1,2,4-Triazole-Based N-Heterocyclic Carbene Nickel Complexes - Synthesis and Catalytic Application

Article abstract of DOI:10.1002/ejic.201500852

Four nickel complexes bearing 1,2,4-triazole-based N-heterocyclic carbene backbones and a cyclopentadienyl ligand were prepared from the corresponding 1,2,4-triazolium salts and nickelocene in tetrahydrofuran (THF) under reflux. The obtained complexes were fully characterized, including by X-ray diffraction analysis. They were then used as catalysts (5 mol-%) for the borylation of aryl bromide derivatives with bis(pinacolato)diboron in the presence of Cs₂CO₃ as the base in THF at 70 C for 20 h to form the corresponding borylated products in moderate yields. Four new nickel complexes bearing 1,2,4-triazole-based N-heterocyclic carbene backbones and a cyclopentadienyl ligand are prepared, fully characterized, and evaluated in the catalytic borylation of aryl bromides with bis(pinacolato)diboron.

Full text of DOI:10.1002/ejic.201500852

FULL PAPER
DOI:10.1002/ejic.201500852
1
,2,4-Triazole-Based N-Heterocyclic Carbene Nickel
Complexes – Synthesis and Catalytic Application
Linus P. Bheeter,[
a][‡]
Duo Wei,[a][‡] Vincent Dorcet,
[b]
[
b]
[c]
[a]
Thierry Roisnel, Prasenjit Ghosh, Jean-Baptiste Sortais,* and
Christophe Darcel*[
a]
Keywords: Homogenous catalysis / Cross-coupling / Nickel / Carbene ligands / Borylation
Four nickel complexes bearing 1,2,4-triazole-based N-het-
erocyclic carbene backbones and a cyclopentadienyl ligand
were prepared from the corresponding 1,2,4-triazolium salts
and nickelocene in tetrahydrofuran (THF) under reflux. The
obtained complexes were fully characterized, including by
X-ray diffraction analysis. They were then used as catalysts
(5 mol-%) for the borylation of aryl bromide derivatives with
bis(pinacolato)diboron in the presence of Cs CO as the base
2 3
in THF at 70 °C for 20 h to form the corresponding borylated
products in moderate yields.
Introduction
ane (H-Bpin, 2), or neopentylglycolborane (3) were classi-
cally used as boron cross-coupling partners.
Aryl- and alkylboronic acid and ester derivatives are im-
In comparison with those with palladium catalysts, the
portant starting materials in molecular synthesis[1] and are nickel-catalyzed borylations of aryl- and alkyl halides have
well-known partners for classical transformations such as been reported less frequently. In a pioneering work, Tour
[
2]
[3]
the Petasis reaction, Chan–Lam coupling, conjugate ad- described the use of Ni(dppp)Cl2 [dppp = bis(diphenyl-
[
4]
dition reactions, and, most impressively, Suzuki–Miyaura phosphanyl)propane] as a catalyst (6 mol-%) in the presence
cross-coupling reactions.[ To prepare such boronic acid de- of a stoichiometric amount of NEt for the borylation of
5]
3
rivatives efficiently, there are currently several methodolo- aryl bromides with 2 to form the corresponding boronic
[
13]
gies, including the traditional route involving a metal–halo- acid derivatives after a hydrolysis step.
gen exchange with an organolithium or Grignard reagent 10 mol-% of dppf [dppf = bis(diphenylphosphanyl)ferro-
The addition of
[
6]
and trialkylborates. Interesting alternatives have emerged cene] to Ni(dppm)Cl [5 mol-%; dppm = 1,1-bis(diphenyl-
2
involving transition-metal-catalyzed C–H activation/bor- phosphanyl)methane] favored the borylation of aryl chlor-
[
14–17]
ylation, the major drawback of which is the control of the ides, mesylates, and tosylates with 3 at 100 °C.
regioselectivity,
It must
and the catalyzed Miyaura borylations be noted that the use of bis(neopentylglycolato)diboron as
of aryl and heteroaryl halides, mainly developed with palla- the coupling partner permitted the borylation of aryl carb-
[
7,8]
[
9]
[10]
[11]
dium, copper, nickel, or other earth-abundant tran- amates and N-arylamides with NiCl (PCy ) or [Ni(cod) /
2
3 2
2
[
12]
sition metals.
For their selectivity and functional-group IMes·HCl] (cod = cyclooctadiene, IMes·HCl = 1,3-di-
[
18,19]
tolerance, bis(pinacolato)diboron (B pin , 1), pinacolbor- mesitylimidazolium chloride) as the catalyst.
Examples
2
2
of nickel catalysts for the borylation of alkyl halides are
scarce. In 2011, Fu et al. described the coupling of alkyl
[
a] UMR 6226 CNRS, Institut des Sciences Chimiques de Rennes,
Team Organometallics: Materials and Catalysis, Centre for
catalysis and Green Chemistry, Université de Rennes 1,
Campus de Beaulieu, 35042 Rennes Cedex, France
E-mail: jean-baptiste.sortais@univ-rennes1.fr
christophe.darcel@univ-rennes1.fr
halides and 1 catalyzed by NiBr ·diglyme/pybox or
2
[
20,21]
2,2Ј;6Ј,2"-terpyridine (terpy).
Substituted allylic
boronates can also be prepared from allylic acetates in the
[22]
presence of catalysts based on Ni(cod)
and PCy
.
It is
2
3
http://scienceschimiques.univ-rennes1.fr/catalyse/
b] UMR 6226 CNRS, Institut des Sciences Chimiques de Rennes,
Centre de Diffraction X, Université de Rennes 1
Campus de Beaulieu, 35042 Rennes Cedex, France
c] Department of Chemistry, Indian Institute of Technology
Bombay,
surprising that only one report deals with the use of nickel
N-heterocyclic carbene (NHC) catalysts, as they are good
[
[
[
[
23]
candidates for catalytic applications,
hydroelementation reactions such as hydrosilylation.
In this report, as a continuation of our work exploring
in particular in
[24]
Powai, Mumbai 400076, India
‡] Equal contribution
[25]
the catalytic potential of nickel complexes in catalysis
Supporting Information and ORCID(s) from the author(s) for
this article are available on the WWW under http://dx.doi.org/
and more especially those derived from N-heterocyclic
carbene ligands, notably with a 1,2,4-triazole scaffold,[ we
26]
10.1002/ejic.201500852.
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describe herein the synthesis of new 1,2,4-triazole-based
NHC cyclopentadienyl (Cp) nickel complexes and their use
in the catalytic borylation reactions of bromoaryl deriva-
tives with bis(pinacolato)diboron.
Results and Discussion
According to the procedure of Cowley,[27] the 1,2,4-tri-
azole NHC nickel complexes CpNi(NHC)X (X = Cl, Br) 5– Scheme 1. Synthesis of 1,2,4-triazole NHC CpNi(NHC)X com-
plexes.
8
were prepared from their corresponding 1,2,4-triazolium
chloride and bromide salts 4a–4d by reaction with nickelo-
cene in THF under reflux for 20 h; the complexes were ob- ingly similar; the nickel atom is bonded to an η -Cp ring, a
tained as crystals in 42–47% isolated yields after recrystalli- triazole moiety, and a chlorido (5 and 7) or bromido (6 and
5
zation from THF/pentane mixtures (Scheme 1).
8) ligand in a two-legged piano-stool geometry (Figure 1
All of the complexes were fully characterized through and Table 1).
1
13
1
classical techniques, H and C{ H} NMR spectroscopy,
X-ray diffraction analysis, HRMS, and elemental analysis.
In 5–8, the Ni–Ccarbene bond lengths [5, 1.870(3) Å; 6,
1.865(3) Å; 7, 1.876(2) Å; 8, 1.875(3) Å] are not signifi-
1
3
1
The C{ H} NMR spectra of the diamagnetic com- cantly different from each other or from those of
plexes 5–8 exhibited characteristic Ni–Ccarbene resonances at CpNi(NHC)Cl complexes bearing imidazol-2-ylidene or
δ = 165.9–167.0 ppm and characteristic Cp resonances at δ 2,5-dihydroimidazol-2-ylidene
ligands
They are slightly shorter than the sum of
those for previously described structures such as CpNi- the individual covalent radii of nickel and carbon (Ni–C
[1.85(2)–
[
26a,28]
=
92.1 ppm. These results are in good accordance with 1.917(9) Å].
[
26a,28]
[29]
(IMes)Cl (δ = 167.2 and 92.3 ppm, respectively).
1.926 Å).
The Ni–Cl bond lengths of 2.2037(8) Å in 5
Complexes 5–8 gave suitable crystals for X-ray diffraction and 2.2084(7) Å in 7 are slightly longer than those reported
analysis, and the obtained molecular structures are strik- for CpNi(NHC)Cl [2.1795(5)–2.199(5) Å]. The differences
Figure 1. ORTEP views of 5–8 with thermal ellipsoids at the 50% probability level. The hydrogen atoms are omitted for clarity.
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Table 1. Selected bond lengths [Å] and angles [°] for 5–8.
was more selective, as no homocoupling adduct was ob-
served, but the cross-coupling product 13a was still ob-
tained in low GC yields (7, 11, and 20%, respectively). Fi-
nally, Cs CO was found to be the best base and afforded
5
(X = Cl)
6 (X = Br) 7 (X = Cl)
8 (X = Br)
Ni–X
Ni–Ccarbene
Ni–C(Cp) average 2.138
2.2037(8)
1.870(3)
2.3294(5)
1.865(3)
2.130
2.2084(7)
1.876(2)
2.138
2.3410(5)
1.875(3)
2.130
2
3
the product 13a in a moderate GC yield (35%) at 85% con-
Ni–C(Cp) max
Ni–C(Cp) min
2.169(3)
2.056(3)
1.350(4),
2.162(3)
2.048(3)
1.343(4),
1.377(3)
129.6(2),
127.7(2)
102.7(3)
95.45(8)
132.50
2.169(3)
2.038(3)
1.348(3),
1.365(3)
129.6(2),
127.7(2)
102.30(19)
96.16(7)
132.15
2.183(3)
2.059(3)
1.339(3),
1.363(3)
130.5(2),
126.4(2)
103.1(2)
94.91(8)
131.97
version. An increase of the quantity of Cs CO to 3 equiv.
2
3
led to the formation of 45% of 13a at 90% conversion; an
increased quantity of base did not improve the reaction.
The nature of the electrophile (1 equiv.) was then evalu-
ated for the reaction with 1.5 equiv. of 1 in the presence of
3 equiv. of Cs CO as the base and 5 mol-% of 5 in THF at
Ccarbene–N
1
.370(4)
130.0(2),
27.3(2)
N–Ccarbene–Ni
1
N–Ccarbene–N
102.7(2)
96.23(9)
2
3
Ccarbene–Ni–X
70 °C for 17 h (Table 2). With p-tosyltoluene (12), no con-
C
carbene–Ni–Cpcent 131.36
132.28
version was observed (Table 2, Entry 4). The use of p-iodo-
and p-chlorotoluene (10 and 11) led to good conversions
X–Ni–Cpcent
131.93
131.51
133.07
(97 and 85%, respectively), but the borylated compound 13
was obtained in poor yield (11%) in both cases (Table 2,
Entries 2 and 3). The best electrophile was p-bromotoluene,
which was converted in 90% and furnished the borylated
compound 13 in 45% yield (Table 2, Entry 1). The four pre-
pared complexes (5–8) were then tested in this reaction, and
complexes 5 and 6 bearing a 1-isopropyl-4-benzyl-1,2,4-tri-
azole ligand led to the borylated product in satisfactory
yields (45–50%; Table 2, Entries 1 and 5–7).
between the carbenoid C–Ni–X angles and those of the
CpNi(NHC)Cl analogues are unimportant [94.91(8)–
96.23(9) vs. 92.06(5)–99.4(6)°]. Thus, the use of triazole li-
gands instead of imidazole ligands did not induce strong
differences in the molecular structures of the nickel com-
plexes.
Borylation is an important reaction in molecular synthe-
sis, and examples of NHC–nickel complexes as catalysts in
the borylation of halide derivatives to form the correspond-
Table 2. Borylation reactions with different electrophiles.[a]
ing borylated compounds are scarce.[
23]
This prompted us
to examine 5–8 as potential catalysts for the coupling of 1
with aryl bromides. As the nature of the base can have a
crucial effect on the selectivity of such cross-coupling reac-
tions, we studied the borylation of 9a with B pin2
2
(1.5 equiv.), 5 mol-% of 5, and 2 equiv. of different types of
bases such as alkoxide, carbonate or phosphate bases to
evaluate the reaction (Scheme 2).
Entry
Cat.
Substrate
Conv. [%][b] Yield [%][b]
1
2
3
4
5
6
7
5
5
5
5
6
7
8
p-Me-C
p-Me-C
p-MeO-C
6
H
4
-Br
-I
9a
10
11
12
9a
9a
9a
90
97
85
45
11
11
0
50
40
40
6 4
H
6
H
4
-Cl
p-Me-C
p-Me-C
p-Me-C
p-Me-C
6
6
6
6
H
4
H
4
H
4
H
4
-Tos
-Br
-Br
-Br
0
Ͼ 98
95
92
[
(
a] Typical procedure: p-Tol-X (1 equiv.), 1 (1.5 equiv.), Cs
2
CO
3
3 equiv.), catalyst (5 mol-%), THF, 70 °C for 17 h. [b] Conversion
and yield determined by GC analysis with dodecane as an internal
standard. The difference between the conversions and GC yields
can be attributed to the formation of toluene as a result of the
6 4 3
dehalogenation of halotoluene; Tos = p-Me-C H -SO .
The scope of the cross-coupling borylation reaction was
Scheme 2. Influence of the base on the selectivity.
then explored with 5 as the catalyst and Cs CO as the base
2
3
(3 equiv.) in THF at 70 °C for 20 h (Table 3). The reaction
Even though tBuOK and NaOtBu led to 90 and 65% led to the corresponding borylated derivatives in 29–40%
conversion, respectively, the expected borylated product 13a yields for electron-donating groups on the arene rings. In-
was obtained in low GC yields (25%). The transformation deed, 90–98% conversions were obtained from para- and
was not selective as significant amounts of dehalogenation ortho-bromotoluene, and the corresponding borylated
product and p-bitolyl were obtained from a homocoupling products were obtained in 40 and 29% yields (determined
reaction. With NaOMe, K CO , and K PO , the reaction by NMR spectroscopy), respectively; therefore an ortho
2
3
3
4
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substituent slightly hampered the reactivity (Table 3, En- tions of aryl bromide derivatives with bis(pinacolato)di-
tries 3 and 4). For the aryl bromide substituted with an elec- boron in the presence of Cs CO as the base in THF at
2
3
tron-donating methoxy group, the corresponding cross-cou- 70 °C for 20 h, the prepared complexes led to the corre-
pling product was obtained in 40% yield (Table 3, Entry 5). sponding borylated compounds with moderate activities
and yields.
Table 3. Borylation reactions with different electrophiles.[a]
Experimental Section
General Procedures: All reagents were obtained from commercial
sources and used as received. THF and pentane were dried with a
Braun MB-SPS-800 solvent-purification system. All solvents were
stored with molecular sieves under an argon atmosphere. All reac-
tions were performed under an argon atmosphere. Technical-grade
petroleum ether and diethyl ether (Et
raphy.
2
O) were used for chromatog-
1H NMR spectra were recorded with samples in CDCl
temperature with Bruker AVANCE 300 and Bruker 400 spectrome-
ters at 300 and 400 MHz, respectively, and the solvent resonance
at ambient
3
Entry Aryl bromide
Conv. Product
[
Yield
[%]
%][
b]
[c]
1
2
3
4
5
6
7
8
9
Ph-Br
p-F-C
p-Me-C
o-Me-C
p-MeO-C
p-(MeO C)-C
p-(Et-OC)-C
o-(CF ) -C
p-(NC)-C
Ph-CH –CH
94
93
90
98
88
71
76
76
79
98
Ph-Bpin
p-F-C
p-Me-C
o-Me-C
p-MeO-C
p-(MeO C)-C
p-(Et-OC)-C
o-(CF ) -C
p-(NC)-C
Ph-CH –CH
37
35
40
29
40
25
23
31
8
was used as the internal standard (δ = 7.26 ppm for CHCl
3
). The
1
3
6
H
6
H
6
H
4
-Br
-Br
-Br
-Br
6
H
6
H
H
6 4
4
-Bpin
-Bpin
-Bpin
-Bpin
-Bpin
-Bpin
-Bpin
-Bpin
–Bpin
C NMR spectra were recorded with samples in CDCl or CD Cl
3
2
2
4
4
and obtained at 75 or 100 MHz. The chemical shifts (δ) and cou-
pling constants (J) are given in ppm and Hz, respectively. The peak
patterns are indicated as follows: s singlet, d doublet, t triplet, q
quartet, m multiplet, and br. broad.
4
6
H
4
6 4
H
2
6
H
H
4
4
-Br
-Br
-Br
-Br
–Br
2
6 4
H
H
6 4
H
4
6
3
6
H
4
3
6
GC analyses were performed with a GC-2014 (Shimadzu) instru-
ment equipped with a 30 m capillary column (Supelco, SPBTM-
6
H
4
6 4
H
10
2
2
2
2
18
20, fused silica capillary column, 30 mϫ 0.25 mmϫ 0.25 mm film
[
a] Typical procedure: Ar-Br (1 equiv.), Cs
2
CO
3
(3 equiv.), 1
thickness), which was used with N /air as the vector gas.
2
(
1.5 equiv.), 5 (5 mol-%), 70 °C for 20 h. [b] Conversion of the aryl
GC–MS was performed with a GCMS-QP2010S (Shimadzu) in-
strument with a GC-2010 chromatograph equipped with a 30 m
capillary column (Supelco, SLBTM-5ms, fused silica capillary col-
umn, 30 mϫ 0.25 mmϫ 0.25 mm film thickness), which was used
with helium as the vector gas. The following GC conditions were
1
bromide determined by H NMR spectroscopy with 1,3,5-tri-
methoxybenzene (0.5 equiv.) as an internal standard. [c] Yields de-
1
termined by H NMR spectroscopy with 1,3,5-trimethoxybenzene
(
0.5 equiv.) as an internal standard.
By contrast, although good conversions (71–79%) can be used: initial temperature 80 °C for 2 min, 10 °C/min to 225 °C,
2
25 °C for 15 min.
reached with electron-deficient aryl bromides after 20 h of
reaction at 70 °C, the borylated compounds were obtained
The HRMS and microanalysis were performed by the correspond-
in lower yields (8–31%): the significant decrease of the yield ing facilities at the Centre Régional de Mesures Physiques de
was mainly due to an increase of the level of debromination l’Ouest (CRMPO), University of Rennes 1, France.
(
Table 3, Entries 6–9). Interestingly, functional groups such
The X-ray diffraction data were collected with an APEXII (Bruker-
AXS) diffractometer equipped with a CCD detector with graphite-
as esters, ketones, and nitriles can be tolerated during the
coupling process. However, for para-nitrobromobenzene or monochromated Mo-K radiation (λ = 0.71073 Å) at T = 150(2) K.
α
3
-bromopyridine, no conversion was observed under similar The structures were solved by direct methods with the SIR97 pro-
conditions. Noticeably, the reaction can also be performed gram[ and then refined through full-matrix least-square methods
30]
2
[31]
[32]
based on F (SHELXL-97) with the aid of the WINGX pro-
with alkyl bromides, for example, 2-phenylethyl bromide,
which led to full conversion but only 18% of the corre-
sponding alkylBpin (Table 3, Entry 10).
gram.
CCDC-1414345 (for 5), -1414343 (6), -1414346 (for 7), and
Notably, this family of half-sandwich NHC catalysts -1414344 (for 8) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
showed better activities than those of the parent Ni(NHC)
Cl square-planar complexes.
2
2
[26c]
1-Isopropyl-4-allyl-1,2,4-triazolium and 1-isopropyl-4-benzyl-1,2,4-
triazolium salts were synthesized according to literature pro-
Conclusions
cedures.[
26a,26b]
A series of nickel complexes bearing 1,2,4-triazole-based
N-heterocyclic carbene backbones and cyclopentadienyl li-
gands were prepared from the corresponding 1,2,4-triazol-
ium salts by reaction with nickelocene in THF under reflux.
General Procedure for the Preparation of 1,2,4-Triazole NHC
CpNi(NHC)X Complexes: In a Schlenk tube, nickelocene (1 equiv.)
and 4-alkyl-1-isopropyl-1,2,4-triazolium halide salt (1 equiv.) were
dissolved in THF (10 mL) under argon atmosphere. The mixture
The complexes have been fully characterized, including by was heated under reflux for 20 h, and the solution slowly turned
X-ray diffraction analysis. In the catalytic borylation reac- from dark green to dark red. The mixture was then filtered through
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a Celite pad and rinsed with THF (3ϫ15 mL). The solvent was
then removed under vacuum, and the resulting solid was washed
with pentane (3 mL), dried, and recrystallized from a THF/pentane
mixture at room temperature. The (cyclopentadienyl)(4-alkyl-1-iso-
propyl-1,2,4-triazol-5-ylidene)nickel halide complex was obtained
as a solid.
[1] a) D. G. Hall (Ed.), Boronic Acids, Wiley-VCH, Weinheim,
Germany, 2011; b) R. Jana, T. P. Pathak, M. S. Sigman, Chem.
Rev. 2011, 111, 1417.
[2] N. Candeias, F. Montalbano, P. M. S. D. Cal, P. Gois, Chem.
Rev. 2010, 110, 6169.
[3] J. Qiao, P. Lam, Synthesis 2011, 829.
(
Cyclopentadienyl)(4-benzyl-1-isopropyl-1,2,4-triazol-5-ylidene)-
[4] G. Berthon-Gelloz, T. Hayashi, Rhodium- and Palladium-Cata-
lyzed Asymmetric Conjugate Addition of Organoboronic Acid,
in: Boronic Acids (Ed.: D. G. Hall), Wiley-VCH, Weinheim,
Germany, 2011.
[5] a) For the Nobel Prize lecture, see: A. Suzuki, Angew. Chem.
Int. Ed. 2011, 50, 6722; Angew. Chem. 2011, 123, 6854; b) N.
Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457; c) A. Suzuki,
J. Organomet. Chem. 1999, 576, 147; d) R. Jana, T. P. Pathak,
M. S. Sigman, Chem. Rev. 2011, 111, 1417; e) B. M. Rosen,
K. W. Quasdorf, D. A. Wilson, N. Zhang, A.-M. Resmerita,
N. K. Garg, V. Percec, Chem. Rev. 2011, 111, 1346.
1
nickel Chloride (5): Persian red solid; yield 46 %. H NMR
(
400 MHz, CDCl
3
): δ = 7.93 (s, 1 H), 7.50–7.30 (m, 5 H), 6.23
(sept, J = 6.8 Hz, 1 H), 6.05 (br. s, 2 H), 5.17 (s, 5 H), 1.58 (d, J =
.8 Hz, 6 H) ppm. 1 C{ H} NMR (75 MHz, CDCl
3
1
6
1
3
): δ = 166.8,
44.0, 136.2, 129.9, 129.4, 128.9, 92.8, 56.2, 53.6, 22.9 ppm.
Ni (325.08): calcd. C 56.64, H 5.59, N 11.66; found C
17 20 3
C H N
5
3
20 3
H N
Ni [M – HCl]+
58
6.44, H 5.63, N 11.53. HRMS: calcd. for C17
24.1011; found 324.1008.
(
Cyclopentadienyl)(4-benzyl-1-isopropyl-1,2,4-triazol-5-ylidene)-
[
[
[
6] a) D. G. Hall, in: Boronic Acids: Preparation and Applications
in Organic Synthesis and Medicine (Ed.: D. G. Hall), Wiley-
VCH, Weinheim, Germany, 2005, p. 1–99; b) E. J. Corey, C.-
M. Yu, S. S. Kim, J. Am. Chem. Soc. 1989, 111, 5495; c)
P. G. M. Wuts, S. S. Bigelow, J. Org. Chem. 1982, 47, 2498; d)
R. W. Hoffmann, B. Kemper, Tetrahedron Lett. 1982, 23, 845.
7] For leading reviews, see: a) J. F. Hartwig, Chem. Soc. Rev. 2011,
40, 1992; b) I. A. I. Mkhalid, J. H. Barnard, T. B. Marder, J. M.
Murphy, J. F. Hartwig, Chem. Rev. 2010, 110, 890; c) T. Ishi-
yama, N. Miyaura, Pure Appl. Chem. 2006, 78, 1369; d) T. Ishi-
yama, N. Miyaura, Chem. Rec. 2004, 3, 271; e) T. Ishiyama, N.
Miyaura, J. Organomet. Chem. 2003, 680, 3.
1
nickel Bromide (6): Persian red solid; yield 42 %. H NMR
400 MHz, CDCl ): δ = 7.85 (s, 1 H), 7.24–7.50 (m, 5 H), 6.19 (br.
s, 1 H), 6.03 (br. s, 2 H), 5.21 (s, 5 H), 1.58 (br. s, 6 H) ppm.
(
3
1
3
1
C{ H} NMR (75 MHz, CDCl
28.6, 128.0, 119.8, 92.1, 55.5, 53.1, 22.2 ppm. C17
404.98): calcd. C 50.42, H 4.98, N 10.38; found C 50.86, H 5.04, N
3
): δ = 167.0, 143.0, 134.9, 129.2,
1
(
H
20BrN Ni
3
79
58
+
1
4
0.41. HRMS: calcd. for C17
03.0197.
20 3
H N Br Ni [M] 403.0194; found
(
Cyclopentadienyl)(4-allyl-1-isopropyl-1,2,4-triazol-5-ylidene)nickel
1
Chloride (7): Firebrick solid; yield 47 %. H NMR (400 MHz,
CDCl ): δ = 7.97 (s, 1 H), 6.25–6.10 (m, 2 H), 5.50–5.24 (m, 4 H),
.23 (s, 5 H), 1.55 (br. s, 6 H) ppm. 1 C{ H} NMR (75 MHz,
CDCl ): δ = 165.9, 142.7, 132.2, 119.8, 92.1, 55.4, 51.7, 22.4 ppm.
18ClN Ni (310.47): calcd. C 50.28, H 5.85, N 13.53; found C
8] For recent examples with iron, see: a) T. Dombray, C. G.
Werncke, S. Jiang, M. Grellier, L. Vendier, S. Bontemps, J.-B.
Sortais, S. Sabo-Etienne, C. Darcel, J. Am. Chem. Soc. 2015,
3
3
1
5
3
137, 4062; b) Y. Ohki, T. Hatanaka, K. Tatsumi, J. Am. Chem.
C
4
2
13
H
3
Soc. 2008, 130, 17174; c) T. Hatanaka, Y. Ohki, K. Tatsumi,
Chem. Asian J. 2010, 5, 1657; d) G. Yan, Y. Jiang, C. Kuang,
S. Wang, H. Liu, Y. Zhang, J. Wang, Chem. Commun. 2010,
18 3
H N
Ni [M – Cl]+
5
8
9.33, H 5.83, N 13.10. HRMS: calcd. for C13
74.0854; found 274.0854.
4
6, 3170; for recent examples with iron and copper, see: e) T. J.
Mazzacano, N. P. Mankad, J. Am. Chem. Soc. 2013, 135,
7258; for a recent example with cobalt, see: f) J. V. Obligacion,
(
Cyclopentadienyl)(4-allyl-1-isopropyl-1,2,4-triazol-5-ylidene)nickel
1
Bromide (8): Deep carmine pink solid; yield 44%. H NMR
400 MHz, CDCl ): δ = 7.97 (s, 1 H), 6.18–6.07 (m, 2 H), 6.00–
.21 (m, 4 H), 5.26 (s, 5 H), 1.54 (br. s, 6 H) ppm. 13C{ H} NMR
1
(
5
(
3
S. P. Semproni, P. J. Chirik, J. Am. Chem. Soc. 2014, 136, 4133;
for examples with nickel, see: g) T. Furukawa, M. Tobisu, N.
Chatani, Chem. Commun. 2015, 51, 6508.
1
75 MHz, CDCl
3
): δ = 166.7, 142.8, 132.1, 119.7, 92.0, 55.4, 51.8,
2
2.2 ppm. C13
H
18BrN
3
Ni (354.92): calcd. C 43.99, H 5.11, N 11.84; [9] For selected examples, see: a) T. Ishiyama, M. Murata, N. Mi-
5
8
yaura, J. Org. Chem. 1995, 60, 7508; b) T. Ishiyama, K. Ishida,
N. Miyaura, Tetrahedron 2001, 57, 9813; c) A. Fürstner, G.
Seidel, Org. Lett. 2002, 4, 541; d) K. L. Billingsley, T. E. Barder,
S. L. Buchwald, Angew. Chem. Int. Ed. 2007, 46, 5359; Angew.
Chem. 2007, 119, 5455; e) S. Kawamorita, H. Ohmiya, T. Iwai,
M. Sawamura, Angew. Chem. Int. Ed. 2011, 50, 8363; Angew.
Chem. 2011, 123, 8513; f) W. Tang, S. Keshipeddy, Y. Zhang,
X. Wei, J. Savoie, N. D. Patel, N. K. Yee, C. H. Senanayake,
Org. Lett. 2011, 13, 1366.
found C 43.42, H 5.02, N 12.46. HRMS: calcd. for C13
18 3
H N Ni
M – Br]+ 274.0854; found 274.0853.
[
General Procedure for Borylation Reactions: A 10 mL Schlenk tube
containing a stirring bar was loaded with Cs CO (3 equiv.), B pin
1.5 equiv.), 5 (5 mol-%), and dry THF (4 mL). The aryl bromide
1.5 equiv.) was then added, and the reaction mixture was stirred
2
3
2
2
(
(
in a preheated oil bath at 70 °C for 20 h. The reaction mixture was
then cooled, 2,4,6-trimethoxybenzene (0.5 equiv.) was added as the
internal NMR standard, and the mixture was stirred for 5 min. The
[
10] a) W. Zhu, D. Ma, Org. Lett. 2006, 8, 261; b) C. Kleeberg, L.
Dang, Z. Lin, T. B. Marder, Angew. Chem. Int. Ed. 2009, 48,
1
conversion and yield were then determined by H NMR spec-
5350; Angew. Chem. 2009, 121, 5454; c) G. Yan, M. Yang, J.
troscopy of the crude mixture. The product can be further purified
by silica gel column chromatography with a petroleum ether/diethyl
ether mixture.
Yu, Lett. Org. Chem. 2012, 9, 71; d) C.-T. Yang, Z.-Q. Zhang,
H. Tajuddin, C.-C. Wu, J. Liang, J.-H. Liu, Y. Fu, M. Czyzew-
ska, P. G. Steel, T. B. Marder, L. Liu, Angew. Chem. Int. Ed.
2012, 51, 528; Angew. Chem. 2012, 124, 543.
[
[
11] For a recent review, see: a) F. S. Han, Chem. Soc. Rev. 2013,
4
2, 5270; b) S. Díez-González, S. P. Nolan, Coord. Chem. Rev.
Acknowledgments
2
007, 251, 874; for NHC–nickel(II) complexes, see: c) V. Rit-
leng, A. M. Oertel, M. J. Chetcuti, Dalton Trans. 2010, 39,
The authors thank the Indo-French Centre for the Promotion of
Advanced Research (IFCPAR), New Delhi (project number 4605-
8153; d) A. M. Oertel, V. Ritleng, M. J. Chetcuti, Organometal-
lics 2012, 31, 2829.
1, PhD grant to L. P. B.) for financial support of this research.
12] Recent examples with iron, see: a) T. C. Atack, R. M. Lecker,
S. P. Cook, J. Am. Chem. Soc. 2014, 136, 9521; b) R. B.
Bedford, P. B. Brenner, E. Carter, T. Gallagher, D. M. Murphy,
D. R. Pye, Organometallics 2014, 33, 5940; recent examples
C. D. and J. B. S. thank the French Ministère de l’Enseignement
Supérieur et de la Recherche and the Centre National de la Recher-
che Scientifique (CNRS) for financial support.
Eur. J. Inorg. Chem. 2015, 5226–5231
5230
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
with zinc: c) S. K. Bose, K. Fucke, L. Liu, P. G. Steel, T. B.
Marder, Angew. Chem. Int. Ed. 2014, 53, 1799; Angew. Chem.
Ghosh, Eur. J. Inorg. Chem. 2015, 1604; e) M. Katari, G. Rajar-
aman, P. Ghosh, J. Organomet. Chem. 2015, 775, 109.
2
014, 126, 1829; d) S. K. Bose, T. B. Marder, Org. Lett. 2014, [24] a) L. P. Bheeter, M. Henrion, L. Brelot, C. Darcel, M. J. Chet-
1
6, 4562.
cuti, J.-B. Sortais, V. Ritleng, Adv. Synth. Catal. 2012, 354,
2619; b) L. P. Beether, M. Henrion, M. J. Chetcuti, C. Darcel,
V. Ritleng, J.-B. Sortais, Catal. Sci. Technol. 2013, 3, 3111; c)
L. Postigo, B. Royo, Adv. Synth. Catal. 2012, 354, 2613; d) J.
Zheng, T. Roisnel, C. Darcel, J.-B. Sortais, ChemCatChem
[
[
13] A. B. Morgan, J. L. Jurs, J. M. Tour, J. Appl. Polym. Sci. 2000,
6, 1257.
7
14] a) B. M. Rosen, C. Huang, V. Percec, Org. Lett. 2008, 10, 2597;
b) D. A. Wilson, C. J. Wilson, B. M. Rosen, V. Percec, Org.
Lett. 2008, 10, 4879; c) C. Moldoveanu, D. A. Wilson, C. J.
Wilson, P. Corcoran, B. M. Rosen, V. Percec, Org. Lett. 2009,
2
013, 5, 2861; e) J. Zheng, C. Darcel, J.-B. Sortais, Catal. Sci.
Technol. 2013, 3, 81.
[
[
25] a) C. Dash, M. M. Shaikh, R. J. Butcher, P. Ghosh, Dalton
Trans. 2010, 39, 2515; b) S. Kumar, A. Narayanan, N. Rao,
M. M. Shaikh, P. Ghosh, J. Organomet. Chem. 2012, 696, 4159;
c) M. K. Samantaray, M. M. Shaikh, P. Ghosh, Organometal-
lics 2009, 28, 2267; d) S. Ray, M. M. Shaikh, P. Ghosh, Eur. J.
Inorg. Chem. 2009, 1932; e) M. Katari, G. Rajaraman, G.
Ghosh, J. Organomet. Chem. 2014, 775, 109.
26] a) C. Dash, M. M. Shaikh, P. Ghosh, Eur. J. Inorg. Chem. 2009,
1608; b) C. Dash, M. M. Shaikh, R. J. Butcher, P. Ghosh, Dal-
ton Trans. 2010, 39, 2515; c) A. Kumar, L. P. Bheeter, M. K.
Gangwar, J.-B. Sortais, C. Darcel, P. Ghosh, J. Organomet.
Chem. 2015, 786, 63.
1
1, 4974; d) C. Moldoveanu, D. A. Wilson, C. J. Wilson, P.
Leowanawat, A.-M. Resmerita, C. Liu, B. M. Rosen, V. Percec,
J. Org. Chem. 2010, 75, 5438.
[
[
[
15] P. Leowanawat, A.-M. Resmerita, C. Moldoveanu, C. Liu, N.
Zhang, D. A. Wilson, L. M. Hoang, B. M. Rosen, V. Percec, J.
Org. Chem. 2010, 75, 7822.
16] D. A. Wilson, C. J. Wilson, C. Moldoveanu, A.-M. Resmerita,
P. Corcoran, L. M. Hoang, B. M. Rosen, V. Percec, J. Am.
Chem. Soc. 2010, 132, 1800.
17] M. Murata, Y. Sogabe, T. Namikoshi, S. Watanabe, Hetero-
cycles 2012, 86, 133.
[
[
27] C. D. Abernethy, A. H. Cowley, R. A. Jones, J. Organomet.
Chem. 2000, 596, 3.
28] a) V. Ritleng, E. Brenner, M. J. Chetcuti, J. Chem. Educ. 2008,
[
[
18] K. Huang, D.-G. Yu, S.-F. Zheng, Z.-H. Wu, Z.-J. Shi, Chem.
Eur. J. 2011, 17, 786.
19] M. Tobisu, K. Nakamura, N. Chatani, J. Am. Chem. Soc. 2014,
8
5, 1646; b) V. Ritleng, C. Barth, E. Brenner, S. Milosevic, M. J.
136, 5587.
Chetcuti, Organometallics 2008, 27, 4223; c) R. A. Kelly III,
N. M. Scott, S. Diez-Gonzalez, E. D. Stevens, S. P. Nolan, Or-
ganometallics 2005, 24, 3442.
[
[
20] A. S. Dudnik, G. C. Fu, J. Am. Chem. Soc. 2012, 134, 10693.
21] J. Yi, J.-H. Liu, J. Liang, J.-J. Dai, C.-T. Yang, Y. Fu, L. Liu,
Adv. Synth. Catal. 2012, 354, 1685.
[
29] L. Pauling, The Nature of The Chemical Bond, 3rd ed., Cornell
University Press, Ithaca, NY, 1960, p. 224–228, p. 256–258.
30] A. Altomare, M. C. Burla, M. Camalli, G. Cascarano, C. Gia-
covazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori, R.
Spagna, J. Appl. Crystallogr. 1999, 32, 115.
31] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112.
32] L. J. Farrugia, J. Appl. Crystallogr. 2012, 45, 849.
Received: July 29, 2015
[
22] P. Zhang, I. A. Roundtree, J. P. Morken, Org. Lett. 2012, 14,
1416.
[
[
23] For recent references, see: a) A. P. Prakasham, P. Ghosh, Inorg.
Chim. Acta 2015, 431, 61; b) M. Henrion, V. Ritleng, M. J.
Chetcuti, ACS Catal. 2015, 5, 1283; c) M. Henrion, M. J. Chet-
cuti, V. Ritleng, Chem. Commun. 2014, 50, 4624; d) M. N. Rao,
M. Haridas, M. K. Gangwar, P. Rajakannu, A. C. Kalita, P.
[
[
Published Online: October 8, 2015
Eur. J. Inorg. Chem. 2015, 5226–5231
5231
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim