Synthesis and structural characterisation of nickel(II) alkyl complexes NiR2, [Ni(Cp)R]2 and a 'head-to-tail' coupled alkyl intermediate compound [NiR(Cl)(R-R)] [R=C(SiMe3)2C5H4N-2, CPh(SiMe3)C5H4N-2 or CH(SiMe3)C5H4N-2; Cp=η5-C5H5

Article abstract of DOI:10.1016/S0022-328X(98)00629-9

Thermally stable nickel(II) alkyls NiR₂ [R=R¹=C(SiMe₃)₂C₅H₄N-2 (1); R=R²=CPh(SiMe₃)C₅H₄N-2 (2),] and [CpNiR]₂ [Cp=η⁵-C₅H₅; R=R³=CH(SiMe₃)C₅H₄N-2 (4)] containing pyridine-functionalised α-substituted alkyl ligands have been prepared by the alkylation of nickel(II) dihalide complexes [NiX₂L₂] (X=Cl, Br; L₂=2 PPh₃, N,N,N′,N′-tetramethylethylenediamine) or nickelocene with appropriate lithium alkyls. However, similar alkylation reaction of [LiR¹]₂ with [NiCl₂(diphos)] (diphos=Ph₂PCH₂CH₂PPh₂) afforded a novel nickel(II)alkylchloride complex [NiR¹(Cl)(R¹-R¹)] (3), in which a 'head-to-tail' coupled organic compound 2-CH(SiMe₃)₂C₅H₄N-5-C(SiMe₃)₂C₅H₄N (R¹-R¹) remained coordinated to the nickel centre via one of the pyridyl nitrogens. Compounds 1-4 have been confirmed by X-ray structure analysis.

Full text of DOI:10.1016/S0022-328X(98)00629-9

Journal of Organometallic Chemistry 564 (1998) 193–200
Synthesis and structural characterisation of nickel(II) alkyl complexes
NiR2, [Ni(Cp)R]2 and a ‘head-to-tail’ coupled alkyl intermediate
compound [NiR(Cl)(R–R)] [R=C(SiMe3)2C5H4N-2,
CPh(SiMe3)C5H4N-2 or CH(SiMe3)C5H4N-2; Cp=p5-C5H5]
Wing-Por Leung *, Hung-Kay Lee, Zhong-Yuan Zhou, Thomas C.W. Mak
Department of Chemistry, The Chinese Uni6ersity of Hong Kong, Shatin, New Territories, Hong Kong
Received 11 March 1998; received in revised form 28 April 1998
Abstract
Thermally stable nickel(II) alkyls NiR2 [R=R1=C(SiMe3)2C5H4N-2 (1); R=R2=CPh(SiMe3)C5H4N-2 (2),] and [CpNiR]2
[Cp=p5-C5H5; R=R3=CH(SiMe3)C5H4N-2 (4)] containing pyridine-functionalised h-substituted alkyl ligands have been
prepared by the alkylation of nickel(II) dihalide complexes [NiX2L2] (X=Cl, Br; L2=2 PPh3, N,N,N%,N%-tetramethylethylenedi-
amine) or nickelocene with appropriate lithium alkyls. However, similar alkylation reaction of [LiR1]2 with [NiCl2(diphos)]
(diphos=Ph2PCH2CH2PPh2) afforded a novel nickel(II)alkylchloride complex [NiR1(Cl)(R1–R1)] (3), in which a ‘head-to-tail’
coupled organic compound 2-CH(SiMe3)2C5H4N-5-C(SiMe3)2C5H4N (R1–R1) remained coordinated to the nickel centre via one
of the pyridyl nitrogens. Compounds 1–4 have been confirmed by X-ray structure analysis. © 1998 Elsevier Science S.A. All rights
reserved.
Keywords: Nickel(II); Alkyls; Pyridine substituted alkyls; Cyclopentadienyl
1. Introduction
In addition to the use of bulky ligands, it has been
known that chelating ligands also impose a stabilizing
effect on the corresponding nickel(II) complexes. For
example, a large number of metallacycle compounds of
composition [Ni(C–E)2] (I) and [{Ni(C–E)Cl}2] (II)
(E=N, P, O, S) with anionic C,N- or C,P-chelates are
known [5–7]. Complexes I are prepared by direct reaction
of metal halides with the appropriate organolithium or
Grignard reagents, whilst complexes II are usually ob-
tainedbydirectmetallationofC–Hbonds.Organo-nickel
compounds of type II are scarcely found, although their
palladium(II) and platinum(II) analogues have been
extensively studied [8–10].
Organonickel species are known to be the intermediate
compounds in nickel catalyzed coupling reaction of
organic halides [1]. Thermally stable nickel(II) complexes
ofthetypes[NiR(X)L2], [NiR2L2], and[(p5-C5H5)NiR(L)]
(R=alkyloraryl;X=halides;L=nitrogen-orphospho-
rus-containing ligands) have been known [1,2]. In con-
trast, nickel dialkyls of the type [NiR2] which contain
Ni–C |-bonds being isolated and fully characterised are
scarcelyreported. Usingstericallydemandingalkyloraryl
ligands, thermally stable nickel dialkyl and diaryl com-
plexes such as bis(trityl)nickel(II) [Ni(CPh3)2] and bis(me-
sityl)nickel(II) [Ni(Mes)2] [1–4] have been synthesised.
The stability of these complexes is attributed to the use
of bulky and i-elimination stabilized ligands which shield
the central metal and block the decomposition pathway.
* Corresponding author.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00629-9

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W.-P. Leung et al. / Journal of Organometallic Chemistry 564 (1998) 193–200
structures of nickel(II) alkyl complexes based on the
pyridine-functionalised alkyl ligands R1, R2 and R3.
2. Results and discussion
2.1. Synthesis of nickel(II) alkyls NiR2
The reaction of [{LiR1}2] with NiCl2 in THF at
ambient temperature afforded a reddish-brown solution
with a black precipitate, apparently metallic nickel. The
solution was filtered, chromatographed and cooled to
give a red crystalline compound, [NiR12] (1) in 6% yield.
This result is similar to the 5% yield of the same
compound reported by Thornton and co-workers by
treating [NiCl2(PEt3)2] with [{LiR1}2], but the structure
of 1 has not been given [25]. In this work, we have
found that the yield of 1 can be improved significantly
to 50% by the reaction of [{LiR1}2] with
[NiCl2(TMEDA)] or [NiCl2(PPh3)2] (Eq. 1).
Pyridine-functionalised bulky alkyl ligands of type
III were of particular interest over the past few years as
they have been used in the synthesis of some novel
main-group metal alkyl complexes [11–20]. They usu-
ally form Y,N-chelates with the metals resulting in the
formation of four-membered metallacycle rings.
Similarly, compound 2, [NiR22], was obtained in 40%
yield
by
treating
[NiCl2(TMEDA)]
with
[LiR2(TMEDA)]. Compound 1 is more soluble in hy-
drocarbon solvents and stable in air than compound 2.
Using [NiCl2L2] as the starting materials, no metallic
nickel, an obvious sign of reduction was observed dur-
ing the course of the reactions. Organolithium com-
pounds are well-known reducing reagents in alkylation
reactions. The use of [NiCl2(TMEDA)] in the prepara-
tion of nickel diaryl complexes has previously been
reported in the literature. Longoni and co-workers have
studied the reaction of [NiCl2(TMEDA)] with o-lithio-
N,N-dimethylbenzylamine and isolated the correspond-
ing diaryl compound [Ni(o-C6H4CH2NMe2)2] which
probably has a trans square-planar geometry [5]. How-
ever, thermal stability of the compound was very low
and was not fully characterised. Moreover, Issleib and
co-workers have synthesized the nickel diaryl [Ni(o-
CH2C6H4PPh2)2] in satisfactory yield by treating
[NiCl2(TMEDA)] with the appropriate lithium aryl [6].
Both compounds were believed to have a five-mem-
bered metallacycle ring from C,N- or C,P-chelation.
We have recently reported the synthesis and struc-
tures of the thermally stable iron(II) and cobalt(II)
dialkyls [MR12] [M=Fe and Co] and p5-cyclopentadi-
enylnickel alkyl complexes [p5-Cp%%NiR] [Cp%%=C5H5 or
C5H3(SiMe3)2; R=R3=CH(SiMe3)C5H4N or R1] [21–
24]. It is noteworthy that the attempted synthesis of
NiR32 by the reaction of [{LiR3(Et2O)}2] with NiCl2,
gave the ‘head-to-head’ coupled organic product
[{CH(SiMe3)C5H4N-2}2] and nickel metal as the by-
product. In this paper, we report the synthesis and
2.2. Synthesis of [NiR1(Cl)(R1–R1)] (3)
When [NiCl2(diphos)] was used as the starting mate-
rial in the alkylation reaction with [{LiR1}2], the

W.-P. Leung et al. / Journal of Organometallic Chemistry 564 (1998) 193–200
195
Scheme 1.
chloroalkylnickel(II) compound, [NiR1(Cl)(R1–R1)] (3)
[R1–R1=2 - CH(SiMe3)2C5H4N - 5 - C(SiMe3)2C5H4N]
was isolated in 35% yield (Eq. 2).
pyridyl ring of a nickelocycle to give the intermediate
compound IV which then re-aromatizes to give the
species containing the ‘head-to-tail’ coupled product 3
(Scheme 1). Nevertheless, the mechanism for the forma-
tion of compound IV as well as the reason why the
formation of the coupled alkyl ligand [R1–R1] was not
observed in the reactions of [{R1Li}2] with
[NiCl2(TMEDA)] and [NiCl2(PPh3)2] still remained un-
known. However, [NiCl2(diphos)] is known to be a
good catalyst for coupling reactions in organic
synthesis.
2.3. Synthesis of [(p5-C5H5)NiR3]2 (4)
In our previous study, the reaction of Ni(p5-C5H5)2
with [{LiR1}2] gave the p5-cyclopentadienylnickel alkyl
complex [(p5-C5H5)NiR1] [23]. However, attempts to
prepare dialkyl 1 by treatment of [(p5-C5H5)NiR1] with
one equivalent of [{LiR1}2] were unsuccessful. The
starting compounds were recovered quantitatively. Sim-
ilarly, the reaction of LiR3 [R3=CH(SiMe3)C5H4N]
with Ni(p5-C5H5)2 afforded a less soluble compound
and was suggested to be [(p5-C5H5)NiR3] (4). Based on
the down-field shift of the methine proton signal in the
1H-NMR spectrum, it was believed that R3 in 4 be-
haved as an aza-ally type ligand. We have recently
obtained the X-ray structure and confirmed that com-
pound to be [(p5-C5H5)NiR3]2 (4), a dimeric compound
with the alkyl ligand forming a bridge between the two
nickel centres (Eq. 3).
X-ray structure analysis has revealed that compound
3 contains a ‘head-to-tail’ coupled product R1–R1 (3b)
coordinated to the nickel centre via one of the pyridine-
nitrogen atoms. Unlike 1, the monoalkyl complex 3 is
only sparingly soluble in hydrocarbon solvents. It is
also unstable towards oxygen in solution, although the
solid-form of 3 can be handled in air for a short period
of time. We have reported earlier that the reaction of
LiR3 with NiCl2 afforded a ‘head-to-head’ coupled
product 2-C5H4NCH(SiMe3)CH(SiMe3)C5H4N(R3–R3)
[23]. The more sterically demanding nature of R1 ren-
ders ‘head-to-head’ coupling of this ligand unfa-
vourable. The ‘head-to-tail’ coupling of R1, on the
other hand, has been reported by Raston and co-work-
ers in their attempted alkylation reaction of BiCl3
([11]k). Furthermore, a ‘tail-to-tail’ coupled product
(3c) was isolated at their studies of the monomeric
dialkyl-aluminum and -gallium radical species [MR22]·
(M=Al, Ga) ([11]j). Compound 3 is one of the rare
examples of an intermediate compound being isolated
in a nickel catalysed reaction. The formation of differ-
ent coupled products is apparently dependent on steric
factors of the alkyl ligands at the h-carbon.
A mechanism for the formation of the ‘head-to-tail’
coupling product was proposed in which a C-centred
carbanionic alkyl ligand R1 attacked position 5 of the

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W.-P. Leung et al. / Journal of Organometallic Chemistry 564 (1998) 193–200
Fig. 3. Crystal structure of 3, non-hydrogen atoms are shown with
˚
35% thermal ellipsoids. Selected bond distances (A) and angles (°) are
shown in Table 3.
Fig. 1. Crystal structure of 1, non-hydrogen atoms are shown with
35% thermal ellipsoids. Selected bond distances (A) and angles are
˚
shown in Table 1.
of alkyl ligands bonded in trans chelate fashion. The
structures are similar to their cobalt(II) analogues CoR21
and CoR22 [22–24]. The Ni–Ch and Ni–N distances of
2.4. X-ray structures
˚
˚
The molecular structures of 1–4 with the atom num-
bering schemes and selected bond distances and angles
are shown in Figs. 1–4 and Tables 1–4.
2.075(8) and 1.889(2) A in 1, 2.065(7) and 1.871(5) A in
2 are shorter than the corresponding distances in
1
2
˚
[CoR2] [2.092(6) and 1.923(4) A] and [CoR2] [2.071(3)
˚
Compound 1 crystallizes in a triclinic system with
and 1.897(3) A]. Furthermore, the Ni–Ch distances in 1
(
space group P1. It contains two independent molecules
and 2 are slightly longer than the corresponding Ni–Ch
5
1
˚
of identical structure with each being located in a
crystallographic inversion centre. Compound 2 crystal-
lizes in a monoclinic system in the space group P2/1.
Both compounds exhibit a square-planar coordination
geometry around each nickel(II) centre, with each pair
distance of 2.018(2) A in [p -CpNiR ] (5) [23], but is
˚
much longer than that of 1.89(1)
A
in cis-
[Ni(CH2SiMe3)2Py2] (6) [26] although the coordination
environments provided by the ligands in 6 are close to
those in 1 and 2. The mean Ni–N distances in 1
˚
(1.889(2)) and 2 (1.871(5) A) are comparable to that of
Fig. 2. Crystal structure of 2, non-hydrogen atoms are shown with
35% thermal ellipsoids. Selected bond distances (A) and angles (°) are
Fig. 4. Crystal structure of 4, non-hydrogen atoms are shown with
35% thermal ellipsoids. Selected bond distances (A) and angles (°) are
˚
˚
shown in Table 2.
shown in Table 4.

W.-P. Leung et al. / Journal of Organometallic Chemistry 564 (1998) 193–200
197
Table 1
Selected bond distances (A) and angles (°) for structure 1
Table 3
Selected bond distances (A) and bond angles (°) for structure 3
˚
˚
˚
˚
Bond lengths (A)
Bond distances (A)
Ni(1)–N(1)
C(1)–C(2)
N(1)–C(6)
C(3)–C(4)
C(5)–C(6)
Si(2)–C(1)
1.887(2) Ni(1)–C(1)
1.486(3) N(1)–C(2)
1.344(3) C(2)–C(3)
1.385(3) C(4)–C(5)
1.379(4) Si(1)–C(1)
1.872(3)
2.078(3)
1.350(4)
1.392(3)
1.368(5)
1.867(2)
Ni(1)–Cl(1)
Ni(1)–N(1)
Si(1)–C(1)
N(1)–C(2)
C(2)–C(3)
C(4)–C(5)
2.166(2)
1.871(4)
1.874(5)
1.334(8)
1.382(9)
Ni(1)–C(1)
Ni(1)–N(2)
C(1)–C(2)
N(1)–C(6)
C(3)–C(4)
2.024(6)
2.000(5)
1.486(7)
1.334(8)
1.375(10)
1.369(9)
1.360(13) C(5)–C(6)
Bond angles (°)
Bond angles (°)
N(1)–Ni(1)–C(1)
C(1)–Ni(1)–N(1A) 109.4(1)
C(1)–Ni(1)–C(1A) 180.0(1)
70.6(1)
N(1)–Ni(1)–N(1A)
N(1)–Ni(1)–C(1A)
N(1A)–Ni(1)–C(1A) 70.6(1)°
180.0(1)
109.4(1)
Cl(1)–Ni(1)–C(1)
C(1)–Ni(1)–N(1)
Cl(1)–Ni(1)–N(2)
N(1)–Ni(1)–N(2)
99.3(2)
70.7(2)
91.6(1)
97.9(2)
Cl(1)–Ni(1)–N(1) 167.8(2)
Cl(1)–Ni(1)–C(2) 136.5(2)
C(1)–Ni(1)–N(2) 168.3(2)
C(2)–Ni(1)–N(2) 130.9(2)
˚
1.856(2) A in 5 but are much shorter than the Ni–N
it is significantly longer than that of 6 [26]. The Ni–
˚
distance of 1.957(8) A in 6 [23,26].
˚
N(1) distance of 1.871(4) A in 3 is shorter than the
Crystals of 3 are monoclinic with space group C2/c.
The alkyl ligand R1 bonds to the nickel centre in a
C,N-chelating manner with Ni–C(1) and Ni–N(1) dis-
˚
Ni–N(2) distance of 2.000(5) A for the coupled dialkyl
ligand. The former is comparable to the corresponding
distance in 5 but is significantly shorter than the Ni–N
distance in 6 [23,26].
˚
tance being 2.024(6) and 1.871(4) A, respetively, with a
bite angle of 70.7(2)°. The coupled product R1–R1 is
bound to the nickel centre via the pyridyl nitrogen N(2)
and is trans to C(1) of ligand R1. The observed Ni–
X-ray structure analysis of cyclopentadienylnickel(II)
alkyl complex 4 had shown that it is a dimer. The
asymmetric unit consists of one and a half molecules.
The pyridine-functionalised alkyl ligand R3 acts as an
inter-bridging ligand between two nickel centres and
forms a ‘chair-like’ eight-membered ring. Such bonding
mode had been found in the dimeric structures of
[FeR42]2 and [CoR24]2 [R4=CH(SiButMe2)C5H4N-2].
The cyclopentadienyl ligand in 4 is bonded to the nickel
metal in a usual pentahapto mode of the metallocene
‘half-sandwich’ ([21]b[24]). The analogous compound 5
bearing the bis(trimethylsily)-substituted ligand R1 is a
monomer. The average Ni–Ch and Ni–N distances in 4
N(2) distance is 2.000(5) and the Ni–Cl(1) distance is
1
˚
2.166(2) A. The bidentate ligand R , N(2) and Cl(1)
constitute a distorted square planar coordination ge-
ometry around the nickel centre with the metal atom
located slightly above the plane formed by the four
groups. The maximum overlap between the pyridyl
nitrogen and the metal would involve the metal and the
heterocyclic ring atoms lying coplanar with each other
as in the case of 1, 2, and the cobalt dialkyls [CoR12]
and [CoR22] [22,24]. This slight deformation in 3 is
believed to take place in order to relieve steric strain at
the metal centre without necessarily decreasing the
pyridine-metal bonding.
˚
are 2.002 and 1.923 A, respectively. The corresponding
˚
distances in 5 are 2.018(2) and 1.856(2) A.
The Ni–Ch distance in the monoalkyl species 3
(2.024(6) A) is only 0.054 A shorter than that of the
˚
˚
2.5. NMR spectroscopy
dialkyl 1 but is comparable to that of 5 [23]. However,
The 1H-NMR spectrum of compound 1 displayed
only one set of SiMe3 peaks, this is consistent with the
Table 2
˚
Selected bond distances (A) and bond angles (°) for structure 2
Table 4
˚
Selected bond distances (A) and bond distances (°) for structure 4
Bond distances
Ni(1)–C(1)
Ni(1)–C(16)
Si(1)–C(1)
C(1)–C(12)
N(1)–C(6)
C(3)–C(4)
C(5)–C(6)
2.065(7)
2.044(6)
1.899(7)
1.496(7)
1.360(9)
Ni(1)–N(1)
Ni(1)–N(2)
C(1)–C(2)
N(1)–C(2)
C(2)–C(3)
1.871(5)
1.862(6)
1.442(11)
1.369(10)
1.394(10)
1.392(12)
˚
Bond distances (A)
Ni(1)–C(1)
Ni(1)–C(3)
Ni(1)–C(5)
Ni(1)–C(25)
C(10)–C(11)
C(2)–C(3)
C(4)–C(5)
N(1)–C(10)
C(7)–C(8)
C(9)–C(10)
2.159(4)
2.164(5)
2.172(5)
2.000(3)
1.473(4)
1.391(6)
1.414(6)
1.365(5)
1.381(7)
1.390(5)
Ni(1)–C(2)
Ni(1)–C(4)
Ni(1)–N(1)
Ni(2)–C(11)
C(1)–C(2)
C(3)–C(4)
N(1)–C(6)
C(6)–C(7)
C(8)–C(9)
2.071(4)
2.158(5)
1.920(3)
2.004(4)
1.419(6)
1.385(7)
1.343(4)
1.374(6)
1.383(5)
1.432(10) C(4)–C(5)
1.313(10)
Bond angles
C(1)–Ni(1)–N(1)
N(1)–Ni(1)–C(16) 107.9(2)
N(1)–Ni(1)–N(2) 178.8(2)
70.9(3)
C(1)–Ni(1)–C(16) 178.5(2)
C(1)–Ni(1)–N(2)
C(16)–Ni(1)–N(2)
109.5(3)
71.7(2)

198
W.-P. Leung et al. / Journal of Organometallic Chemistry 564 (1998) 193–200
Scheme 2.
existence of one geometrical form, the trans-geometry of
the square-planar complex in solution. For compound 2,
due to the substitution at the h-carbon, there are four
possible diastereomers, viz. (R,R), (S,S), (R,S), and
(S,R). The 1H-NMR spectrum of 2 displayed two sets of
SiMe3 signals, which is consistent with the existence of
two sets of diastereoisomers in the ratio of 1:1. They are
assignable to the (R,R)/(S,S) and (R,S)/(S,R)
diastereoisomers. Broad signals were observed in the
1H-NMR spectrum of compound 3. This may suggest
the presence of dynamic behaviour in solution by which
a tetrahedral species could be formed as shown in
Scheme 2. Magnetic moment measurement by Evan’s
NMR method carried out for compound 3 had shown
no significant paramagnetic property.
collected on a Siemens P4/PC diffractometer at 294 K
using graphite-monochromatized Mo–Kh radiation
˚
(u=0.71073 A) with a ꢀ/2q scan model (for compounds
1, 3, 4,) or taking oscillation IP photos (for compounds
2). N unique reflections were measured, and N0 observed
reflections with ꢀF0ꢀ=n|(ꢀF0ꢀ) where n=3 for 1, 10 for
2, 4 for 3 and 4 were used in the structure solution
2 −1
refinement. The weighing scheme w=[|2ꢀF0ꢀ+xꢀF0ꢀ ]
was used with x=0.002 for 1, 0.001 for 2 and 4, and
0.0003 for 3. Computations were performed using the
SHELXTL PC program package on a PC 486 com-
puter. The structures were solved by direct phase
determination and refined by full matrix least-squares
with anisotropic thermal parameters for the non-hydro-
gen atoms. Hydrogen atoms were introduced in their
idealized positions and included in structure factor
calculations with assigned isotropic temperature factors.
Tables of atomic coordinates, thermal parameters and
complete lists of bond lengths and angles have been
deposited at the Cambridge Crystallographic Data
Center.
3. Experimental
3.1. General procedures
All manipulations were carried out under an argon or
dinitrogen atmosphere. Solvents were dried over and
distilled from CaH2 (hexane), and sodium benzophenone
(THF, ether, toluene) and degassed twice prior to use.
Anhydrous NiCl2 was prepared by standard procedure
[27]. Samples of [NiCl2(PPh3)2] (Fluka), [NiCl2(diphos)]
(Aldrich), were used as purchased. The organolithium
3.4. Synthesis of [Ni{C(SiMe3)2C5H4N-2}2] (1)
3.4.1. Method A
A sample of N,N,N%,N%-tetramethylethylenediamine
(0.23 g, 2.0 mmol) was stirred with a suspension of NiCl2
(0.26 g, 2.0 mmol) in THF (20 ml) at 25°C for 8 h. A
solution of [{LiR1}2] (0.97 g, 2.0 mmol) in THF (20 ml)
was then added slowly to the above suspension at
−40°C. After the addition was completed, the mixture
was stirred at ambient temperature for a further 8 h to
give a reddish brown solution. The solvent was removed
in vacuo and the residue was extracted with hexane
followed by filtration and concentration. The concen-
trate was chromatographed on silica gel using pentane
as eluent. All the red fraction was collected. The solvent
was removed under reduced pressure to give 1 as red
crystals (yield 0.53 g, 50%). M.p.: 158–160°C. EI-MS
m/z (%)=531 (9.3) [M]+, 295 (54) [M–R1]+. Anal.
Found: C, 54.22; H, 8.37; N, 5.18%. Calc. for
reagents
[{LiR1}2]
[R1=C(SiMe3)2C5H4N-2],
[LiR2(TMEDA)] [R2=CPh(SiMe3)C5H4N-2] were pre-
pared by published methods [11,20].
3.2. Physical measurements
All NMR spectra were recorded with a Bru¨ker WM-
250 spectrometer. Chemical shifts are referenced to
residual solvent protons of 7.15 ppm for C6D6 and 7.24
ppm for CDCl3. Mass spectra (EI 70 eV) were obtained
on a VG7070F mass spectrometer. Melting points were
recorded on an Electrothermal Melting Point Apparatus
and were uncorrected. Elemental (C, H, N) analyses
were performed by MEDAC, Brunel University, UK.
1
C24H44Si4N2Ni: C, 54.22; H, 8.34; N, 5.27%. H-NMR
(250 MHz, C6D6): l 0.47 (s, 18H), 6.01–6.06 (m, 1H),
3.32 (m, 1H), 6.73–6.79 (dt,J=1.7 and 7.9 Hz, 1H),
7.56–7.58 (m, 1H). 13C{1H}-NMR (62.89 MHz, C6D6):
l 4.10 (SiMe3), 117.64, 125.58, 136.43, 149.15, 179.68
(C5H4N).
3.3. X-ray crystallography for compounds 1–4
The crystals selected for study were mounted in glass
capillaries and sealed under purified nitrogen. Data were

W.-P. Leung et al. / Journal of Organometallic Chemistry 564 (1998) 193–200
199
3.4.2. Method B
brown. After 6 h stirring, the solvent was removed in
vacuo and the residue extracted with hexane. The white
precipitate of LiCp was filtered off and the extract
concentrated, to give dark red crystals which were
recrystallised from benzene (yield 0.61 g, 72%). M.p.:
170–172°C (dec.). EI-MS: m/z (%)=287 (35) [M]+,
272 (9) [M–CH3]+, 214 (23) [M–SiMe3]+. Anal.
Found: C, 58.61; H, 6.62; N, 4.85%. Calc. for
A solution of [{LiR1}2] (0.97 g, 2.0 mmol) in THF
(20 ml) was added slowly to
a suspension of
[NiCl2(PPh3)2] (1.31 g, 2.0 mmol) in THF (30 ml) at
−40°C. The mixture was stirred at room temperature
(r.t.) for 8 h. The resulting reddish brown solution was
worked up by a similar procedure as described in
Method A to give 0.51 g (48%) of the title compound.
1
C14H19NSiNi: C, 58.37; H, 6.65; N, 4.86%. H-NMR
3.4.3. [Ni{CPh(SiMe3)C5H4N-2}2], (2)
(250 MHz, C6D6): l 0.43 (s, SiMe3, 9H), 4.39 (s, CHSi,
1H), 4.76 (s, C5H5, 5H), 6.02–6.05 (m, pyridyl, 1H),
6.27–6.30 (m, pyridyl, 1H), 6.48–6.55 (m, pyridyl, 1H),
8.45–8.46 (m, pyridyl, 1H). 13C{1H}-NMR (62.89
MHz, C6D6): l 1.94 (SiMe3), (CH) obscured, 92.03
(C5H5), 113.60, 120.80, 134.95, 139.40, 156.17 (C5H4N).
N,N,N%,N%-tetramethylethylenediamine (0.16 g, 1.4
mmol) was stirred with a suspension of NiCl2 (0.18 g,
1.4 mmol) in 20 ml THF at 25°C for 8 h. A solution of
[LiR2(TMEDA)] (1.02 g, 2.8 mmol) in THF (30 ml)
was added to the above mixture at −30°C. The solu-
tion was allowed to warm to r.t. and stirring was
continued for 20 h. All volatiles were then removed in
vacuo and the residue was extracted with toluene. The
combined extract was reduced in volume to ca. 10 ml
under reduced pressure. Upon cooling to −30°C, deep
red crystals of 2 were obtained, yielded 0.34 g, 45%.
M.p.: 232–233°C (dec.); EI-MS m/z (%)=539 (23)
[M]+, 299 (64) [M–R2]+, 240 (16) [R2]+, 225 (100)
[R2–CH3]+. 1H-NMR (250 MHz, C6D6): l 0.38 (s,
9H), 5.87–5.93 (dd, J=1.1, 5.4, and 7.4 Hz, 1H),
6.33–6.37 (dt, J=1.1 and 8.0 Hz, 1H), 6.64–6.71 (dt,
J=1.7 and 7.7 Hz, 1H), 7.01–7.08 (dt, J=1.1 and 7.3
Hz, 1H), 7.20–7.26 (dt, J=1.7 and 7.9 Hz, 2H), 7.27–
7.31 (dd, J=1.1, and 1.7, and 5.4 Hz, 2H), 7.76–7.81
(dd, J=1.4 and 8.3 Hz, 1H). 13C{1H}-NMR (62.89
MHz, C6D6): l 1.78 (SiMe3), 116.81, 118.01 (C5H4N),
121.86 (C6H5), 122.05, (C5H4N) 123.75 (C6H5), 136.53,
137.24 (C6H5), 144.76, 145.94 (C5H4N).
Acknowledgements
This research work was supported by the Hong Kong
Research Grants Council, Earmarked Grant CUHK
306/94P.
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200
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