Rhodium assisted C{single bond}H activation of N-(2′-hydroxyphenyl)benzaldimines. Synthesis, structure and electrochemical properties of a group of organorhodium complexes

Article abstract of DOI:10.1016/j.jorganchem.2006.04.020

Reaction of a group of N-(2′-hydroxyphenyl)benzaldimines, derived from 2-aminophenol and five para-substituted benzaldehydes (the para substituents are OCH₃, CH₃, H, Cl and NO₂), with [Rh(PPh₃)₃Cl] in refluxing toluene in the presence of a base (NEt₃) afforded a family of organometallic complexes of rhodium(III). The crystal structure of one complex has been determined by X-ray crystallography. In these complexes the benzaldimine ligands are coordinated to the metal center, via dissociation of the phenolic proton and the phenyl proton at the ortho position of the phenyl ring in the imine fragment, as dianionic tridentate C,N,O-donors, and the two PPh₃ ligands are trans. The complexes are diamagnetic (low-spin d⁶, S = 0) and show intense MLCT transitions in the visible region. Cyclic voltammetry shows a Rh(III){single bond}Rh(IV) oxidation within 0.63-0.93 V vs SCE followed by an oxidation of the coordinated benzaldimine ligand. A reduction of the coordinated benzaldimine is also observed within -0.96 to -1.04 V vs SCE. Potential of the Rh(III){single bond}Rh(IV) oxidation is found to be sensitive to the nature of the para-substituent.

Full text of DOI:10.1016/j.jorganchem.2006.04.020

Journal of Organometallic Chemistry 691 (2006) 3581–3588
www.elsevier.com/locate/jorganchem
Rhodium assisted CAH activation of
N-(20-hydroxyphenyl)benzaldimines. Synthesis, structure
and electrochemical properties of a group of organorhodium complexes
a
a
b
a,
*
Semanti Basu , Swati Dutta , Michael G.B. Drew , Samaresh Bhattacharya
a
Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700 032, India
b
Department of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, UK
Received 21 February 2006; received in revised form 5 April 2006; accepted 11 April 2006
Available online 21 June 2006
Abstract
Reaction of a group of N-(20-hydroxyphenyl)benzaldimines, derived from 2-aminophenol and five para-substituted benzaldehydes
(the para substituents are OCH3, CH3, H, Cl and NO2), with [Rh(PPh3)3Cl] in refluxing toluene in the presence of a base (NEt3) afforded
a family of organometallic complexes of rhodium(III). The crystal structure of one complex has been determined by X-ray crystallog-
raphy. In these complexes the benzaldimine ligands are coordinated to the metal center, via dissociation of the phenolic proton and the
phenyl proton at the ortho position of the phenyl ring in the imine fragment, as dianionic tridentate C,N,O-donors, and the two PPh3
ligands are trans. The complexes are diamagnetic (low-spin d6, S = 0) and show intense MLCT transitions in the visible region. Cyclic
voltammetry shows a Rh(III)ARh(IV) oxidation within 0.63–0.93 V vs SCE followed by an oxidation of the coordinated benzaldimine
ligand. A reduction of the coordinated benzaldimine is also observed within ꢀ0.96 to ꢀ1.04 V vs SCE. Potential of the Rh(III)ARh(IV)
oxidation is found to be sensitive to the nature of the para-substituent.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: CAH activation; Schiff bases; Organorhodium complexes; Structure; Electrochemical properties
1. Introduction
and 2-aminophenol, have been selected as the target mole-
cules for CAH activation and rhodium has been selected as
the transition metal for promoting the CAH activation.
These ligands have two potential donor sites, the pheno-
late-oxygen and the imine-nitrogen, and hence are expected
to bind to metal ions, via dissociation of the phenolic pro-
ton, as bidentate N,O-donors forming five-membered che-
late ring (2). In view of the closeness of the pendent phenyl
ring to the metal center in 2, CAH activation at the ortho
position of the phenyl ring leading to the formation of a
cyclometallated species (3) appears to be a possibility. With
the intention of inducing the said CAH activation of the
N-(20-hydroxyphenyl)benzaldimines (1), their reaction has
been carried out with the Wilkinson’s catalyst, viz.
[Rh(PPh3)3Cl]. This particular complex has been picked
up as the rhodium starting material for this reaction
because of its demonstrated ability to promote CAH
Utilization of transition metals in promoting useful
chemical transformations of organic substrates has been
of considerable current interest [1]. Such transformations
usually proceed via a CAH activation of the organic sub-
strate [2], leading to the formation of a reactive organome-
tallic intermediate, which then undergoes further reactions
to yield the final product. Transition metal mediated CAH
activation of organic molecules is therefore of significant
importance and the present work has originated from our
interest in this area [3]. For the present study, a group of
five Schiff base ligands, viz. N-(20-hydroxyphenyl)benzaldi-
mines (1), derived from para-substituted benzaldehydes
*
Corresponding author. Tel.: +91 3324146223; fax: +91 3324146584.
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.2006.04.020

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S. Basu et al. / Journal of Organometallic Chemistry 691 (2006) 3581–3588
activation, as well as to accommodate tridentate ligands
[3a,4]. Reaction of the N-(20-hydroxyphenyl)benzaldimines
(1) with [Rh(PPh3)3Cl] has indeed afforded a family of
organorhodium complexes, where the benzaldimines are
coordinated to the metal center as in 3. The present report
deals with the chemistry of these organorhodium com-
plexes, with special reference to their formation, structure
and, spectral and electrochemical properties.
R = OCH3, CH3, H,
OH
O
Cl, NO2
M
N
C
N
C
H
H
R
R
1
2
O
M
N
C
Fig. 1. View of the 4-OCH3 molecule.
H
RhAP and RhACl distances (Table 1) are all quite normal
[3a,4b] and so are those within the CNO-coordinated benz-
aldimine. However, the RhAO bond is notably longer than
normal and this elongation may be attributed to the strain
developed due to the formation of two adjacent five-mem-
bered chelate rings by the benzaldimine. As all the five
complexes in this family (4) have been prepared similarly
and they display similar spectral and electrochemical prop-
erties (vide infra), the other four 4-R (R ¼ OCH3) com-
plexes are assumed to have a similar structure as 4-OCH3.
R
3
2. Results and discussion
2.1. Synthesis and characterization
Reactions of the N-(20-hydroxyphenyl)benzaldimines (1)
with [Rh(PPh3)3Cl] proceed smoothly in refluxing toluene
in the presence of triethylamine to afford a group of pink-
ish-orange [5] complexes in decent yields. The preliminary
characterization (microanalytical, magnetic susceptibility,
IR, 1H NMR) data of these complexes indicate that in each
of them one benzaldimine, two triphenylphosphines and a
chloride are coordinated to rhodium. To find out the ste-
reochemistry of the complexes as well as to ascertain the
coordination mode of the benzaldimines in them, structure
of a selected member of this family, viz. that obtained from
the reaction with N-(20-hydroxyphenyl)-4-methoxybenz-
aldimine (1, R = OCH3) has been determined by X-ray
crystallography. The structure (Fig. 1) shows that the benz-
aldimine is coordinated to rhodium as a dianionic triden-
tate C,N,O-donor (3). The coordinated chloride shares
the same equatorial plane with the tricoordinated benzaldi-
mine ligand and the metal center, while the two PPh3
ligands have taken up the remaining two axial positions
and hence they are mutually trans. Rhodium is thus sitting
in a CNOP2Cl environment, which is significantly distorted
from ideal octahedral geometry, as reflected in the bond
parameters around the metal center. The RhAC, RhAN,
R
4-R
PPh3
Rh
OCH3
CH3
H
Cl
NO2
4-OCH3
4-CH3
4-H
4-Cl
4-NO2
O
N
Cl
PPh3
C
R
H
4
Table 1
˚
Selected bond lengths (A) and bond angles (ꢁ) for complex 4-OCH3
˚
Bond lengths (A)
Rh(1)AC(75)
Rh(1)AN(71)
Rh(1)AO(81)
Rh(1)AP(1)
Rh(1)AP(2)
Rh(1)ACl(3)
1.996(9)
1.987(7)
2.167(7)
2.387(4)
2.378(4)
2.387(4)
C(72)AN(71)
C(87)AN(71)
C(82)AO(81)
1.345(11)
1.413(11)
1.329(10)
Bond angles (ꢁ)
C(75)ARh(1)AO(81)
P(1)ARh(1)AP(2)
N(71)ARh(1)ACl(3)
162.5(2)
176.24(10)
179.83(16)
C(75)ARh(1)AN(71)
N(71)ARh(1)AO(81)
82.0(3)
80.6(2)

S. Basu et al. / Journal of Organometallic Chemistry 691 (2006) 3581–3588
3583
˚
The absence of any solvent of crystallization in the crys-
tal lattice indicates the possible existence of some non-
covalent interaction(s) between the individual complex
molecules. A careful inspection of the packing pattern in
the lattice reveals that non-covalent interactions of two dif-
ferent types, viz. CAHꢁ ꢁ ꢁCl and CAHꢁ ꢁ ꢁp interactions, are
active in the lattice (Fig. 2). The coordinated chloride in
each complex molecule is found to be hydrogen-bonded
to two hydrogens, viz. the azomethine hydrogen and one
phenyl hydrogen in the phenol fragment of the benzaldi-
mine ligand of an adjacent complex molecule (Fig. 2a).
The Clꢁ ꢁ ꢁH(azomethine) and Clꢁ ꢁ ꢁH(phenyl) distances are
two carbon atoms constituting the edge are 2.773 A and
˚
2.792 A. The observed CAHꢁ ꢁ ꢁCl and CAHꢁ ꢁ ꢁp interac-
tions have therefore been responsible for holding the crys-
tal lattice together and it may be relevant to note here that
both these interactions are of significant importance in
molecular recognition processes as well as in crystal engi-
neering [6,7].
The exact mechanism of the observed CAH activation is
not completely clear to us. However, the sequences shown
in Scheme 1 seem probable. In the initial step the benzaldi-
mine binds, via loss of the phenolic proton, to the metal
center in [Rh(PPh3)3Cl] as a bidentate N,O-donor with loss
of an electron from the metal center and dissociation of one
triphenylphosphine to afford reactive intermediates of type
5, which then undergo cyclometallation via simultaneous
loss of a proton and an electron affording complex 4. Iso-
lation of the speculated intermediates has not been possi-
ble, probably due to their rapid transformation into the
corresponding cyclometallated species. It is relevant to note
here that cyclometallation of such benzaldimines has prece-
dence in the literature [8].
˚
˚
2.591 A and 2.823 A respectively, and the CAHꢁ ꢁ ꢁCl angles
are 164.76ꢁ and 168.90ꢁ respectively for these two hydro-
gens. One meta-phenyl proton of one coordinated PPh3
ligand in each complex molecule is also found to be hydro-
gen bonded to the p cloud of the phenyl ring in the phenol
fragment of the benzaldimine ligand of a neighboring mol-
ecule. However, this hydrogen-bonding interaction is direc-
ted to an edge of the phenyl ring in a g2 fashion (Fig. 2b).
The Hꢁ ꢁ ꢁC distances from the meta-phenyl hydrogen to the
Fig. 2. The hydrogen bonding interactions in the crystal lattice of 4-OCH3. (a) CAHꢁ ꢁ ꢁCl and (b) CAHꢁ ꢁ ꢁp interaction.

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S. Basu et al. / Journal of Organometallic Chemistry 691 (2006) 3581–3588
new bands (viz. near 1590, 1505, 1394, 1334, 1317 and
OH
1262 cmꢀ1) in the spectra of the 4-R complexes, which
are attributable to the coordinated benzaldimine ligand.
1H NMR spectra of the complexes, recorded in CDCl3
solutions, show broad signals within 7.1–7.8 ppm due to
the coordinated PPh3 ligands. The azomethine proton
signal for the coordinated benzaldimine ligand is observed
as a distinct singlet within 6.6–6.8 ppm. Most of the
expected aromatic proton signals for the coordinated benz-
aldimines have been clearly observed, while few signals
could not be detected due to their overlap with other sig-
nals. In the 4-OCH3 and 4-CH3 complexes signals for the
methoxy and methyl hydrogens are observed at 3.46 and
N
C
H
R
1
[RhI(PPh3)3Cl]
-PPh3, -H+, -e-
PPh3
1
O
Cl
1.92 ppm respectively. The infrared and H NMR spectral
II
Rh
data of the complexes are therefore consistent with their
composition.
PPh3
N
C
Electronic spectra of the complexes have been recorded
in acetonitrile solution. Each complex shows several
intense absorptions in the visible and ultraviolet region
(Table 2). The absorptions in the ultraviolet region are
assignable to transitions within the benzaldimine ligand
orbitals and those in the visible region are probably due
to metal to ligand charge-transfer transition. To have an
insight into the nature of the absorptions in the visible
region, qualitative EHMO calculations have been per-
formed [9] on computer generated models of all the com-
plexes, where phenyl rings of the triphenylphosphines
have been replaced by hydrogens. The results are found
to be similar for all the complexes [10]. Compositions of
selected molecular orbitals are given in Table 3 and partial
MO diagram of a selected complex is shown in Fig. 3. The
highest occupied molecular orbital (HOMO) is localized
primarily on the metal center and the next two filled orbi-
tals (HOMO-1 and HOMO-2) also have major contribu-
tion from the metal. Hence these three filled orbitals may
be considered as the rhodium t2 orbitals. The lowest unoc-
cupied molecular orbital (LUMO) is delocalized almost
entirely on the benzaldimine ligand and is concentrated
mostly on the imine fragment. The LUMO+1 and
LUMO+2 are localized on other parts of the benzaldimine
ligand. Hence the lowest energy absorption in the visible
region may be attributed to the charge-transfer transition
from the filled rhodium t2-orbital to the vacant p*(imine)
orbital of the benzaldimine ligands. The other absorptions
H
R
5
-H+, -e-
PPh3
O
N
Cl
III
Rh
PPh3
C
R
H
4
Scheme 1. Probable steps of the formation of the 4-R complexes.
2.2. Spectral studies
Infrared spectra of all the complexes show several prom-
inent bands within 4000–500 cmꢀ1. Each complex displays
three strong bands near 520, 695 and 745 cmꢀ1, which are
due to the coordinated PPh3 ligands. Comparison with the
spectrum of [Rh(PPh3)3Cl] shows the presence of many
Table 2
Electronic spectral and cyclic voltammetric data
Compound
Electronic spectral data kmax, nm (e, Mꢀ1 cmꢀ1 a
)
Cyclic voltammetric datab E, V vs SCE
Complex 4-OCH3
Complex 4-CH3
Complex 4-H
Complex 4-Cl
Complex 4-NO2
528(2200), 500(2100)c, 352(3400)c, 280(10300),
536(1600), 508(1600)c, 352(2800)c, 288(8500)
534(1600), 504(1800)c, 342(2700)c, 288(8400),
536(1700), 510(1800)c, 352(4400)c, 294(14900)
608(1800), 576(1600), 390(1800)c, 290(8900)
0.63d, 0.99d, ꢀ0.98e
0.67d, 1.00d, ꢀ0.97e
0.71d, 0.95d, ꢀ1.03e
0.78d, 1.10d, ꢀ0.96e
0.93d, 1.27d, ꢀ1.04e
a
In acetonitrile.
b
Solvent, acetonitrile; supporting electrolyte, TBAP; scan rate 50 mV sꢀ1
.
c
d
e
Shoulder.
Epa value.
Epc value.

S. Basu et al. / Journal of Organometallic Chemistry 691 (2006) 3581–3588
3585
Table 3
Composition of selected molecular orbitals
Compounds
Contributing fragmentsa
% contribution of fragments to
HOMO
HOMO-1
HOMO-2
LUMO
LUMO+1
LUMO+2
Complex
4-OCH3
Rh
78
11
40
55
65
29
4
88
–
98
2
93
CNOAOCH3
(C@N, 48)
Complex
4-CH3
Rh
CNOACH3
76
11
42
54
65
28
4
92
–
96
2
96
(C@N, 47)
Complex
4-H
Rh
CNOAH
77
11
43
52
65
29
4
93
–
96
2
95
(C@N, 46)
Complex
4-Cl
Rh
CNOACl
78
11
40
53
65
29
4
87
–
97
2
95
(C@N, 47)
Complex
4-NO2
Rh
CNOANO2
77
11
44
49
65
29
2
98
2
97
–
98
(C@N,15)
(NO2 = 53)
a
The coordinated ligands are referred as CNOAR (R = OCH3, CH3, H, Cl, NO2).
of
R
[11], OCH3 = ꢀ0.27, CH3 = ꢀ0.17, H = 0.00,
Cl = 0.23 and NO2 = 0.78] is linear (Fig. S2) with slopes
(q) of 0.28 V (q = reaction constant of this couple [12]),
which shows that the substituent (R) on the coordinated
benzaldimine ligand, which is four-bonds away from the
metal center, can still influence the metal-centered oxida-
tion potential in a predictable manner. The second oxida-
tive response is tentatively assigned to oxidation of the
coordinated benzaldimine ligand. In view of the nature of
the LUMO, the reductive response on the negative side
of SCE is also attributed to reduction of the benzaldimine
ligand. The ligand-based redox responses do not show any
systematic variation with the electronic nature of the
substituent.
Fig. 3. Partial molecular orbital diagram of 4-OCH3.
3. Conclusions
The present study shows that the N-(20-hydroxyphe-
nyl)benzaldimines (1) can undergo facile CAH activation
at one ortho position of the aryl ring, mediated by
[Rh(PPh3)3Cl]. This study also indicates that similar
CAH activation of organic molecules having structural
similarity with the N-(20-hydroxyphenyl)benzaldimines
may also be possible upon their reaction with [Rh-
(PPh3)3Cl], and such possibilities are currently under
exploration.
may be assigned to transitions from the filled metal t2 orbi-
tals to the higher energy vacant orbitals.
2.3. Electrochemical properties
Electrochemical properties of all the 4-R complexes have
been studied by cyclic voltammetry in acetonitrile solution
(0.1 M TBAP). All the complexes show two irreversible
oxidative responses on the positive side of SCE and an irre-
versible reductive response on the negative side (Table 2,
Fig. S1). In view of the composition of the HOMO, the first
oxidative response is assigned to Rh(III)ARh(IV) oxida-
tion. Potential of this oxidation is found to be sensitive
to the nature of the substituent R in the coordinated benz-
aldimine ligand. The potential increases with increasing
electron-withdrawing character of the substituent R. The
plot of oxidation potential vs r [r = Hammett constant
4. Experimental
Rhodium trichloride was obtained from Arora Matthey,
Kolkata, India. Triphenylphosphine, 2-aminophenol and
the para-substituted benzaldehydes were obtained from
Merck, India. [Rh(PPh3)3Cl] was synthesized by following
a reported procedure [13]. The N-(20-hydroxyphenyl)-

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S. Basu et al. / Journal of Organometallic Chemistry 691 (2006) 3581–3588
Table 4
benzaldimines (1) were prepared by reacting equimolar
amounts of respective para-substituted benzaldehyde and
2-aminophenol in ethanol. Purification of acetonitrile and
preparation of tetrabutylammonium perchlorate (TBAP)
for electrochemical work were performed as reported in
the literature [14]. All other chemicals and solvents were
reagent grade commercial materials and were used as
received. Microanalyses (C, H, N) were performed using
a Heraeus Carlo Erba 1108 elemental analyzer. 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 spec-
trometer using TMS as the internal standard. IR spectra
were obtained on a Shimadzu FTIR-8300 spectrometer
with samples prepared as KBr pellets. Electronic spectra
were recorded on a JASCO V-570 spectrophotometer.
Electrochemical measurements were made using a CH
Instruments model 600A electrochemical analyzer. A plat-
inum disc working electrode, a platinum wire auxiliary
electrode and an aqueous saturated calomel reference elec-
trode (SCE) were used in the cyclic voltammetry experiments.
All electrochemical experiments were performed under a
dinitrogen atmosphere. All electrochemical data were col-
lected at 298 K and are uncorrected for junction potentials.
Selected crystallographic data for complex 4-OCH3
Empirical formula
Fw
C50H41NO2P2ClRh
888.14
Monoclinic, P21/n
Space group
Unit cell dimensions
˚
a (A)
12.166(14)
17.078(18)
20.82(2)
93.688(10)
4317(8)
4
0.71073
0.05 · 0.05 · 0.30
293
0.572
0.0970
0.1642
1.12
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
V (A )
Z
˚
k (A)
Crystal size (mm)
T (K)
l (mmꢀ1
)
a
R1
WR2
b
Goodness-of fitc
P
P
a
R1 = iFoj ꢀ j Fci/ j Foj.
P
P
2
2 1=2
b
c
wR2 ¼ ½ ½wðF 2o ꢀ F c2Þ ꢂ= ½wðF 2oÞ ꢂꢂ
.
P
GOF ¼ ½ ½wðF 2o ꢀ F c2Þ ꢂ=ðM ꢀ NÞꢂ1=2, where M is the number of
2
reflections and N is the number of parameters refined.
7.10–7.60 (2PPh3); 5.74 (d, 2H, J = 3.76); 6.33 (d, H,
J = 8.50); 6.66–6.69 (t, H); 6.81 (s, H); 6.90 (d, H,
J = 8.24); 7.64–7.75 (t, H).
4-Cl. Yield: 68%. Anal. Calc.: C, 65.93; H, 4.26; N, 1.57.
1
Found: C, 65.25; H, 4.30; N, 1.60. H NMR: 5.53 (d, H);
4.1. Synthesis of complexes
6.76–6.91 (t, 3H)*; 7.05 (s, 1H); 7.14–7.57 (2PPh3); 7.62–
7.73 (t, 2H)*.
The 4-R complexes were prepared by following a general
procedure. Specific details for a particular complex are
given below.
4-NO2. Yield: 72%. Anal. Calc.: C, 65.16; H, 4.21; N,
1
3.10. Found: C, 65.09; H, 4.22; N, 3.11. H NMR: 5.74
4-OCH3. N-(20-hydroxyphenyl)-4-methoxybenzaldimine
(25 mg, 0.11 mmol) was dissolved in toluene (50 mL) and
triethylamine (22 mg, 0.22 mmol) was added to it. The
solution was then purged with a stream of dinitrogen for
10 min and to it was added [Rh(PPh3)3Cl] (100 mg,
0.11 mmol). The mixture was refluxed under a dinitrogen
atmosphere for 20 h, whereby a reddish-orange solution
was obtained. Evaporation of this solution afforded a dark
red solid, which was subjected to purification by thin layer
chromatography on a silica plate. With 1:40 acetonitrile-
benzene as the eluant, a distinct pinkish-orange band
separated, which was extracted with 1:3 dichoromethane-
acetonitrile. Evaporation of this extract gave 4-OCH3 as
a crystalline pinkish-orange solid. Yield: 70%. Anal. Calc.:
C, 67.61; H, 4.62; N, 1.58. Found: C, 67.20; H, 4.67; N,
(d, 2H, J = 3.76); 6.33 (d, H, J = 8.50); 6.66–6.69 (t, H)*;
6.81 (s, H); 6.90 (d, H, J = 8.24); 7.10–7.64 (2PPh3);
7.64–7.75 (t, H); 8.10 (s, 1H).
4.2. X-ray structure determination
Single crystals of the 4-OCH3 complex were obtained by
slow evaporation of a 1:3 dichloromethane-acetonitrile
solution of the complex. Selected crystal data and data col-
lection parameters are given in Table 4. Data were col-
lected on a Marresearch Image Plate system using
graphite monochromated Mo Ka radiation. X-ray data
reduction and, structure solution and refinement were done
using SHELXS-97 and SHELXL-97 programs [16]. The struc-
ture was solved by the direct methods.
1
1.61. H NMR [15]: 3.46 (OCH3); 5.73–5.74 (2H)*; 6.26
Acknowledgements
(d, H, J = 8.23); 6.34 (d, H, J = 8.33); 6.52–6.65 (t, H);
6.66 (t, H, J = 2.06); 6.69 (s, 1H); 6.83 (d, H, J = 8.32);
7.09–7.63 (2PPh3).
Financial assistance received from the Department of
Science and Technology New Delhi, [Grant No. SR/S1/
IC-15/2004] is gratefully acknowledged. The authors thank
Professor Saswati Lahiri of the Department of Organic
Chemistry, Indian Association for the Cultivation of Sci-
ence, Kolkata, for her help and the RSIC at Central Drug
Research Institute, Lucknow, India, for the C,H,N analysis
data. Swati Dutta and Semanti Basu thank the Council of
4-CH3. Yield: 70%. Anal. Calc.: C, 68.85; H, 4.71; N,
1.61. Found: C, 68.33; H, 4.75; N, 1.64. H NMR: 1.92
(CH3); 5.73–5.74 (2H);*6.36 (d, H, J = 8.43); 6.50 (d, H,
J = 7.41); 6.53–6.73 (t, 2H);*6.77 (d, H, J = 7.65); 7.01 (s,
H); 7.05–7.61 (2PPh3).
1
4-H. Yield: 67%. Anal. Calc.: C, 68.58; H, 4.55; N, 1.63.
1
Found: C, 68.00; H, 4.59; N, 1.65. H NMR: 7.23 (s, H);

S. Basu et al. / Journal of Organometallic Chemistry 691 (2006) 3581–3588
3587
[3] (a) S. Dutta, S.M. Peng, S. Bhattacharya, J. Chem. Soc., Dalton
Trans. (2000) 4623;
Scientific and Industrial Research, New Delhi, for their fel-
lowship [Grant No. 9/96(410)/2003-EMR-I and 9/96(378)/
2002-EMR-I respectively].
(b) F. Basuli, S.M. Peng, S. Bhattacharya, Inorg. Chem. 40 (2001)
1126;
(c) K. Majumder, S.M. Peng, S. Bhattacharya, J. Chem. Soc., Dalton
Trans. (2001) 284;
Appendix A. Supplementary data
(d) I. Pal, S. Dutta, F. Basuli, S. Goverdhan, S.M. Peng, G.H. Lee,
S. Bhattacharya, Inorg. Chem. 42 (2003) 4338;
(e) P. Gupta, R.J. Butcher, S. Bhattacharya, Inorg. Chem. 42 (2003)
5405;
(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;
Crystallographic data for structural analysis have been
deposited with the Cambridge Crystallographic Data
Centre, CCDC reference number 279097. Copy of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ,
UK [fax. (int code): +44(1223)336 033] or email: depos-
it@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk.
One representative voltammogram (Fig. S1) and least-
squares plots of Epa values of Rh(III)-Rh(IV) couple vs r
for the 4-R complexes (Fig. S2).
(i) R. Acharyya, F. Basuli, S.M. Peng, G.H. Lee, R.Z. Wang,
T.C.W. Mak, S. Bhattacharya, J. Organomet. Chem. 690 (2005) 3908;
(j) P. Gupta, S. Dutta, F. Basuli, S.-M. Peng, G.-H. Lee, S.
Bhattacharya, Inorg. Chem. 45 (2006) 460;
(k) R. Acharyya, S. Dutta, F. Basuli, S.-M. Peng, G.-H. Lee, L.R.
Falvello, S. Bhattacharya, Inorg. Chem. 45 (2006) 1252.
[4] (a) S. Dutta, S.M. Peng, S. Bhattacharya, Inorg. Chem. 39 (2000)
2231;
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