Synthesis, structures and catalytic activities of ruthenium(ii) carbonyl chloride complexes containing pyridine-functionalised N-heterocyclic carbenes

Article abstract of DOI:10.1039/b904882k

A series of ruthenium(ii) carbonyl chloride complexes with pyridine-functionalised N-heterocyclic carbenes, trans(Cl)- and cis(Cl)-[Ru(Py-NHC)(CO)₂Cl₂] [Py-NHC = 3-tert-butyl-1-(2-pyridyl)imidazol-2-ylidene, 1a and 1b; 3-n-butyl-1-(2

Full text of DOI:10.1039/b904882k

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N-Heterocyclic Carbenes
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Westfälische Wilhelms-Universität, Münster, Germany
Published in issue 35, 2009 of Dalton Transactions
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www.rsc.org/dalton | Dalton Transactions
Synthesis, structures and catalytic activities of ruthenium(II) carbonyl chloride
complexes containing pyridine-functionalised N-heterocyclic carbenes†
a
a
a
a
a
b
Yong Cheng, Hui-Jun Xu, Jia-Feng Sun, Yi-Zhi Li, Xue-Tai Chen* and Zi-Ling Xue
Received 10th March 2009, Accepted 15th June 2009
First published as an Advance Article on the web 22nd July 2009
DOI: 10.1039/b904882k
A series of ruthenium(II) carbonyl chloride complexes with pyridine-functionalised N-heterocyclic
carbenes, trans(Cl)- and cis(Cl)-[Ru(Py–NHC)(CO)
2
Cl
2
] [Py–NHC = 3-tert-butyl-1-
(
2-pyridyl)imidazol-2-ylidene, 1a and 1b; 3-n-butyl-1-(2-pyridyl)imidazol-2-ylidene, 2a and 2b;
3-tert-butyl-1-picolylimidazol-2-ylidene, 3a and 3b; 3-n-butyl-1-picolylimidazol-2-ylidene, 4a and 4b;
3
-benzyl-1-picolylimidazol-2-ylidene, 5a and 5b] have been prepared by transmetallation from the
1
corresponding silver carbene complexes and characterised by elemental analyses, infrared and H and
1
3
C NMR spectroscopies. The yields of trans(Cl)- and cis(Cl)-isomers could be controlled by altering
the reaction conditions: the trans-isomers were kinetically formed as the main products in 60–70% yield
in CH Cl at ambient temperature while the thermodynamic cis-isomers were obtained as the major
products in 70–80% yield in toluene at refluxing temperature. The trans-isomer was transformed into
2
2
the thermodynamic cis-isomer by heating in CH
2
Cl in a Teflon-lined stainless autoclave for 24 h at
2
◦
120 C. The molecular structures of 1a, 1b, 2b, and 4b have been determined by single-crystal X-ray
diffraction. These complexes showed catalytic activities in hydrogen transfer reactions of ketones.
Introduction
functionalised NHC Ru(II) nitrosyl complexes and their catalytic
35
activity in hydrogen transfer of ketones.
The Ru(II) carbonyl chloride complexes [Ru(L)(CO)
taining bpy, bipy, dmbpy, or PR ligands have been intensively
N-Heterocyclic carbenes (NHCs) have attracted increasing atten-
tion as they have been proven to act as efficient spectator ligands
2
2
Cl ] con-
3
1
–6
in coordination chemistry and homogeneous catalysis. In many
cases NHC complexes show higher thermal stability and catalytic
activities than their phosphine counterparts partially owing to
the strong metal–NHC bonds and the high s-donating ability of
37–45
studied for nearly twenty years,
but their catalytic activities
in hydrogen transfer of ketones have not been investigated. In
addition, Ru(II) carbonyl chloride complexes with a Py–NHC
ligand have not yet been reported. Herein, we report the prepa-
ration and characterisation of stereoisomers of [Ru(Py–NHC)-
7
NHC ligands. The incorporation of the carbene functionality
into ligand systems containing other “classical” donor groups
offers vast opportunities for ligand design and the discovery of
new efficient catalysts.
Pyridine-functionalised bidentate carbene ligands (Py–NHCs)
have been frequently used as versatile ancillary ligands in
organometallic complexes in recent years. Bidentate pyridine-
(CO)
2
Cl
2
]
with pyridine-functionalised bidentate carbenes
(Py–NHCs, Chart 1). Their catalytic activities in hydrogen transfer
8
–10
of ketones have also been presented.
8
11–15
functionalised NHC complexes including those containing Rh,
12–18
19,20
21–28
29
11,19,30
Ir,
Ni,
Pd,
Cu, and Ag
have been prepared,
some of which showed catalytic activities in hydrosilylation of
1
5
15
acetylenes, cyclization of acetylenic carboxylic acids, hydrogen
15
17
transfer to ketones, reduction of nitroarenes, C–C coupling
2
2,23
19,28
reactions,
ports have been published on Ru
and olefin polymerization.
However, few re-
and Os complexes
3
1–35,14
36
containing bidentate pyridine-functionalised NHC ligands. We
recently reported the synthesis and characterisation of pyridine-
Chart 1
a
State Key Laboratory of Coordination Chemistry, Nanjing National
Laboratory of Microstructures, School of Chemistry and Chemi-
cal Engineering, Nanjing University, Nanjing, 210093, China. E-mail:
xtchen@mail.nju.edu.cn; Fax: +86 25 83314502
Results and discussion
Synthesis and characterisation of [Ru(Py–NHC)(CO)
2
2
Cl ]
b
Department of Chemistry, University of Tennessee, Knoxville, Tennessee
3
7996, USA
Among the reported strategies, the transmetallation route has
proved to be one of the most useful methods in the preparation
of metal–NHC complexes. A silver N-heterocyclic carbene
1
†
Electronic supplementary information (ESI) available: H NMR spectra
, 500 MHz) of 2b, 4b, and 5b. CCDC reference numbers
14989–714992. For ESI and crystallographic data in CIF or other
(
DMSO-d
6
46
7
electronic format see DOI: 10.1039/b904882k
complex, prepared from the reaction of an imidazolium precursor
7
132 | Dalton Trans., 2009, 7132–7140
This journal is © The Royal Society of Chemistry 2009

Scheme 1 Synthesis of ruthenium(II) carbonyl chloride complexes 1a–5a and 1b–5b.
and Ag
2
O, reacts with the metal precursor to give the desired
Crystal structure determination indicated that this is diastereomer
cis(Cl)–cis(CO)–2 (cis-isomer for short), in which one carbonyl
ligand coordinates trans to the pyridine group and one chloride is
trans to the NHC carbene carbon atom.
product. We have employed this route in the current work to
prepare Ru(II) carbonyl chloride complexes 1a–5a and 1b–5b
(
Scheme 1). Reacting imidazolium salts L
1
5
–L with an excess of
Ag O in CH Cl afforded the corresponding silver N-heterocyclic
carbene complexes. The mixture was filtered through Celite
to remove unreacted silver oxide and insoluble residues. The
2
2
2
Complexes 1a–5a and 1b–5b are very soluble in CH
3
OH and
30
CH Cl , but insoluble in Et O and hydrocarbon solvents. These
2
2
2
complexes are stable in air and in the solid state. However, the
yellow methanol solution of the trans-isomers 1a–5a turned dark
green after a few days while the cis compounds 1b–5b are stable in
air in methanol.
filtrate was treated with [Ru(CO)
2
2 n
Cl ] to gave a mixture of
the complexes with trans(Cl)–cis(CO) (trans for short) and
cis(Cl)–cis(CO) (cis for short) configurations, which were sepa-
rated by column chromatography. It was found that the yields of
the products depend on the solvent and the reaction temperature.
1
The H NMR spectra of 1a–5a and 1b–5b do not exhibit the
signals at 10–12 ppm, the imidazolium C
2
–H proton signals of
The reactions in CH
2
Cl at room temperature gave the trans-
2
the precursors, suggesting the coordination of the carbene carbon
11,12
isomers as the main products (yield 60–70%) and the cis-isomers as
the minor products (yield 10–20%), while the reactions in toluene
at refluxing temperature afforded the trans-isomers (5–10% yield)
and cis-isomers (70–80% yield), respectively.
It has been known that the reaction of [Ru(CO)
unsymmetric bidentate ligand leads in principle to the formation
in Py–NHCs ligand to the Ru atoms.
at 5.6–6.0 ppm in trans-isomers 3a, 4a, and 5a, indicating that
the two H atoms of the CH linker between the py and NHC
There is a singlet signal
2
rings are identical. However, two doublet signals of AM pattern
are observed in the cis-isomers 3b (6.15, 5.40 ppm), 4b (5.83,
5.25 ppm), and 5b (5.90, 5.34 ppm), indicating that the two proton
2
2 n
Cl ] with an
of three stereoisomers: trans(Cl)–cis(CO), cis(Cl)–cis(CO) and
atoms of the CH
AB pattern signal centered at 5.63 ppm is observed for the CH
group of Bn in 5b, indicating that the two protons of the CH group
2
linker are diastereotopic. Furthermore, a clear
38
trans(CO)–cis(Cl), as depicted in Chart 2. Few trans(CO)–cis(Cl)
2
39
isomers have been reported, which was suggested to be due to the
2
thermodynamically unfavourable trans positions of both carbonyl
of Bn are also diastereotopic (Fig. 1S, ESI†). This suggests that
there is restricted rotation around the N–C(Bn) bond as a result
of the crowded environment around the ruthenium(II) centre. H
38
ligands. With the N,C bidentate ligands Py–NHCs in the current
work, two diastereoisomeric forms of the cis(Cl)–cis(CO) isomer
are possible. NMR data revealed that only one diastereomer
cis(Cl)–cis(CO) is present, as only one set of resonances was
observed for the pyridine moiety of the Py–NHC ligand.
1
NMR spectra of 2b and 4b also implies the same inequivalence of
the two proton atoms of the CH group of n-Bu, which directly
2
connects with the imdazolyl ring. Two sextet signals at 4.39 and
Chart 2
This journal is © The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7132–7140 | 7133

4
.13 ppm are found for this CH
centered at 4.21 ppm, which can be regarded as the overlapping of
the two sextet signals, is observed for the same CH group in 2b
Fig. 1S, ESI†). The other difference between the H NMR spectra
2
group in 4b. One multiplet signal
2
1
(
of trans- and cis-isomers is that the frequency of the H6 atom
in the Py ring is observed at 9.0–9.1 ppm for the trans-isomers,
1
3
but is found at 9.2–9.4 ppm for the cis-isomers. The C NMR
signals for the carbene carbon atoms of 1a–5a and 1b–5b appear
at 150–180 ppm, locating in the characteristic range reported for
11–36
13
metal complexes bearing Py–NHCs.
The C NMR spectra of
the carbonyl carbon atoms in these complexes show two slightly
different resonances at 201–192, and 196–187 ppm, similar to those
3
8–41
of [Ru(L)(CO)
2
Cl
2
] (L = bpy, bipy, dmbpy and PR
3
).
The IR spectra of complexes 1a–5a and 1b–5b show two
absorptions of terminal CO groups in the range of 2050–2064 and
-
1
1
990–2008 cm . These absorptions do not allow a differentiation
between the trans and cis conformations.
It was found that heating the kinetic trans-isomers 1a–5a in
◦
CH
2
Cl
2
for 24 h at 120 C in a Teflon-lined stainless autoclave
quantitatively gave the thermodynamic cis-isomers 1b–5b. The
isomerization is very clean, as no side product was observed by H
Fig. 2 ORTEP representation of the structure of 1b showing 30%
probability ellipsoids. Hydrogen atoms are omitted for clarity.
1
NMR spectroscopy.
Molecular structures of 1a, 1b, 2b and 4b
Crystals of 1a·2H
2
O for X-ray diffraction structure determination
were obtained by recrystallization from a saturated methanol
◦
solution of 1a at -10 C, while those of 1b, 2b, and 4b were obtained
by evaporation of a methanol solution of 1b, 2b, and 4b in air. The
details of the molecular structures of complexes 1a, 1b, 2b, and 4b
are displayed in Fig. 1–4, respectively. The crystallographic data
for 1a·2H
2
O, 1b, 2b, and 4b are given in Table 1. Selected bond
distances and angles are shown in Table 2.
Fig. 3 ORTEP representation of the structure of 2b showing 30%
probability ellipsoids. Hydrogen atoms are omitted for clarity.
occupying mutually cis positions, one of the CO group trans to the
pyridine nitrogen and the other one trans to the chloride atom.
˚
˚
The Ru–Ccarbene distances of 2.116(4) A (1a), 2.052(4) A (1b),
˚ ˚
2
.014(4) A (2b), 2.027(4) A (4b) are in the range reported for
47–49
Ru–NHC complexes.
It is noteworthy that the Ru–Ccarbene
˚
Fig. 1 ORTEP representation of the structure of 1a showing 30%
probability ellipsoids. Hydrogen atoms are omitted for clarity.
distances in trans-isomer 1a [2.116(4) A] is longer than in cis-
isomers 1b [2.052(4) A˚ ], 2b [2.014(4) A˚ ], and 4b [2.027(4) A˚ ]. The
Ru–Ccarbene bond of 1a is located trans to CO, while it is trans to Cl
in cis-isomers 1b, 2b, and 4b, confirming that CO exerts a strong
trans-influence. The Ru–CCO bond lengths in 1a, 1b, 2b, and 4b are
The ORTEP drawings of 1a, 1b, 2b, and 4b shown in Fig. 1–4
confirm that the coordination geometry around the ruthenium
atom can be rationalised as a slightly distorted octahedron.
˚
in the range of 1.852(4)–1.917(5) A, typical for Ru–CO distances
38–41
The unit cell of 1a·2H
2
O contains two co-crystallized water
of the reported Ru(II) carbonyl complexes.
The Ru–CCO bond
molecules. The structure of 1a shows that two chloride atoms
occupy mutually trans positions and two CO groups are located
trans to the pyridine nitrogen and the carbene carbon, respectively.
The structures of 1b, 2b and 4b are similar, with two chloride atoms
(Ru1–C14) of complex 1a, trans to N-heterocyclic carbene carbon
˚
[1.917(5) A], is longer than that trans to pyridine nitrogen
˚
(Ru1–C13) [1.859(5) A]. It is the longest Ru–CCO bond in all of
these complexes due to the strong s-donation of the trans carbene
7
134 | Dalton Trans., 2009, 7132–7140
This journal is © The Royal Society of Chemistry 2009

Table 1 Summary of crystallographic aata for 1a·2H
2
O, 1b, 2b, and 4b
Compound
1a·2H
2
O
1b
2b
4b
Formula
C
465.29
14
H
15Cl
2
N
3
O
2
Ru·2H
2
O
C
429.26
14
H
15Cl
2
N
3
O
2
Ru
C
429.26
Monoclinic
P2(1)/c
14.7065(12)
9.6796(7)
12.6558(11)
115.0470(10)
1632.2(2)
1.747
14
H
15Cl
2
N
3
O
2
Ru
15 2 3 2
C H17Cl N O Ru
443.29
Formula weight
Crystal system
Space group
a/A˚
Monoclinic
P2(1)/n
11.732(2)
8.9321(16)
18.799(3)
97.904(2)
1951.3(6)
1.584
Monoclinic
P2(1)/c
14.312(12)
6.517(6)
17.998(15)
106.647(11)
1608(2)
1.773
Monoclinic
P2(1)/n
7.7333(16)
17.937(4)
12.653(3)
93.690(3)
1751.5(7)
1.681
b/A˚
c/A˚
◦
b/
V/A˚
3
calc/g cm-
3
D
Z
4
4
4
4
T/K
291(2)
0.71073
936
291(2)
0.71073
856
291(2)
0.71073
856
1.296
2.60 to 26.00
3198/0/200
8525
3198
26.00 (99.7)
0.0361
0.75 and 0.70
1.090
0.0467/0.1018
0.0580/0.1041
0.482/-0.883
291(2)
0.71073
888
Radiation Mo Ka
F (000)
Absorption coefficient/mm-
1
1.098
1.316
1.211
◦
q range for data collection/
Data/restr./paras
Reflections collected
Reflections unique
2.19 to 25.99
3821/0/220
10 192
3821
25.99 (99.9)
0.0398
0.79 and 0.74
1.001
0.0482/0.0995
0.0681/0.1039
0.383/-0.896
2.40 to 26.00
3140/0/202
7795
3140
26.00 (99.6)
0.0399
0.77 and 0.72
1.04
0.0399/0.0819
0.0513/1.039
0.456/-1.024
2.00 to 26.00
3436/0/209
9321
3436
26.00 (99.8)
0.0404
0.79 and 0.76
1.033
0.0434/0.0885
0.0567/0.0903
0.378/-0.837
◦
Completeness to q/ (%)
R
int
Max. and min. transmission
2
Goodness-of-fit on F
R
R
1
/wR
/wR
2
[I > 2s(I)]
a
1
2
(all data)
Larg. peak and hole/e A˚
-1
ꢀ
ꢀ
ꢀ
ꢀ
a
2
2 1/2
R
1
=
ꢀF
o
| - |F
c
ꢀ/ |F
o
|; wR
2
= [ w(|F
o
| - |F
c
|)) / w|F
o
| ]
.
◦
Table 2 Selected bond lengths ( A˚ ) and angles ( ) for 1a, 1b, 2b, and 4b
1
a
1b 2b 4b
Bond length
Ru1–C8
Ru1–N1
Ru1–Cl1
Ru1–Cl2
Ru1–C13
Ru1–C14
C13–O1
2.116(4)
2.159(4)
2.3968(12)
2.3891(12)
1.859(5)
1.917(5)
1.138(5)
1.116(5)
2.052(4)
2.131(3)
2.436(2)
2.431(2)
1.879(4)
1.852(4)
1.113(5)
1.126(5)
2.014(4)
2.156(3)
2.4388(11)
2.4458(11)
1.863(5)
1.866(5)
1.132(5)
1.141(5)
2.027(4)
2.172(3)
2.4344(10)
2.4861(11)
1.868(4)
1.876(4)
1.129(5)
1.109(5)
C14–O2
Bond angle
N1–Ru1–C8
C13–Ru1–C14 87.5(2)
C14–Ru1–C8 170.7(2)
C13–Ru1–C8 101.8(2)
C14–Ru1–N1
C13–Ru1–N1 178.82(18)
C14–Ru1–Cl2
C13–Ru1–Cl2
C8–Ru1–Cl2
N1–Ru1–Cl2
C14–Ru1–Cl1
C13–Ru1–Cl1
C8–Ru1–Cl1
N1–Ru1–Cl1
77.01(16)
78.72(13)
90.09(18)
91.47(17)
102.41(16)
93.82(15)
175.90(16)
88.23(13)
86.12(12)
171.46(11)
92.78(9)
178.12(12)
90.94(14)
89.84(12)
85.12(10)
90.27(4)
77.49(15)
90.1(2)
93.70(19)
98.5(2)
94.72(16)
173.92(18)
87.61(15)
90.84(16)
170.55(13)
93.08(9)
176.52(15)
89.58(16)
89.78(13)
85.86(9)
84.59(15)
88.48(18)
93.59(16)
95.51(16)
94.09(15)
177.41(15)
85.68(12)
90.36(12)
174.07(12)
89.59(10)
176.39(13)
90.69(12)
89.99(10)
86.73(9)
93.65(18)
91.25(15)
91.97(16)
88.75(12)
87.97(10)
91.40(15)
91.20(16)
88.14(12)
88.81(10)
Fig. 4 ORTEP representation of the structure of 4b showing 30%
probability ellipsoids. Hydrogen atoms are omitted for clarity.
Cl2–Ru1–Cl1 175.95(4)
88.93(4)
90.81(3)
˚
˚
carbon. Ru–Npyridine bond lengths of 2.159(4) A (1a), 2.131(3) A
˚ ˚
(
1b), 2.156(3) A (2b), and 2.172(3) A (4b) are similar to those
3
8–41
observed in [Ru(L)(CO)
2
Cl
2
] (L = bpy, bipy, dmbpy, PR
3
).
the chlorine atoms Cl1 and Cl2 are located trans to the carbonyl
(C14O2) and carbene carbon (C8), respectively, in 1b, 2b, and 4b.
The Ccarbene–Ru–Npyridine bond angle in the six-membered
The lengths of the Ru1–Cl bonds in cis-isomers 1b, 2b, and 4b
˚
(
2.436(2)–2.4861(11) A) are longer than those of in trans-isomer
a (2.3968(12) A and 2.3891(12) A), which can be explained by
◦
˚
˚
1
chelating ring of 4b [84.59(15) ] is larger than those in the
◦
◦
the trans influences of carbonyl and carbene carbon groups since
five-membered chelating rings of 1a [77.01(16) ], 1b [78.72(13) ],
This journal is © The Royal Society of Chemistry 2009
Dalton Trans., 2009, 7132–7140 | 7135

◦
and 2b [77.49(15) ]. The N-heterocyclic carbene ring and the
ligand favours the formation of the stable 16-electron interme-
diate, which shows high activity in the transfer hydrogenation
process.
pyridine ring are almost co-planar in 1a, 1b and 2b. They form an
obtuse dihedral angle in 4b [110.3(3) ].
◦
In order to determine the fate of carbonyl ligands in the catalytic
reaction, we have attempted to probe if the carbonyl ligand still
existed in the coordination sphere of ruthenium for the catalytic
reduction of acetophenone with 1b. After the catalytic reaction,
the reaction mixture was evaporated to give a solid. The IR
spectrum of the isolated solid showed the absence of the carbonyl
ligand around the ruthenium atom, indicating that the carbonyl
group did not survive under the reaction conditions. To further
explore the fate of complex 1b before the catalytic reaction starts,
Catalytic transfer hydrogenation of ketones
Ruthenium complexes have been used as active catalysts for
50–53
transfer hydrogenation reactions.
However, only a very limited
number of Ru–NHC complexes have been reported as catalysts
54–55
for this transformation.
Thus 1a–5a and 1b–5b were tested as
catalysts for transfer hydrogenation of ketones.
The reduction of acetophenone to 1-phenylethanol by 2-
propanol was chosen as a model reaction to explore the catalytic
behaviours of complexes 1a–5a and 1b–5b, using 2-propanol
as the hydrogen donor in the presence of base, see eqn (1).
The catalytic trials were carried out using substrate ketone
-
1
complex 1b was added to the solution of 0.1 mol L KOH in
i
PrOH (10 mL) and refluxed for several hours under nitrogen,
then the reaction mixture was evaporated to give a black solid. The
IR spectra of the isolated solids showed the absence of carbonyl
ligands, indicating that the carbonyl group did not survive in the
basic solution, which probably results in a vacant site on the
ruthenium for the catalytic reaction. It is thus reasonable to assume
that these ruthenium complexes just act as precursors to the active
catalysts and the carbonyl ligands probably play no important
role in transfer hydrogenation reactions. It should be noted
that other reported ruthenium carbonyl complexes supported by
Cp analogous ligands are involved in the mechanism of metal
hydride intermediates in which the CO groups still survive in the
coordination sphere of ruthenium for the hydrogenation transfer
(
4.0 mmol), a Ru catalyst precursor (8 mmol), KOH (0.2 mmol),
i
and PrOH (10 mL), with a catalyst : base : substrate ratio of
i
2
: 50 : 1000. An PrOH solution of the base was added to an
i
PrOH solution containing the catalyst and the substrate. The
◦
reaction mixture was kept at 82 C. The conversion was monitored
by GC. In order to evaluate the difference between the various
carbene complexes, the time-dependent conversions were followed
(
Fig. 5).
(
1)
57
reactions.
Since complex 1b was found to be the most efficient catalyst in
transfer hydrogenation of acetophenone, we further explored its
catalytic potentials in the reduction of other aryl and alkyl ketones
with the reaction conditions identical to those used in the transfer
hydrogenation of acetophenone (Table 3). It was found that 1b is
efficient in transfer hydrogenation of 4-methoxyacetophenone to
4
4
-methoxyphenylethanol (85% conversion after 6 h, entry 5) and
-chloroacetophenone to 4-chloroacetophenol (76% conversion
after 6 h, entry 1), moderate active in the case of diphenylketone
47% after 6 h, entry 3) and 2-heptanone (38% after 6 h, entry 7),
(
but shows a poor activity in the reduction of cyclohexanone (14%
after 6 h, entry 6) and 2,4,6-trimethylacetophenone (10% after
6
h, entry 2). These different activities in these substrates may be
attributed to the electron and steric effects of the substituents on
the ketones.
Fig. 5 Conversion vs. reaction time of the catalytic transfer hydrogenation
of acetophenone; 8 mmol catalyst; 0.2 mmol KOH; 4 mmol acetophenone;
solvent PrOH 10 ml, T = 355 K.
Conclusion
i
We have described the preparation, molecular structures and
catalytic activities of trans and cis-isomers of Ru(II) carbonyl com-
plexes bearing pyridine-functionalised N-heterocarbene ligands.
Using the Ag carbene transmetallation route, these new complexes
were readily accessible and were fully characterised. The yields
of the trans- and cis-complexes were controlled by altering the
reaction conditions. Trans-isomers were found to be transformed
into cis-isomers in dichloromethane in a Teflon-lined stainless
autoclave. Their potential as catalyst precursors for transfer
hydrogenation of ketones has also been tested. The presence
of the five-membered ring between the pyridine and imidazole
group is found to be beneficial for the transfer hydrogenation of
acetophenone.
It was found that complexes 1a, 1b, 2a, and 2b are more
active than 3a, 3b, 4a, 4b, 5a, and 5b, suggesting that the
presence of the five-membered ring between the pyridine and
imidazole group is beneficial for the transfer hydrogenation
of acetophenone compared with the six-membered ring. 1b is
the most active catalyst among these complexes. It should be
mentioned that 1b bears a t-butyl group at the nitrogen atom
of the imidazole moiety. Noyori and co-workers have shown that
the true catalyst in transfer hydrogenation reactions is formally
56
a 16-electron intermediate species. It is assumed that the bulky
7
136 | Dalton Trans., 2009, 7132–7140
This journal is © The Royal Society of Chemistry 2009

a
Table 3 Catalytic transfer hydrogenation of ketones with 1b
Elemental analyses were performed in an Elementar Vario
ELIII elemental analyzer. NMR measurements were carried out
Conversion%
(6 h)
1
13
in DMSO-d on a Bruker AM-500 spectrometer. H and C NMR
6
b
Entry Ketone
1
Alcohol
chemical shifts are referenced to the solvent. The IR spectra
were recorded on a Bruker Vector 22 spectrophotometer with
76
10
-
1
KBr pellets in the 4000–400 cm region. The GC analyses of
the catalytic mixtures were performed on a Shimadzu GC-2010
equipment.
2
Syntheses
trans(Cl)-[Ru(Py–NHC)(CO)
2
Cl
2
] (1a–5a) and
cis(Cl)-[Ru(Py–NHC)(CO) Cl
2
2
] (1b–5b)
Route 1. A mixture of L
1.0 mmol) and CH Cl (30 mL) was stirred at room temperature
for 12 h, and was then filtered through Celite to remove unreacted
silver oxide and insoluble residues. [Ru(CO) Cl (1.0 mmol)
was added to the pale yellow solution, stirred for 12 h at room
temperature and then filtered through Celite to remove the silver
halide. The products were chromatographed using silica gel.
1
–L
5
(1.0 mmol), silver oxide
3
4
5
47
91
85
(
2
2
2
2 n
]
Elution with CH
that contained the desired trans-product, and then elution with
CH Cl : MeOH (20 : 1) yielded a yellow band, which is the cis-
2
Cl
2
: MeOH (40 : 1) afforded a pale yellow band
2
2
product. Removal of the volatiles under vacuum gave the trans-
products 1a–5a as pale yellow powders (60–70%) and the cis
complexes 1b–5b as yellow powders (10–20%).
6
14
Route 2. A mixture of L
1.0 mmol) and CH Cl (30 mL) was stirred at room temperature
for 12 h. The mixture was filtered through Celite to remove
unreacted silver oxide and insoluble residues. CH Cl was re-
moved from the reaction mixture under vacuum. [Ru(CO) Cl
1.0 mmol) in toluene (30 mL) was added to the remaining pale
yellow solid, and refluxed for another 12 h. The products were
purified by column chromatography using CH Cl : CH
1
–L
5
(1.0 mmol), silver oxide
(
2
2
2
2
7
38
2
2 n
]
(
2
2
3
OH =
a
◦
Experimental condition: reactions were carried out at 82 C; ace-
40 : 1 to give trans-isomers with a yield of 5–10%; and then with
CH Cl : CH OH (20 : 1) to give cis-isomers in 70–80% yield.
tophenone (4 mmol), complex 1b (8 mmol), KOH (0.2 mmol) in 2-
2
2
3
b
propanol (10 mL); ketone : Ru : KOH = 1000 : 2 : 50. The conversion was
determined by GC analysis.
trans(Cl)-{[3-tert-butyl-1-(2-pyridyl)imidazol-2-
ylidene]Ru(CO)
2
Cl
2
} (1a)
1
Yield, 0.26 g (60%). H NMR (DMSO-d
1
6
, 500 MHz): d 9.08 (d,
3
H, JH–H = 5.0 Hz, 6-H of Py), 8.56 (s, 1H, 4,5-imidazol-2-ylidene
Experimental section
H), 8.40–8.36 (m, 2H, 3,5-H of Py), 7.85 (s, 1H, 4,5-imidazol-
3
Materials and physical methods
2-ylidene H), 7.67 (t, 1H, J
= 5.5 Hz, 4-H of Py), 1.88 (s,
6
H–H
1
3
9
H, [C(CH
CO), d 185.8 (2-imidazol-2-ylidene C), 153.5, 151.9, 143.6 (Py C),
25.1, 123.1, 116.9, 113.9 (Py and 4,5-imidazol-2-ylidene C), 60.2
C(CH ], 32.1 [C(CH ]. Anal. Calcd for C14 Ru: C,
3
)
3
]). C NMR (DMSO-d , 125 MHz): d 200.7, 194.9
Unless otherwise noted, all reactions and manipulations were per-
formed under a dry nitrogen atmosphere using standard Schlenk
techniques. The solvents were purified using standard methods
(
1
[
3
)
3
3
)
3
H
15Cl
2
N
3
O
2
and degassed before use. Methanol and CH
2
Cl were dried over
2
3
9.17; H, 3.52; N, 9.79; Found: C, 39.23; H, 3.66; N, 10.04. IR
Mg/I and P , respectively, and then distilled under nitrogen.
2
2
O
5
-1
(
KBr): n (CO) 2055 and 1990 cm .
Other chemicals were purchased from commercial sources and
used without further purification.
The following starting materials were prepared accord-
trans(Cl)-{[3-n-butyl-1-(2-pyridyl)imidazol-2-
ylidene]Ru(CO)
2
Cl
2
} (2a)
4
0
ing to the literature methods: [Ru(CO)
imidazole, 3-tert-butyl-1-(2-pyridyl)imidazolium bromide (L
2
Cl
2
]
n
,
1-tert-butyl
58
30
1
1
),
Yield, 0.25 g (60%). H NMR (DMSO-d
6
, 500 MHz): d 9.06 (d,
23
3
3
-n-butyl-1-(2-pyridyl)imidazolium bromide (L
2
), 3-tert-butyl-
), 3-n-butyl-1-(2-picoly)-
), 3-benzyl-1-(2-picoly)imidazolium
1H, JH–H = 5.2 Hz, 6-H of Py), 8.54 (s, 1H, 4, 5-imidazol-2-
30
3
1
-(2-picoly)imidazolium bromide (L
3
ylidene H), 8.37 (t, 1H, JH–H = 7.7 Hz, 5-H of Py), 8.31 (d, 1H,
30
3
imidazolium bromide (L
iodide (L
4
J
H–H = 8.2 Hz, 3-H of Py), 7.82 (s, 1H, 4,5-imidazol-2-ylidene
19
3
5
).
H), 7.64 (t, 1H,
J
H–H = 6.4 Hz, 4-H of Py), 4.39 (t, 2H,
Dalton Trans., 2009, 7132–7140 | 7137
This journal is © The Royal Society of Chemistry 2009

3
J
H–H
=
7.3 Hz, NCH
2
CH
2
CH
2
CH
3
), 1.95 (m, 2H,
CH CH ), 0.95 (t,
). C NMR (DMSO-d
25 MHz): d 201.1, 194.4 (CO), d 187.6 (2-imidazol-2-ylidene
N, 8.80; Found: C, 45.22; H, 3.39; N, 8.51. IR (KBr): n (CO) 2053
1
-
NCH
3
1
2
CH
2
CH CH ), 1.42 (m, 2H, NCH
2
3
2
CH
2
2
3
and 1988 cm .
3
13
H, JH–H = 7.3 Hz, NCH
2
CH
2
CH
2
CH
3
6
,
cis(Cl)-{[3-tert-butyl-1-(2-pyridyl)imidazol-2-
ylidene]Ru(CO) Cl } (1b)
C), 153.9, 152.3, 143.5 (Py C), 125.8, 125.40, 118.3, 112.6
Py and 4,5-imidazol-2-ylidene C), 51.6 (NCH CH CH CH ),
3.9 (NCH CH CH CH ), 20.2 (NCH CH CH CH ), 14.8
NCH CH CH CH ). Anal. Calcd for C14 Ru: C,
9.17; H, 3.52; N, 9.79; Found: C, 38.93; H, 3.66; N, 9.88. IR
2
2
(
3
(
3
2
2
2
3
1
Yield, 0.33 g (80%). H NMR (DMSO-d
6
, 500 MHz): d 9.34 (d,
H, JH–H = 4.9 Hz, 6-H of Py), 8.59 (s, 1H, 4,5-imidazol-2-ylidene
H), 8.39 (t, 1H, JH–H = 7.7 Hz, 5-H of Py), 8.34 (d, 1H, JH–H
2
2
2
3
2
2
2
3
3
1
2
2
2
3
H
15Cl
2
N
3
O
2
3
3
=
-
1
8.1 Hz, 3-H of Py), 7.85 (s, 1H, 4,5-imidazol-2-ylidene H), 7.73 (t,
(
KBr): n (CO) 2063 and 2002 cm .
3
13
1
H, JH–H = 6.1 Hz, 4-H of Py), 1.84 (s, 9H, [C(CH
3
) ]). C NMR
3
(
DMSO-d , 125 MHz): d 199.3, 191.5 (CO), d 175.0 (2-imidazol-
6
trans(Cl)-[(3-tert-butyl-1-picolylimidazol-2-ylidene)Ru(CO)
3a)
2
2
Cl ]
2
4
-ylidene C), 152.1, 148.9, 143.5 (Py C), 123.7, 117.6, 113.6 (Py and
(
,5-imidazol-2-ylidene C), 59.9 [C(CH ], 31.4 [C(CH ]. Anal.
3
)
3
)
3 3
1
Calcd for C H Cl N O Ru: C, 39.17; H, 3.52; N, 9.79; Found: C,
39.33; H, 3.76; N, 9.94. IR (KBr): n (CO) 2074 and 2008 cm .
1
4
15
2
3
2
Yield, 0.31 g (70%). H NMR (DMSO-d , 500 MHz): d 9.14 (d,
3
6
-
1
3
1
H, JH–H = 5.4 Hz, 6-H of Py), 8.16 (t, 1H, JH–H = 7.6 Hz, 5-H
3
of Py), 7.77 (d, 1H, JH–H = 7.7 Hz, 3-H of Py), 7.73 (s, 1H, 4,5-
3
imidazol-2-ylidene H), 7.69 (t, 1H, JH–H = 6.2 Hz, 4-H of Py),
cis(Cl)-{[3-n-butyl-1-(2-pyridyl)imidazol-2-ylidene]Ru(CO)
2
Cl
2
}
7
1
1
.65 (s, 1H, 4,5-imidazol-2-ylidene H), 6.00 (s, 2H, CH
2
linker)
, 125 MHz): d 200.5,
(2b)
1
3
.83 (s, 9H, [C(CH
3
)
3
]). C NMR (DMSO-d
6
1
Yield, 0.34 g (80%). H NMR (DMSO-d
1
6
, 500 MHz): d 9.25 (d,
93.8 (CO), d 173.7 (2-imidazol-2-ylidene C), 157.1, 156.9, 141.4
3
H, JH–H = 5.0 Hz, 6-H of Py), 8.53 (s, 1H, 4,5-imidazol-2-ylidene
(
py C), 126.1, 125.8, 123.6, 122.2 (Py and 4,5-imidazol-2-ylidene
C), 61.3 [C(CH ], 54.7 (PyCH N), 32.9 [C(CH ]. Anal. Calcd
Ru: C, 40.64; H, 3.87; N, 9.48; Found: C, 40.33;
3
3
H), 8.37 (t, 1H, JH–H = 7.5 Hz, 5-H of Py), 8.26 (d, 1H, JH–H
=
3
)
3
2
)
3 3
8
1
8
1
.5 Hz, 3-H of Py), 7.80 (s, 1H, 4,5-imidazol-2-ylidene H), 7.70 (t,
for C15
H
17Cl
2
N
3
O
2
3
H, JH–H = 6.5 Hz, 4-H of Py), 4.27–4.15 (m, 2H, J
1
= 7.5 Hz, J
2
=
-
1
H, 3.69; N, 9.64. IR (KBr): n (CO) 2051 and 1980 cm .
Hz, NCH
.37 (m, 2H, NCH
2
CH
2
CH
2
CH
3
), 1.85 (m, 2H, NCH
2
CH CH CH ),
2
2
3
3
2
CH
2
CH
2
CH
3
), 0.93 (t, 3H, JH–H = 7.5 Hz,
6
1
3
trans(Cl)-[(3-n-butyl-1-picolylimidazol-2-ylidene)Ru(CO)
2
Cl
2
]
NCH CH CH CH ). C NMR (DMSO-d , 125 MHz): d 198.5,
2
2
2
3
(
4a)
190.7 (CO), d 178.1 (2-imidazol-2-ylidene C), 152.3, 148.9, 143.2
Py C), 125.6, 123.4, 118.4, 113.2 (Py and 4,5-imidazol-2-ylidene
C), 51.1 (NCH CH CH CH ), 32.9 (NCH CH CH CH ), 19.74
CH ), 14.2 (NCH CH CH CH ). Anal. Calcd for
Ru: C, 39.17; H, 3.52; N, 9.79; Found: C, 39.09; H,
(
1
Yield, 0.30 g (68%). H NMR (DMSO-d
6
, 500 MHz): d 9.09
3
3
2
2
2
3
2
2
2
3
(
d, 1H,
J
H–H = 5.0 Hz, 6-H of Py), 8.17 (t, 1H,
J
H–H
=
(NCH
2
CH
2
CH
2
3
2
2
2
3
3
7
7
2
4
2
0
.3 Hz, 5-H of Py), 7.79 (d, 1H, JH–H = 7.7 Hz, 3-H of Py),
C
14
H
15Cl
2
N
3
O
2
3
.68 (t, 1H,
J
H–H = 6.4 Hz, 4-H of Py), 7.63 and 7.60 (s,
linker),
), 1.89 (m,
CH CH CH ),
). C NMR
, 125 MHz): d 200.5, 193.4 (CO), d 175.5 (2-
imidazol-2-ylidene C), 157.7, 156.6, 141.3 (Py C), 126.7, 125.9,
-
1
3
.36; N, 9.58. IR (KBr): n (CO) 2062 and 1991 cm .
¥ 1H, 4,5-imidazol-2-ylidene H), 5.88 (s, 2H, CH
2
3
.34 (t, 2H,
H, NCH CH
.96 (t, 3H,
J
H–H = 7.8 Hz, NCH
CH CH ), 1.43 (m, 2H, NCH
H–H = 7.3 Hz, NCH CH CH CH
2
CH
2
CH
2
CH
3
cis(Cl)-[(3-tert-butyl-1-picolylimidazol-2-ylidene)Ru(CO)
2
2
Cl ]
2
2
2
3
2
2
2
3
3
13
(3b)
J
2
2
2
3
(
DMSO-d
6
1
Yield, 0.35 g (75%). H NMR (DMSO-d
1
6
, 500 MHz): d 9.37 (d,
3
3
H, JH–H = 5.5 Hz, 6-H of Py), 8.15 (t, 1H, JH–H = 7.5 Hz, 5-
1
23.7, 122.3 (py and 4,5-imidazol-2-ylidene C), 54.1 (PyCH
0.5 (NCH CH CH CH ), 33.9 (NCH CH CH CH ), 20.3
CH CH ), 14.5 (NCH CH CH CH ). Anal. Calcd for
Ru: C, 40.64; H, 3.87; N, 9.48; Found: C, 40.52; H,
2
N),
H of Py), 7.75 (d, 1H, JH–H = 7.5 Hz, 3-H of Py), 7.69 (s, 2 ¥
5
2
2
2
3
2
2
2
3
3
1
H, 4,5-imidazol-2-ylidene H), 7.68 (t, 1H, JH–H = 9.0 Hz, 4-H
(NCH
2
CH
2
2
3
2
2
2
3
2
of Py), 6.15 (d, 1H, JH–H = 15.5 Hz, CHH linker), 5.40 (d, 1H,
C
4
15
H
17Cl
2
N
3
O
2
2
13
J
H–H = 15.5 Hz, CHH linker), 1.80 (s, 9H, [C(CH
3
)
3
]). C NMR
-
1
.03; N, 9.48. IR (KBr): n (CO) 2054 and 1994 cm .
(DMSO-d
6
, 125 MHz): d 201.2, 196.5 (CO), d 165.1 (2-imidazol-
2
-ylidene C), 157.3, 156.7, 142.9 (Py C), 127.1, 126.8, 125.8 (Py
and 4,5-imidazol-2-ylidene C), 63.1[C(CH ], 57.8 (PyCH , C),
Ru: C, 40.64; H,
trans(Cl)-[(3-benzyl-1-picolylimidazol-2-ylidene)Ru(CO)
2
Cl
2
] (5a)
3
)
N
3
2
3
3
2
4.3 [C(CH
3
)
3
]. Anal. Calcd for C15
H
17Cl
2
3
O
2
1
Yield, 0.31 g (65%). H NMR (DMSO-d
6
, 500 MHz): d 9.13 (d,
.87; N, 9.48; Found: C, 40.33; H, 3.54; N, 9.14. IR (KBr): n (CO)
057 and 1988 cm .
3
3
1
H, JH–H = 5.4 Hz, 6-H of Py), 8.19 (t, 1H, JH–H = 7.7 Hz, 5-
-1
3
H of Py), 7.81 (d, 1H, JH–H = 7.6 Hz, 3-H of Py), 7.69 (t, 1H,
3
J
H–H = 6.2 Hz, 4-H of Py), 7.65 (s, 1H, 4,5-imidazol-2-ylidene
3 3
cis(Cl)-[(3-n-butyl-1-picolylimidazol-2-ylidene)Ru(CO)
2
2
Cl ] (4b)
H), 7.41 (t, 2H, JH–H = 7.3 Hz, 3,5-H of Ph), 7.35 (t, 1H, JH–H
=
3
1
7
.1 Hz, 4-H of Ph), 7.27 (d, 2H, JH–H = 8.7 Hz, 2,6-H of Ph); 7.10
Yield, 0.33 g (70%). H NMR (DMSO-d
6
, 500 MHz): d 9.36 (d,
3
3
(
(
s, 1H, 4,5-imidazol-2-ylidene H), 6.00 (br, 2H, CH
2
of Bn), 5.66
, 125 MHz) d 199.6,
93.5 (CO), 176.9 (2-imidazol-2-ylidene C), 157.9, 156.6, 141.4
Py C), 137.6, 129.6, 128.7, 128.1 (Py and 4,5-imidazol-2-ylidene
C), 126.8, 126.1, 124.2, 122.7 (Ph, C), 53.8, 53.7 (PyCH N and
PhCH N). Anal. Calcd for C18 Ru: C, 45.29; H, 3.17;
1H, JH–H = 4.5 Hz, 6-H of Py), 8.14 (t, 1H, JH–H = 3.0 Hz,
1
3
3
s, 2H, CH
2
linker). C NMR (DMSO-d
6
5-H of Py), 7.76 (d, 1H, JH–H = 7.5 Hz, 3-H of Py), 7.68 (t,
3
1
(
1H, JH–H = 5.0 Hz, 4-H of Py), 7.64 (s, 1H, 4,5-imidazol-2-
ylidene H), 7.55 (s, 1H, 4,5-imidazol-2-ylidene H), 5.83 (d, 1H,
2
2
2
J
H–H = 16.0 Hz, CHH linker), 5.25 (d, 1H, JH–H = 16.0 Hz, CHH
2
H
15Cl
2
N
3
O
2
linker), 4.39, 4.13 (two sextet, 2H, NCH
2
CH
2
CH
2
CH ), 1.80 (m,
3
7
138 | Dalton Trans., 2009, 7132–7140
This journal is © The Royal Society of Chemistry 2009

2
(
1
H, NCH
2
CH
t, 3H, JH–H = 7.0 Hz, NCH
25 MHz): d 192.2, 187.4 (CO, C), d 160.9 (2-imidazol-2-ylidene
C), 149.4, 148.4, 134.9 (Py C), 119.2, 119.1, 117.9, 116.8 (Py and
,5-imidazol-2-ylidene C), 48.9 (PyCH , C), 44.2, 27.2, 13.9, 8.2
NCH CH CH CH , C). Anal. Calcd for C15 Ru: C,
0.64; H, 3.87; N, 9.48; Found: C, 40.32; H, 4.11; N, 9.31. IR
2
CH
2
CH
3
), 1.41 (m, 2H, NCH
2
CH
2
CH
2
CH
3
), 0.99
Acknowledgements
3
13
2
CH
2
CH
2
CH
3
). C NMR(DMSO-d
6
,
This work was supported by the National Basic Research Program
of China (No. 2006CB806104 and 2007CB925102), and Natural
Science Grant of China (No. 20721002), and the US National
Science Foundation (CHE-051692).
4
(
4
2
2
2
2
3
H
17Cl
2
N
3
O
2
-
1
(
KBr): n (CO) 2063 and 1992 cm .
References
cis(Cl)-[(3-benzyl-1-picolylimidazol-2-ylidene)Ru(CO)
2
Cl ] (5b)
2
1
A. J. Arduengo, III, R. L. Harlow and M. Kline, J. Am. Chem. Soc.,
1991, 113, 361–363.
1
Yield, 0.30 g (65%). H NMR (DMSO-d
1
6
, 500 MHz): d 9.39 (d,
2
3
F. E. Hahn, Angew. Chew., Int. Ed., 2006, 45, 1348–1352.
W. A. Herrmann, Angew. Chem., Int. Ed., 2002, 41, 1290–1309.
3
3
H, JH–H = 5.6 Hz, 6-H of Py), 8.16 (t, 1H, JH–H = 7.3 Hz, 5-H of
3
3
Py), 7.78 (d, 1H, JH–H = 7.6 Hz, 3-H of Py), 7.72 (t, 1H, JH–H
=
4 W. A. Herrmann and C. K o¨ cher, Angew. Chem., Int. Ed. Engl., 1997,
6, 2162–2187.
5 W. A. Herrmann, O. Runte and G. Artus, J. Organomet. Chem., 1995,
01, C1–C4.
3
6
2
.6 Hz, 4-H of Py), 7.69 (s, 1H, 4,5-imidazol-2-ylidene H), 7.41 (t,
3
3
H, JH–H = 7.4 Hz, 3,5-H of Ph), 7.35 (t, 1H, JH–H = 7.2 Hz, 4-H
5
3
of Ph), 7.27 (s, 1H, 4,5-imidazol-2-ylidene H), 7.17 (d, 2H, JH–H
=
=
6
N. Fr o¨ hlich, U. Pidun, M. Stahl and G. Frenking, Organometallics,
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2
7
5
1
1
.4 Hz, 2,6-H of Ph), 5.90 (d, 2H, JH–H = 16.2 Hz, CHH linker),
2
2
7 D. Bourissou, O. Guerret, F. P. Gabba ¨ı and G. Bertrand, Chem. Rev.,
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.63 (dd, 2H, JH–H = 15.9 Hz, CH
2
of Bn), 5.34 (d, 2H, JH–H
2
1
3
6.2 Hz, CHH linker). C NMR (DMSO-d
6
, 125 MHz) d 197.6,
8
H. M. Lee, C.-C. Lee and P.-Y. Cheng, Curr. Org. Chem., 2007, 11,
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9
(
Py C), 129.7, 129.1, 128.7, 128.1 (Py and 4,5-imidazol-2-ylidene
C), 127.7, 125.5, 124.5, 123.5 (Ph, C), 55.7, 55.5 (PyCH N and
PhCH N). Anal. Calcd for C18 Ru: C, 45.29; H, 3.17;
N, 8.80; Found: C, 45.47; H, 3.21; N, 8.55. IR (KBr): n (CO) 2060
1
1
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2
H
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-
1
and 1987 cm .
1
3 N. Stylianides, A. A. Danopoulos and N. Tsoureas, J. Organomet.
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1
4 X. Wang, S. Liu, L.-H. Weng and G.-X. Jin, Chem.–Eur. J., 2007, 13,
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88–195.
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2
4 h. After evaporation of the solvent, a yellow solid 1b–5b was
1
obtained quantitatively as revealed by H NMR spectrum. No
other product was observed.
1
1
2
8 X.-Q. Xiao and G.-X. Jin, J. Organomet. Chem., 2008, 693, 3363–3368.
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General procedure for the catalytic hydrogen transfer
50–53
The procedure used follows standard literature methods.
hydrogen transfer reactions are carried out using standard Schlenk
glassware.
The
2
22 A. M. Magill, D. S. McGuinness, K. J. Cavell, G. J. P. Britovsek, V. C.
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2
2
Organic substrate ketone (4.0 mmol) and a Ru complex (8 mmol)
i
were dissolved in PrOH (8 mL) in a Schlenk tube. The solution was
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◦
solution was allowed to warm to 82 C for 30 min under nitrogen.
-
1
i
By addition of 2 mL of a 0.1 mol L KOH in PrOH, the reaction
starts immediately. The reaction progress was monitored by GC
analysis.
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2
2
7 A. A. Danopoulos, N. Tsoureas, S. A. Macgregor and C. Smith,
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O, 1b, 2b, and
4b†
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˚
.71073 A) radiation and collected for absorption using SADABS
0
59
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2
32 K. Araki, S. Kuwata and T. Ikariya, Organometallics, 2008, 27, 2176–
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2178.
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