Cyclometallated ruthenium(III) complexes: Synthesis, structure and properties

Article abstract of DOI:10.1016/j.jorganchem.2008.12.064

Reactions of Schiff bases (H₂apahR) derived from acetophenone and acid hydrazides, triethylamine and [Ru(PPh₃)₃Cl₂] (1:2:1 mole ratio) in methanol provide cyclometallated ruthenium(III) complexes of formula tran

Full text of DOI:10.1016/j.jorganchem.2008.12.064

Journal of Organometallic Chemistry 694 (2009) 1482–1486
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Cyclometallated ruthenium(III) complexes: Synthesis, structure and properties
*
Raji Raveendran, Samudranil Pal
School of Chemistry, University of Hyderabad, Hyderabad 500 046, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Reactions of Schiff bases (H2apahR) derived from acetophenone and acid hydrazides, triethylamine and
[Ru(PPh3)3Cl2] (1:2:1 mole ratio) in methanol provide cyclometallated ruthenium(III) complexes of for-
mula trans-[Ru(apahR)(PPh3)2Cl] in 74–81% yields. The complexes have been characterized by elemental
analysis, magnetic susceptibility, spectroscopic (infrared, electronic and EPR) and electrochemical mea-
surements. X-ray crystal structures of two representative complexes have been determined. In each
complex, the metal centre is in distorted octahedral CNOClP2 coordination sphere assembled by the
C,N,O-donor meridionally spanning apahR2À, the chloride and the two mutually trans-oriented PPh3 mol-
Received 25 November 2008
Received in revised form 27 December 2008
Accepted 29 December 2008
Available online 6 January 2009
Keywords:
ortho-Metallation
Ruthenium(III)
ecules. All the complexes are one-electron paramagnetic (leff. = 1.85–1.98 lB) and display rhombic EPR
spectra in frozen (120 K) dichloromethane-toluene (1:1) solution. Electronic spectra of the complexes dis-
play several absorptions within 470–270 nm due to ligand-to-metal charge transfer and ligand centred
transitions. The complexes are redox active and display a Ru(III) ? Ru(II) reduction and a Ru(III) ? Ru(IV)
oxidation in the potential ranges À0.66 to À0.70 V and 0.75 to 0.80 V (vs. Ag/AgCl), respectively.
Ó 2009 Elsevier B.V. All rights reserved.
Acetyl-/aroylhydrazones
Crystal structures
Redox properties
1. Introduction
O
Organometallic chemistry of ruthenium is dominated primar-
ily by its diamagnetic +2 oxidation state [1–3]. Authentic ruthe-
N
C
C
N
R
nium(III) species having M–C
r-bond are very rare [4–15]. A
H
handful of these ruthenium(III) complexes belong to the cyclo-
metallated type of species [11–14]. Among these very few
cyclometallated complexes, only one is X-ray structurally charac-
terized [11]. We have been working on cyclopalladated com-
plexes with C,N,O-donor acid hydrazide based Schiff bases
during the last few years [15,16]. Recently we have reported a
series of trans-chlorobis(triphenylphosphine)ruthenium(III) com-
plexes with the same class of C,N,O-donor Schiff bases derived
from benzaldehyde and various acid hydrazides [17]. These
one-electron paramagnetic and EPR active complexes display a
Ru(III) ? Ru(IV) oxidation in the cyclic voltammetry. This obser-
vation indicates that, this ligand system is not only able to stabi-
lize cyclometallated ruthenium(III) but also makes ruthenium(IV)
accessible. Using the analogous Schiff bases (H2apahR) prepared
from acetophenone and acid hydrazides we have prepared a
new series of cyclometallated ruthenium(III) complexes and com-
pared their physical properties with our previously reported
complexes [17]. In the following account, we describe the
synthesis, characterization and properties of the complexes,
trans-[Ru(apahR)(PPh3)2Cl]. X-ray structures of two representa-
tive complexes are also reported.
CH3
H apahR
2
R = CH , C H , 4-CH -C H ,
3
6
5
3
6 4
4-H CO-C H , 4-Cl-C H
3
6
4
6 4
2. Experimental
2.1. Materials
The Schiff bases H2apahR were prepared in ꢀ80% yields by con-
densation reactions of one mole equivalent of acetophenone with
one mole equivalent of the corresponding acid hydrazide in meth-
anol. [Ru(PPh3)3Cl2] was prepared by following a reported proce-
dure [18]. All other chemicals and solvents were of analytical
grade available commercially and were used as received.
2.2. Physical measurements
Elemental (C, H, N) analysis data were obtained with a Thermo
Finnigon Flash EA1112 series elemental analyzer. Room
* Corresponding author. Tel.: +91 40 2313 4829; fax: +91 40 2301 2460.
E-mail address: spsc@uohyd.ernet.in (S. Pal).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.12.064

R. Raveendran, S. Pal / Journal of Organometallic Chemistry 694 (2009) 1482–1486
1483
Table 1
temperature (298 K) magnetic susceptibilities were measured using
a Sherwood Scientific balance. Diamagnetic corrections calculated
from Pascal’s constants [19] were used to obtain the molar paramag-
netic susceptibilities. Solution electrical conductivities were mea-
sured with a Digisun DI-909 conductivity meter. Infrared spectra
were collected by using KBr pellets on a Nicolet 5700 FT-IR spectro-
photometer. A Cary 100 Bio UV/vis spectrophotometer was used to
record the electronic spectra. EPR spectra were recorded on a Jeol
JES-FA200 spectrometer. A CH-Instruments model 620A electro-
chemical analyzer was used for cyclic voltammetric experiments
with dimethylformamide solutions of the complexes containing tet-
rabutylammonium perchlorate(TBAP) as the supporting electrolyte.
The three electrode measurements were carried out at 298 K under
dinitrogen atmosphere with a platinum disk working electrode, a
platinum wire auxiliary electrode and an Ag/AgCl reference elec-
trode. Under identical condition the Fc+/Fc couple was observed at
0.54 V. The potentials reported in this work are uncorrected for junc-
tion contributions.
Crystal data for trans-[Ru(apahCH3)(PPh3)2Cl] (1) and trans-[Ru(apah4-Cl-C6H4)-
(PPh3)2Cl] (5).
Complex
1
5
Chemical formula
Formula weight
Crystal system
Space group
a (Å)
RuC46H40N2OClP2
835.26
Monoclinic
P21/c
9.9071(12)
19.192(2)
20.429(2)
90
92.441(2)
90
3880.9(8)
4
1.430
0.594
39901
RuC51H41N2OCl2P2
931.77
Triclinic
P1
10.693(3)
10.718(3)
20.654(6)
97.974(4)
101.662(4)
109.545(4)
2129.3(1)
2
1.453
0.611
21820
8244
7393
542
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
q
l
(g cmÀ3
(mmÀ1
)
)
Reflections collected
Reflections unique
Reflections [I P 2
7664
6854
489
r(I)]
Parameters
R1, wR2 [I P 2
r
(I)]
0.0330, 0.0837
0.0378, 0.0867
1.034
0.681, À0.610
0.0330, 0.0769
0.0378, 0.0792
1.031
0.428, À0.321
2.3. Synthesis of [Ru(apahCH3)(PPh3)2Cl] (1)
R1, wR2 [all data]
GOF on F2
Largest peak and hole (e ÅÀ3
)
Solid [Ru(PPh3)3Cl2] (270 mg, 0.28 mmol) was added to a yellow
methanol solution (30 ml) of H2apahCH3 (50 mg, 0.28 mmol) and
N(C2H5)3 (0.08 ml, 58 mg, 0.57 mmol) and the mixture was boiled
under reflux for 2 h. On cooling to room temperature the complex
was precipitated from the reaction mixture as a light brown solid.
It was collected by filtration, washed thoroughly with hexane and
dried in air. This solid was dissolved in minimum amount of
dichloromethane and transferred to a neutral aluminium oxide col-
umn. The first moving light yellow band containing the unreacted
ligand was eluted with dichloromethane and discarded. The sec-
ond brown band containing the complex was eluted with dichloro-
methane containing 5% acetone. Recrystallization of the complex
was performed from dichloromethane-hexane (1:1) mixture. Yield,
190 mg (81%).
The other four complexes having the same general formula
trans-[Ru(apahR)(PPh3)2Cl] (2 (R = C6H5), 3 (R = 4-CH3–C6H4), 4
(R = 4-CH3O–C6H4) and 5 (R = 4-Cl–C6H4)) reported in this work
were synthesized from [Ru(PPh3)3Cl2], the corresponding Schiff
base (H2apahR) and N(C2H5)3 (1:1:2 mole ratio) in 74–80% yields
by following procedures very similar to that described above for
1 (R = CH3).
refinement. The ORTEX6a package [23] was used for molecular
graphics. Selected crystal data are listed in Table 1.
3. Results and discussion
3.1. Synthesis and some properties
Reactions of [Ru(PPh3)3Cl2], corresponding H2apahR and
N(C2H5)3 (1:1:2 mole ratio) in methanol under aerobic condition
provide the complexes 1–5 in very good yields. Elemental analysis
data (Table 2) for the complexes are consistent with the general
molecular formula [Ru(apahR)(PPh3)2Cl]. The complexes are brown
in color and electrically nonconducting in solutions. The room tem-
perature (298 K) effective magnetic moments measured with pow-
dered samples of 1–5 are in the range 1.88–1.98 lB (Table 2). These
values confirm the +3 oxidation state and the low-spin character of
the metal centre in each complex.
3.2. Spectroscopic characteristics
2.4. X-ray crystallography
Absence of the characteristic bands associated with the N–H
and C@O bonds of the amide functionality [24,25] in the infrared
spectra of 1–5 indicates its enolate form in the metal bound
tridentate ligand. The medium to strong band observed within
1609–1574 cmÀ1 is attributed to the C@NAN@C fragment of
The single crystals of 1 and 5 were grown by slow evaporation
of their solutions in dichloromethane-hexane (1:1) mixture. Unit
cell parameters and the intensity data for both 1 and 5 were ob-
tained on a Bruker–Nonius SMART APEX CCD single crystal diffrac-
tometer, equipped with a graphite monochromator and a Mo K
a
apahR2À
.
Three strong bands observed at ꢀ744, ꢀ693 and
fine-focus sealed tube (k = 0.71073 Å) operated at 2.0 kW. The
detector was placed at a distance of 6.0 cm from the crystal and
ꢀ515 cmÀ1 are consistent with the presence of trans-{Ru(PPh3)2}
unit in all the complexes [13,17,26–29].
the data were collected at 298 K with a scan width of 0.3° in
x
Electronic spectra of 1–5 were recorded with their dichlorometh-
ane solutions. The data are listed in Table 2. The spectral profiles of
1–5 are not very different from that of our previously reported anal-
ogous complexes with the acid hydrazide based Schiff bases derived
from benzaldehyde [17]. There are two moderately intense absorp-
tions in the wavelength range 470–350 nm for all the complexes.
These are very likely to be due to the ligand-to-metal charge transfer
transitions expected for low-spin ruthenium(III) complexes
[11–14,17,26,28,29,31]. In the UV region, the very intense band
displayed by all the complexes within the wavelength range 277–
270 nm and the preceding shoulder observed for some of the com-
plexes are believed to be due to ligand based transitions.
and an exposure time of 15 s/frame. The SMART software was used
for data acquisition and the SAINT-Plus software was used for data
extraction [20]. The data were corrected for absorption with the
help of SADABS program [21]. Complexes 1 and 5 crystallize in
the space groups P21/c and P1, respectively. The structures were
solved by direct methods and refined on F2 by full-matrix least-
squares procedures. In each case, the asymmetric unit contains
one complete complex molecule. For both 1 and 5, the chlorine
atom is disordered in two positions. It has been refined with half
occupancy at each position. All non-hydrogen atoms were refined
anisotropically. The hydrogen atoms were included in the structure
factor calculation at idealized positions by using a riding model.
The SHELX-97 programs [22] were used for structure solution and
In frozen (120 K) dichloromethane-toluene (1:1) solution, the
EPR spectra of all the complexes are very similar and display three

1484
R. Raveendran, S. Pal / Journal of Organometallic Chemistry 694 (2009) 1482–1486
Table 2
Elemental analysis, electronic spectroscopic and magnetic susceptibility data.
b
Complex
Found (Calc.) (%)
C
kmax (nm) (10À3
Â
e
(MÀ1 cmÀ1))a
leff. (lB)
H
N
1
2
3
4
5
65.98 (66.14)
68.05 (68.26)
68.21 (68.52)
67.17 (67.35)
65.53 (65.74)
4.65 (4.83)
4.60 (4.72)
4.56 (4.87)
4.63 (4.78)
4.29 (4.43)
3.13 (3.35)
3.02 (3.12)
2.88 (3.07)
2.95 (3.02)
2.89 (3.01)
450 (0.86), 350c (3.7), 275 (29.4)
1.91
1.88
1.90
1.96
1.98
460 (1.9), 385c (3.0), 340c (6.7), 270 (27.4)
465 (2.5), 387c (5.1), 328c (10.8), 277 (37.7)
450 (3.5), 370c (6.5), 270 (37.3)
470 (2.3), 390c (3.7), 345c (9.3), 275 (41.5)
a
In dichloromethane.
At 298 K.
Shoulder.
b
c
distinct signals. The EPR data are listed in Table 3 and a represen-
tative spectrum is shown in Fig. 1. Such rhombic spectra are typical
for low-spin ruthenium(III) species having distorted octahedral
spin–orbit coupling. Therefore within these three levels two li-
gand-field transitions of energies E1 and E2 ( E1 < E2) are pos-
sible. The distortion parameters and the transition energies are
summarized in Table 3. The E1 and E2 transitions for 1–5 are ex-
pected to occur in the ranges 5565–6160 cmÀ1 (1797–1623 nm)
and 15545–19407 cmÀ1 (643–515 nm), respectively. The
/V ra-
tios for 1–5 are in the range 0.95–1.07. It may be noted that the
/V ratios are within 1.01–1.16 for our previously reported ana-
logues complexes [17]. Thus the rhombic component of the distor-
tion is somewhat more dominant in the present series of
complexes. This increase in the rhombicity may be due to the
replacement of the ACH@NA moiety present in the previously re-
ported complexes by the relatively more bulky AC(CH3)@NA moi-
ety in the present series of complexes.
D
D
D
D
coordination geometry. The axial (
D
) and the rhombic (V) compo-
D
D
nents of this distortion have been calculated from the EPR g-values
using the g tensor theory for low-spin d5 metal ion complexes [30].
The axial component splits the t2 level into ‘‘a” and ‘‘e” levels and
the rhombic component removes the degeneracy of ‘‘e” level
(Fig. 1). The energies of these levels are also affected by the
D
D
Table 3
EPR g-values,a distortion parameters and near-IR transitionsb.
Complex
g1
g2
g3
D
/k
V/k
D
E1/k
DE2/k
1
2
3
4
5
2.33
2.36
2.34
2.35
2.32
2.09
2.09
2.10
2.09
2.08
1.95
1.95
1.95
1.95
1.96
10.703
11.089
10.527
11.094
12.699
À10.351
À11.629
À9.831
5.616
5.565
5.698
5.581
6.160
15.981
17.201
15.545
16.796
19.407
3.3. X-ray structures of 1 and 5
The molecular structures of 1 and 5 are illustrated in Figs. 2
and 3, respectively. Structural parameters associated with the me-
tal ion for both complexes are listed in Table 4. In each complex,
the metal centre is in distorted octahedral CNOClP2 coordination
sphere. The tridentate dianionic C,N,O-donor ligand binds the me-
tal centre in a meridional fashion and forms two five-membered
chelate rings. The two phosphine ligands are in mutually trans
positions. The disordered Cl-atom satisfies the remaining equato-
rial position. For clarity only one of the two half occupancy
Cl-atoms are shown in Figs. 2 and 3. The bond lengths in the tri-
dentate ligands are unexceptional and indicate the enolate form
À11.206
À13.241
a
In 1:1 dichloromethane–toluene at 120 K.
The calculations are based on the spin–orbit coupling constant (k) = 1000 cmÀ1
.
b
C18
C19
C26
C17
C30
C31
C20
C29
C25
C27
C21
C28
C16
P1
C22
C24
C32
C23
C33
C11
O
C12
C13
Cl1b
Ru
C9
C10
N1
C8
C1
C2
C3
C4
N2
C47
Cl2
C15
C14
C7
P2
C6
C5
C44
C48
C45
C41
C46
C35
C34
C40
C43
C49
C51
C38
C39
C50
C36
C42
C37
Fig. 2. Molecular structure of trans-[Ru(apahCH3)(PPh3)2Cl] (1) with the atom
labeling scheme. All atoms are represented by their 30% probability thermal
ellipsoids. Hydrogen atoms are omitted for clarity.
Fig. 1. X-band EPR spectrum of trans-[Ru(apahC6H5)(PPh3)2Cl] (2) in frozen (120 K)
dichloromethane-toluene (1:1) solution and the t2 splitting pattern.

R. Raveendran, S. Pal / Journal of Organometallic Chemistry 694 (2009) 1482–1486
1485
Table 5
C21
Cyclic voltammetrica data.
C25
C26
C22
C13
C14
C16
C24
C20
C19
Complex
E1/2 (V) (D
Ep (mV))b
C23
Ru(III) ? Ru(IV)
Ru(III) ? Ru(II)
C27
C11
C17
C15
O
1
2
3
4
5
0.75 (100)
0.80 (150)
0.77 (110)
0.75 (150)
0.80 (130)
–
C18
À0.67 (100)
À0.68 (80)
À0.70 (90)
À0.66 (90)
P1
Clb
C2
C9
N2
Ru
C10
C1
a
In dichloromethane solution (298 K) at a scan rate of 50 mV sÀ1
.
N1
b
E1/2 = (Epa + Epc)/2, where Epa and Epc are anodic and cathodic peak potentials,
respectively;
Ep = Epa À Epc
C3
C8
C43
C7
C6
P2
D
.
C5
C4
C34
C42
C41
C36
C29
C35
C40
C44
for 5) are deviated by a small amount from the ideal trans angle va-
lue of 180°. In each structure, the Ru–Cl bond lengths involving the
two half occupancy Cl-atoms are very similar and within the range
reported for the chloride coordinated ruthenium(III) complexes
[17,26,28,29]. The Ru–P bond lengths are comparable with those
reported for complexes of trans-{Ru(PPh3)2}3+ [11,17,26,28,29].
The Ru–C(ring), Ru–N(imine) and Ru–O(amide) bond lengths are
very similar to the bond lengths observed in trivalent ruthenium
complexes having the same coordinating atoms [11,17,28,29,31].
C33
C32
C46
C37
C30
C39
C38
C31
Fig. 3. Molecular structure of trans-[Ru(apah4-Cl-C6H4)(PPh3)2Cl] (5) with the atom
labeling scheme. All atoms are represented by their 30% probability thermal
ellipsoids. Hydrogen atoms are omitted for clarity.
3.4. Electron transfer properties
of the amide functionality in both complexes. The chelate rings
formed by the tridentate ligand are satisfactorily planar in both
complexes. The mean deviations are in the range 0.002–0.04 Å.
The two rings are also essentially coplanar in each complex. The
dihedral angles between the two ring planes are 3.6(1)° and
3.7(1)° for 1 and 5, respectively. The bite angle (73.59(7)° for 1
and 74.24(6)° for 5) in the chelate ring formed by the amide-O
and the imine-N is slightly smaller than that (75.85(9)° for 1 and
75.38(8)° for 5) in the chelate ring formed by the imine-N and
the ring-C. The P1–Ru–P2 angles (175.51(2)° for 1 and 174.51(2)°
The electron transfer properties of 1–5 have been examined in
dimethylformamide with the help of cyclic voltammetry. The
potential data are summarized in Table 5. Two representative cyc-
lic voltammograms are depicted in Fig. 4. All the complexes dis-
play a quasi-reversible to irreversible Ru(III) ? Ru(IV) oxidation
in the potential range 0.75–0.80 V. In this oxidation response,
Table 4
Selected structural parameters (lengths (Å) and angles (°)) for trans-[Ru(apa-
hCH3)(PPh3)2Cl] (1) and trans-[Ru(apah4-Cl-C6H4)(PPh3)2Cl] (5).
1a
5b
Ru–O
Ru–N(1)
Ru–C(1)
Ru–P(1)
Ru–P(2)
Ru–Cl(a)
Ru–Cl(b)
2.1085(17)
2.0580(19)
2.066(2)
2.3969(6)
2.3924(6)
2.1179(16)
2.019(2)
73.59(7)
149.13(9)
89.71(5)
87.51(5)
75.85(9)
90.70(6)
91.89(6)
94.98(7)
89.21(7)
175.51(2)
92.99(7)
129.50(8)
166.43(8)
156.49(9)
117.68(9)
81.33(10)
87.15(5)
85.64(6)
89.49(5)
93.41(6)
36.62(8)
Ru–O
Ru–N(1)
Ru–C(1)
Ru–P(1)
Ru–P(2)
Ru–Cl(1a)
Ru–Cl(1b)
O–Ru–N(1)
2.1164(16)
2.0464(18)
2.068(2)
2.4226(7)
2.3783(7)
2.0038(15)
2.0026(16)
74.24(6)
149.33(8)
88.87(5)
93.30(5)
75.38(8)
92.05(5)
93.62(6)
96.33(6)
84.49(6)
174.28(2)
88.42(6)
128.00(6)
162.64(7)
156.32(7)
121.83(8)
82.66(8)
88.31(5)
81.52(6)
86.46(5)
93.00(6)
40.65(7)
O–Ru–N(1)
O–Ru–C(1)
O–Ru–P(1)
O–Ru–P(2)
N(1)–Ru–C(1)
N(1)–Ru–P(1)
N(1)–Ru–P(2)
C(1)–Ru–P(1)
C(1)–Ru–P(2)
P(1)–Ru–P(2)
O–Ru–Cl(a)
O–Ru–Cl(b)
N(1)–Ru–Cl(a)
N(1)–Ru–Cl(b)
C(1)–Ru–Cl(a)
C(1)–Ru–Cl(b)
P(1)–Ru–Cl(a)
P(1)–Ru–Cl(b)
P(2)–Ru–Cl(a)
P(2)–Ru–Cl(b)
Cl(a)–Ru–Cl(b)
O–Ru–C(1)
O–Ru–P(1)
O–Ru–P(2)
N(1)–Ru–C(1)
N(1)–Ru–P(1)
N(1)–Ru–P(2)
C(1)–Ru–P(1)
C(1)–Ru–P(2)
P(1)–Ru–P(2)
O–Ru–Cl(1a)
O–Ru–Cl(1b)
N(1)–Ru–Cl(1a)
N(1)–Ru–Cl(1b)
C(1)–Ru–Cl(1a)
C(1)–Ru–Cl(1b)
P(1)–Ru–Cl(1a)
P(1)–Ru–Cl(1b)
P(2)–Ru–Cl(1a)
P(2)–Ru–Cl(1b)
Cl(1a)–Ru–Cl(1b)
Fig. 4. Cyclic voltammograms (scan rate 50 mV sÀ1): (a) reduction of trans-
[Ru(apah4-H3CO-C6H4)(PPh3)2Cl] (4) and (b) oxidation of trans-[Ru(apahCH3)(PPh3)2Cl]
(1) in dimethylformamide (0.1 M TBAP).
a
Both Cl(a) and Cl(b) have half occupancy.
Both Cl(1a) and Cl(1b) have half occupancy.
b

1486
R. Raveendran, S. Pal / Journal of Organometallic Chemistry 694 (2009) 1482–1486
the cathodic peak current is significantly less than the anodic
peak current particularly for complexes 2–5. Barring complex 1
the remaining complexes also show a reversible Ru(III) ? Ru(II)
reduction within À0.66 to À0.70 V. The peak currents for the
reduction response and the anodic peak current for the oxidation
response are comparable with peak currents observed for known
one-electron transfer processes under identical conditions
[11–14,17,27–29]. In the cases of 2–5, the potentials for both
reduction and oxidation reflect a small but noticeable effect of
the electronic nature of the substituent on the tridentate ligand
(Table 5). For the most electron withdrawing substituent Cl (com-
plex 5) the potentials are highest and for the most electron releas-
ing substituent OMe (complex 4) the potentials are lowest.
Satisfactory linear relationships are obtained when the potentials
are plotted against the Hammett constants of the substituents
[32]. Interestingly for our previously reported analogous com-
plexes the Ru(III) ? Ru(II) reduction response is not observed
and except for the complex with acetylhydrazone the Ru(III) ?
Ru(IV) oxidation occurs at lower (by 350–400 mV) potentials
[17]. At present we are not sure about the reasons for the differ-
ences in the electron transfer behavior and the oxidation poten-
tials of the two analogous series of complexes which differ only
in the type of substituent (R) present in the ACR@NA fragment
of the tridentate ligand. Perhaps the change in the extent of dis-
tortions of the coordination geometry and hence in the electron
energy levels due to the change of R from H to CH3 plays some
role in effecting the differences observed [33].
Acknowledgements
Financial support for this work was provided by the Depart-
ment of Science and Technology (DST) (Grant No. SR/S1/IC-10/
2007). Ms. R. Raveendran thanks the Council of Scientific and
Industrial research for a Senior Research Fellowship. X-ray crystal
structures were determined at the National Single Crystal Diffrac-
tometer Facility, School of Chemistry, University of Hyderabad
(established by the DST). We thank the University Grants Commis-
sion, New Delhi for the facilities provided under the UPE and CAS
programs.
References
[1] G. Wilkinson, F.G.A. Stone, E.W. Abel (Eds.), Comprehensive Organometallic
Chemistry, vol. 4, Pergamon, Oxford, 1982, p. 651.
[2] D.F. Schriver, M.I. Bruce (Eds.), Comprehensive Organometallic Chemistry II,
vol. 7, Pergamon, Oxford, 1995, p. 291.
[3] V. Dragutan, I. Dragutan, L. Delaude, A. Demonceau, J. Organomet. Chem. 251
(2007) 765.
[4] A.J. Hewitt, J.H. Holloway, R.D. Peacock, J.B. Raynor, I.L. Wilson, J. Chem. Soc.
Dalton Trans. (1976) 579.
[5] L.H. Pignolet, S.H. Wheeler, Inorg. Chem. 19 (1980) 935.
[6] M.M. Taqui Khan, D. Srinivas, R.I. Kureshy, N.H. Khan, Inorg. Chem. 29 (1990)
2320.
[7] M. Ke, S.J. Rettig, B.R. James, D. Dolphin, J. Chem. Soc. Chem. Commun. (1987)
1110.
[8] J.W. Seyler, C.R. Leidner, Inorg. Chem. 29 (1990) 3636.
[9] M. Ke, C. Sishta, B.R. James, D. Dolphin, J.W. Sparapany, J.A. Ibers, Inorg. Chem.
30 (1991) 4766.
[10] M. Beley, J.P. Collin, R. Louis, B. Metz, J.P. Sauvage, J. Am. Chem. Soc. 113 (1991)
8521.
[11] G.K. Lahiri, S. Bhattacharya, M. Mukherjee, A.K. Mukherjee, A. Chakravorty,
Inorg. Chem. 26 (1987) 3359.
[12] P. Ghosh, A. Pramanik, N. Bag, G.K. Lahiri, A. Chakravorty, J. Organomet. Chem.
454 (1993) 237.
4. Conclusion
[13] R. Hariram, B.K. Santra, G.K. Lahiri, J. Organomet. Chem. 540 (1997) 155.
[14] P. Munshi, R. Samanta, G.K. Lahiri, J. Organomet. Chem. 586 (1999) 176.
[15] S. Das, S. Pal, J. Organomet. Chem. 689 (2004) 352.
[16] S. Das, S. Pal, J. Organomet. Chem. 691 (2006) 2575.
[17] R. Raveendran, S. Pal, J. Organomet. Chem. 692 (2007) 824.
[18] T.A. Stephenson, G. Wilkinson, J. Inorg. Nucl. Chem. 28 (1966) 945.
[19] W.E. Hatfield, in: E.A. Boudreaux, L.N. Mulay (Eds.), Theory and Applications of
Molecular Paramagnetism, Wiley, New York, 1976, p. 491.
[20] SMART version 5.630 and SAINT-plus version 6.45, Bruker-Nonius Analytical
X-ray Systems Inc., Madison, WI, USA, 2003.
Synthesis and characterization of cyclometallated distorted
octahedral ruthenium(III) complexes having the general molecular
formula trans-[Ru(apahR)(PPh3)2Cl] with Schiff bases (H2apahR)
prepared from acid hydrazides and acetophenone have been de-
scribed. The meridionally spanning dianionic ligand (L2À) acts as
C,N,O-donor in these complexes due to ruthenium mediated acti-
vation of ortho-C–H bond of the pendant phenyl group of H2apahR.
The molecular structures of two representative complexes have
been determined by X-ray crystallography. The complexes are
one-electron paramagnetic and display the characteristic rhombic
EPR spectra in frozen solution commonly observed for distorted
octahedral low-spin ruthenium(III) complexes. All the complexes
are redox active and display a metal centred oxidation and except
for one complex a metal centred reduction.
[21] G.M. Sheldrick, SADABS
, Program for Area Detector Absorption Correction,
University of Göttingen, Göttingen, Germany, 1997.
[22] G.M. Sheldrick, SHELX-97 Structure Determination Software, University of
Göttingen, Göttingen, Germany, 1997.
[23] P. McArdle, J. Appl. Crystallogr. 28 (1995) 65.
[24] W. Kemp, in: Organic Spectroscopy, Macmillan, Hampshire, 1987, pp. 62–65.
[25] K. Nakamoto, in: Infrared and Raman Spectra of Inorganic and Coordination
Compounds, Wiley, New York, 1986, pp. 241–244.
[26] F. Basuli, A.K. Das, G. Mostafa, S.M. Peng, S. Bhattacharya, Polyhedron 19
(2000) 1663.
[27] R. Raveendran, S. Pal, Polyhedron 24 (2005) 57.
[28] R. Raveendran, S. Pal, Inorg. Chim. Acta 359 (2006) 3212.
[29] R. Raveendran, S. Pal, Polyhedron 27 (2008) 655.
[30] S. Bhattacharya, A. Chakravorty, Proc. Indian Acad. Sci. (Chem. Sci.) 95 (1985)
159.
[31] S.N. Pal, S. Pal, Eur. J. Inorg. Chem. (2003) 4244.
[32] J. March, in: Advanced Organic Chemistry, 4th ed., Wiley, New York, 1992, p.
280.
5. Supplementary material
CCDC 709287 and 709288 contain the supplementary crystallo-
graphic data for compounds trans-[Ru(apahCH3)(PPh3)2Cl] (1) and
trans-[Ru(apah4-Cl-C6H4)(PPh3)2Cl] (5), respectively. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[33] P. Basu, S.B. Choudhury, S. Pal, A. Chakravorty, Inorg. Chem. 28 (1989) 2680.