Synthesis and characterization of tantalum silyl and disilyl imido complexes that do not contain anionic π-ligands

Article abstract of DOI:10.1021/om000503d

A series of Cp-free d⁰ silyl alkyl, alkylidene, alkylidyne, amide and related complexes were prepared and their chemistry was studied. The synthesis of a Cp-free Ta imido silyl and a Cp-free Ta imido disilyl complex is described. X-ray crystal structure of the compounds show a pseudotetrahedral arrangement in the Ta moiety with different bond angles.

Full text of DOI:10.1021/om000503d

Organometallics 2000, 19, 4191-4192
4191
Syn th esis a n d Ch a r a cter iza tion of Ta n ta lu m Silyl a n d
Disilyl Im id o Com p lexes Th a t Do Not Con ta in An ion ic
π-Liga n d s
Zhongzhi Wu and Ziling Xue*
Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37996-1600
Received J une 15, 2000
Summary: Tantalum disilyl and silyl complexes [(Me3-
Si)2N](Me3SiNd)Ta(SiPh2But)2 (1) and [(Me3Si)2N]-
(Me2N)(Me3SiNd)Ta(SiPh2But) (2) have been prepared
and characterized. They are, to our knowledge, the first
known cyclopentadienyl-free group 5 imido disilyl and
silyl complexes.
interest. (1) To our knowledge, they are the first known
Cp-free group 5 imido silyl and disilyl complexes. So far,
only d0 Cp-free amido disilyl complexes [(Me2N)3Zr-
(SiPh2But)2Li(THF)4]6k and (Me2N)3Ta[Si(SiMe3)3]2,6k
and a few Cp-containing d0 disilyl complexes Cp2M-
(SiR3)2 and Cp2M(SiR2)n have been reported.7 (2) These
Ta complexes with N- and Si-containing ligands are
potential precursors to Ta-Si-N ternary materials that
are of current interest in microelectronic applications.8,9
There have been no reported attempts to use Ta
complexes containing N and Si ligands as single-source
Ta-Si-N precursors.8a
Early-transition-metal silyl chemistry has attracted
increasing interest recently.1 Silyl complexes of the d0
metals have been studied in, for example, insertion
reactions,2 silane dehydropolymerizations,1,3 and hy-
drosilylation.4 Most d0 metal silyl complexes contain
cyclopentadienyl (Cp) or analogous anionic π-ligands;1
relatively fewer Cp-free d0 metal silyl complexes have
been reported.2e,5,6 Cp ligands are believed to lead to
enhanced stability of silyl complexes. Tilley and co-
workers have recently reported Cp-free group 6 imido
The yellow Ta imido silyl complex [(Me3Si)2N](Me2N)-
(Me3SiNd)Ta(SiPh2But) (2) was prepared from the
reaction of {Ta(µ-Cl)Cl(dNSiMe3)[N(SiMe3)2]}2 (3)10 first
with 2 equiv of LiNMe2 and then with 2 equiv of Li-
1
(THF)3SiPh2But 11 (Scheme 1).12 The H, 13C{1H}, and
silyl complexes (2,6-Pri C6H3Nd)2M(R)Si(SiMe3)3 (M )
2
29Si{1H} NMR spectra and elemental analysis of 2 are
consistent with the structural assignment. The X-ray
crystal structure of 2 (Figure 1) shows a pseudo-
tetrahedral arrangement in the Ta moiety with bond
angles around the Ta atom ranging from 100.1(2) to
118.3(3)°. The d0 Ta-Si bond length of 2.704(2) Å is
Mo, W; R ) Cl, CH2But, H).5 We have prepared a series
of Cp-free d0 silyl alkyl, alkylidene, alkylidyne, amide,
and related complexes and studied their chemistry.6 The
synthesis and characterization of a Cp-free Ta imido
silyl and a Cp-free Ta imido disilyl complex are reported
here. We have studied such complexes with a 2-fold
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(7) (a) Cp2Zr(SiMe3)[Si(SiMe3)3]: see ref 2a. (b) Cp2Ti(SiPh3)2: King-
ston, B. M.; Lappert, M. F. J . Chem. Soc., Dalton Trans. 1972, 69. (c)
Cp2Ti(SiPh2)5: Igonin, V. A.; Ovchinnikov, Yu. E.; Dementev, V. V.;
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Organomet. Chem. 1989, 371, 187. (d) Cp2Ti(SiPh2)4: Holtman, M. S.;
Schram, E. P. J . Organomet. Chem. 1980, 187, 147. (e) Cp2Ta(H)-
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10, 3648. (f) [Cp2Ln(SiMe3)2][Li(DME)2] (Ln ) Sm, Lu): Schumann,
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10.1021/om000503d CCC: $19.00 © 2000 American Chemical Society
Publication on Web 09/21/2000

4192 Organometallics, Vol. 19, No. 21, 2000
Communications
Sch em e 1a
of 1.954(6) Å in Ta-NMe2 is slightly shorter than that
(1.993(7) Å) in the bulkier Ta-N(SiMe3)2.
The red Ta imido disilyl complex [(Me3Si)2N](Me3-
SiNd)Ta(SiPh2But)2 (1) was prepared from the reaction
of {Ta(µ-Cl)Cl(dNSiMe3)[N(SiMe3)2]}2 (3) with 4 equiv
of Li(THF)3SiPh2But (Scheme 1).17 The disilyl imido
complex 1 was unstable in solution and photosensitive
in the solid state. In comparison, such decomposition
was not observed in the monosilyl imido complex 2.
Attempts to obtain the X-ray crystal structure of 1 were
unsuccessful. The structure assignment of 1 is based
on its 1H, 13C{1H}, and 29Si{1H} NMR spectra in
comparison to its monosilyl analogue 2 and its elemental
analysis. The 29Si resonance of the silyl ligand in
diamide 2 (64.9 ppm) is shifted upfield from that in
monoamide 1 (95.0 ppm). The additional amido ligand
in 2 and the d-p π bond between its lone-pair electrons
and the Ta atom perhaps increases the electron density
and magnetic shielding around the metal center. This
enhanced shielding may also be reflected in the upfield
shifts of the resonances of â-Si atoms in 2. These 29Si
resonances are -1.9 ppm in -N(SiMe3)2 and -6.5 ppm
in dNSiMe3 in diamido 2. In comparison, 29Si reso-
nances of -N(SiMe3)2 and dNSiMe3 are 7.4 and -2.4
ppm, respectively, in monoamide 1.
a
Legend: (i) +2Li(THF)3SiPh2But; (ii) LiNMe2; (iii) Li(THF)3-
SiPh2But.
The diamido imido silyl complex [(Me3Si)2N](Me2N)-
(Me3SiNd)Ta(SiPh2But) (2) is analogous to dialkyl alky-
lidene silyl complexes (RCH2)2(RCHd)TaSiR′3 (R ) But,
Me3Si; R′3 ) (SiMe3)3, Ph2But) (Scheme 1).6a,d However,
a key difference between the two structural types is that
there are substantial d-p π bonds between the lone-
pair electrons in the amido imido ligands and the metal
atom in 2, and the metal centers in these complexes are
thus more electron rich.16 [(Me3Si)2N](Me3SiNd)Ta-
(SiPh2But)2 (1) is the first known Cp-free amido imido
disilyl complex. Its alkyl alkylidene disilyl analogue
“(RCH2)(RCHd)Ta(SiR′3)2” is, to our knowledge, un-
known. Studies are currently underway to probe the
reactivities of 1 and 2 and to evaluate their potentials
as precursors for the preparation of Ta-Si-N ternary
materials.
F igu r e 1. ORTEP diagram of 2, showing 35% probability
thermal ellipsoids.
longer than, e.g., 2.611(7) Å in (Me3SiCH2)2Ta(dCH-
SiMe3)Si(SiMe3)3,6d 2.624(12)-2.633(2) Å in Cp2Ta(H)-
(SiMe2H)2,7e 2.651(4) Å in Cp2Ta(H)2SiPhMe2,13 2.669(4)
Å in (C5Me5)Ta(SiMe3)Cl3,14 and 2.689(1) Å in Cp*(2,6-
Pri C6H3Nd)Ta[Si(SiMe3)3]H.15 The Ta-Si bond length
2
in 2 is, however, shorter than 2.809(2) Å in Cp*(2,6-
Pri C6H3Nd)Ta(CO)[Si(SiMe3)3]H.15 The TadN(1)-Si-
2
(2) bond angle (167.2(5)°) is close to being linear,
indicating a significant degree of d-p π bonding be-
tween the electron-deficient Ta atom and the lone-pair
electrons on the imido N atom.16 The Ta-N bond length
Ack n ow led gm en t is made to the National Science
Foundation (Grant No. CHE-9904338 and the NSF
Young Investigator program Grant No. CHE-9457368),
Camille Dreyfus Teacher-Scholar program, and DuPont
Young Professor program for financial support of this
research.
(12) [(Me3Si)2N](Me2N)(Me3SiNd)Ta(SiPh2But) (2). To a pale yellow
solution of {Ta(µ-Cl)Cl(dNSiMe3)[N(SiMe3)2]}2 (1.00 g, 1.00 mmol) in
20 mL of diethyl ether was added 2 equiv of LiNMe2 (0.l0 g, 2.0 mmol).
The solution was stirred at room temperature for 4 h. Two equivalents
of Li(THF)3SiPh2But (0.92 g, 2.00 mmol) in 20 mL of diethyl ether was
added dropwise with stirring to the reaction solution at room temper-
ature. After the mixture was stirred at room temperature for 10 h,
the volatiles were removed under vacuum to give a yellow solid.
Extraction of the solid with hexanes, followed by filtration and
crystallization at -20 °C, yielded yellow crystals of 2 (0.33 g, 23%). 1H
NMR (benzene-d6, 250.1 MHz, 23 °C): δ 7.93-7.15 (m, 10H, C6H5),
3.22 (s, 6H, NMe2), 1.36 (s, 9H, CMe3), 0.41 (b, 9H, dNSiMe3), 0.18 [s,
18H, N(SiMe3)2]. 13C{1H} NMR (benzene-d6, 62.9 MHz, 23 °C): 144.2,
143.8, 137.9, 137.6, 128.2, 128.1, 127.8, 127.7 (C6H5), 47.3 (NMe2), 30.4
(CMe3), 23.8 (CMe3), 5.6 [N(SiMe3)2], 4.0 (dNSiMe3). 29Si{1H} NMR
(DEPT, benzene-d6, 79.5 MHz, 23 °C): δ 64.9 (SiPh2But), -1.9
[N(SiMe3)2], -6.5 (dNSiMe3). Anal. Calcd for C27H52N3Si4Ta: C, 45.55;
H, 7.36. Found: C, 45.32; H, 7.28.
Su p p or tin g In for m a tion Ava ila ble: Complete listings
of the crystallographic data for 2. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM000503D
(17) [(Me3Si)2N](Me3SiNd)Ta(SiPh2But)2 (1). To a pale yellow solu-
tion of {Ta(µ-Cl)Cl(dNSiMe3)[N(SiMe3)2]}2 (1.00 g, 1.00 mmol) in 20
mL of hexanes was added 4 equiv of Li(THF)3SiPh2But (1.85 g, 4.00
mmol) in 20 mL of hexanes with stirring at -50 °C. The reaction
solution was slowly warmed to room temperature and stirred for about
30 min. The solvent was removed under vacuum to give a red-brown
solid. Extraction of the solid with hexanes, followed by filtration and
crystallization at -20 °C yielded deep red crystals of 1 (0.96 g, 53%).
1H NMR (benzene-d6, 250.1 MHz, 23 °C): δ 7.81-7.08 (m, 20H, C6H5),
1.28 (s, 18H, CMe3), 0.69 [s, 9H, N(SiMe3)2], 0.36 [s, 9H, N(SiMe3)2],
0.28 (b, 9H, dNSiMe3). 13C{1H} NMR (benzene-d6, 62.9 MHz, 23 °C):
δ 145.1, 143.2, 139.0, 137.9, 128.4, 128.2, 127.8, 127.7 (C6H5), 30.9
(CMe3), 25.3 (CMe3), 6.3 (dNSiMe3), 5.0 [N(SiMe3)2]. 29Si{1H} NMR
(DEPT, benzene-d6, 79.5 MHz, 23 °C): δ 95.02 (SiPh2But), 7.38
[N(SiMe3)2], -2.40 (dNSiMe3). Anal. Calcd for C41H65N2Si5Ta: C,
54.27; H, 7.22. Found: C, 54.56; H, 7.31.
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