Synthesis and crystal structure of the tris(amide) cations [M{N(SiMe3)2}3]+ (M = Zr or Hf ): Evidence for M-Si-C interactions

Article abstract of DOI:10.1039/a706720h

Reaction of the strong Lewis acid B(C₆F₅)₃ with [M{N(SiMe₃)₂}₃Me] (M = Zr or Hf) gave the compounds [M{N(SiMe₃)₂}₃][MeB(C₆F ₅)₃]. Crystallographic analyses of these compounds revealed the formation of multicentre bonds between the SiCH₃ units of the amide ligands and the otherwise electron-deficient metal centre. The new tris(amide) complexes [M{N(Ph)SiMe₃}₃Cl] and [M{N(Ph)SiMe3}3Me] (M = Zr or Hf) have also been synthesized.

Full text of DOI:10.1039/a706720h

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Synthesis and crystal structure of the tris(amide) cations
[M{N(SiMe3)2}3]؉ (M ؍ Zr or Hf): evidence for M᎐Si᎐C
interactions
Jane R. Galsworthy,a Malcolm L. H. Green,*,a Neil Maxteda and Matthias Müllerb
a Inorganic Chemistry Laboratory, South Parks Road, Oxford, UK OX1 3QR
b Chemical Crystallography Laboratory, 9 Parks Road, Oxford, UK OX1 3PD
Reaction of the strong Lewis acid B(C6F5)3 with [M{N(SiMe3)2}3Me] (M = Zr or Hf) gave the compounds
[M{N(SiMe3)2}3][MeB(C6F5)3]. Crystallographic analyses of these compounds revealed the formation of
multicentre bonds between the SiCH3 units of the amide ligands and the otherwise electron-deficient metal
centre. The new tris(amide) complexes [M{N(Ph)SiMe3}3Cl] and [M{N(Ph)SiMe3}3Me] (M = Zr or Hf) have
also been synthesized.
Interaction of the Lewis-acid molecule, B(C6F5)3, with the
metallocene complexes [M(C5H5)2R2] (M = Group IV metal,
R = alkyl) results in addition to the alkyl moiety and formation
of [R(C5H5)2M(µ-R)B(C6F5)3].1 The electrophilic metal centre
thus formed frequently exhibits unusual bonding features as a
means of alleviating its charge deficiency. These compounds
often exist as a solvent-dependent, tight ion pair, exhibiting a
degree of α-agostic interaction between the metal centre and
methyl hydrogen atoms of the anion.2 Alternatively the metal
centre may relieve its electronic deficiency by the addition of a
solvent molecule, as observed for [Zr(C5H5)Me2(η6-C6H5Me)]-
[MeB(C6F5)3] which is formed by the reaction of [Zr(C5H5)Me3]
with B(C6F5)3 in toluene.3
Recently we reported the reaction of [U{N(SiMe3)2}3H]
with B(C6F5)3 which gives the zwitterion [U{N(SiMe3)2}2-
{N(SiMe3)SiMe2CH2B(C6F5)3}] with concomitant elimination
of dihydrogen. This compound has been structurally character-
ised by single-crystal X-ray and neutron diffraction studies
Fig. 1 Structure of [U{N(SiMe3)2}2{N(SiMe3)SiMe2CH2B(C6F5)3}]
(Fig. 1).4 Several reports of M᎐Si᎐CH3 multicentre bonds exist
in the chemistry of lanthanide and actinide complexes although
typically the Si᎐C bond forms part of a metal-bound alkyl
ligand, e.g. [La(η5-C5Me5){CH(SiMe3)2}2]ϩ.5
in the crystal. All black atoms co-ordinate the uranium atom by strong
covalent (N) or weaker multicentre bonds (Si, C). All hydrogen and
fluorine atoms are omitted for clarity
metal centre. The M᎐CH3 distance is 5.527(2) (1) and 5.499(2) Å
(2) and precludes any interaction between the metal atom and
the boron-bound methyl moiety. Close inspection of the co-
ordination sphere around the Group IV atom reveals that each
metal centre is pyramidally co-ordinated by three amide ligands
and the zirconium atom lies 0.688(2) Å above the plane of N(1),
N(2) and N(3) whilst the hafnium atom is 0.707(2) Å above the
analogous N(1)N(2)N(3) plane [Fig. 3(a), 3(b)]. Each amide
ligand has one of its six SiCH3 units located in close proximity
to the metal atom with Zr᎐Si distances of about 3.00 Å, Hf᎐Si
distances of ca. 2.98 Å, Zr᎐C distances of ca. 2.75 Å, Hf᎐C
distances ca. 2.73 Å, Zr᎐H distances of 2.66 Å and Hf᎐H dis-
tances of 2.61 Å (see Tables 2 and 3). These co-ordinated
NSiCH3 moieties, the atoms of which are indicated by black
circles in Figs. 3(a), 3(b) and 4(a), 4(b), are related by local C3
pseudo-symmetry [Fig. 4(a), 4(b)]. The metal atom lies on the
three-fold axis and three SiCH3 units point towards the metal
centre. The three Si᎐C bonds close to the metal centre are sig-
nificantly longer [1.902(1), 1.903(1) and 1.895(1) Å in com-
pound 1, 1.902(1), 1.905(2) and 1.894(2) Å in 2] than the
remaining 15, non-co-ordinating Si᎐C bonds which are in the
ranges 1.854–1.868 (1), 1.853–1.869 Å (2). This bonding con-
trasts with that observed for [M{N(SiMe3)2}3Me], M = Zr or
Hf, where no metal–silyl type interactions were observed.6
However similar features have been observed in [U{N(Si-
Here we report the synthesis of the new Group IV tris(amide)
compounds [M{N(Ph)SiMe3}3Me] (M = Zr or Hf) and the
reactions of these compounds and the previously reported
complexes [M{N(SiMe3)2}3Me] with B(C6F5)3. Our aim was to
explore the generality of the methyl-abstraction reaction using
this Lewis-acid molecule.
Results and Discussion
Treatment of [M{N(SiMe3)2}3Me] (M = Zr or Hf) with 1
equivalent of B(C6F5)3 in pentane yields [M{N(SiMe3)2}3]-
[MeB(C6F5)3] (M = Zr 1 or Hf 2) as white solids which can be
recrystallised from toluene. Complexes 1 and 2 have been char-
acterised by crystal structure determination and by 1H, 11B, 13
C
and 19F NMR spectroscopies (Table 1). An upfield shift of the
11B NMR spectroscopic resonance of B(C6F5)3 (δ 58) to δ
Ϫ14.7 is observed for both species upon reaction. The signal is
characteristic of the [MeB(C6F5)3]Ϫ anion and indicates that,
in solution (C6D6 and CD2Cl2), the MeϪ group has been trans-
ferred from the metal centre to the boron atom and that the
cation and anion are completely dissociated.
The solid-state molecular structures of complexes 1 and 2 are
presented in Fig. 2(a) and 2(b), respectively and display similar
features. The structures contain discrete ionic species in which
the methyl group bonded to boron is fully dissociated from the
J. Chem. Soc., Dalton Trans., 1998, Pages 387–392
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Fig. 2 Structures of compounds 1 (a) and 2 (b) in the crystal. Ellipsoids are drawn at 50% probability. The hydrogen, carbon and fluorine atoms are
not labelled for clarity
Me3)2}2{N(SiMe3)SiMe2CH2B(C6F5)3}] where the electron
deficiency of the metal centre is compensated by the formation
of multicentre bonds between the U atom and SiCH2 units
of the amide ligands.4 The uranium atom is pyramidally co-
ordinated by three amide ligands and lies 0.7 Å above the plane
that these nitrogen atoms form. Each amide ligand has one of
its six SiCH2 entities located in close proximity to the uranium
atom and short U᎐Si and U᎐C distances suggest the formation
of multicentre bonds between the Si᎐C bonds and uranium.
In contrast, work by Horton and co-workers,7,8 describing
the reactions of B(C6F5)3 with zirconium diamide dialkyl
complexes, has uncovered no evidence for the formation of M᎐
Si᎐C multicentre interactions. The complex [Zr{N(SiMe3)2}2-
(CH2Ph)2] reacts with this Lewis acid, eliminating C6H5Me and
state structures of compounds 1 and 2 cannot be detected in
1
their room-temperature H and 13C NMR spectra which are
consistent with the presence of only one type of SiMe3 group.
On cooling a sample of 1 in CD2Cl2 solution to 213 K a broad-
ening and partial splitting of the signal assigned to the SiMe3
groups is observed although slow-exchange conditions of these
molecules could not be achieved. These findings suggest that
M᎐Si᎐CH3 multicentre interactions are present in solution but
that there is a low rotational energy barrier. The compound
[La(η5-C5Me5){CH(SiMe3)2}2]ϩ possesses two types of SiMe3
moieties in the solid state, by virtue of La᎐Si᎐CH3 interactions,
and has been studied by variable-temperature 13C NMR spec-
troscopy. The two different SiMe3 environments cannot be dis-
cerned at room temperature but on cooling to 183 K two signals
1
forming
[Zr(CH2SiMe2NSiMe3){η6-PhCH2B(C6F5)3}{N(Si-
can be resolved.5 For both compounds 1 and 2 a H NMR
Me3)2}], which has been characterised by NMR spectroscopy.7
A similar reaction is observed between [Zr{Me3SiN(CH2CH2-
NSiMe3)2}R2] and B(C6F5)3 when R = CH2Ph. However when
R = Me alkyl abstraction ocurs and NMR spectroscopic data
suggest the presence of a covalent interaction between the
cation, [N3ZrMe]ϩ, and the [MeB(C6F5)3]Ϫ anion.8
spectroscopic resonance due to the methyl group of the
[MeB(C6F5)3]Ϫ anion was not detected, presumably due to line
broadening caused by coupling to the quadrupolar 11B nucleus.
In compounds 1 and 2 the formation of multicentre
M᎐Si᎐CH3 interactions appears to be driven by the need to
relieve the electron deficiency of the metal cation. We wondered
whether these interactions could be displaced by co-ordination
The multicentre M᎐Si᎐C interactions observed in the solid-
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Fig. 3 The co-ordination sphere around the zirconium atom of
compounds 1 (a) and the hafnium atom of 2 (b). All black atoms co-
ordinate the metal atoms by strong covalent (N) or weaker multicentre
(Si, C) bonds
of a two-electron donor ligand to the metal and accordingly
attempted to prepare [M{N(SiMe3)2}3L][MeB(C6F5)3] (L =
PMe3, PPh3, pyridine or ethene) by reaction of the relevant
ligand with compound 1. Both phosphines failed to react indi-
cating that the metal centre is well shielded by the amide
ligands. In light of this finding it is unsurprising that compound
1 also failed to react with ethene, with or without addition of
(MeAlO)n to the reaction. However, reaction of compound 1
with 1 equivalent of pyridine resulted in the formation of
[Zr{N(SiMe3)2}3Me] and C5H5NؒB(C6F5)3.9 One feasible reac-
tion mechanism proceeds via attack at the boron atom by pyri-
dine to generate transient MeϪ which then reacts with the metal
cation to yield [Zr{N(SiMe3)2}3Me]. The strength of the B᎐N
bond may supply the thermodynamic incentive for this reaction
pathway. These findings imply that the N(SiMe3)2 ligands play
a dual role in effectively satisfying the electronic requirements
of the metal centre and providing sufficient steric congestion
around the metal atom to render it inert to addition of
nucleophiles.
In order to explore the reaction of less sterically demanding
(tris)amide complexes with B(C6F5)3 the new compounds
[M{N(Ph)SiMe3}3Cl] (M = Zr 3 or Hf 4) and their methyl
derivatives [M{N(Ph)SiMe3}3Me] (M = Zr 5 or Hf 6) were pre-
pared. The amide, LiN(Ph)SiMe3, has not been reported but is
readily synthesized according to Scheme 1 and can be isolated
as a 2:1 complex with diethyl ether. Characterising data for the
lithium salt are given in Table 1. Compounds 3 and 4 are readily
prepared using the same procedure as colourless, pentane-
soluble, microcrystals. Formation of the methyl derivatives 5
and 6 is easily effected by reaction of 3 and 4 with LiMe. Char-
acterising data for compounds 3–6 are given in Table 1. The
Fig. 4 The co-ordination sphere around the metal centres of com-
pounds 1 (a) and 2 (b) demonstrating the local C3 pseudo-symmetry
(i)
(ii)
(i)
H2NPh
Li(NHPh)
HN(SiMe3)Ph
[{LiN(Ph)SiMe3}2]ؒEt2O
Scheme 1 (i) LiBun, pentane, Ϫ78 ЊC; (ii) SiMe3Cl, Et2O, Ϫ45 ЊC
compounds are quite sensitive and rapidly become yellow at
room temperature, even in the solid state, and satisfactory elem-
ental analyses could not be obtained for 6. The methyl deriv-
atives react with chlorinated solvents to reform the chloro
complexes. It has been previously reported that [Zr{N-
(SiMe3)2}3Me] reacts in solution on exposure to UV radiation
to eliminate methane and form the metallocyclic species
[Zr{N(SiMe3)2}2{N(SiMe3)[SiMe2(µ-CH2)]}].10
The methyl derivatives, 5 and 6, were treated with 1 equiv-
alent of B(C6F5)3 in pentane and yielded green oils. A 11B NMR
spectrum (CDCl3) of the crude mixture from both reactions
exhibited a resonance at δ Ϫ15.4 suggesting that the desired
[M{N(Ph)SiMe3}3][MeB(C6F5)3] species had formed in ca. 50%
yield. Unfortunately attempts to purify the reaction mixture
failed to isolate any products. It was hoped that the reaction of
complexes 5 and 6 with B(C6F5)3 would generate reactive
tris(amide) cations due to the smaller size and decreased elec-
tron-donating power of the N(Ph)SiMe3 ligand. However,
although in situ spectroscopic evidence suggests that the desired
species are formed, it appears that the electronic and steric
properties of the smaller ligand do not stabilise the [M{N(Ph)-
SiMe3}3]ϩ cation sufficiently.
J. Chem. Soc., Dalton Trans., 1998, Pages 387–392
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Table 1 Analytical and spectroscopic data for compounds 1–6 and [{LiN(Ph)SiMe3}2ؒEt2O]
Compounda
Spectroscopic datab
1H:c 0.12 (s, 27 H, CH3)
1 [Zr{N(SiMe3)2}3][MeB(C6F5)3]
C, 39.8 (40.4); H, 5.2 (5.2); B, 0.9 (1.0); N, 3.8 (3.8)
13C:d 148.5 (d, J 226, C6F5), 137.0 (d, J 280, C6F5), 136.7 (d, J 230, C6F5), 11.2 [s (br),
BCH3], 3.4 (s, SiCH3)
11B: Ϫ14.7 (s)
19F:d Ϫ13.60 (d, J 20), Ϫ169.30 (t, J 21), Ϫ172.04 (t, J 24)
1H: 0.13 (s, CH3)
2 [Hf{N(SiMe3)2}3][MeB(C6F5)3]
C, 37.3 (37.5); H, 4.6 (4.81); B, 1.0 (0.93); N, 3.2 (3.54)
13C:d 148.8 (d, J 240, C6F5), 138.2 (d, J 240, C6F5), 137.1 (d, J 250, C6F5), 10.2 [s (br),
BCH3], 2.0 (s, SiCH3)
11B: Ϫ14.6 (s)
19F: Ϫ137.67 (d, J 24), Ϫ165.67 (t, J 21), Ϫ165.89 (t, J 21)
1H: 7.07 (t, J 8.0, 6 H, m-H of C6H5), 6.91 (t, J 7.9, 3 H, p-H of C6H5), 6.12 (d, J 7.5, 6 H,
o-H of C6H5), 0.20 (s, 27 H, SiCH3)
3 [Zr{N(Ph)SiMe3}3Cl]
C, 51.0 (52.4); H, 7.0 (6.8); Cl, 4.9 (5.7); N, 6.5 (6.8)
13C: δ 147.8 (s, ipso-C of C6H5), 129.2 (s, m-C of C6H5), 128.3 (s, p-C of C6H5), 124.5 (s,
o-C of C6H5), 1.0 (s, SiCH3)
4 [Hf{N(Ph)SiMe3}3Cl]
C, 45.2 (45.9); H, 6.1 (6.0); Cl, 4.7 (5.0); N, 5.9 (6.0)
1H: 7.07 (t, J 7.5, 6 H, m-H of C6H5), 6.90 (t, J 6.5, 3 H, p-H of C6H5), 6.55 (d, J 7.0, 6
H, o-H of C6H5), 0.19 (s, 27 H, SiCH3)
13C: 147.9 (s, ipso-C of C6H5), 129.0 (s, m-C of C6H5), 128.4 (s, p-C of C6H5), 124.2 (s,
o-C of C6H5), 1.0 (s, SiCH3)
5 [Zr{N(Ph)SiMe3}3Me]
C, 55.8 (56.2); H, 7.9 (7.5); N, 6.6 (7.0)
1H: 7.13 (t, J 8.5, 6 H, m-H of C6H5), 6.96 (t, J 7.5, 3 H, p-H of C6H5), 6.88 (d, J 8.5, 6
H, o-H of C6H5), 0.39 (s, 3 H, ZrCH3), 0.18 (s, 27 H, SiCH3)
13C: 145.9 (s, ipso-C of C6H5), 129.4 (s, m-C of C6H5), 129.2 (s, p-C of C6H5), 124.2 (s,
o-C of C6H5), 41.2 (s, ZrCH3), 1.0 (s, SiCH3).
6 [Hf{N(Ph)SiMe3}3Me]
[{LiN(Ph)SiMe3}2ؒEt2O]
1H: 7.15 (t, J 7.9, 6 H, m-H of C6H5), 6.95 (t, J 8.5, 3 H, p-H of C6H5), 6.82 (d, J 6.3, 6
H, o-C of C6H5), 0.39 (s, 3 H, ZrCH3), 0.17 (s, 27 H, SiCH3)
13C: 146.1 (s, ipso-C of C6H5), 129.3 (s, m-C of C6H5), 129.2 (s, p-C of C6H5), 124.1 (s,
o-C of C6H5), 45.6 (s, HfCH3), 1.0 (s, SiCH3)
1H: 7.17 (t, J 7.6, 12 H, m-H of C6H5), 6.76 (d, J 8.1, 12 H, o-H of C6H5), 6.65 (t, J 6.3, 6
H, p-H of C6H5), 3.03 (q, J 7.8, 4 H, CH2O), 0.74 (t, J 7.2, 6 H, CH3CH2O), 0.27 (s, 36
H, SiCH3)
a Analytical data given as found (calculated) in %. b NMR data (C6D6, 298 K), unless otherwise stated, given as: chemical shift (δ) [relative intensity,
multiplicity (J in Hz), assignment]. c Methyl resonance too broad to be located. d In CD2Cl2.
Table 2 Selected bond distances (Å) and angles (Њ) for compound 1
Table 3 Selected bond distances (Å) and angles (Њ) for compound 2
Zr᎐N(1)
Zr᎐N(2)
Zr᎐N(3)
Zr᎐Si(10)
Zr᎐Si(20)
Zr᎐Si(30)
Zr᎐C(11)
Zr᎐C(21)
Zr᎐C(31)
2.027(1)
2.022(1)
2.047(1)
2.9843(3)
2.9907(3)
3.0336(3)
2.697(1)
2.736(1)
2.806(1)
Si(10)᎐C(11)
Si(20)᎐C(21)
Si(30)᎐C(31)
Zr᎐H(110)
Zr᎐H(112)
Zr᎐H(210)
Zr᎐H(211))
Zr᎐H(311)
Zr᎐H(312)
1.902(1)
1.903(1)
1.895(1)
2.65(2)
2.58(2)
2.63(2)
2.62(2)
2.75(2)
2.72(2)
Hf᎐N(1)
Hf᎐N(2)
Hf᎐N(3)
Hf᎐Si(10)
Hf᎐Si(20)
Hf᎐Si(30)
Hf᎐C(11)
Hf᎐C(21)
Hf᎐C(31)
2.014(2)
2.015(1)
2.034(1)
2.9631(5)
2.9709(5)
3.0200(4)
2.668(2)
2.716(2)
2.794(2)
Si(10)᎐C(11)
Si(20)᎐C(21)
Si(30)᎐C(31)
Hf᎐H(110)
Hf᎐H(112)
Hf᎐H(210)
Hf᎐H(212)
Hf᎐H(310)
Hf᎐H(311)
1.902(1)
1.905(2)
1.894(2)
2.55(3)
2.54(3)
2.57(3)
2.60(3)
2.64(3)
2.75(3)
Zr᎐N(1)᎐Si(10)
Zr᎐N(2)᎐Si(20)
Zr᎐N(3)᎐Si(30)
104.06(5)
104.61(5)
105.96(5)
Zr᎐N(1)᎐Si(11)
Zr᎐N(2)᎐Si(21)
Zr᎐N(3)᎐Si(31)
134.25(5)
133.07(6)
133.04(6)
Hf᎐N(1)᎐Si(11)
Hf᎐N(2)᎐Si(21)
Hf᎐N(3)᎐Si(31)
135.15(8)
133.72(8)
133.61(8)
Hf᎐N(1)᎐Si(10)
Hf᎐N(2)᎐Si(20)
Hf᎐N(3)᎐Si(30)
103.51(7)
104.04(7)
105.85(7)
Preparations
Experimental
Fourier-transform 1H and 11B NMR spectra were recorded on a
Bruker AM 300 spectrometer at 300 and 96 MHz respectively,
13C NMR spectra on a Bruker AM 300 spectrometer at 75.5
MHz or Varian Unity plus 500 spectrometer at 125 MHz, 19F
NMR spectra on a Varian Unity plus 500 spectrometer at 470
[Zr{N(SiMe3)2}3][MeB(C6F5)3] 1. The compound [Zr{N(Si-
Me3)2}3Me] (265 mg, 0.45 mmol) in pentane (40 cm3) was treat-
ed with B(C6F5)3 (231 mg, 0.45 mmol) in pentane (25 cm3) by
slow addition. There was immediate formation of a white pre-
cipitate and after stirring for 1 h the volatiles were removed in
vacuo. The solid (300 mg, 60% crude yield) was washed with
pentane and extracted with toluene. Concentration of this
solution and cooling to Ϫ20 ЊC gave colourless block shaped
crystals.
1
MHz: H and 13C shifts are reported with respect to δ 0 for
SiMe4, 11B with respect to δ 0 for BF3ؒOEt2, 19F with respect to
δ 0 for CFCl3; all downfield shifts are positive. Microanalyses
were obtained from the microanalytical laboratory of this
department.
[Hf{N(SiMe3)2}3][MeB(C6F5)3] 2. The compound [Hf{N-
(SiMe3)2}3Me] (550 mg, 0.816 mmol) in pentane (80 cm3) was
treated dropwise with B(C6F5)3 (418 mg, 0.816 mmol) in
pentane (40 cm3). There was immediate formation of a white
precipitate. Treatment as above gave colourless block shaped
crystals. Yield 370 mg, 38%.
All reactions were carried out under nitrogen using standard
Schlenk techniques. Solvents were dried over suitable reagents
and freshly distilled under N2 before use. The compounds
NaN(SiMe3)2, ZrCl4, HfCl4, LiMe (1.4  solution in hexane),
LiBun (1.4  solution in pentane), H2NPh and SiMe3Cl were
used as received (Aldrich). The compounds [Zr{N(Si-
Me3)2}3Cl],6 [Hf{N(SiMe3)2}3Cl],6 [Zr{N(SiMe3)2}3Me],6 [Hf-
11
{N(SiMe3)2}3Me]6 and B(C6F5)3 were prepared as previously
LiN(Ph)SiMe3. Aniline (15 g, 0.16 mol) was dissolved in pen-
tane (100 cm3) and cooled to Ϫ78 ЊC. A 2.5  pentane solution
described.
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of LiBun (64.4 cm3, 0.16 mol) was added dropwise and then
stirred for 3 h to give a white precipitate. The reaction mixture
was allowed to warm to room temperature and the supernatant
liquid filtered off to leave an air-sensitive solid. Without further
purification the solid was dissolved in diethyl ether (100 cm3),
cooled to Ϫ45 ЊC, and SiMe3Cl (20.5 cm3, 0.16 mol) added
dropwise. After stirring for 2 h a white precipitate had formed.
All volatiles were removed in vacuo and the resulting solid was
extracted with pentane (3 × 70 cm3). The pentane filtrate was
cooled to Ϫ78 ЊC and LiBun (64.4 cm3, 0.082 mol) added drop-
wise; immediately a cream precipitate formed. The reaction was
allowed to warm to room temperature, stirred for a further hour
and then the solvent removed in vacuo. The product was washed
with pentane and the creamy white solid dried in vacuo before
being extracted with diethyl ether (3 × 40 cm3). The filtrate was
concentrated and recrystallised to yield a white solid. Proton
NMR spectroscopic data of the compound were consistent
with the molecular formula [{LiN(Ph)SiMe3}2]ؒEt2O. Yield
29.03 g, 79%.
solvent was removed in vacuo to give a pale yellow solid. Extrac-
tion with hexane (120 cm3) yielded a white solid which was
1
identified by H and 11B NMR spectroscopy as a mixture of
C5H5NؒB(C6F5)3 and [Zr{N(SiMe3)2}3Me].
With ethene. Compound 1 (320 mg, 0.291 mmol) was dis-
solved in toluene (10 cm3) and ethene was bubbled through the
solution. After 1 h no reaction was observed so (MeAlO)n (320
mg, 0.291 mmol) was added. After a further 1 h no formation
of polyethylene was observed.
Reaction of [Zr{N(Ph)SiMe3}3Me] with B(C6F5)3
The compound [Zr{N(Ph)SiMe3}3Me] (300 mg, 0.50 mmol) in
pentane (60 cm
3) was treated dropwise with B(C F ) (256 mg,
6
5 3
0.50 mmol) in pentane (60 cm3). After stirring for 18 h the
solvent was filtered off from a grey powder. Addition of either
toluene or CH2Cl2 to the solid produced the immediate form-
ation of a green solution which was concentrated in vacuo to
yield a green oil. Examination of the crude product by 11B
NMR spectroscopy revealed two major signals at δ Ϫ5.7 and
Ϫ15.4 but unfortunately no single product could be isolated
from the mixture .
[Zr{N(Ph)SiMe3}3Cl] 3. A solution of [{LiN(Ph)SiMe3}2]ؒ
Et2O (4.02 g, 9.65 mmol) in diethyl ether (60 cm3) was added
to a suspension of ZrCl4 (1.5 g, 6.4 mmol) in diethyl ether
(30 cm3). The reaction was stirred for 18 h before removal of
the solvent under reduced pressure. The solid was extracted
with pentane (3 × 40 cm3) and the filtrate concentrated to 10
cm3; colourless crystals formed on cooling to Ϫ20 ЊC. Yield
2.93 g, 74%.
NMR tube reaction of [Hf{N(Ph)SiMe3}3Me] with B(C6F5)3
The compounds [Hf{N(Ph)SiMe3}3Me] and B(C6F5)3 were
mixed in a 1:1 ratio and then dissolved in C6D6 (0.5 cm3). After
18 h a 11B NMR spectrum of the mixture exhibited peaks at
δ Ϫ5.9 and Ϫ15.4.
[Hf{N(Ph)SiMe3}3Cl] 4. A solution of [{LiN(Ph)SiMe3}2]ؒ
Et2O (1.95 g, 4.68 mmol) in diethyl ether (60 cm3) was added
to a suspension of HfCl4 (1.0 g, 3.1 mmol) in diethyl ether
(30 cm3). The reaction was stirred for 6 h before removal of
the solvent under reduced pressure. The solid was extracted
with pentane (3 × 30 cm3) and the filtrate concentrated to 20
cm3; colourless crystals formed on cooling to Ϫ20 ЊC. Yield
1.07 g, 49%.
Crystallography
Crystals of compounds 1 and 2 were grown from toluene at
253 K and then dried in vacuo. In each case a crystal was im-
mersed in highly viscous perfluoropolyether to exclude oxygen.
It was then mounted on a glass fibre and plunged in a cold
(100 K) nitrogen stream.
Crystal data. Compound 1, C37H57BF15N3Si6Zr, M =
1099.40, triclinic, space group P1, a = 11.360(1), b = 12.860(1),
[Zr{N(Ph)SiMe3}3Me] 5. The compound [Zr{N(Ph)Si-
Me3}3Cl] (1.0 g, 1.6 mmol) in diethyl ether (40 cm3) was cooled
to Ϫ50 ЊC. Methyllithium (1.6 mmol as 1.15 cm3 of a 1.4 
solution in hexane) was added carefully and the reaction stirred
for 2 h before removal of the solvent under reduced pressure.
The solid was extracted with pentane (3 × 40 cm3) and the sol-
vent removed to yield a light brown powder. Yield 0.82 g, 85%.
¯
c = 17.640(1) Å, α = 81.395(2), β = 88.717(2), γ = 78.529(2)Њ,
U = 2479.04 Å3, Z = 2, Dc = 1.462 Mg mϪ3, µ = 4.41 cmϪ1
,
colourless crystals, crystal dimensions 0.2 × 0.2 × 0.3 mm.
Compound 2, C37H57BF15HfN3Si6, M = 1186.67, triclinic, space
¯
group P1, a = 11.354(1), b = 12.863(1), c = 17.616(1) Å, α =
81.367(1), β = 88.676(1), γ = 78.520(1)Њ, U = 2493.0 Å3, Z = 2,
Dc = 1.58 Mg mϪ3, µ = 23.00 cmϪ1, colourless crystals, crystal
dimensions 0.3 × 0.4 × 0.5 mm.
[Hf{N(Ph)SiMe3}3Me] 6. The compound [Hf{N(Ph)Si-
Me3}3Cl] (1.0 g, 1.6 mmol) in diethyl ether (30 cm3) was cooled
to Ϫ50 ЊC. Methyllithium (0.56 mmol as 0.4 cm3 of a 1.4 
solution in hexane) was added carefully and the reaction stirred
for 2 h before removal of the solvent under reduced pressure.
The solid was extracted with pentane (3 × 40 cm3) and the sol-
vent removed to yield a light brown powder. Yield 0.28 g, 72%.
Data collection and processing. The data for compounds 1
and 2 were collected at 100 K on an Enraf-Nonius DIP2020
image-plate diffractometer with graphite-monochromated
Mo-Kα radiation (λ = 0.710 69 Å). An Oxford Cryosystems
CRYOSTREAM cooling system was used. For compound 1
28 322 reflections were measured (1 < θ < 26Њ, h, k, l), 9741
unique of which 8858 had I > 3σ(I). The images were processed
with the DENZO and SCALEPAK programs.12 For compound
2 27 942 reflections were measured (1 < θ < 26Њ, h, k, l),
9728 unique of which 9320 had I > 3σ(I). Corrections for
Lorentz-polarisation effects and for absorption (multiscan)
were performed.
Reactions of [Zr{N(SiMe3)2}3][MeB(C6F5)3] 1 with nucleophiles
With PMe3. The compound [Zr{N(SiMe3)2}3][MeB(C6F5)3] 1
(27 mg, 0.025 mmol) in C6D6 (0.5 cm3) was treated with a small
excess of PMe3 (0.509  toluene solution). The resulting 1H, 11
B
and 31P NMR spectra of the reaction mixture corresponded to
those of the starting reagents.
With PPh3. Compound 1 (20 mg, 0.018 mmol) and PPh3 (7
mg, 0.027 mmol) were dissolved together in C6D6 (0.5 cm3). The
1H, 11B and 31P NMR spectra of the reaction mixture corre-
sponded to those of the starting reagents.
Structure solution and refinement. The crystal structures were
solved by direct methods and refined by the full-matrix least-
squares method. For compound 1 all non-hydrogen atoms were
refined with anisotropic and all hydrogen atoms with isotropic
displacement parameters. 797 Refined parameters and 8858
observations resulted in a ratio observations:refined param-
eters of 11.1:1. A correction for secondary extinction was
applied and refinement completed using a Chebyshev weighting
With pyridine. Compound 1 (320 mg, 0.291 mmol) was dis-
solved in toluene (60 cm3). A 0.1  pyridine solution in toluene
(2.92 cm3, 0.292 mmol) was added and stirred for 2 h. The
J. Chem. Soc., Dalton Trans., 1998, Pages 387–392
391

View Article Online
scheme13 with parameters 0.65, 0.204 and 1.30. Refinement on
F converged at R = 0.024, RЈ = 0.028 and goodness of fit = 1.08.
A final Fourier-difference synthesis showed minimum and max-
2 M. Bochmann and S. J. Lancaster, Organometallics, 1994, 13, 2235.
3 D. J. Gillis, M.-J. Tuboret and M. C. Baird, J. Am. Chem. Soc., 1993,
115, 2543.
4 M. Müller, V. C. Williams, L. H. Doerrer, M. A. Leech, S. A.
Mason, M. L. H. Green and K. Prout, Inorg. Chem., in the press.
5 H. van der Hejden, C. J. Schaverien and A. G. Orpen, Organo-
metallics, 1989, 8, 255.
imum residual electron densities of Ϫ0.29 and 0.36 e ÅϪ3
.
For compound 2 all non-hydrogen atoms were refined in
anisotropic approximation. The positions of the hydrogen
atoms were refined with fixed isotropic displacement param-
eters (Uiso = 0.05 Å2). 740 Refined parameters and 9320 obser-
vations resulted in a ratio observations:refined parameters of
12.6:1. A correction for secondary extinction was applied and
refinement completed using a Chebyshev weighting scheme14
with parameters 2.97, Ϫ1.29 and 2.34 was applied. Refinement
on F converged at R = 0.022, RЈ = 0.025 and goodness of
fit = 1.09. A Fourier-difference synthesis showed minimum and
6 R. Anderson, Inorg. Chem., 1979, 18, 1724.
7 A. D. Horton and J. de With, Chem Commun., 1996, 1375.
8 A. D. Horton, J. de With, A. J. van der Linden and H. van de Weg,
Organometallics, 1996, 15, 2672.
9 J. R. Galsworthy, M. L. H. Green, M. Müller and K. Prout, J. Chem.
Soc., Dalton Trans., 1997, 1309.
10 D. C. Bradley, H. Chudzynska, J. D. J. Backer-Dirks, M. B.
Hursthouse, A. A. Ibrahim, M. Motevalli and A. C. Sullivan,
Polyhedron, 1990, 9, 1423.
11 A. G. Massey and A. J. Park, J. Organomet. Chem., 1964, 2, 245.
12 D. Gewirth, The HKL Manual, written with the co-operation of the
program authors, Z. Otwinowski and W. Minor, Yale University,
1995.
13 E. Prince, Mathematical Techniques in Crystallography and Material
Sciences, Springer, New York, 1982.
maximum residual electron densities of Ϫ0.89 and 0.89 e ÅϪ3
.
All crystallographic calculations were carried out using the
CRYSTALS program package.15
CCDC reference number 186/786.
14 International Tables for Crystallography, Kluwer, Dordrecht, 1992,
vol. C.
15 D. J. Watkin, C. K. Prout, J. R. Carruthers and P. W. Betteridge,
CRYSTALS Issue 10, Chemical Crystallography Laboratory,
University of Oxford, 1996.
Acknowledgements
We thank the University of Oxford for a Violette and Samuel
Glasstone Fellowship (to J. R. G.), the Deutsche Forschung
Gemeinschaft (M. M.) and the EPSRC for support of this
work.
References
1 X. Yang, C. L. Stern and T. J. Marks, J. Am. Chem. Soc., 1991, 113,
3623.
Received 16th September 1997; Paper 7/06720H
392
J. Chem. Soc., Dalton Trans., 1998, Pages 387–392