Reactions of (Me3ECH2)3ZrSi(SiMe3)3 (E = C, Si) with 2,6-dimethylphenyl isocyanide. Preferential isocyanide insertion into Zr-silyl bonds

Article abstract of DOI:10.1021/om980485o

The reactions of alkyl silyl complexes (Me₃ECH₂)₃ZrSi(SiMe₃)₃ [E = C (1), Si (2)] with 2,6-dimethylphenyl isocyanide (ArNC) have been investigated. The first ArNC was found to insert exclusively into the Zr-Si bond, and the second and third ArNC into the Zr-C bonds in 1 and 2. 1 and 2 react with up to 3 equiv of ArNC to give (Me₃ECH₂)₃Zr{η²-C[Si-(SiMe ₃)₃]=NAr} [E = C (3), Si (4)], (Me₃ECH₂)₂Zr[η²-C(CH ₂EMe₃)=NAr]{η²-C[Si(SiMe₃) ₃]=NAr} [E = C (5), Si (6)], and (Me₃ECH₂Zr[η²-C(CH₂EMe ₃)=NAr]₂{η²-C[Si(SiMe₃) ₃]=NAr} [E = C (7), Si (8)]. The tri-insertion complexes 7 and 8 are inert to excess ArNC. The structures of 3 and 7 have been determined by X-ray crystallography. In the structure of 3, the α-hydrogen atoms on one neopentyl ligand lie in close contact (av 2.41 A?) with the metal center giving rise to Zr-C-Hα bond angles of 90 and 92°. The crystal structure of the precursor 1 has also been determined.

Full text of DOI:10.1021/om980485o

Organometallics 1998, 17, 4853-4860
4853
Rea ction s of (Me3ECH2)3Zr Si(SiMe3)3 (E ) C, Si) w ith
2,6-Dim eth ylp h en yl Isocya n id e. P r efer en tia l Isocya n id e
In ser tion in to Zr -Silyl Bon d s
Zhongzhi Wu, Lenore H. McAlexander, J onathan B. Diminnie, and Ziling Xue*
Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37996-1600
Received J une 11, 1998
The reactions of alkyl silyl complexes (Me3ECH2)3ZrSi(SiMe3)3 [E ) C (1), Si (2)] with
2,6-dimethylphenyl isocyanide (ArNC) have been investigated. The first ArNC was found to
insert exclusively into the Zr-Si bond, and the second and third ArNC into the Zr-C bonds
in 1 and 2. 1 and 2 react with up to 3 equiv of ArNC to give (Me3ECH2)3Zr{η2-C[Si-
(SiMe3)3]dNAr} [E ) C (3), Si (4)], (Me3ECH2)2Zr[η2-C(CH2EMe3)dNAr]{η2-C[Si(SiMe3)3]dNAr}
[E ) C (5), Si (6)], and (Me3ECH2)Zr[η2-C(CH2EMe3)dNAr]2{η2-C[Si(SiMe3)3]dNAr} [E ) C
(7), Si (8)]. The tri-insertion complexes 7 and 8 are inert to excess ArNC. The structures of
3 and 7 have been determined by X-ray crystallography. In the structure of 3, the R-hydrogen
atoms on one neopentyl ligand lie in close contact (av 2.41 Å) with the metal center giving
rise to Zr-C-HR bond angles of 90 and 92°. The crystal structure of the precursor 1 has
also been determined.
In tr od u ction
containing π-anionic ligands such as η5-cyclopentadienyl
(Cp).1,2 Our research has been focused on the chemistry
of Cp-free d0 early-transition-metal complexes, such as
alkyl silyl complexes.7 These electronically and coordi-
natively unsaturated complexes present a new and
unique opportunity to directly compare the relative
reactivities of alkyl and silyl ligands.
Early-transition-metal silyl chemistry is becoming
increasingly prominent in organometallic chemistry.1,2
Group 4 d0 metal silyl complexes can undergo insertion
reactions2c,k,3,4 and catalyze silane polymeriza-
tions1g,2a,b,5 and hydrosilation of alkenes and alkynes.6
However, most reactivity studies of d0 early-transition-
metal silyl complexes have been conducted on those
Insertions of isocyanides (RNC) and CO into M-C
bonds are well documented.8 The accepted mechanism
involves addition of CO or RNC to the metal center,
followed by migration of a ligand onto the carbonyl or
isocyanide carbon atoms (Scheme 1). Such insertions
into M-silyl bonds in the absence of alkyl ligands have
been reported by Tilley, Mori, and co-workers.3,9 For
example, Cp2Zr[Si(SiMe3)3]Cl,3b CpCp*Zr[Si(SiMe3)3]Cl,3e
(Me3CO)3ZrSi(SiMe3)3,3f (2,6-iPr2C6H3N)2Mo[Si(SiMe3)3]-
Cl,9a and Cp2ScSi(SiMe3)39c undergo 2,6-dimethylphenyl
* To whom correspondence should be addressed. Fax: (423) 974-
3454. E-mail: xue@utk.edu.
(1) (a) Tilley, T. D. In The Chemistry of Organic Silicon Compounds;
Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1989; Chapter 24.
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Z., Eds.; Wiley: New York, 1991; Chapters 9 and 10. (c) Tilley, T. D.
Comments Inorg. Chem. 1990, 10, 37. (d) Harrod, J . F.; Mu, Y.; Samuel,
E. Polyhedron 1991, 11, 1239. (e) Corey, J . Y. In Advances in Silicon
Chemistry; Larson, G., Ed.; J AI Press: Greenwich, CT, 1991; Vol. 1, p
327. (f) Xue, Z. Comments Inorg. Chem. 1996, 18, 223. (g) Tilley, T. D.
Acc. Chem. Res. 1993, 26, 22. (h) Sharma, H. K.; Pannell, K. H. Chem.
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1992, 114, 7047. (b) Imori, T.; Tilley, T. D. Polyhedron 1994, 13, 2231.
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A. L. J . Am. Chem. Soc. 1995, 117, 3621. (d) Xin, S. X.; Harrod, J . F.
J . Organomet. Chem. 1995, 499, 181. (e) Dioumaev, V. K.; Harrod, J .
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J iang, Q.; Pestana, D. C.; Carroll, P. J .; Berry, D. H. Organometallics
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Chem. 1997, 533, 61. (n) Hengge, E.; Gspaltl, P.; Pinter, E. J .
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X.; Lange, U. E. W.; Reding, M. T.; Buchwald, S. L. J . Am. Chem. Soc.
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10.1021/om980485o CCC: $15.00 © 1998 American Chemical Society
Publication on Web 10/08/1998

4854 Organometallics, Vol. 17, No. 22, 1998
Wu et al.
(2)] were prepared by the reactions of (Me3ECH2)3ZrCl with
Li(THF)3Si(SiMe3)3.7b Infrared spectra were recorded on a Bio-
Rad FST-60A infrared spectrometer. NMR spectra were
recorded on a Bruker AC-250 or AMX-400 Fourier transform
spectrometer and referenced to solvents (residual protons in
Sch em e 1
1
the H spectra). Elemental analyses were performed by E+R
Microanalytical Laboratory (Corona, NY).
(Me3CCH2)3Zr {η2-C[Si(SiMe3)3]dNAr } (3). A solution of
0.21 g (0.38 mmol) of 1 in toluene (2 mL) at room temperature
was treated dropwise with a solution of 0.049 g (0.38 mmol)
of ArNC in toluene (2 mL) over a period of 10 min. The solution
was then stirred at room temperature for 1 h. The bright
yellow solution was then concentrated and cooled to -18 °C,
producing 0.15 g of 3 as bright yellow crystals (58% yield)
suitable for X-ray analysis. IR (KBr, cm-1): 2950 s, 2861 s,
2790 m, 2700 w, 1579 w, 1509 s, 1462 s, 1443 m sh, 1356 s,
1229 s, 1169 w, 1090 w, 996 w, 832 s, 773 s, 689 s, 623 s, 524
isocyanide (ArNC) insertion into M-Si bonds to form
iminosilaacyl complexes. Insertion and addition of more
than 1 equiv of isocyanide to early-transition-metal alkyl
complexes have also been observed. Wilkinson and co-
workers10 reported that in the reaction of (Me3CCH2)4-
Zr with ButNC, the complex undergoes isocyanide
insertion into one of the M-C bonds, followed by
addition of a second ButNC without subsequent migra-
tion of an alkyl ligand. The failure of the remaining
alkyl groups to migrate to the isocyanide carbon atom
was attributed to steric congestion. Multiple isocyanide
insertions to M-alkyl bonds were observed by Rothwell
and co-workers8,11 in the reaction of (R′O)4-xMRx (x )
2, 3; M ) Ti, Zr, Hf) with 2 or 3 equiv of isocyanide; all
M-C bonds undergo isocyanide insertion. Heating of the
products leads to the coupling of the isocyanide ligands
to form metallacyclic compounds.12 Similar reactions
were also recently observed between 2 equiv of iso-
cyanide and [(C5Me4)SiMe2(NBut)]ZrMe2,13 [M(TC-3,n)-
R2] [TC ) tropocoronand; M ) Zr(IV), Hf(IV); n ) 3, 5;
R ) CH2Ph, Ph]14 and [p-But-calix[4]-(OMe)2(O)2ZrR2]
(R ) Me, CH2Ph, p-MeC6H4).15 However, to our knowl-
edge, there are only two reports of the reactions of
isocyanides with metal complexes containing different
reactive ligands.16 Our metal alkyl silyl complexes
(Me3ECH2)3ZrSi(SiMe3)3 [E ) C (1), Si (2)] offer a unique
opportunity to observe the direct competition between
silyl and alkyl ligands in the migration step, and to
study whether silyl or alkyl ligand migration is pre-
ferred. In this paper, we report our investigations of the
reactions between 2,6-dimethylphenyl isocyanide and
(Me3ECH2)3ZrSi(SiMe3)3.
1
w. H NMR (benzene-d6, 250 MHz, 23 °C): δ 6.95, 6.89 (3H,
C6H3), 1.96 (s, 6H, C6H3Me2), 1.23 (s, 27H, CH2CMe3), 1.21 (s,
6H, CH2CMe3), 0.22 [s, 27H, Si(SiMe3)3]. 13C{1H} NMR (benzene-
d6, 62.9 MHz, 23 °C): δ 296.0 (CdN), 155.9, 129.0, 127.6, 126.4
(C6H3), 95.0 (CH2CMe3), 35.5 (CH2CMe3), 35.0 (CH2CMe3), 19.6
(C6H3Me2), 2.6 [Si(SiMe3)3] Anal. Calcd for C33H69NSi4Zr: C,
57.99; H, 10.18. Found: C, 57.63; H, 10.04.
(Me3SiCH2)3Zr {η2-C[Si(SiMe3)3]dNAr } (4). To a pale-
yellow solution of 2 (0.12 g, 0.20 mmol) in toluene (2 mL) was
added slowly 1 equiv of ArNC (0.026 g, 0.20 mmol) in toluene
(2 mL) at room temperature over 10 min. The bright-yellow
solution was concentrated and cooled to -18 °C to afford 0.10
g of 4 as yellow crystals (69% yield). 1H NMR (benzene-d6, 250
MHz, 23 °C): δ 6.95, 6.89 (3H, C6H3), 1.96 (s, 6H, C6H3Me2),
0.78 (s, 6H, CH2SiMe3), 0.24 [s, 27H, Si(SiMe3)3], 0.18 (s, 27H,
CH2SiMe3). 13C{1H} NMR (benzene-d6, 62.9 MHz, 23 °C): δ
297.5 (CdN), 155.3, 129.1, 127.4, 126.6 (C6H3), 65.7 (CH2-
SiMe3), 19.4 (C6H3Me2), 3.1 (CH2SiMe3), 2.4 [Si(SiMe3)3]. Anal.
Calcd for C30H69NSi7Zr: C, 49.25; H, 9.50. Found: C, 49.52;
H, 9.68.
(Me3CCH2)Zr [η2-C(CH2CMe3)dNAr ]2{η2-C[Si(SiMe3)3]d
NAr } (7). To a solution of 50 mg (0.09 mmol) of 1 in benzene-
d6 was added 36 mg (0.27 mmol) of ArNC. The clear, bright-
yellow solution in an NMR tube was then allowed to evaporate
slowly at room temperature. After several days, 50 mg of 7
were isolated as yellow crystals (58% yield), which were used
for X-ray crystal structure determination and elemental
1
analysis. H NMR (benzene-d6, 250 MHz, 23 °C): δ 6.94, 6.89
Exp er im en ta l Section
2
(m, 9H, C6H3), 2.44 (d, J H-H ) 15.2 Hz, 2H, NCCHaHbCMe3),
2.32 (d, 2H, NCCHaHbCMe3), 2.06 (s, 6H, C6H3Me2), 2.03 (s,
6H, C6H3Me2), 1.96 (s, 6H, C6H3Me2), 1.44 (s, 2H, ZrCH2CMe3),
1.14 (s, 9H, ZrCH2CMe3), 0.94 (s, 18H, NdCCH2CMe3), 0.31
[s, 27H, Si(SiMe3)3]. 13C{1H} NMR (benzene-d6, 62.9 MHz, 23
°C): δ 298.8 [NdCSi(SiMe3)3], 261.0 (NdCCH2CMe3), 155.4,
150.2, 129.3, 128.9, 128.4, 127.8, 125.6, 125.3 (C6H3), 75.3
(ZrCH2CMe3), 53.3 (NdCCH2CMe3), 36.4 (ZrCH2CMe3), 35.6
(ZrCH2CMe3), 31.6 (NdCCH2CMe3), 31.1 (NdCCH2CMe3), 20.9
(C6H3Me2), 20.4 (C6H3Me2), 20.3 (C6H3Me2), 3.5 [Si(SiMe3)3].
Anal. Calcd for C51H87N3Si4Zr: C, 64.76; H, 9.27. Found: C,
64.84; H, 9.41.
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)
was used as received. (Me3ECH2)3ZrSi(SiMe3)3 [E ) C (1), Si
(9) (a) Casty, G. L.; Tilley, T. D.; Yap, G. P. A.; Rheingold, A. L.
Organometallics 1997, 16, 4746. (b) Arnold, J .; Tilley, T. D.; Rheingold,
A. L.; Geib, S. J .; Arif, A. M. J . Am. Chem. Soc. 1989, 111, 149. (c)
Campion, B. K.; Heyn, R. H.; Tilley, T. D. Organometallics 1993, 12,
2584. (d) Honda, T.; Satoh, S.; Mori, M. Organometallics 1995, 14, 1548.
(10) Chiu, K. W.; J ones, R. A.; Wilkinson, G.; Galas, A. M. R.;
Hursthouse, M. B. J . Chem. Soc., Dalton Trans. 1981, 2088.
(11) Chamberlain, L. R.; Durfee, L. D.; Fanwick, P. E.; Kobriger,
L.; Latesky, S. L.; McMullen, A. K.; Rothwell, I. P.; Folting, K.;
Huffman, J . C.; Streib, W. E.; Wang, R. J . Am. Chem. Soc. 1987, 109,
390.
(12) Chamberlain, L. R.; Durfee, L. D.; Fanwick, P. E.; Kobriger,
L.; Latesky, S. L.; McMullen, A. K.; Rothwell, I. P.; Folting, K.;
Huffman, J . C.; Streib, W. E. J . Am. Chem. Soc. 1987, 109, 6068.
(13) Kloppenburg, L.; Petersen, J . L. Organometallics 1997, 16,
3548.
(Me3SiCH2)Zr [η2-C(CH2SiMe3)dNAr ]2{η2-C[Si(SiMe3)3]d
NAr } (8). ArNC (0.052 g, 0.39 mmol) was added to 2 (0.078 g,
0.13 mmol) dissolved in toluene (2 mL) to give a bright yellow
solution. The solution was then concentrated and slowly cooled
to -18 °C to give 0.058 g of 8 as yellow crystals (45% yield).
1H NMR (toluene-d8, 400.1 MHz, 27 °C): δ 6.93 (m, 9H, C6H3),
2
2.61 (d, J H-H ) 10.4 Hz, 2H, NCCHaHbSiMe3), 2.57 (d, 2H,
NCCHaHbSiMe3) 2.08 (s, 6H, C6H3Me2), 2.02 (s, 6H, C6H3Me2),
2.01 (s, 6H, C6H3Me2), 0.28 (s, 2H, ZrCH2SiMe3), 0.23 [s, 27H,
Si(SiMe3)3], 0.02 (s, 9H, ZrCH2SiMe3), -0.10 (s, 18H, NdCCH2-
SiMe3). 13C{1H} NMR (toluene-d8, 100.6 MHz, 27 °C): δ 294.8
[NdCSi(SiMe3)3], 258.5 (NdCCH2SiMe3), 155.8, 149.4, 129.5,
128.9, 128.4, 128.1, 125.5, 125.2 (C6H3), 42.1 (ZrCH2SiMe3),
33.6 (NdCCH2SiMe3), 20.4 (C6H3Me2), 20.3 (C6H3Me2), 3.9
(14) Scott, M. J .; Lippard, S. J . Organometallics 1997, 16, 5857.
(15) Giannini, L.; Caselli, A.; Solari, E.; Floriani, C.; Chiesi-Villa,
A.; Rizzoli, C.; Re, N.; Sgmellotti, A. J . Am. Chem. Soc. 1997, 119, 9709.
(16) See refs 3e and Dormond, A.; Aaliti, A.; Moise, C. J . Chem. Soc.,
Chem. Commun. 1985, 1231.

Preferential Isocyanide Insertion into Zr-Silyl Bonds
Organometallics, Vol. 17, No. 22, 1998 4855
Ta ble 1. Cr ysta llogr a p h ic Da ta for 1, 3, a n d 7
1
3
7
empirical formula
cryst size, mm
T, K
C
24H60Si4Zr
C33H69NSi4Zr
0.20 × 0.40 × 0.45
173(2)
C51H87N3Si4Zr
0.56 × 0.38 × 0.16
173(2)
0.32 × 0.20 × 0.10
173(2)
cryst syst
space group
a, Å
b, Å
c, Å
trigonal
P3
16.282(4)
16.282(4)
11.608(4)
90
90
120
2665.0(13)
3
triclinic
P1h
triclinic
P1h
12.032(3)
13.455(4)
14.133(4)
111.99(2)
92.60(2)
93.97(2)
2110.2(10)
2
11.557(3)
14.462(5)
17.228(5)
88.54(2)
89.13(2)
72.95(2)
2752.0(14)
2
R, deg
â, deg
γ, deg
volume, Å3
Z
fw
552.3
1.032
0.453
900
683.5
1.076
0.394
740
945.82
1.141
0.320
1020
d
calc, g/cm3
µ, mm-1
F(000)
scan type
ω-2θ
ω-2θ
ω-2θ
θ range,deg
no. of data [I > 2σ(I)]
abs corr
2.27-22.55
2654
1.56-22.55
5527
1.84-22.55
7236
semiempirical
0.0884 (0.1657)
1.082
semiempirical
0.0409 (0.0948)
1.105
semiempirical
0.0523 (0.1377)
1.117
R1a (wR2)b
GOF
no. of variables
263
0.589, -0.978
376
0.528, -0.383
532
0.828, -0.535
Fmax,min (e Å-3
)
R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) (∑[w(Fo - Fc2)2]/∑[w(Fo2)2)1/2
.
a
b
2
Sch em e 2
1
(ZrCH2SiMe3), 3.1 [Si(SiMe3)3], 0.6 (NdCCH2SiMe3). H NMR
(toluene-d8, 400.1 MHz, 52 °C): δ 6.95 (m, 9H, C6H3), 2.58 (s,
4H, NdCCH2SiMe3), 2.09 (s, 6H, C6H3Me2), 2.01(s, 12H,
C6H3Me2), 0.28 (s, 2H, ZrCH2SiMe3), 0.23 [s, 27H, Si(SiMe3)3],
0.02 (s, 9H, ZrCH2SiMe3), -0.10 (s, 18H, NdCCH2SiMe3).
13C{1H} NMR (toluene-d8, 100.6 MHz, 52 °C): δ 295.3 [Nd
CSi(SiMe3)3], 258.9 (NdCCH2SiMe3), 155.8, 149.6, 129.5, 128.9,
128.4, 128.1, 125.5, 125.2 (C6H3), 42.5 (ZrCH2SiMe3), 33.8
(NdCCH2SiMe3), 20.4 (C6H3Me2), 20.3 (C6H3Me2), 3.9 (ZrCH2-
SiMe3), 3.2 [Si(SiMe3)3], 0.7 (NdCCH2SiMe3). Anal. Calcd for
C
48H87N3Si7Zr: C, 58.00; H, 8.82. Found: C, 57.77; H, 9.10.
X-r a y Da ta Collection a n d Str u ctu r a l An a lyses of 1,
3, a n d 7. 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 Para-
tone 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.
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of Ar NC In ser -
tion P r od u cts 3-8. The alkyl silyl complexes 1 and 2
react with 1 equiv of ArNC instantaneously at room
temperature to produce the silyl insertion products
(Me3ECH2)3Zr{η2-C[Si(SiMe3)3]dNAr} [E ) C (3), Si
(4)]. The mono-insertion products 3 and 4 are highly
soluble in pentane and hexanes, and were purified by
recrystallization from toluene. 3 and 4 are stable under
nitrogen at room temperature. When 2 equiv of ArNC
were added to 1 and 2, di-insertion intermediates (Me3-
ECH2)2Zr[η2-C(CH2EMe3)dNAr]{η2-C[Si(SiMe3)3]d
NAr} [E ) C (5), Si (6)] were clearly identifiable by NMR
(Scheme 2). However, attempts to isolate pure products
were unsuccessful; small amounts of tri-insertion prod-
ucts were present in the isolated materials.17 The tri-
insertion complexes (Me3ECH2)Zr[η2-C(CH2EMe3)d
NAr]2{η2-C[Si(SiMe3)3]dNAr} [E ) C (7), Si (8)] were
obtained by either the reactions of 3 equiv of ArNC with
1 and 2, or addition of 2 equiv of ArNC to 3 and 4
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.
The structures were solved using the Siemens SHELXTL
93 (version 5.0) proprietary software package. For 7, the
zirconium and silicon atoms were located by the Patterson
method, and the structure completed by successive Fourier
syntheses. For 1 and 3, the structures were solved by direct
methods. All non-hydrogen atoms were refined anisotropically.
The R-hydrogen atoms of the neopentyl ligands in 3 were
located from a Fourier difference map and refined isotropically.
The remaining hydrogen atoms in 3 and those in 1 and 7 were
placed in calculated positions and introduced into the refine-
ment as fixed contributors with an isotropic U value of 0.08
Å2.

4856 Organometallics, Vol. 17, No. 22, 1998
Ta ble 2. Selected 13C NMR Da ta a
Wu et al.
complexes
δ(NdCR)
δ(NdCSi)
δ[Si(SiMe3)3]
Np3ZrSi(SiMe3)3 (1)7b
4.2
4.3
2.6
2.4
2.9
2.6
3.5
3.1
2.89
3.30
4.24
2.24
Ns3ZrSi(SiMe3)3 (2)7b
Np3Zr{η2-C[Si(SiMe3)3]dNAr} (3)
296.0
297.5
295.5
297.5
298.8
294.8
299.07
267.6
272.40
299.01
Ns3Zr{η2-C[Si(SiMe3)3]dNAr} (4)
Np2Zr[η2-C(Np)dNAr]{η2-C[Si(SiMe3)3]dNAr} (5)
Ns2Zr[η2-C(Ns)dNAr]{η2-C[Si(SiMe3)3]dNAr} (6)
NpZr[η2-C(Np)dNAr]2{η2-C[Si(SiMe3)3]dNAr} (7)
NsZr[η2-C(Ns)dNAr]2{η2-C[Si(SiMe3)3]dNAr} (8)
Cp2Sc{η2-C[Si(SiMe3)3]dNAr}11c
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
Cp′Zr[η2-C(Me)dNAr]2
251.8
246.3
245.2
13
(2,6-But2C6H3O)2Zr[η2-C(CH2Ph)dNAr](CH2Ph)11
(2,6-But2C6H3O)2Zr[η2-C(Me)dNAr]2
11
a
R ) alkyl; Np ) Me3CCH2; Ns ) Me3SiCH2; Cp′ ) (C5Me4)SiMe2(NBut).
(Scheme 2). 7 and 8, highly soluble in pentane and
hexane, have a lower solubility in toluene, and were
thus purified by recrystallization from toluene. The 14-
electron complexes 7 and 8 are inert to further reaction
with ArNC and were found to be more stable toward
oxidation in air than their 8-electron precursors 1 and
2.
All insertion products have been characterized by 1H
and 13C NMR spectroscopy. The NMR spectra of the
1
mono-insertion complexes 3 and 4 revealed that the H
and 13C resonances of the Si(SiMe3)3 group in 3 and 4
are both upfield-shifted compared to those of their alkyl
silyl precursors. The characteristic η2-iminosilaacyl
carbon resonances for 3 and 4 at 296.0 and 297.5 ppm,
respectively, are similar to those in other η2-imino-
silaacyl complexes (Table 2) and suggest that the first
1
ArNC inserts into the Zr-Si bonds in 1 and 2. The H
NMR spectra of the tri-insertion products 7 and 8 at
206 K show a singlet for the R-protons of the non-
inserted Zr-CH2CMe3 and Zr-CH2SiMe3 ligands as
well as an AB pattern for the methylene protons of the
inserted -CH2CMe3 and -CH2SiMe3 groups. The AB
F igu r e 1. Variable-temperature NMR spectra of (Me3-
SiCH2)Zr(η2-C(CH2SiMe3)dNAr)2{η2-C[Si(SiMe3)3]dNAr}
(8).
1
pattern in the H NMR of 8 is shown in Figure 1. This
AB pattern suggests two motions in 7 and 8. First, there
is a facile rotation (flipping) of the η2-iminosilaacyl
ligand, which makes the two η2-iminoacyl groups chemi-
cally equivalent (Chart 1a). Second, the rotation of the
two η2-iminoacyl ligands (Chart 1b) is fast on the NMR
time scale, which, combined with the rotation of the η2-
iminosilaacyl group, gives rise to one set of diastereo-
topic methylene protons for the η2-iminoacyl ligands in
also consistent with static η2-iminoacyl groups (no
rotation with respect to the Zr centers). Although this
possibility is unlikely, we cannot currently rule it out.
The variable-temperature 1H NMR of 7 and 8 has
been studied. The diastereotopic methylene proton
resonances of the η2-iminoacyl ligands in 8 coalesce to
one single peak at 320 K (Figure 1). The free energy of
activation ∆Gq for the coalescence at 320 K was esti-
mated to be 15.7 ( 0.5 kcal/mol.18 This phenomenon
suggests another dynamic process in 8, namely an
exchange between two η2-iminoacyl ligands (Chart 1c),
which equilibrates their diastereotopic methylene pro-
1
7 and 8. The AB pattern in the H NMR of 7 and 8 is
(17) NMR data for the di-insertion complex (Me3CCH2)2Zr[η2-C(CH2-
CMe3)dNAr]{η2-C[Si(SiMe3)3]dNAr} (5): 1H NMR (benzene-d6, 250
MHz, 23 °C): δ 7.02, 6.95 (m, 6H, C6H3), 2.48 (s, 2H, NdCCH2CMe3),
2.19 (s, 6H, C6H3Me2), 2.16 (s, 6H, C6H3Me2), 1.13 (s, 18H, ZrCH2CMe3),
0.95 (s, 4H, ZrCH2CMe3), 0.89 (s, 9H, NdCCH2CMe3), 0.24 [s, 27H,
Si(SiMe3)3]. 13C{1H} NMR (benzene-d6, 62.9 MHz, 23 °C): δ 295.5 [Nd
CSi(SiMe3)3], 259.9 (NdCCH2CMe3), 156.4, 150.1, 129.1, 128.7, 128.2,
127.6, 125.9, 125.7 (C6H3), 88.9 (ZrCH2CMe3), 52.2 (NdCCH2CMe3),
36.1 (ZrCH2CMe3), 35.1 (ZrCH2CMe3), 31.9 (NdCCH2CMe3), 30.7 (Nd
CCH2CMe3), 20.1 (C6H3Me2), 19.8 (C6H3Me2), 2.9 [Si(SiMe3)3]. NMR
data for the di-insertion complex (Me3SiCH2)2Zr[η2-C(CH2SiMe3)dNAr]-
{η2-C[Si(SiMe3)3]dNAr} (6): 1H NMR (benzene-d6, 250 MHz, 23 °C):
δ 7.04-6.97 (m, 6H, C6H3), 2.78 (s, 2H, NdCCH2SiMe3), 2.28 (s, 6H,
C6H3Me2), 2.19 (s, 6H, C6H3Me2), 0.37 (s, 2H, ZrCH2SiMe3), 0.34 (s,
2H, ZrCH2SiMe3), 0.21 [s, 27H, Si(SiMe3)3] 0.07 (s, 18H, ZrCH2SiMe3),
-0.06 (s, 9H, NdCCH2SiMe3). 13C{1H} NMR (benzene-d6, 62.9 MHz,
23 °C): δ 297.5 [NdCSi(SiMe3)3], 257.7 (NdCCH2SiMe3), 156.0, 148.9,
129.1, 128.8, 127.8, 127.0, 126.0, 125.8 (C6H3), 56.8 (ZrCH2SiMe3), 34.2
(NdCCH2SiMe3), 20.3 (C6H3Me2), 19.9 (C6H3Me2), 3.3 (ZrCH2SiMe3),
2.6 [Si(SiMe3)3], 0.15 (NdCCH2SiMe3).
tons. A similar ligand exchange in (2,6-But C6H3O)Zr[η2-
2
C(CH2Ph)dNAr]2(CH2Ph) has been reported by Roth-
1
well and co-workers.11 The AB pattern in the H NMR
spectra of 7 remains unchanged between 206 and 330
K. This suggests a high degree of steric congestion in 7
compared to that in 8, restricting the ligand-exchange
between the two η2-iminoacyl ligands in 7. The CH2-
(18) For the evaluation of exchange rate constants from the AB case
in NMR spectra, see: Sandstrom, J . Dynamic NMR Spectroscopy;
Academic Press: New York, 1982; p 84.

Preferential Isocyanide Insertion into Zr-Silyl Bonds
Organometallics, Vol. 17, No. 22, 1998 4857
Ch a r t 1
F igu r e 2. ORTEP drawing of (Me3CCH2)3ZrSi(SiMe3)3 (1),
showing 50% thermal ellipsoids.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 1
CMe3 groups in 7 are more sterically demanding than
the CH2SiMe3 groups in 8 [the C-Si bond (ca.1.85 Å) is
longer than the C-C bond (ca. 1.54 Å)] and thus
contribute significantly to the steric congestion in 7.19
Distances
Zr-Si(1)
Zr-C(5)
Zr′-Si(1′)
Zr′-C(5′)
Zr′′-Si(1′′)
Zr′′-C(5′′)
2.74(2)
2.11(3)
2.72(2)
2.09(3)
2.76(2)
2.14(3)
Si(1)-Si(2)
Si(1′)-Si(2′)
Si(1′′)-Si(2′′)
C(4)-C(5)
C(4′)-C(5′)
C(4")-C(5")
2.345(12)
2.347(13)
2.320(9)
1.55(3)
1.55(4)
1.53(4)
Molecu la r Str u ctu r e of (Me3CCH2)3Zr Si(SiMe3)3
(1). The structure of 1, the precursor to 3 and 7, was
determined in part to compare it with those of 3 and 7.
An ORTEP drawing of 1 is shown in Figure 2. There
are three unique but chemically equivalent molecules
in a unit cell, and only one representative molecule is
shown. Selected bond distances and angles are listed
in Table 3. As expected, the structure of 1 is analogous
to that of its titanium analogue (Me3CCH2)3TiSi-
(SiMe3)3.7b The crystal structure reveals a 3-fold axis of
symmetry along the M-Si bond. The alkyl groups on
the Zr metal are staggered with respect to the trimeth-
ylsilyl groups on the central silicon atom. The three
alkyl and the silyl ligands are arranged in a pseudo-
tetrahedral geometry around the metal center, giving
a formally 8-electron species. The angles (C-Zr-C)
between the alkyl ligands are 113.0(7)° (mean). The
angles (C-Zr-Si) between the alkyl and silyl ligands
are 105.6(8)°. These angles are close to those found in
(Me3CCH2)3TiSi(SiMe3)3 and (Me3SiCH2)3TiSi(SiMe3)3.7b
The C-Zr-C angles in 1 are wider than the C-Zr-Si
angles and may indicate that the steric interaction
among the alkyl ligands is greater than that between
alkyl and silyl ligands. The greater Zr-Si bond and Si-
Si distances apparently make the central silicon atom
in the Si(SiMe3)3 group relatively uncrowed; the bonding
about the central silicon atom is not greatly distorted
from tetrahedral [the mean Zr-Si-Si angle: 110.9(5)°].
In contrast, the shorter Zr-C bonds and bulky Me3C
groups on three Me3CCH2 ligands contribute to the
steric strain among these ligands, and perhaps force the
widening of the Zr-C-C angles [av 137(2)°]. No R-
agostic interactions are observed in either the solid-state
structure or solution NMR of 1, which often occurs in
electron deficient early-transition-metal alkyl com-
plexes.20
Angles
C(5)-Zr-C(5A)
Si(1)-Zr-C(5)
104.5(8)
105.9(10) C(5′)-Zr′-C(5′A)
113.9(6)
Si(1′)-Zr′-C(5′)
112.8(8)
112.3(7)
108.2(5)
107.5(6)
Si(1′′)-Zr′′-C(5′′) 106.4(7)
C(5′′)-Zr′′-C(5′′A)
Si(2)-Si(1)-Si(2A)
Si(2′)-Si(1′)-Si(2′A)
Si(2′′)-Si(1′′)-Si(2′′A) 108.2(4)
Zr′-C(5′)-C(4′) 136(3)
Zr-Si(1)-Si(2)
110.7(5)
111.3(5)
Zr′-Si(1′)-Si(2′)
Zr′′-Si(1′′)-Si(2′′) 110.7(4)
Zr-C(5)-C(4)
138(2)
Zr′′-C(5′′)-C(4′′) 138(2)
The mean Zr-C bond distance of 2.11(2) Å in 1 is
slightly shorter than those found in some more electron-
rich Zr(IV) neopentyl complexes, such as Cp2Zr(CH2-
CMe3)2 [2.294(8) Å],19 [(Me3CCH2)3ZrCl]n [2.200(4) Å],21
(F6-acen)Zr(CH2CMe3)2 [2.283(4) and 2.323(5) Å], and
[(F6-acen)Zr(CH2CMe3)(NMe2Ph)][B(C6F5)4] [2.175(5) Å].22
The mean Zr-Si bond distance of 2.74(2) Å is close to
those in (ButO)3ZrSi(SiMe3)3 [2.753(4) Å],3f Cp2Zr[Si-
(SnMe3)3]Cl [2.772(4) Å],1b and Cp2Zr(SiPh3)(H)(PMe3)
[2.721(2) Å]23 but is shorter than those in (Me3SiO)2Zr-
(SiPh2But)Cl(THF)2 [2.848(3) Å],24 Cp2Zr(SiPh3)Cl
[2.813(2) Å],25 and Cp2Zr(SiMe3)(S2CNEt2) (2.815 Å).26
Molecu la r Str u ctu r e of (Me3CCH2)3Zr {η2-C[Si-
(SiMe3)3]dNAr } (3). The insertion of the first ArNC
into Zr-Si bond in (Me3CCH2)3ZrSi(SiMe3)3 (1) was
confirmed by the X-ray crystal structure of 3. An
(20) (a) Brookhart, M.; Green, M. L. H.; Wong, L. Prog. Inorg. Chem.
1988, 36, 1. (b) Crabtree, R. H.; Hamilton, D. G. Adv. Organomet.
Chem. 1988, 28, 299. (c) Grubbs, R. H.; Coates, G. W. Acc. Chem. Res.
1996, 29, 85.
(21) (a) Hoyt, L. K.; Pollitte, J . L.; Xue, Z. Inorg. Chem. 1994, 33,
2497. (b) McAlexander, L. H.; Li, L.; Yang, Y.; Pollitte, J . L.; Xue, Z.
Inorg. Chem. 1998, 37, 1423.
(22) Tjaden, E. B.; Swenson, D. C.; J ordan, R. F.; Petersen, J . L.
Organometallics 1995, 14, 371.
(23) Kreutzer, K. A.; Fisher, R. A.; Davis, W. M.; Spaltenstein, E.;
Buchwald, S. L. Organometallics 1991, 10, 4031.
(24) Wu, Z., Diminnie, J . B.; Xue, Z. Organometallics 1998, 17, 2917.
(25) Muir, K. J . Chem. Soc. A 1971, 2663.
(19) J effery, J .; Lappert, M. F.; Luong-Thi, N. T.; Webb, M. J . Chem.
Soc., Dalton Trans. 1981, 1593.
(26) Tilley, T. D. Organometallics 1985, 4, 1452.

4858 Organometallics, Vol. 17, No. 22, 1998
Wu et al.
angles of 90 and 92° (see Figure 3). The methylene
protons of the three neopentyl ligands were located from
a difference map and refined isotropically. The Zr-H4a
and Zr-H4b bond distances are 2.40(5) and 2.42(5) Å,
respectively, which are comparable to those in the
related early-transition-metal alkyl complexes, such as
CpNb(dN-2,6-C6H3-Pri )(CH2CMe3)2 (Pri ) Me2CH)
2
[2.321(29) and 2.405(33) Å],27 (dmpe)Zr(CH2SiMe3)4
(2.48 Å),28 Cp*Ti(CH2Ph)3 (2.32 and 2.37 Å),29 Tp*NbCl-
(CH2SiMe3)(PhCtCMe) [2.29(6) Å],30 and Cp2Th(CH2-
CMe3)2 [2.597(9) and 2.648(9) Å],31 when the difference
in metal ion radii is taken into account. The Zr-C(4)
distance of 2.213(5) Å is slightly shorter than the other
two Zr-C(alkyl) bonds in 3 [2.237(5) and 2.256(5) Å]
and is very close to that in (dmpe)Zr(CH2SiMe3)4
[2.215(9) Å].26 The infrared spectrum of 3 showed a
medium-strong band at 2790 cm-1 and a weak absorp-
tion at 2700 cm-1, which can be attributed to agostic
C-H stretches in 3.20,32,33
No evidence of an agostic interaction between the
metal center and R-protons of neopentyl ligands is seen
in the solution NMR of 3. From the solid-state structure,
one would expect the NMR spectra of 3 to show two sets
of tert-butyl signals from the CH2CMe3 ligands in a 2:1
ratio. However, only one set of neopentyl resonances
were observed in the variable-temperature NMR spectra
of 3 (193-300 K), indicating either a free rotation of
the iminosilaacyl ligand or a rapid exchange of the three
CH2CMe3 ligands in 3 in solution.
F igu r e 3. ORTEP drawing of (Me3CCH2)3Zr{η2-C[Si-
(SiMe3)3]dNAr} (3), showing 50% thermal ellipsoids.
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 3
Distances
Zr-C(1)
Zr-C(2)
Zr-C(3)
Zr-C(4)
Zr-N(1)
Zr-H(4A)
2.255(4)
2.237(5)
2.256(5)
2.213(5)
2.175(3)
2.40(5)
C(1)-N(1)
C(1)-Si(1)
Si(1)-Si(2)
Si(1)-Si(3)
Si(1)-Si(4)
Zr-H(4B)
1.293(5)
1.897(4)
2.365(2)
2.361(2)
2.368(2)
2.42(5)
The Zr-C(alkyl) bond distances range from 2.213(5)
to 2.257(5) Å and are slightly longer than that in 1
[2.11(3) Å]. The Zr-C(1) [2.255(4) Å] and Zr-N(1)
[2.175(3) Å] bond distances are slightly shorter than
those in Cp2Zr[η2-C(NPh)SiPhBut]Cl (2.28 and 2.19 Å)9d
and CpCp*Zr[η2-C(NAr)Si(SiMe3)3]Cl [2.309(10) and
2.249(8) Å].3e The angles within the ZrCN unit are
similar to those in other Zr iminoacyl and iminosilaacyl
complexes.3e,9d,11,13,15
Angles
C(1)-Zr-C(2)
C(1)-Zr-C(3)
C(1)-Zr-C(4)
C(2)-Zr-C(3)
C(2)-Zr-C(4)
C(3)-Zr-C(4)
C(2)-Zr-N(1)
C(4)-Zr-N(1)
Zr-C(4)-H(4A)
108.5(2)
93.7(2)
128.0(2)
114.0(2)
108.3(2)
103.3(2)
114.1(2)
96.9(2)
90(3)
Zr-C(1)-Si(1)
Zr-N(1)-C(26)
Zr-C(2)-C(5)
Zr-C(3)-C(6)
Zr-C(4)-C(7)
Zr-C(1)-N(1)
C(1)-Zr-N(1)
C(3)-Zr-N(1)
Zr-C(4)-H(4B)
156.5(2)
154.0(3)
134.7(3)
130.1(3)
145.9(3)
69.7(2)
33.87(13)
117.6(2)
92(3)
Molecu la r Str u ctu r e of (Me3CCH2)Zr [η2-C(CH2-
CMe3)dNAr ]2{η2-C[Si(SiMe3)3]dNAr } (7). An ORTEP
drawing of 7 is shown in Figure 4. Selected bond
distances and angles are given in Table 5. The zirconium
atom is bonded to one η2-iminosilaacyl, one neopentyl,
and two η2-iminoacyl ligands to form a seven-coordinate
metal complex. However, an analysis of the calculated
centroids of the CdN bonds shows that the coordination
sphere about the zirconium center is pseudo-tetrahedral.
This coordination sphere, as shown in the simplified
view in Figure 5, is different from that observed in a
ORTEP drawing of complex 3 is shown in Figure 3.
Selected bond distances and angles are listed in Table
4. The zirconium atom is coordinated by one η2-imino-
silaacyl and three CH2CMe3 ligands, giving a formally
10-electron species. The geometry around the metal
atom can be best described as a pseudotetrahedron with
an η2-NdC unit occupying a single coordination site. The
ZrCN unit and one CH2CMe3 ligand closely lie in one
plane with an alkyl ligand on each side of the plane.
One of the three alkyl ligands [C(4)H2CMe3] points
toward the iminosilaacyl ligand while the other two
point away from it. In comparison, in the structure of
the precursor 1, all three CH2CMe3 ligands point away
from the bulky Si(SiMe3)3 ligand. The complex 3 is
perhaps sterically less crowded than 1, allowing the
neopentyl ligands to adopt a different orientation.
It is interesting to note that the R-C angles in the Zr-
alkyl ligands in 3 are 130.2(3), 134.5(3), and 145.9(3)°.
The first two angles are slightly smaller than that in 1
[av 137(2)°]; the other one significantly differs from the
first two and is about 8° larger than that in 1. The
reason for this large Zr-C-C angle may be due to
agostic interactions between the metal center and the
R-protons of the neopentyl methylene. Two hydrogen
atoms on the C(4)H2CMe3 ligand lie in close contact (av
2.41 Å) with the metal center giving rise to Zr-C-HR
tris(η2-iminoacyl) complex (2,6-But C6H3O)Zr[η2-C(CH2-
2
Ph)dNAr]3,11 where two iminoacyl groups are coplanar.
Larger steric repulsion is expected in 7, which contains
bulky Si(SiMe3)3 and neopentyl groups. The CdN
(27) Poole, A. D.; Williams, D. N.; Kenwright, A. M.; Gibson, V. C.;
Clegg, W.; Hockless, D. C. R.; O’Neil, P. A. Organometallics 1993, 12,
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(28) Cayias, J . Z.; Babaian, E. A.; Hrncir, D. C.; Bott, S. G.; Atwood,
J . L. J . Chem. Soc., Dalton Trans. 1986, 2743.
(29) Mena, M.; Pellinghelli, M. A.; Royo, P.; Serrano, R.; Tiripicchio,
A. J . Chem. Soc., Chem. Commun. 1986, 1118.
(30) Etienne, M.; Mathieu, R.; Donnadieu, B. J . Am. Chem. Soc.
1997, 119, 3218.
(31) Bruno, J . W.; Smith, G. M.; Marks, W. J .; Fair, C. K.; Schultz,
A. J .; Williams, J . M. J . Am. Chem. Soc. 1986, 108, 40.
(32) Morse, P. M.; Spencer, M. D.; Wilson, S. R.; Girolami, G. S.
Organometallics 1994, 13, 1646.
(33) McGrady, G. S.; Downs, A. J .; Hamblin, J . M. Organometallics
1995, 14, 3738.

Preferential Isocyanide Insertion into Zr-Silyl Bonds
Organometallics, Vol. 17, No. 22, 1998 4859
F igu r e 4. ORTEP drawing of (Me3CCH2)Zr(η2-C(CH2-
CMe3)dNAr)2{η2-C[Si(SiMe3)3]dNAr} (7), showing 35%
thermal ellipsoids.
F igu r e 5. Simplified ORTEP drawing of the structure of
(Me3CCH2)Zr(η2-C(CH2CMe3)dNAr)2{η2-C[Si(SiMe3)3]d
NAr} (7).
Ta ble 5. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 7
Sch em e 3. P r op osed Mech a n ism of th e F ir st
Ar NC In ser tion in to th e Zr -Si Bon d s in 1 a n d 2
Distances
Zr-C(1)
2.319(5)
2.301(5)
2.265(5)
2.301(5)
2.200(4)
2.270(4)
2.242(4)
1.433(6)
1.454(6)
1.536(7)
C(1)-N(1)
C(2)-N(2)
C(3)-N(3)
C(1)-Si(1)
Si(1)-Si(2)
Si(1)-Si(3)
Si(1)-Si(4)
N(3)-C(27)
C(3)-C(6)
C(4)-C(7)
1.283(6)
1.273(6)
1.283(6)
1.921(5)
2.380(2)
2.369(2)
2.351(2)
1.442(6)
1.506(7)
1.527(7)
Zr-C(2)
Zr-C(3)
Zr-C(4)
Zr-N(1)
Zr-N(2)
Zr-N(3)
N(1)-C(35)
N(2)-C(19)
C(2)-C(5)
Angles
Zr-C(1)-N(1)
Zr-C(1)-Si(1)
Zr-N(1)-C(1)
Zr-N(1)-C(35)
Zr-C(2)-N(2)
Zr-C(2)-C(5)
Zr-N(2)-C(2)
Zr-N(2)-C(19)
Zr-C(3)-N(3)
Zr-C(3)-C(6)
Zr-N(3)-C(3)
Zr-N(3)-C(27)
Zr-C(4)-C(7)
C(1)-Zr-C(3)
C(2)-Zr-C(3)
C(3)-Zr-C(4)
C(2)-Zr-N(2)
68.5(3)
163.1(2)
78.7(3)
151.0(3)
72.5(3)
161.4(4)
75.2(3)
159.1(3)
72.4(3)
N(1)-Zr-N(2)
N(1)-Zr-N(3)
N(1)-Zr-C(2)
N(1)-Zr-C(3)
N(1)-Zr-C(4)
N(2)-Zr-N(3)
N(2)-Zr-C(1)
N(2)-Zr-C(3)
N(2)-Zr-C(4)
N(3)-Zr-C(1)
N(3)-Zr-C(2)
N(3)-Zr-C(4)
C(1)-Zr-C(2)
C(1)-Zr-C(4)
C(2)-Zr-C(4)
C(1)-Zr-N(1)
C(3)-Zr-N(3)
98.58(14)
152.34(14)
90.5(2)
124.2(2)
98.1(2)
107.93(14)
130.1(2)
120.3(2)
93.3(2)
121.9(2)
107.7(2)
88.3(2)
η5-C5Me5) and found that such insertion occurred ex-
clusively to the Zr-Me bond to form an iminoacyl
complex. In contrast, the first insertion of ArNC into
Cp-free alkyl silyl complexes (Me3ECH2)3ZrSi(SiMe3)3
[E ) C (1), Si (2)] occurs to the M-Si bonds to give silyl
insertion complexes 3 and 4. To our knowledge, the
mono-insertion complexes 3 and 4 represent the first
example of isocyanide insertion into a M-Si bond in the
presence of competing M-C bonds.
165.1(4)
74.5(3)
159.7(3)
137.2(4)
103.7(2)
101.7(2)
116.3(2)
32.3(2)
Tilley and co-workers also observed that CO prefer-
entially inserts into the Zr-C bond in Cp2Zr(Me)Si-
121.7(2)
86.7(2)
125.5(2)
32.8(2)
3b
(SiMe3)3 and, in contrast, into the Zr-Si bond in
CpCp*Zr(Me)Si(SiMe3)3.3e In the current studies, inser-
tion into the Zr-Si bonds is exclusive in the reactions
of 1 and 2 with first ArNC. It is not fully understood
what led to such exclusive insertion. The Zr-Si bonds
are usually weaker than Zr-C bonds. The bond disrup-
tion enthalpy (BDE) for the Zr-Si(SiMe3)3 in Cp2Zr[Si-
(SiMe3)3]Cl (BDE ) 56 kcal/mol)34 is smaller than those
of the Zr-alkyl bonds in Zr(CH2CMe3)4 (BDE ) 60 kcal/
mol) and Zr(CH2SiMe3)4 (BDE ) 74 kcal/mol).35 In
addition, the Si(SiMe3)3 ligand is bulkier than CH2CMe3
and CH2SiMe3 ligands; insertion into Zr-Si bonds in 1
and 2 will likely relieve more steric strain than insertion
into Zr-C bonds. The structures of 1 and 3 (Figures 2
and 3) reveal that the average C-Zr-C angle in 1 (113°)
is larger than that in the insertion product 3 (108.5°),
indicating that the steric repulsion between the three
33.1(2)
distances and the internal angles within the three-
membered ZrCN rings are similar to those found in 3
and other zirconium η2-iminoacyl and η2-iminosilaacyl
complexes.3e,9d,11,13,15 The Zr-C(η2-iminosilaacyl) bond
[2.319(5) Å] is slightly longer than the Zr-C(η2-imino-
acyl) bonds [2.301(5) and 2.265(5) Å] (Table 5), perhaps
due to the steric effect of the bulky η2-iminosilaacyl
ligand. In addition, the Zr-C(η2-iminosilaacyl) [2.319(5)
Å], Si-C(dN) [1.921(5) Å], and Zr-C(4) [2.301(5) Å]
distances are longer than the corresponding values
found in the mono-insertion complex 3 [2.255(4), 1.898(4),
and 2.206(5)-2.255(5) Å, respectively]. These are con-
sistent with more steric congestion in the tri-insertion
complex 7.
P r efer en tia l Isocya n id e In ser tion in to Silyl-Zr
Bon d s. Tilley and co-workers3e have investigated the
insertion of ArNC into CpCp*Zr[Si(SiMe3)3]Me (Cp* )
(34) King, W. A.; Marks, T. J . Inorg. Chim. Acta 1995, 229, 343.
(35) Lappert, M. F.; Patil, D. S.; Pedley, J . B. J . Chem. Soc., Chem.
Commun. 1975, 830.

4860 Organometallics, Vol. 17, No. 22, 1998
Wu et al.
CH2CMe3 ligands in 3 decreases compared to that in 1.
These analyses indicate that the silyl migratory inser-
tion in 1 and 2 is favorable. In addition, the results
suggest that the first isocyanide adds between the alkyl
and silyl ligands (cis to the silyl ligand), as shown in
the proposed mechanism in Scheme 3. This addition is
followed by a migration of the bulky Si(SiMe3)3 group
onto the isocyanide carbon. Alternatively, the first ArNC
may add trans to the silyl ligand (among the three
neopentyl ligands). However, such addition is expected
to, in contrast to the experimental observations, be
followed by a neopentyl migration and the formation of
a Zr-C insertion product. Only up to three isocyanide
insertions occur in 1 and 2 to give 7 and 8. This is
perhaps due to steric crowding around the metal atom
in 7 and 8 hindering further ArNC coordination.
first step in the multi-insertion reactions. Steric conges-
tion may limit the number of isocyanide insertions, as
observed in the inertness of the tri-insertion products
7 and 8 toward further ArNC insertion.
Ack n ow led gm en t is made to the National Science
Foundation (Grant CHE-9457368), the DuPont Young
Professor Award, the Camille Dreyfus Teacher-Scholar
Award, the donors of the Petroleum Research Fund,
administered by the American Chemical Society, and
Exxon Education Foundation for support of this re-
search. We thank Professor Arnold L. Rheingold and a
referee for helpful suggestions.
Su p p or tin g In for m a tion Ava ila ble: A complete list of
crystallographic data for 1, 3, and 7 (24 pages). See any current
masthead page for ordering information.
In summary, the isocyanide insertion into Zr-silyl
bonds is preferred in the reactions of Cp-free (Me3ECH2)3-
ZrSi(SiMe3)3 [E ) C (1), Si (2)] with ArNC, and it is the
OM980485O