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Synthesis of Cyclopentadienyl Iron Alkoxycarbene Complexes via
Vinylidene Intermediates: X-ray Structures of
[Fe{C(OMe)Me}(dppe)Cp][I] and [Fe{C(CH2)3O}(dppe)Cp][PF6]
Sarah El-Tarhuni,a Letícia M. Manhães,a Charlotte Morrill,a James Raftery,a Jaskirit K.
Randhawaa and Mark W. Whiteleya*
a
School of Chemistry, University of Manchester, Manchester M13 9PL, UK
Corresponding Author. Email [email protected]
Tel. +441612754634
Abstract
The reaction of [FeI(dppe)Cp], 1 (dppe = Ph2PCH2CH2PPh2) with HC≡CSiMe3 in refluxing
methanol results in formation of a mixture of the vinylidene complex [Fe(=C=CH2)(dppe)Cp]+,
2 and the heteroatom stabilised alkoxycarbene [Fe{C(OMe)Me}(dppe)Cp]+, 3. The carbene 3 is
formed by addition of the alcohol solvent to the reaction intermediate vinylidene 2, and
prolonged reflux in methanol (4 days) resulted in complete conversion of 2 to 3. The
methoxycarbene, 3 was isolated as a stable solid and fully characterised by spectroscopic and
structural methods. Vinylidene 2 also reacts with ethanol to give the ethoxycarbene
[Fe{C(OEt)Me}(dppe)Cp]+, 4 but no reaction was observed in refluxing isopropanol, thus
providing a specific synthesis of vinylidene 2 from 1 and HC≡CSiMe3. An example of an
alcohol based, intramolecular nucleophilic addition to a mono-substituted vinylidene
[Fe(=C=CHR)(dppe)Cp]+ was uncovered in the reaction of 1 with 3-butyn-1-ol which leads to
the synthesis of the cyclic oxacarbene complex [Fe{C(CH2)3O}(dppe)Cp][PF6], 5. X-ray
crystallographic investigations on 3[I] and 5[PF6] determine Fe-Cα bonds lengths of 1.851(5)
and 1.834(2) Å respectively, intermediate between previously reported Fe-Cα distances for
the
amino
carbene
[Fe{C(NH2)Me}(dppe)Cp][PF6]
and
[Fe{=C(H)Me}(dppe)Cp*][PF6].
Keywords
Iron; Vinylidene; Nucleophilic addition; Alcohol; Alkoxycarbene
1
the
alkylidene
complex
Introduction
Metal cumulenylidene complexes have important applications as intermediates in the
functionalization of terminal alkynes [1]. Experimental and theoretical investigations
demonstrate that the regioselectivity of nucleophilic and electrophilic addition to vinylidene
[2,3], allenylidene [4,5] and higher cumulenylidene [6] ligands can be controlled to give a wide
range of products.
Nucleophilic addition at the alpha carbon of a metal vinylidene complex is a well-established
process and reactions with a range of nucleophiles have been investigated [2,7,8]. A frequently
employed protocol involves reaction of a metal halide M-X with a terminal alkyne HC≡CR in an
alcohol solvent R’OH to give the vinylidene intermediate [M(=C=CHR)]+ followed by addition
of R’OH to the vinylidene C=C bond to give the heteroatom-stabilised, Fischer carbene type
complex [M{C(OR’)CH2R}]+ [9-16]. Investigations where M = RuL2Cp (L2 = dppe or 2PPh3)
or RuL2(η-indenyl) (L2 = dppe, 2PPh3, or PPh3/ P(OEt)3) indicate that the process is sensitive to
both steric and electronic factors and is promoted by low steric demand of M, R and R’ and by
electron poor M and R centres which enhance electron deficiency at the vinylidene Cα carbon.
In view of the established reactivity of ruthenium complexes [Ru(=C=CHR)L2(η-L’)]+ (L’ = Cp
or indenyl) towards solvent-based nucleophilic addition, the very limited development of an
analogous chemistry of the corresponding iron system [Fe(=C=CHR)L2Cp]+ (L2 = P-donor
ligand) is surprising. Mixed carbonyl phosphine derivatives [Fe(=C=CHR)(CO)(PPh3)Cp]+ do
react with R’OH [11] and the dppm (dppm = Ph2PCH2PPh2) substituted vinylidene complex
[Fe(=C=CH2)(dppm)Cp]+
has
been
reported
to
react
with
methanol
to
give
[Fe{C(OMe)Me}(dppm)Cp]+ although, to our knowledge, supporting data were not provided
[17]. Very recently, addition of NH3 to [Fe(=C=CH2)(dppe)Cp]+ to give the amino carbene
[Fe{C(NH2)Me}(dppe)Cp]+ has been described [8] but an analogous direct reaction of
[Fe(=C=CHR)(dppe)Cp]+ and related disubstituted vinylidene derivatives with R’OH or water is
reported not to proceed [18, 19].
In this article, we demonstrate that in fact, in very specific cases, vinylidene complexes of the
type [Fe(=C=CHR)(dppe)Cp]+ can be induced to undergo addition at Cα with R’OH based
2
nucleophiles
to
give
synthetically
useful
[20],
heteroatom
stabilised
carbenes
[Fe{C(OR’)CH2R}(dppe)Cp]+, albeit with much reduced reactivity by comparison with Ru
analogues.
Results and discussion
1. Synthetic Studies.
In view of the steric constraints to the addition of alcohols R’OH to vinylidenes
[Fe(=C=CR2)(dppe)Cp]+, the search for a stable alkoxycarbene derivative of the Fe(dppe)Cp
system commenced with an investigation of the reaction of MeOH with the unsubstituted
vinylidene [Fe(=C=CH2)(dppe)Cp]+ (2). Several protocols for the synthesis of 2 have been
developed [18, 21, 22], including the reaction of [FeCl(dppe)Cp] with HC≡CSiMe3 in an
alcohol solvent [22]. In the initial investigation [Fe(=C=CH2)(dppe)Cp][PF6] was reported to be
formed in high yield from the reaction of [FeCl(dppe)Cp] with HC≡CSiMe3 in MeOH [22a]
although a later, independent synthesis employed ButOH as solvent with the explicit purpose of
impeding the formation of an alkoxycarbene by-product [22b]. The reaction of [FeCl(dppe)Cp*]
with HC≡CSiMe3 in refluxing MeOH has also been investigated [23] but again, only the
vinylidene [Fe(=C=CH2)(dppe)Cp*][PF6] was isolated, consistent with the increased steric
demand of the Cp* ring.
The reaction of [FeI(dppe)Cp] (1) [24], with HC≡CSiMe3 and K[PF6] in refluxing methanol
(Scheme 1) was allowed to progress for 3 hours following which the initially brown reaction
mixture had changed to orange-red in colour. A sample of the product was isolated as an orange
solid and spectroscopic characterisation by 1H, 31P{1H} NMR and mass spectrometry confirmed
the successful formation of 2 (identified by comparison with previously reported data).
However, in addition to the spectroscopic data characteristic of vinylidene 2, the isolated
reaction product contained a second, unidentified complex, most apparent in the 31P{1H} NMR
spectrum recorded in CD2Cl2 as a singlet resonance at 113.3 ppm. To explore the possible
involvement of this unidentified complex in an extended reaction sequence, the methanol reflux
was continued with periodic monitoring of the reaction mixture by 31P{1H} NMR spectroscopy.
After a total reflux time of 4 days, the 31P{1H} resonance at 97.1 ppm for vinylidene complex 2
3
was totally absent and only the resonance at 113.3 ppm associated with the unknown remained.
The reaction product was isolated as a yellow solid and was identified by subsequent
spectroscopic and structural (see below) characterisation as the iodide salt of the target
methoxycarbene complex [Fe{C(OMe)Me}(dppe)Cp][I] (3). The formulation as a carbene
complex is supported by a triplet resonance in the 13C{1H} NMR spectrum at 321.6 ppm for the
Cα carbene carbon (shifted to high field by comparison with Cα of vinylidene 2, δ 13C{1H} 354.7
ppm [22]) and by the appearance of resonances at 59.6 and 42.7 ppm consistent with the OMe
and Me substitutents respectively of the methoxycarbene ligand. The low field shift of 16 ppm
in the 31P{1H} spectrum on conversion of 2 to 3 is closely comparable to the equivalent shift for
the Cp* analogues [Fe(=C=CH2)(dppe)Cp*][PF6] and [Fe{C(OMe)Me}(dppe)Cp*][PF6] (δ
31
P{1H}, 90.7 (CDCl3) and 111.9 (CD2Cl2) ppm respectively) [23,25].
Scheme 1: Reagents and conditions (i) HC≡CSiMe3/K[PF6], reflux in R’OH (R’ = Me, Et, Pri),
3 h.; (ii) prolonged reflux in MeOH or EtOH; (iii) HC≡CCH2CH2OH/K[PF6], reflux in MeOH,
2 h.
4
The isolation of 3 principally as an iodide salt rather than as a hexafluorophosphate salt was
unexpected given the inclusion of excess K[PF6] in the reaction mixture. However the iodide salt
3[I] was obtained in two independent ‘one-pot’ preparations and the presence of the iodide
counter-ion was inferred from microanalytical data for iodine and phosphorus (see experimental
section) and was further confirmed by an X-ray structural investigation. Moreover, under similar
reaction conditions (see below), the vinylidene complex 2 was also isolated as an iodide salt
starting from [FeI(dppe)Cp], HC≡CSiMe3 and K[PF6]. As reported previously [8], use of
[NH4][PF6] as an alternative source of the hexafluorophosphate counter-ion led to the formation
of small quantities of the aminocarbene [Fe{C(NH2)Me}(dppe)Cp]+ as a reaction by-product.
However by-products resulting from the iodide-promoted dealkylation of an alkoxycarbene [26,
27] were not observed in the synthesis of 3[I].
The conversion of vinylidene 2 to methoxycarbene 3 represents a new reaction type in the
Fe(dppe)Cp system. However the rate of reaction is very slow (even with the low steric
protection afforded to Cα by the H substituents at Cβ of 2). By comparison [Ru(=C=CH2)L2Cp]+
(L2 = 2PPh3 or dppe) are reported to react rapidly with methanol under mild conditions [12]. To
examine the extent of the reactivity exhibited by [Fe(=C=CH2)(dppe)Cp]+ towards R’OH, the
effect of variation of R’ was investigated. An isolated sample of vinylidene 2 was dissolved in
EtOH and refluxed for 24 h. Subsequent work up led to the isolation of a mixture of unreacted 2,
and the new ethoxycarbene complex [Fe{C(OEt)Me}(dppe)Cp]+, (4); partial separation was
achieved by fractional recrystallization from CH2Cl2/ diethyl ether from which 4 was
precipitated preferentially as the first fraction. The identity of 4 as an ethoxycarbene complex
was confirmed by a triplet resonance in the 13C{1H} NMR spectrum at 321.5 ppm for the Cα
carbene carbon, by the appearance of resonances at 70.3, 12.9 ppm and 43.7 ppm consistent with
the OEt and Me substitutents respectively of the ethoxycarbene ligand and by a characteristic
low field shift in the 31P{1H} NMR resonance (113.6 ppm). However when the reaction of 1
with HC≡CSiMe3 was carried out in 2-propanol, a clean sample of vinylidene 2 was isolated (as
the iodide salt [Fe(=C=CH2)(dppe)Cp][I]) with no evidence observed for the formation of a
secondary alkoxycarbene product. The use of 2-propanol as reaction solvent therefore provides a
reliable protocol for the synthesis of pure samples of vinylidene complex 2 from 1; as discussed
above, an equivalent reaction of [FeCl(dppe)Cp] with HC≡CSiMe3 in ButOH is also reported to
give only vinylidene 2 in high yield [22b].
5
Our attempts to isolate an alkoxycarbene derivative from the extended reaction (18 hours) of the
monosubstituted vinylidene [Fe(C=CHPh)(dppe)Cp][PF6] with refluxing MeOH have been
unsuccessful although mass spectrometry of the isolated product revealed a weak peak with m/z
= 653, consistent with formation of the known complex [Fe{C(OMe)Ph}(dppe)Cp]+, [28]. An
alternative strategy to facilitate the conversion of a monosubstituted vinylidene to an
alkoxycarbene is the promotion of an intramolecular process involving the formation of a
hydroxyvinylidene intermediate [M{=C=CH(CH2)nOH}]+ which subsequently undergoes
intramolecular addition at Cα to give a cyclic oxacarbene product [27, 29-31]. This method has
proved to be effective even at the electron-rich Mo(dppe)(η-C7H7) centre where the large
cycloheptatrienyl ring affords additional steric protection to the vinylidene alpha carbon atom
[30]. The reaction of [FeI(dppe)Cp] with 3-butyn-1-ol, HC≡C(CH2)3OH, in refluxing methanol
in the presence of K[PF6] resulted in a rapid colour change (15 min.) from brown to pale yellow
and subsequent work up led to the isolation of the 2-oxacyclopentylidene (ocp) complex
[Fe{C(CH2)3O}(dppe)Cp][PF6], (5). The carbene character of complex 5 is implicit in the
observation of a triplet resonance at 313.0 ppm for Cα in the 13C{1H} NMR spectrum and the
molecular structure was confirmed by a single crystal X-ray structure determination (see below).
2. X-Ray Structural Investigations
Although a wide range of carbene complexes supported by Ru(dppe)Cp and Ru(PPh3)2Cp
auxiliaries has been structurally characterised, [13, 32-35], structural investigations of analogues
based on the Fe(dppe)Cp’ (Cp’ = Cp or Cp*) system appear to be restricted to
[Fe{C(NH2)Me}(dppe)Cp][PF6],
[8]
and
the
alkylidene
complex
[Fe{=C(H)Me}(dppe)Cp*][PF6], [25]. The X-ray crystal structures of the oxygen heteroatomstabilised carbene complexes 3[I] and 5[PF6] have therefore been determined and important
bond lengths and angles are summarised in Table 1 together with comparative data for related
cyclopentadienyl iron and ruthenium carbene complexes. The molecular structures of 3[I] (as a
CH2Cl2 solvate) and 5[PF6], annotated with atomic numbering schemes are shown in Figures 1
and 2 respectively.
6
Figure 1. Molecular structure of 3[I].CH2Cl2 with thermal ellipsoids plotted at 50% probability.
Figure 2. Molecular structure of 5[PF6] with thermal ellipsoids plotted at 50% probability.
7
Table 1: Key structural data for carbene complexes [M{C(ER’x)R}L2Cp’]+
3[I]
Complex
ML2Cp’
Fe(dppe)Cp
C(ER’x)R
C(OMe)Me
Bond Lengths (Å)
M-Cα
1.851(5)
5[PF6]
Fe(dppe)Cp
ocp a
Cα-E
1.333(6)
1.328(2)
Cα-C(R)
1.495(7)
1.518(3)
M-P
2.1859(12)
2.1991(13)
2.1924(6)
2.2028(6)
1.834(2)
Bond Angles (°)
M-Cα-E
119.0(3)
123.72(14)
M-Cα-C(R)
126.9(4)
129.29(16)
E-Cα-C(R)
114.0(4)
106.92(17)
Data
This work
This work
a ocp
Fe(dppe)Cp
C(NH2)Me
Fe(dppe)Cp*
C(H)Me
Ru(PPh3)2Cp
C(OMe)Me
Ru(dppe)Cp
ocp a
1.9272(15)
1.9251(15)
1.312(2)
1.310(2)
1.518(2)
1.519(2)
2.1756(4)
2.1829(4)
2.2032(4)
2.1860(4)
1.787(8)
1.931(9)
1.92(1)
-
1.321(9)
1.32(1)
1.49(1)
1.50(1)
1.51(1)
2.221(2)
2.239(7)
2.333(2)
2.336(2)
2.267(3)
2.273(3)
128.32(11)
128.61(12)
122.21(11)
121.78(11)
109.4(1)
109.5(1)
ref.8
-
120.9(6)
126.5(7)
141.3(6)
124.8(7)
127.1(8)
-
114.3(8)
106.3(9)
ref. 25
ref. 32
ref. 35
= 2-oxacyclopentylidene
8
The character of the iron to C-alpha bond in a series of alkylidenes and heteroatom (E) stabilised
carbenes has been the focus of a series of theory investigations on complexes of the type
[Fe{C(ER’x)R}L2Cp]+ [36,37]. There is a clear correlation between the extent of heteroatom
stabilisation and the length of the iron to C-alpha bond; heteroatom stabilisation leads to a longer
metal to carbene carbon distance as the acceptor character of the carbene ligand is reduced. The
data in Table 1 permit a direct experimental confirmation of these investigations. The alkylidene
complex [Fe{=C(H)Me}(dppe)Cp*][PF6] exhibits a short Fe-Cα distance (1.787(8) Å), similar
to that reported for the vinylidene [Fe(=C=CH2)(dppe)Cp*][PF6] (1.763(7)Å, [38]) and
consistent with a significant degree of multiple bond character in the Fe-Cα bond. By contrast
the amino carbene ligand of [Fe{C(NH2)Me}(dppe)Cp][PF6] represents the opposite extreme of
the range with a Fe-Cα distance of 1.9272(15), 1.9251(15) Å consistent with extensive N=Cα
double bond character in the heteroatom stabilised carbene and a Fe-Cα bond with little, if any
multiple character [8]. The Fe-Cα distances for 3[I] and 5[PF6] (1.851(5), 1.834(2) respectively)
lie intermediate between the two previously reported examples and agree well with the
computed value of 1.873 Å determined for [Fe{C(OMe)Me}(CO)(PMe3)Cp]+ [36]. The Fe-Cα
distances of 3[I] and 5[PF6] indicate that the oxygen heteroatom stabilised carbene ligands are
also relatively poor acceptor systems with a large contribution from a O=Cα double bond in the
overall structure. In addition to Fe-Cα and O-Cα distances, the Fe-P bond lengths provide an
indirect indicator of the character of the Fe-Cα bond by acting as a monitor of electron density at
the Fe centre. For the alkylidene complex [Fe{=CH(Me)}(dppe)Cp*][PF6], the average Fe-P
distance is 2.23 Å; this quite long bond reflects a reduction in Fe to P back bonding effects as
electron density at the Fe centre is depleted by the strongly accepting alkylidene ligand. By
contrast, average Fe-P distances in the heteroatom stabilised carbene complexes (2.193, 2.198,
2.187 Å for 3[I], 5[PF6] and [Fe{C(NH2)Me}(dppe)Cp][PF6] respectively) are much shorter,
consistent with enhanced Fe-P back bonding and a corresponding reduction in the electron
acceptor capacity of the heteroatom stabilised carbenes. Finally the geometry of the
{C(OMe)Me} and ocp ligands in 3[I] and 5[PF6] may be compared with Ru analogues. With the
obvious exception of M-Cα bond lengths, the bond lengths and angles defining the
alkoxycarbene ligands compare very closely with the corresponding parameters in the analogous
Ru complexes (see Table 1).
9
Conclusions
The nucleophilic addition of alcohols R’OH to Cα of group 8 metal, half-sandwich vinylidene
complexes [M(=C=CHR)L2(η-L’)]+ (M = Fe, Ru, Os) to give heteroatom stabilised
alkoxycarbene products [M{C(OR’)CH2R}L2(η-L’)]+ is controlled by a complex interplay of
steric and electronic factors and dependent upon all the variables M, R, R’, L and L’[11-16, 39].
Where L2 = dppm, dppe or 2PPh3, successful reactions are generally limited to less sterically
demanding options (R = H, R’ = Me, Et) but, as highlighted in the current report, the contrast in
reactivity between cyclopentadienyl iron and ruthenium analogues is quite marked. Thus for iron
complexes [Fe(=C=CHR)L2Cp]+ (L2 = dppm [17], dppe) observation of this reactivity type is
currently limited essentially to R = H, R’ = Me, Et with a prolonged reaction time required
where L2 = dppe. By contrast Ru analogues [Ru(=C=CHR)L2Cp]+ (L2 = dppe, 2PPh3) either
react much more rapidly (R = H, R’ = Me) or show an extended reactivity pattern (R = Me, Ph,
CO2Me, R’ = Me).
The
X-ray
structural
characterisations
of
[Fe{C(OMe)Me}(dppe)Cp][I],
3[I],
and
[Fe{C=C(CH2)3O}(dppe)Cp][PF6], 5[PF6], complete a dataset that permits examination of the
structural differences arising from transition of the series alkylidene, alkoxycarbene,
aminocarbene, against a common support unit. The elongation in the Fe-Cα distance along the
series [Fe{=C(H)Me}(dppe)Cp*][PF6], (1.787(8) Å), [Fe{C(OMe)Me}(dppe)Cp][I], (1.851(5)
Å) and [Fe{C(NH2)Me}(dppe)Cp][PF6], (1.9272(15), 1.9251(15) Å) is consistent with a
reduction in the metal to carbene π-interaction and an increased degree of heteroatom to Cα
multiple bond character.
10
Experimental
General Procedures.
The preparation, purification and reactions of the complexes described were carried out under
dry nitrogen. All solvents were dried by standard methods, distilled and deoxygenated before
use. NMR spectra were recorded on a Bruker Avance III HD (500 MHz 1H, 125 MHz 13C{1H},
202 MHz 31P{1H}) spectrometer. Infrared spectra (solid state) were obtained on a Nicolet iS5
FT-IR spectrometer fitted with an ATR attachment. Electrospay mass spectra were obtained on a
Waters SQD2 instrument and MALDI mass spectra were recorded using a Shimadzu Axima
Confidence spectrometer. Microanalyses were conducted by the staff of the Microanalytical
Service of the School of Chemistry, University of Manchester.
Preparation of [Fe(=C=CH2)(dppe)Cp][I], 2[I]
A solution of [FeI(dppe)Cp] (0.75 g, 1.16 mmol), trimethylsilylacetylene (0.57 g, 5.80 mmol)
and K[PF6] (0.43 g, 2.32 mmol) in isopropanol (40 cm3) was refluxed with stirring for 3h to
give a dark red solution. Reduction of solvent volume in vacuo and cooling resulted in
precipitation of the crude product which was recrystallized from dichloromethane/diethyl
ether to give the product 2[I].CH2Cl2 as a red solid; yield 0.21 g (24%). 1H NMR (CDCl3): δ
3.08, 3.11 (br, 4H, CH2, dppe), 3.92 (t, J(P-H) 3Hz, 2H, C=CH2), 4.93 (s, 5H, Cp), 7.18, 7.41,
7.47 (m, 20H, Ph, dppe). 31P{1H} NMR (CDCl3): δ 97.1. IR: (solid state) ν(C=C)/cm-1, 1624.
MALDI/MS (m/z): 545 [M]+. Anal. 2[I].CH2Cl2: Calcd. (%) for C33H31P2FeI.CH2Cl2: C, 53.9;
H, 4.4; P, 8.2; I, 16.8. Found, C, 54.8; H, 4.6; P, 8.7; I, 14.3. Anal. 2[I] (after recrystallization
from acetone/ether): Calcd. (%) for C33H31P2FeI: C, 58.9; H, 4.6. Found, C, 58.4; H, 4.5.
Preparation of [Fe{C(OMe)Me}(dppe)Cp][I], 3[I]
A solution of [FeI(dppe)Cp] (4.48 g, 6.93 mmol), trimethylsilylacetylene (3.20 g, 32.7 mmol)
and K[PF6] (2.51 g, 13.6 mmol) in methanol (100 cm3) was refluxed with stirring for 4 days
to give an orange solution. Methanol was removed in vacuo and the residue was
recrystallized from CH2Cl2/diethylether to give 3[I].CH2Cl2 as a bright yellow solid; yield
1.65 g (30%). 1H NMR (CD2Cl2): δ 2.43 (s, 3H, Cα-Me), 2.66 (s, 3H, Cα-OMe), 2.80 (br, 2H,
11
CH2, dppe), 2.96 (br, 2H, CH2, dppe), 4.48 (s, 5H, Cp), 7.10, 7.37, 7.45, (m, 20H, Ph, dppe).
13
C{1H} NMR (CD2Cl2): 321.6 (t, JC-P 27 Hz), Cα; 139.6, m, 134.8, m, Phi; 131.9, m, 130.5,
m, Pho; 130.8, s, 130.2, s, Php; 129.0, m, 128.9, m, Phm; 87.1, s, Cp; 59.6, s, Cα-OMe; 42.7, s,
Cα-Me; 29.8, m, CH2 (dppe). 31P{1H} NMR (CD2Cl2): δ 113.3. IR: (solid state) ν(C-O)/cm-1,
1222,
1172.
ES(+)/MS
(m/z):
577
[M]+.
Anal.
3[I].CH2Cl2:
Calcd.
(%)
for
C34H35P2OFeI.CH2Cl2: C, 53.2; H, 4.7. Found, C, 53.0; H, 4.6. A small sample of 3[I].CH2Cl2
was dissolved in acetone (in which it was only sparingly soluble) and precipitated with
diethylether to give 3[I] free from CH2Cl2 of crystallisation. Anal. 3[I]: Calcd. (%) for
C34H35P2OFeI: C, 58.0; H, 5.0; P, 8.8; I, 18.0; Found, C, 57.2; H, 5.3; P, 7.7; I, 15.2.
Preparation of [Fe{C(OEt)Me}(dppe)Cp][I], 4[I]
A solution of [Fe(=C=CH2)(dppe)Cp][I], 2[I], (0.15 g, 0.22 mmol), in ethanol (40 cm3) was
refluxed with stirring for 24 h. Ethanol was removed in vacuo and the residue was
recrystallized from CH2Cl2/diethylether. The first precipitate was collected as a yellow solid
and recrystallized a second time from CH2Cl2/diethylether to give 4[I] as a bright yellow
solid; yield 0.02 g (13%). 1H NMR (CD2Cl2): δ 0.27 (br, 3H, Cα-OCH2Me), 2.51 (s, 3H, CαMe), 2.93 (br, 2H, Cα-OCH2Me), 2.84 (br, 2H, CH2, dppe), 2.98 (br, 2H, CH2, dppe), 4.47 (s,
5H, Cp), 7.09, 7.36, 7.45, (m, 20H, Ph, dppe). 13C{1H} NMR (CD2Cl2): 321.5 (t, JC-P 27 Hz),
Cα; 139.8, m, 134.5, m, Phi; 132.2, m, 130.5, m, Pho; 130.9, s, 130.1, s, Php; 129.0, m, 128.9,
m, Phm; 87.1, s, Cp; 70.3, s, Cα-OCH2Me; 43.7, s, Cα-Me, 12.9, Cα-O-CH2Me; 29.8, m, CH2
(dppe). 31P{1H} NMR (CD2Cl2): δ 113.6. ES(+)/MS (m/z): 591 [M]+.
Preparation of [Fe{C(CH2)3O}(dppe)Cp][PF6], 5[PF6]
A solution of [FeI(dppe)Cp] (0.75 g, 1.16 mmol), 3-butyn-1-ol (0.41 g, 5.86 mmol) and K[PF6] (
0.43 g, 2.32 mmol) in methanol (40 cm3) was refluxed with stirring for 2h resulting in the
precipitation of a bright yellow solid. The solution was then cooled and reduced to half of its
volume in vacuo and the resulting precipitate collected. The crude product was recrystallized
from dichloromethane/diethylether, then acetone/diethylether to give the product 5[PF6], as a
bright yellow solid; yield 0.40 g (47%). 1H NMR (CD2Cl2): δ 1.11 (br, 2H, Hγ), 2.72 (br, 2H,
CH2, dppe), 2.99 (br, 2H, CH2, dppe), 3.20 (br, 4H, Hβ, Hδ), 4.53 (s, 5H, Cp), 7.11, 7.37, (m,
12
20H, Ph, dppe). 13C{1H} NMR (CD2Cl2): 313.0 (t, JC-P 26 Hz), Cα; 139.2, m, 134.7, m, Phi;
131.8, m, 130.6, m, Pho; 130.8, s, 130.3, s, Php; 129.0, m, 128.8, m, Phm; 86.6, s, Cp; 80.5,
Cδ; 58.3, Cβ; 29.4, m, CH2 (dppe); 21.8, s, Cγ.
P{1H} NMR (CD2Cl2): δ 111.0. IR: (solid
31
state) ν(C-O)/cm-1, 1192, 1153. MALDI/MS (m/z): 589 [M]+. Anal. 5[PF6]: Calcd. (%) for
C35H35P2OFePF6: C, 57.2; H, 4.8; P, 12.7; Found, C, 57.3; H, 4.5; P, 12.3.
Crystallography
Single crystals of 3[I] (as a CH2Cl2 solvate) were obtained as yellow plates by vapour diffusion
of diethyl ether into a CH2Cl2 solution of the complex at 4°C; yellow-brown blocks of 5[PF6]
were obtained by vapour diffusion of diethyl ether into an acetone solution of the complex at
4°C. Single crystal X-ray data were collected at 100 K on a Bruker APEX-II CCD
Diffractometer, by a means of Cu-Kα (λ = 1.54178 Å) radiation. SHELXS-97 [40] was
employed for the computing structure solution and SHELXL-97 [41] for the computing
structure refinement. The structure was solved by direct methods with refinement based on F2.
The non-hydrogen atoms were refined anisotropically and H atoms were included in calculated
positions.
Crystal Data for 3[I].CH2Cl2: C35H37P2FeOCl2I, Mr = 789.24, monoclinic, space group P1 21/n1
, a = 14.1508(3) Å, b = 15.8415(4) Å, c = 15.6359(3) Å, β = 101.2849(18)°, U = 3437.32(12)
Å3, Z = 4, μ = 13.082 mm-1, 24787 reflections collected, final wR2(F2) = 0.1421 for all data,
conventional R1 = 0.0491 for 5616 reflections with I>2σ(I), S = 0.993
Crystal Data for 5[PF6]: C35H35P3FeOF6, Mr = 734.39, monoclinic, space group P2(1)/n , a =
12.8715(6) Å, b = 15.1195(8) Å, c = 16.6047(8) Å, β = 95.825(3)°, U = 3214.8(3) Å3, Z = 4, μ =
5.736 mm-1, 21892 reflections collected, final wR2(F2) = 0.0857 for all data, conventional R1 =
0.0337 for 5537 reflections with I>2σ(I), S = 1.032
Appendix. Supplementary material
CCDC 1425807 and CCDC 1425808 contain the supplementary crystallographic data for
complexes 3[I] and 5[PF6] respectively. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
13
Acknowledgements
We thank the Government of Libya for a research studentship (to S.E.-T.) and Cnpq (Conselho
Nacional de Desenvolvimento Científico e Tecnológico, Brazil) for a ‘Science without Borders’
studentship (to L.M.M.).
14
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