Terminal vanadium - Neopentylidyne complexes and intramolecular cross-metathesis reactions to generate azametalacyclohexatrienes

被引:64
作者
Basuli, F
Bailey, BC
Brown, D
Tomaszewski, J
Huffman, JC
Baik, MH [1 ]
Mindiola, DJ
机构
[1] Indiana Univ, Sch Informat, Dept Chem, Bloomington, IN 47405 USA
[2] Indiana Univ, Ctr Mol Struct, Bloomington, IN 47405 USA
关键词
D O I
10.1021/ja0472376
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
Four-coordinate vanadium complexes containing a terminal neopentylidyne functionality have been prepared by two consecutive α-hydrogen abstraction reactions both of which were induced by one-electron oxidations. Among these vanadium-alkylidyne complexes are the neutral and the cation (Nacnac)V≡CtBu(OTf) and [(Nacnac)V≡CtBu(THF)]+, respectively (Nacnac- = [Ar]NC(CH3)CHC(CH3)N[Ar], Ar = 2,6-(CHMe2)2C6H3). The vanadium-alkylidynes have been characterized by 1H, 13C, 51V NMR spectroscopy and single-crystal X-ray diffraction and are consistent with a short VC bond. These alkylidynes were found to transform to azametalacyclohexatriene systems via an intramolecular cross-metathesis reaction. Kinetic studies of the transformation of (Nacnac)V≡CtBu(OTf) in C7D8 reveal the formation of the azametalacyclohexatriene to be independent of solvent (toluene vs THF) and the reaction to be first order in vanadium (k = 3.30(5) × 10-5 s-1 at 80 °C, with activation parameters ΔH‡= 25.4(3) kcal/mol, ΔS‡ = -6(3) cal/molK). High-level DFT calculations on the full model suggest an intramolecular mechanism invoking only one transition state. The overall thermodynamic driving force for the reaction (ΔG) in solution phase was estimated to be -21.3 kcal/mol. Copyright © 2004 American Chemical Society.
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页码:10506 / 10507
页数:2
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