Ruthenium(II) mediated C-H activation of substituted acetophenone thiosemicarbazones: Synthesis, structural characterization, luminescence and electrochemical properties

Article abstract of DOI:10.1016/j.jorganchem.2009.09.010

Treatment of [RuHCl(CO)(AsPh₃)₃] with 4′-substituted acetophenone thiosemicarbazone derivatives in methanol under reflux afford a series of air stable new ruthenium(II) cyclometalated complexes containing thiosemicarbazone of general

Full text of DOI:10.1016/j.jorganchem.2009.09.010

Journal of Organometallic Chemistry 694 (2009) 4170–4177
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Ruthenium(II) mediated C–H activation of substituted acetophenone
thiosemicarbazones: Synthesis, structural characterization, luminescence
and electrochemical properties
*
Rupesh Narayana Prabhu, Devaraj Pandiarajan, Rengan Ramesh
School of Chemistry, Bharathidasan University, Tiruchirappalli 620 024, Tamil Nadu, India
a r t i c l e i n f o
a b s t r a c t
Treatment of [RuHCl(CO)(AsPh3)3] with 40-substituted acetophenone thiosemicarbazone derivatives in
methanol under reflux afford a series of air stable new ruthenium(II) cyclometalated complexes contain-
ing thiosemicarbazone of general formula [Ru(L)(CO)(AsPh3)2]. The 40-substituted acetophenone thio-
semicarbazone ligands behave as a dianionic terdentate C, N and S donors (L) and coordinates to
ruthenium via aromatic carbon, the imine nitrogen and thiol sulfur. The compositions of the complexes
have been established by elemental analysis, and spectral methods (FT-IR, UV–Vis, 1H NMR, ESI-MS) and
X-ray crystallography. In chloroform solution all the complexes exhibit metal-to-ligand charge transfer
transitions (MLCT) in the visible region and are emissive at room temperature with quantum yield of
0.001–0.005. The crystal structure of one of the complexes [Ru(4CAP-PTSC)(CO)(AsPh3)2] (4) has been
solved by single crystal X-ray crystallography and it indicates the presence of a distorted octahedral
geometry in these complexes. All the complexes exhibit a quasi reversible one electron reduction
(RuII/RuI) in the range ꢀ0.83 to ꢀ0.86 V. The formal potential of all the couples correlate linearly with
the Hammett constant of the para substituent in phenyl fragment of the acetophenone thiosemicarba-
zone ligands.
Article history:
Received 2 July 2009
Received in revised form 20 August 2009
Accepted 3 September 2009
Available online 10 September 2009
This paper is dedicated to Professor
Karuppannan Natarajan on the occasion of
his 60th birth anniversary.
Keywords:
Thiosemicarbazone
C–H activation
Ru(II) cyclometalated complex
Crystal structure
Emission
Ó 2009 Elsevier B.V. All rights reserved.
Redox potential
1. Introduction
additional donor atom in a suitable position for chelation, normally
resulting in tricoordination 2 [11,12].
Derivatives of semicarbazones and thiosemicarbazones are
amongst the most widely studied nitrogen and oxygen/sulfur do-
nor ligands [1–4]. Particularly, thiosemicarbazones have emerged
as an important class of sulfur donor ligands for transition metal
ions because of their mixed hard–soft donor character and versa-
tile coordination behaviour. In particular, transition metal com-
plexes of thiosemicarbazones have been receiving considerable
interest largely because of their pharmacological (viz. antiviral,
antifungal, antimicrobial, antitumour, anticancer) property [5–8].
Thiosemicarbazones are versatile ligands with a wide range of
coordination modes in metal complexes. Thiosemicarbazones usu-
ally bind to a metal ion, either in the neutral thione form or in the
anionic thiolate form, as bidentate N, S donor ligands forming five-
membered chelate rings 1 [9,10]. However, the binding capacity of
thiosemicarbazones is further increased by condensation of the
thiosemicarbazide with an aldehyde or ketone containing an
R
R
M
M
H
N
N
H
N
N
S
S
NH2
NH2
1
2
Ever since, the first cyclometalated complex was synthesized
[13], cyclometalation has become an important part of organome-
tallic chemistry and several reviews covering the subject have
appeared [14–16]. The intramolecular activation of aromatic C–H
bonds of coordinated ligands by transition metals represents an
active area of research due to their applications, such as their use
in regiospecific organic and organometallic synthesis, catalysis
[17–19], photochemistry [20,21], the synthesis of new metal
mesogenic compounds [22] and as potential biologically active
materials [23,24]. Bhattacharya et al., reported the reaction of
benzaldehyde thiosemicarbazone ligands with ruthenium(II) and
* Corresponding author. Tel.: +91 431 2407053; fax: +91 431 2407045/2407020.
E-mail address: ramesh_bdu@yahoo.com (R. Ramesh).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.09.010

R.N. Prabhu et al. / Journal of Organometallic Chemistry 694 (2009) 4170–4177
4171
osmium(II) complexes [25,26], where the thiosemicarbazone li-
gand behaved as a monoanionic bidentate N and S donors. Further
the same research group described the different coordination
modes of benzaldehyde thiosemicarbazone ligands with ruthe-
nium in monomeric and dimeric nature [27]. Rhodium mediated
C–H activation of benzaldehyde thiosemicarbazones has been
achieved recently, where the ligand behaved as a dianionic terden-
tate ligand [28]. In addition, palladium cyclometallated complexes
containing acetophenone thiosemicarbazones have been reported
and thiosemicarbazone act as terdentate C, N and S donors [29].
In view of different coordination modes of these ligands, we have
focused our research interest on the reaction of acetophenone thi-
osemicarbazone ligands with ruthenium(II) carbonyl complexes. It
has been observed that, interestingly, these ligands act as terden-
tate C, N and S donors and generate air stable monomeric ruthe-
nium(II) cyclometalated complexes via C–H activation.
Transition metal complexes exhibit an enormous potential for
the discovery of photo redox processes for solar energy conversion
[30], information storage systems [31], laser materials [32], and
biosensors [33]. In particular the photophysical and the excited
state chemistry of Ru(II) diimine complexes has been extensively
studied [34–36]. The complex, [Ru(bpy)3]2+ has been studied in
great detail and is one of the most used sensitizers in research lab-
oratories due to the very favourable photochemical, photophysical
and redox properties [37]. In comparison to the photophysical
properties of polypyridyl complexes, the luminescent chemistry
of cyclometalated ruthenium carbonyl thiosemicarbazone com-
plexes are not well developed.
spectra of the complexes in chloroform solution were recorded
with a Cary 300 Bio UV–Vis Varian spectrophotometer in the range
800–230 nm. Emission intensity measurements were carried out
by using a Jasco FP-6500 spectrofluorimeter with 5 nm exit slit at
Madurai Kamaraj University, Madurai. Electrochemical measure-
ments were made using
a Princeton EG and G-Parc model
potentiostat using a glassy carbon-working electrode and [(n-
C4H9)4N](ClO4) (TBAP) as supporting electrolyte. All the potentials
were referenced to saturated calomel electrode (SCE) and the solu-
tions were purged with N2 before each set of experiments.
2.3. Preparation of thiosemicarbazone ligands
The substituted acetophenone thiosemicarbazone ligands were
prepared by modification of the following reported procedure [29].
A solution of 40-substituted acetophenone (120–165 mg, 1 mmol),
40-substituted-3-thiosemicarbazide (91–165 mg, 1 mmol) in cata-
lytic amount of conc. HCl (0.5 ml) in methanol (20 ml) was stirred
at 27 °C for 6 h. During the course of the reaction, solid formed was
filtered, washed with hexane and dried in air (Scheme 1).
Spectral and analytical data for the ligands:
4-HAP-TSC (R = H, R0 = H): White; Yield: 90%; M.p.: 167 °C; Anal.
Calc. for C9H11N3S: C, 55.93; H, 5.74; N, 21.74; S, 16.59. Found: C,
55.87; H, 5.68; N, 21.64; S, 16.50%. 1H NMR (400 MHz, CDCl3) (d
ppm): 9.3 (s, 1H, NH), 8.8 (s, 2H, NH2), 7.2–7.8 (m, 5H, aromatic),
2.3 (s, 3H, Me).
4-HAP-PTSC (R = H, R0 = Ph): White; Yield: 86%; M.p.: 169 °C;
Anal. Calc. for C15H15N3S: C, 66.88; H, 5.61; N, 15.60; S, 11.90.
Found: C, 66.95; H, 5.54; N, 15.64; S, 11.82%. 1H NMR (400 MHz,
CDCl3) (d ppm): 9.3(s, 1H, NH), 8.8 (s, 1H, NHPh), 7.2–7.7 (m,
10H, aromatic), 2.3 (s, 3H, Me).
In continuation of our research on the synthesis of ruthenium
cyclometalated complexes via direct C–H activation of azo or
thiosemicarbazone ligands [38–42], we describe here the cyclo-
metalation of ruthenium(II) with 40-substituted acetophenone
thiosemicarbazone ligands incorporated with triphenylarsine as
ancillary ligand. All the complexes have been characterized by ana-
lytical and spectral methods. The structure of one of the complexes
has been probed with the help of single crystal X-ray diffraction
analysis. Further, the electrochemical behaviour of the complexes
has been examined by cyclic voltammetry along with lumines-
cence studies.
4-CAP-TSC (R = Cl, R0 = H): White; Yield: 92%; M.p.: 155 °C; Anal.
Calc. for C9H10ClN3S: C, 47.47; H, 4.43; N, 18.45; S, 14.08. Found: C,
47.40; H, 4.33; N, 18.53; S, 14.18%. 1H NMR (400 MHz, CDCl3) (d
ppm): 9.3 (s, 1H, NH), 8.8 (s, 2H, NH2), 7.2–7.7 (m, 4H, aromatic),
2.3 (s, 3H, Me).
4-CAP-PTSC (R = Cl, R0 = Ph): White; Yield: 95%; M.p.: 171 °C;
Anal. Calc. for C15H14ClN3S: C, 59.30; H, 4.64; N, 13.83; S, 10.55.
Found: C, 59.34; H, 4.70; N, 13.73; S, 10.50%. 1H NMR (400 MHz,
CDCl3) (d ppm): 9.3 (s, 1H, NH), 8.8 (s, 1H, NHPh), 7.2–7.7 (m,
9H, aromatic), 2.3 (s, 3H, Me).
2. Experimental
4-MAP-TSC (R = OCH3, R0 = H): White; Yield: 84%; M.p.: 160 °C;
Anal. Calc. for C10H13N3OS: C, 53.79; H, 5.87; N, 18.82; S, 14.36.
Found: C, 53.89; H, 5.89; N, 18.84; S, 14.30%. 1H NMR (400 MHz,
CDCl3) (d ppm): 9.3 (s, 1H, NH), 8.8 (s, 2H, NH2), 7.2–7.7 (m, 4H,
aromatic), 3.9 (s, 3H, OMe), 2.3 (s, 3H, Me).
2.1. Materials and instrumentation
Commercially available RuCl3ꢁ3H2O was used as supplied from
Loba Chemie Pvt. Ltd. All the reagents used were chemically pure
and analar grade. The solvents were freshly distilled using the
standard procedures [43]. Triphenylarsine, all substituted acetoph-
enones and thiosemicarbazides were purchased from Aldrich. The
supporting electrolyte tetrabutyl ammonium perchlorate (TBAP)
was purchased from Fluka and dried in vacuum prior to use. The
precursor complex, [RuHCl(CO)(AsPh3)3], was prepared by re-
ported literature method [44].
R
R
H
N
H
N
CH3OH / HCl
RT 6 hrs
+
H2N
R'
S
H3C
O
H3C
N
HN
S
(R = -H, -Cl, Br, -OH, -NH2, -NO2)
(R' = -H, -C6H5)
HN
2.2. Physical measurements
R'
4HAP-TSC: R = H, R' = H
The microanalysis of carbon, hydrogen, nitrogen and sulfur
were recorded by analytic function testing Vario EL III CHNS ele-
mental analyzer at Sophisticated Test and Instrumentation Centre
(STIC), Cochin University, Kochi. Infrared spectra of complexes
were recorded in KBr pellets with a Perkin–Elmer 597 spectropho-
tometer in the range 4000–400 cmꢀ1. The 1H NMR spectra were re-
corded in CDCl3 and DMSO-d6 with Bruker 400 MHz instrument
using TMS as internal reference. Melting points were recorded in
the Boetius micro heating table and are uncorrected. Electronic
4HAP-PTSC: R = H, R' = C6H5
4CAP-TSC: R = Cl, R' = H
4CAP-PTSC: R = Cl, R' = C6H5
4MAP-TSC: R = CH3, R' = H
4MAP-PTSC: R = CH3, R' = C6H5
4NAP-TSC: R = NO2, R' = H
4NAP-PTSC: R = NO2, R' = C6H5
4AAP-TSC: R = NH2, R' = H
4BAP-PTSC: R = Br, R' = C6H5
4OHAP-TSC: R = OH, R' = H
Scheme 1. Preparation of thiosemicarbazone ligands.

4172
R.N. Prabhu et al. / Journal of Organometallic Chemistry 694 (2009) 4170–4177
4-MAP-PTSC (R = OCH3, R0 = Ph): White; Yield: 82%; M.p.: 173 °C;
II single crystal X-ray diffractometer using monochromated Mo Ka
Anal. Calc. for C16H17N3OS: C, 64.19; H, 5.72; N, 14.04; S, 10.71.
Found: C, 64.13; H, 5.62; N, 14.16; S, 10.75%. 1H NMR (400 MHz,
CDCl3) (d ppm): 9.3 (s, 1H, NH), 8.8 (s, 1H, NHPh), 7.2–7.7 (m,
9H, aromatic), 3.9 (s, 3H, OMe), 2.3 (s, 3H, Me).
radiation (kI = 0.71073 Å). Data were collected at 293 K. the unit
cell parameters were determined by the method of difference vec-
tors using reflections scanned from three different zones of the re-
ciprocal lattice. The intensity data were measured using
x and u
4-NAP-TSC (R = NO2, R0 = H): Yellow; Yield: 85%; M.p.: 175 °C;
Anal. Calc. for C9H10N4O2S: C, 45.37; H, 4.23; N, 23.51; S, 13.46.
Found: C, 45.40; H, 4.18; N, 23.61; S, 13.36%. 1H NMR (400 MHz,
DMSO-d6) (d ppm): 10.5 (s, 1H, NH), 8.7 (s, 1H, NH2), 8.1–8.3 (m,
4H, aromatic), 2.34 (s, 3H, Me).
scan with a frame width of 0.5°. Frame integration and data reduc-
tion were performed using the Bruker SAINT-Plus (Version 7.06a)
software. The multi-scan absorption corrections were applied to
the data using SADABS software.
4-NAP-PTSC (R = NO2, R0 = Ph): Yellow; Yield: 80%; M.p.: 180 °C;
Anal. Calc. for C15H14N4O2S: C, 57.31; H, 4.49; N, 17.82; S, 10.20.
Found: C, 57.35; H, 4.43; N, 17.92; S, 10.15%. 1H NMR (400 MHz,
DMSO-d6) (d ppm): 10.5 (s, 1H, NH), 8.7 (s, 1H, NHPh), 8.1–8.3
(m, 9H, aromatic), 2.34 (s, 3H, Me).
3. Results and discussion
The new ruthenium(II) cyclometalated thiosemicarbazone com-
plexes of 40-substituted acetophenone thiosemicarbazone of the
type [Ru(L)(CO)(AsPh3)2] (Scheme 2) have been obtained in good
yield via C–H activation of 40-substituted acetophenone thiosemi-
carbazone ligand by [RuHCl(CO)(AsPh3)3] in dry methanol in 1:1
molar ratio in the presence of lithium bromide and sodium acetate.
The addition of lithium bromide in basic medium to the reaction
mixture was used to abstract proton and cyclometalation was
achieved [29]. It has been observed that the ligands behave as
dianionic terdentate and replaces one hydride, one chloride and
one triphenylarsine from the ruthenium(II) precursor and the oxi-
dation state of ruthenium remain unchanged during the formation
of cyclometalated species. All the complexes are found to be air
stable in both the solid and the liquid states at room temperature
and are non-hygroscopic in nature. The synthesized ruthenium(II)
complexes are soluble in common solvents such as chloroform,
dichloromethane, acetonitrile, DMF and DMSO producing intense
coloured solutions. The analytical data of all the ruthenium(II)
cyclometallated thiosemicarbazone complexes are given in Table
S1 and are in good agreement with the molecular structure
proposed.
4-AAP-TSC (R = NH2, R0 = H): White; Yield: 80%; M.p.: 153 °C;
Anal. Calc. for C9H12N4S: C, 51.90; H, 5.81; N, 26.90; S, 15.39.
Found: C, 51.99; H, 5.78; N, 26.98; S, 15.42%. 1H NMR (400 MHz,
DMSO-d6) (d ppm): 9.3 (s, 1H, NH), 9.1 (s, 2H, Ar-NH2), 8.8 (br,
2H, NH2), 7.2–7.7 (m, 9H, aromatic), 2.3 (s, 3H, Me).
4-BAP-PTSC (R = Br, R0 = Ph): White; Yield: 86%; M.p.: 163 °C;
Anal. Calc. for C15H14BrN3S: C, 51.73; H, 4.05; N, 12.07; S, 9.21.
Found: C, 51.79; H, 4.10; N, 12.14; S, 9.25%. 1H NMR (400 MHz,
CDCl3) (d ppm): 9.3 (s, 1H, NH), 8.8 (s, 1H, NHPh), 7.2–7.7 (m,
9H, aromatic), 2.3 (s, 3H, Me).
4-HAP-TSC (R = OH, R0 = H): White; Yield: 80%; M.p.: 164 °C;
Anal. Calc. for C9H11N3OS: C, 51.65; H, 5.30; N, 20.08; S, 15.32.
Found: C, 51.58; H, 5.27; N, 20.13; S, 15.26%. 1H NMR (400 MHz,
DMSO-d6) (d ppm): 10.1 (s, 1H, NH), 9.7 (s, 1H, NH2), 7.2–7.7 (m,
9H, aromatic), 6.7 (s, 1H, Ar-OH), 2.3 (s, 3H, Me).
2.4. Synthesis of Ru(II) cyclometalated thiosemicarbazone complexes
All the reactions were carried out under anhydrous conditions
under nitrogen atmosphere and the ruthenium complexes were
prepared by the following general procedure: to a methanolic solu-
tion (20 ml) of [RuHCl(CO)(AsPh3)3] (100 mg, 0.092 mmol) was
added appropriate thiosemicarbazone ligand (17.8–35.7 mg,
0.092 mmol), lithium bromide (16 mg, 0.184 mmol) and sodium
acetate (15.1 mg, 0.184 mmol). The reaction mixture was then re-
fluxed for 6 h. During the course of the reaction solid was formed.
The solvent was evaporated, the residue was washed with light
petroleum ether (60–80 °C) recrystallized from CH2Cl2/CH3OH
and dried under vacuum (Scheme 2). (Yield: 65–75%). The 1H
NMR spectra for a representative complex is shown in Fig. 1. The
analytical data of all the Ru(II) cyclometalated thiosemicarbazone
complexes is given in Table S1 (Supplementary material).
3.1. Characterization
The important IR absorption bands for all the synthesized com-
plexes are given in Table 1. The observed bands may be classified
into those originating from the ligands and those arising from
the bonds formed between Ru(II) and the coordinating sites. The
free ligand displays mC@S absorptions at 834 cmꢀ1 and was disap-
peared upon complexation. This observation may be attributed to
the enolization of –NH–C@S and subsequent coordination through
the deprotonated sulfur [45]. The band observed in the region
1302–1324 cmꢀ1 due to
mC–S, further confirms the coordination
through the deprotonated sulfur. The ligand showed a strong band
at 1611 cmꢀ1 which is characteristic of the azomethine group
(>C@N). Coordination of the ligand to the ruthenium ion through
azomethine nitrogen atom is expected to reduce the electron den-
sity in the azomethine link and thus lowers the mC@N absorption
frequency in the region 1559–1584 cmꢀ1 after complexation indi-
cating the coordination of azomethine nitrogen [46] to ruthenium
2.5. X-ray crystallography
Single crystals of [Ru(4CAP-PTSC)(CO)(AsPh3)2] (4) were grown
by slow evaporation of methanol solution at room temperature.
The data collection was carried out using Bruker AXS Kappa APEX
R
R
CH3OH
AsPh3
+ [RuHCl(CO)(AsPh3)3]
LiBr / NaOAc
CO
N2atm
Reflux
Ru
H3C
N
H3C
S
N
AsPh3
HN
S
N
(R = -H, -Cl, Br, -OH, -NH2, -NO2)
(R' = -H, -C6H5)
NHR'
NHR'
Scheme 2. Synthesis of Ru(II) cyclometalated thiosemicarbazone complexes.

R.N. Prabhu et al. / Journal of Organometallic Chemistry 694 (2009) 4170–4177
4173
Fig. 1. 1H NMR spectrum of complex 4.
1A1g ? 1T1g and 1A1g ? 1T2g are possible in order of the increasing
energy. The low energy bands in the visible region are assigned to
the charge transfer (CT) transitions. The charge transfer bands ob-
served in all the complexes due to M ? L transitions are possible in
the visible region in the range of 457–580 nm [47–49]. The other
high intensity bands in the region 242–398 nm region were assign-
able to ligand-centered (LC) transitions and have been designated
Table 1
IR data of ruthenium(II) cyclometalated thiosemicarbazone complexes.
Sl. no.
Complexes
m(C„O)
m(C@N)
m(C–S)
(cmꢀ1
)
(cmꢀ1
)
(cmꢀ1
)
1
2
3
4
5
6
7
8
[Ru(4-HAP-TSC)(CO)(AsPh3)2]
[Ru(4-HAP-PTSC)(CO)(AsPh3)2]
[Ru(4-CAP-TSC)(CO)(AsPh3)2]
[Ru(4-CAP-PTSC)(CO)(AsPh3)2]
[Ru(4-MAP-TSC)(CO)(AsPh3)2]
[Ru(4-MAP-PTSC)(CO)(AsPh3)2]
[Ru(4-NAP-TSC)(CO)(AsPh3)2]
[Ru(4-NAP-PTSC)(CO)(AsPh3)2]
[Ru(4-AAP-TSC)(CO)(AsPh3)2]
[Ru(4-BAP-PTSC)(CO)(AsPh3)2]
[Ru(4-OHAP-TSC)(CO)(AsPh3)2]
1916
1914
1929
1921
1916
1916
1926
1928
1912
1926
1926
1568
1567
1567
1564
1566
1577
1574
1580
1584
1559
1578
1317
1315
1324
1309
1312
1302
1310
1313
1310
1311
1315
as p–
p* and n–p* transitions. The absorption spectrum of a repre-
Table 2
9
10
11
Absorption and luminescence data of ruthenium(II) cyclometalated thiosemicarba-
zone complexes.
Complexes
kmax (nm)a;
e
(dm3 molꢀ1 cmꢀ1
)
Luminescence data
kmax (nm)b
/
em
c
1
2
3
4
5
6
7
8
476(2,030), 307(16,400), 242(45,100)
481(1,990), 339(22,370), 245(44,300)
478(3,090), 309(25,490), 243(46,400)
480(1,390), 331(20,720), 249(45,800)
462(4,150), 344(10,110), 249(46,700)
470(3,920), 328(28,130), 250(44,250)
580(3,520), 398(12,650), 242(49,320)
573(2,690), 398(15,520), 245(48,670)
457(4,140), 349(13,110), 243(42,670)
480(1,380), 331(20,620), 249(45,570)
459(3,320), 303(25,340), 242(44,530)
594
594
596
596
590
590
598
598
590
596
590
0.0034
0.0029
0.0046
0.0032
0.0022
0.0027
0.0042
0.0050
0.0017
0.0042
0.0015
ion. For all complexes, a strong band in the region 1912–1929 cmꢀ1
is due to the terminally coordinated carbonyl group and is ob-
served at higher frequency than in the precursor complexes. In
addition, other characteristic bands due to triphenylarsine are also
present at 1480 cmꢀ1 in the spectra of all the complexes.
The electronic absorption spectra of all the complexes in chloro-
form showed three to four bands in the region 242–580 nm (Table
2). All the ruthenium(II) complexes are diamagnetic, indicating the
presence of ruthenium in the +2 oxidation state. The ground state
of ruthenium(II) in an octahedral environment is 1A1g, arising from
9
10
11
a
Linear absorption maximum in CHCl3 solution.
Room temperature emission maximum in CHCl3 (10ꢀ4 M) solution
(kex = 450 nm).
b
6
the t2g configuration, and the excited states corresponding to the
t2g5eg1 configuration are 3T1g, 3T2g, 1T1g and 1T2g. Hence, four bands
c
Room temperature emission quantum yield in CHCl3 solution using
[Ru(bpy)3]2+ in acetonitrile as standard, with /em = 0.062.
corresponding to the transitions 1A1g ? 3T1g
,
1A1g ? 3T2g
,

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R.N. Prabhu et al. / Journal of Organometallic Chemistry 694 (2009) 4170–4177
sentative complex is shown in Fig. 2. The pattern of the electronic
1.00
0.50
0.00
spectra of all the complexes indicated the presence of an octahe-
dral environment around the ruthenium(II) ion, similar to that of
other ruthenium(II) octahedral complexes [50,51].
The 1H NMR spectra of all the complexes were recorded to con-
firm the binding of the thiosemicarbazone ligands to the ruthe-
nium(II) ion (Table 3). Multiplets are observed in the region d
6.4–7.9 ppm in all the complexes and have been assigned to the
aromatic protons of triphenylarsine and thiosemicarbazone li-
gands [52]. The CH3 protons of azomethine group appeared as a
singlet at d 2.1–2.3 ppm. All the complexes showed a singlet at d
8.7–8.8, which has been assigned to NH2 or NH–R protons. The
HN–C@S, protons present in the ligand are absent in the com-
plexes. The 1H NMR spectra of all the complexes are therefore con-
sistent with their composition.
350
400
450
500
550
600
650
700
Wavelength (nm)
Fig. 2. Normalised lowest energy absorption band (—) and luminescence (- - -)
spectra of complex 4 (10ꢀ4 M) at 298 K in chloroform and deaerated chloroform,
respectively, with 450 nm as the excitation wavelength.
3.2. Luminescence property
All the complexes are diamagnetic with the bivalent nature of
ruthenium in low-spin d6 in these complexes. The light emitting
property of all the complexes (10ꢀ4 M) was investigated in de-
gassed chloroform at room temperature (Table 2) with 450 nm as
the excitation wavelength. The emission maxima fall in the range
590–598 nm for the complexes. The luminescence spectrum of a
representative complex is shown in Fig. 2. It is likely that the
emission originates from the lowest energy metal-to-ligand
charge transfer (MLCT) state, probably derived from the excitation
Table 3
1H NMR data of ruthenium(II) cyclometalated thiosemicarbazone complexes.
Complexes
1H NMR data (ppm)
NH–R0 (s)
Ar–H (m)
CH3 (s)
R
1
2
3
4
5
6
7
8
8.8
8.8
8.8
8.8
8.8
8.8
8.7
8.7
8.7
8.8
8.8
6.4–7.7
6.4–7.9
6.4–7.7
6.4–7.8
6.4–7.8
6.4–7.8
6.4–7.7
6.4–7.7
6.4–7.7
6.4–7.7
6.4–7.9
2.1
2.3
2.3
2.3
2.2
2.3
2.1
2.3
2.2
2.3
2.2
7.4
7.4
–
involving dp(Ru) ? p
* (ligand) transitions, similar to the MLCT ob-
–
served in Ru(II) bipyridyl complexes [53,54]. All the complexes are
weakly emissive at room temperature in chloroform with a quan-
tum yield of 0.001–0.005 (using [Ru(bpy)3]2+ in acetonitrile as
standard, with /em = 0.062 [55]). The present result shows that
the cyclometalated Ru(II) carbonyl thiosemicarbazone complexes
have low emission intensity/quantum yield, when compared to
other ruthenium(II) bipyridyl complexes.
3.9
3.9
–
–
10.2
–
9
10
11
8.3
Fig. 3. The ORTEP diagram of the complex [Ru(4CAP-PTSC)(CO)(AsPh3)2] (4). For reasons of clarity, hydrogen atoms have been omitted.

R.N. Prabhu et al. / Journal of Organometallic Chemistry 694 (2009) 4170–4177
4175
3.3. X-ray structure
The summary of the data collection and refinement parameters
are given in Table 4 where as selected bond lengths and bond an-
gles are given in Table 5. The complex crystallizes in P21/n space
group. The thiosemicarbazone ligand coordinates in a terdentate
manner to the ruthenium(II) ion via thiolate sulfur, azomethine
nitrogen and one ortho carbon of the phenyl ring in the acetophe-
none fragment in addition to two AsPh3 and one carbonyl ligands.
Ruthenium is therefore sitting in a C2NSAs2 coordination environ-
ment, which is distorted octahedral in nature as reflected in all the
bond parameters around ruthenium. The bite angles around Ru(II)
are S–Ru–N(1) = 79.05(6)°, C(8)–Ru–N(1)= 78.41(9)°, C(8)–Ru–
C(52) = 92.23(11)° and S–Ru–C(52) = 110.30(9)°, and bond lengths
of 2.061(3) Å Ru–C(8), 2.0732(19) Å Ru–N(1), 2.4641(7) Å Ru–S and
1.838(3) Å Ru–C(52). The thiosemicarbazone ligand binds the me-
tal center at C, N and S forming two five-membered chelate rings.
The coordinated acetophenone thiosemicarbazone ligand and car-
bonyl ligand constitute one equatorial plane with the metal at the
center where the carbonyl ligand is trans to the azomethine
(>C@N) nitrogen. The two AsPh3 ligands are mutually trans to each
other. Usually the AsPh3 ligands prefer to occupy mutually cis posi-
The molecular structure of one of the complexes [Ru(4CAP-
PTSC)(CO)(AsPh3)2] (4) has been determined by single crystal X-
ray diffraction to find out the coordination mode of the acetophe-
none thiosemicarbazone in the complexes and stereochemistry of
the complexes. The ORTEP view of complex 4 is shown in Fig. 3.
Table 4
Crystal data and structure refinement for complex 4.
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system, space group
Unit cell dimensions
a (Å)
C52H42As2ClN3ORuS
1043.31
293(2)
0.71073
Monoclinic, P21/n
12.4945(4)
28.4182(11)
13.7331(5)
b (Å)
c (Å)
a
(°)
90
b (°)
113.174(2)
90
4482.8(3)
4, 1.546
1.964
2104
0.30 ꢂ 0.20 ꢂ 0.20
1.43 to 31.15
ꢀ18 ꢃ h ꢃ 17, ꢀ40 ꢃ k ꢃ 38,
ꢀ19 ꢃ l ꢃ 16
59 554/14 141 [0.0381]
100.0%
c
(°)
Volume (Å3)
tions for better
p-interaction [56]. However, in these complexes
Z, calculated density (Mg/m3)
Absorption coefficient (mmꢀ1
F(0 0 0)
the presence of CO, which is stronger
p
-acidic ligand, has probably
)
forced the bulky AsPh3 to take up mutually trans position for steric
reasons.
Crystal size (mm)
Theta range for data collection (°)
Limiting indices
3.4. Electrochemical study
Reflections collected/unique [R(int)
Completeness to theta = 25.00
Absorption correction
Maximum and minimum
transmission
]
Electrochemical study was carried out for all the free ligands
and the Ru(II) carbonyl thiosemicarbazone complexes in acetoni-
trile solution under N2 atmosphere in the potential range of 0 to
ꢀ1.5 V. The supporting electrolyte used was 0.05 M tetrabutyl
ammonium perchlorate (TBAP) and the concentration of the com-
plex was 10ꢀ3 M. We have not observed any redox waves within
the potential limits of 0 to ꢀ1.5 V for free ligands and whatever
the reductive responses observed within this potential limits were
due to metal center only. All the complexes display a quasi revers-
ible reduction at a scan rate of 100 mV sꢀ1 and the one electron
nature of reduction has been confirmed by comparing its current
height with that of a standard ferrocene–ferrocenium couple under
identical experimental conditions. The potentials are summarized
in Table 6 and cyclic voltammogram of complex 4 is shown in
Fig. 4. All the complexes show well-defined waves, with E1/2 in
the range of ꢀ0.82 to ꢀ0.86 V. The redox processes are quasi-
reversible in nature, characterized by a rather large peak-to-peak
Semi-empirical from equivalents
0.68 and 0.55
Refinement method
Full-matrix least-squares on F2
14141/1/556
1.067
R1 = 0.0387, wR2 = 0.0893
R1 = 0.0754, wR2 = 0.1099
0.00158(12)
1.071 and ꢀ0.519
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
Extinction coefficient
Largest difference peak and hole
(e Aꢀ3
)
Table 5
Selected bond lengths (Å) and angles (°) for complex 4.
Bond lengths (Å)
Bond angles (°)
Ru–As
Ru–As
Ru–C8
Ru–N1
Ru–S
Ru–C52
As1–C16
As1–C22
As1–C28
As2–C34
As2–C40
As2–C46
C1–C3
C3–C8
C6–Cl
C9–S
C52–O1
N1–N2
N1–C1
N2–C9
N3–C9
1 2.4695(3)
2 2.4379(3)
2.061(3)
2.0732(19)
2.4641(7)
1.838(3)
1.953(3)
1.942(3)
1.944(3)
1.944(3)
1.947(3)
1.945(3)
1.443(4)
1.424(3)
1.739(3)
1.755(2)
1.146(3)
1.377(3)
1.301(3)
1.292(3)
1.363(3)
S–Ru–As
S–Ru–As2
S–Ru–C8
1 87.191(18)
88.078(19)
157.42(7)
79.05(6)
110.30(9)
175.180(13)
93.59(6)
88.81(5)
92.16(8)
90.43(6)
89.39(5)
separation (DEp) of 100–140 mV [57]. The redox potentials are vir-
tually independent of scan rates, indicating quasi-reversibility.
The potentials of reduction (RuII/RuI) have been found to be
sensitive to the nature of the substituent (R) in the acetophenone
S–Ru–N1
S–Ru–C52
As1–Ru–As2
As1–Ru–C8
As1–Ru–N1
As1–Ru–C52
As2–Ru–C8
As2–Ru–N1
As2–Ru–C52
C8–Ru–N1
C8–Ru–C52
N1–Ru–C52
Ru–S–C9
Ru–N1–N2
Ru–N1–C1
N2–N1–C1
N1–N2–C9
Ru–C52–O1
N1–C1–C3
S–C9–N2
Table 6
Electrochemical data of ruthenium(II) cyclometallated thiosemicarbazone complexes.
Complexes
(RuII/RuI)
Epc (V)
Epa (V)
E1/2 (V)
DEp (mV)
90.34(8)
78.41(9)
1
2
3
4
5
6
7
8
ꢀ0.91
ꢀ0.89
ꢀ0.93
ꢀ0.94
ꢀ0.91
ꢀ0.90
ꢀ0.95
ꢀ0.96
ꢀ0.89
ꢀ0.95
ꢀ0.90
ꢀ0.77
ꢀ0.79
ꢀ0.81
ꢀ0.80
ꢀ0.79
ꢀ0.80
ꢀ0.83
ꢀ0.83
ꢀ0.77
ꢀ0.81
ꢀ0.78
ꢀ0.84
ꢀ0.84
ꢀ0.87
ꢀ0.87
ꢀ0.85
ꢀ0.85
ꢀ0.89
ꢀ0.89
ꢀ0.83
ꢀ0.88
ꢀ0.84
140
100
120
140
120
100
120
130
120
140
120
92.23(11)
170.64(11)
94.81(9)
125.34(15)
118.15(18)
116.5(2)
114.0(2)
174.6(3)
114.3(2)
126.6(2)
9
10
11
S–C9–N3
N2–C9–N3
115.3(2)
118.1(2)
Supporting electrolyte: [Bu4N](ClO4) (0.05 M); solvent = acetonitrile; all potentials
referenced to SCE; E1/2 = 0.5(Epc + Epa), where Epa and Epc are anodic and cathodic
peak potentials, respectively;
D .
Ep = (Epc + Epa); scan rate: 100 mV sꢀ1
ESD in parenthesis.

4176
R.N. Prabhu et al. / Journal of Organometallic Chemistry 694 (2009) 4170–4177
80
60
40
20
0
entate C, N and S donors) have been synthesized from the
reactions of [RuHCl(CO)(AsPh3)3] with 40-substituted acetophe-
none thiosemicarbazone ligand. The characterization of the com-
plexes were accomplished by analytical and spectral (IR, UV–Vis,
1H NMR) methods. X-ray diffraction study of complex 4 confirms
the C, N and S coordination mode of acetophenone thiosemicarba-
zone ligands and reveals the presence of a distorted octahedral
geometry around Ru(II) ion. The present result shows that the terd-
entate C, N and S coordination mode of acetophenone thiosemicar-
bazone to ruthenium(II) ion via C–H activation. All the complexes
are luminescent but have low quantum yield, when compared to
other ruthenium(II) bipyridyl complexes. All the complexes show
one electron nature of reduction and the electronic effects of the
substituents (R) have direct influence on the redox potential.
-20
0
-400
-800
-1200
-1600
Potential (mV)
Acknowledgements
Fig. 4. Cyclic voltammogram of complex 4. Supporting electrolyte: [Bu4N](ClO4)
(0.05 M); solvent = acetonitrile; scan rate: 100 mV sꢀ1
.
We sincerely thank Council of Scientific and Industrial Research
(CSIR), New Delhi for financial support [Scheme. No. 10-2(5)/426
2007(i)-E.U.II; 01(2156)/07/EMR-II] and for Junior Research Fel-
lowship to R.N.P. We express sincere thanks to SAIF, Indian Insti-
-0.82
-0.83
-0.84
-0.85
-0.86
-0.87
tute of Technology
crystallographic studies.
–
Madras, for single crystal X-ray
Appendix A. Supplementary material
CCDC 703225 contains the supplementary crystallographic data
for complex 4. 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.2009.09.010.
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-0.50
0.00
Substituent constant (σ)
0.50
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