A. Kanchanadevi et al. / Journal of Organometallic Chemistry 808 (2016) 68e77
69
relatively less. Thioamides (tautomeric forms Ia and Ib) are versa-
tile ligands which can coordinate to metal as neutral thione or in
their deprotonated thiol form (Scheme 1). It has been found in the
literature that the thiocarboxamide ligands are known to coordi-
nate metal ions usually in a bidentate fashion with an N,S donor
forming a five membered chelate ring. However, sulphur contain-
ing SCS pincers have gained recognition because of the added
stability via tridentate coordination imparts to the formation of
pincer complex. In terms of sulphur Lewis base donors, thioamides
are a relatively unexplored compound class in the design of ligands.
Palladium(II), gold(III), and platinum(II) complexes have been re-
ported for the bidentate coordination [25]. Arene ruthenium met-
allacycles containing anionic chelating thioamides have been
reported [26]. Recently, deprotonation-induced structural changes
in ruthenium pincer complexes with secondary thioamide groups
have been reported [27].
chromatography (GC) using Bruker 436-GC using GC-FID detector
equipped with a column (15 m - 0.25 mm - 0.25 mm) and high
purity nitrogen as carrier gas.
2.3. Synthesis of new ruthenium(II) arene thioamide complexes
A
mixture containing [Ru(h
6-p-cymene)Cl2]2 (50 mg,
0.082 mmol), thioamide (37.4e40.8 mg, 0.164 mmol) and PPh3
(42.8 mg, 0.164 mmol) in MeOH (20 mL) and Et3N (1 mL) was
heated to reflux for 2 h. To the hot solution was added solid NaBPh4
(58.6 mg, 0.164 mmol), which caused precipitation of an orange to
brown solid on cooling. The product was isolated by filtration,
washed with H2O, a little cold MeOH, diethyl ether and was sub-
sequently dried in vacuum. The resulting complexes were recrys-
tallized from CH2Cl2/Pet.ether and dried under vacuum. The purity
of the complexes was checked by TLC. Yield ¼ 78e84%.
With the objective of promoting the catalysts for TH reactions,
we focus our interest on synthesis of ruthenium(II) arene com-
plexes and its catalytic application towards TH reaction [28].
Herein, we describe the report on synthesis of ruthenium(II) arene
p-cymene complexes containing pyridine-2-thioamide ligands and
triphenylphosphine. The composition of the complexes has been
established by analytical and spectral (IR, UV-Vis, and NMR)
methods. The molecular structure of complex 4 has been deter-
mined by diffraction analysis on single crystals. Further, the new
cationic ruthenium complexes were demonstrated to be efficient
catalysts for the TH of the various aromatic/heterocycle and
aliphatic ketones to their corresponding secondary alcohols.
2.4. Analytical and spectral data for the complexes
2.4.1. [(
h
6-p-cymene)Ru[
k
2-S,N-C6H4CS¼N-(2-
MePh)(PPh3)]þ[BPh4]-] (1)
Brown solid.Yield: 82%, M.p. 182 ꢁC (with decomposition).
Found: C, 74.80%; H, 5.78%; N, 2.63%; S, 3.09%. Calc. for
C
65H60BN2PRuS: C, 74.77%; H, 5.79%; N, 2.68%; S, 3.07%. FT-IR (KBr
cmꢀ1): 1586 (ʋC]N); 1325 (ʋC-S). UVꢀVis (CH2Cl2;
l, nm): 425, 268,
229. NMR (CDCl3): dH (400 MHz): 6.71e8.47 (m, 43H, Ar, PPh3,
BPh4), 4.85e6.70 (d, 4H, cymene AreH), 2.3 (s, 3H, CH3), 1.3 (s, 3H,
cymene-CH3), 0.88e0.92 (d, 6H, cymene-i-propyl methyl). 13C NMR
(100 MHz, CDCl3) (d ppm): 171.5, 168.9, 167.5, 164.1, 162.3, 161.3,
152.4, 148.1, 137.9, 135.3, 131.9, 129.6, 129.3, 128.8, 128.0, 126.7,
123.2, 117.7, 105.5, 94.5, 81.2, 29.6, 21.7, 20.9, 20.2, 17.1.
2. Experimental section
2.1. Materials
2.4.2. [(
h
6-p-cymene)Ru[
k
2-S,N-C6H4CS¼N-(3-
MePh)(PPh3)]þ[BPh4]-] (2)
Commercially available RuCl3$3H2O was used as supplied from
Loba Chemie. All the reagents used were chemically pure and
analytical grade. The solvents were freshly distilled using the
standard procedures. 2-methyl pyridine, sulphur, aniline de-
rivatives and the ketones used for catalysis were purchased from
Sigma-Aldrich and were used as received. The precursor complex
Brown solid.Yield: 73%, M.p. 202 ꢁC (with decomposition).
Found: C, 74.81%; H, 5.81%; N, 2.61%; S, 3.07%. Calc. for
C
65H60BN2PRuS: C, 74.77%; H, 5.79%; N, 2.68%; S, 3.07%. FT-IR (KBr
cmꢀ1): 1591 (ʋC]N); 1334 (ʋC-S). UVꢀVis (CH2Cl2;
l, nm): 430, 271,
228. NMR (CDCl3): dH (400 MHz): 6.71e8.54 (m, 43H, Ar, PPh3,
BPh4), 4.84e5.66 (d, 4H, cymene AreH), 2.34 (s, 3H, CH3), 1.33 (s,
3H, cymene-CH3), 1.29e2.1 (d, 6H, cymene-i-propyl methyl). 13C
[Ru(h
6-p-cymene)Cl2]2 [29] and the substituted pyridine-2-
thioamide ligands [30] were prepared by the literature reports.
NMR (100 MHz, CDCl3) (d ppm): 168.5, 166.9, 163.7, 162.1, 161.7,
161.2, 158.9, 146.2, 138.9, 136.4, 132.1, 131.8, 130.9, 129.5, 127.8,
124.8, 121.9, 116.6, 111.2, 99.1, 86.1, 32.7, 23.7, 22.3, 21.7, 19.2.
2.2. Physical measurements
6-p-cymene)Ru[
k
2-S,N-C6H4CS ¼ N-(4-
Melting points were recorded in the Boetius micro-heating table
and are uncorrected. The analysis of carbon, hydrogen, nitrogen and
sulphur were performed at Sophisticated Test and Instrumentation
Centre (STIC), Cochin University of Science and Technology, Kochi.
Infrared spectra of complexes were recorded in KBr pellets with a
2.4.3. [(
h
MePh)(PPh3)]þ[BPh4]-] (3)
Brown solid.Yield: 78%, M.p. 196 ꢁC (with decomposition).
Found: C, 74.71%; H, 5.78%; N, 2.65%; S, 3.06%. Calc. for
C
65H60BN2PRuS: C, 74.77%; H, 5.79%; N, 2.68%; S, 3.07%. FT-IR (KBr
Perkin-Elmer 597 spectrophotometer in the range 4000e400 cmꢀ1
.
cmꢀ1): 1599 (ʋC]N); 1317 (ʋC-S). UVꢀVis (CH2Cl2;
l, nm): 421, 271,
Electronic spectra of the complexes were recorded in CH2Cl2 so-
lution with a Cary 300 Bio UVeVis Varian Spectrophotometer in the
range 800e200 nm. The 1H NMR spectra were recorded in CDCl3 on
Bruker (400 MHz) equipment with TMS (d 0.00) as an internal
standard. Organic compounds in catalysis were identified by gas
231. NMR (CDCl3): dH (400 MHz): 6.82e7.3 (m, 43H, Ar, PPh3, BPh4),
4.88e5.67 (d, 4H, cymene AreH), 2.36 (s, 3H, CH3), 1.36 (s, 3H,
cymene-CH3), 0.91e0.96 (d, 6H, cymene-i-propyl methyl). 13C NMR
(100 MHz, CDCl3) (d ppm): 169.5, 164.9, 164.4, 163.9, 163.4, 160.2,
156.7, 147.3, 138.1, 136.4, 134.1, 133.7, 131.3, 129.5, 128.7, 125.7, 122.0,
113.9, 106.9, 95.6, 82.8, 30.7, 24.7, 21.3, 21.2, 18.2.
S
2.4.4. [(h k
6-p-cymene)Ru[
2-S,N-C6H4CS ¼ N-(2,3,4-
SH
N
tautomeric equlibrium
R
R
TriMePh)(PPh3)]þ[BPh4]-] (4)
N
R
R
Brown solid.Yield: 75%, M.p. 206 ꢁC (with decomposition).
Found: C, 75.10%; H, 6.05%; N, 2.59%; S, 2.89%. Calc. for
H
amino-thione
imino-thiol
C
67H64BN2PRuS: C, 75.06%; H, 6.02%; N, 2.61%; S, 2.99%. FT-IR (KBr
Ia
Ib
cmꢀ1): 1594 (ʋC]N); 1338 (ʋC-S). UVꢀVis (CH2Cl2;
l, nm): 425, 268,
Scheme 1. Thione and thiol forms of thioamide.
229. NMR (CDCl3): dH (400 MHz): 6.63e8.38 (m, 41H, Ar, PPh3,