Cyclometallation of bis-benzimidazole derivatives with rhodium(III) halides

Article abstract of DOI:10.1016/S0277-5387(99)00129-1

Treatment of rhodium(III) halides with the N-heterocycles (LH), 1,3-bis(benzimidazolyl)benzene (bBzlH₂bzH; Ia) and its N-methyl derivative (bBzlMe₂bzH; Ib) in methanol gave halobridged binuclear cyclometallated products of the compos

Full text of DOI:10.1016/S0277-5387(99)00129-1

Polyhedron 18 (1999) 2351–2360
Cyclometallation of bis-benzimidazole derivatives with rhodium(III) halides
*
V. Gayathri, E.G. Leelamani, N.M.N. Gowda , G.K.N. Reddy
Department of Chemistry, Bangalore University, Central College Campus, Bangalore 560001, India
Received 16 December 1998; accepted 27 April 1999
Abstract
Treatment of rhodium(III) halides with the N-heterocycles (LH), 1,3-bis(benzimidazolyl)benzene (bBzlH2bzH; Ia) and its N-methyl
derivative (bBzlMe2bzH; Ib) in methanol gave halobridged binuclear cyclometallated products of the composition [RhX2L]2 (X5Cl, Br
or I). The chloro complex undergoes halobridge cleavage reactions to yield several new mononuclear complexes of the types
RhCl2(bBzlH2bz)(AsPh3), RhCl(bBzlH2bz)(OClO3)(L9/N-N) (L95AsPh3; N-N52,29-bipyridine or 1,10-phenanthroline) and the
heterocycle bridged binuclear complexes of the composition [RhCl2(bBzlH2bz)]2(m-N-N) (N-N5pyrazine or 4,49-bipyridine). Passage of
CO through [RhCl2(bBzlH2bz)]2 in DMF yielded mononuclear carbonyl complex RhCl2(CO)(bBzlH2bz)?2H2O. Treatment of
carbonylated solution of rhodium trichloride with Ia produced non-cyclometallated mononuclear complex of the type
[Rh(CO)2(bBzlH2bzH)]Cl. The complexes are characterised by 1H, 13C NMR, IR, Far-IR, electronic and FAB-mass spectral studies.
1999 Elsevier Science Ltd. All rights reserved.
Keywords: Cyclometallation; Rhodium; 1,3-Bis(benzimidazolyl)benzene; 1,3-Bis(N-methylbenzimidazolyl)benzene; Binuclear complexes; Multidentate
N-heterocycles
1. Introduction
Williams et al. [18] have synthesised a trimer of the
6-metallated acetato palladium(II) complex (IIIb, R5
CH3; M5Pd) whose crystal structure has been established
by X-ray crystallography, the pendant benzimidazole
group serving as a donor to another cyclometallated
palladium(II). In continuation of our recent publication
[19] on the reactions of rhodium and iridium salts with
multidentate N-heterocycles, herein we report cyclometal-
lation reactions of rhodium(III) with bis(benzimidazole)
derivatives (I).
The chemistry of a variety of organorhodium complexes
of several N-heterocycles and their derivatives has been
widely investigated in recent years [1–8]. However, a
relatively small number of N-heterocycles are observed to
undergo cyclometallation to give five-membered metal-
locycles (II) [9–16]. Furthermore, the chemistry of
cyclometallated complexes is gaining importance as such
complexes have been successively used in organic syn-
thesis, asymmetric synthesis, homogeneous catalysis, liq-
uid crystals and photochemistry [17].
Cyclometallation of the N-heterocycles Ia and Ib could
give rise to products corresponding to (i) mononuclear
closed metallo-bicycle (IIIa; 2-metallation), (ii) mono-
nuclear open metallo-monocycle (IIIb; 4- or 6-metalla-
tion), or (iii) binuclear open metallo-bicycle (IIIc; 4- and
6-metallation, or IIId, 2 and 4-, or 2 and 6-metallation),
the coordination being symmetrical (IIIa, c) or un-
symmetrical (IIIb, d).
*Corresponding author. Tel.: 191-80-221-1679; fax: 191-80-221-
1679.
0277-5387/99/$ – see front matter
PII: S0277-5387(99)00129-1
1999 Elsevier Science Ltd. All rights reserved.

2352
V. Gayathri et al. / Polyhedron 18 (1999) 2351–2360
2.3. Preparation of the complexes
2.3.1. [RhX2(bBzlH2bz)]2 and [RhX2(bBzlMe2bz)]2 (X5
Cl, Br or I)
Rhodium trichloride/bromide (1 mmol) dissolved in
methanol (5 cm3) was treated with a methanolic solution
(5 cm3) of the N-heterocycle (3 mmol). The mixture was
heated under reflux for about 5 h during which a yellow or
brown solid was separated. The solid was washed with
methanol and dried in vacuo. Yield: 60–80%.
Metathesis reaction of the chloro complexes with 15-
fold excess of sodium iodide on prolonged refluxing in
methanol (24 h) gave yellowish-brown iodo complexes.
Yield: 80%.
2.3.2. RhCl2(bBzlH2bz)(AsPh3 )
[RhCl2(bBzlH2bz)]2 (0.5 mmol) was treated with tri-
phenyl arsine (1 mmol) in methanol (50 cm3) and the
mixture was refluxed for 2 days when a yellow solid got
separated. It was washed with methanol and dried in
vacuo. Yield: 50%.
2. Experimental
2.1. Materials
The N-heterocycles bBzlH2bzH and bBzlMe2bzH were
prepared according to a previously published report [20].
Rhodium trichloride was purchased from Arora-Matthey,
India. Hydrated rhodium tribromide was prepared as
described elsewhere [21].
2.3.3. RhCl(bBzlH2bz)(L9/N-N)(OClO3 ) (L95AsPh3 ; N-
N5bipy or phen)
To a suspension of [RhCl2(bBzlH2bz)]2 (1 mmol) in
methanol (50 cm3), triphenyl arsine or 2,29-bipyridine
(bipy) or 1,10-phenanthroline (phen) (2 mmol) and sodium
perchlorate (10 mmol) were added and the mixture was
refluxed for 24 h when a yellow solid got separated. It was
washed with methanol and water and dried in vacuo. Yield:
60%.
2.2. Physical measurement
The IR spectra were recorded on
a Carl-Zeiss
SPECORD 75-IR and Nicolet FT-IR spectrometer. The
electronic spectra were recorded on a Hitachi 150-20
spectrophotometer. The Far-IR spectra were recorded in
polyethylene powder on a Bruker IFS 113V spec-
trophotometer. The 1H and 13C NMR spectra were re-
corded at ambient temperatures on a Bruker WH-270 and
AMX-400 spectrometer with TMS as the internal refer-
ence. Rotating frame Overhauser effect spectroscopy
(ROESY) experiments [22,23] were performed in DMSO-
d6. A spin-lock mixing time of 250 ms was used. Nearly
512 FIDs were collected (each of 1024 complex data
points) with t1 incrementation. The resulting data were
Fourier transformed along F1 and F2 dimensions with zero
filling the t1 data points to 1024. The data were multiplied
by squared sinebell window function shifted by 908 on
both t2 and t1 dimensions prior to Fourier transformation.
1H and 13C spin lattice (T1) relaxation measurements were
performed using inversion recovery method. The FAB-
mass spectra were recorded on a JEOL SX 102/DA-6000
mass spectrometer (using Xenon as the FAB gas and
m-nitrobenzyl alcohol as the matrix) at CDRI, Lucknow,
India. Microanalyses were obtained from 240B Perkin
Elmer elemental analyser. The molar conductivities were
determined using an Elico model CM-82T conductivity
bridge with a conventional dip type conductivity cell.
2.3.4. [RhCl2(bBzlH2bz)]2(m-N-N) (N-N5pyz or bpy)
[RhCl2(bBzlH2bz)]2 (1 mmol) and pyrazine (pyz) or
4,49-bipyridine (bpy) (1 mmol) in methanol (100 cm3)
were refluxed for 24 h when a yellow solid got separated.
It was washed with methanol and dried in vacuo. Yield:
80%.
2.3.5. RhCl2(CO)(bBzlH2bz)?2H2O
CO was bubbled through [RhCl2(bBzlH2bz)]2 (1 mmol)
suspended in dimethyl formamide (10 cm3) and heated to
refluxing temperature. Gradually the complex dissolved to
give a yellow solution. Passage of CO was continued for 6
h and the resultant solution was evaporated to dryness
under reduced pressure when a yellow solid was obtained.
It was washed with acetone and dried in vacuo. Yield:
60%.
2.3.6. [Rh(CO)2(bBzlH2bzH)]Cl
CO was bubbled through an ethanolic solution (10 cm3)
of rhodium trichloride (1 mmol) at refluxing temperature

V. Gayathri et al. / Polyhedron 18 (1999) 2351–2360
2353
until yellow. To this an ethanolic solution (5 cm3) of the
3. Results and discussion
heterocycle (1 mmol) was added. Passage of CO was
continued for about 2 h and the resultant solution was
evaporated under CO atmosphere to a small volume when
a light yellow solid got separated. The solid was washed
quickly with acetone and dried in vacuo. Yield: 60%.
The reaction of rhodium(III) halides with the multiden-
tate N-heterocycles (I, LH) in methanol resulted in yellow
dimeric complexes of the composition [RhX2L]2 (X5Cl or
Br). Metathesis reaction of the chloro complex with
sodium iodide in methanol produced the iodo analogues in
a low state of purity. The complexes are diamagnetic and
are insoluble in common organic solvents except for
[RhX2(bBzlH2bz)]2 (X5Cl, Br or I) when dissolved in
dimethyl formamide and dimethyl sulfoxide, result in
solutions being non-conducting.
The solid state IR spectra of the complexes (Table 1) are
comparable with those of the uncoordinated N-heterocy-
cles barring minor shifts in the positions of the ligand
bands. The NH stretching and N-Me deformation vibra-
tions are observed around 3150 and 1415 cm21, respec-
2.3.7. [Rh(CO)2(bBzlH2bzH)]ClO4
[Rh(CO)2(bBzlH2bzH)]Cl (1 mmol) was suspended in
methanol (20 cm3) and to this sodium perchlorate (2
mmol) was added. CO was passed through the mixture at
refluxing temperature for 4 h. The complex gradually
dissolved to give a yellow solution. It was evaporated to
dryness under reduced pressure to obtain a yellow solid.
The resultant solid was washed with acetone followed by
water and dried in vacuo. Yield: 60%.
Table 1
Analytical and IR data of the complexes
Complex
Analytical data (%)
found (calc.)
IR spectral data (cm21
)
C
H
N
nNH/
dN-Me
nC=N &
nC=C
nRh–Xt
nRh–Xb
nRh–C
nCO
nClO4
[RhCl2(bBzlH2bz)]2
[RhBr2(bBzlH2bz)]2
[RhI2(bBzlH2bz)]2
49.5
(49.6)
42.2
(41.9)
37.2
(36.0)
51.9
(51.9)
43.7
(44.0)
37.0
(38.1)
57.8
(57.8)
3.1
(2.9)
2.1
(2.5)
2.2
(2.1)
3.4
(3.5)
2.9
(3.0)
2.4
(2.5)
3.8
(3.6)
11.0
(11.6)
9.6
(9.8)
8.3
(8.4)
10.9
(10.9)
8.7
(9.3)
7.3
3167
3157
3153
1416
1413
1413
3167
1620
1585
1614
1587
1613
1592
1604
1580
1602
1577
1603
1580
1626
1595
354
264
205
356
281
212
301
215
150
316
223
152
275a
354
334
327
356
304
315
372
[RhCl2(bBzlMe2bz)]2
[RhBr2(bBzlMe2bz)]2
[RhI2(bBzlMe2bz)]2
RhCl2(bBzlH2bz)(AsPh3)
(8.1)
8.3
(7.1)
322,
332,
337
317,
334
RhCl(bBzlH2bz)(AsPh3)(OClO3)
RhCl(bBzlH2bz)(bipy)(OClO3)
RhCl(bBzlH2bz)(phen)(OClO3)
53.7
(53.5)
3.6
(3.3)
6.5
(6.6)
3155
3200
3181
1636
1610
275a
340
369
363
1180,
1103,
628
1114,
1054,
628
1105,
1057,
628
51.5
(51.2)
3.0
(3.0)
12.0
(12.0)
1624
1590
317,
352
–
–
–
52.5
(52.8)
2.9
(2.9)
11.4
(11.6)
1621
1586
316,
363
[RhCl2(bBzlH2bz)]2(pyz)
[RhCl2(bBzlH2bz)]2(bpy)
RhCl2(CO)(bBzlH2bz).2H2O
[Rh(CO)2(bBzlH2bzH)]Cl
[Rh(CO)2(bBzlH2bzH)]ClO4
49.8
(50.5)
53.5
(53.5)
45.7
(46.1)
52.1
(51.9)
46.6
(46.5)
3.1
(2.9)
3.3
(3.1)
3.9
(3.1)
3.3
(2.8)
2.8
(2.3)
13.0
(13.4)
12.4
(12.5)
9.9
(10.2)
10.9
(11.1)
9.1
(9.9)
3193
3103
3172
3140
3181
1625
1594
1594
1580
1629,
1603
1620
298,
351
300,
358
321 (trans),
303, 336 (cis)
–
366
358
336
–
–
–
2019,
2091
2000,
2080
2029,
2091
1620,
1600
–
–
1098,
628
a nRh–As.

Table 2
1H NMR spectral data in DMSO-d6 (d in ppm)a,b
Complex
49
59
69
79
2
4,6
5
NH
bBzlH2bzH
[RhCl2(bBzlH2bz)]2
7.65m
7.71d
7.25m
7.41m
(0.16)
7.42m
(0.17)
7.40m
(0.15)
7.50m
(0.25)
7.68m
(0.43)
7.25m
7.41m
(0.16)
7.42m
(0.17)
7.40m
(0.15)
7.50m
(0.25)
7.68m
(0.43)
7.65m
8.01d
(0.36)
8.01d
(0.36)
8.04d
(0.39)
7.82m
(0.17)
7.81d
(0.16)
9.07s
–
8.28d
8.66d
(0.38)
8.84m
(0.56)
9.09m
(0.81)
8.49d
(0.21)
8.57d
(0.29)
7.75t
7.51t
(20.24)
7.52t
(20.23)
7.52t
(20.23)
8.00t
(0.25)
7.42m
(20.33)
13.14s
14.28s
(1.14)
14.28s
(1.14)
14.29s
(1.15)
–
.
(0.06)
7.73m
(0.08)
7.71m
(0.06)
7.82m
(0.17)
6.37d
[RhBr2(bBzlH2bz)]2
–
–
[RhI2(bBzlH2bz)]2
[Rh(CO)2(bBzlH2bzH)]Cl
RhCl2(AsPh3)(bBzlH2bz)
9.20s
(0.13)
–
14.24s
(1.10)
AsPh3 (7.37
to 7.47m)
aa9
(21.28)
1
bb9
cc9
dd9
ee9
bipy
8.68d
7.39d
7.93t
7.31t
7.44t
8.00t
(0.56)
8.83t
(1.39)
7.77m
8.62d
(0.85)
9.45m
(1.68)
8.39d
8.70d
(0.31)
9.12d
(0.73)
9
RhCl(bipy)(bBzlH2bz)(OClO3)
6.00d
(21.65)
7.06t
(20.19)
7.26t
(0.01)
7.65d
–
–
8.23d
(20.05)
7.78t
(0.03)
14.44s
(1.30)
(21.29)
10.24d
(1.56)
9.10m
7.71d
(21.39)
10.50d
(1.4)
(20.62)
8.48t
(0.55)
8.48m
7.63t
(20.85)
8.81m
(0.33)
2
2
phen
7.97s
RhCl(phen)(bBzlH2bz)(OClO3)
5.73d
(21.92)
6.88t
(20.37)
7.17t
(20.08)
7.59d
(20.06)
8.26m
(20.02)
7.82t
(0.07)
14.45s
(1.31)
8.26m
(0.29)
8.57d
(0.60)
a Values in parentheses are coordination induced shifts (c.i.s.5d complex – d ligand).
b s5singlet, d5doublet, t5triplet, m5multiplet.

Table 3
13C NMR spectral data in DMSO-d6 (d in ppm)a
Complex
29
49
59
69
79
89
99
1,3
2
4,6
5
bBzlH2bzH
[RhCl2(bBzlH2bz)]2
150.85 119.04
158.08 117.73
122.04 122.95 111.67 135.21
123.57 123.80 112.77 133.10
143.84
140.77
131.03
132.77
124.84
127.65
129.82
124.31
181.63b, 124.62
.
(7.23) (21.31) (1.53) (0.85) (1.10) (22.11) (23.07) (1.74)
23.91c
(23.03) (25.51)
(56.79)
[RhBr2(bBzlH2bz)]2
RhCl2(CO)(bBzlH2bz).2H2O
[Rh(CO)2(bBzlH2bzH)]Cl
bipy
158.34 118.30
123.45 123.80 112.60 133.11
141.14
132.73
(1.70)
181.97b 124.70
124.36
(22.95) (25.46)
(7.49) (20.74) (1.41) (0.85) (0.93) (22.10) (22.7)
24.45c
(57.13)
150.65 115.18
(20.2) (23.86) (0.92) (0.01) (3.51) (3.57)
122.96 122.96 115.18 138.78
138.78
(25.06) (2.34)
133.37
184.10b 129.97
130.30
(0.48)
(CO) 181.51b,
79.9c
20.0c
(2.32)
(59.26)
130.56
148.95 114.67
(21.9) (24.37) (2.82) (1.91) (3.0)
124.86 124.86 114.67 135.01
135.01 127.30
(28.83) (23.73) (5.72)
130.22
(2.57)
126.72
(1.88)
(CO) 181.80b,
72.62c
(20.2)
1
aa9
bb9
cc9
dd9
ee9
ff9
149.07 137.03
151.68 128.04
120.29 123.93 155.18
139.96 124.07 156.46
9
RhCl(bipy)(bBzlH2bz)(OClO3) 158.15 113.31
124.07 124.07 113.31 132.70
139.42
133.52
184.94b 125.21
125.59
(7.30) (25.73) (2.03) (1.12) (1.64) (22.51) (24.42) (2.49)
22.28c
(60.1)
(22.44) (24.23) (2.61) (28.99) (19.67) (0.14) (1.28)
5
150.63 128.34
141.34
154.59
(1.56) (28.69) (21.05)
(20.59)
2
phen
149.94 136.19
152.64 126.69
126.66 128.45 123.30
139.02 130.22 127.80
(12.36) (1.77) (4.5)
139.99 130.50 128.31
(13.33) (2.05) (5.0)
145.54
146.77
(1.23)
145.49
(20.05)
RhCl(phen)(bBzlH2bz)(OClO3) 158.29 113.34
123.75 123.75 113.18 132.75
(1.71) (0.8) (1.51) (22.46) (24.20) (2.88)
139.64
133.91
184.93b 125.34
125.49
(7.44) (25.7)
22.71c
(22.31) (24.33) (2.7)
151.64 127.19
(1.7) (29.0)
(29.5)
(60.09)
a Values in parentheses are coordination induced shifts (c.i.s.5d complex – d ligand).
b Doublet.
c
JRh–C in Hz.

2356
V. Gayathri et al. / Polyhedron 18 (1999) 2351–2360
tively and are suggestive of the coordination of the N-
heterocycles to the metal ion via the tertiary nitrogens. The
Far-IR spectra of the complexes displayed peaks corre-
sponding to rhodium–halogen stretches and are indicative
of the presence of both terminal and bridged types of
halides [24]. The spectra also displayed a peak due to
nRh–C in the range 300–360 cm21; the result pointing to
cyclometallation [25] of the bis-benzimidazole derivative.
1
Cyclometallation is further supported by the H and 13C
NMR spectra of the complexes and also the FAB-mass
spectra.
The PMR spectra of bBzlH2bzH and [RhX2L]2 in
DMSO-d6 (Table 2) exhibited resonances due to the
central benzene and the benzimidazole ring protons. The
resonance due to the imine proton is observed around 14 d.
The resonance at 9.07 d arising from the proton on
carbon-2 of the central benzene/phenylene ring of the
un-coordinated heterocycle bBzlH2bzH is absent in the
spectra of the complexed species. Furthermore, the 13C
resonance of C-2 which appeared as a singlet at 129.82 d
for the free heterocycle is split into a doublet [26–28] and
has shifted downfield by nearly 50 d on complexation
(Table 3). The splitting is due to the interaction of 13C
with 103Rh (100%, I51/2) the coupling constant being 24
Hz is diagnostic of rhodium–carbon direct linkage. The
resonances due to C-49 and C-99 of bBzlH2bz unit have
undergone an upfield shift on complexation.
The FAB-MS of [RhCl2L]2 (LH5bBzlH2bzH) has
confirmed the dinuclear nature of the complex. The
spectrum showed a parent ion peak at m/z 966 [M112H].
The parent ion loses Cl, HCl or [HCl1H] to give peaks at
m/z 931, 930 and 929, respectively. These further lose
(HCl1H), HCl or Cl, respectively to give a peak at m/z
894 due to Rh2Cl2L2. Subsequent fragmentation produced
the mononuclear species RhL2 (by loss of RhCl1Cl) and
RhClL (due to loss of RhClL). These molecular ions lose L
or Cl, respectively, to give RhL (m/z 412), which in turn
loses (Rh12H) to give a peak (L –2H) at m/z 307. The
fragmentation reactions are summarised in Scheme 1.
The electronic spectra of [RhX2L]2 exhibited weak
absorption bands in the range 400–500 nm (Table 4) and
are ascribed to d–d transitions of octahedral spin paired d6
system [29]. An intense peak at 370 nm is attributed to
metal-to-ligand charge transfer transition.
The N-heterocycles can serve as bidentate or tridentate
ligands. Earlier, it has been observed that the heterocycles
have displayed a bidentate non-cyclometallated behaviour
[20] in CoX2(LH) (X5Cl, Br or I; LH5Ia or Ib) and
Co(LH)2(ClO4)2 complexes and a bridging tridentate
cyclometallated behaviour in [PdL(OOCCH3)]3?9CH3CN
complex [18]. In the present investigation a tridentate
behaviour of the N-heterocycles (N–C–N) leading to non-
bridging cyclometallation but dihalobridged binuclear na-
ture has been observed. Considering the N-heterocycles as
planar and by taking the N–C–N skeleton, two structures
can be conceived for such complexes, the one being
Scheme 1. Fragmentation pathway of [RhCl2L]2.
centrosymmetric (trans, IVa) and the other being non-
centrosymmetric (cis, IVb). Molecular models favour the
former (IVa) which has less steric hindrance than the latter.
1
Further with both in the H and 13C NMR spectra, only
one set of resonances have been observed implying the
chemical equivalence of the corresponding protons as well
as the carbons of the two heterocycles in each of the
binuclear complexes.
The complex [RhCl2(bBzlH2bz)]2 undergoes halobridge
cleavage reaction. It reacts with AsPh3 in methanol at
refluxing temperature to give a monomeric complex
RhCl2(bBzlH2bz)(AsPh3) (V). In the presence of excess of
sodium
perchlorate,
complex
of
the
type
RhCl(bBzlH2bz)(AsPh3)(OClO3) has been isolated. The
dimer [RhCl2(bBzlH2bz)]2 reacts with chelating bidentate
ligands like 2,29-bipyridine (bipy) and 1,10-phenanthroline
(phen) in the presence of excess of sodium perchlorate to
form yellow crystalline monomeric complexes of the type
RhCl(bBzlH2bz)(N-N)(OClO3) (VI) (N-N5bipy or phen).
On the other hand with bridging bidentate ligands,
[RhCl2(bBzlH2bz)]2 in methanol yielded complexes of the
type [RhCl2(bBzlH2bz)]2(m-N-N) (VII) (N-N5pyrazine

V. Gayathri et al. / Polyhedron 18 (1999) 2351–2360
2357
Table 4
Electronic spectral data in DMF (nm)
Complex
Electronic transitionsa
Ligand bands
M→L
d→d transitions
Charge transfer
Transition
bBzlH2bzH
300 (44231)
309 (51442)
324 (35817)
335 (2599)
299 (29170)
309 (31340)
336 (16585)
304 (37409)
339 (15855)
[RhCl2(bBzlH2bz)]2
[RhBr2(bBzlH2bz)]2
[RhI2(bBzlH2bz)]2
370(9434)
384(7774)
367(12863)
384(11593)
443(98), 469(34), 517(5)
405(737),434(208),
475(83), 548(18)
299(28333)
310(29925)
325(22895)
340(16855)
309(36509)
345(22209)
373(11391)
386(8358)
459(266), 591(27)
RhCl2(bBzlH2bz)(AsPh3)
376(10816)
386(8899)
395(4763)
396(4512)
388(7406)
440(140), 468(64)
439(58), 469(71)
RhCl(bBzlH2bz)(AsPh3)(OClO3)
308(43478)
338(28225)
343(24792)
297(30027)
360(18283)
278(30425)
292(29621)
358(18703)
304(53888)
367(24078)
RhCl(bBzlH2bz)(bipy)(OClO3)
RhCl(bBzlH2bz)(phen)(OClO3)
388(9835)
398(3004)
389(9162)
397(3759)
418(905), 466(42)
447(66), 466(31)
[RhCl2(bBzlH2bz)]2(pyz)
386(23056)
392(1200)
394sh(11341)
382(29670)
393(13894)
375(2288)
395(809)
439(258), 471(94)
440(207), 474(119)
422(244), 450(74)
[RhCl2(bBzlH2bz)]2(bpy)
294(47525)
300(39142)
305(35605)
RhCl2(CO)(bBzlH2bz).2H2O
a e values are in parentheses.
1
(pyz) or 4,49-bipyridyl (bpy)). A similar reaction with
phenazine also produced a binuclear complex, though in a
low state of purity. Reaction of CO with
[RhCl2(bBzlH2bz)]2 in dimethylformamide at refluxing
temperature gave monomeric yellow rhodium(III) carbonyl
complex of the composition RhCl2(CO)(bBzlH2bz)?2H2O
(VIII).
ported by H and 13C NMR spectra of the complexes. The
carbonyl complex exhibits two intense nCO peaks at 2019
and 2091 cm21 indicating the presence of two isomers
(VIII; CO trans to Cl and trans to C). The Far-IR spectra
of the complexes exhibit peaks corresponding to nM-Cl,
nM-N and nM-C, and are diagnostic of terminal halides.
1
The H NMR spectra of the complexes displayed peaks
The complexes are insoluble in common organic sol-
vents but soluble in dimethyl formamide or dimethyl
sulfoxide in which the solutions are non-conducting. The
physical properties and analytical data of the complexes
are listed in Table 1.
The complexes exhibit nNH in the range 3100–3200
cm21as a broad peak. The perchlorate complexes (being
non-electrolytes in DMSO/DMF) in addition to the
heterocycle bands exhibit peaks around 1100 and 628
cm21, the former peak is split indicating the coordination
of perchlorate to the metal ion [30]. In view of the above,
it is likely that the heterocycle bipy or phen is behaving as
a monodentate rather than bidentate ligand. This is sup-

2358
V. Gayathri et al. / Polyhedron 18 (1999) 2351–2360
uncoordinated part of the heterocycle and the other set in
the downfield region to the coordinated part. Surprisingly,
the heterocycle, bipy or phen is neither chelating nor
bridging bidentate in the complexes. Such a coordination
with pendant nitrogen is rather unusual in organometallic
chemistry. The monodentate behaviour of bipy or phen in
the complexes is also supported by ROESY measurements.
The ROESY spectra of the complexes have revealed the
interaction of all the protons (a9 to d9) of the coordinated
part of bipy or phen with H-49 of bBzlH2bz as evidenced
by the interligand NOE measurements. The H-49 shows
NOE to a9, b9, c9 and d9 in the bipy complex and a9, b9 and
c9 in the phen complex. The results indicate that the
coordinated part of the bipy or phen is much closer to
bBzlH2bz than the uncoordinated part. The spin lattice
relaxation times of the protons and carbons of the coordi-
nated part of the bipy in RhCl(bBzlH2bz)(bipy)(OClO3)
are observed to be lower compared to those of the
uncoordinated part implying more flexibility of the latter
unit. Detailed 2D NMR studies on the complexes are in
progress. The monodentate behaviour of the ligand may be
attributed to the electronic factor rather than the steric
hindrance around the metal ion. The complexes exhibit
negative c.i.s values for C-49 and C-99 of bBzlH2bz. The
13C NMR spectrum of the carbonyl complex displayed two
doublets one at 182 and the other at 184 d. The 103Rh –
13C coupling constant of the former is 80 Hz (due to
Rh–CO) whereas that of the latter is 20 Hz (due to
Rh–C-2 of bBzlH2bz).
The FAB-MS of RhClL(N-N)(OClO3) (LH5
bBzlH2bzH) have confirmed the mononuclear nature of the
complexes. The spectra consist of molecular ion peaks at
m/z 702 (N-N5bipy) and 726 (N-N5phen). Both the
complexes first lose perchlorate to produce RhClL(N-N)
and then Cl to give RhL(N-N). Subsequent loss of N-N
gives RhL (m/z 412). Both RhL(N-N) and RhL lose
Rh12H to give a ligand peak at m/z 307. In the case of
the FAB-MS of [RhCl2(bBzlH2bz)]2(m-bpy) the molecu-
lar ion peak corresponding to the dimer (m/z 1120) was
not observed, but the peaks due to the fragmentation
products RhClL2 (m/z 757), RhL2 (m/z 712), RhClL (m/z
447) and Rh(bBzlH2bz) (m/z 412) were observed.
A
dicarbonyl
complex
of
rhodium(I)
RhCl(CO)2(bBzlH2bzH) as a light yellow solid was
isolated by treating an alcoholic carbonylated solution of
rhodium trichloride with bBzlH2bzH. In the case of
bBzlMe2bzH, a blue coloured dicarbonyl (nCO, 1993 and
2068 cm21) of low state of purity was obtained. The
chloro carbonyl is insoluble in nitrobenzene and acetoni-
trile but soluble in dimethyl formamide and alcohol in
which its electrolytic behaviour is uni-univalent.
due to bBzlH2bz and the substituted ligands. The reso-
nance due to the imine proton is observed around 14 d. The
resonance of H-49 of bBzlH2bz has undergone an upfield
shift as compared to that of the parent complex. A negative
c.i.s. has been observed and this is probably due to metal-
The IR spectrum of the chloro carbonyl in addition to
the ligand peaks exhibited two intense peaks around 2000
and 2080 cm21 due to nCO. The nNH of the coordinated
heterocycle is observed at 3140 cm21. The complex has
1
to-ligand p-back donation [31]. Interestingly the H and
13C NMR spectra of the complexes RhCl(bBzlH2bz)(N-
N)(OClO3) (N-N5bipy or phen) exhibited two sets of
resonances due to bipy or phen (Figs. 1 and 2). One set of
proton resonances in the upfield region assignable to the
1
not undergone metallation reaction as evidenced by its H
and 13C NMR spectra. The PMR spectrum has displayed a

V. Gayathri et al. / Polyhedron 18 (1999) 2351–2360
2359
Fig. 1. 1H NMR spectrum of RhCl(bBzlH2bz)(bipy)(OClO3).
Fig. 2. 13C NMR spectrum of RhCl(bBzlH2bz)(phen)(OClO3).

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V. Gayathri et al. / Polyhedron 18 (1999) 2351–2360
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peaks (2029 and 2091 cm21) and also peaks due to ionic
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Acknowledgements
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Radiochem. 28 (1984) 255.
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The authors are thankful to the UGC, New Delhi for the
DRS programme, Professor C.L. Khetrapal and G.A.
Nagana Gowda, SIF and Dr H.S. Vasan, SSCU, IISc,
Bangalore for NMR and Far-IR spectra. The authors are
also indebted to the referees for valuable suggestions.