Highly active homoleptic nickel(II) bis-N-heterocyclic carbene catalyst for Suzuki–Miyaura and Heck cross-coupling reactions

Article abstract of DOI:10.1016/j.poly.2018.10.028

New homoleptic nickel(II) biscarbene complex was synthesized and structurally characterized. The complex depicted the excellent catalytic activities with only 3 mol% catalyst loading along with wide substrate scope for the Suzuki–Miyaura cross-coupling reactions (twenty six examples) and Heck coupling reactions (eighteen examples).

Full text of DOI:10.1016/j.poly.2018.10.028

Accepted Manuscript
Highly Active Homoleptic Nickel(II) Bis-N-heterocyclic Carbene Catalyst for
Suzuki–Miyaura and Heck Cross-coupling Reactions
Nirmala Muthukumaran, Arruri Sathyanarayana, Moulali Vaddamanu,
Karupnaswamy Ramesh, Mannarsamy Maruthupandi, Mannaem Adinarayana,
Ganesan Prabusankar
PII:
S0277-5387(18)30664-8
https://doi.org/10.1016/j.poly.2018.10.028
POLY 13502
DOI:
Reference:
To appear in:
Polyhedron
Received Date:
Revised Date:
Accepted Date:
4 September 2018
7 October 2018
9 October 2018
Please cite this article as: N. Muthukumaran, A. Sathyanarayana, M. Vaddamanu, K. Ramesh, M. Maruthupandi,
M. Adinarayana, G. Prabusankar, Highly Active Homoleptic Nickel(II) Bis-N-heterocyclic Carbene Catalyst for
Suzuki–Miyaura and Heck Cross-coupling Reactions, Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.
2
018.10.028
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Highly Active Homoleptic Nickel(II) Bis-N-heterocyclic Carbene Catalyst
§
for Suzuki–Miyaura and Heck Cross-coupling Reactions
a
a
a
Nirmala Muthukumaran, Arruri Sathyanarayana, Moulali Vaddamanu,
a
a
a
Karupnaswamy Ramesh, Mannarsamy Maruthupandi, Mannaem Adinarayana, and
Ganesan Prabusankar*a
aDepartment of Chemistry, Indian Institute of Technology Hyderabad, Kandi, Telangana,
INDIA. 502 285 Fax: +91 40 2301 6032; Tel: +91 40 23016089; E-mail: prabu@iith.ac.in
§
-Equal Contribution
Keywords: Nickel(II), bis-N-heterocyclic carbene, Suzuki-Miyaura cross-coupling, Heck
coupling
Abstract
New homoleptic nickel(II) biscarbene complex was synthesized and structurally characterized.
The complex depicted the excellent catalytic activities with only 3 mol% catalyst loading along
with wide substrate scope for the Suzuki–Miyaura cross-coupling reactions (twenty six examples)
and Heck coupling reactions (eighteen examples).
1
. Introduction
The application of Ni(II)-NHC’s (NHC’s = N-heterocyclic carbenes) in Suzuki-Miyaura and Heck
cross coupling reactions have attracted much of attentions towards basic research to industrial
applications [1]. Several Ni(II)-NHC systems have been demonstrated with superior catalytic
activity over their expensive Pd(II) analogues [2-6]. Thus, a great success of Ni-NHC complexes
in Suzuki-Miyaura and Heck cross-coupling chemistry has been accomplished mostly through
ligand manipulation. For example, the sterically and electronically controlled mono, bis, tris and
tetra NHC ligands have been employed to isolate the Ni(II)-NHC catalysts [1].
In particular, the application of mono-NHC supported nickel complexes have been
extensively investigated for the Suzuki-Miyaura and Heck cross coupling reactions. For example,
the SciFinder search for “nickel carbene” (945 references) followed by refine search on “Suzuki-
Miyaura” resulted forty references, while “nickel carbene” followed by refine search on “Heck”
th
gave twenty eight references (as on 04 September 2018). Though, the catalytic applications of
nickel NHC have been extensively investigated, only sixteen plus homoleptic nickel NHC
derivatives have been reported as of now. Surprisingly, only one reference has been described for

2
+
-
the homoleptic [{(PhCH N(CH) N(C:))CH } Ni(II)] 2Br (I) precatalyst mediated Suzuki-
2
2
2 2
Miyaura and Heck coupling reactions [7]. Heck reaction of aryl bromides catalyzed by 5mol% of
I with poor yield (4-56%). However, the quantitative yield was obtained in the Heck coupling
reaction between iodobenzene and butyl acrylate in the presence of Na CO or NEt . Suzuki–
2
3
3
Miyaura cross-coupling of aryl halides with phenylboronic acid using 5mol% precatalyst catalyst
I gave quantitative yield only for phenyl bromide, while substituted bromo or chloro or fluro aryl
derivatives gave very poor yield (3-42% yield). Thus, the following challenges remain unexplored
with homoleptic Ni(II)NHC’s: (i) catalytic activities of well defined homoleptic nickel(II)NHC
catalyst mediated Suzuki–Miyaura and Heck reactions; (ii) optimization of catalyst loading and
scope of the well defined homoleptic nickel(II)NHC catalysts in Suzuki–Miyaura and Heck
reactions. Continuing our interest in NHC-metal based catalytic reactions [8], in this paper we
reported
the
new
sterically
less
hindered
homoleptic
nickel(II)
complex
2
+
-
[
{(CH CHN(CH) N(C:))CH CH } Ni(II)] .2Br .2H O] (2) from the reaction between
2
2
2
2 2
2
2
+
-
[
{(CH CHN(CH) N(CH))CH CH } .2Br ] (1) and Ni(OAc) . Subsequently, catalyst 2 depicted
2
2
2
2
2
the superior activity towards Suzuki–Miyaura and Heck coupling with less catalyst loading.
N
N
2Br
N
N
N
N
N
N
N
N
N
N
2
+
2
+
Ni
Ni
.2Br
.
2H O
2
N
N
N
N
Foley et. al, 2012
This work
Chart 1. Known homoleptic nickel(II) biscarbene complex for Suzuki–Miyaura cross-coupling
and Heck coupling reactions
2
. Results and discussion
2
.1. Synthesis and characterization of 2
The 1,1'-divinyl-3,3-ethylenediimidazolium dibromide salt 1 was obtained by reacting
vinylimidazole with 1,2-dibromoethane [8]. The neat reaction of 1 with anhydrous nickel(II)
acetate and tetra butyl ammonium bromide (TBAB) at 128 °C yielded bis(1,1’-ethylene-3,3’-
divinylimidazole-2,2’-diylidene)nickel(II) dibromide dihydrate (2) as a light yellow solid in very
good yield (Scheme 1). 2 is soluble in CH Cl , CHCl , CH CN, DMSO and insoluble in diethyl
2
2
3
3
ether. The formation of 2 was confirmed by FT-IR, multinuclear NMR and elemental analysis, and

the structure was confirmed by single crystal X-ray crystallography. Upon complex 2 formation,
1
the absence of imidazolium (NCHN) proton was observed in H NMR spectrum of 2. The signature
1H NMR peaks for the backbone of NHC ring was observed at about 7.61-7.72 ppm.
2+
N
N
N
N
N
N
TBAB
.2Br
.2H O
Ni
N
N
+ Ni(OAc)2
o
6
0 C, 1h
N
N
.
2Br
2
o
1
28 C, 6 h
N
N
1
2
Scheme 1. Synthesis of 2.
1
3
The presence of downfield C NMR signal of NCN carbene carbon at 169.71 ppm in 2
confirms the Ni-Ccarbene bond formation [7]. The peaks appeared between 124.22 and 120.52 ppm
1
3
were attributed to NHC carbon. In C NMR, the vinyl carbon appeared at 106.94 ppm and -NCH -
2
carbon appeared at 47.34 ppm.
The structure of 2 was confirmed through single-crystal X-ray diffraction technique. The
structural parameters are listed in table 1. 2 was crystallized in the triclinic space group, Pī with
bis(1,1’-ethylene-3,3’-divinylimidazole-2,2’-diylidene)nickel(II), one bromide ion along along
with couple of water molecules in the asymmetric unit. Figure 1 depicts the solid state structure of
2
. The selected bond lengths and angles are tabulated in table 2. As shown in figure 1, the nickel
atom in 2 displays a square-planar geometry with four C-donor atoms lying on the same plan. The
distances of the Ni-Ccarbene bonds (1.892(4) and 1.916(4) Å) in 2 are comparable to those of the
t
square-planar
I
(1.896(2)
Å
and
1.906(2)
Å)
and
[{(p- Bu-
2
+
-
C H CH N(CH) N(C:))CH } Ni(II)] 2Br (1.894(3) Å and 1.899(3) Å) [7]. The C(8)–Ni–C(3)
6
4
2
2
2 2
and C(8)–Ni–C(3)’ bond angles (90.30° and 89.70°) show negligible deviation from 90°. These
(93.90(10)o and 86.10(10)o) and [{(p- Bu-
t
are comparable with that of
I
2
+
-
o
o
C H CH N(CH) N(C:))CH } Ni(II)] 2Br (93.75(11) and 86.25(11) ) [7]. The C(8)–Ni–C(8)’
6
4
2
2
2 2
and C(3)–Ni–C(3)’ angles are 180°. The coordination environment around nickel is satisfied by
four carbene carbons, C(3), C(8), C(3)’ and C(8)’ forming the basal plane. One of -CH -CH ,
2
2
proton shows a weak C–H···Ni hydrogen bonding interaction at the apical position of NiC plan.
4
The C–H···Ni angle is 100.9° with H···Ni distance of 2.866 Å, which is much stronger than C–
H···Ni hydrogen bonding interaction fond in the earlier reports [9-11].

Figure 1.
2
2
.2 Catalysis
.2.1. Suzuki-Miyaura cross coupling
The 2 was investigated for the Suzuki-Miyaura cross coupling. In order to optimize the
catalytic systems, the coupling of iodobenzene and phenylboronic acid in the presence of 2 and
K CO was fixed as the prototype reaction (Table 3). The catalytic reactions were carried out in
2
3
different mid-polar and polar solvents (Table 3, Entries 1-9). Among different solvents (toluene,
acetonitrile, 1,4-dioxane, EtOH, DMF, DMF/H O, p-xylene, DMSO, and water), the mixture of
2
DMF/H O seems to be the ideal choice (Table 3, Entry 6). To explore the choices of base, various
2
bases (such as K CO NaHCO KHCO NaOH, KOH, KOtBu and NaOtBu) (Table 3, Entries 10-
2
3,
3,
3,
1
5) were screened. Among various bases, a mild, inexpensive yet effective base K CO was found
2 3
to be the best (Table 3, Entry 6). To understand the role of catalyst, the catalytic experiment was
carried-out without the base (Table 3, Entry 16) or the catalyst (Table 3, Entry 17). As expected,
there was no reaction even after an extended reaction time (12 h) (Table 3, Entry 18).
Subsequently, we have further investigated the capacity of catalyst loading (Figure 2). The
reactions were performed by changing the quantity of the catalysts ranging from 0.5 to 4 mol%.
The catalytic loading of 3 mol% was found to be the optimized amount to get better out-come. No
significant increase in the efficiency of the reaction was observed on further raise of catalyst
loading to 4 mol% (Figure 2). Compared to the known protocols documented in in the literature
[1, 7], the catalyst 2 was active enough to promote the Suzuki-Miyaura cross coupling reactions
under milder conditions in DMF/H O mixture under aerobic conditions [7, 9, 10].
2
Figure 2.
Besides, the scope of the catalytic reactions was explored between a wide range of aryl
boronic acid derivatives and substituted/unsubstituted aryl halides (Table 4). The reactions take
place gently and furnished the corresponding biphenyls in good to high yield (Table 4, entries 1-
2
6). The reaction of 4-formylphenylboronic acid with iodobenzene or 4-bromo-nitrobenzene
reacted gently to offer the corresponding biphenyl compounds in 99 % yield (Table 4, Entries 4
and 17). Both the electron rich and electron poor aryl bromides were fruitfully transformed to the
corresponding products in excellent yields (Table 4, Entries 6,7,9,16-19,21,22,24,25). The electron
poor phenyl boronicacids afforded the desired biphenyls in good yields (Table 4, Entries
4
,17,21,23,24). The coupling of 1-bromonaphthalene with phenylboronic acid and 4-methoxy
phenylboronic acids gives the coupled products in excellent yield (Table 4, Entries 8 and 20).

Furthermore, aryl iodides were excellent substrates for the coupling reaction could be converted
effectively (Table 4, Entries 1-5 and 10-15). Subsequently, the reaction scope of 2 was examined
with few aryl chlorides comprising electron withdrawing and donating substituents underwent
coupling reactions with arylboronic acids to provide the expected biaryls in moderate to good
yields (Table 4, Entries 21 and 26). Notably, our present catalytic system 2, shows greater activity
-
towards Suzuki-Miyaura cross-coupling reactions compared to [Ni(diNHC) ].2Br [7, 9, 10].
2
Notably, all these reactions were performed under phosphine free condition [11-13].
Based on the literature [11-14], we assume that in C-C cross-coupled bond formation
reaction, the bis-carbene Ni(II)-NHC systems are supposed to be reduced in-situ to active zero-
valent nickel, which catalyzes the coupling reaction via a Ni(0)↔Ni(II) cycle. Our current
homoleptic Ni(NHC ) X catalytic system gives a different tactic to revamp the coordination
2
2
2
sphere of the metal by contemplating both the electronic and steric atmosphere of the nickel center
for incoming catalytic substrates.
3
.2. Heck coupling reaction
Heck coupling is a straightforward and excellent method to synthesis C -C single bonds
sp2
sp2
through base-promoted cross-coupling strategy within aryl halides and olefins [15-20]. For the
better optimizing condition, a screening was done for a prototype reaction of iodobenzene with
butyl acrylate. Figure 3 summarizes the influence of base and catalyst loading on heck reaction,
while figure 4 depicts the choice of solvent in catalyst 2 mediated Heck coupling reaction. In order
to determine the essential role of base, various bases such as TBAE, NaOAc, K CO Na CO
2
3,
2
3,
Cs CO and K PO were screened. Among the bases employed, an excellent yield of desired
2
3
3
4
product was isolated in the presence of K CO or Cs CO . However, Cs CO is not economical
2
3
2
3
2
3
compared to K CO . Out of different solvents tested, DMF was identified as the best solvent
2
3
towards the Heck cross-coupling reaction (with 96 % yield, Figure 4). Water was found to be
ineffective for this system.
Figure 3.
Figure 4.
Thus, the reactions of different arylchlorides with olefins were carried out under the
optimized condition (3 mol% catalyst, 2 eq. K CO , DMF, 100˚C, 4 h). Table 5, summarizes the
2
3
obtained product yield. The observation revealed that the coupling between aryl iodides and
ethyl/butyl acrylates proceeded in excellent yield (Table 5, Entries 1-7). Similarly, the styrene was

successfully coupled with various aryl halides produced the appropriate products with the yield
ranging from 83 to 99 % (Table 5, Entries 11-18). The electron-rich as well as the electron-
deficient aryl bromides showed a high activity when electron-deficient olefins are used (Table 5,
entries 7-10). By adopting the identical reaction condition, the aryl chloride was successfully
converted to the desired product in 83-98 % yield (Table 5, Entry 17). Even, bromonaphthalene
reacted nicely with electron poor butyl acrylate (Table 5, Entry 10).
On the basis of earlier literature report [21], we believe that Ni(II) in 2 is reduced in-situ to
active zero-valent nickel, and the activation of aryl halides was further achieved by the oxidative
addition. In the second step, an olefin substrate coordinates to the nickel metal with the subsequent
insertion of the alkene at the C-Ni. Final step is an intramolecular β-hydride elimination, which
led to the formation of desired product by removal of HX.
4
. Conclusions
In conclusion, the first sterically less crowded well defined homoleptic nickel(II)
biscarbene 2 mediated Suzuki–Miyaura cross coupling reactions and Heck coupling reactions were
1
demonstrated. 2 was isolated and characterized by elemental analysis, FT-IR and NMR ( H and
13C) spectrometry. The structure of 2 was confirmed by single-crystal X-ray diffraction technique.
The nickel center in 2 adopts a square planar geometry with chelating di-NHC ligands along with
two non-coordinating bromide counter ions and two water molecules. 2 was found to be highly
active catalyst in Suzuki–Miyaura cross coupling reactions (eighteen different examples) and Heck
coupling reactions (twenty four different examples). Catalyst 2 depicted the excellent functional
group tolerance towards wide range of reactants in Suzuki–Miyaura and Heck cross-coupling
reactions with only 3 mol% catalyst loading.
5
. Experimental
5
.1. General procedures and methods
All manipulations were carried out under argon using Schlenk-vaccum line techniques and
argon filled glove box. The solvents were puchased from commercial sources and purified
according to standard procedures [22]. Unless otherwise stated, the chemicals were purchased
from commercial sources. 1 was synthesiszed as reported [8]. FT-IR measurement (neat) was
carried out on a Bruker Alpha-P Fourier transform spectrometer. NMR spectra were recorded on
Bruker Ultrashield-400 spectrometers at 25 °C unless otherwise stated. Chemical shifts are given
relative to TMS and were referenced to the solvent resonances as internal standards. The crystal

structure of 2 was measured on an Oxford Xcalibur 2 diffractometer. Data were collected at 150
K. The structure of 2 was solved by direct methods using the Olexprogram [23] and refined with
a full matrix least-squares method on F2 using the SHELXL-97 program [24, 25]. 2 depicts three
“
B level” alerts. The U(eq) value of an C(7) atom is compared with the average U(eq) for to non-
hydrogen atoms bonded to it. Large differences may indicate that the high thermal parameter of
terminal carbon atom. The short non-bonding inter H(2B)..H((12A) contact could be due to the
strong bite angle of NHC ligand. Potential hydrogen bond donors are checked for the presence of
suitable acceptors using commonly used (Jeffrey) H-bond criteria. As a general rule there should
be an acceptor for each donor. In 2, this could be due to the absence of acceptor for O(2)-H(2B)as
the hydrogen atoms have been fixed by calculated position. CCDC 1832286 contains 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 or from
the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44
1
223 336 033; or e-mail: deposit@ccdc.cam.ac.uk.
.2. Synthesis of 2
5
A mixture of bisvinyl imidazolium dibromide salt 1 (0.100 g, 0.26 mmol), anhydrous
nickel(II) acetate (0.047 g, 0.26 mmol) and tetra butyl ammonium bromide (0.400 g, 1.24 mmol)
were mixed and heated under vacuum in Schlenk tube at 60 °C for 1 h, followed by at 128 °C for
5
h. The molten reaction mixture was allowed to attain at room temperature, water (10 mL) was
added to the reaction mixture. The resulting mixture was extracted with dichloromethane (40 mL).
The organic layer was collected, dried on sodium sulphate and concentrated then stored at room
temperature to get the desired product as light yellow crystals. Yield: 65% (Based on nickel(II)
acetate) M.p.: 260-262 °C (decomp.). Anal. Calcd (%) for C H Br N Ni (648.0481): C, 44.27;
2
4
32
2
8
1
H, 4.95; N, 17.21; found: C, 44.2; H, 5.0; N, 17.21. H NMR (CDCl 400 MHz): δ 4.79-4.84 (4H,
3
,
3
3
m, NCH ), 3.66-3.70, 4.99-5.01 (4H, d, J =7.6 Hz, NCH=CHH ), 5.28-5.31 (4H, d, J =15.3
2
HH
cis
HH
Hz,NCH=CHHtrans), 5.57-5.62 (4H, m, NCH ), 7.16-7.22 (4H, dd, vinylCH), 7.61(4H, s, ImH),
2
1
3
7
1
.72 (4H, s, ImH). C NMR (100 MHz, CDCl ): δ 169.71 (Ni-C), 131.61(NCN), 124.22 (ImC),
3
‒
1
20.52 (ImC), 106.94 (vinyl-C), 47.34 (NCH ). FT‒IR (neat, ῡ, cm ): 3419 (w), 3371 (w), 3082
2
(w), 3055 (w), 2970 (w), 1632 (s), 1444 (m), 1398 (s), 1329 (m), 1246 (s), 1188 (m), 1080 (w)
1
040 (m), 960 (m), 913 (s), 730 (m) 680 (s).
5
.3. General procedure for the Suzuki-Miyaura reactions

The typical procedure is as follows. Oven dried Schlenk tube was charged with aryl halides
(
1 mmol), aryl phenylboronic acid (1.2 mmol), K CO (2 mmol) and catalyst 2 (3 mol %) in1:1
2
3
mixture of DMF/H O medium. The reaction mixture was stirred in an oil bath at 100 °C in the
2
presence of air. After completion of the reaction, the reaction mixture was then cooled to room
temperature and diluted with Et O/H O (1:1, 20 mL). The organic layer was separated and dried
2
2
with anhydrous MgSO . The product was filtered and dried under vacuum. The resulting crude
4
compound was purified by column chromatography on silica gel to afford the corresponding
products.
5
.4. General procedure for the Heck reactions
The typical procedure is as follows. Oven dried Schlenk tube was equipped with stirrer bar, was
charged with aryl halides (1 mmol), acrylates (1.2 mmol), K CO (2 mmol) and catalyst 2 (3 mol
2
3
%) in DMF medium. The reaction mixture was stirred in an oil bath at 100 ⁰C under argon
atmosphere for an appropriate period of time. After completion of the reaction, the reaction mixture
was then cooled to room temperature and diluted with Et O/H O (1:1, 20 mL). The organic layer
2
2
was separated and dried with anhydrous MgSO . The product was filtered and dried under vacuum.
4
The resulting crude compound was purified by column chromatography on silica gel to afford the
corresponding products.
Appendix A. Supplementary data
1
13
Supplementary data: ( H and C NMR spectra of the synthesized complex. Catalysis protocols
and characterization data of coupling products) related to this article can be found. CCDC. CCDC
1
832286 contains the supplementary crystallographic data for 2. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-
0
33; or e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgment
GP gratefully acknowledge the Council of Scientific and Industrial Research (No:
0
1(2884)/17/EMR-II) for financial support. NM thank DST-NPDF (PDF/2016/001834) for
fellowship.
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24]G. M. Sheldrick, SHELXL-97, Program for Crystal Structure Refinement, Universität
Göttingen, Göttingen, 1997.
25]P. van der Sluis, A. L. Spek, Acta Cryst A, 46 (1990) 194.
Fig. 1. Top: The solid state structure of 2. Two water molecules and two bromide ions have been
omitted for clarity. Bottom: The geometrical representation of nickel center in 2. Two water
molecules, two bromide ions and hydrogen atoms on carbons have been omitted for clarity.
Fig. 2. Effect of catalyst (mol%) with respect to time.
Fig. 3. Effect of catalyst (mol%) and base on Heck coupling of iodobenzene with butyl acrylate.
Fig. 4. Effect of solvent on Heck coupling of iodobenzene with butyl acrylate.
Table 1. Crystal data and structure refinement parameters of 2.
Parameters
Empirical formula
2
C H Br N NiO
2
4
36
2
8
4
Formula weight
Temperature (K)
719.14
150
Crystal system
Space group
Triclinic
Pī
a/Å
b/Å
c/Å
α/°
β/°
7.6367(5)
10.7808(7)
11.0785(7)
114.455(6)
96.028(5)
107.167(6)
765.73(9)
1
γ/°
3
Volume (Å )
Z

ρcalc/mg mm-3
Absorption coefficient (mm )
F(000)
1.560
4.328
366
Table 2. Selected structural
parameters of 2
-1
Table 3. Evaluation of
Data collected
Unique data
Rint
5016
2863
0.0410
1.075
conditions for the Suzuki-
Miyaura cross-coupling
reaction using 2a,b
2
GOF on F
R1 (I>2σ(I))
0.0711
HO
OH
B
I
0.2026
wR (I>2σ(I))
2
+
R1 values (all data)
0.0748
0.2062
wR values (all data)
2
Interatomic distances (Å)
C(3)−Ni(1)
C(8)−Ni(1)
C(3)−N(1)
C(3)-N(2)
C(8)-N(3)
C(8)-N(4)
1.892(4)
1.916(4)
1.361(6)
1.347(6)
1.353(6)
1.373(6)
Bond angles(ᵒ)
N(2)−C(3)−N(1)
N(2)−C(3)−Ni(1)
N(1)−C(3)−Ni(1)
N(3)−C(8)−N(4)
N(3)−C(8)−Ni(1)
N(4)−C(8)−Ni(1)
C(3)−Ni(1)−C(3)
C(8)−Ni(1)−C(8)
C(8)–Ni–C(3)
C(8)–Ni–C(3)
104.1(4)
124.8(3)
130.9(4)
104.1(4)
129.6(4)
126.1(3)
180.000(1)
180.000(1)
89.70 (19)
90.30(19)

Entry
Base
Solvent
Toluene
Temp (˚C)
110
82
101
78
Time (h)
8
8
8
8
8
8
12
12
12
12
12
12
12
12
12
12
8
Yield (%)b Table 4.
1
2
3
4
5
K CO
69
2
3
3
3
3
3
3
3
3
3
Complex
56
K CO
Acetonitrile
1,4-dioxane
C H OH
2
K CO
62
24
79
97
32
61
n.r
22
17
59
61
53
47
n.r
n.r
n.r
2
2
K CO
2
2
5
catalyzed
Suzuki-
Miyaura
coupling
of aryl
halides
and
K CO
DMF
DMF/H O
p-xylene
DMSO
150
100
138
140
100
100
100
100
100
100
100
100
100
100
2
e
6
K CO
2
2
7
8
9
K CO
2
K CO
2
K CO
H O
2
2
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
NaHCO3
KHCO3
NaOH
KOH
KOtBu
NaOtBu
-
DMF/H O
DMF/H O
DMF/H O
DMF/H O
DMF/H O
DMF/H O
DMF/H O
DMF/H O
2
2
2
2
2
2
c
2
d
d
K CO
2
3
2
1
K CO
2
DMF/H O
24
3
2
a
Reaction conditions: iodo benzene (1 mmol), phenylboronic acid (1.2 mmol), base
2 mmol) and catalyst (3 mol %) in solvent (4 mL).
Isolated yield based on column chromatography.
(
b
c
The reaction was carried out using iodo benzene (1 mmol), phenylboronic acid (1.2
mmol), without base, catalyst (3 mol %).
d
The reaction was carried out using iodo benzene (1 mmol), phenylboronic acid (1.2
mmol), base (2 mmol), without catalyst.
e
Better optimization condition.
X
B(OH)2
Catalyst (3 mol%)
DMF/H O (1:1), K CO
3
R1
R2
2
2
R1
o
R2
100 C, 8 h
arylboronicacids.a,b
X = Br, Cl, I
Aryl boronic
acid
Yield
(%)
Entry Aryl halide
Product
b
HO
OH
B
I
1
96
99
HO
OH
B
O
I
2
O

HO
HO
OH
B
I
O
3
99
O
O
O
B
OH
I
I
O
4
5
99
90
O
HO
OH
B
HO
HO
HO
OH
OH
OH
B
B
B
6
7
8
99
85
99
Br
Br
O
O
NO2
O N
2
Br
Br
HO
OH
B
9
90
HO
HO
OH
OH
B
B
I
1
1
0
1
H N
91
94
2
H N
2
I

HO
HO
OH
OH
B
B
OH
OH
I
1
1
2
3
96
94
O
OH
OH
O
I
O
HO
OH
B
1
1
4
5
O
88
76
I
HO
HO
OH
OH
O
B
B
O
I
Br
1
1
1
1
6
7
8
9
O
40
99
97
99
O
B
HO
OH
NO2
O
O N
2
Br
Br
Br
O
OH
HO
HO
B
O
O
O
O
O
O
O
O
O
B
OH
O

HO
OH
Table 5.
B
O
Br
Complex 2
catalyzed
Heck
2
2
2
0
1
2
89
97
99
O
HO
HO
OH
Br
coupling of
aryl halides
B
Cl
and
Cl
B
acrylates.a,b
OH
Br
O
O
O
O
O
O
B
O
HO
HO
HO
OH
OH
O
2
2
3
4
F
99
97
Cl
F
Br
B
F
F
OH
Br
B
2
5
6
O
O
99
42
O
O
B
HO
OH
Cl
2
O
O
a
Reaction conditions: aryl halide (1 mmol), arylboronic acid (1.2 mmol),
K CO (2 mmol) and catalyst (3 mol %) in DMF/H O (1:1, v/v) (4 mL).
2
3
2
b
Isolated yield based on column chromatography.

X
Catalyst (3 mol%)
R2
R2
DMF, K CO3
2
R1
o
R1
100 C, 4 h
X = Br, Cl, I
Yield
Entry Aryl halide
Acrylate
Product
b
(%)
O
O
I
O
O
O
1
2
3
O
O
82
83
79
O
O
O
I
O
O
O
I
O
O
O
O
O
I
O
O
O
O
4
5
OH
63
64
OH
O
O
O
I
O
O
O
I
O
O
6
7
O
O
96
78
O
O
Br
Br
Br
NO2
NO2
O
O
O
O
O
8
9
96
89
O
O
O
O
O

Br
Graphical
Abstract
Highly
O
O
1
1
0
1
97
89
O
O
active
homoleptic
nickel(II)
bis-N-
I
heterocyclic
carbene
catalyst for
Suzuki–
Miyaura
and Heck
cross-
coupling
reactions
are
I
1
1
2
3
89
99
H N
2
NH2
Br
reported.
OH
OH
I
1
1
4
5
99
93
I
I
O
O
1
6
97
O
O
Cl
1
1
7
8
83
95
Br
NO2
NO2
a
Reaction conditions: aryl halide (1 mmol), acrylate(1.2 mmol), K CO (2 mmol)
2
3
and catalyst (3 mol %) in DMF (4 mL).
b
Isolated yield based on column chromatography.