A Density Functional Study of Ethene Hydrogenation Reactions Catalyzed by Titanocene Complexes

Abstract

Density functional calculations have been carried out to investigate the mechanisms of ethene hydrogenation reactions catalyzed by four different titanocene complexes, Cp2Ti(CO)2, Cp2Ti(CH3)2, Cp2Ti(C6H5)2, and Cp2Ti(p-C6H4CH3)2 (Cp: cyclopentadienyl group = η5-C5H5). The molecular geometries of the ground and transition states in these reactions have also been evaluated. The hybrid density functional method B3PW91 showed the best agreement with the experimental geometries of Cp2Ti(CO)2. B3PW91 computations of activation parameters for the thermal decomposition of Cp2TiMe2 also showed good agreement with previous experimental data on a similar complex, (η5-C5Me5)2TiMe2. Ethene hydrogenation by Cp2Ti(CO)2 proceeds in the following order: first and second bond dissociations of Ti−C(CO) bonds followed by the formation of Cp2TiH2 from (Cp2Ti + H2) and then ethene hydrogenation by Cp2TiH2. B3PW91 computations indicated that continuous heating of the system is necessary until the activation barrier of ethene ...