Synthesis and characterisation of new PCsp3P-supported nickel complexes

Article abstract of DOI:10.1016/j.jorganchem.2014.02.013

The coordination behaviour of the aliphatic pincer ligand cis-1,3-bis-((di-tert-butylphosphino)methyl)cyclohexane with NiCl₂ and NiBr₂ was studied. Reflux in toluene afforded cyclometalated, tridentate PC_sp3P pincer complexes, that were characterised by elemental analysis and NMR spectroscopy; the solid state structures were determined by X-ray diffraction showing an unusually long Ni-Br bond in the bromo complex. A preliminary account of their reactivity is reported and they were found to be unreactive towards base and hydride sources and to be poor catalysts in Kumada coupling reactions.

Full text of DOI:10.1016/j.jorganchem.2014.02.013

Journal of Organometallic Chemistry 759 (2014) 15e18
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and characterisation of new PC P-supported nickel
sp3
complexes
Klara J. Jonasson, Ola F. Wendt*
Centre for Analysis and Synthesis, Department of Chemistry, Lund University, P.O. Box 124, S-221 00 Lund, Sweden
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 December 2013
Received in revised form
The coordination behaviour of the aliphatic pincer ligand cis-1,3-bis-((di-tert-butylphosphino)methyl)
cyclohexane with NiCl and NiBr was studied. Reflux in toluene afforded cyclometalated, tridentate
2 2
PCsp3P pincer complexes, that were characterised by elemental analysis and NMR spectroscopy; the solid
state structures were determined by X-ray diffraction showing an unusually long NieBr bond in the
bromo complex. A preliminary account of their reactivity is reported and they were found to be
unreactive towards base and hydride sources and to be poor catalysts in Kumada coupling reactions.
Ó 2014 Elsevier B.V. All rights reserved.
12 February 2014
Accepted 20 February 2014
Keywords:
Aliphatic pincer complexes
PCP pincer ligands
Nickel
Cyclometalation
Coordination
1. Introduction
several known examples where the nature of the coordinating
carbon alters the reactivity of a pincer complex, illustrating how a
Over the last 30 years, pincer metal complexes have earned
recognition as potent and versatile compounds in homogeneous
catalysis [1]. However, replacement of precious metals with
cheaper and more abundant first row transition metal alterna-
tives remains one of the great challenges for the field [2]. One
problem in this aspect might be the reluctance of 3d metals to
undergo 2-electron oxidative addition and reductive elimination
reactions. In combination with the weaker MeC bonds of the 3d
metals this usually makes CeH activation and cyclometalation
reactions more difficult. On the other hand, in the case of nickel
complexes, 1-electron processes are more frequently occurring,
opening up for catalytic pathways that may not be accessible for
heavier analogues [3]. Recent advances of nickel pincer com-
plexes in the literature involve various cross-coupling reactions
strongly s-donating Csp3-hybridised ligand can be a useful tool for
electrochemical tuning [12], and this has opened up NeH oxidative
addition pathways unavailable with traditional aromatic pincer li-
gands [13]. We have previously reported on the synthesis of the
cyclohexyl-based PCsp3
P ligand cis-1,3-bis-((di-tert-butylphos-
phino)methyl)cyclohexane (1), and we and others have shown its
ability to cyclometalate with second and third row transition
metals, such as palladium [14], platinum [15], rhodium [16] and
iridium [17]. Here we report on the first complexation of this ligand
with nickel, together with some reactivity data of these PCsp3P-
coordinated complexes.
2. Experimental section
[
3,4], direct alkylations [5] alkene hydrogenations [6], hydro-
2
.1. General considerations
aminations [7], hydrosilylations [8] and reduction of carbon di-
oxide to methanol [9].
Amongst the published work on PCP pincer complexes, pincer
ligands with aromatic backbones are in vast majority and this is also
true for nickel complexes, although a number of aliphatic nickel
pincer complexes have been reported [10,11]. In general, there are
All manipulations were performed under a nitrogen or argon
atmosphere using standard Schlenk or glovebox techniques, except
where noted. Solvents were purified by vacuum distillation from
sodium/benzophenone ketyl radical. The ligand cis-1,3-bis-((di-
tert-butylphosphino)methyl)cyclohexane (1) was synthesized ac-
cording to previously reported procedures [14]. All other chemicals
where purchased from Acros, Alfa Aesar or Sigma Aldrich and used
1
13
31
as received. H, C and P NMR spectroscopy experiments were
recorded on a Varian Unity INOVA 500 spectrometer, operating at
*
Corresponding author. Tel.: þ46 46 2228153.
E-mail address: ola.wendt@chem.lu.se (O.F. Wendt).
http://dx.doi.org/10.1016/j.jorganchem.2014.02.013
022-328X/Ó 2014 Elsevier B.V. All rights reserved.
0

16
K.J. Jonasson, O.F. Wendt / Journal of Organometallic Chemistry 759 (2014) 15e18
1
4
99.76 MHz ( H). Chemical shifts are given in ppm downfield from
3. Results and discussion
1
13
31
3 4
TMS, using residual solvent peaks ( H and C) or H PO ( P) as
reference. Multiplicities are abbreviated as follows: (s) singlet, (d)
doublet, (t) triplet, (q) quartet, (m) multiplet, (v) virtual. Elemental
analyses were performed by H. Kolbe Microanalytisches Labo-
ratorium, Mülheim an der Ruhr, Germany. XRD-quality crystals of
The straightforward synthesis of pincer complexes 2a and 2b is
illustrated in Scheme 1, following the synthetic protocol of Zar-
garian and coworkers for the non-cyclic 1,5-bis(phosphinito)
pentane ligand [10b], but increasing the amount of NiX
equivalents.
2
from 2 to 3
2
a and 2b were obtained through recrystallisation from pentane.
Intensity data were collected with an Oxford Diffraction Excalibur 3
The products were isolated in moderate to good yields, and no
phosphorus containing species apart from the products could be
ꢀ
system, using
u
-scans and Mo K
a
(l
¼ 0.71073 A) radiation [18]. The
31
data were extracted and integrated using Crysalis RED [19]. The
observed in the crude reaction mixture by means of P NMR
spectroscopy. Thus, there is no indication that byproducts such as
previously reported binuclear 16-atom ring chelate complexes or
mononuclear complexes with cis-coordination to the P atoms are
formed [22]. This however does not rule out the formation of such
16-atom cyclic dimers, since these compounds are known to be
highly fluxional and sometimes low-soluble which makes them
hard to detect by NMR spectroscopy. The somewhat limited yields
could also be accounted for by formation of phosphorus containing
nickel salts, but the solid residues formed during the reactions are
highly insoluble and probably NMR silent, and any attempted
characterization has been unsuccessful. The group of Zargarian has
reported that nickelation of the 1,5-bis(phosphino)pentane ligand
gives a byproduct with low solubility identified as a zwitterionic
complex with an anionic tetrahedral nickel centre and a mono-
coordinated pincer ligand with one protonated non-coordinated
phosphine. The protonation is suggested to take place by in situ
generated HX, which supports their and our observation that
addition of DMAP or other bases improves the yield for the
complexation reaction [10a].
structure was solved by direct methods and refined by full-matrix
least-squares calculations on F using SHELXTL5.1 [20]. Molecular
graphics were generated using CrystalMaker 8.3.5 [21]. All crys-
tallographic data are available in CIF format (CCDC reference
numbers 978220-21).
2
2.2. Preparation of trans-[NiCl{cis-1,3-bis-((di-tert-
butylphosphino)methyl)}cyclo-hexane] (2a)
DMAP (15.2 mg, 0.125 mmol) was added to a stirred mixture of
the
ligand (50.0 mg, 0.125 mmol) and anhydrous NiCl
.374 mmol) in toluene (5 mL). The reaction mixture was heated to
cis-1,3-bis-[(di-tert-butylphosphino)methyl]cyclohexane
2
(48.5 mg,
0
reflux for 24 h under a nitrogen atmosphere. The cooled suspension
was concentrated in vacuo, dispersed in ethyl acetate and filtered in
air through a pad of silica. Removal of the solvent afforded 2a as a
1
yellow crystalline powder. Yield: 36.9 mg (69% based on 1). H NMR
(
C
6
D
6
):
d 1.82e1.77 (m, Cy, 2H), 1.74e1.70 (m, Cy, 1H), 1.69e1.63 (m,
t
PCH
.45 (vt, J ¼ 13.0 Hz, Bu, 18H), 1.27 (t, JPH ¼ 11.0 Hz, HCeNi), 1.29e
.24 (m, Cy, 1H), 1.11e1.03 (m, PCH CH, 2H), 0.82e0.74 (m, Cy, 2H).
2
CH, 2H), 1.55e1.45 (m, Cy, 2H), 1.48 (vt, J ¼ 13.0 Hz, Bu, 18H),
t
31
1
1
The P{ H} NMR spectra of 2a and 2b display a sharp singlet
resonance that confirms the equivalence of the phosphorus nuclei
in agreement with an expected trans geometry; this is also
1
2
1
3
1
2
C{ H} NMR (C
PC ¼ 21 Hz, CH), 35.7 (vt, JPC ¼ 19 Hz, CHCH
vt, JPC ¼ 11 Hz, C(CH ), 34.6 (vt, JPC ¼ 14 Hz, C(CH
PC ¼ 18 Hz, PeCH ), 30.4 (vt, JPC ¼ 5.0 Hz, C(CH
PC ¼ 4.0 Hz, C(CH
61.79 (s). Anal. Calcd for C24
Found: C, 58.24; H, 10.12.
6
D
6
):
d
53.3 (t,
J
PC ¼ 11 Hz, HCeNi), 49.5 (vt,
CH ), 35.2
), 32.3 (vt,
), 29.6 (vt,
). P{ H} NMR (C ):
(493.74): C, 58.38; H, 10.00.
t
J
(
J
J
d
2
2
consistent with the appearance of the Bu protons as virtual triplets
1
3
)
3
3
)
3
in H NMR spectra. The characteristic pattern of virtual triplets is
13
1
2
3
)
3
also observed in the C{ H} NMR spectra, where all nuclei except
the most remote methylene carbons of the cyclohexyl ring display
coupling to phosphorus.
31
1
3
)
3
), 27.2 (s, CH
2
CH
2
CH
2
6 6
D
H49ClNiP
2
To confirm the cyclometalated structures, crystals of both
complexes were subjected to an X-ray diffraction experiment. The
details of the crystal structure solution and refinement are given in
Table 1. The molecular structures, including selected bond distances
and angles, of compound 2a and 2b are shown in Figs. 1 and 2,
respectively. As expected from the NMR spectroscopy results, the
cis-1,3-bis-((di-tert-butylphosphino)methyl)cyclohexane ligand is
coordinated meridionally with the P atoms positioned trans to each
other. The Ni atom adopts a distorted square planar geometry, with
2.3. Preparation of trans-[NiBr{cis-1,3-bis-((di-tert-
butylphosphino)methyl)}-cyclohexane] (2b)
The compound was synthesized according to the same pro-
cedure and in the same scale as the corresponding chloride
1
complex (2a). Yield: 42.9 mg (71% based on 1). H NMR (C
6
D
6
):
CH, 2H),
.55e1.50 (m, Cy, 2H), 1.49 (vt, J ¼ 12.5 Hz, Bu, 18H), 1.46 (vt,
d
1.83e1.79 (m, Cy, 2H), 1.73e1.67 (m, Cy, 1H and m, PCH
2
t
ꢀ
1
P(1)eNieP(2) angles around 170 . The cyclohexyl ring has a chair
t
J ¼ 12.0 Hz, Bu, 18H), 1.30e1.22 (m, Cy, 1H), 1.27 (t, JPH ¼ 11.0 Hz,
conformation and the three coordinated positions are all equato-
rially oriented in agreement with previous observations [14,15].
The NieCl bond in 2a is longer than in the analogous aromatic
compounds [23], and very close to the reported bond length for a
1
3
HCeNi), 1.11e1.05 (m, PCH
2
CH, 2H), 0.81e0.73 (m, Cy, 2H).
C
1
2
{
H} NMR (C
PC ¼ 26 Hz, CH), 35.7 (vt, JPC ¼ 19 Hz, CHCH
PC ¼ 11 Hz, C(CH ), 35.1 (vt, JPC ¼ 14 Hz, C(CH
vt, JPC ¼ 18 Hz, PeCH ), 30.7 (vt, JPC ¼ 4.7 Hz, C(CH ), 29.7 (vt,
), 27.2 (s, CH ). P{ H} NMR (C ):
(493.74): C, 53.56; H,
6
D
6
):
d
56.3 (t,
J
PC ¼ 11 Hz, HCeNi), 49.3 (vt,
CH ), 35.5 (vt,
), 32.8
J
J
2
2
tBu
3
)
3
3
)
3
similar non-cyclic PCsp3P nickel complex [10a], underpinning the
3
(
2
3
)
3
greater trans-influence from a sp -hybridized coordinated carbon
31
1
2
J
d
PC ¼ 4.5 Hz, C(CH
3
)
3
2
CH
49BrNiP
2
CH
2
6
D
6
compared to its sp -hybridized aromatic counterpart. However, the
ꢀ
61.47 (s). Anal. Calcd for C24
.18. Found: C, 53.44; H, 9.11.
H
2
NieBr bond in 2b (2.4303(4) A) is significantly longer than NieBr
9
2.4. General procedure for attempted Kumada coupling
RMgCl (0.27 mmol, 3 M THF solution) was added to a solution of
RX (0.26 mmol) and the catalyst (3 mol%) in THF (0.5 mL). The
ꢀ
mixture was heated to 120 C for the desired time. A sample of the
reaction was then withdrawn, quenched with 0.5 M HCl and diluted
with THF. The organic phase was dried over MgSO
the resultant solution was analyzed by GC.
4
and filtered, and
Scheme 1. Synthesis of 2a and 2b.

K.J. Jonasson, O.F. Wendt / Journal of Organometallic Chemistry 759 (2014) 15e18
17
Table 1
Crystal data and collection and refinement details for compounds 2a and 2b.
2a
2b
Formula
Fw
C
24
H
49ClNiP
2
C
24
H
49BrNiP
538.16
P2 /c
2
493.71
Pna2
22.9163(5)
8.4324(3)
14.4279(4)
90
90
90
2788.04
4
1.176
Space group
1
1
ꢀ
a/A
11.4024(2)
15.8824(3)
15.6999(4)
90
98.245(2)
90
2813.83
4
1.270
ꢀ
b/A
ꢀ
c/A
a
/deg
/deg
b
g
/deg
ꢀ
3
V/A
Z
ꢁ
3
D
calcd/g cm
ꢁ
1
m
/mm
0.915
2.231
q
/range/deg
2.57e28.88
46,663
6821
0.0563
0.1242
1.095
2.44e28.97
61,313
6895
0.0450
0.1005
1.254
No. reflns collected
No. of unique reflns
R(F) (I > 2
wR2(F ) (all data)
a
s(I))
2
b
c
S
R
int
0.0975
0.0665
P
P
P
Fig. 2. Molecular structure of 2b at the 30% probability level. Hydrogen atoms are
a
R ¼ ðjF
wR2 ¼ ½ wðjF
S ¼ ½ wðjF
o
j ꢁ jF
c
jÞ= jF
o
j.
ꢀ
ꢀ
omitted for clarity. Selected bond lengths (A) and bond angles ( ) with estimated
standard deviations: Ni1eC1 ¼ 1.998(2), Ni1eP1 ¼ 2.2402(7), Ni1eP2 ¼ 2.2325(7),
Ni1eBr1 ¼ 2.4303(4), C1eNi1eBr1 ¼ 169.48(7), P1eNi1eP2 ¼ 168.42(3), P1eNi1e
P
P
b
c
2
jÞ2ꢂ1=2.
jÞ2ꢂ1=2.
o
j ꢁ jF
c
jÞ = jF
o
P
2
o
j ꢁ jF
c
jÞ = jF
o
C1
¼
85.09(7), P2eNi1eC1
¼
85.15(7), P1eNi1eBr1
¼
95.476(19), P2eNi1e
Br1 ¼ 95.26(2).
ꢀ
bonds in both aromatic (2.3290e2.3601 A) [10d,24,25] and
ꢀ
aliphatic (2.3712e2.3866 A) [10a,10d] PCP nickel bromide com-
plexes in literature. It approaches the bond length for the aromatic
NCN nickel bromide complexes reported by van Koten and co-
bromide deviates slightly from the coordination plane and it is also
possible that the NieCl distance is underestimated by the crystal
structure due to libration [27].
i
workers (NCN
¼
C
H
6 3
-2,6-{CH
2
N( Pr)Me}
2
and
6 3
C H -2,6-
t
ꢀ
ꢀ
The complexes showed no sign of decomposition upon
exposure to air in solution, and could be stored under air as solids
{
CH
2
N( Bu)Me}
2
, NieBr ¼ 2.437(2) A and 2.4459(30) A) [26], and
thus is one of the longest Ni(II)eBr distances reported to this date.
The reason for this deviation is not obvious to us especially since
the trans influence of the cyclohexyl ring in 2a is no different from
ꢀ
at room temperature or in pentane solution at ꢁ30 C for several
weeks. Initial studies confirm a low reactivity of these complexes;
3
4
refluxing 2a in toluene/ethanol (1:1) with NaBH did not result in
any conversion to the corresponding hydride, as is reported for
the analogous aromatic nickel pincer complex [28], nor did
other sp -hybridized ligands. It can be noted that the position of the
treatment with LiAlH
synthesis of similar phosphinite pincer hydride complexes [9b].
Piers and co-workers have reported on the conversion of a PCsp3
nickel bromide complex to a rare nickel carbene complex through
dehydrobromination with KN(SiMe [29], but under the same
4
in toluene that has been used for the
P
3 2
)
reaction conditions 2b did not display any such reactivity. This
rather unexpected lack of reactivity towards the strongly
donating hydride and amide is more likely attributed to the bulky
t
Bu-substituents than to the electronic environment at the metal
centre. 2a and 2b have also been tested as catalysts for Kumada
coupling of alkyl and aryl halides with alkyl Grignard reagents,
but the best GC yields were around 15%, for the coupling of
EtMgCl and PhBr. Zargarian et al. have shown that the steric bulk
of the phosphorus substituents strongly influences the reactivity
t
in such reactions [10d], and a replacement of the Bu-groups for
i
less sterically demanding Pr-groups is
investigations.
a topic for future
4. Conclusion
The complexation behaviour of the cyclohexyl-based PCsp3
ligand cis-1,3-bis-((di-tert-butylphosphino)methyl)cyclohexane
towards NiCl and NiBr has been studied, giving two new PCsp3P-
supported nickel complexes. The bond distances found in the mo-
lecular structures indicate a high reactivity but they were found to
be more or less unreactive in a number of standard reactions for
these types of complexes.
P
Fig. 1. Molecular structure of 2a at the 30% probability level. Hydrogen atoms are
2
2
ꢀ
ꢀ
omitted for clarity. Selected bond lengths (A) and bond angles ( ) with estimated
standard deviations: Ni1eC1 ¼ 1.990(4), Ni1eP1 ¼ 2.2346(11), Ni1eP2 ¼ 2.2251(11),
Ni1eCl1 ¼ 2.2497(14), C1eNi1eCl1 ¼ 178.81(18), P1eNi1eP2 ¼ 170.83(5), P1eNi1e
C1
¼
85.97(13), P2eNi1eC1
¼
85.06(13), P1eNi1eCl1
¼
94.70(5), P2eNi1e
Cl1 ¼ 94.46(5).

18
K.J. Jonasson, O.F. Wendt / Journal of Organometallic Chemistry 759 (2014) 15e18
Acknowledgements
25 (2006) 602;
(
(
(
b) V. Pandarus, D. Zargarian, Organometallics 26 (2007) 4321;
c) V. Pandarus, D. Zargarian, Chem. Commun. (2007) 978;
d) A. Castonguay, A.L. Beauchamp, D. Zargarian, Organometallics 27 (2008)
Financial support from the Swedish Research Council, the Knut
and Alice Wallenberg Foundation and the Royal Physiographic So-
ciety in Lund is gratefully acknowledged. We thank Mr. David
Ahlstrand for experimental assistance in the Kumada coupling
reactions.
5723.
[
11] For a thorough kinetic and mechanistic study on the nickelation of aromatic
versus aliphatic PCP and POCOP ligands, see: B. Vabre, M.L. Lambert, A. Petit,
D.H. Ess, D. Zargarian Organometallics 31 (2012) 6041.
[12] (a) W. Leis, H.A. Mayer, W.C. Kaska, Coord. Chem. Rev. 252 (2008) 1787;
b) D. Gelman, S. Musa, ACS Catal. 2 (2012) 2456.
(
[
[
[
13] J. Zhao, A.S. Goldman, J.F. Hartwig, Science 307 (2005) 1080.
14] S. Sjovall, O.F. Wendt, C. Andersson, J. Chem. Soc. Dalton (2002) 1396.
15] D. Olsson, A. Arunachalampillai, O.F. Wendt, Dalton Trans. (2007) 5427.
References
[1] (a) M.E. van der Boom, D. Milstein, Chem. Rev. 103 (2003) 1759;
[16] V.F. Kuznetsov, A.J. Lough, D.G. Gusev, Inorg. Chim. Acta 359 (2006) 2806.
[17] A. Arunachalampillai, D. Olsson, O.F. Wendt, Dalton Trans. (2009) 8626.
[18] Crysalis CCD, Oxford Diffraction Ltd., Abingdon, Oxfordshire, UK, 2005.
[19] Crysalis RED, Oxford Diffraction Ltd., Abingdon, Oxfordshire, UK, 2005.
[20] G.M. Sheldrick, SHELXTL5.1, Program for Structure Solution and Least Squares
Refinement, University of Göttingen, Göttingen, Germany, 1998.
[21] CrystalMakerÒ Software, Begbroke Science Park, Sandy Lane, Yarnton,
Oxfordshire, OX5 1PF, United Kingdom, 2010.
[22] (a) V. Pandarus, A. Castonguay, D. Zargarian, Dalton Trans. (2008) 4756;
(b) M.T. Johnson, O.F. Wendt, Inorg. Chim. Acta 367 (2011) 222.
[23] B.J. Boro, D.A. Dickie, K.I. Goldberg, R.A. Kemp, Acta Crystallogr. E64 (2008)
m1304.
[24] A.R. Kennedy, R.J. Cross, K.W. Muir, Inorg. Chim. Acta 231 (1995) 195.
[25] F. Bachechi, Struct. Chem. 14 (2003) 263.
[26] J.A.M. Vanbeek, G. van Koten, M.J. Ramp, N.C. Coenjaarts, D.M. Grove,
K. Goubitz, M.C. Zoutberg, C.H. Stam, W.J.J. Smeets, A.L. Spek, Inorg. Chem. 30
(1991) 3059.
(
(
(
(
b) M. Albrecht, M.M. Lindner, Dalton Trans. 40 (2011) 8733;
c) J. Choi, A.H.R. MacArthur, M. Brookhart, A.S. Goldman, Chem. Rev. 111
2011) 1761;
d) N. Selander, K.J. Szabo, Chem. Rev. 111 (2011) 2048.
[
2] R.M. Bullock (Ed.), Catalysis without Precious Metals, Wiley-VCH, Hoboken, NJ,
010.
2
[
[
3] X.L. Hu, Chem. Sci. 2 (2011) 1867.
4] (a) O. Vechorkin, X.L. Hu, Angew. Chem. Int. Ed. 48 (2009) 2937;
(
(
b) O. Vechorkin, V. Proust, X.L. Hu, J. Am. Chem. Soc. 131 (2009) 9756;
c) O. Vechorkin, D. Barmaz, V. Proust, X.L. Hu, J. Am. Chem. Soc. 131 (2009)
12078;
(
d) O. Vechorkin, R. Scopelliti, X.L. Hu, Angew. Chem. Int. Ed. 50 (2011) 11777.
[5] O. Vechorkin, V. Proust, X.L. Hu, Angew. Chem. Int. Ed. 49 (2010) 3061.
[6] K.V. Vasudevan, B.L. Scott, S.K. Hanson, Eur. J. Inorg. Chem. (2012) 4898.
[7] A. Castonguay, D.M. Spasyuk, N. Madern, A.L. Beauchamp, D. Zargarian, Or-
ganometallics 28 (2009) 2134.
[
[
8] S. Chakraborty, J.A. Krause, H. Guan, Organometallics 28 (2009) 582.
9] (a) S. Chakraborty, J. Zhang, J.A. Krause, H.R. Guan, J. Am. Chem. Soc. 132
[27] J.P. Clusker, M. Lewis, M. Rossi, Crystal Structure Analysis for Chemists and
Biologists, Wiley-VCH, 1994.
[28] C.J. Moulton, B.L. Shaw, J. Chem. Soc. Dalton (1976) 1020.
[29] D.V. Gutsulyak, W.E. Piers, J. Borau-Garcia, M. Parvez, J. Am. Chem. Soc. 135
(2013) 11776.
(
(
2010) 8872;
b) S. Chakraborty, Y.J. Patel, J.A. Krause, H.R. Guan, Polyhedron 32 (2012) 30.
[10] For synthesis and characterization of aliphatic nickel pincer complexes, see:
(
a) A. Castonguay, C. Sui-Seng, D. Zargarian, A.L. Beauchamp, Organometallics