A bifunctional strategy for N-heterocyclic carbene-stabilized iridium complex-catalyzed: N -alkylation of amines with alcohols in aqueous media

Article abstract of DOI:10.1039/c8gc02298d

Through the strategy of combining bifunctional 2-hydroxypyridine and a thermally stable N-heterocyclic carbene ligand, an Ir-catalyzed N-monoalkylation reaction has been developed in aqueous media under base-free conditions. This reaction proceeds smoothly with high yields of various aromatic amines and sulfonamides with a wide range of primary alcohols. Experimental and computational studies revealed a metal-ligand cooperative mechanism and its thermal stability during the bifunctional catalysis in aqueous media.

Full text of DOI:10.1039/c8gc02298d

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A bifunctional strategy for N-heterocyclic
carbene-stabilized iridium complex-catalyzed
N-alkylation of amines with alcohols in aqueous
media†
Cite this: DOI: 10.1039/c8gc02298d
Received 24th July 2018,
Accepted 10th December 2018
DOI: 10.1039/c8gc02298d
a
a
a
a
b
Ming Huang,
Yinwu Li, Jiahao Liu,
Xiao-Bing Lan,
Yan Liu,
a
a
rsc.li/greenchem
Cunyuan Zhao and Zhuofeng Ke
*
Through the strategy of combining bifunctional 2-hydroxypyridine xypyridine (2-HP) has emerged as a new class of scaffolds in
and a thermally stable N-heterocyclic carbene ligand, an Ir-cata- bifunctional ligand design. These ligands could be tuned by
−
lyzed N-monoalkylation reaction has been developed in aqueous deprotonation of the ortho-OH group (producing OH/O var-
media under base-free conditions. This reaction proceeds iants), facilitating the transfer of protons via a metal–ligand
smoothly with high yields of various aromatic amines and sulfona- cooperative mechanism. Importantly, Yamaguchi, Fujita, and
mides with a wide range of primary alcohols. Experimental and their co-workers have explored a series of Cp*Ir (Cp* =
5
computational studies revealed
a
metal–ligand cooperative η -C Me ) complexes with bidentate 2-HP ligands, which have
5
5
mechanism and its thermal stability during the bifunctional cataly- led to promising applications in hydrogenation and dehydro-
1
0
sis in aqueous media.
genation reactions.
Encouraged by these pioneering studies, we became inter-
ested in designing a new bifunctional ligand that comprises
N-heterocyclic carbene (NHC) and 2-HP moieties. With the
strong σ-donor ability of the NHC, it would be a promising
ligand to increase the thermal stability of the catalyst in
N-Alkylated amines are valuable reactive intermediates with
numerous applications in the pharmaceutical, polymer
1
materials, and synthetic industries. One of the most appeal-
ing synthetic approaches for their preparation is the “borrow-
ing hydrogen” methodology, in which the amines are formed
by using sustainable and abundant alcohols as coupling
2
reagents (Scheme 1a). In principle, in these transformations,
only water is generated as the byproduct, which minimizes the
environmental hazards and maximizes the atom efficiency.
Although a variety of catalytic systems based on transition-
3
4
5
6
7
metal catalysts (e.g., based on Ru, Ir, Co, Fe and Mn ) have
been developed, these reactions usually have to be carried out
under reflux in organic solvents such as toluene or diglyme,
and require the usage of a base, which to some extent compro-
mise their applicability (Scheme 1b). Thus, the development of
new catalytic systems which can perform in a greener solvent
8
such as water and without any additive is highly desirable.
Bifunctional ligands and their complexes are of high inter-
est to organometallic and organic chemists, and they are
9
widely and successfully applied in catalysis. Recently, 2-hydro-
a
School of Materials Science and Engineering, PCFM Lab, School of Chemistry,
Sun Yat-sen University, Guangzhou 510275, China. E-mail: kezhf3@mail.sysu.edu.cn
b
School of Chemical Engineering and Light Industry, Guangdong University of
Technology, Guangzhou 510006, P. R. China
†
Electronic supplementary information (ESI) available. CCDC 1828919. For ESI
and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c8gc02298d
Scheme 1 The design of bifunctional Cp*Ir complexes with a bidentate
NHC-2-HP ligand in this study.
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1
1
a
water. Interestingly, NHCs have been combined with pyridi- Table 1 Optimization of reaction conditions
nol rings in Ru and Ir catalysts for hydrogenation of carbon
dioxide, and dehydrogenation of formic acid and alcohols in
1
0b,c
aqueous media through bifunctional mechanisms.
The
bidentate picolyl–NHC scaffolds have been proven to be potent
ligands for improving catalytic activity in N-alkylation of
b
Entry
Catalysts
Conv. (%)
Imine (%)
Amine (%)
3
e
amines in the presence of toluene and KOH. Inspired by
these results, we are looking forward to developing a bifunc-
tional NHC-2-HP ligand (Scheme 1c) for improving catalytic
activity in N-alkylation of amines under the aqueous and base-
free conditions. Furthermore, the picoline arm of NHC-2-HP
has the potential to perform an extra bifunctional action
through the dearomatization–rearomatization process, resem-
bling Milstein’s picolyl–phosphine ligands (Scheme 1c).
Therefore, NHC-2-HP could serve as a potential bifunctional
ligand bearing multi-functional sites, which would lead to a 12
1
2
3
4
5
6
—
(Cp*IrCl
8a
10
9a
9b
8a
8b
8c
8d
8e
7a
8a
8a
8a
8a
—
—
—
2
)
2
17.7
71.1
4.3
54.1
5.1
96.5
34.0
51.3
75.8
60.3
93.3
89.4
78.8
78.9
94.1
7.4
0.8
1.1
1.6
1.2
0.1
1.3
1.4
1.0
0.8
1.1
46.5
2.1
3.1
0.6
10.3
70.3
3.2
52.5
3.9
96.4
32.7
49.6
74.8
59.5
92.2
42.9
76.7
75.8
93.5
c
7
c
8
c
9
c,12
9
c
1
1
0
1
c
c
c,d
c,e
c, f
f,g
1
1
1
3
4
5
versatile platform to manipulate metal–ligand cooperation
1
3
under different reaction conditions.
Herein, we report the synthesis of Cp*Ir(NHC-2-HP) com- 16
plexes, which showed high catalytic performance for the
N-alkylation of aromatic amines and sulfonamides with a wide 2 mol% [Ir], 1 mL H O, 110 °C, 9 h, N . GC yield. 24 h. Without N2.
range of primary alcohols in aqueous media. The combination
of experimental and computational studies demonstrated the
bifunctional feature of Cp*Ir(NHC-2-HP) through the outer-
sphere mechanism for the studied N-alkylation reactions.
a
Reaction conditions: 0.5 mmol aniline, 0.5 mmol benzyl alcohol,
b
c
d
2
2
e
f
g
1
00 °C. 1 mol%. 48 h.
mark reaction (Table 1). The control experiments showed that
The synthesis of ligands 6 was straightforward (see the N-alkylation reaction did not proceed well in the absence
t
2 2
Scheme S1 in the ESI†) with O Bu serving as a protected of the catalyst or using a simple [Cp*IrCl ] as a catalyst
1
0c
group. The new Ir complexes 7 were prepared via a transme- (entries 1 and 2). It is clear that 8a showed higher catalytic per-
tallation procedure, involving a stepwise reaction of the appro- formance than 10 (entries 3 and 4), which suggested that the
priate proligands 6 with Ag
2
O followed by the addition of bidentate picolyl–NHC scaffold is more appropriate for
(Scheme 2). Under reflux in a N-alkylation. Complex 9a gave a slightly lower yield than 8a
[
Cp*IrCl and sufficient KPF
2
]
2
6
MeCN solution, 7 could be transformed into hydroxyl deriva- (entries 5 and 3), while a dramatically decreased yield was
tives 8. Meanwhile, we also synthesized the structurally similar obtained when 9b (entry 6) was used. These results demon-
1
0c,14
complexes 9a, 9b, and 10.
stable and can be stored in air for months without decompo- action for 8a with respect to 9b and indicated that the OCH
sition. The structure of complex 8a was confirmed by X-ray group could reserve to some extent the bifunctional ability
All of the Ir complexes are very strated the significant contribution of the bifunctional inter-
3
4
c
diffraction, which is revealed to be a typical half-sandwich similar to the OH group. To our delight, the yield could be
complex. The Ir1–C9 and Ir1–N1 distances are 2.116 and increased to 96.4% with 8a as a catalyst, when the reaction
2
.050 Å, respectively. The dihedral angle between the time is prolonged to 24 h (entry 7). Then, the substituents on
N-heterocyclic carbene plane with the picolyl plane is 48.1°, the NHC wingtip and the backbone of the imidazole were
1
4
which is comparable to that of the congener of 9b (50.0°).
modified aiming at improving the catalytic reactivity. However,
Initially, the coupling of benzyl alcohol and aniline in water when the isopropyl or phenyl group (entries 8 and 9) was used
at 110 °C to afford N-benzylaniline was chosen as the bench- as a wingtip substituent, a lower yield was obtained. The cata-
lytic performance of 8d with methyl substituents on the imid-
azole backbone or 8e with a benzimidazole ring is also inferior
both in terms of activity and selectivity (entries 10 and 11).
These results reveal that both the steric effects and the elec-
tronic properties of the ligand apparently influenced the cata-
lytic activity. Notably, 7a showed comparable catalytic activity
to 8a (entry 12), presumably as a result of deprotection of the
t
O Bu group under the reaction conditions (see Fig. S2†).
However, low yield was obtained when the reaction was per-
formed under air atmosphere and at lower temperature
(
entries 13 and 14). Furthermore, an attempt to lower the cata-
lyst loading to 1 mol% resulted in the decrease of yield
(entry 15). The reaction time was prolonged to 48 h, which
Scheme 2 Sythesis of Ir complexes 8, 9 and 10.
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could increase the yield up to 93.5% (entry 16). This result
gives evidence for the stability of the catalyst under the reac-
tion conditions.
In order to determine the potential applicability of this
catalytic system, we then extended the reaction to a wider
range of amines and alcohols (Scheme 3). The N-alkylation of
anilines bearing either electron-donating or electron-withdraw-
ing substituents at the para-position with benzylic alcohol gave
the corresponding products 13a–f in 70–90% yields. Similarly,
anilines with ortho-substituted groups such as Me, Br, and the
t
bulky Bu were converted to desired products 13g–i in 65–78%
yields. Transformations of 1-naphthylamine, 2-naphthylamine
and 2-pyridylamine afforded the desired products 13j–l in
8
0–92% yields, as well. In the meantime, the coupling reac-
tions of aniline with a variety of benzyl alcohols bearing elec-
tron-donating groups, as well as electron-withdrawing groups,
also could take place efficiently to obtain the expected pro-
ducts in good yields (13m–13q). The sensitive boronic ester
substituted alcohol and 2-naphthalenemethanol were compati-
ble, affording 13r and 13v in 46% and 86% yields, respectively.
Scheme 4 Scope of the N-alkylation of p-methylbenzenesulfonamide.
Reaction conditions: 0.5 mmol p-methylbenzenesulfonamide, 0.5 mmol
However, the catalytic performance was found to be less alcohol, 0.5 mmol Na CO , 2 mol% 8a, 1 mL H O, 110 °C, 24 h, N ; iso-
2
3
2
2
efficient when heteroaryl or aliphatic alcohols were used, and lated yield.
the corresponding products (13s–13u and 13w–13x) were iso-
lated in 25–70% yields.
N-Alkylsulfonamides are also an important class of nitro- benzenesulfonamide with alcohols was then investigated
gen-containing compounds, which have displayed a wide (Scheme 4). Reactions of p-methylbenzenesulfonamide with
1
5
range of biological activities. To further expand the generality benzyl alcohol or benzylic alcohols bearing an electron-
of the catalytic system, the N-alkylation of p-methyl- donating or electron-withdrawing group afforded the desired
products 15a–j in 43–92% yields. The system was also applied
to 2-naphthalenemethanol and heterocyclic methanols, giving
the desired products 15k–n in 43–91% yields. For aliphatic
alcohols, the desired products 15o–p were obtained in 52–60%
yields.
To gain insights into the mechanism of the N-alkylation
reaction, experimental and computational studies were per-
formed. Firstly, the mercury poisoning experiment was con-
ducted. Adding one drop of elemental mercury (1.1 equiv.)
showed no retardation to the 8a-catalyzed N-alkylation of
aniline with benzylalcohol, suggesting that the catalytic reac-
1
6
tion is homogeneous (Scheme 5a). Then, the reaction of the
corresponding imine 16a with benzylic alcohol under the
optimal conditions gave 13a in
a
quantitative yield
(
Scheme 5b). These results indicate that the N-alkylation
process follows the “borrowing hydrogen” pathway with imine
as the key intermediate. Also, a variable temperature NMR
experiment of 8a was conducted to explore the potential hemil-
1
7
ability of the picoline moieties. However, no changes in the
1
8
a H resonances were observed, even at 110 °C. Although VT
NMR results cannot totally exclude the possibility of a low
concentration of the pyridine-dissociated intermediate in the
catalytic system, DFT calculations suggested that the free
energy of a pyridine-dissociated intermediate is as high as
3.7 kcal mol− (IM-6 in Fig. 1). In addition, the studies of the
1
2
stepwise deprotonation of 8a (Scheme 5c) showed that the OH
group of the 2-HP is facile to be deprotonated. Further depro-
tonation of the picolyl arm, the methylene, of 8a was not
Scheme 3 Scope of the N-alkylation of aromatic amines. Reaction
conditions: 0.5 mmol amine, 0.5 mmol alcohol, 2 mol% 8a, 1 mL H O,
10 °C, 24 h, N ; isolated yield.
2
1
2
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12a in water at 110 °C for 24 h gave a mixture of N-alkylated
products 13a (53%), 13a-d1 (41%) and 13a-d2 (6%) in 59%
yield (Scheme 5d). These results reveal that the alcohol
oxidation step is reversible. The intermolecular competition
reactions of 11a and 11a-d2 with 12a were studied under the
standard catalytic conditions, and the observed products are
1
3a (74%), 13a-d1 (23%) and 13a-d2 (3%) on the basis of
1
H NMR. Apart from the influence of the H/D exchange, the
calculated KIE (k /k ) was 2.09. Furthermore, in the parallel
H D
1
8a
reaction of 11a and 11a-d2 with 12a, the observed kinetic
isotope effect (k /k ) was 2.47. These experimental findings
H
D
suggest that the alcohol oxidation was involved in the rate-
determining step (RDS) of this reaction.
To better understand the details of the catalytic cycle and
investigate the bifunctional mechanism further, DFT calcu-
lations were performed (Fig. 1, S9, S10, and S11 in the ESI†).
The reaction is initiated with the formation of species Cat-1
0.0 kcal mol− , Fig. 1), which is assumed to be formed via the
1
(
1
0b
elimination of HCl from 8a with the assistance of aniline.
There are two possible reaction pathways for the catalytic
cycles: one is the outer-sphere pathway and the other is the
inner-sphere β-H elimination/insertion pathway. The outer-
sphere dehydrogenation (Fig. 1) begins with the formation of
−
1
an agostic interaction intermediate IM-2 (9.9 kcal mol ), after
the coordination of the alcohol substrate 11a (Cat-1 → IM-1,
1
4
.7 kcal mol− ). Then, the dehydrogenation of 11a would occur
−
1
via transition state TS-1 (25.3 kcal mol ) to yield the aldehyde
and iridium hydride intermediate IM-4 (8.9 kcal mol ). The
Scheme 5 Preliminary mechanistic studies.
−1
bifunctional TS-1 operates in an outer-sphere manner, in
which the α-hydrogen and the proton of the alcohol would
observed under the excess base under our catalytic conditions. transfer synchronously to the metal center and the pyridone
However, the potential of the (de)aromatization of the picolyl oxygen, respectively. The inner-sphere mechanism consists of
arm in metal–ligand cooperation should be studied in other several steps (Fig. 1). Firstly, the proton of the alcohol in IM-1
−
1
reaction systems, which is in progress in our laboratory. transfers to the pyridone oxygen to give IM-5 (11.7 kcal mol ),
Moreover, the kinetic isotope effect (KIE) studies (Schemes 5d via TS-2 (10.4 kcal mol− ). Then, the dissociation of the pyri-
and e) were carried out to gain more information concerning dine ligand led to IM-6 (23.7 kcal mol− ) and a subsequent β-H
1
1
1
8
−1
the reaction pathway. The reaction of 11a-d2 (97% D) with agostic interaction species IM-7 (25.3 kcal mol ). From IM-7,
Fig. 1 Free energy profile for 8a-catalyzed N-alkylation of aniline and benzylalcohol. Free energies are given in kcal mol−1
.
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−
1
β-hydride elimination (TS-3, 30.9 kcal mol ) takes place to
S. J. Mehrman, Org. Process Res. Dev., 2006, 10, 971–1031;
(c) A. Seayad, M. Ahmed, H. Klein, R. Jackstell, T. Gross and
M. Beller, Science, 2002, 297, 1676–1678; (d) S. Kobayashi
and H. Ishitani, Chem. Rev., 1999, 99, 1069–1094.
2 (a) A. Corma, J. Navas and M. J. Sabater, Chem. Rev., 2018,
118, 1410–1459; (b) X. Ma, C. Su and Q. Xu, Top. Curr.
Chem., 2016, 374, 27; (c) A. J. A. Watson and
J. M. J. Williams, Science, 2010, 329, 635–636.
−1
provide IM-8 (26.6 kcal mol ). The overall barrier for the
inner-sphere dehydrogenation is 30.9 kcal mol relative to
Cat-1, which is 5.6 kcal mol higher than that of the outer-
sphere pathway. The yielded aldehyde reacts with an amine to
form an imine for the subsequent hydrogenation step. DFT
−
1
−
1
results suggest that the outer-sphere hydrogenation (TS-5,
1
1
5.2 kcal mol− ) is also more favored than the inner-sphere
−
1
hydrogenation (TS-6, 33.7 kcal mol ). Therefore, both the
dehydrogenation and hydrogenation steps prefer the outer-
sphere mechanism, and the RDS is the dehydrogenation of the
alcohol, which is consistent with our KIE results (KIE = 2.47).
Moreover, DFT results support the bifunctional role of the
NHC-2-HP ligand, which is in accordance with the signifi-
cantly reduced activity observed when the hydroxyl group was
replaced with hydrogen (entry 6, Table 1). It should be noted
that we observed comparable activity for complex 9a with the
OMe group (entry 5, Table 1), which might be attributed to the
electron donation effect, the possible second coordination
sphere hydrogen-bonding effect, or the conversion of the OMe
group to the OH group to a certain extent under reaction
3 (a) J. J. A. Celaje, X. Zhang, F. Zhang, L. Kam, J. R. Herron
and T. J. Williams, ACS Catal., 2017, 7, 1136–1142;
(b) K. O. Marichev and J. M. Takacs, ACS Catal., 2016, 6,
2205–2210; (c) X. Xie and H. V. Huynh, ACS Catal., 2015, 5,
4143–4151; (d) A. B. Enyong and B. Moasser, J. Org. Chem.,
2014, 79, 7553–7563; (e) F. E. Fernández, M. C. Puerta and
P. Valerga, Organometallics, 2012, 31, 6868–6879;
(f) M. H. S. A. Hamid, C. L. Allen, G. W. Lamb,
A. C. Maxwell, H. C. Maytum, A. J. A. Watson and
J. M. J. Williams, J. Am. Chem. Soc., 2009, 131, 1766–1774.
4 (a) P. Liu, R. Liang, L. Lu, Z. Yu and F. Li, J. Org. Chem.,
2017, 82, 1943–1950; (b) J.-Q. Li and P. G. Andersson,
Chem. Commun., 2013, 49, 6131–6133; (c) A. Bartoszewicz,
R. Marcos, S. Sahoo, A. K. Inge, X. Zou and B. Martín-
1
9
conditions.
In conclusion, we have developed a series of bifunctional
Cp*Ir complexes 8a–e, which bear picolyl-functionalized
N-heterocyclic carbene ligands with a pendant OH group.
These complexes are efficient catalysts for the N-alkylation of
anilines or sulfonamides with alcohols in aqueous media
under base-free conditions. A wide variety of primary alcohols
and (hetero)aromatic amines or p-methylbenzenesulfonamide
were efficiently converted into mono-N-alkylated amines in
good-to-excellent isolated yields. Notably, the present bifunc-
tional catalytic system through an outer-sphere (de)hydrogen-
ation mechanism provides guidelines for the development of
NHC complexes for reactions in aqueous media.
Matute, Chem.
(d) S. Michlik and R. Kempe, Chem. – Eur. J., 2010, 16,
13193–13198.
–
Eur. J., 2012, 18, 14510–14519;
5 (a) G. Zhang, Z. Yin and S. Zheng, Org. Lett., 2016, 18, 300–
303; (b) M. Mastalir, G. Tomsu, E. Pittenauer, G. Allmaier
and K. Kirchner, Org. Lett., 2016, 18, 3462–3465;
(c) S. Rösler, M. Ertl, T. Irrgang and R. Kempe, Angew.
Chem., Int. Ed., 2015, 54, 15046–15050.
6 (a) T. Yan, B. L. Feringa and K. Barta, ACS Catal., 2016, 6,
381–388; (b) H.-J. Pan, T. W. Ng and Y. Zhao, Chem.
Commun., 2015, 51, 11907–11910; (c) T. Yan, B. L. Feringa
and K. Barta, Nat. Commun., 2014, 5, 5602; (d) M. Bala,
P. K. Verma, U. Sharma, N. Kumar and B. Singh, Green
Chem., 2013, 15, 1687–1693.
Conflicts of interest
7 (a) S. Elangovan, J. Neumann, J.-B. Sortais, K. Junge,
C. Darcel and M. Beller, Nat. Commun., 2016, 7, 12641;
There are no conflicts to declare.
(
b) A. Bruneau-Voisine, D. Wang, V. Dorcet, T. Roisnel,
C. Darcel and J.-B. Sortais, J. Catal., 2017, 347, 57–62.
8
9
(a) A. Fernandes and B. Royo, ChemCatChem, 2017, 9,
Acknowledgements
3912–3917; (b) P. Qu, C. Sun, J. Ma and F. Li, Adv. Synth.
Catal., 2014, 356, 447–459; (c) R. Kawahara, K. Fujita and
R. Yamaguchi, Adv. Synth. Catal., 2011, 353, 1161–
This work was supported by the NSFC (21473261, 21673301,
and 21502023), the Guangdong Natural Science Funds for
Distinguished Young Scholar (No. 2015A030306027), the Tip-
top Youth Talents of Guangdong special support program
1
168; (d) O. Saidi, A. J. Blacker, M. M. Farah, S. P. Marsden
and J. M. J. Williams, Chem. Commun., 2010, 46,
541–1543.
(a) T. P. Goncalves and K.-W. Huang, J. Am. Chem. Soc.,
017, 139, 13442–13449; (b) P. A. Dub, B. L. Scott and
J. C. Gordon, J. Am. Chem. Soc., 2017, 139, 1245–1260;
c) J. R. Khusnutdinova and D. Milstein, Angew. Chem., Int.
1
(No. 20153100042090537) and the Fundamental Research
Funds for the Central Universities. Computing facilities were
supported in part by the National Supercomputing Center in
Guangzhou and Zhengzhou.
2
(
Ed., 2015, 54, 12236–12273; (d) T. Zell and D. Milstein,
Acc. Chem. Res., 2015, 48, 1979–1994; (e) S. Kuwata and
T. Ikariya, Chem. Commun., 2014, 50, 14290–14300;
(f) H. Grützmacher, Angew. Chem., Int. Ed., 2008, 47,
1814–1818.
Notes and references
1
(a) E. Vitaku, D. T. Smith and J. T. Njardarson, J. Med.
Chem., 2014, 57, 10257–10274; (b) A. F. Abdel-Magid and
This journal is © The Royal Society of Chemistry 2018
Green Chem.

View Article Online
Communication
Green Chemistry
1
0 (a) L. Wang, R. Kanega, H. Kawanami and Y. Himeda,
Chem. Rec., 2017, 17, 1071–1094; (b) K. Fujita, R. Tamura,
Y. Tanaka, M. Yoshida, M. Onoda and R. Yamaguchi, ACS
D. Song, Inorg. Chem., 2017, 56, 11956–11970; (c) C. Hou,
Z. Zhang, C. Zhao and Z. Ke, Inorg. Chem., 2016, 55, 6539–
6551.
Catal., 2017, 7, 7226–7230; (c) S. Siek, D. B. Burks, 13 (a) A. V. Polezhaev, C.-H. Chen, Y. Losovyj and
D. L. Gerlach, G. Liang, J. M. Tesh, C. R. Thompson, F. Qu,
J. E. Shankwitz, R. M. Vasquez, N. Chambers,
G. J. Szulczewski, D. B. Grotjahn, C. E. Webster and
E. T. Papish, Organometallics, 2017, 36, 1091–1106;
K. G. Caulton, Chem. – Eur. J., 2017, 23, 8039–8050;
(b) C. Hou, J. Jiang, Y. Li, C. Zhao and Z. Ke, ACS Catal.,
2017, 7, 786–795; (c) E. Fogler, J. A. Garg, P. Hu, G. Leitus,
L. J. W. Shimon and D. Milstein, Chem. – Eur. J., 2014, 20,
15727–15731.
(d) K. Fujita, T. Wada and T. Shiraishi, Angew. Chem., Int.
Ed., 2017, 56, 10886–10889; (e) Z. Xu, P. Yan, H. Li, K. Liu, 14 X.-Q. Xiao and G.-X. Jin, J. Organomet. Chem., 2008, 693,
X. Liu, S. Jia and Z. C. Zhang, ACS Catal., 2016, 6, 3784– 3363–3368.
788; (f) C. M. Moore, E. W. Dahl and N. K. Szymczak, 15 (a) A. Gopalsamy, M. Shi, B. Stauffer, R. Bahat, J. Billiard,
3
Curr. Opin. Chem. Biol., 2015, 25, 9–17; (g) J. B. Geri and
N. K. Szymczak, J. Am. Chem. Soc., 2015, 137, 12808–12814;
H. Ponce-de-Leon, L. Seestaller-Wehr, S. Fukayama,
A. Mangine, R. Moran, G. Krishnamurthy and P. Bodine,
J. Med. Chem., 2008, 51, 7670–7672; (b) J. Drews, Science,
2000, 287, 1960–1964.
(h) K. Fujita, Y. Tanaka, M. Kobayashi and R. Yamaguchi,
J. Am. Chem. Soc., 2014, 136, 4829–4832; (i) F. Li, J. Ma and
N. Wang, J. Org. Chem., 2014, 79, 10447–10455; ( j) C. Hou, 16 K. Chakrabarti, B. Paul, M. Maji, B. C. Roy, S. Shee and
J. Jiang, S. Zhang, G. Wang, Z. Zhang, Z. Ke and C. Zhao, S. Kundu, Org. Biomol. Chem., 2016, 14, 10988–10997.
ACS Catal., 2014, 4, 2990–2997; (k) R. Kawahara, K. Fujita 17 D. Gnanamgari, E. L. O. Sauer, N. D. Schley, C. Butler,
and R. Yamaguchi, J. Am. Chem. Soc., 2012, 134, 3643–
C. D. Incarvito and R. H. Crabtree, Organometallics, 2009,
28, 321–325.
18 (a) M. Vellakkaran, K. Singh and D. Banerjee, ACS Catal.,
2017, 7, 8152–8158; (b) E. M. Simmons and J. F. Hartwig,
Angew. Chem., Int. Ed., 2012, 51, 3066–3072.
3
2
646; (l) K. Fujita, N. Tanino and R. Yamaguchi, Org. Lett.,
007, 9, 109–111.
1
1
1 (a) E. Peris, Chem. Rev., 2018, 118, 9988–10031;
(b) M. Iglesias and L. A. Oro, Chem. Soc. Rev., 2018, 47,
2
772–2808; (c) M. N. Hopkinson, C. Richter, M. Schedler 19 (a) W.-H. Wang, J. F. Hull, J. T. Muckerman, E. Fujita and
and F. Glorius, Nature, 2014, 510, 485–496; (d) D. J. Nelson
and S. P. Nolan, Chem. Soc. Rev., 2013, 42, 6723–6753;
Y. Himeda, Energy Environ. Sci., 2012, 5, 7923–7926;
(b) W.-H. Wang, S. Xu, Y. Manaka, Y. Suna, H. Kambayashi,
J. T. Muckerman, E. Fujita and Y. Himeda, ChemSusChem,
2014, 7, 1976–1983; (c) K. T. Ngo, M. McKinnon,
B. Mahanti, R. Narayanan, D. C. Grills, M. Z. Ertem and
J. Rochford, J. Am. Chem. Soc., 2017, 139, 2604–2618.
(e) T. Dröge and F. Glorius, Angew. Chem., Int. Ed., 2010, 49,
6
940–6952.
2 (a) Q. Liang, A. Salmon, P. J. Kim, L. Yan and D. Song,
J. Am. Chem. Soc., 2018, 140, 1263–1266; (b) Q. Liang and
Green Chem.
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