The C-H activation of pendant naphthyl group of 1-alkyl-2-(naphthyl- α-azo)imidazole by rhodium(III). spectral, structural characterization and, DFT computation

Article abstract of DOI:10.1016/j.jorganchem.2013.02.013

The reaction of RhCl₃ with 1-alkyl-2-(naphthyl-α-azo) imidazole (α-NaiR, N, N′chelator) (R = CH₃, CH ₂-CH₃, CH₂-Ph) has synthesized a coordination compound, [Rh(α-NaiR-N, N′)(PPh₃)Cl₃] (2) from boiling methanol in the presence of PPh₃ while the reaction under similar condition in the presence of Et₃N has synthesized cyclometallated complex, [Rh(α-NaiR-N, N′, C)(PPh ₃)Cl₂] (3). The structures of both types of complexes are confirmed by single crystal X-ray diffraction study in representative cases. All the complexes have been characterized by spectral data (FT-IR, UV-VIS, MS, ¹H-NMR) and elemental analyses. Density functional theory calculation has also been performed to rationalize the electronic structures and their spectral properties.

Full text of DOI:10.1016/j.jorganchem.2013.02.013

Journal of Organometallic Chemistry 732 (2013) 109e115
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
The CeH activation of pendant naphthyl group of 1-alkyl-2-(naphthyl-a-azo)
imidazole by rhodium(III). Spectral, structural characterization and, DFT
computation
,
,
,
Dibakar Sardar a 1, Papia Datta a 2, Rajat Saha b, Pallepogu Raghavaiah c, Chittaranjan Sinha a
*
a Department of Chemistry, Jadavpur University, Kolkata 700 032, India
b Department of Physics, Jadavpur University, Kolkata 700 032, India
c School of Chemistry, National Single Crystal X-ray Diffractometer Facility, University of Hyderabad, Hyderabad 500 046, India
a r t i c l e i n f o
a b s t r a c t
-NaiR, N, N0chelator) (R ¼ CH3, CH2
Article history:
The reaction of RhCl3 with 1-alkyl-2-(naphthyl-a-azo)imidazole (a
eCH3, CH2ePh) has synthesized
a coordination compound, [Rh(a
-NaiR-N, N0)(PPh3)Cl3] (2) from
Received 12 November 2012
Received in revised form
4 February 2013
boiling methanol in the presence of PPh3 while the reaction under similar condition in the presence of
Et3N has synthesized cyclometallated complex, [Rh(
a
-NaiR-N, N0, C)(PPh3)Cl2] (3). The structures of both
Accepted 12 February 2013
types of complexes are confirmed by single crystal X-ray diffraction study in representative cases. All the
complexes have been characterized by spectral data (FT-IR, UVeVIS, MS, 1H-NMR) and elemental ana-
lyses. Density functional theory calculation has also been performed to rationalize the electronic
structures and their spectral properties.
Keywords:
Rhodium(III) complexes
Naphthylazoimidazole
Cyclometallation
Structure
Ó 2013 Elsevier B.V. All rights reserved.
DFT computation
1. Introduction
terest because of potential application in organic synthesis and
catalysis [21e25], material science [26,27], mesogens and metal-
The azo functionalized (eN]Ne) compounds are versatile dyes
and pigments and have been used in the development of various
types of transition metal complexes [1e8]. These complexes have
exhibited different exciting properties related to electron transfer
reaction, photochromism, liquid crystals, photoluminescence etc
[9e20]. Some of the azo ligands are used for metal assisted organic
transformation, and such type of reaction has a considerable in-
lomesogens [28], and biological activity [29]. A major goal of cur-
rent chemical research is to achieve metal-catalysed activation of
the CeH bond who could be used for the synthesis of new mole-
cules those are otherwise difficult to synthesize or even impossible.
The presence of suitable donor centre to the coordinating ligand
used for metal mediated CeH activation may synthesize cyclo-
metallated compounds (Eq. (1)).
(1).
We have been engaged for the last several years to design azo
functionalized imidazoles and their derivatives such as 1-alkyl-2-
(arylazo)imidazole [16]. Imidazole is very interesting molecule to
chemistry and biology [30,31]. Imidazolyl group carries two N-
centers of different hardness and can bridge two metal centers [32].
If we block one of the N-centers by alkyl group to synthesize 1-
alkyl-2-(arylazo)imidazole then molecule may primarily serve as
* Corresponding author. Fax: þ91 033 2413 7121.
E-mail address: c_r_sinha@yahoo.com (C. Sinha).
1
Present address: Dinabandhu Andrews College, Garia, Kolkata 700084, India.
Present address: RCC Institute of Information Technology, Canal South Road,
2
Kolkata 700015, India.
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.02.013

110
D. Sardar et al. / Journal of Organometallic Chemistry 732 (2013) 109e115
bidentate NeN0-chelator [16e20]. 1-Alkyl-2-(naphthyl-
imidazole ( -NaiR, Scheme 1) has some interesting ability to syn-
thesise both coordination and cyclopalladated complexes [33]. The
ligand, -NaiR has two specific donor centreseN(imidazolyl) (N),
N(azo) (N0), and is abbreviated as -NaiR-N, N0; in the cyclo-
a
-azo)
2.3. Preparation of compounds
a
2.3.1. Synthesis of [Rh(
RhCl3$3H2O (0.10 g, 0.379 mmol) was added to a methanol so-
lution of -NaiMe (0.089 g, 0.379 mmol) and PPh3 (0.102 g,
a
-NaiMe-N,N0)(PPh3)Cl3] (2a)
a
a
a
palladated product the CeH group ortho to the eN]Ne function of
0.379 mmol). The mixture was refluxed for 5 h under stirring
condition. The red colour solution was cooled slowly in air and the
products so obtained were collected by filtration, washed with cold
methanol and ether and dried under vacuum. The yield was 0.16 g
(58%).
the pendant naphthyl group serves as cyclometallation centre and
is abbreviated as a
-NaiR-N, N0,C. This reaction has stimulated us to
synthesize organometallics of other platinum group metals. In the
present work, we have characterized the complexes of Rh(III) with
a
-NaiR (R ¼ CH3, CH2eCH3, CH2ePh) (Scheme 1); the manipulation
of the reaction condition has synthesized either coordination
complex, [Rh(
-NaiR-N, N0)(PPh3)Cl3] (2) or the cyclometallated
derivative, [Rh(
-NaiR-N, N0, C)(PPh3)Cl2] (3). The products are
All other complexes were prepared following the identical
procedure. The yield varied from 55 to 65%.
a
a
2.3.1.1. [Rh(a
-NaiMe-N,N0)(PPh3)Cl3] (2a). Microanalytical data:
structurally characterized by single crystal X-ray diffraction study
and the electronic spectra are explained by DFT computation of
optimized geometry.
Found: C, 54.24; H, 3.78; N, 7.87%. Calc. for C32H27N4Cl3PRh: C,
54.27; H, 3.82; N, 7.91%. MS(FAB): m/z 709 (M þ H)þ. FT-IR (KBr disc,
cmꢀ1):
n(N]N), 1367(m); n(C]N),1560(s); n(Rh-Cl), 322, 330, 337;
n
(PPh3), 524, 692, 749. (w ¼ weak; s ¼ strong; vs ¼ very strong;
2. Experimental
m ¼ medium). Electronic spectral data in acetonitrile solution:
(
lmax, nm (
, 103 Mꢀ1 cmꢀ1)): 278(17.45), 336(7.59), 374(7.32), 474
3
2.1. Materials
(5.897). 1H NMR (CDCl3): 4.11 (s, eNeCH3, 3H), 6.86 (d, 1H
J ¼ 8.0 Hz), 7.10 (d, 1H, J ¼ 8.0 Hz), 7.18(m, 1H), 7.05e7.55 (PPh3),
7.60 (m, 2H), 7.81 (d, 1H, J ¼ 8.0 Hz), 7.98 (m, 1H), 8.12 (m, 1H), 8.92
(d, 1H, J ¼ 8.0 Hz).
RhCl3$3H2O was obtained from Arora-Mathy, India and used as
it was received. Triphenylphosphine, triethylamine and the sol-
vents used were obtained from E. Merck, India. The ligands used in
this work were 1-alkyl-2-(naphthyl-
a
-azo)imidazole
(a
-NaiR,
2.3.1.2. [Rh(a
-NaiEt-N,N0)(PPh3)Cl3] (2b). Microanalytical data:
R ¼ CH3, CH2eCH3, CH2ePh) (Scheme 1) and were prepared by
reported procedure [34]. Chemicals used for syntheses were of
analytical grade and solvents were dried before use [35]. The so-
lution spectral studies were carried out by spectroscopic grade
solvents obtained from Lancester.
Found: C, 54.84; H, 4.06; N, 7.81%. Calc. for C33H29N4Cl3PRh: C,
54.88; H, 4.02; N, 7.76%. MS(FAB): m/z 723 (MþH)þ. FT-IR (KBr disc,
cmꢀ1):
n(N]N), 1365(m); n(C]N), 1552(s); n(Rh-Cl), 321, 329, 338;
n
(PPh3), 527, 694, 750. (w ¼ weak; s ¼ strong; vs ¼ very strong;
m ¼ medium). Electronic spectral data in acetonitrile solution:
(
lmax, nm (
, 103 Mꢀ1 cmꢀ1)): 279(19.39), 337 (7.82), 374(6.94), 475
3
2.2. Physical measurements
(5.553). 1H NMR (CDCl3): 1.49 (t, (eNeCH2e)CH3, 3H, J ¼ 8.0 Hz),
4.48 (q, Hz, eNeCH2, 2H, J ¼ 7.5 Hz), 6.97 (d, 1H, J ¼ 8.0 Hz), 7.16 (d,
1H, J ¼ 8.0 Hz), 7.17 (m, 1H), 7.05e7.60 (PPh3), 7.61 (m, 2H), 7.81 (d,
1H, J ¼ 8.0 Hz), 7.96 (m, 1H), 8.14 (m, 1H), 8.90 (d, 1H, J ¼ 8.0 Hz).
Microanalyses (C, H, N) were performed using PerkineElmer
2400 CHN elemental analyser. Spectroscopic measurements were
carried out using the following instruments: UVeVis spectra,
Lambda 25 Perkin Elmer; IR spectra (KBr disk), RX-1 Perkin Elmer;
1H NMR spectra in DMSO-d6, Bruker 300 MHz FT-NMR spectrom-
eters in presence of TMS as internal standard. FAB-MS data were
collected from Jeol-AX 500 instrument.
2.3.1.3. [Rh(a
-NaiCH2Ph-N,N0)(PPh3)Cl3] (2c). Microanalytical data:
Found: C, 58.22; H, 3.90; N, 7.11%. Calc. for C38H31N4Cl3PRh: C,
58.20; H, 3.96; N, 7.15%. MS(FAB): m/z 785 (M þ H)þ. FT-IR (KBr disc,
cmꢀ1):
n(N]N), 1366(m); n(C]N), 1563(s); n(Rh-Cl), 320, 327, 337;
PPh3
Cl
Cl
N
N
R
Rh
Methanol
N
4
5
Cl
N
Reflux
(5 hrs)
N
N
R
Red
N
RhCl3
Et3N
PPh3
+
+
2
N
9
DMF
13
10
PPh3
Cl
7
12
11
N
N
Methanol
Et3N
8
R
Rh
Cl
N
N
Reflux
1
(10 hrs)
3
Green
-NaiR (1); R = -CH3 (1a, 2a, 3a), -CH2CH3 (1b, 2b, 3b), -CH2Ph (1c, 2c, 3c)
Scheme 1. The ligands (a-NaiR, 1) and the complexes, [Rh(a a
-NaiR-N,N0)(PPh3)Cl3] (2) [Rh( -NaiR-N,N0C)(PPh3)Cl2] (3).

D. Sardar et al. / Journal of Organometallic Chemistry 732 (2013) 109e115
111
n
(PPh3), 526, 692, 749. (w ¼ weak; s ¼ strong; vs ¼ very strong;
2.3.2.4. [Rh(a
-NaiMe-N,N0)(PPh3)Cl3] (2a). (0.1 mg, 0.141 mmol)
m ¼ medium). Electronic spectral data in acetonitrile solution:
was dissolved in 50 ml DMF and Et3N (0.014 g, 0.141 mmol) was
added. Then it was refluxed for 7 h under stirring condition in inert
atmosphere (N2) to yield a deep green solution. Slow evaporation of
this solution gave a dark green solid, which was subjected to pu-
rification by silica gel column chromatography prepared in
petroleumeether (60e80 ꢁC fraction). A green portion was eluted
with 1:1(v/v) benzeneeacetonitrile mixture which upon evapora-
tion afforded analytically pure product 3a. Yield was 0.055 g (59%).
(
lmax, nm (
, 103 Mꢀ1 cmꢀ1)): 278(16.57), 337 (6.92), 373(6.21), 475
3
(5.234). 1H NMR (CDCl3): 5.54 (s, eNeCH2, 2H), 7.09 (d, 1H,
J ¼ 8.0 Hz), 7.22 (d, 1H, J ¼ 8.0 Hz), 7.20 (m, 1H), 7.05e7.55 (PPh3),
7.25e7.35 (eNe(CH2)Ph, 5H), 7.60 (m, 2H), 7.84 (d, J ¼ 8.0 Hz, 1H),
7.99 (m, 1H), 8.11 (m, 1H), 8.85 (d, 1H, J ¼ 8.0 Hz).
2.3.2. Synthesis of [Rh(a
-NaiMe-N,N0,C)(PPh3)Cl2] (3a)
(a) Direct synthesis
2.4. X-ray diffraction study
1-Methyl-2-(naphthyl-a-azo)imidazole (a-NaiMe) (0.089 g,
Details of crystal analyses,data collection and structurerefinement
data are given in Table 1. Single crystal data were collected by fine
0.379 mmol) was dissolved in 50 ml methanol and Et3N (0.038 g,
0.376 mmol) was added. The solution was stirred for 5 min. Then
RhCl3$3H2O (0.1 g, 0.379 mmol) and PPh3 (0.102 g, 0.379 mmol)
were added and the mixture was refluxed for 12 h under stirring
condition to yield a deep green solution. Evaporation of this solu-
tion gave a dark green solid, which was subjected to purification by
silica gel column chromatography prepared in petroleumeether
(60e80 ꢁC fraction). A green portion was eluted with 1:1(v/v)
benzeneeacetonitrile which upon evaporation afforded analyti-
cally pure product 3a. Yield was 0.17 g (67%).
focus sealed tube using fine focus graphite monochromator Bruker
ꢀ
Smart CCD Area Detector (Mo-K
a
radiation, (
l
¼ 0.71073 A) for [Rh(
a-
NaiEt-N, N0)(PPh3)Cl3] (2b) (crystal size, 0.44 ꢂ 0.08 ꢂ 0.06 mm) at
293(2) K and for [Rh(a
-NaiEt-N, N0,C)(PPh3)Cl2] (3b) (crystal size,
0.50 ꢂ 0.16 ꢂ 0.04 mm) at 298(2) K. Unit cell parameters were
determined from least-squares refinement of setting angles with q in
the range 2.49 ꢃ
q
ꢃ 26.01ꢁ (2b) and 1.67 ꢃ
q
ꢃ 25.00ꢁ (3b). Out of
16,493 collected data 5906 for 2b and 28,001 collected data 5177 for
3b with I > 2
are ꢀ12
2b, ꢀ10 ꢃ h ꢃ 10; ꢀ26 ꢃ k ꢃ 26; ꢀ17 ꢃ l ꢃ 17 for 3b. Reflection data
were recorded using the scan technique. Data were corrected for
s
(I) were used for structure solution. The hkl range
All other complexes were prepared by the same procedure. The
yield varied from 60 to 65%.
ꢃ
h
ꢃ
14; ꢀ19 17; ꢀ21 21 for
ꢃ
k
ꢃ
ꢃ
l
ꢃ
u
2.3.2.1. [Rh(a
-NaiMe-N,N0,C)(PPh3)Cl2] (3a). Microanalytical data:
Lorentz polarization effects and for linear decay. The structure was
solved by direct method for all these compounds using SHELXS-97
[36] and successive difference Fourier syntheses. Largest difference
Found: C, 57.18; H, 3.90; N, 8.36%. Calc. for C32H26N4Cl2PRh: C,
57.22; H, 3.87; N, 8.35. MS(FAB): m/z 672 (M þ H)þ. FT-IR (KBr disc,
cmꢀ1):
n(N]N), 1381(m); n(C]N), 1576(s); n(Rh-Cl), 321, 327;
ꢀꢀ3
inpeakandhole(e.A )are ꢀ0.323,0.806(2b)andꢀ0.239, 0.466(3b).
n
(PPh3), 524, 695, 749. (w ¼ weak; s ¼ strong; vs ¼ very strong;
All non-hydrogen atoms were refined anisotropically. The hydrogen
atoms were fixedgeometricallyand refined using the riding model. All
calculations were carried out using SHELXL-97 [37], ORTEP-32 [38],
and PLATON-99 [39] programs.
m ¼ medium). Electronic spectral data in acetonitrile solution:
(
lmax, nm (
, 103 Mꢀ1 cmꢀ1)): 277 (37.22), 384 (29.17), 429 (21.00),
3
622 (11.45). 1H NMR (CDCl3): 4.06 (s, eNeCH3, 3H), 7.09 (d, 1H,
J ¼ 8.0 Hz), 7.17(d, 1H, J ¼ 8.0 Hz), 7.26e7.45 (PPh3), 7.46 (m, 2H),
7.59 (m, 1H), 7.71 (m, 1H), 7.91 (m, 1H), 8.08 (d, 1H, J ¼ 8.0 Hz).
2.5. Computational details
2.3.2.2. [Rh(a
-NaiEt-N,N0,C)(PPh3)Cl2] (3b). Microanalytical data:
All computations were performed using the Gaussian03 (G03)
software package running under Windows [40]. The Becke’s three-
Found: C, 57.80; H, 4.10; N, 8.15%. Calc. for C33H28Cl2N4PRh: C, 57.81;
H, 4.09; N, 8.18%. MS(FAB): m/z 686 (M þ H) þ. FT-IR (KBr disc,
cmꢀ1):
n(N]N),1371(m); n(C]N), 1573(s); n(Rh-Cl), 321, 328;
Table 1
Selected crystallographic data for 2b and 3b.
n
(PPh3), 521, 697, 762. (w ¼ weak; s ¼ strong; vs ¼ very strong;
m ¼ medium). Electronic spectral data in acetonitrile solution:
[Rh(
(PPh3)Cl3] (2b)
33H29N4PCl3Rh$H2O
739.85
298(2)
a
-NaiEt-N,N0)
[Rh(a
-NaiEt-N,N0,C)
(PPh3)Cl2] (3b)
(
lmax, nm (
, 103 Mꢀ1 cmꢀ1)): 277 (37.22), 385(29.16), 430(15.65),
3
622(7.84). 1H NMR (CDCl3): 1.41 (t, (eNeCH2e)CH3, 3H, J ¼ 8.0 Hz),
4.27 (q, eNeCH2, 2H, J ¼ 7.5 Hz), 7.11 (d, 1H, J ¼ 8.0 Hz), 7.16(d, 1H,
J ¼ 8.0 Hz), 7.26e7.42 (PPh3), 7.43 (m, 2H), 7.58 (m,1H), 7.71 (m,1H),
7.89 (m, 1H), 8.06 (d, 1H, J ¼ 8.0 Hz).
Empirical formula
Formula weight
T, K
C
C33H28N4PCl2 Rh
685.37
298 (2)
Crystal system
Space group
Orthorhombic
Pna2(1)
11.5353(8)
15.4737(11)
17.4878(12)
90.00
3121.5(4)
4
1.574
Monoclinic
P2(1)/n
ꢀ
a, A
9.1216(8)
21.8811(19)
14.7889(13)
94.437(2)
2942.9(4)
4
1.547
0.71073
0.847
ꢀ
-NaiCH2Ph-N,N0,C)(PPh3)Cl2]
(3c). Microanalytical
b, A
2.3.2.3. [Rh(
a
ꢀ
c, A
data: Found: C, 61.06; H, 4.03; N, 7.47%. Calc. for C38H30Cl2N4PRh: C,
ꢁ
b
,
61.04; H, 4.02; N, 7.49%. MS(FAB): m/z 748 (M þ H)þ. FT-IR (KBr disc,
3
ꢀ
V, A
cmꢀ1):
n(N]N), 1372(m); n(C]N), 1575 (s); n(Rh-Cl), 321, 330;
Z
Dcalc (mg mꢀ3
)
n
(PPh3), 525, 698, 750. (w ¼ weak; s ¼ strong; vs ¼ very strong;
ꢀ
l
(A)
0.71073
0.885
m ¼ medium). Electronic spectral data in acetonitrile solution:
m
(Mo-K
a
) (mmꢀ1
)
(
lmax, nm (
, 103 Mꢀ1 cmꢀ1)): 277 (32.09), 384 (17.02), 429 (15.90),
3
Total reflection
Unique reflections
[I > 2 (I)]
17,036
6055
28,001
5177
622 (8.23). 1H NMR (CDCl3): 5.52 (q, eNeCH2, 2H, J ¼ 7.8 Hz), 7.16
(d, 1H, J ¼ 8.0 Hz), 7.28(d, 1H, J ¼ 8.0 Hz), 7.20e7.45 (PPh3), 7.44 (m,
2H), 7.56 (m, 1H), 7.73 (m, 1H), 7.92 (m, 1H), 8.09 (d, 1H, J ¼ 8.0 Hz).
s
Refined parameters
Goodness-of-fit on F2
389
0.999
1.76e26.01
0.0465
0.0961
371
1.062
1.67e25.00
0.0312
0.0764
q
range (ꢁ)
(b) Conversion of coordination to cyclometallated Rh(III)
complexes
R (Fo)a [I > 2
s(I)]
wR (Fo)b [I > 2
s(I)]
a
R ¼ SjjFoj ꢀ jFcjj/SjFoj.
[Rh(
Cl2] (3a)
a a
-NaiMe-N,N0)(PPh3)Cl3] (2a) / [Rh( -NaiMe-N,N0,C)(PPh3)
b
wR ¼ [Sw(F2o ꢀ Fc2)2/Sw(F2o)2]1/2, w ¼ 1/[
s
2(Fo)2 þ (0.0433P)2 þ 0.0000P] (2b) and
w ¼ 1/[
s
2(Fo)2 þ (0.0377P)2 þ 1.4388P] (3b) where P ¼ ((Fo2 þ 2F2c)/3.

112
D. Sardar et al. / Journal of Organometallic Chemistry 732 (2013) 109e115
parameter hybrid exchange functional and the LeeeYangeParr
nonlocal correlation functional (B3LYP) was used throughout this
computation [41]. For heavy atoms like rhodium, phosphorus and
chlorine the Los Alamos effective core potential plus double zeta
(LanL2DZ) basis set were employed [42] while other elements were
assigned by 6-31G basis set. The geometric structures of the ligand
and the complexes in the ground state (S0) were fully optimized at
the B3LYP level. Geometry optimization was carried out from the
geometry obtained from the crystal structure without any sym-
metry constraints. In all cases, vibrational frequencies were calcu-
lated to ensure that optimized geometries represented local
minima. Using the respective optimized S0 geometries we
employed time dependent density functional theory (TD-DFT) at
the B3LYP level to predict their absorptions characteristics [43].
Although CAM-B3LYP could improve excitation energies and the
assignment would be more appropriate but the configuration of
computation workstation has not been sustained. We have been
failed to carry out calculation using CAM-B3LYP functional.
3. Results and discussion
Fig. 1. Single crystal X-ray structure of [Rh(
a
-NaiR-N, N0)(PPh3)Cl3] (2b).
3.1. Synthesis
ꢀ
The RheN(imidazolyl), (N(3)) (2.271(2) A) of 3b, trans to RheC, is
1-Alkyl-2-(naphthyl-a-azo)imidazole (Scheme 1: a-NaiR, 1;
ꢀ
longer than RheN(imidazolyl), (N(1)) (2.000(4) A) of 2b which may
be due to the stronger trans effect of aryl carbon (RheC) and the
angular strain developed in the ligand frame due to double chela-
tion. The RheP bond distances (Rh(1)eP(1), 2.3133(4) A in 2b and
R ¼ CH3 (a), CH2-CH3 (b), CH2Ph (c)) generally serve as N,
N0chelating ligand where, N(imidazolyl) and N(azo) are assigned to
N and N0 respectively. The reaction of RhCl3 with
a-NaiR (1) and
ꢀ
PPh3 in methanol under refluxing condition has synthesized a red
colour complex, 2. The X-ray structure of one of the complexes, 2b
ꢀ
Rh(1)eP(1), 2.2995(7) A in 3b) are comparable with the published
reveals that a
-NaiEt binds to Rh(III) centre as N, N0 chelating agent.
results [45].
These two structures are optimized using DFT computation
technique. The experimental bond distances are lower than calcu-
On the other hand, upon addition of Et3N to the same reaction
mixture has synthesized a green colour rhodium(III) complex, 3,
where the ligand has been found to undergo CeH activation. The
CeH activation at the 13th-position (C(13)eH) of the naphthyl ring
has been confirmed by the X-ray crystal structure of complex 3b,
ꢀ
lated lengths in general by 0.02e0.15 A while the bond angles are
elongated by 1e2ꢁ (Table 2). This implies compatibility of methods
used for calculation and hence the derived functions are closer to
the experiments.
where the ligand a-NaiR coordinates with rhodium as monoanionic
tridentate N, N0, C chelating agent. The cyclomtallated complexes, 3,
can be synthesised by refluxing 2 in basic medium (Et3N) (shown in
Scheme 1). The formulation of the complexes is also consistent with
the microanalytical and spectroscopic data. All the complexes are
diamagnetic, indicating the presence of rhodium in the þ3 oxida-
tion state (d6).
The packing of molecular structure 2b shows the presence of
crystallized H2O molecule which is hydrogen bonded with one of
the Cl of three RheCl groups (Fig. 3) (O(1)eH(2)—Cl(3): H(2)—Cl(3),
ꢀ
ꢀ
2.69 (2) A; O(1)——Cl(3), 3.448(8) A and :O(1)eH(2)—Cl(3),
149.0 ꢁ). Each unit is then connected by CeH—
p interaction,
ꢀ
ꢀ
C(20)eH(20)—Cg(1) (H(20)—Cg(1), 2.91 A; C(20)—Cg(1), 3.485(6) A
and :C(20)eH(20)—Cg(1), 121ꢁ at symmetry ꢀ1/2 þ x, 3/2 ꢀ y, z
3.2. Molecular structure of [Rh(
[Rh(
-NaiEt-N, N0,C)(PPh3)Cl2] (3b)
a
-NaiEt-N, N0)(PPh3)Cl3] (2b) and
a
The complexes 2b and 3b were crystallized by slow diffusion of
hexane into dichloromethane solution of the respective complexes.
Suitable crystals were picked up for X-ray analyses. The structures
are shown in Figs. 1 and 2 and the relevant bond parameters are
given in Table 2. The ligand is coordinated to Rh(III) as a bidentate
(N, N0) donor in 2b and makes a five-member chelate ring with a
bite angle :N(4)eRh(1)eN(1), 77.47(19)ꢁ (Table 2) and as a mon-
oanionic tridentate (N, N0, C) donor, forming two adjacent five-
member chelate rings with bite angles :N(3)eRh(1)eN(1),
74.86(9)ꢁ and :N(1)eRh(1)eC(30), 82.92(10)ꢁ (Table 2) in 3b.
a-
NaiEt acts as a N, N0 chelator in 2b and the coordination geometry
for the central Rh atom is based on an octahedron defined by a
N2PCl3 coordination set. The Rh-Cl distances are comparable with
reported Rh(III)-1-alkyl-2-(arylazo)imidazole complexes [44].
However, the N(azo)eRheN(imidazolyl) chelate angles are shorter
than 2b which may be due to the structural strain originated from
bulkier naphthyl pendant group and coordinated PPh3 [44]. In 3b,
a
-NaiEt acts as a tridentate chelator where one of the donor centres
is naphthyl carbanion, (C(30)) along with N and N0 donor centres.
Fig. 2. Single crystal X-ray structure of [Rh(a
-NaiEt-N, N0, C)(PPh3)Cl2] (3b).

D. Sardar et al. / Journal of Organometallic Chemistry 732 (2013) 109e115
113
Table 2
ꢁ
Selected experimental and theoretical bond lengths (A) and angles ( ) for the complexes [Rh(a a
-NaiEt-N, N0)(PPh3)Cl3] (2b) and [Rh( -NaiEt-N, N0, C)(PPh3)Cl2] (3b).
ꢀ
Bond angle (ꢁ)
Experimental value
Theoretical value
ꢀ
Bond length (A)
Experimental value
Theoretical value
[Rh(a
-NaiEt-N,N0)(PPh3)Cl3] (2b)
Rh(1)eN(1)
Rh(1)eN(4)
Rh(1)eP(1)
Rh(1)eCl(1)
Rh(1)eCl (2)
Rh(1)eCl (3)
N(3)eN(4)
N(1)eC(3)
2.000(4)
2.084(5)
2.313(13)
2.330(14)
2.344(12)
2.425(14)
1.270(6)
1.332(7)
1.367(6)
1.811(5)
1.833(5)
1.836(5)
2.023
2.138
2.475
2.425
2.443
2.457
1.314
1.354
1.372
1.880
1.889
1.889
N(4)eRh(1)eN(1)
N(4)eRh(1)eCl(2)
N(4)eRh(1)eCl(3)
N(4)eRh(1)eP(1)
N(1)eRh(1)eCl(1)
N(1)eRh(1)eCl(3)
N(1)eRh(1)eP(1)
Cl(2)eRh(1)eCl(1)
Cl(2)eRh(1)eCl(3)
Cl(2)eRh(1)eP(1)
Cl(1)eRh(1)eP(1)
Cl(1)eRh(1)eCl(3)
N(4)eRh(1)eCl(1)
N(1)eRh(1)eCl(2)
P(1)eRh(1)eCl(3)
77.43(18)
100.44(13)
84.77(13)
95.61(13)
89.50(15)
85.61(11)
92.76(11)
92.40(6)
91.38(6)
91.24(5)
87.86(6)
91.38(6)
77.70
99.33
84.64
98.17
89.59
86.29
93.89
93.34
92.83
87.14
85.37
91.80
166.98
176.97
177.16
N(3)eC(3)
P(1)eC(16)
P(1)eC(22)
P(1)eC(28)
166.60(12)
175.64(13)
178.20(6)
[Rh(a
-NaiEt-N,N0)(PPh3)Cl2] (3b)
Rh(1)eN(1)
Rh(1)eN(3)
Rh(1)eP(1)
Rh(1)eC(30)
Rh(1)eCl(1)
Rh(1)eCl(2)
N(1)eN(2)
N(2)eC(23)
N(3)eC(23)
P(1)eC(1)
1.982(2)
2.271(2)
2.2995(7)
2.003(3)
2.3577(8)
2.3897(7)
1.269(3)
1.370(4)
1.347(4)
1.826(3)
1.834(3)
1.822(3)
2.006
2.253
2.464
2.018
2.448
2.448
1.305
1.382
1.360
1.888
1.890
1.882
N(1)eRh(1)eN(3)
N(1)eRh(1)eC(30)
N(1)eRh(1)eCl(2)
N(1)eRh(1)eP(1)
N(3)eRh(1)eCl(1)
N(3)eRh(1)eCl(2)
N(3)eRh(1)eP(1)
C(30)eRh(1)eCl(1)
C(30)eRh(1)eCl(2)
C(30)eRh(1)eP(1)
P(1)eRh(1)eCl(1)
Cl(1)eRh(1)eCl(2)
N(1)eRh(1)eCl(1)
N(3)eRh(1)eC(30)
P(1)eRh(1)eCl(2)
74.86(9)
82.92(10)
84.78(6)
95.53(6)
109.57(6)
88.50(6)
86.24(6)
92.51(8)
88.89(7)
96.64(8)
89.99(3)
90.11(3)
173.19(7)
157.77(10)
174.46(3)
76.41
82.73
84.82
95.40
102.90
86.84
91.68
97.63
88.57
92.89
89.13
90.62
175.54
158.93
178.38
P(1)eC(7)
P(1)eC(13)
where Cg(1) refers to C(22)eC(23)eC(24)eC(25)eC(26)eC(27) and
is leading to the formation of 1D supramolecular chain along
crystallographic a-axis (Fig. 4).
3.3. Spectroscopic characterization
The IR spectra of the complexes display a moderately strong
band in the region 1365e1380 cmꢀ1 for
n
(N]N) stretching vibra-
tions and a weak band in the region 1560e1575 cmꢀ1 for
n
(C]N)
stretching vibrations which are significantly shifted to lower value
Fig. 3. Water molecule is bounded to the moiety through hydrogen bonding in-
teractions in 2b.
Fig. 4. 1D supramolecular chain is formed by CeH—
graphic a-axis in 2b.
p
interactions along crystallo-

114
D. Sardar et al. / Journal of Organometallic Chemistry 732 (2013) 109e115
compared to free ligand by 25e30 cmꢀ1. This supports the coor-
dination of ligand ( -NaiR) to Rh(III) through N(azo) and N(imi-
a
dazolyl). The spectra also show three characteristics strong bands
around 750, 695 and 525 cmꢀ1 for coordinated PPh3 ligand.
The electronic spectra of the complexes were recorded in
acetonitrile solution. The colour of the solution of 2 is red and that
of 3 is green. Both the complexes (2, 3) show four major peaks of
high intensity (
, 104 Mꢀ1 cmꢀ1) in 250e650 nm (Fig. 5). The
3
transitions at ultraviolet region may be assigned as intraligand
transitions and that of visible regions are probably due to metal-to-
ligand charge transfer transitions. Multiple charge-transfer transi-
tions in such mixed-ligand complexes may result from lower
symmetry splitting of the metal level, the presence of different
acceptor orbitals, and the mixing of singlet and triplet configura-
tions in the excited state through spin-orbit coupling [46e48]. The
spectral assignment have been done by theoretical computation of
optimized geometries using DFT and TD-DFT technique (vide infra).
The spectra of 3 differ from 2 in the longer wavelength region
(>600). The cyclometallated compound (3) has characteristic low
energy band and may be due to the lowering of symmetry of double
chelation that restricts vibrational relaxation.
Fig. 6. Correlation diagram between [Rh(
NaiEt-N, N0, C)(PPh3 Cl2)] (3b).
a a-
-NaiEt-N, N0)(PPh3)Cl3] (2b) and [Rh(
observed electronic spectra. The electronic structure and configu-
ration are dependent on the composition and stereochemistry in
the molecule. The HOMO of 3b lies at higher energy by 0.4 eV than
that of 2b (3b, EHOMO ¼ ꢀ5.44 eV; 2b, EHOMO ¼ ꢀ5.84 eV). The
LUMO also follows same trend and the energy difference is 0.25 eV
(3b, ELUMO ¼ ꢀ3.05 eV; 2b, ELUMO ¼ ꢀ3.30 eV) (Fig. 6). Other
occupied MOs are closely spaced in 2b (HOMO-1, ꢀ5.87 eV; HOMO-
2, ꢀ5.97 eV) and 3b (HOMO-1, ꢀ5.61 eV; HOMO-2, ꢀ5.64 eV) but a
substantial energy gap is observed between LUMO and LUMO þ 1
The 1H-NMR spectra of the complexes are studied in DMSO-d6
and assignment has been made on comparing with free ligand data
[33,34] and intensity measurement of the signals corresponds to
the total number of protons in the respective complexes. In the
coordination complexes, 2, the protons suffer significant downfield
shifting compared to the ligands values, which may be due to the
electron-withdrawing effect of the coordinated rhodium(III). The
imidazole protons, 4-H and 5-H experience w0.05e0.20 ppm
downfield shift compared to free ligand values and appeared as
singlets. In the cyclometallated complexes, 3, the imidazole protons
shift to upperfield region compared to the coordination complexes
(2). This indicates that the cyclometallated complexes (3) have
more contribution of metal d-orbital in the formation of molecular
orbital compare to coordination complexes. The DFT calculation
also supports the contribution of orbitals of Rh to HOMO (Supple-
mentary materials, Table S1). The resonances of the phenyl protons
of PPh3 were observed as multiplets at 7.00e7.60 ppm.
(D
E > 0.3 eV) (Table S1, Supplementary materials). In 2b, the HOMO
is dominated by Cl (84%) function with a small contribution from
rhodium (9%); whereas in 3b, it is composed of -NaiEt (61%), Cl
a
(18%) and Rh (19%). Other occupied MOs (HOMO-1 to HOMO-5) for
2b have the major contribution from Cl function (65e85%) with
contribution from rhodium as well (4e25%). The similar observa-
tion is recorded in 3b. The LUMO is dominated by ligand function
(92%) in these complexes; in addition to that in 3b, the unoccupied
MOs like LUMO þ 1 to LUMO þ 4 have contribution from PPh3 (55e
85%).
To gain an insight about the nature of electronic transitions and
to explain the electronic spectra, the TD-DFT calculations were
performed. The experimental spectra correlate well with the
theoretical spectra (Supplementary materials, Fig. S1). The calcu-
lations also interpret multiple charge transfer transitions for these
complexes. For complex 2b, the experimental spectrum shows
transition at 475 nm which has been correlated with admixture of
HOMO / LUMO and HOMO-n / LUMO in the calculated spectrum
(501 nm) (Supplementary materials, Table S2). The bands in the
experimental spectrum of 2b at 275e380 nm are assigned to the
mixture of multiple transitions originated from ILCT, XLCT, XMCT
3.4. DFT and TD-DFT calculation
The DFT computations of [Rh(
[Rh(
-NaiEt-N, N0,C)(PPh3)Cl2] (3b) have been performed with
optimized geometry to correlate the electronic structure with the
a
-NaiEt-N, N0)(PPh3)Cl3] (2b) and
a
(pp (Cl) / dp (Rh)) etc. For complex 3b, the lowest energy tran-
sition near 622 nm is originated from HOMO / LUMO. The other
transition near 430 nm region is due to transition from HOMO-2/
HOMO-3 / LUMO and can be assigned as chloride-to-ligand and
intraligand charge transfer transitions. The transitions at shorter
wavelengths are mixture of mainly PPh3-to-ligand (YLCT), intra-
ligand (ILCT), chloride-to-ligand charge transfer transitions (XLCT).
4. Conclusion
The coordination and cyclometallated complexes of Rh(III)
incorporating 1-alkyl-2-(naphthyl-
described in this paper. Organorhodium complexes are obtained on
treatment of -NaiR with RhCl3 in presence of Et3N. The coordi-
a-azo)imidazole (a-NaiR) are
a
a a
-NaiEt-N, N0)(PPh3)Cl3] (2b) and [Rh( -NaiEt-N, N0,
nation complexes also transfer to the organometallic complexes
with the treatment of Et3N. The complexes are characterized by IR,
Fig. 5. UVevisible spectra of [Rh(
C) (PPh3)Cl2] (3b) in acetonitrile.

D. Sardar et al. / Journal of Organometallic Chemistry 732 (2013) 109e115
115
UVeVIS, 1H-NMR spectral data and the structures of both types of
complexes are confirmed by single crystal X-ray diffraction study.
The electronic properties are explained by DFT and TD-DFT calcu-
lations. We will study the CeH activation reaction by other plat-
inum group metals and the reactivity of the MeC bonds.
[18] P. Byabartta, J. Dhinda, P.K. Santra, C. Sinha, K. Panneerselvam, F.-L. Liao, T.-
H. Lu, J. Chem. Soc. Dalton Trans. (2001) 2825e2832.
[19] J. Otsuki, K. Suwa, K. Narutaki, C. Sinha, I. Yoshikawa, K. Araki, J. Phys. Chem. A
109 (2005) 8064e8069.
[20] K.K. Sarker, B.G. Chand, K. Suwa, J. Cheng, T.-H. Lu, J. Otsuki, C. Sinha, Inorg.
Chem. 46 (2007) 670e680.
[21] A.D. Ryabov, Synthesis (1985) 233e252.
[22] J.P. Collman, L.S. Hegedus, J.R. Norton, R.G. Finke, Principles and Applications
of Organotransition Metal Chemistry. Mill Valley, CA (1987).
[23] M. Bellar, C. Bolm, Transition Metals for Organic Synthesis 1e2, Wiley-VCH,
Weinheim, 1998.
[24] B. Cornils, W.A. Hermann (Eds.), Applied Homogenous Catalysis with Organ-
ometallic Compounds: A Comprehensive Handbook in Two Volumes, VCH,
Weinheim, 1996.
Acknowledgements
Financial support from Council of Scientific and Industrial
Research, and Department of Science and Technology, New Delhi
are gratefully acknowledged.
[25] J. Tsuji, Transition Metal Reagents and Catalysts, Wiley-VCH, Weinheim, 2000.
[26] I. Aiello, A. Crispini, M. Ghedini, M. La Deda, F. Barigelletti, Inorg. Chim. Acta
308 (2000) 121e128.
Appendix A. Supplementary material
[27] D.P. Lydon, G.W.V. Cave, J.P. Rourke, J. Mater. Chem. 7 (1997) 403e406.
[28] L. Dıez, P. Espinet, J.A. Miguel, M.P.R. Medina, J. Organomet. Chem. 690 (2005)
261e268.
[29] C.N. Ranninger, I.L. Solera, J. Rodriguez, J.L.G. Ruano, P.R. Raithby,
J.R. Masaguer, C. Alosona, J. Med. Chem. 36 (1993) 3795e3801.
[30] W. Kaim, B. Schwederski, Bioinorganic Chemistry: Inorganic Elements in the
Chemistry of Life, J. Wiley & Sons, ChichestereNew YorkeBrisbaneeToronto
Singapore, 1994.
[31] S.J. Lippard, J.M. Berg, Principles of Bioinorganic Chemistry, University Science
Books, Mill Valley, CA, 1994.
[32] E. Gómez, M.A. Huertos, J. Pérez, L. Riera, A. Menéndez-Velázquez, Inorg.
Chem. 49 (2010) 9527e9534.
Energy and composition of the selected frontier molecular or-
bitals calculated by DFT and electronic transition data from TDDFT
calculation are given in Supplementary material. Crystallographic
data for the structural analysis are in the Cambridge Crystallo-
graphic Data Centre, and CCDC No. 907997, [Rh(
a-NaiEt-N,
N0)(PPh3)Cl3] (2b) and 907996 [Rh( -NaiEt-N, N0,C)(PPh3)Cl2] (3b).
a
Copies of this information may be obtained free of charge from the
Director, CCDC, 12 Union Road, Cambridge, CB2 1FZ, UK (email:
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
[33] J. Dinda, D. Das, P.K. Santra, C. Sinha, L.R. Falvello, J. Organomet. Chem. 629
(2001) 28e38.
[34] J. Dinda, K. Bag, C. Sinha, G. Mostafa, T.-H. Lu, Polyhedron 22 (2003) 1367e
1376.
References
[35] A.I. Vogel, A Text Book of Practical Organic Chemistry, Longmann, London,
1959.
[36] G.M. Sheldrick, SHELXS-97, Program for the Solution of Crystal Structure,
University of Gottingen, Germany, 1997.
[37] G.M. Sheldrick, SHELXL 97, Program for the Refinement of Crystal Structure,
University of Gottingen, Germany, 1997.
[38] L.J. Farrugia, J. Appl. Cryst. 30 (1997) 565.
[1] K. Venkataraman, The Chemistry of Synthetic Dyes, Academic Press, New
York, 1956.
[2] H. Zollinger, Color Chemistry: Syntheses, Properties and Application of
Organic Dyes and Pigments, second ed., VCH, Weinheim, 1991.
[3] S. Kawata, Y. Kawata, Chem. Rev. 100 (2000) 1777e1788.
[4] J.A. Delaire, K. Nakatani, Chem. Rev. 100 (2000) 1817e1845.
[5] I. Sener, F. Karc, N. Ertan, E. Kılıc, Dyes Pigments 70 (2006) 143e148.
[6] W. Huang, Dyes Pigments 79 (2008) 69e75.
[7] G. Pavlovic, L. Racane, H. Cicak, V. Tralic-Kulenovic, Dyes Pigments 83 (2009)
354e362.
[8] F. Hamon, F. Djedaini-Pilard, F. Barbot, C. Len, Tetrahedron 65 (2009) 10105e
10123.
[9] B.K. Ghosh, A. Chakravorty, Coord. Chem. Rev. 95 (1989) 239e266.
[10] N. Bag, A. Pramanik, G.K. Lahiri, A. Chakravorty, Inorg. Chem. 31 (1992) 40e45.
[11] A.C.G. Hotze, H. Kooijman, A.L. Spek, J.G. Haasnoot, J. Reedijk, New J. Chem. 28
(2004) 565e569.
[12] C. Das, A. Saha, C.-H. Hung, G.-H. Lee, S.-M. Peng, S. Goswami, Inorg. Chem. 42
(2003) 198e204.
[13] K.N. Mitra, S. Goswami, Proc. Indian Acad. Sci. (Chem. Sci) 111 (1999)
461e467.
[14] B.K. Santra, G.K. Lahiri, J. Chem. Soc. Dalton Trans. (1998) 1613e1618.
[15] G.K. Lahiri, S. Bhattacharya, S. Goswami, A. Chakravorty, J. Chem. Soc. Dalton
Trans. (1990) 561e565.
[39] A.L. Spek, PLATON, Molecular Geometry Program, University of Utrecht, The
Netherlands, 1999.
[40] M.J. Frisch, G.W. Trucks, H.B. Schlegel, P.M.W. Gill, B.G. Johnson, M.A. Robb,
J.R. Cheeseman, T.A. Keith, G.A. Petersson, J.A. Montgomery, K. Raghavachari,
M.A. Al-Laham, V.G. Zakrzewski, J.V. Ortiz, J.B. Foresman, J. Cioslowski,
B.B. Stefanov, A. Nanayakkara, M. Challacombe, C.Y. Peng, P.Y. Ayala, W. Chen,
M.W. Wong, J.L. Andres, E.S. Replogle, R. Gomperts, R.L. Martin, D.J. Fox,
J.S. Binkley, D.J. Defrees, J. Baker, J.P. Stewart, M. Head-Gordon, C. Gonzalez,
J.A. Pople, Gaussian98, Gaussian, Inc., Pittsburgh, PA, 1998.
[41] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785e789.
[42] P.J. Hay, W.R. Wadt, J. Chem. Phys. 82 (1985) 270e283.
[43] M. Cossi, V.J. Barone, J. Chem. Phys. 115 (2001) 4708e4717.
[44] D. Sardar, P. Datta, S. Das, B. Saha, S. Samanta, D. Bhattacharya, P. Karmakar,
C.-D. Chen, C.-J. Chen, C. Sinha, Inorg. Chim. Acta 394 (2013) 98e106.
[45] R. Acharyya, S. Dutta, F. Basuli, S.-M. Peng, G.-H. Lee, L.R. Falvello,
S. Bhattacharya, Inorg. Chem. 45 (2006) 1252e1259.
[46] B.J. Pankuch, D.E. Lacky, G.A. Crosby, J. Phys. Chem. 84 (1980) 2061e2068.
[47] A. Ceulemans, L.G. Vanquickenborne, J. Am. Chem. Soc. 103 (1981) 2238e
2241.
[16] T.K. Misra, D. Das, C. Sinha, P. Ghosh, C.K. Pal, Inorg. Chem. 37 (1998) 1672e
1678.
[17] P. Byabartta, Sk. Jasimuddin, B.K. Ghosh, C. Sinha, A.M.Z. Slawin, J.D. Woollins,
New J. Chem. 26 (2002) 1415e1424.
[48] E.M. Kober, T.J. Meyer, Inorg. Chem. 21 (1982) 3967e3977.