Synthesis, solid-state structures, solution behaviour and catalysis studies of nickel complexes of bis(benzimidazolin-2-ylidene)pyridine pincer ligands

Article abstract of DOI:10.1071/CH12044

N-Heterocyclic carbenenickel complexes with five- and four-coordinate geometries [(CNC)NiBr₂] and [(CNC)NiBr]X (X=PF₆ or BPh₄) have been prepared with the pincer ligands 2,6-bis(N- octylbenzimidazolin-2-ylidene)pyridine and 2,6-bis(N-butyl-5,6- dimethoxybenzimidazolin-2-ylidene)pyridine. The addition of the n-octyl substituent significantly extends the solubility of the complexes and has allowed UV-vis solution studies of the complexes in dichloromethane and methanol. The four- and five-coordinate species exist in equilibrium in solution and this equilibrium has been explored by UV-vis studies. The complexes have also been characterized by NMR studies, and single crystal X-ray diffraction studies have been performed on [(CNC)NiBr₂] (where CNC=2,6-bis(N-octylbenzimidazolin-2-ylidene)pyridine) and [(CNC)NiBr]BPh ₄ (where CNC=2,6-bis(N-butyl-5,6-dimethoxybenzimidazolin-2-ylidene) pyridine).

Full text of DOI:10.1071/CH12044

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2012, 65, 823–833
Full Paper
http://dx.doi.org/10.1071/CH12044
Synthesis, Solid-state Structures, Solution Behaviour
and Catalysis Studies of Nickel Complexes
of Bis(benzimidazolin-2-ylidene)pyridine
Pincer Ligands*
A
A
B
Karen D. M. MaGee, Guy Travers, Brian W. Skelton,
A
A
A C D
, ,
Massimilliano Massi, Alan D. Payne, and David H. Brown
A
Department of Chemistry, Curtin University, GPO Box U1987, Perth,
WA 6845, Australia.
B
Centre for Microscopy, Characterisation and Analysis, The University of Western
Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
C
School of Biomedical, Biomolecular and Chemical Sciences, The University
of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
D
Corresponding author. Email: d.h.brown@curtin.edu.au
N-Heterocyclic carbene–nickel complexes with five- and four-coordinate geometries [(CNC)NiBr2] and [(CNC)NiBr]X
(X ¼ PF6 or BPh4) have been prepared with the pincer ligands 2,6-bis(N-octylbenzimidazolin-2-ylidene)pyridine and 2,6-
bis(N-butyl-5,6-dimethoxybenzimidazolin-2-ylidene)pyridine. The addition of the n-octyl substituent significantly
extends the solubility of the complexes and has allowed UV-vis solution studies of the complexes in dichloromethane
and methanol. The four- and five-coordinate species exist in equilibrium in solution and this equilibrium has been explored
by UV-vis studies. The complexes have also been characterized by NMR studies, and single crystal X-ray diffraction
studies have been performed on [(CNC)NiBr2] (where CNC ¼ 2,6-bis(N-octylbenzimidazolin-2-ylidene)pyridine) and
[(CNC)NiBr]BPh4 (where CNC ¼ 2,6-bis(N-butyl-5,6-dimethoxybenzimidazolin-2-ylidene)pyridine).
Manuscript received: 25 January 2012.
Manuscript accepted: 16 February 2012.
Published online: 24 April 2012.
six-coordinate nickel complex.[17] The five-coordinate com-
plexes 2 displayed surprisingly low solubility in a range of
organic solvents, and our studies suggested dissolution of these
purple [(CNC)NiX2] complexes resulted in formation of yellow
solutions containing [(CNC)NiX]þ cations 3 (X ¼ Cl, Br).[13]
In this paper, we report our continued exploration of these
nickel complexes bearing 2,6-bis(benzimidazolin-2-ylidene)
pyridine ligands, including catalysis studies in Kumada cou-
pling reactions. Incorporation of octyl substituents has allowed
us to explore the solution behaviour of these complexes in
solvents other than highly polar solvents such as methanol.
In addition, we have explored the incorporation of methoxy
groups into the periphery of the benzimidazole moiety, because
incorporation of these groups in the 5,6-positions should not
influence the coordination environment based on sterics, but
may influence the electronic properties of the carbene donor
atom. Several studies have incorporated methoxy groups onto
benzimidazolin-2-ylidenes in an effort to explore the influence
they have on metal complexation.[18–23]
Introduction
Metal complexes of ‘pincer’ ligands bearing N-heterocyclic
carbenes (NHCs) have been studied extensively, involving a
range of additional donor types.[1–3] Within this class of com-
pounds, NHC ‘pincer’ ligands with a pyridyl core are common
(e.g. 1 in Fig. 1). Although there is now an extensive variety of
different NHC structural motifs, the pyridyl-core CNC pincer
has predominantly been explored with imidazole-derived
NHCs. Metal complexes of 2,6-bis(imidazol-2-ylidene)pyridine
type ligands cover the majority of the d-block elements,
with significant interest in catalysis applications.[1,2,4–8] By
comparison, complexes of the benzimidazole-based 2,6-
bis(benzimidazolin-2-ylidene)pyridine ligand system have only
been reported with Pd, Ag, Os and recently Ni.[4,9–14]
In our recent exploration of nickel complexes of the 2,6-
bis(benzimidazolin-2-ylidene)pyridine ligand system, we
identified the formation of the five-coordinate [(CNC)NiX2]
complexes 2 (where CNC ¼ 2,6-bis(3-n-butylbenzimidazolin-
2-ylidene)pyridine, X ¼ Cl, Br),[13] an unusual coordination
geometry for this CNC ligand system. Other studies of
nickel complexes with 2,6-bis(imidazol-2-ylidene)pyridine
ligands have predominantly identified only four-coordinate
[(CNC)NiX]þ geometries,[7,15–17] with one example of a
Results and Discussion
The syntheses reported here are derived from the previously
reported procedures for the synthesis of
2
(X ¼ Br),
*Dedicated to Professor Allan H. White on the occasion of his 75th birthday.
Journal compilation Ó CSIRO 2012
www.publish.csiro.au/journals/ajc

824
K. D. M. MaGee et al.
3ꢀPF6 (X ¼ Br) and the bis(benzimidazolium) dibromide
salt used as the ligand precursor.[10,13] Treatment of 5,6-
dimethoxybenzimidazole[24] with sodium hydride and then
reaction of the resulting benzimidazolate anion with 2,6-
dichloropyridine in DMF at 708C for 24 h and then 1408C for a
further 24 h afforded 1,3-bis(5,6-dimethoxybenzimidazol-1-yl)
pyridine (4) in good yield (Scheme 1). Alkylation of 4 with a large
excess of 1-bromobutane afforded the bis(benzimidazolium)
salt 5ꢀ2Br. A solution of 5ꢀ2Br and nickel acetate tetrahydrate in
DMF was heated from room temperature to ,1108C over the
course of ,10 min, and then immediately allowed to cool,
which resulted in the formation of the five-coordinate nickel
complex 6 as a purple precipitate, which could be further puri-
fied by recrystallization from nitromethane. Treatment of a
mixture 6 and potassium hexafluorophosphate in methanol
afforded the four-coordinate complex salt 7ꢀPF6 as an orange
powder in high yield (Scheme 1). Attempts to grow single
crystals of either 6 or 7ꢀPF6 proved difficult, routinely affording
extremely fine needles that were not suitable for single-crystal
X-ray studies. Such behaviour was also observed for the pre-
viously studied non-methoxy analogues 2 (X ¼ Br) and 3ꢀPF6
(X ¼ Br).[13] The salt 7ꢀBPh4 was prepared similarly to 7ꢀPF6,
using sodium tetraphenylborate instead of potassium hexa-
fluorophosphate. Recrystallization of the tetraphenylborate salt
7ꢀBPh4 afforded single crystals that were suitable for X-ray
studies (see Solid-State Studies). Dissolution of 7ꢀPF6 in
methanol or dichloromethane afforded bright yellow solutions.
In the case of 6, solutions in methanol are bright yellow whereas
solutions in dichloromethane are yellow to orange, depending
on concentration.
insoluble nature of 2. In an effort to improve the solubility of
such systems, and to further explore the solution behaviour of
these complexes, we synthesized the n-octyl-substituted bis
(benzimidazolium) salt 8ꢀ2Br and the five- and four-coordinate
complexes 9 and 10ꢀPF6 in good yields using procedures similar
to those described above (Fig. 2). As with 2 (X ¼ Br) and 3ꢀPF6
(X ¼ Br), attempts to grow crystals of 9 and 10ꢀPF6 invariably
afforded extremely fine needles; however, we were fortunate
that when using THF and methanol as recrystallization solvents,
dark purple crystals of 9 suitable for X-ray studies were isolated
H
H3CO
H3CO
N
2
N
(i) NaH, DMF
(ii) 2, 6-dichloropyridine
70ЊC → 140ЊC
H3CO
H3CO
OCH3
OCH3
N
N
N
N
N
4 65 %
1-bromobutane
DMF, 100ЊC
OCH3
OCH3
H3CO
H3CO
Our previous solution studies of the five-coordinate com-
plex 2 (X ¼ Br) were restricted to polar solvents owing to the
N
N
N
ϩ
ϩ
ϩ
2 BrϪ
N
N
Bu
Bu
BrϪ
N
N
N
5⋅2Br 57 %
N
H3C
N
CH3
Ni
Br
DMF, 110ЊC
Ni(OAc)2⋅4H2O
1⋅Br
OCH3
H3CO
H3CO
OCH3
N
N
N
N
Bu
N
Bu
Ni
N
N
N
Br
Br
N
N
Bu
6 54 %
Ni
Bu
X
X
KPF6 CH3OH
2
ϩ
OCH3
OCH3
H3CO
H3CO
ϩ
Ϫ
PF6
N
N
N
PFϪ6
N
N
N
N
Bu
N
Bu
Ni
Br
N
Bu
N
Bu
Ni
X
7⋅PF6 85 %
3⋅PF6
Scheme 1. Synthesis of the pyridyl-bis(dimethyoxybenzimidazolium) salt
5ꢀ2Br and the bis(dimethyloxybenzimidazolin-2-ylidene)pyridine nickel
complexes 6 and 7ꢀPF6.
Fig. 1.

NHC Pincer Complexes
825
(see Solid-State Studies). The addition of the octyl substituents
significantly improved the solubility of the complexes, particu-
larly the five-coordinate complex 9, which proved to be soluble
in chlorinated solvents such as dichloromethane, affording
purple–brown coloured solutions. This contrasts with the butyl-
substituted complex 2 (X ¼ Br), which only displayed appreci-
able solubility in more polar solvents such as methanol, and on
dissolution (of the purple solid) afforded yellow solutions.
Solid-State Studies of 9 and 7ꢀBPh4ꢀEt2O
Table 1 summarizes selected coordination geometries for the
two structures 9 and 7ꢀBPh4ꢀEt2O.
The structure for 9 displays a distorted trigonal bipyramidal
geometry around the nickel centre, with the two bromide atoms
and N21 forming the horizontal plane and the carbene carbons
C12 and C32 occupying the axial positions (Fig. 3). The geometry
in 9 is similar to that of the crystallographically characterized
chlorido complex 2 (X ¼ Cl)[13] and a related [(CNC)PdI2]
complex.[11] The structure of 9 represents only the third crystallo-
graphically characterized example of this unusual five-coordinate
geometry for nickel or palladium complexes of this class of pincer
ligand system.[11,13] Group 10 metal complexes of these types of
N-heterocyclic carbene CNC pincer ligands typically display
four-coordinate planar geometries.[10,15–17,25] Interestingly, the
five-coordinate geometries have been only observed with CNC
ligands based on benzimidazolin-2-ylidenes and not the more
common imidazol-2-ylidenes.[11,13]
1
All compounds were characterized by H and 13C NMR
studies. The 13C NMR spectra of the nickel complexes were
obtained using relatively concentrated solutions of the com-
plexes. Solutions were prepared using [D]chloroform (with a
drop of [D3]methanol) for the five-coordinate complexes 6
(orange in colour) and 9 (dark brown–purple in colour),
and [D]chloroform (with [D6]dimethylsulfoxide) for the four-
coordinate materials 7ꢀPF6 and 10ꢀPF6. Each of the 13C NMR
spectra displayed a relatively sharp downfield signal attributed
to the carbene carbons bound to each nickel centre (dC 166.4 (6);
172.0 (9); 165.6 (7ꢀPF6); 169.8 (10ꢀPF6)). However, at these
concentrations the 1H NMR spectra often displayed broadened
signals for the solutions of the five-coordinate complexes 6 and
9. Dilution of the solutions resulted in sharper spectra from
which accurate data could be obtained.
The cation 7 shows an essentially coplanar molecule with the
exception of the pendant butyl chains and methoxy groups
(Fig. 4). The most deviant atoms from the plane are C24
˚
˚
(d 0.122(2) A) and C35 (d 0.166(2) A). The dihedral angles
between the planes of the two benzimidazolin-2-ylidene groups
and the pyridyl groups are 3.60(6)8 (between planes 1 and 2) and
5.17(6)8 (between planes 2 and 3). The dihedral angle between
the two benzimidazolin-2-ylidene groups (planes 1 and 3) is
1.68(5)8. The unit cell containing 7ꢀBPh4 also includes one
molecule of diethyl ether (solvent) per molecule of compound
(Fig. 5). The cations are arranged in the cell as centrosymme-
trically related pairs (Figs 6, 7) with the Ni1?Ni1 (1 ꢁ x,
N
N
N
ϩ
ϩ
2 BrϪ
N
N
C8H17
H
17C8
8⋅2Br
˚
1 ꢁ y,1 ꢁ z) distance being 3.4767(3) A and Ni1?N21(1 ꢁ x,
˚
1 ꢁ y,1 ꢁ z) 3.583(2) A. The coordination geometry around the
nickel centre is approximately square planar. There is no
significant deflection of the bromide atom away from planarity,
with an N21–Ni1–Br1 angle of 179.54(5)8 and a total deviation
N
N
N
˚
of the bromide atom out of the NC2Ni plane of 0.019(3) A,
˚
N
H17C8
N
C8H17
Ni
compared with 166.68(9)8 and 0.528(4) A for the non-methoxy
analogue 3ꢀPF6 (X ¼ Br).[13] The ‘cavity’ for the bromido ligand
to occupy in the ideal square-planar geometry, as measured by
the distance between the two benzimidazole-bound methylene
carbons C1?C5, is only slightly larger in the methoxy-
Br
Br
9
˚
functionalized complex, at 6.594(2) A, compared with
[13]
ϩ
˚
6.547(6) A for 3ꢀPF6 (X ¼ Br).
A comparison of the solid-
PFϪ6
state structures for the cations in 7 and 3 (X ¼ Br) does not reveal
any obvious reasons as to why the coordination geometry around
the nickel centres should vary so significantly; however, the
variation in their geometries appears to correlate with the
observed differences in their solution behaviour.
N
N
N
N
H17C8
N
C8H17
Ni
Br
UV-vis Studies
10⋅PF6
In our earlier studies of the five-coordinate [(CNC)NiBr2] 2, the
low solubility of the complex in various organic solvents limited
Fig. 2. n-Octyl-substituted compounds reported in this paper.
˚
Table 1. Selected bond lengths [A] and angles [8] for 7 and 9, and relevant literature examples
RꢀꢀꢀRA [A]
NC2Ni?XB [A]
˚
C–Ni [A]
˚
N–Ni [A]
˚
Ni–X [A]
˚
˚
Complex
C–Ni–C [8]
N–Ni–X[8]
179.54(5)
7ꢀBPh4
1.929(2), 1.933(1) 1.866(2) 2.2989(4)
3ꢀPF6 (X ¼ Br)[13] 1.924(4), 1.932(4) 1.866(3) 2.2955(6)
162.73(8)
6.594(2)
6.547(6)
6.341(4)
0.019(3)
163.08(14) 166.68(9)
161.7(1) 127.50(6), 132.46(6)
0.528(4)
9
1.894(2), 1.890(2) 1.876(2) 2.5177(5), 2.4404(4)
1.998(3), 1.797(3)
2 (X ¼ Cl)[13]
1.897(6), 1.900(7) 1.871(5) 2.2791(18), 2.4324(19) 162.0(3)
141.38(17), 115.64(17) 6.270(10) 2.192(4), 1.424(6)
AThe distance between the two carbon atoms, of the alkyl substituents, bound to the azolyl nitrogen. BThe distance of the halide out of the NC2Ni plane.

826
K. D. M. MaGee et al.
C24
N21
C23
C22
C25
C26
C15
C34
C14
C35
C36
N13
N11
N33
C16
C12
C32
C17
C37
Ni1
Br1
N31
C109
C101
C110
Br2
C102
C104
C107
C106
C105
C111
C113
C103
C108
C112
C114
C115
C116
Fig. 3. Molecular structure of 9.
C151
C15
C24
C351
O35
O15
C23
C22
C25
C26
C34
C14
C35
C36
N13
N33
O36
N21
Ni1
Br1
O16
C12
C16
C32
C37
C161
C17
C361
N31
C6
N11
C1
C5
C7
C2
C3
C8
C4
Fig. 4. Structure of cation 7 projected onto the coordination plane.
our solution studies to polar solvents such as methanol.[13] In
these studies, the UV-vis spectra of solutions of [(CNC)NiBr2] 2
in methanol were almost identical to those of the four-coordinate
[(CNC)NiBr]PF6 3ꢀPF6 in methanol, which suggested the
dissolution of the five-coordinate [(CNC)NiBr2] 2 afforded
solutions of the four-coordinate cation [(CNC)NiBr]þ.[13] The
improved solubility of the octyl-substituted [(CNC)NiBr2] 9 in
chlorinated solvents compared with the butyl analogue 2
(X ¼ Br) allowed further studies of the solution behaviour of
these types of complexes.
Solutions of 9 in dichloromethane were brown–purple
(Fig. 8), whereas solutions in methanol were bright yellow.
The differences in solution colour are consistent with the
dramatically different UV-vis spectra (Fig. 9). The spectrum
for a methanol solution of 9 (Fig. 9) is very similar to that of the
spectra for solutions of the four-coordinate [(CNC)NiBr]
PF6 10ꢀPF6 in methanol or dichloromethane (Fig. 9), which
excludes the possibility that the absorption profile of 9 in
methanol originates from the cationic solvato-complex with a
distorted trigonal bipyramidal geometry. These data are consis-
tent with the dissolution of [(CNC)NiBr]PF6 10ꢀPF6 in either
methanol or dichloromethane resulting in solutions with the
four-coordinate species [(CNC)NiBr]þ 10, as well as dissolution
of 9 in methanol forming the same four-coordinate species. We
assume that the spectrum of 9 in dichloromethane (Fig. 9) is a
spectrum of the five-coordinate species in solution, based on the
stark differences in colour in solution (brown–purple for 9 in
dichloromethane; bright yellow for 10 in dichloromethane) that
parallel their solid-state appearances (purple powders for 9;
yellow powders for 10ꢀPF6) (see Supplementary Material).
The additions of tetrabutylammonium bromide to a dichloro-
methane solution of [(CNC)NiBr]PF6 10ꢀPF6 results in a signif-
icant change in the UV-vis spectra (Fig. 10). With subsequent
additions of tetrabutylammonium bromide, the intensity of the
peaks at ,450 and 540 nm increases and at the same time,
the intensity the peak at ,395 mn slightly decreases. After the
addition of excess bromide (.5 equiv.) the spectrum is similar
to that of solutions of the five-coordinate [(CNC)NiBr2] 9.

NHC Pincer Complexes
827
Br1 N31
N33
O36
Ni1
N11
O15
b
c
Fig. 5. Unit cell contents of 7ꢀBPh4 ꢀEt2O projected along the a axis.
7ꢀPF6 are remarkably similar (Fig. 12). Although there is an
increase in the absorbance at ,550 nm in the solution of 6 in
dichloromethane, it is not as pronounced as in the spectrum of
9 in dichloromethane. The addition of a large excess of tetra-
butylammonium bromide to the solution of 6 in dichloro-
methane resulted in a small enhancement of the absorbance at
550 nm (Fig. 13). It would appear that in the case of 6, the
addition of the methoxy substituents causes the nickel to favour,
though possible not exclusively, a four-coordinate geometry in
solution. However, in the solid state, the colour of 6 (dark
purple) is consistent with the five-coordinate geometry. This
may be a result of the subtle differences in the complex structure
(see Solid-State Studies) or a result of an electronic influence of
the methoxy groups on the carbene donor atoms.
O36
N31
O16
Ni1
N13
Br1
Fig. 6. A pair of centrosymmetrically related cations of 7 projected oblique
to the coordination plane.
Catalysis Studies
The catalytic activity of complexes 6 and 2 (X ¼ Br) was eval-
uated in Tamao–Kumada–Corriu coupling reactions against
several aryl substrates of varying electronic and steric properties
(Table 2). Despite the very low solubility of both complexes in
THF, the addition of the Grignard reagent to the mixture
afforded a dark red solution, presumably as a result of the dis-
solution of the complex. The results show that only moderate
yields of coupling products were obtained, with complex 2
(X ¼ Br) proving to be the ‘better’ catalyst (Table 2). Both
complexes show little tolerance for sterically hindered sub-
strates. Significant quantities of the homo-coupled products
(from the Grignard reagents) were found in all reactions, which
has been previously reported for similar systems.[26] This side
reaction is believed to be responsible for lower than expected
yields, as the Grignard reagent is consumed in the formation of
the homo-coupled product. The catalyst only showed reactivity
towards aryl halides. The attempted coupling of alkyl halides
(e.g. (4-bromobutoxy)benzene) did not form the desired
In methanol solutions of [(CNC)NiBr]PF610ꢀPF6, there was no
significant change in the spectra on the addition of tetrabutyl-
ammonium bromide. This solution behaviour is consistent with
an equilibrium existing involving the four- and five-coordinate
species (Scheme 2). It would appear that the ability of the
solvent to solvate bromide ions is a major contributing factor
as to the position of the equilibrium. The isosbestic point at
,420 nm in Fig. 10 is consistent with the equilibrium involving
only two species that absorb in the visible spectrum, presumably
[(CNC)NiBr2] 9 and [(CNC)NiBr]þ 10. When solutions of 9 in
dichloromethane were treated with increasing amounts of water
(within solubility limits), the position of the equilibrium shifted
away from the five-coordinate 9. This change in the equilibrium
position was observed by the decrease of the absorbance peaks at
,450 and 550 nm and an increase in the peak at ,390 nm
(Fig. 11), and is consistent with the increased solvation of the
free bromide by water.
1
product; instead, H NMR analysis indicated the formation of
alkenes (e.g. 4-phenoxybut-1-ene), suggesting a b-hydride
elimination pathway. Without the addition of the nickel
The methoxy-functionalized complex 6 appeared to behave
differently in dichloromethane solutions compared with 9.
The UV-vis spectra for dichloromethane solutions of 6 and

828
K. D. M. MaGee et al.
N33
N31
N13
N21
Ni1
N11
Br1
Fig. 7. A pair of centrosymmetrically related cations of 7 projected onto the coordination plane. The molecule at 1 – x, 1 – y, 1 – z is shown with blackened
bonds.
0.5
10
6
6
9
9
10 ϩ 0.5 eq BrϪ
10 ϩ 1 eq BrϪ
10 ϩ 2 eq BrϪ
10 ϩ 10 eq BrϪ
0.4
0.3
0.2
0.1
0
10Ϫ3 M
10Ϫ4 M
10Ϫ3 M
10Ϫ4 M
Fig. 8. Solutions of
1 ꢂ 10ꢁ4 M).
6
and
9
in dichloromethane (1 ꢂ 10ꢁ3 and
350
400
450
500
550
600
650
Wavelength [nm]
0.5
0.4
0.3
0.2
0.1
0
9 in CH2Cl2
Fig. 10. UV-vis spectra of a solution of 10ꢀPF6 in dichloromethane
(,10ꢁ4 M) with successive additions of tetrabutylammonium bromide.
10.PF6 in CH2Cl2
9 in CH3OH
10.PF6 in CH3OH
Conclusions
Solution studies of the octyl-substituted bis(benzimidazolin-2-
ylidene)pyridyl pincer five-coordinate nickel complex [(CNC)
NiBr2] suggest that the complex, with a five-coordinate geo-
metry, can exist in solution, unlike what was observed in earlier
studies.[13] The five-coordinate species is in an equilibrium
with the four-coordinate species [(CNC)NiBr]þ, and the equi-
librium is strongly influenced by the nature of the solvent
system, in addition to ligand variations (pincer and halide), as
reported previously.[13] The addition of methoxy groups to the
periphery of the benzimidazolin-2-ylidene appears to result in
the favouring of the four-coordinate geometry in solution,
though the exact reason for this preference is unknown. The
nickel complexes displayed only moderate activity in Tamao–
Kumada–Corriu coupling reactions.
350
400
450
500
550
600
650
Wavelength [nm]
Fig. 9. UV-vis spectra of solutions of 9 and 10ꢀPF6 in methanol and
dichloromethane (,10ꢁ4 M).
complexes, there was no reaction between (4-bromobutoxy)-
benzene and the Grignard reagent. The more soluble complexes
7ꢀPF6 and 3ꢀPF6 were also tested, and found to have similar
activity to their parent compounds. In comparison with the
imidazole-based analogue 1ꢀBr, the benzimidazolin-2-ylidene
pincer complexes studied here proved to be less efficient cata-
lysts in Tamao–Kumada–Corriu coupling reactions.[26] The
complexes also displayed less activity than a benzimidazolin-2-
ylidene nickel complex of the type [(NHC)2NiBr2] bearing a
cis-chelating dibenzimidazolin-2-ylidene ligand.[27]
Experimental
Nuclear magnetic resonance (NMR) spectra were recorded
using a Bruker AV400N (400.13 MHz for 1H, 100.61 MHz for
1
13C) spectrometer at 300 K. H and 13C chemical shifts were
referenced to the residual solvent resonances. Assignments of
NMR spectra were made with the aid of DEPT, 1H–1H COSY,
1
HSQC (one-bond H–13C correlations) and HMBC (two- and

NHC Pincer Complexes
829
ϩ
N
N
N
N
N
N
BrϪ
ϩ
N
H17C8
N
C8H17
N
H17C8
N
C8H17
Ni
Br
Ni
Br
Br
9
10
Scheme 2. Equilibria involving 9 and 10 in solution.
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
6
9
6 ϩ 10 eq BrϪ
7.PF6
9 ϩ 250 mg LϪ1 H2O
9 ϩ 1150 mg LϪ1 H2O
9 ϩ 2150 mg LϪ1 H2O
0.30
0.25
0.20
0.15
0.10
0.05
0
7 ϩ 200 eq BrϪ
400
450
500
550
600
650
350
400
450
500
550
600
650
Wavelength [nm]
Wavelength [nm]
Fig. 11. UV-vis spectra of a solution of 9 in dichloromethane (,10ꢁ4 M)
with successive additions of water.
Fig. 13. UV-vis spectra of solution of 6 and 7ꢀPF6 in dichloromethane
(,10ꢁ4 M), with the addition of tetrabutylammonium bromide.
1,3-Bis(5,6-dimethoxybenzimidazol-1-yl)pyridine 4
0.40
6 in CH2Cl2
A solution of 5,6-dimethoxybenzimidazole (2.0 g, 11 mmol) in
dimethylformamide (10 mL) was added dropwise to a cooled
(ice-bath) suspension of sodium hydride (60 % dispersion in oil,
0.50 g, 12 mmol) in dimethylformamide (10 mL). The reaction
mixture was warmed to room temperature and stirred for 1 h,
and then 2,6-dichloropyridine (0.68 g, 4.6 mmol) was added.
The resulting mixture was then heated at 708C for 24 h, and then
at 1408C for a further 24 h. The mixture was cooled and
then diluted with water (20 mL). The resulting precipitate was
collected, washed with diethyl ether (2 ꢂ 10 mL) and recrys-
tallized from toluene (,50 mL) to produce a light-pink powder
(1.62 g, 65 %). dH (CDCl3) 3.76 (s, 6H, 2 ꢂ OCH3), 3.97 (s, 6H,
2 ꢂ OCH3), 7.34 (s, 2H, 2 ꢂ benzimidazolyl CH), 7.50 (d, J 8.0,
2H, pyridyl H3 and H5), 7.80 (s, 2H, 2 ꢂ benzimidazolyl CH),
8.11 (t, J 8.0, 1H, pyridyl H4), 8.46 (s, 2H, 2 ꢂ benzimidazolyl
CH). dC (CDCl3) 56.3 (OCH3), 56.3 (OCH3), 96.7 (CH, benzi-
midazolyl C4 or C7), 102.4 (CH, benzimidazolyl C7 or C4),
110.3 (CH, pyridyl C3/C5), 125.7 (C, benzimidazolyl C8 or C9),
138.3 (C, benzimidazolyl C9 or C8), 139.1 (benzimidazole
C2), 141.9 (CH, pyridyl C4), 147.6 (C, benzimidazolyl C5
or C6), 148.2 (C, benzimidazolyl C6 or C5), 149.7 (C, pyridyl
C2/C6). Anal. calc. for C23H21N5O4: C 64.03, H 4.91, N 16.23.
Found: C 63.99, H 4.78, N 16.08 %.
0.35
7.PF6 in CH2Cl2
8 in CH3OH
0.30
0.25
0.20
0.15
0.10
0.05
0
7.BPh4 in CH3OH
400
450
500
550
600
650
Wavelength [nm]
Fig. 12. UV-vis spectra of 6 and 7 (7ꢀPF6, 7ꢀBPh4) in dichloromethane and
methanol solutions (,10ꢁ4 M).
three-bond 1H–13C correlations) experiments. Coupling
reactions were analysed using an HP 5890A gas chromatograph
with a flame ionization detector (FID). Microanalyses were
performed by the Central Science Laboratory, University of
Tasmania, or locally using a Perkin Elmer 2400 CHNS/O
Analyser. UV-vis spectra were collected using Perkin–
Elmer Lambda 35 or GBC 916 UV-vis spectrophotometers.
Quoted peak maxima are for the range 350–700 nm.
5,6-Dimethoxybenzimidazole,[24]1,3-bis(benzimidazol-1-yl)
pyridine,[10] the five-coordinate [(CNC)NiBr2] complex 2[13]
and the four-coordinate [(CNC)NiBr]PF6 salt 3ꢀPF[613] were
synthesized by literature procedures.
1,10-(2,6-Pyridyl)bis(3-n-butyl-5,6-
dimethoxybenzimidazolium) Dibromide 5ꢀ2Br
A mixture of 1-bromobutane (5.0 mL, 29 mmol) and 4 (0.84 g,
1.9 mmol) in dimethylformamide (10 mL) was sealed in a
screw-capped flask and then heated at 1008C for 48 h. The
mixture was cooled and a precipitate was collected. The filtrate

830
K. D. M. MaGee et al.
Table 2. Tamao Kumada Corriu coupling reactions catalyzed by complexes 6 and 2 (X 5 Br)
]
Conditions: aryl halide (1.0 mmol), ArMgX (1.5 mmol) and catalyst (0.05 mmol) in THF (1.5 mL); 24 h, 308C under Ar
]
X
R
6 or 2
RMgX
ϩ
THF
30ЊC
R1
R1
ArX
RMgX
Product
Catalyst
Yield [%]A
Br
2
6
58
54
PhMgBr
Br
2
53
Br
2
6
38
17
Br
2
6
51
33
OMe
MeO
MeO
Br
2
2
18
0B
OMe
–
Br
O
Cl
Cl
2
6
53
33
2
27
Cl
OMe
2
2
2
2
2
2
27
6
MeO
MeO
MeO
MeO
Cl
OMe
Br
OMe
4-MePhMgCl
44
6
MeO
Br
OMe
Cl
OMe
20
5
MeO
Cl
OMe
AYield determined by GC-FID using bis(ethyleneglycol) dibutyl ether as an internal standard from an average of two runs. BYield determined by 1H NMR.

NHC Pincer Complexes
831
was diluted with diethyl ether (50 mL) and the resulting pre-
cipitate collected. The solids were combined, and then recrys-
tallized from 1-propanol (,10 mL) to afford a colourless
powder (0.79 g, 57 %). dH (CDCl3) 1.04 (t, J 7.36, 6H, 2 ꢂ CH3),
1.56 (m, 4H, 2 ꢂ CH2), 2.14 (m, 4H, 2 ꢂ CH2), 4.03 (s, 6 H,
OCH3), 4.08 (s, 6 H, OCH3), 4.86 (t, J 7.34, 4H, 2 ꢂ NCH2),
7.17 (s, 2H, 2 ꢂ benzimidazolyl H4 or H7), 7.93 (s, 2H,
2 ꢂ benzimidazolyl H7 or H4), 8.45 (t, J 8.10, 1H, pyridyl H4),
8.67 (d, J 8.0, 2H, pyridyl H3 and H5), 11.88 (s, 2H, NCHN). dC
(CDCl3) 13.6 (CH3), 19.9 (CH2), 31.4 (CH2), 48.1 (NCH2), 57.0
(OCH3), 57.9 (OCH3), 94.7 (CH, benzimidazolyl C4 or C7),
97.3 (CH, benzimidazolyl C7 or C4), 117.6 (CH, pyridyl C3/
C5), 123.5 (C, benzimidazolyl C8), 125.7 (C, benzimidazolyl
C9), 139.7 (CH, benzimidazolyl C2), 146.1 (CH, pyridyl C4),
146.3 (C, pyridyl C2/C6), 150.1 (C, benzimidazolyl C6 or C5),
151.6 (C, benzimidazolyl C5 or C6). Anal. calc. for
C31H39Br2N5O4 ꢀ0.6CH3CH2CH2OHꢀ1.5H2O: C 51.26, H 6.14,
N 9.11. Found: C 51.44, H 5.92, N 8.99 %.
(C, benzimidazolyl C9), 147.7 (CH, pyridyl C4), 149.2
(C, benzimidazolyl C5 or C6), 149.7 (C, benzimidazolyl C6 or
C5), 150.4 (C, pyridyl C2/C6) 166.4 (C, C–Ni). Anal. calc. for
C31H37Br2N5NiO4ꢀH2O: C 47.72, H 5.04, N 8.98. Found:
C 47.63, H 5.12, N, 8.99 %.
Bromido[1,10-(2,6-pyridyl)bis(3-n-butyl-5,6-
dimethoxybenzimidazolin-2-ylidene)]nickel(II)
Hexafluorophosphate 7ꢀPF6
A mixture 6 (0.11 g, 0.17 mmol) and potassium hexa-
fluorophosphate (60 mg, 0.33 mmol) in methanol (20 mL) was
warmed for 5 min until an orange precipitate developed. The
solid was collected, washed with water (5 mL) and diethyl ether
(2 ꢂ 10 mL), and dried to afford an orange powder (0.10 g,
85 %). lmax/nm (e/Mꢁ1 cmꢁ1) (CH2Cl2) 464 (3200). dH (90 %
CDCl3, 10 % (CD3)2SO) 0.95 (t, J 7.2, 6H, 2 ꢂ CH3), 1.45 (m,
4H, 2 ꢂ CH2), 1.82 (m, 4H, 2 ꢂ CH2), 3.92 (s, 6H, OCH3), 3.97
(s, 6H, OCH3), 4.76 (m, 4H, 2 ꢂ NCH2), 7.04 (s, 2H, 2 ꢂ
benzimidazolyl H4 or H7), 7.43 (s, 2H, 2 ꢂ benzimidazolyl H7
or H4), 7.97 (d, J 8.4, 2H, pyridyl H3 and H5), 8.40 (t, J 8.4, 1H,
pyridyl H4). dC (90 % CDCl3, 10 % (CD3)2SO) 13.0 (CH3), 18.8
(CH2), 31.5 (CH2), 45.9 (CH2), 55.8 (OCH3), 56.2 (OCH3), 94.2
(CH, benzimidazolyl C4 or C7), 94.6 (CH, benzimidazolyl C7 or
C4), 107.3 (CH, pyridyl C3/C5), 121.5 (C, benzimidazolyl C8 or
C9), 128.6 (C, benzimidazolyl C9 or C8), 146.0 (CH, pyridyl
C4), 148.4 (C, benzimidazolyl C5 or C6), 148.8 (C, benzimi-
dazolyl C6 or C5), 150.1 (C, pyridyl C2/C6), 165.6 (C, C–Ni).
Anal. calc. for C31H37BrN5NiO4PF6ꢀH2O: C 44.05, H 4.65,
N 8.29. Found: C 44.04, H 4.61, N 8.26 %.
1,10-(2,6-Pyridyl)bis(3-n-octylbenzimidazolium)
Dibromide 8ꢀ2Br
A
mixture of 1,3-bis(benzimidazol-1-yl)pyridine (8.0 g,
25 mmol) and 1-bromooctane (50 mL, 0.29 mol) in dimethyl-
formamide (70 mL) was heated at 1208C for 24 h and then at
1408C for 48 h. The reaction mixture was cooled and the
resulting precipitate was collected and washed with diethyl ether
(2 ꢂ 20 mL) to afford a colourless powder (11.4 g, 63 %). dH
((CD3)2SO) 0.86 (m, 6H, 2 ꢂ CH3), 1.27–1.47 (m, 20H, 10 ꢂ
CH2), 2.07 (m, 4H, 2 ꢂ CH2), 4.70 (t, J 7.6, 4H, 2 ꢂ NCH2), 7.80
(m, 2H, benzimidazolyl H5 or H6), 7.82 (m, 2H, benzimidazolyl
H6 or H5), 8.30 (d, J 8.0, 2H, benzimidazolyl H4 or H7), 8.41 (d,
J 8.0, 2H, benzimidazolyl H7 or H4), 8.48 (d, J 8.4, 2H, pyridyl
H3 and H5), 8.78 (t, J 8.0, 1H, pyridyl H4), 10.90 (s, 2H,
NCHN). dC ((CD3)2SO) 13.9 (CH3), 22.0 (CH2), 25.8 (CH2),
28.5 (2 ꢂ CH2), 31.2 (2 ꢂ CH2), 47.4 (NCH2), 114.3 (CH,
benzimidazolyl C7 or C4), 115.7 (CH, benzimidazolyl C4 or
C7), 117.9 (CH, pyridyl C3/C5), 127.3 (CH, benzimidazolyl C5
or C6), 127.9 (CH, benzimidazolyl C6 or C5), 129.5 (C, ben-
zimidazolyl C8 or C9), 131.6 (C, benzimidazolyl C9 or C8),
142.9 (CH, benzimidazolyl C2), 144.5 (CH, pyridyl C4), 146.4
(C, pyridyl C2/C6). Anal. calc. for C35H47Br2N5: C 60.26,
H 6.79, N 10.04. Found: C 59.97, H 6.77, N 9.81 %.
Bromido[1,10-(2,6-pyridyl)bis(3-n-butyl-5,6-
dimethoxybenzimidazolin-2-ylidene)]nickel(II)
Tetraphenylborate (7ꢀBPh4)
Amixtureof6(0.15 g, 0.19 mmol)andsodiumtetraphenylborate
(0.14 g, 0.40 mmol) in methanol (10 mL) was warmed for 5 min.
The mixture was then diluted with water (10 mL) and the
resulting precipitate was collected. The solid was washed with
water (10 mL) and methanol (10 mL) to afford an orange solid.
The solid was recrystallized by the diffusion of vapours between
a diethyl ether solution and a solution of the salt in dichlor-
omethane to afford orange crystals (0.14 g, 71 %). lmax/nm
(e/Mꢁ1 cmꢁ1) (CH3OH) 456 (3000). dH (90 % CDCl3, 10 %
(CD3)2SO) 0.90 (t, 6H, J 7.2, 2 ꢂ CH3), 1.41 (m, 4H, CH2), 1.79
(m, 4H, CH2), 3.82 (s, 6H, OCH3), 3.86 (s, 6H, OCH3), 4.72 (t, J
7.6, 4H, NCH2), 6.67 (t, 4H, J 7.0, 4 ꢂ BPh4 p-ArH), 6.79–6.85
(m, 10H, 8 ꢂ BPh4 m-ArH, 2 ꢂ benzimidazolyl C4 or C7), 7.07
(s, 2H, 2 ꢂ benzimidazolyl C4 or C7), 7.13 (d, J 8.3, 2H, pyridyl
H3 and H5), 7.23 (br s, 8H, 8 ꢂ BPh4 o-ArH), 7.36 (t, J 8.2, 1H,
pyridyl H4). dC (90 % CDCl3, 10 % (CD3)2SO) 13.6 (CH3), 19.6
(CH2), 32.2 (CH2), 46.7 (CH2), 56.5 (OCH3), 56.9 (OCH3), 94.6
(CH, benzimidazolyl C4 or C7), 95.1 (CH, benzimidazolyl C7 or
C4), 107.1 (CH, pyridyl C3/C5), 121.5 (CH, BPh4 C4), 122.3 (C,
benzimidazolyl C8), 125.4 (CH, BPh4 C3/C5), 129.3 (C, ben-
zimidazolyl C9), 135.8 (CH, BPh4 C2/C6), 146.7 (CH, pyridyl
C4), 149.2 (C, benzimidazolyl C5 or C6), 149.6 (benzimidazolyl
C6 orC5), 150.6(C, pyridylC2/C6), 163.8 (C, q, J 49, BPh4 ipso-
Ar)166.6(C, C–Ni). Anal. calc. forC55H57BBrN5NiO4;C65.96,
H 5.74, N 6.99. Found: C 66.26, H 5.72, N 6.89 %. Crystals
suitable for X-ray studies were grownby the diffusion of vapours
between a diethyl ether solution and a solution of the salt in
dichloromethane.
Dibromido[1,10-(2,6-pyridyl)bis(3-n-butyl-5,6-
dimethoxybenzimidazolin-2-ylidene)]nickel(II) 6
A mixture of nickel acetate tetrahydrate (0.52 g, 2.1 mmol) and
5ꢀ2Br (1.0 g, 1.4 mmol) in dimethylformamide (4 mL) was
heated from room temperature to 1108C over the course of
,10 min and then immediately allowed to cool. The resulting
precipitate was collected, washed with diethyl ether (10 mL) and
recrystallized from nitromethane (,150 mL) to yield a purple
fine crystalline solid (0.58 g, 54 %). lmax/nm (e/Mꢁ1 cmꢁ1
)
(CH2Cl2) 462 (3300); (CH3OH) 455 (3600). dH (CDCl3 þ 1
drop CD3OD) 0.97 (t, J 7.2, 2 ꢂ 6H, CH3), 1.48 (m, 4H, 2 ꢂ
CH2), 1.85 (m, 4H, 2 ꢂ CH2), 3.92 (s, 6H, OCH3), 4.11 (s, 6H,
OCH3), 4.80 (t, J 7.6, 4H, 2 ꢂ NCH2), 6.98 (s, 2H, benzimida-
zolyl H4 or H7), 7.62 (s, 2H, benzimidazolyl H7 or H4), 8.23 (d,
J 8.4, 2H, pyridyl H3 and H5), 8.72 (t, J 8.4, 1H, pyridyl H4). dC
(CDCl3 þ 1 drop CD3OD) 13.8 (CH3), 19.9 (CH2), 32.4 (CH2),
47.0 (NCH2), 57.4 (OCH3), 57.8 (OCH3), 95.0 (CH, benzimi-
dazolyl C4 or C7), 95.9 (CH, benzimidazolyl C7 or C4), 108.9
(CH, pyridyl C3/C5), 122.4 (C, benzimidazolyl C8), 129.2

832
K. D. M. MaGee et al.
Dibromido[1,10-(2,6-pyridyl)bis(3-n-octylbenzimidazolin-
2-ylidene)]nickel(II), [(CNC)NiBr2] 9
1 M) and extracted with ethyl acetate (2 ꢂ 5 mL) and dried with
CaCl2. Product yields were determined by GC.
A mixture of 8ꢀ2Br (1.9 g, 2.8 mmol) and nickel acetate tetra-
hydrate (0.88 g, 3.1 mmol) in dimethylsulfoxide (11 mL) was
heated to 1208C for ,30 min and then allowed to cool. The
mixture was diluted with diethyl ether (20 mL) and then stirred
overnight. The resulting solid was collected and dried under
vacuum to afford dark purple crystals (2.5 g, 81 %). lmax/nm
(e/Mꢁ1 cmꢁ1) (CH2Cl2) 538 (1600), 453 (3700); (CH3OH) 434
(2100), 392 (3500). dH (CDCl3 þ 1 drop CD3OD) 0.90 (m, 6H,
2 ꢂ CH3), 1.25–1.37 (m, 16H, 8 ꢂ CH2), 1.61 (m, 4H, 2 ꢂ CH2),
2.10 (m, 4H, 2 ꢂ CH2), 4.82 (m, 4H, 2 ꢂ NCH2), 7.47–7.52 (m,
4H, benzimidazolyl H5 and H6), 7.53 (m, 2H, benzimidazolyl
H7), 7.87 (d, J 8.4, 2H, pyridyl H3 and H5), 8.02 (m, 2H, ben-
zimidazolyl H4), 8.40 (t, J 8.4, 1H, pyridyl H4). dC (CDCl3 þ 1
drop CD3OD) 13.9 (CH3), 22.5 (CH2), 26.5 (CH2), 29.1 (CH2),
29.1 (CH2), 30.0 (CH2), 31.7 (CH2), 47.8 (NCH2), 108.0 (CH,
pyridyl C3/C5), 112.2 (CH, benzimidazolyl C4 or C7), 112.5
(CH, benzimidazolyl C7 or C4), 125.9 (CH, benzimidazolyl C5
or C6), 126.7 (CH, benzimidazolyl C6 or C5), 128.8 (C, ben-
zimidazolyl C8), 135.6 (C, benzimidazolyl C9), 145.8 (CH,
pyridyl C4), 150.6 (C, pyridyl C2/C6), 171.9 (C, C–Ni). Anal.
calc. for C35H45Br2N5Ni: C 55.73, H 6.01, N 9.28. Found:
C 55.42, H 6.24, N, 9.11 %. Crystals suitable for X-ray studies
were grown by the diffusion of vapours between a solution of
THF and a solution of the complex in methanol.
X-Ray Structure Determinations
The crystal data for 9 and 7ꢀBPh4 ꢀEt2O are summarized below,
with the structures depicted in Figs 3 and 4, where ellipsoids
have been drawn at the 50 % probability level, and also in
Figs 5–7. Selected coordination geometries are shown in Ta-
ble 1. Crystallographic data for the structures were collected at
100(2) K on an Oxford Diffraction Xcalibur diffractometer (for
9) or an Oxford Diffraction Gemini diffractometer (for 7ꢀBPh4),
both fitted with Mo Ka radiation. Following analytical
absorption corrections and solution by direct methods, the
structures were refined against F2with full-matrix least-squares
using the program SHELXL-97.[28] Anisotropic displacement
parameters were employed for the non-hydrogen atoms. All H
atoms were added at calculated positions and refined by use of a
riding model with isotropic displacement parameters based on
those of the parent atom. Crystallographic data have been
deposited with the Cambridge Crystallographic Data Centre
(CCDC) (http://www.ccdc.cam.ac.uk), CCDC No. 862648 (9)
and 862649 (7ꢀBPh4ꢀEt2O).
Crystal Data for 9
ꢀ
C35H45Br2N5Ni, M ¼ 754.29, triclinic, space group P1, a ¼
˚
9.6767(4), b ¼ 12.7864(6), c ¼ 13.9272(7) A; a ¼ 90.991(4),
3
˚
b ¼ 99.678(4), g ¼ 102.541(4)8; V ¼ 1655.57(13) A ; Z ¼ 2;
Bromido[1,10-(2,6-pyridyl)bis(3-n-octylbenzimidazolin-
2-ylidene)]nickel(II) Hexafluorophosphate,
[(CNC)NiBr]PF6 10ꢀPF6
Dc ¼ 1.513 Mg mꢁ3; m ¼ 3.032 mmꢁ1; specimen: 0.26 ꢂ 0.12
ꢂ 0.02 mm3; ymax ¼ 33.08; 20784 reflections collected; 11527
unique (Rint ¼ 0.0338); Tmax/min ¼ 0.95/0.65; GoF ¼ 1.085;
R1 ¼ 0.0486, wR2 ¼ 0.0824 [I . 2s(I)].
A mixture of 9 (0.16 g, 0.22 mmol) and potassium hexa-
fluorophosphate (0.68 g, 3.7 mmol) in methanol (10 mL) was
heated at reflux for 5 min. Water (9 mL) was added and the
mixture was heated for a further 5 min. The reaction was allowed
to cooled to room temperature, and then cooled in an ice-bath.
The resulting precipitate was collected, washed with methanol
(10 mL) and water (10 mL), and dried to afford a yellow solid
(0.078 g, 43 %). lmax/nm (e/Mꢁ1 cmꢁ1) (CH2Cl2) 432 (1700),
387 (2900); (CH3OH) 440 (1400), 394 (2400). dH (90 % CDCl3,
10 % (CD3)2SO) 0.57 (m, 6H, 2 ꢂ CH3), 1.0–1.21 (m, 20H,
10 ꢂ CH2), 1.65 (m, 4H, 2 ꢂ CH2), 4.60 (m, 4H, 2 ꢂ NCH2),
7.26–7.34 (m, 4H, benzimidazolyl H5 and H6), 7.38 (d, J 7.2,
2H, benzimidazolyl H4 or H7), 7.73 (d, J 8.0, 2H, pyridyl H3 and
H5) 7.85 (d, J 7.6, 2H, H7 or H4), 8.20 (t, J 8.4, 1H, pyridyl H4).
dC (90 % CDCl3, 10 % (CD3)2SO) 13.4 (CH3), 21.6 (CH2), 25.8
(CH2), 27.4 (CH2), 28.3 (CH2), 29.6 (CH2), 30.8 (CH2), 46.7
(NCH2), 107.6 (CH, pyridyl C3/C5), 111.8 (CH, benzimidazolyl
C4 or C7), 111.9 (CH, benzimidazolyl C7 or C4), 125.7 (CH,
benzimidazolyl C5 or C6), 126.3 (CH, benzimidazolyl C6 or
C5), 128.0 (C, benzimidazolyl C8), 135.0 (C, benzimidazolyl
C9), 145.9 (CH, pyridyl C4), 150.4 (C, pyridyl C2/C6), 169.8
(C, C–Ni). Anal. calc. for C35H45BrN5NiPF6: C 51.31, H 5.54,
N 8.55. Found: C 51.55, H 5.36, N, 8.42 %.
Crystal Data for 7ꢀBPh4 ꢀEt2O
ꢀ
C59H67BBrN5NiO5, M ¼ 1075.61, triclinic, space group P1,
˚
a ¼ 13.3548(4), b ¼ 13.9625(4), c ¼ 17.3927(5) A; a ¼ 91.903
3
˚
(2), b ¼ 110.563(3), g ¼ 117.055(3)8; V ¼ 2630.82(18) A ;
Z ¼ 2; Dc ¼ 1.358 Mg mꢁ3
;
m ¼ 1.183 mmꢁ1
;
specimen:
0.52 ꢂ 0.15 ꢂ 0.12 mm3; ymax ¼ 35.08; 63735 reflections col-
lected; 21593 unique (Rint ¼ 0.0451); Tmax/min ¼ 0.468/0.329;
GoF ¼ 0.903; R1 ¼ 0.0414, wR2 ¼ 0.0970 [I . 2s(I)].
Supplementary Material
Images of 6, 9, 7ꢀPF6 and 10ꢀPF6 in the solid-state form are
provided in Supplementary Material.
Acknowledgements
We thank Curtin University for a Curtin University Research and Teaching
Fellowship (to DHB), a Curtin University Internal Research Grant (to DHB)
and a Curtin University Postgraduate Scholarship (to GT). The authors
acknowledge the facilities, scientific and technical assistance of the
Australian Microscopy and Microanalysis Research Facility at the Centre for
Microscopy, Characterisation and Analysis, The University of Western
Australia, a facility funded by the University, State and Commonwealth
Governments.
Catalysis Studies
Typical procedure for nickel-catalyzed Tamao–Kumada–
Corriu coupling reaction: Grignard reagent (1.5 mL, 1 M in
tetrahydrofuran) was added to a mixture of aryl halide (1 mmol),
nickel complex (5 mol %, 0.05 mmol) and bis(ethyleneglycol)
dibutyl ether (45 mg) in an argon-purged tube. The reaction was
heated at 308C for 24 h in a Radleys parallel synthesizer. After
cooling, the reaction mixture was quenched with HCl (2 mL,
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