Synthesis, characterisation and theoretical studies on some piano-stool ruthenium and rhodium complexes containing substituted phenyl imidazole ligands

Article abstract of DOI:10.1016/j.jorganchem.2009.11.011

Reactions of the chloro-bridged arene ruthenium complexes [{(η⁶-arene)RuCl(μ-Cl}₂] (η⁶-arene = benzene, p-cymene) and structurally analogous rhodium complex [{(η⁵-C₅Me₅)RhCl(μ-Cl}₂

Full text of DOI:10.1016/j.jorganchem.2009.11.011

Journal of Organometallic Chemistry 695 (2010) 567–573
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, characterisation and theoretical studies on some piano-stool
ruthenium and rhodium complexes containing substituted phenyl imidazole ligands
*
Ashish Kumar Singh, Prashant Kumar, Mahendra Yadav, Daya Shankar Pandey
Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221005, UP, India
a r t i c l e i n f o
a b s t r a c t
6-arene)RuCl(
5-C5Me5)RhCl(
l
l
-Cl}2] (
-Cl}2] with imidazole
g
6-arene = ben-
Article history:
Reactions of the chloro-bridged arene ruthenium complexes [{(
zene, p-cymene) and structurally analogous rhodium complex [{(
g
g
Received 25 September 2009
Received in revised form 10 November 2009
Accepted 11 November 2009
Available online 17 November 2009
based ligands viz., 1-(4-nitro-phenyl)-imidazole (NOPI), 1-(4-formylphenyl)-imidazole (FPI) and 1-(4-
hydroxyphenyl)-imidazole (HPI) have been investigated. The resulting complexes have been character-
ised by elemental analyses, IR, 1H and 13C NMR, electronic absorption and emission spectral studies.
Crystal structure of the representative complex [(g
5-C5Me5)RhCl2(NOPI)] has been determined crystallo-
Keywords:
Ruthenium
Rhodium
graphically. Geometrical optimisation on the complexes have been performed using exchange correlation
functional B3LYP. Optimised bond lengths and angles of the complexes have been found to be in good
agreement with our earlier reports and single crystal X-ray data of the complex [(g
5-C5Me5)RhCl2(NOPI)].
g
6-Arene
Ó 2009 Elsevier B.V. All rights reserved.
Pentamethylcyclopentadienyl
Weak-interactions
1. Introduction
internal charge transfer (TICT) and its ability to behave as a good
bridging ligand [26,27].
The dimeric chloro-bridged arene ruthenium [{(
g
6-arene)Ru(
l
-
In this direction to develop the chemistry of CPI and related li-
gands, we have examined reactivity of the arene ruthenium com-
Cl)Cl}2] (arene = benzene and their derivatives) and structurally
analogous rhodium and iridium complexes [{(
5-C5Me5)M(
Cl)Cl}2] (M = Rh or Ir) imparting
6-/ 5-cyclic hydrocarbon ligands
g
l
-
plexes [{(
with 1-(4-cyanophenyl)-imidazole and have reported first exam-
ples of luminescent complexes containing (
6-arene)Ru- moiety
g l-Cl)Cl}2] (arene = benzene, p-cymene)
6-arene)Ru(
g
g
are versatile and valuable synthetic intermediates that have seen
g
many applications in coordination, organometallic chemistry and
[27–29]. It is expected that the replacement of cyanophenyl group
in CPI by nitro phenyl, phenyl carbaldehyde or phenolic group may
lead to substantial changes in the properties of the resulting com-
plexes. With this view-point we have examined reactivity of the
catalysis [1–6]. These complexes undergo
a rich variety of
chemistry via intermediacy of the chloro-bridge cleavage reactions
leading to the formation of a series of interesting neutral and cat-
ionic mononuclear half-sandwich complexes [7–13]. Air-stable,
arene ruthenium [{(
g
6-arene)Ru(
l
-Cl)Cl}2] (arene = benzene,
water-soluble complexes containing
(g
6-arene)Ru- and
(
g5
-
p-cymene) and rhodium complexes [{(
g
5-C5Me5)Rh(
l-Cl)Cl}2]
C5Me5)Rh- moieties find wide applications in many areas including
homogeneous catalysis, polymeric materials, nano-cages and
nano-particle precursors [14–19]. These are also, being explored
for their medicinal properties as anticancer agents [20–25]. Fur-
ther, it have been shown that certain acceptor–donor molecules
exhibit twisted internal charge transfer (TICT) which appears
attractive for molecular switching, since there is an almost perfect
orbital decoupling in the twisted internal charge transfer state. It is
expected that the complexes in which redox sites are bridged by
this type of molecule could be a good model to test the possibility
of molecular switching. In this regard, 1-(4-cyanophenyl)-imidaz-
ole (CPI) have drawn special attention due to occurrence of twisted
with 1-(4-nitrophenyl)-imidazole (NOPI), 1-(4-formylphenyl)-
imidazole (FPI) and 1-(4-hydroxyphenyl)-imidazole (HPI). In this
paper we report syntheses and spectral characterisation of a series
of neutral mononuclear complexes containing (
5-C5Me5)Rh- moieties and aforesaid ligands. Also, we present
herein crystal structure of the representative rhodium complex
[(
5-C5Me5)RhCl2(NOPI)].
g
6-arene)Ru- and
(g
g
2. Experimental
2.1. Materials and physical measurements
All the chemicals were obtained from commercial sources and
used without further purifications. Pentamethylcyclopentadiene,
hydrated rhodium(III) chloride, hydrated ruthenium(III) chloride,
* Corresponding author. Tel.: + 91 542 2307321 105.
E-mail address: dspbhu@bhu.ac.in (D.S. Pandey).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.11.011

568
A.K. Singh et al. / Journal of Organometallic Chemistry 695 (2010) 567–573
4-fluronitrobenzene, 4-fluorobenzaldehyde, 4-imidazol-yl-phenol
and imidazole were procured from Sigma–Aldrich. The ligands 1-
(4-nitrophenyl)-imidazole (NOPI) [30], 1-(4-formylphenyl)-imid-
93.9 (C–CH3), 9.1 (C–CH3). UV–vis. {CH2Cl2, knm
(4.48 Â 103), 289 (1.79 Â 104), 258 (1.75 Â 104).
(e)}: 400
azole (FPI) [31] and precursor complexes [{(
g
6-arene)Ru(
5-C5Me5)Rh(
l
l
-Cl)Cl}2]
-Cl)Cl}2]
2.2.4. Preparation of complex [(
It was prepared following the procedure for 1 using FPI (86 mg,
0.50 mmol) and [{( -Cl}2] (125 mg, 0.25 mmol).
6-C6H6)RuCl(
g
6-C6H6)RuCl2(FPI)] 4
(arene = benzene [32], p-cymene [33]), [{(
g
[34] were prepared and purified following the literature proce-
dures. Elemental analyses on the complexes were performed on
an Exter CE-440 CHN Analyzer. IR and electronic absorption spec-
tra were recorded on a Perkin Elmer-577 and Shimadzu-UV 1700
spectrophotometers, respectively. 1H and 13C NMR spectra of the
complexes were recorded on a JEOL AL 300 FT-NMR machine in
d-chloroform at 298 K using TMS as an internal reference. Emission
spectra were recorded in dichloromethane on a Varian Carry Eclips
spectrophotometer.
g
l
Yield: 171 mg, 81%. Microanalytical data: Anal. Calc. C16H14N2OCl2-
Ru, requires: C, 45.51; H, 3.34; N, 6.63. Found: C, 45.37; H, 3.63; N,
6.52%. IR(KBr cmÀ1): 3482 (vbr), 3122 (m), 2960 (w), 1698 (vs),
1601(vs), 1519 (s), 1487 (vs), 1375 (w), 1303 (vs), 1216 (w),
1171 (s), 1120 (m), 1056 (s), 957 (w), 828 (s), 510 (w). 1H NMR
(CDCl3, d ppm): 10.03 (s, 1H), 8.47 (s, 1H), 8.29 (d, 2H, J = 9.0 Hz),
7.58 (s, 1H), 7.52 (d, 2H, J = 6.6 Hz), 7.32 (s, 1H), 6.45 (s, 6H). 13C
NMR (75.45 MHz, CDCl3, d ppm): 190.1, 140.0, 136.9, 135.6,
131.5, 122.3, 118.6, 87.3(C
g
6-C6H6). UV–vis. {CH2Cl2, knm (d)}:
451 (1.43 Â 103), 284 (1.88 Â 104), 240 (1.69 Â 104).
2.2. Syntheses
g
6-C6H6)RuCl2(NOPI)] 1
2.2.5. Preparation of complex [(
It was prepared following the method for 1 using FPI (86 mg,
0.50 mmol) and [{( -Cl}2] (153 mg, 0.25 mmol).
6-C10H14)RuCl(
g
6-C10H14)RuCl2(FPI)] 5
2.2.1. Preparation of [(
To a solution of NOPI (95 mg, 0.50 mmol) in methanol (25 mL),
the ruthenium complex [{( -Cl}2] (125 mg, 0.25
6-C6H6)RuCl(
g
l
g
l
Yield: 187 mg, 78%. Microanalytical data: Anal. Calc. C20H22N2OCl2-
Ru, requires: C, 50.21; H, 4.64; N, 5.86. Found: C, 50.06; H, 4.55; N,
5.59%. IR (KBr cmÀ1): 3455 (vbr), 3126 (m), 2918 (w), 1693 (vs),
1602 (vs), 1517 (s), 1490 (vs), 1376 (w), 1304 (vs), 1213 (w),
1168 (s), 1120 (m), 1061 (s), 829 (vs), 759 (w), 478 (w). 1H NMR
(CDCl3, d ppm): 10.07 (s, 1H), 8.52 (s, 1H), 8.45 (d, 2H, J = 8.7 Hz),
8.02 (d, 2H, J = 9.0 Hz), 7.55 (s, 1H), 7.37 (s, 1H), 5.61 (d, 2H,
J = 5.7 Hz), 5.41 (d, 2H, J = 5.4 Hz), 3.00 (m, 1H), 2.26 (s, 3H), 1.38
(d, 6H, J = 6.6 Hz). 13C NMR (75.45 MHz, CDCl3, d ppm): 190.5,
141.1, 137.8, 134.7, 132.4, 121.2, 119.1, 101.8, 97.9, 81.2, 79.6,
30.3((CH3)2CH), 23.3 ((CH3)2CH), 20.1 (CH3). UV–vis. {CH2Cl2, knm
mmol) was added and the resulting suspension was stirred at room
temperature for 4 h. Clear pale red solution thus obtained was fil-
tered through celite to remove any solid impurities. Addition of
petroleum ether (60–80 °C) to the filtrate afforded pale red crystal-
line product. It was separated by filtration, washed with methanol
(2 Â 10 mL), diethyl ether (2 Â 10 mL) and dried under vacuum.
Yield: 176 mg, 80%. Microanalytical data: Anal. Calc. C15H13N3-
O2Cl2Ru, requires: C, 41.02; H, 2.98; N, 9.57. Found: C, 40.82; H,
3.23; N, 9.43%. IR (KBr cmÀ1): 3449 (vbr), 3086 (s), 1595 (vs),
1514 (s), 1432 (s), 1339 (vs), 1304 (vs) 1270 (vs), 1199 (w), 1111
(vs), 1064 (vs), 1008 (w), 957 (w), 845 (s), 747 (s), 688 (w), 621
(vs), 506 (w). 1H NMR (CDCl3, d ppm): 8.48 (s, 1H), 8.09 (d, 2H,
J = 9.3 Hz), 8.00 (d, 3H, J = 9.0 Hz), 7.55 (s, 1H), 6.61 (s, 6H). 13C
NMR (75.45 MHz, CDCl3, d ppm): 146.2, 140.4, 139.4, 128.3,
(e
)}: 446 (1.44 Â 103), 290 (1.96 Â 104), 241 (1.62 Â 104).
2.2.6. Preparation of complex [(
This complex was prepared using FPI (86 mg, 0.50 mmol) and
5-C5Me5)RhCl(
-Cl}2] (155 mg, 0.25 mmol) following the
g
5-C5Me5)RhCl2(FPI)] 6
125.5, 121.5, 118.6, 87.63(C
g
6-C6H6). UV–vis. {CH2Cl2, knm
(e
)}:445 (1.58 Â 103), 290 (2.13 Â 104), 242 (1.76 Â 104).
[{(g
l
method for 1. Yield: 197 mg, 82%. Microanalytical data: Anal. Calc.
C20H23N2OCl2Rh, requires: C, 49.92; H, 4.82; N, 5.82. Found: C,
49.71; H, 4.57; N, 5.63%. IR (KBr cmÀ1): 3478 (vbr), 3123 (m),
3060 (w), 2960 (br), 1698 (vs), 1600 (vs), 1519 (vs), 1485 (m),
1376 (w), 1302 (vs) 1215 (vs), 1170 (s), 1118 (s), 1055 (vs), 826
(s), 509 (w). 1H NMR (CDCl3, d ppm): 10.05 (s, 1H), 8.50 (s, 1H),
8.02 (d, 2H, J = 8.4 Hz), 7.57 (d, 2H, J = 8.4 Hz), 7.44 (s, 1H), 7.37
(s, 1H), 1.58 (s, 15H). 13C NMR (75.45 MHz, CDCl3, d ppm):190.6,
140.3, 137.5, 135.6, 131.7, 121.3, 119.0, 93.9 (C–CH3), 9.1(C–CH3).
2.2.2. Preparation of [(
This complex was prepared from NOPI (95 mg, 0.50 mmol) and
6-C10H14)RuCl(
-Cl}2] (153 mg, 0.25 mmol) following the
g
6-C10H14)RuCl2(NOPI)].1/2(Et2O) 2
[{(g
l
method 1. Yield: 196 mg, 79%. Microanalytical data: Anal. Calc.
C19H21N3O2Cl2Ru, requires: C, 46.07; H, 4.27; N, 8.48. Found: C,
45.93; H, 4.15; N, 8.27%. IR (KBr cmÀ1): 3450 (vbr), 3099 (m),
2917 (w), 1598 (s), 1514 (s), 1339 (vs), 1302 (s), 1250 (w), 1111
(m), 1058 (s), 1023 (w), 848 (s), 754 (s), 686 (w), 509 (w). 1H
NMR (CDCl3, d ppm): 8.43 (s, 1H), 8.36 (d, 2H, J = 8.7 Hz), 7.54 (d,
3H, J = 9.0 Hz), 7.36 (s, 1H), 5.51 (d, 2H, J = 5.4 Hz), 5.35 (d, 2H,
J = 5.4 Hz), 3.47 (q, 2H, J = 7.2 Hz), 3.01 (m, 1H), 2.24 (s, 3H), 1.32
(d, 6H, J = 6.9 Hz), 1.208 (t, 3H, J = 6.9 Hz). 13C NMR (75.45 MHz,
CDCl3, d ppm): 146.4, 140.1, 139.0, 128.5, 125.0, 122.1, 118.0
103.2, 96.9, 82.2, 81.0, 29.9((CH3)2CH), 23.0 ((CH3)2CH), 19.0
UV–vis. {CH2Cl2, knm (
e
)}: 402 (3.44 Â 103), 282 (1.77 Â 104), 254
(1.80 Â 104).
2.2.7. Preparation of complex [(
It was prepared from HPI (80 mg, 0.50 mmol) and [{(g6
C6H6)RuCl( -Cl}2] (125 mg, 0.25 mmol) following the method for
g
6-C6H6)RuCl2(HPI)] 7
-
l
1.Yield: 164 mg, 80%. Microanalytical data: Anal. Calc. C15H14N2-
OCl2Ru, requires: C, 43.91; H, 3.44; N, 6.83. Found: C, 43.68; H,
3.22; N, 6.76%. IR (KBr cmÀ1): 3543 (vbr), 3145 (m), 2940 (br),
1602 (vs), 1522 (s), 1425 (br), 1391 (vs), 1310 (vs) 1265 (vs),
1185 (w), 1120 (vs), 1066 (vs), 965 (w), 842 (s), 771 (s), 661 (w),
622 (vs), 565 (w). 1H NMR (CDCl3, d ppm): 9.95 (s, 1H, OH),
8.52(s, 1H), 8.37 (d, 2H, J = 8.7 Hz), 7.61 (s, 1H), 7.52 (d, 2H,
J = 6.6 Hz), 7.32 (s, 1H), 5.85 (s, 15H). 13C NMR (75.45 MHz, CDCl3,
(CH3). UV–vis. {CH2Cl2, knm
(e
)}: 442 (1.10 Â 103), 290
(2.11 Â 104), 241 (1.73 Â 104).
2.2.3. Preparation of complex [(
This complex was prepared from NOPI (95 mg, 0.50 mmol) and
5-C5Me5)RhCl(
-Cl}2] (155 mg, 0.25 mmol) following the pro-
g
5-C5Me5)RhCl2(NOPI)] 3
[{(g
l
cedure for 1. Yield: 202 mg, 81%. Microanalytical data: Anal. Calc.
C19H22N3O2Cl2Rh, requires: C, 45.81; H, 4.45; N, 8.43% Found: C,
45.65; H, 4.87; N, 8.22%. IR (KBr cmÀ1): 3451 (vbr), 3140 (m),
2960 (w), 1602 (s), 1522 (s), 1463 (s), 1337 (vs), 1302 (s), 1267
(w), 1220 (s), 1109 (m), 1065 (s), 797 (s), 621 (w), 478 (w). 1H
NMR (CDCl3, d ppm): 8.52 (s, 1H), 8.37 (d, 2H, J = 9.0 Hz), 7.58 (d,
2H, J = 8.7 Hz), 7.42 (m, 2H), 1.61(s, 15H). 13C NMR (75.45 MHz,
CDCl3, d ppm): 146.8, 140.5, 137.5, 132.2, 125.8, 121.4, 119.2,
d ppm): 157.2, 137.5, 131.9, 128.3, 122.7, 118.5, 117.0, 88.1(C g6
-
C6H6).
2.2.8. Preparation of complex [(
This complex was prepared from HPI (80 mg, 0.50 mmol) and
6-C10H14)RuCl(
-Cl}2] (153 mg, 0.25 mmol) following the same
procedure as employed for 1. Yield: 189 mg, 81%. Microanalytical
g
6-C10H14)RuCl2(HPI)] 8
[{(g
l

A.K. Singh et al. / Journal of Organometallic Chemistry 695 (2010) 567–573
569
data: Anal. Calc. C19H22N2OCl2Ru, requires: C, 48.93; H, 4.94; N,
b = 12.503(3) Å, c = 13.912(3) Å,
90.00°, V = 2090.9(7) Å3, Z = 4, Dcalc = 1.583, F(0 0 0) = 1008,
= 1.091, T(K) = 293(2), k = 0.71073, R(all) = 0.0446, R(I > 2 (I)) =
a = 90.00°, b = 102.39(3)°, c =
5.97. Found: C, 48.82; H, 4.75; N, 5.86%. IR (KBr cmÀ1); 3540
(vbr), 3141 (m), 2925 (br), 1597 (vs), 1525 (s), 1422 (br), 1388
(vs), 1310 (vs) 1268 (vs), 1184 (w), 1125 (vs), 1070 (vs), 964 (w),
839 (s), 773 (s), 656 (w), 623 (vs), 560 (w). 1H NMR (CDCl3, d
ppm): 9.86(s, 1H, OH), 8.37(s, 1H), 8.06 (d, 2H, J = 8.7 Hz), 7.59
(d, 2H, J = 9.0 Hz), 7.36 (d, 2H, J = 8.7 Hz), 5.72 (d, 2H, J = 6.3 Hz),
5.55 (d, 2H, J = 6.6 Hz), 3.06(s, 1H), 2.32 (s, 3H), 1.39(d, 6H,
J = 6.6 Hz). 13C NMR (75.45 MHz, CDCl3, d ppm): 157.0, 138.0,
132.4, 128.1, 122.3, 119.1, 116.6, 102.8, 97.5, 82.7, 81.4,
30.7((CH3)2CH), 22.2 ((CH3)2CH), 18.7 (CH3).
l
r
0.0308, wR2 = 0.0644, wR2 [I > 2r(I)] = 0.0612, GOF = 1.249.
2.4. Computational methods
Calculations were performed using hybrid B3LYP density func-
tional method which uses Becke’s 3-parameter non-local exchange
functionals mixed with the exact (Hartree–Fock) exchange func-
tional and Lee–Yang–Parr’s non-local correlation functional
[36,37]. Geometries of the complexes were optimised without
g
5-C5Me5)RhCl2(HPI)] 9
**
2.2.9. Preparation of complex [(
It was prepared following exactly the same procedure as em-
ployed for 1 starting from HPI (80 mg, 0.50 mmol) and [{(g5
C5Me5)RhCl( -Cl}2] (155 mg, 0.25 mmol) in methanol.. Yield:
185 mg, 79%. Microanalytical data: Anal. Calc. C19H23N2OCl2Rh, re-
quires: C, 48.64; H, 4.94; N, 5.97. Found: C, 48.30; H, 4.15; N, 6.16%.
IR (KBr cmÀ1): 3440 (vbr), 2932 (br), 1599 (vs), 1525 (s), 1425 (br),
1385 (vs), 1323 (vs), 1274 (vs), 1190 (w), 1120 (vs), 1065 (vs), 963
(w), 835 (s), 763 (s), 650 (w), 624 (vs), 565 (w). 1H NMR (CDCl3, d
ppm): 9.90(s, 1H, OH), 8.49(s, 1H), 8.37 (d, 2H, J = 9.0 Hz), 7.58 (d,
2H, J = 8.7 Hz), 7.42 (m, 2H), 1.61(s, 15H). 13C NMR (75.45 MHz,
CDCl3, d ppm): 157.1, 137.5, 132.2, 128.1, 122.7, 118.6, 116.9,
94.2 (C–CH3), 9.3(C–CH3).
any symmetry restrictions with standard 6-31G
basis sets
[38,39] for N, C, H, O and Cl elements and LANL2DZ [40–42] for
Ru and Rh which combines quasi-relativistic effective core poten-
tials with a valence double-basis set. Frequency calculations were
performed to determine whether the optimised geometries were
minima on the potential energy surface. The electronic structure
of the complexes were examined by natural charges at each atom
computed using Kohn–Sham orbitals obtained from DFT calcula-
-
l
**
tions [43]. 6-31G basis sets for N, C, H, O and Cl elements and
LANL2DZ for Ru and Rh elements. The calculations were performed
using GAUSSIAN 03 program [44].
3. Results and discussion
2.3. X-ray crystallography
Reactions of the chloro-bridged dimeric arene ruthenium com-
plexes [{(
rhodium complex [{(
g
6-arene)RuCl(
l
-Cl}2] (arene = benzene, p-cymene) and
g
5-C5Me5)RhCl(
l-Cl}2] with imidazole con-
2.3.1. Details of single crystal X-ray diffraction study
Details about the data collection, solution and refinement are
summarised in Section 2.3.2. Intensity data for 3 were collected
on a Rigaku AFC-7R diffractometer equipped with graphite Mo
taining ligands 1-(4-nitrophenyl)-imidazole (NOPI), 1-(4-formyl-
phenyl)-imidazole (FPI) and 1-(4-hydroxyphenyl)-imidazole (HPI)
were carried out in methanol under stirring conditions at RT.
These reactions afforded neutral mononuclear complexes [(g6
-
Ka
radiation (k = 0.71073 Å) at 293(2) K. The structure was solved
by direct methods (SHELXS 97) and refined by full-matrix least
squares procedure based on F2
SHELX 97) [35]. All non-hydrogen
C6H6)RuCl2(NOPI)] (1), [(
RhCl2(NOPI)] (3), [(
6-C6H6)RuCl2(FPI)] (4), [(
(FPI)] (5), [(
5-C5Me5)RhCl2(FPI)] (6), [( 6-C6H6)RuCl2(HPI)] (7),
[(
6-C10H14)RuCl2(HPI)] (8), [( 5-C5Me5)RhCl2(HPI)] (9) reasonably
g
6-C10H14)RuCl2(NOPI)] (2), [(
g
5-C5Me5)-
6-C10H14)RuCl2-
(
g
g
atoms were refined anisotropically and hydrogen atoms were lo-
cated at calculated positions and refined using a riding model with
isotropic thermal parameters fixed at 1.2 times the Ueq value of the
appropriate carrier atom.
g
g
g
g
good yields. A simple scheme showing the synthesis of the com-
plexes is depicted in Scheme 1.
All the complexes are air-stable solid and not shows any sign of
decomposition when placed in air for several days. All the
complexes are of crystalline nature. They are soluble in common
organic solvent like dichloromethane, acetone, acetonitrile,
2.3.2. Selected crystallographic data of 3
Formula = C19H22Cl2N3O2Rh, Mw = 498.21, specimen 0.15 mm Â
ꢀ
0.13 mm  0.12 mm, Triclinic space group P1, a = 12.306(3) Å,
X
N
R
Rh
Ru
Cl
Cl
Cl
Cl
N
N
i
ii
N
N
N
X=NO2, CHO,
OH
X=NO2, Ar-R=benzene (1)
Ar-R=p-cymene(2)
X
X
X=NO2 (3)
CHO(6)
OH (9)
X=CHO, Ar-R=benzene(4)
Ar-R=p-cymene(5)
X=OH, Ar-R=benzene (7)
Ar-R=p-cymene (8)
Scheme 1. Synthesis of complexes 1–9 (i)[{
g
6-arene)RuCl(
l
-Cl)}2] (arene = C6H6, C10H14) (ii)[{
g
5-C5Me5)RhCl(
l
-Cl)}2].

570
A.K. Singh et al. / Journal of Organometallic Chemistry 695 (2010) 567–573
dimethylsulphoxide (DMSO) and dimethylformamide (DMF) but
insoluble in n-hexane, diethyl ether, benzene and toluene. The
complexes have been characterised by elemental analyses, IR,
NMR and electronic spectral studies. Density functional theoretical
calculations have been performed to authenticate the structures
and electronic structure of these complexes.
In the IR spectra of respective complexes characteristic bands
corresponding to mN@O, mC@O and mO–H of the coordinated NOPI,
FPI and HPI were displayed at ꢀ1339, 1598 and 3550 cmÀ1, respec-
tively [30–34]. The band corresponding to imidazole ring vibra-
tions appeared at ꢀ1600 cmÀ1 as compared to that in the free
ligand (1610 cmÀ1 in NOPI, 1615 cmÀ1 in FPI and 1608 cmÀ1 in
ing coordination of ligands with ruthenium/rhodium centres.
The 1H NMR spectrum of the complexes displayed resonances
between 7.2–8.5 ppm corresponding to the protons of the coor-
dinated ligand, while characteristic signals due to aldehyde and
phenol appeared at ꢀ9–11 ppm and 8–10 ppm, respectively.
Downfield shift in the position of peak corresponding to the
imidazole ring suggested coordination of the metal through
imidazolyl nitrogen. Peaks corresponding to the arene precursors
appeared at almost the same position as in the precursor
complexes without any significant change. Peaks corresponding
to the
g
6-C6H6 protons appeared at ꢀ6 ppm and the one corre-
sponding to the
protons associated with
g
5-C5Me5 protons at ꢀ1.5 ppm. As expected the
HPI). The shift in the position of
m
C@N bands suggested coordination
g
6-p-cymene also appeared in the
of the ligand to metal centre through imidazole nitrogen. IR spectra
of the complexes also exhibited characteristic bands associated
normal range [33].
13C NMR spectra also supported formulations of the respective
complexes. Resulting data are summarised in the experimental
section and representative spectra of the complexes 1, 3, 6 and 8
are depicted in Figs. S1–S4. Resonances associated with aromatic
carbons of phenyl and imidazolyl groups of ligands are observed
between 115–150 ppm while characteristic peak of aldehyde
group of ligand FPI observed at ꢀ190 ppm and peak corresponding
with
positions.
g g g
6-C6H6, 6-C10H14 and 5-C5Me5 rings at their usual
1H NMR spectral data of the complexes are recorded in CDCl3
and presented in the experimental section. Position and inte-
grated intensity of the various signals corresponding to ligands
and the arene precursors corroborated well to a system involv-
to C–OH of HPI observed at ꢀ157 ppm. Similarly, In (
related complexes, pentamethylcyclopentadienyl carbons reso-
nated at 8.6(C–CH3), 94.8(C5Me5) ppm, for (
6-C6H6)Ru- related
g
5-C5Me5)Rh-
g
complexes carbons resonated at ꢀ87 ppm (Figs. S1–S3). Similarly,
Peaks associated with carbon of
the normal range (Fig. S4).
g
6-p-cymene also appeared in
The electronic absorption spectra of complexes 1–6 were re-
corded in acetonitrile solutions at room temperature and resulting
data are summarised in the experimental section. The low spin d6
orbitals on ruthenium(II)/Rhodium(III) provides filled metal orbi-
tals of proper symmetry to interact with relatively low lying p*
orbitals on the ligand. It is expected to give a band associated with
metal to ligand charge transfer (MLCT) transition (t1g ?
position varies with nature of the metal ion and ligands acting as
p
*) whose
p
acceptor. Electronic spectra of the complexes 1–6 displayed MLCT
bands at ꢀ450 and ꢀ400 nm for Ru and Rh complexes, respectively
(Fig. 1). Peaks around 290 nm and 230 nm ascribed as intra-ligand
transition [45,46]. On the basis of its position and intensity the low
energy bands in the region 400–450 nm has been assigned to MLCT
transitions [Ru(II)/Rh(III) ? p* orbital of L] while, the absorptions
in the region 247–293 nm has been attributed to the ligand field
Fig. 1. UV–vis spectra of complexes 1–6.
Fig. 2. Emission spectra of complex 1–3 upon excitation (a) at MLCT band (b) at intra-ligand transition.

A.K. Singh et al. / Journal of Organometallic Chemistry 695 (2010) 567–573
571
or intra-ligand transitions (
port formation of the complexes [25,47,48].
p
?
p
*). Presence of MLCT bands sup-
Coordination geometry about the metal centre rhodium is com-
pleted by imidazolyl nitrogen, two chloro- groups and C5Me5 ring
Emission spectra of the complexes 1–3 were acquired in dichlo-
romethane at room temperature and the resulting spectra are
shown in (Figs. 2a and b). Upon excitation at the respective MLCT
bands, complexes 1–3 results moderate emissions [655, 445 nm
(exc), 1; 650, 442 nm (exc), 2 and 622, 400 nm (exc), 3. (Fig. 2a)
These bands may be due to triplet metal-to-ligand charge transfer
state (3MLCT). In addition, these exhibited strong emissions in the
region 320–350 nm upon excitation at ꢀ290 nm.(Fig. 2b) It has
been ascribed to ligand based transitions, which originate from
NOPI. Hence, these compounds are luminescent materials.
Molecular structure of 3 has been determined crystallographi-
cally. Details about the data collection, solution and refinement
are summarised in crystallographic section, selected geometrical
parameters are gathered in Table S1 and ORTEP view at 30% ther-
mal ellipsoid probability is depicted in Fig. 3. The metal centre rho-
dium in this complex adopted typical piano-stool geometry.
coordinated in g
5-manner. The Rh–N and Rh–Cl bond distances
[Rh–N1 = 2.107 Å, Rh–Cl1 = 2.399 Å, Rh–Cl2 = 2.418 Å) are normal
[49]. The Cl–Rh–Cl and N–Rh–Cl angles are less than 90° which
are consistent with the ‘‘piano-stool” arrangement of various
groups about the metal centre (Table S1) [49]. The
g
5-C5Me5 ring
is essentially planar and coordinated to rhodium centre with an
average bond distance of 2.145 Å [range 2.134(3)–2.251(3) Å] and
metal to centroid of
g
5-C5Me5 distance of 1.766 Å) [49].
Weak interaction studies on the complex 3 revealed that two C–
HÁÁÁO intermolecular contacts (C16–H16Á Á ÁO1 = 3.632 Å, C8–
H8BÁ Á ÁO2 = 3.407 Å[50]) between hydrogen of the phenyl group
of NOPI and oxygen of the nitro group results in a structural motif
having slipper shaped cavities along the crystallographic-‘c’-axis
with the dimensions of 14.813 Â 11.118 Å (Fig. 4). Significant
interaction parameters along with the symmetry are listed in
Table 1.
Fig. 3. Molecular structure of complex 3.
Fig. 4. Cavity resulting from H-bonding interaction in 3.

572
A.K. Singh et al. / Journal of Organometallic Chemistry 695 (2010) 567–573
Table 1
(NBO) charge distributions are presented in the Scheme S1. One
Matrices for weak-interactions in 3.
can see that the calculated NPA charge distributions for the metals
(Ru/Rh), arene/cyclopentadiene and imidazolyl based ligands are
positive, while that for the chloro groups are negative. It is note-
worthy that the charge distribution in all the complexes are similar
hence, their electronic properties. To visualise the Ru/Rh–N1, Ru/
Complex 1
Donor–HÁÁÁacceptor
1 C(13)–H(13)ÁÁÁCl(2)a
1 C(11)–H(11)ÁÁÁCl(1)b
1 C(16)–H(16)ÁÁÁO(1)c
1 C(8)–H(8B)ÁÁÁO(2)d
1 C(6)–H(6A)ÁÁÁCl(2)e
1 C(7)–H(7B)ÁÁÁCl(2)e
1 C(19)–H(19)ÁÁÁCl(2)e
D–H
HÁÁÁA
2.83
2.92
2.72
2.71
2.95
2.86
2.78
DÁÁÁA
D–HÁÁÁA
164
165
168
130
168
157
130
0.93
0.93
0.93
0.96
0.96
0.96
0.96
3.734
3.831
3.632
3.407
3.891
3.761
3.453
Rh–Cl1, Ru/Rh–Cl2, Ru–(
g5-C10H14) bonding, envelope plots of
some of the relevant molecular orbitals of 2 are depicted in Fig.
S14. Similar conclusions may be extended to other complexes un-
der study
a
b
c
= 2 À x, À1/2 + y, 1/2 À z.
= 2 À x,1 À y,Àz.
4. Conclusions
=3 À x, Ày, Àz.
d
e
=À1 + x, 1/2 À y, 1/2 + z.
=x, 1/2 À y, À1/2 + z.
In the present work we have described synthesis, spectral and
structural characterisation of characterisation of a series of neutral
mononuclear complexes containing
(g ( -
6-arene)Ru- and g5
C5Me5)Rh- moieties and imidazole based ligands. To compare the
geometrical parameters from theoretical studies with the single
crystal X-ray data, theoretical studies have performed. NBO calcu-
lations suggested that there is an overall charge flow in the direc-
tion M ? L.
Acknowledgements
Thanks are due to the Department of Science and Technology,
New Delhi, India for providing financial assistance (SR/S1/IC-15/
2006). A.K.S. acknowledges CSIR for awarding JRF 09/013(0127)/
2007, EMR-I. We are also thankful to the Head, Department of
Chemistry, Banaras Hindu University, Varanasi, UP, India and Prof.
Q. Xu, National Institute of Advanced Industrial Science and Tech-
nology (AIST), Osaka, Japan for providing single crystal X-ray data.
Appendix A. Supplementary material
Fig. 5. C–HÁÁÁ
p
interaction in 3.
CCDC 742147 contains the supplementary crystallographic data
for complex 3. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via <www.ccdc.cam.ac.uk/
data_request/cif>. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.jorganchem.2009.11.011.
Furthermore, the methyl protons of C5Me5 ring are intramolec-
ularly involved in long range C–HÁÁÁ interactions with the phenyl
ring. The methyl hydrogen H10C approaches C17 of the phenyl ring
interactions with a contact distance of 2.878 Å
(H10C to centroid distance 2.874 Å) (Fig. 5) [50]. Further, crystal
structure of 3 revealed the presence of extensive inter-molecular
C–HÁÁÁCl interactions (C13–H13ÁÁÁCl2 = 3.734 Å, C11–H11ÁÁÁCl1 =
3.831 Å, C6–H6AÁÁÁCl2 = 3.891 Å, C7–H7BÁÁÁCl2 = 3.761 Å, C19–
H19ÁÁÁCl2 = 3.453 Å). Various interaction distances are consistent
with the values reported in the literature [50].
p
resulting in C–HÁÁÁ
p
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