Acta Chimica Sinica ›› 2005, Vol. 63 ›› Issue (15): 1383-1390. Previous Articles     Next Articles

Original Articles

取代基对有机钼化合物中α-氢转移反应势垒和产物稳定性的影响

王长生*,高坤,张艳,刘阳   

  1. (辽宁师范大学化学化工学院 大连 116029)
  • 收稿日期:2004-12-31 修回日期:2005-03-24 出版日期:2005-08-15 发布日期:2010-12-10
  • 通讯作者: 王长生

Effects of Substituents on the Reaction Barriers and the Product Relative Stabilities of the α-Hydrogen Shift Reactions in Organomolybdenum Complexes

WANG Chang-Sheng*, GAO Kun, ZHANG Yan, LIU Yang   

  1. (Department of Chemistry, Liaoning Normal University, Dalian 116029)
  • Received:2004-12-31 Revised:2005-03-24 Online:2005-08-15 Published:2010-12-10
  • Contact: WANG Chang-Sheng

The theoretical studies on a series of α-hydrogen shift reactions between the alkylidene and alkylidyne organometallic molybdenum complexes R3R4Mo(≡CH)(CHR1R2) and R3R4Mo(=CH2)(=CR1R2) were carried out with the density functional theory B3LYP method. The optimal structures of the reactants, transition states, and products were obtained and the reaction barriers and the relative energies of the reactants and products were calculated. Calculated results indicate that in all of the 16 transition states studied in this paper the sp2 hybridization has been adopted by the central carbon atoms, from which the hydrogen atom has been shifted. The reaction barrier will be lowered by the substituents that delocalize the unpair electron in pz orbital of the central carbon atom. The most preferable substituents are methyl groups for positions R1 and/or R2, due to the existence of a hyperconjugation effect between the pz orbital of the central carbon atom and one of the C—H bond orbitals in methyl group. For the positons R3 and R4, the SiH3 group is a favorite substituent. Calculated results also show that the first methyl group lowers the barriers as twice as the second one. The first silyl group lowers the barriers twice more than the second one. The second methyl group for positions R1 and/or R2 stabilizes the product as much as the first one. For positions R3 and/or R4, the first silyl group stabilizes the product while the second one will destabilize it.

Key words: organometallic molybdenum complex, α-hydrogen shift reaction, hyperconjugation effect