α-Alkylation of arylacetonitriles with primary alcohols catalyzed by backbone modified N-heterocyclic carbene iridium(i) complexes

Article abstract of DOI:10.1039/d0dt04082g

A series of backbone-modified N-heterocyclic carbene (NHC) complexes of iridium(i) (1d-f) have been synthesized and characterized. The electronic properties of the NHC ligands have been assessed by comparison of the IR carbonyl stretching frequencies of thein situprepared [IrCl(CO)₂(NHC)] complexes in CH₂Cl₂. These new complexes (1d-f), together with previously prepared1a-c, were applied as catalysts for the α-alkylation of arylacetonitriles with an equimolar amount of primary alcohols or 2-aminobenzyl alcohol. The catalytic activities of these complexes could be controlled by modifying the N-substituents and backbone of the NHC ligands. The NHC-Ir^Icomplex1fbearing 4-methoxybenzyl substituents on the N-atoms and 4-methoxyphenyl groups at the 4,5-positions of imidazole exhibited the highest catalytic activity in the α-alkylation of arylacetonitriles with primary alcohols. Various α-alkylated nitriles and aminoquinolines were obtained in high yields through a borrowing hydrogen pathway by using 0.1 mol%1fand a catalytic amount of KOH (5 mol%) under an air atmosphere within significantly short reaction times.

Full text of DOI:10.1039/d0dt04082g

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α-Alkylation of arylacetonitriles with primary
alcohols catalyzed by backbone modified
N-heterocyclic carbene iridium(I) complexes†
Cite this: Dalton Trans., 2021, 50,
1788
Burcu Arslan and Süleyman Gülcemal
*
A series of backbone-modified N-heterocyclic carbene (NHC) complexes of iridium(I) (1d–f) have been
synthesized and characterized. The electronic properties of the NHC ligands have been assessed by com-
parison of the IR carbonyl stretching frequencies of the in situ prepared [IrCl(CO)2(NHC)] complexes in
CH2Cl2. These new complexes (1d–f), together with previously prepared 1a–c, were applied as catalysts
for the α-alkylation of arylacetonitriles with an equimolar amount of primary alcohols or 2-aminobenzyl
alcohol. The catalytic activities of these complexes could be controlled by modifying the N-substituents
and backbone of the NHC ligands. The NHC–IrI complex 1f bearing 4-methoxybenzyl substituents on the
N-atoms and 4-methoxyphenyl groups at the 4,5-positions of imidazole exhibited the highest catalytic
activity in the α-alkylation of arylacetonitriles with primary alcohols. Various α-alkylated nitriles and ami-
noquinolines were obtained in high yields through a borrowing hydrogen pathway by using 0.1 mol% 1f
and a catalytic amount of KOH (5 mol%) under an air atmosphere within significantly short reaction times.
Received 29th November 2020,
Accepted 30th December 2020
DOI: 10.1039/d0dt04082g
rsc.li/dalton
times, or an excess amount of alkylating alcohols for the selec-
tive formation of the desired alkylnitrile product over the
Introduction
The transition-metal (TM) catalyzed borrowing hydrogen (BH) undesired olefinic nitrile intermediate. Homogeneous TM
strategy, also called hydrogen autotransfer, has become an complexes, including Ru,8 Os,9 Ir,10 Rh,11 Mn,12 Fe,13 and Ni,14
important alternative for alkylation reactions in which in- have also been developed for this transformation; however,
expensive and environmentally friendly alcohols are used as most of these catalysts suffer from high catalyst loadings, the
alkylating agents.1 This highly valuable process has emerged necessity of using an excess amount of alkylating alcohols, or
as a powerful approach to construct C–C and C–N bonds for inert reaction conditions. There exist only two reports wherein
the one-step synthesis of highly complicated molecules includ- equimolar amounts of arylacetonitrile and alkylating alcohol
ing α-alkylated ketones,1c–g β-alkylated alcohols,1d–g,2 were used for this transformation.9,11 In the first report, Yus
α-alkylated nitriles,1c,d,e,g quinolines,1d,e,3 and amines.1e–g et al. discussed the alkylation of arylacetonitriles with primary
Among these valuable molecules, α-alkylated nitriles are versa- alcohols catalyzed by an N-heterocyclic carbene (NHC)–
tile building blocks in organic synthesis because they can osmium(II) complex (1.0 mol%, giving TONs up to 98), which
easily be converted to carboxylic acids, ketones, amines, required the removal of the in situ formed water molecule
amides, and various biologically active compounds.4 In the tra- during the reaction.9 In the second report, Wang and co-
ditional synthesis of α-alkylated nitriles, toxic alkyl halides are workers discussed the α-alkylation or olefination of nitriles
employed as alkylating reagents with a stoichiometric or with primary alcohols by using 0.5 equivalent of NaOH and a
excess amount of a strong base. Alternatively, the α-alkylation 0.5 mol% rhodium complex at 110 °C and the total TON for
of nitriles with alcohols as green alkylating reagents through a the α-alkylation reaction was reported to be up to 198.11
BH strategy was first explored by Grigg et al.5 Subsequently, Recently, the Kundu group reported the first example of the
heterogeneous Ru6 or Pd7 catalysts were employed for the TM-free base-catalyzed α-alkylation of nitriles by using primary
α-alkylation of nitriles with alcohols; however, these systems alcohols; however, the main limitation of this system is that it
require very high temperatures (180 °C), prolonged reaction requires 0.8 equivalent of KOtBu as the base and an excess of
alkylating alcohol (3.0 equivalents).15
However, the electronic and steric properties of the NHC
Department of Chemistry, Ege University, 35100 Bornova, Izmir, Turkey.
ligand are important for homogeneous TM catalysis. For classi-
E-mail: suleyman.gulcemal@ege.edu.tr
†Electronic supplementary information (ESI) available: Traces of 1H, 13C NMR,
cal NHCs, N-substituents and backbone modifications primar-
ily change their electronic and steric properties.16 NHC–Ir
and HRMS spectra (PDF). See DOI: 10.1039/d0dt04082g
1788 | Dalton Trans., 2021, 50, 1788–1796
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complexes have been utilized in various catalytic reactions understand the electronic effects of the NHC ligands, which
including transfer hydrogenation, (de)hydrogenation, and BH are important for homogeneous catalysis.23 Thus, the corres-
reactions.16c,17 Our group recently demonstrated that the ponding [IrCl(CO)2(NHCa–f)] complexes were prepared in situ
N-substituents and backbone modifications on the NHC by passing carbon monoxide gas through a dichloromethane
ligand play a critical role in the catalytic activity of the related solution (0.01 M) of complexes 1a–f at room temperature for
NHC–Ir complexes in the transfer hydrogenation of carbo- 1 h to compare the electronic properties of the NHC ligands
nyls18 and acceptorless dehydrogenation of alcohols.19 with one another. However, these [IrCl(CO)2(NHCa–f)] species
Inspired by these studies, we subsequently prepared a set of were not isolated. Subsequently, these solutions were analyzed
[IrCl(cod)(NHC)] (cod = 1,5-cyclooctadiene) complexes and by IR spectroscopy. The IR spectra showed two strong νCO
reported their superior catalytic activities for the alkylation of bands for each complex. The average carbonyl stretching fre-
av
secondary alcohols or ketones with primary alcohols to give quencies ν in the IR spectra were then used to calculate the
CO
α-alkylated ketones,20a β-alkylated alcohols,20b quinoline deri- Tolman electronic parameters (TEP)24 by using the linear
vatives,20b α,α-disubstituted ketones,20c and β,β-disubstituted regression equation described by Crabtree23a and Nolan23b
alcohols.20c Encouraged by these results, we herein describe (see Table 1). The results revealed that both the benzylic
the synthesis of
a set of [IrCl(cod)(NHC)] complexes wingtip substituents on the N-atoms and backbone modifi-
(Scheme 1) with different NHC skeletons and explore the cata- cations played important roles in the electron-donating pro-
lytic activities of these complexes in the α-alkylation of nitriles perties of the NHC ligands. NHCf bearing 4-methoxybenzyl
with primary alcohols.
groups at the 1,3-positions and 4-methoxyphenyl groups at the
4,5-positions appeared as the most strongly electron-donating
ligand assessed in this study.
To probe the potential of NHC–IrI catalysts 1a–f for the
α-alkylation of arylacetonitriles with primary alcohols, benzyl
cyanide (2a) and benzyl alcohol (3a) were selected as model
Results and discussion
Scheme 1 shows the route to the synthesis of NHC–IrI com-
1
19
21
substrates (see Table 2). The yields are based on the H NMR
plexes (1a–f). The NHC precursors La–d and Le,f and com-
plexes 1a–c20a were synthesized according to the published
procedures. The new complexes 1d–f were obtained in 71–83%
yields as air- and moisture-stable yellow solids by a two-step
process that involved transmetalation from the in situ formed
NHC–Ag species.22 The formation of 1d–f was confirmed by
NMR spectroscopy, HRMS, and elemental analysis. Complexes
1d–f exhibited characteristic Ir–Ccarbene signals at δ = 192.4,
180.9, and 180.3 ppm, respectively. Meanwhile, the character-
istic downfield signals for the NCHN+ protons of NHC precur-
sors Ld–f disappeared from the 1H NMR spectrum.
analysis of the crude reaction mixtures by using 1,3,5-tri-
methoxybenzene as an internal standard. In the presence of
1a–f as the catalyst (0.1 mol%), respectively, and KOH
(10 mol%), the reaction was performed in toluene (1 mL) at
135 °C (oil-bath temperature) open to the air for 1 h (entries
1–6). In the presence of complexes 1a–e, poor to moderate con-
versions were observed; additionally, 30–77% yield of the
desired product 4a and 5–14% yield of the unsaturated olefin
intermediate 4′a along with unreacted starting materials were
obtained (entries 1–5). To our delight, NHC–IrI complex 1f
with a strongly electron donating NHC ligand demonstrated
the highest catalytic activity to give 4a in 93% NMR yield as
the sole product where the unsaturated olefin intermediate 4′a
could not be detected (entry 6). Considering complexes 1a–f
bearing NHC ligands, the significant differences in the cata-
lytic ability among these iridium complexes could be attribu-
ted to the different electron densities at the iridium centers.16a
Measuring the carbonyl stretching frequencies of the [IrCl
(CO)2(NHC)] complexes by infrared spectroscopy allows us to
Table 1 νCO, νaCvO, and TEP values for [IrCl(CO)2(NHCa–f)] complexes
derived from 1a–fa
νCO (cm−1
)
ν
(cm−1
)
TEPb (cm−1
)
TEPc (cm−1
)
av
NHC
CO
NHCa
NHCb
NHCc
NHCd
NHCe
NHCf
1985.4; 2068.9
1987.7; 2071.4
1984.6; 2068.1
1988.7; 2071.6
1984.2; 2067.3
1983.5; 2066.5
2027.2
2029.6
2026.4
2030.2
2025.8
2025.0
2056.6
2058.4
2056.1
2058.8
2055.6
2055.1
2053.0
2055.1
2052.4
2055.6
2051.9
2051.2
a The IR spectra of the in situ prepared [IrCl(CO)2(NHCa–f)] complexes
were recorded in a CH2Cl2 solution as the film using NaCl plates.
Scheme 1 Synthesis route to the NHC–IrI complexes used in this
study.
b
c
+ 593 cm−1
.
av
Calculated using Crabtree’s equation: 0.722 × ν
CO
Calculated using Nolan’s equation: 0.847 × ν + 336 cm−1
.
av
CO
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Table 2 Optimization of the reaction conditionsa
Base
(mol%)
Time Yield 4ab Yield 4′ab
Entry Cat.
(h)
(%)
(%)
1
2
3
4
5
6
7
1a
1b
1c
1d
1e
1f
1f
1f
1f
1f
1f
1f
1f
—
KOH (10)
KOH (10)
KOH (10)
KOH (10)
KOH (10)
KOH (10)
KOH (5)
KOH (5)
KOH (5)
KOtBu (5)
NaOH (5)
NaOtBu (5)
—
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
38
29
56
53
77
93
95
94
91
87
78
65
—
—
26
6
4
8
9
5
—
—
—
—
4
20
17
—
—
3
8c
9d
10
11
12
13
14
15
KOH (5)
[IrCl(cod)(IMe)] KOH (5)
a Reaction conditions: 2a (1.0 mmol), 3a (1.0 mmol), 1a–f (0.1 mol%),
base (5–10 mol%), toluene (1.0 mL), 135 °C (oil bath temperature),
open to the air. b Yields were determined by the 1H NMR analysis of
the crude reaction mixture using 1,3,5-trimethoxybenzene as an
internal standard. c A drop of mercury was added to the reaction
mixture. d The reaction was performed under an argon atmosphere.
Pleasingly, decreasing the KOH loading to 5 mol% resulted in
95% NMR yield with complete chemoselectivity in 2 h (entry
7), and 4a was isolated in 90% yield. A similar yield was
observed upon adding a drop of mercury to the reaction
mixture, indicating the homogeneous nature of the catalytic
system (entry 8). Noteworthily, an inert atmosphere seemed to
be unnecessary (entry 9). The use of other strong bases includ-
ing KOtBu, NaOH, and NaOtBu resulted in a decrease in the
yield and selectivity (entries 10–12). Control experiments
showed no activity in the absence of KOH or complex 1f
(entries 13 and 14). In addition, the catalytic performance of
the [IrCl(cod)(IMe)] complex was evaluated in the present reac-
Scheme 2 Scope of the α-alkylation of arylacetonitriles with primary
alcohols catalyzed by complex 1f. Reaction conditions: arylacetonitrile
(1.0 mmol), primary alcohol (1.0 mmol), 1f (0.1 mol%), KOH (5 mol%),
toluene (1.0 mL), 135 °C (oil bath temperature), open to the air. Isolated
yields. aThe reaction was performed on a 0.5 mmol scale. bDetermined
by 1H NMR analysis.
tion and only 26% yield of the desired product was observed position of the phenyl ring gave the corresponding products
(entry 15). Considering the TEP value of the [IrCl(CO)2(IMe)] 4g–4l in 60–91% isolated yields. Furthermore, the reaction of
complex (2051 cm−1, Nolan’s equation),25 which is very close benzyl cyanide with ferrocenemethanol derivatives afforded
to that of [IrCl(CO)2(NHCf)], the significant differences in the the desired products 4m and 4n in 89% and 86% isolated
catalytic abilities (entry 15 compared to entry 7) among these yields, respectively. In the case of heterocycles containing
iridium complexes could be related to the different wingtip primary alcohols 2-pyridinemethanol and 2-thiophenemetha-
and backbone substituents on the NHC ligands.
nol, long reaction time (16) was required for obtaining high
Under the optimized conditions (Table 2, entry 7) in hand, yields, and the corresponding alcohols 4o and 4p were isolated
we next explored the scope of the reaction (Scheme 2). in 76% and 92% yields, respectively. However, applications of
Pleasingly, all the reactions resulted in the selective formation long-chain alcohols such as 1-heptanol and 1-octanol and
of the desired α-alkylated nitrile products 4a–p. The reaction ortho-substituted benzyl alcohols were not successful in con-
of substituted arylacetonitriles bearing 4-Me, 4-OMe, 4-Cl, version to the desired product, and we observed only a trace
4-Br, and 2-Cl substituents with benzyl alcohols gave the amount of conversions to the desired products under the stan-
desired products 4b–4f in 52–96% isolated yields. We also dard conditions.
explored the reactions with respect to primary alcohols. For
Thereafter, the α-alkylation of electronically different aryl
instance, the reactions with various benzyl alcohols bearing acetonitriles (2a–e) with 2-aminobenzyl alcohol (5) to give
substituents with different electronic properties at the para- 2-aminoquinolines8c,26 was investigated to extends the poten-
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Scheme 3 Synthesis of 2-aminoquinolines catalyzed by complex 1f
(isolated yields).
tial of complex 1f (Scheme 3). The reaction of equimolar
amounts of arylacetonitriles (2a–e), respectively, with 2-amino-
benzyl alcohol (5) in the presence of complex 1f (0.1 mol%)
and KOH (5 mol%) at 135 °C in toluene for 4–8 h gave moder-
ate to high isolated yields (65%–84%) of the desired 2-amino-
quinoline derivatives 6a–e.
Then, we monitored the progress of the model reaction of
benzyl cyanide (2a) and benzyl alcohol (3a) as a function of
time under the reaction conditions as in Table 2, entry 7 by
performing individual experiments over different reaction
times (Fig. 1). 1H NMR monitoring of the reaction progress
confirmed the complete conversion of the starting materials in
120 min. The formation of the desired product 4a and the
unsaturated intermediate 4′a was also observed. After 1 h, 4a
was formed with 79% yield, accompanied by 8% of unsatu-
rated intermediate 4′a. During this time, the amount of unsa-
turated intermediate 4′a was almost constant (ca. 10%).
Further completion of the reaction by the consumption of
benzyl cyanide and benzyl alcohol occurred at a slow rate over
a 2 h period. From these observations, it can be suggested that
the dehydrogenation of benzyl alcohol is most likely the rate-
limiting step.
Scheme 4 Control experiments.
effect of the catalyst on the formation of olefinic nitrile inter-
mediate 4′b by the aldol condensation of 4-methoxybenzyl
nitrile (2b) with benzaldehyde (7) (Scheme 4, eqn (1)). The
reaction with both the most active catalyst 1f and the least
active catalyst 1b resulted in a complete conversion, whereas
the reaction without any catalyst was inefficient (7% yield in
comparison with >99% yield with 1b or 1f). This indicates that
the NHC–Ir complex was involved in this step of the reaction.
The reduction of olefinic nitrile intermediate 4′b to 4b using
benzyl alcohol as
a hydrogen source was also studied
(Scheme 4, eqn (2)). However, the conversion to 4b varies with
the nature of the catalyst. Thus, 4b was obtained in 36% yield
with 0.1 mol% of 1f in 15 min, whereas 4b was obtained in
17% yield in the presence of 0.1 mol% of 1b under the same
conditions. The electronic nature of the NHC ligand in the
corresponding NHC–Ir complex seems to be highly important
in the transfer hydrogenation of the olefinic nitrile intermedi-
ate. Increasing the reaction time to 30 min in the presence of
1f resulted in >95% conversion to 4b. Without an NHC–Ir cata-
lyst, 4′b could also be reduced by benzyl alcohol to give 4b only
in 14% conversion under the conditions employed. Upon
replacing benzyl alcohol with 1-phenylethanol (8), 4′b was
reduced to 4b in 38% yield in the presence of 0.1 mol% 1f
within 15 min (Scheme 4, eqn (3)). Notably, the reaction of
benzyl cyanide (2a) and benzyl alcohol (3a) was carried out in
a sealed reaction tube for 15 min, resulting in the formation of
4a (45%) together with unsaturated olefin intermediate 4′a
(16%) and the presence of free hydrogen in the gas phase of
the reaction was detected by GC analysis (Fig. S30, see the
ESI†) (Scheme 4, eqn (4)).
Several control experiments were performed to elucidate
the reaction mechanism (Scheme 4). First, we investigated the
Fig. 1 Monitoring of the reaction progress. Reaction conditions: 2a
(1 mmol), 3a (1 mmol), 1f (0.1 mol%), KOH (5 mol%), toluene (1 mL),
135 °C (oil bath temperature), open to the air. % Mol values were deter-
mined by 1H NMR analyses of the independent reaction mixtures using
1,3,5-trimethoxybenzene as the internal standard.
On the basis of relevant studies involving similar catalysts
in our earlier work20 and experimental evidence obtained in
this study, a plausible mechanism for this transformation can
be proposed as shown in Scheme 5. The mechanism involves
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was filtered through Celite®. The remaining solid was washed
with CH2Cl2 (2 × 5 mL), and the solvent of the filtrate was evap-
orated. The residue was purified by silica gel column chrom-
atography using a CH2Cl2 and hexane (9 : 1) mixture as an
eluent to give a pure complex as a yellow solid. Complexes 1d–f
are new compounds and their spectroscopic data are given in
the following text.
Complex 1d. Yield: 74%, 257 mg. 1H NMR (400 MHz, CDCl3,
TMS, 25 °C, ppm): δ = 7.37 (d, J = 7.6 Hz, 4H), 6.98–7.03 (m,
4H), 6.88 (d, J = 8.8 Hz, 4H), 6.18 (d, J = 15.2 Hz, 2H), 5.89 (d,
J = 15.6 Hz, 2H), 4.77 (t, J = 3.0 Hz, 2H), 3.78 (s, 6H), 2.96 (t, J =
2.8 Hz, 2H), 2.27–2.05 (m, 4H), 1.81–1.73 (m, 2H), 1.62–1.57
(m, 2H). 13C {1H} NMR (100.6 MHz, CDCl3, TMS, 25 °C, ppm):
δ = 192.4, 159.2, 135.0, 128.6, 127.9, 122.5, 114.2, 111.2, 87.1,
55.3, 52.9, 52.2, 33.5, 29.3. Anal. Calcd for C31H34ClIrN2O2: C,
53.63; H, 4.94; N, 4.03. Found: C, 53.72; H, 4.88; N, 3.96.
HRMS (ESI) m/z: [M − Cl]+ Calcd for C31H34IrN2O2 659.2250;
Found: 659.2291.
Scheme 5 Plausible reaction mechanism.
the decoordination of Cl in the presence of KOH to generate
an [Ir(COD)(NHC)]+ intermediate. Thereafter, the dehydrogena-
tion of primary alcohol (3) to the corresponding aldehyde (7)
generates transient iridium hydride.20a Next, an NHC–Ir-cata-
lyzed condensation of 2 and 7 gives the olefinic nitrile inter-
mediate 4′. Finally, 4′ is reduced to afford 4 using iridium
hydride.
Complex 1e. Yield: 71%, 283 mg. 1H NMR (400 MHz, CDCl3,
TMS, 25 °C, ppm): δ = 7.18–7.08 (m, 6H), 6.97 (d, J = 8.8 Hz,
4H), 6.92 (d, J = 8.8 Hz, 4H), 6.66 (d, J = 8.8 Hz, 4H), 5.99 (d, J =
14.8 Hz, 2H), 5.53 (d, J = 14.8 Hz, 2H), 4.66 (t, J = 2.8 Hz, 2H),
3.72 (s, 6H), 2.95 (t, J = 2.8 Hz, 2H), 2.22–2.00 (m, 4H),
1.73–1.65 (m, 2H), 1.54–1.49 (m, 2H). 13C {1H} NMR
(100.6 MHz, CDCl3, TMS, 25 °C, ppm): δ = 180.9, 158.7, 132.1,
130.5, 129.1, 129.0, 128.7, 128.3, 128.1, 113.5, 84.5, 55.2, 52.7,
52.1, 33.5, 29.4. Anal. Calcd for C39H40ClIrN2O2: C, 58.82; H,
5.06; N, 3.52. Found: C, 58.75; H, 5.02; N, 3.57. HRMS (ESI)
m/z: [M − Cl]+ Calcd for C39H40IrN2O2 761.2719; Found:
761.2735.
Experimental
General considerations
Experiments that involved air- or moisture-sensitive reagents
were performed under an atmosphere of dry argon by using
standard Schlenk techniques. Unless otherwise specified, all
the reagents and solvents were commercially obtained and
1
Complex 1f. Yield: 83%, 355 mg. H NMR (400 MHz, CDCl3,
19
used without further purification. Imidazolium salts La–d
TMS, 25 °C, ppm): δ = 7.00 (d, J = 8.4 Hz, 4H), 6.82 (d, J = 8.0
Hz, 4H), 6.69 (d, J = 8.0 Hz, 4H), 6.63 (d, J = 8.0 Hz, 4H), 5.92
(d, J = 15.2 Hz, 2H), 5.50 (d, J = 14.8 Hz, 2H), 4.64 (t, J = 3.2 Hz,
2H), 3.73 (s, 6H), 3.71 (s, 6H), 2.91 (t, J = 3.0 Hz, 2H), 2.16–2.02
(m, 4H), 1.70–1.63 (m, 2H), 1.53–1.46 (m, 2H). 13C {1H} NMR
(100.6 MHz, CDCl3, TMS, 25 °C, ppm): δ = 180.3, 159.4, 158.6,
131.8, 131.8, 129.4, 128.9, 121.0, 113.6, 113.5, 84.2, 55.2, 55.1,
52.6, 52.0, 33.5, 29.3. Anal. Calcd for C41H44ClIrN2O4: C, 57.50;
H, 5.18; N, 3.27. Found: C, 57.39; H, 5.25; N, 3.30. HRMS (ESI)
m/z: [M − Cl]+ Calcd for C41H44IrN2O4 821.2930; Found:
821.2967.
21
and Ld,f and complexes 1a–c20a were synthesized according
to the published procedures, and the physical properties and
spectroscopic data of the obtained compounds were in accord-
ance with previous reports. The NMR spectra were recorded on
a Varian AS 400 Mercury NMR spectrometer and reported in
the unit of parts per million (ppm) relative to CDCl3 (δ =
1
7.26 ppm for H and δ = 77.0 ppm for 13C NMR). The elemen-
tal analyses were performed using a PerkinElmer PE 2400
elemental analyzer. FTIR spectra were recorded using a
PerkinElmer Spectrum 100 series system. HRMS was per-
formed using an Agilent 6530 Accurate-Mass Q-TOF mass
spectrometer at the East Anatolia High Technology Application
and Research Center, Atatürk University. GC analysis for the
H2 evolution experiment was performed using an Agilent
7890A GC instrument, and gas products were identified
according to the standard gas mixture (Agilent P/N 5190-0519).
General procedure for the α-alkylation of arylacetonitriles with
primary alcohols
To a 20 mL reaction tube (1 cm × 20 cm) with a condenser,
were added KOH (2.8 mg, 0.05 mmol, 5 mol%), arylacetonitrile
(1.0 mmol), primary alcohol (1.0 mmol), and a solution of
complex 1f (0.001 mmol, 0.1 mol%) in toluene (1.0 mL) under
Synthesis of the NHC–IrI complexes used in this study
A mixture of La–f (0.5 mmol) and Ag2O (60 mg, 0.26 mmol) was open air conditions. The reaction mixture was then vigorously
suspended in CH2Cl2 (10 mL) under an argon atmosphere and stirred (1200 rpm) in a preheated oil bath at 135 °C for 2–16 h.
stirred at ambient temperature for 1 h shielded from light. Thereafter, the reaction mixture was cooled down to ambient
[IrCl(COD)]2 (168 mg, 0.25 mmol) was then added to the sus- temperature, and CH2Cl2 (5.0 mL) was added to the reaction
pension, and the reaction mixture was stirred at ambient mixture. After filtration, the filtrate was concentrated under
temperature for an additional 12 h. The resulting suspension reduced pressure. The crude product was purified by silica gel
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column chromatography using a hexane and ethyl acetate (100.6 MHz, CDCl3, TMS, 25 °C, ppm): δ = 134.7, 134.5, 133.3,
(9 : 1) mixture as an eluent to afford the desired product.
130.6, 129.0, 128.7, 128.3, 127.4, 120.0, 41.3, 39.5.
2,3-Diphenylpropanenitrile (4a).8c,d,12b,14 White solid. Yield:
3-(4-Bromophenyl)-2-phenylpropanenitrile (4j).8d,15 White
1
187 mg, 90%. H NMR (400 MHz, CDCl3, TMS, 25 °C, ppm): δ solid. Yield: 238 mg, 83%. 1H NMR (400 MHz, CDCl3,
= 7.40–7.26 (m, 8H), 7.16 (d, J = 7.6 Hz, 2H), 4.02 (t, J = 7.2 Hz, TMS, 25 °C, ppm): δ = 7.42–7.22 (m, 7H), 6.98 (dd, J1 = 5.6
1H), 3.24–3.12 (m, 2H). 13C {1H} NMR (100.6 MHz, CDCl3, Hz, J2 = 1.6 Hz, 2H), 3.99 (t, J = 7.2 Hz, 1H), 3.18–3.07 (m, 2H).
TMS, 25 °C, ppm): δ = 136.2, 135.2, 129.1, 128.9, 128.5, 128.1, 13C {1H} NMR (100.6 MHz, CDCl3, TMS, 25 °C, ppm): δ =
127.4, 127.3, 120.3, 42.1, 39.7.
135.0, 134.7, 131.7, 130.9, 129.0, 128.3, 127.4, 121.4, 120.0,
2-(4-Methoxyphenyl)-3-phenylpropanenitrile
(4b).8c,d,15 41.4, 39.4.
White solid. Yield: 228 mg, 96%. 1H NMR (400 MHz, CDCl3,
2-Phenyl-3-(4-(trifluoromethyl)phenyl)propanenitrile (4k).8d,14
TMS, 25 °C, ppm): δ = 7.33–7.14 (m, 7H), 6.90–6.87 (m, 2H), White solid. Yield: 165 mg, 60%. 1H NMR (400 MHz, CDCl3,
3.96 (t, J = 7.2 Hz, 1H), 3.81 (s, 3H), 3.21–3.08 (m, 2H). 13C {1H} TMS, 25 °C, ppm): δ = 7.56 (d, J = 8.0 Hz, 2H), 7.40–7.24 (m,
NMR (100.6 MHz, CDCl3, TMS, 25 °C, ppm): δ = 159.3, 136.3, 2H), 4.05 (t, J = 7.4 Hz, 1H), 3.28–3.18 (m, 2H). 13C {1H} NMR
129.2, 128.5, 128.5, 127.2, 127.1, 120.6, 114.3, 55.2, 42.2, 38.9.
(100.6 MHz, CDCl3, TMS, 25 °C, ppm): δ = 140.1, 134.5, 129.9,
3-Phenyl-2-(p-tolyl)propanenitrile (4c).8c,d,14,15 Yellow solid. 129.6, 129.1, 128.4, 127.4, 125.5, 125.5, 125.4, 125.4, 122.7,
Yield: 201 mg, 91%. 1H NMR (400 MHz, CDCl3, TMS, 25 °C, 119.8, 41.7, 39.3. 19F NMR (376 MHz, CDCl3, TMS, 25 °C,
ppm): δ = 7.35–7.16 (m, 9H), 3.98 (t, J = 7.4 Hz, 1H), 3.22–3.10 ppm): δ = −62.6.
(m, 2H), 2.37 (s, 3H). 13C {1H} NMR (100.6 MHz, CDCl3, TMS,
25 °C, ppm): δ = 137.9, 136.4, 132.2, 129.6, 129.1, 128.5, 127.3, Yellow solid. Yield: 208 mg, 83%. H NMR (400 MHz, CDCl3,
3-(4-(Dimethylamino)phenyl)-2-phenylpropanenitrile (4l).27
1
127.2, 120.5, 42.1, 39.3, 21.0.
TMS, 25 °C, ppm): δ = 7.40–7.26 (m, 5H), 7.03 (dd, J1 = 6.8 Hz,
2-(4-Chlorophenyl)-3-phenylpropanenitrile (4d).8d,14 White J2 = 2.0 Hz, 2H), 6.68 (dd, J1 = 6.8 Hz, J2 = 2.0 Hz, 2H), 3.95 (dd,
solid. Yield: 225 mg, 93%. 1H NMR (400 MHz, CDCl3, TMS, J1 = 8.4 Hz, J2 = 6.4 Hz, 1H), 3.15–3.03 (m, 2H), 2.94 (s, 6H). 13
C
25 °C, ppm): δ = 7.34–7.26 (m, 5H), 7.19–7.10 (m, 4H), 3.99 (t, {1H} NMR (100.6 MHz, CDCl3, TMS, 25 °C, ppm): δ = 149.8,
J = 7.2 Hz, 1H), 3.22–3.09 (m, 2H). 13C {1H} NMR (100.6 MHz, 135.6, 129.8, 128.9, 127.9, 127.5, 124.0, 120.7, 112.6, 41.4, 40.5,
CDCl3, TMS, 25 °C, ppm): δ = 135.7, 134.2, 133.6, 129.2, 129.1, 40.2.
128.8, 128.5, 127.5, 119.9, 41.9, 39.0.
2-Phenyl-3-(ferrocene-1-yl)propanenitrile (4m). Yellow solid.
2-(4-Bromophenyl)-3-phenylpropanenitrile (4e).8c,14,15 White Yield: 281 mg, 89%. 1H NMR (400 MHz, CDCl3, TMS, 25 °C,
solid. Yield: 149 mg, 52%. 1H NMR (400 MHz, CDCl3, TMS, ppm): δ = 7.38–7.23 (m, 5H), 4.11 (s, 8H), 4.04–4.03 (m, 1H),
25 °C, ppm): δ = 7.48 (d, J = 8.4 Hz, 2H), 7.33–7.11 (m, 7H), 3.82 (dd, J1 = 8.0 Hz, J2 = 6.0 Hz, 1H), 3.04–2.89 (m, 2H). 13C
3.98 (t, J = 7.2 Hz, 1H), 3.21–3.08 (m, 2H). 13C {1H} NMR {1H} NMR (100.6 MHz, CDCl3, TMS, 25 °C, ppm): δ = 135.5,
(100.6 MHz, CDCl3, TMS, 25 °C, ppm): δ = 135.7, 134.1, 132.0, 128.8, 128.0, 127.3, 120.7, 82.7, 69.2, 68.9, 68.6, 68.0, 68.0,
129.1, 128.6, 127.4, 122.2, 119.8, 41.8, 39.1.
39.9, 37.2. HRMS (ESI) m/z: [M]+ Calcd for C19H17FeN
2-(2-Chlorophenyl)-3-phenylpropanenitrile (4f).15 Yellow 315.0710; Found: 315.0711.
solid. Yield: 198 mg, 82%. 1H NMR (400 MHz, CDCl3, TMS,
2-Phenyl-3-([1′-(diphenylphosphorothioyl)]ferrocene-1-yl)pro-
25 °C, ppm): δ = 7.53–7.24 (m, 9H), 4.54 (q, J = 4.6 Hz, 1H), panenitrile (4n). Dark yellow solid. Yield: 228 mg, 86%. 1H
3.26–3.06 (m, 2H). 13C {1H} NMR (100.6 MHz, CDCl3, TMS, NMR (400 MHz, CDCl3, TMS, 25 °C, ppm): δ = 7.74–7.66 (m,
25 °C, ppm): δ = 136.0, 132.9, 132.5, 129.9, 129.6, 129.1, 129.1, 4H), 7.44–7.19 (m, 11H), 4.47–4.43 (m, 2H), 4.36–4.33 (m, 2H),
128.6, 127.5, 127.4, 119.6, 40.0, 37.2.
4.16–4.15 (m, 2H), 4.03–4.00 (m, 2H), 3.79 (t, J = 7.0 Hz, 1H),
3-(4-Methoxyphenyl)-2-phenylpropanenitrile (4g).14,15 White 2.73 (d, J = 7.2 Hz, 2H). 13C {1H} NMR (100.6 MHz, CDCl3,
solid. Yield: 216 mg, 91%. 1H NMR (400 MHz, CDCl3, TMS, TMS, 25 °C, ppm): δ = 135.2, 134.9, 134.8, 133.9, 131.6, 131.5,
25 °C, ppm): δ = 7.43–7.26 (m, 7H), 7.03–6.94 (m, 2H), 4.48 (t, 128.8, 128.2, 128.1, 128.0, 127.4, 120.5, 84.4, 75.9, 75.0, 71.4,
J = 7.0 Hz, 1H), 3.87 (s, 3H), 3.22–3.14 (m, 2H). 13C {1H} NMR 71.2, 69.8, 39.5, 36.1. HRMS (ESI) m/z: [M + H]+ Calcd for
(100.6 MHz, CDCl3, TMS, 25 °C, ppm): δ = 155.8, 136.9, 129.3, C31H27FeNPS 532.0951; Found: 532.0961.
128.9, 128.2, 128.2, 126.9, 123.4, 120.6, 120.4, 110.6, 55.3, 39.7,
33.9.
2-Phenyl-3-(pyridin-2-yl)propanenitrile (4o).12b,14 Yellow
liquid. Yield: 158 mg, 76%. H NMR (400 MHz, CDCl3, TMS,
1
2-Phenyl-3-(p-tolyl)propanenitrile (4h).8c,12b,14,15 Yellow 25 °C, ppm): δ = 8.60 (d, J = 4,8 Hz, 1H), 7.62–7.38 (m, 1H),
solid. Yield: 195 mg, 88%. 1H NMR (400 MHz, CDCl3, TMS, 7.36–7.26 (m, 5H), 7.18 (dd, J1 = 7.6 Hz, J2 = 4.8 Hz, 1H), 7.11
25 °C, ppm): δ = 7.42–7.30 (m, 5H), 7.15 (d, J = 8.0 Hz, 2H), (d, J = 7.6 Hz, 1H), 4.48 (dd, J1 = 9.2 Hz, J2 = 6.4 Hz, 1H),
7.08 (d, J = 8.0 Hz, 2H), 4.01 (t, J = 7.4 Hz, 1H), 3.18–3.14 (m, 3.39–3.25 (m, 2H). 13C {1H} NMR (100.6 MHz, CDCl3, TMS,
2H), 2.37 (s, 3H). 13C {1H} NMR (100.6 MHz, CDCl3, TMS, 25 °C, ppm): δ = 156.0, 149.6, 136.6, 135.4, 129.0, 128.0, 127.3,
25 °C, ppm): δ = 136.8, 135.2, 133.1, 129.1, 128.9, 128.8, 128.0, 123.8, 122.2, 120.5, 44.0, 37.1.
127.3, 120.3, 41.6, 39.7, 20.9.
2-Phenyl-3-(thiophen-2-yl)propanenitrile (4p).12b,15 Yellow
3-(4-Chlorophenyl)-2-phenylpropanenitrile (4i).8d,14,15 White liquid. Yield: 196 mg, 92%. H NMR (400 MHz, CDCl3, TMS,
solid. Yield: 208 mg, 86%. 1H NMR (400 MHz, CDCl3, TMS, 25 °C, ppm): δ = 7.41–7.30 (m, 6H), 7.19 (dd, J1 = 5.2 Hz, J2 =
25 °C, ppm): δ = 7.39–7.23 (m, 7H), 7.05 (d, J = 12.4 Hz, 2H), 1.2 Hz, 1H), 6.95 (dd, J1 = 5.2 Hz, J2 = 3.6 Hz, 1H), 4.06 (dd, J1 =
3.99 (t, J = 7.2 Hz, 1H), 3.19–3.09 (m, 2H). 13C {1H} NMR 8.4 Hz, J2 = 6.4 Hz, 1H), 3.48–3.33 (m, 2H). 13C {1H} NMR
1
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(100.6 MHz, CDCl3, TMS, 25 °C, ppm): δ = 137.9, 134.7, 129.0, 137.1, 129.5, 129.1, 128.9, 128.1, 127.4, 125.6, 125.0, 124.2,
128.3, 127.4, 127.0, 126.9, 124.8, 120.0, 40.0, 36.1.
122.7.
Procedure for the time profile of the reaction
General procedure for the synthesis of 2-aminoquinolines
Six identical reactions were performed in different reaction
tubes at different time intervals (5, 15, 30, 60, 90, and
120 min). To a 20 mL reaction tube (1 cm × 20 cm) with a con-
denser, were added KOH (2.8 mg, 0.05 mmol, 5 mol%), aryl-
acetonitrile (1.0 mmol), primary alcohol (1.0 mmol), and a
solution of complex 1f (0.001 mmol, 0.1 mol%) in toluene
(1.0 mL) under open air conditions. The reaction mixture was
then vigorously stirred (1200 rpm) in a preheated oil bath at
135 °C for 5–120 min. After completion of the reactions,
conversions and yields were determined by 1H NMR analysis
of the crude reaction mixture using 1,3,5-trimethoxybenzene
as an internal standard.
To a 20 mL reaction tube with a condenser, were added KOH
(1.4 mg, 0.025 mmol, 5 mol%), arylacetonitrile (0.5 mmol),
2-aminobenzy alcohol (0.5 mmol), and a solution of complex
1f (0.0005 mmol, 0.1 mol%) in toluene (1.0 mL) under open
air conditions. The reaction mixture was then vigorously
stirred (1200 rpm) in a preheated oil bath at 135 °C for 4–8 h.
Thereafter, the reaction mixture was cooled to ambient temp-
erature, and ethyl acetate (5.0 mL) was added to the reaction
mixture. After filtration, the filtrate was concentrated under
reduced pressure. The crude product was purified by silica gel
column chromatography using
a
hexane : ethyl-acetate :
triethyl-amine (7 : 3 : 0.1) mixture as an eluent to afford the
desired 2-aminoquinolines.
3-Phenylquinolin-2-amine (6a).8c,26c,28 Yellow solid. Yield:
88 mg, 80%. 1H NMR (400 MHz, CDCl3, TMS, 25 °C, ppm): δ =
7.77 (s, 1H), 7.69 (d, J = 8.4 Hz, 1H), 7.63 (dd, J1 = 8.0 Hz, J2 =
1.2 Hz, 1H), 7.56–7.41 (m, 6H), 7.26 (td, J1 = 7.2 Hz, J2 = 0.8 Hz,
1H), 5.12 (s, 2H). 13C {1H} NMR (100.6 MHz, CDCl3, TMS,
25 °C, ppm): δ = 155.2, 147.2, 137.6, 137.1, 129.5, 129.1, 128.9,
128.1, 127.4, 125.6, 125.0, 124.2, 122.7.
Conclusions
We have successfully synthesized and characterized a series of
backbone-modified [IrCl(cod)(NHC)] complexes. The variation
of the benzyl groups at the 1,3-positions and aryl groups at the
4,5-positions of imidazole affects the electronic nature of the
NHC ligands, as confirmed by the comparison of the IR carbo-
nyl stretching frequencies of the in situ prepared [IrCl
(CO)2(NHC)] complexes. The electronic nature of the NHC
ligands seemed to play an important role in determining the
reaction efficiency of the NHC–Ir-catalyzed α-alkylation of
nitriles with primary alcohols. Complex 1f with an NHC ligand
bearing 4-methoxybenzyl groups at the 1,3-positions and
4-methoxyphenyl groups at the 4,5-positions proved that it is a
general and highly productive catalyst for this transformation
under an air atmosphere requiring significantly short reaction
times. To the best of our knowledge, one of the highest turn-
over numbers (TONs up to 960) is reported for the α-alkylation
of nitriles with primary alcohols among all the reported TM
complexes as catalysts for these transformations.
3-(4-Methoxyphenyl)quinolin-2-amine (6b).28 Yellow solid.
Yield: 105 mg, 84%. 1H NMR (400 MHz, CDCl3, TMS, 25 °C,
ppm): δ = 7.73 (s, 1H), 7.67 (d, J = 8.4 Hz, 1H), 7.61 (dd, J1 = 8.0
Hz, J2 = 1.2 Hz, 1H), 7.54 (td, J1 = 6.8 Hz, J2 = 1.2 Hz, 1H), 7.43
(dd, J1 = 6.4 Hz, J2 = 2.0 Hz, 2H), 7.24 (td, J1 = 6.8 Hz, J2 = 0.8
Hz, 1H), 7.00 (dd, J1 = 6.8 Hz, J2 = 2.0 Hz, 2H), 5.16 (s, 2H),
3.85 (s, 3H). 13C {1H} NMR (100.6 MHz, CDCl3, TMS, 25 °C,
ppm): δ = 159.5, 155.6, 147.0, 136.9, 130.0, 129.7, 129.3, 127.3,
125.5, 124.2, 122.6, 114.5, 55.3.
3-(p-Tolyl)quinolin-2-amine (6c).26c,28 Yellow solid. Yield:
95 mg, 81%. 1H NMR (400 MHz, CDCl3, TMS, 25 °C, ppm): δ =
7.75 (s, 1H), 7.68 (dd, J1 = 8.6 Hz, J2 = 0.8 Hz, 1H), 7.62 (dd, J1 =
8.0 Hz, J2 = 1.2 Hz, 1H), 7.55 (td, J1 = 7.6 Hz, J2 = 1.2 Hz, 1H),
7.41 (dd, J1 = 6.0 Hz, J2 = 2.0 Hz, 2H), 7.30–7.23 (m, 3H), 5.17
(s, 2H), 2.42 (s, 3H). 13C {1H} NMR (100.6 MHz, CDCl3, TMS,
25 °C, ppm): δ = 155.4, 147.1, 138.0, 136.9, 134.6, 129.7, 129.4,
128.7, 127.5, 125.5, 125.0, 124.2, 122.6, 21.2.
3-(4-Chlorophenyl)quinolin-2-amine (6d).26c Yellow solid.
Yield: 90 mg, 71%. 1H NMR (400 MHz, CDCl3, TMS, 25 °C,
ppm): δ = 7.76 (s, 1H), 7.69 (dd, J1 = 8.2 Hz, J2 = 0.8 Hz, 1H),
7.64 (dd, J1 = 8.0 Hz, J2 = 1.2 Hz, 1H), 7.57 (td, J1 = 7.6 Hz, J2 =
2.0 Hz, 1H), 7.47 (s, 4H), 7.27 (td, J1 = 7.6 Hz, J2 = 2.0 Hz, 1H),
4.93 (s, 2H). 13C {1H} NMR (100.6 MHz, CDCl3, TMS, 25 °C,
ppm): δ = 154.8, 147.3, 137.3, 136.0, 134.3, 130.3, 129.9, 129.4,
127.5, 125.7, 124.1, 123.7, 122.9.
Conflicts of interest
There are no conflicts to declare.
Acknowledgements
We are grateful to the Ege University Scientific Research
3-(4-Bromophenyl)quinolin-2-amine (6e).26c,28 Yellow solid. Projects Coordination (FBG-2020-21867) for financial support.
Yield: 97 mg, 65%. 1H NMR (400 MHz, CDCl3, TMS, 25 °C, We also thank the Ege University Directorate of Library and
ppm): δ = 7.77 (s, 1H), 7.70 (d, J = 8.4 Hz, 1H), 7.64 (d, J = 8.0 Documentation, EGE-PIK and Enago for providing editing
Hz, 1H), 7.60–7.53 (m, 2H), 7.38 (td, J1 = 7.6 Hz, J2 = 6.0 Hz, service and Osman Nuri Aslan (Atatürk University-DAYTAM)
3H), 7.28 (t, J = 7.0 Hz, 1H), 4.88 (s, 2H). 13C {1H} NMR for the HRMS analyses. B. A. thanks the Council of Higher
(100.6 MHz, CDCl3, TMS, 25 °C, ppm): δ = 155.2, 147.2, 137.6, Education (YÖK 100/2000) for the fellowship.
1794 | Dalton Trans., 2021, 50, 1788–1796
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13 W. Ma, S. Cui, H. Sun, W. Tang, D. Xue, C. Li, J. Fan, J. Xiao
References
and C. Wang, Chem. – Eur. J., 2018, 24, 13118–13123.
1 (a) M. H. S. A. Hamid, P. A. Slatford and J. M. J. Williams, 14 S. Bera, A. Bera and D. Banerjee, Chem. Commun., 2020, 56,
Adv. Synth. Catal., 2007, 349, 1555–1575; (b) C. Gunanathan 6850–6853.
and D. Milstein, Science, 2013, 341, 1229712; (c) Y. Obora, 15 B. C. Roy, I. A. Ansari, S. A. Samim and S. Kundu, Chem. –
ACS Catal., 2014, 4, 3972–3981; (d) F. Huang, Z. Q. Liu and Asian J., 2019, 14, 2215–2219.
Z. K. Yu, Angew. Chem., Int. Ed., 2016, 55, 862–875; 16 (a) J. W. Ogle and S. A. Miller, Chem. Commun., 2009, 5728–
(e) A. Corma, J. Navas and M. J. Sabater, Chem. Rev., 2018,
118, 1410–1459; (f) B. G. Reed-Berendt, K. Polidano and
L. C. Morrill, Org. Biomol. Chem., 2019, 17, 1595–1607;
(g) T. Irrgang and R. Kempe, Chem. Rev., 2019, 119, 2524–
2549.
5730; (b) H. V. Huynh, Chem. Rev., 2018, 118, 9457–9492;
(c) G. Sipos and R. Dorta, Coord. Chem. Rev., 2018, 375, 13–
68; (d) D. Munz, Organometallics, 2018, 37, 275–289;
(e) D.-H. Li, X.-X. He, C. Xu, H.-D. Huang, N. Liu,
D.-S. Shen and F.-S. Liu, Organometallics, 2019, 38, 2539–
2552.
2 H. Lundberg and H. Adolfsson, Synthesis, 2016, 48, 644–
652.
17 (a) D. Wang and D. Astruc, Chem. Rev., 2015, 115, 6621–
6686; (b) V. César, L. H. Gade and S. Bellemin-Laponnez,
NHC-Cobalt, -Rhodium, and -Iridium Complexes in
Catalysis, in N-heterocyclic carbenes: From laboratory curios-
ities to efficient synthetic tools, ed. S. Díez-González, Royal
Society of Chemistry, Cambridge, 2nd edn, 2017, pp.
302–335; (c) S. Gülcemal and B. Çetinkaya, Reduction
Reactions with NHC-Bearing Complexes, in N-heterocyclic
carbenes: From laboratory curiosities to efficient synthetic
tools, ed. S. Díez-González, Royal Society of Chemistry,
Cambridge, 2nd edn, 2017, pp. 484–533; (d) E. Peris, Chem.
Rev., 2018, 118, 9988–10031; (e) M. Iglesias and
L. A. A. Oro, Chem. Soc. Rev., 2018, 47, 2772–2808.
3 G. Chelucci and A. Porcheddu, Chem. Rec., 2017, 200–216.
4 (a) S. S. Kulp and M. J. McGee, J. Org. Chem., 1983, 48,
4097–4098; (b) H. Takaya, K. Yoshida, K. Isozaki, H. Terai
and S.-I. Murahashi, Angew. Chem., Int. Ed., 2003, 42, 3302–
3304; (c) F. F. Fleming, L. Yao, P. C. Ravikumar, L. Funk
and B. C. Shook, J. Med. Chem., 2010, 53, 7902–7791;
(d) M. Szostak, B. Sautier, M. Spain and D. J. Procter, Org.
Lett., 2014, 16, 1092–1095; (e) N. Kurono and T. Ohkuma,
ACS Catal., 2016, 6, 989–1023; (f) J.-T. Yu, F. Teng and
J. Cheng, Adv. Synth. Catal., 2017, 359, 26–38.
5 R. Grigg, T. R. B. Mitchell, S. Sutthivaiyakit and
N. Tongpenyai, Tetrahedron Lett., 1981, 22, 4107–4110.
6 (a) K. Motokura, D. Nishimura, K. Mori, T. Mizugaki, 18 (a) S. Gülcemal, A. G. Gökçe and B. Çetinkaya, Inorg.
K. Ebitani and K. Kaneda, J. Am. Chem. Soc., 2004, 126,
5662–5663; (b) K. Motokura, N. Fujita, K. Mori,
T. Mizugaki, K. Ebitani, K. Jitsukawa and K. Kaneda, Chem.
– Eur. J., 2006, 12, 8228–8239.
Chem., 2013, 52, 10601–10609; (b) S. Gülcemal, A. G. Gökçe
and B. Çetinkaya, Dalton Trans., 2013, 42, 7305–7311;
(c) D. Gülcemal, A. G. Gökçe, S. Gülcemal and B. Çetinkaya,
RSC Adv., 2014, 4, 26222–26230.
7 A. Corma, T. Ródenas and M. J. Sabater, J. Catal., 2011, 19 S. Gülcemal, D. Gülcemal, G. F. S. Whitehead and J. Xiao,
279, 319–327. Chem. – Eur. J., 2016, 22, 10513–10522.
8 (a) T. Kuwahara, T. Fukuyama and I. Ryu, Chem. Lett., 2013, 20 (a) S. Genç, S. Günnaz, B. Çetinkaya, S. Gülcemal and
42, 1163–1165; (b) S. Thiyagarajan and C. Gunanathan, ACS
Catal., 2017, 7, 5483–5490; (c) B. C. Roy, S. Debnath,
K. Chakrabarti, B. Paul, M. Maji and S. Kundu, Org. Chem.
Front., 2018, 5, 1008–1018; (d) Z.-H. Zhu, Y. Li, Y.-B. Wang,
Z.-G. Lan, X. Zhu, X.-Q. Hao and M.-P. Song,
Organometallics, 2019, 38, 2156–2166.
D. Gülcemal, J. Org. Chem., 2018, 83, 2875–2881;
(b) S. Genç, B. Arslan, S. Gülcemal, S. Günnaz, B. Çetinkaya
and D. Gülcemal, J. Org. Chem., 2019, 84, 6286–6297;
(c) S. Genç, S. Gülcemal, S. Günnaz, B. Çetinkaya and
D. Gülcemal, J. Org. Chem., 2020, 85, 9139–9152.
21 F. Hackenberg, G. Lally, H. Müller-Bunz, F. Paradisi,
D. Quaglia, W. Streciwilk and M. Tacke, J. Organomet.
Chem., 2012, 717, 123–134.
9 M. L. Buil, M. A. Esteruelas, J. Herrero, S. Izquierdo,
I. M. Pastor and M. Yus, ACS Catal., 2013, 3, 2072–2075.
10 (a) C. Löfberg, R. Grigg, M. A. Whittaker, A. Keep and 22 H. M. J. Wang and I. J. B. Lin, Organometallics, 1998, 17,
A. Derrick, J. Org. Chem., 2006, 71, 8023–8027; 972–975.
(b) M. Morita, Y. Obora and Y. Ishii, Chem. Commun., 2007, 23 (a) A. R. Chianese, X. Li, M. C. Janzen, J. W. Faller and
2850–2852; (c) T. Sawaguchi and Y. Obora, Chem. Lett.,
2011, 40, 1055–1057; (d) B. Anxionnat, D. Gomez Pardo,
G. Ricci and J. Cossy, Org. Lett., 2011, 13, 4084–4087;
(e) Y.-Y. Kong and Z.-X. Wang, Asian J. Org. Chem., 2020, 9,
1192–1198.
R. H. Crabtree, Organometallics, 2003, 22, 1663–1667;
(b) R. A. Kelly III, H. Clavier, S. Giudice, N. M. Scott,
E. D. Stevens, J. Bordner, I. Samardjiev, C. D. Hoff,
L. Cavallo and S. P. Nolan, Organometallics, 2008, 27, 202–
210; (c) T. Dröge and F. Glorius, Angew. Chem., Int. Ed.,
2010, 49, 6940–6952; (d) D. J. Nelson and S. P. Nolan,
Chem. Soc. Rev., 2013, 42, 6723–6753.
11 J. Li, Y. Liu, W. Tang, D. Xue, C. Li, J. Xiao and C. Wang,
Chem. – Eur. J., 2017, 23, 14445–14449.
12 (a) A. Jana, C. B. Reddy and B. Maji, ACS Catal., 2018, 8, 24 C. A. Tolman, Chem. Rev., 1977, 77, 313–348.
9226–9231; (b) J. C. Borghs, M. A. Tran, J. Sklyaruk, 25 S. C. Zinner, C. F. Rentzsch, E. Herdtweck, W. A. Herrmann
M. Rueping and O. El-Sepelgy, J. Org. Chem., 2019, 84,
7927–7935.
and F. E. Kühn, Dalton Trans., 2009, 42, 7055–
7062.
This journal is © The Royal Society of Chemistry 2021
Dalton Trans., 2021, 50, 1788–1796 | 1795

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Paper
Dalton Transactions
26 (a) M. Maji, K. Chakrabarti, B. Paul, B. C. Roy and 27 S. Lieber, F. Scheer, W. Meissner, S. Naruhn, T. Adhikary,
S. Kundu, Adv. Synth. Catal., 2018, 360, 722–729;
(b) S. Shee, K. Ganguli, K. Jana and S. Kundu, Chem.
S. Müller-Brüsselbach, W. E. Diederich and R. Müller,
J. Med. Chem., 2012, 55, 2858–2868.
Commun., 2018, 54, 6883–6886; (c) K. Das, A. Mondal, 28 G. Chakraborty, R. Sikari, S. Das, R. Mondal, S. Sinha,
D. Pal and D. Srimani, Org. Lett., 2019, 21, 3223–
S. Banerjee and N. D. Paul, J. Org. Chem., 2019, 84, 2626–
3227.
2641.
1796 | Dalton Trans., 2021, 50, 1788–1796
This journal is © The Royal Society of Chemistry 2021