取代基对有机金属钽化合物中分子内α-H转移势垒的影响

Effects of Substituents on the Reaction Barriers of the Intramolecular α-Hydrogen Transfer in Organometallic Tantalum Complexes

运用B3LYP方法研究了有机钽化合物中分子内α-氢转移反应,探讨了不同取代基对α-氢转移反应势垒的影响.确定了反应物、过渡态和产物的几何构型和反应势垒.结果表明,过渡金属钽有机化合物中,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杂化的pz轨道上单电子的离域作用.Ta(CH3)4CH(SiMe3)2的α-氢转移反应势垒最低.

Theoretical calculations on a series of intramolecular α-hydrogen transfer reactions for organometallic tantalum complexes were carded out using the B3LYP method. Optimal structures for reactants, transition states, and products were located. Calculated results indicate that sp^2 hybridization is adopted by the central carbon atoms, from which the hydrogen atom shifts, for all 16 transition states. Both electron donating groups and electron withdrawing groups will delocalize the unpaired electron in the pz orbital of the central carbon atom in some way and will thus result in a lower reaction barrier. The reaction barrier of Ta（CH3）4CH（SiMe3）2 had the lowest value.