Efficient and versatile transfer hydrogenation catalysts: Iridium (III) and ruthenium (II) complexes with 4-acetylbenzyl-N-heterocyclic carbenes

Article abstract of DOI:10.1016/j.molcata.2014.06.004

New 4-acetylbenzyl-N-heterocyclic carbene ligands (1-4) have been used to synthesize iridium complexes 6-9 and ruthenium complex 10. All complexes were characterized by FT-IR, ¹H and ¹³C NMR spectroscopy, elemental analysis, and in the case of 6, by X-ray diffraction studies. The catalytic performance of these iridium and ruthenium complexes for transfer hydrogenation of ketones and imines and N-alkylation of amines with primary alcohols were tested in a range of substrates, and showed high catalytic activity with 1 mol% catalytic loading. The neutral complex 8 with two acetyl groups also showed good catalytic efficiency under lower catalyst loading (0.01 mol%), with the maximum TON of 8000, while on the other hand, the cationic complex 9 with PF₆^- as counteranion showed good to excellent catalytic activity toward the N-alkylation of amines in a wide scope of substrates. We also found out that the Ir complex 6′ was formed through the intramolecular CH activition of 6 under the transfer hydrogenation conditions.

Full text of DOI:10.1016/j.molcata.2014.06.004

Journal of Molecular Catalysis A: Chemical 393 (2014) 134–141
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Efficient and versatile transfer hydrogenation catalysts: Iridium (III)
and ruthenium (II) complexes with 4-acetylbenzyl-N-heterocyclic
carbenes
Xiao-Han Zhu1, Li-Hua Cai1, Chen-Xi Wang, Ya-Nong Wang, Xu-Qing Guo, Xiu-Feng Hou∗
Department of Chemistry, Fudan University, 220 Handan Road, Shanghai 200433, China
a r t i c l e i n f o
a b s t r a c t
Article history:
New 4-acetylbenzyl-N-heterocyclic carbene ligands (1–4) have been used to synthesize iridium com-
plexes 6–9 and ruthenium complex 10. All complexes were characterized by FT-IR, 1H and 13C NMR
spectroscopy, elemental analysis, and in the case of 6, by X-ray diffraction studies. The catalytic perfor-
mance of these iridium and ruthenium complexes for transfer hydrogenation of ketones and imines and
N-alkylation of amines with primary alcohols were tested in a range of substrates, and showed high cat-
alytic activity with 1 mol% catalytic loading. The neutral complex 8 with two acetyl groups also showed
good catalytic efficiency under lower catalyst loading (0.01 mol%), with the maximum TON of 8000, while
Received 21 April 2014
Received in revised form 30 May 2014
Accepted 3 June 2014
Available online 12 June 2014
Keywords:
Iridium
Ruthenium
N-Heterocyclic carbenes
Transfer hydrogenation
Alkylation
−
on the other hand, the cationic complex 9 with PF6 as counteranion showed good to excellent catalytic
activity toward the N-alkylation of amines in a wide scope of substrates. We also found out that the Ir
complex 6ꢀ was formed through the intramolecular C H activition of 6 under the transfer hydrogenation
conditions.
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
Crabtree et al. [2c] reported the chelated iridium (III) bis-carbene
complexes. Then, several Ir(I)/Ir(III)–NHC [3] and Ru(II)–NHC [4]
The transfer hydrogenation reaction refers to the addition of
hydrogen to a molecule from a source other than gaseous H2. It is
a powerful strategy to access various alcohols and amines via the
reduction of ketones or imines using organic or inorganic reagents
acting as hydrogen donors [1], for it avoiding the inconvenience and
expense of employing the gaseous H2. Metal catalysts for transfer
hydrogenation present significant practical advantages, particu-
larly in large-scale synthesis, since there is no need to employ a
high dihydrogen pressure or hazardous reducing agents [2].
N-Heterocyclic carbenes (NHCs) as ligands have been applied
for homogeneous catalysis in recent years. The NHC ligands have
strong coordination ability and, because of their tunable charac-
ter, can adjust the steric and electronic properties on the metal
center. Iridium and ruthenium complexes with NHC ligands have
been developed to catalyze the transfer hydrogenation of C O and
complexes with chelating or non-chelating groups were applied as
precatalysts for hydrogen transfer from 2-propanol to ketones.
In addition, the N-alkylation of amines with alcohols is an attrac-
tive method of the formation of C N bonds for replacing the toxic
halides as alkylation reagents and water as sole byproducts [5], and
a number of highly efficient metal complexes catalysts have been
reported [6]. A recent computational study shows that N-alkylation
of amines with alcohols catalyzed by iridium compounds includes
the step of metal-catalyzed reduction of the imines [7], which
implies that the catalysts for transfer hydrogenation prabably work
on N-alkylation of amines with alcohols. However, versatile and
active catalysts both for transfer hydrogenation of ketones and
imines and N-alkylation of amines with alcohols have been rarely
developed [6j,8].
Our group has been interested in the synthesis and catalytic
performance of the functionalized N-heterocyclic carbene metal
complexes during the past few years [9]. In this work, we describe
the preparation of 4-acetylbenzyl-N-heterocyclic carbene iridium
and ruthenium complexes. The catalytic activity of these new
complexes has been studied in a wide set of reactions. Further-
more, the stability of the ligand was evaluated under catalytic
conditions.
C
N groups. In 2001, Nolan et al. [2a] first applied iridium(I)–NHC
complexes to the transfer hydrogenation of cyclohexanone. Later,
∗
Corresponding author. Tel.: +86 21 55664878; fax: +86 21 65641740.
E-mail address: xfhou@fudan.edu.cn (X.-F. Hou).
These authors contributed equally to this work.
1
http://dx.doi.org/10.1016/j.molcata.2014.06.004
1381-1169/© 2014 Elsevier B.V. All rights reserved.

X.-H. Zhu et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 134–141
135
Table 1
Optimization
Br
N
of
reaction
conditions
of
transfer
hydrogenation.a
1: R= methyl
O
OH
R
N
2: R= 2,4,6-trimethylphenyl
3: R= 4-acetylbenzyl
4: R= pyrimidyl
O
OH
Ir/Ru-NHC
tBuOK
+
+
.
O
Entry
Cat. (mol%)
Yieldb (%)
TONc
Fig. 1. Imidazolium salt precursors for NHC ligands.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25d
26d
27[d]
5 (1)
6 (1)
7 (1)
8 (1)
9 (1)
10 (1)
94
95
95
96
94
96
95
97
95
96
97
95
94
97
95
98
95
96
67
71
70
80
70
72
49
60
76
94
95
95
96
94
2. Results and discussion
2.1. Synthesis of precursors for NHC ligands
96
5 (0.5)
6 (0.5)
7 (0.5)
8 (0.5)
9 (0.5)
10 (0.5)
5 (0.1)
6 (0.1)
7 (0.1)
8 (0.1)
9 (0.1)
10 (0.1)
5 (0.01)
6 (0.01)
7 (0.01)
8 (0.01)
9 (0.01)
10 (0.01)
5 (0.01)
6 (0.01)
8 (0.01)
190
194
190
192
194
190
940
970
950
980
950
960
6700
7100
7000
8000
7000
7200
4900
6000
7600
The imidazolium salt precursors for 4-acetylbenzyl-N-
heterocyclic carbene ligands were prepared by alkylation of
1-substituted imidazole with the alkyl bromide (Fig. 1). Reactions
of 1-[4-(bromomethyl)phenyl]ethanone with 1-methyl-, 2,4,6-
trimethylphenyl-, 4-acetylbenzyl- and pyrimidylimidazole gave
4-acetylbenzyl-substituted imidazolium salts (1–4) with different
bulk, respectively. The imidazolium salts (1–4) were isolated in
excellent yields and were characterized by FT-IR, 1H and 13C NMR
spectroscopy and elemental analysis. In FT-IR spectra of 1–4, the
ꢀC
absorptions were found at 1660 cm−1. The characteristic
O
downfield shifted resonances of the NCHN imidazolium fragment
of 1–4 were observed in the 1H and 13C NMR spectra in CDCl3 (or
DMSO) at ı 9.43, 10.74, 9.48, 10.96 ppm and 140.4, 141.4, 140.1,
159.9 ppm, respectively.
2.2. Synthesis of iridium(III) and ruthenium(II) complexes
a
Reaction conditions: acetophenone (1.0 mmol), tBuOK (10 mol%), iPrOH (3 mL),
The iridium complex 5 without acetylbenzyl group was pre-
pared by reported method [10]. The new neutral iridium(III)
complexes with acetylbenzyl-functonalized NHC ligands 6–8
were synthesized according to the established protocol from
the corresponding silver carbene complexes with [IrCp*Cl2]2 in
dichloromethane and purified by column chromatography as yel-
low solids in moderate yield (Fig. 2). The cationic iridium (III)
complex 9 was obtained by the reaction of the pyrimidyl-subtituted
silver carbene complex with [IrCp*Cl2]2 and followed by an anion-
exchange procedure with KPF6. The ruthenium complex 10 was
prepared in an analogous manner with 6, using [Ru(p-cymene)Cl2]2
as metalation reagent.
82 ◦C, 24 h.
b
Isolated yield.
TON = (mmol of product)/(mmol of catalyst).
Acetophenone (10.0 mmol).
c
d
spectra of 6–10, the disappearance of the downfield-shift NCHN
resonance indicated the deprotonation of the proton of imidaz-
olium fragment. In addition, the metalation becomes evident, as
the low-field resonance around ı 157.4, 155.2, 158.7 159.5 and
175.0 ppm were observed in the 13C NMR spectra of 6–10 respec-
tively. Notably, signals at 7.83, 7.68 and 7.07 ppm in the 1H NMR
spectrum of 9 showed the characteristic set of three distinct peaks
for the pyrimidyl ring, which is caused by the loss of symmetry,
and indicated the N atom in the pyrimidyl group coordinating to
the metal iridium.
The complexes 6–10 were characterized by FT-IR, 1H and 13C
NMR spectroscopy, elemental analysis and in the case of 6, by X-ray
crystallography. In the IR spectra of 6–10, the characteristic band
around 1660 cm−1 for ꢀC absorption remained. In the 1H NMR
O
In order to obtain more detailed information on the structural
parameters, crystals of complex 6 suitable for X-ray diffrac-
tion were obtained by layering diethyl ether onto a saturated
dichloromethane solution. The structure of 6 and the most repre-
sentative bond lengths and angles are shown in Fig. 3. The Ir center
is in a distorted octahedral environment, Cp* occupies three coordi-
nation sites, and other ones are occupied by carbene carbon and two
chlorine atoms, respectively. The bond length of Ir–Ccarbene and the
Ir–Ccarbene resonance in its 13C NMR spectrum are typical of most
iridium (III) complexes containing an NHC ligand [10,11,2c,2d]. The
dihedral angle between the Cp* ring, the phenyl ring and the imid-
azole ring are 28.1◦ and 57.5◦, respectively.
Cl
Ir
Cl
Cl
Ir
Cl
R
N
N
N
N
5
O
6
:R = methyl
7: R= 2,4,6-trimethylphenyl
8: R= 4-acetylbenzyl
-
PF6
Cl Ru Cl
Cl
Ir
2.3. Transfer hydrogenation of acetophenone catalyzed by Ir and
Ru complexes
N
N
N
N
N
N
The neutral and cationic iridium and ruthenium complexes with
4-acetylbenzyl-NHCs have been explored as catalysts for transfer
hydrogenation of unsaturated substrates, and the results are shown
in Table 1.
O
O
10
9
Fig. 2. Neutral and cationic iridium and ruthenium complexes.

136
X.-H. Zhu et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 134–141
Fig. 3. Crystal structure of 6. Ellipsoids at the 30% probability level. Hydrogen atoms and solvent molecules have been omitted for clarity. Selected bond lengths [Å] and
angles [◦]: Ir(1)–C(12) 2.036(12), Ir(1)–Cl(1) 2.465(3), Ir(1)–Cl(2) 2.478(2), Ir(1)–Cp*(centroid) 1.832(2); Cl(1)–Ir(1)–Cl(2) 86.18(9), C(12)–Ir(1)–Cl(1) 93.1(4), C(12)–Ir(1)–Cl(2)
91.7(3).
The known complex 5 was introduced to gain insight into the
influence of the acetyl group on the transfer hydrogenation. The
reduction of acetophenone to 1-phenylethanol was chosen as a
model reaction to screen the performance of Ir and Ru catalysts
in the presence of 10 mol% of potassium tert-butoxide (tBuOK) as
the base. Several catalytic runs have been carried out at differ-
ent catalyst concentrations using substrate/catalyst (S/C) ratios of
100:1, 200:1, 1000:1, and 10,000:1 in order to gain more details
of the transfer hydrogenation of acetophenone. First, a standard
catalyst loading of 1 mol% was used and all the complexes exhib-
ited excellent catalytic activity (above 94% isolated yield, Table 1,
Entries 1–6). Acetophenone kept excellent yields when decreasing
the catalyst loading even to 0.1 mol% (above 94% isolated yield,
Table 1, Entries 7–18). Although the decrease of the catalyst load-
ing to 0.01 mol% lowered the yields, the Ir complex 8 with two
acetylbenzyl substituents still showed good catalytic activity (80%
isolated yield, Entry 22). When increasing the amount of substrate
(10.0 mmol acetophenone), the Ir complex 8 (0.01 mol%) still exhib-
ited good catalytic activity (above 76% isolated yield and a TON of
7600), while 5 and 6 were less efficient (Entries 25–27). The result
shows that catalytic activity of complex 8 with two acetylbenzyl
groups is better than the ones of other complexes under lower
catalyst loading conditions.
In order to explore the stability of the ligand with acetylben-
zyl group and investigate whether the acetyl group participates in
the transfer hydrogenation reaction, the stoichiometric reaction of
complex 6 with equimolar tBuOK proceeded with no addition of
the ketone. We found that the Ir complex 6 would be converted
to a new complex 6ꢀ, which is relatively stable and can be iso-
lated in 70% yield. Comparison of the 1H NMR spectra of 6 and
6ꢀ, complex 6ꢀ could arise from intramolecular C H activation. The
protons of the CH2 of benzyl group of these two Ir complexes 6 and
6ꢀ are diastereotopic and display signals at d = 6.20 (J = 14.0 Hz) and
5.21 ppm (J = 14.0 Hz) for 6 and at d = 4.85 (J = 14.4 Hz) and 4.73 ppm
(J = 14.0 Hz) for 6ꢀ, which are consistent with previous works in
our laboratory and the research of Peris et al. [9a,10]. The result
suggested these ligands with acetylbenzyl group were stable in
the basic conditions and the acetyl would not be converted to a
hydroxyl-ethyl group via transfer hydrogenation (Fig. 4).
hydrogenation reactions of different ketones and imines were car-
ried out, as shown in Table 2. Obviously, p-methyl-acetophenone,
p-chloro-acetophenone, benzophenone and 2-decanone exhibited
good yields with the TON around 8000 at the S/C ratio of 10,000,
and almost quantitative yields at the S/C ratio of 100. The results
indicate that these electron-withdrawing or electron-donating aryl
ketones and alkyl ketones could be tolerated under these condi-
tions.
Imine hydrogenation has several important drawbacks such
as the imine nitrogen lone pair coordination to the metal cen-
ter, which inhibits the ꢁ2 (C N) coordination required for the
insertion into metal-hydride bonds, or the poisoning effect of
the resultant amines on the catalyst [3b]. Therefore, finding suit-
able catalytic systems with high activities for the hydrogenation
of imines has attracted much attention. We found out that the
neutral iridium complex 8 with bis-(4-acetylbenzyl)NHC ligand
worked effectively in the transfer hydrogenation of imines with
both electron-withdrawing and electron-donating groups in good
yields (Table 2, Entries 5–7). All these results demonstrate the ver-
satility of 8 toward the transfer hydrogenation of both ketones and
imines.
2.5. N-alkylation of amines with alcohols catalyzed by Ir
complexes or Ru complexes
The neutral and cationic iridium and ruthenium complexes in
hand were tested for activity in N-alkylation of amines with alco-
hols. Initially, the N-alkylation of aniline with benzyl alcohol was
used as the model reaction and the optimization was carried out
(Table 3). The catalytic activity of iridium complex 6 was similar to
the corresponding ruthenium comple−x 10 (Entries 2 and 6), and the
cationic iridium complex 9 with PF6 as counteranion was effec-
tive as the neutral ones under the same conditions (Entries 1–6).
Besides, the Ir complex 8 with two acetyl groups, which showed
the highest catalytic activity toward the transfer hydrogenation,
was nearly as effective as the complex 9. Several bases were also
employed in this reaction (Entries 7–10), and 0.5 mmol tBuOK was
found most effective (Entry 7).
Various amines and alcohols were then chosen to explore the
activity of 9 and the results were summarized in Table 4. Benzyl
alcohols with electron-withdrawing and electron-donating group
(Entries 1–2) and even aliphatic alcohol (Entry 3) could react with
aniline in excellent yield. We also tested various amines with ben-
zyl alcohol as substrates. Aniline with halo substituent obtained
excellent yield (Entry 4) but decreased sharply with p-methoxyl
2.4. Transfer hydrogenation of ketones and imines catalyzed by Ir
complex 8
In the presence of the Ir complex 8 as a catalyst, tBuOK as a
base, and iPrOH as the solvent as well as hydrogen donor, transfer

X.-H. Zhu et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 134–141
137
Table 2
X
XH
R2
O
OH
8, tBuOK
+
+
R1
R2
X = O, NR'
R1
Transfer hydrogenation with different substrates.a
.
Entry
Substrate
Yieldb (%)
TONc
O
1
93 (74)
98 (75)
93 (7400)
O
Cl
2
98 (7500)
O
3
4
95 (84)
98 (80)
95 (8400)
98 (8000)
O
( )7
N
N
N
OMe
5
6
86
86
79
75
79
75
Cl
7
a
Reaction conditions: substrate (1.0 mmol), 8 (1 mol%), tBuOK (10 mol%), iPrOH (3 mL), 82 ◦C, 24 h.
Isolated yield.
TON = (mmol of product)/(mmol of catalyst). The yield and TON given in parentheses are using 8 (0.01 mol%).
b
c
Table 3
N-alkylation of aniline with benzyl alcohols catalyzed by Ir or Ru complexes.a
NH2
H
N
OH
Catalyst
+
Base, MS
.
Entry
Substrate
Base (mmol)
Yieldb (%)
1
2
3
4
5
6
7
8
9
5
6
7
8
9
10
9
9
9
9
tBuOK (1)
tBuOK (1)
tBuOK (1)
tBuOK (1)
tBuOK (1)
tBuOK (1)
tBuOK (0.5)
NaHCO3 (0.5)
K2CO3 (0.5)
KOH (0.5)
79
78
76
80
82
77
88
73
76
86
10
a
Reaction conditions: aniline (1.1 mmol), benzyl alcohol (1.0 mmol), catalyst (1 mol%), base, 4 A molecular sieves (MS), toluene (0.5 mL), 110 ◦C, 48 h.
Isolated yield.
˚
b

138
X.-H. Zhu et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 134–141
Fig. 4. C H activition of Ir complex 6.
substituent (Entry 5). Besides, aliphatic (Entry 6) and heterocyclic
amines (Entries 7 and 8) exhibited excellent catalytic activity
(above 80% isolated yield). Moreover, both amine and benzyl alco-
hol with electron-withdrawing group showed good performance
with yields up to 80% (Entry 9). It is noteworthy that the complex
9 also showed excellent catalytic activity toward transfer hydro-
genation of acetophenone, with above 94% isolated yield (Table 1,
Entries 5, 11, 17). These results demonstrate that 9 can be tolerated
under a wide range of substrates and can also have an excellent cat-
alytic performance toward both transfer hydrogenation of ketones
and N-alkylation of amines with alcohols.
9 exhibited more effective activity compared to the neutral ones
toward the N-alkylation for typical substrates.
4. Experimental
General. The starting materials [Ru(p-cymene)Cl2]2 [12] and
[IrCp*Cl2]2 [13] were synthesized according to the literature pro-
cedures. All manipulations were carried out under a nitrogen
atmosphere using standard Schlenk techniques unless otherwise
stated. Solvents were distilled under nitrogen from sodium ben-
zophenone (acetonitrile, diethyl ether, THF, toluene) or calcium
hydride (dichloromethane), and methanol was distilled over Mg/I2.
Other chemical reagents were obtained from commercial sources
and used without further purification. NMR spectra were recorded
at room temperature in CDCl3 and [d6]DMSO unless otherwise
stated, using Bruker spectrometers operating at 400 or 500 (1H)
and 100 or 125 MHz (13C), respectively. Elemental analysis was per-
formed using an Elementar Vario EL III analyzer. IR spectra were
recorded using Nicolet AVATAR-360IR.
Synthesis of 1-[4-(bromomethyl)phenyl]ethanone. p-Methyl-
acetophenone (2.0 mL, 14.9 mmol) was dissolved in acetonitrile
(10 mL) under nitrogen. N-bromosuccinimide (NBS) (2.92 g,
16.4 mmol) and benzoyl peroxide (BPO) (0.36 g, 1.49 mmol) were
added and the reaction mixture was stirred for 2 h at 90 ◦C to give
a yellow solution. The solvent was removed in vacuo, the residue
was dissolved in toluene (20 mL) and filtrated. The filtrate was con-
centrated under reduced pressure and purified by silica gel column
chromatography yielded as a white solid (3.0 g, 93%)
3. Conclusions
We successfully synthesized and characterized 4-acetylbenzyl-
N-heterocyclic carbene iridium complexes 6–9 and ruthenium
complex 10. The X-ray structure of 6 shows an ideal distorted
octahedral geometry around Ir center. Cp* is a three-coordinated
ligand, and other three coordination sites are occupied by car-
bene carbon and two chlorine atoms, respectively. These complexes
were applied to transfer hydrogenation of ketones and imines and
to N-alkylation of amines, and proved to be highly active. The Ir
complex 6 with carbonyl substituent showed better catalytic per-
formance than that 5 without carbonyl substituent at low catalyst
loadings. The stoichiometric reaction without the reactant ketone
indicated that the Ir complex converted to complex 6ꢀ through an
intramolecular C H activition process under the reaction condi-
tions. Iridium complex 8 with bis(4-acetylbenzyl)NHC exhibited
excellent to good performance toward transfer hydrogenation of
ketones and imines for typical substrates with a lower catalyst load-
ing, and good yield was also obtained in the N-alkylation of amines
with alcohols with 1 mol% 8. Notably, the cationic iridium complex
Synthesis of 1. 1-Methylimidazole (41.1 mg, 0.5 mmol) was
added to
a solution of 1-[4-(bromomethyl)phenyl]ethanone
(106 mg, 0.5 mmol) in toluene (5 mL) while stirring. The mix-
ture was refluxed for 12 h at 110 ◦C. The solvent was removed

X.-H. Zhu et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 134–141
139
Table 4
N-alkylation of amines with alcohols catalyzed by Ir complex 9.a
H
N
9, tBuOK, MS
R2
R1 NH2
HO
R2
+
R1
Toluene
.
Entry
Amine
Alcohol
Yieldb (%)
NH2
NH2
NH2
OH
Cl
1
2
3
88
91
88
OH
OH
( )5
NH2
OH
Cl
4
90
NH2
OH
OH
OH
OH
O
5
6
7
8
50
80
75
80
NH2
NH2
NH2
N
N
N
NH2
OH
Cl
Cl
9
80
a
Reaction conditions: amine (1.1 mmol), alcohol (1.0 mmol), 9 (1 mol%), tBuOK (0.5 mmol), 4 A molecular sieves (MS), toluene (0.5 mL), 110 ◦C, 48 h.
Isolated yield.
˚
b
in vacuo. The oily residue was washed with diethyl ether several
(Ph), 137.62 (Ph), 134.16 (Ph), 130.67 (Ph), 129.93 (Ph), 129.51
(Ph), 129.26 (Ph), 123.58 (CHimidazole), 123.33 (CH imidazole), 52.39
(CH2 Ph), 26.84 (CH3C O), 21.16 (p-CH3 Ph), 17.14 (o-CH3 Ph).
Elemental analysis calcd (%) for C21H23BrN2O: C 63.16, H 5.81, N
7.02; found: C 63.15, H 5.82, N 7.04.
Synthesis of 3. Following the same procedure as described for 1,
reaction 1-[4-(bromomethyl)phenyl]ethanone (106 mg, 0.5 mmol)
with corresponding imidazole (206.5 mg, 0.5 mmol) yielded 3 as a
white solid (153 mg, 85%). 1H NMR([d6]DMSO, 400 MHz, ppm): ı
9.48 (s, 1H, NCHN),7.97 (d, J = 7.2 Hz, 4H, Ph), 7.85 (s, 2H, NCHCHN),
7.53 (d, J = 7.6 Hz, 4H, Ph), 5.52 (s, 4H, CH2 Ph), 2.55 (s, 6H,
CH3C O).13C NMR([d6]DMSO, 100 MHz, ppm): ı 198.11 (C O),
140.13 (NCN), 137.47 (Ph), 137.34 (Ph), 129.36 (Ph), 129.09 (Ph),
123.65 (NCHCHN), 52.14 (CH2 Ph), 27.39 (CH3C O). Elemental
analysis calcd (%) for C21H21BrN2O2: C 61.03, H 5.12, N 6.78; found:
C 61.04, H 5.13, N 6.77.
times and dried to afford the imidazolium salt 1 as a pale yellow
solid. Yield: 132 mg (90%). 1H NMR ([d6]DMSO, 400 MHz, ppm):
ı 9.43 (s, 1H, NCHN), 8.05 (d, J = 7.2 Hz, 2H, Ph), 7.92 (s, 1H,
CHimidazole), 7.83 (s, 1H, CHimidazole), 7.64 (d, J = 7.6 Hz, 2H, Ph),
5.63 (s, 2H, CH2 Ph), 3.94 (s, 3H, N CH3), 2.63 (s, 3H, CH3C O).
13C NMR ([d6]DMSO, 100 MHz, ppm): ı 198.14 (C O), 140.39
(NCN), 137.43 (Ph), 137.36 (Ph), 129.29 (Ph), 129.04 (Ph), 124.62
(CHimidazole), 122.93 (CHimidazole), 51.78 (CH2 Ph), 36.49 (N CH3),
27.43 (CH3C O). Elemental analysis calcd (%) for C13H15BrN2O: C
52.90, H 5.12, N 9.49; found: C 52.89, H 5.14, N 9.50.
Synthesis of 2. Following the same procedure as described for 1,
reaction 1-[4-(bromomethyl)phenyl]ethanone (106 mg, 0.5 mmol)
with corresponding imidazole (93.6 mg, 0.5 mmol) yielded 2 as a
light gray solid (160 mg, 80%). 1H NMR (CDCl3, 400 MHz, ppm): ı
10.74 (s, 1H, NCHN), 8.00 (d, J = 7.6 Hz, 2H, Ph), 7.76 (d, J = 7.6 Hz,
2H, Ph), 7.59 (s, 1H, CHimidazole), 7.10 (s, 1H, CHimidazole), 7.01
(s, 2H, CHmesityl), 6.10 (s, 2H, CH2 Ph), 2.61 (s, 3H, CH3C O),
2.35 (s, 3H, p-CH3 Ph), 2.07 (s, 6H, o-CH3 Ph). 13C NMR (CDCl3,
100 MHz, ppm): ı 197.64 (C O), 141.39 (NCN), 138.91 (Ph), 137.71
Synthesis of 4. Following the same procedure as described for 1a,
reaction 1-[4-(bromomethyl)phenyl]ethanone (106 mg, 0.5 mmol)
with corresponding imidazole (73.5 mg, 0.5 mmol) yielded 4 as a
light gray solid (153 mg, 85%). 1H NMR (CDCl3, 400 MHz, ppm): ı

140
X.-H. Zhu et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 134–141
10.96 (s, 1H, NCHN), 8.87 (d, J = 4.4 Hz, 2H, Ph), 8.16 (d, J = 6.0 Hz,
2H, Ph), 7.90 (m, 4H, CHimidazole and CHpyrimidine), 7.59 (t, J = 4.8 Hz,
1H, CHpyrimidine), 6.32 (s, 2H, CH2 Ph), 2.56 (s, 3H, CH3C O).
13C NMR (CDCl3, 100 MHz, ppm): ı 197.71 (C O), 159.90 (pyrimi-
dine), 152.12 (NCN), 138.27 (Ph), 137.67 (Ph), 135.84 (pyrimidine),
135.78 (pyrimidine), 129.94 (Ph), 129.22 (Ph), 124.33 (CHimidazole),
122.51 (CHimidazole), 118.83 (pyrimidine), 53.07 (CH2 Ph), 26.91
(CH3C O). Elemental analysis calcd (%) for C16H15BrN4O: C 53.50,
H 4.21, N 15.60; found: C 53.52, H 4.23, N 15.61.
Synthesis of 6. Silver oxide (0.5equiv) was added to a solution
of 1 (0.2 mmol) in CH2Cl2 (10 mL). The suspension was stirred at
room temperature for 4–6 h under the exclusion of light. The sus-
pension was filtered to the solution of [Cp*IrCl2]2 (0.1 mmol) in
dichloromethane. After the mixture was stirred at room temper-
ature for 12 h, the suspension was filtered and the filtrate was
concentrated. The residue was purified by column chromatogra-
phy with CH2Cl2/CH3OH (100:1–50:1) and yielded a yellow solid.
Yield: 71 mg (58%). 1H NMR (CDCl3, 500 MHz, ppm): ı 7.93 (d, 2H,
J = 5.0 Hz, Ph), 7.47 (d, 2H, J = 10.0 Hz, Ph), 6.95 (d, 1H, J = 2.0 Hz,
CHimidazole), 6.66 (d, 1H, J = 2.0 Hz, CHimidazole), 6.20–6.17 (d, 1H,
J = 15.0 Hz, CH2 Ph), 5.21–5.18 (d, 1H, J = 14.5 Hz, CH2 Ph), 4.01
(s, 3H, N CH3), 2.59 (s, 3H, CH3C O), 1.60 (s, 15H, Cp*). 13C
NMR (CDCl3, 125 MHz, ppm): ı 197.63 (C O), 157.36 (C Ir), 142.15
(Ph), 136.70 (Ph), 128.59 (Ph), 128.55 (Ph), 123.66 (CHimidazole),
121.71 (CHimidazole), 88.87 (Cp*), 54.06 (CH2 Ph), 38.70 (N CH3),
26.61 (CH3C O), 9.15 (Cp*, CH3). Elemental analysis calcd (%) for
(Ph), 129.19 (Ph), 123.98 (CHimidazole), 121.26 (CHimidazole), 118.51
(pyrimidine), 93.21 (Cp*), 53.55 (CH2 Ph), 28.82 (CH3C O), 9.43
(Cp*, CH3). Elemental analysis calcd (%) for C26H29ClF6IrN4OP: C
39.72, H 3.72, N 7.13; found: C 40.26, H 4.10, N 7.57.
Synthesis of 10. Following the same procedure as described
for 6, reaction of 1 (0.2 mmol) with Ag2O (0.5 equiv) in CH2Cl2
(10 mL) and subsequently with [Ru(p-cymene)Cl2]2 (0.1 mmol)
yielded 10 as an gray solid. Yield: 57 mg (55%). 1H NMR(CDCl3,
400 MHz, ppm): ı 7.94–7.92 (d, 2H, J = 8.0 Hz, Ph), 7.40–7.38 (d, 2H,
J = 8.0 Hz, Ph), 7.03 (s, 1H, CHimidazole), 6.81 (s,1H,CHimidazole), 5.96
(br, 1H, CH2 Ph), 5.61 (br, 1H, CH2 Ph), 5.36 (s, 2H, Cymene),
5.04 (s, 2H, Cymene), 4.05 (s, 3H, CH3 imidazole), 2.95–2.69 (sep-
tuplet, 1H, Ph CH(CH3)2), 2.60 (s, 3H, CH3C O), 2.06 (s, 3H, CH3
cymene), 1.25–1.24 (d, 6H, J = 6.8 Hz, Ph CH(CH3)2). 13C NMR(CDCl3,
100 MHz, ppm): ı 197.79 (C O), 174.90 (C Ru), 142.95 (Ph),
136.72 (Ph), 128.80 (Ph), 128.15 (Ph), 124.47 (CHimidazole), 122.86
(CHimidazole), 108.87, 98.97, 85.73, 82.25 (Cymene), 54.54 (CH2 Ph),
39.80 (N CH3), 30.87 (CH(CH3)2 cymene), 26.78 (CH3C O), 22.28
(CH(CH3)2 cymene), 18.78 (CH3 cymene). Elemental analysis calcd (%)
for C23H28Cl2RuN2O: C 53.08, H 5.42, N 5.38; found: C 53.06, H 5.40,
N 5.37.
General procedure for hydrogen transformation. Ketone
(1.0 mmol) or imine (1.0 mmol), tBuOK (0.1 mmol) and cata-
lyst (0.01 mmol) were weighed into an oven-dried Schlenk flask.
Dry iPrOH (3.0 mL) was added to the flask, and the mixture was
refluxed for the time specified under nitrogen. The reaction was
cooled, and an aliquot was filtered through a pad of Celite and
the crude product was purified by column chromatography using
petroleum ether and ethyl acetate. The analytical data of all
products are consistent with the data reported in literature [2,3].
C
23H29Cl2IrN2O: C 45.09, H 4.77, N 4.57; found: C 45.10, H 4.78, N
4.55.
Synthesis of 7. Following the same procedure as described for 6,
reaction of 2 (0.2 mmol) with Ag2O (0.5equiv) in CH2Cl2 (10 mL) and
subsequently with [Cp*IrCl2]2 (0.1 mmol) yielded 7 as an orange
solid. Yield: 72 mg (50%). 1H NMR (CDCl3, 400 MHz, ppm): ı 8.00 (d,
2H, J = 7.6 Hz, Ph), 7.55 (d, 2H, J = 8.0 Hz, Ph), 6.87 (s, 2H, CHmesityl),
6.83 (s, 1H, CHimidazole), 6.67 (s, 1H, CHimidazole), 5.91–5.87 (d, 1H,
J = 12.0 Hz, CH2 Ph), 5.71–5.67 (d, 1H, J = 12.0 Hz, CH2 Ph), 2.61
(s, 3H, CH3C O), 2.31 (s, 3H, p-CH3 Ph), 2.10 (s, 6H, o-CH3 Ph),
1.51 (s, 15H, Cp*). 13C NMR (CDCl3, 100 MHz, ppm): ı 197.76 (C O),
155.19 (C Ir), 142.36 (Ph), 138.66 (Ph), 136.95 (Ph), 136.89 (Ph),
128.96 (Ph), 128.72 (Ph), 125.75 (CHimidazole), 121.58 (CHimidazole),
89.27 (Cp*), 55.81 (CH2 Ph), 28.79 (CH3C O), 21.37 (p-CH3 Ph),
19.18 (o-CH3 Ph), 9.35 (Cp*, CH3). Elemental analysis calcd (%) for
Intramolecular
C H activation of complex 6. Complex 6
(0.04 mmol) and tBuOK (1 eq) were weighed into an oven-dried
Schlenk flask. Dry iPrOH (3.0 mL) was added to the flask, and the
mixture was refluxed for 48 h under nitrogen. After cooling, the
mixture was filtered through a pad of Celite and the crude prod-
uct was purified by column chromatography using CH2Cl2/CH3OH
(1000:1 – 600:1) and yielded 6ꢀ as a yellow solid. Yield: 17 mg
(70%). 1H NMR (CDCl3, 500 MHz, ppm): ı 8.19 (d, 1H, J = 2.0 Hz,
Ph), 7.46–7.43 (q, 1H, J = 1.8 Hz, Ph), 7.04–7.02 (d, 1H, J = 8.0 Hz,
Ph), 6.98–6.96 (d, 1H, J = 2.0 Hz, CHimidazole), 6.93 (d, 1H, J = 2.0 Hz,
CHimidazole), 4.85–4.82 (d, 1H, J = 14.4 Hz, CH2 Ph), 4.73–4.68(d, 1H,
J = 14.0 Hz, CH2 Ph), 3.93 (s, 3H, N CH3), 2.59 (s, 3H, CH3C O), 1.68
(s, 15H, Cp*). 13C NMR (CDCl3, 125 MHz, ppm): ı 199.95 (C O),
156.65 (C Ir), 144.73 (Ph), 144.16 (Ph), 142.25 (Ph), 136.37 (Ph),
124.47 (Ph), 121.77 (Ph), 121.48 (CHimidazole), 120.55(CHimidazole),
90.37 (Cp*), 56.96 (CH2 Ph), 36.92 (N CH3), 29.72(CH3C O), 9.46
(Cp*, CH3). Elemental analysis calcd (%) for C23H28ClIrN2O: C 47.95,
H 4.90, N 4.86; found: C 47.57, H 4.78, N 4.56.
C
31H37Cl2IrN2O: C 51.95, H 5.20, N 3.91; found: C 51.97, H 5.21, N
3.93.
Synthesis of 8. Following the same procedure as described for 6,
reaction of 3 (0.2 mmol) with Ag2O (0.5 equiv) in CH2Cl2 (10 mL)
and subsequently with [Cp*IrCl2]2 (0.1 mmol) yielded 8 as a yel-
low solid. Yield: 102 mg (70%). 1H NMR (CDCl3, 400 MHz, ppm):
ı 7.95 (d, 4H, J = 8.0 Hz, Ph), 7.50 (d, 4H, J = 8.0 Hz, Ph), 6.70 (s, 2H,
NCHCHN), 6.22 (d, 2H, J = 15.2 Hz, CH2 Ph), 5.35 (d, 2H, J = 15.6 Hz,
CH2 Ph), 2.59 (s, 6H, CH3C O), 1.63 (s, 15H, Cp*). 13C NMR (CDCl3,
100 MHz, ppm): ı 197.74 (C O), 158.65 (C Ir), 141.97 (Ph), 136.90
(Ph), 128.83 (Ph), 128.68 (Ph), 122.30 (NCHCHN), 89.37 (Cp*), 54.41
(CH2 Ph), 28.80 (CH3C O), 9.38 (Cp*, CH3). Elemental analysis
calcd (%) for C31H35Cl2IrN2O2: C 50.95, H 4.83, N 3.83; found: C
50.94, H 4.84, N 3.85.
Synthesis of 9. Following the same procedure as described
for 6, reaction of 4 (0.2 mmol) with Ag2O (0.5equiv) in CH2Cl2
(10 mL) and subsequently with [Cp*IrCl2]2 (0.1 mmol) and KPF6
(0.1 mmol) yielded 9 as a bright yellow solid. Yield: 90 mg (54%).
1H NMR (CDCl3, 400 MHz, ppm): ı 8.93–8.86 (m, 2H, CHimidazole),
7.95 (d, 2H, J = 8.0 Hz, Ph), 7.83 (s, 1H, CHpyrimidine), 7.68–7.64 (m,
1H, CHpyrimidine), 7.61–7.59 (d, 2H, J = 8.0 Hz, Ph), 7.07–7.04 (m,
1H, CHpyrimidine), 5.58 (d, 2H, J = 14.0 Hz, CH2 Ph), 2.57 (s, 3H,
CH3C O), 1.83 (s, 15H, Cp*). 13C NMR (CDCl3, 100 MHz, ppm): ı
197.68 (C O), 166.29 (pyrimidine), 161.19 (pyrimidine), 159.48
(pyrimidine), 157.63 (C Ir), 138.86 (Ph), 137.58 (Ph), 129.31
General procedure for amine N-alkylation. Alcohol (1.00 mmol)
and amine (1.10 mmol) were weighed into an oven-dried Schlenk
˚
flask containing 4 A molecular sieves (60 mg). tBuOK (0.50 mmol)
was added, followed by dry toluene (0.50 mL). The mixture was
put under an atmosphere of nitrogen, and catalyst (0.01 mmol)
was added before stoppering the flask and immersing it in a pre-
heated oil bath (110 ◦C) for 48 h. Then, the solvent was evaporated
and the crude solid was purified by column chromatography using
petroleum ether and triethylamine. The analytical data of all prod-
ucts are consistent with the data reported in literature [6j,8,11e].
X-ray crystallography. Intensity data for the Ir complex 6 were
collected on Bruker Smart APEX (at 293 K), equipped with 2.4 kW
˚
sealed tube X-ray source (Mo-K␣ radiation, ꢂ = 0.71073 A) oper-
ating at 50 kV and 30 mA. A hemisphere of intensity data was
collected at room temperature with a scan width of 0.60◦ in ω.
Empirical absorption corrections were based on SADABS program
[14]. The structures were solved by direct methods and refined
by full-matrix least-squares refinement using the SHELXTL-97

X.-H. Zhu et al. / Journal of Molecular Catalysis A: Chemical 393 (2014) 134–141
141
Table 5
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Crystal data and structure refinement for 6.
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(c) M. Albrecht, J.R. Miecznikowski, A. Samuel, J.W. Faller, R.H. Crabtree,
Organometallics 21 (2002) 3596–3604;
(d) J.R. Miecznikowski, R.H. Crabtree, Organometallics 23 (2004) 629–631;
(e) J.R. Miecznikowski, R.H. Crabtree, Polyhedron 23 (2004) 2857–2872;
(f) E. Mas-Marzá, M. Poyatos, M. Sanaú, E. Peris, Organometallics 23 (2004)
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(g) F.E. Hahn, C. Holtgrewe, T. Pape, M. Martin, E. Sola, L.A. Oro, Organometallics
24 (2005) 2203–2209;
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6
Formula
Mr
Crystal system
Space group
a (Å)
C23 H29 Cl2 Ir N2O
612.58
Monoclinic
P2(1)/n
14.110(5)
9.027(3)
c = 18.930(6)
90
104.025(4)
90
2339.2(13)
4
5.953
1.739
1200
293(2)
2.06–25.01
9414/4098
0.0647
4098/12/262
0.992
b (Å)
c (Å)
˛(◦)
ˇ (◦)
(i) A.P. da Costa, M. Viciano, M. Sanaú, S. Merino, J. Tejeda, E. Peris, B. Royo,
Organometallics 27 (2008) 1305–1309.
ꢃ (◦)
V (Å3)
Z
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ꢄ (mm−1
)
ꢅcalcd (mg m−3
F (0 0 0)
)
T (K)
 range (◦)
Reflns collected/indep reflns
R(int)
Data/restraints/params
GOF
R1 (I > 2ꢆ(I))
wR2
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Financial support from the National Natural Science Foundation
of China (Grant No. 20871032, 20971026 and 21271047), Shanghai
Leading Academic Discipline Project, Project Number: B108, and
Shanghai Key Laboratory Green Chemistry and Chemical Process is
gratefully acknowledged.
(b) X.-F. Hou, Y.-N. Wang, I. Göttker-Schnetmann, Organometallics 30 (2011)
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