Download Bidentate mixed ligand ruthenium(III) complexes containing

Indian Journal of Chemistry
Vol. 40A , June 2001 , pp. 573 -576
Bidentate mixed ligand ruthenium(III) complexes containing triphenylphosphine
or triphenylarsine and their antibacterial activity
T Daniel Thangadurai & K Natarajan*
Department of Chemi stry , Bharathiar Uni ve rsity , Coimbatore 641 046, India
Received II September 2000; revised 28 February 2001
Ruthenium( III ) mi xed ligand co mplexes of the type [RuX 2(LL')(EPh 3h ] ( X = Cl or Br; LL' = a, f3-un saturated-f3ketoaminate; E = P or As) have been synthesized by the reactions of [RuC1 3(PPh 3 h]. [RuC1 3(AsPh 3) 3] , [RuBr 3(AsPh 3 hl or
[RuBr 3(PPh1h( MeOH )] with appropri ate bidentate chelating li gand s. The complexes have been characteri sed by ele mental
analy ses, spectral (IR, electro ni c and EPR) and e lectro chemical data. An octahedral structure has been tentatively proposed
for all these complexes. The antibacteri al acti vities of some of the ligands and their complexes have also been carri ed out.
A few ruthenium(III) complexes with tertiaryarsine as
one of the ligands are known 1-4. Though mixed ligand
complexes of ruthenium(III) containing 13-diketones
and other related ligands have been reported 5- 7 , the
study of the reactions of tertiaryphosphine or
tertiaryarsine complexes of ruthenium(III) with a ,l3unsaturated-13-ketoamine appears to have not been
undertaken.
During the course of our systematic investigations
on the reactions of a,l3- un saturated-l3-ketoamine and
related ligands with ruthenium(lll) complexes, we
intended to study the effect of electron donating
groups present in the phenyl group of the ligands on
the antibacterial studies. The 13-ketoamine ligands that
have been used in the present study are of the
fo llowing type (Structure I):
R~
/
HzG_
c
~C
/
0
Preparation of [RuXl( EPh 3 )(LL' )]
(X = Cl or Br; E = P or As;LL' = a, /3-unsaturated-/3ketoaminate)
NR"
R'
(I)
where,
R
CH3
CH3
CH3
R'
C6Hs
C6Hs
C6Hs
R"
-C6Hs
-C6H4-CH3
-C6H4-0CH3
Materials and Methods
All the reagents used were of AR or chemically
pure grade. Elemental analyses were performed at
II Sc., Bangalore. IR spectra were recorded in KBr
a
Shimadzu
Ff-IR
8200
pellets
with
spectrophotometer. Electronic spectra were recorded
in dich loromethane with a Hitachi-Perkin-Elmer
20/200 spectrophotometer. EPR spectra of the
powdered samples were recorded on a Bruker ER2000-SRC instrument in X-band frequencies at room
temperature. The cyclic voltammetric studies were
carried out in acetoni trile solu tion using a glassycarbon worki ng electrode and all the potentials were
referenced to saturated calomel electrode. Melting
points were recorded in a Boetius Micro heating table
and are uncorrected.
[RuCI 3(PPh 3h ]8,
The
starting
complexes
[RuCb(AsPh3h] 9 ,
[RuBr3(AsPh 3h] 10
and
11
[RuBr3(PPh3h(MeOH)] and the ligands 12 ·13 were
prepared according to the reported procedures.
abbreviation
bzac-ani
bzac-o-tol
bzac-o-anz
To a benzene (20 mL) solution of [RuX 3(EPh 3h ]
(1.00- 1.20 g; 0.01 mmol) or [RuBr3(PPh 3h(MeOH)]
(0.90 g; 0.01 mmol), the appropriate ligand (0. 10 0.14 g; 0.01 mmol) was added. The resulting solution
was heated under reflux for 5 h and then concentrated
to 3 mL. The complex was separated by the addition
of small quantity of pet. ether (60-80°C). It was
filtered and recrystallised from CH 2CI 2/ pet. ether and
dried in vacuo (yield ca. 75-85 %).
INDIAN 1 CHEM, SEC. A, JUNE 2001
574
Results and Discussion
Hexa-coordinated ruthenium(HI) complexes of the
type [RuX 2 (EPh 3MLL')] (X = CI or Br; E = P or As;
LL' = cx,B-unsaturated-B-ketoaminate) have been
obtained from the reactions of [RuX 3(EPh 3h] (X = CI,
E = P; X = Cl or Br, E = P or As) or
[RuBr3(PPh 3h(MeOH)] with various cx,B-unsaturatedB-ketoamines. The analytical data (Table 1) are in
good agreement with general molecular formula.
In the infrared spectra of the ligand, the Vc=o
stretching frequency is observed in the 1640-1620
cm- 1 region . This band is shifted to 1610-1590 cm- 1
region in the complexes, indicating the coordination
of the ligand through the oxygen atom 12 (Table 1).
The bands appearing in the region 1580-1560 em_,
have been assigned to the mixed mode of vibration
arising from Vc=N and Vc=c stretching vibrations 14 .
This clearly indicates that nitrogen atom of the cx,Bunsaturated-B-ketoamine is the second donor atom to
coordinate with metal. For all the complexes, the
1
v (Ru -Ctl absorption has been observed -320 cm- region
indicating that two halide groups are in cis position 15 •
All the other characteristic bands due to
triphenylphosphine/arsine and ligands were also
present in the expected region .
The ground state of ruthenium(III) is 2T28 and the
first excited doublet levels in the order of increasing
energy are 2 T 1,j and 2A 28 which arise from the t2/
configuration 1 • The
electronic
spectra
of
ruthenium(III) complexes show two to three bands in
the region 575-345 nm (Table 1). In most of the
ruthenium(III) complexes, the UV and visible spectra
show only charge transfer bands 11 • The bands
appearing in the region - 575-490 nm have been
assigned to 2T 28 --7 2A 2g transition. The bands -425345 nm are charge-transfer bands. In general, the
electronic spectra of all the complexes are
characteristic of an octahedral environment around
ruthenium(III) atoms.
e/
Cyclic voltammetric studies have been carried out
for the complexes in acetonitrile solution at a glassycarbon working electrode. The oxidations and
reductions of some complexes are achieved by welldefined waves with £1 values in the range from 0.63 V
to 0.74 V (oxidation) and from -0.37 V to -0.77 V
(reduction) against saturated calomel electrode
(Table 2). The redox process observed from these
complexes are metal centered only. Most of the
complexes showed reversible redox couples with
peak-to-peak separation values (f..£1:) ranging from 60
to 100 mV, indicating a single-step one-electron
transfer 16• 17 process. The complexes namely,
Table 1-Analytical, IR and electronic spectral data of ruthenium(III) complexes
Complex
Colour
M.pt
oc
c
Found (Calcd),%
H
Vc=O
N
(cm- 1)
Vc =N
+
Vc=C
Amax
(nm)
(cm- 1)
[RuCI 2(bzac-ani)(PPh 3hl
Brown
120
[RuCI 2(bzac-ani)(AsPh 3hl
Brown
117
[RuBribzac-ani)(AsPhJh l
Black
122
(RuBr2(bzac-ani)(PPh Jhl
Black
119
(RuCI 2(bzac-o-tol)(PPh 3) 2]
Black
109
[RuC1 2(bzac-o-tol)(AsPh 3h ]
Black
Ill
[RuBr 2(bzac-o-tol)(AsPh3) 2]
Brown
113
[RuBr2(bzac-o-tol)(PPh 3 h l
Black
107
[RuC1 2(bzac-o-anz)(PPh 3)2 ]
Brown
114
[RuCI 2(bzac-o-anz)(AsPhJhl
Brown
131
[RuBr2(bzac-o-anz)(AsPh 3) 2]
Brown
136
[RuBr2(bzac-o-anz)(PPhJhl
Brown
127
66.87
(66.93)
61.20
(61.16)
56.30
(56.35)
61.30
(61.21)
67.29
(67.20)
61.76
(61.50)
53.80
(53 .84)
61.50
(61.54)
66.15
(66.09)
60.70
(60.56)
56.00
(55.92)
59.50
(59.47)
4.80
(4.76)
4.40
(4.34)
3.98
(4.00)
4.39
(4.35)
4.95
(4.89)
4.52
(4.48)
3.87
(3.92)
4.50
(4.48)
4.90
(4.81)
4.50
(4.41)
4.00
(4.07)
4.40
(4.33)
1.55
(1 .50)
1.40
(1 .37)
1.30
( 1.26)
1.41
(1 .37)
1.50
( 1.48)
1.40
(1.35)
1.22
( 1.18)
1.40
( 1.36)
1.50
( 1.45)
1.40
(1.33)
1.19
( 1.23)
1.29
( 1.31)
1590
1570
490,350
1600
1565
490,360
1590
1570
510,425, 365
1600
1560
505,420,360
1590
1570
520, 360
1590
1575
515 , 345
1590
1570
510,350
1600
1560
500, 415,355
1610
1570
500, 360
1590
1575
575 , 350
1600
1570
530, 420, 355
1590
1575
510, 360
THANGADURAI eta/.: RUTHENIUM(III) COMPLEXES
575
Tab le 2-Cyclic vo ltammetric data* of ruthenium(III) complexes
Epc(V)
Ep,(V)
Et{V)
1'-.Ep(mV)
Ep,(V)
Ru 111 - Ru 11
Et{V)
Epc(V)
Rul v - Rulli
Complexes
1'-.Ep( mV )
[RuC1 2(bzac-ani)(PPh 3h l
0.71
0.62
0.67
90
-0.68
-0.76
-0.72
80
[RuCI 2(bzac-ani)(AsPh 3h l
0.66
0.60
0.63
60
-0.72
-0.81
-0.77
90
0.70
0.74
80
[RuBri bzac-ani)(AsPhJhl
0.78
-0.56
-0.50
-0.53
60
[RuBr2(bzac-ani )(PPh 3h ]
0.80
-0.49
-0.58
-0.54
90
[RuBr2(bzac-o-tol)(AsPh 3) 2]
0.78
-0.59
-0.66
-0.63
70
[Ru Br2(bzac-o-tol)(PPh 3) 2 ]
-0.48
-0.58
-0.53
100
[RuC1 2(bzac-o-anz)(AsPh 3h]
0.70
0.62
0.66
80
-0.32
-0.4 1
-0.37
90
[RuB r2(bzac-o-anz )(As Ph 3h 1
0.7 8
0.70
0.74
80
-0.59
-0.52
-0.56
70
[RuBr2(bzac-o-anz)( PPh 3h ]
0.77
0.69
0.73
80
*Supporting electrol yte: [NBu 4 ]Cl04 (0.05 M); Conce ntrati on of the com plexes: 0.001 M; Scan rate: 50 mvs- 1; all the potenti als are
referred to silver-sil ver chloride e lectrode; Er =0.5 (Epa + Epc) where Epa and Epc are the anodi c and cathodic peak pote nti als respective ly.
[RuBr2(bzacani)(PPh 3)2], [RuBr2(bzac-o-toi)(AsPh 3h ]
and
[RuBr2(bzac-o-tol)(PPh 3h ]
showed
only
reduction potential and the complex [RuBr2(bzac-oanz)(PPh3h] showed only oxidation potential. The
reason for the irreversibility for these complexes may
18
be due to short lived oxidation state of the metal ion
or due to oxidative degradation of the ligands 19 .
The room temperature EPR spectra of powdered
samples were recorded at X-band frequencies. Most
of the complexes exhibit only one signal with 'g'
values between 2.34-2.46 indicating a high symmetry
around ruthenium ion . Such isotropic lines are due to
occupancy of the unpaired electron in a degenerate
orbital. Overall, the position of the lines and the
nature of the EPR spectra are characteristic of
octahedral ruthenium(III) complexes 20 ·2 1•
Antibacterial activities of the complexes and the
ligands have been carried out against Enterobacteria
feacalis and Aeromonas hydrophilla using nutrient
22
agar (NA) medium by agar-well diffusion method
with an incubation period of 24-48 h at 35 °C. The test
solutions were prepared in DMF. It has also been
observed from the studies that ruthenium chelates
have a higher activity than the other respective free
ligands against the same micro-organism under
identical experimental conditions (Table 3) which is
consistent with the earlier reports 23 . The mode of
action of the compounds may involve the formation
of hydrogen bond through the azomethi ne (>C=N)
group with the active centres of cell constituents
resulting in the interference with normal cell
24
process . The complexes containing more electrondonating group (-OCH 3) showed more activity than
the other complexes.
Table 3-Antibacteri al activity data of ruthenium(lll) complexes
Compound
Diameter of inhibition zone
(mm)
E. Jeacalis
A. hydrophilla
1%
2%
1%
2%
(bzac-ani )
10
12
8
II
[RuC1 2(bzac-ani )(AsPh 3) 2]
13
14
15
17
19
[RuBribzac-ani )(PPh 3h l
15
17
18
(bzac-o-tol)
12
15
16
18
[RuC1 2(bzac-o-tol )(PPh 3) 2]
15
18
18
20
[RuBribzac-o-tol )(AsPh 3h ]
17
20
22
23
(bzac-o-anz)
15
17
20
21
[RuCI 2(bzac-o-anz)(AsPh 3) 2 ]
18
24
23
25
[RuBr2(bzac-o-anz)(PPh 3h ]
26
28
29
32
Based on the analytical, spectral (IR, UV -visible
and EPR) and electrochemical data, the following
octahedral structure II has been tentatively proposed
for all the ruthenium(III) complexes.
x--........._
Ph,
)
/R
_.........- o -- c ~
. . . . . . ._Ru_.. . . . >H
X / ~N====C""-""--R·
1
EPh 3
R"
(II)
X = Cl or Br; E = P or As; R
C6H4CH3 or -C 6H4 OCH 3
= CH 3; R' = C6H5 ; R" = -C6H5 or -
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