A theoretical study of the photochemical reductive elimination and thermal oxidative addition of molecular hydrogen from and to the Ir-complex

The electronic mechanisms of the cyclic processes of photochemical reductive elimination of H₂ from [IrClH₂(PH₃)₃] and thermal oxidative addition of H₂ to [IrCl(PH₃)₃] are investigated theoretically. The geometries of the ground and excited states are optimized using the Hartree-Fock and single excitation configuration interaction methods, respectively, and higher level calculations for the ground and excited states are carried out by the symmetry adapted cluster (SAC)/SAC-configuration interaction method. The present calculation shows that the reductive elimination of H₂ from [IrClH₂(PH₃)₃] dose not occur thermally but photochemically through diabatic conversion from the lowest A′ excited state to the ground state (A′), while the oxidative addition of H₂ to [IrCl(PH₃)₃] easily proceeds thermally. The lowest ¹A′ excited state involves the nature of the Ir-H₂ antibonding.