Effective core potential study of transition metal and lanthanide catalyzed hydrogen exchange

Abstract

An effective core potential study of H2 activation by the sigma-bond metathesis mechanism is reported for a range of simple Cl2MH catalyst models: M=Sc, Y, La, Lu, Zr+, B, and Al. Several points of interest are noted. Effective core potentials methods allow the study of metals from the transition, lanthanide and main group series with near equal facility. A single-determinant wavefunction is found to be sufficient for a qualitatively correct description of the ground and transition states in these reactions; changes in optimized geometries are minimal upon inclusion of correlation at the multiconfiguration self-consistent field (MCSCF) level. Calculated barriers are the highest using restricted Hartree-Fock (RHF) and multiconfiguration self-consistent field wavefunctions and lowest using Møller-Plesset second-order perturbation theory and second-order configuration interaction (SOCI) methods. Trends as a function of metal species on H2 activation barriers are consistent for all wavefunctions employed. As MP2 and RHF wavefunctions are most amenable to larger, more experimentally relevant systems, the use of RHF wavefunctions to determine stationary point geometries followed by MP2 calculations to assess their relative energies seems to be an attractive theoretical approach for computational investigations of hydrogenation and important related reactions.