Efficient catalysis of transfer hydrogenation of ketones and oxidation of alcohols with newly designed half-sandwich rhodium(III) and iridium(III) complexes of half-pincer chalcogenated pyridines

Article abstract of DOI:10.1021/om300169p

The in situ generated ArE^- (E = S or Se) reacts with (2-chloromethyl)pyridine in N₂ atmosphere, resulting in half-pincer (N, S/Se) ligands (2-arylchalcogenomethyl)pyridine (L1-L3; aryl = Ph/2-pyridyl for S, Ph for Se). Half-sandwich complexes [(η⁵-Cp*)Rh(L) Cl][PF₆] (1, 2), [(η⁵-Cp*)Rh(L2)CH ₃CN][PF₆]₂ (3), and [(η⁵- Cp*)Ir(L)Cl][PF₆] (4-6), where L = L1-L3, have been synthesized by reacting L with [(η⁵-Cp*)RhCl(ν-Cl)]₂ and [(η⁵-Cp*)IrCl(ν-Cl)]₂ respectively. The ligands and complexes have been characterized by IR, HR-MS, and ¹H, ¹³C{¹H}, and ⁷⁷Se{¹H} NMR spectra. The single-crystal structures of all the complexes (1-6) have been determined with X-ray crystallography [Rh-S, Rh-Se, Ir-S, Ir-Se bond distances: 2.383(2)/2.353(2), 2.4867(9), 2.343(2)/2.341(3), 2.453(1) A, respectively]. Each metal has pseudo-octahedral half-sandwich "piano-stool" geometry. The PF₆^- ions in crystals are packed between half-sandwich complex molecules, resulting in various H...F secondary interactions. Complexes 1-6 have been explored for catalysis of oxidation of secondary alcohols with N-methylmorpholine-N-oxide and transfer hydrogenation reaction of ketones with 2-propanol and found very efficient, as revealed by TON values, which are up to 9.6 × 10³ and 9.8 × 10³ respectively for the two catalytic reactions. The formation of the M-H bond has been noticed in the intermediates of both the catalytic reactions. DFT calculations indicate a reactivity order for the complexes of Rh > Ir, which is also found for the two catalytic reactions experimentally. The calculated (DFT) and observed bond distances and angles of 1-6 are reasonably close.

Full text of DOI:10.1021/om300169p

Article
pubs.acs.org/Organometallics
Efficient Catalysis of Transfer Hydrogenation of Ketones and
Oxidation of Alcohols with Newly Designed Half-Sandwich
Rhodium(III) and Iridium(III) Complexes of Half-Pincer Chalcogenated
Pyridines
Om Prakash, Pradhumn Singh, G. Mukherjee, and Ajai K Singh*
Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016, India
S
* Supporting Information
ABSTRACT: The in situ generated ArE¯ (E = S or Se) reacts with (2-
chloromethyl)pyridine in N2 atmosphere, resulting in half-pincer (N, S/Se)
ligands (2-arylchalcogenomethyl)pyridine (L1−L3; aryl = Ph/2-pyridyl for
S, Ph for Se). Half-sandwich complexes [(η5-Cp*)Rh(L)Cl][PF6] (1, 2),
[(η5-Cp*)Rh(L2)CH3CN][PF6]2 (3), and [(η5-Cp*)Ir(L)Cl][PF6] (4−
6), where L = L1−L3, have been synthesized by reacting L with [(η5-
Cp*)RhCl(μ-Cl)]2 and [(η5-Cp*)IrCl(μ-Cl)]2 respectively. The ligands
1
and complexes have been characterized by IR, HR-MS, and H, 13C{1H},
and 77Se{1H} NMR spectra. The single-crystal structures of all the
complexes (1−6) have been determined with X-ray crystallography [Rh−S,
Rh−Se, Ir−S, Ir−Se bond distances: 2.383(2)/2.353(2), 2.4867(9), 2.343(2)/2.341(3), 2.453(1) Å, respectively]. Each metal
−
has pseudo-octahedral half-sandwich “piano-stool” geometry. The PF6 ions in crystals are packed between half-sandwich
complex molecules, resulting in various H···F secondary interactions. Complexes 1−6 have been explored for catalysis of
oxidation of secondary alcohols with N-methylmorpholine-N-oxide and transfer hydrogenation reaction of ketones with 2-
propanol and found very efficient, as revealed by TON values, which are up to 9.6 × 103 and 9.8 × 103 respectively for the two
catalytic reactions. The formation of the M−H bond has been noticed in the intermediates of both the catalytic reactions. DFT
calculations indicate a reactivity order for the complexes of Rh > Ir, which is also found for the two catalytic reactions
experimentally. The calculated (DFT) and observed bond distances and angles of 1−6 are reasonably close.
units ligated with chalcogen ligands, particularly those
containing selenium and tellurium. Half-sandwich iridium(III)
and rhodium(III) complexes with organochalcogen (S, Se)
ligands based on N-methylimidazole have been synthesized and
used as catalysts12 for norbornene polymerization. [(η5-
Cp*)Ir(CO)(ETol)2] (E = Se, S; Tol = p-tolyl) has been
synthesized and reacted with [Pt(PPh3)3] to form tri- or
dinuclear mixed-metal complexes with bridging chalcogenido or
chalcogenolato ligands.13,14 The coordination of chalcogen-
functionalized carboranes15−18 with η5-Cp*Rh(III)/Ir(III) has
been investigated. The synthesis and structural aspects of
complexes of chalcogenated phosphines with η5-Cp*Rh(III)
have also been investigated.19,20 There is only one report to our
knowledge in which selenoethers and telluroethers have been
reacted with η5-Cp*Rh(III)/Ir(III).21 Considering the fact that
selenoethers have been found recently to be important building
blocks for efficient catalysts for C−C coupling22−24 [(Se, C, Se)
and (Se, N, Se) pincer and (Se, N, C−) ligands], transfer
hydrogenation, and oxidation of alcohols25,26 [(E, N, S) ligand
E = S, Se or Te], and species η5-Cp/Cp*Rh(III)/Ir(III) have
been used to design catalysts for asymmetric transfer
INTRODUCTION
■
η5-Cyclopentadienyl (Cp) and η5-pentamethylcyclopentadienyl
(Cp*) groups are efficient ancillary ligands in organometallic
complexes. There are reports on the synthesis, structure, and
reactivity of a number of Cp or Cp* transition-metal complexes
in the literature.1 Rhodium(III) and iridium(III) are two
important metal ions that give with Cp/Cp* and other
coligands species of interesting reactivity. Although Cp and
Cp* ligands stabilize metal centers by tridentate coordination
in a facial fashion, it is rather difficult to modify the electronic
and steric properties of these ligands. Therefore, other ligands
are used to tune properties of transition metals attached to Cp
or Cp*. The complexes of the species η5-CpRh(III)/Ir(III) and
η5-Cp*Rh(III)/Ir(III) with a variety of coligands have been
found to show very promising catalytic activity for various
organic transformations. The η5-Cp*Ir(III) complexes bearing
N-heterocyclic carbene coligands are effective catalysts for
Oppenauer-type oxidation of alcohols.2,3 Multialkylation of
aqueous ammonia with alcohols has been catalyzed by water-
soluble η5-Cp*Ir-ammine complexes.4 A variety of (N, N) and
(N, O) ligands are able to tune the catalytic activity of η5-
Cp*Rh(III)/Ir(III) for efficient asymmetric transfer hydro-
genation,5−11 even in water. There are not many examples of
species having η5-CpRh(III)/Ir(III) and η5-Cp*Rh(III)/Ir(III)
Received: February 29, 2012
Published: April 3, 2012
© 2012 American Chemical Society
3379
dx.doi.org/10.1021/om300169p | Organometallics 2012, 31, 3379−3388

Organometallics
Article
optimized geometries to characterize the stationary points as minima.
The molecular orbital plots were made using the Chemcraft program
package (http://www.chemcraftprog.com).
hydrogenation, it was thought worthwhile to study the
complexes of η5-Cp*Rh(III)/Ir(III) with chalcogenated pyr-
idine (half-pincer) ligands (L1−L3; see Chart 1) for catalyzing
Synthesis of L1. Sodium hydroxide (0.224 g, 6 mmol) dissolved in
5 cm3 of water was added dropwise to thiophenol (0.5 mL, ∼5 mmol)
taken in 50 cm3 of ethanol and refluxed for 0.5 h under N2
atmosphere. (2-Chloromethyl)pyridine hydrochloride (0.82 g, 5
mmol) dissolved in 20 cm3 of ethanol was added dropwise, and
refluxing of the mixture continued further for 3 h. After cooling to
room temperature the mixture was poured into 100 cm3 of distilled
water, neutralized with dilute sodium hydroxide, and extracted with
100 cm3 of chloroform. The extract was washed with water (3 × 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: 0.95 g, 95%. 1H NMR
(CDCl3, 25 °C vs Me4Si) δ (ppm): 4.26 (s, 2H, H5), 7.17−7.60 (m,
Chart 1
3
8H, H1−3, H7−9), 8.52 (d, JHH = 4.5 Hz, 1H, H10). 13C{1H} NMR
(CDCl3, 25 °C vs Me4Si) δ (ppm): 40.4 (C5), 122.0 (C7), 122.9 (C9),
126.2 (C3), 128.8 (C2), 129.5 (C1), 135.8 (C4), 136.5 (C8), 149.3
(C10), 157.6 (C6). HR-MS (CH3CN) [M + H]+ (m/z) = 202.0685;
calcd value for C12H12NS = 202.0685 (δ 0.00 ppm). IR (KBr, cm−1):
3056 (m; νC−H (aromatic)), 2924 (s; νC−H (aliphatic)), 1585 (m; νCN), 1474
(m; νCC (aromatic)), 748 (m; νC−H (aromatic)).
transfer hydrogenation of ketones and oxidation of secondary
alcohols. The results are promising and given in the present
paper. DFT studies have also been made and found to support
experimental results.
Synthesis of L2 and L3. Diphenyl diselenide/dipyridyl disulfide
(2.0 mmol) dissolved in 30 cm3 of ethanol was treated with a solution
(made in 5% NaOH) of NaBH4 (0.149 g, 4.0 mmol) (added
dropwise) under N2 atmosphere until it become colorless due to the
formation of PhSeNa/PySNa. (2-Chloromethyl)pyridine hydrochlor-
ide (0.6560 g, 4.0 mmol) dissolved in 5 cm3 of ethanol was mixed with
this colorless solution with constant stirring. The mixture was stirred
further for 3−4 h and poured into 100 cm3 of ice-cold distilled water
and extracted into CHCl3 (5 × 40 cm3). The extract was washed with
water (3 × 50 cm3) and dried over anhydrous sodium sulfate. Its
solvent was evaporated off under reduced pressure on a rotary
evaporator, resulting in a pale yellow oil, L2/L3, respectively.
L2: Yield: 0.92 g, 93%. 1H NMR (CDCl3, 25 °C vs Me4Si) δ
(ppm): 4.23 (s, 2H, H5), 7.08−7.61 (m, 8H, H1−3, H7−9), 8.51 (d, 3JHH
= 5.7 Hz, 1H, H10). 13C{1H} NMR (CDCl3, 25 °C vs Me4Si) δ (ppm):
33.7 (C5), 121 (C7), 122.9 (C9), 127.2 (C1), 128.9 (C2), 129.7 (C4),
133.4 (C3), 136.2 (C8), 149.2 (C10), 158.5 (C6). 77Se{1H} NMR
(CDCl3, 25 °C vs Me2Se) δ (ppm): 365.7. HR-MS (CH3CN) [M +
Na]+ (m/z) = 271.9949; calcd value for C12H12NSe = 271.9949 (δ 0.0
ppm). IR (KBr, cm−1): 3056 (m; νC−H (aromatic)), 2925 (s; νC−H (aliphatic)),
1585 (m; νCN (aromatic)), 1474 (m; νCC (aromatic)), 739 (m;
νC−H (aromatic)).
EXPERIMENTAL SECTION
■
Diphenyldiselenide, thiophenol, bis(2-pyridyl)disulfide, NaBH4, (2-
chloromethyl)pyridine hydrochloride, and ammonium hexafluoro-
phosphate procured from Sigma-Aldrich (USA) were used as received.
27
[(η5-Cp*)RhCl(μ-Cl)]2 and [(η5-Cp*)IrCl(μ-Cl)]228 were prepared
according to literature methods. All the solvents were dried and
distilled before use by standard procedures.29 Common reagents and
chemicals available locally were used. The H, 13C{1H}, and 77Se{1H}
1
NMR spectra were recorded on a Bruker Spectrospin DPX-300 NMR
spectrometer at 300.13, 75.47, and 57.24 MHz, respectively, with
chemical shifts reported in ppm relative to normal standards. Yields
refer to isolated yields of compounds that have purity ≥ 95%
1
[established by H NMR]. All reactions were carried out in glassware
dried in an oven, under ambient conditions, except the synthesis of L1,
L2, and L3. 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. Nitrogen atmosphere if required was created using
Schlenk techniques. IR spectra in the range 4000−400 cm−1 were
́
recorded on a Nicolet Protege 460 FT-IR spectrometer as KBr pellets.
L3: Yield: 0.74 g, 92%. 1H NMR (CDCl3, 25 °C vs Me4Si) δ
(ppm): 4.58 (s, 2H, H6), 6.96−7.62 (m, 6H, H2−4, H8−10), 8.43−8.45
(m, 1H, H1), 8.54−8.56 (m, 1H, H11). 13C{1H} NMR (CDCl3, 25 °C
vs Me4Si) δ (ppm): 35.8 (C6), 119.5 (C4), 121.9 (C2), 121.9 (C8),
123.1 (C10), 135.9 (C3), 136.5 (C9), 149.1 (C11), 149.2 (C1), 157.4
(C7), 158.1 (C5). HR-MS (CH3CN) [M + H]+ (m/z) = 203.0637;
calcd value for C11H11N2S = 203.0640 (δ −1.1 ppm). IR (KBr, cm−1):
3048 (m; νC−H (aromatic), 2924 (s; νC−H (aliphatic)), 1579 (m; νCN), 1475
(m; νCC (aromatic)), 746 (m; νC−H (aromatic)).
The C, H, and N analyses were carried out with a Perkin-Elmer 2400
Series II C, H, and N analyzer. For single-crystal structures the data
were collected with a Bruker AXS SMART Apex CCD diffractometer
using Mo Kα (0.71073 Å) radiation at 298(2) K. The software
SADABS30 was used for absorption correction (if needed) and
SHELXTL for space group, structure determination, and refine-
ments.31 Hydrogen atoms were included in idealized positions with
isotropic thermal parameters set at 1.2 times that of the carbon atom
to which they are attached in all cases. The catalytic oxidation yields
were determined with a NUCON Engineers (New Delhi, India) gas
chromatograph (with FID detector), model 5765, equipped with an
Alltech (EcTM‑1) column of 30 m length and 0.25 mm diameter and
having liquid film of 0.25 mm thickness. High-resolution mass spectral
measurements were performed with electron spray ionization (10 eV,
180 °C source temperature, sodium formate as reference compound)
on a Bruker MicroTOF-Q II, taking samples in CH3CN.
Synthesis of Complexes 1 and 2. The solid [(η5-Cp*)RhCl(μ-
Cl)]2 (0.05 g, 0.1 mmol) and L1 or L3 (0.2 mmol) dissolved in
CH3OH (15 cm3) were mixed, 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 cm3) with a rotary evaporator.
It was mixed with solid NH4PF6 (0.032 g, 0.2 mmol), and the resulting
orange-colored microcrystalline solid was filtered, washed with 10 cm3
of ice-cold CH3OH, and dried in vacuo. Single crystals of 1 or 2 were
obtained by diffusion of diethyl ether into its solution (1 cm3) made in
a mixture (1:4) of CH3OH and CH3CN.
All DFT calculations were carried out at the Department of
Chemistry, Supercomputing Facility for Bioinformatics and Computa-
tional Biology, IIT Delhi, with the GAUSSIAN-0332 programs with an
immediate objective of identifying the reactivity in the present series of
compounds. The geometry of complexes 1 to 6 was optimized at the
B3LYP33 level using a SDD basis set for metal atoms and chalcogen
and 6-31G* basis sets for C, N, and H. Geometry optimizations were
carried out without any symmetry restriction with X-ray coordinates of
the molecule. Harmonic force constants were computed at the
1: Yield: 0.076 g, 78%. Anal. Calcd for C22H26ClNRhS·[PF6]: C,
42.63; H, 4.23; N, 2.26. Found: C, 42.59; H, 4.19; N, 2.25. Mp: 206.0
°C. 1H NMR (CD3CN, 25 °C vs Me4Si) δ (ppm): 1.74 (s, 15H, H of
Me5Cp), 4.58−4.68 (m, 2H, H5), 7.01−8.08 (m, 8H, H1−3, H7−9), 8.60
(d, 3JHH = 4.8 Hz, 1H, H10). 13C{1H} NMR (CD3CN, 25 °C vs Me4Si)
δ (ppm): 8.0 (C of Me5Cp), 45.4 (C5), 99.2 (C of Cp), 123.7 (C7),
3380
dx.doi.org/10.1021/om300169p | Organometallics 2012, 31, 3379−3388

Organometallics
Article
Scheme 1. Synthesis of Ligands L1−L3 and Complexes 1−6
125.8 (C9), 126.9 (C3), 128.7 (C2), 129.1 (C1), 130.6 (C4), 140.1
(C8), 153.7 (C10), 159.4 (C6). HR-MS (CH3CN) [M]+ (m/z) =
474.0524; calcd value for C22H26ClNRhS = 474.0541 (δ −3.6 ppm).
IR (KBr, cm−1): 3068 (m; νC−H (aromatic)), 2928 (s; νC−H (aliphatic)), 1605
(m; νCN), 1477 (m; νCC (aromatic)), 837 (s; νP−F),762 (m;
νC−H(aromatic)).
(CH3CN) [M]+ (m/z) = 521.9967; calcd value for C22H26ClNRhSe =
521.9962 (δ 1.0 ppm). IR (KBr, cm−1): 3040 (m; νC−H (aromatic)), 2920
(s; νC−H (aliphatic)), 1605 (m; νCN), 1478 (m; νCC (aromatic)), 841 (s;
νP−F), 765 (m; νC−H (aromatic)).
Synthesis of Complexes 4−6. The solid [(η5-Cp*)IrCl(μ-Cl)]2
(0.05 g, 0.1 mmol) and L1, L2, or L3 (0.2 mmol) dissolved in CH3OH
(15 cm3) were mixed, and the mixture was stirred for 10 h at room
temperature. The resulting yellow solution was filtered. After reducing
the volume of the filtrate to ∼7 cm3 with a rotary evaporator, it was
mixed with solid NH4PF6 (0.032 g, 0.2 mmol). The resulting yellow-
colored microcrystalline solid was filtered, washed with 10 cm3 of ice-
cold CH3OH, and dried in vacuo. Single crystals of 4−6 were obtained
by diffusion of diethyl ether into their solution (1 cm3) made in a
mixture (1:4) of CH3OH and CH3CN:
2: Yield: 0.078 g, 80%. Anal. Calcd for C21H25ClN2RhS·[PF6]: C,
40.63; H, 4.06; N, 4.51. Found: C, 40.64; H, 4.02; N, 4.53. Mp: 210.0
°C. 1H NMR (CD3CN, 25 °C vs Me4Si) δ (ppm): 1.77 (s, 15H, H of
Me5Cp), 4.49−4.55 (m, 2H, H6), 7.19−8.04 (m, 6H, H2−4, H8−10),
3
8.22−8.24 (m, 1H, H1), 8.54 (d, JHH = 5.4 Hz, 1H, H11). 13C{1H}
NMR (CD3CN, 25 °C vs Me4Si) δ (ppm): 8.1 (C of Me5Cp), 42.1
(C6), 99.3 (C of Cp), 123.2 (C4), 123.7 (C2), 125.2 (C8), 125.9 (C10),
136.4 (C3), 139.5 (C9), 147.2 (C11), 149.4 (C1), 152.8 (C7), 160.6
(C5). HR-MS (CH3CN) [M]+ (m/z) = 475.0477; calcd value for
C21H25ClN2RhS = 475.0481 (δ −1.0). IR (KBr, cm−1): 3045 (m;
νC−H (aromatic)), 2922 (s; νC−H (aliphatic)), 1608 (m; νCN), 1453 (m;
νCC (aromatic)), 843 (s; νP−F), 765 (m; νC−H (aromatic)).
4: Yield: 0.096 g, 85%. Anal. Calcd for C22H26ClNIrS·[PF6]: C,
37.26; H, 3.70; N, 1.98. Found: C, 37.37; H, 3.47; N, 1.90. Mp: 221.0
°C. 13C{1H} NMR (CD3CN, 25 °C vs Me4Si) δ (ppm): 1.71 (s, 15H,
CpMe5), 4.40−4.46 (m, 2H, H5), 6.99−8.02 (m, 8H, H1−3, H7−9), 8.60
(d, 3JHH = 4.8 Hz, 1H, H10). 13C{1H} NMR (CD3CN, 25 °C vs Me4Si)
δ (ppm): 8.0 (C of Me5Cp), 47.9 (C5), 92.6 (C of Cp), 123.5 (C7),
126.6 (C9), 129.1 (C3), 129.6 (C2), 130.0 (C1), 130.1 (C4), 140.8
(C8), 154.5 (C10), 160.5 (C6). HR-MS (CH3CN) [M]+ (m/z) =
564.1089; calcd value for C22H26ClN2IrS = 564.1094 (δ −0.9 ppm). IR
(KBr, cm−1): 2967 (m; νC−H (aromatic)), 2924 (s; νC−H (aliphatic)), 1609
(m; νCN), 1479 (m; νCC (aromatic)), 845 (s; νP−F), 770 (m;
νC−H (aromatic)).
Synthesis of Complex 3. The mixture of solid [(η5-Cp*)RhCl(μ-
Cl)]2 (0.05 g, 0.1 mmol) and L2 (0.2 mmol) dissolved in CH3OH (15
cm3) was stirred for 10 h at room temperature. The resulting orange
solution was mixed with AgOTf (0.05 g, 0.2 mmol) dissolved in
CH3CN (15 cm3), and the mixture refluxed for 6 h. The precipitated
AgCl was filtered off. The yellow filtrate was mixed with solid NH4PF6
(0.064 g, 0.4 mmol), and the volume of the solution was reduced to
∼7 cm3 with a rotary evaporator. On addition of diethyl ether (7 cm3)
to the concentrate, 3 was precipitated. It was filtered, washed with 10
cm3 of CH3CN−diethyl ether mixture (1:5), dried in vacuo, and
recrystallized with a CH3CN−diethyl ether mixture (1:5). Single
crystals of 3 were obtained by diffusion of diethyl ether into its
solution (1 cm3) made in CH3CN. Yield: 0.10 g, 80%. Anal. Calcd for
C24H29N2RhSe·[PF6]2: C, 35.27; H, 3.58; N, 3.43. Found: C, 35.10; H,
5: Yield: 0.100 g, 85%. Anal. Calcd for C22H26ClNIrSe·[PF6]: C,
34.95; H, 3.47; N, 1.85. Found: C, 34.76; H, 3.34; N, 1.91. Mp: 203.0
1
°C. H NMR (CD3CN, 25 °C vs Me4Si) δ (ppm): 1.74 (s, 15H,
CpMe5), 4.38−4.86 (m, 2H, H5), 7.04−8.07 (m, 8H, H1−3, H7−9), 8.69
(d, 3JHH = 5.7 Hz 1H, H10). 13C{1H} NMR (CD3CN, 25 °C vs Me4Si)
δ (ppm): 7.8 (C of Me5Cp), 41.4 (C5), 91.6 (C of Cp), 124.1 (C7),
126.0 (C9), 128.9 (C1), 129.7 (C2), 129.8 (C4), 130.95 (C3), 140.0
(C8), 154.8 (C10), 161.0 (C6). 77Se{1H} NMR (CD3CN, 25 °C vs
Me2Se) δ (ppm): 339.4. HR-MS (CH3CN) [M]+ (m/z) = 612.0534;
calcd value for C22H26ClNIrSe = 612.0562 (δ: −4.6 ppm). IR (KBr,
cm−1): 3045 (m; νC−H (aromatic)), 2922 (s; νC−H (aliphatic)), 1608 (m;
νCN), 1453 (m; νCC (aromatic)), 843 (s; νP−F), 765 (m; νC−H (aromatic)).
6: Yield: 0.095 g, 85%. Anal. Calcd for C21H25ClN2IrS·[PF6]: C,
35.52; H, 3.55; N, 3.94. Found: C, 35.26; H, 3.42; N, 4.24. Mp: 213.0
1
4.69; N, 3.39. Mp: 199.0 °C. H NMR (CD3CN, 25 °C vs Me4Si) δ
(ppm): 1.55 (s, 15H, H of Me5Cp), 2.19 (s, 3H, CH3CN), 4.55−4.79
3
(m, 2H, H5), 7.23−8.05 (m, 8H, H1−3, H7−9), 8.67 (d, JHH = 5.4 Hz
1H, H10). 13C{1H} NMR (CD3CN, 25 °C vs Me4Si) δ (ppm): 8.5 (C
of Me5Cp), 23.7 (CH3 of CH3CN), 40.1 (C5), 99.1 (C of Cp), 125.0
(C7), 125.8 (C9), 129.2 (C1), 129.8 (C2), 130.3 (C4), 131.9 (C3),
134.1 (CN of CH3CN), 140.1 (C8), 154.63 (C10), 161.5 (C6).
77Se{1H} NMR (CD3CN, 25 °C vs Me2Se) δ (ppm): 380.8. HR-MS
3381
dx.doi.org/10.1021/om300169p | Organometallics 2012, 31, 3379−3388

Organometallics
Article
1
°C. H NMR (CD3CN, 25 °C vs Me4Si) δ (ppm): 1.77 (s, 15 H,
free L2. This kind of variation on coordination is not unusual in
view of the fact that iridium is a 5d element. In 1H and 13C{1H}
NMR spectra of 1−6 signals of protons and carbon atoms
generally appear at higher frequencies relative to those of free
ligands that coordinate with Rh and Ir in a half-pincer mode.
The magnitude of shift to higher frequency is large for CH2(E)
(E = S, Se): up to 4.24 ppm in 13C{1H) NMR, and for protons
attached to them up to 0.65 ppm. These observations imply the
coordination of ligands through S or Se. In the 1H and 13C{1H}
NMR spectra of 1−3, the signals of η5-pentamethylcyclopenta-
dienyl group (singlet in 1H NMR) were found shifted to lower
frequency by up to 0.3 and 3.3 ppm, respectively, with respect
to those of [(η5-Cp*)RhCl(μ-Cl)]2. This may be due to
substitution of Cl with S and Se, which have relatively lower
electronegativity. Similar observations regarding shifting of
signals with respect to those of [(η5-Cp*)IrCl(μ-Cl)]2 were
CpMe5), 4.39−4.82 (m, 2H, H6), 7.21−8.05 (m, 6H, H2−4, H8−10),
8.25−8.26 (m, 1H, H1), 8.46 (d, JHH = 5.9 Hz, 1H, H11). 13C{1H}
3
NMR (CD3CN, 25 °C vs Me4Si) δ (ppm): 9.0 (CpMe5), 45.6 (C6),
93.6 (Cp), 124.4 (C4), 125.0 (C2), 127.0 (C8), 127.4 (C10), 137.8
(C3), 141.1 (C9), 147.6 (C11), 150.9 (C1), 154.6 (C7), 162.6 (C5).
HR-MS (CH3CN) [M]+ (m/z) = 565.1042; calcd value for
C21H25ClN2IrS = 565.1067 (δ −4.5 ppm). IR (KBr, cm−1): 2943
(m; νC−H (aromatic)), 2923 (s; νC−H (aliphatic)), 1611 (m; νCN), 1453 (m;
νCC (aromatic)), 843 (s; νP−F), 768 (m; νC−H (aromatic)).
Mass and 77Se{1H} NMR, 1H NMR, and 13C{1H} NMR spectra are
given in the Supporting Information (Figures S1−S10, S18−S35).
Procedure for Catalytic Transfer Hydrogenation. The ketone
(1 mmol), KOH (2 cm3 of a 0.2 M solution in 2-propanol), and a
complex from 1 to 6 (0.01 mol % dissolved in CH3CN) were added to
15 cm3 of 2-propanol, and the mixture was refluxed (80 °C) for 3 (1−
3) or 5 h (4−6). 2-Propanol was removed on a rotary evaporator, and
the resulting semisolid was extracted with diethyl ether (3 × 20 cm3).
The extract was passed through a short column (∼8 cm) of silica gel.
The column was washed with ∼50 cm3 of diethyl ether. All the eluates
from the column were mixed, and the solvent from the mixture was
evaporated off on a rotary evaporator. The resulting residue was
dissolved in 2−3 cm3 of hexane and subjected to GC. The final
conversions are reported as an average of two runs of each catalytic
reaction.
1
made in H and 13C{1H} NMR spectra of 4−6.
Crystal Structures. The crystallographic and refinement
data for 1−6 are summarized in the Supporting Information
(Tables S1 and S2). L1, L2, and L3 exhibit an identical bonding
mode in all complexes 1−6; that is, a five-membered ring is
formed by their coordination to both the metal centers. The
rhodium and iridium complexes have similar molecular
structures. The ORTEP diagrams of cations of 1−6 are given
in Figures 1 to 6 with selected bond lengths and angles. In these
Procedure of Catalytic Oxidation of Alcohols with NMO. A
solution of a complex from 1−6 (0.01 mol %) dissolved in 20 cm3 of
CH2Cl2 was mixed with alcohol substrate (1 mmol), K2CO3 (1.2
mmol), and solid NMO (1.2 mmol). The mixture was refluxed for 3
(1−3) or 4 h (4−6). Thereafter the solvent was evaporated off with a
rotary evaporator. The residue having an oxidized product was
extracted with 20 cm3 of petroleum ether (60−80 °C). The complex-
catalyst undissolved in petroleum ether was recovered almost
quantitatively for the next catalytic cycle. The oxidized product
present in petroleum ether extract was analyzed by GC.
RESULTS AND DISCUSSION
■
The syntheses of L1−L3 and their complexes have been
summarized in Scheme 1. The present procedures for the
synthesis of L1 and L2 are distinct from earlier known
ones34 40 and give relatively higher yields, up to 95%. The
−
important modifications are (i) ArS− or ArSe− was prepared in
refluxing conditions and reacted with 2-chloromethylpyridine
hydrochloride under similar conditions. Thus the reaction time
for maximum yield in our case was short, and (ii) extraction of
reaction product was carried out with chloroform, resulting in
higher purity. Complex 3 was synthesized by substitution of Cl
with CH3CN, as single crystals of the species containing a
chloro group could not be grown. The ligands L1−L3 have
good solubility in common organic solvents, viz., CHCl3,
CH2Cl2, CH3OH, and CH3CN, while complexes 1−6 are
moderately soluble in common organic solvents such as CHCl3,
CH2Cl2, and CH3OH, but have good solubility in CH3CN. The
pale yellow liquids L1−L3 are stable in air and moisture and
can be stored at room temperature for several months. The
solutions of complexes 1−6 made in CH3CN are also stable for
several months under ambient conditions.
NMR Spectra. The NMR spectral data for ligands L1−L3
and complexes 1−6 are consistent with their structures, which
are established by single-crystal X-ray diffraction in the case of
the complexes. The signal in the 77Se{1H} NMR spectrum of 3
appears shifted to a higher frequency by ∼15 ppm in
comparison to that of free L2. Probably it arises due to
coordination of L2 with Rh through Se. In the case of complex
5 the signal in the 77Se{1H} NMR spectrum has been observed
shifted to lower frequency by ∼24 ppm with respect to that of
Figure 1. ORTEP diagram of the cation of 1 with ellipsoids at the 30%
probability level. Hydrogen atoms and the PF6 anions have been
omitted for clarity. Bond lengths (Å): Rh−S(1) 2.383(2), Rh−N(1)
2.133(5), Rh(1)−Cl(1) 2.407(2), Rh−C 2.154(6)−2.202(7). Bond
angles (deg): S(1)−Rh(1)−N(1) 81.60(2), C(1)−S(1)−Rh(1)
112.2(2), S(1)−Rh(1)−Cl(1) 84.34(6).
−
cations there is a pseudo-octahedral half-sandwich “piano-stool”
disposition of donor atoms around the metal center (Rh and
Ir). The centroid of the η5-Cp* ring occupies nearly the center
of a triangular face of an octahedron. A chelate ring with the
metal center is formed through nitrogen and chalcogen atoms,
and a chlorine atom completes the coordination sphere. This
results in an overall three-legged piano-stool conformation.
The structures of cations of complexes 1 to 3 are similar,
with a five-membered chelate ring, except that in 3 in place of
Cl there is a CH3CN molecule coordinated with metal (Figures
1−3). The Rh−S bond distances in 1 [2.383(2) Å] and 2
[2.353(2) Å] are consistent with each other and with the values
reported for complexes [η5-Cp*RhCl(1,1′-(1,2-ethanediyl)bis-
(3-methylimidazole-2-thione)]Cl [2.3967(11) Å]12 and [η5-
Cp*RhCl{η2-S,P-Ph2P(S)NHPPh2}]BF4 [2.404(3) Å].41 The
Rh−Se bond length of cation 3 [2.487(1) Å] is a little shorter
than that of complex [η5-Cp*RhCl{η2-(SePPh2)2N}]BF4
3382
dx.doi.org/10.1021/om300169p | Organometallics 2012, 31, 3379−3388

Organometallics
Article
Figure 2. ORTEP diagram of the cation of 2 with ellipsoids at the 30%
−
probability level. Hydrogen atoms and the PF6 anions have been
Figure 4. ORTEP diagram of the cation of 4 with ellipsoids at the 30%
probability level. Hydrogen atoms and the PF6 anions have been
omitted for clarity. Bond lengths (Å): Ir−S(1) 2.343(2), Ir−N(1)
2.105(5), Ir(1)−Cl(1) 2.391(2), Ir−C 2.165(7)−2.184(6). Bond
angles (deg): S(1)−Ir(1)−N(1) 81.70(2), C(1)−S(1)− Ir(1)
115.8(2), S(1)− Ir(1)−Cl(1) 96.12(6).
−
omitted for clarity. Bond lengths (Å): Rh−S(1) 2.353(2), Rh−N(1)
2.091(4), Rh(1)−Cl(1) 2.376(2), Rh−C 2.143(5)−2.160(7). Bond
angles (deg): S(1)−Rh(1)−N(1) 81.70(2), C(1)−S(1)−Rh(1)
112.70(2), S(1)−Rh(1)−Cl(1) 96.66(6).
Figure 3. ORTEP diagram of the cation of 3 with ellipsoids at the 30%
−
probability level. Hydrogen atoms and the PF6 anions have been
omitted for clarity. Bond lengths (Å): Rh−Se(1) 2.487(1), Rh−N(1)
2.129(5), Rh−N(2) 2.074(6), Rh−C 2.156(6)−2.171(6). Bond angles
(deg): Se(1)−Rh(1)−N(1) 82.80(2), C(1)−Se(1)−Rh(1) 107.1(2),
Se(1)−Rh(1)−N(2) 92.40(2), N(2)−−Rh(1)−−N(1) 84.2(2).
Figure 5. ORTEP diagram of the cation of 5 with ellipsoids at the 30%
probability level. Hydrogen atoms and the PF6 anions have been
omitted for clarity. Bond lengths (Å): Ir−Se(1) 2.453(1), Ir−N(1)
2.106(6), Ir(1)−Cl(1) 2.388(2), Ir−C 2.174(8)−2.178(7). Bond
angles (deg): Se(1)−Ir(1)−N(1) 82.40(2), C(1)−Se(1)− Ir(1)
113.4(3), Se(1)− Ir(1)−Cl(1) 95.84(6).
−
[2.5266(8) Å]19 and somewhat larger than the values reported
for the half-sandwich complex of Rh(III) with the [1,2-dicarba-
closo-dodecaborane-1,2-dichalcogenolato] ligand [2.3833(5)−
2.4706(6) Å].15 The Rh−N bond distance of 1 [2.133(5) Å] is
consistent with those of 2 and 3 [2.091(4) and 2.129(5) Å,
respectively] and also with those of complex [η5-Cp*Rh(2,6-
(mesityl)2C6H3S)(bpy)][B(3,5-(CF3)2C6H3)4] [2.099(3)−
2.103(3) Å].42 The Rh−C (Cp* centroid) distances of
complexes 1−3 are in the range 1.780−1.795 Å, which is
normal.41
The molecular structures of cations of iridium complexes 4−
6 are shown in Figures 4−6. The Ir−S bond distance for 4 is
2.343(2) Å, consistent with that of 6 [2.341(3) Å]. Both are
also within the range of 2.318(1)−2.3872(10) Å for the
reported Ir−S bond lengths of [η5-Cp*Ir-(CO)(μ-STol)Pt-
(STol)(PPh3)],13 [η5-Cp*Ir(η2-ppy-S-p-tol)(H2O)][OTf]2,43
[η5-Cp*Ir(4,6-di-tert-butyl-(2-methylthiophenylimino)-o-
benzoquinone](PF6)·CH2Cl2,44 and [η5-Cp*Ir(nBuPPh2)({7-
(S)PPh2}-8-S-7,8-C2B9H10)].45 The Ir−Se distance [2.453(1)
Å] in 5 is longer than the values reported for complex [η5-
Cp*Ir{Se2C2(CO2Me)2}] (2.3494(7) and 2.3520(7) Å).46 The
Ir−Se bond distances reported for half-sandwich complexes
[η5-Cp*IrCl(μ-SeCOC6H5)(κ2-SeCOC6H4−)Ir(η5-Cp*)]
(2.445(2)−2.495(1) Å)47 and [η5-Cp*Ir(μ3-Se)2{PtTol-
(PPh3)}2] [2.416(1)−2.422(1) Å]13 are consistent with those
of 5. The Ir−N bond length of the cation of 4, 2.105(5) Å, is
similar to that of cations of 5 and 6 [2.106(6) and 2.099(8) Å,
respectively]. They are shorter than the values of the half-
sandwich complex of Ir(III) with 2-(1-benzyl-1H-1,2,3-triazol-
4-yl)pyridine (2.151(2)−2.159(7) Å).48 The Ir−η5-Cp*-
(centroid) distances (Å) in 4 [1.800 Å], 5 [1.801 Å], and 6
[1.781 Å] are consistent with each other and with the reported
49
values for complexes [(η5-Cp*)Ir(phpy)Cl] [1.863 Å]. PF6
−
has been found involved in C−H···F secondary interactions in
all the complexes 1−6, resulting in chains. In Figure 7 they are
shown for complex 2 along with the distances. The secondary
interactions for other complexes are given in the Supporting
Information, Figures S13−S17. The noncovalent interactions of
C−H···F distances (Å) of 1−6 have also been included in the
Supporting Information, Table S6.
3383
dx.doi.org/10.1021/om300169p | Organometallics 2012, 31, 3379−3388

Organometallics
Article
Scheme 2
Table 1. Complexes 3 and 5 are the most efficient catalysts
among 1−6. On monitoring the transfer hydrogenation
reactions catalyzed with 3 and 5 by 77Se{1H} NMR
spectroscopy, it is observed that the signals in the spectra
shift to higher frequency (18−23 ppm), indicating that
probably the M−Cl (in the case of 3, Rh−NCCH3) bond is
cleaved or weakened very significantly to make a coordination
site on the metal center available so that formation of an
intermediate having a M−H bond can take place.53 The
transfer hydrogenation reactions catalyzed with 3 and 5 were
monitored with 1H NMR spectra. After 1 h a broad singlet was
noticed around δ −8.8 and −12.1 ppm, respectively. These
signals are characteristic of hydrides and indicate the formation
of a M−H bond.2 Thus catalytic reactions with the present
complexes probably proceed via formation of a metal−hydride
complex intermediate
The catalytic efficiency varies with chalcogen ligands in the
order Se > S, when other coligands are the same, which may be
tailored by a stronger electron-donating tendency of Se toward
the metal center, thus promoting the formation of hydride with
it. The rhodium complexes show better catalytic efficiency in
comparison to analogous iridium complexes.54 The formation
of a M−H-containing intermediate and the absence of a NH
group in the system suggest that transfer hydrogenation by 1−6
is catalyzed by a conventional mechanism. The Rh(III) species
appears to be a better catalyst than Ir(III), which is supported
by DFT calculation results, which suggest greater reactivity for
rhodium species.
Figure 6. ORTEP diagram of the cation of 6 with ellipsoids at the 30%
probability level. Hydrogen atoms and the PF6 anions have been
omitted for clarity. Bond lengths (Å): Ir−S(1) 2.341(3), Ir−N(1)
2.099(8), Ir(1)−Cl(1) 2.379(3), Ir−C 2.110(1)−2.150(1). Bond
angles (deg): S(1)−Ir(1)−N(1) 82.0(3), C(1)−S(1)− Ir(1) 114.7(4),
S(1)− Ir(1)−Cl(1) 95.40(1).
−
CATALYTIC STUDIES
■
Transfer Hydrogenation of Ketones. The transfer
hydrogenation reaction in which hydrogen is transferred from
one organic molecule to another is of great importance in
organic synthesis since one can avoid the use of molecular
hydrogen.50 Transfer hydrogenation of ketones has been
catalyzed by a number of ruthenium species including half-
sandwich ones.25,26 However, Rh and Ir complexes, particularly
half-sandwich type, are little explored. The catalytic reactions in
their presence many times necessitate high temperature and
inert atmosphere.51 However, transfer hydrogenation reactions
of ketones (Scheme 2) can be catalyzed with present complexes
1−6 (0.01 mol %) at a moderate temperature of 80 °C. The
high efficiency of the reduction of ketones to their
corresponding alcohols with 2-propanol as hydrogen donor
was exhibited in the presence of KOH, which was earlier
reported to be the best inorganic base for such reactions.52 The
most efficient conversions (up to 98%) were found in the case
of acetophenone with all the catalysts, while in the case of
aliphatic secondary ketones the conversions were up to 92%.
The details of percent conversions and TONs are given in
Oxidation of Secondary Alcohols. A number of
transition-metal systems have been used for the catalysis of
oxidation of alcohols using oxygen or hydrogen peroxide as an
oxidant.55 Oppenauer-type oxidation of alcohols in which
acetone has been used as an oxidant is among the promising
methods for the oxidation.3 We have examined the oxidation of
Figure 7. Noncovalent interaction diagram showing the C−H···F interactions in 2. Distances [Å]: C(5)−H(5)···F(2) 2.447(6), C(9)−H(9)···F(3)
2.452(6), C(17)−H(17A)···F(4) 2.490(1).
3384
dx.doi.org/10.1021/om300169p | Organometallics 2012, 31, 3379−3388

Organometallics
Article
Table 1. Transfer Hydrogenation of Ketones
secondary alcohols in the presence of 1−6 (0.01 mol %)
(Scheme 3) in which NMO has been used as an oxidant at 80
°C with K2CO3 in CH2Cl2. Maximum conversions were
reached in 3 h with catalysts 1−3 and in 4 h with catalysts
4−6 (Scheme 3). The products were identified by GC after
recovering the catalyst and doing the required workup. The
percent conversion and TON results has been summarized in
Table 2. On monitoring the reactions catalyzed with 3 and 5 by
Scheme 3
Table 2. Oxidation of Secondary Alcohols
3385
dx.doi.org/10.1021/om300169p | Organometallics 2012, 31, 3379−3388

Organometallics
Article
catalyzing oxidation than their S analogues containing similar
coligands. Similarly Rh(III) species are somewhat better
catalysts than Ir(III) species, which has been corroborated by
the DFT calculations given below
Scheme 4. Proposed Mechanism of Oxidation of Alcohol
DFT Calculations. In an attempt to further understand the
nature of bonding within these complexes and the reactivity,
density functional theory (DFT) calculations (see Experimental
Section for details) were performed for all six complexes 1−6.
While the accuracy of calculations incorporating late transition
metals is insufficient to warrant a detailed discussion of MO
energy levels, an analysis of the lowest energy configurations
and frontier orbitals can provide a qualitative insight into the
bonding, etc., characteristics of the complexes. The HOMOs
(highest occupied molecular orbitals) of all complexes are
essentially identical and are positioned primarily over the metal
center and Cp* ring, with some contribution toward chalcogen
and Cl (if present) donors (see Figure 8 for complexes 1, 3, 4,
and 5, and for complexes 2 and 6 see the Supporting
Information, Figure S16). The agreement between the
experimentally observed bonding parameters and the calculated
one is better for M−Cl, M−N, and M−Cp* (centroid). For
details see the Supporting Information (Table S4). The
differences between calculated and observed M−E (E = S or
Se) bond distances (0.13−0.19 Å) are not very unusual. The
calculated and experimentally found bond angles are also very
close (Table S4) except in a few cases, e.g., S−Rh−Cl.
1
77Se{1H} and H NMR spectra, as examples, it has been found
that the signal in the 77Se{1H} NMR spectrum is shifted to
higher frequency (20−27 ppm) in the course of the reaction. In
the H NMR spectra new signals at δ −9.1 and −12.5 ppm
appear in the case of 3 and 5, respectively. These signals may be
ascribed to the formation of metal hydride species.3 Thus the
oxidation of secondary alcohols appears to be catalyzed by 1−6
via a pathway suggested in Scheme 4. Like transfer hydro-
genation, Se ligand containing complexes are more efficient for
1
The absolute values for the HOMO energy levels cannot be
reliably determined for complexes of heavy metals. However,
relative energy levels are informative. It has been previously
reported that there is a direct correlation between the
HOMO−LUMO energy gap of a complex and its chemical
reactivity.56−58 The larger gap reflects lower reactivity. The
Figure 8. Graphical representations of HOMOs for 1, 3, 4, and 5.
3386
dx.doi.org/10.1021/om300169p | Organometallics 2012, 31, 3379−3388

Organometallics
Article
Figure 9. Partial charges in coordination spheres of 1, 3, 4, and 5.
HOMO−LUMO energy gaps between 1 and 4, 2 and 6, and 3
and 5 sufficiently differ in energy (Table S5), indicating that
reactivities of Rh complexes are greater than those of Ir
complexes. This is consistent with the observed catalytic
efficiency of complexes of two metals. Mulliken partial charge
analyses for 1−6 show that the partial atomic charge on the Rh
center is greater than that on the Ir center (Figure 9), which
further supports the above conclusion. The charges on the
other atoms are given in the Supporting Information (Table S5,
Figure S17).
ASSOCIATED CONTENT
* Supporting Information
Crystal and refinement data, bond lengths and angles,
■
S
1
secondary interaction distances and their figures, H NMR,
13C{1H} NMR, 77Se{1H} NMR, and mass spectra, CIFs, and
DFT calculation data [figures of HOMOs, partial charge
diagrams, table of calculated bond lengths and angles, table of
HOMO−LUMO energy gap and partial charges] are included.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Notes
The authors declare no competing financial interest.
■
CONCLUSION
■
Half-sandwich “piano-stool” complexes [(η5-Cp*)Rh(L)Cl]-
[PF6], [(η5-Cp*)Rh(L2)CH3CN][PF6]2, and [(η5-Cp*)Ir(L)-
Cl][PF6] (1−6) of chalcogenated pyridine ligands (L1−L3)
have been synthesized and characterized by multinuclei NMR,
HR-MS, and X-ray crystallography. The complexes are the first
examples of half-sandwich complexes of rhodium(III)/iridium-
(III) with (Se/S, N) ligands explored for transfer hydro-
genation of ketones and oxidation of secondary alcohols. They
show promising TON values [transfer hydrogenation reactions
of ketones up to 9.8 × 103, oxidation of secondary alcohols up
to 9.6 × 103]. Their air and moisture stability is an additional
advantage. The catalytic activities follow the orders Rh > Ir and
Se > S, which are corroborated by DFT studies. The formation
of the M−H bond has been noticed in the intermediates of
both catalytic reactions.
ACKNOWLEDGMENTS
■
The authors thank the Department of Science and Technology,
New Delhi (India), for project no. SR/S1/IC-40/2010. The
partial financial assistance given by DST (India) to establish
single-crystal X-ray diffraction and mass spectral facilities at IIT
Delhi, New Delhi (India), under its FIST programme is
gratefully acknowledged. O.P. and P.S. thank University Grants
Commission (India) for the award of a Junior/Senior Research
Fellowship. The authors thank Prof. B. Jayaram for computa-
tional facilities.
REFERENCES
■
(1) Crabtree, R. H. In The Organometallic Chemistry of the Transition
Metals, 3rd ed.; Wiley-Interscience: New York, 2001; Chapter 5, p 129.
3387
dx.doi.org/10.1021/om300169p | Organometallics 2012, 31, 3379−3388

Organometallics
Article
(2) Hanasaka, F.; Fujita, K.; Yamaguchi, R. Organometallics 2005, 24,
4322.
(3) Hanasaka, F.; Fujita, K.; Yamaguchi, R. Organometallics 2004, 25,
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.
1490.
(33) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.;
Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(34) Canovese, L.; Visentin, F.; Chessa, G.; Uguagliati, P.; Levi, C.;
Dolmella, A. Organometallics 2005, 24, 5537.
(4) Kawahara, R.; Fujita, K.; Yamaguchi, R. J. Am. Chem. Soc. 2010,
132, 15108.
(5) Wu, X.; Vinci, D.; Ikariya, T.; Xiao, J. Chem. Commun. 2005,
4447.
(35) Tresoldi, G.; Baradello, L.; Lanza, S.; Cardiano, P. Eur. J. Inorg.
Chem. 2005, 2423.
(36) Reisner, E.; Abikoff, T. C.; Lippard, S. J. Inorg. Chem. 2007, 46,
(6) Cross, D. J.; Houson, I.; Kawamoto, A. M.; Wills, M. Tetrahedron
Lett. 2004, 45, 843.
(7) Thorpe, T.; Blacker, J.; Brown, S. M.; Bubert, C.; Crosby, J.;
Fitzjohn, S.; Muxworthy, J. P.; Williamsa, J. M. J. Tetrahedron Lett.
2001, 42, 4041.
10229.
(37) Haviv, F.; DeNet, R. W.; Michaels, R. J.; Ratajczyk, J. D.; Carter,
G. W.; Young, P. R. J. Med. Chem. 1983, 26, 218.
(38) Lim, S. F.; Harris, B. L.; Blanc, P.; White, J. M. J. Org. Chem.
2011, 76, 1673.
(39) (a) Grieco, P. A.; Jaw, J. Y. J. Org. Chem. 1981, 46, 1215.
(b) Trost, B. M.; Braslau, R. J. Org. Chem. 1988, 53, 532.
(40) Jones, R. C.; Skelton, B. W.; Tolhurst, V.-A.; White, A. H.;
Wilson, A. J.; Canty, A. J. Polyhedron 2007, 26, 708.
(8) Cortez, N. A.; Aguirre, G.; Parra-Hake, M.; Somanathan, R.
Tetrahedron Lett. 2007, 48, 4338.
(9) Wu, X.; Li, X.; Zanotti-Gerosa, A.; Pettman, A.; Liu, J.; Mills, A.
J.; Xiao, J. Chem.Eur. J. 2008, 14, 2209.
(10) Ahlford, K.; Lind, J.; Maler, L.; Adolfsson, H. Green Chem. 2008,
̈
10, 832.
(11) Furegati, M.; Rippert, A. J. Tetrahedron: Asymmetry 2005, 16,
3947.
(12) Jia, W.-G.; Huang, Y.-B.; Lin, Y.-J.; Jin, G.-X. Dalton Trans.
2008, 5612.
(13) Nakagawa, T.; Seino, H.; Mizobe, Y. Organometallics 2010, 24,
́
(41) Simοn-Manso, E.; Valderrama, M.; Gantzel, P.; Kubiak, C. P. J.
Organomet. Chem. 2002, 651, 90.
(42) Sakamoto, M.; Ohki, Y.; Tatsumi, K. Organometallics 2010, 29,
1761.
(43) Sau, Y. K.; Yi, X. Y.; Chan, K. W.; Lai, C. S.; Williams, I. D.;
Leung, W. H. J. Organomet. Chem. 2010, 695, 1399.
2254.
(14) Nakagawa, T.; Seino, H.; Nagao, S.; Mizobe, Y. Angew. Chem.,
Int. Ed. 2006, 45, 7758.
(15) Herberhold, M.; Yan, H.; Milius, W.; Wrackmeyer, B.
(44) Hubner, R.; Weber, S.; Strobel, S.; Sarkar, B.; Zal
Organometallics 2011, 30, 1414.
́
is,
̌
S.; Kaim, W.
̈
(45) Huo, X. K.; Su, G.; Jin, G. X. Chem.Eur. J. 2010, 16, 12017.
(46) Nagao, S.; Seino, H.; Okada, T.; Mizobe, Y.; Hidai, M. J. Chem.
Soc., Dalton Trans. 2000, 3546.
(47) Kumbhare, L. B.; Wadawale, A. P.; Jain, V. K.; Sieger, M.; Kaim,
W. Inorg. Chem. Commun. 2010, 13, 475.
Organometallics 2000, 19, 4289.
(16) Xiao, X.-Q.; Lin, Y.-J.; Jin, G.-X. Dalton Trans. 2008, 2615.
(17) Zhang, J.-S.; Lin, Y.-J.; Jin, G.-X. Dalton Trans. 2009, 111.
(18) Huo, X.-K.; Su, G.; Jin, G.-X. Dalton Trans. 2010, 39, 1954.
(19) Valderrama, M.; Contreras, R.; Lamata, M. P.; Viguri, F.;
Carmona, D.; Lahoz, F. J.; Elipe, S.; Oro, L. A. J. Organomet. Chem.
2000, 607, 3.
(48) Lalrempuia, R.; Muller-Bunz, H.; Albrecht, M. Angew. Chem., Int.
̈
Ed. 2011, 50, 9969.
(49) Liu, Z.; Salassa, L.; Habtemariam, A.; Pizarro, A. M.; Clarkson,
G. J.; Sadler, P. J. Inorg. Chem. 2011, 50, 5777.
(20) Bhattacharyya, P.; Slawin, A. M. Z.; Smith, M. B. J. Chem. Soc.,
Dalton Trans. 1998, 2467.
(50) (a) Palmer, M. J.; Wills, M. Tetrahedron: Asymmetry 1999, 2045.
(b) Gladiali, S.; Mestroni, G. In Transition Metals for Organic Synthesis;
Beller, M., Bolm, C., Eds.; Wiley-VCH: Weinheim, 1998; p 97.
(51) (a) Cortez, N. A.; Aguirre, G.; Parra-Hake, M.; Somanathan, R.
Tetrahedron Lett. 2009, 50, 2228. (b) Wu, X.; Xiao, J. Chem. Commun.
2007, 46, 2449. (c) Raja, M. U.; Ramesh, R.; Ahn, K. H. Tetrahedron
Lett. 2009, 50, 7014.
(21) Levason, W.; Orchard, S. D.; Reid, G.; Street, J. M. J. Chem. Soc.,
Dalton Trans. 2000, 2537.
(22) Das, D.; Rao, G. K.; Singh, A. K. Organometallics 2009, 28, 6054.
(23) Yao, Q.; Kinney, E. P.; Zheng, C. Org. Lett. 2004, 6, 2997.
(24) Rao, G. K.; Kumar, A.; Ahmed, J.; Singh, A. K. Chem. Comun.
2010, 46, 5954.
(25) Singh, P.; Singh, A. K. Organometallics 2010, 29, 6433.
(26) Singh, P.; Singh, A. K. Eur. J. Inorg. Chem. 2010, 4187.
(27) Kang, W.; Moseley, K.; Maitlis, P. M. J. Am. Chem. Soc. 1969, 91,
5970.
(28) White, C.; Yates, A.; Maitlis, P. M. Inorg. Synth. 1992, 29, 228.
(29) 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 UK Ltd., 1989.
(52) Turkmen, H.; Pape, T.; Hahn, F. E.; C
metallics 2008, 27, 571.
̧
etinkaya, B. Organo-
̈
(53) 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.
(54) (a) Ito, M.; Endo, Y.; Tejima, N.; Ikariya, T. Organometallics
2010, 29, 2397. (b) Singh, S. K.; Dubey, S. K.; Pandey, R.; Mishra, L.;
Zou, R.-Q.; Xu, Q.; Pandey, D. S. Polyhedron 2008, 27, 2877.
(55) (a) Sato, K.; Aoki, M.; Takagi, J.; Noyori, R. J. Am. Chem. Soc.
1997, 119, 12386. (b) Nishimura, T.; Onoue, T.; Ohe, K.; Uemura, S.
Tetrahedron Lett. 1998, 39, 6011. (c) Mori, K.; Yamaguchi, K.; Hara,
T.; Mizugaki, T.; Ebitani, K.; Kaneda, K. J. Am. Chem. Soc. 2002, 124,
11572. (d) Jensen, D. R.; Schultz, M. J.; Mueller, J. A.; Sigman, M. S.
Angew. Chem., Int. Ed. 2003, 42, 3810. (e) Iwasawa, T.; Tokunaga, M.;
Obora, Y.; Tsuji, Y. J. Am. Chem. Soc. 2004, 126, 6554.
(56) (a) Mebi, C. A. J. Chem. Sci. 2011, 123, 727. (b) Chattaraj, P. K.;
Maiti, B. J. Am. Chem. Soc. 2003, 125, 2705.
(57) (a) Pearson, R. G. Acc. Chem. Res. 1993, 26, 250. (b) Parr, P. G.;
Pearson, R. G. J. Am. Chem. Soc. 1983, 105, 7512.
(58) (a) Parr, R. G.; Szentpaly, L.; Liu, S. J. Am. Chem. Soc. 1999,
121, 1922. (b) Liu, S. J. Chem. Sci. 2005, 117, 477.
(30) Sheldrick, G. M. SADABS V2.10; 2003.
(31) (a) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. 1990, 46,
467. (b) Sheldrick, G. M. SHELXL-NT, Version 6.12; University of
Gottingen: Germany, 2000.
(32) Frisch, M. J.; Trucks, G. W.; Schlegel, H. A.; Scuseria, G. E.;
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.;
3388
dx.doi.org/10.1021/om300169p | Organometallics 2012, 31, 3379−3388