A convenient route to vinylsiloxane-tertiary phosphine-nickel(0) complexes; The molecular structure of [(Ni{P(C6H4Me-4)3}) 2{μ-(L′′L′′)2}] {(L′′L′′)2=[CH 2=CH(Me)Si(μ-O)]4}

Article abstract of DOI:10.1016/S0022-328X(00)00316-8

A simple one pot synthesis in Et₂O at ambient temperature, from the readily available starting materials [Ni(cod)₂], PR₃ and LL or (L′′L′′)₂, provides an essentially quantitative route to the known vinylsiloxanenickel(0) complexes [Ni(LL)PR₃] and the new binuclear analogues [{Ni(PR₃)}₂{μ-(L′′L′′) ₂}] (5) {LL=[CH₂=CH(Me)₂Si]₂O, (L′′L′′)₂=[CH ₂=CH(Me)Si(μ-O)]₄ and R=Ph, C₆H₄Me-4 or C₆H₁₁-c}. The X-ray crystal structure of 5b (R=C₆H₄Me-4) shows it to be a centrosymmetric binuclear complex containing (L′′L′′)₂ as a chair-shaped bridging ligand. It is bound to each Ni(PR₃) moiety by a pair of μ²-vinyl groups (having M and M′ as centroids) and each NiMSiOSi′M′ metallacycle is also of chair conformation.

Full text of DOI:10.1016/S0022-328X(00)00316-8

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 605 (2000) 221–225
A convenient route to vinylsiloxane-tertiary phosphine-nickel(0)
complexes; the molecular structure of
[(Ni{P(C6H4Me-4)3})2{m-(L%%L%%)2}]
{(L%%L%%)2=[CH2ꢀCH(Me)Si(m-O)]4}
Peter B. Hitchcock, Michael F. Lappert *, Hieronim Maciejewski 1
The Chemical Laboratory, Uni6ersity of Sussex, Brighton BN1 9QJ, UK
Received 18 April 2000; accepted 18 May 2000
Abstract
A simple one pot synthesis in Et2O at ambient temperature, from the readily available starting materials [Ni(cod)2], PR3 and
LL or (L%%L%%)2, provides an essentially quantitative route to the known vinylsiloxanenickel(0) complexes [¸N¹i(¹LLº)PR3] and the new
¸¹¹¹º
¸¹¹¹º
binuclear analogues [{Ni(PR3)}2{m-(L%%L%%)2}] (5) {LL=[CH2ꢀCH(Me)2Si]2O, (L%%L%%)2=[CH2ꢀCH(Me)Si(m-O)]4 and R=Ph,
C6H4Me-4 or C6H11-c}. The X-ray crystal structure of 5b (R=C6H4Me-4) shows it to be a centrosymmetric binuclear complex
containing (L%%L%%)2 as a chair-shaped bridging ligand. It is bound to each Ni(PR3) moiety by a pair of m2-vinyl groups (having M
and M% as centroids) and each NiMSiOSi%M% metallacycle is also of chair conformation. © 2000 Elsevier Science S.A. All rights
reserved.
Keywords: Nickel; Vinylsiloxane complexes
1. Introduction
LL)] (2) was isolated [5]. Complex 2 was shown to be a
Karstedt catalyst; with sty¸re¹nºe as substrate,¸t¹raºnsient
14-electron intermediates [Pt(LL)(LL)] and [Pt(LL)(h2-
CH2ꢀCHPh)] were identified by NMR spectroscopy [6].
Complex 2 was also shown to be a convenient source of
Hydrosilylation is widely used in the silicone industry
for the synthesis of monomers containing SiꢁC bonds,
the cross-linking of polymers and as a source of various
silane coupling reagents, while in organic chemistry it
has a role for the synthesis of alcohols by reduction of
carbonyl compounds [1]. Such processes generally re-
quire the use of a highly active platinum-containing
catalyst. The silicone-soluble Karstedt catalyst is com-
mercially important for hydrosilylation. It is obtained,
in presence of the silane, by reaction of chloroplatinic
acid H2[PtCl6]xH2O (1) (Speier’s catalyst) with a vinyl-
silicon-containing compound, such as sym-divinylte-
tra(methyl)disiloxane [CH2ꢀCH(Me)2Si]2O (ꢂLL) [2,3].
Our earlier studies had established that 1 and LL in
further well characterised siloxanep¸la¹tiºnum(0) ¸c¹oºm-
¸¹º
plexes, suc¸h¹aºs [Pt(LL)(PR3)] [4,7], [{Pt(LL)}2(m-dppe)]
[8] and [{Pt(LL)}3(m3-triphos)] [8] [dppe=(Ph2PCH2)2,
triphos=(Ph2PCH2)3CMe or (Ph2PCH2CH2)2PPh]. A
¸¹¹º
¸¹º
series of palladium(0) complexes [{Pd(LL)}2(m-LL)]
¸¹¹º
(from [PdCl2(cod)2], Li2cot and LL) and [Pd(LL)D]
i
t
(D=C2H4 or PR3; R=Me, Pr, Bu, Ph or C6H4Me-2)
has also been reported [9].
The high cost of platinum has led to much research
on various nickel complexes as potential hydrosilylation
catalysts [1]. Also relevant to the present study is the
fact that tertiary phosphine ligands have a pervasive
place in many industrially important noble metal-
catalysed organic reactions, including hydrosilylation;
complexes of Rh(I), Pd(0 or II) and Pt(0) are particu-
larly prominent [10]. The other pertinent ligand compo-
nent for this report relates to a vinylsilane. Previous
the absence of a silane yielded a solution A [4], from
which the crystalline platinum(0) complex [{Pt(LL)}2(m-
¸¹¹º
* Corresponding author. Fax: +44-1273-677196.
E-mail address: m.f.lappert@sussex.ac.uk (M.F. Lappert).
1 Present address. Adam Mickiewicz University, 60–780 Poznan,
Poland.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00316-8

222
P.B. Hitchcock et al. / Journal of Organometallic Chemistry 605 (2000) 221–225
work dealing with these parameters concerned the for-
tiary phosphine ligands, study their structures and ex-
plore their potential as hydrosilylation catalysts;
catalytic aspects will be considered in a later paper.
An improved synthesis (cf. [7] and [11]) of the com-
plexes 3 was accomplished, using the readily available
[Ni(cod)2] as precursor (Eq. 1). The displaced volatile
cyclooctadiene was easily removed in vacuo, providing
the essentially pure residue of the appropriate complex
3 in quantitative yield. Each of the crystalline com-
plexes 3a, 3b and 3c was authenticated by showing it to
have identical NMR spectra to those of the previously
characterised specimens [7].
¸¹º
mation of (a) [Ni(LL)(PR3)] (R=Ph, C6H4Me-4 or
C6H11-c) (3) from trans,trans,trans-cyclododeca-
trienenickel(0) {ꢂ[Ni(CDDT]} and LL [7,11], and (b)
¸¹º
¸¹¹¹º
[Ni(LL)(PPh3)]
or
[Ni(LPhLPh)(PPh3)]
from
[NiCl2(PPh3)2], zinc dust and LL or LPhLPh
{ꢂ[CH2ꢀCH(Ph)2Si]2O}
[7].
The
compound
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
[Ni{CH2ꢀCH(Me)2SiOSi(Me)2CHꢀCHSi(Me)2OSi(Me)2-
¸ ¹ ¹ º
¹¹º
CHꢀCH2}] was obtained from nickel atoms and LL
under metal vapour synthesis conditions [12]. Other
vinylsilanes which have been employed as ligands in
Group 10 metal chemistry include (CH2ꢀCH)2SiMe2
(ꢂL%L%) and [CH2ꢀCH(Me)Si(m-O)]4 [ꢂ(L%%L%%)2] (4).
Thus, [NiCl2(PPh3)2], zinc dust and L%L% afforded
[{Ni(m-L%L%)(PPh3)}2] [8]; and 4 has been used in plat-
inum chemistry [7,13] to generate hydrosilylation cata-
lysts related to 2 [13].
2. Results and discussion
2.1. Synthetic studies
(1)
In a similar fashion, but using cyclotetrakis[vinyl(-
methyl)siloxane] (4) [ꢂL%%L%%)2] in place of LL, there were
obtained the binuclear nickel(0) complexes 5, Eq. (2).
Each of the crystalline, yellow complexes 5a, 5b and 5c
gave satisfactory analyses and appropriate NMR spec-
Our objective was to develop convenient syntheses
for nickel(0) complexes having h2-vinylsilicon and ter-
1
1
tra. The various Hꢁ1H, and Hꢁ31P and 31Pꢁ29Si cou-
pling constants, Fig. 2, were similar for each of 5a–5c,
and also to those found for 3a–3c [7]. Like their
analogues 3 [7], it is interesting that 5c is the rac-
diastereoisomer in the solid state.
Fig.
1.
The
molecular
structure
of
[(Ni{P(C6H4Me-
¸¹¹º
4)3})2[CH2ꢀCH(Me)S(m-O)]4 (5b) with atom labelling.
i
Fig. 2. Schematic representation of 1Hꢁ31P and 31Pꢁ29Si coupling
constants (Hz), from 1H- and 29Si-NMR spectra, for 5a, 5b, 5c,
respectively in C6D6 at 298 K.
(2)

P.B. Hitchcock et al. / Journal of Organometallic Chemistry 605 (2000) 221–225
223
Table 1
3. Experimental
a
,
Selected bond lengths (A) and angles (°) for 5b
3.1. General procedures and starting silicon reagents
Bond lengths
NiꢁP
2.180(1)
2.005(3)
2.000(3)
1.887(3)
1.392(4)
NiꢁC(1)
NiꢁC(3)
NiꢁM(1)
C(1)ꢁC(2)
2.008(3)
2.023(3)
1.882(3)
1.393(4)
All manipulations and instruments were as described
earlier [7,8,14]. The silicon reagents used in Sections
3.2, 3.3, 3.4 and 3.5 were kindly provided by Dow
Corning, Ltd.
NiꢁC(2)
NiꢁC(4)
NiꢁM(2)
C(3)ꢁC(4)
Bond angles
M(1)ꢁNiꢁM(2)
M(2)ꢁNiꢁP
131.85(11)
116.00(9)
M(1)ꢁNiꢁP
111.18(9)
129.08(11)
122.4(2)
113.05(13)
123.4(2)
3.2. Synthesis of
¸¹¹¹¹¹¹¹º
Si(1)ꢁO(1)ꢁSi(2)
C(2)ꢁC(1)ꢁSi(1)
Si(1)ꢁC(1)ꢁNi
C(4)ꢁC(3)ꢁSi(2)
Si(2)ꢁC(3)ꢁNi
C(12)ꢁC(7)ꢁC(8)
[{Ni(PPh3)}2{v-(p-CH2ꢀCH(Me)Si(v-O))4}] (5a)
Si(1)ꢁO(2)ꢁSi(2)% 148.67(12)
C(2)ꢁC(1)ꢁNi
C(1)ꢁC(2)ꢁNi
C(4)ꢁC(3)ꢁNi
C(3)ꢁC(4)ꢁNi
69.6(2)
69.8(2)
68.9(2)
70.7(2)
Cyclotetrakis[vinyl(methyl)siloxane] (1.0 ml) was
added slowly to a stirred red suspension of [Ni(cod)2]
(0.50 g, 1.8 mmol) and PPh3 (0.47 g, 1.8 mmol) in
diethyl ether (10 ml) at ambient temperature, yielding a
yellow solution. The reaction mixture was allowed to
stir overnight. The volatiles were removed in vacuo to
give a yellow oil, which was extracted into pentane
(2×2 ml). The extract was filtered through Celite. The
filtrate was concentrated, then set aside at −30°C to
yield the yellow solid compound 5a (0.77 g, 0.8 mmol,
86%). Yellow crystals of 5a, m.p. 212–214°C (dec) were
obtained by recrystalisation from benzene, at ambient
temperature. Anal. Found: C, 58.3; H, 5.49.
113.03(13)
117.5(2)
a M(1) and M(2) are the centres of the C(1)ꢁC(2) and C(3)ꢁC(4)
bonds, respectively. Symmetry transformations used to generate
equivalent atoms:,−x, −y, −z.
A
platinum analogue of 5c, prepared from
¸¹¹º
[Pt(LL){P(C6H11-c)3}] and 4, had been reported [4]; its
structure was conjectured to be similar to that now
established for 5b ( see Section 2.2).
1
C48H54Ni2O4P2Si4 Calc.: C, 58.4; H, 5.52%. H-NMR
(C6D6, 298 K, 500 MHz): l 0.39 (s, 12H), 2.56 (td, 4H),
3
3.07 (dd, 8H), 7.03–7.64 (m, 30H), J(1H1ꢁ1H2)=12.6
Hz, 3J(1H1ꢁ1H3)=16.5 Hz, 3J(1H1ꢁ31P)=4.8 Hz,
3J(1H2ꢁ31P)=7.9 Hz, 3J(1H3ꢁ31P)=6.4 Hz. 13C{1H}-
NMR (C6D6, 298 K, 125.8 MHz): l 0.61 (s, Me), 58.17
(s, ꢀCHꢁ), 63.15 (s, ꢀCH2), 127.81–136.60 (m, Ph).
29Si{1H}-NMR (C6D6, 298 K, 99.4 MHz):l −24.0 (d),
3J(29Siꢁ31P)=4.0 Hz. 31P{1H}-NMR (C6D6, 298 K,
101.2 MHz): l 41.2 (s).
2.2. The X-ray molecular structure of
[(Ni{P(C6H4Me-4)3})2{v-(L%%L%%)2}] (5b)
Crystalline 5b, obtained from benzene, is a cen-
trosymmetric binuclear nickel(0) complex, the inversion
centre being the mid-point of the chair-shaped (SiO)4
ring, Fig. 1. Selected bond lengths and angles are listed
in Table 1. There is a molecule of benzene solvate in a
general position.
3.3. Sy¸nt¹he¹s¹is¹o¹f ¹[{¹NºiP(C6H4Me-4)3}2-
{v-(p-CH2ꢀCH(Me)Si(v-O))4}] (5b)
The local geometry at each three-coordinate nickel
atom is planar, taking its vertices to be the phosphorus
atom and the centroids M of adjacent h2-vinyl groups.
The M(1)ꢁNiꢁM(2) angle is wider [131.8(1)°] than
Compound 5b ( 0.83 g, 0.8 mmol, 85%) was prepared
in a similar manner as 5a, except that P(C6H4Me-4)3
was used in place of PPh3. Yellow crystals of 5b, m.p
224–226°C (dec) suitable for X-ray diffraction, were
grown from benzene at ambient temperature over a
period of 24 h. Anal. Found: C, 60.7; H, 6.54.
C54H66Ni2O4P2Si4 Calc.: C, 60.6; H, 6.21%. H-NMR
(C6D6, 298 K, 500 MHz): l 0.48 (s, 12H), 2.03 (s, 9H),
2.61 (td, 4H), 3.16 (dd, 8H), 6.93–7.65 (m, 24H),
M(1)ꢁNiꢁP [111.2(1)°] or M(2)ꢁNiꢁP [116.0(1)°]. This
¸¹¹º
situation is similar to that in [Ni(LL){P(C6H11-c)3}], the
corresponding angles being 130.1(1), 113.9(1) and
115.1(1)° [7]. Likewise, the NiꢁP and average NiꢁCa
and NiꢁCb bond lengths in that compound of 2.206(1),
1
3J(1H1ꢁ1H2)=12.1
3J(1H1ꢁ31P)=4.6
Hz,
Hz,
3J(1H1ꢁ1H3)=16.4
3J(1H2ꢁ31P)=6.0
Hz,
Hz,
,
2.000(3) and 2.027(3) A are close to the 2.179(1),
,
2.003(3) and 2.015(3) A in 5b. Each six-membered
¸¹¹¹¹¹¹¹¹¹¹º
3J(1H3ꢁ31P)=10.5 Hz. 13C{1H}-NMR (C6D6, 298 K,
125.8 MHz): l 0.69 (s, Me), 21.01 (s, Me), 57.68 (s,
ꢀCHꢁ), 63.00 (s, ꢀCH2), 127.80–139.22 (m, tol).
29Si{1H}-NMR (C6D6, 298 K, 99.4 MHz): l −23.9 (d),
3J(29Siꢁ31P)=3.8 Hz. 31P{1H}-NMR (C6D6, 298 K,
101.2 MHz): l 39.1 (s)
metallacyclic ring [NiM(1)Si(1)OSi(2)M(2)] (5b) adopts
a chair conformation, as had previously been observed
¸¹º
for (M¸et¹)M¹¹(1¹)S¹i(¹1¹)O¹S¹i(¹2¹)Mº(2) rings in Ni(LL) [7],
¸¹º
¸¹º
¸¹¹º
Pt(LL) [4,5,7,8], Rh(LL) [14] and Rh(LPhLPh) [14] com-
plexes (Met=Ni, Pt or Rh).

224
P.B. Hitchcock et al. / Journal of Organometallic Chemistry 605 (2000) 221–225
3.4. Synthesis¸o¹f¹[{¹Nºi(P(C6H11-c)3)}2-
{v-(p-CH2ꢀCH(Me)Si(v-O))4}] (5c)
O{P(C6H11-c)3}] (3c) was authenticated by showing it
to have identical NMR spectra to those of the previ-
ously characterised specimens [7].
Compound 5c ( 0.70 g, 0.7 mmol, 76%) was prepared
in similar manner as 5a, except that P(C6H11-c)3 was
used in place of PPh3. Yellow crystals of 5c, m.p.
235–237°C (dec) were obtained by recrystalisation from
benzene, at ambient temperature. Anal. Found: C, 57.3;
H, 9.01. C48H90Ni2O4P2Si4 Calc.: C, 56.4; H, 8.87%.
1H-NMR (C6D6, 298 K, 500 MHz): l 0.51 (s, 12H),
1.1–1.8 (m, 33H), 2.53 (td, 4H), 3.06 (dd, 8H),
3.6. X-ray structure determination of 5b
Intensities were measured on a Enraf–Nonius CAD
4 difractometer with monochromated Mo–Ka radiation
,
(u=0.71073 A). Structure solution was by SHELXS-86
[15]. Refinement was by full-matrix least-squares on F2
using all reflections and SHELXL-93 [16]. Non-hydrogen
atoms were refined anisotropically. Hydrogen atoms
were included in riding mode with Uiso(H) equal to
1.2Ueq(C) or 1.5Ueq(C) for methyl groups. The 4-tolyl
methyl H atoms were included as disordered equally
over two sets of positions related by a 60° rotation.
Further details are in Table 2.
3J(1H1ꢁ1H2)=12.6
3J(1H1ꢁ31P)=3.4
Hz,
Hz,
3J(1H1ꢁ1H3)=16.3
3J(1H2ꢁ31P)=5.6
Hz,
Hz,
3J(1H3ꢁ31P)=8.2 Hz. 13C{1H}-NMR (C6D6, 298 K,
125.8 MHz): l 0.65 (s, Me), 26.99–36.54 (m, C6H11-c),
55.60 (s, ꢀCHꢁ), 58.95 (s, ꢀCH2). 29Si{1H}-NMR
3
(C6D6, 298 K, 99.4 MHz): l −23.6 (d), J(29Siꢁ31P)=
3.2 Hz. 31P{1H}-NMR (C6D6, 298 K, 101.2 MHz): l
39.4 (s).
4. Supplementary material
3.5. Typical synthesis of
[Ni{v-CH2ꢀCH(Me)2Si }2O(PR3)] (3)
¸¹¹¹¹º
Crystallographic data for the structural analysis have
been deposited at the Cambridge Crystallographic Data
Centre: CCDC no. 142037. Copies of this information
may be obtained free of charge from The Director,
CCDC, Cambridge CB2 1EZ, UK (fax: +44-1223-336-
033; e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
Divinyltetramethyldisiloxane (1.0 ml) was added
slowly to a stirred red suspension of [Ni(cod)2] (0.56 g,
2.5 mmol) and PR3 (2.5 mmol; R=Ph, C6H4Me-4 or
C6H11-c) in diethyl ether (10 ml) at ambient tempera-
ture, yielding a yellow solution. The reaction mixture
was allowed to stir overnight and the volatiles were
removed under reduced pressure to yield a yellow oil.
This was taken up into pentane (2×2 ml) and filtered
through Celite. Concentration of the filtrate and cool-
ing to −30°C yielded yellow crystals of 3. Each of
Acknowledgements
We thank Dow Corning Ltd. (Barry) for gifts of
chemicals, the Royal Society for the award of a R.S.-
NATO postdoctoral fellowship to H.M. and EPSRC
for other support
t¸h¹e ¹¹¹ºcrystalline
CH(Me)2Si}2O(PPh3)], (3b), [Ni{m-CH2ꢀCH(Me)2Si}2-
O{P(C6H4Me-4)3}] 3a and [Ni{m-CH2ꢀCH(Me)2Si}2-
complexes
¸[¹N¹i{¹m¹-CºH2ꢀ
¸¹¹¹¹º
Table 2
References
Crystal data and structural refinement parameters for 5b
Formula
Formula weight
C54H66Ni2O4P2Si4·2(C6H6)
1227.0
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10.045(5)
11.529(3)
14.179(9)
80.65(4)
76.86(4)
85.47(3)
1576.3(13)
1
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(
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R1 [for I\2|(I)]
25
5527
4543
0.035
0.083
wR2 (for all data)

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