化学学报 ›› 2004, Vol. 62 ›› Issue (16): 1503-1508. 上一篇    下一篇

研究论文

取代基对有机钨化合物中α-氢转移势垒的影响

王长生, 刘阳, 齐学洁   

  1. 辽宁师范大学化学系, 大连, 116029
  • 投稿日期:2003-09-01 修回日期:2004-04-18 发布日期:2014-02-17
  • 通讯作者: chwangcs2003@yahoo,com.cn
  • 作者简介:王长生:E-mail:chwangcs2003@yahoo,com.cn
  • 基金资助:
    国家自然科学基金(No.20173025),辽宁省科学技术基金和辽宁省教育厅基金资助项目.

Effect of Substitutes on the Reaction Barriers of α-Hydrogen Shift Reactions in Organotungsten Complexes

WANG Chang-Sheng, LIU Yang, QI Xue-Jie   

  1. Department of Chemistry, Liaoning Normal University, Dalian 116029
  • Received:2003-09-01 Revised:2004-04-18 Published:2014-02-17

使用密度泛函理论的B3LYP方法,以有机过渡金属钨化合物中的α-氢转移反应为研究对象,探讨不同位置上不同的取代基对α-氢转移反应势垒影响.确定了反应物、产物和过渡态的几何构型和反应势垒.研究结果表明,过渡金属钨有机化合物中,发生α-氢转移的碳原子在过渡态中采用sp2杂化.取代基对α-氢转移势垒的影响取决于取代基对过渡态中碳原子的未参与sp2杂化的pz轨道上单电子的离域作用.R1,R2位置上为氢原子时,由于H的s轨道与过渡态中单电子所占领的碳原子的Pz轨道对称性不匹配,没有有效的成键作用,所以此时α-氢转移反应有最大的反应势垒.当R1,R2位置是Me基团时,由于碳原子的Pz轨道与甲基的一个C-H键轨道对称性匹配,存在强的超共轭效应,从而可以最大程度地降低α-氢转移过程的反应势垒.对于R3,R4位置,相比于本研究中的其他基团,SiH3与金属原子轨道间的有效成键作用最大,所以当R3,R4位置是SiH3基团时,可以最大程度地降低α-氢转移过程的反应势垒.

关键词: 过渡金属钨有机化合物, 氢转移反应, 超共轭效应

The theoretical studies on a series of α-hydrogen shift reactions of the organometallic tungsten complexes were carried out with the density functional theory B3LYP method.The optimal structures of the reactants, transition states and the products were determined.Calculated results indicate that in all of the 12 transition states studied in this work the sp2 hybridization has been adopted by the central carbon atoms, from which the hydrogen atom has shifted.Both electron donating group and electron withdrawing group, that delocalize the unpair electron in pz orbital of the carbon atom in some way, will lead to a lower reaction barrier.There exists the highest barrier when the substituent in the position R1 or R2 is a hydrogen atom, because the 1s orbital of hydrogen atom cannot lead to an effective match with the pz orbital of the central carbon atom.The most preferable substituents are methyl groups for positions R1 and 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 in methyl group.For the positions R3 and R3 the most favorite substituents are silyl groups SiH 3, which stablize the unpair electron of the central carbon atom by the orbital interaction through the metal atom.

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