Synthesis and Characterization of (Me3ECH2)2Ta(=CHEMe3)Si(SiMe3)3 (E = C, Si). Kinetic and Mechanistic Studies of the Formation of a S
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- 作者：Liting Li ; Jonathan B. Diminnie ; Xiaozhan Liu ; Jonathan L. Pollitte ; and Ziling Xue
- 刊名：Organometallics
- 出版年：1996
- 出版时间：August 6, 1996
- 年：1996
- 卷：15
- 期：16
- 页码：3520 - 3527
- 全文大小：429K
- 年卷期：v.15,no.16(August 6, 1996)
- ISSN：1520-6041
文摘
Silyl alkylidene complexes(Me3ECH2)2Ta(=CHEMe3)Si(SiMe3)3(E = C, 1; E = Si, 2), whichare free of anionic 
-ligands such as cyclopentadienyl (Cp), wereprepared through thereactions of(Me3ECH2)3TaCl2with 2 equiv ofLiSi(SiMe3)3(THF)3.An unprecedentedpreferential elimination of silaneHSi(SiMe3)3 leads to the formation of thealkylidene bondsin 1 and 2. An intermediate(Me3SiCH2)3Ta(Cl)Si(SiMe3)3(9) was observed in the formationof 2. 9 was found to react withLiSi(SiMe3)3(THF)3 andLiCH2SiMe3 to form 2 and(Me3SiCH2)3Ta=CHSiMe3(6), respectively. The reaction of 9 withLiSi(SiMe3)3(THF)3 toformthe silyl alkylidene complex 2 follows a pathwaydifferent from the reaction of(Me3ECH2)4TaCl (E = C, Si) with LiCH2EMe3 to formalkyl alkylidene complexes(Me3ECH2)2Ta=CHEMe3. The decomposition of 9 wasfound to follow first-order kinetics, with
H
=17.2(1.0) kcal/mol and S = -4(4)eu, and give an unstable dimeric alkylidene complex(Me3SiCH2)4(Cl)2Ta(=CHSiMe3)2(12). The reaction between 9 andLiSi(SiMe3)3(THF)3toform 2 and HSi(SiMe3)3 wasobserved to follow first-order kinetics, and the reactionrateswere independent of the concentration ofLiSi(SiMe3)3(THF)3.In addition, the rates of thisreaction (k2) are almost equal to the rates ofthe decomposition of 9 (k1).These results areconsistent with the presence of"(Me3SiCH2)2Ta(=CHSiMe3)Cl"as an intermediate in theconversion of 9 to 2. Kinetic andmechanistic studies of the formation of 2 will bediscussed.A thermodynamic analysis of the preferential silane eliminationshows that this preferencemay not be thermodynamic in origin, and could be attributedto a kinetic effect.
-ligands such as cyclopentadienyl (Cp), wereprepared through thereactions of(Me3ECH2)3TaCl2with 2 equiv ofLiSi(SiMe3)3(THF)3.An unprecedentedpreferential elimination of silaneHSi(SiMe3)3 leads to the formation of thealkylidene bondsin 1 and 2. An intermediate(Me3SiCH2)3Ta(Cl)Si(SiMe3)3(9) was observed in the formationof 2. 9 was found to react withLiSi(SiMe3)3(THF)3 andLiCH2SiMe3 to form 2 and(Me3SiCH2)3Ta=CHSiMe3(6), respectively. The reaction of 9 withLiSi(SiMe3)3(THF)3 toformthe silyl alkylidene complex 2 follows a pathwaydifferent from the reaction of(Me3ECH2)4TaCl (E = C, Si) with LiCH2EMe3 to formalkyl alkylidene complexes(Me3ECH2)2Ta=CHEMe3. The decomposition of 9 wasfound to follow first-order kinetics, withH =17.2(1.0) kcal/mol and S = -4(4)eu, and give an unstable dimeric alkylidene complex(Me3SiCH2)4(Cl)2Ta(=CHSiMe3)2(12). The reaction between 9 andLiSi(SiMe3)3(THF)3toform 2 and HSi(SiMe3)3 wasobserved to follow first-order kinetics, and the reactionrateswere independent of the concentration ofLiSi(SiMe3)3(THF)3.In addition, the rates of thisreaction (k2) are almost equal to the rates ofthe decomposition of 9 (k1).These results areconsistent with the presence of"(Me3SiCH2)2Ta(=CHSiMe3)Cl"as an intermediate in theconversion of 9 to 2. Kinetic andmechanistic studies of the formation of 2 will bediscussed.A thermodynamic analysis of the preferential silane eliminationshows that this preferencemay not be thermodynamic in origin, and could be attributedto a kinetic effect.