as linear two–
coordinated, [Cd(PC6H11)2]+2.(67)
In contrast to tertiary phosphines and arsines, very few examples of
Lewis acid-base adducts between mercury(II) halides and tertiary stibines are
known, although the donor character of antimony in the R3Sb compounds is
well established.
The reactions of tertiary stibines in benzene with mercury(II) halides,
at room temperature, lead to the formation of 1:1 adducts according to the
following equation: (68)
R3Sb + HgX2
R3Sb.HgX2
(R= Ph, o–and p–olyl; X = Cl, Br or I)
Both spectroscopic and conductometric evidences suggest that, these
compounds should be formulated as donor- acceptor complexes containing
Sb-Hg bond:
X
R3Sb
Hg
X
Triphenyl stibine was also found to react with the halides of other d10
metals such as Cu(I) and Ag(I). For instance some 1:2 binuclear complexes
of these metals formulated as [(Ph3Sb)2M(µ-X)2M(SbPh3)2] (where M= Cu,
Ag; X = Cl, Br and I) were prepared. Based on x–ray diffraction studies,
these complexes were found to contain four– coordinated metals in a
halogen–bridged tetrahedral geometry.(69,70)
According to recent reports, adducts of triphenyl stibine, along with
triphenyl phosphine and arsine analogues, with silver(I) bromate(71) and
silver(I) nitrite(72) have been synthesized and characterized both in solution
and solid state. These adducts can be formulated as (Ph3E)xAgBrO3 (where
E= P, As, Sb; X = 1–4) and [AgNO2(Ph3E)x] (where E= P, As, Sb; X = 1–3)
respectively. The topology of the structure was found to depend on the nature
of EPh3 and on the stoichiometric ratio Ag salt/EPh3.
Generally unidentate tertiary phosphines and arsines are known to
afford complexes with coinage metals Cu(I), Ag(I) and Au(I) in different
stoichiometrics Lm(MX)n where L is a tertiary phosphine or arsine and X is a
coordinating anion and M a group 11 metal. The known geometries for
various classes are shown below: (73)
X
L
M
L
M
L
L
L
L
L
[L4 M] +X–
[L3 MX]
X
M
L
X
L
M
Or
L
L
M
L
L
X
L2MX
L
X
L
L
M
X
X
M
M
M
,
L
L
X
M
X
L
M
X
L
X
M
X
X
M
M
L
L
Dialkyl-aminophsphines of the formula (R2N)3 P (R=Me or Et) form
complexes with a vast array of transition metals salts. Thus they react with
divalent cadmium and mercury iodides to give adducts with different
stiochiometries e.g. [(CH3)2N)3 P. MI2] and [(CH3)2N)3 P] 2 MI2 (where M =
Cd or Hg).(74)
The crystal data of the dimeric zinc(П) iodide dimethylamino
phosphine complex [(ZnI2 P(NMe2)3)]
was reported
(14)
and found to be
closely in agreement with those of [ZnI2(PEt3)]2.(13) Both complexes exhibit
close regular tetrahedral geometries for the zinc(П) metal centers.
Dialkylamino phosphines can be prepared readily by reaction of
phosphorus(Ш) chloride and secondary amines in an inert solvent like
benzene, ether or light petroleum at lower temperature in accordance with the
general equation: (75)
PCl3 + 6R2NH
(R2N)3P + 3R2NH.HCl
(R = Me or Et)
Dialkylamino arsine can be formed in analogous manner.(76) However,
reactions of SbCl3 and secondary amines lead to the formation of the highly
stable adduct SbCl3.3NHR2 according to the following equation:
SbCl3 + 3R2NH
SbCl3.3NHR2
Thus Sb(NR2)3 can be readily synthesized by an indirect synthetic
route developed by Moeritzer.(77)
n-BuLi + HNR2
3LiNR2 + SbCl3
LiNR2 + Bu-H
Sb(NR2)3 + 3LiCl
Both (R2N)3P and (R2N)3As were found to form adduct complexes
with copper(I) and silver(I) halides in different metal : ligand ratios up to 1:4.
The corresponding complexes were identified by infra-red spectroscopy.(78, 79)
Tris dialkylamino phosphines and arsines contain two basic sites
(namely the phosphorus and the nitrogen donor atoms). The basicity of the
phosphorus atom is enhanced relative to the nitrogen atom due to the
formation of the π- bonding between the nitrogen lone pair of electrons and
vacant d–orbital of phosphorus or arsenic.(80) Based on this fact coordination
would be through the P or As atoms rather than the N atom.
The dialkyl dithiocarbamates of group 15 can be prepared by the
insertion reactions between an amino derivative of group 15 element (P, As
or Sb) and carbon disulfide which can be represented by the generic reaction:
M-N + U
M-U-N
U = CS2 or CO2, OCS, SO2 … etc.
The above reaction involves the insertion of a ligand, usually
unsaturated, across the M–N bond (where M is P, As or Sb). These reactions
filled a considerable area of literature and are widely used in the synthesis of
dialkyl dithiocarbamate complexes since R.W light et al (81) have investigated
several reactions proceed to products in which CS2, CO2 or COS have
undergone insertion in the P–N bond; the insertion products being prepared
have the empirical formula P(CSSNR2)3.
The direct reaction of a metal chloride, secondary amine and carbon
disulphide has been extensively employed in the syntheses of dithio
carbamates of some of group 15 elements.
The direct reaction method has the advantage of eliminating the
separate preparation of dialkyl amino derivative. Thus tris dithio carbamate
of arsenic and antimony with pipyridine, diisobutyl amine and dibenzyl
amine were readily prepared by directly mixing either AsCl3 or SbCl3 with
CS2 and the corresponding amine, the reactions were carried out in carbon
tetra chloride as a solvent at room temperature.(82)
Tris (N,N–diethyl dithiocarbamate ) arsenic(III) was prepared by
Manoussakis(83) by direct reaction of AsCl3, HNEt2 and CS2 in petroleum
ether at –80°C according to the following reaction:
o
AsCl3 + 6HNEt2 + 3CS2
-80 C
As(CS2NEt2)3 + 3Et2NH.HCl
1
H-NMR and I.R spectra of the product were reported. Tris–(diethyl
dithiocarbamate) phosphine can also be prepared in an analogous manner.(84)
Alternatively, use of the oxides of arsenic and antimory offered a
simplified method for the preparation of the dialkyl dithiocarbamates of these
elements in aqueous solution.(85)
A convenient method has been applied recently for preparation of
Sb(CS2NR2)3 by reacting SbCl3 and sodium salt of dialkyl dithio carbamate
Na(CS2NR2) in an ethanolic solution. Thus tris (diethyl dithiocarbamate)
stibine was successfully prepared via the reaction of Na(CS2NEt2) and SbCl3
in absolute ethanol in accordance with the following equation: (86)
SbCl3 + 3Na(CS2NEt2)
Sb(CS2NEt2)3 + 3NaCl
CHAPTER TWO
EXPERIMENTAL
2.1 General Techniques:
All experiments in this work were performed under an inert gas
atmosphere of dry oxygen-free argon ( BTS catalyst, molecular seive) using
a schlenk-type apparatus on two manifold vacuum line or an argon filled
glove box (m-Braun labmaster 130) with a high-capacity recirculator (<
0.1ppm of H20, 02) in order to eliminate traces of air and moisture.
Quick-fit glassware was used throughout this work; it is usually dried
in an air oven at 120 C for 24 hours, sealed in vacuo and moderately heated
using a heating gun and then allowed to cool under argon. Silicon grease was
used as a lubricant.
Vacuum techniques are sometimes used for fresh distillation of
reactants, removing of solvents and drying of solid compounds and products.
2.2 Melting point:
Melting points were measured on a Thomas-Hoover capillary melting
point apparatus and recorded without corrections.
2.3 Elemental Analysis:
Elemental content of carbon, hydrogen and nitrogen were determined
using a Vario EL CHN elemental analyzer.
2.4 NMR spectra:
1
H and
31
P NMR spectra were recorded on a Bruker ARX 250
instrument with a variable temperature unit. The chemical shifts are reported
in ppm using residual protons signals of the deteurated solvents as internal
standards.
2.5 Purification of chemicals:
Solid samples such as zinc(II) iodide, cadmium(II) iodide, mercury(II)
iodide, antimony(III) chloride, copper(II) sulphate pentahydrate, potassium
iodide, sodium thiosulphate, silver(I) nitrate, zinc(II) chloride, cadmium(II)
bromide and mercury(II) bromide were obtained from (Merk) and Aldrich
chemicals and were used without further purification.
Solvents used in this work such as dichloromethane, diethyl ether,
light petroleum ( 40-60°C ) are analar grade and are usually dried by reflux
with calcium hydride and distilled prior to use. Carbon tetrachloride and
chloroform were distilled and stored under argon.
Deteurated NMR solvents, obtained from (Cambridge isotope
laboratory all 99 atom % D), were degassed, dried by reflux with calcium
hydride and distilled.
Analar phosphorus trichloride, arsenic trichloride and carbon
disulphide were used as supplied.
n-Butyl lithium was supplied as nitrogen-packed solution in hexane
(1.6M) and was used without treatment.
Absolute methanol was dried by reflux with magnesium turnings for
six hours, distilled and stored under argon.
Diethyl amine, analar grade (Merk), was shaken with potassium
hydroxide pellets, filtered and distilled. The fraction boiling at 54°C was
collected and stored over molecular sieve.
Dimethyl amine was carefully evaporated under vacuum from an
aqueous solution into a liquid nitrogen-cooled schlenk tube for three times
and stored at –18°C over molecular sieve.
2.6 Preparation of starting materials:
2.6.1 Preparation of phosphorus(III) tris (N,N-dimethyl amide): (75)
The corresponding compound was prepared according to the following
synthetic scheme:
PCl3 + 6HNMe2
P(NMe2)3 + 3Me2NH.HCl
A dry three necked quick-fit 500 ml round bottom flask was facilitated
with a mechanical stirrer, a dropping funnel, a pressure equalizing tube and
gas inlet tube. The apparatus was flushed with a continuous flow of dry
argon throughout the reaction course.
Dimethyl amine, 7.9g (18 mmol), in 100 ml. of light petroleum was
charged into the flask, while the flask was immediately immersed in
isopropanol- liquid nitrogen sluch bath at –30° C.
Phosphorus trichloride ,(3.0 mmol), in light petroleum ,25 ml., was
added drop-wise while the contents of the flask were continuously stirred;
meanwhile the temperature of the bath was adjusted to –30° C. After the
addition was completed the reaction mixture was stirred for a further hour at
room temperature.
Dimethyl ammonium chloride was filtered off under argon using a predried sintered glass flask and washed several times with light petroleum;
excess dimethyl amine and the solvent were removed carefully by normal
distillation. A faint yellow liquid was left in the flask (yield 70%) as
P(Me2N)3. The crude product was used without further purification.
2.6.2 Preparation of phosphorus(III) tris (N,N-dimethyl
dithiocarbamate):
The preparation of phosphorus(III) tris (N,N-dimethyl dithio
carbamate) was according to R. W. Light et al. (81) method:
[(CH3)2N]3P + 3CS2
[(CH3)2NCS2]3P
Under dry conditions, phosphorus(III) tris dimethyl amide (2.0 mmol.)
was mixed with excess carbon disulfide in a pre-dried 100 ml two-necked
round- bottom flask facilitated with a reflux condenser and magnetic stirrer.
The reaction mixture was refluxed under argon for 24 hours, and after
cooling, the compound was obtained as a yellow powder which was collected
by filtration under argon, washed with dry diethyl ether and then dried under
vacuum (yield 90%).
The analytical data demonstrates the compound as P[CS2NMe2]3
Analysis:
N%
1
31
Found
10.89
C%
27.8
Calculated for C9H18N3PS6
10.75
27.6
H%
4.8
4.6
H-NMR spectrum of this compound is given in chart [1] page 55.
P-NMR spectrum of this compound is shown in chart [2] page 56.
2.6.3 Preparation of phosphorus(III) tris diethyl amide:
This compound was prepared according to the following method:(75)
PCl3 + 6HNEt2
P(NEt2)3 + 3Et2NH.HCl
Under anhydrous conditions of using argon as an atmosphere, a
mixture of, 8.0 g (110 mmol.), of freshly distilled Diethyl amine and 150 ml.
of petroleum ether were placed in a dry 500 ml. three necked round bottom
flask equipped with mechanical stirrer, dropping funnel with pressure
equalizing tube and stop-cock, a slow flow of argon was passed through the
system to maintain inert atmosphere. The reaction flask was cooled to –30°C
using liquid nitrogen-isopropanol sluch bath. Phosphorus trichloride, 2.21 g
(16.1 mmol.), was added drop-wise from the dropping funnel. The flask
contents were continuously and rapidly stirred. During the course of the
reaction, a white precipitate of diethyl ammonium hydrochloride was formed.
After the addition was completed the bath was removed and the stirring was
continued for a further hour. The white precipitate of diethylammonium
chloride (C2H5)2NH.H+Cl- was allowed to be in contact with the solution and
then filtred off through a sintered glass flask and washed several times with
petroleum ether. The solvent and excess diethyl amine was removed by
distillation; the phosphorus amide was obtained as a pale yellow oily liquid
(4.2 g, yield 70%). The crude product was used without further purification.
2.6.4 Preparation of phosphorus(III) tris (N,N-diethyl dithiocarbamate):
This compound was prepared according to the following method:(87)
[(C2H5)2N]3P + 3CS2
[(C2H5)2NCS2]3P
Tris diethyl amino phosphine, 2.47g (10 mmol), was dissolved in 20
ml. of benzene in a 100 ml pre-dried round bottom flask with teflon-coated
magnetic bar and entry for argon. Excess carbon disulfide was syringed in
portion-wise while maintaining continuous stirring of the flask contents. The
resulting dark-brown solution was refluxed for half an hour and allowed to
settle at room temperature. After standing for several days, the corresponding
compound was obtained as a slightly golden cubic crystal (yield 4.2 g, 85%),
mp: 131°C (lit: 130-132° C).(87)
The compound was characterized by means of elemental analysis for
C, N and H; and 1H, 31P-NMR spectroscopy.
Analysis:
N%
1
Found
8.89
C%
38.2
Calculated for C15H30N3PS6
8.84
38.0
H%
6.67
6.40
H-NMR (CDCl3 solution) spectrum of this compound is recorded in
chart [3] page (57)
31
P-NMR spectrum of this compound is shown in chart [4] page (58)
2.6.5 Preparation of arsenic(III) tris (N,N-diethyl dithiocarbamate):(85)
As2O3 + 6HNEt2 + 3CS2
2As(CS2NEt2)3 + 3H2O
In a two-necked round bottom flask equipped with a mechanical stirrer
and a dropping funnel, diethyl amine, 4.4 g (60 mmol), was mixed with 50
ml. of distilled water and treated with arsenic trioxide, As2O3, 2.4g (20
mmol). To this mixture carbon disulfide, 4.56 g (60 mmol), was added dropwise from the funnel with continuous rapid stirring. After the addition was
completed the reaction mixture was refluxed for half an hour and the yellow
precipitate was filtred off and recrystallized from carbon tetrachloride to give
arsenic(III) tris (N,N-diethyl dithiocarbamate) as yellow crystals, in 90%
yield, mp:144°C [lit144-145°C].(85)
Analysis:
N%
C%
H%
8.0
34.4
5.7
Calculated for C15H30AsN3S 6 8.0
34.6
5.7
found
1
H-NMR spectrum of this compound is given in chart [5] page 59
2.6.6 Preparation of antimony(III) tris (N,N-diethyl dithiocarbamate):
This compound was prepared according to synthetic scheme developed
by G. E. Manoussakis et al :( 82)
SbCl3 + 6HNEt2 + 3CS2
Sb(CS2NEt2)3 + 3Et2NH.HCl
Antimony trichloride 4.55 g (20 mmol) was placed in a 500 ml. quickfit round- bottom flask equipped with a magnetic stirrer, carbon tetrachloride
(150 ml.) and carbon disulfide, 4.56 g (60 mmol), were added with
continuous and rapid stirring till most of the antimony trichloride was
dissolved. To this mixture a solution of diethylamine, 8.76 g (120 mmol.), in
50 ml. of carbon tetrachloride was added portion-wise. After the addition was
completed the reaction mixture was refluxed with rapid stirring for two
hours. After cooling the white precipitate of diethylammonium hydrochloride
Et2NH.HCl was filtred off through a sintered glass funnel and the filtrate was
concentrated to a reduced volume by vacuum distillation and shaked with 40
ml. of methanol to induce crystalization.
Upon standing overnight, tris (N,N-diethyl dithiocarbamate) stibine
was obtained as bright yellow crystals. The product was isolated by filtration
and dried under vacuum. A second crop of the compound was obtained upon
keeping the filtrate for several days (overall yield 80%), melting point 109110°C.
The product was identified by 1H-NMR and elemental analysis of C,
N, and H.
Analysis:
1
N%
C%
H%
found
7.4
31.9
5.3
Calculated for C15H30N3S6Sb
7.4
31.8
5.3
H-NMR spectrum of this compound is given in chart [6] page 60
2.6.7 Preparation of lithium diethyl amide:
This compound was prepared according to Nudelmann(88) et al.
method:
n-BuLi + HNEt2
LiNEt2 + Bu-H
In a vacuum -dried 100 ml. round bottom flask equipped with a tefloncoated stirring bar, glass stopper and inlet for argon, n-butyl lithium 2.86 g
(44.0 mmol) solution in hexane (1.6M) was cooled to –78 °C using acetoneliquid nitrogen sluch bath. To this solution freshly distilled diethyl amine
2.93 g (44.0 mmol) was added, drop-wise, under argon with continuous rapid
stirring. After the addition the stirring was continued for further 10 minutes
at room temperature and the white lithium diethyl amide was filtred off and
washed several times with n-hexane to remove excess n-butyl Lithium, dried
under vacuum and then stored in the glove box.
Lithium diethyl amide was obtained in 90% yield as an extremely air
sensitive white compound which was characterized by 1HNMR; chart [7]
page 61.
2.6.8 Preparation of antimony(III) tris (N,N-diethyl amide):(77)
This compound was prepared according to the general equation:
3LiNEt2 + SbCl3
Sb(NEt2)3 + 3LiCl
A quantity of 4.8 g (6.0 mmol )of lithium diethyl amide was weighed
inside the glove-box and placed in a carefully- dried 250 ml round bottom
flask with magnetic bar and glass stopper, the flask was taken out of the
glove box and connected to the vacuum line. Lithium diethyl amide was then
dissolved in freshly distilled diethyl ether (50 ml.) and subsequently the flask
was immersed in acetone- liquid nitrogen sluch bath at –78° C. To this
solution, a solution of antimony trichloride, 0.45 g (2.0 mmol), and 25 ml. of
diethyl ether was added, drop-wise, under argon over half an hour
maintaining continuous and rapid stirring of the reaction mixture. During the
course of the reaction a white precipitate of lithium chloride was formed.
After the addition was completed, stirring was continued for further
half an hour followed by refluxing for two hours. Solid lithium chloride was
filtred off by transferring the clear solution through a glass fibre filter to a
pre-dried round bottom flask. Diethyl ether was removed by vacuum
distillation and the antimony(III) tris (N,N-diethyl amide), Sb(NEt2)3, was
obtained as a brown undistillable oily liquid.
The product is extremely air-sensitive and was characterized by 1HNMR spectroscopy; chart [8] page 62.
2.6.9 Preparation of copper(I) iodide:(89)
2CuSO4 + 2KI + 2Na2S2O3
2CuI + Na2SO4 + K2SO4 +
Na2S4O6
Copper(II) sulphate pentahydrate, 25.0 g (0.1 mol), was placed in 400
ml beaker and dissolved in 150 ml. of distilled water. A second solution was
prepared by placing potassium iodide, 36.5 g (0.22 mol), and sodium
thiosulphate, 28.0 g (0.11 mol), in 100 ml. of water in a volumetric flask. The
second solution was added to the first solution from a burette with
continuous rapid stirring until no further precipitation occurred in the course
of the titration. The dense white precipitate was allowed to settle down for
about 15 minutes and then collected in a sintered glass funnel, washed
several times with distilled water, ethanol, and finally with dry diethyl ether.
The product was dried under vacuum, powdered, and stored inside the
glove box.
2.6.10 Preparation of silver(I) iodide:(90)
AgNO3 + KI
AgI + KNO3
Potassium iodide, 8.3 g (0.05 mol.), was dissolved in distilled water
and added to silver nitrate, 8.5 g (0.05 mol.). solution slowly with continuous
stirring. The supernatant liquid was siphoned off. The precipitate was then
transferred to a one-litre bottle and about 500 ml. of distilled water were
added. The mixture was shaken vigorously to disperse the small lumps of
iodide. The precipitate settled rapidly and the clear supernatant liquid was
siphoned off after about 5 minutes, the product was washed several times
with water containing 1% nitric acid. The wash water was allowed to remain
in contact with the precipitate overnight to remove all possibly adsorbed
electrolytes. The precipitate was filtred, dried at 110°C and then stored inside
the glove box in a brown bottle.
2.7 Reactions:
2.7.1 Reaction of phosphorus(III) tris (N,N-diethyl dithiocarbamate) [1]
with group 12 metals halides:
2.7.1.1 Reaction of compound [1] with zinc(II) iodide:
Under dry conditions, zinc(II) iodide, 0.319 g (1.0 mmol), was
dissolved in minimal volume of methanol in a pre-dried 50 ml. schlenk tube
equipped with magnetic bar and entry for argon. To this solution
phosphorus(III) tris (N,N-diethyl dithiocarbamate), 0.950 g (2.0 mmol), in 15
ml. of dichloromethane was added. The mixture was stirred for few minutes
and then stored in a refrigerator overnight; pale yellow crystals were
obtained. The crystalline product was separated by filtration under argon and
vacuum dried, mp: 178-179°C.
This compound was structurally characterized by single-crystal x-ray
diffraction method and found to be zinc(II) bis (N,N-diethyl dithiocarbamate)
complex. Zn(CS2NEt2)2.
Analysis:
N%
C%
H%
Found
7.69
33.16
5.6
Calculated for
7.75
33.20
5.53
C10H20N2S4Zn
1
H-NMR spectrum of this compound is given in chart [9] page 63. The
compound gave no 31P-NMR signals.
2.7.1.2 Reaction of compound [1] with cadmium(II) iodide:
Phosphorus(III) tris (N,N-diethyl dithiocarbamate), 0.950 g (2.0
mmol), and cadmium(II) iodide, 0.366 g (1.0 mmol), were mixed under dry
argon and stirred in a schlenk tube using dichloromethane as a solvent, few
millilitres of methanol were added to dissolve the cadmium iodide.
The mixture was stirred until a clear solution was obtained, the
reaction mixture was allowed to stand overnight in the cold. Colourless shiny
crystals of the complex were obtained. The complex was isolated by
filtration through a glass fibre filter and dried under vacuum, mp: 255°C.
The complex was characterized by means of 1H-NMR, 31P-NMR and
elemental analysis, structurally characterized by single-crystal x-ray
diffraction
method
and
found
to
dithiocarbamate) complex, Cd(CS2NEt2)2.
be
cadmium
bis
(N,N-diethyl
Analysis:
Found
Calculated for
C10H20CdN2S4
1
N%
C%
H%
7.0
29,8
5.2
6.8
29.6
4.9
H-NMR spectrum of this compound is given in chart [10] page 64.
The complex gave no signals for the 31P-NMR..
2.7.1.3 Reaction of compound [1] with mercury(II) iodide:
In a dry schlenk tube facilitated with magnetic bar and entry for
vacuum and argon, phosphorus (III) tris (N,N-diethyl dithiocarbamate),
0.475 g (1.0 mmol), was dissolved in 15 ml. of dichloromethane, to this
solution solid mercury(II) iodide, 0.454 g (1.0 mmol), was added with
constant stirring until all mercury(II) iodide was completely dissolved. The
resulting solution was concentrated by pumping off almost half of the
solvent; the remaining solution was kept in a refrigerator. After standing for
several days pale yellow crystalline compound was formed which was
isolated by filtration and dried under vacuum, mp: 159°C
Elemental analysis for C, H, N and melting point indicated the
compound is mercury(II) iodo (N,N-diethyl dithiocarbamate) complex,
HgI[CS2NEt2].
Analysis:
Found
Calculated for
C5H10HgINS2
N%
C%
H%
3.2
13.1
2.28
2.9
12.6
2.1
The 1H-NMR spectrum was not recorded as this complex is not soluble
in most of the organic solvent.
2.7.1.4 Reaction of compound [1] with zinc(II) chloride:
To a stirred solution of zinc(II) chloride, 0.136 g (1.0 mmol), in 10 ml.
of methanol in a schlenk tube under an inert atmosphere of pure and dry
argon, was added a solution of phosphorus(III) tris (N,N-diethyl
dithiocarbamate), 0.950 g (2.0 mmol), in 20 ml of dichloromethane. The
stirring was continued for another 10 minutes; the reaction mixture was left
standing overnight in a refrigerator.
The pale yellow crystals that formed were isolated by filtration through
a glass fibre filter under argon pressure, washed with methanol and vacuum
dried, mp: 179°C.
The
product
was
found
to
be
zinc(II)
bis
(N,N-diethyl
dithiocarbamate), Zn(CS2NEt2)2, according to the elemental content of C, N,
and H. and 1H-NMR spectrum, chart [9] page 63.
Analysis:
N%
C%
H%
Found
7.68
33.2
5.8
Calculated for
C10H20N2S4Zn
7.75
33.2
5.5
2.7.1.5 Reaction of compound [1] with cadmium(II) bromide:
Phosphorus(III) tris (N,N-diethyl dithiocarbamate), 0.950 g (2.0
mmol), was dissolved in 20 ml. of dichloromethane and then transferred to a
stirred methanolic solution of cadmium(II) bromide, 0.272 g (1.0 mmol).The
resulting solution was stirred for few minutes and then the clear solution was
stored at 4˚C overnight.
Pale yellow crystals were formed which were isolated by filtration,
washed with cold dichloromethane and vacuum dried, mp: 253-255°C.
The compound was shown to be cadmium(II) bis (N,N-diethyl
dithiocarbamate) complex.
Analysis:
Complex
C10H20CdN2S4
1
N%
C%
H%
Found Calc. Found Calc. Found Calc.
6.7
6.8
29.2
29.3
4.89
4.89
H-NMR spectrum for Cd(CS2NEt2)2 is shown in chart [10] page 64.
2.7.1.6 Reaction of compound [1] with mercury(II) bromide:
Phosphorus(III) tris (N,N-diethyl dithiocarbamate), 0.475g (1.0 mmol),
dissolved in 15 ml of dichloromethane, was added to a stirred methanolic
solution of equimolar mercury(II) bromide. The clear resulting solution was
stirred and allowed to stand in the cold for several days. Bright yellow
crystals were formed. These were separated by filtration and dried under
vacuum, mp: 129°C.
The resulting complex was characterized by the elemental contents of
C, N, and H as mercury(II) bis (N,N-diethyl dithiocarbamate).
Analysis:
Complex
N%
C%
H%
Found
5.55
24.20
4.42
5.63
24.1
4.00
Calculated for
C10H20HgN2S4
1
H-NMR spectrum for Hg(CS2NEt2)2 is reported in chart [11] page 65.
2.7.2 Reaction of arsenic(III) tris (N,N-diethyl dithiocarbamate) [2] with
group 12 metals halides:
2.7.2.1 Reaction of compound [2] with zinc(II) iodide:
To a solution of 0.319 g (1.0 mmol) of zinc (II) iodide in 10 ml. of
mehtanol, another solution consisting of arsenic(III) tris (N,N-diethy
dithiocarbamate), 0.519 g ( 1.0 mmol), and 15.0 ml. of dichloromethane was
added with constant stirring. After the addition the schlenk tube was
connected to the vacuum line and the solution was concentrated by vacuum
pumping.
After the passage of 24 hours the tertiary arsine ligand was recovered
unreacted as its melting point and analytical data were similar to those of the
original ligand.
2.7.2.2 Reaction of compound [2] with cadmium(II) iodide:
Methanolic solution of cadmium(II) iodide, 0.366 g (1.0 mmol), was
placed in a schlenk tube, facilitated with a stirring bar. To this solution
another solution of arsenic(III) tris (N,N-diethyl dithiocarbamate), 0.519 g
(1.0 mmol), was added with stirring. The reaction mixture was kept in the
cold overnight. The resulting yellow compound was isolated by filtration and
dried under vacuum.
The compound was identified by elemental analysis as cadmium(II)
iodo (N,N-diethyl dithiocarbamate), Cd I [CS2NEt2], mp: 248°C.
Analysis:
N%
C%
H%
found
3.9
16.0
2.5
Calculated for
3.6
15.6
2.5
C5H10CdINS2
2.7.2.3 Reaction of compound [2] with mercury (II) iodide:
Arsenic(III) tris (N,N-diethyl dithiocarbamate), 0.519 g(1.0 mmol),
dissolved in 10 ml. of dichloromethane, was added drop-wise to methanolic
solution of mercury(II) iodide, 0.454 g (1.0 mmol ), in a schlenk tube with a
stopper and a magnetic bar. After the addition was completed the reaction
mixture was stirred for few minutes and stored in the cold overnight. A
yellow crystalline compound was formed. This was filtred and dried under
vacuum; a second crop of crystals was obtained when the filtrate was kept for
several days in the cold. The overall yield was 70%, mp: 158°C.
As indicated by elemental analysis the compound was found to be
mercury(II) iodo (N,N-diethyl dithiocarbamate) complex.
Analysis:
N%
C%
H%
Found
2.9
13.5
2.4
Calculated for
2.9
12.6
2.1
C5H10HgINS2
2.7.2.4 Reaction of compound [2] with cadmium(II) bromide:
Arsenic(III) tris (N,N-diethyl dithiocarbamate), 0.519 g (1.0 mmol),
was dissolved in 20 ml. of dichloromethane and then transferred to a stirred
methanolic solution of cadmium(II) bromide, 0.272 g (1.0 mmol).The
resulting solution was stirred for few minutes and then the clear solution was
stored at 4˚C overnight.
A yellow compound was formed which was isolated by filtration,
washed with cold dichloromethane and vacuum dried, mp: 248°C.
The compound was shown to be cadmium(II) bromo (N,N-diethyl
dithiocarbamate) complex.
Analysis:
Complex
C5H10BrCdNS2
N%
C%
H%
Found Calc. Found Calc. Found Calc.
3.8
4.11
17.6
17.6
3.2
2.9
2.7.3 Reaction of antimony(III) tris (N,N-diethyl dithiocarbamate) [3]
with group 12 metals halides:
2.7.3.1 Reaction of compound [3] with zinc(II) iodide:
A dichloromethane solution of antimony(III) tris (N,N-diethyl
dithiocarbamate), 0.566 g (1.0 mmol), was added to a stirred concentrated
methanolic solution of zinc(II) iodide, 0.319 g (1.0 mmol), in 50 ml- schlenk
tube. A yellow compound was obtained upon standing which was isolated by
filtration and dried under vacuum.
Results of elemental analysis for C, N, and H are not consistent with
the expected pattern of reactivity of antimony(III) tris (N,N-diethyl
dithiocarbamate).
2.7.3.2 Reaction of compound [3] with cadmium(II) iodide:
Cadmium(II) iodide, 0.366 g (1.0 mmol), was dissolved in minimal
volume of absolute methanol in a schlenk tube fitted with stirring bar. To this
solution antimony(III) tris (N,N-diethyl dithiocarbamate), 0.566g (1.0
mmol), in 15 ml. of dichloromethane was transferred maintaining continuous
and rapid stirring of the tube contents.
The resulting solution was then allowed to stand overnight at 0°C. The
resulting compound was isolated by filtration as a yellow powder and dried
under vacuum, mp: 248-249°C.
The analytical data showed the compound to be cadmium(II) iodo
(N,N-diethyl dithiocarbamate) complex.
Analysis:
Found
Calculated for
C5H10CdINS2
N%
C%
H%
3.17
15.26
2.56
3.5
15.5
2.5
2.7.3.3 Reaction of compound [3] with mercury(II) iodide:
Antimony(III) tris (N,N-diethyl dithiocarbamate), 0.566 g ( 1.0 mmol),
was dissolved in 15 ml. of dichloromethane in a schlenk tube. Solid
mercury(II) Iodide, 0.45 g (1.0 mmol), was added with constant stirring till
all the mercuric iodide was dissolved, few millilitres of methanol were added
to induce crystallization. Yellow crystals were obtained upon standing for 24
hours in the cold. These were isolated by filtration and vacuum dried, mp:
158°C.
The complex was characterized by C, N, H elemental analysis as
mercury(II) iodo (N,N-diethyl dithiocarbamate ) complex.
Analysis:
Found
Calculated for
C5H10HgINS2
N%
C%
H%
2.76
12.70
2.3
2.9
12.61
2.1
2.7.3.4 Reaction of compound [3] with cadmium(II) bromide:
Antimony(III) tris (N,N-diethyl dithiocarbamate), 0.566 g (1.0 mmol),
was dissolved in 20 ml. of dichloromethane and then transferred to a stirred
methanolic solution of cadmium(II) bromide, 0.272 g (1.0 mmol),.The
resulting solution was stored at 4˚C overnight.
A yellow compound was formed which was isolated by filtration,
washed with cold dichloromethane and vacuum dried, mp: 248°C.
The compound was shown to be cadmium(II) bromo (N,N-diethyl
dithiocarbamate) complex.
Analysis:
Complex
C5H10BrCdNS2
N%
C%
H%
Found Calc. Found Calc. Found Calc.
3.8
4.11
17.6
17.6
3.2
2.9
2.7.4 Reactions of phosphorus(III) tris (N,N-dimethyl dithiocarbamate)
[4] with ZnI2, CdI2 and HgI2:
Under
dry
conditions,
phosphorus(III)
tris
(N,N-dimethyl
dithiocarbamate), 0.391g (1.0 mmol), was dissolved in 15 ml. of freshly
distilled chloroform in a dry 50 ml quick-fit schlenk tube fitted with
magnetic bar, a slow flow of dry argon was used throughout the course of the
reactions. This solution was transferred under argon pressure to another
solution of equimolar quantity of metal halide MI2 (where M= Zn, Cd, and
Hg) dissolved in minimal volume of methanol in another schlenk tube. After
the addition, the reaction mixture was stirred for a while and kept in a
refrigerator. Upon standing for at least 24 hours the resulting compounds
were isolated by filtration under argon using a glass fibre filter and dried
under vacuum.
The analytical and spectroscopic data of the resulting compounds were
in complete agreement with bis (N,N-dimethyl dithiocarbamate) complexes
of zinc(II), cadmium(II) and mercury(II), with the formula M[CS2N(CH3)2]2.
Analysis:
N%
Complex
C6H12N2S4Zn
C%
H%
found Calc. found Calc. found Calc. appearance MP.°C
8.82
9.11
23.45 23.50
4.32
3.95 White pwd
C6H12CdN2S4 7.14
7.35
19.0
18.9
3.45
3.15
,, pwd
298-299
C6H12HgN2S4 6.28
6.30
16.29
16.3
2.76
2.70
Yellow ,,
261
1
255
H-NMR spectrum for the Zn[CS2N(CH3)2]2 is recorded in chart [12]
page 66.
As Cd[CS2N(CH3)2]2 and Hg[CS2N(CH3)2]2 are not soluble in the
common solvents, NMR spectra were not recorded for these complexes.
2.7.5 Reaction of antimony(III) tris (N,N-diethyl amide) with copper(I)
iodide in 1:1 molar ratio:
Copper(I) iodide, 0.19 g ( 1.0 mmol), was weighed in the glove box
and placed in a perfectly dried 50 ml schlenk tube facilitated with a stirring
bar, the schlenk tube was then taken out of the glove box and connected to
the vacuum line and freshly distilled diethyl ether (25 ml) was added.
Equimolar quantity of antimony tris (N,N-diethyl amide) was syringed under
argon into the stirred suspension of copper(I) iodide in diethyl ether with
continuous vigorous stirring of the tube contents. Subsequently the reaction
mixture was stirred for about four hours. However, the same quantity of CuI
was recovered unreacted, indicating that the reaction did not occur.
This reaction was repeated several times using different organic
solvents such as dichloro methane, tetra hydrofuran, acitonitrile and ethanol
with reflux for many hours.
After each experiment copper(I) iodide was recovered unchanged and
similar to authentic sample of CuI.
2.7.6 Reaction of antimony(III) tris (N,N-diethyl amide) with silver(I)
iodide in 1:1 molar ratio:
Antimony(III) tris (N,N-diethyl amide), 1.0 mmol, was placed in a dry
50 ml schlenk tube facilitated with a stirring bar and mixed with 25 ml. of
diethyl ether. This solution was transferred under argon to another brown
schlenk tube containing solid silver(I) iodide, 0.23 g (1.0 mmol),. The
reaction mixture was then stirred overnight. No dissolution of AgI was
observed and the same quantity of the metal salt was recovered unchanged.
The reaction was carried out many times in different conditions using
other organic solvents including dichloromethane, chloroform, tetra
hydrofuran, acetonitrile and ethanol with reflux for a convenient time;
however in each time no reaction between AgI and the antimony amide was
observed.
Futile attempts were made to react antimony(III) tris (N,N-diethyl amide)
with CuCl and AgCl similar to that with CuI and AgI in different organic
solvents with stirring in the cold and under reflux.
CHAPTER THREE
RESULTS AND DISCUSSION
3.1 Preparation of phosphorus(III), arsenic(III), and antimony(III) tris
(N,N-dialkyl dithiocarbamate):
Dialkyldithiocarbamates of phosphorus (III) were prepared by the
reaction of the respective dialkyl amino phosphine with stoichiometric
amount of carbon disulphide in benzene in accordance with the following
equation:
P(NR2)3 + 3CS2
P(CS2NR2)3
(Where R=Me or Et)
Phosphorus (III) tris (N,N-dimethyl dithiocarbamate) was obtained as
extremely air-sensitive yellow powder which was identified by C, N, H
elemental analysis, 1H-NMR spectra, chart [1], and
31
P-NMR spectra ,chart
[2].
Phosphorus (III) tris (N,N-diethyl dithiocarbamate) was obtained as a
slightly golden cubic crystals which melted at 131°C ( lit. 130-131°C).(87)
The compound was characterized by C, N, H elemental analysis, 1H-NMR
spectra [chart 3], and
31
P-NMR spectra [chart 4]. The reactions probably
proceed by insertion of CS2 molecules across the P–N bond in two steps as
shown below:
P(NR2)3 + 2CS2
(R2N)P(CS2NR2)2
CS2
P(CS2NR2)3
A mechanism involving electrophilic attack by CS2 on the phosphorus
atom has been proposed as an initial step for this reaction: (91)
Arsenic (III) tris (N,N-diethyl dithiocarbamate) was prepared via
simultaneous mixing of arsenic trioxide, diethyl amine, and carbon
disulphide in water:
As2O3 + 6HNEt2 + 3CS2
2As(CS2NEt2)3 + 3H2O
As (CS2NEt2)3 was obtained as air stable yellowish crystals that melted
at 144°C (lit.144-145°C)
(85)
and was identified by C, N, H elemental
analysis, and 1H-NMR spectra [chart 5].
Antimony(III) tris (N,N-diethyl dithiocarbamate) was prepared via
simultaneous mixing of antimony trichloride, carbon disulphide, and diethyl
amine in carbon tetrachloride according to the following reaction:
SbCl3 + 6HNEt2 + 3CS2
Sb(CS2NEt2)3 + 3Et2NH.HCl
The formation of the amino derivative of antimony was proposed as an initial
step followed by insertion of carbon disulphide.(82)
The compound was obtained as air stable yellow shiny crystals that
melted at 110°C (lit. 109-110°C)(82) and was identified by C, N, H elemental
analysis, and 1H-NMR spectra [chart 6].
3.2 Reactions of tris dialkyl dithiocarbamates of phosphorus(III),
arsenic(III), and antimony(III) with the dihalides of group 12 (Zn, Cd
and Hg):
These reactions were conducted by directly adding the dithiocarbamate
ligand solution in dichloromethane to another solution of a stoichiometric
amount of metal halide dissolved in methanol; under anhydrous conditions
owing to the instability of some dithiocarbamate ligands and some metal
halides towards hydrolysis.
The reactions, instead of forming simple adducts, seem to proceed by
substitution of either one or both iodine atoms on metal atom by
dithiocarbamate ligands depending upon the reaction molar ratio. Thus the
reactions can be presented by the general equation:
(R2NCS2)3Y + MX2
2(R2NCS2)3Y + MX2
(R2NCS2)2YX + MX(CS2NR2)
(R2NCS2)2YX + M(CS2NR2)2
(Where Y=P, As or Sb; M=Zn, Cd, and Hg)
The molecular structure of the resulting M(CS2NR2)2 and
MX(CS2NR2) complexes was established by the following methods:
(I)
The elemental analysis of carbon, hydrogen, and nitrogen
(II)
1
H-NMR spectroscopy:
The 1H-NMR spectra of these complexes exhibited triplet and quartet
bands for protons of the corresponding methyl and methylene groups
respectively in the region of chemical shifts that have been previously
recorded for similar complexes.
(III) Single crystal x-rays diffraction: the full crystal structure of
cadmium (II) bis( diethyl dithiocarbamate) was established by
single crystal x-rays diffraction. The complex was recrystallized
from mixture of methanol and methylene chloride by standing
overnight at –12 C. The complex is binuclear; thus the molecule
should be formulated as [Cd2(S2CNEt2)4].(92) The two halves of the
binuclear molecule are related by a centre of symmetry as shown
below:
H
C
S
S
SS
Cd
3-
S
Cd
S
C
H
SS
C
S S+
H
+
S
S
Cd
3-
Cd
S
S
C
SS
H
Two of the four diethyl dithiocarbamate groups are acting as
bidentate ligands, and the other two as bridging ligands, giving rise to a
puckered eight-membered ring, comprising two cadmium, two carbon and
four sulphur atoms. The two symmetry-related cadmium atoms are fivecoordinate.
Zinc (II) bis (diethyl dithiocarbamate) was also structurally
characterized and found to be iso-structural with the cadmium analogue.(92)
The remaining solutions were evaporated to dryness and the existence
of YI(CS2NR2)2 was established from elemental analysis of iodine by
precipitation as silver(I) iodide.
The substitution of only one of three dithiocarbamate groups of the
Y(CS2NR2)3 (where Y= P, As, and Sb) seems reasonable and consistent with
the fact that in As (CS2NEt2)3 one of the As–S bond lengths of one
dithiocarbamate is significantly longer relative to the others.(91) Thus this
dithiocarbamate group is weakly bounded to the arsenic atom and can be
displaced by iodine atom, giving rise to the formation of the mono-iodide
compound, AsI(CS2NEt2)2.
The Person’s concept of hard-soft acids and bases seems to be
operative in the substitution reactions of the dithiocarbamate of group 15 and
the halides of group 12. The transition metal ions of Hg(II), Cd(II), and
Zn(II) are soft acids and tend to interact with the softer sulphur atom as base;
whereas the phosphorus atom, being the harder acid, interacts with the harder
iodine, the latter interacts as a base.
In line with this explanation, the reaction of arsenic(III) tris (N,Ndimethyl dithiocarbamate) with iodine gave a mono iodide complex and tetra
methyl thioraum disulphide according to the equation given below:(93)
S
(R2NCS2)As + I2
S
(R2NCS2)2AsI + R2N-C-S-S-C-NR2
Dialkyl dithiocarbamates of group 15 elements (P, As, and Sb) act as
ligands with two possible basic sites for coordination to metals; the lone pair
of electrons on group 15 element and those on the sulphur atom, in other
word the sulphur atom competes with the phosphorus in the coordination to
metals. Of these the coordination through the sulphur lone pair of electrons is
favoured. This could be attributed to the greater б-donation ability of sulphur
atom compared to group 15 element which could be explained by the
electronegativity difference between the two atoms.
The preference of metal-sulphur coordination can also be understood in
terms of the possibility of use of p- and d- orbitals of sulphur for both б- and
л-bond formation in the corresponding complexes.
The dithiocarbamate ligands can act as л-electrons acceptor because
they have two sulphur atoms with vacant 3d orbitals and л* molecular
orbitals which could overlap with filled d-orbital on the metal in d л – d л
interaction. The ability of dithiocarbamate ligands to act as л- acceptor is
supported by the possible existence of conjugation. (94)
As the electron – releasing ability of (-NR2) groups increases, the
electron density on the sulphur atom also increases, and consequently the
dithiocarbamate ligand becomes a weaker л- acceptor. The contribution of
this л-component to the total strength of the bond would depend mainly upon
two factors:
(a) The relative availability of d-electron pairs in metal atom containing a
complete sub-shell of 10 electrons (e.g. Zn(II), Cd(II), and Hg(II) ).
(b) The relative overlap of the two orbitals, which is dependent upon the
relative sizes of the metal and the ligand coordinating atom.
Strong dл – dл contribution requires a metal with filled d-orbital such
as Zn (II), Cd (II), and Hg (II) and a donor atom with vacant and fairly low
energy d-orbital such as sulphur. The stability of such complexes depends on
the strength of attachment of the ligand, the nature of the ligand donor atom
and the metal acceptor. Such bonding may be illustrated pictorially as:
+
+
M
+
δ
S
+
Overlap of metal filled d-orbital with sulphur empty d-orbital.
Tris (N,N-dialkyl dithiocarbamate) of phosphorous(III), arsenic(III) or
antimony(III) can be described as very bulky ligands and the congestion
around the bonding face of group 15 element is high. Thus their adduct
complexes with group 12 metals dihalides are expected to be very unstable
and dissociated extensively in solutions. The steric effect of large dialkyl
dithiocarbamate group in the ligands can have important electronic
consequences. For example, increasing the angles between substituents will
decrease the percentage of s-character in the lone pair of group 15 element.
This reason, among others, makes the σ-type bonding through (P, As or Sb)
uninvocable.
Generally the steric effect of tertiary phosphine ligands has been
investigated in much greater detail than any of its congeners. Tolman (95) has
made valuable attempts to establish an order of steric effect of a number of
tertiary phosphines; he found that the ability of phosphorus ligands to
compete for coordination position on Ni(0) could be explained in terms of
ligands size rather than their electronic character. Ni(0) complexes NiL4 and
various phosphine ligands (L') were equilibrated in toluene as follows:
NiL4 + 4L
NiL(4-n)Ln + nL
The extent of exchange was semi-quantitatively measured from the
relative intensities of free and bound ligand resonance in the
31
P-NMR
spectra of the equilibrated solutions and each ligand assigned a position in a
relative stability series. The order of ligand in the series is not correlated with
electronic properties of the phosphine ligand but does seem to bear some
resemblance to intuitive ideas of the steric size about the phosphine.
Tolman(95) used atomic models to construct molecular models, for
various phosphine ligands, based upon a Ni–P distance of 2.28A˚
and
determined the apex angle of the subtending cone which encloses the van
der waals radii of the outermost atoms of the ligand with free rotation about
the Ni–P bond. As shown below:
P
o
2.28 A
Ni
The ligand cone
The ligand cone angle θ, as a steric parameter of various ligands,
increases with increasing the size of substituents attached to phosphorus. The
value of the cone angle of a certain ligand can quantitatively be measured by
using molecular model of the ligand with a scale of 1.25 cm/A˚.
The cone angle θ of some common tertiary phosphine ligands are given
below :( 50)
Phosphine ligand
Cone angle
PH3
87˚
PF3
104˚
P(OMe)3
107˚
PMe3
118˚
P(OPh)3
121˚
PEt3
132˚
PPh3
145˚
PPr3i
160˚
PCy3
170˚
Pbu3t
182˚
P(o-tolyl)3
194˚
The cone angle values of group 15 elements dialkyl dithio carbamates
are expected to be large and comparable to that in PBu3t (θ = 182˚). Thus the
steric factor is anticipated to play a dominant role in coordination of these
dithiocarbamate ligands with transition metals such as Zn(II), Cd(II), and
Hg(II). This could explain that reactions, of dithiocarbamates of group 15 (P,
As, and Sb) with the dihalides of group 12 (Zn, Cd and Hg), proceed by
substitution and transfer of dithiocarbamate fragments to metals as complex–
formation through (P, As and Sb) to metals is sterically not allowed.
In further investigation(61), reaction of the bulky o-tolyl stibine (cone
angle = 194˚) with HgCl2 in tetrahydrofuran yields R2SbCl and RHgCl these
results were interpreted in terms of scrambling occurring via a five –
coordinate antimony labile intermediate formed via oxidative addition of the
stibine by HgCl2 as shown below:
HgCl
R3Sb + HgCl2
R
Sb(v) R
R
R2SbCl + RHgCl
Cl
(Where R=o-tolyl)
Reaction of phosphorus(III) dimethyl dithiocarbamate with HgX2
(where X = Cl, SCN) were carried out by Klein,(96) using ethanol as solvent.
These reactions proceed by transference of dithiocarbamate group from
phosphorus(III) dimethyl dithiocarbamate to transition metal ion giving rise
to the formation of Hg(CS2 NMe2)2. Since in this case the solvent was
ethanol, a mechanism involves ''alcholysis'' reaction of the phosphorus(III)
dimethyl dithiocarbamate was proposed:
(Me2NCS2)3P + Et-OH
2Me2NCS2H + HgX2
(Me2NCS2)2P-OEt + Me2NCS2H
Hg(CS2NMe2)2 + 2HX
3.3 Reaction of antimony(III) tris (N,N–diethyl amine) with copper (I)
and silver(I) halides:
The ligation capability of antimony(III) tris (N,N – diethyl amine)
towards group 11 metals has been investigated by reacting this ligand with
Cu(I) and Ag(I) halides inorder to isolate Lewis acid – base adduct
complexes.
These reactions were manipulated under an inert atmosphere of dry
oxygen–free argon by injecting the tertiary stibine ligand into a suspension of
Cu(I) and Ag(I) iodide in a suitable organic solvent. The starting materials of
these reactions are sensitive to air and moisture which could be attributed to
the rapid oxidation and disproportionation of copper(I) halides to Cu(II)
species and also to the high sensitivity of the ligand towards hydrolysis: (21)
2Sb(NEt2)3 + 3H2O
Sb2O3 + 6HNEt2
Many futile attempts were made to react antimony(III) tris (N,N –
diethyl amine) with copper(I) and silver(I) iodides in different solvents such
as diethyl ether, dichloromethane, tetrahydrofuran ......etc with stirring and
reflux for a convenient time. Under the various conditions attempted no
reaction was observed and the metal halides were recovered unchanged.
The inertness of copper(I) and silver(I) halides towards tris (N,N –
diethyl amine) stibine and the instability of their proposed complexes can be
attributed to the fact that for constant R the σ-donor power varies PR3>
AsR3>SbR3 therefore, tertiary stibines are, in general, poorer σ-donors
relative to its higher congeners. Additionally the base strength of antimony in
Sb(NEt2)3 is expected to decrease due to the electronegative –NR2
substituents as the interaction (2pπ–5dπ) of the lone pair of electrons on
nitrogen atom with empty d –orbital in antimony is not favoured owing to the
great difference in size of both orbitals.(50)
In contrast, the basicity of phosphorus(III) and arsenic(III) – nitrogen
compounds is enhanced relative to their alkyl derivatives by partial 2pπ–3dπ
and 2pπ–4dπ interaction for phosphorus and arsenic respectively; therefore
reactions for phosphorus(III) and arsenic(III) dialkyl amines with Cu(I) and
Ag(I) are facile and their reactivity can be best explained in terms of the
possibility of use of p and d–orbitals for both б- and π- bond formation in
their complexes.(97)
The coordination affinity of group 15 tertiary ligands towards Lewis
acids which have no d –electrons, such as boron halides, increases with
increasing the electronegativity, NR3>PR3>AsR3>SbR3, however in case of
coordination with metals to the right of the transition series such as Ni(II),
Cu(II), Ag(I), and Au(I) the bond strength depends upon the extent of both σand π-bondings, since group 15 tertiary ligands, with exception of nitrogen,
have vacant d-orbitals, being capable of interacting with filled d-orbitals of
the transition metal.
The coordination can then be thought of as having two components.
The primary component is σ–donation and the second component is back
donation from a filled metal d-orbital to an empty d-orbital on the ligand of
the same symmetry. The л–bonding in tertiary phosphines, as an example,
depends substantially on oxidation state and nature of the metal, and
Metal oxidation state
electronegativity of the substituents attached to phosphorus. (50)
Condition least
favorable for π-bonding
Condition most
favorable for π-bonding
0
But
R,Ph NR2 OR,Cl OPh CF3
Electronegativity
F
As electron-withdrawing (electronegative) groups are attached to
phosphorus, the σ–donation of the phosphine ligand tends to decrease. At the
same time, the electron density around phosphorus is lowered providing an
increase in back donation ability. Therefore phosphines can exhibit a range of
σ–donor and л–acceptor capabilities:
PR3 > PPh3 > P(OR)3 > P(OPh)3 > P(NR2)3 > PCl3 > PF3
Greater π− acidity
Greater δ − donation
The inertness of antimony (III) tris (N,N-diethyl amine), towards Ag(I)
and Cu(I) halides, can probably be explained in terms of steric effect of the
bulky –N(CH3CH2)2 substituents.
3.4 31P, 1H NMR spectra:
NMR- samples were prepared by dissolving 1 – 2 mg of the compound
in the suitable NMR deteurated solvent under argon inside a glove box or by
using a flow of argon. 1H-NMR spectra of ligands and complexes, in this
study, are routinely recorded and serve not only to characterize the
compounds, but also as reasonably simple purity check.
Chemical shifts are reported using ppm and referenced to the residual protons
of deteurated NMR-solvents.
Chart [1]: 1H-NMR spectrum of P(CS2NMe2 )3
1.000
SpinWorks 2.4:
PPM
7.2
6.8
6.4
6.0
file: C:\Dokumente und Einstellungen\Noor\Desktop\5\fid expt: <zg>
transmitter freq.: 250.131047 MHz
time domain size: 16384 points
width: 3030.30 Hz = 12.114862 ppm = 0.184955 Hz/pt
number of scans: 8
5.6
5.2
4.8
4.4
4.0
3.6
3.2
2.8
2.4
2.0
1.6
1.2
0.8
0.4
freq. of 0 ppm: 250.130000 MHz
processed size: 16384 complex points
LB: 0.000 GB: 0.0000
1
H-NMR spectrum of this compound was measured (CDCl3 solution)
and the chemical shifts were recorded on ppm using the residual proton
signal of the solvent as internal standard. The spectra showed a singlet band
for the protons of the corresponding methyl group.
Chart [2]: 31P-NMR spectrum of P(CS2NMe2)
SpinWorks 2.4:
x 1.000
400.0
PPM
360.0
340.0
320.0
300.0
file: C:\Dokumente und Einstellungen\Noor\Desktop\1\fid expt: <zgpg30>
transmitter freq.: 101.273087 MHz
time domain size: 41665 points
width: 45454.55 Hz = 448.831440 ppm = 1.090953 Hz/pt
number of scans: 126
31
280.0 260.0
240.0
390.0
220.0
380.0
200.0
180.0
370.0
160.0
140.0 120.0
100.0
80.0
60.0
40.0
20.0
0.0
-20.0
freq. of 0 ppm: 101.254355 MHz
processed size: 65536 complex points
LB: 1.000 GB: 0.0000
P-NMR spectrum of the complex showed a singlet for the lone
phosphorus atom.
Chart [3]: 1H-NMR spectrum of P(CS2NEt2 )3
PPM
7.2
6.8
6.4
6.0
5.6
file: C:\Dokumente und Einstellungen\Noor\Desktop\8\fid expt: <zg>
transmitter freq.: 250.131047 MHz
time domain size: 16384 points
width: 3030.30 Hz = 12.114862 ppm = 0.184955 Hz/pt
number of scans: 8
5.2
4.8
4.4
4.0
1.948
1.000
SpinWorks 2.4:
3.6
3.2
2.8
2.4
2.0
1.6
1.2
0.8
0.4
freq. of 0 ppm: 250.130000 MHz
processed size: 16384 complex points
LB: 0.000 GB: 0.0000
The 1H-NMR (CDCl3 solution) spectrum consists of a triplet at 1.25
ppm and a quartet at 3.82 ppm for the corresponding methyl and methylene
protons respectively.
Chart [4]: 31P-NMR spectrum of P(CS2NEt2)3
SpinWorks 2.4:
x 1.000
400.0
360.0
PPM
340.0
320.0
300.0
file: C:\Dokumente und Einstellungen\Noor\Desktop\1\fid expt: <zgpg30>
transmitter freq.: 101.273087 MHz
time domain size: 41665 points
width: 45454.55 Hz = 448.831440 ppm = 1.090953 Hz/pt
number of scans: 126
396.0
392.0
280.0 260.0
388.0
240.0
384.0
220.0
380.0
200.0
376.0
180.0
372.0
160.0
140.0 120.0
100.0
80.0
60.0
40.0
20.0
freq. of 0 ppm: 101.254355 MHz
processed size: 65536 complex points
LB: 1.000 GB: 0.0000
31
P-NMR spectrum of the compound showed a singlet at 392 ppm.
Chart [5]: 1H-NMR spectrum of As(CS2NEt2)3
0.0
-20.0
3.6
PPM
3.4
3.2
file: C:\Dokumente und Einstellungen\Noor\Desktop\2\fid expt: <zg>
transmitter freq.: 250.131047 MHz
time domain size: 16384 points
width: 3030.30 Hz = 12.114862 ppm = 0.184955 Hz/pt
number of scans: 8
3.0
1.456
1.000
SpinWorks 2.4:
2.8
2.6
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
freq. of 0 ppm: 250.130000 MHz
processed size: 16384 complex points
LB: 0.000 GB: 0.0000
1
H-NMR (CDCl3 solution) showed a quartet and a triplet (integration
2:3) corresponding to methylene and methyl protons respectively.
Chart [6]: 1H-NMR spectrum of Sb(CS2NEt2)3
0.6
6.8
PPM
6.4
6.0
5.6
5.2
4.8
4.4
4.0
file: C:\Dokumente und Einstellungen\Noor\Desktop\4\fid expt: <zg>
transmitter freq.: 250.131047 MHz
time domain size: 16384 points
width: 3030.30 Hz = 12.114862 ppm = 0.184955 Hz/pt
number of scans: 8
1.487
1.000
SpinWorks 2.4:
3.6
3.2
2.8
2.4
2.0
1.6
1.2
0.8
0.4
freq. of 0 ppm: 250.130000 MHz
processed size: 16384 complex points
LB: 0.000 GB: 0.0000
1
H-NMR (CDCl3 solution) showed a quartet and a triplet (intensities
2:3) for the protons of the corresponding methylene and methyl groups
respectively.
Chart [7]: 1H-NMR spectrum of LiNEt2
-0.0
PPM
3.6
3.4
3.2
file: C:\Dokumente und Einstellungen\Noor\Desktop\2\fid expt: <zg>
transmitter freq.: 250.131047 MHz
time domain size: 16384 points
width: 3030.30 Hz = 12.114862 ppm = 0.184955 Hz/pt
number of scans: 8
3.0
1.456
1.000
SpinWorks 2.4:
2.8
2.6
2.4
2.2
2.0
1.8
freq. of 0 ppm: 250.130000 MHz
processed size: 16384 complex points
LB: 0.000 GB: 0.0000
Chart [8]: 1H-NMR spectrum of Sb(NEt2 )3
1.6
1.4
1.2
1.0
0.8
0.6
PPM
6.8
6.4
6.0
5.6
file: C:\Dokumente und Einstellungen\Noor\Desktop\3\fid expt: <zg>
transmitter freq.: 250.131047 MHz
time domain size: 16384 points
width: 3030.30 Hz = 12.114862 ppm = 0.184955 Hz/pt
number of scans: 8
5.2
4.8
4.4
4.0
3.6
3.2
1.473
1.000
SpinWorks 2.4:
2.8
freq. of 0 ppm: 250.130000 MHz
processed size: 16384 complex points
LB: 0.000 GB: 0.0000
Chart [9]: 1H-NMR spectrum of Zn(CS2NEt2)2
2.4
2.0
1.6
1.2
0.8
0.4
6.8
PPM
6.4
6.0
file: C:\Dokumente und Einstellungen\Noor\Desktop\23\fid expt: <zg>
transmitter freq.: 250.131047 MHz
time domain size: 16384 points
width: 3030.30 Hz = 12.114862 ppm = 0.184955 Hz/pt
number of scans: 8
5.6
5.2
4.8
4.4
4.0
1.495
1.000
SpinWorks 2.4:
3.6
3.2
2.8
2.4
2.0
1.6
1.2
0.8
0.4
freq. of 0 ppm: 250.130000 MHz
processed size: 16384 complex points
LB: 0.000 GB: 0.0000
1
H-NMR (CDCl3 solution, solvent residual protons signal was used as
internal standard CDCl3 = 7.3 ppm) showed a quartet and a triplet (intensities
2:3 for the corresponding protons of methylene and methyl groups
respectively.
Chart [10]: 1H-NMR spectrum of Cd(CS2NEt2)2
6.8
PPM
6.4
6.0
file: C:\Dokumente und Einstellungen\Noor\Desktop\9\fid expt: <zg>
transmitter freq.: 250.131047 MHz
time domain size: 16384 points
width: 3030.30 Hz = 12.114862 ppm = 0.184955 Hz/pt
number of scans: 8
5.6
5.2
4.8
4.4
4.0
2.193
1.000
SpinWorks 2.4:
3.6
3.2
2.8
2.4
2.0
1.6
1.2
0.8
0.4
freq. of 0 ppm: 250.130000 MHz
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LB: 0.000 GB: 0.0000
1
H-NMR (CDCl3 solution) consists of a quartet and a triplet for the
corresponding methylene and methyl protons respectively.
Chart [11]: 1H-NMR spectrum of Hg(CS2NEt2)2
7.2
PPM
6.8
6.4
6.0
file: C:\Dokumente und Einstellungen\Noor\Desktop\26\fid expt: <zg>
transmitter freq.: 250.130013 MHz
time domain size: 16384 points
width: 7575.76 Hz = 30.287279 ppm = 0.462388 Hz/pt
number of scans: 8
5.6
5.2
4.8
4.4
4.0
1.551
1.000
SpinWorks 2.4:
3.6
3.2
2.8
2.4
2.0
1.6
1.2
0.8
0.4
-0.0
-0.4
-0.8
freq. of 0 ppm: 250.130000 MHz
processed size: 16384 complex points
LB: 0.000 GB: 0.0000
1
H-NMR spectrum for Hg(CS2NEt2)2 is run (CDCl3 solution) consists
of a quartet at 4.2 ppm and a triplet at 1.8 ppm (integration 2:3) for the
corresponding methylene and methyl protons respectively.
Chart [12]: 1H-NMR spectrum of Zn(CS2NMe2)2
-1.2
1.000
SpinWorks 2.4:
7.6
PPM
7.2
6.8
6.4
6.0
file: C:\Dokumente und Einstellungen\Noor\Desktop\25\fid expt: <zg>
transmitter freq.: 250.130013 MHz
time domain size: 16384 points
width: 7575.76 Hz = 30.287279 ppm = 0.462388 Hz/pt
number of scans: 8
5.6
5.2
4.8
4.4
4.0
3.6
3.2
2.8
2.4
2.0
1.6
1.2
0.8
0.4
-0.0
freq. of 0 ppm: 250.130000 MHz
processed size: 16384 complex points
LB: 0.000 GB: 0.0000
1
H-NMR spectrum for the Zn[CS2N(CH3)2]2 (CDCl3 solutions) was
recorded in ppm and showed a singlet band for the corresponding methyl
groups
3.5 Conclusion:
Reactions of group 15 dialkyl dithiocarbamates with the halides of
group 12 divalent metals were investigated. These reactions can be classified
as substitution reactions and proceed by substitution of either one or both
halogen atoms on metal atom by dithiocarbamate ligands. The bulkiness of
the dialkyl dithiocarbamates may be the principal factor in deriving the
reactions to proceed by substitution excluding the formation of simple
adducts.
Two main substitution products of the formula: M(CS2NR2)2 and
MX(CS2NR2) ( where M=Zn, Cd and Hg; X=Cl, Br and I; R= Me and Et)
were isolated which was characterized by elemental analysis, 1H,
31
P NMR
spectroscopy and fortunately complete x-ray diffraction studies for two
representitve compounds; Zn(CS2NEt2)2 and Cd(CS2NEt2)2.
The other substitution products of the formula: XY(CS2NR2)2 ( where
Y=P, As or Sb) were identified by the elemental analysis for iodine.
The results of this study are consistent with the cone angle theory and Person
theory for hard and soft acids and bases and can serve as reasonable
alternative methods for synthesis of other metal dialkyl dithiocarbamates that
have potential catalytic activity or biological importance.
Further investigation in this field of study is suggested inorder to shed
more light on the role of electronic and steric factors in Lewis acid-base
reactions pathways.
References
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