Perimidin-2-ylidene rhodium(I) complexes; Unexpected halogen exchange and catalytic activities in transfer hydrogenation reaction

Article abstract of DOI:10.1016/j.jorganchem.2014.04.033

Four new [(NHC)RhCl(COD)] (NHC = perimidin-2-ylidene; COD = 1,5-cyclooctadiene) rhodium complexes (4a-c and 5a) have been prepared by the reaction of [Rh(μ-OMe)(COD)]₂ with perimidinium bromides (2a-c and 3a). The halogen exchange, abstracted f

Full text of DOI:10.1016/j.jorganchem.2014.04.033

Journal of Organometallic Chemistry 765 (2014) 23e30
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Perimidin-2-ylidene rhodium(I) complexes; unexpected halogen
exchange and catalytic activities in transfer hydrogenation reaction
,
b
c
P. Arzu Akıncı a, Süleyman Gülcemal a , Olga N. Kazheva , Grigorii G. Alexandrov ,
*
Oleg A. Dyachenko b, Engin Çetinkaya a, Bekir Çetinkaya a
a Ege University, Department of Chemistry, Catalyst Research Laboratory, 35100 Bornova, Izmir, Turkey
b Institute of Problems of Chemical Physics, Russian Academy of Sciences, Semenov Av. 1, Chernogolovka, 142432 Moscow Region, Russia
c N.S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninskii Prosp. 31, 119991 Moscow, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
Four new [(NHC)RhCl(COD)] (NHC ¼ perimidin-2-ylidene; COD ¼ 1,5-cyclooctadiene) rhodium com-
Received 17 February 2014
Received in revised form
24 April 2014
plexes (4aec and 5a) have been prepared by the reaction of [Rh(m-OMe)(COD)]2 with perimidinium
bromides (2aec and 3a). The halogen exchange, abstracted from 1,2-dichloroethane was observed during
the reaction and [(NHC)RhCl(COD)] complexes were obtained instead of [(NHC)RhBr(COD)]. All ligand
precursors and complexes have been fully characterized by 1H, 13C NMR, IR spectroscopy, elemental
analysis and mass spectroscopy. X-ray diffraction studies on single crystals of 4a and 5a confirm the
square planar geometry. The y(CO) values of [(NHC)RhCl(CO)2] complexes (6aec and 7a) revealed that the
Accepted 29 April 2014
Keywords:
Perimidine
N-Heterocyclic carbenes
Rh(I) complexes
Transfer hydrogenation
NHC ligands are not good
ketones has been comparatively studied by using complexes 4aec and 5a as catalysts.
Ó 2014 Elsevier B.V. All rights reserved.
s-donors. Transfer hydrogenation (TH) reaction of aliphatic and aromatic
Introduction
against this s-donation ability [6a,b]. Therefore, we wished to pay
more attention to investigate synthesis, characterization and
properties of new perimidin-2-ylidene complexes bearing alky-
lated benzyl substituent(s) on the nitrogen atom(s) and their cat-
alytic properties.
N-Heterocyclic carbenes (NHCs) exhibit good s-donor and weak
-acceptor electronic properties and have emerged as a versatile
p
class of ligands since they often give more stable organometallic
complexes due to the strength of the metal-NHC bond [1]. This
strong metaleNHC bond avoids decomposition to free and inactive
metal under catalytic conditions in many cases [2]. Additionally,
their tunable nature allows for the control of the electronic and
steric properties at the metal center [3]. In this respect, the most
popular NHC scaffolds derived from five-membered heterocycles
such as imidazol-2-ylidenes, imidazolin-2-ylidenes and benzimi-
dazol-2-ylidenes have been successfully applied as ligands in
transition metal-catalyzed reactions [4].
Results and discussion
Syntheses of NHC precursors and NHCeRh(I) complexes
The synthesis of the desired dissymmetric perimidinium salts
(2aec and 3a) was carried out by stepwise substitution re-
actions. In the first step, N-alkylperimidines (2 and 3) were
prepared from literature-known 1H-perimidine [7] and alkyl
halides in the presence of NaH and obtained as air stable yellow
solids (Scheme 1). Then, N-alkylperimidines (2 and 3) were
treated with 2-bromopropane, 2-bromoethyl methyl ether or
2,4,6-trimethylbenzyl bromide to give corresponding peri-
midinium bromides (2aec and 3a) as air and moisture stable
yellow solids in good yields (Scheme 1). All these ligand pre-
cursors were spectroscopically characterized. The IR data clearly
indicate the presence of the C]N group with a y(C]N) vibrations
between 1655 and 1664 cmꢀ1, and the 1H NMR spectra were
consistent with the proposed structures; characteristic NCHN
Perimidine-based NHCs and their metal complexes have first
been investigated by Richeson [5] and other research groups [6]. In
some of these studies
s-donation of perimidin-2-ylidenes were
reported to be stronger than their five-membered analogs. Pri-
marily, from these observations it is expected that this donor
property should be reflected in the catalytic activity of derived
complexes. In the other hand, there are some recent examples
* Corresponding author. Tel.: þ90 232 3111581; fax: þ90 232 3888264.
E-mail address: suleyman.gulcemal@ege.edu.tr (S. Gülcemal).
proton resonance at
d
¼ 6.69e8.78 ppm as sharp singlets.
http://dx.doi.org/10.1016/j.jorganchem.2014.04.033
0022-328X/Ó 2014 Elsevier B.V. All rights reserved.

24
P.A. Akıncı et al. / Journal of Organometallic Chemistry 765 (2014) 23e30
Scheme 1. Synthesis of 1-alkylperimidine, perimidinium salts and NHCeRh(I) complexes: i) NaH, ReBr, THF, reflux; ii) R0eBr, PhMe, 60 ꢁC or reflux; iii) [Rh(
ClCH2CH2Cl, reflux.
m-OMe)(COD)]2,
[(NHC)RhCl(COD)] complexes (4aec and 5a) were obtained, by
deprotonation of two equivalents of perimidinium salt (2aec and
3a) with [Rh(m-OMe)(COD)]2 in 1,2-dicholoroethane, as yellow
solids in moderate yields (Scheme 1). All new [(NHC)RhCl(COD)]
complexes (4aec and 5a) with perimidin-2-ylidene ligands were
characterized by NMR spectroscopy and elemental analysis. The
characteristic downfield signals for the NCHN protons of the cor-
responding perimidinium salts disappeared in the 1H NMR spectra
of complexes 4aec and 5a. In the 13C NMR spectra, chemical shifts
showed that Ccarbene is substantially deshielded. Values of Ccarbene
of chloride instead of bromide clearly has proven by elemental
analysis and X-ray crystallography (for 4a and 5a). In a detailed
study on the AgeNHC complexes by Jin, it has been proposed that
the source of chloride is the chlorinated solvents (1,2-
dichloroethane or dichloromethane) and the halogen exchange
reaction occurred unambiguously during the synthesis and not
during recrystallization [9]. As far as we are aware this type of
halogen exchange for Rh(I)eNHC complexes have not been
observed so far.
Measuring of carbonyl stretching frequencies in [(NHC)
M(X)(CO)2] (M ¼ Rh or Ir, X ¼ halogen) complexes with IR spec-
troscopy allows us to compare donor properties of NHC ligands,
which is an important criteria for homogeneous catalysis [10]. Thus,
the corresponding [(NHC)RhCl(CO)2] complexes (6aec and 7a)
were prepared in order to compare the electronic properties of the
NHC ligands. The complexes 6aec and 7a were easily obtained by
passing carbon monoxide gas through a dichloromethane solution
of the 4aec and 5a at room temperature (Scheme 2). These re-
actions resulted in almost quantitative substitution of COD by CO
ligands. The cis conformation of the CO ligands in complex 6aec
and 7a were confirmed by NMR and IR spectroscopies. 13C NMR
spectra exhibit three signals at w182, w185.4 and w204 ppm as
were in the
d
¼ 214.4e215.2 ppm range and coupling constants JRhe
C were in the range 47.8e49.1 Hz for the new complexes and these
values were similar to those found for other perimidin-2-ylidene
rhodium(I) complexes [5,6a,b,d,i,j]. The carbon atoms in the two
cyclooctadiene double bonds are coupled with the rhodium center
differently (JRheC ¼ w6.8 and w14.5 Hz), which is consistent with
their position trans to NHC and the halide atom, respectively.
In principle, deprotonation of azolium bromides with basic
[Rh(m-OMe)(COD)]2 give the corresponding bromide complexes
[(NHC)RhBr(COD)] with MeOH elimination [8]. However, in this
work the presence of chloride coordinated to the Rh atom in
complexes 4aec and 5a and occurred (Scheme 1). The coordination
Scheme 2. Synthesis of [(NHC)RhCl(CO)2] complexes (6aec and 7a).

P.A. Akıncı et al. / Journal of Organometallic Chemistry 765 (2014) 23e30
25
doublets in 6aec and 7a for the two CO and Ccarbene ligands. The
compounds [5,6a,i,j,13]. Rh(1)eCl(1) bond lengths are 2.3599(6)
and 2.3709(6) A for 4a and 5a respectively, which is a bit shorter
than in works [14].
Crystal structures of 4a and 5a are presented if Figs. 2 and 3. In
the crystal structure of 4a water molecules as solvent were
discovered.
ꢀ
average carbonyl stretching frequency in the IR spectra was found
av
to be nCO ¼ 2047, 2045, 2045 and 2047 cmꢀ1 for complexes 6aec
and 7a respectively.
The Tolman electronic parameters (TEP) [11] could also be used
to compare the donor strength of a NHC ligand. By applying the
modified relationship introduced by Plenio and Nolan [12] the CO
stretching frequencies of [(NHC)MX(CO)2] complexes (M ¼ Ir or Rh)
can be converted to the corresponding TEP value. The calculated
TEP value was found to be 2054, 2056, 2056 and 2054 cmꢀ1
(Nolan’s equation: TEP ¼ 0.847 ꢂ nCO avþ336; Plenio’s equation:
Catalysis
Transfer hydrogenation (TH) is a metal-catalyzed process that
requires a hydrogen donor atom, typically 2-propanol, in combi-
nation with a strong base. This process is preferred for large-scale
industrial use in the hope of developing a greener process by
reducing waste production, energy use and lowering toxicity. TH is
a safer and more valuable atom-efficient method when compared
with the conventional hydrogenation reaction using the highly
flammable H2 gas [4b]. In this study, Rh(I)eNHC complexes with a
perimidin-2-ylidene scaffold has been used in such reduction re-
action for the first time. For this purpose, [(NHC)RhCl(COD)] com-
plexes (4aec and 5a) were tested as catalysts for TH of
cyclohexanone to cyclohexanol using 2-propanol as a hydrogen
donor in the presence of KOH. The catalytic experiments were
carried out using 0.5 mmol of ketone, 0.005 mmol (1 mol%) of 4aec
or 5a 0.025 mmol of KOH (5 mol%), 2.5 mL of 2-propanol, with a
catalyst/base/substrate ratio of 1:5:100. The catalyst was added to a
solution of 2-propanol containing KOH, which was kept at 82 ꢁC for
5 min and corresponding ketone was added into this solution.
Percentage conversions were screened by GC analysis and results
were summarized in Table 3.
The catalytic activity of the complexes 4aec and 5a decreases in
order 5a > 4a > 4b > 4c (Table 3, entries 1e4). The catalyst 5a with
iPr and 2,4,6-triisopropylbenzyl groups attached to the nitrogen
atoms of perimidine scaffold was found to be the most active
catalyst within all complexes examined and reaches to 83% con-
version in 4 h (Table 3, entry 4) for the TH of cyclohexanone to
cyclohexanol. The most active catalyst 5a was also examined for TH
of different substituted aromatic and aliphatic ketones (Table 3,
entries 5e9). In the presence of acetophenone 68% conversion was
achieved in 4 h with the catalyst 5a (Table 3, entry 5). When
compared with the other [(NHC)RhX(COD)] analogs with a five-
membered imidazol-2-ylidene or benzimidazol-2-ylidene ligand,
catalytic activity of perimidine-2-ylidene ligand in TH reaction was
av
nIr ¼ 0.8695 ꢂ nRh avþ250.7) for complexes 6aec and 7a respec-
tively (Table 1).
There are number of reports on IR data for related neutral per-
imidin-2-ylidene complexes carrying various alkyl groups attached
to the nitrogen atoms [5,6a,b,i,j]. Comparison of the CO stretching
frequencies (nCO av) and the subsequent TEP values are not consis-
tent. Furthermore, the complex 6aec and 7a are weaker
s-donors.
Molecular structures of complexes 4a and 5a
The molecular view and selected bond lengths of 4a and 5a are
presented in Fig.1 and Table 2 respectively. The structures of 4a and
5a show a three-coordinate environment for C(1), a planar geom-
etry around the N atoms and carbene center, short NeCcarbene dis-
ꢀ
tances with an average of 1.354(2) and 1.359(2) A for 4a and 5a,
respectively, which are consistent with a carbene structure. The
maximal deviations of N(1), N(2) and C(1) atoms out of the bonded
ꢀ
ꢀ
atoms’ plane don’t exceed 0.03 A for 4a and 0.04 A for 5a. The sums
of valent angles of the corresponding atoms are extremely close to
360ꢁ. The longer NeCnaphth bond lengths (average 1.412(2) and
ꢀ
1.417(3) A) suggest that N atoms lone pairs are more involved with
bonding to Ccarbene than to the naphthyl ring, as described in work
[5]. The NeCcarbeneeN angles of 117ꢁ also close to the previously
described analogs [5].
Perimidine tricycles are approximate planar, maximal deviation
ꢀ
of non-hydrogen atoms out of their planes don’t exceed 0.18 A for
ꢀ
4a (N(2) atom) and 0.09 A for 5a (N(2) atom).
Rh(1) coordination geometry is a distorted square plane,
perpendicularly oriented to the carbene plane, as in work [5]. Dis-
ꢀ
tances Rh(1)eC(1) are 2.060(2)e2.062(2) A, which corresponds to
ꢀ
the wide range of 2.04e2.09 A values reported in similar rhodium
Table 1
Stretching frequencies and TEP values of the [(NHC)RhX(CO)2] complexes.
nCO (cmꢀ1
)
n
(cmꢀ1
)
TEP (cmꢀ1
)
Reference
av
Complex
Solvent
CO
8A (X ¼ Cl)
8A (X ¼ I)
8B (X ¼ Cl)
8B (X ¼ Cl)
8C (X ¼ Cl)
8D (X ¼ I)
8E (X ¼ I)
8F (X ¼ I)
6a
CH2Cl2
CH2Cl2
No info
No info
No info
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
2007, 2085
2004, 2075
1985, 2073
1989, 2073
2000, 2079
2000, 2073
1999, 2072
2001, 2075
2006, 2084
2008, 2085
2008, 2086
2006, 2083
2046
2040
2029
2031
2040
2037
2036
2038
2045
2047
2047
2045
2055
2051
2043
2044
2051
2049
2048
2049
2054
2056
2056
2054
[6a]
[6j]
[5]
[6i]
[6b]
[6j]
[6j]
[6j]
This study
This study
This study
This study
6b
6c
7a

26
P.A. Akıncı et al. / Journal of Organometallic Chemistry 765 (2014) 23e30
Fig. 1. Molecular view of complexes 4a and 5a with the atom labeling scheme.
found to be lower even with a higher catalyst loading [8a,b,e]. A
black precipitation was observed during the catalytic process in all
cases and this observation could be attributed to the low stability of
catalysts in these reaction conditions.
hexane and toluene over Na and dichloromethane over CaH2). The
reagents were purchased from SigmaeAldrich, Merck, Alfa Aesar
and Acros Organics. 1H-perimidine [7], [Rh(m-OMe)(COD)]2 [15],
2,4,6-trimethylbenzyl bromide and 2,4,6-triisopropylbenzyl bro-
mide [16] were prepared according to the published procedures. 1H
(400 MHz) and 13C NMR (100.6 MHz) spectra were acquired on a
Varian AS 400 Mercury spectrometer with CDCl3 as solvent and
Conclusions
tetramethylsilane (TMS) as internal standard. Chemical shifts (d)
This report was devoted to the design of perimidine derivatives
and their NHC-metal complexes, we presented here simple syn-
thetic strategies for the construction of new type of 1,3-
disubstituted perimidine salts and perimidin-2-ylidenes. Despite
were reported in units (ppm) by assigning TMS resonance in the 1H
spectrum as 0.00 ppm and CDCl3 resonance in the 13C spectrum as
77.0 ppm. All coupling constants (J values) were reported in Hertz
(Hz). Melting points were recorded with Gallenkamp electro-
thermal melting point apparatus. FTIR spectra were recorded on a
Perkin Elmer Spectrum 100 series. Elemental analyses were per-
formed on a PerkineElmer PE 2400 elemental analyzer. The chro-
matographic analyses (GC) were performed with an Agilent 7820A
instrument equipped with a flame ionization detector and an Agi-
the acidity of C2eH (
ture has a dramatic effect on the deprotonation behavior and is base
selective. The deprotonation/coordination was successfully ach-
d
¼ 6.69e8.78 ppm), perimidinium architec-
ieved only by [Rh(m-OMe)(COD)]2 in boiling 1,2-dichloroethane.
The halogen exchange reaction of Rh(I)eNHC complexes from a
chlorinated solvent during the synthetic process was observed for
the first time. The catalytic activities for rhodium(I) complexes with
a perimidine scaffold were evaluated for TH reaction of cyclohex-
anone and acetophenone. The catalytic efficiency of complexes is
lent 19091J-413 column (30 m ꢂ 320
mm ꢂ 0.5
mm).
Synthesis of 1-alkylperimidine derivatives (2 and 3)
low, which may be attributed to the weak
disubstituted perimidin-2-ylidene ligands.
s-donocity of 1,3-
A suspension of NaH (0.86 g; 35.7 mmol) in THF (15 mL) was
transferred drop wise into the solution of 1H-perimidine (5.0 g;
29.7 mmol) in 60 mL of THF and the resulting mixture was refluxed
for 24 h. Then 2,4,6-trimethylbenzyl bromide or 2,4,6-
triisopropylbenzyl bromide (35.7 mmol) was added and the
Experimental
General considerations
Unless otherwise noted all manipulations were carried out un-
der an argon atmosphere by using Schlenk techniques. All solvents
were dried rigorously, freshly distilled prior to use and stored under
argon atmosphere (tehrahydrofuran over Na/benzophenone, n-
Table 2
ꢀ
Selected bond lengths [A] for 4a and 5a.
4a
5a
Rh(1)eC(1)
Rh(1)eC(25)
Rh(1)eC(32)
Rh(1)eC(29)
Rh(1)eC(28)
Rh(1)eCl(1)
N(1)eC(1)
2.062(2)
2.107(2)
2.130(2)
2.185(2)
2.215(2)
2.3599(6)
1.349(2)
1.360(2)
Rh(1)eC(1)
Rh(1)eC(31)
Rh(1)eC(38)
Rh(1)eC(35)
Rh(1)eC(34)
Rh(1)eCl(1)
N(1)eC(1)
2.060(2)
2.114(2)
2.138(2)
2.188(2)
2.225(2)
2.3709(6)
1.359(2)
1.359(2)
N(2)eC(1)
N(2)eC(1)
Fig. 2. Crystal structure of 4a.

P.A. Akıncı et al. / Journal of Organometallic Chemistry 765 (2014) 23e30
27
24.5, 24.2 (CH3). Elemental analysis (%) calc. for C27H32N2: C, 84.33;
H, 8.39; N, 7.28; found: C, 84.28; H, 8.42; N, 7.25.
Synthesis of perimidinium salts (2aec and 3a)
To a solution of 2 or 3 (5 mmol) in toluene (10 mL), 1.1 eq. of 2-
bromopropane (for 2a and 3a), 2-bromoethyl methyl ether (for 2b)
or 2,4,6-trimethylbenzyl bromide (for 2c) was added. The mixture
was stirred for 24 h at 60 ꢁC (for 2a and 3a) or 110 ꢁC (for 2b and 2c).
Following the completion of the process, the solid formed was
filtered off and the resulting precipitate was recrystallized from
CH2Cl2/Et2O as yellow solid.
Fig. 3. Crystal structure of 5a.
2a: 1.79 g (85%), mp 189 ꢁC. FTIR (film) n(C]N) 1655 cmꢀ1 1H
.
mixture was refluxed for additional 24 h. The solvent was removed
under reduced pressure. The oily residue was treated with CH2Cl2
and filtered off, then was purified by column chromatography over
silica gel using CH2Cl2/MeOH (98:2) as the eluent to give pure
compounds as yellow solid.
NMR (CDCl3):
d
/ppm ¼ 8.78 (s, 1H, NCHNþ), 7.42e7.36 (m, 3H,
CHarom), 7.26 (t, J ¼ 8.4 Hz, 1H, CHarom), 7.07 (d, J ¼ 7.2 Hz, 1H,
CHarom), 6.85 (s, 2H, CH2C6H2(CH3)3-2,4,6), 6.84 (d, J ¼ 6.8 Hz, 1H,
CHarom), 5.40 (s, 2H, CH2C6H2(CH3)3-2,4,6), 4.67 (sept, J ¼ 6.4 Hz,1H,
CH(CH3)2), 2.34, 2.20 (s, 9H, CH2C6H2(CH3)3-2,4,6), 1.52 (d,
2: 6.0 g (67%), mp 159e160 ꢁC. FTIR (film) n(C]N) 1628 cmꢀ1. 1H
J ¼ 4.0 Hz, 6H, CH(CH3)2). 13C NMR (CDCl3):
d/ppm ¼ 148.8
NMR (CDCl3):
d
/ppm ¼ 7.28e7.16 (m, 4H, CHarom), 6.94 (s, 2H,
(NCHNþ), 139.8 (AreC), 137.8 (AreC), 135.2 (AreC), 132.1 (AreC),
131.2 (AreC), 130.7 (AreC), 128.6 (AreC), 128.5 (AreC), 124.9 (Are
C), 124.2 (AreC), 121.8 (AreC), 108.8 (AreC), 108.6 (AreC), 53.8
(CH(CH3)2), 51.7 (CH2C6H2(CH3)3-2,4,6), 21.1, 20.9 (CH2C6H2(CH3)3-
2,4,6), 20.8 (CH(CH3)2). Elemental analysis (%) calc. for C24H27BrN2:
C, 68.08; H, 6.43; N, 6.62; found: C, 68.12; H, 6.46; N, 6.61.
CH2C6H2(CH3)3-2,4,6), 6.81 (d, J ¼ 6.8 Hz, 1H, CHarom), 6.77 (s, 1H,
NCHN), 6.37 (d, J ¼ 6.8 Hz, 1H, CHarom), 4.39 (s, 2H, CH2C6H2(CH3)3-
2,4,6), 2.31, 2.28 (s, 9H, CH2C6H2(CH3)3-2,4,6). 13C NMR (CDCl3):
d/
ppm ¼ 145.3 (NCHN), 143.6 (AreC), 139.3 (AreC), 139.1 (AreC),
138.4 (AreC), 135.7 (AreC), 129.9 (AreC), 129.1 (AreC), 127.7 (Are
C), 126.0 (AreC), 123.2 (AreC), 120.5 (AreC), 120.0 (AreC), 115.4
(AreC), 100.3 (AreC), 46.6 (CH2C6H2(CH3)3-2,4,6), 21.3, 19.9
(CH2C6H2(CH3)3-2,4,6). Elemental analysis (%) calc. for C21H20N2: C,
83.96; H, 6.71; N, 9.33; found: C, 83.99; H, 6.70; N, 9.30.
2b: 1.67 g (76%), mp 209e210 ꢁC. FTIR (film) n(C]) 1659 cmꢀ1. 1H
NMR (CDCl3):
d
/ppm ¼ 8.57 (s, 1H, NCHNþ), 7.50e7.37 (m, 4H,
CHarom), 7.07 (d, J ¼ 7.6 Hz, 1H, CHarom), 6.97 (s, 2H, CH2C6H2(CH3)3-
2,4,6), 6.93 (d, J ¼ 7.6 Hz, 1H, CHarom), 5.13 (s, 2H, CH2C6H2(CH3)3-
2,4,6), 4.44 (t, J ¼ 4.4 Hz, 2H, CH2CH2OCH3), 3.73 (t, J ¼ 5.2 Hz, 2H,
CH2CH2OCH3), 3.23 (s, 3H, CH2CH2OCH3), 2.44, 2.31 (s, 9H,
3: 9.9 g (87%), mp 167 ꢁC. FTIR (film) n(C]N) 1629 cmꢀ1. 1H NMR
(CDCl3):
CH2C6H2(CHMe2)3-2,4,6), 6.83 (s, 1H, NCHN), 6.82 (d, J ¼ 6.8 Hz, 1H,
CHarom), 6.43 (d, 7.2 Hz, 1H, CHarom), 4.43 (s, 2H,
CH2C6H2(CHMe2)3-2,4,6), 2.96 (sept, 7.2 Hz, 3H,
d/ppm
¼
7.29e7.19 (m, 4H, CHarom), 7.10 (s, 2H,
CH2C6H2(CH3)3-2,4,6). 13C NMR (CDCl3):
d
/ppm ¼ 151.2 (NCHNþ),
J
¼
140.3 (AreC), 138.6 (AreC), 135.2 (AreC), 132.6 (AreC), 131.4 (Are
C),130.6 (AreC), 128.7 (AreC), 128.5 (AreC), 124.9 (AreC), 124.6
(AreC), 123.3 (AreC), 121.6 (AreC), 108.6 (AreC), 108.2 (AreC), 66.5
(CH2C6H2(CH3)3-2,4,6), 58.9 (CH2CH2OCH3), 52.0 (CH2CH2OCH3),
50.8 (CH2CH2OCH3), 21.3, 20.6 (CH2C6H2(CH3)3-2,4,6). Elemental
analysis (%) calc. for C24H27BrN2O: C, 65.60; H, 6.19; N, 6.38; found:
C, 65.65; H, 6.21; N, 6.36.
J
¼
CH2C6H2(CHMe2)3-2,4,6), 1.28 (d, J ¼ 6.4 Hz, 6H, CH3), 1.24 (d,
J ¼ 6.8 Hz, 12H, CH3). 13C NMR (CDCl3):
/ppm ¼ 150.8 (NCHN),
d
149.0 (AreC), 145.6 (AreC), 143.6 (AreC), 139.0 (AreC), 135.7 (Are
C), 129.1 (AreC), 127.7 (AreC), 123.2 (AreC), 122.2 (AreC), 120.4
(AreC), 120.1(AreC), 115.5 (AreC), 100.2 (AreC), 44.6
(CH2C6H2(CHMe2)3-2,4,6), 34.7, 30.1 (CH2C6H2(CHMe2)3-2,4,6),
2c: 2.20 g (86%), mp 217e218 ꢁC. FTIR (film) n(C]N) 1664 cmꢀ1. 1H
NMR (CDCl3):
d
/ppm ¼ 7.60e7.53 (m, 4H, CHarom), 7.39 (d, J ¼ 7.2 Hz,
2H, CHarom), 6.73 (s, 4H, CH2C6H2(CH3)3-2,4,6), 6.69 (s, 1H, NCHNþ),
4.92 (s, 4H, CH2C6H2(CH3)3-2,4,6), 2.32, 2.11 (s,18H, CH2C6H2(CH3)3-
Table 3
Catalytic TH of ketones with catalysts 4aec and 5a.a
2,4,6). 13C NMR (CDCl3):
d
/ppm ¼ 145.7 (NCHNþ), 140.4 (AreC),
138.4 (AreC), 134.9 (AreC), 132.4 (AreC), 129.9 (AreC), 129.0 (Are
C), 125.2 (AreC), 122.7 (AreC), 121.2 (AreC), 109.2 (AreC), 49.9
(CH2C6H2(CH3)3-2,4,6), 21.4, 19.7 (CH2C6H2(CH3)3-2,4,6). Elemental
analysis (%) calc. for C31H33BrN2: C, 72.51; H, 6.48; N, 5.46; found: C,
72.46; H, 6.50; N, 5.45.
Entry Catalyst
Ketone
Time/conversion [%]b
3a: 2.13 g (84%), mp 199 ꢁC. FTIR (film) n(C]N) 1662 cmꢀ1 1H
.
0.5 h 1 h 1.5 h 2 h 4 h
NMR (CDCl3):
d
/ppm ¼ 7.53e7.45 (m, 4H, CHarom), 7.43 (s, 1H,
1
2
3
4
5
6
7
8
4a
4b
4c
5a
5a
5a
5a
5a
5a
Cyclohexanone
Cyclohexanone
Cyclohexanone
Cyclohexanone
Acetophenone
22
26
18
29
28
39 51
41 46
24 29
54 66
42 49
55 58
49 51
32 36
78 83
64 68
12 14
21 27
33 36
77 79
NCHNþ), 7.35 (d, J ¼ 6.6 Hz, 1H, CHarom), 7.30 (d, J ¼ 7.6 Hz, 1H,
CHarom), 7.14 (s, 2H, CH2C6H2(CHMe2)3-2,4,6), 5.13 (s, 2H,
CH2C6H2(CHMe2)3-2,4,6), 4.87 (sept, J ¼ 6.4 Hz, 1H, CHMe2), 3.00
(sept, J ¼ 7.2 Hz, 2H, CH2C6H2(CHMe2)3-2,4,6), 2.91 (sept, J ¼ 7.2 Hz,
1H, CH2C6H2(CHMe2)3-2,4,6), 1.24 (d, J ¼ 6.4 Hz, 6H, CH3), 1.23 (d,
J ¼ 7.6 Hz, 12H, CH3), 1.21 (d, J ¼ 6.4 Hz, 6H, CH(CH3)2). 13C NMR
20-Chloroacetophenone <1
5
8
40-Bromoacetophenone
Propiophenone
2-Heptanone
5
12
20
11 18
23 29
42 61
e
9
(CDCl3):
d
/ppm ¼ 152.7 (NCHNþ), 149.4 (AreC), 145.6 (AreC), 139.6
10c
11d
RheNHC [8a] Acetophenone
RheNHC [8a] Acetophenone
e
e
>99
e
(AreC),135.2 (AreC),132.1 (AreC),131.0 (AreC), 128.9 (AreC),128.8
(AreC), 125.4 (AreC), 125.1 (AreC), 122.9 (AreC), 121.5 (AreC),
120.4 (AreC), 109.6 (AreC), 108.9 (AreC), 94.3 (AreC), 53.3
e
>99
e
e
e
a
Ketone (0.5 mmol), KOH (5 mol%), catalyst (1 mol%), IPA (2.5 mL), 82 ꢁC.
Determined by using GC from an average of at least two runs.
RheNHC ¼ bromo(
b
c
(CH(CH3)2),
48.4
(CH2C6H2(CHMe2)3-2,4,6),
34.5,
30.1
h
4-cycloocta-1,5-diene)-1,3-bis(2,4,6-trimethylbenzyl)imi-
(CH2C6H2(CHMe2)3-2,4,6), 24.6, 24.0 (CH3), 20.8 (CH(CH3)2).
Elemental analysis (%) calc. for C30H39BrN2: C, 70.99; H, 7.75; N,
5.52; found: C, 71.04; H, 7.79; N, 5.49.
dazol-2-ylidene rhodium(I) (0.5 mol%).
d
RheNHC ¼ bromo(
h
4-cycloocta-1,5-diene)-1,3-bis(2,4,6-trimethylbenzyl)imi-
dazolin-2-ylidene rhodium(I) (0.5 mol%).

28
P.A. Akıncı et al. / Journal of Organometallic Chemistry 765 (2014) 23e30
Synthesis of the [(NHC)RhCl(COD)] complexes (4aec and 5a)
To a solution of perimidinium salt (2aee or 3a) (0.5 mmol) in
5a: 175 mg (52%). 1H NMR (CDCl3):
6.8 Hz, 1H, CH(CH3)2), 7.43 (d,
d
/ppm ¼ 7.70 (sept,
J
¼
J
¼
15.2 Hz, 1H,
CH2C6H2(CHMe2)3-2,4,6), 7.29e7.21 (m, 2H, CHarom), 7.10 (d,
J ¼ 8.4 Hz, 1H, CHarom), 7.00 (d, J ¼ 7.2 Hz, 1H, CH2C6H2(CHMe2)3-
10 mL of 1,2-dicholoroethane, [Rh(m-OMe)(COD)]2 (121 mg;
0.25 mmol) was added under argon atmosphere. The reaction
mixture was stirred 1 h at 25 ꢁC and then refluxed for 48 h.
Meanwhile the reaction progress was monitored with thin layer
chromatography. After removal of the solvent under reduced
pressure, the residue was purified by column chromatography on
silica gel using CH2Cl2/acetone (98:2) as the eluent to give a yellow
solid.
2,4,6), 6.94 (t,
CH2C6H2(CHMe2)3-2,4,6), 6.28 (d,
J
¼
8.0 Hz, 2H, CHarom), 6.90 (s, 1H,
J
¼
15.6 Hz, 1H,
CH2C6H2(CHMe2)3-2,4,6), 6.21 (d, J ¼ 7.6 Hz, 1H, CHarom), 5.10e5.08
(m, 1H, COD-CH), 5.00e4.95 (m, 1H, COD-CH), 3.62e3.54 (m, 1H,
COD-CH), 3.43 (br, 1H, COD-CH), 2.81 (sept, J ¼ 6.8 Hz, 1H,
CH2C6H2(CHMe2)3-2,4,6), 2.55e2.45 (m, 2H, CH2C6H2(CHMe2)3-
2,4,6), 2.42e2.28 (m, 2H, COD-CH2), 2.08e2.04 (m, 2H, COD-CH2),
1.90 (d, J ¼ 5.2 Hz, 3H, CH(CH3)2), 1.88 (d, J ¼ 5.2 Hz, 3H, CH(CH3)2),
4a: 124 mg (42%). 1H NMR (CDCl3):
d/ppm ¼ 7.72 (sept,
J ¼ 7.2 Hz, 1H, CH(CH3)2), 7.32e7.26 (m, 2H, CHarom), 7.19 (d,
J ¼ 8.8 Hz, 1H, CH2C6H2(CH3)3-2,4,6), 7.13 (s, 1H, CHarom), 7.06e7.01
(m, 2H, CHarom), 6.78 (s, 1H, CH2C6H2(CH3)3-2,4,6), 6.71 (s, 1H,
CH2C6H2(CH3)3-2,4,6), 6.49 (d, J ¼ 16.8 Hz, 1H, CHarom), 6.16 (d,
J ¼ 8.4 Hz, 1H, CH2C6H2(CH3)3-2,4,6), 5.09e5.04 (m, 1H, COD-CH),
5.01e4.96 (m, 1H, COD-CH), 3.65e3.61 (m, 1H, COD-CH), 3.48e3.42
(m, 1H, COD-CH), 2.51e2.38 (m, 4H, COD-CH2), 2.32 (d, J ¼ 9.2 Hz,
6H, CH(CH3)2), 2.03e1.95 (m, 4H, COD-CH2), 1.91, 1.89, 1.86 (s, 3H,
1.91e1.83 (m, 4H, COD-CH2), 1.21, 1.19 (d, J ¼ 4.4 Hz, 18H, CH3). 13
C
NMR (CDCl3):
d/ppm ¼ 215.1 (d, JRheCarbene ¼ 47.8 Hz, Ccarbene),
147.8, 146.8, 145.1, 133.6, 132.4, 130.9, 125.9, 125.7, 124.1, 121.7, 121.1,
120.2, 119.9, 119.3, 106.6, 105.2 (AreC), 97.0 (d, J ¼ 6.9 Hz, COD-CH),
95.8 (d, J ¼ 6.9 Hz, COD-CH), 69.9 (d, J ¼ 14.5 Hz, COD-CH), 69.2 (d,
J ¼ 14.5 Hz, COD-CH), 60.9 (CH(CH3)2), 54.9 (CH2C6H2(CHMe2)3-
2,4,6), 32.9 (s, COD-CH2), 32.4 (CH2C6H2(CHMe2)3-2,4,6), 29.0 (s,
COD-CH2), 24.7, 24.4 (CH2C6H2(CHMe2)3-2,4,6), 22.9 (d, J ¼ 9.1 Hz,
CH3), 22.5, 21.9 (CH3), 18.6, 18.2 (CH(CH3)2). Elemental analysis (%)
calc. for C38H50ClN2Rh: C, 67.80; H, 7.49; N, 4.16; found: C, 67.75; H,
7.53; N, 4.17.
CH2C6H2(CH3)3-2,4,6). 13C NMR (CDCl3):
d
/ppm ¼ 214.4 (d, JRhe
¼ 48.1 Hz, Ccarbene), 136.7, 136.4, 135.1, 134.7, 133.7, 132.2,
Carbene
131.2, 130.6, 127.7, 127.6, 127.2, 121.5, 121.3, 121.0, 108.0, 105.6 (Are
C), 97.9 (d, J ¼ 6.8 Hz, COD-CH), 97.1 (d, J ¼ 6.9 Hz, COD-CH), 71.5 (d,
J ¼ 14.5 Hz, COD-CH), 70.0 (d, J ¼ 14.5 Hz, COD-CH), 61.9 (CH(CH3)2),
33.3 (s, COD-CH2), 29.6 (s, COD-CH2), 21.4, 21.1 (CH(CH3)2), 20.9,
20.2, 19.0 (CH2C6H2(CH3)3-2,4,6). Elemental analysis (%) calc. for
Synthesis of the [(NHC)RhCl(CO)2] complexes (6aec and 7a)
Complexes 4aec or 5a (0.1 mmol) was dissolved in CH2Cl2
(5 mL) and carbon monoxide was bubbled through the solution for
1 h. Color of the solution changed from yellow to pale yellow. The
solution was concentrated ca 1 mL and pentane was added. The
pale yellow solid that separated out was filtered, washed with
pentane and discarded.
C
32H38ClN2Rh: C, 62.25; H, 6.50; N, 4.76; found: C, 62.19; H, 6.47; N,
4.79.
4b: 169 mg (56%). 1H NMR (CDCl3):
d
/ppm ¼ 7.37e7.30 (m, 2H,
CHarom), 7.23 (d, J ¼ 15.2 Hz, 1H, CH2C6H2(CH3)3-2,4,6), 7.12e7.04
(m, 2H, CHarom), 6.91 (d, J ¼ 7.2 Hz, 1H, CHarom), 6.80 (s, 1H,
CH2C6H2(CH3)3-2,4,6), 6.72 (s, 1H, CH2C6H2(CH3)3-2,4,6), 6.65e6.49
(br, 1H, CH2CH2OCH3), 6.38 (d, J ¼ 16.4 Hz, 1H, CH2C6H2(CH3)3-
2,4,6), 6.20 (d, J ¼ 8.0 Hz, 1H, CHarom), 5.07 (s, 2H, COD-CH), 4.88e
4.65 (br, 1H, CH2CH2OCH3), 4.30e4.21 (m, 1H, CH2CH2OCH3), 3.88e
3.82 (m, 1H, CH2CH2OCH3), 3.52 (s, 3H, CH2CH2OCH3), 3.47e3.39
(m, 2H, COD-CH), 2.51e2.36 (m, 4H, COD-CH2), 2.33 (s, 3H,
CH2C6H2(CH3)3-2,4,6), 2.30 (s, 3H, CH2C6H2(CH3)3-2,4,6), 2.22 (s,
3H, CH2C6H2(CH3)3-2,4,6), 1.99e1.88 (m, 4H, COD-CH2). 13C NMR
6a: 51 mg (95%). FTIR (CH2Cl2) nCO 2006 and 2084 cmꢀ1. 1H NMR
(CDCl3):
CHarom), 6.91 (s, 1H, CHarom), 6.83 (s, 1H, CH2C6H2(CH3)3-2,4,6), 6.82
(d, 16.8 Hz, 1H, CH2C6H2(CH3)3-2,4,6), 6.70 (s, 1H,
d/ppm ¼ 7.35e7.26 (m, 3H, CHarom), 7.11e7.05 (m, 2H,
J
¼
CH2C6H2(CH3)3-2,4,6), 6.66 (sept, J ¼ 6.8 Hz, 1H, CH(CH3)2), 6.27 (d,
J ¼ 7.6 Hz, 1H, CHarom), 6.16 (d, J ¼ 16.8 Hz, 1H, CH2C6H2(CH3)3-
2,4,6), 2.48 (s, 3H, CH2C6H2(CH3)3-2,4,6), 2.24 (s, 3H,
CH2C6H2(CH3)3-2,4,6), 2.21 (s, 3H, CH2C6H2(CH3)3-2,4,6), 1.80 (d,
J ¼ 7.6 Hz, 3H, CH(CH3)2), 1.74 (d, J ¼ 7.6 Hz, 3H, CH(CH3)2). 13C NMR
(CDCl3):
d
/ppm ¼ 215.2 (d, JRheCarbene ¼ 49.1 Hz, Ccarbene), 136.5,
136.4, 134.7, 133.9, 133.8, 131.2, 130.7, 127.9, 127.8, 127.5, 121.6, 121.3,
120.3, 105.9, 105.6 (AreC), 98.8 (d, J ¼ 6.9 Hz, COD-CH), 98.3 (d,
J ¼ 6.9 Hz, COD-CH), 71.5 (d, J ¼ 14.6 Hz, COD-CH), 71.2 (d,
J ¼ 14.6 Hz, COD-CH), 68.6 (CH2CH2OCH3), 59.5 (CH2CH2OCH3), 58.5
(s, CH2C6H2(CH3)3-2,4,6), 54.3 (CH2CH2OCH3), 32.8 (d, J ¼ 7.6 Hz,
(CDCl3):
d
/ppm ¼ 202.6 (d, JRheCarbene ¼ 41.3 Hz, Ccarbene), 185.5 (d,
JRheC ¼ 55.2 Hz, CO), 182.4 (d, JRheC ¼ 75.9 Hz, CO), 136.9, 134.9,
133.4, 131.6, 131.0, 130.4, 128.7, 127.5, 127.0, 126.9, 122.1, 121.9, 121.8,
108.7, 106.7 (AreC), 63.0 (CH(CH3)2), 58.3 (CH2C6H2(CH3)3-2,4,6),
28.5 (CH2C6H2(CH3)3-2,4,6), 21.1, 20.7 (CH2C6H2(CH3)3-2,4,6), 19.0,
17.6 (CH(CH3)2).
COD-CH2), 29.0 (d,
J
¼
9.1 Hz, COD-CH2), 21.5, 21.2, 21.0
(CH2C6H2(CH3)3-2,4,6). Elemental analysis (%) calc. for
32H38ClN2ORh: C, 63.53; H, 6.33; N, 4.63; found: C, 63.49; H, 6.34;
N, 4.65.
4c: 156 mg (46%). 1H NMR (CDCl3):
6b: 50 mg (91%). FTIR (CH2Cl2) nCO 2008 and 2085 cmꢀ1. 1H NMR
C
(CDCl3)
d
/ppm ¼ 7.39e7.36 (m, 2H, CHarom), 7.32 (d, J ¼ 8.0 Hz, 1H,
CHarom), 7.12 (t, J ¼ 4.0 Hz, 1H, CHarom), 6.89 (d, J ¼ 16.0 Hz, 1H,
CH2C6H2(CH3)3-2,4,6), 6.78 (s,1H, CH2C6H2(CH3)3-2,4,6), 6.74 (s, 1H,
CH2C6H2(CH3)3-2,4,6), 6.32 (d, J ¼ 8.0 Hz, 1H, CHarom), 5.49 (d,
d
/ppm ¼ 7.26 (d, J ¼ 8.4 Hz,
2H, CHarom), 7.10 (t, J ¼ 8.0 Hz, 2H, CHarom), 6.92 (d, J ¼ 8.0 Hz, 4H,
CH2C6H2(CH3)3-2,4,6), 6.85 (d, J ¼ 4.8 Hz, 4H, CH2C6H2(CH3)3-2,4,6),
6.40 (d, J ¼ 8.0 Hz, 2H, CHarom), 5.08 (s, 2H, COD-CH), 3.62 (s, 2H,
COD-CH), 2.52 (s, 6H, CH2C6H2(CH3)3-2,4,6), 2.34 (s, 6H,
CH2C6H2(CH3)3-2,4,6), 2.28 (s, 6H, CH2C6H2(CH3)3-2,4,6), 2.22e2.10
J
¼
16.4 Hz, 1H, CH2C6H2(CH3)3-2,4,6), 5.51e5.34 (br, 1H,
CH2CH2OCH3), 4.90e4.78 (br, 1H, CH2CH2OCH3), 3.96e3.86 (m, 2H,
CH2CH2OCH3), 3.42 (s, 3H, CH2CH2OCH3), 2.47 (s, 3H,
CH2C6H2(CH3)3-2,4,6), 2.25 (s, 6H, CH2C6H2(CH3)3-2,4,6). 13C NMR
(br, 4H, COD-CH2), 1.90e1.84 (m, 4H, COD-CH2). 13C NMR (CDCl3):
d/
(CDCl3):
d
/ppm ¼ 204.3 (d, JRheCarbene ¼ 42.9 Hz, Ccarbene), 185.4 (d,
ppm ¼ 214.8 (d, JRheCarbene ¼ 49.1 Hz, Ccarbene), 135.7, 135.5, 135.3,
135.2, 135.0, 133.5, 133.3, 133.1, 129.7, 129.6, 129.0, 128.6, 127.1,
126.6, 126.4, 120.2, 118.8, 118.4, 104.7, 104.1 (AreC), 96.8 (d,
J ¼ 6.9 Hz, COD-CH), 69.9 (d, J ¼ 13.7 Hz, COD-CH), 58.4
(CH2C6H2(CH3)3-2,4,6), 31.50, 27.7 (COD-CH2), 20.0, 19.7, 19.5
(CH2C6H2(CH3)3-2,4,6). Elemental analysis (%) calc. for
JRheC ¼ 54.4 Hz, CO), 182.4 (d, JRheC ¼ 75.9 Hz, CO), 136.9, 136.0,
135.1, 134.7, 133.7, 133.3, 131.1, 130.4, 127.8, 127.6, 126.9, 122.3, 122.0,
120.8, 106.9, 106.1 (AreC), 67.6 (CH2CH2OCH3), 59.1 (CH2CH2OCH3),
58.8 (CH2C6H2(CH3)3-2,4,6), 55.1 (CH2CH2OCH3), 21.2, 20.7
(CH2C6H2(CH3)3-2,4,6).
6c: 60 mg (96%). FTIR (CH2Cl2) nCO 2008 and 2086 cmꢀ1. 1H NMR
C
4.10.
39H44ClN2Rh: C, 68.97; H, 6.53; N, 4.12; found: C, 69.03; H, 6.55; N,
(CDCl3)
d
/ppm ¼ 7.27 (d, J ¼ 2.11 Hz, 2H, CHarom), 7.09 (t, J ¼ 2.11 Hz,
2H, CHarom), 6.82e6.93 (br, 2H, CH2C6H2(CH3)3-2,4,6), 6.75e6.82

P.A. Akıncı et al. / Journal of Organometallic Chemistry 765 (2014) 23e30
29
(br, 2H, CH2C6H2(CH3)3-2,4,6), 6.71 (d,
CH2C6H2(CH3)3-2,4,6), 6.39 (d, J ¼ 2.01 Hz, 2H, CHarom), 5.69 (d,
4.22 Hz, 2H, CH2C6H2(CH3)3-2,4,6), 2.40e2.56 (br, 6H,
CH2C6H2(CH3)3-2,4,6), 2.29e2.40 (br, 6H, CH2C6H2(CH3)3-2,4,6),
2.25 (s, 6H, CH2C6H2(CH3)3-2,4,6). 13C NMR (CDCl3)
J
¼
4.22 Hz, 2H,
measured reflections, 16,674; the number of independent re-
flections, 7648; the number of refined parameters, 379; R-factor
0.032 for 6013 reflections with [F0 > 4s(F0)].
J
¼
d
/ppm ¼ 205.6
Acknowledgments
(d, JRheCarbene ¼ 42.9 Hz, Ccarbene), 185.4 (d, JRheC ¼ 54.4 Hz, CO),
182.6 (d, JRheC ¼ 75.9 Hz, CO), 137.3, 136.4, 134.6, 133.8, 130.8, 127.7,
127.5, 122.4, 121.1, 107.4 (AreC), 59.8 (CH2C6H2(CH3)3-2,4,6), 21.0,
20.7 (CH2C6H2(CH3)3-2,4,6).
We thank to Ege University Research Fund (Project Number: 11-
FEN-048) for financial support of this work and Mr. Salih Günnaz
for NMR analyses.
7a: 58 mg (94%). FTIR (CH2Cl2) nCO 2006 and 2083 cmꢀ1 1H
.
NMR (CDCl3):
d
/ppm ¼ 7.31e7.29 (m, 2H, CHarom), 7.20 (d,
Appendix A. Supplementary material
J ¼ 8.4 Hz, 1H, CHarom), 7.08 (s, 1H, CH2C6H2(CHMe2)3-2,4,6),
7.04e6.98 (m, 2H, CHarom), 6.95 (s, 1H, CH2C6H2(CHMe2)3-2,4,6),
6.85 (d, J ¼ 15.6 Hz, 1H, CH2C6H2(CHMe2)3-2,4,6), 6.73 (sept,
J ¼ 6.8 Hz, 1H, CH(CH3)2), 6.44 (d, J ¼ 7.6 Hz, 1H, CHarom), 5.50 (d,
J ¼ 15.6 Hz, 1H, CH2C6H2(CHMe2)3-2,4,6), 3.68 (sept, J ¼ 6.8 Hz,
CCDC 985038 and 985039 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
1H, CH2C6H2(CHMe2)3-2,4,6), 3.35 (sept,
CH2C6H2(CHMe2)3-2,4,6), 2.85 (sept,
J
¼
¼
6.8 Hz, 1H,
6.8 Hz, 1H,
J
References
CH2C6H2(CHMe2)3-2,4,6), 1.81 (d, J ¼ 6.8 Hz, 3H, CH(CH3)2), 1.68
(d, J ¼ 6.8 Hz, 3H, CH(CH3)2), 1.38, 1.31, 1.22, 1.19 (4 ꢂ d,
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Efficient Synthetic Tools, RSC Catalysis Series No. 6, Royal Society of Chem-
istry, Cambridge, 2011;
J ¼ 6.4 Hz, 18H, CH2C6H2(CH(CH3)2)3-2,4,6). 13C NMR (CDCl3):
d/
ppm ¼ 203.9 (d, JRheCarbene ¼ 41.4 Hz, Ccarbene), 185.7 (d, JRhe
¼ 54.5 Hz, CO), 182.1 (d, JRheC ¼ 75.9 Hz, CO), 148.6, 147.6, 147.2,
C
(d) L. Benhamou, E. Chardon, G. Lavigne, S. Bellemin-Laponnaz, V. César,
Chem. Rev. 111 (2011) 2705;
(e) D. Tapu, D.A. Dixon, C. Roe, Chem. Rev. 109 (2009) 3385;
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134.7, 133.7, 131.5, 128.7, 127.1, 126.7, 125.4, 122.5, 122.3, 121.9,
121.8, 121.5, 108.5, 107.4 (AreC), 63.1 (CH(CH3)2), 56.4
(CH2C6H2(CHMe2)3-2,4,6), 34.1 (CH2C6H2(CHMe2)3-2,4,6), 30.2,
30.0 (CH2C6H2(CHMe2)3-2,4,6), 28.0, 25.5, 24.5, 23.9, 23.6, 23.2
(CH2C6H2(CH(CH3)2)3-2,4,6), 19.2, 17.4 (CH(CH3)2).
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General procedure for the transfer hydrogenation reaction
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Under inert atmosphere, in a vial fitted with a screw cap, an
aliquot of the tested complex (1 mol%), from a stock solution in
dichloromethane was added. The solvent was removed under
vacuum and solution of KOH (0.25 mmol, 5 mol%) in 2-propanol
(2.5 mL) was added. Mesitylene (0.1 mmol) was added to the so-
lution as internal standard. The solution was heated to 82 ꢁC for
5 min. Subsequently, cyclohexanone (0.5 mmol) was added. After
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the desired reaction time an aliquot (10 mL) of the mixture was
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taken and quenched with 2 mL of dichloromethane. The resulting
solution was filtered to remove insoluble inorganic material and
the reaction progress was monitored by GC. The results for each
experiment are averages over two runs.
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X-ray diffraction studies
X-ray diffraction studies were carried out on a Bruker SMART
APEX2 CCD diffractometer at room temperature, Mo-Ka radiation.
The crystal structure was solved by direct methods and following
Fourier synthesis using SHELXS-97 [17]. The structure was refined
by full-matrix least squares procedures using an anisotropic
approximation for all non-hydrogen atoms with the SHELXL-97
program [18]. Hydrogen atoms were put in idealized positions
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Crystallographic data for 4a: C32H40ClN2ORh, M ¼ 605.00,
monoclinic, space group P21/c, a ¼ꢁ 15.720(1), b ¼ 9.7813(9) and
3
ꢀ
ꢀ
c ¼ 19.672(2) A,
b
¼ 103.050(1) , V ¼ 2946.6(5) A , Z ¼ 4,
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l
¼ 0.7107 A, dcalc ¼ 1.36 g cmꢀ3
,
m
¼ 0.697 mmꢀ1. The number of
ꢀ
measured reflections, 34,320; the number of independent re-
flections, 8905; the number of refined parameters, 334; R-factor
0.039 for 7877 reflections with [F0 > 4s(F0)].
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Crystallographic data for 5a:
C
38H50ClN2Rh,
M
¼
673.16,
monoclinic, space group P21/c, a ¼ 10.7829(6), b ¼ 15.6629(9) and
3
ꢀ
ꢁ
ꢀ
c ¼ 20.467(1) A,
b
¼ 104.103(1) , V ¼ 3352.6(3) A , Z ¼ 4,
ꢀ
l
¼ 0.7107 A, dcalc ¼ 1.33 g cmꢀ3
,
m
¼ 0.617 mme1. The number of
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30
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