Complexes LNi(Cp)X with alkylamino-substituted N-heterocyclic carbene ligands (L) and their catalytic activity in the Suzuki—Miyaura reaction

Article abstract of DOI:10.1007/s11172-021-3212-5

New nickel(ii) complexes of the general formula LNi(Cp)X (L is an N-heterocyclic carbene (NHC) ligand of the 1,2,4-triazole or imidazole series; Cp is the cyclopentadienyl anion; X = Cl, I) are reported. In these complexes, the NHC ligands (L) contain an alkylamino group at the 3 or 4 position of the heterocycle. The synthesized complexes and structurally similar complexes without an alkylamino group were tested for catalytic activity in the Suzuki—Miyaura reaction. The introduction of an alkylamino group into the NHC ligand leads to the enhancement of the catalytic activity of complexes with N,N′-diaryl-substituted NHC ligands of the imidazole series and a decrease in the activity of the complexes with N,N′-dialkyl-substituted NHC ligands of the 1,2,4-triazole series.

Full text of DOI:10.1007/s11172-021-3212-5

Russian Chemical Bulletin, International Edition, Vol. 70, No. 7, pp. 1281—1289, July, 2021
1281
Complexes LNi(Cp)X with alkylamino-substituted
N-heterocyclic carbene ligands (L)
and their catalytic activity in the Suzuki—Miyaura reaction
V. V. Chesnokov,a M. A. Shevchenko,a S. B. Soliev,a V. A. Tafeenko,b and V. M. Chernysheva
aPlatov South-Russian State Polytechnic University (NPI),
132 ul. Prosveschenya, 346428 Novocherkassk, Russian Federation.
E-mail: chern13@yandex.ru
bLomonosov Moscow State University,
1 Leninskie Gory, 119991 Moscow, Russian Federation
New nickel(II) complexes of the general formula LNi(Cp)X (L is an N-heterocyclic carbene
(NHC) ligand of the 1,2,4-triazole or imidazole series; Cp is the cyclopentadienyl anion;
X = Cl, I) are reported. In these complexes, the NHC ligands (L) contain an alkylamino group
at the 3 or 4 position of the heterocycle. The synthesized complexes and structurally similar
complexes without an alkylamino group were tested for catalytic activity in the Suzuki—Miyaura
reaction. The introduction of an alkylamino group into the NHC ligand leads to the enhance-
ment of the catalytic activity of complexes with N,N´-diaryl-substituted NHC ligands of the
imidazole series and a decrease in the activity of the complexes with N,N´-dialkyl-substituted
NHC ligands of the 1,2,4-triazole series.
Key words: N-heterocyclic carbenes, nickel, catalysis, Suzuki—Miyaura reaction.
Metal-catalyzed cross-coupling reactions serve as an
indispensable tool for state-of-the-art organic synthe-
sis.1—6 Palladium plays a significant role in the catalysis
of various cross-coupling reactions.1,3,6—8 However,
a drawback of palladium is its high cost. Hence, great ef-
forts are being made to develop new efficient catalysts
based on more available non-noble metals. Nickel is con-
sidered as a promising alternative for palladium in many
reactions of organic synthesis.1,9—11 Ligands have a sig-
nificant effect on the efficiency of nickel catalysts.1,4,10,11
For instance, nickel complexes with N-heterocyclic carb-
enes (NHC) are becoming increasingly popular in the
catalysis of many cross-coupling reactions,1,9,10,12 includ-
ing the Suzuki—Miyaura reaction commonly employed
for the carbon—carbon bond formation.13—17 Advantages
of NHCs over many other ligands, for example, phos-
phines, are the relative ease of the preparation, lower
toxicity, high variability of the steric and electronic pa-
rameters, and considerable stability of the Ni—NHC bond
due to high σ-donor ability of these ligands.18—21 Readily
available and air-stable complexes LNi(Cp)X (Cp is the
cyclopentadienyl anion, X is halogen, L is a NHC li-
gand),17,22—27 produced in one step from the azolium salts
NHC•HX (NHC proligands) and nickelocene [Ni(Cp)2],14 are
widely used in the catalysis of the Suzuki—Miyaura reaction.
Special electron-donating or -withdrawing groups,
which are either ionizable or charge-bearing, are often
introduced into NHC ligands in order to change the elec-
tronic and steric parameters, polarity, solubility, and other
properties of the complexes, in particular their catalytic
activity.28 For example, the introduction of alkylamino
and dialkylamino groups as substituents at the 4 and 5
positions of the imidazole ring makes it possible to increase
the activity of Pd complexes with NHC ligands in the
Buchwald—Hartwig reaction due to the electron-donating
effect of alkylamino groups and the so-called buttressing
effect of N-aryl substituents.29—33 Palladium complexes
with 3-arylamino-substituted NHC ligands of the 1,2,4-tri-
azole series exhibit high activity in the Suzuki—Miyaura
reaction.34 It is assumed that the electron-donating and
buttressing effects of a substituted amino group accelerate
the oxidative addition of aryl halide and the subsequent
reductive elimination of the cross-coupling product.29—33
However, the effect of the alkylamino group, which is
capable of conjugation with the aromatic system of the
NHC ligand, on the catalytic activity of nickel complexes
has not been investigated, and Ni complexes with 3(4)-al-
kylamino-substituted NHC ligands of the 1,2,4-triazole
and imidazole series are not described in the literature.
Herein, we report the synthesis of new complexes
LNi(Cp)X with 3(4)-alkylamino-substituted NHC ligands
of the 1,2,4-triazole and imidazole series and the investi-
gation of the effect of the alkylamino group on the catalytic
activity of the complexes in the Suzuki—Miyaura reaction.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1281—1289, July, 2021.
1066-5285/21/7007-1281 © 2021 Springer Science+Business Media LLC

Chesnokov et al.
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Russ. Chem. Bull., Int. Ed., Vol. 70, No. 7, July, 2021
Scheme 2
To evaluate the effect of alkylamino groups on the
catalytic activity, it was reasonable to compare the catalytic
properties of structurally similar complexes, which differ
only by the presence of the corresponding alkylamino
group in the NHC ligand. Therefore, we synthesized
N,N´-dialkyl-1,2,4-triazolium and N,N´-diarylimid-
azolium salts as NHC proligands needed for the synthesis
of the corresponding Ni complexes.
The alkylation of triazoles 1a,b35,36 with iodomethane
afforded NHC proligands of the 1,2,4-triazole series 2a,b,
and the acylation of compound 2b with acetic anhydride
gave compound 2c (Scheme 1).
Scheme 1
2, 3: Ar is 2,4,6-trimethylphenyl (Mes) (2d,e, 3a),
2,6-diisopropylphenyl (DiPP) (2f, 3b);
2, 4, 5: R = H, R´ = But (2d,f, 4a, 5a,b); R—R´ = (CH2)4 (2e, 4b, 5c)
Reagents and conditions: i. DIPEA, DMA, 140 C; ii. (CF3SO2)2O,
CH2Cl2, 2,4,6-trimethylpyridine, –75 C.
a general procedure26,40 (Scheme 3). The synthesis of
complexes 6d—f from triflates 2d—f was accomplished in
the presence of tetraethylammonium chloride as a source
of chloride ions (see Scheme 3).
Scheme 3
Reagents and conditions: i. CH3I, acetonitrile, 80 C, 12 h;
ii. Ac2O, reflux, 2 h.
Com-
pound 2, 6
2, 6
2
6
X
I
R1
R2
Me
Me
R3
H
Y
Imidazolium NHC proligands 2d—f containing alkyl-
and dialkylamino groups at the 4 position of the imidazole
ring were synthesized based on the approach proposed
previously (Scheme 2)37,38 by the alkylation of form-
amidines 3a,b with chloroacetic acid amides 4a,b followed
by the cyclization of alkylation products 5a,b with tri-
fluoromethanesulonic anhydride. The use
Z
N
N
N
CH
CH
CH
CH
CH
a
b
c
d
e
f
But
But
But
I
I
I
ButNH
Ac(But)N
ButNH
C4H8N*
ButNH
H
Me
I
Mes
Mes
DiPP
Mes
DiPP
Mes
Mes
DiPP
Mes
DiPP
CF3SO3
CF3SO3
CF3SO3
Cl
Cl
Cl
Cl
Cl
Cl
g
h
H
Cl
of N,N-diisopropylethylamine (DIPEA)
instead of Et3N as a base made it possible
to significantly reduce the time of synthe-
sis compared to the procedure described
Reagents and conditions: i. THF, 70 C for 2a—c,g,h; ii. [Et4N]Cl,
THF, 70 C for 2d—f.
previously.37,38
Proligands 2g and 2h were synthesized
Ar = Mes (g),
DiPP (h)
by known procedures.39
The synthesized complexes are air-stable red-purple
crystalline compounds. The structures of new complexes
The complexes LNi(Cp)X (6a—h) were prepared by
heating proligands 2a—h with nickelocene in THF using
6a—f were confirmed by H and 13C NMR spectroscopy
1

LNi(Cp)X complexes in Suzuki—Miyaura reaction
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 7, July, 2021
1283
in the plane of the triazole ring; the maximum deviation
(0.209(8) Å) from the mean C(1),N(1),C(2),N(2),N(3)
plane is observed in compound 6b. The Ni(1)—I(1) bond
is nearly perpendicular to the C(1)—Ni(1) bond. The
I(1)—Ni(1)—C(1) bond angle is 92.9(1) in compound
6a, 98.2(2) in compound 6b, and 93.8(2) in compound
6c. The C(1)—Ni(1) bond length (1.890(5), 1.888(5), and
1.882(9) Å in molecules 6a, 6b, and 6c, respectively) only
slightly depends on the nature of the alkylamino group in the
NHC ligand and is quite similar to the typical values
published in the literature (1.860—1.876 Å).41,42 In com-
pound 6b, the alkylamino group adopts a planar configur-
ation (the sum of the bond angles at the N(4) atom is
360) and is nearly coplanar with the triazole ring (the
C(9)—N(4)—C(2)—N(2) torsion angle is 4.6(8), the
deviation of the N(4) atom from the mean plane of the
triazole ring is as small as 0.050(8) Å). This is indicative
of the possible conjugation of the N atom lone pair of the
alkylamino group with the π system of the NHC ligand.
In compound 6c, the N(4) atom of the Ac(But)N group
is significantly flattened (the sum of the bond angles at the
N(4) atom is 359.1). However, unlike the tert-butylamino
group of compound 6b, the Ac(But)N group of molecule
6c is nearly orthogonal to the plane of the triazole ring;
the C(9)—N(4)—C(2)—N(2) torsion angle is 84.8(9).
To evaluate the effect of the alkylamino group of the
NHC ligand on the catalytic activity of Ni/NHC com-
plexes, compounds 6a—f were tested in the catalysis of the
cross-coupling of 4-chloroacetophenone (7a) with phenyl-
boronic acid (8a) in dioxane containing H2O (1 vol.%) in
the presence of KOH as a base (Scheme 4, Table 1). The
conditions for the preliminary evaluation of the catalytic
activity of the complexes were chosen taking into account
that the aqueous dioxane—KOH system proved to be
highly efficient in the Ni/L-catalyzed Suzuki—Miyaura
С(12)
С(10)
С(9)
C(11)
I(1)
Ni(1)
С(4)
С(1)
N(3)
С(2)
С(3)
N(2)
С(7)
С(6)
N(1)
С(8)
С(5)
Fig. 1. X-ray molecular structure of compound 6a.
and elemental analysis. The structures of compounds 6a—c
were also determined by X-ray diffraction (Figs 1—3). The
1H NMR spectra show characteristic signals of substituents
of the NHC ligands and a singlet of the Cp ligand at δH
4.5—5.3. The complexes containing the ButNH substitu-
ent give a singlet of NH at δH 3.5 (6b) or 2.8 (6d,f), which
1
disappears upon deuteration. In the H NMR spectrum
of complex 6c, the signals of the acetyl and N-methyl
groups and the signal of the Cp ligand are split due appar-
ently to hindered rotation of the Ac(But)N group.
According to the X-ray diffraction data, the geometric
parameters of molecules 6a—c are similar to those of the
complexes LNi(Cp)X with NHC ligands of the triazole
series described previously.41,42 The nickel atom is nearly
С(15)
С(16)
С(14)
С(13)
С(1)
I(1)
N(2)
С(12)
Ni(1)
С(4)
N(3)
С(2)
С(3)
С(7)
С(6)
С(10)
N(1)
С(9)
N(4)
С(8)
С(5)
C(11)
Fig. 2. X-ray molecular structure of compound 6b.

Chesnokov et al.
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Russ. Chem. Bull., Int. Ed., Vol. 70, No. 7, July, 2021
С(16)
С(15)
С(13)
С(14)
С(18)
N(3)
O(1)
С(17)
N(2)
С(6)
С(1)
C(11)
С(4)
С(3)
С(2)
N(4)
С(5)
N(1)
Ni(1)
С(9)
С(10)
С(8)
С(12)
С(7)
I(1)
Fig. 3. X-ray molecular structure of compound 6c.
reaction.16 It is worth noting that the complexes contain-
ing the tert-butylamino group (6b) or the N-acetyl-N-tert-
butylamino group (6c) showed lower catalytic activity
(runs 2 and 3) than complex 6a, in which the NHC ligand
at the 3 position is not replaced (run 1). The opposite ef-
fect of the alkylamino group is observed in complexes
6d—h containing the imidazol-2-ylidene NHC ligands
with aryl substituents at the nitrogen atoms of the imid-
azole ring. The introduction of an alkylamino group leads
to a significant increase in the activity of the complexes
with N-mesityl substituents at the nitrogen atoms of the
NHC ligand. For example, the yield of compound 9a in
the reaction catalyzed by complex 6g, which does not
contain an alkylamino group at the 4 position of the im-
idazole ring, is 62% (run 4), whereas the yield in the reac-
tion catalyzed by complexes 6d,e with functionalized NHC
ligands is 90% and 89%, respectively (runs 5 and 6). A com-
parison of the activity of complexes 6h (run 7) and 6f (run 8)
shows that in the case of the bulkier 2,6-diisopropylphenyl
substituents at the nitrogen atoms of the NHC ligand, the
introduction of an alkylamino group (complex 6f) also
leads to a slight increase in the catalytic activity.
The factors responsible for the different effects of the
alkylamino group on the catalytic activity of the complexes
with 1,2,4-triazol-5-ylidene and imidazol-2-ylidene li-
gands are unclear. In our opinion, the opposite effects of
the alkylamino group on the activity of complexes 6b,c
and 6e,f,h can be attributed primarily to the nature of
substituens at the nitrogen N atoms of the NHC ligand
rather than to the structure of the heterocycle. Complexes
6a—c contain aliphatic substituents at the N atoms.
Apparently, steric interactions between the alkylamino
group and N-alkyl substituents in the 1,2,4-triazolylidene
ligands induce destabilizing steric hindrance in the transi-
tion state of the Suzuki—Miyaura reaction. However,
according to the literature data, specific non-covalent
interactions can occur in complexes with N,N´-diaryl-
imidazol-2-ylidene ligands between N-aryl substituents
and aryl groups coordinated to the metal.43,44 These in-
teractions reduce the energy of the transition state.43,44
The alkylamino group can exert the buttressing effect of
N-aryl substituents, thereby enhancing non-covalent in-
teractions in the transition state, which can lead to the
acceleration of the Suzuki—Miyaura reaction.32 The
Scheme 4
Reaction conditions: 7a (0.25 mmol), 8a (0.35 mmol), base (0.35 mmol), catalyst 6a—h, solvent (2 mL), argon, 120 C, 12 h.

LNi(Cp)X complexes in Suzuki—Miyaura reaction
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 7, July, 2021
1285
Table 1. Catalytic activity of complexes 6a—h in the reaction of 4-chloroacetophenone (7a) with phenyl-
boronic acid (8a)
Run
Catalyst
(mol.%)a
Solvent
Base
Cb
(%)
Yield (%)c
9a
10a
11a
d
1
2
3
4
5
6
7
8
6a (1)
6b (1)
6c (1)
6g (1)
6d (1)
6e(1)
6h (1)
6f (1)
6f (3)
6f (0.5)
6f (0.1)
6f (1)
6f (1)
6f (1)
6f (1)
6f (1)
6f (1)
Dioxane + 1% H2O
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
K3PO4
Cs2CO3
NaOBut
KOH
K3PO4
81
77
45
65
91
90
91
93
96
68
34
65
5
79
75
42
62
90
89
89
92
92
68
34
52
5
2
2
3
3
1
1
2
1
3
0
0
8
0
—
d
The same
—
d

—

0
d

—
d

—
d

—
d

—
d
9

—
d
10
11
12
13
14
15
16
17

—
d

—
Dioxane
Dioxane
Dioxane
Dioxane
Toluene
Toluene
0
d
—
d
25
26
44
42
24
25
42
40
—
1
0
2
2
0
d
—
d
—
a The amount of the catalyst (mol.%) relative to aryl halide 7a.
b The conversion of compound 7a.
c GC-MS data.
d Traces.
mechanism of the effect of the alkylamino group on the
catalytic activity of the complexes under study requires an
additional more detailed investigation.
Among the characterized complexes, compound 6f
showed the highest activity (see Table 1, run 8). Since the
variation of the used amounts of the catalyst, solvent, and
base did not lead to an increase in the yield of the target
product 9a (see Table 1, runs 9—17), the conditions
of run 8 were accepted as optimal. Under the opti-
mized conditions, the coupling of aryl chlorides 7a—f
Table 2. Yields of biaryls 9a—n in the reaction of aryl halides 7a—f and 3-chloropyridine 7g with
arylboronic acids 8a—c catalyzed by complex 6fa
Run
7
8
C
b (%)
Product
X
R
R´
Yield of 9 (%)c
1
2
3
4
5
6
7
8
7a
7b
7c
7d
7e
7f
7g
7a
7b
7e
7f
8a
8a
8a
8a
8a
8a
8a
8b
8b
8b
8b
8b
8c
8c
8c
92
93
63
59
92
99
90
63
55
65
66
85
73
65
60
9a
9b
9c
9d
9e
9f
9g
9h
9f
9i
9j
9k
9l
9m
9n
CH
CH
CH
CH
CH
CH
N
CH
CH
CH
CH
N
COMe
H
H
H
92
92
61
56
86
98
87
61
52
63
65
83
71
64
58
Me
H
OMe
CN
CF3
H
COMe
H
CN
CF3
H
COMe
CN
H
H
H
H
H
CF3
CF3
CF3
CF3
CF3
OMe
OMe
OMe
9
10
11
12
13
14
15
7g
7a
7e
7g
CH
CH
N
a Reaction conditions: halide 7a—g (0.25 mmol), arylboronic acid 8a—c (0.35 mmol), KOH (0.35 mmol),
complex 6f (1.5 mg, 2.5 μmol, 1 mol.%), aqueous dioxane (1 vol.% H2O, 2 mL), 120 C, 12 h.
b The conversion of aryl halide 7a—g.
c GC-MS data.

Chesnokov et al.
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Russ. Chem. Bull., Int. Ed., Vol. 70, No. 7, July, 2021
a closed tube (high pressure!) for 16 h. Then the solvent was
distilled off in vacuo, and the residue was recrystallized from
acetone, washed on a filter with Et2O, and dried in vacuo.
1-tert-Butyl-4-methyl-1H-1,2,4-triazolium iodide (2a). The
yield was 0.18 g (67%), colorless crystals, m.p. 196—198 C
(acetone). High-resolution MS: found m/z 140.1186 [M – I]+;
and 3-chloropyridine 7g with arylboronic acids 8a—c af-
forded biaryls 9a—n in 52—98% yields (Scheme 5, Table 2).
Therefore, complex 6f can serve as a new catalyst for the
Suzuki—Miyaura reaction involving aryl chlorides.
calculated for C7H14N3 140.1182. 1H NMR (DMSO-d6), δ:
+
Scheme 5
1.60 (s, 9 H, But); 3.88 (s, 3 H, Me); 9.15 (s, 1 H, CaromH); 10.19
(s, 1 H, CaromH). 13C{1H} NMR (DMSO-d6), δ: 28.0, 33.9, 62.5,
141.4, 145.1. Found (%): C, 31.54; H, 5.31; N, 15.66. C7H14N3I.
Calculated (%): C, 31.48; H, 5.28; N, 15.73.
1-tert-Butyl-3-(tert-butylamino)-4-methyl-1H-1,2,4-triazol-
ium iodide (2b). The yield was 0.25 g (74%), colorless crystals,
m.p. 174—176 C (EtOAc). High-resolution MS: found m/z
211.1913 [M – I]+; calculated for C11H23N4+ 211.1917. 1H NMR
(CDCl3), δ: 1.48 (s, 9 H, But); 1.65 (s, 9 H, But); 4.04 (s, 3 H,
Me); 5.70 (s, 1 H, NH); 10.25 (s, 1 H, CaromH). 13C{1H} NMR
(CDCl3), δ: 28.5, 28.7, 33.7, 53.8, 62.4, 136.6, 153.0. Found (%):
C, 39.16; H, 6.74; N, 16.51. C11H23IN4. Calculated (%):
C, 39.06; H, 6.85; N, 16.56.
Reagents and conditions: 6f (1 mol.%), KOH, aqueous dioxane
(1 vol.% H2O), 120 C, 12 h.
1-tert-Butyl-3-[tert-butyl(acetyl)amino]-4-methyl-1H-1,2,4-
triazolium iodide (2c). A solution of salt 2b (0.34 g, 1 mmol) and
Ac2O (0.15 g, 1.5 mmol) in MeCN (3 mL) was refluxed for 2 h.
Then the solvent was distilled off, and the residue was recrystal-
lized from water and dried in vacuo. The yield was 0.32 g (84%),
colorless crystals, m.p. 190—192 C (EtOAc). High-resolution
MS: found m/z 253.2019 [M – I]+; calculated for C13H25N4O+
253.2023. 1H NMR (DMSO-d6), δ: 1.35 (s, 9 H, But); 1.62
(s, 9 H, But); 1.78 (s, 3 H, Ac); 3.80 (s, 3 H, N—Me); 10.33
(s, 1 H, CaromH). 13C{1H} NMR (DMSO-d6), δ: 24.4, 27.5, 27.7,
32.7, 60.7, 63.3, 143.6, 50.1, 169.6. Found (%): C, 41.14; H, 6.64;
N, 14.85. C13H25N4OI. Calculated (%): C, 41.06; H, 6.63;
N, 14.73.
Synthesis of 4-aminoimidazolium triflates 2d—f (general
procedure). A mixture of N,N´-diarylformamidine 3a,b52
(0.5 mmol), chloroacetamide 4a,b (0.6 mmol), DIPEA (97 mg,
0.75 mmol), and KI (5 mg, 0.03 mmol) in DMA (2 mL) was
stirred in a tightly closed tube at 140 C for 2 h. Then the solution
was cooled and poured with stirring onto crushed ice (100 g).
The amorphous precipitate that formed was filtered off, thor-
oughly washed with water, and dried to constant weight in vacuo
at 40 C. Amides 5a,b38 prepared by this procedure were used in
the next step of the synthesis without additional purification.
A solution of compound 5a,b (0.5 mmol) and 2,4,6-trimethyl-
pyridine (91 mg, 0.75 mmol) in dry CH2Cl2 (4 mL) was cooled
to –75 C, and trifluoromethanesulfonic anhydride [(CF3SO2)2O]
(155 mg, 0.55 mmol) was added with stirring. The reaction
mixture was stirred at –75 C for 1 h and then at room tem-
perature for 2 h. A saturated aqueous NaHCO3 solution (5 mL)
was added, and the mixture was stirred at room temperature for
30 min. The organic layer was separated, washed with a NaHCO3
solution and water, and dried over Na2SO4. The solvent was
distilled off in vacuo, and the residue was treated with diethyl
ether (10 mL). The crystalline precipitate that formed was filtered
off, washed with diethyl ether, recrystallized from EtOH, and
dried in vacuo at 80 C.
In summary, we developed methods for the synthesis
of new (NHC)Ni(Cp)X complexes with NHC ligands
containing alkylamino and N-acetyl-N-alkylamino groups
at the 3 or 4 position of the NHC ligand. The introduction
of an alkylamino group into the NHC ligand was found
to increase the catalytic activity of the complexes with
N,N´-diaryl-substituted NHC ligands of the imidazole
series and decrease the activity of the complexes with
N,N´-dialkyl-substituted NHC ligands of the 1,2,4-tri-
azole series in the Suzuki—Miyaura reaction. Synthesized
complex 6f was proposed as a new efficient catalyst for the
cross-coupling of aryl halides with arylboronic acids.
Experimental
The 1H and 13C{1H} NMR spectra were recorded on a Bruker
AV-300 spectrometer (300 and 75 MHz, respectively) using
residual signals of the solvent as the internal standard. High-
resolution electrospray ionization (ESI) mass spectra were ob-
tained on a Bruker maXis Q-TOF mass spectrometer. Elemental
analysis was performed on a Perkin Elmer 2400 analyzer. Gas
chromatography mass spectrometry (GC-MS) was carried out
on an Agilent 7890A chromatograph equipped with an Agilent
5975C mass-selective detector (EI, 70 eV) and an HP-5MS
capillary column (30 m×0.25 mm×0.25 μm). The cross-coupling
products were identified by comparing their mass spectra with
those of the reference samples and the NIST mass spectral library.
The melting points were determined in sealed capillary tubes on
a PTP-1 instrument. Triazoles 1a,b,35 salts 2d,e,39 complexes
6g,h,40,45 N-(tert-butyl)chloroacetamide (4a),46 2-chloro-1-
(pyrrolidin-1-yl)ethanone (4b),47 and authentic samples of
cross-coupling products 9a—n48—51 were prepared according to
procedures described in the literature. Other reagents were com-
mercially available.
4-tert-Butylamino-1,3-bis(2,4,6-trimethylphenyl)-1H-imid-
azolium triflate (2d). The yield was 124 mg (47%), colorless
powder, m.p. 157—159 C (EtOH). High-resolution MS: found
1-tert-Butyl-4-methyl-1H-1,2,4-triazolium iodides (2a,b).
A solution of 1-tert-butyl[1,2,4]triazole (1a) or 1-tert-butyl-3-
(tert-butylamino)[1,2,4]triazole (1b) (1 mmol) and MeI (0.21 g,
1.5 mmol) in MeCN (3 mL) was heated with stirring at 80 C in
m/z 376.2745 [M – CF3SO3–]+; calculated for C25H34N3
+
376.2747. 1H NMR (DMSO-d6), δ: 1.23 (s, 9 H, But); 2.09

LNi(Cp)X complexes in Suzuki—Miyaura reaction
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 7, July, 2021
1287
(s, 6 H, Me); 2.16 (s, 6 H, Me); 2.34 (s, 3 H, Me); 2.35 (s, 3 H,
Me); 5.06 (s, 1 H, NH); 7.18 (s, 2 H, Ar); 7.19 (s, 2 H, Ar); 7.46
(d, 1 H, Ar, J = 1.8 Hz); 9.10 (d, 1 H, Ar, J = 1.8 Hz). 13C{1H}
NMR (DMSO-d6), δ: 16.8, 17.2, 20.65, 20.74, 27.9, 51.3, 103.6,
127.6, 129.3, 129.5, 131.6, 131.8, 134.3, 135.7, 138.3, 140.3,
140.6, the signal of CF3 is at the background level. Found (%):
C, 59.51; H, 6.60; N, 8.04. C26H34N3F3SO3. Calculated (%):
C, 59.41; H, 6.52; N, 7.99.
H, 6.01; N, 12.05. C16H27N4INi. Calculated (%): C, 41.69;
H, 5.90; N, 12.15.
{1-tert-Butyl-5-[N-acetyl-N-tert-butylamino]-4-methyl-1H-
1,2,4-triazol-3-ylidene}(η5-cyclopentadienyl)(iodo)nickel (6c).
The yield was 168 mg (67%), dark-purple needles, t.decomp.
>150 C (CH2Cl2—hexane, 1 : 5). 1H NMR (CDCl3), δ: 1.35
(br.s, 9 H, But); 1.65 and 1.68 (both s, total 3 H, Ac); 1.99 (s, 9 H,
But); 4.26 and 4.27 (both s, total 3 H, N—Me); 5.32 and 5.33
(both s, total 5 H, C5H5). 13C{1H} NMR (CDCl3), δ: 24.3; 24.6;
28.2; 28.3; 31.1; 36.2; 36.4; 60.4; 60.9; 62.8; 93.6; 151.0; 151.1;
169.8; 170.5; 170.7. Found (%): C, 43.07; H, 5.84; N, 11.05.
C18H29N4INiO. Calculated (%): C, 42.98; H, 5.81; N, 11.14.
[4-tert-Butylamino -1,3-bis(2,4,6-trimethylphenyl)imidazol-
2-ylidene](η5-cyclopentadienyl)(chloro)nickel (6d). The yield was
166 mg (62%). Lilac powder, t.decomp. >150 C (toluene).
1H NMR (CDCl3), δ: 1.15 (s, 9 H, But); 2.16 (s, 6 H, Me); 2.22
(s, 6 H, Me); 2.42 (s, 3 H, Me); 2.44 (s, 3 H, Me); 2.80 (s, 1 H,
NH); 4.50 (s, 5 H, C5H5); 6.31 (s, 1 H, Ar); 7.09 (s, 2 H, Ar);
7.13 (s, 2 H, Ar). 13C{1H} NMR (CDCl3), δ: 18.5; 18.6; 21.4;
21.5; 29.0; 51.6; 92.1; 104.5; 129.2; 129.7; 132.3; 136.2; 137.4;
137.5; 138.8; 139.7; 156.8; 164.9. Found (%): C, 67.44; H, 7.19;
N, 7.81. C30H38N3ClNi. Calculated (%): C, 67.38; H, 7.16; N, 7.86.
[4-(Pyrrolidin-1-yl)-1,3-bis(2,4,6-trimethylphenyl)imidazol-
2-ylidene](chloro)(η5-cyclopentadienyl)nickel (6e). The yield was
224 mg (84%), dark-red crystals, t.decomp. >150 C (CH2Cl2—
hexane, 1 : 5). 1H NMR (CDCl3), δ: 1.71—1.79 (m, 4 H, 2 CH2);
2.18 (s, 6 H, Me); 2.23 (s, 6 H, Me); 2.41 (s, 3 H, Me); 2.43
(s, 3 H, Me); 2.66—2.77 (m, 4 H, 2 CH2); 4.48 (s, 5 H, C5H5);
6.30 (s, 1 H, Ar); 7.08 (s, 2 H, Ar); 7.09 (s, 2 H, Ar). 13C{1H}
NMR (CDCl3), δ: 18.6; 19.0; 21.4; 21.5; 24.8; 50.4; 92.2; 106.8;
129.2; 129.3; 135.7; 136.2; 137.1; 137.4; 138.8; 139.0; 145.6;
160.7. Found (%): C, 67.57; H, 6.83; N, 7.78. C30H36N3ClNi.
Calculated (%): C, 67.63; H, 6.81; N, 7.89.
[4-tert-Butylamino-1,3-bis(2,6-diisopropylphenyl)imidazol-
2-ylidene](chloro)(η5-cyclopentadienyl)nickel (6f). The yield was
167 mg (54%), red powder, t.decomp. >175 C (CH2Cl2—hex-
ane). 1H NMR (CDCl3), δ: 1.00—1.23 (m, 21 H, 4 CH3 + But);
1.38—1.45 (m, 12 H, 4 CH3); 2.80 (s, 1 H, NH); 2.84—3.07
(m, 4 H, 4 CHMe2); 4.46 (s, 5 H, C5H5); 6.30 (s, 1 H, Ar);
7.38 (d, 2 H, Ar, J = 7.7 Hz); 7.45 (d, 2 H, Ar, J = 7.7 Hz);
7.51 (t, 1 H, Ar, J = 7.7 Hz); 7.61 (t, 1 H, Ar, J = 7.8 Hz).
13C{1H} NMR (CDCl3), δ: 22.8; 23.8; 25.4; 26.3; 28.3;
28.5; 28.8; 51.1; 92.1; 105.7; 124.0; 124.8; 129.8; 130.8; 132.5;
137.6; 139.5; 146.5; 148.3; 159.3. Found (%): C, 70.02; H, 8.19;
N, 6.73. C36H50N3ClNi. Calculated (%): C, 69.86; H, 8.14;
N, 6.79.
4-(Pyrrolidin-1-yl)-1,3-bis(2,4,6-trimethylphenyl)-1H-imid-
azolium triflate (2e). The yield was 84 mg (32%), colorless pow-
der, m.p. 142—145 C (EtOH). High-resolution MS: found m/z
374.2590 [M – CF3SO3]+; calculated for C25H32N3+ 374.2591.
1H NMR (DMSO-d6), δ: 1.78 (m, 4 H, CH2); 2.16 (s, 6 H, Me);
2.17 (s, 6 H, Me); 2.34 (s, 3 H, Me); 2.35 (s, 3 H, Me); 2.85
(m, 4 H, CH2); 7.18 (s, 2 H, Ar); 7.19 (s, 2 H, Ar); 7.36 (d, 1 H,
Ar, J = 2.0 Hz); 9.15 (d, 1 H, Ar, J = 2.0 Hz). 13C{1H} NMR
(DMSO-d6), δ: 16.7; 17.1; 20.6; 20.7; 24.6; 49.6; 103.9; 120.7
(q, CF3, J = 322.7 Hz); 129.3; 129.4; 129.6; 131.4; 132.8; 134.2;
135.3; 140.3; 140.8; 142.4. Found (%): C, 59.68; H, 6.20; N, 8.09.
C26H32F3N3O3S. Calculated (%): C, 59.64; H, 6.16; N, 8.03.
4-tert-Butylamino-1,3-bis(2,6-diisopropylphenyl)-1H-imid-
azolium triflate (2f). The yield was 204 mg (67%), colorless
powder, t.decomp. 245—250 C (EtOH). High-resolution MS:
found m/z 460.3689 [M – CF3SO3]+; calculated for C31H46N3
+
460.3686. 1H NMR (DMSO-d6), δ: 1.13 (d, 6 H, CHMe2,
J = 6.8 Hz); 1.18 (d, 6 H, CHMe2, J = 6.8 Hz); 1.25 (s, 9 H, But);
1.29 (d, 6 H, CHMe2, J = 6.8 Hz); 1.31 (d, 6 H, CHMe2,
J = 6.9 Hz); 2.38—2.47 (m, 2 H, CHMe2); 2.38—2.47 (m, 2 H,
CHMe2, overlaps with the signal of DMSO); 5.18 (s, 1 H, NH);
7.47—7.54 (m, 4 H, Ar); 7.61—7.70 (m, 3 H, Ar); 9.50 (d, 1 H,
Ar, J = 1.9 Hz). 13C{1H) NMR (DMSO-d6), δ: 22.5; 23.4; 24.16;
24.24; 27.8; 28.6; 28.8; 51.5; 103.6; 120.7 (q, CF3, J = 322.4 Hz);
124.4; 124.9; 126.5; 130.8; 131.4; 131.9; 132.3; 139.1; 144.9;
146.0. Found (%): C, 63.11; H, 7.62; N, 6.83. C32H46F3N3O3S.
Calculated (%): C, 63.03; H, 7.60; N, 6.
Synthesis of complexes 6a—h (general procedure). The reac-
tion was performed under an argon atmosphere. A solution of
salt 1a—f (0.5 mmol) and nickelocene (104 mg, 0.55 mmol) in
anhydrous THF (15 mL) was heated at 70 C with stirring for
20 h (in the synthesis of compounds 6e,f,h, [Et4N]Cl (166 mg,
1 mmol) was added to the reaction mixture). Then the reaction
mixture was filtered, without cooling, through a thin layer of
celite, and the solvent was distilled off in vacuo. The product was
isolated by silica gel column chromatography (CH2Cl2 as the
eluent) and additionally purified by recrystallization from an
appropriate solvent.
(1-tert-Butyl-4-methyl-1H-1,2,4-triazol-3-ylidene)(iodo)-
(η5-cyclopentadienyl)nickel (6a). The yield was 107 mg (55%),
purple needles, t.decomp. >150 C (CH2Cl2—hexane, 1 : 5).
1H NMR (CDCl3), δ: 2.00 (s, 9 H, But); 4.40 (s, 3 H, Me); 5.31
(s, 5 H, C5H5); 7.97 (s, 1 H, Ar). 13C{1H} NMR (CDCl3), δ:
31.3; 37.8; 62.3; 93.6; 142.7; 166.6. Found (%): C, 37.16; H, 4.60;
N, 10.61. C12H18N3INi. Calculated (%): C, 36.97; H, 4.65;
N, 10.78.
[1-tert-Butyl-5-(tert-butylamino)-4-methyl-1H-1,2,4-tri-
azol-3-ylidene](iodo)(η5-cyclopentadienyl)nickel (6b). The yield
was 99 mg (43%), dark-purple needles, t.decomp. >150 C
(CH2Cl2—hexane, 1 : 5). 1H NMR (CDCl3), δ: 1.36 (s, 9 H,
But); 1.95 (s, 9 H, But); 3.51 (s, 1 H, NH); 4.18 (s, 3 H, N—Me);
5.28 (s, 5 H, C5H5). 13C{1H} NMR (CDCl3), δ: 28.8; 31.2;
34.8; 52.6; 60.8; 93.4; 151.9; 159.4. Found (%): C, 41.72;
Evaluation of catalytic activity of compounds 6a—h in the
Suzuki—Miyaura reaction (general procedure). The reaction was
performed under an argon atmosphere in a 7-mL glass tube
equipped with a magnetic stirrer bar and a screw cap. A solution
of the catalyst (7.5 μmol, 1 mol.%) in the appropriate solvent
(1.5 mL) (see Tables 1 and 2) was added to a solution of the ap-
propriate base (0.35 mmol), aryl halide 7a—g (0.25 mmol), and
arylboronic acid 8a—c (0.35 mmol) in the corresponding solvent
(0.5 mL). The tube was sealed and heated to the specified tem-
perature with stirring during a required time (see Tables 1 and 2).
Then the mixture was cooled to room temperature, and a solution
of naphthalene (16 mg, 0.125 mmol) in acetonitrile (2 mL) was
added as the internal standard. An aliquot (2 μL) of the resulting
mixture was dissolved in acetonitrile (1 mL) and analyzed by
GC-MS (see Tables 1 and 2).

Chesnokov et al.
1288
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 7, July, 2021
Table 3. Crystallographic data and the structure refinement parameters for compounds 6a—c
Parameter
6a
6b
6c
Molecular formula
C
12H18IN3Ni
389.90
C16H27IN4Ni
461.02
Monoclinic
C2/c
36.1170(14)
10.9892(4)
10.1206(4)
90
C18H29IN4NiO
503.06
Monoclinic
P21
11.8453(6)
8.0500(4)
12.5201(7)
90
М/g
Crystal system
Monoclinic
P21/n
7.0225(2)
17.1910(8)
12.4220(3)
90
Space group
a/Å
b/Å
c/Å
α/deg
/deg
97.985(2)
90
90.010(8)
90
112.993(4)
90
1099.00(10)
γ/deg
V/Å3
1485.09(10)
8
4016.8(3)
2
Z 4
dcalc/g cm–3
F(000)
1.744
768
3.37
0.092
28.3
2.0
1.525
1.520
508
2.3
0.101
28.2
1.8
1856
/mm–1
2.51
Rint
max/deg
min/deg
0.118
28.3
1.9
Number of reflections
measured
39352
3613
26169
4776
16155
5068
2756
235
0.043
0.069
unique
with I > 2(I)
Number of refined parameters
R1
2178
2139
159
206
0.045
0.054
wR2 (I > 2(I))
S 0.89
0.105
0.130
0.87
0.81
Residual electron density
0.74/−1.28
0.53/−1.01
0.58/−0.95
(max/min)/e Å–3
X-ray diffraction study. Single crystals of complexes 6a—c
were obtained by the crystallization from dichloromethane in
hexane vapor. The unit cell parameters were measured on
a StadiVari Pilatus 100K diffractometer using Cu-Kα radiation
from a GeniX3D generator equipped with a microfocus X-ray
tube and a FOX3D HF Xenocs multilayer thin-film ellipsoidal
monochromator. The X-ray diffraction data were collected, the
unit cell parameters were determined and refined, and the dif-
fraction data were processed using the STOE X-Area software
package (STOE & Cie GmbH, Darmstadt, Germany, 2013). The
intensities of reflections were scaled with the LANA module of
the X-Area software suite to minimize the differences in the
intensities of symmetry-equivalent reflections (multi-scan meth-
od). The crystal structures were solved by direct methods using
the SHELXS-97 program package.53,54 The positional and ther-
mal parameters of nonhydrogen atoms were refined by the full-
matrix method with anisotropic displacement parameters. The
hydrogen atoms were positioned geometrically and refined using
a riding model with fixed isotropic displacement parameters
(Uiso(H) = 1.2Ueq(C)).
helpful advice. We thank the staff of the Center for
Collective Use "Nanotechnology" of the Platov South-
Russian State Polytechnic University (NPI) and the Center for
Collective Use of the Zelinsky Institute of Organic Chem-
istry, Russian Academy of Sciences, for performing anal-
ytical experiments. X-ray diffraction studies of complexes
6a—c were performed using equipment granted by the Lomo-
nosov Moscow State University Program of Development.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 19-03-01053).
This paper does not contain descriptions of studies on
animals or humans.
The authors declare no competing interests.
References
1. N. Hazari, P. R. Melvin, M. M. Beromi, Nature Rev. Chem.,
2017, 1, 0025; DOI: 10.1038/s41570-017-0025.
2. R. Takise, K. Muto, J. Yamaguchi, Chem. Soc. Rev., 2017, 46,
5864; 10.1039/C7CS00182G.
3. A. Biffis, P. Centomo, A. Del Zotto, M. Zecca, Chem. Rev.,
2018, 118, 2249; DOI: 10.1021/acs.chemrev.7b00443.
4. D. Balcells, A. Nova, ACS Catal., 2018, 8, 3499; DOI: 10.1021/
acscatal.8b00230.
Tables of atomic coordinates, bond lengths, bond angles,
torsion angles, and anisotropic displacement parameters for all
the compounds were deposited with the Cambridge Crystallo-
graphic Data Centre (CCDC 2041135 (6a), 2041141 (6b),
2041132 (6c)), and are available at www.ccdc.cam.ac.uk.
We are grateful to Academician of the Russian Academy
of Sciences V. P. Ananikov for valuable discussion and
5. R. I. Khusnutdinov, N. A. Shchadneva, Russ. Chem. Rev.,
2019, 88, 800; DOI: 10.1070/RCR4881.

LNi(Cp)X complexes in Suzuki—Miyaura reaction
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 7, July, 2021
1289
6. D. S. Kopchuk, O. S. Taniya, A. F. Khasanov, A. P. Krino-
chkin, I. S. Kovalev, T. A. Pospelova, G. V. Zyryanov, V. L.
Rusinov, O. N. Chupakhin, Chem. Heterocycl. Compd.
(Engl. Transl.), 2019, 55, 490; DOI: 10.1007/s10593-019-02487-5.
7. P. S. Gribanov, G. A. Chesnokov, P. B. Dzhevakov, N. Y.
Kirilenko, S. A. Rzhevskiy, A. A. Ageshina, M. A. Topchiy,
M. V. Bermeshev, A. F. Asachenko, M. S. Nechaev, Mendeleev
Commun., 2019, 29, 147; DOI: 10.1016/j.mencom.2019.03.009.
8. E. S. Matyugina, A. L. Khandazhinskaya, S. N. Kochetkov,
K. L. Seley-Radtke, Mendeleev Commun., 2020, 30, 231; DOI:
10.1016/j.mencom.2020.03.034.
32. Y. Zhang, G. Lavigne, N. Lugan, V. César, Chem. Eur. J.,
2017, 23, 13792; DOI: 10.1002/chem.201702859.
33. N. Fukaya, T. Mizusaki, K. Hatakeyama, Y. Seo, Y. Inaba,
K. Matsumoto, V. Y. Lee, Y. Takagi, J. Kuwabara, T. Kanbara,
Y.-K. Choe, J.-C. Choi, Organometallics, 2019, 38, 375; DOI:
10.1021/acs.organomet.8b00757.
34. M. Sevim, S. B. Kavukcu, A. Kınal, O. Şahin, H. Türkmen,
Dalton Trans., 2020, DOI: 10.1039/D0DT02937H.
35. S. V. Voitekhovich, A. S. Lyakhov, L. S. Ivashkevich, V. E.
Matulis, Y. V. Grigoriev, P. N. Gaponik, O. A. Ivashkevich,
Tetrahedron, 2012, 68, 4962; DOI: 10.1016/j.tet.2012.04.063.
36. A. V. Astakhov, O. V. Khazipov, A. Y. Chernenko, D. V.
Pasyukov, A. S. Kashin, E. G. Gordeev, V. N. Khrustalev, V.
M. Chernyshev, V. P. Ananikov, Organometallics, 2017, 36,
1981; DOI: 10.1021/acs.organomet.7b00184.
9. S. Z. Tasker, E. A. Standley, T. F. Jamison, Nature, 2014,
509, 299; DOI: 10.1038/nature13274.
10. V. P. Ananikov, ACS Catal., 2015, 5, 1964; DOI: 10.1021/
acscatal.5b00072.
11. Z. N. Gafurov, A. A. Kagilev, A. O. Kantyukov, A. A.
Balabaev, O. G. Sinyashin, D. G. Yakhvarov, Russ. Chem.
Bull., 2018, 67, 385; DOI: 10.1007/s11172-018-2086-7.
12. A. V. Astakhov, O. V. Khazipov, E. S. Degtyareva, V. N.
Khrustalev, V. M. Chernyshev, V. P. Ananikov, Organometallics,
2015, 34, 5759; DOI: 10.1021/acs.organomet.5b00856.
13. F.-S. Han, Chem. Soc. Rev., 2013, 42, 5270; DOI: 10.1039/
C3CS35521G.
14. Ł. Banach, P. A. Guńka, J. Zachara, W. Buchowicz, Coord.
Chem. Rev., 2019, 389, 19; DOI: 10.1016/j.ccr.2019.03.006.
15. I. P. Beletskaya, F. Alonso, V. Tyurin, Coord. Chem. Rev.,
2019, 385, 137; DOI: 10.1016/j.ccr.2019.01.012.
37. V. César, J.-C. Tourneux, N. Vujkovic, R. Brousses, N. Lugan,
G. Lavigne, Chem. Commun., 2012, 48, 2349; 10.1039/
C2CC17870B.
38. A. A. Danopoulos, P. Braunstein, Chem. Commun., 2014, 50,
3055; DOI: 10.1039/c3cc49517e.
39. M. Hans, J. Lorkowski, A. Demonceau, L. Delaude, Beilstein
J. Org. Chem., 2015, 11, 2318; DOI: 10.3762/bjoc.11.252.
40. C. D. Abernethy, A. H. Cowley, R. A. Jones, J. Organomet.
Chem., 2000, 596, 3; DOI: 10.1016/S0022-328X(99)00557-4.
41. O. R. Luca, B. A. Thompson, M. K. Takase, R. H. Crabtree,
J. Organomet. Chem., 2013, 730, 79; DOI: 10.1016/
j.jorganchem.2012.10.038.
16. S. B. Soliev, A. V. Astakhov, D. V. Pasyukov, V. M. Chernyshev,
Russ. Chem. Bull., 2020, 69, 683; DOI: 10.1007/s11172-020-2818-3.
17. J. Buchspies, M. M. Rahman, M. Szostak, Catalysts, 2020,
10, 372; DOI: 10.3390/catal10040372.
18. M. N. Hopkinson, C. Richter, M. Schedler, F. Glorius,
Nature, 2014, 510, 485; DOI: 10.1038/nature13384.
19. H. V. Huynh, Chem. Rev., 2018, 118, 9457; DOI: 10.1021/
acs.chemrev.8b00067.
42. L. P. Bheeter, D. Wei, V. Dorcet, T. Roisnel, P. Ghosh, J.-B.
Sortais, C. Darcel, Eur. J. Inorg. Chem., 2015, 2015, 5226;
DOI: 10.1002/ejic.201500852.
43. T. Szilvási, T. Veszprémi, ACS Catal., 2013, 3, 1984; DOI:
10.1021/cs400429j.
44. N. I. Saper, A. Ohgi, D. W. Small, K. Semba, Y. Nakao,
J. F. Hartwig, Nature Chem., 2020, 12, 276; DOI: 10.1038/
s41557-019-0409-4.
20. A. V. Astakhov, S. B. Soliev, E. G. Gordeev, V. M. Chernyshev,
V. P. Ananikov, Dalton Trans., 2019, 48, 17052, DOI:; 10.1039/
c9dt03266e.
21. V. M. Chernyshev, E. A. Denisova, D. B. Eremin, V. P. Anani-
kov, Chem. Sci., 2020, 11, 6957; DOI: 10.1039/D0SC02629H.
22. V. Ritleng, A. M. Oertel, M. J. Chetcuti, Dalton Trans., 2010,
39, 8153; DOI: 10.1039/C0DT00021C.
45. R. A. Kelly, N. M. Scott, S. Díez-González, E. D. Stevens,
S. P. Nolan, Organometallics, 2005, 24, 3442; DOI: 10.1021/
om0501879.
46. J. A. Lowe, D. L. Hageman, S. E. Drozda, S. McLean,
D. K. Bryce, R. T. Crawford, S. Zorn, J. Morrone, J. Bordner,
J. Med. Chem., 1994, 37, 3789; DOI: 10.1021/jm00048a015.
47. H. Seguin, D. Gardette, M.-F. Moreau, J.-C. Madelmont,
J.-C. Gramain, Synth. Commun., 1998, 28, 4257; DOI:
10.1080/00397919809458707.
23. A. M. Oertel, V. Ritleng, M. J. Chetcuti, Organometallics,
2012, 31, 2829; DOI: 10.1021/om201101g.
24. Y. Wei, A. Petronilho, H. Mueller-Bunz, M. Albrecht,
Organometallics, 2014, 33, 5834; DOI: 10.1021/om500593s.
25. J. Yau, K. E. Hunt, L. McDougall, A. R. Kennedy, D. J.
Nelson, Beilstein J. Org. Chem., 2015, 11, 2171; DOI: 10.3762/
bjoc.11.235.
26. F. P. Malan, E. Singleton, P. H. van Rooyen, M. Landman,
J. Organomet. Chem., 2016, 813, 7; DOI: 10.1016/j.jor-
ganchem.2016.03.017.
27. S. Ando, H. Matsunaga, T. Ishizuka, J. Org. Chem., 2017, 82,
1266; DOI: 10.1021/acs.joc.6b02666.
28. E. Peris, Chem. Rev., 2018, 118, 9988; DOI: 10.1021/acs.
chemrev.6b00695.
29. Y. Zhang, V. César, G. Storch, N. Lugan, G. Lavigne, Angew.
Chem., Int. Ed., 2014, 53, 6482; DOI: 10.1002/anie.201402301.
30. Y. Zhang, V. César, G. Lavigne, Eur. J. Org. Chem., 2015,
2015, 2042; DOI: 10.1002/ejoc.201500030.
31. Y. Zhang, G. Lavigne, V. César, J. Org. Chem., 2015, 80,
7666; DOI: 10.1021/acs.joc.5b01272.
48. L.-Y. Xu, C.-Y. Liu, S.-Y. Liu, Z.-G. Ren, D. J. Young,
J.-P. Lang, Tetrahedron, 2017, 73, 3125; DOI: 10.1016/j.tet.
2017.04.034.
49. L. Liu, Y. Zhang, B. Xin, J. Org. Chem., 2006, 71, 3994; DOI:
10.1021/jo060122v.
50. B. Xin, J. Chem. Res., 2008, 2008, 412; DOI: 10.3184/
030823408785702544.
51. M.-X. Li, Y.-L. Tang, H. Gao, Z.-W. Mao, Tetrahedron Lett.,
2020, 61; DOI: 10.1016/j.tetlet.2020.151784.
52. K. E. Krahulic, G. D. Enright, M. Parvez, R. Roesler, J. Am.
Chem. Soc., 2005, 127, 4142; DOI: 10.1021/ja050129e.
53. G. Sheldrick, Acta Crystallogr., Sect. A., 2008, 64, 112; DOI:
10.1107/S0108767307043930.
54. G. Sheldrick, Acta Crystallogr. Sect. A., 2015, 71, 3; DOI:
10.1107/S2053273314026370.
Received November 30, 2020;
in revised form December 28, 2020;
accepted February 1, 2021