Interaction of 2-(arylazo)phenols with rhodium. Usual coordination vs. C-H and C-C activation

Article abstract of DOI:10.1016/j.jorganchem.2006.10.063

Reaction of 2-(2′-hydroxyphenylazo)phenol with [Rh(PPh₃)₃Cl] in refluxing benzene in presence of triethylamine afforded a red complex in which the ligand is coordinated to rhodium as a tridentate O,N,O-donor. However, similar reaction of [Rh(PPh₃)₃Cl] with 2-(2′-carboxyphenylazo)-4-methylphenol yielded two complexes, viz. a blue one and a green one. In both the complexes the ligand is coordinated as C,N,O-donor. However, in the blue complex orthometallation takes place from the ortho-carbon atom, which bears -COOH group via decarboxylation and in green one orthometallation occurs from the other ortho-carbon. Structures of all the three complexes were determined by X-ray crystallography. In all the three complexes rhodium is sharing the equatorial plane with the tridentate ligand and a chloride, and the two triphenylphosphines are axially disposed. All of the complexes show intense MLCT transitions in the visible region. Cyclic voltammetry on these complexes shows a Rh(III)-Rh(IV) oxidation on the positive side of SCE and a reduction of the coordinated azophenolate ligand on the negative side.

Full text of DOI:10.1016/j.jorganchem.2006.10.063

Journal of Organometallic Chemistry 692 (2007) 1025–1032
www.elsevier.com/locate/jorganchem
Interaction of 2-(arylazo)phenols with rhodium. Usual coordination
vs. C–H and C–C activation
a
a
a
b
Suparna Baksi , Rama Acharyya , Swati Dutta , Alexander J. Blake ,
c
a,
*
Michael G.B. Drew , Samaresh Bhattacharya
a
Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700 032, India
b
School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK
c
Department of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, UK
Received 2 August 2006; received in revised form 13 October 2006; accepted 27 October 2006
Available online 7 November 2006
Abstract
Reaction of 2-(20-hydroxyphenylazo)phenol with [Rh(PPh3)3Cl] in refluxing benzene in presence of triethylamine afforded a red com-
plex in which the ligand is coordinated to rhodium as a tridentate O,N,O-donor. However, similar reaction of [Rh(PPh3)3Cl] with 2-(20-
carboxyphenylazo)-4-methylphenol yielded two complexes, viz. a blue one and a green one. In both the complexes the ligand is coordi-
nated as C,N,O-donor. However, in the blue complex orthometallation takes place from the ortho-carbon atom, which bears –COOH
group via decarboxylation and in green one orthometallation occurs from the other ortho-carbon. Structures of all the three complexes
were determined by X-ray crystallography. In all the three complexes rhodium is sharing the equatorial plane with the tridentate ligand
and a chloride, and the two triphenylphosphines are axially disposed. All of the complexes show intense MLCT transitions in the visible
region. Cyclic voltammetry on these complexes shows a Rh(III)–Rh(IV) oxidation on the positive side of SCE and a reduction of the
coordinated azophenolate ligand on the negative side.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: 2-(Arylazo)phenols; Rhodium; Usual coordination; C–H and C–C activation
1. Introduction
we have selected two modified 2-(arylazo)phenols, viz. 2-
(20-hydroxyphenylazo)phenol (3) and 2-(20-carboxypheny-
lazo)-4-methylphenol (4), in both of which one ortho-posi-
tion of the phenyl ring in the arylazo fragment is
strategically blocked by a hydroxy group and a carboxy
group respectively. These two ligands are known to bind
metal ions usually as dianionic tridendate O,N,O-donors
forming stable chelates (5 and 6) [4]. However, in view of
the possible free rotation of the phenyl ring in the arylazo
fragment around the C–N bond, cylometallation of these
ligands is also, in principle, possible (7 and 8). The present
study was initiated to explore these possibilities in these
two ligands (3 and 4), and rhodium has been chosen as
the platinum metal to interact with these selected ligands.
As the source of rhodium the Wilkinson’s catalyst,
[Rh(PPh3)3Cl], has been utilized. This particular complex
has been picked up as the rhodium starting material
There is considerable current interest in the reactions of
transition metals with suitable organic ligands leading to
the formation of metal–carbon bond(s) via C–H or C–C
activation [1]. Formation of such organometallic com-
plexes is of particular importance as they often serve as
reactive intermediates in metal-mediated transformation
of organic substrates [1,2]. The present work has originated
from our interest in this area [3]. During our recent studies
we have observed that 2-(arylazo)phenols (1) readily
undergo cyclometallation (2) via platinum metal mediated
C–H activation at one ortho-position of the phenyl ring
in the arylazo fragment [3a,3c,3g,3j]. In the present study
*
Corresponding author.
E-mail address: samaresh_b@hotmail.com (S. Bhattacharya).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.10.063

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S. Baksi et al. / Journal of Organometallic Chemistry 692 (2007) 1025–1032
because of its recognized efficiency to undergo facile reac-
tion with phenolic ligands and, more importantly, its dem-
onstrated ability to accommodate tridentate ligands via
dissociation of a triphenylphosphine [3a,3d,3k,3l]. Reac-
tion of [Rh(PPh3)3Cl] with the ligands 3 and 4 has been
found to afford complexes, where the ligands have dis-
played interesting modes of binding. Herein we wish to
report the chemistry of all these complexes, with special ref-
erence to their formation, structure, and electrochemical
properties.
(9) in a decent yield. Preliminary (microanalytical, mag-
netic, spectral, etc.) characterizations on complex 9 indicate
that ligand 3 is probably coordinated to the metal center in
the expected dianionic tridentate O,N,O-fashion (5) along
with two triphenylphosphines and a chloride. To authenti-
cate the structure of complex 9, as well as the binding mode
of ligand 3 in it, its structure has been determined by X-ray
crystallography. The structure is shown in Fig. 1 and
selected bond parameters are listed in Table 1. The struc-
ture shows that ligand 3 is indeed bound to rhodium in
the expected dianionic tridentate fashion (5), forming two
adjacent five- and six-membered rings with bite angles of
77.45ꢁ and 98.08ꢁ, respectively. The other three coordina-
tion sites are occupied by two triphenylphosphines and a
chloride. The overall structure is a distorted octahedron
with the O,N,O-donor ligand and the chloride occupying
the equatorial plane with the metal at the center and two
axially disposed PPh3 ligands. The observed Rh–Cl, Rh–
P, Rh–O, and Rh–N bond distances, as well as the C–O
and N–N lengths in the O,N,O-chelate, are all quite normal
[3a,5]. In complex 9 rhodium is existing in its +3 oxidation
state, and hence its formation from the rhodium(I) starting
material (Scheme 1) involves loss of two electrons from the
metal center. In the presence of triethylamine ligand 3 also
undergoes loss of two protons. So in effect the doubly
deprotonated ligand 3 binds oxidatively to the metal center
OH
O
M
H3C
N
N
H3C
N
N
R
R
1
2
OH
OH
N
N
OH
H3C
N
N
COOH
with simultaneous dissociation of
[Rh(PPh3)3Cl] during the formation of complex 9.
a
PPh3 from
3
4
Reaction of the other chosen ligand, viz. 2-(20-carbo-
xyphenylazo)-4-methylphenol (4), with [Rh(PPh3)3Cl] also
proceeds smoothly under similar experimental condition
as before. This reaction, however, yielded two complexes
O
M
H3C
O
M
O
N
N
O
N
N
C O
5
6
O
O
M
M
N
N
H3C
N
N
HO
HOOC
7
8
2. Results and discussion
2.1. Synthesis and characterization
Reaction of 2-(20-hydroxyphenylazo)phenol (3) with
[Rh(PPh3)3Cl] has been carried out in refluxing benzene
in the presence of triethylamine to afford a red complex
Fig. 1. View of complex 9.

S. Baksi et al. / Journal of Organometallic Chemistry 692 (2007) 1025–1032
1027
Table 1
Selected bond lengths (A) and bond angles (ꢁ) for complexes 9–11
˚
Complex 9
Complex 10
Complex 11
˚
Bond lengths (A)
Rh(1)–Cl(1)
Rh(1)–P(11)
Rh(1)–P(12)
Rh(1)–O(1)
Rh(1)–N(1)
Rh(1)–O(2)
C(1)–O(1)
N(1)–N(2)
C(6)–N(1)
C(7)–N(2)
C(12)–O(2)
2.3643(6)
2.3827(8)
2.3720(8)
2.0263(17)
1.998(4)
2.0119(17)
1.325(3)
1.273(5)
1.499(4)
1.393(5)
1.300(3)
Rh(1)–Cl(1)
Rh(1)–P(1)
Rh(1)–P(2)
2.398(3)
2.371(3)
2.389(3)
2.209(4)
1.960(4)
2.005(4)
1.317(5)
1.296(4)
1.401(5)
1.394(5)
1.418(5)
Rh–Cl(1)
Rh–P(1)
Rh–P(2)
Rh–O(1)
Rh–N(1)
Rh–C(12)
C(1)–O(1)
N(1)–N(2)
C(6)–N(1)
C(7)–N(2)
C(7)–C(12)
C(8)–C(14)
C(14)–O(2)
C(14)–O(3)
2.3868(10)
2.3717(12)
2.3641(12)
2.195(3)
1.956(3)
2.008(4)
1.294(5)
1.270(4)
1.380(5)
1.390(5)
1.417(5)
1.498(5)
1.338(6)
1.204(6)
Rh(1)–O(85)
Rh(1)–N(78)
Rh(1)–C(71)
C(84)–O(85)
N(77)–N(78)
C(811)–N(77)
C(79)–N(78)
C(71)–C(811)
Bond angles (ꢁ)
P(11)–Rh(1)–P(12)
O(1)–Rh(1)–O(2)
Cl(1)–Rh(1)–N(1)
N(1)–Rh(1)–O(1)
N(1)–Rh(1)–O(2)
175.96(3)
P(1)–Rh(1)–P(2)
173.72(4)
159.47(12)
178.67(9)
80.07(11)
79.43(13)
P(1)–Rh–P(2)
O(1)–Rh–C(12)
Cl–Rh–N(1)
N(1)–Rh–O(1)
N(1)–Rh–C(12)
O(2)–C(14)–O(3)
173.37(4)
175.51(7)
168.98(11)
77.45(12)
98.08(12)
O(85)–Rh(1)–C(71)
Cl(1)–Rh(1)–N(78)
N(78)–Rh(1)–O(85)
N(78)–Rh(1)–C(71)
159.39(13)
174.78(10)
80.02(12)
79.38(14)
119.6(4)
with distinctly different colors, viz. a blue complex (10) and
a green complex (11). The preliminary characterization
data of these complexes have failed to indicate any definite
coordination mode of ligand 4 in them. To find out the
binding mode(s) of ligand 4 in these complexes, as well as
their stereochemistries, structure of both the complexes
has been determined by X-ray crystallography. The struc-
tures are shown in Fig. 2 (complex 10) and Fig. 3 (complex
11) and relevant bond parameters are given in Table 1.
Structure of complex 10 (Fig. 2) shows that in it ligand 4
is coordinated to rhodium as a dianionic C,N,O-donor
via decarboxylation, forming two adjacent five-membered
rings with bite angles of 80.07ꢁ and 79.43ꢁ. Two triphenyl-
phosphines and a chloride are also coordinated to the
metal center as before. The C,N,O-coordinated ligand, rho-
dium and the chloride are sharing one equatorial plane and
the two PPh3 ligands are occupying the axial positions. The
observed bond parameters compare well with those
observed in complex 9. However, the Rh–O bond is signif-
icantly longer than the corresponding Rh–O bond in com-
plex 9, which may be attributed to the strain developed due
to formation of two five-membered chelate rings by the
C,N,O-bound ligand. Structure of the complex 11 (Fig. 3)
shows that in it ligand 4 is again coordinated to rhodium
as a C,N,O-donor, but in a different fashion. In this com-
plex orthometallation has taken place from the other
ortho-carbon, which does not bear the carboxy group.
Besides presence of the –COOH group in the C,N,O-donor
ligand, other structural features in this green complex are
comparable to those observed in the complex 10.
P = PPh3
P
OH
Cl
O
III
[RhIP3Cl], Et3N
-P, -2H+, -2e-
Rh
O
N
N
OH
N
N
P
3
9
Scheme 1. Formation of complex 9.
Fig. 2. View of complex 10.

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S. Baksi et al. / Journal of Organometallic Chemistry 692 (2007) 1025–1032
OH
H3C
N
N
COOH
4
-P
[RhIP3Cl]
Et3N
-2H+
-e-
P = PPh3
P
P
II
Rh
O
O
Cl
P
Cl
P
II
Rh
COO-
H3C
N
N
H3C
N
N
-OOC
A
B
-e-
-CO2
-e-
Fig. 3. View of complex 11.
Formation of these two complexes from the same reac-
tion has been quite interesting, and the speculated steps
involved in the synthetic reaction are illustrated in Scheme
2. In the presence of NEt3 both the phenolic and carboxylic
protons of ligand 4 are believed to get dissociated and the
resulting dianionic ligand coordinates the metal center in
[Rh(PPh3)3Cl] as a N,O-donor with loss of an electron
from the metal center and dissociation of a PPh3, to gener-
ate a reactive pentacoordinated rhodium(II) intermediate.
During the free rotation of the pendent phenyl ring around
the C–N bond the ortho-carbons come in close proximity
to the metal center, facilitating either a C–C activation
(in rotamer A) or a C–H activation (in rotamer B). It is
interesting to note that in the rotamer A the carboxylate
fragment, though may appear close to the metal center, is
actually disposed so far away from the metal center that
it cannot participate in coordination [6]. Thus complex 10
is believed to form from rotamer A via loss of carbondiox-
ide [7] along with loss of an electron from the metal center,
while complex 11 is formed from rotamer B via loss of a
proton and a one-electron oxidation of the metal center.
The free carboxylate fragment in complex 11 is likely to
remain in the deprotonated form in the presence of NEt3
(as the HNEtþ3 salt). However, during the work-up the
HNEtþ3 salt probably undergoes usual hydrolysis to afford
the free COOH fragment in complex 11. It is interesting to
note that similar cylometallation of some phenolic Schiff
bases mediated by [Rh(PPh3)3Cl] has been observed before
[3l,8]. It may also be noted here that in the first synthetic
reaction between ligand 3 and [Rh(PPh3)3Cl] no orthomet-
allated product (containing 7) is obtained, probably due to
the much higher acidity of the phenolic O–H compared to
the phenyl C–H.
P
P
Cl
Cl
O
N
O
N
III
III
Rh
Rh
H3C
H3C
P
P
N
N
HOOC
10
11
Scheme 2. Probable steps for the formation of complexes 10 and 11.
2.2. Spectral studies
Infrared spectra of all the complexes show many bands
of varying intensities within 400–4000 cmꢀ1. Assignment of
each individual band to a specific vibration has not been
attempted. However, three strong bands observed around
746, 695, and 516 cmꢀ1 are attributable to the coordinated
PPh3 ligands [3]. Spectrum of the complex 11 shows a
strong band at 1730 cmꢀ1, which is absent in complex 10,
is due to the COOH fragment. Magnetic susceptibility
measurements show that all the three complexes are dia-
magnetic, which corresponds to the trivalent state of rho-
dium (low-spin d6, S = 0) in them. H NMR spectra of
1
complexes 9–11 have been recorded in CDCl3 solution.
The spectral data of each complex, given in experimental
section, are found to be in good agreement with its compo-
sition. The methyl signals of the coordinated azo ligand in
complexes 10 and 11 are observed around 2.00 ppm. In the
spectrum of complex 11, the carboxylic proton signal is
observed clearly at 12.41 ppm.
All the three complexes (9–11) are found to be readily
soluble in dichloromethane, sparingly soluble in acetoni-
trile and acetone, and poorly soluble in alcoholic solvents.

S. Baksi et al. / Journal of Organometallic Chemistry 692 (2007) 1025–1032
1029
Table 2
Electronic spectral and cyclic voltammetric data of the complexes
Compound
Electronic spectral dataa
k
max, nm (e, Mꢀ1 cmꢀ1
)
Cyclic voltammetric datac
Complex 9
Complex 10
Complex 11
534(5600), 503(4800)b, 339(7600)b, 304(19000), 230(52000)
635(2500), 591(2200)b, 341(4300)b, 291(10900), 232(19000)
702(12300), 649(10600), 373(13700)b, 346(16300)b, 296(38900), 230(64700)
1.08d (70)e, ꢀ1.31f
0.82d (75)e, ꢀ1.30f
1.01d (81)e, ꢀ1.00f
Where Epa and Epc are anodic and cathodic peak potentials, respectively.
a
In dichloromethane solution.
Shoulder.
b
c
Solvent: 1:9 dichloromethane–acetonitrile; supporting electrolyte, TBAP; reference electrode, SCE, scan rate, 50 mV sꢀ1
.
d
E1/2 = 0.5(Epa + Epc); where Epa and Epc are anodic and cathodic peak potentials, respectively.
e
DEp = Epa ꢀ Epc
.
f
Epc value.
Table 3
Composition of selected molecular orbitals
Compounds
Contributing fragments
% Contribution of fragments to
HOMO
HOMO ꢀ 1
HOMO ꢀ 2
LUMO
LUMO + 1
LUMO + 2
Complex 9
Rh
Chloride
81
5
70
–
34
–
13
–
–
–
–
–
Tridentate ligand (ONO)
7
20
60
81 (N@N, 54)
98
98
Complex 10
Complex 11
Rh
Chloride
Tridentate ligand (CNO)
78
4
8
43
–
52
53
4
33
15
–
–
–
96
–
–
95
81 (N@N, 48)
Rh
Chloride
79
5
39
–
56
4
12
–
–
–
–
–
Tridentate ligand (CNO)
8
57
33
83 (N@N, 41)
95
96
Fig. 4. Partial molecular orbital diagram of complex 9.
Electronic spectra of all the complexes have been recorded
in dichloromethane solution. Each complex shows several
intense absorptions in the visible and ultraviolet region
(Table 2). The absorptions in the ultraviolet region are
believed to be due to transitions within the ligand orbi-
tals. To have an insight into the nature of absorptions

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S. Baksi et al. / Journal of Organometallic Chemistry 692 (2007) 1025–1032
in the visible region, EHMO calculations have been per-
formed [9] on computer generated models of the all the
three complexes, where phenyl rings of the PPh3 ligands
have been replaced by hydrogens. Compositions of
selected molecular orbitals are given in Table 3 and par-
tial MO diagram of complex 9 is shown in Fig. 4. Partial
MO diagrams of complexes 10 and 11 are deposited as
Supplementary material (Figs. S1 and S2). The calcula-
tions reveal that the highest occupied molecular orbital
(HOMO) has major (P78%) contribution from the metal
d-orbitals, whereas the lowest unoccupied molecular orbi-
tal (LUMO) is primarily (P81%) delocalized over the
coordinated O,N,O- or C,N,O-donor ligand and is con-
centrated heavily (P41%) on the azo fragment. Hence
the lowest energy absorption in the visible region is
assignable to a charge-transfer transition from the filled
rhodium orbital (HOMO) to the p*-(azo) orbital (LUMO)
of the tridentate ligand. The other absorptions in the vis-
ible region are attributable to transitions occurring from
the other filled orbitals to the higher energy vacant
orbitals.
4. Experimental
Rhodium trichloride was obtained from Arora Matthey,
Kolkata, India. All other chemicals and solvents were
reagent grade commercial materials and were used as
received. [Rh(PPh3)3Cl] was synthesized by following a
reported procedure [11]. The 2-(20-hydroxyphenylazo)phe-
nol and 2-(20-carboxyphenylazo)-4-methylphenol were pre-
pared following reported procedures [12]. Purification of
dichloromethane and acetonitrile, and preparation of tetra-
butylammonium perchlorate (TBAP) for electrochemical
work were performed as before [13]. Microanalyses (C,
H, N) were performed using a Heraeus Carlo Erba 1108
elemental analyzer. IR spectra were obtained on a Shima-
dzu FTIR-8300 spectrometer with samples prepared as
KBr pellets. Electronic spectra were recorded on a JASCO
V-570 spectrophotometer. Magnetic susceptibilities were
measured using a PAR 155 vibrating sample magnetometer
fitted with a Walker scientific L75FBAL magnet. 1H NMR
spectra were recorded in CDCl3 solution on a Bruker
Avance DPX 300 NMR spectrometer using TMS as the
internal standard. Electrochemical measurements were
made using a CH Instruments model 600 A electrochemical
analyzer. A platinum disc working electrode, a platinum
wire auxiliary electrode and an aqueous saturated calomel
reference electrode (SCE) were used in a three electrode
configuration. All electrochemical experiments were per-
formed under a dinitrogen atmosphere. All electrochemical
data were collected at 298 K and are uncorrected for junc-
tion potentials.
2.3. Electrochemical properties
Electrochemical properties of complexes 9–11 have been
studied in 1:9 dichloromethane–acetonitrile solution (0.1 M
TBAP) by cyclic voltammetry [10]. Voltammetric data are
presented in Table 2 and a selected voltammogram is pre-
sented as Supplementary material (Fig. S3). Each complex
shows an oxidative response on the positive side of SCE
and a reductive response on the negative side. The oxida-
tive response is reversible in nature, characterized by a
peak-to-peak separation (DEp) of ꢁ75 mV and the anodic
peak-current (ipa) is almost equal to the cathodic peak-cur-
rent (ipc) as expected for a reversible response. In view of
the composition of the HOMO, this oxidation is assigned
to a Rh(III)–Rh(IV) oxidation. Similarly in view of the
composition of the LUMO, the irreversible reductive
response is attributed to reduction of the azo group of
the tridentate ligand. One electron nature of the signals is
established by comparing their current heights (ipa) with
those of the ferrocene–ferrocenium couple (DEp = 76 mV)
under similar experimental conditions.
4.1. Synthesis of complexes
Complex 9. 2-(20-Hydroxyphenylazo)phenol (23 mg,
0.11 mmol) was dissolved in benzene (30 mL) and to it
was added triethylamine (25 mg, 0.25 mmol). Then
[Rh(PPh3)3Cl] (100 mg, 0.11 mmol) was added and the
mixture was heated at reflux under dinitrogen atmosphere,
for 5 h to yield a deep red solution. Evaporation of this
solution gave a dark red solid, which was subjected to puri-
fication by thin layer chromatography on a silica plate.
With benzene as the eluant, a red band separated, which
was extracted with acetonitrile. Upon evaporation of the
acetonitrile extract complex 9 was obtained as a crystalline
red solid. Yield: 88%. Anal. Calc. for C48H38N2O2P2ClRh:
C, 65.87; H, 4.35; N, 3.20. Found: C, 65.43; H, 4.37; N,
3. Conclusions
1
The present study shows that 2-(arylazo)phenols, having
a suitable substituent in one ortho-position in the phenyl
ring of the arylazo fragment, can undergo facile C–H or
C–C activation mediated by transition metals. This is man-
ifested in the reaction of 2-(20-carboxyphenylazo)-4-meth-
3.18%. H NMR [14]: 6.18 (t, 1H, J = 7.5); 6.31 (t, 1H,
J = 7.5); 6.60 (d, 1H, J = 6.0); 6.69 (d, 1H, J = 9.0); 6.87
(t, 1H, J = 7.5); 6.97 (d, 1H, J = 9.0); 7.06 (d, 1H,
J = 6.0); 7.14–7.46 (2PPh3).
Complex 10 and complex 11. 2-(20-Carboxyphenylazo)-
4-methylphenol (28 mg, 0.11 mmol) was dissolved in ben-
zene (30 mL) and to it was added triethylamine (25 mg,
0.25 mmol). Then [Rh(PPh3)3Cl] (100 mg, 0.11 mmol) was
added and the mixture was heated at reflux under dinitro-
gen atmosphere for 5 h to yield a bluish-green solution.
Evaporation of this solution gave a dark green solid, which
ylphenol (4) with [Rh(PPh3)3Cl], where ligand
4
undergoes C–H as well as C–C activation. While 2-(20-
hydroxyphenylazo)phenol (3), upon similar reaction
with[Rh(PPh3)3Cl], binds to rhodium only in the O,N,O-
fashion (5) and no C–H activation of this ligand takes
place.

S. Baksi et al. / Journal of Organometallic Chemistry 692 (2007) 1025–1032
1031
was subjected to purification by thin layer chromatography
on a silica plate. With 1:10 acetonitrile–benzene as the elu-
ant, a blue band separated followed by a green one, which
were extracted with acetonitrile. Upon evaporation of these
extracts complex 10 and 11 were obtained as crystalline
blue (yield: 35%) and green (yield: 55%) solids, respectively.
Complex 10: Anal. Calc. for complex C49H40N2OP2ClRh:
C, 67.39; H, 4.58; N, 3.21. Found: C, 67.04; H, 4.56; N,
atom model for each N atom was introduced and geomet-
˚
˚
ric restraints applied: N@N 1.28 A, Cꢂ ꢂ ꢂN 2.28 A and sim-
ilarity restraints on C–N distances. This model refined well,
in one molecule the occupancies converged at 0.537(6) and
0.463(6), while in the other the values were 0.600(6) and
0.400(6). Such disorder typically extends to a lesser extent
into the phenyl rings but no further modeling was deemed
necessary in this case.
1
3.19%. H NMR: 2.00 (CH3); 5.80 (s, 1H); 6.19 (d, 1H,
J = 9.0); 6.35 (t, 1H, J = 7.5); 6.46 (d, 1H, J = 6.0); 6.68
(t, 1H, J = 7.5); 6.99–7.48 (2PPh3); 7.54–7.63 (2H).ast Com-
plex 11: Anal. Calc. for complex C50H40N2O2P2ClRh: C,
65.18; H, 4.35; N, 3.04. Found: C, 65.61; H, 4.33; N,
3.07%. H NMR: 1.82 (CH3); 5.62 (s, 1H); 6.25 (d, 1H,
J = 9.0); 6.54 (t, 1H, J = 7.5); 6.63 (d, 1H, J = 9.0); 7.17–
Acknowledgements
The authors thank the referees for their constructive
comments, which have been helpful in preparing the re-
vised manuscript. Financial assistance received from the
Department of Science and Technology, New Delhi [Grant
No. SR/S1/IC-15/2004] is gratefully acknowledged. A.J.B.
thanks EPSRC (UK) for the provision of a diffractometer.
M.G.B.D. thanks EPSRC (UK) and the University of
Reading for funds for the Image Plate System. S.D. thanks
the Council of Scientific and Industrial Research, New Del-
hi, for her fellowship [9/96(410)/2003-EMR-I].
1
7.58 (2PPh3); 12.41 (COOH).
4.2. X-ray structure determination
Single crystals of complexes 9–11 were grown by slow
diffusion of hexane into dichloromethane solutions of the
respective complexes. Selected crystal data and data collec-
tion parameters are given in Table 4. Data on the crystals
of the complexes 9 and 11 were collected on a Bruker
SMART 1000 CCD diffractometer, while those on the crys-
tal of complex 10 were collected on a Marresearch Image
Plate system, using graphite monochromated MoKa radi-
ation. X-ray data reduction, structure solution and refine-
ment were done using the SHELXS-97 and SHELXL-97
packages [15]. The structures were solved by the direct
methods. In the crystal of complex 9 disorder was identified
in the central –N@N– unit of each azo ligand by unrealistic
geometry and poor refinement as ordered groups. A split
Appendix A. Supplementary material
CCDCs 613285, 613286, and 613287 contain the supple-
mentary crystallographic data for this paper. The data can
be obtained free of charge via htpp://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: depos-
it@ccdc.cam.ac.uk. Partial MO diagrams for complex 10
and 11 (Figs. S1 and S2), and cyclic voltammogram of
complex 11 (Fig. S3). Supplementary data associated with
Table 4
Crystallographic data for complexes 9–11
Complex 9
Complex 10
Complex 11
Empirical formula
Fw
C
875.10
48H38N2O2P2ClRh
C49H40N2OP2ClRh
868.65
C50H40N2O3P2ClRh, 0.5(CH2Cl2)
959.60
ꢀ
Space group
Unit cell dimensions
a (A)
Monoclinic, P21/c
Monoclinic, P21/c
Triclinic, P1
˚
23.4822(10)
17.6758(8)
20.9611(9)
90
114.532
90
12.346(14)
19.05(2)
18.65(2)
90
108.338(10)
90
10.4131(9)
11.9353(10)
19.150(2)
103.681(2)
91.955(2)
95.044(2)
2299.8(4)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
7914.9(6)
8
4164(8)
4
Z
˚
k (A)
0.71073
0.23 · 0.27 · 0.40
150
0.71073
0.05 · 0.05 · 0.30
293
0.71073
0.06 · 0.15 · 0.50
150
0.601
0.0459
Crystal size (mm)
T (K)
l (mmꢀ1
R1
)
0.623
0.565
a
0.0295
0.0794
1.02
0.0473
0.1055
1.11
b
wR2
GOFc
0.1560
1.05
P
P
a
R1 = iFoj ꢀ jFci/ jFoj.
P
P
2
2 1=2
b
c
wR2 ¼ ½ ½wðF 2o ꢀ F c2Þ ꢃ= ½wðF 2oÞ ꢃꢃ
.
P
2
GOF ¼ ½ ½wðF 2o ꢀ F c2Þ ꢃ=ðM ꢀ NÞꢃ1=2, where M is the number of reflections and N is the number of parameters refined.

1032
S. Baksi et al. / Journal of Organometallic Chemistry 692 (2007) 1025–1032
(f) R. Acharyya, S.M. Peng, G.H. Lee, S. Bhattacharya, Inorg.
Chem. 42 (2003) 7378;
(g) R. Acharyya, F. Basuli, R.-Z. Wang, T.C.W. Mak, S. Bhattach-
arya, Inorg. Chem. 43 (2004) 704;
(h) S. Nag, P. Gupta, R.J. Butcher, S. Bhattacharya, Inorg. Chem.
43 (2004) 4814;
this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2006.10.063.
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