Chemistry of ruthenium with some phenolic ligands: Synthesis, structure and redox properties

Article abstract of DOI:10.1016/S0277-5387(00)00404-6

Reaction of three phenolate ligands, viz. salicylaldehyde (HL¹), 2-hydroxyacetophenone (HL²) and 2-hydroxynaphthylaldehyde (HL³), (abbreviated in general as HL, where H stands for the phenolic proton) with [Ru(PPh₃)₃Cl₂] in 1:1 mole ratio gives complexes of the type [Ru(PPh₃)₂(L)Cl₂]. The structure of the [Ru(PPh₃)₂(L²)Cl₂] complex has been solved by X-ray crystallography. The coordination sphere around ruthenium is O₂P₂Cl₂ with a cis-trans-cis geometry, respectively. The [Ru(PPh₃)₂(L)Cl₂] complexes are one-electron paramagnetic (low-spin d⁵, S = 1/2) and show rhombic ESR spectra in 1:1 dichloromethane-toluene solution at 77 K. In dichloromethane solution the [Ru(PPh₃)₂(L)Cl₂] complexes show several intense LMCT transitions in the visible region. Reaction between the phenolic ligands and [Ru(PPh₃)₃Cl₂] in 2:1 mole ratio in the presence of a base affords the [Ru(PPh₃)₂(L)₂] complexes in two isomeric forms, ¹H NMR spectra of one isomer shows that it does not have any C₂ symmetry and has the cis-cis-cis disposition of the three sets of donor atoms. ¹H NMR spectra of the other isomer shows that it has C₂ symmetry. The structure of the isomer of the [Ru(PPh₃)₂(L¹)₂] complex has been solved by X-ray crystallography. The coordination sphere around ruthenium is O₄P₂ with a cis-trans-cis disposition of the carbonylic oxygens, phenolate oxygens and phosphorus atoms, respectively. The [Ru(PPh₃)₂(L)₂] complexes are diamagnetic (low-spin d⁶, S = O) and show intense MLCT transitions in the visible region. Cyclic voltammetry on the [Ru(PPh₃)₂(L)Cl₂] complexes shows a ruthenium(III)-ruthenium(II) reduction near - 0.3 V versus SCE and a ruthenium(III)-ruthenium(IV) oxidation in the range 1.08-1.24 V versus SCE. Cyclic voltammetry on both isomers of the [Ru(PPh₃)₂(L)₂] complexes shows a ruthenium(II)-ruthenium(III) oxidation within 0.09-0.41 V versus SCE, followed by a ruthenium(III)-ruthenium(IV) oxidation within 1.31-1.52 V versus SCE. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(00)00404-6

www.elsevier.nl/locate/poly
Polyhedron 19 (2000) 1663–1672
Chemistry of ruthenium with some phenolic ligands: synthesis,
structure and redox properties
Falguni Basulia, Anjan Kumar Das a, Golam Mostafa b, Shie-Ming Peng c,
Samaresh Bhattacharya a,*
a Department of Chemistry, Inorganic Chemistry Section, Jada6pur Uni6ersity, Calcutta 700032, India
b Department of Physics, Krishnath College, Berhampur, West Bengal, India
c Department of Chemistry, National Taiwan Uni6ersity, Taipei, Taiwan, ROC
Received 11 January 2000; accepted 11 April 2000
Abstract
Reaction of three phenolate ligands, viz. salicylaldehyde (HL1), 2-hydroxyacetophenone (HL2) and 2-hydroxynaphthylaldehyde
(HL3), (abbreviated in general as HL, where H stands for the phenolic proton) with [Ru(PPh3)3Cl2] in 1:1 mole ratio gives
complexes of the type [Ru(PPh3)2(L)Cl2]. The structure of the [Ru(PPh3)2(L2)Cl2] complex has been solved by X-ray crystallogra-
phy. The coordination sphere around ruthenium is O2P2Cl2 with a cis–trans–cis geometry, respectively. The [Ru(PPh3)2(L)Cl2]
complexes are one-electron paramagnetic (low-spin d5, S=1/2) and show rhombic ESR spectra in 1:1 dichloromethane–toluene
solution at 77 K. In dichloromethane solution the [Ru(PPh3)2(L)Cl2] complexes show several intense LMCT transitions in the
visible region. Reaction between the phenolic ligands and [Ru(PPh3)3Cl2] in 2:1 mole ratio in the presence of a base affords the
1
[Ru(PPh3)2(L)2] complexes in two isomeric forms. H NMR spectra of one isomer shows that it does not have any C2 symmetry
1
and has the cis–cis–cis disposition of the three sets of donor atoms. H NMR spectra of the other isomer shows that it has C2
symmetry. The structure of the isomer of the [Ru(PPh3)2(L1)2] complex has been solved by X-ray crystallography. The
coordination sphere around ruthenium is O4P2 with a cis–trans–cis disposition of the carbonylic oxygens, phenolate oxygens and
phosphorus atoms, respectively. The [Ru(PPh3)2(L)2] complexes are diamagnetic (low-spin d6, S=O) and show intense MLCT
transitions in the visible region. Cyclic voltammetry on the [Ru(PPh3)2(L)Cl2] complexes shows a ruthenium(III)ꢀruthenium(II)
reduction near −0.3 V versus SCE and a ruthenium(III)ꢀruthenium(IV) oxidation in the range 1.08–1.24 V versus SCE. Cyclic
voltammetry on both isomers of the [Ru(PPh3)2(L)2] complexes shows a ruthenium(II)ꢀruthenium(III) oxidation within 0.09–0.41
V versus SCE, followed by a ruthenium(III)-ruthenium(IV) oxidation within 1.31–1.52 V versus SCE. © 2000 Elsevier Science
Ltd. All rights reserved.
Keywords: Ruthenium; Phenolic ligands; Synthesis; Structure; Redox properties
states, which in turn depend on the nature of ligands
bound to the metal. Complexation of ruthenium by
1. Introduction
ligands of different types has thus been of particular
The chemistry of ruthenium has currently been re-
interest. In the present study, which has originated
ceiving a lot of attention [1–10] primarily because of
from our interest in the chemistry of ruthenium in
the fascinating electron-transfer and energy-transfer
different coordination environments [11–18], we have
properties displayed by the complexes of this metal.
Ruthenium offers a wide range of oxidation states and
chosen phenolic ligands of type 1 as the principal
ligand, which are abbreviated in general as HL where H
the reactivities of the ruthenium complexes depend on
stands for the dissociable phenolic proton. The depro-
the stability and interconvertibility of these oxidation
tonated ligands are known to coordinate metal ions as
bidentate O,O-donor forming six-membered chelate
rings (2) [19,20]. Three different phenolic ligands have
been used in this study, which are shown in 1 along
with their specific abbreviations.
* Corresponding author. Fax: +91-33-473-4266.
E-mail address: samaresh b@hotmail.com (S. Bhattacharya).
–
0277-5387/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(00)00404-6

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F. Basuli et al. / Polyhedron 19 (2000) 1663–1672
While phenolate oxygen is a recognized hard donor, and
coordination by it is known to stabilize the higher
oxidation states of ruthenium [21–23], coordination of
metals by carbonylic oxygen has also recently been of
considerable interest in bioinorganic chemistry [24–28].
It may be mentioned here that ruthenium chemistry of
these ligands has not been explored much [19]. Stability
of different oxidation states of ruthenium is expected to
depend on the number of phenolate and carbonylic
oxygen in the coordination sphere and in the case of
mixed-ligand complexes, on the nature of coligands
also. Herein we have restricted our studies to some
mono- and bis-phenolate complexes of ruthenium,
which have been synthesized by reacting the phenolic
ligands with [Ru(PPh3)3Cl2] under different experimen-
tal conditions. The chemistry of complexes of the type
[Ru(PPh3)2(L)Cl2] and [Ru(PPh3)2(L)2] has been de-
scribed in this paper with special reference to synthesis,
stereoisomerism and electron-transfer properties.
solid, which was collected by filtration, washed with
ethanol and dried in air. The yield was 55 mg (64%).
2.2.2. [Ru(PPh3)2(L2)Cl2]
This was synthesized by following the same procedure
above using HL2 instead of HL1. The yield was 60 mg
(69%).
2.2.3. [Ru(PPh3)2(L3)Cl2]
Dichloromethane (40 cm3) was added to a solid
mixture of [Ru(PPh3)3Cl2] (100 mg, 0.10 mmol) and HL3
(20 mg, 0.12 mmol) and the solution was stirred for 3 h
to afford a green solution. On evaporation of the
solvent, a green solid was obtained, which was washed
with ethanol and dried in air. Purification of this
product was achieved by chromatography through a
silica gel column. Using toluene as the eluent a green
band resulted, which was collected. Evaporation of the
eluate gave [Ru(PPh3)2(L3)Cl2] as a green microcrys-
talline solid. The yield was 55 mg (61%).
2.2.4. ctc and ccc isomers of [Ru(PPh3)2(L1)2]
2. Experimental
2.2.4.1. Method A. [Ru(PPh3)3Cl2] (100 mg, 0.10 mmol)
was added to a hot solution of HL1 (30 mg, 0.24 mmol)
in ethanol (40 cm3), followed by NEt3 (30 mg, 0.30
mmol). The mixture was refluxed for 2 h to produce a
red solution. On partial evaporation of solvent, a micro-
crystalline red solid precipitated, which was collected by
filtration, washed thoroughly with water and dried in
vacuo over P4O10. Purification was achieved by chro-
matography through silica gel column. Using toluene
and 1:4 acetonitrile–toluene as the eluents, two different
red bands resulted, which were collected separately and
evaporation of the eluates, respectively, gave the ctc and
ccc isomers of [Ru(PPh3)2(L1)2]. The yield was 30 mg
(33%) for the ctc isomer and 32 mg (35%) for the ccc
isomer.
2.1. Materials
Commercial ruthenium trichloride was purchased
from Arora Matthey, Calcutta, India, and was con-
verted into RuCl3·3H2O by repeated evaporation with
concentrated hydrochloric acid. Triphenylphosphine
(PPh3), triethylamine (NEt3) and salicylaldehyde (HL1)
were obtained from SD, India. 2-Hydroxyacetophenone
(HL2) and 2-hydroxynaphthaldehyde (HL3) were pur-
chased, respectively, from Spectrochem, India and
Aldrich. All other chemicals and solvents were reagent
grade commercial materials and were used as received.
[Ru(PPh3)3Cl2] was prepared following a reported pro-
cedure [29]. Purification of acetonitrile and preparation
of tetraethylammonium perchlorate (TEAP) for electro-
chemical work were performed as before [30,31].
2.2.4.2. Method B. [Ru(PPh3)2(L1)Cl2] (50 mg, 0.06
mmol) was dissolved in a minimum volume of dichloro-
methane and to it a solution of HL1 (10 mg, 0.08 mmol)
in ethanol (30 cm3) was added, followed by NEt3 (10
mg, 0.10 mmol). The solution was refluxed for 4 h.
Upon evaporation of the solution, a red crystalline solid
was obtained, which was washed with water and dried
in vacuo over P4O10. The solid was then purified as in
Method A. The ctc and ccc isomers of [Ru(PPh3)2(L1)2]
were obtained in 36 and 32% yields, respectively.
2.2. Preparation of complexes
2.2.1. [Ru(PPh3)2(L1)Cl2]
HL1 (15 mg, 0.12 mmol) was added to a suspension
of [Ru(PPh3)3Cl2] (100 mg, 0.10 mmol) in ethanol (40
cm3) and the mixture was stirred for 5 h to produce a
green solution. On partial evaporation of the solvent,
[Ru(PPh3)2(L1)Cl2] separated out as a green crystalline

F. Basuli et al. / Polyhedron 19 (2000) 1663–1672
1665
2.2.5. ctc and ccc isomers of [Ru(PPh3)2(L2)2]
were recorded on a Bruker AC-200 spectrometer using
TMS as the internal standard. ESR spectra were
recorded on a Varian Model 109C E-line X-band spec-
trometer fitted with a quartz Dewar for measurements
at 77 K (liquid dinitrogen). All spectra were calibrated
with the help of DPPH (g=2.0037). Electrochemical
measurements were made using a PAR model 273
potentiostat. A platinum disc working electrode, a plat-
inum wire auxiliary electrode and an aqueous saturated
calomel reference electrode (SCE) were used in a three
electrode configuration. Dinitrogen gas was purified by
successively bubbling it through alkaline dithionite and
concentrated sulfuric acid. All electrochemical experi-
ments were performed under a dinitrogen atmosphere.
All electrochemical data were collected at 298 K and
are uncorrected for junction potentials. An RE 0089
X-Y recorder was used to trace the voltammograms.
These isomers have been prepared by following the
above procedures. In method A, HL2 was used instead
of HL1. The ctc and ccc isomers of [Ru(PPh3)2(L2)2]
were obtained in 30 and 34% yields. In method B
[Ru(PPh3)2(L2)Cl2] and HL2 were used instead of
[Ru(PPh3)2(L1)Cl2] and HL1, respectively. Yields of the
ctc and ccc isomers were 35 and 33%, respectively.
2.2.6. ctc and ccc isomers of [Ru(PPh3)2(L3)2]
These isomers have been prepared by following the
above procedures (Section 2.2.4). In method A, HL3
was used instead of HL1. The ctc and ccc isomers of
[Ru(PPh3)2(L3)2] were obtained in 32 and 36% yields. In
method B, [Ru(PPh3)2(L3)Cl2] and HL1 were used in-
stead of [Ru(PPh3)2(L1)Cl2] and HL1, respectively.
Yields of the ctc and ccc isomers were 32 and 34%,
respectively.
2.4. Crystallography
2.3. Physical measurements
Single crystals of [Ru(PPh3)2(L2)Cl2] were grown by
slow diffusion of hexane into a dichloromethane solu-
tion of the complex. Selected crystal data and data
collection parameters are given in Table 1. Data were
collected on a Siemens Smart CCD diffractometer using
graphite monochromated Mo Ka radiation (u=
Microanalyses (C, H, N) were performed using a
Perkin–Elmer 240C elemental analyzer. IR spectra
were obtained on a Perkin–Elmer 783 spectrometer
with samples prepared as KBr pellets. Electronic spec-
tra were recorded on Shimadzu UV 240 spectrophoto-
meter. Magnetic susceptibilities were measured using a
PAR 155 Vibrating sample magnetometer fitted with a
,
0.71073 A) by v scans within the angular range 1.57B
qB25.00°. X-ray data reduction, structure solution and
refinement were done using SHELXTL-PLUS package.
1
Walker scientific L75FBAL magnet. H NMR spectra
The structure was solved by direct methods.
Table 1
Crystallographic data
Single crystals of ctc-[Ru(PPh3)2(L1)2] were grown by
slow diffusion of benzene into an acetonitrile solution
of the complex. Selected crystal data and data collec-
tion parameters are given in Table 1. The unit cell
dimensions were determined by a least-squares fit of 25
centered reflections (10.805q520.94°). Data were col-
lected on an Enraf–Nonius CAD-4 diffractometer us-
ing graphite monochromated Mo Ka radiation
[Ru(PPh3)2(L2)Cl2]
ctc-[Ru(PPh3)2(L1)2]
Formula
Formula weight
Space group
C44H37Cl2O2P2Ru
831.65
orthorhombic, Pnma triclinic, P1
10.5844(10)
23.817(2)
15.407(2)
90
90
90
3884.0(8)
4
0.50×0.30×0.15
293(2)
C50H40O4P2Ru
867.87
(
,
a (A)
10.7368(19)
11.637(4)
16.732(7)
96.18(3)
91.78(3)
99.44(3)
2047.7(12)
2
,
b (A)
,
(u=0.71073 A) by q−2q scans within the angular
,
c (A)
range 3.0B2qB45.0°. Three standard reflections, used
to check the crystal stability towards X-ray exposure,
showed no significant intensity variation over the
course of data collection. X-ray data reduction, and
structure solution and refinement were carried out using
the SHELXS-97 package. The structure was solved by
the direct methods.
h (°)
i (°)
k (°)
3
,
V (A )
Z
Crystal size (mm)
0.40×0.30×0.20
298
T (K)
v (cm−1
)
6.60
4.951
R
R1=0.0522 a
Rf=0.046 d
Rw=0.047 c
2.01 f
b
wR2=0.1390
GOF
1.082 e
3. Results and discussion
a R1=ꢀꢁFoꢂ−ꢂFcꢁ/ꢀꢂFoꢂ.
b wR2=[ꢀ[w(Fo2−Fc2)2]/ꢀ[w(F2o)2]]1/2
.
3.1. Preparation and characterization
c GOF=[ꢀ[w(Fo2−Fc2)2]/(M−N)1/2, where M is the number of
reflections and N is the number of parameters refined.
d Rf=ꢀꢁFoꢂ−ꢂFcꢁ/ꢀꢂFoꢂ.
3.1.1. [Ru(PPh3)2(L)Cl2] complexes
Reaction of [Ru(PPh3)3Cl2] with an equimolar quan-
tity of each phenolic ligand (HL) proceeds smoothly in
dichloromethane solution at ambient temperature to
e Rw=[ꢀw(ꢂFoꢂ−ꢂFcꢂ)2/ꢀw(Fo)2]1/2
.
f GOF=[ꢀw(ꢂFoꢂ−ꢂFcꢂ)2/(M−N)]1/2, where M is the number of
reflections and N is the number of parameters refined.

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F. Basuli et al. / Polyhedron 19 (2000) 1663–1672
Table 2
Microanalytical, electronic spectral and cyclic voltammetric data
Compound
Microanalytical data a
Electronic spectral data b
Cyclic voltammetric date c
E1/2 (V) (DEp, mV)
umax (nm) (m, M−1 cm−1
)
%C
%H
[Ru(PPh3)2(L1)Cl2]
Ru(PPh3)2(L2)Cl2]
[Ru(PPh3)2(L3)Cl2]
63.5
(63.2)
4.4
(4.3)
656 (423), 492 d (966),
396 (4700), 304 (19300),
272 d (22 000) 240 (25 600)
624 (907), 388 (5200),
300 d (15 100), 268 d (23 100),
236 (38800)
−0.28 (120),
1.16 (120)
62.6
(63.5)
4.9
(4.5)
−0.37 (120),
1.08 (120)
65.3
(65.1)
4.5
(4.3)
588 (855), 400 d (2000),
312 d (3300), 260 d (10700),
232 (19300)
−0.30 (120),
1.24 (120)
ctc-[Ru(PPh3)2(L1)2]
ccc-[Ru(PPh3)2(L1)2]
ctc-[Ru(PPh3)2(L2)2]
69.7
(69.2)
69.5
(69.2)
70.1
(69.7)
4.7
(4.6)
4.5
(4.6)
5.0
(4.9)
504 (2300), 404 d (7000),
364 (10 400), 232 (78 300)
500 (1300), 408 d (3700),
356 (5000), 232 (38600)
492 (1800), 388 d (5000),
340 (7800), 260 (22 900),
236 (23600)
0.23 (80),
1.35 (100)
0.28 (80),
1.41 (100)
0.09 (80),
1.31 (110)
ccc-[Ru(PPh3)2(L2)2]
ctc-[Ru(PPh3)2(L3)2]
69.9
(69.7)
72.1
4.9
(4.9)
4.7
500 d (2300), 400 (6300),
336 (8200), 232 (64 600)
490 (3000), 390 (9600),
340 d (12 200), 320 d (17 700),
280 (32 700), 232 (77 600)
490 (3000), 398 (7400),
340 (11 200), 320 d (17 200),
276 (30 000), 232 (61 300)
0.21 (80),
1.52 (120)
0.35 (80),
1.46 (100)
(72.0)
(4.6)
ccc-[Ru(PPh3)2(L3)2]
72.2
(72.0)
4.6
(4.6)
0.41 (80),
1.52 (110)
a Calculated values are in parenthesis.
b Dichloromethane solution.
c Solvent, acetonitrile; supporting electrolyte, TEAP; reference electrode, SCE; E1/2=0.5(Epa+Epc), where Epa and Epc are anodic and cathodic
peak potentials, respectively; DEp=Epa−Epc; scan rate, 50 mV s−1
.
d Shoulder.
afford complexes of the type [Ru(PPh3)2(L)Cl2]. It is
interesting to note here that ruthenium has undergone a
one-electron oxidation during the course of this syn-
thetic reaction. In view of the ruthenium(III)–rutheniu-
m(II) reduction potentials in these complexes (vide
infra), oxygen in air appears to have served as the
oxidant. Compositions of the complexes have been
confirmed by their microanalytical data (Table 2). As
all the three phenolate ligands used in the present study
selected bond distances and angles are presented in
Table 3. The O2P2Cl2 coordination sphere around
ruthenium is distorted octahedral in nature, which is
are
asymmetric
bidentate
in
nature,
the
[Ru(PPh3)2(L)Cl2] complexes may exist in three geomet-
ric isomeric forms (3–5).
To distinguish between the possible three isomers,
molecular structure of a representative complex, viz.
[Ru(PPh3)2(L2)Cl2], has been determined by X-ray crys-
tallography. The structure is shown in Fig. 1 and
Fig. 1. View of the [Ru(PPh3)2(L2)Cl2] molecule.

F. Basuli et al. / Polyhedron 19 (2000) 1663–1672
1667
Table 3
[19,32–34]. This structure determination thus shows
that [Ru(PPh3)2(L2)Cl2] has structure 3. As all the three
[Ru(PPh3)2(L)Cl2] complexes display similar properties
(vide infra), the other two [Ru(PPh3)2(L)Cl2] complexes
are assumed to have a similar structure as [Ru(PPh3)2-
(L2)Cl2].
,
Selected bond distances (A) and bond angles (°) for
[Ru(PPh3)2(L2)Cl2]
RuꢀCl(1)
RuꢀCl(2)
RuꢀP(1)
RuꢀO(1)
RuꢀO(2)
2.324(2)
2.304(2)
2.415(2)
1.995(5)
2.025(6)
O(2)ꢀC(7)
O(1)ꢀC(1)
C(1)ꢀC(2)
C(2)ꢀC(3)
C(3)ꢀC(4)
C(4)ꢀC(5)
C(5)ꢀC(6)
C(6)ꢀC(7)
C(1)ꢀC(6)
C(7)ꢀC(8)
1.298(12)
1.267(10)
1.405(14)
1.45(3)
1.39(5)
1.22(4)
1.44(2)
1.42(2)
1.38(2)
1.494(13)
Infrared spectra of the [Ru(PPh3)2(L)Cl2] complexes
show many sharp and strong vibrations in the 1600–300
cm−1 region, of which the vibrations near 520, 700 and
745 cm−1 are also observed in [Ru(PPh3)3Cl2] and hence
these are attributable to the Ru(PPh3)2 fragment of the
[Ru(PPh3)2(L)Cl2] complexes. One new band, observed
near 1580 cm−1 in all these complexes, is assigned to the
w(CꢁO) vibration of the coordinated phenolate ligand.
The w(RuꢀCl) stretching vibration appears as a strong
band in all the complexes near 330 cm−1. The infrared
spectral data thus correspond to the composition of the
complexes. The [Ru(PPh3)2(L)Cl2] complexes are soluble
in common polar organic solvents, like dichloro-
methane, chloroform, acetonitrile, etc., producing green
solutions. Electronic spectra of these complexes have
been recorded in dichloromethane solution. A selected
spectrum is shown in Fig. 2 and spectral data are listed
in Table 2. Each complex shows few intense absorptions
in the visible region together with some very intense
absorptions in the ultraviolet region. The absorptions in
the ultraviolet region may be assigned to transitions
occurring within the ligand orbitals. To have an insight
into the nature of transitions appearing in the visible
region, qualitative EHMO calculations have been per-
formed [35,36] on a model of the [Ru(PPh3)2(L)Cl2]
complexes, which was computer generated from
[Ru(PPh3)2(L1)Cl2] by replacing the phenyl groups of
the PPh3 ligands with hydrogen. A partial MO diagram
is shown in Fig. 3. The highest occupied (singly occu-
pied) molecular orbital (MO-1) and the next two filled
orbitals (MO-2 and MO-3) of this model are predomi-
nantly (]80%) ruthenium t2 in character. There are
two filled molecular orbitals (MO-4 and MO-5) below
these metal t2 orbitals, which are localized almost en-
tirely (]96%) on the phenolate ligand. The intense
absorptions observed in the visible region may therefore
be assigned to the allowed ligand-to-metal charge-trans-
fer transitions occurring from the filled orbitals of the
phenolate ligand (MO-4 and MO-5) to the half-filled
ruthenium t2 orbital (MO-1).
O(2)ꢀRuꢀCl(2)
P(1)ꢀRuꢀP(1A)
O(1)ꢀRuꢀCl(1)
O(1)ꢀRuꢀO(2)
O(2)ꢀRuꢀCl(1)
O(1)ꢀRuꢀP(1)
Cl(2)ꢀRuꢀP(1)
176.9(2)
179.41(8)
173.2(2)
86.4(2)
86.9(2)
89.73(4)
89.88(5)
O(1)ꢀRuꢀCl(2)
C(2)ꢀRuꢀCl(1)
O(2)ꢀRuꢀP(1)
Cl(1)ꢀRuꢀP(1)
90.5(2)
96.27(11)
90.10(5)
90.28(4)
Fig. 2. Electronic spectra of (a) [Ru(PPh3)2(L3)Cl2] and (b) ctc-
[Ru(PPh3)2(L1)2] (—) and ccc-[Ru(PPh3)2(L1)2] (------) in
dichloromethane solution.
Magnetic susceptibility show that all the three
[Ru(PPh3)2(L)Cl2] complexes are one-electron paramag-
netic, which is in accordance with the +3 oxidation
state of ruthenium (low-spin d5, S=1/2) in these com-
plexes. Electron spin resonance spectra of the
[Ru(PPh3)2(L)Cl2] complexes, recorded in 1:1
dichloromethane–toluene solution at 77 K, show rhom-
bic spectra with three distinct signals (g1, g2 and g3 in the
order of decreasing magnitude). A representative spec-
trum is shown in Fig. 4 and the spectral data are
reflected in the bond parameters. The two bulky PPh3
ligands are in trans positions, as is usually observed in
complexes of ruthenium(III) having the Ru(PPh3)2 moi-
ety [32–34], while the two chloride ligands have occu-
pied cis positions. The observed bond distances are all
quite normal as observed in structurally characterized
complexes of ruthenium containing similar ligands

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F. Basuli et al. / Polyhedron 19 (2000) 1663–1672
Fig. 3. Qualitative molecular orbital diagram of [Ru(PPh3)2(L)Cl2].
presented in Table 4. The observed rhombicity of the
ESR spectra is understandable in terms of the gross
molecular symmetry of these complexes containing the
three non-equivalent PꢀRuꢀP, O(phenolic)–RuꢀCl and
O(carbonylic)ꢀRuꢀCl axes. The rhombic distortion can
be thought of a combination of axial distortion (Z,
which splits t2 into a and e) and rhombic distortion (V,
which splits e). The splitting pattern is illustrated in Fig.
4. Spin-orbit coupling causes further changes in the
energy gaps. Thus two electronic transitions (transition
energies DE1 and DE2; DE1BDE2) are possible within
these three levels. All these energy parameters have
been computed (Table 4) using the observed g values,
the g tensor theory of low-spin d5 complexes and a
reported method [37–39]. The axial distortion is ob-
served to be much stronger than the rhombic one. The
DE1 transition falls in the infrared region (3200–3700
cm−1) and could not be detected. The DE2 transition,
which is expected to occur near 6000 cm−1 (ꢀ1667
nm), could not be verified either because of the non-
transparency of the solvent in this region. However, the
ESR data analysis shows that the [Ru(PPh3)2(L)Cl2]
complexes are significantly distorted from ideal octahe-
dral geometry, which was also observed in the struc-
tural analysis of [Ru(PPh3)2(L2)Cl2].
ands (HL) with [Ru(PPh3)3Cl2] in 2:1 mole ratio pro-
ceeds smoothly in refluxing ethanol in the presence of a
base to afford the bis complexes of type [Ru(PPh3)2-
(L)2]. These complexes can also be prepared from
[Ru(PPh3)2(L)Cl2] by reacting them with one equivalent
of the respective phenolic ligand (HL) in the presence
of a base. Thin layer chromatographic experiments
indicated the presence of two isomers (isomer-I and
isomer-II) in all [Ru(PPh3)2(L)2] complexes, which have
3.1.2. [Ru(PPh3)2(L)2] complexes
These complexes have been prepared in two different
ways (Scheme 1). Direct reaction of the phenolic lig-
Fig. 4. ESR spectrum of [Ru(PPh3)2(L2)Cl2] in 1:1 dichloromethane–
toluene solution at 77 K.

F. Basuli et al. / Polyhedron 19 (2000) 1663–1672
1669
Table 4
Magnetic moment and ESR g values a and derived parameters b of the [Ru(PPh3)2(L)Cl2] complexes
Compound
veff (BM)
g1
g2
g3
D/u
V/u
DE1/u
DE2/u
[Ru(PPh3)2(L1)Cl2]
[Ru(PPh3)2(L2)Cl2]
[Ru(PPh3)2(L3)Cl2]
1.85
1.93
1.97
2.497
2.428
2.407
2.212
2.233
2.258
1.791
1.828
1.795
4.313
4.574
4.065
−2.450
−1.976
−1.264
3.236
3.691
3.515
5.801
5.830
5.029
a In 1:1 dichloromethane–toluene solution at 77 K.
b Spin-orbit coupling constant (u) for complexed ruthenium(III) is ꢀ1000 cm−1
.
been separated by column chromatography. Microana-
lytical data of these complexes are in good agreement
with their compositions (Table 2). Both isomers of
these complexes are diamagnetic, which corresponds to
the bivalent state of ruthenium (low-spin d6, S=O) in
these complexes.
the molecular structure of isomer-I of [Ru(PPh3)2(L1)2]
has been determined by X-ray crystallography. The
structure is shown in Fig. 5 and selected bond distances
and angles are presented in Table 5. Ruthenium has a
distorted octahedral O4P2 coordination sphere with the
two PPh3 ligands in cis positions, the two phenolate
oxygens in trans positions and the two carbonylic oxy-
gens in cis positions. Therefore isomer-I of
[Ru(PPh3)2(L1)2] has structure 9 (henceforth referred to
as the ctc isomer to indicate the cis–trans–cis disposi-
tions of the carbonylic oxygens, phenolate oxygens and
phosphines, respectively). The observed bond parame-
ters are all quite normal. In view of the similarity in
synthetic procedure and properties, isomer-I of the
other two [Ru(PPh3)2(L)2] complexes are assumed to
have similar ctc structure.
As all three phenolate ligands used in the present
study are asymmetric, the [Ru(PPh3)2(L)2] complexes
may exist in five geometrical isomeric forms (6–10).
Isomers 6–9 have a C2 axis, while isomer 10 does not
have any C2 symmetry. 1H NMR spectra have been
recorded on both isomers of all three [Ru(PPh3)2(L)2]
complexes in CDCl3 solution. Isomer-I of all three
complexes clearly shows the presence of a C2 axis, while
isomer-II indicates the absence of C2 symmetry. For
example, isomer-I of [Ru(PPh3)2(L1)2] shows only one
aldehydic proton signal at 8.68 ppm, while isomer-II of
[Ru(PPh3)2(L1)2] shows two aldehydic proton signals
(1H each) at 8.36 and 8.53 ppm. This shows that
isomer-II has structure 10, where the three sets of
donor atoms are in cis positions and henceforth this
isomer will be labeled as the cis–cis–cis or ccc isomer.
Scheme 1.
It has not been possible to assign specific stereochem-
istry of isomer-I on the basis of 1H NMR spectral
results alone. However, as complexes of ruthenium with
the Ru(PPh3)2 are known to Prefer cis-disposition of
PPh3 ligands [33,34,40], these [Ru(PPh3)2(L)2] com-
plexes may be assumed to have either structure 8 or 9.
To sort out this problem of stereochemistry of isomer-I,
Fig. 5. View of the ctc-[Ru(PPh3)2(L1)2] molecule.

1670
F. Basuli et al. / Polyhedron 19 (2000) 1663–1672
Table 5
because of the lower symmetry splitting of the metal
1
,
Selected bond distances (A) and bond angles (°) for [Ru(PPh3)2(L )2]
orbitals and presence of different accepting orbitals.
For proper assignment of the absorptions in the visible
region, qualitative EHMO calculations have been per-
formed as before on models of the ctc and ccc isomersa
of [Ru(PPh3)2(L1)2], where phenyl groups of the PPh3
ligands have been replaced by hydrogen. The results of
these calculations are qualitatively very similar for both
the isomers. A partial MO diagram for one isomer is
shown in Fig. 6. The highest occupied molecular orbital
(HOMO) and the next two filled orbitals (HOMO-1
and HOMO-2) are basically (\75%) ruthenium t2 or-
bitals. There are two relatively close vacant molecular
orbitals above these filled orbitals, the lowest unoccu-
pied molecular orbital (LUMO) and the next unoccu-
pied orbital (LUMO+1), which are primarily (\95%)
p-orbitals of the phenolate ligands. The intense absorp-
tions observed in the visible region may therefore be
assigned to the charge-transfer transitions occurring
from the filled ruthenium t2 orbitals to the vacant
p-orbitals of the phenolate ligands.
RuꢀP(1)
RuꢀP(2)
RuꢀO(1)
RuꢀO(2)
RuꢀO(3)
RuꢀO(4)
2.2929(18)
2.3031(17)
2.057(3)
2.090(4)
2.052(3)
2.128(4)
O(1)ꢀC(1)
O(2)ꢀC(7)
O(3)ꢀC(8)
O(4)ꢀC(14)
1.295(6)
1.239(7)
1.313(6)
1.262(7)
P(1)ꢀRuꢀO(2)
P(2)ꢀRuꢀO(4)
O(1)ꢀRuꢀO(3)
P(1)ꢀRuꢀP(2)
P(1)ꢀRuꢀO(1)
P(1)ꢀRuꢀO(3)
P(1)ꢀRuꢀO(4)
P(2)ꢀRuꢀO(1)
P(2)ꢀRuꢀO(2)
169.48(11)
169.69(11)
173.61(14)
99.22(6)
90.17(11)
93.05(11)
91.07(11)
97.04(11)
91.08(11)
P(2)ꢀRuꢀO(3)
O(1)ꢀRuꢀO(2)
O(1)ꢀRuꢀO(4)
O(2)ꢀRuꢀO(3)
O(2)ꢀRuꢀO(4)
O(3)ꢀRuꢀO(4)
87.90(11)
90.75(14)
83.48(14)
85.08(14)
78.62(14)
90.94(14)
Infrared spectra of ctc and ccc isomers of the
[Ru(PPh3)2(L)2] complexes are very similar. Each shows
characteristic vibrations near 500, 700, 750 cm−1, indi-
cating the presence of the Ru(PPh3)2 moiety. The
w(CꢁO) vibration is observed as a strong band near
1580 cm−1 in all these complexes. The [Ru(PPh3)2(L)2]
complexes are soluble in common organic solvents like
dichloromethane, chloroform, acetone, acetonitrile,
etc., forming intense red solutions. Electronic spectra of
these complexes, recorded in dichloromethane solution,
show several intense absorptions in the visible region
and few absorptions of very high intensity in the ultra-
violet region (Fig. 2, Table 2). The latter absorptions
are assigned to transitions within the ligand orbitals.
The former absorptions in the visible region are proba-
bly due to allowed metal-to-ligand charge-transfer tran-
sitions. Multiple charge-transfer transitions are
common in such mixed ligand complexes, primarily
3.2. Electron-transfer properties
Electron-transfer properties of the [Ru(PPh3)2(L)Cl2]
and [Ru(PPh3)2(L)2] have been studied in acetonitrile
solution by cyclic voltammetry. Representative voltam-
mograms are shown in Fig. 7 and voltammetric data
are presented in Table 2.
Each [Ru(PPh3)2(L)Cl2] complex shows a reductive
response on the negative side of SCE and an oxidative
response on the positive side. Both responses are quasi-
reversible in nature. The reduction, observed near
−0.3 V (all potentials are referenced to SCE), is tenta-
tively assigned to ruthenium(III)-ruthenium(II) reduc-
tion and the oxidation, which occurs within 1.08–
Fig. 6. Qualitative molecular orbital diagram of [Ru(PPh3)2(L)2].

F. Basuli et al. / Polyhedron 19 (2000) 1663–1672
1671
Acknowledgements
Financial assistance received from the Council of
Scientific and Industrial Research, New Delhi [Grant
No. 01(1408)/96/EMR-II] is gratefully acknowledged.
Thanks are also due to the Third World Academy of
Sciences for financial support for the purchase of an
electrochemical cell system. F.B. thanks the University
Grants Commission, New Delhi, for her fellowship.
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