Quinoline-functionalized N-heterocyclic carbene complexes of iridium: Synthesis, structures and catalytic activities in transfer hydrogenation

Article abstract of DOI:10.1016/j.jorganchem.2009.02.007

Iridium complexes containing quinoline-functionalized N-heterocyclic carbene (NHC) ligands have been synthesized by the transmetalation route from silver carbene precursors. The silver complexes undergo a facile reaction with [Ir(COD)Cl]₂ (COD

Full text of DOI:10.1016/j.jorganchem.2009.02.007

Journal of Organometallic Chemistry 694 (2009) 2096–2105
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Journal of Organometallic Chemistry
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Quinoline-functionalized N-heterocyclic carbene complexes of iridium:
Synthesis, structures and catalytic activities in transfer hydrogenation
a
a
b
a
a
a
Jia-Feng Sun , Fei Chen , Brenda A. Dougan , Hui-Jun Xu , Yong Cheng , Yi-Zhi Li ,
a,
b,
*
*
Xue-Tai Chen , Zi-Ling Xue
Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructures,
School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China
a
b
Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 August 2008
Received in revised form 2 February 2009
Accepted 10 February 2009
Available online 21 February 2009
Iridium complexes containing quinoline-functionalized N-heterocyclic carbene (NHC) ligands have been
synthesized by the transmetalation route from silver carbene precursors. The silver complexes undergo a
facile reaction with [Ir(COD)Cl]
(NHC)Ir(COD)Cl] (NHC = 3-methyl-1-(8-quinolylmethyl)imidazole-2-ylidene (2a); 3-n-butyl-1-(8-quin-
olylmethyl)imidazole-2-ylidene (2b); 3-benzyl-1-(8-quinolylmethyl)imidazole-2-ylidene (2c); 1,3-di
8-quinolylmethyl)imidazole-2-ylidene (2d). The coordinated COD was replaced by carbon monoxide
to yield the corresponding carbonyl species [(NHC)Ir(CO) Cl] (3). Complexes 2 and 3 have been charac-
terized by IR, ESI-MS, 1H and C NMR and elemental analyses. The molecular structures of complexes
b and 2c have been confirmed by single-crystal X-ray diffraction. Two analogous Ir(I) complexes 5
2
(COD = 1,5-cyclooctadiene) to yield a series of carbene complexes
[
(
Keywords:
N-heterocyclic carbene
Iridium
Transfer hydrogenation
Catalysis
2
13
2
and 6 with naphthalene-containing NHC have also been synthesized and characterized. These Ir(I) com-
plexes in the current work have been proved to be active catalysts in the transfer hydrogenation of
ketones to alcohols using 2-propanol as the hydrogen source.
Ó 2009 Elsevier B.V. All rights reserved.
1
. Introduction
In the past decade, N-heterocyclic carbenes (NHCs), in particu-
In comparison to the electronically similar phosphine ligand
systems [35], NHC-based catalysts are considered to be stable
against heat, moisture, and oxygen [36]. Recently, research has also
been devoted to the synthesis of nitrogen-functionalized ligands
containing NHC moieties, in order to modify the ligand properties
and catalytic activities [37–40]. The nitrogen donor atom would act
as a hemilabile arm, capable of reversible dissociation from the
metal center. For example, the combination of pyridine and NHC
leads to a large diverse group of ligands, some of which have
shown interesting coordination chemistry and efficient catalytic
applications [15,16,41]. Some Ir(I) and Ir(III) complexes with pyri-
dine-functionalized HNCs have been prepared and showed active
transfer hydrogenation of ketones [15,16]. Here we report the
synthesis and characterization of a series of new quinoline-func-
tionalized NHC iridium(I) cyclooctene and carbonyl complexes
[(NHC)Ir(COD)Cl] (NHC = 3-methyl-1-(8-quinolylmethyl)imidaz-
ole-2-ylidene (2a); 3-n-butyl-1-(8-quinolylmethyl)imidazole-2-
ylidene (2b); 3-benzyl-1-(8-quinolylmethyl)imidazole-2-ylidene
(2c); 1,3-di(8-quinolylmethyl)imidazole-2-ylidene (2d) and
lar imidazolin-2-ylidenes, have attracted much attention because
their transition metal complexes display rich coordination chemis-
try [1–4], and the complexes demonstrate high homogeneous cat-
alytic activities [5–8]. Among the various metal complexes,
applications of the iridium NHC complexes in catalysis have been
actively studied. It is known that Ir–NHC complexes can catalyze
a variety of reactions including the Oppenauer-type oxidation [9],
transfer hydrogenation of carbonyl [10–16] and nitro [17]
compounds, cyclization of alkynylcarboxylic acids [15,18],
hydrogenation of olefins [19–23], hydrosilylation [15,24–26],
hydroamination [27], and bornylation [28], among which transfer
hydrogenation of ketone is an important synthesis with applica-
tions in many fields [29,30]. In comparison to the commonly used
reduction processes [30], catalytic transfer hydrogenation employs
hydrogen donors, e.g., 2-propanol. The process is safer, highly
selective, economic, and eco-friendly [31–34]. A broad range of
alcohols are accessible by transfer hydrogenation under mild reac-
tions in the presence of various metal catalysts [10–16].
[(NHC)Ir(CO)
2
Cl] (3) and their catalytic activities toward the trans-
fer hydrogenation of ketones. In addition, two analogous iridium(I)
complexes with naphthalene-containing NHC have also been pre-
pared and examined in order to probe the influence of the quino-
line nitrogen donor in the transfer hydrogenation reaction. It is
noted that when this paper is under review, Li et al. reported the
*
Corresponding authors. Tel.: +86 25 83597147; fax: +86 25 83314502. (X.-T.
Chen).
E-mail address: xtchen@netra.nju.edu.cn (X.-T. Chen).
0
022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.02.007

J.-F. Sun et al. / Journal of Organometallic Chemistry 694 (2009) 2096–2105
2097
preparation of complex 2b and a few other iridium(I), iridiium(III)
42] and palladium complexes [43] with quinoline-functionalized
NHC.
Supplementary material for 3c), indicating the two protons are dia-
stereotopic, perhaps as a result of restricted ligand rotation. As the
temperature was raised to 40 °C, they gradually coalesced into a
broad peak at 6.15 ppm. Fast ligand rotation makes the two pro-
[
tons in the –CH
spectra (Supplementary material) remains an AB system till at least
0 °C.
linker equivalent. For 2b and 3d, its VT 1H NMR
2
2
. Results and discussion
.1. Synthesis and characterization
Quinoline-functionalized imidazolium salts were used as
4
2
The positive ion ESI-MS analyses for 2a–2d and 3a–3d in each
case showed a major m/z peak corresponding to the [MCl]+
fragment.
precursors to N-heterocyclic carbene ligands. The salts were syn-
thesized by reacting 8-bromomethylquinoline with the corre-
sponding substituted imidazoles according to Scheme 1. The salts
The analogous naphthalene-functionalized imidazolium salt 4
and the corresponding iridium(I) complexes 5 and 6 were prepared
by the same procedures (Schemes 1 and 2). Complexes 4–6 were
1
a–1d were found to be hygroscopic and soluble in chlorinated sol-
1
13
characterized by IR, ESI-MS, H and C NMR and elemental analy-
ses. Their spectroscopic data are consistent with their suggested
compositions and structures.
vents. The NMR spectroscopic data of 1a–1d agree with the pro-
1
posed structures. In the
H NMR spectra of 1a–1d, the
imidazolium protons appear at d 10.28–10.60 ppm.
Transmetalation from Ag–NHC complex has been shown to be
an efficient method for the preparation of NHC complexes of tran-
sition metals [44]. Here, a two-step process was used to prepare
the iridium(I) cyclooctene complexes. The first involves deprotona-
2
.2. Structural studies
Detailed coordination spheres around the metal center of 2b
and 2c are confirmed by the X-ray crystal analyses. The molecular
structures of 2b and 2c in the solid state are depicted in Figs. 2 and
3
graphically nonequivalent molecules A and B, whose structures are
almost identical, with only small differences in bond distances and
bond angles.
tion of the imidazolium salts with Ag
cies [45–49]. Although these complexes can be isolated, we used
our Ag–NHC complexes in situ. The addition of [Ir(COD)Cl] to
the mixture gave the yellow complexes 2a–2d in good yields
2
O to form the Ag–NHC spe-
, respectively. For 2b, the asymmetric unit contains two crystallo-
2
(
see Scheme 2).
The 1H NMR spectra of 2a–2d do not exhibit a signal at
Crystallographic analysis confirms the C
b and 2c. The coordination sphere is square planar for both com-
2
binding mode in both
1
2
0–11 ppm, where the imidazolium C -H signals of the precursors
2
are found, indicating the formation of iridium–carbene bond. The
chemical shifts of the quinolyl rings are essentially similar to those
of the corresponding precursors, indicating that the quinolyl nitro-
gen donor remains uncoordinated. Furthermore, 1H NMR spectra
plexes, and the selected bond distances, bond angles and torsion
angles are given in Table 1. The Ir–Ccarbene distances of
2
.024(10), 2.033(10) Å for 2b and 2.024(7) Å for 2c are typical
for this type of carbene coordination [17,50]. The C–C distances
of 1.335(14), 1.307(16) Å for 2b and 1.346(11) Å for 2c in the
imidazole ring are consistent with a double bond and supports
the perturbed aromatization [4] proposed to occur upon carbene
formation. The average distance of Ir–CCOD trans to the carbene
donor (2.16 Å for 2b and 2c) appears to be longer than those in
the cis arrangement (2.10 Å for 2b and 2c), suggesting that the
show diastereotopic protons for the CH
2
linker (e.g., d = 6.45 and
2
13
6
.29, JHH = 14.5 Hz in 2a). C NMR data for the coordinating car-
bene carbons appear at d 180.1–181.5 ppm, suggesting the forma-
tion of the Ir–C bond. These signals are in the typical range for
Ir–Ccarbene analogues [15,17,18,25,50].
Complexes 2a–2d were converted to the corresponding dicar-
bonyl complexes 3a–3d through reactions with excess CO in
r
-donor nature of the diaminocarbene is stronger than that of
2 2
CH Cl at room temperature (Scheme 2). Cyclooctadiene is easily
the chloride. The torsion angles for N–C–Ir–Cl (Table 1) indicated
that the imidazole ring is almost orthogonal to the square plane,
displaced in minutes, as shown by a color change from bright to
pale yellow. The cis geometry proposed in Scheme 2 is supported
by IR spectroscopy, which shows two CO stretching vibrations of
similar intensity. Inequivalent CO carbon atoms were also ob-
2
which accounts for the diastereotopic N-CH protons if Ir–C rota-
tion is slow.
1
3
served in C NMR spectroscopy. The geometry is consistent with
1
2.3. IR and electrochemistry
the
H
NMR spectrum, in which the N-CH
2
protons are
diastereotopic.
1
The infrared carbonyl stretching frequencies of the iridium
complexes cis-[(L)Ir(CO) Cl] are well documented as a good evalu-
ation of the electron-donating properties of L ligand [50–53]. In Ta-
ble 2, the carbonyl frequencies of [(NHC)Ir(CO) Cl] (3a–3d and 6)
are listed and compared with those of analogous complexes. The
carbonyl stretching frequencies show that the av(CO) values are
nearly the same for 3a–3d, leading to the close values of Tolman
electronic parameter (TEP) of NHCs ligands. However, TEP values
of these quinoline-functionalized carbenes are significantly higher
than those commonly used NHCs reported in the literature, indi-
cating that these quinoline-containing NHCs are less electron-
donating. It is also very interesting to note that TEP value of the
naphthalene-containing NHC derived from the imidazolium salt 4
is lower than the quinoline-functionalized NHCs, indicating that
the electronic effect induced by the substitution of nitrogen atom
in place of carbon is very significant and naphthalene-containing
NHC is more electron-donating than the quinoline-functionalized
NHC. The TEP values of these quinoline-functionalized NHC of
Variable-temperature H NMR studies of 2b, 3a, 3c, and 3d were
1
conducted from ꢀ10 to 40 °C. The VT H NMR spectra of 3a from
2
ꢀ
10 to 40 °C are given in Fig. 1. Additional spectra are given in
the Supplementary material. These VT NMR spectra show that
the signals of the quinoline groups are independent with the tem-
perature with no indication of quinoline nitrogen coordination to
Ir(I) atoms.
2
v
In the case of both 3a and 3c, the –CH
shows an AB system around 6.1 ppm at ꢀ10 °C (Fig. 1 for 3a and
2 2
linker, the NCH Qu,
+
Br
acetone
N
N
N
N
+
R
-
R
Br
H
X
X
H
X = N, R = Me, 1a;
Qu=8-quinolylmethyl
X = C, R =
-Bu, 4
n
-Bu, 1b;Bn, 1c;Qu, 1d
n
[
2 3
(NHC)Ir(CO) Cl] (3) display nearly the same values as [(PCy )Ir
Scheme 1.
(CO) Cl]. Therefore, the quinoline-functionalized NHCs ligands
2

2
098
J.-F. Sun et al. / Journal of Organometallic Chemistry 694 (2009) 2096–2105
N
N
R
+
X
N
N
1)Ag O
2
Cl
R
Ir
-
Br
2)[Ir(COD)Cl]2
H
X
X = N, R = Me, 2a;
X = C, R = n-Bu, 5
n-Bu, 2b ;Bn, 2c; Qu, 2d
CO
N
N
R
X
Cl
Ir
OC
CO
X = N, R = Me, 3a;
X = C, R = n-Bu, 6
n-Bu, 3b;Bn, 3c; Qu, 3d
Scheme 2.
Fig. 1. 1H NMR spectra of 3a between ꢀ10 and 40 °C in CDCl
3
.
have almost the same electron-donating capacity as PCy
the most donating phosphine ligands known.
3
, one of
0.531 V when the scan direction was reversed. Moreover, the peak
current for the anodic process is larger than that of the cathodic
process, indicating that the oxidized species are not stable. The oxi-
dized species undergoes some chemical reactions after the anodic
process [42]. We also examined the naphthalene-containing irid-
ium(I) complex 5 under the same condition. The cyclic voltammo-
gram of 5 (Fig. 4) shows one anodic peak, but no obvious cathodic
peak is observed. The more positive Epa value of 0.926 V indicated
that complex 5 is more difficult to be oxidized than 2a–2d. In other
The electrochemical properties of transition metal complexes of
NHCs have been probed previously [54–56]. CV of complexes
ꢀ1
2
a–2d was performed at a scan rate of 100 mV s at a GC elec-
trode in CH Cl and the results are shown in Table 3. These com-
2
2
plexes undergo a one-electron oxidation process with the anodic
peak potential (Epa) in the range 0.642–0.701 V and one reduction
process with the cathodic peak potential (Epc) ranging 0.501–

J.-F. Sun et al. / Journal of Organometallic Chemistry 694 (2009) 2096–2105
2099
Fig. 2. Molecular structure and atom numbering scheme for complex 2b (drawn with 30% probability ellipsoids). Hydrogen atoms have been omitted for clarity.
Fig. 3. Molecular structure and atom numbering scheme for complex 2c (drawn with 30% probability ellipsoids). Hydrogen atoms have been omitted for clarity.
words, naphthalene-containing NHC is more electron-donating
than quinoline-functionalized carbenes, which is consistent with
the conclusions from IR results.
and 3a–3d. Complexes 5 and 6 were also tested under the same
catalytic conditions to probe the possible influence of the quinoline
nitrogen atom. The reduction of acetophenone to 1-phenylethanol
by 2-propanol was chosen as a model reaction in the current work
to explore the catalytic behavior in transfer hydrogenation
2.4. Catalytic studies
(
Scheme 3). Thus, in a typical experiment, the catalyst precursor
i
Complexes of type (COD)Ir(NHC)X (X = Br, NHC = 1,3-di(pro-
pyl)benzimidazol-2-ylidene [12]; X = Cl, 1,3-mesitylimidazol-2-
ylidene [13]; X = Cl, NHC = 3-methyl-1-(6-methylpicolyl)imida-
(0.05 mol%) was added to a solution of KOH (1.5 mol%) and PrOH
(10 mL). Acetophenone (8 mmol) was then add at 82 °C. The
reaction was monitored by gas chromatograph (GC) and time-
dependent conversion for transfer hydrogenation of acetophenone
were followed (Fig. 5). Among all the quinoline-functionalized NHC
Ir complexes, 2a and 2b are very active, giving more than 90% con-
zol-2-ylidene
imidazol-2-ylidene [16], and X = Br, annulated NHC derived from
-methylaminopiperidine [17]) have been tested for the transfer
[16];
X = Cl,
3-methyl-1-(6-mesityllpicolyl)
2
hydrogenation of some ketones such as cyclohexanone and aceto-
phenone. It should be noted that these catalytic studies were re-
ported to be carried out under different reaction conditions and
even with different substrates and bases. These results promoted
us to investigate the transfer hydrogenation of ketone by 2a–2d
2
version after 40 min. The complexes of the type [(NHC)Ir(CO) Cl]
(3, 6) are generally less active than [(NHC)Ir(COD)Cl] ( 2, 5),
probably due to the fact that COD is more easily removed from
the metal center than CO. Among the tested complexes, 2b is the
most efficient in the transfer hydrogenation of acetophenone to

2
100
J.-F. Sun et al. / Journal of Organometallic Chemistry 694 (2009) 2096–2105
Table 1
Selected bond distances ( ÅA ) and angles (°) for 2b and 2c.
0
2
b
2c
Molecule A
Bond distances
Ir1–C1
Molecule B
2.024(10)
2.366(2)
Ir2–C26
Ir2–Cl2
Ir2–C43
Ir2–C44
Ir2–C47
Ir2–C48
C27–C28
2.033(10)
2.366(2)
Ir1–C1
2.024(7)
2.3569(18)
2.150(8)
2.119(8)
2.100(9)
2.178(9)
1.346(11)
Ir1–Cl1
Ir1–Cl1
Ir1–C21
Ir1–C24
Ir1–C25
Ir1–C28
C2–C3
Ir1–C18
Ir1–C19
Ir1–C22
Ir1–C23
C2–C3
2.107(11)
2.119(16)
2.152(11)
2.166(10)
1.335(14)
2.109(10)
2.077(10)
2.165(11)
2.159(11)
1.307(16)
Bond angles
C1–Ir1–C18
C1–Ir1–C19
C1–Ir1–C22
C1–Ir1–C23
C1–Ir1–Cl1
Cl1–Ir1–C18
Cl1–Ir1–C19
Cl1–Ir1–C22
Cl1–Ir1–C23
N1–C1–N2
N1–C1–Ir1
N2–C1–Ir1
91.7(4)
93.2(4)
164.2(5)
161.2(5)
90.9(3)
164.1(4)
159.0(4)
88.5(3)
C26–Ir2–C43
C26–Ir2–C44
C26–Ir2–C47
C26–Ir2–C48
C26–Ir2–Cl2
Cl2–Ir2–C43
Cl2–Ir2–C44
Cl2–Ir2–C47
Cl2–Ir2–C48
N4–C26–N5
N4–C26–Ir2
N5–C26–Ir2
93.4(4)
91.6(4
160.2(5)
164.7(5)
89.3(3)
160.0(3)
162.6(3)
92.4(3)
C1–Ir1–C21
C1–Ir1–C24
C1–Ir1–C25
C1–Ir1–C28
C1–Ir1–Cl1
Cl1–Ir1–C21
Cl1–Ir1–C24
Cl1–Ir1–C25
Cl1–Ir1–C28
N1–C1–N2
N1–C1–Ir1
N2–C1–Ir1
161.9(3)
81.8(3)
95.8(3)
158.7(3)
89.5(2)
90.3(3)
161.8(2)
159.5(2)
89.9(2)
103.0(6)
130.9(6)
125.0(5)
91.2(3)
90.0(3)
104.1(8)
130.0(8)
125.3(8)
104.8(8)
129.1(8)
126.1(8)
Torsion angles
N1–C1–Ir1–Cl1
N2–C1–Ir1–Cl1
ꢀ94.3(10)
N4–C26–Ir2–Cl2
N5–C26–Ir2–Cl2
ꢀ88.2(8)
N1–C1–Ir1–Cl1
N2–C1–Ir1–Cl1
76.4(7)
ꢀ89.5(6)
75.0(9)
90.0(7)
Table 2
5
0
2
Carbonyl stretching frequencies for [(L)Ir(CO) Cl].
La
v
(CO) (cm
ꢀ1
)
v
av(CO) (cm
ꢀ1
)
TEP (cm
ꢀ1
)
Ref.
*
*
*
b
1
1
1
1
4
a
b
c
2069.6, 1986.0
2068.8, 1984.9
2070.2, 1986.6
2068.5, 1985.8
2062.5, 1978.8
2063, 1976
2027.8
2026.9
2028.4
2027.2
2020.7
2020
2057.1
This work
This work
This work
This work
b
2056.4
b
-5
2057.5
*
b
d
2056.6
*
b
2051.9
This work
-
-
-
10
15
20
tmiy
biy
ItBu
IAd
ICy
2050
2051
50
50
53
53
53
53
53
50
i
2062, 1978
2020
2064.6, 1980.0
2063.4, 1979.8
2064.8, 1981.2
2066.8, 1981.0
2066.4, 1979.8
2072, 1984
2022.3
2021.6
2023.0
2023.9
2023.1
2028.0
2050.1
2049.5
2049.6
2051.5
2050.7
2056.4
IPr
IMes
PCy
3
a
1
a*–1d*, 4* represent the carbenes derived from precursors 1a–1d and 4.
tmiy = 1,3-di(4-tolylmethyl)imidazole-2-ylidene, biy = 1,3-di-n-butylimidazole-2-
ylidene, ItBu = 1,3-di-t-butylimidazole-2-ylidene, IAd = 1,3-diadamantylimidazole-
1.0
0.8
0.6
0.4
0.2
E / V vs. Ag/AgCl
2
-ylidene, ICy = 1,3-di cyclohexylimidazole-2-ylidene, IPr = 1,3-di(2,6-diisopropyl-
phenyl)imidazole-2-ylidene,
IMes = 1,3-di(2,4,6-trimethylphenyl)imidazole-2-
Fig. 4. Cyclic voltammograms of 1 mM solutions of complexes 2b (solid line) and 5
ylidene.
b
ꢀ1
(dashed line) performed at a 2 mm diameter GC electrode in CH
2
Cl
2
(containing
Values calculated by equation TEP = 0.722
v
av(CO) + 593 cm [50].
ꢀ
1
4 4
0.1 M Bu NClO ) at a scan rate of 100 mV s .
Table 3
Redox potentials of the [(NHC)Ir(COD)Cl] complexes in CH
2
Cl
2
(scan rate
O
OH
ꢀ
1 a
1
00 mV s ).
O
OH
0.05 mol % catalyst
[
(NHC)Ir(COD)Cl]
E
pa (V)
E
pc (V)
i
pa/ipc
+
+
1.5 mol % KOH
2
2
2
2
5
a
b
c
0.656
0.674
0.701
0.642
0.926
0.503
0.513
0.531
0.501
–
2.660
2.820
2.704
2.086
–
Scheme 3.
d
hydrogenation. The iridium(I) complexes 5 and 6 with naphtha-
lene-containing NHC have lower activities than those quinoline-
containing complexes, indicating that the employment of
quinoline tether is beneficial for the catalytic reaction. The possible
reasons for this improvement could be due to the probable coordi-
nation of the quinolyl group in the catalytic cycle. Li et al. have
demonstrated that the quinolyl group would coordinate to the irid-
a
E
pa and Epc is the anodic and cathodic peak potentials (vs. Ag/AgCl in 0.1 M
NClO ), respectively. ipa and ipc is the anodic and cathodic peak currents,
respectively.
Bu
4
4
1
-phenylethanol. These data indicated that the influence of the
substituents at the ring nitrogen atom on the catalytic activity.
The comparison between 2b and 5, 3b and 6 would provide the
possible influence of the quinolyl group in the catalytic transfer
6
ium atom when [(NHC)IrCl] was treated with KPF [42]. It is possi-
ble that similar coordination of quinolyl group could occur in the
unsaturated active catalytic species, which is favorable for the

J.-F. Sun et al. / Journal of Organometallic Chemistry 694 (2009) 2096–2105
2101
1
00
drawing group has generally been found to facilitate the hydrogen
transfer reaction [57–59], and this has been attributed to the hyd-
ridic nature of the reducing species involved. Furthermore, it has
been shown to be less efficient in the reduction of benzophenone
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
2
2
a
b
(
entry 5) and dialkyl ketones (entries 6 and 7) compared to aceto-
phenone (entry 1). These differences in the catalytic activities
could be attributed to the electronic and steric effects of the sub-
stituents in ketones.
2c
2
3
3
3
3
5
6
d
a
b
c
d
3
. Experimental
3.1. Reagents and general procedures
All reactions and manipulations were carried out in either a
nitrogen-filled glove-box or under nitrogen using standard
Schlenk-line techniques. Dichloromethane was dried over P
and distilled under nitrogen. Other solvents were used as received.
-Bromomethylquinoline and 1-bromomethylnaphthalene [60,61]
and metal precursor [Ir(COD)Cl] [62] were synthesized according
0
20
40
60
80
100 120 140
2 5
O
Time (min)
8
Fig. 5. Time dependence of the catalytic transfer hydrogenation of acetophenone.
Conditions: reactions were carried out at 82 °C using 8 mmol of acetophenone.
Ketone/complex/KOH ratio: 2000:1:30. Yield of 1-phenylethanol determined by GC
analysis.
2
to the literature methods. All other chemicals were purchased from
commercial sources and used without further purification.
1
13
H and C NMR spectra were recorded on a Bruker DRX-500
1
13
catalytic reaction. Another possible reason is the different elec-
tronic effect between the NHCs derived from 1b and 4.
spectrometer operating at 500 MHz ( H NMR) and 125 MHz ( C
NMR), respectively, and referenced to SiMe (d in parts per million,
4
1
On the basis of the high activity shown by 2b in the transfer
hydrogenation of acetophenone, we decided to further explore its
catalytic potential in the reduction of other ketones. The results
are listed in Table 4. Generally, a good efficiency of 2b as a precat-
alyst has been observed for all the ketones employed. The higher
TOF (11400 h ) were obtained for the acetophenone derivatives
with electro-withdrawing group (Cl) in the para position (Table
, entry 2). In comparison, slower reduction was observed for its
J in hertz). Variable-temperature H NMR spectra were recorded on
a Bruker AMX-400 spectrometer and referenced to residual proton
in CDCl . Electrospray mass spectra (ESI-MS) were recorded using
3
an LCQ electron spray mass spectrometer (Finnigan). Infrared spec-
tra were measured on a Nicolet NEXUS870 FT-IR spectrometer. Ele-
mental analyses were performed on a Perkin–Elmer 240C analytic
instrument. GC measurements were made on Shimadzu GC-2010
equipment. Cyclic voltammetric measurements were performed
on a 273A Potentiostat/Gawanostat (EG&G) using a glassy carbon
ꢀ1
4
electro-donating groups (OMe, Me) substituted derivatives (entries
and 4; TOF = 670, 620 h ). The presence of an electron-with-
ꢀ1
3
working electrode, a platinum wire counter electrode, and Bu N-
4
Table 4
a
Catalytic transfer hydrogenation of ketones by complex 2b.
Yield% (min)b
0(20)
Final TOF (h )c
ꢀ1
Entry
1
Ketone
Product
O
OH
9
5400
O
O
OH
OH
2
3
95(10)
11400
670
Cl
Cl
67(120)
OCH
3
OCH
3
O
OH
62(120)
620
4
O
OH
5
6
91(60)
1800
O
OH
OH
7
9
5(60)
1(30)
1500
3600
O
7
a
Conditions: reactions were carried out at 82 °C using 8 mmol of ketone. Ketone/complex/KOH ratio: 2000:1:30.
Yield determined by GC analysis.
Turnover frequency (mol of product per mol of complex per hour).
b
c

2
102
J.-F. Sun et al. / Journal of Organometallic Chemistry 694 (2009) 2096–2105
ClO
4
(TBAP) as supporting electrolyte. All the potentials were refer-
of H
anhydrous MgSO
removed under reduced pressure to give a brown liquid as pure
2
O (20 mL). After separation, the organic layer was dried with
+
enced to Ag /Ag electrode and the solutions were purged with N
before each set of experiments.
2
4
. The solution was filtered, and the solvent was
1
3
product. Yield: 2.173 g (74%). H NMR (CDCl , 25 °C): d 8.93 (d,
3
2
3
4
3
3
.2. Preparation of ligands and iridium complexes
1H, JHH = 3.2 Hz, QuH ), 8.14 (d, 1H,
J
HH = 7.9 Hz, QuH ), 7.76 (d,
3
7
5
1
H,
J
HH = 8.2 Hz, QuH ), 7.72 (s, 1H, NCHN), 7.46-7.42 (m, 2H,
6
3
3
.2.1. 3-Methyl-1-(8-quinolylmethyl)imidazolium bromide (1a)
QuH and QuH ), 7.31 (d, 1H,
J
HH = 6.9 Hz, QuH ), 7.05 (s, 2H,
Qu). C NMR (CDCl
1
3
To a solution of 8-bromomethylquinoline (2.615 g, 11.78 mmol)
in acetone (20 mL) was added 1-methylimidazole (0.967 g,
1.78 mmol). The mixture was stirred for 24 h at room tempera-
HCCH), 5.80 (s, 2H, NCH
2
3
, 25 °C): 150.3,
146.0, 138.3, 136.7, 135.3, 129.4, 128.7, 128.6, 128.5, 126.7,
1
122.0, 120.2 (Qu and Im), 47.3 (NCH Qu).
2
ture, and the desired product precipitated as a white solid from
the solution. The solid was collected and washed with THF
3.2.5. 1,3-Di(8-quinolylmethyl)imidazolium bromide (1d)
(
2 ꢁ 10 mL) and then dried under vacuum. Yield: 3.410 g (95%).
A procedure analogous to the synthesis of 1a, except using 8-
bromomethylquinoline (2.306 g, 10.38 mmol) and 2-(1H-imida-
zol-1-ylmethyl)quinoline (2.173 g, 10.39 mmol) in acetone
1
3
3
H NMR (CDCl
3
, 25 °C): d 10.39 (s, 1H, NCHN), 8.96 (d, 1H,
2
3
4
J
J
HH = 2.1 Hz, QuH ), 8.30 (d, 1H,
J
J
HH = 6.7 Hz, QuH ), 8.20 (d, 1H,
5
3
7
1
HH = 8.0 Hz, QuH ), 7.86 (d, 1H,
HH = 8.0 Hz, QuH ), 7.73 (s, 1H,
(20 mL), gave 1d as a solid. Yield: 3.757 g (84%). H NMR (CDCl
3
,
3
6
3
3
2
HCCH), 7.55 (t, 1H,
and 4.0 Hz, QuH ), 7.36 (s, 1H, HCCH), 6.14 (s, 2H, NCH
(
1
4
J
HH = 7.5 Hz, QuH ), 7.47 (dd, 1H,
J
HH = 7.8
Qu), 4.01
, 25 °C): 150.3, 145.5, 136.8, 136.4,
31.4, 131.2, 129.7, 128.1, 126.3, 123.1, 122.7, 121.6 (Qu and Im),
8.7 (NCH Qu), 36.5 (NCH ). Anal. Calc. for C14 14BrN : C, 55.28;
25 °C): d 10.60 (s, 1H, NCHN), 8.84 (d, 2H, JHH = 2.6 Hz, QuH ),
HH = 8.1 Hz, QuH ),
7.80 (d, 2H, JHH = 8.1 Hz, QuH ), 7.62 (s, 2H, HCCH), 7.50 (t, 2H,
3
3
4
3
5
2
8.28 (d, 2H, JHH = 6.8 Hz, QuH ), 8.13 (d, 2H,
J
1
3
3
7
s, 3H, NCH
3
). C NMR (CDCl
3
3
6
3
3
J
HH = 7.6 Hz, QuH ), 7.40 (dd, 2H,
J
HH = 8.1 and 4.1 Hz, QuH ),
C NMR (CDCl , 25 °C): 150.7, 146.3,
1
3
2
3
H
3
6.07 (s, 4H, NCH
2
Qu).
3
H, 4.64; N, 13.81. Found: C, 55.21; H, 4.57; N, 13.80%.
137.7, 137.0, 132.4, 131.9, 130.3, 128.8, 127.1, 122.8, 122.1 (Qu
and Im), 49.4 (NCH Qu). Anal. Calc. for C23 19BrN : C, 64.05; H,
4.44; N, 12.99. Found: C, 63.89; H, 4.37; N, 12.92%.
2
H
4
3.2.2. 3-n-Butyl-1-(8-quinolylmethyl)imidazolium bromide (1b)
To a solution of 8-bromomethylquinoline (2.683 g, 12.08 mmol)
in acetone (20 mL) was added 1-n-butylimidazole (1.500 g,
2.08 mmol). After it was stirred for 48 h at room temperature,
the solvent was removed under vacuum to afford thick brown syr-
up. The syrup was redissolved in CH Cl (10 mL). Addition of ether
20 mL) caused an oil to separate out. The solvent was decanted off,
3.2.6. [3-Methyl-1-(8-quinolylmethyl)imidazole-2-ylidene][(1,2,5,6-
)-1,5-cyclooactadiene]chloroiridium (2a)
1
g
A mixture of Ag
0.49 mmol) in CH Cl
for 12 h. [Ir(COD)Cl]
2
O (0.118 g, 0.51 mmol) and 1a (0.149 g,
(20 mL) was stirred at room temperature
2
(0.161 g, 0.24 mmol) was then added. The
2
2
2
2
(
and the oily solid that formed was triturated with THF (20 mL) to
mixture was stirred for 12 h and filtered through Celite, and the
volatile components were removed under reduced pressure. The
residue was chromatographied through a column of silica gel using
give a powder. This was further washed with THF (2 ꢁ 10 mL)
1
and then dried under vacuum. Yield: 3.636 g (87%). H NMR (CDCl
3
,
2
2
5 °C): d 10.39 (s, 1H, NCHN), 8.90 (br, 1H, QuH ), 8.27 (d, 1H,
ethyl acetate to give analytically pure products after the removal of
3
4
3
5
1
J
J
HH = 4.0 Hz, QuH ), 8.14 (d, 1H, JHH = 6.7 Hz, QuH ), 7.79 (d, 1H,
ethyl acetate. Yield: 0.197 g (72%). H NMR (CDCl
3
, 25 °C): d 8.98
3
7
6
2
3
4
HH = 6.8 Hz, QuH ), 7.70 (s, 1H, HCCH), 7.47 (t, 1H, QuH ), 7.40
(br, 1H, QuH ), 8.20 (d, 1H,
JHH = 7.4 Hz, QuH ), 7.97 (d, 1H,
3
3
J
HH = 6.8 Hz, QuH ), 7.79 (d, 1H, 3JHH = 8.0 Hz, QuH ), 7.54 (t, 1H,
5
7
(
m, 2H, QuH and HCCH), 6.11 (s, 2H, NCH
2
Qu), 4.21 (br, 2H,
CH CH ), 0.81
, 25 °C): 150.7, 146.1,
37.3, 136.8, 132.1, 131.8, 130.2, 128.7, 126.9, 123.3, 122.3, 122.1
Qu), 49.9, 32.3, 19.6, 13.6
). Anal. Calc. for C17 20BrN : C, 58.97; H, 5.82;
3JHH = 7.5 Hz, QuH ), 7.47 (dd, 1H, 3JHH = 7.3 and 3.6 Hz, QuH ),
6
3
NCH ), 1.77 (br, 2H, NCH CH ), 1.24 (br, 2H, NCH
2
2
2
2
2
2
13
2
(
1
br, 3H, NCH
2
CH CH
2 2
CH
3
). C NMR (CDCl
3
6.91 (s, 1H, HCCH), 6.74 (s, 1H, HCCH), 6.45 (d, 1H, JHH = 14.5 Hz,
2
NCH
2
Qu), 6.29 (d, 1H,
J
HH = 14.5 Hz, NCH
2
Qu), 4.62 (m, 2H,
(
(
Qu and Im), 49.2 (NCH
NCH CH CH CH
2
CHCOD), 3.99 (s, 3H, NCH
3
), 3.07 (m, 2H, CHCOD), 2.22 (m, 4H,
1
3
2
2
2
3
H
3
(CH COD), 1.57 (m, 4H, (CH )COD). C NMR (CDCl , 25 °C): 180.6
2
)
2
3
N, 12.14. Found: C, 56.88; H, 5.65; N, 10.66%. This compound is
highly hydroscopic, and this may have led to the current EA results.
The identity of this compound was confirmed in its subsequent
(C–Ir), 150.0, 146.4, 136.6, 134.9, 131.0, 128.4, 128.3, 126.9,
121.8, 121.4, 121.2 (Qu and Im), 84.7, 84.2, 52.2, 51.6 (CHCOD),
49.3 (NCH
Calc. for C22
.57; N, 7.54%. ESI-MS (m/z): calc., 523.68, [MꢀCl] ; found, 524.25.
2 3 2
Qu), 37.6 (NCH ), 34.2, 33.2, 30.1, 29.4 ((CH )COD). Anal.
reaction with Ag
2
O and then [Ir(COD)Cl]
2
to give 2b.
H
25ClIrN : C, 47.26; H, 4.51; N, 7.52. Found: C, 47.16; H,
3
+
4
3
.2.3. 3-Benzyl-1-(8-quinolylmethyl)imidazolium bromide (1c)
A procedure analogous to the synthesis of 1b, except using 8-bro-
momethylquinoline (3.063 g, 13.79 mmol) and 1-benzylimidazole
2.181 g, 13.79 mmol) in acetone (20 mL), gave 1c as a solid. Yield:
3.2.7. [3-n-Butyl-1-(8-quinolylmethyl)imidazole-2-ylidene][(1,2,5,6-
g)-1,5-cyclooactadiene]chloroiridium (2b)
(
4
The procedure for the preparation of 2b was similar to that for
1
.192 g (80%). H NMR (CDCl
3
, 25 °C): d 10.28 (s, 1H, NCHN), 8.79
2a, from Ag
[Ir(COD)Cl]
2
O (0.178 g, 0.77 mmol), 1b (0.258 g, 0.75 mmol) and
(0.242 g, 0.36 mmol). Yield: 0.278 g (62%). Crystals
2
4
5
(
br, 1H, QuH ), 8.10 (br, 1H, QuH ), 8.03 (br, 1H, QuH ), 7.69 (br,
2
7
6
3
1
7
NCH
H, QuH ), 7.58 (s, 1H, HCCH), 7.33 (m, 5H, QuH , QuH and Ph),
.12 (m, 3H, Ph and HCCH), 5.94 (s, 2H, NCH Qu), 5.44 (s, 2H,
, 25 °C): 150.3, 145.6, 136.6, 134.1, 131.7,
suitable for X-ray crystallography were obtained by layering a
1
2
2 2 3
CH Cl solution with hexane. H NMR (CDCl , 25 °C): d 8.97 (d,
1
3
3
2
3
4
2
Ph). C NMR (CDCl
3
1H, JHH = 2.7 Hz, QuH ), 8.19 (d, 1H, JHH = 8.2 Hz, QuH ), 7.94 (d,
3
5
3
7
1
31.1, 129.9, 129.1, 128.7, 128.3, 126.5, 123.0, 121.5, 119.4 (Qu, Im
and Ph), 52.9 (NCH Ph), 49.2 (NCH Qu). Anal. Calc. for C20 18BrN
C, 63.17; H, 4.77; N, 11.05. Found: C, 63.02; H, 4.79; N, 10.90%.
1H,
1H,
JHH = 7.0 Hz, QuH ), 7.78 (d, 1H, JHH = 8.0 Hz, QuH ), 7.53 (t,
3
6
3
2
2
H
3
:
J
HH = 7.7 Hz, QuH ), 7.46 (dd, 1H,
JHH = 8.2 and 4.2 Hz,
3
QuH ), 6.88 (s, 1H, HCCH), 6.77 (s, 1H, HCCH), 6.44 (d, 1H,
2
2
J
HH = 14.6 Hz, NCH
4.62 (m, 2H, CHCOD), 4.40 (m, 2H, NCH
2.20 (m, 4H, (CH COD), 1.72-1.56 (m, 6H, (CH
1.45 (m, 2H, NCH CH CH ), 1.01 (t, 3H, NCH
NMR (CDCl
131.0, 128.3, 128.2, 126.9, 121.4, 121.2, 120.0 (Qu and Im), 84.2,
84.0, 52.0, 51.9 (CHCOD), 49.4 (NCH Qu), 33.9, 33.6, 29.8, 29.7
2
Qu), 6.27 (d, 1H,
J
HH = 14.6 Hz, NCH
), 3.06 (m, 2H, CHCOD),
2
Qu),
3
.2.4. 2-(1H-Imidazol-1-ylmethyl)quinoline
A mixture of 8-bromomethylquinoline (3.122 g, 14.06 mmol),
imidazole (0.958 g, 14.07 mmol), and potassium hydroxide
2.363 g, 42.11 mmol) in THF (20 mL) was refluxed for 48 h. The
solvent was completely removed under reduced pressure. CH Cl
20 mL) was added, and thoroughly washed by several portions
2
2
)
2
)
COD and NCH
2
CH
2
),
3
C
1
2
2
2
2
CH CH CH ).
2
2
3
(
3
, 25 °C): 180.1 (C–Ir), 150.0, 146.4, 136.6, 134.9,
2
2
(
2

J.-F. Sun et al. / Journal of Organometallic Chemistry 694 (2009) 2096–2105
2103
4
3
5
(
C
6
(CH
2
)
COD), 50.4, 33.1, 20.2, 14.0 (NCH
31ClIrN : C, 49.94; H, 5.20; N, 6.99. Found: C, 50.07; H, 5.19; N,
.94%. ES-MS (m/z): calc., 565.76, [MꢀCl] ; found, 566.33.
2
CH
2
CH
2
CH
3
). Anal. Calc. for
QuH ), 7.97 (d, 1H, JHH = 7.7 Hz, QuH ), 7.67 (d, 1H, 3JHH = 6.4 Hz,
7
6
3
25
H
3
QuH ), 7.60 (m, 2H, QuH and QuH ), 7.51 (s, 1H, HCCH), 7.45 (s,
+
2
1H, HCCH), 6.37 (d, 1H,
HH = 13.8 Hz, NCH
J
HH = 13.8 Hz, NCH
Qu), 4.37 (m, 2H, NCH
), 1.40 (m, 2H, NCH CH CH ), 0.97 (t, 3H,
CH CH , 25 °C): 181.7 (C–Ir), 173.5,
). 13C NMR (CDCl
2
Qu), 6.01 (d, 1H,
2
J
2
2
), 1.91 (m, 2H,
3
g
.2.8. [3-Benzyl-1-(8-quinolylmethyl)imidazole-2-ylidene][(1,2,5,6-
)-1,5-cyclooactadiene]chloroiridium (2c)
NCH
NCH
2
CH
CH
2
2
2
2
2
2
2
3
3
The procedure for the preparation of 2c is similar to that for 2a,
168.3 (CO), 150.2, 146.3, 136.5, 134.1, 130.8, 128.8, 128.5, 126.6,
122.7, 121.6, 121.0 (Qu and Im), 50.6 (NCH Qu), 51.3, 32.9, 19.9,
13.8 (N CH CH CH CH ). FT-IR (CHCl ): (CO) 2068.8,
1984.9 cm . Anal. Calc. for C19 19ClIrN : C, 41.56; H, 3.49; N,
from Ag
Ir(COD)Cl]
suitable for X-ray crystallography were obtained by layering a
2
O (0.139 g, 0.60 mmol), 1c (0.221 g, 0.58 mmol) and
2
[
2
(0.188 g, 0.28 mmol). Yield: 0.256 g (69%). Crystals
2
2
2
3
3
v
ꢀ1
H
3 2
O
1
CH
2
Cl
2
solution with hexane. H NMR (CDCl
3
, 25 °C): d 8.98 (br,
7.65. Found: C, 41.66; H, 3.17; N, 7.83%. ESI-MS (m/z): calc.,
2
4
+
1
H, QuH ), 8.21 (d, 1H, 3JHH = 7.7 Hz, QuH ), 8.00 (d, 1H,
513.60, [MꢀCl] ; found, 514.17.
3
5
3
7
J
J
HH = 6.4 Hz, QuH ), 7.81 (d, 1H,
JHH = 7.9 Hz, QuH ), 7.57 (t, 1H,
3
HH = 7.6 Hz, QuH ), 7.47 (dd, 1H, 3JHH = 7.3 and 3.7 Hz, QuH ),
6
3
3.2.12. [3-Benzyl-1-(8-quinolylmethyl)imidazole-2-
ylidene]dicarbonylchloroiridium (3c)
7
6
.37-7.31 (m, 5H, Ph), 6.91 (s, 1H, HCCH), 6.61 (s, 1H, HCCH),
2
Qu), 6.32 (d, 1H, 2
.50 (d, 1H,
J
HH = 14.5 Hz, NCH
2
J
HH = 14.5 Hz,
Ph), 5.67 (d, 1H,
Ph), 4.66 (m, 2H, CHCOD), 3.10 (m, 2H, CHCOD),
The procedure for the preparation of 3c is similar to that for 3a,
2
1
6
NCH
2
Qu), 5.75 (d, 1H,
HH = 14.8 Hz, NCH
.22 (m, 4H, (CH
J
HH = 14.8 Hz, NCH
2
from 2c (0.121 g, 0.19 mmol). Yield: 0.096 g (87%). H NMR (d -
2
3
2
J
2
acetone, 25 °C): d 9.01 (d, 1H,
J
HH = 2.4 Hz, QuH ), 8.41 (d, 1H,
13
3
HH = 7.5 Hz, QuH ), 7.99 (d, 1H, 3JHH = 7.6 Hz, QuH ), 7.74 (d, 1H,
4
5
2
2
1
8
3
5
2
)COD), 1.57 (m, 4H, (CH
2
)
COD). C NMR (CDCl
3
,
J
3JHH = 6.9 Hz, QuH ), 7.61–7.34 (m, 9H, QuH
7
6
QuH , Ph and HCCH),
3
5 °C): 181.1 (C–Ir), 150.3, 146.7, 136.9, 136.8, 135.1, 131.3,
29.2, 128.6, 128.4, 127.2, 121.9, 121.7, 120.5 (Qu, Im and Ph),
,
2
2
6.41 (d, 1H,
NCH
JHH = 15.5 Hz, NCH
2
Qu), 6.04 (d, 1H,
J
HH = 15.5 Hz,
1
3
5.1, 85.0, 52.7, 52.4 (CHCOD), 54.7 (NCH
4.1, 33.8, 30.1, 29.8 ((CH COD). Anal. Calc. for C28
2.94; H, 4.60; N, 6.62. Found: C, 52.93; H, 4.79; N, 6.97%. ESI-MS
2 2
Ph), 49.7 (NCH Qu),
2
Qu), 5.63 (s, 2H, NCH
2
Ph). C NMR (CDCl
3
): 181.4 (C–Ir),
2
)
3
H29ClIrN : C,
174.0, 168.0 (CO), 150.1, 146.3, 136.4, 135.5, 133.8, 130.9, 129.0,
128.8, 128.5, 128.4, 128.3, 126.5, 123.0, 121.5, 120.9 (Qu, Im and
+
(
m/z): calc., 599.78, [MꢀCl] ; found, 600.42.
Ph), 55.0 (NCH
2
Ph), 50.6 (NCH
2
Qu). FT-IR (CHCl
3
): v(CO) 2070.2,
ꢀ
1
1
986.6 cm . Anal. Calc. for C22
H
17ClIrN : C, 45.32; H, 2.94; N,
3 2
O
3
.2.9. [1,3-Di(8-quinolylmethyl)imidazole-2-ylidene][(1,2,5,6-
g
)-1,5-
7.21. Found: C, 45.21; H, 3.37; N, 6.91%. ESI-MS (m/z): calc.,
547.61, [MꢀCl] ; found, 548.08.
+
cyclooactadiene]chloroiridium (2d)
The procedure for the preparation of 2d is similar to that for 2a,
from Ag O (0.171 g, 0.74 mmol), 1d (0.312 g, 0.72 mmol) and
2
3.2.13. [1,3-Di(8-quinolylmethyl)imidazole-2-
ylidene]dicarbonylchloroiridium (3d)
1
[
Ir(COD)Cl]
2
(0.228 g, 0.34 mmol). Yield: 0.284 g (57%). H NMR
2
3
(
CDCl , 25 °C): d 8.97 (br, 2H, QuH ), 8.20 (d, 2H,
3
J
HH = 7.6 Hz,
The procedure for the preparation of 3d is similar to that for 3a,
4
3
HH = 6.5 Hz, QuH ), 7.80 (d, 2H, 3JHH = 7.9 Hz,
5
1
QuH ), 7.99 (d, 2H,
QuH ), 7.56 (t, 2H,
and 3.9 Hz, QuH ), 6.85 (s, 2H, HCCH), 6.52 (d, 2H,
NCH
J
from 2d (0.130 g, 0.19 mmol). Yield: 0.106 g (88%). H NMR (CDCl
3
,
7
3
6
3
3
2
3
J
HH = 7.5 Hz, QuH ), 7.46 (dd, 2H,
J
HH = 7.6
25 °C): d 8.98 (d, 2H, JHH = 2.6 Hz, QuH ), 8.22 (d, 2H, JHH = 8.1 Hz,
3
2
4
3
5
3
J
HH = 14.6 Hz,
QuH ), 7.99 (d, 2H,
J
HH = 6.9 Hz, QuH ), 7.85 (d, 2H, JHH = 8.0 Hz,
HH = 7.6 Hz, QuH ), 7.49 (dd, 2H,
2
7
3
6
3
2
Qu), 6.33 (d, 2H,
J
HH = 14.6 Hz, NCH
2
Qu), 4.67 (m, 2H,
COD), 1.60 (m, 4H,
, 25 °C): 180.8 (C–Ir), 150.2, 146.7,
36.8, 135.3, 131.2, 128.6, 128.5, 127.2, 121.6, 121.5 (Qu and Im),
4.6, 52.7 (CHCOD), 49.8 (NCH Qu), 34.0, 30.0, ((CH COD). Anal. Calc.
30ClIrN : C, 54.25; H, 4.41; N, 8.16. Found: C, 54.21; H,
.40; N, 8.11%. ESI-MS (m/z): calc., 650.82, [MꢀCl] ; found, 651.33.
QuH ), 7.58 (t, 2H,
J
J
HH = 8.1
3
2
CHCOD), 3.20 (m, 2H, CHCOD), 2.20 (m, 4H, (CH
2
)
and 4.0 Hz, QuH ), 7.21 (s, 2H, HCCH), 6.36 (d, 2H,
JHH = 14.5 Hz,
1
3
2
13
(
CH
2
)
COD). C NMR (CDCl
3
2 2 3
NCH Qu), 6.13 (d, 2H, JHH = 14.5 Hz, NCH Qu). C NMR (CDCl ,
1
8
25 °C): 181.7 (C–Ir), 173.9, 168.1 (CO), 150.0, 146.2, 136.4, 134.0,
2
2
)
130.6, 128.7, 128.4, 126.5, 122.3, 121.5 (Qu and Im), 50.5
ꢀ1
for C31
4
H
4
(NCH
for C25
.87; N, 8.81%. ESI-MS (m/z): calc., 598.66, [MꢀCl] ; found, 599.08.
2
Qu). FT-IR (CHCl
3
): v(CO) 2068.5, 1985.8 cm . Anal. Calc.
+
H
18ClIrN : C, 47.35; H, 2.86; N, 8.84. Found: C, 47.41; H,
4 2
O
+
2
3
.2.10. [3-Methyl-1-(8-quinolylmethyl)imidazole-2-
ylidene]dicarbonylchloroiridium (3a)
3.2.14. 3-n-Butyl-1-(8-naphthylmethyl)imidazolium bromide (4)
To solution of 1-bromomethylnaphthalene (2.000 g,
CO gas was passed though a solution of 2a (0.089 g, 0.16 mmol)
a
in CH
2
Cl
2
(20 mL) with stirring for 30 min. The solvent was evapo-
9.05 mmol) in acetone (20 mL) were added 1-n-butylimidazole
(1.123 g, 9.05 mmol). After it was stirred for 12 h at room temper-
ature, and the desired product precipitated as a white solid from
the solution. The solid was collected and washed with THF
rated under pressure at room temperature. The pale yellow pow-
der obtained was washed with hexane (3 ꢁ 5 mL) and dried in
1
6
vacuo. Yield: 0.076 g (94%). H NMR (d -acetone, 25 °C): d 9.00
3
3
2
3
4
(
(
(
d, 1H,
d, 1H,
J
J
HH = 3.1 Hz, QuH ), 8.40 (d, 1H, JHH = 8.2 Hz, QuH ), 7.97
(2 ꢁ 10 mL) and then dried under vacuum. Yield: 2.874 g (92%).
5
3
7
1
HH = 8.2 Hz, QuH ), 7.67 (d, 1H,
J
HH = 7.0 Hz, QuH ), 7.60
3
H NMR (CDCl , 25 °C): d 10.71 (s, 1H, NCHN), 8.12 (d, 1H, naph-
6
3
m, 2H, QuH and QuH ), 7.50 (s, 1H, HCCH), 7.40 (s, 1H, HCCH),
thyl-H), 7.88 (t, 2H, naphthyl-H), 7.68 (d, 1H, naphthyl-H), 7.57
6
.35 (br, 1H, NCH
2
Qu), 6.03 (br, 1H, NCH
, 25 °C): 181.5 (C–Ir), 174.0, 168.1 (CO), 150.0,
46.2, 136.4, 133.9, 130.7, 128.8, 128.4, 126.5, 122.6, 122.4, 121.5
Qu), 38.5 (NCH ). FT-IR (CHCl ): (CO)
069.6, 1986.0 cm . Anal. Calc. for C16 13ClIrN : C, 37.91; H,
2 3
Qu), 3.95 (s, 3H, NCH ).
(d, 1H, naphthyl-H), 7.52–7.45 (m, 2H, naphthyl-H), 7.35 (s, 1H,
1
3
C NMR (CDCl
3
HCCH), 7.17 (s, 1H, HCCH), 6.08 (s, 2H, naphthyl-NCH
2H, NCH ), 1.85 (m, 2H, NCH CH ), 1.31 (m, 2H, NCH
0.90 (t, 3H, NCH CH CH CH ). C NMR (CDCl
134.0, 131.0, 130.7, 129.3, 129.2, 128.5, 127.9, 126.7, 125.6,
123.0, 122.4, 122.1 (naphthyl and Im), 51.2 (naphthyl-NCH ),
50.0, 32.1, 19.5, 13.5 (NCH CH CH CH ). Anal. Calc. for C18 20BrN
2
), 4.26 (t,
CH CH ),
3
, 25 °C): 136.8,
1
2
2
2
3
2
2
2
1
(
Qu and Im), 50.3 (NCH
2
3
3
v
2
2
2
3
ꢀ
1
2
2
4
H
3 2
O
.58; N, 8.29. Found: C, 38.01; H, 2.53; N, 8.24%. ESI-MS (m/z): calc.,
2
+
71.51, [MꢀCl] ; found, 472.08.
2
2
2
3
H
2
:
C, 62.61; H, 6.13; N, 8.11. Found: C, 62.57; H, 6.01; N, 8.07%.
3.2.11. [3-n-Butyl-1-(8-quinolylmethyl)imidazole-2-
ylidene]dicarbonylchloroiridium (3b)
3.2.15. [3-n-Butyl-1-(8-naphthylmethyl)imidazole-2-
The procedure for the preparation of 3b is similar to that for 3a,
ylidene][(1,2,5,6-
The procedure for the preparation of 5 was similar to that for 2a,
from Ag O (0.301 g, 1.30 mmol), 4 (0.345 g, 1.00 mmol) and
g)-1,5-cyclooactadiene]chloroiridium (5)
1
6
from 2b (0.138 g, 0.23 mmol). Yield: 0.114 g (90%). H NMR (d -
2
3
acetone, 25 °C): d 9.00 (br, 1H, QuH ), 8.40 (d, 1H,
J
HH = 6.4 Hz,
2

2
104
J.-F. Sun et al. / Journal of Organometallic Chemistry 694 (2009) 2096–2105
Table 5
Crystal data and structure refinements for 2b and 2c.
2
b
2c
Crystal size (mm)
Empirical formula
Formula weight
0.19 ꢁ 0.16 ꢁ 0.15
31ClIrN
601.20
293(2)
0.20 ꢁ 0.16 ꢁ 0.14
C
25
H
3
28 3
C H29ClIrN
635.19
291(2)
T (K)
0
k ( AÅ )
Crystal system
0.71073
Triclinic
P1
0.71073
Triclinic
P1
ꢀ
ꢀ
Space group
0
a ( AÅ )
10.3150(11)
10.6590(10)
0
b ( AÅ )
11.6587(12)
11.188(3)
0
c ( AÅ )
21.351(2)
11.649(2)
a
(°)
b (°)
(°0)
76.8960(10)
79.4780(10)
73.2850(10)
2376.1(4)
74.949(2)
75.733(3)
63.079(2)
1182.7(4)
c
3
V ( AÅ )
Z
4
2
Absorption coefficient (mmꢀ1)
Index ranges
5.748
5.780
ꢀ12 6 h 6 12, ꢀ13 6 k 6 13, ꢀ16 6 l 6 25
ꢀ13 6 h 6 11, ꢀ13 6 k 6 11, ꢀ11 6 l 6 14
Reflections collected
12053
6421
Independent reflections (Rint
)
8280(0.1246)
98.8
0.42 and 0.35
8280/2423/537
0.987
4546(0.0276)
97.8
0.45 and 0.34
4546/0/298
1.080
Completeness to h = 25.02 (%)
Maximum and minimum transmission
Data/restraints/parameters
Goodness-of-fit (GOF)
Final R indices [I > 2
R indices (all data)
r
(I)]a
R
R
1
= 0.0580, wR
= 0.0735, wR
2
= 0.1485
= 0.1634
R
R
1
= 0.0476, wR
= 0.0568, wR
2
2
= 0.1038
= 0.1055
0
1
2
1
Largest difference in peak and hole (e ÅA ꢀ3)
2.385 and ꢀ1.920
Pw(|F
1.629 and ꢀ3.039
a
R
1
=
P||F
o
| ꢀ |F
c
||/P
|F
o
|; wR
2
= [P
w(|F
o
| ꢀ |F
c
|) / w|F
P
o
o
| ꢀ |F
c
|) /(n
o
–n
v
2
|2]1/2; GOF = [
2
)]1/2
.
[
(
Ir(COD)Cl]
CDCl , 25 °C): d 8.23 (d, 1H, naphthyl-H), 7.92–7.88 (m, 2H, naph-
2
(0.336 g, 0.50 mmol). Yield: 0.391 g (65%). 1H NMR
(10 mL) in a Schlenk tube. The solution was heated to 82 °C for
30 min. Subsequently, ketone (8 mmol) was added and the reac-
tion progress was monitored by GC analysis.
3
thyl-H), 7.61 (t, 1H, naphthyl-H), 7.55 (t, 1H, naphthyl-H), 7.48 (t,
1
6
5
4
H, naphthyl-H), 7.40 (d, 1H, naphthyl-H), 6.80 (d, 1H, HCCH),
2
.56 (d, 1H, HCCH), 6.27 (d, 1H,
J
HH = 14.9 Hz, Naphthyl-NCH
HH = 15.0 Hz, naphthyl-NCH ), 4.67 (m, 2H, CHCOD),
.45 (m, 2H, NCH ), 3.09 (m, 2H, CHCOD), 2.55-1.65 (m, 10H,
CH ), 1.49 (m, 2H, NCH CH CH ), 1.05 (t, 3H,
). C NMR (CDCl , 25 °C): 180.4 (C–Ir), 133.9,
2
),
3.4. X-ray crystallographic structure determination
2
.98 (d, 1H,
J
2
2
Data for 2b and 2c were collected on a SMART APEX CCD dif-
fractometer with graphite monochromated Mo Ka (k = 0.71073 ÅA )
0
(
CH
2
)
COD and NCH
2
2
2
2
2
1
3
NCH
2
CH CH
2 2
CH
3
3
and corrected for absorption using SADABS program [63]. These
two structures were solved by direct methods and refined on F2
against all reflections by full-matrix least-squares methods with
SHELXTL (version 6.10) program [64]. The hydrogen atoms in these
compounds were positioned geometrically and refined in the rid-
ing-model approximation. All non-hydrogen atoms were refined
with anisotropic thermal parameters. Table 5 summarized the
crystal data, data collection and refinement parameters for both
compounds.
1
1
31.9, 131.6, 129.3, 128.8, 127.4, 127.3, 126.4, 125.5, 124.0,
20.3, 120.1 (naphthyl and Im), 84.8, 84.6, 51.8 (CHCOD), 52.3
(
naphthyl-NCH
2
), 33.8, 29.6 ((CH
2
)
COD), 50.7, 33.2, 20.2, 14.0
32ClIrN : C, 52.03; H, 5.37;
(
NCH CH CH CH
2
2
2
3
). Anal. Calc. for C26
H
2
N, 4.67. Found: C, 51.92; H, 5.30; N, 4.57%. ESI-MS (m/z): calc.,
+
5
65.78, [MꢀCl] ; found, 565.17.
3.2.16. [3-n-Butyl-1-(8-naphthylmethyl)imidazole-2-
ylidene]dicarbonylchloroiridium (6)
The procedure for the preparation of 6 was similar to that for 3a,
Acknowledgements
1
from 5 (0.108 g, 0.18 mmol). Yield: 0.085 g (86%). H NMR (CDCl
3
,
2
(
5 °C): d 8.11 (d, 1H, naphthyl-H), 7.91 (d, 2H, naphthyl-H), 7.56
m, 2H, naphthyl-H), 7.50 (t, 1H, naphthyl-H), 7.42 (d, 1H, naph-
thyl-H), 6.90 (s, 1H, HCCH), 6.67 (s, 1H, HCCH), 6.05 (d, 1H,
This work was supported by National Basic Research Program of
China (Nos. 2006CB806104 and 2007CB925102), and US National
Science Foundation (CHE-0516928).
2
), 5.86 (d, 1H, 2
), 1.91 (m, 2H, NCH
J
HH = 14.7 Hz, naphthyl-NCH
thyl-NCH ), 4.34 (m, 2H, NCH
CH CH ), 1.02 (t, 3H, NCH
2
J
HH = 14.8 Hz, naph-
CH ), 1.44 (m,
). C NMR (CDCl
2
2
2
3
2
Appendix A. Supplementary material
1
2
2
1
H, NCH
2
2
2
2
CH CH
2 2
CH
3
3
,
5 °C): 181.5 (C–Ir), 173.7, 168.4 (CO), 134.1, 131.4, 130.7, 139.9,
29.0, 128.1, 127.3, 126.5, 125.5, 123.7, 121.3, 121.1 (naphthyl
CCDC 697147 and 697146 contain the supplementary crystallo-
graphic data for 2b and 2c. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2009.02.007.
and Im) 53.4 (naphthyl-NCH
CH CH CH CH ). FT-IR (CHCl ):
Calc. for C20 20ClIrN
3.97; H, 3.68; N, 5.04%. ESI-MS (m/z): calc., 513.62, [MꢀCl] ;
found, 513.00.
2
), 51.5, 33.0, 19.9, 13.8 (N
v
(CO) 2062.5, 1978.8 cm 1. Anal.
ꢀ
2
2
2
3
3
H
2 2
O : C, 43.83; H, 3.68; N, 5.11. Found: C,
+
4
References
3.3. General conditions of catalytic studies
[
[
1] J.C. Garrison, W.J. Youngs, Chem. Rev. 105 (2005) 3978.
2] D. Pugh, A.A. Danopoulos, Coord. Chem. Rev. 251 (2007) 610.
Under an inert atmosphere, the tested complex (4 lmol) was
dissolved in a solution of KOH (0.12 mmol) and isopropanol
[3] F.E. Hahn, M.C. Jahnke, Angew. Chem., Int. Ed. 47 (2008) 3122.

J.-F. Sun et al. / Journal of Organometallic Chemistry 694 (2009) 2096–2105
2105
[
[
[
[
[
[
4] D. Bourissou, O. Guerret, F.P. Gabba, G. Bertrand, Chem. Rev. 100 (2000) 39.
5] W.A. Herrmann, Angew. Chem., Int. Ed. 41 (2002) 1290.
6] M.C. Perry, K. Burgess, Tetrahedron: Asymmetry 14 (2003) 951.
7] W.A. Herrmann, C. Köcher, Angew. Chem., Int. Ed. Engl. 36 (1997) 2163.
8] F. Boeda, S.P. Nolan, Annu. Rep. Prog. Chem., Sect. B 104 (2008) 184.
9] F. Hanasaka, K. Fujita, R. Yamaguchi, Organometallics 25 (2006) 4643.
[34] H.-U. Blaser, C. Malan, B. Pugin, F. Spindler, H. Steiner, M. Studer, Adv. Synth.
Catal. 345 (2003) 103.
[35] J.C. Green, R.G. Scurr, P.L. Arnold, F.G.N. Cloke, Chem. Commun. (1997) 1963.
[36] K. Öfele, W.A. Herrmann, D. Mihalios, M. Elison, E. Herdtweck, J. Organomet.
Chem. 498 (1995) 1.
[37] S.T. Liddle, I.S. Edworthy, P.L. Arnold, Chem. Soc. Rev. 36 (2007) 1732.
[38] O. Kühl, Chem. Soc. Rev. 36 (2007) 592.
[39] H.M. Lee, C.-C. Lee, P.-Y. Cheng, Curr. Org. Chem. 11 (2007) 1491.
[40] A.T. Normand, K.J. Cavell, Eur. J. Inorg. Chem. (2008) 2781.
[41] P.L. Chiu, C.Y. Chen, C.-C. Lee, M.-H. Hsieh, C.-H. Chuang, H.M. Lee, Inorg. Chem.
45 (2006) 2520. and references cited therein.
[42] H.M. Peng, R.D. Webster, X. Li, Organometallics 27 (2008) 4484.
[43] H.M. Peng, G. Song, Y. Li, X. Li, Inorg. Chem. 47 (2008) 8031.
[44] I.J.B. Lin, C.S. Vasam, Comments Inorg. Chem. 25 (2004) 75.
[45] J.C. Garrison, R.S. Simons, J.M. Talley, C. Wesdemiotis, C.A. Tessier, W.J. Youngs,
Organometallics 20 (2001) 1276.
[
10] M. Albrecht, J.R. Miecznikowski, A. Samuel, J.W. Faller, R.H. Crabtree,
Organometallics 21 (2002) 3596.
11] J.R. Miecznikowski, R.H. Crabtree, Organometallics 23 (2004) 629.
12] F.E. Hahn, C. Holtgrewe, T. Pape, M. Martin, E. Sola, L.A. Oro, Organometallics
4 (2005) 2203.
13] I. Kownacki, M. Kubicki, K. Szubert, B. Marciniec, J. Organomet. Chem. 693
2008) 321.
14] W.A. Herrmann, D. Baskakov, E. Herdtweck, S.D. Hoffmann, T.
Bunlaksananusorn, F. Rampf, L. Rodefeld, Organometallics 25 (2006) 2449.
15] E. Mas-Marzá, M. Sanaú, E. Peris, Inorg. Chem. 44 (2005) 9961.
[
[
2
[
[
(
[
[
16] C.-Y. Wang, C.-F. Fu, Y.-H. Liu, S.-M. Peng, S.-T. Liu, Inorg. Chem. 46 (2007)
[46] J.C. Garrison, R.S. Simons, W.G. Kofron, C.A. Tessier, W.J. Youngs, Chem.
Commun. (2001) 1780.
5
779.
17] H. Türkmen, T. Pape, F.E. Hahn, B. Cetinkaya, Organometallics 27 (2008)
71.
18] E. Mas-Marzá, E. Peris, I. Castro-Rodriguez, K. Meyer, Organometallics 24
2005) 3158.
[
[
[47] J. Pytkowicz, S. Roland, P. Mangeney, J. Organomet. Chem. 631 (2001) 157.
[48] C.K. Lee, K.M. Lee, I.J.B. Lin, Organometallics 21 (2002) 10.
[49] K.M. Lee, H.M.J. Wang, I.J.B. Lin, J. Chem. Soc., Dalton Trans. (2002) 2852.
[50] A.R. Chianese, X. Li, M.C. Janzen, J.W. Faller, R.H. Crabtree, Organometallics 22
(2003) 1663.
[51] G. Song, Y. Zhang, X. Li, Organometallics 27 (2008) 1936.
[52] A.R. Chianese, A. Kovacevic, B.M. Zeglis, J.W. Faller, R.H. Crabtree,
Organometallics 23 (2004) 2461.
5
(
[
[
[
19] H.M. Lee, T. Jiang, E.D. Stevens, S.P. Nolan, Organometallics 20 (2001) 1255.
20] L.D. Vázquez-Serrano, B.T. Owens, J.M. Buriak, Chem. Commun. (2002) 2518.
21] M.G. Perry, X. Cui, M.T. Powell, D.-R. Hou, J.H. Reibenspies, K. Burgess, J. Am.
Chem. Soc. 125 (2003) 113.
[
[
22] S. Nanchen, A. Pfaltz, Chem. Eur. J. 12 (2006) 4550.
23] D. Baskakov, W.A. Herrmann, E. Herdtweck, S.D. Hoffmann, Organometallics
[53] R.A. Kelly III, H. Clavier, S. Giudice, N.M. Scott, E.D. Stevens, J. Bordner, I.
Samardjiev, C.D. Hoff, L. Cavallo, S.P. Nolan, Organometallics 27 (2008) 202.
[54] L. Mercs, G. Labat, A. Neels, A. Ehlers, M. Albrecht, Organometallics 25 (2006)
5648.
[55] M. Süßner, H. Plenio, Chem. Commun. (2005) 5417.
[56] S. Leuthäußer, D. Schwarz, H. Plenio, Chem. Eur. J. 13 (2007) 7195.
[57] I. Yamada, R. Noyori, Org. Lett. 2 (2000) 3425.
[58] M.J. Palmer, M. Wills, Tetrahedron: Asymmetry 10 (1999) 2045.
[59] J.W. Faller, A.R. Lavoie, Organometallics 20 (2001) 5245.
[60] X.H. Bu, D.L. An, Y.T. Chen, M. Shionoya, E. Kimura, J. Chem. Soc., Dalton Trans.
(1995) 2289.
[61] N.K. Dalley, G.P. Xue, J.S. Bradshaw, X.X. Zhang, R.G. Harrison, P.B. Savage, K.E.
Krakowiak, R.M. Izatt, J. Heterocyclic Chem. 38 (2001) 1.
[62] J.L. Herdé, J.C. Lambert, C.V. Senoff, Inorg. Synth. 15 (1974) 18.
[63] G.M. Sheldrick, Program for Empirical Absorption Correction, University of
Göttingen, Germany, 2000.
2
6 (2007) 626.
[
[
[
24] A.R. Chianese, R.H. Crabtree, Organometallics 24 (2005) 4432.
25] E. Mas-Marzá, M. Poyatos, M. Sanaú, E. Peris, Inorg. Chem. 43 (2004) 2213.
26] C. Vicent, M. Viciano, E. Mas-Marzá, M. Sanaú, E. Peris, Organometallics 25
(
2006) 3713.
27] L.D. Field, B.A. Messerle, K.Q. Vuong, P. Turner, Organometallics 24 (2005)
241.
[
[
[
[
4
28] G.D. Frey, C.F. Rentzsch, D. van Preysing, T. Scherg, M. Müehlhofer, E.
Herdtweck, W.A. Herrmann, J. Organomet. Chem. 691 (2006) 5725.
29] G.W. Kabalka, R.S. Verma, in: B.M. Trost, I. Fleming (Eds.), Comprehensive
Organic Synthesis, Pergamon: Oxford, UK, 1991.
30] R.C. Larock, Comprehensive Organic Transformations: A Guide to Functional
Group Preparation, 2nd ed., Wiley-VCH, New York, 1999.
31] S. Gladiali, E. Alberico, Chem. Soc. Rev. 35 (2006) 226.
32] G. Zassinovich, G. Mestroni, S. Gladiali, Chem. Rev. 92 (1992) 1051.
33] R. Noyori, S. Hashiguchi, Acc. Chem. Res. 30 (1997) 97.
[
[
[
[64] G.M. Sheldrick, Program for Crystal Structure Solution and Refinement,
University of Göttingen, Germany, 2000.