Multi-insertion reactions of isocyanides with zirconium amido silyl complexes

Article abstract of DOI:10.1021/om980979l

The reactions of (Me₂N)₃ZrSi(SiMe₃)₃ (1), (Me₂N)₃ZrSiPh₂Bu^t(THF)o.5 (2), and (Me₂N)₂[(Me₃Si)₂N]ZrSi(SiMe ₃)₃ (3) with 2,6-dimethylphenyl isocyanide (ArNC) or tert-butyl isocyanide (Bu^tNC) have been investigated. The first ArNC was found to insert exclusively into the Zi-Si bond in complex 3 and, in contrast, into the Zi-N bonds in complex 1. Up to 4 equiv of ArNC react with 1 and 2 to give (Me₂N)₂Zr[Si(SiMe₃)₃][η ³-C(NMe₂)=NAr] (4), (Me2N)Zr[Si(SiMe₃)₃][η³-C(NMe ₂)=NAr]₂ (5), (Me₂N)Zr[η²-C(NMe₂)=NAr] ₂{η²-C[Si(SiMe₃)₃]=NAr} (6), Zr[η²-C(NMe₂)=NAr]₃{η ³-C[Si(SiMe₃)₃]=NAr} (7), and Zr[η²-C(NMe₂)=NAr]₃[η ²-C(SiPh₂Bu^t) =NAr] (8). However, 3 reacts with only 2 equiv of ArNC to yield (Me₂N)₂[(Me₃Si)₂N]Zr{η ²-C[Si(SiMe₃)₃]=NAr} (9) and (Me₂N)[(Me₃Si)₂N]Zr[η ²-C(NMe₂)=NAr]{η2-C[Si(SiMe3)3]=NAr} (10). Complex 2 was found to react with 2 equiv of Bu^tNC to yield a ketenimine complex (Me2N)3Zr[N(Bu^t)C(SiPh2Bu^t)=C=NBu^t] (12). The reactions of Zr(NMe₂)₄ with ArNC and Bu'NC were also studied and gave tetrainsertion products Zr[η²-C(NMe2)=NR]4 [R = Bu*(13), 2,6-dimethylphenyl (14)]. The structures of 7,12,13, and 14 have been determined by X-ray crystallography.

Full text of DOI:10.1021/om980979l

1002
Organometallics 1999, 18, 1002-1010
Mu lti-in ser tion Rea ction s of Isocya n id es w ith Zir con iu m
Am id o Silyl Com p lexes
Zhongzhi Wu, J onathan B. Diminnie, and Ziling Xue*
Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37996-1600
Received December 3, 1998
The reactions of (Me2N)3ZrSi(SiMe3)3 (1), (Me2N)3ZrSiPh2But(THF)0.5 (2), and (Me2N)2[(Me3-
Si)2N]ZrSi(SiMe3)3 (3) with 2,6-dimethylphenyl isocyanide (ArNC) or tert-butyl isocyanide
(ButNC) have been investigated. The first ArNC was found to insert exclusively into the
Zr-Si bond in complex 3 and, in contrast, into the Zr-N bonds in complex 1. Up to 4 equiv
of ArNC react with 1 and 2 to give (Me2N)2Zr[Si(SiMe3)3][η2-C(NMe2)dNAr] (4), (Me2N)Zr-
[Si(SiMe3)3][η2-C(NMe2)dNAr]2 (5), (Me2N)Zr[η2-C(NMe2)dNAr]2{η2-C[Si(SiMe3)3]dNAr} (6),
Zr[η2-C(NMe2)dNAr]3{η2-C[Si(SiMe3)3]dNAr} (7), and Zr[η2-C(NMe2)dNAr]3[η2-C(SiPh2But)
dNAr] (8). However, 3 reacts with only 2 equiv of ArNC to yield (Me2N)2[(Me3Si)2N]Zr{η2-
C[Si(SiMe3)3]dNAr} (9) and (Me2N)[(Me3Si)2N]Zr[η2-C(NMe2)dNAr]{η2-C[Si(SiMe3)3]dNAr}
(10). Complex 2 was found to react with 2 equiv of ButNC to yield a ketenimine complex
(Me2N)3Zr[N(But)C(SiPh2But)dCdNBut] (12). The reactions of Zr(NMe2)4 with ArNC and
ButNC were also studied and gave tetrainsertion products Zr[η2-C(NMe2)dNR]4 [R ) But
(13), 2,6-dimethylphenyl (14)]. The structures of 7, 12, 13, and 14 have been determined by
X-ray crystallography.
In tr od u ction
cyclopentadienyl (Cp).1,2 The chemistry of Cp-free d0
metal silyl complexes is a relatively young and unex-
plored area. The research interests in our laboratory
have recently been focused on the chemistry of Cp-free
d0 early-transition-metal complexes, such as alkyl silyl7
and amido silyl complexes.8 These electronically and
coordinatively unsaturated complexes present a new
and unique opportunity to directly compare the relative
reactivities of alkyl, amido, and silyl ligands.
Early-transition-metal d0 silyl chemistry has attracted
special attention in the past decade.1,2 Group 4 d0 metal
silyl complexes were found to undergo insertion and
σ-bond
metathesis
reactions
involving M-Si
bonds.2a-c,k,3-6 However, reactivity studies of d0 metal
silyl complexes have been mainly concentrated on those
containing π-anionic auxiliary ligands such as η5-
We reported recently that in the reactions of alkyl
silyl complexes (Me3ECH2)3ZrSi(SiMe3)3 with ArNC, the
first isocyanide insertion occurred exclusively into the
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10.1021/om980979l CCC: $18.00 © 1999 American Chemical Society
Publication on Web 02/24/1999

Multi-insertion Reactions of Isocyanides
Organometallics, Vol. 18, No. 6, 1999 1003
Sch em e 1
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were performed
under a dry nitrogen atmosphere with the use of either
standard Schlenk techniques or a glovebox. Solvents were
purified by distillation over potassium/benzophenone ketyl.
Benzene-d6 was dried over activated molecular sieves and
stored under nitrogen. 2,6-Dimethylphenyl isocyanide (Fluka)
and ButNC (Aldrich) were used as received. (Me2N)3ZrSi-
(SiMe3)3 (1), (Me2N)3ZrSiPh2But‚THF0.5 (2), and (Me2N)2[(Me3-
Si)2N]ZrSi(SiMe3)3 (3) were prepared by the reactions of
(Me2N)3ZrCl or (Me2N)2[(Me3Si)2N]ZrCl with the corresponding
silyllithium reagents.8 NMR spectra were recorded on a Bruker
AC-250 Fourier transform spectrometer and referenced to
solvents (residual protons in the 1H spectra). Elemental
analyses were performed by E+R Microanalytical Laboratory,
Corona, NY.
(Me2N)Zr [η2-C(NMe2)dNAr ]2{η2-C[Si(SiMe3)3]dNAr } (6).
To a pale yellow solution of 1 (0.50 g, 1.06 mmol) in 20 mL of
pentane at -20 °C was added dropwise 2,6-dimethylphenyl
isocyanide (0.42 g, 3.18 mmol) in 20 mL of pentane with
vigorous stirring. The reaction solution rapidly turned bright
yellow. After stirring at room temperature overnight, the
reaction solution was concentrated and slowly cooled to -18
°C to yield 0.86 g of 6 as a pale yellow solid (94% yield). 1H
NMR (benzene-d6, 250 MHz, 23 °C): δ 6.93-6.86 (m, 9H,
C6H3), 3.06 (s, 6H, ZrNMe2), 2.92 (s, 6H, NdCNMe2), 2.22 (s,
6H, NdCNMe2), 2.05 (s, 6H, C6H3Me2), 2.03 (s, 6H, C6H3Me2),
1.96 (s, 6H, C6H3Me2), 0.31 [s, 27H, Si(SiMe3)3]. 13C{1H} NMR
(benzene-d6, 62.9 MHz, 23 °C): δ 297.1 [NdCSi(SiMe3)3], 211.6
(NdCNMe2), 156.6, 150.2, 131.5, 131.2, 128.6, 127.4, 124.9,
123.4 (C6H3), 46.7 (NdCNMe2), 45.9 (ZrNMe2), 36.1 (Nd
CNMe2), 19.4 (C6H3Me2), 19.0 (C6H3Me2), 2.8 [Si(SiMe3)3]. Anal.
Calcd for C42H72N6Si4Zr: C, 58.34; H, 8.39. Found: C, 58.50;
H, 8.50.
Zr-Si bonds (Scheme 1).9 This preferential isocyanide
insertion into the Zr-Si bonds in the alkyl silyl system
prompted us to study the reactions of the amido
analogues (Me2N)3ZrSiR3 [SiR3 ) Si(SiMe3)3 (1), SiPh2-
But (2)] and (Me2N)2[(Me3Si)2N]ZrSi(SiMe3)3 (3) with
isocyanide. Insertions of isocyanides (RNC) into
M-C,10-16 M-N,10,17 and M-Si3,18 bonds of early-
transition-metal complexes are well documented; how-
ever, there are only a few reports of the reactions of
isocyanides with metal complexes containing different
reactive ligands.3e,9,19 The reactions of isocyanides with
complexes involving both M-Si and M-N bonds, to our
knowledge, have not been investigated. Our amido silyl
complexes 1-3 offer a unique opportunity to observe the
direct competition between silyl and amido ligands in
the migration step and to study whether silyl or amido
ligand migration is preferred. In this paper, we report
our investigations of the reactions of isocyanides with
(Me2N)3ZrSi(SiMe3)3 (1), (Me2N)3ZrSiPh2But(THF)0.5 (2),
and (Me2N)2[(Me3Si)2N]ZrSi(SiMe3)3 (3).
(9) Wu, Z.; McAlexander, L. H.; Diminnie, J . B.; Xue, Z. Organo-
metallics 1998, 17, 4853.
Zr [η2-C(NMe2)dNAr ]3{η2-C[Si(SiMe3)3]dNAr } (7). To a
pale yellow solution of 1 (0.50 g, 1.06 mmol) in hexanes (20
mL) was added dropwise with stirring 0.56 g (4.24 mmol) of
2,6-dimethylphenyl isocyanide in hexanes (20 mL) at room
temperature. The bright yellow solution was allowed to stir
overnight at room temperature. The solution was then filtered,
concentrated to about 5 mL, and slowly cooled to -20 °C to
give 1.00 g of 7 as yellow crystals (95% yield). 1H NMR
(benzene-d6, 250 MHz, 23 °C): δ 8.90, 6.88 (d, 12H, C6H3), 2.89
(s, 9H, NdCNMe2), 2.20 (s, 9H, NdCNMe2), 1.96 (s, 6H,
C6H3Me2), 1.94 (s, 18H, C6H3Me2), 0.27 [s, 27H, Si(SiMe3)3].
13C{1H} NMR (benzene-d6, 62.9 MHz, 23 °C): δ 291.4 [NdCSi-
(SiMe3)3], 212.3 (NdCNMe2), 156.4, 151.2, 131.7, 129.2, 128.7,
127.5, 124.8, 123.0 (C6H3), 47.0 (NdCNMe2), 36.6 (NdCNMe2),
20.3 (C6H3Me2), 20.0 (C6H3Me2), 3.9 [Si(SiMe3)3]. Anal. Calcd
for C51H81N7Si4Zr: C, 61.51; H, 8.20. Found: C, 61.45; H, 8.40.
Zr [η2-C(NMe2)dNAr ]3[η2-C(SiP h 2Bu t)dNAr ] (8). Com-
plex 2 (0.10 g, 0.20 mmol) and 2,6-dimethylphenyl isocyanide
(0.11 g, 0.84 mmol) were placed into a Schlenk tube and
dissolved in 5 mL of benzene at room temperature to give a
yellow-orange solution. After 30 min, the solvent was removed,
and the yellow solid was redissolved in 5 mL of pentane. The
solution was concentrated and cooled to -18 °C to afford 0.15
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Houseknecht, K. L.; Stockman, K. E.; Sabat, M.; Finn, M. G.; Grimes,
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L.; Latesky, S. L.; McMullen, A. K.; Rothwell, I. P.; Folting, K.;
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and references therein.
1
g of yellow microcrystalline 8 (73% yield). H NMR (benzene-
(15) Scott, M. J .; Lippard, S. J . Organometallics 1997, 16, 5857.
(16) Giannini, L.; Caselli, A.; Solari, E.; Floriani, C.; Chiesi-Villa,
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9709.
d6, 250 MHz, 23 °C): δ 7.52-6.50 (m, 22H, C6H5, C6H3), 2.85
(s, 9H, NdCNMe2), 2.22 (s, 9H, NdCNMe2), 1.98 (s, 18H,
C6H3Me2), 1.77 (s, 6H, C6H3Me2), 1.28 (s, 9H, SiPh2But). 13C-
{1H} NMR (benzene-d6, 62.9 MHz, 23 °C): δ 292.9 (NdCSiPh2-
But), 212.7 (NdCN), 154.1, 151.4, 137.2, 135.5, 131.7, 128.8,
128.5, 127.8, 127.5, 127.1, 124.6, 123.0 (C6H5, C6H3), 46.5 (Nd
CNMe2), 36.5 (NdCNMe2), 29.3 (SiPh2CMe3), 20.1 (SiPh2CMe3),
19.9 (SiCdNC6H3Me2), 19.7 (NCdNC6H3Me2). Anal. Calcd for
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A.; Aaliti, A.; Moise, C. J . Chem. Soc., Chem. Commun. 1985, 1231.
C
58H73N7SiZr: C, 70.54; H, 7.45. Found: C, 70.31; H, 7.37.
(M e 2 N )[(M e 3 S i )2 N ]Zr [η2 -C (N M e 2 )dN Ar ]{η2 -C [S i -
(SiMe3)3]dNAr } (10). To a pale yellow solution of 3 (0.11 g,
0.18 mmol) in benzene was added 2 equiv of 2,6-dimethylphe-

1004 Organometallics, Vol. 18, No. 6, 1999
Ta ble 1. Cr ysta llogr a p h ic Da ta for 7, 12, 13, a n d 14
Wu et al.
7
12
13
14
formula
cryst size, mm3
T, K
C
51H81N7Si4Zr
C32H55N5SiZr
0.50 × 0.44 × 0.40
173(2)
C28H60N8Zr
0.46 × 0.42 × 0.42
173(2)
C44H60N8Zr
0.40 × 0.20 × 0.20
0.62 × 0.50 × 0.50
173(2)
173(2)
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
triclinic
P1h
monoclinic
P21/c
12.136(6)
17.126(7)
17.217(8)
90
99.45(3)
90
3530(3)
4
tetragonal
I4h
13.053(3)
13.053(3)
7.790(4)
90
triclinic
P1h
10.980(4)
15.015(6)
16.995(7)
90.13(3)
95.08(3)
97.48(3)
2767(2)
2
11.380(3)
12.240(3)
16.703(5)
94.49(3)
96.45(3)
112.09(2)
2123.7(10)
2
90
90
1668.0(9)
2
Z
fw
995.81
1.195
0.324
1064
629.12
1.184
0.372
1344
600.2
1.195
0.358
648
792.22
1.239
0.299
840
d
calc., g/cm3
µ, mm-1
F(000)
scan type
ω-2θ
ω-2θ
ω-2θ
ω-2θ
θ range, deg
no. of data [I > 2σ(I)]
abs corr
1.81-22.55
7257
1.69-22.57
4647
2.21-22.51
642
1.81-25.05
7501
semiempirical
0.0920(0.1408)
1.093
semiempirical
0.0593(0.1136)
1.098
semiempirical
0.0301(0.0780)
1.136
semiempirical
0.0483(0.1272)
1.076
R1a (wR2)b
GOF
no. of variables
568
0.489, -0.475
352
0.403, -0.371
84
478
0.561, -0.476
Fmax,min (e Å-3
)
0.343, -0.284
R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) (∑[w(Fo - Fc2)2]/∑[w(Fo2)2)1/2
.
a
b
2
nyl isocyanide (0.05 g, 0.37 mmol) at room temperature. The
bright yellow reaction solution was allowed to stand at room
temperature for 24 h. The solvent was then removed in vacuo
to give a bright yellow solid, which was redissolved in pentane.
The pentane solution was concentrated and slowly cooled to
-18 °C to yield bright yellow crystals of 10 (0.11 g, 71% yield).
1H NMR (benzene-d6, 250 MHz, 23 °C): δ 6.92-6.85 (m, 6H,
C6H3), 2.88 (s, 6H, ZrNMe2), 2.84 (s, 3H, NdCNMe2), 2.18 (s,
3H, NdCNMe2), 2.14 (s, 3H, C6H3Me2), 2.05 (s, 3H, C6H3Me2),
1.89 (s, 3H, C6H3Me2), 1.76 (s, 3H, C6H3Me2), 0.39 (s, 18H,
N(SiMe3)2], 0.30 [s, 27H, Si(SiMe3)3]. 13C{1H} NMR (benzene-
d6, 62.9 MHz, 23 °C): δ 295.8 [NdCSi(SiMe3)3], 207.6 (Nd
CNMe2), 154.9, 149.3, 131.8, 131.6, 127.7, 127.5, 125.5, 124.2
(C6H3), 46.4 (NdCNMe2), 44.1 (ZrNMe2), 36.7 (NdCNMe2), 19.9
(C6H3Me2), 19.5 (C6H3Me2), 19.3 (C6H3Me2), 18.9 (C6H3Me2), 6.6
[N(SiMe3)2], 3.6 [Si(SiMe3)3]. Anal. Calcd for C37H75N5Si6Zr: C,
52.30; H, 8.90. Found: C, 51.94; H, 8.61.
0.44 mmol) were placed in an NMR tube and dissolved in
benzene-d6 at room temperature. An instantaneous reaction
was observed to give the tetrainsertion product 14 in almost
quantitative yield as shown by NMR. The reaction solution
was slowly evaporated at room temperature to give 65 mg of
14 as colorless crystals (73% yield). 1H NMR (benzene-d6, 250
MHz, 23 °C): δ 7.00, 6.93 (m, 12H, C6H3), 2.89 (s, 12H, Nd
CNMe2), 2.25 (s, 12H, NdCNMe2), 2.04 (s, 24H, C6H3Me2). 13C-
{1H} NMR (benzene-d6, 62.9 MHz, 23 °C): δ 212.8 (Nd
CNMe2), 151.5, 131.1, 127.5, 122.6 (C6H3), 46.4 (NdCNMe2),
36.2 (NdCNMe2), 19.1 (C6H3Me). Anal. Calcd for C44H60N8Zr:
C, 66.71; H, 7.63. Found: C, 66.83; H, 7.72.
X-r a y Da ta Collection a n d Str u ctu r a l An a lyses of 7,
12, 13, a n d 14. All crystal structures were determined on a
Siemens R3m/V diffractometer equipped with a Nicolet LT-2
low-temperature device. Suitable crystals were coated with
Paratone oil (Exxon) and mounted under a stream of nitrogen
at -100 °C. The unit cell parameters and orientation matrix
were determined from a least-squares fit of the orientation of
at least 25 reflections obtained from a rotation photograph and
an automatic peak search routine. The refined lattice param-
eters and other pertinent crystallographic information are
given in Table 1.
(Me2N)3Zr [NBu tC(SiP h 2Bu t)dCdNBu t] (12). A solution
of 0.27 g (0.53 mmol) of 2 in benzene was added to a solution
of ButNC (0.18 g, 2.13 mmol) in benzene at room temperature.
The clear, bright yellow solution was then allowed to stand at
room temperature for 30 min. The solvent was then removed
to give a yellow solid. The solid was redissolved in pentane
and slowly cooled to -18 °C to afford 0.30 g of 12 as pale yellow
1
Intensity data were measured with graphite-monochro-
mated Mo KR radiation (λ ) 0.710 73 Å). Background counts
were measured at the beginning and end of each scan with
the crystal and counter kept stationary. The intensities of three
standard reflections were measured after every 97 reflections.
The intensity data were corrected for Lorentz and polarization
effects and an empirical absorption correction based upon ψ
scans.
crystals (66% yield). H NMR (benzene-d6, 250 MHz, 23 °C):
δ 8.05-7.22 (m, 10H, C6H5), 3.00 (s, 18H, ZrNMe2), 1.31 (s,
9H, SiCMe3), 1.23 (s, 9H, NCMe3), 1.20 (s, 9H, NCMe3). 13C-
{1H} NMR (benzene-d6, 62.9 MHz, 23 °C) δ 182.2 (NdCdCSi),
137.3, 129.1, 127.7, 127.0 (C6H5), 64.4 (NdCdCSi), 58.5
(NCMe3), 57.4 (NCMe3), 42.9 (ZrNMe2), 30.9 (NCMe3), 30.5
(NCMe3), 29.2 (SiCMe3), 20.8 (SiCMe3). Anal. Calcd for C32H55N5-
SiZr: C, 61.09; H, 8.81. Found: C, 61.13; H, 8.82.
F or m a tion of Zr [η2-C(NMe2)dNBu t]4 (13). To a pale
yellow solution of Zr(NMe2)4 (30 mg, 0.11 mmol) in benzene-
d6 in an NMR tube was added 4 equiv of ButNC (38 mg, 0.45
mmol) at room temperature. The solution was placed at room
temperature in a drybox for 1 week to yield 53 mg of 13 as
colorless crystals (78% yield). The crystals were found to be
almost insoluble in aliphatic and aromatic solvents. The
structural assignment was thus based on its elemental analy-
sis and X-ray crystal structure. Anal. Calcd for C28H60N8Zr:
C, 56.05; H, 10.08. Found: C, 56.05; H, 9.90.
The structures were solved by direct methods using the
Siemens SHELXTL 93 (version 5.0) proprietary software
package. All non-hydrogen atoms were refined anisotropically.
All hydrogen atoms were placed in calculated positions and
introduced into the refinement as fixed contributors with an
isotropic U value of 0.08 Å2.
Resu lts a n d Discu ssion
F or m a tion of Zr [η2-C(NMe2)dNAr ]4 (14). (Me2N)4Zr (30
mg, 0.11 mmol) and 2,6-dimethylphenyl isocyanide (59 mg,
Syn th esis a n d Ch a r a cter iza tion of In ser tion
P r od u cts 4-14. The reaction of the amido silyl complex

Multi-insertion Reactions of Isocyanides
Organometallics, Vol. 18, No. 6, 1999 1005
Ta ble 2. Selected 13C NMR Da ta
δ (NdCR)a
complex
δ (NdCSi)
δ Si(SiMe3)3
(Me2N)3ZrSi(SiMe3)3 (1)8
5.1
5.6
5.6
6.3
2.8
3.9
(Me2N)2[(Me3Si)2N] ZrSi(SiMe3)3 (3)8
(Me2N)2 Zr[Si(SiMe3)3][η2-C(NMe2)dNAr] (4)
(Me2N)Zr[Si(SiMe3)3][η2-C(NMe2)dNAr]2 (5)
(Me2N)Zr[η2-C(NMe2)dNAr]2{η2-C[Si(SiMe3)3]dNAr} (6)
Zr[η2-C(NMe2)dNAr]3{η2-C[Si(SiMe3)3]dNAr} (7)
Zr[η2-C(NMe2)dNAr]3[η2-C(SiPh2But)dNAr] (8)
(Me2N)2[(Me3Si)2N]Zr{η2-C[Si(SiMe3)3]dNAr} (9)
(Me2N)[(Me3Si)2N]Zr[η2-C(NMe2)dNAr]2{η2-C[Si(SiMe3)3]dNAr} (10)
(Me2N)3Zr[η2-C(SiPh2But)dNBut] (11)
208.8
205.2
211.6
212.3
212.7
297.1
291.4
292.9
287.8
295.8
287.6
3.1
3.6
207.6
Zr[η2-C(NMe2)dNAr]4 (14)
212.8
194, 213
Mo[η2-C(NMe2)dNAr]4
17b
Np3Zr{η2-C[Si(SiMe3)3]dNAr}9
296.0
297.5
295.5
297.5
298.8
294.8
299.07
267.6
272.40
299.01
269.7
2.6
2.4
2.9
2.6
3.5
3.1
2.89
3.30
4.24
2.24
Ns3Zr{η2-C[Si(SiMe3)3]dNAr}9
Np2Zr[η2-C(Np)dNAr[{η2-C[Si(SiMe3)3]dNAr}9
Ns2Zr[η2-C(Ns)dNAr]{η2-C[Si(SiMe3)3]dNAr}9
NpZr[η2-C(Np)dNAr]2{η2-C[Si(SiMe3)3]dNAr}9
NsZr[η2-C(Ns)dNAr]2{η2-C[Si(SiMe3)3]dNAr}9
Cp2Sc{η2-C[Si(SiMe3)3]dNAr}18c
259.9
257.7
261.0
258.5
Cp2Zr{η2-C[Si(SiMe3)3]dNAr}Cl3b
CpCp*Zr{η2-C[Si(SiMe3)3]dNAr}Cl3e
(ButO)3Zr{η2-C[Si(SiMe3)3]dNAr}3f
Cp2Zr[η2-C(SiPh2But)dNPh]Cl18d
14
Cp′2Zr[η2-C(Me)dNAr]2
251.8
246.3
245.2
(2,6-But2C6H3O)2Zr[η2-C(CH2Ph)dNAr] (CH2Ph)13a
13a
(2,6-But2C6H3O)2Zr[η2-C(Me)dNAr]2
a
R ) alkyl or amido ligand; Np ) Me3CCH2; Ns ) Me3SiCH2; Ar ) 2,6-dimethylphenyl.
Sch em e 2
(Me2N)3ZrSi(SiMe3)3 (1) with 4 equiv of 2,6-dimeth-
ylphenyl isocyanide (ArNC) proceeds instantaneously
at room temperature to give the tetra-insertion product
7. The mono-insertion and di-insertion intermediates 4
and 5 were detected as well by NMR, when 1 and 2
equiv of ArNC were added to 1 (Scheme 2).20 However,
4 and 5 are not stable in solution, and over days the
NMR spectra showed their decomposition to HSi-
(SiMe3)3 and unidentified products. Attempts to isolate
pure mono- (4) and di-insertion (5) products were
unsuccessful. The tri-insertion intermediate 6 was
obtained by the reaction of 1 with 3 equivalents of
isocyanide (Scheme 2). The reaction of ArNC with
(Me2N)3ZrSiPh2But(THF)0.5 (2) is extremely rapid, and
only the tetra-insertion product 8 was isolated.
In the reaction of 1 with ArNC, the first and second
equivalents of isocyanide were found to insert into Zr-N
bonds. The insertion products were identified by the
1
presence of the characteristic H and 13C NMR reso-
nances of the Zr-Si(SiMe3)3 moiety in 4 (0.46 and 5.6
1
ppm) and 5 (0.54 and 6.3 ppm) (see Table 2).20 Both H
and 13C NMR resonances of the Zr-Si(SiMe3)3 moiety
in 4 and 5 are downfield shifted from those (0.39 and
5.1 ppm) in the precursor 1 (Table 2). In addition, the
characteristic 13C NMR resonances for the (η2-ArNd
CNMe2) ligands in 4 and 5 are at 208.8 and 205.2 ppm,
respectively, and are close to those reported for Mo[η2-
C(NMe2)dNAr]4.17b They are, however, upfield shifted
from that of an iminosilaacyl ligand (ca. 295 ppm) (Table
2). The third and fourth equivalents of ArNC were found
to insert into the Zr-Si and remaining Zr-N bond to
form 6 and 7 (Scheme 2).
The reaction of ArNC with 3 is very fast at both room
and low temperature. A di-insertion complex 10 was
isolated and characterized. The NMR spectra of the di-
insertion complex 10 show the characteristic 13C NMR
resonances of ArNdCSi and ArNdCNMe2 at 295.8 and
207.6 ppm, respectively, and are similar to those in 4-8
(Table 2). The four 2,6-dimethylphenyl methyl groups
(20) NMR data for the mono-insertion complex (Me2N)2Zr[Si(SiMe3)3]-
[η2-C(NMe2)dNAr] (4): 1H NMR (benzene-d6, 250 MHz, 23 °C) δ 6.93-
6.86 (m, 3H, C6H3), 3.00 (s, 12H, ZrNMe2), 2.90 (s, 3H, NdCNMe2),
2.11 (s, 3H, NdCNMe2), 2.00 (s, 6H, C6H3Me2), 0.46 [s, 27H, Si(SiMe3)3];
13C{1H} NMR (benzene-d6, 62.9 MHz, 23 °C) δ 208.8 (NdCNMe2),
148.9, 130.4, 128.9, 124.7 (C6H3), 44.7 (NdCNMe2), 40.5 (ZrNMe2), 36.2
(NdCNMe2), 19.1 (C6H3Me2), 5.6 [Si(SiMe3)3]. NMR data for di-
insertion complex (Me2N)Zr[Si(SiMe3)3][η2-C(NMe2)dNAr]2 (5): 1H
NMR (benzene-d6, 250 MHz, 23 °C) δ 6.93-6.86 (m, 6H, C6H3), 3.05
(s, 6H, ZrNMe2), 3.03 (s, 6H, NdCNMe2), 2.14 (s, 6H, NdCNMe2), 2.00
(s, 6H, C6H3Me2), 1.75 (s, 6H, C6H3Me2), 0.52 [s, 27H, Si(SiMe3)3]; 13C-
{1H} NMR (benzene-d6, 62.9 MHz, 23 °C) δ 205.2 (NdCNMe2), 149.3,
130.6, 128.0, 124.4 (C6H3), 47.4 (NdCNMe2), 42.7 (ZrNMe2), 36.2 (Nd
CNMe2), 19.6 (C6H3Me2), 19.0 (C6H3Me2), 6.3 [Si(SiMe3)3].
1
of 10 are inequivalent in the H NMR spectrum at 23
°C. This suggests a high degree of steric crowding in
the molecule, leading to restricted rotations about the
N-Ar bonds in 10. This result is also consistent with

1006 Organometallics, Vol. 18, No. 6, 1999
Wu et al.
Sch em e 3
Sch em e 4
the fact that 10 is inert to further insertion by ArNC.
Although it could not be isolated, the mono-insertion
intermediate 9 was clearly identified in the reaction of
3 with ArNC.21 The NMR data of 9 indicate that the
insertion occurs first at the Zr-Si bond in the reaction
of 3 with ArNC (Scheme 3) with the characteristic 13C
NMR of ArNdCSi in 9 at 287.8 ppm.
F igu r e 1. ORTEP drawing of Zr[η2-C(NMe2)dNAr]3{η2-
C[Si(SiMe3)3]dNAr} (7), showing 35% thermal ellipsoids.
Sch em e 5
The reactions of 1 and 2 with ArNC are fast and
difficult to control; we thus turned to the reactions of 1
and 2 with ButNC. However, no reaction was observed
between 1 and ButNC at 23 °C over 1 day. The reaction
of excess ButNC with (Me2N)3ZrSiPh2But(THF)0.5 (2)
resulted in an instantaneous formation of a red-orange
solution, which rapidly changed to a pale yellow solu-
tion. From this solution, 12 was isolated as pale yellow
crystals. An X-ray crystal structure determination
revealed that 12 was a di-isocyanide addition product
containing a ketenimine functionality. A possible mech-
anism for the formation of 12 is shown in Scheme 4.
The insertion of ButNC into the Zr-Si bond produces
an η2-iminosilaacyl 11, which then undergoes nucleo-
philic addition of the second equivalent of ButNC to form
12. The di-isocyanide adduct 12 was found to be inert
to further insertion by ButNC. The intermediate 11 was
observed by NMR.22 Similar ketenimine complexes have
been proposed, though not observed, as intermediates
in the reactions of isocyanides with Cp2ScSi(SiMe3)3,18c
3,3)(CH2Ph)](BPh4) and 2 equiv of ButNC.25 12, to our
knowledge, is the first structurally characterized keten-
imine complex through isocyanide insertion to a M-silyl
bond.
Although no insertion of ButNC into the Zr-NMe2
bonds was observed in the reaction of 2 with excess But-
NC, such insertion was observed in the reactions of Zr-
(NMe2)4 with excess ButNC to give a tetra-insertion
product Zr[η2-C(NMe2)dNBut]4 (13) (Scheme 5). The
reaction of Zr(NMe2)4 with ButNC is very slow at room
temperature, and 13 crystallizes from a benzene solu-
tion after a week. The reaction of Zr(NMe2)4 with 4 equiv
of ArNC instantaneously gives a similar product, Zr-
[η2-C(NMe2)dNAr]4 (14), at room temperature.
Molecu la r Str u ctu r e of Zr [η2-C(NMe2)dNAr ]3{η2-
C[Si(SiMe3)3]dNAr } (7). The structure of 7 has been
determined by X-ray crystallogaphy. An ORTEP draw-
ing of 7 is shown in Figure 1. Selected bond distances
and angles are listed in Table 3. Complex 7 contains
one η2-iminosilaacyl and three η2-amidino ligands. The
coordination sphere around the Zr atom can be de-
scribed as a pseudotetrahedron with an η2-CdN unit
occupying a single coordination site. As seen in a
simplified view of 7 in Figure 2, the iminosilaacyl and
one of the amidino ligands [C(3)-N(3)] lie closely in a
plane with carbon atoms cis to each other, and the other
two amidino ligands arrange in another plane with
carbon atoms trans to each other. These two planes are
nearly perpendicular to each other with the C(1)-Zr-
N(2) [167.3(3)°] and N(3)-Zr-N(4) [169.6(3)°] angles
near 170°.
(2,6-Pri C6H3O)2Ta(H)Cl2(PMe2Ph),23 and [(Me3Si)2N]2-
2
VMe(THF).24 Recently, Scott and Lippard structurally
characterized two ketenimine complexes {M(TC-3,3)-
[NButC(CH2Ph)dCdNBut]}(BPh4) (M ) Zr, Hf; TC )
tropocoronand), prepared from alkyl complexes [M(TC-
(21) NMR data for the mono-insertion intermediate (Me2N)2[(Me3-
Si)2N]Zr{η2-C[Si(SiMe3)3]dNAr} (9): 1H NMR (benzene-d6, 250 MHz,
23 °C) δ 6.91 (s, 3H, C6H3), 2.97 (s, 12H, ZrNMe2), 1.99 (s, 6H,
C6H3Me2), 0.34 [s, 18H, N(SiMe3)2], 0.24[s, 27H, Si(SiMe3)3]; 13C{1H}
NMR (benzene-d6, 62.9 MHz, 23 °C) δ 287.8 [NdCSi(SiMe3)3], 156.7,
129.1, 128.6, 125.9 (C6H3), 44.4 (ZrNMe2), 19.5 (C6H3Me2), 5.8
[N(SiMe3)2], 3.1 [Si(SiMe3)3].
(22) NMR data for the intermediate (Me2N)3Zr[η2-C(SiPh2But)d
NBut] (11): 1H NMR (benzene-d6, 250 MHz, 23 °C) δ 7.60, 7.17 (m,
10H, C6H5), 3.05 (s, 18H, ZrNMe2), 1.36 (s, 9H, CMe3), 1.15 [s, 9H,
CMe3]; 13C{1H} NMR (benzene-d6, 62.9 MHz, 23 °C) δ 287.6 [Nd
CSiPh2But], 136.7, 129.5, 128.2, 127.2 (C6H5), 56.9 (NCMe3), 43.1
(ZrNMe2), 30.1 (NCMe3), 28.6(SiCMe3), 19.4 (SiCMe3).
(23) (a) Clark, J . R.; Fanwick, P. E.; Rothwell, I. P. J . Chem. Soc.,
Chem. Commun. 1993, 1233. (b) Clark, J . R.; Fanwick, P. E.; Rothwell,
I. P. Organometallics 1996, 15, 3232.
The Zr-N bond lengths [2.235(9)-2.310(8) Å] are
similar to those in (Me3CCH2)3Zr{η2-C[Si(SiMe3)3]d
NAr} [2.175(3) Å]9 and (Me3CCH2)Zr[η2-C(CH2CMe3)d
(24) Gerlach, C. P.; Arnold, J . J . Chem. Soc., Dalton Trans. 1997,
4795.
(25) Scott, M. J .; Lippard, S. J . Organometallics 1998, 17, 1769.

Multi-insertion Reactions of Isocyanides
Organometallics, Vol. 18, No. 6, 1999 1007
F igu r e 3. ORTEP drawing of (Me2N)3Zr[NButC(SiPh2-
But)dCdNBut] (12), showing 35% thermal ellipsoids.
F igu r e 2. Simplified ORTEP drawing of the structure of
Zr[η2-C(NMe2)dNAr]3{η2-C[Si(SiMe3)3]dNAr} (7).
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 12
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 7
Distances
Zr-N(1)
Zr-N(2)
Zr-N(3)
Zr-N(4)
Si-C(7)
Si-C(17)
Si-C(27)
2.047(6)
2.044(6)
2.062(6)
2.067(5)
1.888(6)
1.922(7)
1.899(7)
N(4)-C(7)
N(4)-C(9)
C(7)-C(8)
N(5)-C(8)
N(5)-C(13)
Si-C(21)
1.457(7)
1.499(7)
1.335(9)
1.226(8)
1.498(8)
1.885(7)
Distances
Zr-C(1)
2.293(10)
2.240(10)
2.225(11)
2.347(10)
2.253(8)
2.310(8)
2.285(9)
2.235(9)
1.341(12)
1.447(13)
1.427(12)
1.417(13)
C(1)-N(1)
C(2)-N(2)
C(3)-N(3)
C(4)-N(4)
C(4)-Si(1)
Si(1)-Si(2)
Si(1)-Si(3)
Si(1)-Si(4)
N(4)-C(35)
C(2)-N(6)
C(3)-N(7)
1.308(12)
1.306(12)
1.301(13)
1.270(12)
1.932(11)
2.396(5)
2.373(5)
2.362(5)
1.441(12)
1.361(12)
1.365(13)
Zr-C(2)
Zr-C(3)
Zr-C(4)
Zr-N(1)
Zr-N(2)
Zr-N(3)
Angles
111.6(2)
Zr-N(4)
N(1)-Zr-N(2)
N(1)-Zr-N(3)
N(1)-Zr-N(4)
N(2)-Zr-N(3)
N(2)-Zr-N(4)
N(3)-Zr-N(4)
Zr-N(4)-C(7)
Zr-N(4)-C(9)
C(7)-Si-C(27)
C(17)-Si-C(27)
C(7)-N(4)-C(9)
C(7)-C(8)-N(5)
C(8)-N(5)-C(13)
N(4)-C(7)-Si
117.7(5)
170.7(7)
127.0(6)
124.9(4)
118.6(5)
115.8(6)
110.7(3)
107.7(3)
111.3(3)
109.5(3)
C(1)-N(5)
N(1)-C(11)
N(2)-C(19)
N(3)-C(27)
101.8(2)
108.0(2)
103.1(2)
115.3(2)
116.4(2)
116.6(4)
125.5(4)
113.0(3)
104.7(3)
C(8)-C(7)-Si
N(4)-C(7)-C(8)
C(7)-Si-C(17)
C(7)-Si-C(21)
C(17)-Si-C(21)
C(21)-Si-C(27)
Angles
Zr-C(1)-N(1)
Zr-C(1)-N(5)
Zr-N(1)-C(1)
Zr-N(1)-C(11)
Zr-C(2)-N(2)
Zr-C(2)-N(6)
Zr-N(2)-C(2)
Zr-N(2)-C(19)
N(1)-Zr-N(2)
N(1)-Zr-N(3)
N(1)-Zr-N(4)
N(1)-Zr-C(2)
N(1)-Zr-C(3)
N(1)-Zr-C(4)
N(2)-Zr-N(3)
N(2)-Zr-N(4)
N(2)-Zr-C(1)
N(2)-Zr-C(3)
N(2)-Zr-C(4)
C(2)-Zr-C(4)
C(1)-N(5)-C(5)
C(1)-N(5)-C(6)
C(5)-N(5)-C(6)
C(3)-N(7)-C(9)
C(9)-N(7)-C(10)
71.6(6)
158.0(8)
74.9(6)
154.0(7)
76.3(6)
153.7(8)
70.4(6)
158.0(7)
134.9(3)
92.1(3)
Zr-C(3)-N(3)
Zr-C(3)-N(7)
Zr-N(3)-C(3)
Zr-N(3)-C(27)
Zr-C(4)-N(4)
Zr-C(4)-Si(1)
Zr-N(4)-C(4)
Zr-N(4)-C(35)
N(3)-Zr-N(4)
N(3)-Zr-C(1)
N(3)-Zr-C(2)
N(3)-Zr-C(4)
N(4)-Zr-C(1)
N(4)-Zr-C(2)
N(4)-Zr-C(3)
C(1)-Zr-C(2)
C(1)-Zr-C(3)
C(1)-Zr-C(4)
C(2)-Zr-C(3)
C(3)-Zr-C(4)
C(2)-N(6)-C(7)
C(2)-N(6)-C(8)
C(7)-N(6)-C(8)
C(3)-N(7)-C(10)
75.8(6)
157.8(8)
70.7(6)
156.5(7)
69.1(6)
160.5(6)
78.8(6)
148.9(7)
169.6(3)
88.2(3)
91.1(3)
140.2(4)
87.1(3)
bulky Si(SiMe3)3 group. The Si-C(dN) bond distance
[1.932(11) Å] in 7 is close to those in (Me3CCH2)Zr[η2-
C(CH2CMe3)dNAr]2{η2-C[Si(SiMe3)3]dNAr} [1.921(5)
Å],9 CpCp*Zr{η2-C[Si(SiMe3)3]dNAr}Cl [1.949(11) Å],3e
Cp2Zr[η2-C(SiPh2But)dNPh]Cl (1.92 Å), and a silaacyl
complex Cp2Zr(η2-COSiMe3)Cl [1.927(2) Å],3a but is
longer than that found in the mono-insertion complex
(Me3CCH2)3Zr{η2-C[Si(SiMe3)3]dNAr} [1.897(4) Å].9 The
C-NMe2 bond distances range from 1.341(12) to 1.365-
(13) Å and are between the CdN [1.270(12)-1.308(12)
Å] and N-CAr bonds [1.417(13)-1.447(13) Å]. The short
C-NMe2 bonds in 7 suggest some degree of p-π
bonding in the Me2N-CdN moiety. This bonding fea-
ture is consistent with the fact that the sums of the
angles around the Me2N group are near 360°, and the
ZrCN unit and Me2N group are nearly coplanar.
89.0(3)
101.7(4)
112.4(3)
114.4(3)
87.3(3)
99.2(3)
167.3(3)
90.9(3)
98.8(3)
137.5(4)
135.0(4)
91.9(4)
98.0(3)
93.1(3)
111.2(4)
106.8(4)
119.5(9)
125.4(9)
114.2(9)
125.9(9)
110.4(4)
119.4(9)
128.2(9)
112.1(9)
118.1(9)
115.6(9)
Molecu la r St r u ct u r e of (Me2N)3Zr [NBu t C(Si-
P h 2Bu t)dCdNBu t] (12). An ORTEP drawing of the
ketenimine complex 12 is shown in Figure 3. Selected
bond distances and angles are listed in Table 4. The Zr
atom is bonded to a ketenimine and three NMe2 ligands
to form a distorted tetrahedron; the bond angles be-
tween the N(4) atom of the ketenimine ligand and
nitrogen atoms of the three amido ligands range from
108.0(2)° to 116.4(2)°. These angles are larger than the
Si-M-N angles in (Me2N)3ZrSi(SiMe3)3 (1) [105.91(11)°]
and (Me2N)3TiSiPh2But [104.6(2)°],8 suggesting that the
NAr]2{η2-C[Si(SiMe3)3]dNAr} [2.200(4)-2.270(4) Å]9
and are consistent with dative Zr(IV)-N bond dis-
tances.26 The Zr-C(4) (iminosilaacyl) bond [2.347(10)
Å] is longer than the average Zr-C(amidino) bond
[2.252(10) Å]. Such difference was also observed in (Me3-
CCH2)Zr[η2-C(CH2CMe3)dNAr]2{η2-C[Si(SiMe3)3]d
NAr}9 and can be ascribed to the steric effect of the
(26) Chisholm, M. H.; Hammond, C. E.; Huffman, J . C. Polyhedron
1988, 7, 2515.

1008 Organometallics, Vol. 18, No. 6, 1999
Wu et al.
F igu r e 5. ORTEP drawing of Zr[η2-C(NMe2)dNAr]4 (14),
F igu r e 4. ORTEP drawing of Zr[η2-C(NMe2)dNBut]4 (13),
showing 35% thermal ellipsoids.
showing 35% thermal ellipsoids.
Ta ble 6. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 14
Ta ble 5. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 13
Distances
Zr-C(1)
2.263(4)
2.282(4)
2.267(3)
2.206(3)
1.314(5)
1.315(5)
1.345(5)
1.344(5)
Zr-C(12)
Zr-C(34)
Zr-N(3)
2.267(3)
2.303(4)
2.259(3)
2.194(3)
1.306(4)
1.317(5)
1.348(4)
1.344(5)
Distances
Zr-C(23)
Zr-N(1)
Zr-N(1)
2.235(3)
2.302(4)
1.514(9)
1.525(7)
1.462(8)
C(1)-N(1)
C(1)-N(2)
C(2)-C(4)
N(2)-C(6)
1.299(9)
1.356(8)
1.529(7)
1.439(8)
Zr-C(1)
Zr-N(5)
Zr-N(7)
C(2)-C(3)
C(2)-C(5)
N(2)-C(7)
C(1)-N(1)
C(23)-N(5)
C(1)-N(2)
C(23)-N(6)
C(12)-N(3)
C(34)-N(7)
C(12)-N(4)
C(34)-N(8)
Angles
C(1)-Zr-N(1)
Zr-C(1)-N(1)
Zr-N(1)-C(1)
C(1)-N(1)-C(2)
33.2(2)
70.6(2)
76.2(3)
138.3(5)
Zr-C(1)-N(2)
Zr-N(1)-C(2)
N(1)-C(1)-N(2)
156.8(4)
145.5(5)
132.6(5)
Angles
Zr-C(1)-N(1)
Zr-C(23)-N(5)
Zr-C(1)-N(2)
Zr-N(3)-C(13)
Zr-C(23)-N(6)
Zr-C(34)-N(8)
N(1)-Zr-N(3)
N(1)-Zr-C(12)
N(1)-Zr-C(34)
N(3)-Zr-C(34)
N(5)-Zr-C(34)
73.3(2)
69.8(2)
Zr-C(12)-N(3)
Zr-C(34)-N(7)
Zr-N(1)-C(4)
Zr-C(12)-N(4)
Zr-N(5)-C(24)
Zr-N(7)-C(35)
N(1)-Zr-N(5)
N(1)-Zr-C(23)
72.9(2)
68.5(2)
160.1(3)
149.7(2)
162.4(3)
164.7(3)
91.66(10)
90.62(11)
170.27(12) N(3)-Zr-C(23)
87.55(11)
93.60(12)
152.0(2)
158.8(3)
148.2(2)
149.6(2)
93.48(11)
88.67(12)
171.80(12)
104.51(12)
102.78(13)
ketenimine ligand in 12 is more sterically demanding
than the silyl ligands in 1 and (Me2N)3TiSiPh2But. The
Zr-N bonds range from 2.044(6) to 2.067(5) Å and are
similar to those found in other known Zr(IV) amido
complexes.26,27 The CdC [1.335(9)] and CdN [1.226(8)
Å] bond distances of the CdCdN moiety are similar to
those found in other complexes containing a CdCdN
functionality, such as [p-But-calix[4]-(OMe)2(O)2Zr-
{N(But)C(Me2)C(CNBut)N(But)}] [1.324(15) and 1.227-
(14) Å],16 [(Me3Si)N]2Zr[ButNdCMeC(dCdNBut)NBut]
[1.345(4) and 1.205(4) Å],24 [(2,6-Pri2C6H3)2Cl2]Ta[ButNd
CHC(dCdNBut)NBut] [1.338(6) and 1.206(5) Å],23 [Zr-
(TC-3,3){NButC(CH2Ph)dCdNBut}](BPh4) [1.314(8) and
1.230(8) Å], and [Hf(TC-3,3){NButC(CH2Ph)dCdNBut}]-
(BPh4) [1.328(9) and 1.229(9) Å].25
Molecu la r Str u ctu r es of Zr [η2-C(NMe2)dNBu t]4
(13) a n d Zr [η2-C(NMe2)dNAr ]4 (14). An ORTEP
drawing of 13 is shown in Figure 4. Selected bond
distances and angles are given in Table 5. The coordina-
tion sphere around the metal center is similar to that
in 7. However, the orientation of four η2-amidino ligands
is different from that in 7. In 13, four ZrCN units lie in
two different, nearly perpendicular planes which bisect
each other, and the carbon atoms in each plane are cis
N(5)-Zr-C(12)
N(7)-Zr-C(1)
C(23)-Zr-C(34) 93.49(12)
C(12)-Zr-C(34) 94.05(12)
to one another. The Zr-N, Zr-C, CdN and C-N(amido)
bond distances [2.235(3) 2.302(4), 1.299(9), and 1.356-
(8) Å, respectively] are similar to those in 7. An ORTEP
drawing of 14 is shown in Figure 5. Selected bond
distances and angles are listed in Table 6. The zirco-
nium atom is coordinated by four η2-amidino ligands,
and the coordination sphere around it is similar to those
in 7 and 13. In 14, the carbon atoms of η2-amidino
ligands in the same plane are trans to each other, as is
observed in Mo[η2-C(NMe2)dNAr]4.17b The orientation
of the four η2-amidino ligands in 14 is thus different
from those in 7 and 13. The average Zr-C and Zr-N
bond distances are 2.276(13) and 2.232(11) Å, respec-
tively, and are close to the corresponding values in 7
and 14.
In flu en ce of Ster ic Effects on Isocya n id e In ser -
tion s in to Zr -Am id o a n d Zr -Silyl Bon d s. Although
isocyanide insertion into metal amido17b,c or metal
silyl3,18 bonds has been previously observed, the current
work reports, to our knowledge, the first isocyanide
insertions involving complexes containing both amido
and silyl ligands. It is interesting to note that the first
ArNC inserts into a Zr-N bond in the amido silyl
(27) (a) Brenner, S.; Kempe, R.; Arndt, P. Z. Anorg. Allg. Chem.
1995, 621, 2021. (b) Nugent, W. A.; Harlow, R. L. Inorg. Chem. 1979,
18, 2030. (c) Diamond, G. M.; J ordan, R. F.; Petersen, J . L. J . Am.
Chem. Soc. 1996, 118, 8024. (d) Christopher, J . N.; Diamond, G. M.;
J ordan, R. F.; Petersen, J . L. Organometallics 1996, 15, 4038. (e)
Bradley, D. C.; Chudzynska, H.; Becker-Dirks, J . D.; Hursthouse, M.
B.; Ibrahim, A. A.; Montevalli, M.; Sullivan, A. C. Polyhedron 1990, 9,
1423. (f) Wu, Z.; Dimmine, J . B.; Xue, Z. Inorg. Chem. 1998, 37, 2570.

Multi-insertion Reactions of Isocyanides
Organometallics, Vol. 18, No. 6, 1999 1009
F igu r e 7. Space-filling drawings of (Me2N)3ZrSi(SiMe3)3
(1): (a) axial view along Zr-Si bond; (b) equatorial view.
F igu r e 6. Space-filling drawings of (Me3CCH2)3ZrSi-
(SiMe3)3:9 (a) axial view along Zr-Si bond; (b) equatorial
view.
Sch em e 6
complex (Me2N)3ZrSi(SiMe3)3 (1). In contrast, the first
ArNC was found to insert exclusively into the Zr-Si
bond in alkyl silyl complexes (Me3ECH2)3ZrSi(SiMe3)3
(E ) C, Si).9 The reason for the difference in the
reactivities of 1 and (Me3ECH2)3ZrSi(SiMe3)3 (E ) C,
Si) toward isocyanide is not clear. Space-filling drawings
of 18 and (Me3CCH2)3ZrSi(SiMe3)39 are shown in Figures
6 and 7, respectively. The largest open area of the
zirconium atom in 1 for the attack of ArNC is between
the amido ligands. We believe that the addition of the
first isocyanide to the metal center in 1 may take place
exclusively trans to the silyl ligand (Scheme 6) and that
the reason for the amide migration is steric. The silyl
ligand in 1 is not in a position to migrate onto the
isocyanide carbon, and the amide migration is irrevers-
ible. An attack trans to the silyl ligand may also be
preferred for the second equivalent of isocyanide. How-
ever, after two isocyanide insertions, the attack trans
to the silyl ligand may become hindered, causing the
third isocyanide attack to take place cis to the silyl
ligand. In other words, the arrangement of the ligands
in 1 directs the attack of the first and second isocyanide
molecules to a position where only amide migration is
feasible.
isocyanide addition between the alkyl and silyl ligands
(cis to the silyl ligand, equatorial view) preferred
(Scheme 1). This addition is followed by a migration of
the bulky Si(SiMe3)3 group onto the isocyanide carbon.
Tilley and co-workers have also observed the influence
of the steric effects on CO insertions to the Zr-C and
Zr-Si bonds in the reactions of CO with Cp2Zr(Me)Si-
(SiMe3)3 and CpCp*Zr(Me)Si(SiMe3)3 (Cp* ) η5-C5-
3b
Me5).3e It was found that CO preferentially inserts into
3b
the Zr-C bond in Cp2Zr(Me)Si(SiMe3)3 and, in con-
trast, into the Zr-Si bond in the more bulky complex
CpCp*Zr(Me)Si(SiMe3)3 (Cp* ) η5-C5Me5).3e
To confirm the influence of the steric effects on the
insertion reaction of ArNC with (Me2N)3ZrSi(SiMe3)3 (1),
we studied the reaction of (Me2N)2[(Me3Si)2N]ZrSi-
(SiMe3)3 (3) with ArNC. Compared to 1, 3 contains a
bulky (Me3Si)2N ligand, which would block the open
area between the amido ligands for the attack of ArNC.
We indeed found that in the reaction of 3 with ArNC
In (Me3CCH2)3ZrSi(SiMe3)3,9 the space between the
alkyl ligands (trans to the silyl ligand, axial view) is
much more crowded than that in 1, perhaps making the

1010 Organometallics, Vol. 18, No. 6, 1999
Wu et al.
Sch em e 7
In conclusion, we have investigated the reactivities
of Cp-free amido silyl complexes toward isocyanides. The
current studies indicate that isocyanide insertion into
Zr-silyl bonds is in general preferred and is often the
first step in multi-insertion reactions. However, steric
effects may play an important role in the insertion and
may direct, for example, the first ArNC insertion to an
M-amide bond in 1. Steric congestion may also limit
the number of isocyanide insertions, as observed in the
inertness of complex 10 and 12 toward further isocya-
nide insertion.
the first ArNC inserted into the Zr-Si bond to give a
mono-insertion product 9 (Scheme 7). (Me2N)3ZrSiPh2-
But(THF)0.5 (2) also reacts with ButNC to give exclu-
sively the Zr-Si insertion products 11 and 12, in
contrast to the reactivity observed with (Me2N)3ZrSi-
(SiMe3)3 (1). THF coordination trans to the silyl ligand
was found in the crystal structure of 2,8 which may
prevent the ArNC approach to the Zr atom from this
position. In addition, the exclusive formation of silyl
insertion products 11 and 12 suggests that once the Zr-
Si and Zr-N bonds are both available for the insertion
of isocyanide, the silyl migration is more favorable than
the amido migration, perhaps because the Zr-amide
bonds are usually stronger than the Zr-silyl bonds.28
Ack n ow led gm en t is made to the National Science
Foundation (Grant CHE-9457368), the DuPont Young
Professor Award, and the Camille Dreyfus Teacher-
Scholar Award for financial support.
Su p p or tin g In for m a tion Ava ila ble: Complete listings
of crystallographic data for 7, 12, 13 and 14. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM980979L
(28) King, W. A.; Marks, T. J . Inorg. Chim. Acta 1995, 229, 343.