A RuII-N-heterocyclic carbene (NHC) complex from metal-metal singly bonded diruthenium(I) precursor: Synthesis, structure and catalytic evaluation

Article abstract of DOI:10.1016/j.jorganchem.2010.11.003

A mononuclear Ru(II)-N-heterocyclic carbene (NHC) complex [Ru ^II(CO)₂(κ²C,N-BIN)(H₂O)Br] [OTf] (OTf = trifluoromethane sulphonate) (1) has been synthesized in high-yield by the oxidative cleavage of the metal-metal singly-bonded diruthenium(I) precursor [Ru₂(CO)₄(CH₃CN)₆(OTf) ₂] with 1,8-naphthyridine functionalized NHC precursor 1-benzyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazolium bromide (BIN·HBr) at room temperature. Compound 1 catalyzes transfer hydrogenation of ketones to alcohols, and carbene-transfer from ethyl diazoacetate to a variety of substrates. It is shown to be an excellent catalyst for the insertion of carbene into the O-H and N-H bonds of alcohols and amines.

Full text of DOI:10.1016/j.jorganchem.2010.11.003

Journal of Organometallic Chemistry 696 (2011) 1248e1257
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
II
A Ru eN-heterocyclic carbene (NHC) complex from metalemetal singly bonded
diruthenium(I) precursor: Synthesis, structure and catalytic evaluation
Arup Sinha , Prosenjit Daw, S.M. Wahidur Rahaman, Biswajit Saha, Jitendra K. Bera*
*
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
a r t i c l e i n f o
a b s t r a c t
A
2 2
mononuclear Ru(II)eN-heterocyclic carbene (NHC) complex [Ru (CO) (k2C,N-BIN)(H O)Br][OTf]
(
II
Article history:
Received 29 September 2010
Received in revised form
OTf ¼ trifluoromethane sulphonate) (1) has been synthesized in high-yield by the oxidative cleavage of
the metalemetal singly-bonded diruthenium(I) precursor [Ru (CO) (CH CN) (OTf) ] with 1,8-naph-
2
4
3
6
2
2
November 2010
thyridine functionalized NHC precursor 1-benzyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazolium
bromide (BIN$HBr) at room temperature. Compound 1 catalyzes transfer hydrogenation of ketones to
alcohols, and carbene-transfer from ethyl diazoacetate to a variety of substrates. It is shown to be an
excellent catalyst for the insertion of carbene into the OeH and NeH bonds of alcohols and amines.
Ó 2010 Elsevier B.V. All rights reserved.
Accepted 3 November 2010
Keywords:
Ruthenium
N-Heterocyclic carbene
Metalemetal bond
Oxidative addition
Catalysis
1. Introduction
been shown to transfer NHC to Au, Pd and Ru [14]. Several other
procedures have also been developed in recent years [15].
N-heterocyclic carbenes (NHC) have emerged as a useful class of
ligands in the development of homogeneous organic [1] and
organometallic catalysts [2]. These are strong s-donors, sterically
Oxidative addition of C2eH bond of imidazolium cations to low-
valent metal complex is a facile but less explored path. Advantage of
this protocol is that no base is required for the activation. Nolan [16]
and Crabtree [17] independently proposed oxidative addition of the
imidazolium CeH to Pd(0) for the synthesis of Pd -NHC
3 2 4
compounds. Isolation of a hydride complex [Pt(H)(dmiy)(PR ) ]BF
and electronically tunable, and form thermally stable compounds
with different metal ions. Such qualities have rendered NHC ligands
as surrogates to phosphines in organometallic catalysis [3]. Last few
decades have witnessed an extensive exploration of metal-NHC
complexes as catalysts for a wide variety of organic transformations
including olefin metathesis [4], hydrosilylation [5], hydroformy-
lation [6], hydrogenation [7], copolymerization [8], and CeC [9] and
CeN [10] coupling reactions and asymmetric transformations [11].
In general, NHCs are shown to be good ancillary ligands; however,
recent reports on the reductive elimination of corresponding imi-
II
(dmiy ¼ 1,3-dimethylimidazolin-2-ylidene and R ¼ Phenyl, Cyclo-
hexyl) by Cavell, following a similar procedure, provides support
for this hypothesis [18]. Subsequently several reports have
appeared implicating oxidative addition pathway for the activation
process [19]. Though this method is successfully employed for low-
valent electron-rich coordinatively unsaturated Group 10 metal
complexes, there are limited examples known for other metals [20].
The prospect of functionalization at the N atoms and in the
backbone of imidazole has brought about a new dimension in NHC
chemistry [21]. Hetero-arene derivatized NHC ligands exhibit wide
diversity in ligand topology and binding mode, offering greater
control over the coordination environment of metal and its cata-
lytic activities [22]. Introduction of 1,8-naphthyridine (NP) unit in
NHC afforded 1-benzyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imi-
dazol-2-ylidene (BIN) which exhibits diversity in metalecarbene
chemistry by virtue of its multiple binding sites and topological
flexibility (Fig.1) [23]. We have recently demonstrated multifaceted
coordination of this NP-NHC hybrid ligand BIN generating a host of
transition metal complexes involving W, Ag, Pd, Ir and Rh are
synthesized [24]. However, our efforts to access a mononuclear
II
dazolium salt from NHC-Pd -alkyl complex have cast doubt on an
all-out ‘spectator’ description [12].
The complexation protocols in NHC chemistry are mainly
based on the following routes: 1. the complexation of the free, pre-
isolated NHC with metal; 2. in situ deprotonation of the azolium salt
by base, either exogenous or embedded in the metal precursor, and
2
subsequent metal-complexation; 3. use of basic Ag O to generate
a Ag-NHC complex, followed by the NHC transfer to a late transition
I
metal via transmetallation [13]. Recently, Cu -NHC complexes have
*
Corresponding authors. Tel.: þ91 512 259 7336; fax: þ91 512 259 7436.
E-mail address: jbera@iitk.ac.in (J.K. Bera).
0
022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.11.003

A. Sinha et al. / Journal of Organometallic Chemistry 696 (2011) 1248e1257
1249
Fig. 1. Schematic representation of 1-benzyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)
imidazol-2-ylidene (BIN).
ruthenium complex remained thus far unsuccessful from a variety
II
of conventional mononuclear Ru precursors such as Ru
2
(p-cyme-
(CO)(H)
In this contribution, we report oxidative cleavage of the
metalemetal single bond in the diruthenium(I) precursor [Ru
Fig. 2. ORTEP diagram (50% probability thermal ellipsoid) of the cationic unit [Ru
2
þ
*
(CO)
2
(
k
C,N-BIN)(H
2
O)Br]
in compound
1
with important atoms labeled.
ne)
2
Cl
4
, Ru
2
(Cp )
2
Cl
4
, [Ru(COD)Cl
2
]
2
and Ru(PPh
3
)
3
2
.
ꢀ
Hydrogen atoms omitted for the sake of clarity. Selected bond distances (A) and
angles (deg): Ru1eC23 2.013(5), Ru1eN2 2.194(4), Ru1eO3 2.158(3), Ru1eBr1
2
-
2
.5151(7), Ru1eC1 1.901(6), Ru1eC2 1.892(5), N3eC23 1.374(6), N4eC23 1.348(6),
N2eC17 1.361(6), N2eC20 1.332(6), N1eC12 1.329(6), N3eC20 1.405(6), N3eC21
.392(6), N4eC22 1.399(7), N4eC24 1.453(7), C1eO1 1.118(7), C2eO2 1.122(6).
N4eC23eN3 104.5(4), C2eRu1eC1 90.5(2), C2eRu1eC23 97.7(2), C1eRu1eC23
2.89(19), C1eRu1eO3 93.06(18), C2eRu1eO3 90.66(18), C23eRu1eO3 169.69(16),
II
2
(
(
4 3 6 2 2 2
CO) (CH CN) (OTf) ] affording [Ru (CO) (k C,N-BIN)(H O)Br][OTf]
1
OTf ¼ trifluoromethane sulphonate) (1). The catalytic activities of
this complex are evaluated with special emphasis on the carbene-
transfer reactions from ethyl diazoacetate (EDA).
9
C23eRu1eN2 77.20(17), C23eRu1eBr1 91.08(12), O3eRu1eBr1 83.37(10),
C20eN2eC17 117.0(4), C12eN1eC17 118.0(4), C23eN3eC20 128.8(4), N2eC20eN3
114.3(4), N1eC17eN2 115.9(4). Dihedral Angles (deg): N2eC20eN3eC23 1.8(6),
Ru1eC23eN4eC24 0.6(8).
2
. Results and discussions
2
.1. Synthesis and characterization of aqua-bromo-dicarbonyl-[1-
II
benzyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazol-2-ylidene]
comparable with other Ru eaqua complexes carrying NHCeli-
ruthenium(II) trifluomethylsulphonate (1)
gands [25].
1
All ligand protons have been assigned in the H NMR spectra for
The NP substituted NHC-ligand precursor 1-benzyl-3-(5,7-
dimethyl-1,8-naphthyrid-2-yl)imidazolium bromide (BIN$HBr)
was obtained by the direct linkage between 2-imidazolyl-1,8-
naphthyridine and benzyl bromide as reported earlier [24]. Room
complex 1. Protons of the coordinated BIN show marginal shifts
reflecting its coordination to the metal. The methylene protons
2
undergo geminal coupling ( JHH ¼ 16 Hz), appearing as a doublet of
doublet at
d 5.55 ppm with characteristic ‘roof’ shape, which indi-
13
temperature treatment of [Ru
2
(CO)
4
(CH
3
CN)
6
][OTf]
2
with two
cate their inequivalent chemical environment. The C NMR signal
corresponding to the carbene carbon atom (NCImN) undergoes
considerable downfield shift, appearing at 178.9 ppm. Such a large
equivalents of BIN$HBr in dichloromethane provided a mono-
nuclear Ru(II)ecarbene complex 1 (Scheme 1) in high-yield (80%).
Formation of 1 involves metal-oxidation from RuI to Ru
accompanied by the metalemetal bond cleavage, clearly suggesting
an ‘oxidative addition’ step in the mechanism. Homolytic oxidative
scission of the diruthenium(I) system in presence of BIN$HBr
results in a mononuclear ruthenium(II) species incorporating one
chelated BIN and two carbonyl ligands. Two incipient vacant sites
are subsequently occupied by one bromide from NHC precursor and
an adventitious water molecule providing 1.
II
shift (Δd 42.7 ppm) is credited to the highly deshielded chemical
shielding tensor associated with the diamino carbenes [26]. Two
carbonyl carbon atoms resonate at 194.2 and 187.3 ppm. The ESI-
MS spectrum of 1 reveals the molecular ion signal at m/z 571 (20%).
The base signal which is attributed to the dehydrated molecular ion
þ
[M ꢀ H
2
O] appears at m/z 553.
2.2. Catalysis
Detail of the molecular structure was established by single
crystal X-ray diffraction studies. Molecular structure of the complex
RueNHC complexes constitute an important class of molecules
in the field of catalysis [27], known to catalyze numerous organic
transformations such as metathesis [4], hydrogenation [7], CeH
bond activation and CeC bond formation [9], tandem catalytic
reactions [28], and cyclopropanation reactions of alkenes with
diazo compounds [29]. Examination of the molecular structure of 1
reveals a metal-coordinated water which is trans to the carbene
unit, presumably labile and offers accessible site for substrate
binding. Accordingly, we evaluated the catalytic properties of 1 for
1, as depicted in Fig. 2, reveals the chelate binding of the ligand
involving carbene carbon and nitrogen atom of the naphthyridine
unit. The Ru1eC23 and Ru1eN2 bond distances of the C^N BIN are
ꢀ
ꢀ
2
.013(5) A and 2.194(4) A. The octahedral coordination sphere
about ruthenium atom is fulfilled by a bromide and two carbonyl
ligands, while the sixth position is occupied by a water molecule.
The water molecule occupies the position trans to the carbene
ꢀ
carbon atom (C23) with a RueO distance of 2.158(3) A which is
2 2
Scheme 1. Synthesis of [Ru(CO) ( O)Br][OTf] (1).
k2C,N-BIN)(H

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A. Sinha et al. / Journal of Organometallic Chemistry 696 (2011) 1248e1257
II
Table 1
Ru eNHC complexes found their applications in this field, though
a
Transfer hydrogenation reaction of ketones catalyzed by 1.
the studies are limited to cyclopropanation reactions. We subjected
complex 1 for the carbene-transfer reactions from ethyl diazo-
acetate (EDA).
To examine the reactivity of 1 towards EDA, the latter was added
to a methylene chloride solution of 1 resulting in the rapid
formation of the olefins diethyl maleate and diethyl fumarate in
1
mol % 1
O
i
OH
KO Pr
i
Ar
R
PrOH
Ar
R
8
0:20 ratio (Scheme 2). Complete decomposition of EDA was
Entry
Ketone
Yield (%)b
observed in less than 2 h (EDA/catalyst 1: 100/1). In the absence of
1, no dimer formed and the chlorinated product ethyl 1,2-dichlor-
opropanoate was observed after 16 h of stirring. This observation is
consistent with the formation of metalecarbene adduct from EDA
with the extrusion of nitrogen. Furthermore, observed selectivity in
the olefin products is indicative of possible stereoselectivity in the
product from the carbene-transfer reactions catalyzed by 1.
1
2
3
4
5
6
7
Benzophenone
Acetophenone
85
83
80
79
77
77
76
65
59
<1
2-Methylacetophenone
4-Methoxyacetophenone
3-Nitroacetophenone
2,4-Dimethoxyacetophenone
2-Fluroacetophenone
Acetylthiazole
c
8
c
9
1
Acetylpyridine
Acetylpyrrole
0d
2.2.3. Cyclopropanation of olefins
Reaction of EDA with alkene is among the conventional reac-
tions to evaluate the efficiency of the catalysis in carbene-transfer
reactions. Room temperature addition of a 1.5 mmol of EDA to
a dichlormethane solution of 1 (1 mol%) and substituted olefins
(10 mmol) resulted in the formation of the cis and trans cyclopro-
panes (Scheme 3, Table 2). Dilute EDA solution and excess olefins
were added to minimize the dimerization of EDA relative to the
desired cyclopropane products. Products were identified by GC and
a
i
Reaction conditions: 1 mmol substrate, 1 mol% 1, 0.5 mL 0.1 M KOH in PrOH,
C, 5 h, unless mentioned otherwise.
ꢁ
3
0
b
c
Isolated yield.
ꢁ
1
2
2 h, 80 C.
d
ꢁ
4 h, 80 C.
transfer hydrogenation reaction and carbene-transfer reactions.
The results are discussed in the preceding sections.
1
H NMR, and yields were obtained by isolation of the products or by
integration of peaks in the GC traces relative to that of an internal
standard.
2
.2.1. Catalytic transfer hydrogenation reaction
Complex 1 showed moderate activity in the transfer hydroge-
Styrene gave moderate cyclopropanation yield (60%) in 6 h
nation reaction of aromatic and heteroaromatic ketones to the
corresponding secondary alcohols from PrOH/KOH at room
i
(entry 1). Substituted styrenes containing electron donating
substituent provided slightly better conversion (entries 2 and 3)
compared to those containing electron withdrawing substituent
temperature. For aromatic ketones, yields exceed 75% irrespective
of the substituents on the phenyl groups (entries 1e7, Table 1).
The catalyst exhibits diminished activity towards the hetero-
aromatic ketones; acetylpyridine and acetylthiazole afforded
moderate yields (55e65%) at elevated temperature (entries 8 and
(
entry 4). The
cyclopropanations.
sion similar to styrene derivatives; whereas, cinnamonitrlie (entry
) gave very poor conversion (<5%). Even a longer duration and
b
-substituted styrenes were also examined for
b-Methylstyrene (entry 5) afforded a conver-
6
9
). No conversion was observed for acetylpyrrole (entry 10) even
higher temperature did not improve the conversion. Among all
compounds studied in this work, ethyl vinyl ether afforded the best
conversion (90%) (entry 7) though the selectivity is poor (55:45).
The cyclic aliphatic alkenes had shown slightly lower reactivity
after prolonged heating.
2.2.2. Carbene-transfer reactions
Transition metalecatalyzed transfer of carbene moiety from an
(entries 8e11). Longer reaction times improved the yields only
aliphatic diazo source to organic substrates has received consider-
able interests in the last few decades [30]. These reactions are
mostly catalyzed by rhodium and copper catalysts [31]. Recently
marginally. In case of the cyclic dialkene 1,5-cyclooctadiene,
cyclopropanation occurred in one double bond (entry 11).
Scheme 2. Dimerization of EDA catalyzed by 1.
Scheme 3. Cyclopropanation reaction catalyzed by 1.

A. Sinha et al. / Journal of Organometallic Chemistry 696 (2011) 1248e1257
1251
Table 2
a
Complex 1 catalyzed cyclopropanation of alkene.
CO Et
2
N2
1
mol % 1
DCM
R
R
H
CO Et
2
R
R
.
Entry
1
Reactant
Product
Time (h)
Conversionb
Yield (%)c
6
6
62
60
66
COOEt
MeO
MeO
2
3
70
65
COOEt
6
6
62
55
COOEt
COOEt
F
F
4
5
59
65
6
60
COOEt
CN
6
6
6
<5
e
CN
COOEt
O
7d
O
90
70
COOEt
COOEt
8
9
8
8
62
58
55
50
COOEt
COOEt
COOEt
1
0e
10
10
58
55
56
50
1
1
a
ꢁ
Reaction conditions: 1.5 mmol EDA in 3 mL dichloromethane was slowly added to the mixture of 10 mmol alkene, 1 mol% 1 in 5 mL dichloromethane at 40 C. E/Z ratio: in
the range of 70/30, unless mentioned otherwise.
b
Determined by GCeMS after reaction.
Combined yields of E and Z isomer after chromatography.
E/Z ratio 55:45.
E/Z ratio 60:40.
c
d
e

1252
A. Sinha et al. / Journal of Organometallic Chemistry 696 (2011) 1248e1257
2
.2.4. Ylide formation and aldehydeeolefination
Aldehydeeolefination via reaction with the ylide is one of the
aldehydes (1 mmol) using 1.5 mmol ethyl diazoacetate (EDA),
1.2 mmol of PPh , 1 mol% catalyst in toluene.
3
important synthetic transformations in synthetic organic chemistry.
Classically Wittig and its numerous variants are used for this process
Treatment of benzaldehyde with EDA/PPh
3
/catalyst 1 in toluene
ꢁ
at 60 C provided ethyl cinnamate in 75% conversion after 6 h of
reaction time with an E/Z ratio of 92:8. Purification of the product
by silica gel column chromatography with petroleum ether/ethyl
acetate (9:1 v/v) afforded 73% isolated yield (entry 7) and the
product was characterized by NMR. Ethyl maleate and fumarate
were also observed in GCeMS as side products resulting from the
dimerization of carbene although the combined yields are less than
10%. All results are collected in Table 3.
[32]. Multistep synthetic methods, low selectivity and possible
epimerization of base-sensitive substrates are the major short-
comings of the ylide generation. Development of metal-mediated
carbene-transfer reactions have appeared as a potential substitute
for these widely used classical methods [33]. The carbene-transfer
ability of 1 was tested in the aldehydeeolefination reactions. Car-
benes are transferred to tertiary phosphines providing corre-
sponding phosphorous ylides which subsequently participate in the
olefination reaction. The reactions were carried out with variety of
Among the aldehydes studied, those containing electron with-
drawing groups were found to be more reactive as compared to
Table 3
a
Olefination of aldehydes with EDA catalyzed by 1.
CO
2
Et
Ph
N
2
O
1 mol % 1
PPh
3
3
P
O
H
CO
2
Et
Toluene
R
R
ꢁ
Conversionb
100
E/Z (%)c
99/1
Yield (%)c
Entry
1
Aldehyde
Product
Temp. ( C)
Time (h)
1
COOEt
COOEt
O
25
95
O N
NO
2
NO2
2
O
2
N
O
2
3
4
5
25
25
60
25
2
2
6
2
95
85
88
85
98/2
99/1
91/9
93/7
92
80
82
80
O N
2
2
O N
COOEt
O
NO2
NO
2
COOEt
COOEt
COOEt
O
O
NC
F3C
Br
NC
F3C
O
6
7
8
60
60
60
6
6
6
83
75
60
98/2
92/8
99/1
75
73
54
Br
COOEt
O
COOEt
O
OH
OH

A. Sinha et al. / Journal of Organometallic Chemistry 696 (2011) 1248e1257
1253
Table 3 (continued )
ꢁ
Conversionb
70
E/Z (%)c
93/7
Yield (%)c
Entry
Aldehyde
Product
Temp. ( C)
Time (h)
6
COOEt
COOEt
O
9
60
60
47
O
1
1
0
60
6
55
96/4
97/3
Me N
2
2
Me N
COOEt
O
1
2
60
60
10
6
38
30
10
MeO
MeO
O
COOEt
1
w10
a
3
Reaction conditions: To a stirred solution of 1 mol % complex 1, 1 mmol aldehyde, and 1.2 mmol of Ph P in 5 mL of toluene at room temperature was added drop-wise
a solution of 1.5 mmol of EDA in 3 mL of toluene.
b
Determined by GCeMS after reaction.
Combined yields of E and Z isomer after chromatography.
c
Scheme 4. Reaction of p-nitrobenzaldehyde with EDA in absence of 1.
aldehydes with electron donating groups. Incorporation of nitro
groups in aromatic ring provided higher yield and E-selectivity.
Quantitative conversion (100%) of product was achieved for
carbene is transferred to the phosphine resulting in the phos-
phorane, Ph
3
P ¼ CHCOOEt. The ylide then undergoes Wittig type
reaction with aldehyde to produce the new olefin and phosphine
oxide. The intermediacy of the phosphorane is confirmed by
a controlled experiment, where the phosphorane was identified by
2
,4-dinitrobenzaldehyde (entry 1) at ambient temperature in 1 h
with excellent selectivity (99:1). Similar conversion and selectivity
was also observed for p-nitrobenzaldehyde (entry 2). o-Nitro-
benzaldehyde and p-trifluoromethylbenzaldehyde showed similar
conversion (85%) with slightly less E-selectivity for the later (93:7)
31
P NMR spectroscopy in absence of aldehyde. Involvement of the
Wittig type reaction in the process also explains the higher reac-
tivity of the electron deficient aldehydes which make the carbonyl
carbon more electronegative facilitating the nucleophilic attack of
the ylide carbon to aldehyde. It should be pointed out that the
formation of ylide that is catalyzed and not the subsequent Wittig
reaction.
(
entries 3 and 5). Only 53% conversion was achieved for p-cyano-
benzaldehyde at room temperature; increase of temperature and
reaction time drastically improved conversion to 88% (entry 4).
Electron-rich aldehyde exhibited reduced reactivity. Lower
conversions (<70%) were observed for o-hydroxy, p-tolyl and
p-(N,N-dimethyl)aminobenzaldehyde after 6 h of reaction time and
2.2.5. Carbene insertion into NeH and OeH bonds
Transition metal-mediated insertion reaction of carbenes into
polar NeH and OeH bonds have become a convenient method for
ꢁ
at elevated temperature (60 C) (entries 8, 9, 10). p-methox-
ybenzaldehyde (entry 11) was found to be the least reactive among
the aromatic aldehydes, and the reaction could be completed only
after prolonged reaction time (10 h). Excellent E-selectivities
were observed in every case. The aliphatic aldehyde 2-phenyl-
acetaldehyde was found to be inactive and only w10% conversion
was observed (entry 12).
The presence of triphenylphosphine was found to be essential
for this reaction. No olefin was observed in absence of triphenyl-
phosphine. Invariably, the formation of triphenylphosphine oxide
was observed from GCeMS. The reaction is catalytic since no ole-
fination product was observed without the application of the
catalyst under identical conditions. Azine was identified as the only
product when p-nitrobenzaldehyde was reacted with EDA for 2
days in absence of catalyst (Scheme 4).
Based on this information, a catalytic cycle is proposed in
Scheme 5 [33d]. In the initial step, EDA reacts with the ruthenium
II
(
(
II) catalyst 1 and forms a metal-carbenoid intermediate [Ru ¼ CH
COOEt)] with the extrusion of N
2
. In the next step, the incipient
Scheme 5. Mechanism for Ru(II) catalyzed aldehyde olefination reaction.

1254
A. Sinha et al. / Journal of Organometallic Chemistry 696 (2011) 1248e1257
Scheme 6. Carbene insertion reaction into NeH and OeH bonds catalyzed by 1.
the synthesis of
a-amino and a-alkoxycarboxylic acid derivatives
[34]. The NeH bonds of aromatic and aliphatic amine, as well as the
OeH bonds of aliphatic alcohols, were functionalized. The reactions
were carried out with variety of primary/secondary amines and
alcohols (1 mmol) using 1.5 mmol ethyl diazoacetate (EDA) and
Table 4
a
Complex 1 catalyzed insertion of carbene into NeH and OeH bonds.
1
mol% catalyst in DCM (Scheme 6).
The results are collected in Table 4. This reaction was found to be
N2
1
mol % 1
DCM
X
H
X
CO Et
2
excellent for aromatic amines and aliphatic alcohols. The insertions
of EDA into the NeH bond of primary aromatic amines (entries 1, 2
and 3) and that into OeH bond of primary aliphatic alcohols
H
CO Et
2
X = R N, RO
2
(entries 7 and 8) were found to be very high exceeding 90%.
Aliphatic secondary amines (entries 4 and 5) and alcohols (entry 9)
show relatively less activity with a conversion w80%, while benzyl
amine shows least activity (entry 6).
Entry
1
Reactant
Product
Conversion
98
NH2
N
H
COOEt
3. Conclusion
We have reported a new high-yield synthetic protocol for
COOEt
accessing metal-NHC complex from metalemetal singly bonded
dimetal precursor. Oxidative addition of the imidazolium C2eH
2
NH
2
N
96
H
bond into [RuI
BIN)(H
(CO)
O)Br][OTf] (1). The NHC$HBr addition occurs at the expense
II
2
2
4 3 6 2 2
(CH CN) ][OTf] afforded [Ru (CO) (k C,N-
2
of the metalemetal bond cleavage. Complex 1 exhibits good
activities in catalyzing transfer hydrogenation of ketone to alcohols.
It is also shown to be a carbene-transfer catalyst from EDA to
various organic substrates. The best results are obtained for carbene
insertion into OeH and NeH bonds of alcohols and amines.
NC
NH2 NC
N
H
3
4
5
COOEt 96
N
N
NH
NH
88
80
COOEt
4. Experimental section
COOEt
4.1. General procedures, materials and physical measurements
All reactions with metal complexes were carried out under an
atmosphere of purified nitrogen using standard Schlenk-vessel and
vacuum line techniques. Solvents were dried by conventional
methods, distilled under nitrogen and deoxygenated prior to use.
COOEt
N
6
NH2
45
H
RuCl
3
$H
2
O
was purchased from Arora Matthey, India. The
(CO) (CH CN) (OTf) [35] and 1-Benzyl-3-(5,7-
compounds Ru
2
4
3
6
2
O
dimethyl-1,8-naphthyrid-2-yl)imidazolium bromide [24] were
synthesized following the literature procedure. Substrates for
catalysis were purchased from commercial suppliers and used as
received.
O
COOEt
H
7
8
95
95
OH
O
COOEt
1
H NMR spectra were obtained on JEOL JNM-LA 500 MHz
1
spectrometers. H NMR chemical shifts were referenced to the
residual hydrogen signal of the deuterated solvents. Elemental
analyses were performed on a Thermoquest EA1110 CHNS/O
analyzer. The crystallized compounds were powdered, washed
several times with dry diethyl ether and dried in vacuum for at least
9
OH
O
COO Et
72
4
8 h prior to elemental analyses. Infrared spectra were recorded in
a
Reaction conditions: 1.5 mmol EDA in 3 mL dichloromethane was slowly added
ꢀ1
the range of 4000e400 cm on a Vertex 70 Bruker spectropho-
tometer. ESI-MS was recorded on a Waters Micromass Quattro
to the mixture of 1 mmol amine or alcohol, 1 mol% 1 in 5 mL dichloromethane at
0
ꢁ
4
C and the reaction was continued for 6 h.

A. Sinha et al. / Journal of Organometallic Chemistry 696 (2011) 1248e1257
1255
Micro triple-quadrupole mass spectrometer. ESI-MS of compound 1
was recorded in acetonitrile. GCeMS experiments were performed
on an Agilent 7890A GC and 5975C MS system.
then it was extracted with diethyl ether (3 ꢂ 20 mL). The ethereal
solution was washed with brine (3 ꢂ 10 mL) and dried over MgSO
4
and filtered. After removing the solvent under vacuum, the product
was purified by chromatography on a silica gel column using
a mixture hexane/EtOAc as eluent.
4
.2. Synthesis of aqua-bromo-dicarbonyl-[1-benzyl-3-(5,7-dimethyl-
,8-naphthyrid-2-yl)imidazol-2-ylidene]ruthenium(II) trifluomethyl-
sulphonate (1)
1
4.3.4. NeC bond formation
3
mL dichloromethane solution of EDA (1.5 mmol, 0.14 mL) was
1
-Benzyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazolium
drop-wise added to the mixture of amine (1 mmol) and catalyst 1
bromide (42 mg, 0.106 mmol) was added to a dichloromethane
(0.01 mmol) in dichloromethane under nitrogen atmosphere over
a period of 30 min. Then the solution was stirred for 6 h at 40 C. The
ꢁ
solution of Ru
2
(CO)
4
(CH
3
CN)
6
(OTf)
2
(45 mg, 0.052 mmol) and
stirred at room temperature for 6 h. Resulting greenish-yellow
solution was concentrated under reduced pressure and diethyl
ether was added to induce precipitation. The yellowish-brown solid
was washed with diethyl ether and dried under vacuo. Crystals
suitable for X-ray diffraction were grown by layering petroleum
progress of the reactionwas monitored by GC. After the reactionwas
over, the reaction mixture was extracted with diethyl ether
(3 ꢂ 20 mL). The ethereal solution was washed with brine
(3 ꢂ 10 mL) and dried over MgSO
4
and filtered. After removing the
solvent under vacuum, the product was purified bychromatography
ether over a concentrated dichloromethane solution of the
on a silica gel column using a mixture hexane/EtOAc as eluent.
1
compound. Yield: 56 mg (80%). H NMR (500 MHz, CD
3
CN, 293K):
8
8
.998e8.976 (1H, d, J ¼ 8.75 Hz, NP), 8.20 (1H, d, J ¼ 2.3 Hz, Im),
4.3.5. OeC bond formation
.07 (1H, d, J ¼ 8.75 Hz, NP), 7.52 (s, 1H, NP), 7.434e7.33(6H, m, Im,
3 mL dichloromethane solution of EDA (1.5 mmol, 0.14 mL) was
drop-wise added to the mixture of alcohol (1 mmol) and catalyst 1
(0.01 mmol) in dichloromethane under nitrogen atmosphere over
Ph), 5.55 (2H, dd, J ¼ 50 Hz, J ¼ 16 Hz, methylene), 2.77 (3H, s, Me),
.73 (3H, s, Me). 13C NMR (127.7 MHz, CD
CN, 293K): 194.2 (CO),
87.3 (CO), 178.9 (NCNIm), 165.7 (NCNNP), 154.2 (NCCNP), 153.8
NCCNP), 147.99 (CCCNP), 141.9 (CHNP), 134.7 (CHPh), 129.1 (CHPh),
28.6 (CHPh), 127.3 (CHPh), 125.9 (CHNP), 125.2 (CHIm), 120.4 (CCCNP),
19.2 (CHNP), 110.7 (CHIm), 54.5 (CH Ph), 24.8 (CH ), 17.5 (CH ). IR
(CO): 2073 (s), 2011 (s),; (OTf): 1257. ESI-MS,
2
1
(
1
3
ꢁ
a period of 30 min. Then the solution was stirred for 6 h at 40 C. The
progress of the reaction was monitored by GC. After the reaction
was over, the reaction mixture was extracted with diethyl ether
(3 ꢂ 20 mL). The ethereal solution was washed with brine
1
2
3
3
ꢀ
1
(
KBr) data (cm ):
n
n
(3 ꢂ 10 mL) and dried over MgSO
4
and filtered. After removing the
þ
þ
m/z (fragment): 594 [MeH
2
O
þ
CH
3
CN] , 571 [M] , 553
(BIN)(H O)Br.
BrRu: C, 38.45; H, 2.80; N, 7.80.
Found: C, 38.55; H, 2.97; N, 7.87.
solvent under vacuum, the product was purified bychromatography
þ
þ
[
M ꢀ H
2
O] , 525 [MeH
2
OeCO] where M is Ru(CO)
SO
2
2
on a silica gel column using a mixture hexane/EtOAc as eluent.
Anal. Calcd for C23
H
20
N
4
F
3
6
4.4. X-ray data collections and refinement
4
4
.3. General procedures for catalysis
Single crystal X-ray structural studies were performed on a CCD
Bruker SMART APEX diffractometer equipped with an Oxford
Instruments low-temperature attachment. Data were collected at
.3.1. Transfer hydrogenation
Aromatic ketone (1 mmol) and 1 (0.01 mmol) were placed in
a Schlenk flask and the vessel was flushed with nitrogen. 12 mL
-propanol was added to the mixture and stirred for 5 min. 0.5 mL
of 0.1 M KOH in 2-propanol was added to the mixture. Reaction
was continued under the conditions mentioned in Table 1. After
completion of reaction, as monitored by GC, the reaction mixture
was evaporated and the crude product was purified by silica gel
column chromatography using 10% ethyl acetate/petroleum ether.
100(2) K using graphite-monochromated Mo-K
a
radiation (
l
¼
a
ꢀ
0.71073 A). The frames were indexed, integrated and scaled using
SMART and SAINT software package [36], and the data were cor-
rected for absorption using the SADABS program [37]. The
2
Table 5
Crystallographic data and pertinent refinement parameters for 1.
Empirical formula
Formula weight
Crystal system
Space group
3 4 6
C23H18BrF N O SRu
716.45
Triclinic
P ꢀ 1
4
.3.2. Cyclopropanation reaction
mL dichloromethane solution of EDA (1.5 mmol, 0.14 mL) was
added drop-wise to the mixture of alkene (10 mmol) and catalyst 1
0.01 mmol) in dichloromethane under nitrogen atmosphere over
3
ꢀ
a (A)
8.2654(7)
ꢀ
b (A)
10.2658(9)
16.3288(14)
95.5860(10)
91.7690(10)
107.6390(10)
1311.4(2)
2
ꢀ
(
c (A)
a
b
g
(deg)
a period of 30 min. Then the solution was stirred for 6 h at room
temperature. The progress of the reaction was monitored by GC.
After the reaction was over, the reaction mixture was extracted
with diethyl ether (3 ꢂ 20 mL). The ethereal solution was washed
(deg)
(deg)
ꢀ
3
V (A )
Z
ꢀ3)
with brine (3 ꢂ 10 mL) and dried over MgSO
4
and filtered. After
r
calcd (g cm
1.814
2.269
m
(mm 1
ꢀ
)
removing the solvent under vacuum, the product was purified
by chromatography on a silica gel column using a mixture
hexane/EtOAc as eluent.
F(000)
708
Reflections
Collected
11700
6247
5127
354
1.102
Independent
Observed [I > 2
No. of variables
GooF
s
(I)]
4
.3.3. Aldehydeeolefination reaction
mL toluene solution of EDA (1.5 mmol, 0.14 mL) was added
drop-wise to the mixture of triphenylphosphine (1.2 mmol,
14 mg), aldehyde (1 mmol) and catalyst 1 (0.01 mmol) in toluene
3
R
int
0.0242
R1 ¼ 0.0480
Final R indices [I > 2s
(I)]a
3
over a period of 30 min under nitrogen atmosphere. The reactions
were performed under the conditions mentioned in Table 3. The
progress of the reaction was monitored by GC. After the reaction
was over, the resulting mixture was cooled to room temperature,
wR
2
¼ 0.1235
R indices (all data)a
R
¼ 0.0644
2
1
wR
¼ 0.1542
a
2
2
2
2
2
2 2
j ]1/2.
R
1
¼ SkF
o
j e jF
c
k/SjF
o
j with F
o
> 2
s(F
o
). wR
2
¼ [Sw(jF
o
j e jF
c
j) /SjF
o

1256
A. Sinha et al. / Journal of Organometallic Chemistry 696 (2011) 1248e1257
structures were solved and refined using SHELX suite of programs
38] while additional crystallographic calculations were performed
by the programs PLATON [39]. Figures were drawn using ORTEP32
40]. The hydrogen atoms were included into geometrically calcu-
lated positions in the final stages of the refinement and were
refined according to ‘riding model’. Hydrogen atoms of the coor-
dinated water molecule were not included in the structure. All non-
hydrogen atoms were refined with anisotropic thermal parameters.
Crystallographic data and pertinent refinement parameters for 1
are presented in Table 5.
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This work was financially supported by the Department of
Science and Technology (DST), India. J.K.B. thanks DST for the
Swarnajayanti Fellowship and Ramanna Fellowship. A.S. and B.S.
thank CSIR, S.M.W.R. thanks UGC, India for fellowships, P.D. thanks
CSIR for the Shyama Prasad Mukherjee Fellowship.
Macromolecules 36 (2003) 6953.
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CCDC-793941 contains the supplementary crystallographic data
for compound 1. This data can be obtained free of charge from The
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