The first structurally characterised σ-bonded organonickel(I) compound: Crystal structures of some organonickel and organopalladium compounds (see abstract)

Article abstract of DOI:10.1039/b000374n

The reaction between [NiCl₂(PPh₃)₂] and [Li{C(SiMe₃)₂(SiMe₂C₅H₄N-2)}] in tetrahydrofuran gave the monomeric Ni(I) compound [Ni{C(SiMe₃)₂(SiMe₂C₅H₄N-2)}(PPh₃)], which shows planar coordination at Ni with Ni-C 2.025(4) A, together with the Ni(II) silanolato compound [Ni{C(Si-Me₃)(SiMe₂C₅H₄N-2)(SiMe₂O)}]₂ as a minor product, however, the corresponding reaction with [PdCl₂(PPh₃)₂] gave [Pd(μ-Cl){C(SiMe₃)₂(SiMe₂C₅H₄N-2)}]₂, which has a chloride-bridged structure with an unusual fold angle of 60°at the Cl···Cl axis.

Full text of DOI:10.1039/b000374n

The first structurally characterised s-bonded organonickel( ) compound.
I
Crystal structures of [Ni{C(SiMe3)2(SiMe2C5H4N-2)}(PPh3)],
[Ni{C(SiMe3)(SiMe2C5H4N-2)(SiMe2O)}]2 and
[Pd(m-Cl){C(SiMe3)2(SiMe2C5H4N-2)}]2
Colin Eaborn,* Michael S. Hill, Peter B. Hitchcock and J. David Smith*
School of Chemistry, Physics and Environmental Science, University of Sussex, Brighton, UK BN1 9QJ.
E-mail: j.d.smith@sussex.ac.uk;c.eaborn@sussex.ac.uk
Received (in Basel, Switzerland) 20th December 1999, Accepted 5th March 2000
Published on the Web 3rd April 2000
pyridine ring and the NiCNP coordination plane is 22°, the Ni–P
The reaction between [NiCl2(PPh3)2] and [Li{C(SiMe3)2(Si-
Me2C5H4N-2)}] in tetrahydrofuran gave the monomeric
bond distance is normal, and the Ni–C and Ni–N distances,
2.025(4) and 2.007(3) Å, suggest that the covalent radius for
Ni( ) compound [Ni{C(SiMe3)2(SiMe2C5H4N-2)}(PPh3)],
I
Ni( ) is ca. 1.25 Å. Longer Ni–C and shorter Ni–N distances are
I
which shows planar coordination at Ni with Ni–C 2.025(4)
found in [Ni{C(SiMe3)2(C5H4N-2)}Cp] and [Ni{C(Si-
Me3)2(C5H4N-2)}2],7 reflecting the greater strain in the four-
membered metallacycles than in the five-membered ring of 2.
We have found no evidence for the presence of an
alkylnickel(II) chloride in the products from the reaction
between [NiCl2(PPh3)2] and 1. Nevertheless such a species is
probably formed at the surface of the sparingly soluble
[NiCl2(PPh3)2] and rapidly reduced to 2 by the excess of 1.
Compound 2 is probably prevented by the steric requirements of
the ligand from giving aggregates with Ni–Ni bonds and
Å, together with the Ni(II) silanolato compound [Ni{C(Si-
Me3)(SiMe2C5H4N-2)(SiMe2O)}]2 as a minor product, how-
ever, the corresponding reaction with [PdCl2(PPh3)2] gave
[Pd(m-Cl){C(SiMe3)2(SiMe2C5H4N-2)}]2, which has a chlo-
ride-bridged structure with an unusual fold angle of 60° at
the Cl···Cl axis.
Organonickel compounds have been widely studied, partic-
ularly because of their applications as catalysts.1 Some catalytic
ultimately metallic nickel, and remains in solution as a Ni( )
I
processes are thought to involve Ni(
although triorganophosphine and amine complexes have been
obtained,3 attempts to isolate organo–Ni(
) compounds com-
I
) intermediates2 but,
species stabilised by the soft PPh3 and C5H4N ligands.
Compound 2 was also the principal product from a 1+1
[NiCl2(PPh3)2]+1 mixture but in this case we isolated a few
crystals of a second compound identified‡ as the silanolato
compound 3 (Fig. 2). Our [NiCl2(PPh3)2] probably contained a
trace of hydroxide and intra- or inter-molecular elimination of
I
monly lead to precipitation of elemental nickel.
We have previously isolated organometallic compounds of
the s-, p- and f-elements containing ligands C(SiMe3)n(Si-
Me2X)32n in which the groups X have lone pairs of electrons.4
We reasoned that, if the substituents X had p-acceptor
properties, it might be possible to obtain compounds of d-block
elements without unwanted reduction. Reactions of the pre-
CH4 from [Ni(OH){C(SiMe3)2(SiMe2C5H4N-2)}] could lead to
compound 3. Cleavage of C–Si bonds under mild conditions is
highly unusual, but a few examples are known where an OH
group is held in a favourable position with respect to an SiMe3
group.5b,8 Trialkylsilanolatonickel derivatives have not appar-
ently been reported before.
cursor Li{C(SiMe3)2(SiMe2C5H4N-2)} 1 to give the novel
derivatives 2–4, show that this is indeed the case.
The Ni(
compound to contain a Ni(
I
) compound 2 (the first structurally characterised
I
)–C s-bond, and, apart from the
electrochemically characterised dimeric species [Cu2R2]2+ [R =
C(SiMe3)2(C5H4N-2)],5a the first d9 s-bonded organometallic
compound) was obtained from the reaction of NiCl2(PPh3)2
with 2 equivalents of 1,† and crystals suitable for an X-ray
study‡ (Fig. 1) were isolated from hexane. Compound 2
appeared to be stable in the solid state under Ar, but solutions in
hexane deposited metallic nickel. The EPR spectrum in toluene
at 298 K (g = 2.239) was broad but similar to that of
[NiCl(PPh3)3],6 and the magnetic moment of 1.55 mB at room
temperature was as expected for a d9 complex with one unpaired
electron. The coordination at Ni is planar (sum of angles 360°)
with a bite angle of 98° for the bidentate ligand and a wide C–
Ni–P angle, reflecting the repulsion between the SiMe3 groups
and the phosphine ligand. The dihedral angle between the
Fig. 1 The molecular structure of 2. Selected bond lengths (Å) and angles
(°). For mean values, e.s.d’s of individual measurements are given in
parentheses: Ni–N 2.007(3), Ni–C 2.025(4), Ni–P 2.200(1), Si(1)–C(1)
1.826(4), Si(2,3)–C(1) 1.857(4), mean Si–Me 1.880(4); N–Ni-C(1)
98.28(14), N–Ni–P 105.81(10), C(1)–Ni–P 155.67(11), mean Si–C–Si
114.1(2), mean Me–Si–Me 105.4(2), mean C–Si–Me 113.2(2), C(1)–Si–
C(4) 105.36(18), Si–C(4)–N 114.0(3), C(4)–N–Ni 111.8(3), Ni–C(1)–Si
97.20(17), Ni–C(1)–Si(3) 102.52(18), Ni–C(1)–Si(2) 112.85(18).
DOI: 10.1039/b000374n
Chem. Commun., 2000, 691–692
This journal is © The Royal Society of Chemistry 2000
691

became dark brown as it was allowed to warm to room temperature. The
solvent was then removed, the solid residue extracted with hexane (40 cm3),
and the extract filtered. The filtrate was reduced to 20 cm3 and kept at 230
°C, and the brown solid that separated was filtered off and recrystallised
three times from hexane at 230 °C to give bright orange–red crystals of 2
(0.20 g, 30%), mp 167–168 °C (Found: C, 62.5; H, 7.1; N, 2.2.
C32H43NNiPSi3 requires C, 62.4; H, 7.0; N, 2.2%); m/z 614 (12, M); 599 (4,
M 2 Me), 352 [43, M 2 PPh3 (RNi)], 337 (30, RNi 2 Me), 322 (32, RNi
2 2Me), 294 (35, R), 279 (65, R 2 Me), 262 (100, PPh3), 221 (45, R 2
SiMe3). The reaction between 1 (2.14 mmol), prepared as above, and
[NiCl2(PPh3)2] (2.14 mmol) in thf also gave mainly 2 but a few deep red
crystals observed in the products were separated manually and shown to be
3 (m/z 706.1181. C26H50N2Ni2O2Si6 requires 706.1195).
‡ Crystal data: for 2: M = 615.6; monoclinic, space group P21/n; a =
16.476(2), b = 9.142(3), c = 21.687(5) Å, b = 91.22(2)°, U = 3266(1) Å3,
Z = 4, m = 0.77 mm21; 5932 reflections collected, 5732 unique (Rint
=
0.038), 3974 with I > 2s(I); R1, wR2 0.049, 0.102 [I > 2s(I)] and 0.089,
0.118 (all data). For 3: M = 708.64; triclinic, space group P1; a =
Fig. 2 The molecular structure of 3. Selected bond lengths (Å) and angles
(°): Ni–N 1.881(5), Ni–O 1.891(45), Ni–OA 1.918(4), Ni–C(1) 1.980(6),
mean Si–C(1) 1.852(6), Si–Me 1.875(7), Si–O 1.651(4); O–Ni–O
84.00(18), Si–O–Ni 93.2(2), Ni–O–NiA 96.00(18), Si–C(1)–Si 126.0(3),
115.0(3), 115.6(3), Ni–C–Si(2) 84.5(2), C(1)–Ni–O 84.2(2), Ni–O–Si(2)
93.2(2), Si(2)–C(1)–Ni 84.5(2).
¯
8.8600(8), b = 10.1220(10), c = 10.6164(11) Å, a = 91.437(6), b =
111.283(7), g = 92.595(5)°, U = 885.4 Å3, Z = 1; m = 1.29 mm21; 8262
reflections collected, 3091 unique (Rint = 0.058); 2618 with I > 2s(I); R1,
wR2 0.066, 0.154 [I > 2s(I)], 0.079, 0.160 (all data). For 4: M = 873.0;
orthorhombic, space group Pbca; a = 13.465(5), b = 23.390(12), c =
25.032(9) Å, U = 7884(6) Å3, Z = 8, m = 1.25 mm21; 13619 reflections
collected, 6907 unique (Rint = 0.128), 3750 with I > 2s(I); R1, wR2 0.082,
0.187 [I > 2s(I)] and 0.154, 0.226 (all data). A CAD4 diffractometer was
used for 2 and 4 and a Kappa CCD diffractometer for 3. Structures were
refined by full matrix least squares refinement (SHELXL-97) with non-H
atoms anisotropic and H atoms in riding mode. For 4 the structure was
disordered 80:20 with only Pd sites located for the low occupancy
orientation.
CCDC 182/1571. See http://www.rsc.org/suppdata/cc/b0/b000374n/ for
crystallographic files in .cif format.
§ A solution of 1 (1.22 mmol) in thf (30 cm3) was added to a slurry of
[PdCl2(PPh3)2] (0.86 g, 1.22 mmol) in thf (25 cm3) at 278 °C and the
resulting solution allowed to warm to room temperature. The solvent was
pumped away, the dark brown residue extracted with hexane (3 3 25 cm3),
and the extract filtered. The filtrate was reduced to 25 cm3 and kept at 5 °C
to give pale yellow crystals of 4 (0.28 g, 53%), mp 193–195 °C (decomp.),
darkens 104 °C (Found: C, 38.7; H, 6.4; N, 3.2. C28H56Cl2N2Pd2Si6 requires
C, 38.7; H, 6.5; N, 2.8%.); dH(C6D6) 0.07 (18 H, s, SiMe3), 0.43 (6 H, s,
SiMe2), 6.70 (1 H, m, 4-H), 7.09 (1 H, t, 5-H), 7.23 (1 H, d, 3-H), 8.63 (1
H, d, 6-H); dC(C6D6) 1.3 (1JSiC 51.8 Hz, SiMe2), 3.4 (1JSiC 51.2 Hz, SiMe3),
15.9 (1JSiC 37.1 Hz, CSi3), 122.3 (4-C), 128.4 (5-C), 133.6 (3-C), 150.9
(6-C), 170.2 (1JSiC 77.4 Hz, 2-C); dSi (C6D6) 26.1 (1JSiC 39.4, 52.2, 77.8
Hz, SiMe2), 20.09 (1JSiC 37.4, 50.7 Hz, SiMe3); m/z 857, (30, M 2 Me),
764 (15, M 2 SiMe3Cl), 402, (12, RPd), 385 (22, RPd 2 Me), 370, (27, RPd
Fig. 3 The molecular structure of 4. Selected mean bond lengths (Å) and
angles (°): Pd···Pd 3.1433(15), Pd–N 2.026(10), Pd–C 2.123(12), Pd–Cl
2.325(3), 2.465(3), Si–C(1,15) 1.877(12), Si–Me 1.873(13), Si–
C(py)1.864(15), N–C(Si) 1.362(16); N–C(C) 1.329(16), N–Pd–C 89.9(4),
N–Pd–Cl 92.0(3), Cl–Pd–Cl, 82.62(11), C-Pd-Cl, 95.6(3); Pd–Cl–Pd 81.95,
Pd–C–Si(py) 100.0(5), C–Si–C(py) 102.6(6), Si–C–N 113.6(8), C(py)–N–
Pd 118.7(8), Si–C–Si 112.8(6), Me–Si–Me 106.4(6). Angles between
pyridyl and Pd coordination planes 26.5, 30°.
2 2Me), 312 (100, RPd 2 SiMe4), 206 (80, R 2 SiMe4) [R
=
C(SiMe3)2(SiMe2C5H4N)].
The palladium compound 4 is obtained from equimolar
quantities of 1 and [PdCl2(PPh3)2].§ It is stable in the solid state
under Ar but Pd metal is deposited slowly from solutions in
hexane at room temperature. The dimer‡ (Fig. 3) shows no
crystallographic symmetry but there is an approximate C2 axis
perpendicular to and bisecting the Pd···Pd and Cl···Cl vectors.
The coordination at Pd is square planar and the Pd–Cl bonds
trans to C [2.465(3) Å] are longer than those trans to N
1 A. K. Smith in Comprehensive Organometallic Chemistry II, ed. E. W.
Abel, F. G. A. Stone and G. Wilkinson, Pergamon, Oxford, 1995, vol.
9, pp. 29–106; P. W. Jolly in Comprehensive Organometallic Chem-
istry, ed. G. Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon,
Oxford, 1982, vol. 6, pp. 37–100 and vol. 8, pp. 613–797.
2 T. T. Tsou and J. K. Kochi, J. Am. Chem. Soc., 1979, 101, 7547.
3 L. Sacconi, F. Mani and A. Bencini, in Comprehensive Coordination
Chemistry, ed. G. Wilkinson, R. D. Gillard and J. A. McCleverty
Pergamon, Oxford, 1987, vol. 5, pp. 1–347.
[2.325(3) Å], as in similar compounds containing the NCPd(m-
4 C. Eaborn, P. B. Hitchcock, J. D. Smith and S. E. Sözerli, Organome-
tallics, 1997, 16, 5653; 1998, 17, 4322; S. S. Al-Juaid, C. Eaborn, S. M.
El-Hamruni, P. B. Hitchcock and J. D. Smith, Organometallics, 1999,
18, 45 and references therein.
5 (a) R. I. Papasergio, C. L. Raston and A. H. White, J. Chem. Soc., Chem.
Commun., 1983, 1419; J. Chem. Soc., Dalton Trans., 1987, 3085; (b)
L. M. Engelhardt, R. I. Papasergio, C. L. Raston and A. H. White,
J. Chem. Soc., Dalton Trans., 1984, 311.
6 M. J. Nilges, E. K. Barefield, R. L. Belford and P. H. Davis, J. Am.
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Chem., 1993, 462, 7; 1998, 564, 193 and references therein.
8 C. Eaborn and P. B. Hitchcock, J. Chem. Soc., Perkin Trans. 2, 1991,
1137.
Cl)2PdCN core. The Pd–N bond lengths are normal and the Pd–
C lengths are at the upper end of the usual range. The most
intriguing feature of the structure is the large fold angle (60°) at
the Cl···Cl axis since most Cl-bridged Pt(II) dimers with
bidentate C,N-ligands are planar or nearly so. Two compounds
with fold angles of 37–39°, and one with a fold angle of 58°,
have been reported.9,10 That the palladium compound 4 is much
more easily isolated than the nickel analogue is in accord with
the generalisation that the stabilities of M(II) organometallic
compounds increase in the series from Ni to Pt.
We thank the EPSRC for financial support.
9 A. Crispini, G. De Munno, M. Ghedini and F. Neve, J. Organomet.
Chem., 1992, 427, 409; M. Ghedini, S. Armentano, G. De Munno, A.
Crispini and F. Neve, Liq. Cryst., 1990, 8, 739.
Notes and references
† Formation of complexes 2 and 3: (Me3Si)2[(C5H4N)Me2Si]CH (0.63 g,
2.13 mmol) in thf (15 cm3) was treated with a solution of LiMe (2.16 mmol)
in thf (10 cm3). The resulting solution of 1 was then added to a slurry of
[NiCl2(PPh3)2] (0.70 g, 1.07 mmol) in thf (20 cm3) at 278 °C. The solution
10 A. G. Constable, W. S. McDonald, L. C. Sawkins and B. L. Shaw,
J. Chem. Soc., Dalton Trans., 1980, 1992; S. Armentano, A. Crispini, G.
De Munno, M. Ghedini and F. Neve, Acta Crystallogr., Sect. C, 1991,
47, 966.
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Chem. Commun., 2000, 691–692