Disilyl complexes of zirconium, hafnium, and tantalum. Their synthesis, characterization, and exchanges with silyl anions

Article abstract of DOI:10.1021/om050302f

Cyclopentadienyl-free disilyl amide complexes [(Me₂N) ₃M(SiBu^tPh₂)₂]^- (M = Zr, 1; Hf, 2 as [Li(THF)₄]⁺ salts), K(18-crown-6) _3/2{(Me₂N)₃M[(Me₃Si) ₂Si-(CH₂)₂-Si(SiMe₃)₂]} (M = Zr, 3; Hf, 4), (Me₂N)₃Ta[Si(SiMe₃) ₃]₂ (5), (Me₂N)₃Ta(SiBu ^tPh₂)₂ (6), and (Me₂N) ₃Ta(SiBu^tPh₂)[Si(SiMe₃) ₃] (7) have been prepared. The structures of 1-4 have been determined by X-ray single-crystal diffraction. The two -Si(SiMe ₃)₃^- ligands in (Me₂N) ₃Ta[Si(SiMe₃)₃]₂ (5) were replaced sequentially by the -SiBu^tPh₂^- anions to give (Me₂N)₃Ta(SiBu^tPh₂)[Si(SiMe ₃)₃] (7) and (Me₂N)₃Ta(SiBu ^tPh₂)₂ (6). The silyl ligand in (Me ₂N)₃Zr-Si(SiMe₃)₃ was found to undergo a reversible exchange with SiBu^tPh₂^-, probably through a disilyl intermediate, to reach the following equilibrium: (Me₂N)₃ZrSi(SiMe₃)₃ + SiBu ^tPh₂^- (Me₂N)₃ZrSiBu ^tPh₂ + Si(SiMe₃)₃-with ΔH° = 4.6(0.5) kcal/mol and ΔS° = -7(2) eu. A similar exchange involving [(Me₂N)₃M(SiBu^tPh ₂)₂]^- (M = Zr, 1; Hf, 2) was observed: (Me ₂N)₃ZrSiBu^tPh₂ + SiBu ^tPh₂^- ? 1 with the estimated free energy of activation ΔG? = 14.1(0.5) kcal/mol. (Me ₂N)₃Ta(SiBu^tPh₂)₂ (6) and (Me₂N)₃Ta(SiBu^tPh₂)[Si(SiMe ₃)₃] (7) are thermally unstable. Kinetic studies give the activation parameters of the decomposition of 7: ΔH? = 22.8(1.3) kcal/mol and ΔS? = -3(5) eu.

Full text of DOI:10.1021/om050302f

4190
Organometallics 2005, 24, 4190-4197
Disilyl Complexes of Zirconium, Hafnium, and Tantalum.
Their Synthesis, Characterization, and Exchanges with
Silyl Anions
He Qiu, Hu Cai, Jaime B. Woods, Zhongzhi Wu, Tianniu Chen,
Xianghua Yu, and Zi-Ling Xue*
Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37996
Received April 18, 2005
Cyclopentadienyl-free disilyl amide complexes [(Me2N)3M(SiButPh2)2]- (M ) Zr, 1; Hf, 2
as [Li(THF)4]+ salts), K(18-crown-6)3/2{(Me2N)3M[(Me3Si)2Si-(CH2)2-Si(SiMe3)2]} (M ) Zr, 3;
Hf, 4), (Me2N)3Ta[Si(SiMe3)3]2 (5), (Me2N)3Ta(SiButPh2)2 (6), and (Me2N)3Ta(SiButPh2)[Si-
(SiMe3)3] (7) have been prepared. The structures of 1-4 have been determined by X-ray
-
single-crystal diffraction. The two -Si(SiMe3)3 ligands in (Me2N)3Ta[Si(SiMe3)3]2 (5) were
replaced sequentially by the -SiButPh2- anions to give (Me2N)3Ta(SiButPh2)[Si(SiMe3)3] (7)
and (Me2N)3Ta(SiButPh2)2 (6). The silyl ligand in (Me2N)3Zr-Si(SiMe3)3 was found to undergo
-
a reversible exchange with SiButPh2 , probably through a disilyl intermediate, to reach the
-
following equilibrium: (Me2N)3ZrSi(SiMe3)3 + SiButPh2- h (Me2N)3ZrSiButPh2 + Si(SiMe3)3
with ∆H° ) 4.6(0.5) kcal/mol and ∆S° ) -7(2) eu. A similar exchange involving
-
[(Me2N)3M(SiButPh2)2]- (M ) Zr, 1; Hf, 2) was observed: (Me2N)3ZrSiButPh2 + SiButPh2
h 1 with the estimated free energy of activation ∆Gq ) 14.1(0.5) kcal/mol. (Me2N)3Ta(Si-
ButPh2)2 (6) and (Me2N)3Ta(SiButPh2)[Si(SiMe3)3] (7) are thermally unstable. Kinetic studies
give the activation parameters of the decomposition of 7: ∆Hq ) 22.8(1.3) kcal/mol and ∆Sq
) -3(5) eu.
Silyl derivatives of transition metals are of intense
chelating disilyl ligand have been prepared: [(Me2N)3-
M(SiButPh2)2]- (M ) Zr, 1;11 Hf, 2 as [Li(THF)4]+ salts),
K(18-crown-6)3/2{(Me2N)3M[(Me3Si)2Si-(CH2)2-Si-
(SiMe3)2]} (M ) Zr, 3; Hf, 4), (Me2N)3Ta[Si(SiMe3)3]2 (5),
(Me2N)3Ta(SiButPh2)2 (6), and (Me2N)3Ta(SiButPh2)[Si-
(SiMe3)3] (7). The two silyl ligands in (Me2N)3Ta[Si-
(SiMe3)3]2 (5) were substituted sequentially by the
interest for their unique structures, reactivities, and
catalytic applications.1-3 Many early transition metal
silyl complexes contain cyclopentadienyl (Cp) ligands or
analogous anionic π-ligands,1 and there are relatively
fewer Cp-free d0 silyl complexes, especially those with
two silyl ligands.2d,4-9 In comparison, multi-alkyl com-
plexes of these transition metals are well known includ-
ing the peralkyl complexes M(CH2R)n (n ) 4; M ) Ti,
Zr, Hf; n ) 5, M ) Ta; n ) 6, M ) W).10 We recently
studied Cp-free d0 transition metal silyl complexes.11
Novel d0 bis(silyl) complexes containing two silyl or one
SiButPh2 anions to give (Me2N)3Ta(SiButPh2)[Si-
-
(SiMe3)3] (7) and then (Me2N)3Ta(SiButPh2)2 (6). In
(4) (a) Xue, Z.; Li, L.; Hoyt, L. K.; Diminnie, J. B.; Pollitte, J. L. J.
Am. Chem. Soc. 1994, 116, 2169. (b) McAlexander, L. H.; Hung, M.;
Li, L.; Diminnie, J. B.; Xue, Z.; Yap, G. P. A.; Rheingold, A. L.
Organometallics 1996, 15, 5231. (c) Diminnie, J. B.; Hall, H. D.; Xue,
Z. Chem. Commun. 1996, 2383. (d) Li, L.; Diminnie, J. B.; Liu, X.;
Pollitte, J. L.; Xue, Z. Organometallics 1996, 15, 3520. (e) Diminnie,
J. B.; Xue, Z. J. Am. Chem. Soc. 1997, 119, 12657. (f) Wu, Z.; Diminnie,
J. B.; Xue, Z. Organometallics 1998, 17, 2917. (g) Wu, Z.; McAlexander,
L. H.; Diminnie, J. B.; Xue, Z. Organometallics 1998, 17, 4853. (h)
Chen, T.; Wu, Z.; Li, L.; Sorasaenee, K. R.; Diminnie, J. B.; Pan, H.;
Guzei, I. A.; Rheingold, A. L.; Xue, Z. J. Am. Chem. Soc. 1998, 120,
13519. (i) Wu, Z.; Cai, H.; Yu, X.; Blanton, J. R.; Diminnie, J. B.; Pan,
H.-J.; Xue, Z. Organometallics 2002, 21, 3973. (j) Fischer, R.; Zirngast,
M.; Folck, M.; Baumgartner, J.; Marschner, C. J. Am. Chem. Soc. 2005,
127, 70.
(5) Casty, G. L.; Tilley, T. D.; Yap, G. P. A.; Rheingold, A. L.
Organometallics 1997, 16, 4746.
(6) An early reported tetrasilyl complex Ti(SiPh3)4 was found later
to be Ti(OSiPh3)4. (a) Hengge, E.; Zimmermann, H. Angew. Chem., Int.
Ed. Engl. 1968, 7, 142. (b) Kingston, B. M.; Lappert, M. F. J. Chem.
Soc., Dalton Trans. 1972, 69.
(1) (a) Tilley, T. D. In The Silicon-Heteroatom Bond; Patai, S.,
Rappoport, Z.; Eds.; Wiley: New York, 1991; Chapters 9 and 10. (b)
Eisen, M. S. In The Chemistry of Organic Silicon Compounds, Vol. 2;
Rappoport, Z.; Apeloig, Y.; Eds.; Wiley: New York, 1998; Part 3, p 2037.
(c) Corey, J. Y. In Advances in Silicon Chemistry; Larson, G., Ed.; JAI
Press: Greenwich, CT, 1991; Vol. 1, p 327. (d) Gauvin, F.; Harrod, J.
F.; Woo, H. G. Adv. Organomet. Chem. 1998, 42, 363. (e) Sharma, H.
K.; Pannell, K. H. Chem. Rev. 1995, 95, 1351. (f) Yu, X.-H.; Morton, L.
A.; Xue, Z.-L. Organometallics 2004, 23, 2210.
(2) (a) Campion, B. K.; Falk, J.; Tilley, T. D. J. Am. Chem. Soc. 1987,
109, 2049. (b) Arnold, J.; Engeler, M. P.; Elsner, F. H.; Heyn, R. H.;
Tilley, T. D. Organometallics 1989, 8, 2284. (c) Elsner, F. H.; Tilley,
T. D.; Rheingold, A. L.; Geib, S. J. Organomet. Chem. 1988, 358, 169.
(d) Heyn, R. H.; Tilley, T. D. Inorg. Chem. 1989, 28, 1768. (e) Campion,
B. K.; Heyn, R. H.; Tilley, T. D. J. Am. Chem. Soc. 1990, 112, 2011. (f)
Radu, N. S.; Engeler, M. P.; Gerlach, C. P.; Tilley, T. D.; Rheingold, A.
L. J. Am. Chem. Soc. 1995, 117, 3621.
(3) (a) Imori, T.; Tilley, T. D. Polyhedron 1994, 13, 2231. (b)
Dioumaev, V. K.; Harrod, J. F. Organometallics 1994, 13, 1548; 1997,
16, 2798. (c) Procopio, L. J.; Carroll, P. J.; Berry, D. H. Polyhedron
1995, 14, 45. (d) Huhmann, J. L.; Corey, J. Y.; Rath, N. P. J.
Organomet. Chem. 1997, 533, 61. (e) Hengge, E.; Gspaltl, P.; Pinter,
E. J. Organomet. Chem. 1996, 521, 145. (f) Banovetz, J. P.; Suzuki,
H.; Waymouth, R. M. Organometallics 1993, 12, 4700. (g) Verdaguer,
X.; Lange, U. E. W.; Reding, M. T.; Buchwald, S. L. J. Am. Chem. Soc.
1996, 118, 6784. (h) Fu, P.-F.; Marks, T. J. J. Am. Chem. Soc. 1995,
117, 10747.
(7) Ti(SiMe3)4 was reported to exist at -78 °C, but no characteriza-
tion was offered for this complex. Razuvaev, G. A.; Latyaeva, V. N.;
Vyshinskaya, L. I.; Malysheva, A. V.; Vasileva, G. A. Dokl. Akad. Nauk.
SSSR 1977, 237, 605.
(8) Several zerovalent Zr-polytin complexes have been reported. (a)
[K(15-crown-5)2]2[Zr(CO)5(SnMe3)2]: Ellis, J. E.; Yuen, P.; Jang, M. J.
Organomet. Chem. 1996, 507, 283. (b) [n-Pr4N]2[(Ph3Sn)4M(CO)4] (M
) Zr, Hf): Ellis, J. E.; Chi, K. M.; DiMaio, A. J.; Frerichs, S. R.; Stenzel,
J. R.; Rheingold, A. L.; Haggerty, B. S. Angew. Chem., Int. Ed. Engl.
1991, 30, 194.
10.1021/om050302f CCC: $30.25 © 2005 American Chemical Society
Publication on Web 07/16/2005

Disilyl Complexes of Zr, Hf, and Ta
Organometallics, Vol. 24, No. 17, 2005 4191
experiments were conducted at a given temperature. The
maximum random uncertainty in the equilibrium constants
was combined with the estimated systematic uncertainty, ca.
5%. The estimated uncertainty in the temperature measure-
ments for an NMR probe was 1 K. The enthalpy (∆H°) and
entropy (∆S°) changes were calculated from an unweighted
nonlinear least-squares procedure contained in the SigmaPlot
Scientific Graph System. The uncertainties in ∆H° and ∆S°
were computed from the following error propagation formulas,
which were derived from -RT ln Keq ) ∆H° - T∆S°:16
addition, the silyl ligand in (Me2N)3Zr-Si(SiMe3)3 un-
dergoes an exchange with SiButPh2-, probably through
a disilyl intermediate. The preparation of these new
disilyl complexes, structures of 1-4, and studies of the
silyl exchanges and thermal decomposition of 6 and 7
are reported here.
(σ∆H°)2 )
2
2
(σT/T)2R2(Tmax Tmin4 + Tmin Tmax4)[ln(Keq(max)/Keq(min))]2/
2
∆T4 + 2R2Tmax Tmin2(σKeq/Keq)2/∆T2
(σ∆S°)2 )
2R2Tmin Tmax2[ln(Keq(max)/Keq(min))]2(σT/T)2/∆T4 +
2
R2(Tmax2 + Tmin2)(σKeq/Keq)2/∆T2
where ∆T ) (Tmax - Tmin); σT ) 1 K; T ) the mean of Tmin and
Experimental Section
17
Tmax
.
Preparation of [Li(THF)4][(Me2N)3Zr(SiButPh2)2] (1 as
a [Li(THF)4]+ salt). To a solution of (Me2N)3ZrSiButPh2-
(THF)0.5 (0.568 g, 1.14 mmol) in 3 mL of toluene was added 1
equiv of Li(THF)3SiButPh2 (0.534 g, 1.14 mmol) in 3 mL of
toluene at room temperature. 1 gradually crystallizes from the
solution as orange crystals (0.75 g, 0.75 mmol, 66% yield). 1H
NMR (benzene-d6, 250.1 MHz, 23 °C): δ 7.87, 7.34, 7.20 (m,
20H, C6H5), 3.41 (m, 16H, OCH2CH2), 2.82 (s, 18H, NMe2), 1.40
(b, 18H, SiCMe3), 1.29 (m, 16H, OCH2CH2). 13C{1H} NMR
(benzene-d6, 62.9 MHz, 23 °C): δ 149.1, 137.2, 127.1, 125.8
(C6H5), 68.2 (OCH2CH2), 40.6 (NMe2), 31.3 (SiCMe3), 25.4
(OCH2CH2), 21.3 (SiCMe3). Anal. Calcd for C54H88N3O4Si2-
LiZr: C, 65.01; H, 8.89. Found: C, 65.18; H, 8.78.
All manipulations were performed under a dry nitrogen
atmosphere with the use of either a drybox or standard
Schlenk techniques. Solvents were purified by distillation from
potassium/benzophenone ketyl and stored under nitrogen prior
to use. TaCl5 (Strem) was sublimed prior to use. (Me2N)3MCl
(M ) Zr; Hf),12a (Me2N)3MSiButPh2(THF)0.5 (M ) Zr; Hf),12b
(Me2N)3TaCl2,13 (Me2N)3Ta(SiButPh2)Cl,4i [K(18-crown-6)]2-
[(Me3Si)2Si(CH2)2Si(SiMe3)2] (8),14 Li(THF)3Si(SiMe3)3,15a and
Li(THF)3SiButPh215b were prepared according to the literature
procedures. Benzene-d6, THF-d8, and toluene-d8 were dried
over activated molecular sieves. 1H and 13C{1H} NMR spectra
were recorded on a Bruker AC-250 or AMX-400 spectrometer
and referenced to solvent (residual protons in the 1H spectra).
29Si{1H} data were obtained by a Bruker AMX-400 spectrom-
eter and referenced to SiMe4. Elemental analyses were per-
formed by Complete Analysis Laboratories Inc., Parsippany,
NJ.
Preparation of [Hf(NMe2)3(SiButPh2)2][Li(THF)4] (2 as
a [Li(THF)4]+ salt). Hf(NMe2)3(SiButPh2)(THF)0.5 (0.293 g,
0.500 mmol) was mixed with Li(THF)3SiButPh2 (0.231 g, 0.499
mmol). To this mixture, 3 mL of toluene was added at room
temperature. Yellow crystals of 2 precipitated immediately
(0.368 g, 0.339 mmol, 68% yield). 1H NMR (benzene-d6, 400.11
MHz, 23 °C): δ 8.04-7.17 (m, 20H, C6H5), 3.42 (m, 16H, OCH2-
CH2), 2.83 (s, 18H, NMe2), 1.53 and 1.29 (two broad peaks,
SiCMe3), 1.29 (m, 16H, OCH2CH2). 13C{1H} NMR (benzene-
d6, 100.62 MHz, 23 °C): δ 137.35, 137.11, 136.06, 127.50,
127.26, 126.86, 124.76 (C6H5), 68.11 (OCH2CH2), 39.33 (NMe2),
31.89 and 30.26 (two broad peaks, SiCMe3), 27.64 (SiCMe3),
25.42 (OCH2CH2). A NOESY spectrum revealed an exchange
of the two [SiButPh2]- groups in 2. Anal. Calcd for C54H88N3O4-
Si2HfLi: C, 59.78; H, 8.18. Found: C, 59.64; H, 7.95.
Preparation of K(18-crown-6)3/2{(Me2N)3Zr[(Me3Si)2Si-
(CH2)2Si(SiMe3)2]} (3). (Me2N)3ZrCl (0.203 g, 0.687 mmol) and
[K(18-crown-6)]2[(Me3Si)2Si(CH2)2Si(SiMe3)2] (8, 0.675 g, 0.686
mmol) were added to a Schlenk flask and then dissolved in
toluene (5 mL). After 45 min of stirring, all volatiles were
removed in vacuo. The resulting mixture of a yellow-orange
solid and oil was washed with hexanes to give bright yellow
powders of 3. The yellow powders were dissolved in toluene.
An oil formed at the bottom of the flask. The flask containing
the oil and the toluene solution was kept in a freezer at -30
°C for two weeks to give crystals of 3‚toluene (0.592 g, 83.3%
yield). In a separate experiment, the yellow powders were
dissolved in benzene, and the solution was filtered. Removal
in vacuo of volatiles in the filtrate, followed by washing of the
For the thermodynamic studies, the equilibrium constants
Keq were obtained from 1H NMR spectra. At least two separate
(9) For metallocene-based disilyl complexes of early transition and
lanthanide metals, see, e.g., Cp2Zr(SiMe3)[Si(SiMe3)3];2a Cp2Ti(SiPh3)2;6b
Cp2Ti(SiPh2)5: Igonin, V. A.; Ovchinnikov, Yu. E.; Dementev, V. V.;
Shklover, V. E.; Timofeeva, T. V.; Frunze, T. M.; Struchkov, Yu. T. J.
Organomet. Chem. 1989, 371, 187. Cp2Ti(SiPh2)4: Holtman, M. S.;
Schram, E. P. J. Organomet. Chem. 1980, 187, 147. Cp2Ta(H)-
(SiMe2H)2: Jiang, Q.; Carroll, P. J.; Berry, D. H. Organometallics 1991,
10, 3648. [Cp2Ln(SiMe3)2][Li(DME)2] (Ln ) Sm, Lu): Schumann, H.;
Nickel, S.; Hahn, E.; Heeg, M. J. Organometallics 1985, 4, 800. Cp2M-
[Si(SiMe3)3]2 (M ) Zr, Hf): Kayser, C.; Frank, D.; Baumgartner, J.;
Marschner, C. J. Organomet. Chem. 2003, 667, 149. Cp2NbH(SiCl3)2:
Dorogov, K. Yu.; Churakov, A. V.; Kuzmina, L. G.; Howard, J. A. K.;
Nikonov, G. I. Eur. J. Inorg. Chem. 2004, 771, and references therein.
(10) (a) Li, L.; Hung, M.; Xue, Z. J. Am. Chem. Soc. 1995, 117, 12746.
(b) Davidson, P. J.; Lappert, M. F.; Pearce, R. Chem. Rev. 1976, 76,
219. (c) Schrock, R. R.; Parshall, G. W. Chem. Rev. 1976, 76, 243. (d)
Wu, Y.-D.; Chan, K. W. K.; Xue, Z. J. Am. Chem. Soc. 1995, 117, 9259.
(e) Wu, Y.-D.; Peng, Z.-H.; Xue, Z. J. Am. Chem. Soc. 1996, 118, 9772.
(11) Wu, Z.; Diminnie, J. B.; Xue, Z. J. Am. Chem. Soc. 1999, 121,
4300.
(12) (a) Wu, Z.; Diminnie, J. B.; Xue, Z. Inorg. Chem. 1998, 37, 2570.
(b)Wu, Z.; Diminnie, J. B.; Xue, Z. Inorg. Chem. 1998, 43, 6366.
(13) Chisholm, M. H.; Huffman, J. C.; Tan, L.-S. Inorg. Chem. 1981,
20, 1859.
(14) Blanton, J. R.; Diminnie, J. B.; Chen, T.; Wiltz, A. M.; Xue, Z.
Organometallics 2001, 20, 5542. For related potassium silyl complexes,
see, e.g.: (a) Marschner, C. Eur. J. Inorg. Chem. 1998, 221. (b) Jenkins,
D. M.; Teng, W.; Englich, U.; Stone, D.; Ruhlandt-Senge, K. Organo-
metallics 2001, 20, 4600. (c) Teng, W.; Ruhlandt-Senge, K. Organo-
metallics 2004, 23, 2694. (d) Fischer, R.; Konopa, T.; Ully, S.;
Baumgartner, J.; Marschner, C. J. Organomet. Chem. 2003, 685, 79.
(15) (a) Gutekunst, G.; Brook, A. G. J. Organomet. Chem. 1982, 225,
1. (b) Campion, B. K.; Heyn, R. H.; Tilley, T. D. Organometallics 1993,
12, 2584.
(16) Levine, I. N. Physical Chemistry, 3rd ed.; McGraw-Hill: New
York, 1988; pp. 307-309.
(17) Taylor, J. R. An Introduction to Error Analysis. The Study of
Uncertainties in Physical Measurements; University Science Books:
Mill Valley, CA, 1982; Chapter 4, p 93.

4192 Organometallics, Vol. 24, No. 17, 2005
Qiu et al.
solid with hexanes, yielded an analytically pure solid of 3. 1H
NMR (250.1 MHz, benzene-d6, 23 °C): δ 3.56 (s, 18H, NMe2),
3.32 (s, 36H, O-CH2), 1.63 (s, 4H, Si-CH2), 0.67 (s, 36H,
SiMe3). 1H NMR (250.1 MHz, toluene-d8, 23 °C): δ 3.50 (s, 18H,
NMe2), 3.35 (s, 36H, O-CH2), 1.56 (s, 4H, Si-CH2), 0.59 (s,
36H, SiMe3). 1H NMR (400.1 MHz, THF-d8, 23 °C): δ 3.63 (s,
36H, O-CH2), 2.99 (s, 18H, NMe2), 1.07 (s, 4H, Si-CH2), 0.51
(s, 36H, SiMe3). 13C{1H} NMR (62.9 MHz, benzene-d6, 23 °C):
δ 70.30 (O-CH2), 44.64 (NMe2), 15.83 (Si-CH2), 4.52 (SiMe3).
13C{1H} NMR (62.9 MHz, toluene-d8, 23 °C): δ 70.71 (O-CH2),
44.60 (NMe2), 15.82 (Si-CH2), 4.43 (SiMe3). 13C{1H} NMR
(100.6 MHz, THF-d8, 23 °C): δ 71.20 (O-CH2), 44.50 (NMe2),
15.61 (Si-CH2), 4.12 (SiMe3). 29Si{1H} NMR (79.5 MHz, THF-
d8, 23 °C): δ -8.01 (SiMe3), -73.11 (Si-SiMe3). Anal. Calcd
for the toluene-free solid of 3, C38H94KN3O9Si6Zr: C, 44.06;
H, 9.15. Found: C, 43.89; H, 9.08.
HSiButPh2, HSi(SiMe3)3, and other unknown species. The
structural assignment for 7 was thus based on its spectroscopic
data. 1H NMR (benzene-d6, 250.1 MHz): δ 7.61-7.15 (m, 10H,
C6H5), 3.14 (s, 18H, NMe2), 1.08 (s, 9H, CMe3), 0.32 (s, 27H,
SiMe3). 13C{1H} NMR (benzene-d6, 62.9 MHz): δ 147.3, 137.2,
127.2, 127.1 (C6H5), 44.8 (NMe2), 30.9 (CMe3), 24.7 (CMe3), 6.8
(SiMe3). 29Si{1H} NMR (benzene-d6, 79.5 MHz, 8 °C): δ 40.9
(SiButPh2), -11.1 (SiSiMe3), -19.8 (SiSiMe3).
Kinetic Study of the Decomposition of (Me2N)3Ta-
(SiButPh2)2 (6) and (Me2N)3Ta(SiButPh2)[Si(SiMe3)3] (7).
Complex 7 was prepared in situ at 23 °C from a 1:1 mixture
of (Me2N)3Ta(SiButPh2)Cl and Li(THF)3Si(SiMe3)3 in a toluene-
d8 solution containing 4,4′-dimethylbiphenyl as an internal
standard. The NMR spectrometer was preset to the temper-
ature between 298 and 323 K, and 1H spectra were recorded.
Complex 6 was also prepared in situ from a mixture of 1 equiv
of (Me2N)3TaCl2 and 2 equiv of Li(THF)3SiButPh2 in a toluene-
d8 solution containing 4,4′-dimethylbiphenyl as an internal
standard. At least two separate experiments were conducted
at a given temperature. The maximum random uncertainty
in the rate constants was combined with the estimated
systematic uncertainty, ca. 5%. The estimated uncertainty in
the temperature measurements for an NMR probe was 1 K.
The activation enthalpy (∆Hq) and entropy (∆Sq) were calcu-
lated from the Eyring equation using an unweighted nonlinear
least-squares procedure contained in the SigmaPlot Scientific
Graph System. The uncertainties in ∆Hq and ∆Sq were
computed from the error propagation formulas derived by
Girolami and co-workers.18
Preparation of K(18-crown-6)3/2{(Me2N)3Hf[(Me3Si)2-
Si(CH2)2Si(SiMe3)2]} (4). To a mixture of (Me2N)3HfCl (0.300
g, 0.867 mmol) and [K(18-crown-6)]2[(Me3Si)2Si(CH2)2Si-
(SiMe3)2] (8, 0.863 g, 0.878 mmol) was added toluene (15 mL).
All volatiles were removed in vacuo after the reaction mixture
was stirred for 45 min. The resulting brown solid was washed
with hexanes (3 × 15 mL) to give a bright yellow solid. This
solid was dissolved in toluene, and the oil-containing solution
was cooled at -35 °C to give yellow crystals of 4‚toluene (0.494
1
g, 0.439 mmol, 51% yield). H NMR (400.0 MHz, THF-d8, 23
°C): δ 3.61 (s, 36H, O-CH2), 3.01 (s, 18H, NMe2), 1.19 (s, 4H,
Si-CH2), 0.59 (s, 36H, SiMe3). 13C{1H} NMR (100.60 MHz,
THF-d8, 23 °C): δ 71.37 (O-CH2), 44.31 (NMe2), 15.73 (Si-
CH2), 4.23 (SiMe3). 29Si{1H} NMR (79.5 MHz, THF-d8, 23 °C):
δ -5.5 (SiMe3), -48.8 (SiSiMe3). The crystals of 4‚toluene were
washed with pentane, and the solid was then dried in vacuo.
1H NMR of the solid showed that there was one toluene
molecule per three molecules of 4 in the solid. This sample
was then submitted for elemental analysis. Anal. Calcd for
The kinetics of the decomposition of 6 was conducted at 303
K.
X-ray Crystal Structure Determination of 1, 2, 3‚tolu-
ene, and 4‚toluene. The crystal structure of 1 was deter-
mined on a Siemens R3m/V diffratometer equipped with a
Nicolet LT-2 low-temperature device. A suitable crystal was
coated with Paratone oil 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 orienta-
tion of at least 25 reflections obtained from a rotation
photograph and an automatic peak search routine. Intensity
data were measured with graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å). Background counts were measured
at the beginning and the 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 structure was solved by direct methods using the
Siemens SHELXTL 93 (version 5.0) proprietary software
package. All hydrogen atoms were placed in calculated posi-
tions and introduced into the refinement as fixed contributors
with an isotropic U value of 0.008 Å2.
The crystal structures of 2, 3‚toluene, and 4‚toluene were
determined on a Bruker AXS Smart 1000 X-ray diffratometer
with Mo KR radiation. Yellow crystals were selected in
Paratone oil and mounted on a hairloop under a N2 stream at
-100 °C. The structures of 2, 3‚toluene, and 4‚toluene were
solved by direct methods. Non-hydrogen atoms in 2 were
anistropically refined. In SHELXTL, the normal L.S. 4 pro-
cedure was performed to refine non-hydrogen atoms isotropi-
cally. The L.S. 4 procedure could not be used in the anisotropic
refinement because of the large size of the cell. The CGLS
procedure is much faster and more suitable in most macro-
molecule refinements.20,21 Hence the CGLS and, subsequently,
the L.S./BLOC procedures were used in the next, anisotropic
refinement. The CGLS procedure does not provide estimated
standard deviations (esd), therefore, in the final refinement,
C
121H290K3N9O27Si18Hf3: C, 41.98; H, 8.44. Found: C, 41.67;
H, 8.32.
Preparation of (Me2N)3Ta[Si(SiMe3)3]2 (5). To a yellow
slurry of (Me2N)3TaCl2 (0.511 g, 1.33 mmol) in pentane (25
mL) was added 2 equiv of Li(THF)3Si(SiMe3)3 (1.25 g, 2.66
mmol) at room temperature. The reaction solution immediately
turned deep purple. After stirring for 3 h at room temperature,
the volatiles were removed in vacuo, yielding a purple solid.
Extraction of the solid with pentane, followed by filtration and
crystallization at -20 °C, afforded deep red crystals of 5 (0.31
g, 0.38 mmol, 29% yield). 1H NMR (toluene-d8, 400.1 MHz, -30
°C): δ 3.22 (s, 18H, NMe2), 0.37 (s, 54H, SiMe3). 13C{1H} NMR
(toluene-d8, 100.6 MHz, -30 °C): δ 44.9 (NMe2), 6.5 (SiMe3).
29Si{1H} NMR (DEPT, toluene-d8, 79.5 MHz, -30 °C): δ 0.95
(SiSiMe3), -6.25 (SiSiMe3). Anal. Calcd for C24H72N3Si8Ta: C,
35.65; H, 8.98. Found: C, 35.42; H, 8.75.
Preparation of (Me2N)3Ta(SiButPh2)2 (6). Li(THF)2Si-
ButPh2 (0.041 g, 0.11 mmol) was added to a mixture of (Me2N)3-
TaCl2 (0.020 g, 0.052 mmol) and 4,4′-dimethylbiphenyl (0.010
g, 0.055 mmol) in benzene-d6 at room temperature. After 10
min, 6 was observed by NMR (0.041 mmol, 78% yield). 6 was
found thermally unstable, and it decomposed to HSiButPh2 and
other unknown species. The structural assignment for 6 was
thus based on its spectroscopic data. 1H NMR (benzene-d6,
250.1 MHz): δ 7.58-7.14 (m, 20H, C6H5), 2.99 (s, 18H, NMe2),
1.07 (s, 18H, CMe3). 13C{1H} NMR (benzene-d6, 62.9 MHz): δ
148.7, 137.3, 127.1, 126.8 (C6H5), 44.5 (NMe2), 31.1 (CMe3), 24.2
(CMe3). 29Si{1H} NMR (benzene-d6, 79.5 MHz): δ 48.9 (Si-
ButPh2).
Preparation of (Me2N)3Ta(SiButPh2)[Si(SiMe3)3] (7).
(Me2N)3Ta(SiButPh2)Cl (0.022 g, 0.037 mmol) in benzene-d6
was treated with Li(THF)3Si(SiMe3)3 (0.017 g, 0.036 mmol) and
4,4′-dimethylbiphenyl (0.014 g, 0.077 mmol) at room temper-
ature. The reaction solution immediately turned purple. 7 was
observed by NMR (0.031 mmol, 86% yield). The complex was
found unstable at room temperature, and it decomposed to
(18) Morse, P. M.; Spencer, M. D.; Wilson, S. R.; Girolami, G. S.
Organometallics 1994, 13, 1646.
(19) See Supporting Information for details.

Disilyl Complexes of Zr, Hf, and Ta
Organometallics, Vol. 24, No. 17, 2005 4193
Table 1. Equilibrium Constants (Keq) for
Scheme 1
-
(Me2N)3Zr-Si(SiMe3)3 + SiButPh2
h
-
(Me2N)3Zr-SiButPh2 + Si(SiMe3)3
a
T (K)
[Keq ( δKeq(ran)]
293(1)
288(1)
283(1)
278(1)
273(1)
268(1)
263(1)
82.83(0.02)
89.82(0.01)
101.73(0.03)
125.42(0.02)
145.95(0.01)
173.03(0.03)
192.51(0.01)
Scheme 2
a The total uncertainty σKeq/Keq of 6% was calculated from
σKeq(ran)/Keq ) 3%, and the estimated systematic uncertainty
σKeq(sys)/Keq ) 5% by σKeq/Keq ) [(σKeq(ran)/Keq)2 + (σKeq(sys)/Keq)2]1/2
.
L.S. 1 and BLOC 1 procedures were used to obtain estimated
standard deviations of bond lengths and bond angles in
3‚toluene and 4‚toluene. All hydrogen atoms were included in
the structure factor calculation at idealized positions and were
allowed to ride on the neighboring atoms with relative isotropic
displacement coefficients. The SHELXTL (version 5.1) propri-
etary software package was used for all structure solution and
refinement calculations.
Results and Discussion
Preparation and Characterization of Disilyl
Complexes 1-7. The anionic disilyl complexes
[M(NMe2)3(SiButPh2)2][Li(THF)4] (M ) Zr, 1; Hf, 2 as
[Li(THF)4]+ salts) were prepared by the addition of Li-
(THF)3SiButPh215b to (Me2N)3M(SiButPh2)12b in toluene,
from which [Li(THF)4]‚1 and [Li(THF)4]‚2 crystallized
at room temperature (Scheme 1). [Li(THF)4]‚1 is ther-
mally unstable in solution but may be stored indefinitely
as a solid at -20 °C.
Figure 1. Plot of ln Keq vs 1/T of the equilibrium (Me2N)3-
-
Zr-Si(SiMe3)3 + SiButPh2 h (Me2N)3Zr-SiButPh2 + Si-
-
(SiMe3)3
.
Scheme 3
1
There is a sharp -NMe2 signal in the H and 13C-
{1H} NMR spectra of 1 or 2 at room temperature. Both
1H (400.1 MHz) and 13C{1H} (100.6 MHz) NMR peaks
of the But groups in the Zr complex 1 are broad at 23
°C, and at 0 °C, these resonances of the But groups
resolve into two separate broad signals, which are close
to those of (Me2N)3Zr(SiButPh2)12b and Li(THF)3Si-
ButPh2. This indicates that the -SiButPh2 ligand in
(Me2N)3Zr(SiButPh2)12b is in a rapid exchange with Li-
(THF)3SiButPh2 in solution at room temperature (Scheme
1). The dynamic NMR of this exchange reaction in 1 was
studied in the current work. The signals of the two
-SiButPh2 ligands were found to coalesce at 20 °C. The
free energy of activation ∆Gq was estimated to be 14.1-
(0.5) kcal/mol for the exchange in 1 at the coalescence
temperature. A similar exchange was also observed in
the Hf analogue 2. Unlike the exchange in its Zr
to confirm NMR assignments. In addition, the exchange
in 2 was observed in its 2-D NOESY spectrum.
The silyl ligand in (Me2N)3Zr-Si(SiMe3)3 was found
to undergo a reversible exchange with the SiButPh2
-
anion as well to reach the following equilibrium: (Me2N)3-
-
ZrSi(SiMe3)3 + SiButPh2 h (Me2N)3Zr-SiButPh2
+
Si(SiMe3)3-. Although this exchange does not involve
disilyl complexes, it was studied in the current work to
provide a better understanding of silyl exchanges in d0
transition metal complexes. Once Li(THF)3SiButPh2 was
added to the solution of (Me2N)3Zr-Si(SiMe3)3, (Me2N)3-
Zr-SiButPh2 and Li(THF)3Si(SiMe3)3 were observed in
the solution at room temperature (Scheme 2). The
equilibrium constants for the exchange were measured
1
analogue 1, both H (400.1 MHz) and 13C{1H} (100.6
MHz) NMR spectra of 2 at 23 °C show two broad peaks
for the But groups. The coalescence of the peaks does
not occur until 43 °C. The free energy of activation ∆Gq
was estimated to be 15.3(0.5) kcal/mol for the exchange
in 2 at the coalescence temperature. This is slightly
higher than 14.1(0.5) kcal/mol for the exchange in the
Zr analogue 1. 2-D HMQC spectra of 1 and 2 were used
1
between 263 and 293 K from H NMR spectra and are
listed in Table 1. A plot of ln Keq vs 1/T (Figure 1) gave
a linear fit and yielded ∆H° ) 4.6(0.5) kcal/mol and ∆S°
) -7(2) eu.16
The reaction of (Me2N)3MCl12a (M ) Zr, Hf) with
[K(18-crown-6)]2[(Me3Si)2Si-(CH2)2-Si(SiMe3)2] (8) in tolu-
ene was found to give chelating disilyl complexes 3 and
4 (Scheme 3).
(20) Sheldrick, G. M. A Program for Empirical Absorption Correction
of Area Detector Data; University of Gottingen: Gottingen, Germany,
1996.
(21) Sheldrick, G. M. A Program for the Refinement of Crystal
Structures; University of Gottingen: Gottingen, Germany, 1997.
The concentrations of both (Me2N)3MCl12a and [K(18-
crown-6)]2[(Me3Si)2Si(CH2)2Si(SiMe3)2] (8)14 were found
to be important to the success of the preparation. Solids

4194 Organometallics, Vol. 24, No. 17, 2005
Qiu et al.
Scheme 4
Figure 2. ORTEP diagram of the bis(silyl) anion in 2,
showing 35% thermal ellipsoids.
Table 2. 29Si NMR of Complexes Containing the
-SiPh2But or -Si(SiMe3)3 Ligands
[Li(THF)3]SiButPh2
7.54 (SiButPh2)
-185.4 [Si(SiMe3)3]
-5.3 (Me3Si)
a,15b
a,15a
[Li(THF)3]Si(SiMe3)3
.
(Me2N)3Zr-SiButPh2 0.5 THFb,12b
19.6 (SiButPh2)
-4.4 (SiMe3)
b,12b
(Me2N)3Zr-Si(SiMe3)3
-124.6 [Si(SiMe3)3]
46.8 (SiButPh2)
-2.1 (SiMe3)
.
(Me2N)3Hf-SiButPh2 0.5 THFb,12b
b,12b
(Me2N)3Hf-Si(SiMe3)3
-103.5 [Si(SiMe3)3]
49.04 (SiButPh2)
-84.12 [Si(SiMe3)3]
64.6 (SiButPh2)
4.39 (SiMe3)
Cp2Hf(SiButPh2)Meb,22
Cp2Hf[Si(SiMe3)3]Meb,22
(Me2N)3Ta(SiButPh2)Clb,4i
(Me2N)3Ta[Si(SiMe3)3]Clb,4i
-51.34 [Si(SiMe3)3]
-189.0 (SiButPh2)
-4.0 (SiMe3)
b,4i
(Me2N)4Ta-SiButPh2
b,4i
(Me2N)4Ta-Si(SiMe3)3
-98.4 [Si(SiMe3)3]
48.94 (SiButPh2)
0.95 (SiMe3)
Figure 3. ORTEP diagram of the anion in bis(silyl) Hf
complex 4‚toluene, showing 30% thermal ellipsoids.
(Me2N)3Ta(SiButPh2)2 (6)b
(Me2N)3Ta[Si(SiMe3)3]2 (5)b
-6.25 [Si(SiMe3)3]
40.9 (SiButPh2)
-11.1 (SiSiMe3)
-19.8 (SiSiMe3)
(Me2N)3Ta(SiButPh2)[Si(SiMe3)3] (7)c
Si(SiMe3)3 (-85.5 ppm), (Me3SiCH2)3Zr-Si(SiMe3)3 (-75.7
ppm),4a,b and Cp2Zr[Si(SiMe3)3]Cl (-85.5 ppm).2a In the
29Si NMR spectra of its Hf analogue 4, the Hf-Si-SiMe3
peak was observed at -48.8 ppm. In comparison, the
R-Si resonances of, for example, (Me2N)3Hf-Si-
a Benzene-d6. b Room temperature, benzene-d6. c 8 °C, benzene-
d6.
ButPh2‚0.5THF, CpCp*Hf(SiButPh2)Cl,22 and (Me2N)3-
12b
of both reagents were mixed in one flask and dissolved
in a small amount of toluene (5-15 mL) to start the
reaction. The products, after washing with hexanes,
were crystallized from toluene at -30 °C to give crystals
of 3‚toluene or 4‚toluene.
Hf-Si(SiMe3)3
were observed at 46.8, 51.48, and
-103.5 ppm, respectively.
No exchange between the chelating silyl ligands in 4
and excess Li(THF)3SiButPh2 was observed after the
two species were mixed in THF-d8 for 24 h. This is
perhaps not surprising, as the substitution of the
chelating [(Me3Si)2Si(CH2)2Si(SiMe3)2]2- ligand in 4 by
Four resonances were observed in the 1H NMR
spectra of 3 and 4, respectively. In the 1H NMR
spectrum of 3, the -SiMe3 resonance (0.67 ppm) of the
disilyl ligand and -O-CH2 resonances (3.32 ppm) of 18-
crown-6, respectively, are only slightly shifted from
those in [K(18-crown-6)]2[(Me3Si)2Si-(CH2)2-Si(SiMe3)2]
(8). The -CH2- resonance in 3 is 0.3 ppm downfield
shifted from that of 8. Only one resonance attributed
the mono silyl SiButPh2 anion is thermodynamically
-
unfavorable.
The tantalum disilyl complex (Me2N)3Ta[Si(SiMe3)3]2
(5) was readily prepared either by the reactions of the
silyl chloride complex (Me2N)3Ta[Si(SiMe3)3]Cl with 1
equiv of Li(THF)3Si(SiMe3)3 or by the reaction of (Me2N)3-
TaCl2 with 2 equiv of Li(THF)3Si(SiMe3)3 (Scheme 3).
(Me2N)3Ta(SiButPh2)2 (6), an analogue of 5, was simi-
larly prepared. The mixed bis(silyl) complex (Me2N)3-
Ta(SiButPh2)[Si(SiMe3)3] (7) was prepared from the
reaction of (Me2N)3Ta(SiButPh2)Cl4i with 1 equiv of
Li(THF)3Si(SiMe3)3 (Scheme 4).
1
to the -NMe2 ligands was observed at 23 °C in the H
1
NMR spectrum of 3 at 250 MHz. However, in the H
NMR spectrum of 3 at 400 MHz, two nearly overlapping
amide and -SiMe3 peaks were found at 23 °C, which
were more separated at lower temperatures,19 suggest-
ing dynamic exchanges of these groups. In the 13C{1H}
NMR spectra of 3 in benzene-d6, the -SiMe3 resonance
of 3 at 4.48 ppm is upfield shifted from that (5.74 ppm)
in [K(18-crown-6)]2[(Me3Si)2Si(CH2)2Si(SiMe3)2] (8). One
-NMe2 peak was observed for 3 at 44.61 ppm at 23 °C.
In the 29Si{1H} NMR spectrum of 3 at 23 °C, the Zr-
Si-SiMe3 peak at -73.11 ppm is consistent with those
in other Zr-Si complexes such as (Me3CCH2)3Zr-
The NMR spectra of 5-7 are consistent with the
1
structural assignment of the complexes. The H NMR
spectra of bis(silyl) complexes 5-7 show only one
resonance for -NMe2 ligands at both low and room
temperatures, suggesting that 5-7 may adopt a trigonal
(22) Sadow, A. D.; Tilley, T. D. J. Am. Chem. Soc. 2003, 125, 9462.

Disilyl Complexes of Zr, Hf, and Ta
Table 3. Crystal Data of 1, 2, 3·toluene, and 4·toluene
3‚toluene
Organometallics, Vol. 24, No. 17, 2005 4195
1
2
4‚toluene
(C54H88Li N3O4Si2Zr) (C54H88LiN3O4Si2Hf) (C180H408K4N12O36Si24Zr4) (C180H408K4N12O36Si24Hf4)
fw
997.61
monoclinic
C2/c
21.195(6)
17.434(5)
17.801(5)
1084.88
monoclinic
C2/c
21.139(4)
17.466(3)
17.762(3)
90
4512.60
4861.68
cryst syst
space group
lattice params
triclinic
triclinic
P1h
P1h
a (Å)
b (Å)
c (Å)
13.077(3)
24.797(5)
41.823(8)
101.06(3)
92.00(3)
13.114(7)
24.704(14)
41.71(2)
R (deg) 90
100.870(9)
91.881(9)
101.425(10)
12974(12)
2
â (deg)
γ (deg)
119.76(2)
90
5710(3)
4
1.160
0.277
2144
119.699(3)
90
101.05(3)
13028(5)
2
V (Å3)
5696.8(17)
4
Z
dcalcd (Mg m-3
)
1.265
1.153
1.248
µ (mm-1
F(000)
)
1.916
0.388
1.828
2272
4888
5144
θ (deg)
no. of data collected
completeness
1.61-22.54
3880
1.61-28.30
29 219
1.07-27.05
119 093
1.00-28.99
141 993
96.8% to θ ) 28.30°
6865 (Rint ) 0.0642)
13 215/2/599
92.4% to θ ) 27.05°
52 829 (Rint ) 0.1100)
52 829/0/2419
89.2% to θ ) 28.99°
61 492 (Rint ) 0.0670)
61 492/0/2420
no. of indep data
no. of data/restraints/
params
3761 (Rint ) 0.0256)
3758/0/295
index ranges
0 e h e 22
0 e k e 18
-19 e l e 16
R1 ) 0.0465
wR2 ) 0.1240
1.083
-23 e h e 23
-23 e k e 23
-25 e l e 25
R1 ) 0.0401
wR2 ) 0.1096
0.907
-16 e h e 16
-30 e k e 30
-52 e l e 52
R1 ) 0.1076
wR2 ) 0.2790
0.991
-17 e h e 17
-33 e k e 33
-55 e l e 55
R1 ) 0.0621
wR2 ) 0.1476
0.965
R indices [I > 2σ(I)]
goodness-of-fit on F2
wR2 ) [∑w(Fo - Fc )2/∑w(Fo2)2]1/2; R ) ∑||Fo| - |Fc||/∑|Fo|; w ) 1/[σ2(Fo2) + (aP)2 + bP]; P ) [2Fc + Max(Fo2,0)]/3.
a
2
2
2
Table 4. Selected Bond Distances (Å) and Bond
bipyramidal structure with two silyl ligands in the axial
and three amide ligands in the equatorial positions. In
the 29Si NMR spectra of (Me2N)3Ta[Si(SiMe3)3]2 (5) and
(Me2N)3Ta(SiButPh2)2 (6), the R-Si resonances appear
at -6.25 (SiSiMe3) and 48.9 (SiButPh2) ppm, respec-
tively. This follows the general trend of chemical shifts
for the silyl ligands -Si(SiMe3)3 and -SiButPh2 in the
complexes listed in Table 2: The former usually is
further upfield shifted than the latter with the exception
of (Me2N)4Ta-SiButPh2 and (Me2N)4Ta-Si(SiMe3)3. On
the basis of this observation, the two R-Si resonances
in (Me2N)3Ta(SiButPh2)[Si(SiMe3)3] (7) at 40.9 and
-19.8 ppm are assigned to those of -SiButPh2 and
-SiSiMe3, respectively. Thermal decomposition of 7, to
be discussed below, prevented us from taking more
scans during the NMR data acquisition to observe the
1JSi-Si couplings, which would have helped the assign-
ment.
Angles (deg) in 2 and 419
[(Me2N)3Hf(SiButPh2)2]- in 2
Hf(1)-N(2)
Hf(1)-N(3)
Hf(1)-Si(2)
2.035(16) Hf(1)-N(1)
2.029(15)
2.918(7)
2.063(5)
2.896(7)
N(2)-Hf(1)-N(1) 117.9(2)
N(1)-Hf(1)-N(3) 122.5(9)
N(1)-Hf(1)-Si(1) 89.8(4)
N(2)-Hf(1)-Si(2) 86.4(4)
N(3)-Hf(1)-Si(2) 93.4(6)
Hf(1)-Si(1)
N(2)-Hf(1)-N(3)
119.7(8)
N(2)-Hf(1)-Si(1) 93.5(4)
N(3)-Hf(1)-Si(1) 88.6(6)
N(1)-Hf(1)-Si(2) 88.2(4)
Si(1)-Hf(1)-Si(2) 177.71(15)
(Me2N)3Hf[(Me3Si)2Si(CH2)2Si(SiMe3)2]- in 4
2.043(7) Hf(1)-N(2)
2.063(7)
Hf(1)-N(3)
2.047(7)
2.846(2)
1.554(10)
1.960(8)
97.2(3)
Hf(1)-N(1)
Hf(1)-Si(1)
C(7)-C(8)
Hf(1)-Si(4)
2.863(2)
1.945(7)
109.4(3)
97.9(3)
C(7)-Si(1)
C(8)-Si(4)
N(3)-Hf(1)-N(2)
N(2)-Hf(1)-N(1)
N(2)-Hf(1)-Si(1)
N(3)-Hf(1)-Si(4)
N(1)-Hf(1)-Si(4)
C(8)-C(7)-Si(1)
N(3)-Hf(1)-N(1)
N(3)-Hf(1)-Si(1)
N(1)-Hf(1)-Si(1)
N(2)-Hf(1)-Si(4)
Si(1)-Hf(1)-Si(4)
C(7)-C(8)-Si(4)
96.8(2)
96.1(2)
155.7(2)
123.5(2)
70.78(7)
111.1(5)
126.3(2)
84.9(2)
108.4(5)
When a solution of (Me2N)3Ta[Si(SiMe3)3]2 (5) in
benzene-d6 was added to Li(THF)3SiButPh2, the forma-
tion of (Me2N)3Ta(SiButPh2)[Si(SiMe3)3] (7), (Me2N)3Ta-
(SiButPh2)2 (6), and Li(THF)3Si(SiMe3)3 was observed,
4 are summarized in Table 3. Selected bond distances
and bond angles of 2 and 4 are given in Table 4.
-
indicating that one -Si(SiMe3)3 ligand in 5 was
In the structure of 2 (Figure 2), the Hf atom is five-
coordinate to form an anion with two silyl ligands and
three -NMe2 ligands. The two -SiButPh2 ligands,
which are trans to each other, occupy the axial positions
to form trigonal bipyramidal geometry in 2 with the
nearly linear Si-Hf-Si angle of 177.93(5)°. Unlike the
trigonal bipyramidal anion [(Me2N)3Hf(SiButPh2)2]- (2),
the {(Me2N)3Hf[(Me3Si)2Si-(CH2)2-Si(SiMe3)2]}- anion in
4 (Figure 3) is severely distorted from either the trigonal
bipyramidal or the square pyramidal geometry. In this
case the two Si atoms in the chelating bisilyl ligand are
cis to each other in the pseudoaxial and pseudoequato-
rial positions, respectively, with the Si-Hf-Si angle of
70.8°. The Hf-Si bond lengths [2.846(2)-2.863(2) Å] in
4 are slightly shorter than [2.896(7)-2.918(7) Å] in
substituted by a -SiButPh2 anion to give 7. Subse-
-
-
quently, the remaining -Si(SiMe3)3 ligand in 7 was
replaced by another -SiButPh2- anion to give 6. 6 was
found, however, to be inert to the exchange with the
-
-Si(SiMe3)3 anion. Both 6 and 7 are thermally un-
stable and decompose to silanes and unknown species.
The kinetic studies of their decompositions are discussed
below.
Crystal and Molecular Structures of 1, 2, 3‚
toluene, and 4‚toluene. ORTEP views of the bis(sily)
anion 1 and 4‚toluene are shown in Figures 2 and 3.
ORTEP views of 1 and 3 with structures similar to those
of 2 and 4, respectively, are given in the Supporting
Information.19 The crystallographic data of 1, 2, 3, and

4196 Organometallics, Vol. 24, No. 17, 2005
Qiu et al.
Figure 4. ORTEP diagram of the cations in two different molecules of 4‚toluene, showing 30% thermal ellipsoids.19
Table 5. Rate Constants k for the Decomposition
Scheme 5
of 7a
T (K)
[k ( δk(ran)] × 105 (s-1
)
298(1)
303(1)
308(1)
313(1)
318(1)
323(1)
2.48(0.01)
4.33(0.16)
8.7(0.3)
16.9(0.3)
31.9(1.7)
47.1(0.7)
[(Me2N)3Hf(SiButPh2)2]- (2). In comparison, the Hf-Si
bond [2.807(4) Å] in the monosilyl complex (Me2N)3Hf-
a The total uncertainty of δk/k ) 7.3% was calculated from
δk(ran)/k ) 5.3% and δk(sys)/k ) 5%.
SiPh2 Bu is shorter than in both 2 and 4.12b The Hf-N
t
bond lengths [2.043(7)-2.063(7) Å] are also similar to
2.029(3)-2.063(5) Å in (Me2N)3Hf(SiButPh2)2 (2) and
2.019(9)-2.030(9) Å in (Me2N)3HfSiButPh2.12b
There are two types of cations in 4 (Figure 4): K(18-
crown-6)+ and K(18-crown-6)2+. The K+ ion in the
former was coordinated to one 18-crown-6 ligand. There
is also weak interaction between K+ and two toluene
molecules. In the latter, the two 18-crown-6 ligands use
six and two O atoms, respectively, to bond to the K+
ion.
The triamide disilyl complexes 5-7 may adopt a
trigonal bipyramidal structure with the two silyl ligands
in the axial positions (Scheme 5), as observed in the
triamide disilyl anion 1. However, we were not able to
obtain a crystal structure of these disilyl Ta compounds.
6 and 7 were thermally unstable, which is discussed
below. Crystals of 5 were found to rapidly decompose
on the X-ray diffractometer, precluding attempts to
confirm its structure.
Figure 5. Kinetic plots of the thermal decomposition of
7.
Kinetic Studies of the Decomposition of (Me2N)3-
Ta(SiButPh2)2 (6) and (Me2N)3Ta(SiButPh2)[Si-
(SiMe3)3] (7). Both 6 and 7 are thermally unstable and
decompose at 23 °C to HSiButPh2, HSiButPh2, and HSi-
(SiMe3)3, respectively, and other unknown species. 5,
containing two -Si(SiMe3)3 ligands, is thermally stable
at room temperature under nitrogen.
The decomposition reactions were not characterized,
and not all products of the thermal decomposition are
known. To compare the rates of the decomposition of
the two complexes, the decomposition kinetics was
studied. The decomposition was found to follow first-
order (irreversible) kinetics. The sample of 7 used in the
kinetic studies was prepared in situ from 5 and 1 equiv
of Li(THF)3Si(SiMe3)3 in toluene-d8. The kinetic studies
were conducted between 298 and 323 K in toluene-d8
to give plots of ln(C0/C) (C ) [7]) vs time t (Figure 5)
and the first-order rate constants k of the conversion
(Table 5). An Eyring plot (Figure 6) gives activation
parameters of the thermal decomposition: ∆Hq ) 22.8-
(1.3) kcal/mol, ∆Sq ) -3(5) eu, and ∆Gq298 K ) 24(3) kcal/
mol.
Figure 6. Eyring plot of the thermal decomposition of 7.
The thermal decomposition of 6 was studied by NMR
in toluene-d8. The decomposition was found to follow
the first-order kinetics as well. The rate constant k for
this decomposition at 303 K is 7.2(0.2) × 10-5 s-1, larger
than the rate constant [4.33(0.16) × 10-5 s-1, Table 5]
for the thermal decomposition of 7 at this temperature,
suggesting that 7, with one -Si(SiMe3)3 and one -Si-

Disilyl Complexes of Zr, Hf, and Ta
Organometallics, Vol. 24, No. 17, 2005 4197
ButPh2 ligand, decomposes slower than 6, containing
two -SiButPh2 ligands.
support of the research. We thank the reviewers for
helpful suggestions.
Acknowledgment is made to the National Science
Foundation (CHE-9457368, CHE-9904338, and CHE-
0212137), DuPont Young Professor Award, and the
Camille Dreyfus Teacher-Scholar program for financial
Supporting Information Available: This material is
available free of charge via the Internet at http://pubs.acs.org.
OM050302F