Silylenenickel(0) or silyl(silylene)platinum(II) complexes by reaction of Si[(NCH2But)2C6H4-1,2] with [NiCl2(PPh3)2], [Ni(cod)2], or [PtCl2(PPh3)2]

Article abstract of DOI:10.1021/om980818h

The stable silylene Si[(NCH₂Bu^t)₂C₆H₄-1,2] [abbreviated as Si(NN)] (1) (4 equiv) with 1 equiv each of [NiCl₂(PPh₃)₂], [Ni(cod)₂], or [PtCl₂(PPh₃)₂) in benzene affords the crystalline diamagnetic complex [NifPPhs)-{Si(NN)}₃] (2), [Ni{Si(NN)}₄] (3), or trans-[Pt{Si(NN)Cl}₂{Si(NN)}₂] (4), while from 1 (5 equiv) and [NiCl₂(PPh₃)₂] the product was 3. The diversity of behavior of 1, functioning as (i) a neutral ligand, (ii) a reducing agent, and / or (iii) a source of the anionic ligand [Si(NN)Cl]^- is noteworthy.

Full text of DOI:10.1021/om980818h

Organometallics 1998, 17, 5599-5601
5599
Silylen en ick el(0) or Silyl(silylen e)p la tin u m (II)
Com p lexes by Rea ction of Si[(NCH2Bu t)2C6H4-1,2] w ith
[NiCl2(P P h 3)2], [Ni(cod )2], or [P tCl2(P P h 3)2]
Barbara Gehrhus, Peter B. Hitchcock, Michael F. Lappert,* and
Hieronim Maciejewski
The Chemistry Laboratory, University of Sussex, Brighton, BN1 9QJ U.K.
Received September 29, 1998
Summary: The stable silylene Si[(NCH2But)2C6H4-1,2]
Sch em e 1
[abbreviated as Si(NN)] (1) (4 equiv) with 1 equiv each
of [NiCl2(PPh3)2], [Ni(cod)2], or [PtCl2(PPh3)2] in benzene
affords the crystalline diamagnetic complex [Ni(PPh3)-
{Si(NN)}3] (2), [Ni{Si(NN)}4] (3), or trans-[Pt{Si(NN)-
Cl}2{Si(NN)}2] (4), while from 1 (5 equiv) and [NiCl2-
(PPh3)2] the product was 3. The diversity of behavior of
1, functioning as (i) a neutral ligand, (ii) a reducing
agent, and/ or (iii) a source of the anionic ligand
Sch em e 2
[Si(NN)Cl]- is noteworthy.
The chemistry of transient silylenes SiX2 (X- being a
monodentate anionic ligand) has been extensively stud-
ied, but there is no record of the trapping of such a
silylene on a transition metal (M), generating [M(SiX2)n-
(L)m]. Details have appeared on just two cases of a
stable divalent silicon compound, the silylene SiN(But)-
(CH)2NBut or Si(η5-C5Me5)2, functioning as a ligand
(2),6 [Ni{Si(NN)}4] (3),7 and trans-[Pt{Si(NN)Cl}2{Si-
(NN)}2] (4),8 obtained from 1 and [NiCl2(PPh3)2] (2 and
3), [Ni(cod)2] (3), or [PtCl2(PPh3)2] (4), Schemes 1 and
2. Thus, 1 (i) is a nucleophile, displacing triphenylphos-
phine or cycloocta-1,4-diene from a group 10 metal; (ii)
reduces a Ni(II) chloride to the Ni(0) complex 3; and (iii)
inserts into two Pt-Cl bonds of [PtCl2(PPh3)2] in yield-
ing 4. Variable-temperature, multinuclear (1H, 29Si{1H},
yielding [Ni(CO)2{SiN(But)(CH)2NBut}2]1 or [AuCl{Si-
(η1-C5Me5)(η5-C5Me5)}]2 from [Ni(CO)4] or [Au(Cl)CO],
respectively; also mentioned have been the crystalline
[Fe(CO)4{SiN(But)(CH)2NBut}] and [Cr(CO)2(Mes){SiN-
(But)(CH)2NBut}].1b There are a few other examples of
metal (Ru(II) or Pt(II)) complexes containing three-
coordinate silicon (but these were invariably obtained
from a tetravalent silicon precursor): [Ru(η5-C5Me5)-
1
195Pt{1H}) as well as H saturation transfer (at 213 K)
and 2D EXSY (at 243 K) NMR spectroscopic experi-
ments on 4 in CDCl3, to be described in the full paper,
revealed that the compound underwent fluxional pro-
cesses, involving as major components 4, its cis-analogue
(PMe3)2(SiX2)]+ (X ) SEt,3a SC6H4Me-4,3b Me,3b or Ph3b
)
and trans-[PtH{P(C6H11-c)3}2(SiX2)]+ (X ) SEt).4
We now report that the thermally stable silylene Si-
4a , and the six-coordinate isomer cis-[PtCl2{Si(NN)}4]
(4b), Scheme 3.
The outcome of the reaction between the silylene 1
and [NiCl2(PPh3)2] (1 equiv) was stoichiometry-depend-
ent. Complex 2 was obtained from 1 (4 equiv), whereas
[(NCH2But)2C6H4-1,2] [abbreviated as Si(NN)]5 (1) can
behave with a suitable transition metal complex not
only as (i) an SiX2 ligand but also as (ii) a reducing agent
and/or (iii) a source of an [SiX2X′]- ligand. This diversity
is illustrated by the isolation of the three X-ray-
(5) Gehrhus, B.; Lappert, M. F.; Heinicke, J .; Boese, R.; Bla¨ser, D.
J . Chem. Soc., Chem. Commun. 1995, 1931. Gehrhus, B.; Hitchcock,
P. B.; Lappert, M. F.; Heinicke, J .; Boese, R.; Bla¨ser, D. J . Organomet.
Chem. 1996, 521, 211.
authenticated crystalline complexes [Ni(PPh3){Si(NN)}3]
(1) (a) Denk, M.; Hayashi, R. K.; West. R. J . Chem. Soc., Chem.
Commun. 1994, 33. (b) West, R.; Denk, M. Pure Appl. Chem. 1996,
68, 785.
(2) J utzi, P.; Mo¨hrke, A. Angew. Chem., Int. Ed. Engl. 1990, 29, 893.
(3) (a) Straus, D. A.; Grumbine, S. D.; Tilley, T. D. J . Am. Chem.
Soc. 1990, 112, 7801. (b) Grumbine, S. K.; Tilley, T. D.; Arnold, F. P.;
Rheingold, A. L. J . Am. Chem. Soc. 1994, 116, 5495, and references
therein.
(6) Selected data for 2: Yellow crystals, mp 106-108 °C (decomp).
NMR (C6D6, 293 K): 1H δ 0.78 (s, 54 H), 3.26 (s, 12 H), 6.96 (m, 21 H),
7.7 (m, 6 H); 13C{1H} δ 29.46 (CMe3), 34.08(CMe3), 52.47 (CH2), 110.99,
117.52, 141.22 (phenyl); 31P{1H} δ 47.31 (s); 29Si{1H} δ 136.19.
(7) Selected data for 3: Yellow crystals, mp 84-86 °C (decomp).
NMR (C6D6, 293 K): 1H δ 0.87 (s, 72 H), 3.76 (s, 16 H), 6.96 (m, 8 H),
7.08 (m, 8 H); 13C{1H} δ 29.94 (CMe3), 34.32 (CMe3), 52.96 (CH2),
110.84, 118.06 and 141.30 (phenyl); 29Si{1H} δ 145.9.
(4) Grumbine, S. D.; Tilley, T. D.; Arnold, F. P.; Rheingold, A. L. J .
Am. Chem. Soc. 1993, 115, 7884.
(8) Compound 4: Orange crystals, mp 158-160 °C (decomp).
10.1021/om980818h CCC: $15.00 © 1998 American Chemical Society
Publication on Web 12/04/1998

5600 Organometallics, Vol. 17, No. 26, 1998
Communications
F igu r e 2.
resolved)] of 4 in CDCl3/toluene at 213 K was at a
significantly higher frequency than in the free silylene
1 (δ 96.92);5 this shift is substantially greater than that
between [Ni(CO)2{SiN(But)(CH)2NBut}2] (δ 97.5)1 and
SiN(But)(CH)2NBut (δ 78.4).9 The 29Si NMR spectral
F igu r e 1.
Sch em e 3
chemical shift attributed to the [Si(NN)Cl]- ligand in 4
and 4a was at δ 53.7 and 57.3 [with 1J (29Si-195Pt) )
957 and 934 Hz] and may be compared with δ(29Si)
values for the [Si(NN)X]- ligand in Sn(Ar){Si(NN)Ar}
[δ 48.1, Ar ) C6H3(NMe2)2-2,6].10 The 195Pt{1H} NMR
spectrum of the crystalline 4 in CDCl3/toluene at 213
K showed two major signals at δ -5474 and -5497
attributed to 4/4a and one minor signal (4b) at δ -5540.
Crystalline complex 211 (Figure 1) lies on a crystal-
lographic 3-fold axis, the central Ni atom being almost
tetrahedrally surrounded by the three silicons and the
phosphorus of the four ligands, the Si-Ni-P angles of
106.4(1)° being somewhat narrower than the Si-Ni-
Si′ of 112.4(1)°. The Si-Ni bond distances of 2.165(2) Å
formation of 3 required the use of 5 equiv of 1. The
homoleptic nickel(0) silylene complex 3 was also acces-
sible from [Ni(cod)2] (1 equiv) and 1 (4 equiv). Each of
these high-yield reactions was accomplished in benzene
at ambient temperature. The coproduct of these reac-
5
tions were Si(NN)Cl2 and PPh3 (i or ii in Scheme 1)
and cycloocta-1,4-diene (iii in Scheme 1).
In contrast to reaction ii of Scheme 1 involving [NiCl2-
(PPh3)2], the isoleptic platinum compound was not
reduced by 1 under similarly mild conditions, but
instead underwent insertion into each of the Pt-Cl
bonds, affording stereoselectively (Scheme 2) the crys-
talline trans-bis(chlorosilyl)bis(silylene)platinum(II) prod-
uct 4. It is therefore possible that a transient (chlorosilyl)-
nickel(II) compound may have been an intermediate in
the reduction (i or ii of Scheme 1) of the nickel(II)
chloride. Experiments to test this hypothesis are in
hand.
The yellow (26 or 37) or orange (4),8 crystalline,
diamagnetic complexes gave satisfactory analyses, multi-
nuclear NMR, and mass (parent ion observed) spectra.
Single-crystal X-ray diffraction data established their
molecular structures, shown in Figures 1 (for 2) and 2
(for 4); the structure of 3 will appear in the full paper.
The 29Si{1H} NMR spectra showed that the 29Si
are between the 2.207(2) Å of [Ni(CO)2{SiN(But)-
(CH)2NBut}2]1 (the only other base-free silylenenickel
complex) and the 2.137(1) Å for the Ni-SiMe2 bond in
the base-stabilized silylene(silyl)nickel(II) complex 5, the
Ni-Si(SiMe3)2Me bond length in 5 being 2.240(1) Å.12
Each silicon atom in 2 is slightly (0.214 Å) out of the
(9) Denk, M.; Lennon, R.; Hayashi, R.; West, R.; Belyakov, A. V.;
Verne, H. P.; Haaland, A.; Wagner, M.; Metzler, N. J . Am. Chem. Soc.
1994, 116, 2691.
(10) Drost, C.; Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F. Chem.
Commun. 1997, 1845.
(11) Crystal data for 2: C66H93N6NiPSi3, M ) 1216.6, cubic, space
group Pa3 (No. 205), a ) 23.841(4) Å, U ) 13551(4) Å3, F(000) ) 5264,
Z ) 8, Dc ) 1.19 Mg m-3, µ(Mo KR) ) 0.41 mm-1, specimen 0.3 × 0.2
× 0.2 mm, 2119 independent reflections [R(int) ) 0.0468], R1 ) 0.060
for 1248 reflections with I > 2σ(I), wR2 ) 0.15 (for all data). Intensities
were measured on θmax 20° on an Enraf-Nonius CAD4-diffractometer
[T ) 173(2) K] using monochromated Mo KR radiation (λ ) 0.710 73
Å). Full-matrix least-squares refinement, on all F2, with SHELXL-93,
H atoms in riding mode and all non-H atoms anisotropic. There are
two molecules of pentane solvate disordered across the crystallographic
3h site.
chemical shift of the Si(NN) ligand in 2 (δ 136.2), 3 (δ
145.9), and the three isomers 4, 4a , and 4b [4/4a : δ
142.5 and 146.9 with 1J (29Si-195Pt) ) 2265 and 2259
Hz, respectively; 4b: δ 143.0 and 146.5 (coupling not
(12) Nlate, S; Herdtweck, E; Fischer, R. A. Angew. Chem., Int. Ed.
Engl. 1996, 35, 1861.

Communications
Organometallics, Vol. 17, No. 26, 1998 5601
corresponding NiN2 plane, which, together with the
small deviation from trigonal planarity at Si (sum of
angles at each Si 355.8°), points to imperfect Ni-Si
π-bonding. The Ni-P bond length of 2.210(4) Å is
unexceptional.
2.426(1) Å being unexceptional {e.g., 2.401(3) Å in [Pt-
(OPri)(SiBut OH){(PMe2CH2)2}]14}, as is the Si-Cl,
2
2.100(1) Å.
Crystalline [Ni{Si(NN)}4] (3) is a new member of the
rare class of homoleptic four-coordinate nickel(0) com-
plexes and only the second (cf.15 a homoleptic stan-
nylene-Ni complex) having a group 14 element-cen-
tered ligand, joining the recently described [Ni{In{C(Si-
Me3)3}4}]16 in extending the boundaries of such com-
plexes to the left of the group 15 elements. The
coordination chemistry of the heavier group 14 element
carbene congeners M′X2 (M′ ) Ge, Sn, or Pb) is well-
established,17 as is that of carbenes18a,b or their dimers.18c
Related homoleptic d10 metal complexes to 3 are the two-
coordinate [M(CX2)2]19 and the three-coordinate [M′-
(GeX′2)3]20 and [M′(SnX′2)3],20 prepared from the appro-
priate [M(cod)2], [M′(cod)Cl2], and CX2, GeX′2, or SnX′2
The centrosymmetric, crystalline Pt(II) complex 413
(Figure 2) has a square-planar coordination environ-
ment for Pt, Si(1)-Pt-Si(1)′ 180.0°, Si(1)-Pt-Si(2)
90.86(3)°. In each silylene ligand, the neopentyl sub-
stituents are trans-disposed to one another (in contrast
to their being cis in 1),5 probably in order to accom-
[M ) Ni or Pt, M′ ) Pd or Pt, CX2 ) CN(C6H2Me3-2,4,6)-
CHCHNC6H2Me3-2,4,6, X′ ) N(SiMe3)2]. The different
coordination numbers for these complexes and 3 are
probably largely controlled by steric effects.
The present results, together with those of refs 1 and
2, thus complete the series and offer a prelude of the
significant extensions that will surely follow.
modate the mutually trans chlorines on the [Si(NN)Cl]-
ligands. The three-coordinate silicons, Si(1), are in a
planar environment (sum of angles at Si, 359.9°), with
the average N-Si(1)-Pt bond angle being 133.3° and
Si only 0.04 Å out of the PtNN′ plane. The Pt-Si(1) bond
length, 2.266(1) Å, is almost identical to the 2.270(2) Å
in the cationic Pt(II) complex trans-[PtH{P(C6H11-c}3}2-
{Si(SEt)2}]+.4 The geometric parameters within the
silylene are somewhat different from those (shown
Ack n ow led gm en t. We are grateful for support from
EPSRC and the Royal Society, especially for the fellow-
ships for B.G. (EPSRC) and H.M. (Royal Society-NATO),
and to Dr. A. G. Avent for valuable NMR spectroscopic
data on 4.
successively in parentheses) for the [Si(NN)Cl]- ligand
of 4, 2, and the free silylene 1:5 N-Si-N′ 93.2(1)° [89.7-
(1), 89.5(3), 88.2(1)°], Si-N 1.713(2) Å [1.76(1), 1.75(1),
1.75(1) Å], N-C 1.41(1) Å [1.41(1), 1.40(1), 1.38(1) Å],
and C-C 1.405(4) Å [1.407(4), 1.40(1), 1.415(5) Å]. The
four-coordinate silicons, Si(2), of 4 are in a distorted
tetrahedral environment, the Pt-Si(2) bond length of
Su p p or tin g In for m a tion Ava ila ble: Tables giving X-ray
diffraction data for 2 and 4 (22 pages). Ordering information
is given on any current masthead page.
OM980818H
(14) Goikhman, R.; Aizenberg, M.; Shimon, L. J . W.; Milstein, D. J .
Am. Chem. Soc. 1996, 118, 10894.
(13) Crystal data for 4: C64H104Cl2N8PtSi4‚5(C6H6), M ) 1754.4,
triclinic, space group P1h (No. 2), a ) 13.755(2) Å, b ) 13.857(4) Å, c )
13.999(3) Å, R ) 85.36(2)°, â ) 60.89(2)°, γ ) 77.61(2)°, U ) 2275.7(9)
(15) Veith, M.; Stahl, L.; Huch, V. J . Chem. Soc., Chem. Commun.
1990, 359.
(16) Uhl, W.; Pohlmann, M.; Wartchow, R. Angew. Chem., Int. Ed.
Engl. 1998, 37, 961.
(17) A review: Lappert, M. F.; Rowe, R. S. Coord. Chem. Rev. 1990,
100, 267.
(18) Reviews: (a) Herrmann, W. A.; Ko¨cher, C. Angew. Chem., Int.
Ed. Engl. 1997, 36, 2163. (b) Arduengo, A. J .; Krafczyk, R. Chem. Z.
1998, 32, 6. (c) Lappert, M. F. J . Organomet. Chem. 1988, 358, 185.
(19) Arduengo, A. J .; Gamper, S. F.; Calabrese, J . C.; Davidson, F.
J . Am. Chem. Soc. 1994, 116, 4391.
Å3, F(000) ) 922, Z ) 1, Dc ) 1.28 Mg m-3, µ(Mo KR) ) 1.70 mm-1
,
specimen 0.3 × 0.25 × 0.25 mm, 7994 independent reflections, R1 )
0.025 for 7819 reflections with I > 2σ(I), wR2 ) 0.058 (for all data).
Intensities were measured on θmax 25° on an Enraf-Nonius CAD4-
diffractometer [T ) 173(2) K] using monochromated Mo KR radiation
(λ ) 0.710 73 Å). Full-matrix least-squares refinement, on all F2, with
SHELXL-93, H atoms in riding mode and all non-H atoms anisotropic.
There is a molecule of the platinum complex on an inversion center,
two ordered benzene solvate molecules in general positions, and one
disordered benzene solvate molecule on an inversion center.
(20) Hitchcock, P. B.; Lappert, M. F.; Misra, M. C. J . Chem. Soc.,
Chem. Commun. 1985, 863.