Half-sandwich ruthenium(II) complexes of click generated 1,2,3-triazole based organosulfur/-selenium ligands: Structural and donor site dependent catalytic oxidation and transfer hydrogenation aspects

Article abstract of DOI:10.1021/om400057e

1-Benzyl-4-((phenylthio)-/(phenylseleno)methyl)-1H-1,2,3-triazole (L1/L2) and 4-phenyl-1-((phenylthio)-/(phenylseleno)methyl)-1H-1,2,3-triazole (L3/L4) synthesized using the click reaction have been reacted for the first time with [{(η⁶-C₆H₆)RuCl(μ-Cl)}₂] and NH₄PF₆ to design the half-sandwich complexes [(η⁶-benzene)RuLCl]PF₆ (1-4 for L = L1-L4), which have been characterized by single-crystal X-ray diffraction and explored for the catalytic oxidation of alcohols with N-methylmorpholine N-oxide (NMO) and transfer hydrogenation of ketones with 2-propanol. There is a pseudo-octahedral "piano-stool" disposition of donor atoms around Ru in 1-4. In 1 and 2, N(3) of the triazole skeleton coordinates with Ru, whereas in other complexes the nitrogen involved is N(2). The Ru-S and Ru-Se bond distances are 2.3847(11)/2.3893(10) and 2.497(5)/2.4859(9) A, respectively. The catalytic processes are more efficient with 3 and 4 (compared to 1 and 2), in which N(2) of the triazole is involved in coordination with Ru. The nature of the chalcogen and steric factors together also appear to affect the efficiency of complexes. HOMO-LUMO energy gaps are lower for 3 and 4 than for 1 and 2. The formation of Ru^IV=O species probably results in oxidation and transfer hydrogenation involves an intermediate containing Ru-H. Bond distances and angles based on DFT calculations are generally consistent with experimental values.

Full text of DOI:10.1021/om400057e

Article
pubs.acs.org/Organometallics
Half-Sandwich Ruthenium(II) Complexes of Click Generated 1,2,3-
Triazole Based Organosulfur/-selenium Ligands: Structural and
Donor Site Dependent Catalytic Oxidation and Transfer
Hydrogenation Aspects
Fariha Saleem, Gyandshwar Kumar Rao, Arun Kumar, Goutam Mukherjee, and Ajai K. Singh*
Department of Chemistry, Indian Institute of Technology Delhi, New Delhi-110016, India
S
* Supporting Information
ABSTRACT: 1-Benzyl-4-((phenylthio)-/(phenylseleno)methyl)-1H-
1,2,3-triazole (L1/L2) and 4-phenyl-1-((phenylthio)-/(phenylseleno)-
methyl)-1H-1,2,3-triazole (L3/L4) synthesized using the click reaction
have been reacted for the first time with [{(η6-C6H6)RuCl(μ-Cl)}2] and
NH4PF6 to design the half-sandwich complexes [(η6-benzene)RuLCl]PF6
(1−4 for L = L1−L4), which have been characterized by single-crystal X-
ray diffraction and explored for the catalytic oxidation of alcohols with N-
methylmorpholine N-oxide (NMO) and transfer hydrogenation of
ketones with 2-propanol. There is a pseudo-octahedral “piano-stool”
disposition of donor atoms around Ru in 1−4. In 1 and 2, N(3) of the
triazole skeleton coordinates with Ru, whereas in other complexes the
nitrogen involved is N(2). The Ru−S and Ru−Se bond distances are
2.3847(11)/2.3893(10) and 2.497(5)/2.4859(9) Å, respectively. The
catalytic processes are more efficient with 3 and 4 (compared to 1 and 2), in which N(2) of the triazole is involved in
coordination with Ru. The nature of the chalcogen and steric factors together also appear to affect the efficiency of complexes.
HOMO−LUMO energy gaps are lower for 3 and 4 than for 1 and 2. The formation of RuIVO species probably results in
oxidation and transfer hydrogenation involves an intermediate containing Ru−H. Bond distances and angles based on DFT
calculations are generally consistent with experimental values.
Scheme 1. Synthesis of Ligands L1−L4 and Their
Complexes 1−4
INTRODUCTION
■
Transition-metal-based catalysis provides efficient and sustain-
able routes for organic synthesis, including oxidations of
alcohols1 and transfer hydrogenations of ketones,2 which are
important in synthetic organic chemistry. Many transition-
metal complexes,3 including half-sandwich ruthenium(II)
complexes,4 have been studied for these transformations. The
promise of organochalcogen ligands has been demonstrated in
the catalysis of various chemical transformations,5a−j and
ruthenium(II) complexes (including half-sandwich species)
have been designed in the recent past using such ligands to
catalyze the oxidation of alcohols and transfer hydrogenation of
ketones.5k,l The promising efficiency of these catalysts may be
partially attributed to the strong electron-donating ability of the
chalcogen donor site, particularly in the case of sulfur and
selenium.
The functionalized 1,2,3-triazole derivatives have emerged as
interesting ligands for transition metals and organometallic
species because they have the potential to act as N donors
through two types of nitrogen atoms: viz., N(2) and N(3)
(Scheme 1). A wide range of mono-,6 bi-,7 tri-,8 and
polydentate9 ligands containing the 1,2,3-triazole skeleton has
been synthesized and studied for their coordination chemistry.
The synthesis of such ligands has become quite easy after the
discovery of the 1,3-dipolar Cu(I)-catalyzed azide−alkyne
cycloaddition (CuAAC)10 reaction, which yields 1,4-disubsti-
tuted 1,2,3-triazoles and has become the archetypal example of
“click chemistry”11 due to its reliability, simplicity, and mild
Received: January 23, 2013
© XXXX American Chemical Society
A
dx.doi.org/10.1021/om400057e | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(10 eV, 180 °C source temperature, and sodium formate as calibrant)
on a Bruker MicroTOF-Q II instrument, with the sample taken up in
CH3CN. All DFT calculations have been carried out at the
Department of Chemistry, Supercomputing Facility for Bioinformatics
and Computational Biology, IIT Delhi, with the GAUSSIAN-0319
programs. The geometries of complexes 1−4 have been optimized at
the B3LYP20 level using an SDD basis set for metal atoms and
chalcogen and 6-31G* basis sets for C, N, and H. Geometry
optimizations have been carried out without any symmetry restriction
with X-ray coordinates of the molecule. Harmonic force constants
have been computed at the optimized geometries to characterize the
stationary points as minima. The molecular orbital plots have been
created using the Chemcraft program package (http://www.
chemcraftprog.com).
Chemicals and Reagents. The reported methods have been used
for the synthesis of [{(η6-C6H6)RuCl(μ-Cl)}2],21 benzyl azide,22
azidomethyl phenyl sulfide,14a azidomethyl phenyl selenide,23 and
propargyl phenyl sulfide.24 Thiophenol, diphenyl diselenide, NaBH4,
propargyl bromide, benzyl bromide, and NH4PF6 have been procured
from Sigma-Aldrich (USA) and used as received. Common reagents
(such as alcohols and ketones) have been procured from locally
available sources. All of the solvents have been dried and distilled
before use by standard procedures.25
Synthesis of Ligands L1 and L2. Azidomethylbenzene (0.266 g,
2 mmol) taken up in 30 mL of t-BuOH was added to propargyl phenyl
sulfide (0.296 g, 2 mmol)/propargyl phenyl selenide (0.390 g, 2
mmol) placed in a round-bottom reaction flask. In two separate
vessels, CuSO4·5H2O (10 mol %, 0.050 g) and sodium ascorbate (20
mol %, 0.079 g) were each dissolved separately in 2 mL of distilled
water. Both solutions were mixed, and the resulting dark brown
mixture was quickly added to the reaction flask. The reaction mixture
was stirred at room temperature for 12 h. It was then poured into cold
water (30 mL). The aqueous phase was extracted with CHCl3 (4 × 25
mL), and the organic layers were combined and washed with water
(20 mL), 20% ammonia solution (50 mL), and brine (20 mL). The
organic phase was dried with anhydrous Na2SO4. Its solvent was
evaporated under reduced pressure on a rotary evaporator to give
ligands L1 and L2 as off-white solids.
L1: yield 0.533 g (95%); mp 65 °C. Anal. Found: C, 68.32; H, 5.35;
N, 14.90. Calcd for C16H15N3S: C, 68.30; H, 5.37; N, 14.93. 1H NMR
(CDCl3, 25 °C, TMS; δ (ppm)): 4.16 (s, 2H, H5), 5.41 (s, 2H, H8),
7.13−7.48 (m, 11H, H1−H3, H7, H10−H12). 13C{1H} NMR (CDCl3,
25 °C, TMS; δ (ppm)): 28.9 (C5), 54.1 (C8), 122.0 (C12), 126.4 (C7),
127.8 (C11), 128.2 (C4), 128.6 (C1) 128.9 (C10), 129.0 (C2), 129.7
(C3), 134.5 (C9), 135.2 (C6). IR (cm−1): 464 (m), 689 (s), 738 (s;
νC−H(aromatic)), 814 (b), 1045 (m), 1208 (m), 1338 (m), 1431 (b;
νC−C(aromatic)), 1550 (m; νCN), 1577 (m; νNN), 2094 (s), 2362
(m), 2923 (m; νC−H(aliphatic)), 3063 (m; νC−H(aromatic)), 3139
(m). HR-MS (CH3CN; m/z): [M + Na]+ 304.0879; calcd value for
C16H15N3NaS 304.0879 (δ 0.1 ppm).
reaction conditions. The easy synthetic strategy has not only
made such compounds attractive as ligands but also has led to
their extensive applications in areas ranging from biology and
medicine to materials science.12 The Ru(II) complexes of 1,2,3-
triazole-based ligands have been explored13 for catalytic water
oxidation, antitumor activity, dye-sensitized solar cells and
cyclometalating bridging ligands.
To date, only a few reports have appeared on the synthesis of
1,2,3-triazole-based organochalcogen ligands and applications
of their metal complexes as catalysts.14 To the best of our
knowledge, ruthenium(II) complexes of 1,2,3-triazole-based
organochalcogen ligands have not been reported so far.
Envisaging the importance of such complexes and their
applications, we have thus synthesized organochalcogenated
1,2,3-triazole derivatives (L1−L4; Scheme 1) by the 1,3-dipolar
cycloaddition of azides to terminal alkynes. The resulting
bidentate ligands have potential coordination sites N(2) or
N(3) and S/Se. During the course of a metal-mediated
reaction, such a set of donor groups may stabilize intermediate
species via chelation and encourage reactivity and low-energy
transition states by partial dissociation, which in turn may
improve the catalytic efficiency of the complex.15 The (η6-
benzene)ruthenium(II) complexes of L1−L4 have been
synthesized (Scheme 1) and explored for the catalytic oxidation
of alcohols and transfer hydrogenation of ketones. It has been
found that the catalytic activity of a complex in which nitrogen
N(2) of 1,2,3-triazole is coordinated with metal (3 and 4) is
unexpectedly higher than that of the corresponding analogue in
which the N(3) nitrogen is involved in coordination (1 and 2).
The coordination with N(3) makes the complex more stable
with respect to that in which ligation is through N(2),16 and
thus the former complex may be less reactive than the latter
species. Further, the catalytic efficiencies of sulfur and
analogous selenium ligated complexes have been found not
to differ much. DFT calculations support the structural features
of newly synthesized half-sandwich complexes. All of these
results are presented in this paper.
EXPERIMENTAL SECTION
■
1
Physical Measurements. The H, 13C{1H}, and 77Se{1H} NMR
spectra have been recorded on a Bruker Spectrospin DPX-300 NMR
spectrometer at 300.13, 75.47, and 57.24 MHz, respectively. The
chemical shifts are reported relative to normal standards. Yields refer
to isolated yields of compounds (except for some products of
catalysis) which have purity ≥95% (established by 1H NMR). All
reactions have been carried out in glassware dried in an oven, under
ambient conditions. Commercial nitrogen gas was used after passing it
successively through traps containing solutions of alkaline anthraqui-
none sodium dithionite, alkaline pyrogallol, concentrated H2SO4, and
KOH pellets. A nitrogen atmosphere, if required, has been created
using Schlenk techniques. IR spectra in the range 4000−400 cm−1
L2: yield 0.610 g (93%); mp 70 °C. Anal. Found: C, 58.52; H, 4.63;
N, 12.82. Calcd for C16H15N3Se: C, 58.54; H, 4.61; N, 12.80. 1H NMR
(CDCl3, 25 °C, TMS; δ (ppm)): 4.14 (s, 2H, H5), 5.43 (s, 2H, H8),
7.08−7.20 (m, 6H, H1, H2, H11, H12), 7.25−7.29 (m, 3H, H3, H7), 7.37
(dd, 3JH−H = 7.2 Hz, 1.8 Hz, 2H, H10). 13C{1H} NMR (CDCl3, 25 °C,
TMS; δ (ppm)): 20.7 (C5), 53.9 (C8), 121.5 (C12), 127.0 (C7), 127.5
(C2), 128.2 (C1), 128.6 (C11), 128.7 (C3), 129.3 (C4), 133.0 (C10),
134.5 (C3), 145.3 (C6). 77Se{1H} NMR (CDCl3, 25 °C, Me2Se; δ
(ppm)): 364.6. IR (cm−1): 457 (m), 696(s), 735 (s; νC−H(aromatic)),
1020 (m), 1055 (m), 1213 (m), 1334 (m), 1436 (b; νC−C(aromatic)),
1542 (m; νCN), 1575 (m; νNN), 2359 (b), 2922 (s;
νC−H(aliphatic)), 3054 (m; νC−H(aromatic)), 3100 (m). HR-MS
(CH3CN; m/z): [M + Na]+ 352.0330; calcd value for C16H15N3NaSe
352.0324 (δ 1.2 ppm).
Synthesis of Ligands L3 and L4. Azidomethyl phenyl sulfide
(0.330 g, 2 mmol)/azidomethyl phenyl selenide (0.424 g, 2 mmol)
taken up in 30 mL of t-BuOH was added to phenylacetylene (0.204 g,
2 mmol) placed in a reaction flask. In two separate vessels,
CuSO4·5H2O (10 mol %, 0.050 g) and sodium ascorbate (20 mol
%, 0.079 g) were each dissolved in 2 mL of distilled water. Both
́
have been recorded on a Nicolet Protege 460 FT-IR spectrometer as
KBr pellets. The C, H, and N analyses were carried out with a Perkin-
Elmer 2400 Series II C, H, and N analyzer. Single-crystal structure
determination data were collected with a Bruker AXS SMART Apex
CCD diffractometer using Mo Kα (0.71073 Å) radiation at 298(2) K.
The software SADABS17 has been used for absorption correction (if
needed) and SHELXTL for space group, structure determination, and
refinement.18 Hydrogen atoms have been included in idealized
positions with isotropic thermal parameters set at 1.2 times those of
the carbon atoms to which they were attached in all cases. The least-
squares refinement cycles on F2 were performed until the model
converged. The melting points determined in an open capillary have
been reported as such. High-resolution mass spectral (HR-MS)
measurements have been carried out using electron spray ionization
B
dx.doi.org/10.1021/om400057e | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
solutions were mixed together, and the resulting dark brown mixture
was quickly added to the reaction flask. The reaction mixture was
stirred at room temperature for 12 h. L3 and L4 were obtained after a
workup similar to that used for L1 and L2.
3: yield 0.102 g (82%); mp 210 °C dec. Anal. Found: C, 40.20; H,
3.08; N, 6.75. Calcd for C21H19N3ClRuS[PF6]: C, 40.23; H, 3.05; N,
1
6.70. H NMR (CD3CN, 25 °C, TMS; δ (ppm)): 5.27−5.40 (m, 2H,
H5), 5.84 (m, 6H, Ru−ArH), 7.30−7.46 (m, 2H, H9), 7.46−7.52 (m,
6H, H1−H2, H10−H11), 7.94−8.00 (m, 2H, H3), 8.54 (s, 1H, H6).
13C{1H} NMR (CD3CN, 25 °C, TMS; δ (ppm)): 58.5 (C5), 88.3
(Ru−ArC), 124.0 (C11), 125.9 (C10), 129.2 (C2), 129.3 (C1,), 129.7
(C6), 130.5 (C9), 130.7 (C3), 132.1 (C8), 132.4 (C4), 151.2 (C7). IR
(cm−1): 439 (b), 559 (s), 752 (s; νC−H(aromatic)), 842 (s; νP−F), 1083
(m), 1188 (b), 1433 (b), 1479 (m; νC−C(aromatic)), 1610 (b; νNN),
2361 (m), 3070 (m; νC−H(aliphatic)), 3162 (m; νC−H(aromatic)). HR-
MS (CH3CN; m/z): [M]+ 482.0026, calcd value for C21H19ClN3RuS
482.0028 (δ 0.5).
L3: yield 0.499 g (93%); mp 90 °C. Anal. Found: C, 67.36; H, 4.87;
N, 15.70. Calcd for C15H13N3S: C, 67.39; H, 4.90; N, 15.72. 1H NMR
(CDCl3, 25 °C, TMS; δ (ppm)): 5.66 (s, 2H, H5), 7.33−7.43 (m, 8H,
H1−H2, H9−H11), 7.79−7.81 (m, 3H, H3, H6). 13C{1H} NMR
(CDCl3, 25 °C, TMS; δ (ppm)): 53.9 (C5), 119.0 (C11), 125.7 (C10),
128.3 (C6), 128.7 (C1), 128.9 (C2), 129.6 (C9), 130.3 (C4), 131.9
(C8), 132.3 (C3), 148.3 (C7). IR (cm−1): 467 (m), 690(s), 740 (s;
νC−H(aromatic)), 765 (m), 1040 (m), 1074 (s), 1186 (m), 1227 (m),
1350 (m), 1432 (b; νC−C(aromatic)), 1578 (m; ν), 2361 (m), 3052
(m; νC−H(aromatic)), 3087 (m), 3118 (m). HR-MS (CH3CN; m/z):
[M + Na]+ 290.0726, calcd value for C15H13N3NaS 290.0722 (δ 1.4
ppm).
4: yield 0.114 g (85%); mp 200 °C dec. Anal. Found: C, 37.40; H,
2.80; N, 6.22. Calcd for C21H19N3ClRuSe[PF6]: C, 37.43; H, 2.84; N,
1
6.24. H NMR (CD3CN, 25 °C, TMS; δ (ppm)): 5.28−5.36 (m, 2H,
H5), 5.97 (s, 6H, Ru−ArH), 7.31−7.57 (m, 8H, H1−H2, H9−H11),
7.79−8.00 (m, 2H, H3), 8.47 (s, 1H, H6). 13C{1H} NMR (CD3CN, 25
°C, TMS; δ (ppm)): 50.9 (C5), 87.7 (Ru−ArC), 124.6 (C11), 125.8
(C10), 128.3 (C4), 129.2 (C2), 129.3 (C8), 129.7 (C1), 130.4 (C9),
131.7 (C6), 131.8 (C3,), 151.0 (C7). 77Se{1H} NMR (CD3CN, 25 °C,
Me2Se; δ (ppm)): 472.0. IR (cm−1): 438 (b), 558 (b), 694 (m), 743
(s; νC−H(aromatic)), 854 (s; νP−F), 1083 (m), 1155 (m), 1187 (m),
1274 (b), 1433 (m; νC−C(aromatic)), 1480(m), 1579 (b; νNN), 2361
(m), 3068 (m; νC−H(aliphatic)), 3161 (m; νC−H(aromatic)). HR-MS
(CH3CN; m/z): [M]+ 529.9449, calcd value for C21H19ClN3RuSe
529.9476 (δ 4.9 ppm).
L4: yield 0.602 g (96%); mp 70 °C. Anal. Found: C, 57.30; H, 4.15;
N, 13.35. Calcd for C15H13N3S: C, 57.33; H, 4.17; N, 13.37. 1H NMR
(CDCl3, 25 °C, TMS; δ (ppm)): 5.72 (s, 2H, H5), 7.23−7.42 (m, 6H,
H1−H2, H10−H11), 7.48 (d, 3JH−H = 6.6 Hz, 2H, H9), 7.63 (s, 1H, H6),
7.74−7.77 (m, 2H, H3). 13C{1H} NMR (CDCl3, 25 °C, TMS; δ
(ppm)): 44.6 (C5), 119.3 (C11), 125.6 (C10), 127.3 (C4), 128.2 (C6),
128.8 (C2), 128.9 (C1), 129.5 (C9), 130.2 (C8), 134.2 (C3), 148.1
(C7). 77Se{1H} NMR (CDCl3, 25 °C, Me2Se; δ (ppm)): 430.8. IR
(cm−1): 469 (m), 692 (s), 743 (s; νC−H(aromatic)), 766(m), 1039
(m), 1070 (s), 1185 (m), 1229 (m), 1352 (m), 1432 (b;
νC−C(aromatic)), 1578 (m; νNN), 2364 (m), 3052 (m;
νC−H(aromatic)), 3085 (m), 3119 (m). HR-MS (CH3CN; m/z): [M
+ Na]+ 338.0174, calcd value for C15H13N3NaSe 338.0167 (δ 2 ppm).
Synthesis of Ruthenium Complexes 1−4. To a solution of L1
(0.056 g, 0.2 mmol)/L2 (0.065 g, 0.2 mmol)/L3 (0.053 g, 0.2 mmol)/
L4 (0.063 g, 0.2 mmol) made up in CH3OH (5 mL) was added a
solution of [{(η6-C6H6)RuCl(μ-Cl)}2] (0.050 g, 0.1 mmol) in
CH3OH (5 mL), and the mixture was stirred for 8 h at room
temperature. The resulting orange solution was filtered, and the
volume of the filtrate was reduced (∼7 mL) with a rotary evaporator.
It was mixed with solid NH4PF6 (0.032 g, 0.2 mmol), and the resulting
orange microcrystalline solid was filtered, washed with 5 mL of ice-
cold CH3OH, and dried in vacuo. Single crystals of each of the four
complexes were obtained by diffusion of diethyl ether into a solution
made up in a mixture (1/4) of CH3OH and CH3CN.
Catalytic Oxidation of Alcohols with NMO. One of the four
complexes (1/2 (0.1−1 mol %) and 3/4 (0.01−0.1 mol %)) taken up
in 20 mL of CH2Cl2 was mixed with the alcohol (1 mmol) and solid
NMO (3 mmol). The mixture was refluxed for 3 h. Thereafter solvent
was evaporated off using a rotary evaporator. The residue having an
oxidized product was extracted with 20 mL of diethyl ether. The
solvent from the extract was evaporated off, and the residue was
purified by column chromatography on silica gel. The products were
1
analyzed with H and 13C{1H} NMR spectra.
Catalytic Transfer Hydrogenation Reaction. Ketone (1 mmol),
KOH (2 mL of a 0.2 M solution in 2-propanol), and one of the
complexes (1/2 (0.1−1 mol %) and 3/4 (0.01−0.1 mol %)) was
heated under reflux (80 °C) in 10 mL of 2-propanol for 3 h.
Thereafter 2-propanol was removed with a rotary evaporator and the
product that formed was extracted with diethyl ether. The solvent
from the extract was evaporated off, resulting in a residue which was
purified by column chromatography on silica gel using a mixture of
hexane and ethyl acetate as eluent. The products were analyzed with
1H and 13C{1H} NMR spectra.
1: yield 0.099 g (78%); mp 140 °C dec. Anal. Found: C, 41.25; H,
3.31; N, 6.50. Calcd for C22H21N3ClRuS[PF6]: C, 41.22; H, 3.30; N,
6.56. 1H NMR (CD3CN, 25 °C, TMS; δ (ppm)): 3.95 (d, 1H, 3JH−H
=
3
16.8 Hz, H5), 4.10 (d, 1H, JH−H = 16.8 Hz, H5), 5.72−5.83 (m, 6H,
H16, Ru−ArH), 7.43−7.58 (m, 10H, H1−H3, H10−H12), 7.97 (s, 1H,
H7). 13C{1H} NMR (CD3CN, 25 °C, TMS; δ (ppm)): 36.4 (C5), 55.7
(C8), 87.4 (Ru−ArC), 123.2 (C12), 128.6 (C3), 129.2 (C1), 129.2
(C2,), 129.8 (C11), 130.2 (C10), 131.2 (C7), 133.9 (C4), 135.0 (C9),
146.9 (C6). IR (cm−1): 484 (b), 557 (s), 748 (m; νC−H(aromatic)),
841 (s; νP−F), 1090 (b), 1133 (b), 1256 (b), 1439 (m;
νC−C(aromatic))], 1574 (b; νNN), 2361 (m), 2921 (m;
νC−H(aliphatic)), 3095 (m; νC−H(aromatic)]). HR-MS (CH3CN; m/
z): [M]+ 496.0182, calcd value for C22H21ClN3RuS 496.0185 (δ 0.5
ppm).
RESULTS AND DISCUSSION
■
The syntheses of L1−L4 and their complexes are summarized
in Scheme 1. L1−L4 have good solubility in common organic
solvents, viz., CHCl3, CH2Cl2, CH3OH, and CH3CN, while
complexes 1−4 are only moderately soluble in the first three
solvents. They have good solubility in DMSO as well as
CH3CN. L1−L4 and their complexes 1−4 are stable to air and
moisture and can be stored at room temperature for several
months under ambient conditions. The 1H, 13C{1H}, and
77Se{1H} NMR and mass spectra of L1−L4 as well as their
complexes 1−4 are given in the Supporting Information
(Figures S1−S29).
2: yield 0.109 g (80%); mp 170 °C dec. Anal. Found: C, 38.41; H,
3.08; N, 6.11. Calcd for C22H21N3ClRuSe[PF6]: C, 38.43; H, 3.05; N,
6.15. 1H NMR (CD3CN, 25 °C, TMS; δ (ppm)): 3.80 (d, 1H, 3JH−H
=
15.3 Hz, H5), 4.00 (d, 1H, 3JH−H = 5.3 Hz, H5), 5.72 (s, 2H, H8), 5.79
(s, 6H, Ru−ArH), 7.41−7.55 (m, 10H, H1−H3, H10−H12), 7.93 (s,
1H, H7). 13C{1H} NMR (CD3CN, 25 °C, TMS; δ (ppm)): 28.6 (C5),
55.6 (C8), 86.8 (Ru−ArC), 123.6 (C12), 128.6 (C3), 129.16 (C7),
129.23 (C1, C2), 130.2 (C11), 131.1 (C4), 131.1 (C10), 134.0 (C9),
147.7 (C6). 77Se{1H} NMR (CD3CN, 25 °C, Me2Se; δ (ppm)): 450.2.
IR (cm−1): 557 (b), 707 (m), 744 (s; νC−H(aromatic)), 848 (s; νP−F),
1087 (m), 1144 (m), 1245 (b), 1437 (m; νC−C(aromatic)), 1571 (b;
νNN), 2362 (m), 3099 (m; νC−H(aliphatic)), 3155 (m;
νC−H(aromatic)). HR-MS (CH3CN; m/z): [M]+ 543.9633, calcd
value for C22H21ClN3RuSe 543.9632 (δ 0.2 ppm).
NMR Spectra. The 1H, 13C{1H}, and 77Se{1H} NMR
spectra of L1−L4 as well as their complexes 1−4 were found to
be in agreement with the molecular structures depicted in
Scheme 1. These structures are supported by single-crystal
structures determined with X-ray diffraction. The signal in the
77Se{1H} NMR spectrum of L2 (364.6 ppm) is at a 10 ppm
lower frequency with respect to that of the selenated alkyne
(375.8 ppm), whereas the signal for L4 in 77Se{1H} NMR
C
dx.doi.org/10.1021/om400057e | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
appears at 430.8 ppm, which is at 55 ppm higher frequency
with respect to that of selenated azide (375.1 ppm). The signals
in the 77Se{1H} NMR spectra of 2 and 4 shifted to higher
frequencies by 85.6 and 41.2 ppm, respectively, with respect to
those of the corresponding free ligands. Probably the shift arises
due to coordination of L2/L4 with Ru via Se. The signals of H5
in the 1H NMR spectra of 1−4 appear at a lower frequency (up
to 0.3 ppm) relative to those of free ligands. Similarly the
signals of C5 in the 13C{1H} NMR spectra of these complexes
have been observed at a higher frequency (up to 7.9 ppm) with
respect to those of free ligands. These observations imply the
coordination of ligands with the metal through S or Se,
probably in a half-pincer mode.
Figure 3. ORTEP diagram of the cation of 3 with ellipsoids given at
the 30% probability level. H atoms, the O atom, and the PF6 anion
¯
Crystal Structures. The crystal structures of complexes 1−
4 have been solved. The crystal data and refinement parameters
are given in the Supporting Information (Table S1). ORTEP
diagrams of the cations of 1−4 are shown in Figures 1−4 with
have been omitted for clarity. Bond distances (Å): Ru(1)−S(1) =
2.3893(10), Ru(1)−N(2) = 2.075(2), Ru(1)−Cl(1) = 2.3928(10),
Ru(1)−C = 2.154(4)−2.198(4). Bond angles (deg): N(2)−Ru(1)−
S(1) = 80.80(7), N(2)−Ru(1)−Cl(1) = 86.95(7), S(1)−Ru(1)−
Cl(1) = 82.46(3).
Figure 4. ORTEP diagram of the cation of 4 with ellipsoids given at
¯
the 30% probability level. H atoms, the O atom, and the PF6 anion
Figure 1. ORTEP diagram of the cation of 1 with ellipsoids given at
the 30% probability level. H atoms and the PF6 anion have been
have been omitted for clarity. Bond distances (Å): Ru(1)−N(2) =
2.072(5), Ru(1)−Se(1) = 2.4859(9), Ru(1)−Cl(1) = 2.3894(18),
Ru(1)−C = 2.157(7)−2.195(8). Bond angles (deg): N(2)−Ru(1)−
Se(1) = 82.10(14), N(2)−Ru(1)−Cl(1) = 86.86(15), Cl(1)−Ru(1)−
Se(1) = 81.28(5).
¯
omitted for clarity. Bond distances (Å): Ru(1)−N(3) = 2.079(3),
Ru(1)−S(1) = 2.3847(11), Ru(1)−C = 2.171(4)−2.194(4), Ru(1)−
Cl(1) = 2.3872(10). Bond angles (deg): N(3)−Ru(1)−S(1) =
80.17(7), N(3)−Ru(1)−Cl(1) = 87.15(8), S(1)−Ru(1)−Cl(1) =
80.67(3).
of triazole and E (S/Se) to the metal center in all of the
complexes. There is a pseudo-octahedral half-sandwich “piano-
stool” disposition of donor atoms around the Ru metal center
in the cations of complexes 1−4. The benzene ring occupies
one face of an octahedron in the cations of all the four
complexes. The nitrogen and chalcogen atoms form a chelate
ring with the metal center, and a chlorine donor atom
completes the coordination sphere. This results in an overall
three-legged piano-stool conformation. The Ru−S(1) bond
lengths (2.3847(11) Å in 1 and 2.3893(10) Å in 3) are
consistent with each other and with the values reported for
[(η6-C6H6)RuCl(N-{2-(phenylthio)ethyl}pyrrolidine)]+
(2.3649(19) Å)5l and [(η6-C6H6)Ru(2-MeSC6H4CH
NCH2CH2SC6H5)]2+ (2.3921(19) Å).5m The Ru−Se bond
distance in the cation of 2 (2.497(5) Å) is somewhat longer
than that of the cation of 4 (2.4859(9) Å), which is consistent
with the values reported for [(η6-C6H6)RuCl(N-{2-
(phenylseleno)ethyl}pyrrolidine)]+ (2.480(11) Å)5l and [(η6-
C6H6)Ru(2-MeSC6H4CHNCH2CH2SeC6H5)]2+ (2.4848(8)
Å).5m However, Ru−Se bond distance of [RuCp(CO)(C
CPh)(μ-Se)ZrCp2] (2.494(1) Å)5k is consistent with that of
the cation of 2. The Ru−N bond lengths of 1−4 have been
found to vary in a narrow range (2.072(5)−2.101(4) Å) and
are consistent with Ru−N bond length values reported for
Figure 2. ORTEP diagram of the cation of 2 with ellipsoids given at
the 30% probability level. H atoms and the PF6 anion have been
¯
omitted for clarity. Bond distances (Å): Ru(1)−N(3) = 2.101(4),
Ru(1)−Se(1) = 2.497(5), Ru(1)−C = 2.179(6)−2.22(6), Ru(1)−
Cl(1) = 2.420(4). Bond angles (deg): N(3)−Ru(1)−Se(1) =
80.82(12), N(3)−Ru(1)−Cl(1) = 86.61(19), Se(1)−Ru(1)−Cl(1) =
79.12(12).
selected bond lengths and angles. Other bond angles and
lengths are given in the Supporting Information (Table S2). A
five-membered ring is formed on coordination of the nitrogen
D
dx.doi.org/10.1021/om400057e | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 5. Noncovalent C−H···F interactions in 1.
Figure 6. Noncovalent C−H···F interactions in 3.
[Ru(2,6-bis(1-benzyl-1,2,3-triazol-4-yl)pyridine)2](PF6)2
(2.050(3) Å)26 and [(η6-C6H6)Ru(2-MeSC6H4CHN−
CH2CH2SC6H5)]2+ (2.073(6) Å).5m The Ru−C bond lengths
(2.154(4)−2.22(6) Å) and C−Ru−C bond angles of cations of
Table 1. Catalytic Oxidation of Alcohols Using Complexes
1−4 as Catalysts
a
yield, %
b
c
b
c
1−4 are in the normal range.5m,27 The PF6 group has been
−
entry no.
alcohol
1
2
3
4
1
2
3
4
5
benzyl alcohol
1-phenylethanol
diphenylmethanol
2-pentanol
85
90
93
95
84
86
80
87
90
93
95
82
83
79
88
95
95
95
93
91
86
90
92
95
97
89
92
88
found to be involved in C−H···F secondary interactions in all
of the complexes (1−4) and are shown for complexes 1 and 3
in Figures 5 and 6, respectively. The secondary interactions for
2 and 4 are given in the Supporting Information (Figures S30
and S31). The C−H···F distances (Å) of 1−4 have been
included in the Supporting Information (Table S3).
4-chlorobenzyl alcohol
1-octanol
d
6
d
7
2-octanol
Catalytic Studies. Oxidation of Secondary Alcohols. The
catalytic performance of complexes 1−4 has been evaluated in a
classical oxidation system developed for the oxidation of
primary and secondary alcohols in CH2Cl2 in the presence of
NMO as oxidant (Table 1). The present oxidation protocol is
simple to operate and gives the corresponding carbonyl
compound in good to excellent yield. N-Methylmorpholine
and water are the byproducts during the course of oxidation
reactions. Optimization studies have shown that dichloro-
methane is the best solvent and 3 mmol of NMO as oxidant is
sufficient for the present catalytic system designed for 1 mmol
of substrate. A series of blank experiments (carried out under
identical conditions) suggest that neither a ruthenium(II)
complex from 1−4 nor the oxidant NMO alone causes the
oxidation under identical reaction conditions. Maximum
conversions have been obtained in 3 h with catalyst loadings
of 0.1−1 mol % for 1 and 2 and 0.01−0.1 mol % for 3 and 4
(Scheme 2). A higher catalyst loading (1 mol % for 1 and 2 and
0.1 mol % for 3 and 4) is required for good conversions in the
cases of 1-octanol and 2-octanol. Thus complexes 3 and 4, in
a
Reaction conditions: catalysts 1 and 2 (0.1 mol %) and 3 and 4 (0.01
mol %), alcohol (1 mmol), NMO (3 mmol), solvent DCM, bath
temperature 80 °C, reaction time 3 h. Isolated yield after column
chromatography. NMR percent yield. Catalysts 1 and 2 (1 mol %)
and 3 and 4 (0.1 mol %).
b
c
d
Scheme 2. Oxidation of Alcohol
which N(2) coordinates with Ru along with chalcogen, appear
to be better catalysts than complexes 1 and 2, as they give
almost similar yields under similar reaction conditions but at
low catalyst loading (Table 1). Among the all four half-
sandwich complexes of Ru, 3 appears to be somewhat more
efficient as a catalyst (Table 1) relative to the other three. On
E
dx.doi.org/10.1021/om400057e | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
the basis of earlier work,1b,c,e,g,5m,28,29 the possible mechanism
of catalytic oxidation appears to involve RuIVO species,
which are probably formed by free radicals (generated by
heterolytic cleavage of oxidant NMO) as reported in the earlier
work.5m,o When the reactions catalyzed with 2 and 4 were
monitored by 77Se{1H} NMR spectroscopy, it was found that
the signals are shifted to higher frequencies by ≥375 ppm in the
course of the reaction. This is due to oxidation of Ru(II) to
Ru(IV),5m,o and thus the formation of RuIVO species is
responsible for the oxidation of alcohols. A new shoulder at
390−395 nm appearing in the UV−visible spectra recorded in
dichloromethane for each of 1−4 in the presence of NMO
supports the formation of the RuIVO species. A very strong
band at 848−855 cm−1 (νP−F at 841−854 cm−1 is of medium
intensity only) has been found in the IR spectra of residues
obtained by evaporating off solvent from their dichloromethane
solutions containing NMO. The formation of RuIVO species
probably contributes to this intense band. Both of these
observations1a,b,j,4h,28a,29,30 favor the fact that the species
responsible for transfer of the oxygen to alcohol substrates,
resulting in their catalytic oxidation, is RuIVO. The short
lifetime of RuIVO transient species restricted us from
acquiring direct evidence of a mass spectrum for its existence
Table 2. Catalytic Transfer Hydrogenation of Ketones Using
Complexes 1−4 as Catalysts
a
yield, %
b
c
b
c
entry no.
ketone
1
2
3
4
1
2
3
4
5
cyclopentanone
cyclohexanone
90
89
93
90
87
82
78
90
92
95
93
85
80
81
95
91
97
92
90
89
90
95
95
97
95
90
93
86
acetophenone
benzophenone
2-pentanone
d
6
d
4-chlorobenzophenone
4-methoxybenzophenone
7
a
Reaction conditions: catalysts 1 and 2 (0.1 mol %) and 3 and 4 (0.01
mol %), ketone (1 mmol), KOH (2 mL of a 0.2 M solution in 2-
propanol), solvent 2-propanol, bath temperature 80 °C, reaction time
b
c
3 h. Isolated yield after column chromatography. NMR percent
d
yields. Catalysts 1 and 2 (1 mol %) and 3 and 4 (0.1 mol %).
bond takes place.32 In H NMR spectra a broad singlet has
1
been noticed around −7.8 to −11.0 ppm during the course of
the catalytic reaction. The signal at this position is characteristic
of a metal hydride and indicates the formation of a Ru−H
bond.33 Thus, catalytic transfer hydrogenation reactions with
the present complexes probably proceed via formation of a
metal hydride intermediate. The efficiencies of sulfur-ligated
complexes for catalyzing transfer hydrogenation and of their
corresponding Se analogues are not much different. This
observation differs from earlier reports5l−o in which complexes
of Se ligands have been found to be generally better than their S
analogues. However, the present results might have arisen due
to the overall ligating characteristics of L1−L4 and their steric
influences.
1
during the course of catalytic oxidation. The H NMR spectra
of ruthenium complexes recorded after adding oxidants become
broad, indicating the formation of paramagnetic species as
intermediates, which further indirectly supports the formation
of RuIVO. Generally complexes of Se ligands have been
found to be more efficient5l−o than their S analogues, but the
nature of other donor sites and steric factors may modify such a
trend, and thus Se derivatives are not distinctly efficient in
comparison to S derivatives in the present case.
Transfer Hydrogenation of Ketones. Transfer hydro-
genation reaction (in which one organic molecule transfers
hydrogen to another) has an advantage in organic synthesis that
one can avoid the use of molecular hydrogen.2b We have
studied the catalysis of transfer hydrogenation reactions of
ketones (Scheme 3) at 80 °C using 1/2 (0.1−1 mol %) and 3/
DFT Calculations. The accuracy of density functional
theory (DFT) calculations made on complexes 1−4 incorpo-
rating the late transition metal Ru is insufficient to warrant a
detailed discussion of MO energy levels. At most, a qualitative
analysis of the lowest energy configurations, frontier orbitals,
and charge distribution of the complexes can be done. The
HOMOs (highest occupied molecular orbitals) of complexes 1
and 2 are positioned primarily over the Ru and Cl atoms. A d
orbital of Ru(II) interacting with a π orbital of the η6-benzene
ring, a p orbital of one N of the triazole ring, and a chalcogen
atom constitute their HOMO. In the case of complexes 3 and 4
HOMOs are composed of a π orbital of 4-phenyl-1,2,3-triazole
and a d orbital of the metal. However, an interaction between a
d orbital of Ru(II) with a π orbital of the η6-benzene ring, a p
orbital of one N of the triazole ring, and a chalcogen donor
atom has been observed in HOMO-1. The HOMO−LUMO
energy gap of a complex and its chemical reactivity have been
correlated earlier.34−36 Generally, when the energy gaps are
low, the reactivity is higher. However, differences in HOMO−
LUMO energy gaps (Figure 7) between complexes 1 and 2 and
between 3 and 4 are inadequate to infer a difference in
reactivity between S and Se. The HOMO−LUMO energy gaps
calculated by DFT for 3 and 4 are lower relative to those of 1
and 2, respectively. This suggests that the relatively higher
reactivities of complexes 3 and 4, having coordination with
N(2), may be at least partially ascribed to their low energy gaps.
The electron densities (Figure 8) at coordinated N(3) of the
triazole ring in the case of complexes 1 and 2 are higher as
compared to those of N(2) in 3 and 4. Probably there is a
strong coordination of N(3) of triazole with Ru in complexes 1
and 2, which makes them more stable in comparison to 3 and
Scheme 3. Transfer Hydrogenation of Ketone
4 (0.01−0.1 mol %) as catalysts. 2-Propanol has been used as a
hydrogen donor in the presence of KOH, which is known to be
the best inorganic base for this reaction.31 High conversions
(Table 2) have been found in the case of acetophenone (up to
97%) with all catalysts 1−4, while in the case of aliphatic
secondary ketones the conversion has been observed to be up
to 95% in case of cyclopentanone. Complexes 3 and 4, having
the involvement of N(2) of the triazole ring in coordination
with Ru, are the most efficient catalysts among 1−4, as their
low catalyst loading is sufficient for high conversions. When the
reactions catalyzed with 2 and 4 were monitored with 77Se{1H}
NMR spectroscopy, it was observed that the signals in the
spectra shift to higher frequency (17−20 ppm), indicating that
probably the Ru−Cl bond is cleaved or weakened very
significantly to make a coordination site on metal center
available so that formation of an intermediate having a Ru−H
F
dx.doi.org/10.1021/om400057e | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Figure 7. Frontier molecular orbital diagrams of complexes 1−4.
Figure 8. Mulliken partial charges of complexes 1−4.
4, respectively.16,37 Thus, the latter species are more reactive.
There is also a possibility of a somewhat steric blockade for the
substrate in the case of 1 and 2. The experimentally observed
bond distances and the calculated distances match better for
Ru−Cl, Ru−N, and Ru−C (centroid) (Supporting Informa-
tion; Table S4). However, some differences between calculated
and observed Ru−E (E = S/Se) bond distances (0.083−0.138
Å) exist. The calculated and experimentally found bond angles
are also very close (Supporting Information; Table S4) to each
other.
coordinated to Ru (1 and 2), and in the other two (3 and 4)
N(2) is bonded to Ru. They have been explored as catalysts for
the oxidation of alcohols and transfer hydrogenation of ketones.
The species in which N(2) is bonded to ruthenium are more
efficient than those involving N(3) in coordination. The
oxidation is probably via a RuIVO species, and transfer
hydrogenation involves an intermediate containing Ru−H.
DFT calculation based bond lengths/angles are generally
consistent with experimental values. The HOMO−LUMO
energy gaps of 3 and 4 are lower than those of 1 and 2.
ASSOCIATED CONTENT
CONCLUSION
■
■
Four half-sandwich complexes of (η6-benzene)RuII with 1,2,3-
triazole-based organosulfur/-selenium ligands (obtained using a
click reaction) have been synthesized for the first time and
characterized structurally with single-crystal X-ray diffraction
studies. The disposition of donor atoms around Ru is a pseudo-
octahedral “piano-stool” type. Two of the complexes have N(3)
S
* Supporting Information
Tables, figures, and CIF files giving crystal data and refinement
details, bond lengths and angles, secondary interaction figures
and distances, NMR and mass spectra, crystallographic data for
1 (CCDC no. 919781), 2 (CCDC no. 919782), 3 (CCDC no.
919783), and 4 (CCDC no. 919784), and bond lengths and
G
dx.doi.org/10.1021/om400057e | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(p) Prakash, O.; Singh, P.; Mukherjee, G.; Singh, A. K. Organometallics
2012, 31, 3379−3388.
angles calculated by DFT. This material is available free of
charge via the Internet at http://pubs.acs.org.
(4) (a) Matsumura, K.; Hashiguchi, S.; Ikariya, T.; Noyori, R. J. Am.
Chem. Soc. 1997, 119, 8738−8739. (b) Everaere, K.; Mortreux, A.;
Bulliard, M.; Brussee, J.; van der Gen, A.; Nowogrocki, G.; Carpentier,
J.-F. Eur. J. Org. Chem. 2001, 275−2291. (c) da Silva, A. C.; Piotrowski,
H.; Mayer, P.; Polborn, K.; Severin, K. Eur. J. Inorg. Chem. 2001, 685−
691. (d) Ogo, S.; Abura, T.; Watanabe, Y. Organometallics 2002, 21,
2964−2969. (e) Ogo, S.; Uehara, K.; Abura, T.; Watanabe, Y.;
Fukuzumi, S. Organometallics 2004, 23, 3047−3052. (f) Canivet, J.;
AUTHOR INFORMATION
Corresponding Author
*A.K.S.: e-mail, aksingh@chemistry.iitd.ac.in, ajai57@hotmail.
com; fax, +91 11 26581102; tel, +91 11 26591379.
■
Notes
The authors declare no competing financial interest.
Labat, G.; Stoeckli-Evans, H.; Suss-Fink, G. Eur. J. Inorg. Chem. 2005,
̈
4493−4500. (g) Carrion
́
, M. C.; Jalon
́
, F. A.; Manzano, B. R.;
ACKNOWLEDGMENTS
■
Rodríguez, A. M.; Sepulveda, F.; Maestro, M. Eur. J. Inorg. Chem. 2007,
́
A.K.S. thanks the Council of Scientific and Industrial Research
(CSIR) of India (Project No. 01(2421)10/EMR-II) and
Department of Science and Technology of India (Project No.
SR/S1/IC-40/2010) for financial support. F.S. thanks the
University Grants Commission (UGC) for SRF. G.K.R. and
A.K. thank the CSIR of India for SRF and RA, respectively. We
also thank Prof. B. Jayaram (Coordinator, SCFBio) and the
Supercomputing Facility for Bioinformatics and Computational
Biology (SCFBio), Department of Chemistry, IIT Delhi, for
providing access to the computational facilities.
3961−3973. (h) Kumar, K. N.; Venkatachalam, G.; Ramesh, R.; Liu, Y.
Polyhedron 2008, 27, 157−166. (i) Do, Y.; Ko, S.-B.; Hwang, I.-C.;
Lee, K.-E.; Lee, S. W.; Park, J. Organometallics 2009, 28, 4624−4627.
(j) Touge, T.; Hakamata, T.; Nara, H.; Kobayashi, T.; Sayo, N.; Saito,
T.; Kayaki, Y.; Ikariya, T. J. Am. Chem. Soc. 2011, 133, 14960−14963.
̈
̈
̈
̇
(k) Gurbuz, N.; Ozcan, E. O.; Ozdemir, I.; C
̧
etinkaya, B.; S
̧ahin, O.;
̈
̈
Buyukgungor, O. Dalton Trans. 2012, 41, 2330−2339.
̈
̈
̈
̈
(5) (a) Kumar, A.; Rao, G. K.; Kumar, S.; Singh, A. K. Dalton Trans.
2013, 42, 5200−5223. (b) Kumar, A.; Rao, G. K.; Singh, A. K. RSC
Adv. 2012, 2, 12552−12574. (c) Kumar, A.; Rao, G. K.; Saleem, F.;
Singh, A. K. Dalton Trans. 2012, 41, 11949−11977. (d) Rao, G. K.;
Kumar, A.; Kumar, B.; Singh, A. K. Dalton Trans. 2012, 41, 4306−
4309. (e) Rao, G. K.; Kumar, A.; Kumar, B.; Kumar, D.; Singh, A. K.
Dalton Trans. 2012, 41, 1931−1937. (f) Rao, G. K.; Kumar, A.;
Ahmed, J.; Singh, A. K. Chem. Commun. 2010, 46, 5954−5956.
(g) Kumar, A.; Agarwal, M.; Singh, A. K. Inorg. Chim. Acta 2009, 362,
3208−3218. (h) Kumar, A.; Agarwal, M.; Singh, A. K. J. Organomet.
Chem. 2008, 693, 3533−3545. (i) Kumar, A.; Agarwal, M.; Singh, A. K.
Polyhedron 2008, 27, 485−492. (j) Saleem, F.; Rao, G. K.; Singh, P.;
Singh, A. K. Organometallics 2013, 32, 387−395. (k) Sunada, Y.;
Hayashi, Y.; Kawaguchi, H.; Tatsumi, K. Inorg. Chem. 2001, 40, 7072−
7078. (l) Singh, P.; Singh, M.; Singh, A. K. J. Organomet. Chem. 2009,
694, 3872−3880. (m) Singh, P.; Singh, A. K. Organometallics 2010, 29,
6433−6442. (n) Das, D.; Singh, P.; Singh, A. K. J. Organomet. Chem.
2010, 695, 955−962. (o) Singh, P.; Singh, A. K. Eur. J. Inorg. Chem.
2010, 4187−4195.
REFERENCES
■
(1) (a) Leung, W.-H.; Che, Chi.-M. Inorg. Chem. 1989, 28, 4619−
4622. (b) Catalano, V. J.; Heck, R. A.; Immoos, C. E.; Ohman, A.; Hill,
̈
M. G. Inorg. Chem. 1998, 37, 2150−2157. (c) Fung, W.-H.; Yu, W.-Y.;
Che, C.-M. J. Org. Chem. 1998, 63, 2873−2877. (d) Chatterjee, D.;
Mitra, A.; Mukherjee, S. Polyhedron 1999, 18, 2659−2663.
(e) Gonsalvi, L.; Arends, I. W. C. E.; Sheldon, R. A. Org. Lett. 2002,
4, 1659−1661. (f) Sheldon, R. A.; Arends, I. W. C. E.; Brink, G.-J. T.;
Dijksman, A. Acc. Chem. Res. 2002, 35, 774−781. (g) Gonsalvi, L.;
Arends, I. W. C. E.; Moilanen, P.; Sheldon, R. A. Adv. Synth. Catal.
2003, 345, 1321−1328. (h) Hanasaka, F.; Fujita, K.; Yamaguchi, R.
Organometallics 2006, 25, 4643−4647. (i) Cheung, W.-M.; Ng, H.-Y.;
Williams, I. D.; Leung, W.-H. Inorg. Chem. 2008, 47, 4383−4391.
(j) Raja, M. U.; Gowri, N.; Ramesh, R. Polyhedron 2010, 29, 1175−
1181. (k) Raju, V. V.; Balasubramanian, K. P.; Jayabalakrishnan, C.;
Chinnusamy, V. Nat. Sci. 2011, 3, 3542−550. (l) Trivedi, M.;
Nagarajan, R.; Kumar, A.; Singh, N. K.; Rath, N. P. J. Mol. Struct. 2011,
994, 29−38. (m) Gunasekaran, N.; Remya, N.; Radhakrishnan, S.;
Karvembu, R. J. Coord. Chem. 2011, 64, 491−501. (n) Tamizh, M. M.;
Mereiter, K.; Kirchner, K.; Karvembu, R. J. Organomet. Chem. 2012,
700, 194−201.
(6) (a) Aucagne, V.; Hanni, K. D.; Leigh, D. A.; Lusby, P. J.; Walker,
̈
D. B. J. Am. Chem. Soc. 2006, 128, 2186−2187. (b) Suijkerbuijk, B. M.
J. M.; Aerts, B. N. H.; Dijkstra, H. P.; Lutz, M.; Spek, A. L.; van Koten,
G.; Gebbink, R. J. M. K. Dalton Trans. 2007, 1273−1276. (c) Maeda,
C.; Yamaguchi, S.; Ikeda, C.; Shinokubo, H.; Osuka, A. Org. Lett. 2008,
10, 549−552. (d) Mullen, K. M.; Gunter, M. J. J. Org. Chem. 2008, 73,
3336−3350.
(2) (a) Li, Y.-H.; Ding, X.-H.; Zhang, Y.; He, W.-R.; Huang, W. Inorg.
Chem. Commun. 2012, 15, 194−197. (b) Palmer, M. J.; Wills, M.
Tetrahedron: Asymmetry 1999, 10, 2045−2061.
(3) (a) Krohn, K.; Vinke, I.; Adam, H. J. Org. Chem. 1996, 61, 1467−
1472. (b) Sato, K.; Aoki, M.; Takagi, J.; Noyori, R. J. Am. Chem. Soc.
(7) (a) Detz, R. J.; Heras, S. A.; de Gelder, R.; van Leeuwen, P. W. N.
M.; Hiemstra, H.; Reek, J. N. H.; van Maarseveen, J. H. Org. Lett.
2006, 8, 3227−3230. (b) Monkowius, U.; Ritter, S.; Konig, B.; Zabel,
̈
M.; Yersin, H. Eur. J. Inorg. Chem. 2007, 4597−4606. (c) Fukuzawa, S.;
Oki, H.; Hosaka, M.; Sugasawa, J.; Kikuchi, S. Org. Lett. 2007, 9,
5557−5560. (d) Richardson, C.; Fitchett, C. M.; Keene, F. R.; Steel, P.
J. Dalton Trans. 2008, 2534−2537. (e) Schweinfurth, D.; Hardcastle,
K. I.; Bunz, U. H. F. Chem. Commun. 2008, 2203−2205. (f) Maisonial,
1997, 119, 12386−12387. (c) Marko,
́
I. E.; Giles, P. R.; Tsukazaki, M.;
Chelle-Regnaut, I.; Urch, C. J.; Brown, S. M. J. Am. Chem. Soc. 1997,
́
119, 12661−12662. (d) Nishimura, T.; Onoue, T.; Ohe, K.; Uemura,
S. Tetrahedron Lett. 1998, 39, 6011. (e) Miyata, A.; Murakami, M.; Irie,
R.; Katsuki, T. Tetrahedron Lett. 2001, 42, 7067−7070. (f) Mori, K.;
Yamaguchi, K.; Hara, T.; Mizugaki, T.; Ebitani, K.; Kaneda, K. J. Am.
Chem. Soc. 2002, 124, 11572−11573. (g) Jensen, D. R.; Schultz, M. J.;
Mueller, J. A.; Sigman, M. S. Angew. Chem.; Int. Ed. 2003, 42, 3810−
3813. (h) Iwasawa, T.; Tokunaga, M.; Obora, Y.; Tsuji, Y. J. Am. Chem.
Soc. 2004, 126, 6554−6555. (i) Hanasaka, F.; Fujita, K.; Yamaguchi, R.
Organometallics 2005, 24, 3422−3433. (j) Hanasaka, F.; Fujita, K.;
Yamaguchi, R. Organometallics 2006, 25, 4643−4647. (k) Ikariya, T.;
́
A.; Serafin, P.; Traïkia, M.; Debiton, E.; Thery, V.; Aitken, D. J.;
Lemoine, P.; Bernard, V.; Gautier, A. Eur. J. Inorg. Chem. 2008, 298−
305.
(8) (a) Mindt, T. L.; Struthers, H.; Brans, L.; Anguelov, T.;
́
Schweinsberg, C.; Maes, V.; Tourwe, D.; Schibli, R. J. Am. Chem. Soc.
2006, 128, 15096−15097. (b) Li, Y.; Huffman, J. C.; Flood, A. H.
Chem. Commun. 2007, 2692−2694. (c) Meudtner, R. M.; Ostermeier,
M.; Goddard, R.; Limberg, C.; Hecht, S. Chem. Eur. J. 2007, 13, 9834−
́
9840. (d) Colasson, B.; Save, M.; Milko, P.; Roithova, J.; Schroder, D.;
̈
Blacker, A. J. Acc. Chem. Res. 2007, 40, 1300−1308. (l) Canivet, J.;
̌
Reinaud, O. Org. Lett. 2007, 9, 4987−4990. (e) van Assema, S. G. A.;
Tazelaar, C. G. J.; de Jong, G. B.; van Maarseveen, J. H.; Schakel, M.;
Lutz, M.; Spek, A. L.; Slootweg, J. C.; Lammertsma, K. Organometallics
Suss-Fink, G.; Step
̌
nick
̌
a, P. Eur. J. Inorg. Chem. 2007, 4736−4742.
̈
(m) Singh, P.; Das, D.; Singh, M.; Singh, A. K. Inorg. Chem. Commun.
2010, 13, 988−991. (n) Ramasubramanian, A. S.; Bhat, B.; Dileep, R.;
Rani, S. J. Serb. Chem. Soc. 2011, 76, 75−83. (o) Kawahara, R.; Fujita,
K.; Yamaguchi, R. J. Am. Chem. Soc. 2012, 134, 3643−3646.
2008, 27, 3210−3215. (f) Mindt, T. L.; Muller, C.; Melis, M.; de Jong,
̈
M.; Schibli, R. Bioconjugate Chem. 2008, 19, 1689−1695.
H
dx.doi.org/10.1021/om400057e | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(9) (a) David, O.; Maisonneuve, S.; Xie, J. Tetrahedron Lett. 2007, 48,
6527−6530. (b) Camp, C.; Dorbes, S.; Picard, C.; Benoist, E.
Tetrahedron Lett. 2008, 49, 1979−1983. (c) Ziegler, T.; Hermann, C.
Tetrahedron Lett. 2008, 49, 2166−2169.
(10) (a) Tornøe, C. W.; Christensen, C.; Meldal, M. J. Org. Chem.
2002, 67, 3057−3064. (b) Rostovtsev, V. V.; Green, L. G.; Fokin, V.
V.; Sharpless, K. B. Angew. Chem., Int. Ed. 2002, 41, 2596−2599.
(c) Meldal, M.; Tornøe, C. W. Chem. Rev. 2008, 108, 2952−3015.
(11) (a) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int.
Ed. 2001, 40, 2004−2021.
(12) (a) Moses, J. E.; Moorhouse, A. D. Chem. Soc. Rev. 2007, 36,
1249−1262. (b) Fournier, D.; Hoogenboom, R.; Schubert, U. S. Chem.
Soc. Rev. 2007, 36, 1369−1380. (c) Lutz, J.-F. Angew. Chem., Int. Ed.
2007, 46, 1018−1025. (d) Ladmiral, V.; Mantovani, G.; Clarkson, G.
J.; Cauet, S.; Irwin, J. L.; Haddleton, D. M. J. Am. Chem. Soc. 2006,
128, 4823−4830. (e) Punna, S.; Kuzelka, J.; Wang, Q.; Finn, M. G.
Angew. Chem., Int. Ed. 2005, 44, 2215−2220. (f) Bodine, K. D.; Gin, D.
Y.; Gin, M. S. J. Am. Chem. Soc. 2004, 126, 1638−1639. (g) Wu, P.;
Feldman, A. K.; Nugent, A. K.; Hawker, C. J.; Scheel, A.; Voit, B.;
(22) Hou, D.-R.; Kuan, T.-C.; Li, Y.-K.; Lee, R.; Huang, K.-W.
Tetrahedron 2010, 66, 9415−9420.
(23) Seus, N.; Saraiva, M. T.; Alberto, E. E.; Savegnago, L.; Alves, D.
Tetrahedron 2012, 68, 10419−10425.
(24) Arnau, N.; Moreno-Manas, M.; Pleixats, R. Tetrahedron 1993,
̃
49, 11019−11028.
(25) Furniss, B. S.; Hannaford, A. J.; Smith, P. W. G.; Tatchell, A. R.
Vogel’s Textbook of Practical Organic Chemistry, 5th ed.; ELBS,
Longman Group: London, 1989.
(26) Zhang, C.; Shen, X.; Sakai, R.; Gottschaldt, M.; Schubert, U. S.;
Hirohara, S.; Tanihara, M.; Yano, S.; Obata, M.; Xiao, N.; Satoh, T.;
Kakuchi, T. J. Polym. Sci., Part A: Polym. Chem. 2011, 49, 746−753.
(27) (a) Ahmed, S. J.; Hyder, M. I.; Kabir, S. E.; Miah, M. A.;
Deeming, A. J.; Nordlander, E. J. Organomet. Chem. 2006, 691, 309−
322. (b) Singh, A. K.; Kadarkaraisamy, M.; Misra, M.; Sooriyakumar,
J.; Drake, J. E.; Hursthouse, M. B.; Light, M. E.; Jasinski, J. P. Inorg.
Chim. Acta 2001, 320, 133−140. (c) Mishra, H.; Mukherjee, R. J.
Organomet. Chem. 2006, 691, 3545−3555.
(28) (a) Drago, R. S. Coord. Chem. Rev. 1992, 117, 185−213.
(b) Cundari, T. R.; Drago, R. S. Inorg. Chem. 1990, 29, 3904−3907.
(c) Che, C.-M.; Lai, T.-F.; Wong, K.-Y. Inorg. Chem. 1987, 26, 2289−
2290.
(29) (a) El-Hendawy, A. M.; Alkubaisi, A. H.; Koarashy, A. E.;
Shanab, M. M. Polyhedron 1993, 12, 2343−2350. (b) Goldstein, A. S.;
Drago, R. S. J. Chem. Soc., Chem. Commun. 1991, 21−22.
(30) (a) El-Shahawi, M. S.; Shoir, A. F. Spectrochim. Acta, Part A
2004, 60, 121−127. (b) Chatterjeea, D.; Mitra, A.; Roy, B. C. J. Mol.
Catal. A 2000, 161, 17−21.
́
Pyun, J.; Frechet, J. M. J.; Sharpless, K. B.; Fokin, V. V. Angew. Chem.,
Int. Ed. 2004, 43, 3928−3932. (h) Kolb, H. C.; Sharpless, K. B. Drug
Discovery Today 2003, 8, 1128−1138.
(13) (a) Bernet, L.; Lalrempuia, R.; Ghattas, W.; Mueller-Bunz, H.;
Vigara, L.; Llobet, A.; Albrecht, M. Chem. Commun. 2011, 47, 8058−
8060. (b) Bratsos, I.; Urankar, D.; Zangrando, E.; Genova-Kalou, P.;
̂
Kosmrlj, J.; Alessio, E.; Turel, I. Dalton Trans. 2011, 40, 5188−5199.
(c) Wang, L.; Yang, W.-W.; Zheng, R.-H.; Shi, Q.; Zhong, Y.-W.; Yao,
J. Inorg. Chem. 2011, 50, 7074−7079. (d) Stengel, I.; Mishra, A.;
(31) Turkmen, H.; Pape, T.; Hahn, F. E.; C
metallics 2008, 27, 571−575.
̧
etinkaya, B. Organo-
̈
Pootrakulchote, N.; Moon, S.-J.; Zakeeruddin, S. M.; Gratzel, M.;
̈
Bauerle, P. J. Mater. Chem. 2011, 21, 3726−3734.
̈
(32) Bacchi, A.; Balordi, M.; Cammi, R.; Elviri, L.; Pelizzi, C.;
Picchioni, F.; Verdolino, V.; Goubitz, K.; Peschar, R.; Pelagatti, P. Eur.
J. Inorg. Chem. 2008, 4462−4473.
(14) (a) Schuster, E. M.; Botoshansky, M.; Gandelman, M. Angew.
Chem., Int. Ed. 2008, 47, 4555−4558. (b) Schuster, E. M.; Nisnevich,
G.; Botoshansky, M.; Gandelman, M. Organometallics 2009, 28, 5025−
5031. (c) Struthers, H.; Spingler, B.; Mindt, T. L.; Schibli, R. Chem.
Eur. J. 2008, 14, 6173−6183.
(33) Deb, B.; Sarmah, P. P.; Dutta, D. K. Eur. J. Inorg. Chem. 2010,
1710−1716.
(34) (a) Mebi, C. A. J. Chem. Sci. 2011, 123, 727−731. (b) Chattaraj,
P. K.; Maiti, B. J. Am. Chem. Soc. 2003, 125, 2705−2710.
(35) (a) Pearson, R. G. Acc. Chem. Res. 1993, 26, 250−255. (b) Parr,
P. G.; Pearson, R. G. J. Am. Chem. Soc. 1983, 105, 7512−7516.
(36) (a) Parr, R. G.; Szentpaly, L.; Liu, S. J. Am. Chem. Soc. 1999,
121, 1922−1924. (b) Liu, S. J. Chem. Sci. 2005, 117, 477−483.
(37) Bastero, A.; Font, D.; Pericas, M. A. J. Org. Chem. 2007, 72,
2460−2468.
(15) (a) Reetz, M. T.; Waldvogel, S. R.; Goddard, R. Tetrahedron
Lett. 1997, 38, 5967−5970. (b) Jung, I. G.; Son, S. U.; Park, K. H.;
Chung, K.-C.; Lee, J. W.; Chung, Y. K. Organometallics 2003, 22,
4715−4722. (c) Kostas, I. D.; Steele, B. R.; Terzis, A.; Amosova, S. V.
Tetrahedron 2003, 59, 3467−3473.
(16) (a) Kilpin, K. J.; Crowley, J. D. Polyhedron 2010, 29, 3111−
3117. (b) Kilpin, K. J.; Gavey, E. L.; McAdam, C. J.; Anderson, C. B.;
Lind, S. J.; Keep, C. C.; Gordon, K. C.; Crowley, J. D. Inorg. Chem.
2011, 50, 6334−6346.
(17) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
1990, 46, 467.
(18) Sheldrick, G. M. SHELXL-NT, Version 6.12; University of
Gottingen, Gottingen, Germany, 2000.
(19) Robb, M. A.; Cheeseman, J. A.; Montgomery, J. A.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi., J.;
Barone, V.; Mennucci, M.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, M.; Honda, Y.; Kitao,
K.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J.
B.; Bakken, V.; Adamo, V.; Jaramillo, J.; Gomperts, R.; Stratmann, R.
E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.;
Ayala, P. Y.; Morokuma, K.; Voth, J. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas,
O.; Malick, D. A.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, G.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. A.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian-03; Gaussian,
Inc., Wallingford, CT, 2004.
(20) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648−5652. (b) Lee,
C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785−789.
(21) Zelonka, R. A.; Baird, M. C. Can. J. Chem. 1972, 50, 3063−3072.
I
dx.doi.org/10.1021/om400057e | Organometallics XXXX, XXX, XXX−XXX