Half sandwich complexes of Ru(II) and complexes of Pd(II) and Pt(II) with seleno and thio derivatives of pyrrolidine: Synthesis, structure and applications as catalysts for organic reactions

Article abstract of DOI:10.1016/j.jorganchem.2009.08.004

The reactions of PhSe^-, PhS^- and Se^2- with N-{2-(chloroethyl)}pyrrolidine result in N-{2-(phenylseleno)ethyl}pyrrolidine (L1), N-{2-(phenylthio)ethyl}pyrrolidine (L2), and bis{2-pyrrolidene-N-yl)ethyl selenide (L3), respectively, which have been explored as ligands. The complexes [PdCl₂(L1/L2)] (1/7), [PtCl₂(L1/L2)] (2/8), [RuCl(η⁶-C₆H₆)(L1/L2)][PF₆] (3/9), [RuCl(η⁶-p-cymene)(L1/L2)][PF₆] (4/10), [RuCl(η⁶-p-cymene)(NH₃)₂][PF₆] (5) and [Ru(η⁶-p-cymene)(L1)(CH₃CN)][PF₆]₂·CH₃CN (6) have been synthesized. The L1-L3 and complexes were found to give characteristic NMR (Proton, Carbon-13 and Se-77). The crystal structures of complexes 1, 3-6, 9 and 10 have been solved. The Pd-Se and Ru-Se bond lengths have been found to be 2.353(2) and 2.480(11)/2.4918(9)/2.4770(5) A?, respectively. The complexes 1 and 7 have been explored for catalytic Heck and Suzuki-Miyaura coupling reactions. The value of TON has been found up to 85 000 with the advantage of catalyst's stability under ambient conditions. The efficiency of 1 is marginally better than 7. The Ru-complexes 3 and 9 are good for catalytic oxidation of primary and secondary alcohols in CH₂Cl₂ in the presence of N-methylmorpholine-N-oxide (NMO). The TON value varies between 8.0 × 10⁴ and 9.7 × 10⁴ for this oxidation. The 3 is somewhat more efficient catalyst than 9.

Full text of DOI:10.1016/j.jorganchem.2009.08.004

Journal of Organometallic Chemistry 694 (2009) 3872–3880
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Half sandwich complexes of Ru(II) and complexes of Pd(II) and Pt(II) with seleno
and thio derivatives of pyrrolidine: Synthesis, structure and applications
as catalysts for organic reactions
1
*
Pradhumn Singh, Monika Singh , Ajai K. Singh
Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016, India
a r t i c l e i n f o
a b s t r a c t
The reactions of PhSeꢀ, PhSꢀ and Se2ꢀ with N-{2-(chloroethyl)}pyrrolidine result in N-{2-(phenylsele-
no)ethyl}pyrrolidine (L1), N-{2-(phenylthio)ethyl}pyrrolidine (L2), and bis{2-pyrrolidene-N-yl)ethyl sel-
enide (L3), respectively, which have been explored as ligands. The complexes [PdCl2(L1/L2)] (1/7),
Article history:
Received 19 June 2009
Received in revised form 29 July 2009
Accepted 4 August 2009
Available online 8 August 2009
[PtCl2(L1/L2)] (2/8), [RuCl(
g g
6-C6H6)(L1/L2)][PF6] (3/9), [RuCl( 6-p-cymene)(L1/L2)][PF6] (4/10),
[RuCl(
g
6-p-cymene)(NH3)2][PF6] (5) and [Ru(
g
6-p-cymene)(L1)(CH3CN)][PF6]2ꢁCH3CN (6) have been syn-
thesized. The L1–L3 and complexes were found to give characteristic NMR (Proton, Carbon-13 and Se-77).
The crystal structures of complexes 1, 3–6, 9 and 10 have been solved. The Pd–Se and Ru–Se bond lengths
have been found to be 2.353(2) and 2.480(11)/2.4918(9)/2.4770(5) Å, respectively. The complexes 1 and
7 have been explored for catalytic Heck and Suzuki–Miyaura coupling reactions. The value of TON has
been found up to 85 000 with the advantage of catalyst’s stability under ambient conditions. The effi-
ciency of 1 is marginally better than 7. The Ru-complexes 3 and 9 are good for catalytic oxidation of pri-
mary and secondary alcohols in CH2Cl2 in the presence of N-methylmorpholine-N-oxide (NMO). The TON
value varies between 8.0 ꢂ 104 and 9.7 ꢂ 104 for this oxidation. The 3 is somewhat more efficient catalyst
than 9.
Keywords:
Seleno/thio pyrrolidine derivatives
Ruthenium
Palladium
Platinum
C–C coupling
Oxidation of alcohols
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
Half sandwich complexes having
g
6-benzene)Ru(II) units are well known [8,9]. The impetus for
(g
6-p-cymene)Ru(II) and
(
The biological aspects of pyrrolidine derivatives have got atten-
tion as they show potential for anti-cancer therapy [1,2], selective
inhibition activity against matrix metalloproteinase-2 [3] and
characteristics of potent anti-tumor agents [4]. The binding of ent-
antiomers of chiral platinum(II) complex of N-methyl-2-aminom-
ethylpyrrolidine to dG, d(GpG) and a 52-mer oligonucleotide has
been investigated [5]. Copper(II) complex of pyrrolidine dithiocar-
bamate has been reported to have potent anti-cancer activity
against cisplatin resistant neuroblastoma cells [6]. Recently pyrrol-
idine based inhibitors of the drug resistant mutant of HIV-1 prote-
ase have been reported [7]. We are unaware of any investigation
made on any selenated pyrrolidine derivatives (including their li-
gand chemistry). It was therefore thought worthwhile to synthe-
size L1 and L3 and investigate their ligand chemistry with ‘Soft’
metallic species (Pd(II), Pt(II) and Ru(II)), with which they are ex-
pected to coordinate preferably. The L3 was found unstable and
therefore its ligation could not be investigated. The L2 also not ex-
plored as a ligand, has been included for a comparative study.
the synthesis of new derivatives having these units arises, owing
to their catalytic potential in a range of organic transformations
[10–25] and very promising cytotoxic properties [26]. The [(g6
-
benzene)Ru(en)Cl]+ (en = 1,2-diaminoethane) shows very promis-
ing anti-cancer activity [27–29]. The properties of such complexes
may be fine tuned by the presence of chelating ligands, particularly
when the ligand or its skeleton has biological activity. We are una-
ware of any half sandwich complex of ruthenium(II) of piano stool
geometry that has L1 or any other (Se, N) ligand. The tellurium
analog of L1 is known [30] but its structurally characterized half
sandwich complex is unknown so far. Therefore, such complexes
having (
g
6-p-cymene)Ru(II) or (
g
6-benzene)Ru(II) unit and L1/L2
6-ben-
have been studied. The complexes of L1 and L2 with (
g
zene)Ru(II) have shown promise for catalytic oxidation of primary
and secondary alcohols, which has been studied in detail. The pres-
ent investigations on half sandwich complexes of Ru(II) with L1/L2
are not only expected to be helpful in understanding the effect of
these bidentate ligands on relative strength of Ru–benzene ring
bonding but also reveal a variety of non-covalent interactions. Re-
cently, palladium complex of a selenium ligand has been reported
very promising for Heck C–C coupling reaction [31]. Therefore
some palladium complexes of present (Se/S, N) ligands have been
* Corresponding author. Tel.: +91 11 26591379; fax: +91 11 26581102.
E-mail addresses: ajai57@hotmail.com, aksingh@chemistry.iitd.ac.in (A.K. Singh).
1
Contributed in crystallographic analysis.
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.08.004

P. Singh et al. / Journal of Organometallic Chemistry 694 (2009) 3872–3880
3873
explored for catalytic C–C coupling of Heck and Suzuki–Miyaura
type. The results of all these studies are the part of present paper.
low colored 2 was filtered, washed with hexane (10 cm3) and dried
in vacuo. Single crystals of 1 were grown by slow evaporation of its
solution in chloroform–hexane mixture (3:2).
1: Yield: 0.076 g (ꢃ70%). m.p. 145 °C. KM = 7.9 S cm2 molꢀ1
.
2. Experimental
Anal. Calc. for C12H17Cl2NPdSe: C, 33.48; H, 3.75; N, 3.25%. Found:
C, 34.06; H, 4. 01; N, 3.58%. NMR: (1H, CDCl 3, 25 °C versus TMS)
d (ppm): 1.76–2.06 (m, 4H, H8), 2.55–2.88 (m, 4H, H7), 3.01–3.34
(m, 2H, H5), 3.98–4.29 (m, 2H, H6), 7.50–7.52 (m, 3H, H1, H2),
8.22–8.25 (m, 2H, H3), (13C {1H}, CDCl3, 25 °C versus TMS) d
(ppm): 21.6 (C8), 32.4 (C5), 59.2 (C7), 63.3 (C6), 126.6 (C1), 130.3
(C2), 130.7 (C3), 133.5 (C4), (77Se{1H}, CDCl 3, 25 °C versus Me2Se)
d (ppm): 472.3.
Perkin–Elmer 2400 Series II C, H, N analyzer was used for ele-
mental analysis. The 1H, 13C{1H} and 77Se{1H}NMR spectra were re-
corded on a Bruker Spectrospin DPX-300 NMR spectrometer at
300.13, 75.47 and 57.24 MHz, respectively. IR spectra in the range
4000–400 cmꢀ1 were recorded on a Nicolet Protége 460 FT–IR
spectrometer as KBr pellets. The UV–Vis spectra were recorded
on Lambda BIO-20, Perkin–Elmer (USA); model 330. The conduc-
tivity measurements were carried out in CH3CN (concentration
ca. 1 mM) using ORION conductivity meter model 162. Single crys-
tal data were collected (at IIT Delhi and IIT Kanpur, India) on a Bru-
2: Yield: 0.091 g (ꢃ70%). m.p. 150 °C. KM = 9.6 S cm2 molꢀ1
.
Anal. Calc. for C12H17Cl2NPtSe.: C, 27.77; H, 3.11; N, 2.70%. Found:
C, 28.10; H, 3.39; N, 3.01%. NMR: (1H, DMSO-d6, 25 °C versus TMS)
d (ppm): 1.78–1.87 (m, 4H, H8), 2.41–2.81 (m, 4H, H7), 2.89–3.34
(m, 2H, H5), 3.84–4.10 (m, 2H, H6), 7.51–7.61 (m, 3H, H1, H2),
8.14–8.19 (m, 2H, H3), (13C{1H}, DMSO-d6, 25 °C versus TMS) d
(ppm): 22.2 (C8), 33.9 (C5), 62.2 (C7), 64.6 (C6), 125.8 (C1), 130.1
(C2), 130.8 (C3), 133.4 (C4), (77Se{1H}, DMSO-d6, 25 °C versus
Me2Se) d (ppm): 428.2 (t, 1J (195Pt–Se) 366.53 Hz).
ker AXS SMART Apex CCD diffractometer using Mo Ka (0.71073 Å)
radiations at 298(2) K. The software SADABS was used for absorption
correction (if needed) and SHELXTL for space group, structure deter-
mination and refinements [32–33]. The catalytic oxidation yields
were determined with NUCON Engineers (New Delhi, India) gas
chromatograph (with FID detector), model 5765 equipped with
an Alltech (EcTM-1) column of 30 m length, 0.25 mm diameter and
2.3. Synthesis of [RuCl(g g
6-C6H6)(L1)][PF6] (3) and [RuCl( 6-p-cymene)
(L1)][PF6] (4)
having liquid film of 0.25 lm thickness. The cyclic voltammetric
studies were performed on BAS CV 50 W instrument at University
of Delhi (Department of Chemistry), India. A three-electrode con-
figuration composed of a Pt disk working electrode (3.1 mm2 area),
a Pt wire counter electrode, and an Ag/AgCl reference electrode
was used for the measurements. Ferrocene was used as an internal
standard (E1/2 = 0.500 V versus Ag/AgCl) and all the potentials are
expressed with reference to Ag/AgCl. The melting points deter-
mined in open capillary are reported as such. The complexes
The solid [{( -Cl)}2] (0.05 g, 0.1 mmol) or
g
6-C6H6)RuCl(
l-Cl)}2] (0.12 g, 0.2 mmol) and L1 (0.051 g,
l
[{(
g
6-p-cymene)RuCl(
0.2 mmol) dissolved in CH3OH (15 cm3) were stirred together for
10 or 14 h at room temperature. The resulting yellow solution
was filtered and the volume of the filtrate was reduced (ꢃ7 cm3)
with
a rotary evaporator. It was mixed with solid NH4PF6
(0.032 g, 0.2 mmol) and the resulting yellow colored microcrystal-
line solid 3 or 4 was filtered, washed with ice-cold 10 cm3 CH3OH
and dried in vacuo. Single crystals of 3 or 4 were obtained by dif-
fusion of diethyl ether into its solution (1 cm3) made in a mixture
(1:4) of CH3OH and CH3CN.
[{(g l-Cl)}2] and [{(g l-Cl)}2], were
6C6H6)RuCl( 6-p-cymene)RuCl(
prepared according to literature methods [34–35].
2.1. Synthesis of L1
3: Yield 0.1 g (ꢃ85%); m.p. 178 °C. KM = 148.4 S cm2 molꢀ1
.
Diphenyldiselenide (0.62 g, 2.0 mmol) dissolved in 30 cm3 of
ethanol was treated with a solution (made in 5% NaOH) of NaBH4
(0.14 g, 4.0 mmol) (added drop wise) under N2 atmosphere until
it become colorless due to the formation of PhSeNa. (2-Chloro-
ethyl)pyrrolidine hydrochloride (0.72 g, 4.0 mmol) dissolved in
5 cm3 of ethanol was mixed to this colorless solution with constant
stirring. The mixture was stirred further for 3–4 h and poured into
ice-cold 1% (w/v) NaOH (20 cm3), from which L1 was extracted
into CHCl3 (5 ꢂ 40 cm3). The extract was washed with water
(3 ꢂ 50 cm3) and dried over anhydrous sodium sulfate. Its solvent
was evaporated off under reduced pressure on a rotary evaporator,
resulting in pale yellow oil (L1). Yield 0.81 g (ꢃ80%). NMR: (1H,
CDCl3, 25 °C, versus TMS) d (ppm): 1.62 (m, 4H, H8), 2.37 (m, 4H,
H7), 2.65 (t, 3J = 7.5 Hz, 2H, H5), 2.91 (t, 3J = 7.5 Hz, 2H, H6), 7.06–
7.10 (m, 3H, H1, H2), 7.36 (d, 3J = 6.0 Hz, 2H, H3), (13C{1H}, CDCl3,
25 °C versus TMS) d (ppm): 23.4 (C8), 26.4 (C5), 53.9 (C7), 56.5
(C6), 126.7 (C1), 129.0 (C2), 130.4 (C3), 132.3 (C4), (77Se {1H}, CDCl3,
25 °C versus Me2Se) d (ppm): 281.3.
Anal. Calc. for C18H23ClNRuSeꢁPF6: C, 35.23; H, 3.78; N, 2.28%.
Found: C, 35.46; H, 3.97; N, 2.35%. NMR: (1H, CD3CN, 25 °C versus
TMS) d (ppm): 1.95–1.98 (m, 4H, H8), 2.54–3.16 (m, 4H, H7), 3.43–
3.61 (m, 2H, H5), 3.69–4.10 (m, 2H, H6), 5.64 (s, 6H, RuAr–H), 7.39–
7.44 (m, 1H, H1), 7.64–7.66 (m, 2H, H2), 7.87–7.89 (m, 2H, H3),
(
13C{1H}, CD3CN, 25 °C versus TMS) d (ppm): 33.9 (C8), 55.1 (C5),
65.2 (C7), 68.3 (C6), 87.4 (Ar–C–Ru), 130.1 (C1), 131.2 (C2), 132.1
(C3), 133.1(C4), (77Se {1H},CD3CN, 25 °C versus Me2Se) d (ppm):
384.5.
4: Yield 0.11 g (ꢃ80%); m.p. 165 °C KM = 142.7 S cm2 molꢀ1
.
Anal. Calc. For C22H31ClNRuSeꢁPF6: C, 39.45; H, 4.66; N, 2.09%.
Found: C, 39.41; H, 4.61; N, 2.07%. NMR: (1H, CDCl3, 25 °C, versus
TMS) d (ppm): 1.29 (d, 3J = 6.6 Hz, 3H, CH3 of i-Pr), 1.34 (d,
3J = 6.6 Hz, 3H, CH3 of i-Pr), 1.99–2.11 (m, 4H, H8), 2.37 (s, 3H,
CH3 p to i-Pr), 2.51 (sp, 3J = 6.9 Hz, 1H, CH of i-Pr), 2.61–2.86 (m,
4H, H7), 2.97–3.13 (m, 2H, H5), 3.67–3.89 (m, 2H, H6), 5.33–5.81
(m, 4H, Ar–H of p-cymene), 7.61–7.70 (m, 3H, H1, H2), 7.81–7.83
(m, 2H, H3), (13C{1H}, CDCl3, 25 °C versus TMS) d (ppm): 18.1
(CH3, p to i-Pr), 21.4, 23.3 (CH3 of i-Pr), 31.0 (CH of i-Pr), 32.7
(C8), 53.2 (C5), 63.6 (C7), 66.3 (C6), 82.9–105.8 (Ar–C of p-cymene),
129.9 (C1), 130.4 (C2), 131.2 (C3), 132.0 (C4), (77Se {1H}, CDCl3, 25 °C
versus Me2Se) d (ppm): 385.8.
2.2. Synthesis of [PdCl2(L1)] (1) and [PtCl2(L1)] (2)
The solution of L1 (0.065 g, 0.25 mmol) made in 10 cm3 of ace-
tone and Na2PdCl4 (0.08 g, 0.25 mmol) or K2PtCl4 (0.1 g,
0.25 mmol) dissolved in 10 cm3 of deoxygenated water were stir-
red together for 30 min at room temperature and poured into
100 cm3 of distilled water. The complex was extracted into chloro-
form (2 ꢂ 50 cm3). The extract was dried over anhydrous sodium
sulfate, concentrated to ꢃ10 cm3 with a rotary evaporator and
mixed with hexane (20 cm3). The resulting orange colored 1 or yel-
2.4. Synthesis of [RuCl(g
6-p-cymene)(NH3)2][PF6] (5)
The filtrate left after removing 4 (Section 2.3) was stirred for 1 h
with solid NH4PF6 (0.032 g, 0.2 mmol) and CH3OH (15 cm3) and
kept aside for one week. The slow evaporation of solvent resulted
in single crystals of 5. m.p. 155 °C. KM = 155.6 S cm2 molꢀ1. Anal.

3874
P. Singh et al. / Journal of Organometallic Chemistry 694 (2009) 3872–3880
Calc. For C10H20ClN2RuꢁPF6: C, 26.71; H, 4.48; N, 6.23%. Found: C,
26.68; H, 4.45; N, 6.27%. NMR: (1H, CD3CN, 25 °C, versus TMS) d
(ppm): 1.19 (d, 3J = 6.6 Hz, 6H, CH3 of i-Pr), 1.88 (s, 6H, NH3),
2.01 (s, 3H, CH3 p to i-Pr), 2.73 (sp, 3J = 6.9 Hz, 1H, CH of i-Pr),
5.33–5.75 (m, 4H, Ar–H of p-cymene), (13C{1H}, CD3CN, 25 °C ver-
sus TMS) d (ppm): 18.4 (CH3, p to i-Pr), 22.3 (CH3 of i-Pr), 31.5
(CH of i-Pr), 81.3–104.0 (Ar–C of p-cymene).
(ppm): 22.6 (C8), 41.8 (C5), 59.8 (C7), 63.0 (C6),130.7 (C1), 130.8
(C2), 132.0 (C3), 134.2 (C4).
8: Yield: 0.083 g (ꢃ70%). m.p. 156.8 °C. KM = 11.4 S cm2 molꢀ1
.
Anal. Calc. for C12H17Cl2NPtS: C, 30.46; H, 3.62; N, 2.96%. Found:
C, 29.97; H, 3.39; N, 2.75%. NMR: (1H, DMSO-d6, 25 °C versus
TMS): (d, ppm): 1.69–1.87 (m, 4H, H8), 2.41–2.51 (m, 4H, H7),
2.77–2.97 (m, 2H, H5), 3.07–3.34 (m, 2H, H6), 7.51–7.61 (m, 3H,
H1, H2), 8.14–8.19 (m, 2H, H3), (13C{1H}, DMSO-d6, 25 °C versus
TMS) d (ppm): 22.2 (C8), 33.9 (C5), 62.2 (C7), 64.6 (C6), 125.8 (C1),
130.1 (C2), 130.8 (C3), 133.4 (C4).
2.5. Synthesis of [Ru(
g
6-p-cymene)(L1)(CH3CN)][PF6]2ꢁCH3CN (6)
The 4 (0.13 g, 0.2 mmol) dissolved in CH3CN (10 cm3) and AgOTf
(0.05 g, 0.2 mmol) were mixed and refluxed for 6 h. The precipi-
tated AgCl was filtered off. The yellow filtrate was mixed with solid
NH4PF6 (0.032 g, 0.2 mmol) and the volume of solution was re-
duced to 3 cm3 with a rotary evaporator. The 6 precipitated on
the addition of diethyl ether (5 cm3) was filtered, washed with
10 cm3 of CH3CN–diethyl ether mixture (1:5), dried in vacuo and
recrystallized with CH3CN–diethyl ether mixture (1:5). Single crys-
tals of 6 were obtained by diffusion of diethyl ether into its solu-
tion (1 cm3) made in CH3CN. Yield 0.12 g, (ꢃ70%); m.p. 185 °C.
KM = 240.9 S cm2 molꢀ1. Anal. Calc. for C24H34N2RuSeꢁ[PF6]2: C,
35.14; H, 4.18; N, 3.41%. Found: C, 35.05; H, 4.16; N, 3.38%. NMR
(1H, CD3CN, 25 °C versus TMS) d (ppm): 1.28 (d, 3J = 6.6 Hz, 3H,
CH3 of i-Pr), 1.32 (d, 3J = 6.6 Hz, 3H, CH3 of i-Pr), 2.19 (s, 3H,
CH3CN), 1.94–2.00 (m, 4H, H8), 2.36 (s, 3H, CH3 p to i-Pr), 2.41–
2.52 (m, 4H, H7), 2.86 (sp, 3J = 6.9 Hz, 1H, CH of i-Pr), 3.09–3.15
(m, 2H, H5), 3.31–3.36 (m, 2H, H6), 5.51–5.72 (m, 4H, Ar–H of p-
cymene), 7.35–7.45 (m, 3H, H1, H2), 7.52–7.60 (m, 2H, H3),
2.8. Synthesis of [RuCl(g g
6-C6H6)(L2)][PF6] (9) and[RuCl( 6-p-Cymene)
(L2)][PF6] (10)
The ligand L2 (0.042 g, 0.2 mmol) dissolved in CH3OH (15 cm3)
was reacted with solid [{( -Cl)}2] (0.05 g, 0.1 mmol)
6-C6H6)RuCl(
or [{( -Cl)}2] (0.06 g, 0.1 mmol) as described
6-p-cymene)RuCl(
g
l
g
l
for 3 and 4 in Section 2.4. The 9 and 10 including their single crys-
tals were obtained in a similar fashion (Section 2.4).
9: Yield 0.09 g, (ꢃ85%); m.p. 167 °C. Molecular conductance
KM = 150.1 S cm2 molꢀ1
. Anal. Calc. for C18H23ClNRuSPF6: C,
38.14; H, 4.09; N, 2.47%. Found: C, 37.97; H, 3.99; N, 2.45%.
NMR: (1H, CD3CN, 25 °C versus TMS) d (ppm): 1.93–1.96 (m, 4H,
H8), 2.53–2.95 (m, 4H, H7), 3.06–3.58 (m, 2H, H5), 3.71–3.91 (m,
2H, H6), 5.55 (s, 6H, RuAr–H), 7.42 (m, 1H, H1), 7.67 (m, 2H, H2),
7.87 (m, 2H, H3), (13C{1H}, CD3CN, 25 °C versus TMS) d (ppm):
40.1 (C8), 55.4 (C5), 65.2 (C7), 67.6 (C6), 88.0 (RuAr–C), 129.9 (C1),
131.5 (C2), 132.3 (C3), 132.6 (C4).
(
13C{1H}, CD3CN, 25 °C versus TMS) d (ppm): 18.8 (CH3, p to i-Pr),
10: Yield 0.1 g, (ꢃ80%) m.p. 179 °C. KM = 144.8 S cm2 molꢀ1
.
23.7 (CH3 of CH3CN), 22.1, 22.3 (CH3 of i-Pr), 30.3 (CH of i-Pr),
31.8 (C8), 55.4 (C5), 65.3 (C7), 68.4 (C6), 82.6–105.9 (Ar–C of p-cym-
ene), 128.6 (C1), 129.0 (C2), 131.0 (C3), 131.5 (C4), 134.1 (CN of
CH3CN). (77Se{1H}, CD3CN, 25 °C versus Me2Se) (d, ppm). 360.8.
Anal. Calc. For C22H31ClNRuSꢁPF6: C, 42.42; H, 5.02; N, 2.25%.
Found: C, 42.46; H, 5.09; N, 2.27%. NMR: (1H, CD3CN, 25 °C TMS)
d (ppm): 1.30 (d, 3J = 6.6 Hz, 6H, CH3 of i-Pr), 1.95–2.10 (m, 4H,
H8), 2.23 (s, 3H, CH3 p to i-Pr), 2.52–2.75 (m, 4H, H7), 2.89 (sp,
3J = 6.9 Hz, 1H, CH of i-Pr), 3.02–3.20 (m, 2H, H5), 3.39–3.53 (m,
2H, H6), 5.30–5.85 (m, 4H, Ar–H of p-cymene), 7.41–7.60 (m, 5H,
H1, H2, H3), (13C{1H}, CD3CN, 25 °C versus TMS): d (ppm): 18.0
(CH3, p to i-Pr), 22.2, 22.3 (CH3 of i-Pr), 30.9 (CH of i-Pr), 31.8
(C8), 55.1 (C5), 64.7 (C7), 66.5 (C6), 82.1–106.0 (Ar–C of p-cymene),
128.0 (C1), 128.4 (C2), 129.9 (C3), 130.7 (C4).
2.6. Synthesis of L2
Sodium hydroxide (0.440 g, 11 mmol) dissolved in 5 cm3 of
water was added dropwise to thiophenol (0.5 ml, ꢃ5 mmol) re-
fluxed for 0.5 h in 50 cm3 of dry ethanol under N2 atmosphere.
(2-Chloroethyl)pyrrolidine hydrochloride (0.85 g, 5 mmol) dis-
solved in 20 cm3 of ethanol was added dropwise to the reaction
mixture and its refluxing continued further for 3 h. The reaction
mixture after cooling to room temperature was poured into
100 cm3 of distilled water, neutralized with dilute sodium hydrox-
ide and extracted with 100 cm3 of chloroform. The L2 (pale yellow
liquid) was recovered from the extract by a procedure similar to
that of L1. Yield: 0.65 g (ꢃ78%). NMR: (1H, CDCl3, 25 °C versus
TMS) d (ppm): 1.77–1.81 (m, 4H, H8), 2.52–2.57 (m, 4H, H7), 2.73
(t, 3J = 7.5 Hz, 2H, H5), 3.08 (t, 3J = 7.5 Hz, 2H, H6), 7.14–7.19 (m,
1H, H1), 7.25–7.30 (m, 2H, H2) 7.32–7.36 (m, 2H, H3), (13C{1H},
CDCl3, 25 °C versus TMS) d (ppm): 23.4 (C8), 32.3 (C5), 54.0 (C7),
55.5 (C6), 125.7 (C1), 128.7 (C2), 128.8 (C3), 132.4 (C4).
2.9. Synthesis of L3
Selenium powder (0.40 g, 5 mmol) and sodium borohydride
(0.38 g, 10.0 mmol) solution (made in 10 cm3 of 2.0 M NaOH) were
stirred in 50 cm3 of water for 1 h under nitrogen atmosphere at
room temperature. To the resulting thin slurry of Na2Se, was added
dropwise with constant stirring, (2-chloroethyl) pyrrolidine hydro-
chloride (1.7 g, 10.0 mmol) dissolved in 5 cm3 of ethanol. The mix-
ture was stirred further for 2–3 h and poured into 100 cm3 of
distilled water. The L3 was extracted into diethyl ether
(3 ꢂ 20 cm3) from the aqueous phase. The ether extract was
washed with distilled water (2 ꢂ 10 cm3) and dried over anhy-
drous sodium sulfate. On evaporating off ether under reduced pres-
sure on rotary evaporator L3 was obtained as a yellow liquid,
unstable under ambient conditions. Yield: 1.78 g (ꢃ65%). NMR:
(1H, CDCl3, 25 °C versus TMS) d (ppm): 1.78–1.83 (m, 4H, H4),
2.54–2.56 (m, 4H, H3), 2.69–2.78 (m, 4H, H1, H2), (13C{1H}, CDCl3,
25 °C versus TMS) d (ppm): 22.3 (C4), 23.1 (C1), 53.7 (C3), 56.9
(C2), (77Se {1H}, (CDCl3, 25 °C versus Me2Se) d (ppm): 143.1.
2.7. Synthesis of [PdCl2(L2)] (7) and [PtCl2(L2)] (8)
The solution of L2 (0.052 g, 0.25 mmol) made in 10 cm3 of ace-
tone was reacted with Na2PdCl4 (0.08 g, 0.25 mmol) or K2PtCl4
(0.1 g, 0.25 mmol) dissolved in 10 cm3 of deoxygenated water as
described in Section 2.1 for 1/2. The resulting 7 or 8 was filtered,
washed with hexane and dried in vacuo.
7: Yield: 0.072 g (ꢃ75%). m.p. 140.9 °C. KM = 8.1 S cm2 molꢀ1
.
2.10. Procedure for catalytic Suzuki reaction
Anal. Calc. for C12H17Cl2NPdS: C, 37.47; H, 4.45; N, 3.64%. Found:
C, 37.12; H, 4.65; N, 3.35%. NMR: (1H, CD3CN, 25 °C versus TMS)
d (ppm): 1.93–1.98 (m, 4H, H8), 2.75–3.06 (m, 4H, H7), 3.12–3.37
(m, 2H, H5), 3.73–4.01 (m, 2H, H6), 7.57–7.61 (m, 3H, H1, H2),
8.23–8.26 (m, 2H, H3). (13C {1H}, CD3CN, 25 °C versus TMS) d
Bromobenzene or its derivative (1 mmol), benzeneboronic acid
(0.183 g, 1.5 mmol), K2CO3 (0.276 g, 2 mmol), distilled water
(0.5 cm3), DMF (4 ml) and catalyst (complex 1/7) (0.001 mol%)
were mixed and stirred under reflux over an oil bath for 24 h at

P. Singh et al. / Journal of Organometallic Chemistry 694 (2009) 3872–3880
3875
100 °C under ambient conditions. After cooling to room tempera-
ture, 20 cm3 of distilled water was added to reaction mixture.
The product was extracted with a mixture of hexane–diethyl ether
(25–50 cm3). The solvent of extract was partly evaporated on a ro-
tary evaporator to get white crystalline solid product, which was
filtered, washed with 3–4 cm3 of hexane and authenticated by
NMR (1H and 13C{1H}) spectra and m.p.
ble. The solutions of all the complexes in DMSO showed the sign of
decomposition after 1–2 days. The molar conductance values of
half sandwich ruthenium(II) complexes 3, 4, 5, 9 and 10 are close
to the values expected for a 1:1 electrolyte. In case of 6 the molar
conductance value concurrs with its 1:2 electrolytic nature. In IR
spectra of 3–6 and 9–10 the band around 850 cmꢀ1 may be as-
signed to P–F vibrations. IR data are further detailed in supplemen-
try material.
2.11. Procedure for catalytic Heck reaction
3.1. NMR spectra
A mixture of alkene (1.5 mmol), aryl halide (1 mmol), Na2CO3
(0.212 g, 2.0 mmol), DMF (4.0 cm3) and catalyst (complex 1/7)
(0.001 mol%) was stirred under reflux on oil bath for 24 h at
100 °C under nitrogen atmosphere. After cooling the reaction mix-
ture to room temperature, 20 cm3 of water was added to it. The
product was extracted into dichloromethane (40 cm3) and the ex-
tract filtered. To obtain (E)-1-(4-chloro/nitrophenyl)-2-phenyleth-
ene, the filtrate was washed with water (3 ꢂ 25 cm3) and
evaporated on a rotary evaporator. The residue was purified by sil-
ica gel column chromatography using hexane–ethylacetate mix-
ture (9:1). In case of (E)-3-(4-chloro/nitrophenyl)acrylic acid, the
cooled reaction mixture was mixed with NaHCO3 (0.50 g) and
water (30 cm3). It was stirred for 1 h at room temperature and fil-
tered. The filtrate was washed with CH2Cl2 (3 ꢂ 20 cm3). The aque-
ous phase was acidified with 5 N HCl and cooled to 0 °C. The
resulting solid precipitate of the product was filtered, washed with
cold water and air dried. The NMR (1H and 13C{1H}) spectra and
m.p. authenticated the product.
The characteristic signal in 77Se{1H} NMR spectra of L1 shifts to
a high frequency on complex formation (Shift: ꢃ191, 147, 103.2–
104.5 and 79.5 ppm for 1, 2, 3/4 and 6 respectively), implying the
coordination of Pd, Pt or Ru through Se of L1. The signals at almost
similar frequency in the spectra of 3 and 4 indicate that electronic
effects on selenium of p-cymene and benzene ligands are not much
different.
On complexation of L1 with metal ions the signals of H3, H5, H6
and H7 in 1H NMR spectra shift to higher frequency
(0.41–1.24 ppm) relative to those of free L1, implying the coordina-
tion of L1 through Se and N donor sites. In 13C{1H} NMR spectra of
complexes of L1 the signals of C3, C5, C6 and C7 appear at higher fre-
quency (up to ꢃ19 ppm) relative to those of free L1, corroborating
with the proton NMR spectra. The 1H NMR spectra of complexes of
L2 exhibit signals of H3, H5, H6 and H7 at higher frequency (up to
0.91 ppm) with respect to those of free L2. Thus L2 appears to coor-
dinate with Pd, Pt and Ru like L1. This is corroborated by 13C{1H}
NMR spectra of complexes of L2 as the signals of C3, C4, C5, C6
and C7 are shifted to higher frequency (up to ꢃ22.8 ppm) with re-
spect to those of free ligand. These observations suggest that L1
and L2 in all the complexes behave as (S/Se, N) donors, as revealed
by single crystal structures (Section 3.3).
The cyclic voltammetric (CV) experiments performed at 298 K
in CH3CN (0.01 M NBu4ClO4 as supporting electrolyte) for both 3
and 9 at scan rate 100 mV sꢀ1 (anodic sweep) show two metal cen-
tered voltammetric responses (Fig. 1). A quasi-reversible oxidation
with E1/2 values +0.452 and +0.612 V (versus Ag/AgCl) respectively
for 3 and 9 has been observed. The higher value of E1/2 for 9 in com-
parison to that of 3 suggests that substitution of (N, S) ligand with a
(N, Se) at ruthenium centre leads to a less thermodynamically
favorable oxidation. However these E1/2 values indicate that 3
and 9 are expected to be reasonably efficient catalyst for the redox
process [36].
2.12. Procedure for catalytic oxidation of alcohols
Oxidations of primary alcohols to aldehydes and secondary
ones to ketones with N-methylmorpholine-N-oxide (NMO) were
catalyzed by the presence of half sandwich compounds [RuCl(g6
-
C6H6)(L1)][PF6] (3) and [RuCl(g
6-C6H6)(L2)][PF6] (9). A typical
reaction using the complexes 3 or 9 as catalyst is as follows. A solu-
tion of complex 3 or 9 (0.001 mol%) in 20 cm3 of CH2Cl2 was added
to the mixture of substrate (1 mmol) and NMO (3 mmol). The mix-
ture was refluxed for 3 h and the solvent was evaporated under re-
duced pressure with a rotary evaporator resulting in a solid mass,
which contained the complex 3 or 9 and the oxidized product. It
was shaken with petroleum ether (60–80 °C) (20 cm3). The com-
plex 3 or 9 remained as precipitate was recovered almost quantita-
tively. The oxidized product extracted into petroleum ether was
analyzed by GC.
3.2. Crystal structures
3. Results and discussion
The data of single crystals of 1, 3–6, 9 and 10 and structural
refinement parameters are given in Supplementary material (Table
S1 and S2). The molecular structure of 1 is shown in Fig. 2 along
with important bond lengths and angles. More bond lengths and
angles are given in Supplementary material (Table S3). The geom-
etry around Pd is slightly distorted square planar. The Pd–Se, Pd–N
and Pd–Cl bond distances 2.353(2), 2.085(14) and 2.340(5)/
2.303(5) Å, respectively are consistent with values 2.3669(11),
2.003(7) and 2.305(2) Å, respectively reported recently [37] for
Pd(II) complex of a tridentate selenated Schiff base. In Figs. 3–5
molecular structures of complexes 3, 4 and 6 are given along with
selected bond lengths and angles (see Table S3 in Supplementary
material for further details). The molecular structure of 5 is shown
in Supplementary material (Fig S3). In all complexes 3–6 the cation
exhibits the pseudo-octahedral half sandwich ‘‘piano-stool” dispo-
sition around Ru. The benzene ring or ring of p-cymene occupies
one face of octahedron. The Ru–C distances (2.170(8)–2.215(8) Å
for 3, 2.165(6)–2.235(7) Å for 4 and 2.164(3)–2.208(3) Å for 5 are
normal and consistent with the earlier reports [38,39]. The 6 has
The syntheses of L1–L3 and their complexes (1–10) are summa-
rized in Scheme 1. There is no reference in literature for the syn-
thesis of L2 except the registry number 398472-84-9, indicating
its commercial availability. The bridge-cleavage reactivity of chloro
bridged dimers [((
uCl( -Cl))2] with L1 and L2 and subsequent treatment with NH4PF6
g l-Cl))2] and [((g
6-C6H6)RuCl( 6-p-cymene)R-
l
have resulted in the formation of 3, 4, 9 and 10. The 6 was formed
by substitution of Cl with CH3CN. The formation of 5 resulted due
to reaction of unreacted chlorobridged dimeric compound of Ru
with NH4PF6. The L3 is unstable and therefore its complexes of
good purity could not be isolated. On contrary its tellurium analoge
is stable [30]. All the ligands were found soluble in common organ-
ic solvents. The L1 and L2 were found stable for a week in referiger-
ator (ꢃ5 °C). The solid complexes 1–10 were found stable and
could be stored for six months easily under ambient conditions.
They exhibit solubility in common organaic solvents except hexane
or petroleum ether in which they were found only sparingly solu-

3876
P. Singh et al. / Journal of Organometallic Chemistry 694 (2009) 3872–3880
Scheme 1. Synthesis of ligands and complexes.
some what longer Ru–C bond lengths (2.190(4)–2.253(4) Å) in
comparison to those of 3, 4 or 5. The trans influence of MeCN ap-
pears to contribute partly to this elongation. The formation of
hydrogen bond by anion PFꢀ6 in the crystals of 3–6 (Figs. S1, S2,
S4 and S6 and Table S4 in Supplementary material) results in ex-
tended solid state structures. In the crystals of 4 and 5 intra and in-
ter molecular hydrogen bonds between Cl and various H atoms
have also been observed (Table S4 and Fig. S5 in Supplementary
material). The Ru–N bond lengths of 3 and 4 (2.201(5) Å) are some
what longer than those of 5 (2.146(3)/2.154(3) Å, partly due to ste-
ric effects of bidentate L1 in 3 and 4. However, Ru–N bond lengths
of 3–5 are consistent with the recent literature reports
(2.0511(17)–2.163(10) Å) [38–39]. We are unaware of any crystal-
lographic study carried out on a Ru-complex of a selenoether li-
gand. Therefore, comparisons of present Ru–Se bond distances
are made with those present in cluster or bimetallic species having
bridging selenide or diselenide ligand(s). The Ru–Se bond lengths
of 3 and 4 [2.4918(9) and 2.480(11) Å, respectively] fall within
the range 2.4756(10)–2.5240(9) Å reported for Ru–Se bond lengths
in clusters [Ru3(l3-Se)(CO)7(l3-CO)(l-dppm)] and [Ru3(l3-Se)

P. Singh et al. / Journal of Organometallic Chemistry 694 (2009) 3872–3880
3877
0.000012
0.000010
0.000008
0.000006
0.000004
0.000002
0.000000
-0.000002
-0.000004
-0.000006
0.00003
0.00002
0.00001
0.00000
-0.00001
-0.00002
-0.00003
-1000 -800 -600 -400 -200
0
200 400 600 800 1000
-1500
-1000
-500
0
500
1000
1500
3
9
Fig. 1. Cyclic voltammogram of 3 and 9.
C7
C5
C5
C6
Se1
C3
C2
C8
C4
C7
C4
C3
N1
Pd1
C9
C10
C2
C9
C12
C6
C1
C8
C11
C1
C18
C10
C19
Ru1
Se1
C16
Cl2
Cl1
C17
0
C14
C13
Fig. 2. ORTEP diagram of 1 with 50% probability ellipsoids; bond length (AÅ):
Pd(1)–Se(1) 2.353(2), Pd(1)–N(1) 2.085(14), Pd(1)–Cl(1) 2.340(5), Pd(1)–Cl(2)
2.303(5); bond angle (o): Cl(1)–Pd(1)–Se(1)169.2(17), Cl(2)–Pd(1)–Se(1) 86.6(15),
N(1)–Pd(1)–Se(1) 89.2(4), N(1)–Pd(1)–Cl(1) 93.4(4), N(1)–Pd(1)–Cl(2) 173.7(4),
Cl(2)–Pd(1)–Cl(1) 91.6(19).
N1
Cl1
C20
C15
C12
C11
C22
C21
Fig. 4. ORTEP diagram of 4 with 50% probability ellipsoids; hydrogen atoms and PF6
0
are omitted due to clarity. bond length (ÅA): Ru(1)–Se(1) 2.4918(9), Ru(1)–N(1)
2.201(5), Ru(1)–Cl(1) 2.3815(17), Ru(1)–C 2.165(6)–2.235(7); bond angle (o): Cl(1)–
Ru(1)–Se(1) 90.00(5), N(1)–Ru(1)–Se(1) 84.12(13), N(1)–Ru(1)–Cl(1) 86.37(13).
C23
C24
C7
N2
C5
C3
C4
Fig. 3. ORTEP diagram of 3 with 50% probability ellipsoids; hydrogen atoms and PF6
0
C6
C2
are omitted due to clarity. bond length (ÅA): Ru(1)–Se(1) 2.480(11), Ru(1)–N(1)
2.201(5), Ru(1)–Cl(1) 2.406(2), Ru(1)–C 2.170(8)–2.215(8); bond angle (o): Cl(1)–
Ru(1)–Se(1) 80.87(6), N(1)–Ru(1)–Se(1) 83.81(15), N(1)–Ru(1)–Cl(1) 85.73(15).
C8
C9
Ru1
Se1
C10
C1
C18
C19
C20
*
(
l
3-S)(CO)7(
l
-dppm)] [40]. For Ru(IV) complex [Cp Ru{
g
2-Se2P
C11
C16
(i-Pr)2}{
g
2-SeP(i-Pr)2}][PF6] the Ru–Se bond lengths [41] are re-
N1
N3
C17
C25
ported in the range 2.538(2)–2.590(2) Å, longer than those of 3
and 4 due to steric crowding. The Ru–Se and Ru–N (L1) bond dis-
tances of 6 (2.4770(5) and 2.190(3) Å, respectively) are somewhat
shorter than those of 3/4. The Ru–Se bond distance found in bime-
C15
C13
C14
C12
C22
C26
C21
tallic species [CpRu(CO)(C„CPh)(
l
-Se)ZrCp2] 2.494(1) Å [42], is
Fig. 5. ORTEP diagram of 6 with 50% probability ellipsoids; hydrogen atoms and PF6
5-C5Me5)Ru(
l
2-SeR)3Ru(
g
5-C5Me5)]Cl
0
closer to that of 3. In [(
g
are omitted due to clarity. bond length (ÅA): Ru(1)–Se(1) 2.4770(5), Ru(1)–N(1)
2.190(3), Ru(1)–N(3) 2.041(4), Ru(1)–C 2.190(4)–2.253(4); bond angle (o): N(1)–
Ru(1)–Se(1) 84.96(9), N(3)–Ru(1)–Se(1) 88.99(9), N(3)–Ru(1)–N(1) 84.70(13).
(R = Tol) Ru–Se bond distances are in the range 2.446(4)–
2.466(4) Å [43] and shorter than those of 3 and 4, because RSeꢀ

3878
P. Singh et al. / Journal of Organometallic Chemistry 694 (2009) 3872–3880
0
in comparison to 2.3649(13) ÅA found for 9. The Ru–S bond distance
in case [{RuCl2(p-cymene){ -o-C5H4-(CH2SMe)2}] is reported as
2.4021(10) ÅA, longer than those of 9 and 10 both. The formation
of chelate ring in 9 and 10 appears to be responsible for short
Ru–S distances.
C5
C2
Ru1
C6
C8
C4
C3
C16
l
0
C1
C9
C10
C12
C11
3.3. Catalytic Heck and Suzuki–Miyaura reactions
C15
C14
C7
N1
One of the most important facets of electronic properties of
selenium is its strong electron donating ability which has been
responsible for the efficiency of Pd(II)–selenium ligand complex
for Heck reaction [31]. There is current interest in phosphine-free
catalysts for Heck coupling [45–46]. Thus palladium complex 1
having Se–ligand has been explored for Heck reactions given in
Scheme 2 (Eq. (1)). The palladium complex 7, which is sulfur ana-
log of 1 has been explored for comparison and found to be only
marginally less efficient than 1. In Table 1 substrates, percentage
conversions and values of turnover number (TON) are given. The
TOF values are in the ranges 1.46 ꢂ 103–3.46 ꢂ 103 hꢀ1 and
1.04 ꢂ 103–3.13 ꢂ 103 hꢀ1, respectively for 1 and 7. The air stabil-
ity of 1 and 7 is the major advantage of using them. The conver-
sions are higher for ArI in comparison to ArBr. The TON values of
1 and 7 (up to 83 000) for many substrates are comparable to those
reported for Pd-complex of Se–C–Se pincer ligand [31].
C13
S1
Cl1
C17
C18
Fig. 6. ORTEP diagram of 9 with 50% probability ellipsoids; hydrogen atoms and PF6
0
are omitted due to clarity. bond length (ÅA): Ru(1)–S(1) 2.3649(13), Ru(1)–N(1)
2.187(3), Ru(1)–Cl(1) 2.3914(12), Ru(1)–C 2.168(5)–2.193(5); bond angle (o): Cl(1)–
Ru(1)–S(1) 82.39(4), N(1)–Ru(1)–S(1) 83.08(10), N(1)–Ru(1)–Cl(1) 85.56(9).
C7
C5
C3
C4
C2
C6
C8
C9
Ru1
S1
C16
Suzuki–Miyaura reaction given in Scheme 2 (Eq. (2)), is also
among the most important palladium-catalyzed cross-coupling
reactions of both academic and industrial interest. In view of air
and moisture sensitivity of complexes of phosphorus ligands, there
is a current interest in palladium complexes of phosphine-free li-
gands for the Suzuki–Miyaura reaction [47–49] as well. Complexes
1 and 7 have been explored for Suzuki–Miyaura reaction as they
offer the advantage of stability under ambient conditions. In Table
1 substrates, percentage conversions and values of turnover num-
ber (TON) are given. The TOF values are in the range 1.46 ꢂ 103–
3.54 ꢂ 103 hꢀ1 for 1 and 1.04 ꢂ 103–3.42 ꢂ 103 hꢀ1 for 7. The
TON values dependent on R have been found up to 85000 and bet-
ter for some substrates than those reported earlier [47–49]. The Se
containing complex is some what more efficient than its sulfur
analog.
C1
C18
C10
C19
C17
N1
C14
C13
Cl1
C20
C15
C12
C11
C22
C21
Fig. 7. ORTEP diagram of 10 with 50% probability ellipsoids; hydrogen atoms and
0
PF6 are omitted due to clarity. bond length (AÅ): Ru(1)–S(1) 2.389(16), Ru(1)–N(1)
2.192(4), Ru(1)–Cl(1) 2.383(16), Ru(1)–C 2.184(6)–2.228(5); bond angle (o): Cl(1)–
Ru(1)–S(1) 89.78(6), N(1)–Ru(1)–S(1) 83.87(12), N(1)–Ru(1)–Cl(1) 86.79(11).
is expected to be bonded strongly in comparison to a selenoether.
In a diselenide bridged complex [(MeCp)Ru(PPh3)]2(l-Se2)2(Otf)2.
3.4. Catalytic oxidation of alcohols
Ru–Se bond distances are 2.518(1) and 2.556(1) Å [44], somewhat
longer than those of 3 and 4. The molecular structures of 9 and 10
are shown in Fig. 6 and 7 whereas secondary interactions observed
in their crystals are shown in Figs. S7–S10 of Supplementary mate-
The catalytic performances of Ru-complexes 3 and 9 have been
explored for oxidation of primary and secondary alcohols in a clas-
sical oxidation system developed in CH2Cl2 in the presence of NMO
(Scheme 3). In Table 2 percentage conversions and values of turn
over number (TON) are given. The conversion is between 80%
and 97%, whereas TON value varies between 8.0 ꢂ 104 and
9.7 ꢂ 104. These values commensurate with the redox potentials
derived by CV studies. The TOF values in case of 3 are in the range
rial. The Ru–S and Ru–N bond distances of 9 and 10 are nearly sim-
*
ilar (see Figs.
6
and 7). For [Cp Ru(PMe3)2(SC6F4H)] and
*
[Cp Ru(NO)(SC6F4H)2] [41] the Ru–S bond distances are reported
as 2.4104(9)/2.4156(9) and 2.3899(6)/2.3880(6) Å, respectively.
These values are closer to the value 2.389(16) Å observed for 10
Scheme 2. Heck and Suzuki reactions.

P. Singh et al. / Journal of Organometallic Chemistry 694 (2009) 3872–3880
3879
Table 1
Yields (%) in Suzuki and Heck reactions.
Substituents on reactants
Complex
1
7
Ar–X
Y
TON (yield of trans product %)
Heck reaction
COOH
8.3 ꢂ 104 (83)
8.0 ꢂ 104 (80)
3.7 ꢂ 104 (37)
8.0 ꢂ 104 (80)
7.8 ꢂ 104 (78)
3.5 ꢂ 104 (35)
7.5 ꢂ 104 (75)
7.2 ꢂ 104 (72)
2.5 ꢂ 104 (25)
7.2 ꢂ 104 (72)
7.0 ꢂ 104 (70)
2.8 ꢂ 104 (28)
O2N
Cl
I
COOH
COOH
Ph
I
I
O2N
O2N
Cl
Br
I
Ph
Ph
O2N
Br
R
TON (yield %)
Suzuki reaction
OMe
H
3.5 ꢂ 104 (35)
6.0 ꢂ 104 (60)
8.5 ꢂ 104 (85)
2.5 ꢂ 104 (25)
5.0 ꢂ 104 (50)
8.2 ꢂ 104 (82)
NO2
Scheme 3. Catalytic oxidation of alcohols.
Table 2
Oxidation of alcohols to corresponding aldehydes and ketones with NMO catalyzed by complexes 3 and 9.
Entry
Substrate
Product
TON (% conversion)
3
9
1
8.5 ꢂ 104 (85)
8.0 ꢂ 104 (80)
CHO
O
OH
2
3
9.2 ꢂ 104 (92)
9.6 ꢂ 104 (96)
8.9 ꢂ 104 (89)
9.2 ꢂ 104 (92)
OH
OH
O
4
5
9.3 ꢂ 104 (93)
9.4 ꢂ 104 (94)
9.0 ꢂ 104 (90)
9.1 ꢂ 104 (91)
OH
OH
O
O
6
7
9.8 ꢂ 104 (98)
9.7 ꢂ 104 (97)
9.6 ꢂ 104 (96)
9.4 ꢂ 104 (94)
OH
OH
O
O

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P. Singh et al. / Journal of Organometallic Chemistry 694 (2009) 3872–3880
2.84 ꢂ 104–3.27 ꢂ 104 hꢀ1, whereas for 9 the range is 2.67 ꢂ 104–
3.20 ꢂ 104 hꢀ1. It has been observed that neither 3/9 nor NMO
alone causes these organic transformations under identical reac-
tion conditions. The 3 and 9 both effectively catalyze the oxidation
of benzyl alcohol with maximum selectivity to aldehyde, impor-
tantly, with no further oxidation to carboxylic acid. It appears that
probably NMO reacts with Ru-complex to yield ruthenium(IV)-oxo
species, which in turn oxidizes the alcohols. On addition of NMO to
a dichloromethane solution of 3 or 9 a new shoulder at 391 nm in
UV–Vis spectrum appears, which supports the formation of
Ru(IV)@O species. The IR of residue left after evaporating solvent
from the mixture of 3 or 9 with NMO exhibits a very strong band
at 856 cmꢀ1 which appears to have contribution from Ru(IV)@O
species [50]. The band of moderate intensity around this position
due to PF6 is also present therefore unequivocal assignment of this
band is not possible but the occurrence of more intense band is an
indication of contribution by Ru(IV)@O species. The earlier reports
on the oxidation of various substrates including alcohols by oxo-
ruthenium species [51–53] further support our proposition. The
complex 3 is somewhat more efficient catalyst than 9.
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Acknowledgements
Authors thank Department of Science and Technology (India)
for research Project No. SR/S1/IC-23/06 and for partial financial
assistance given to establish single crystal X-ray diffraction facility
at IIT Delhi, New Delhi (India) under its FIST program. P.S. thanks
University Grants Commission (India) for the award of Junior/Se-
nior Research Fellowship.
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CCDC 735502, 699208, 735503, 735504, 735505, 735506 and
735507 contain the supplementary crystallographic data for 1, 3,
5, 9, 10, 4, and 6. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif.
Supplementary data associated with this article can be found, in
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