Reaction of H₂ with a binuclear zirconium dinitrogen complex - Evaluation of theoretical models and hybrid approaches

Molecular orbital and hybrid ONIOM (both IMOMO and IMOMM) calculations have been carried out on the important reaction of H₂ with a binuclear zirconium dinitrogen complex to test the efficacy of several structural models of the ancillary ligand. The complete experimental ligand, PhP(CH ₂SiMe₂NSiMe₂CH₂)₂PPh, in the zirconium complex has been treated at the IMOMM level, while two smaller approximations of the ligand, HP(CH₂SiH₂NSiH ₂CH₂)₂PH and (PH₃) ₂(NH₂)₂, have received the full molecular orbital treatment. The mechanism of dihydrogen addition has been compared with our earlier study (Basch, Musaev, and Morokuma J. Am. Chem. Soc. 1999, 121, 5754-5761). We find that the substituent effects do cause some small changes in both the structures of the complexes studied and the activation energies of the transition structures. However for the most part the potential energy profiles are very similar to our earlier study and lend support to our use of simple theoretical models to represent moderately large experimental structures.