A closer look at the formation of bicyclometalated and cyclometalated ruthenium carbonyl complexes

Article abstract of DOI:10.1016/j.ica.2012.11.011

To study steric and electronic factors that affect the C-H activation of Schiff bases by the complex [Ru(PPh₃)₂(CO) ₂Cl₂], systematic spectroscopic analyses were performed for a family of Ru(II) complexes of type [Ru(PPh₃)₂(CO)L]. Among eight Schiff bases [H₂Ln (n = 1-8)], synthesized by condensation of methyl-4-formyl benzoate with 4-aminoacetophenone, 1-naphthylamine, 2-amino-5-chloropyridine, 8-aminoquinoline, semicarbazide hydrochloride, 2-aminophenol, thiosemicarbazide and 2-aminothiophenol, it was observed that the C-H activation was dependent on the kind as well as the position of the coordinating atoms. The C-H activation of the Schiff bases was most facile in the formation of a Ru-CNO configuration followed by Ru-CNS, Ru-CNN, and Ru-CNC configurations, whereas for a Ru-NC(methine) configuration the activation was the slowest. X-ray crystal structures for five cycloruthenated complexes are reported. Detailed electrochemical studies reveals the redox behavior of the complexes and DFT calculations were performed to obtain geometry optimized structure of all other complexes and to get an insight of the electronic spectral behavior.

Full text of DOI:10.1016/j.ica.2012.11.011

Inorganica Chimica Acta 397 (2013) 10–20
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
A closer look at the formation of bicyclometalated and cyclometalated
ruthenium carbonyl complexes
Soumik Mandal a, Dipravath K. Seth b, Parna Gupta a,
⇑
a Department of Chemical Sciences, Indian Institute of Science Education and Research, Kolkata, BCKV Main Post Office, Mohanpur, West Bengal 741252, India
b Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata 700032, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 March 2012
Received in revised form 17 August 2012
Accepted 12 November 2012
Available online 27 November 2012
To study steric and electronic factors that affect the C–H activation of Schiff bases by the complex
[Ru(PPh3)2(CO)2Cl2], systematic spectroscopic analyses were performed for a family of Ru(II) complexes
of type [Ru(PPh3)2(CO)L]. Among eight Schiff bases [H2Ln (n = 1–8)], synthesized by condensation of
methyl-4-formyl benzoate with 4-aminoacetophenone, 1-naphthylamine, 2-amino-5-chloropyridine, 8-
aminoquinoline, semicarbazide hydrochloride, 2-aminophenol, thiosemicarbazide and 2-aminothiophe-
nol, it was observed that the C–H activation was dependent on the kind as well as the position of the
coordinating atoms. The C–H activation of the Schiff bases was most facile in the formation of a
Keywords:
C–H activation
Ruthenium
Ru-CNO configuration followed by Ru-CNS, Ru-CNN, and Ru-CNC configurations, whereas for
a
Ru-NC(methine) configuration the activation was the slowest. X-ray crystal structures for five cycloruth-
enated complexes are reported. Detailed electrochemical studies reveals the redox behavior of the
complexes and DFT calculations were performed to obtain geometry optimized structure of all other
complexes and to get an insight of the electronic spectral behavior.
Schiff base
Bicyclometalation
Structure elucidation
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
ruthenium(II) where, electronic and steric environment of the li-
gands were varied significantly [13]. To get an idea of ease of acti-
Alkyl or aryl C–H bond cleavage reaction by a ruthenium com-
plex was first reported by Chatt and Davidson in 1965 [1]. Since
then, the cyclometalation reaction through C–H activation and
cyclometalated complexes continue to be of interest for its applica-
tion in the synthesis of organic molecules [2–4], particularly in the
field of novel materials [5,6] and medicines [7,8]. In these reactions
intramolecular C–H activation initiating a cyclometalation reaction
has been the key step. Cyclometalation is possible through C–C or
C–H eteroatom bond activation. If selective functionalization of al-
kyl or aryl C–H bonds can be developed, it would have broad appli-
cation and serve as powerful tool for transformations in organic
synthesis. Owing to the easy availability and cost viability, ruthe-
nium complexes are attractive choice for the activation of C–H,
C–C and C–N bonds in the alkyl or arene compounds [9–11]. Intu-
itively it is expected that for ligands with the increase in coordina-
tion sites, and with more electronegative atom available for
coordination, reaction rates will increase. However, it is not clear
whether stable ring formation, electronegativity or steric factor af-
fects the mechanistic pathway significantly or not [12].
vation of C–H bond, the progress of the reactions were simply
monitored by UV-spectroscopy. The reactions of [Ru(PPh3)2(CO)2-
Cl2] with ligands H2Ln (n = 1,2, 5–8, where H stands for dissociable
proton) and HLn (n = 3 and 4, where H stands for dissociable pro-
ton) (Fig. 1) afforded a group of organoruthenium complexes of
composition [Ru(PPh3)2(CO)HL1], [Ru(PPh3)2(CO)L4]+ (2, 3, 5–8;
L = L2, L3, L5–L8). The reactions, coordination environments and
exact molecular structures are shown in Scheme 1. Depending on
the proximity of methine or aryl C-atom, only in one of the cases
a methine C–H bond (HL3) and in all other cases an aryl C–H bond
has been activated.
Comparatively rare bicyclometalated ruthenium complex (2)
has been formed in reaction of H2L2 with [Ru(PPh3)2(CO)2Cl2],
where two aryl C–H atoms have been activated [14]. The com-
plexes formed by the reaction of [Ru(PPh3)2(CO)2Cl2] with the li-
gands HL4, H2L5–H2L8 exhibits quite expected coordination
mode having CNN(S/O) environment [12,15,16]. Single crystal X-
ray study of complex 8 indicates an unprecedented mononuclear
cycloruthenated complex of aminothiophenol derived Schiff base.
The present manuscript illustrates the detailed syntheses, spec-
tral and structural characterization, electrochemistry, DFT study
and the dependence of the reaction rates for C–H activation with
systematic variation of the ligand structure and coordinating
atoms.
To address some of these issues, we have initiated investiga-
tions on the C–H activation of some Schiff bases H2Ln or HLn by
⇑
Corresponding author. Tel.: +91 3473279130; fax: +91 3473279131.
E-mail address: parna.gupta@gmail.com (P. Gupta).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.11.011

S. Mandal et al. / Inorganica Chimica Acta 397 (2013) 10–20
11
chosen as the basis function and 6-31g(d,p) basis set was taken for
H, C, N, O and Cl and SDD basis set for Ru.
COCH3
Ar
Ar
N
Ar
N
2.3. X-ray crystallography
H2L1
H2L2
X-ray diffraction data of five Ru complexes, crystallized mainly
by solvent evaporation, were collected on a Bruker SMART APEXII
CCD area-detector diffractometer using graphite monochromated
Cl
Mo Ka radiation (k = 0.71073 Å). Data reduction included multi-
N
scan corrections for absorption. Structure solution and refinement
were done using the SHELXL-TL program package [19]. Selected crys-
tal data and data collection parameters for all the complexes are gi-
ven in Table 1. Graphic representations of the complexes were
generated with program MERCURY [20].
Ar
N
N
N
HL3
HL4
H
N
NH2
O
Ar
N
2.4. Synthesis of ruthenium complexes
Ar
N
OH
SH
2.4.1. [Ru(PPh3)2(CO)(HL1)Cl] (1)
H2L5
H2L6
Ligand H2L1 (28 mg, 0.10 mmol) along with triethylamine
(0.014 mL, 0.10 mmol) was dissolved in toluene (50 mL), refluxed
and [Ru(CO)2(PPh3)2Cl2] (75 mg, 0.10 mmol) was added to the
refluxing solution. The reaction mixture was then refluxed for
12 h. The solution was dried under reduced pressure. The resulting
light red colored solid was purified by preparative TLC using 14%
acetonitrile in toluene (Rf = 0.15) and identity of the complex was
confirmed by ESI-MS. Yield: 71 mg (73%); Elemental Anal. Calc.
for C54H44ClNO4P2Ru: C, 66.90; H, 4.57; N, 1.44. Found: C, 67.06;
H, 4.45; N, 1.63%. ESI-MS (m/z): 935.52 [MÀCl]+; 933.49(M+À2H);
671.56(M+À2H-PPh3); 412.93(M+À2H-2PPh3); IR (KBr, cmÀ1):
H
N
NH2
Ar
N
Ar
N
S
H2L7
H2L8
COOCH3
Ar =
519, 695, 744(
mPPh3), 1720, 1578(mC@N), 1940(mCO), 2858, 2928
Fig. 1. Molecular structure of ligands H2L1–H2L8.
(m
C–H). 1H NMR (400 MHz, CDCl3, d ppm); 2,62(s, 3H), 3.96(s, 3H),
7.24–7.27(m, 12H), 7.40(s, 1H), 7.7(d, 2H, J = 8.56 Hz), 7.82(d, 1H,
J = 7.86 Hz), 7.98–8.01(m, 18H), 8.15(d, 2H, J = 8.56 Hz), 8.49(s,
1H); 13C NMR(125 MHz, CDCl3, d ppm): 47.27, 52.36, 111.72,
120.83, 127.00, 128.53, 128.90, 129.44, 129.76, 130.09, 130.76,
132,84, 134.96, 139.44, 143.63, 151.59, 155.76, 160.53, 166.43,
197.18.
2. Experimental
2.1. Materials
The starting materials RuCl3Á3H2O, triphenylphosphane, formal-
dehyde, KOH, methyl-4-formylbenzoate, p-amino acetophenone,
1-naphthyl amine, 5-chloro-2-aminopyridine, 8-amino quinoline,
semicarbazide, 2-aminophenol, thiosemicarbazide, and 2-amino-
benzenethiol were purchased from Sigma–Aldrich and used with-
out purification. All the solvents were dried by usual methods prior
to use. [Ru(PPh3)2(CO)2Cl2] were prepared according to the re-
ported procedure [17] and ligand syntheses are given in supporting
information.
2.4.2. [Ru(PPh3)2(CO)(L2)] (2)
Ligand H2L2 (29 mg, 0.10 mmol) and triethylamine (0.028 mL,
0.20 mmol) was dissolved in toluene (50 mL), refluxed and
[Ru(PPh3)2(CO)2Cl2] (75 mg, 0.10 mmol) was added to the boiling
solution. The reaction mixture was then refluxed for 2 h. The solu-
tion was dried under reduced pressure. The resulting blue solid
was purified by preparative TLC using dichloromethane (Rf = 0.5)
and identity of the complex was confirmed by ESI-MS and X-ray
crystallography. Yield: 75.20 mg (80%). Elemental Anal. Calc. for
2.2. Physical measurements
C56H43NO3P2Ru: C, 71.48; H, 4.61; N, 1.49. Found: C, 70.87; H,
4.34; N, 1.38%. ESI-MS (m/z): 942.32[MÀCl]+; IR (KBr, cmÀ1): 520,
Microanalyses (C, H, N) were performed using a Heraeus Carlo
Erba 1108 elemental analyzer. IR spectra were obtained on a
Perkin-Elmer Spectrum RXI spectrophotometer with samples
prepared as KBr pellets. Electronic spectra were recorded on a
U-4100, HITACHI spectrometer. 1H NMR spectra were obtained
on a JEOL ECS-400 NMR spectrometer using TMS as the internal
standard. Electrochemical measurements were made using a PAR
model 273 potentiostat. A platinum disk working electrode, a plat-
inum wire auxiliary electrode and an aqueous Ag/AgCl were used
in a three electrode configuration. Electrochemical measurements
were made under a dinitrogen atmosphere. All electrochemical
data were collected at 298 K and are uncorrected for junction po-
tential. Mass spectra were recorded on a Q-Tof Micromass spec-
trometer by positive-ion mode electrospray ionization.
Optimization of ground-state structures and energy calculations
for all the complexes were carried out by density functional theory
(DFT) method using the GAUSSIAN 03 package [18], where B3LYP was
695, 743 (mPPh3), 1689, 1716(mC@N), 1927 (mCO), 2864, 2929(mC–H);
1H NMR (400 MHz, CDCl3,
d ppm): 3.93(s, 3H), 6.33(d, 1H,
J = 7.32 Hz), 6.77(t, 1H, J = 7.32 Hz), 6.87–6.91(m, 2H), 6.96(d, 1H,
J = 7.92 Hz), 7.00–7.04(m, 12H), 7.11–7.15(m, 18H), 7.28(s, 1H),
7.36(d, 2H, J = 7.92 Hz), 7.66(d, 1H, J = 6.72 Hz), 8.87(s, 1H); 13C
NMR (125 MHz, CDCl3, d ppm): 51.81, 108.93, 117.98, 121.87,
122.98, 126.28, 126.87, 126.92, 126.97, 127.02, 127.32, 127.70,
128.82, 132.65, 132.86, 133.58, 133.63, 133.68, 146.99, 154.28,
160.93, 168.27.
2.4.3. [Ru(PPh3)2(CO)(L3)Cl] (3)
Ligand HL3 (27 mg, 0.10 mmol) along with triethylamine
(0.014 mL, 0.10 mmol) was dissolved in toluene (50 mL), refluxed
and [Ru(PPh3)2(CO)2Cl2] (75 mg, 0.10 mmol) was added to the boil-
ing solution. The reaction mixture was then refluxed for 2 h. The
solution was dried under reduced pressure and the resulting yel-
low solid was purified by preparative TLC using toluene (Rf = 0.2)

12
S. Mandal et al. / Inorganica Chimica Acta 397 (2013) 10–20
O-H/ S-H
C-H
[Ru] = [Ru(CO)2(PPh3)2Cl2]
H
H
COCH3
N
N
H
H
H3COOC
H
H3COOC
[Ru], -CO, - 2Cl-, -2H+
[Ru], -CO, - Cl-, -H+
N
N
H3COOC
Ru(PPh3)2(CO)Cl
Ru(PPh3)2(CO)
1
COOCH3
2
Cl
H
N
N
N
H
H3COOC
N
H3COOC
H
[Ru], -CO, - Cl-
+
[Ru], -Cl-
+
Cl
H
N
N
N
N
+
H
H3COOC
H3COOC
Ru
Ru
+
-
-H , -Cl-, +PF6
PF6
Cl
N
Ru
H
N
N
N
-H+
Ru(PPh3)2(CO)
Cl
N
N
COOCH3
Ru(PPh3)2(CO)Cl
4
H3COOC
3
N
NH2
H
N
X
N
H
H3COOC
X
H
H
H3COOC
[Ru], -CO, - Cl-, -H+
[Ru], -CO, - Cl-, -H+
N
NH2
N
N
X
X
H3COOC
H
Ru
-Cl-, -H+
NH2
H3COOC
H
Ru
-Cl-, -H+
X
N
N
X
N
Ru(PPh3)2(CO)
Ru(PPh3)2(CO)
COOCH3
COOCH3
5 X= O
7 X= S
6 X= O
8 X= S
Scheme 1. Probable step for the formation of 1–8.

S. Mandal et al. / Inorganica Chimica Acta 397 (2013) 10–20
13
Table 1
Crystallographic data for 2ÁCH3CN, 3, 6ÁC2H5OH, 7Á /2(CH2OH)2 and 8ÁCH2Cl2.
1
1
2ÁCH3CN
3
6ÁC2H5OH
7Á /2(CH2OH)2
8ÁCH2Cl2
Empirical formula
F.W.
Space group
a (Å)
b (Å)
C58H46N2O3P2Ru
981.98
triclinic, P1
C51H40Cl2N2O3P2Ru
962.76
C54H47NO5P2Ru
952.94
triclinic, P1
C48H42N3O4P2RuS
888.91
triclinic, P1
C54H45Cl4NO3P2RuS
1092.79
ꢀ
ꢀ
ꢀ
monoclinic, P2(1)/c
11.9613(15)
29.818(4)
13.3927(15)
90.00
114.918(4)
90.00
4332.0(9)
4
monoclinic, P2(1)/c
13.0091(11)
13.9293(12)
26.838(2)
90.00
91.268(2)
90.00
4862.1(7)
4
10.1621(19)
21.344(4)
22.796(5)
102.307(4)
96.644(4)
100.736(4)
4683.7(16)
4
11.9458(5)
12.9001(6)
17.0701(8)
71.556(2)
72.860(2)
63.978(2)
2204.62(17)
2
12.6670(9)
12.9370(9)
13.4361(10)
89.007(4)
68.689(4)
80.316(4)
2019.7(3)
2
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Crystal, size (mm)
Color
0.43 Â 0.11 Â 0.03
0.20 Â 0.13 Â 0.11
0.21 Â 0.12 Â 0.10
0.21 Â 0.12 Â 0.10
0.55 Â 0.35 Â 0.33
blue
yellow
blue
orange
green
T (K)
l
100
0.452
100
0.606
100
0.480
100
0.565
100
0.697
(mmÀ1
)
Absorption correction method
Transmission (minimum/
maximum)
multi-scan
0.942/0.987
multi-scan
0.910/0.936
multi-scan
0.933/0.953
multi-scan
0.903/0.929
multi-scan
0.746/0.795
Data/parameters
h Range (°)
20415/1181
0.93–27.00
2.737, À1.481
R1 = 0.0552,
wR2 = 0.0978
R1 = 0.1206,
wR2 = 0.1242
0.999
6490/539
9362/571
4186/425
10617/596
2.11–27.00
1.805, À1.742
R1 = 0.0494,
wR2 = 0.1367
R1 = 0.0548,
wR2 = 0.1415
1.083
1.81–23.93
0.639, À0.482
R1 = 0.0543,
wR2 = 0.1135
R1 = 0.0823,
wR2 = 0.1229
1.296
1.28–27.00
2.538, À1.547
R1 = 0.0488,
wR2 = 0.1236
R1 = 0.0650,
wR2 = 0.1309
1.079
1.60–20.83
1.470, À0.831
R1 = 0.0664,
wR2 = 0.1810
R1 = 0.0818,
wR2 = 0.1874
1.289
D
qmax, Dqmin
Final R indices [F2 > 2 (F2)]
r
Final R indices (all data)
Goodness-of-fit
and identity of the complex was confirmed by ESI-MS and X-ray
crystallography. Yield: 54.24 mg (56%). Elemental Anal. Calc. for
2H, J = 2.72 Hz); 13C NMR (125 MHz, DMSO-d6, d ppm): 109.26,
117.35, 127.00, 128.15, 128.24, 128.70, 128.80, 131.43, 131.52,
132.03, 132.05, 132.31, 133.13, 136.70, 145.63, 158.50, 166.00.
C
51H40Cl2N2O3P2Ru: C, 63.62; H, 4.19; N, 2.91. Found: C, 64.06;
H, 4.42; N, 2.80%. ESI-MS (m/z): 927.09 [MÀCl] +; 664.98 (M+ÀH-
PPh3); IR (KBr, cmÀ1): 519, 694, 743 (
1936 (
m
PPh3), 1605, 1716(
m
C@N),
2.4.4. [Ru(PPh3)2(CO)(L4)](PF6) (4)
m
CO), 2856, 2927(
m
C–H); 1H NMR (400 MHz, DMSO-d6, d
Ligand HL4 (29 mg, 0.10 mmol) and triethylamine (0.014 mL,
0.10 mmol) was dissolved in toluene (50 mL), refluxed and
[Ru(CO)2(PPh3)2Cl2] (75 mg, 0.10 mmol) was added to the refluxing
ppm): 3.90(s, 3H), 7.24–7.31(m, 12H), 7.37(s, 1H), 7.41(d, 2H,
J = 2.76 Hz), 7.64–7.59(m, 18H), 7.78(s, 1H), 7.80(s, 1H), 7.87(d,
Fig. 2. Molecular structure of 2ÁCH3CN with all atoms labeled and thermal ellipsoids at the 50% probability level. Hydrogen atoms and solvent molecule are omitted for
clarity.

14
S. Mandal et al. / Inorganica Chimica Acta 397 (2013) 10–20
Fig. 3. Molecular structure of 3 with all atoms labeled and thermal ellipsoids at the 50% probability level. Hydrogen atoms are omitted for clarity.
solution. The reaction mixture was then refluxed for 6 h. The solu-
tion was dried under reduced pressure and the resulting red col-
ESI-MS (m/z): 942.87 [MÀCl]+, 680.87 (M+ÀH-PPh3); IR (KBr,
cmÀ1): 513, 696, 768(
mPPh3), 1702, 1556(mC@N), 1888(mCO), 2357.
ored solid was dissolved in dichloromethane.
A
methanolic
1H NMR(CDCl3, 400 MHz): 3.96(s, 3H), 7.07(t, 3H, J = 7.32 Hz),
7.14–7.18(m, 9H), 7.29–7.32(m, 9H), 7.40(b, 12H), 7.46–7.53(m,
3H), 7.64–7.72(m, 3H), 8.12(s, 1H). 13C NMR(CDCl3, 100 MHz):
52.33, 118.28, 118.28, 121.57, 125.58, 126.75, 127.48, 128.07,
128.12, 128.42, 128.48, 128.67, 129.00, 129.13, 129.83, 132.10,
133.52, 133.57, 133.64, 136.12, 136.35, 150.29, 161.63.
solution of NH4PF6 (16.30 mg, 0.10 mmol) was added to the dichlo-
romethane solution, slow evaporation of the solution give red col-
ored precipitate and identity of the complex was confirmed by ESI-
MS. Yield: 75.86 mg (70%); Elemental Anal. Calc. for C55H44F6N2O3-
P3Ru: C, 60.66; H, 4.07; N, 2.57. Found: C, 61.06; H, 4.05; N, 2.41%.
Fig. 4. Molecular structure of 6ÁC2H5OH with all atoms labeled and thermal ellipsoids at the 50% probability level. Hydrogen atoms and solvent molecule are omitted for
clarity.

S. Mandal et al. / Inorganica Chimica Acta 397 (2013) 10–20
15
Fig. 5. Molecular structure of 7Á1/2(CH2OH)2 with all atoms labeled and thermal ellipsoids at the 50% probability level. Hydrogen atoms and solvent molecule are omitted for
clarity.
Fig. 6. Molecular structure of 8ÁCH2Cl2 with all atoms labeled and thermal ellipsoids at the 50% probability level. Hydrogen atoms and solvent molecule are omitted for
clarity.

16
S. Mandal et al. / Inorganica Chimica Acta 397 (2013) 10–20
Table 2
1
Key bond lengths (Å) and angles (°) of complexes 2ÁCH3CN, 3, 6ÁC2H5OH, 7Á /2(CH2OH)2, 8ÁCH2Cl2.
Bond lengths
Bond angles
Bond angles
2ÁCH3CN
Ru1–P1
Ru1–P2
Ru1–N1
Ru1–C37
Ru1–C49
Ru1–C56
Ru2–P3
2.3618(14)
2.3707(13)
2.093(4)
2.147(5)
2.128(5)
1.848(5)
2.3654(14)
2.3828(14)
2.101(4)
C56–Ru1–N1
C56–Ru1–C49
N1–Ru1–C49
C56–Ru1–C37
N1–Ru1–C37
C49–Ru1–C37
P1–Ru1–P2
176.14(18)
105.7(2)
C112–Ru2–N2
C112–Ru2–C93
N2–Ru2–C93
C112–Ru2–C105
N2–Ru2–C105
C93–Ru2–C105
P3–Ru2–P4
176.37(17)
97.33(19)
79.04(17)
106.48(18)
77.15(16)
156.17(18)
175.37(5)
78.09(17)
97.81(19)
78.41(17)
156.10(19)
177.87(5)
Ru2–P4
Ru2–N2
Ru2–C93
Ru2–C105
Ru2–C112
2.122(4)
2.165(4)
1.826(5)
3
Ru1–P1
Ru1–P2
Ru1–Cl2
Ru1–N2
Ru1–C42
Ru1–C51
2.3818(19)
2.3907(19)
2.4999(17)
2.140(6)
2.048(7)
1.829(8)
C51–Ru1–C42
C51–Ru1–N2
C42–Ru1–N2
N2–Ru1–Cl2
97.9(3)
174.0(2)
76.6(2)
C51–Ru1–Cl2
C42–Ru1–Cl2
P1–Ru1–P2
98.1(2)
164.0(2)
177.38(7)
87.47(15)
6ÁC2H5OH
Ru1–P1
Ru1–P2
Ru1–N1
Ru1–O3
Ru1–C45
Ru1–C52
2.3722(11)
2.3808(11)
2.082(4)
2.228(3)
2.049(4)
C52–Ru1–C45
C52–Ru1–N1
C45–Ru1–N1
C52–Ru1–O3
100.28(17)
179.63(16)
79.70(16)
103.25(14)
C45–Ru1–O3
N1–Ru1–O3
P1–Ru1–P2
156.46(14)
76.78(12)
175.14(4)
1.876(5)
1
7Á /2(CH2OH)2
Ru1–P1
Ru1–P2
Ru1–S1
Ru1–N3
Ru1–C1
Ru1–C5
2.388(3)
2.375(3)
2.467(3)
2.119(9)
1.830(13)
2.092(11)
C1–Ru1–C5
C1–Ru1–N3
C5–Ru1–N3
C1–Ru1–S1
97.4(5)
176.3(5)
78.9(4)
106.3(4)
C5–Ru1–S1
N3–Ru1–S1
P2–Ru1–P1
156.3(3)
77.4(3)
175.14(12)
8ÁCH2Cl2
Ru1–P1
Ru1–P2
Ru1–N1
Ru1–S1
Ru1–C45
Ru1–C52
2.3728(9)
2.3619(9)
2.113(3)
2.4591(9)
2.064(3)
1.844(3)
C52–Ru1–C45
C52–Ru1–N1
C45–Ru1–N1
C52–Ru1–S1
94.27(14)
173.31(13)
79.07(12)
105.34(10)
C45–Ru1–S1
N1–Ru1–S1
P2–Ru1–P1
160.09(10)
81.34(8)
177.43(3)
2.4.5. [Ru(PPh3)2(CO)L5] (5)
sure and the resulting blue solid was purified by TLC using 10% ace-
tonitrile in toluene (Rf = 0.25) and identity of the complex was
confirmed by ESI-MS and X-ray crystallography. Yield: 80.48 mg
(89%). Elemental Anal. Calc. for C52H42NO4P2Ru: C, 68.79; H, 4.66;
N, 1.54. Found: C, 67.98; H, 5.02; N, 1.47%. ESI-MS (m/z): 906.63
Ligand H2L5 (22 mg, 0.10 mmol) was dissolved in toluene
(50 mL), triethylamine (0.014 ml, 0.10 mmol) was added. The
resulting solution was refluxed and [Ru(CO)2(PPh3)2Cl2] (75 mg,
0.10 mmol) was added. The reaction mixture was refluxed for
2 h. The solution was dried under reduced pressure and the result-
ing light orange colored solid was purified by preparative TLC using
20% acetonitrile in toluene (Rf = 0.6) and identity of the complex
was confirmed by elemental analysis and ESI-MS. Yield:
49.57 mg (57%); Elemental Anal. Calc. for C47H40N3O4P2Ru: C,
64.67; H, 4.61; N, 4.81. Found: C, 64.93; H, 4.54; N, 4.65%. ESI-
[MÀCl]+; IR (KBr, cmÀ1): 518, 694, 770(
mPPh3), 1715, 1588(mC@N),
1934(mCO), 2851, 2922(m
C–H). 1H (400 MHz, CDCl3 d ppm): 3.90(s,
3H), 7.22–7.35(m, 18H), 7.46–7.50(m, 4H), 7.62(d, 2H,
J = 8.72 Hz), 7.99–8.18(m, 12H), 8.33(s, 1H), 8.35(s, 1H). 13C NMR
(125 MHz, CDCl3, d ppm): 30.61, 52.51, 65.90, 111.08, 125.11,
126.10, 127.54, 127.89, 129.34, 129.50, 129.60, 129.98, 130.35,
132.12, 133.32, 133.41, 141.35, 150.33, 165.49, 192.85.
MS (m/z): 874.08 [MÀCl]+; IR (KBr, cmÀ1): 516, 693, 769(
m
PPh3),
1698, 1578(mC@N), 1727(mCO), 2858, 2928(mC–H), 3180(m
N–H); 1H
NMR (400 MHz, CDCl3, d ppm); 3.34(s, 3H), 5.22(s, 2H) 7.90–
8.10(m, 32H), 8.30(s, 1H), 9.19(s, 1H), 10.95(s, 1H); 13C NMR
(125 MHz, CDCl3, d ppm): 52.22, 127.14, 127.63, 128.24, 128.46,
128.55, 129.87, 131.96, 132.05, 132.13, 132.30, 132.86, 133.95,
134.11, 166.51.
2.4.7. [Ru(PPh3)2(CO)L7] (7)
Ligand H2L7 (24 mg, 0.10 mmol) was dissolved in toluene
(50 mL), triethylamine (0.014 mL, 0.10 mmol) was added, refluxed
and [Ru(CO)2(PPh3)2Cl2] (75 mg, 0.10 mmol) was added to the boil-
ing solution. The reaction mixture was then refluxed for 2 h. The
solution was dried under reduced pressure and the resulting or-
ange solid was purified by preparative TLC using 5% acetonitrile
in toluene (Rf = 0.2) and identity of the complex was confirmed
by ESI-MS and X-ray crystallography. Yield: 66.58 mg (75%); Ele-
mental Anal. Calc. for C47H40N3O3P2RuS: C, 63.43; H, 4.53; N,
4.72. Found: C, 63.24; H, 4.43; N, 4.62%. ESI-MS (m/z): 889.91
2.4.6. [Ru(PPh3)2(CO)L6] (6)
Ligand H2L6 (26 mg, 0.10 mmol) was dissolved in toluene
(50 mL), triethylamine (0.014 mL, 0.10 mmol) was added, refluxed
and [Ru(CO)2(PPh3)2Cl2] (75 mg, 0.10 mmol) was added to the
refluxing solution. The reaction mixture was then refluxed for
2 h. The greenish yellow solution was dried under reduced pres-
[MÀCl]+; IR (KBr, cmÀ1): 516, 693, 769(
mPPh3), 1698, 1578(mC@N),

S. Mandal et al. / Inorganica Chimica Acta 397 (2013) 10–20
17
Table 3
3. Results and discussion
Selected orbital contribution of complexes 1–8.
Complex
Contributing fragments
%Contribution of fragments to
Reaction of potentially [C,N,X], (X = O, S, N, C) terdentate Schiff
bases (H2L1–H2L8) with [Ru(PPh3)2(CO)2Cl2] in refluxing toluene
afforded a group of cyclometalated complexes (1–8) in moderate
yield. To envisage the C–H activation of the ligands by [Ru(PPh3)2
(CO)2Cl2], extensive spectral and structural studies were done with
the resulting ruthenium complexes. The complexes described in
this paper were characterized by elemental analysis, IR spectros-
copy, 1H and 13C{1H} NMR spectroscopy, ESI-MS and X-ray crystal-
lography. As we are interested in C–H activation, one methine or
aryl carbon atom was kept in the vicinity of the ruthenium. The
ruthenium(II) has successfully activated methine or aryl C–H bond
HOMO
LUMO
1
Ru
Cl
CO
L1
35.62
46.32
10.86
6.46
15.04
6.41
5.26
72.61
0.68
PPh3
0.74
2
3
Ru
CO
L2
56.28
5.18
8.13
1.53
38.75
0.79
89.63
0.71
PPh3
Ru
Cl
CO
L3
36.16
43.75
4.37
11.26
3.21
1.29
to form metal–carbon(sp2C)
r-bond in every complex (Scheme 1).
The ligands coordinate Ru in terdentate fashion, except for
[Ru(PPh3)2(CO)(HL1)Cl] (1) and [Ru(PPh3)2(CO)(L3)Cl] (3). Two aryl
C–H bonds have been activated to generate bicyclometalated
ruthenium(II) complex [Ru(PPh3)2(CO)(L2)Cl] (2). The composi-
tions of the complexes were confirmed by elemental analyses,
ESI-MS as well as structures of the complexes 2ÁCH3CN, 3, 6ÁC2H5
15.05
0.67
83.62
0.62
PPh3
4
5
6
7
8
Ru
CO
L4
55.58
2.43
12.58
5.23
41.17
0.82
81.44
0.75
PPh3
1
OH, 7Á /2(CH2OH)2, 8ÁCH2Cl2 were determined by single crystal X-
Ru1
CO
L5
58.10
3.71
37.46
0.73
5.32
16.67
77.36
0.65
ray diffraction. The structures are shown in Figs. 2–6 and selected
bond parameters are presented in Table 2.
The complexes (1–8, Scheme 1) have one carbonyl and two tri-
phenylphosphanes attached to the ruthenium center and all of
them have the P1–Ru–P2 angle around 180 3° [21]. The average
Ru–P (2.3758 Å) and Ru–CO (1.8468 Å) bond lengths are quite nor-
mal and comparable with similar type of complexes of ruthe-
nium(II) [17]. The average Ru–C (methine or aryl) distance
(2.0607 Å) is quite normal for 3, 6–8 [15,22,23], but a little longer
in case of 2 [14].
PPh3
Ru1
CO
L6
52.98
3.06
5.78
8.02
43.33
0.63
85.66
0.54
PPh3
Ru1
CO
L7
58.36
2.23
5.78
0.54
5.97
8.89
84.65
0.49
PPh3
Treatment of [Ru(PPh3)2(CO)2Cl2] with H2L1 and H2L2 and sub-
sequent purification results in the formation of 1 and 2. The ele-
mental analysis, ESI-MS and NMR spectroscopic data clearly
Ru1
CO
L8
45.21
2.44
4.96
7.78
12.39
0.78
86.69
0.57
indicate that the H2L1 is j
2-C,N bonded [22,23] to the ruthenium
PPh3
center in case of 1 and the expected composition of synthesized
complex is [Ru(PPh3)2(CO)(HL1)Cl]. ESI-MS of 1 (Fig. S1) shows
molecular ion peak at m/z 935.52(M+) attributable to [Ru(PPh3)2
(CO)(HL1)]+. Geometry optimized structure of 1 (Fig. S2) has been
obtained using DFT calculation as good quality single crystal could
not be grown. Obtained bond parameters are given in Table S1. An
interesting bicyclometalated complex has formed, when
[Ru(PPh3)2(CO)2Cl2] reacts with H2L2, where, both benzene and
napthyl ring C–H have been activated. Molecular structure of 2
(Fig. 2) shows monomeric compound in which ruthenium sits in
the center of a distorted octahedron, coordinated to C(37), C(49)
and N1(imine nitrogen) of dianionic tridentate L2. The fourth coor-
dination site in the equatorial plane is occupied by carbonyl C(56).
Extensive literature survey could not find any single example of
bicyclometalated complex like 2 [14]. The angles around the ruthe-
nium center deviate significantly from 90°. The angles C56–Ru1–
C49, C56–Ru1–C37 opened up to 105.7(2), and 97.81(19) whereas,
N1–Ru1–C49 and N1–Ru1–C37 angles have reduced to 78.09(17),
78.41(17). Moreover, the C49–Ru1–C37 angle of 156.10(19) sug-
gests significant distortion from octahedral geometry.
The X-ray crystal structure of 3 (Fig. 3) reveals that ligand HL3 is
coordinated to six-coordinated ruthenium center as L3, through
pyridine-N and the iminoacyl-carbon to form a stable five-mem-
bered chelate with a C39–Ru1–N1 angle of 76.58°(19). The ruthe-
nium has a C2NP2Cl coordination sphere in this complex. The
ligand L3, ruthenium, carbonyl and chloride constitute the equato-
rial plane of the octahedron with the metal at the center, and as
mentioned earlier, two triphenylphosphane ligands take up the
two axial positions. The carbonyl lie trans to the pyridine(py) nitro-
gen atom of the py–N@CHAr (L3) and the chloride is trans to the
1921(mCO), 2858, 2928(mC–H), 3255(m
N–H); 1H NMR (400 MHz,
CDCl3, d ppm): 3.84(s, 3H), 4.57(d, 2H, J = 6.32 Hz), 7.1–7.6(m,
32H), 7.91(s, 1H), 7.93(s, 1H); 13C NMR (125 MHz, CDCl3, d ppm):
51.94, 62.33, 126.28, 127.93, 128.68, 128.77, 129.00, 129.54,
129.75, 131.40, 131.49, 132.00, 133.10, 148.40, 166.21.
2.4.8. [Ru(PPh3)2(CO)L8] (8)
Ligand H2L8 (27 mg, 0.10 mmol) was dissolved in toluene
(50 mL), triethylamine (0.014 mL, 0.10 mmol) was added, refluxed
and [Ru(CO)2(PPh3)2Cl2] (75 mg, 0.10 mmol) was added to the boil-
ing solution. The reaction mixture was then refluxed for 2 h. The
solution was concentrated under reduced pressure and the result-
ing orange solid was purified by preparative TLC using dichloro-
methane in toluene (Rf = 0.4) and identity of the complex was
confirmed by ESI-MS and X-ray crystallography. Yield: 78.68 mg
(85%); Elemental Anal. Calc. for C52H42NO3P2RuS: C, 67.59; H,
4.58; N, 1.52. Found: C, 67.57; H, 4.43; N, 1.52%. ESI-MS (m/z):
922.82 [MÀCl]+; IR (KBr, cmÀ1): 528, 682, 728(
mPPh3), 1710,
1564(mC@N), 1904(mCO), 2893, 2947(m
C–H). 1H NMR (400 MHz, CDCl3,
d ppm): 3.83(s, 3H), 5.91(d, 1H, J = 7.92 Hz), 6.07(t, 1H, J = 6.72 Hz),
6.37(t, 1H, J = 7.32 Hz), 6.55(d, 1H, J = 7.96 Hz), 6.94(d, 1H,
J = 7.96 Hz), 7.09–7.18(m, 18H), 7.25(t, 1H, J = 7.32 Hz), 7.34–
7.39(m, 1H), 7.44–7.50(m, 12H), 7.80(s, 1H); 13C NMR(100 MHz,
DMSO-d6, d ppm): 51.74, 116.16, 121.56, 127.37, 127.41, 127.45,
128.39, 128.84, 129.51, 132.26, 132.48, 132.70, 133.47, 133.52,
133.56, 142.02, 143.56, 153.04, 153.28, 166.60.

18
S. Mandal et al. / Inorganica Chimica Acta 397 (2013) 10–20
Table 4
Electrochemical and electronic spectral data of complexes 1–8.
a
Complex
Electronic spectral data kmax, nm (€ Â 10À4, MÀ1cmÀ1
)
Cyclic voltammetric datab, E, V vs. SCE
1
2
3
4
5
6
7
8
378(0.77), 315c(8.5)
1.24f, 1.04f, À1.37g
524(0.17), 379(0.50)
0.903f, À1.224g, À1.644g
1.04, 1.39, À1.11g, À1.60g
0.685, 1.22, À0.99g
403(0.21), 310c(0.85)
560(0.24), 376(0.72), 325(1.56), 288c(2.10)
324(2.20)
0.51d(80)e, 0.71f, À.03g, À1.44d(70)e
0.58d(70)e, 1.30f, À1.15g, À1.59g
0.65d(80)e1.18f, À1.04g
594(0.086), 471(0.091), 409(0.23), 371c(0.37)
464(0.057), 357(0.37), 290(1.10)
419c(0.43), 373(0.93), 297(0.32)
0.36(70), 0.693, 1.22f, À1.65g
a
b
c
d
e
f
Dichloromethane solution.
Dichloromethane/acetonitrile (1:9), TBAP supporting electrolyte.
Shoulder.
E1/2 = 0.5(Epa + Epc), where Epa and Epc are anodic and cathodic peak potentials, respectively, scan rate 50 mV sÀ1
.
D
Ep = Epa À Epc in mV.
Epa value.
Epc value.
g
imine carbon (N@C) atom. All bond lengths are in the expected
limit, except Ru–N and Ru–Cl bonds [21,24,25], which are a little
longer, may be due to the presence of two trans-PPh3 ligands.
Earlier report by Kirchner group [26,27] shows ligand with coordi-
to 6 is available in literature [28], no report of complex similar to 8
is available in the literature. This is the first ever report of cyclo-
ruthenated complex coordinated to anionic sulfur attached to an
aromatic ring. The Ru–S bond [Ru1–S1 2.4591(9)] is comparable
to the Ru–S bond in complex 7.
nation environment similar to HL3, provides either
j
2-N,N-
coordinated or aminocarbene ruthenium complexes, where the
Ru–C bond length varies from 1.83 to 1.93 Å [13]. However, an
interesting coordination mode of py–N@CHAr (HL3) with ruthe-
nium is being revealed here with Ru–C bond length of
Infrared spectra of all the complexes show multiple bands of
varying intensities within the range 4000 to 400 cmÀ1. The me-
tal–carbon stretching band in the region 740–800 cmÀ1 cannot
be assigned from the spectra, because of overlap by strong triphen-
ylphosphane bands. Three strong bands observed around 520, 695,
730–770 and 1940 cmÀ1 in all the complexes are attributable to
the coordinated triphenylphosphanes and carbonyl respectively,
for all the complexes. The bands at around 1570 and 1700 cmÀ1
(2.045(5) Å), indicating the presence of metal–carbon
They have proposed that steric restrictions and presence of
strongly -accepting PPh3, CO ligands prevent an oxidative addi-
tion step in the formation of
2-N,C coordinated complex. Presence
of PPh3 and CO together, due to strong -accepting character and
r-bond.
p
j
p
(2–6) are due to mC@N which were absent in the precursor complex.
steric factor, probably prevents the formation of ruthenium car-
bene and facilitates the formation of more stable five-membered
iminoacyl ruthenium complex. Reaction of HL4 with [Ru(PPh3)2
(CO)2Cl2] generate cationic complex 4 with C2N2P2 (Scheme 1)
coordination environment, where ligand provides tridentate NNC
coordinating environment. The complex has precipitated out from
the solution as PF6-salt. Lack in quality of the single crystal pre-
vented further detailed structural studies of this complex. Compo-
sition of the complex was confirmed by elemental analysis, ESI-MS
(Fig. S3) and NMR studies. Geometry optimized structure (Fig. S4)
has been obtained from DFT study and bond parameters are given
in Table S1.
Each complex shows several intense absorptions in the visible
and UV region. The absorptions in the UV region are believed to
be due to transitions within the ligand orbitals. In order to assign
the lowest energy absorption in the visible region, DFT (1–8) and
TD-DFT (1, 3) calculations were performed using the crystallo-
graphic coordinates (for complex 2, 3, 6, 7, 8). Selected orbital con-
tribution of all the complexes are given in Table 3. It is interesting
to note that, for the complexes 1 and 3, coordinated chloride ligand
has considerable contribution in highest occupied molecular orbi-
tal (HOMO). Because of the mixed Ru d(p)–Clp(p) character of the
HOMO, a mixed MLCT/XLCT character of the transition is inaccu-
rate because of the delocalised character of the relevant orbitals.
This assignment proposed [29], with the Cl to HL1 or L3 XLCT con-
tribution prevailing. Of course this description is further supported
by the following comparison. The absorption spectrum of 1 closely
resembles that of 3 (see Table 4). In case of all other complexes (2,
4–8), HOMO holds maximum contribution from metal center and
LUMO possesses predominant ligand contribution. Hence, we as-
sign the lowest absorption band in the spectra to this HOMO ? LU-
Ligands H2L5–H2L8, on reaction with [Ru(PPh3)2(CO)2Cl2], af-
fords mononuclear complexes where the ligand bind as tridentate
j
3-C,N,O/S (Scheme 1), replacing two chloride and one carbonyl
from the ruthenium precursor. The structural studies on
[Ru(PPh3)2(CO)L6] (6) (Fig. 4), [Ru(PPh3)2(CO)L7] (7) (Fig. 5) and
[Ru(PPh3)2(CO)L8] (8) (Fig. 6) confirm that six-coordinated ruthe-
nium center bound to one dianionic tridentate CNO/S-donor li-
gand, one carbonyl, and two axial triphenylphosphanes. ESI-MS
and geometry optimized structure of 5, is shown in Figs. S5 and
S6, respectively. Extensive study by Bhattacharya group [12,15]
on the possible coordination mode of the benzaldehyde semicarba-
zone and thiosemicarbazones reveals that, formation of five-mem-
bered chelate ring is difficult but possible for these ligands, as they
have a rigid geometry across the C@N bond. But, ortho-metalation
of the pendant phenyl ring by C–H bond activation under suitable
reaction condition is possible. The crystal structure of 7 (Fig. 5)
shows that, the thiosemicarbazone ligand gets coordinated to
ruthenium as an CNS(anionic) donor. The Ru–S bond length is
2.469(3) comparable [15]. The geometry around the ruthenium
in complexes 6 and 8 are similar, only oxygen (6) is being replaced
by sulfur (8). Though complexes with similar coordination pattern
MO transition, which can be best be viewed as rmetal–
p⁄
L
transition. The other absorptions in the visible region are attribut-
able to transitions occurring from the ruthenium t2 orbitals to the
higher energy vacant orbitals. The absorptions in the UV region are
due to transitions within the ligand orbitals. Frontier orbital sur-
face diagram of complexes 3 and 4 are shown in Fig. 7.
To get an idea regarding the oxidation and reduction processes,
the complexes have been studied by cyclic voltammetry in 1:9
dichloromethane–acetonitrile solution (0.1 M TBAP) and voltam-
metric data are presented in Table 4. Each of the complexes shows
one to two oxidative and reductive responses. The origin of
reduction and oxidation are assigned from the HOMO and LUMO
population. For the complexes 1 and 3, there occurs halogen med-
iated metal oxidation, as HOMO posses mixed chloride and metal

S. Mandal et al. / Inorganica Chimica Acta 397 (2013) 10–20
19
the metal–ligand complex formation and that too, is reflected in
formation of complex 3. If, metal center prefers to coordinate the
more electronegative atom over carbon, we should end up at a
four-membered cationic complex as 3. It is significant to note that,
electronic and steric environment along with the stable ring for-
mation directs the bonding pattern as well as control the rate of
the reaction.
LUMO(3)
HOMO(3)
4. Conclusions
The present study shows that a series of Schiff base ligands
(H2L1–H2L8) can undergo facile C–H activation mediated by
[Ru(PPh3)2(CO)2Cl2] under mild reaction condition. The experi-
mental condition helps to activate both the acyl C–H and aryl
C–H bond. The C–H bond activation of ligands with varying coordi-
nation environment, were studied by a simple experiment. The
synthesis, reactivity and kinetic study reported here will definitely
provide useful insight for the templated designing of organic mol-
ecule through C–H activation. Further study in this direction is
presently being carried out in our laboratory.
LUMO(4)
HOMO(4)
Fig. 7. Contour plots of HOMO and LUMO of the complexes 3 and 4 (hydrogen
atoms are omitted for clearity).
Table 5
Time to complete the formation of ruthenium
complexes 1–8.
Acknowledgments
Complex
Time of
completion
(min)
P.G. would like to thank the Department of Science and Tech-
nology, India, Research Grant SR/FT/CS-057/2009 and IISER Kolkata
central XRD facility. S.M. and D.K.S. thank the CSIR, India for finan-
cial support. Authors are grateful to Prof. Samaresh Bhattacharya,
Jadavpur University, Dr. Indranil Bhattacharyya, ND College, How-
rah for their help.
1
2
3
4
5
6
7
8
850
651
31
198
37
15
32
71
Appendix A. Supplementary data
CCDC 841461, 821627, 821629, 821628 and 842508 contain the
supplementary crystallographic data for complexes 2ÁCH3CN, 3,
character. Since the metal contribution is predominant in the
HOMO of all other six complexes, first oxidation is assigned to me-
tal oxidation. The reductive response arose are due to imine-ligand
reduction. The first oxidative response is irreversible in nature for
complexes 1–4, whereas, for 5–8 it is reversible in nature charac-
1
6ÁC2H5OH, 7Á /2(CH2OH)2 and 8ÁCH2Cl2, respectively. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via http://www.ccdc.cam.ac.uk/data_request/
cif. Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.ica.2012.11.
011.
terized by a peak-to-peak separation (DEp) of 70–80 mV. The irre-
versible reductive response observed around 1.0–1.1 V may be
assigned to reduction of the imine fragment in the coordinated
ligands.
References
To study the C–H activation of H2L1–H2L8 by ruthenium(II), a
very simple experiment has been done. The time required for com-
pletion and the changes in the UV–vis spectrum with time during
the reaction of [Ru(PPh3)2(CO)2Cl2] with ligands H2L1–H2L8 were
plotted (Fig. S7). The time required for completion of the reactions
has been tabulated in Table 5. For the sake of our study, reaction
parameters like solvent, solvent volume, concentration and tem-
perature were kept constant. The slowest rate of formation of com-
plex is observed with H2L1, where single aryl C–H bond has been
activated and the ligand binds to the metal center in bidentate
fashion. Except, rate of formation of 1, 2 and 4, all other reactions
are quite fast and comparable. The plausible mechanism for every
case was suggested in Scheme 1. The closer look at the time of
completion suggests that the aryl C–H activation is the second
and rate determining step of the reactions and the initial binding
of metal to aryl carbon(along with imine nitrogen), in case of 1
and 2 render the reactions slow. In all other cases, the initial bind-
ing to N/O/S present in the ligand along with imine nitrogen brings
the pendent phenyl ring closer to the metal center to make the
otherwise difficult C–H bond activation easier. This is not applica-
ble for 4 and the unusual rate of formation of complex 4 is due to
difficulty in releasing the H+ from a cationic species. Definitely, sta-
ble chelate ring formation is one of the most important criteria of
[1] J. Chatt, J.M. Davidson, J. Chem. Soc. (1965) 843.
[2] S. Murahashi, Ruthenium in Organic Synthesis, Wiley, New York, 2004.
[3] T. Naota, T. Hikaru, S. Murahashi, Chem. Rev. 98 (1998) 2599.
[4] G. Dyker, Handbook of C–H Transformations: Applications in Organic
Synthesis, Wiley, New York, 2000.
[5] G. van Koten, R.J.M.(Bert)K. Gebbink, Dalton Trans. 40 (2011) 8731.
[6] M.E. van der Boom, D. Milstein, Chem. Rev. 103 (2003) 1759.
[7] R. Anand, J. Maksimoska, N. Pagano, E.Y. Wong, P.A. Gimotty, S.L. Diamond, E.
Meggers, R. Marmorstein, J. Med. Chem. 52 (2009) 1602.
[8] N.B. Johnson, I.C. Lennon, P.H. Moran, J.A. Ramsden, Acc. Chem. Res. 40 (2007)
1291.
[9] G.C. Vougioukalakis, R.H. Grubbs, Chem. Rev. 110 (2010) 1746.
[10] S.I. Murahashi, H. Takaya, Acc. Chem. Res. 33 (2000) 225.
[11] C. Gunanathan, D. Milstein, Acc. Chem. Res. 44 (2011) 588.
[12] F. Basuli, S.M. Peng, S. Bhattacharya, Inorg. Chem. 40 (2001) 1126.
[13] H.A. Zhong, J.A. Labinger, J.E. Bercaw, J. Am. Chem. Soc. 124 (2002) 1378.
[14] X.W. Li, F. Chen, W.F. Xu, Y.Z. Li, X.T. Chen, Z.L. Xue, Inorg. Chem. Commun. 14
(2011) 1673.
[15] S. Dutta, F. Basuli, A. Castineiras, S.M. Peng, G.H. Lee, S. Bhattacharya, Eur. J.
Inorg. Chem. 29 (2008) 4538.
[16] L.R. Hanton, T. Kemmitt, Chem. Commun. 10 (1991) 700.
[17] A. Ahmed, S.D. Robinson, M.F. Uttley, J. Chem. Soc., Dalton Trans. 7 (1972) 843.
[18] A.D. Becke, J. Chem. Phys. 98 (1993) 5648.
[19] G.M. Sheldrick, Acta. Crystallogr., Sect. A 64 (2008) 112.
[20] C.F. Macrae, I.J. Bruno, J.A. Chisholm, P.R. Edgington, P. McCabe, E. Pidcock, L.
Rodriguez-Monge, R. Taylor, J. van de Streek, P.A. Wood, J. Appl. Crystallogr. 41
(2008) 466.
[21] S. Nag, P. Gupta, R.J. Butcher, S. Bhattacharya, Inorg. Chem. 43 (2004) 4814.
[22] K. Ghosh, S. Kumar, R. Kumar, U.P. Singh, N. Goel, Inorg. Chem. 49 (2010) 7235.

20
S. Mandal et al. / Inorganica Chimica Acta 397 (2013) 10–20
[23] W.R. Roper, L.I. Wright, J. Organomet. Chem. 142 (1977) Cl.
[24] K. Omura, T. Uchida, R. Irie, T. Katsuki, Chem. Commun. 18 (2004) 2060.
[25] C.G. Roy, S.S. Sen, S. Dutta, G. Mostafa, S. Bhattacharya, Polyhedron 26 (2007)
3876.
[27] C. Slugovc, K. Mereiter, R. Schmid, K. Kirchner, Organometallics 17 (1998) 827.
[28] N.S. Chowdhury, D.K. Seth, M.G.B. Drew, S. Bhattacharya, Inorg. Chim. Acta 372
(2011) 183.
ˇ
[29] M.P. Aarnts, D.J. Stufkens, M.P. Wilms, E.J. Baerends, A. Vlcek Jr., I.P. Clark, M.W.
[26] C.M. Standfest-Hauser, K. Mereiter, R. Schmid, K. Kirchner, Organometallics 21
(2002) 4891.
George, J.J. Turner, Chem. Eur. J. 2 (1996) 1556.