Molecular Mechanics Force Field for Octahedral Organometallic Compounds with Inclusion of the Trans Influence

Efficient calculation of the properties of metal-containing complexes relevant to catalysis is of major interest for better characterizing and optimizing the catalysts. For this, a new force field, called VALBOND-TRANS here, is proposed. It is based on the existing VALBOND force field of Landis and co-workers, extended by adding terms that account for electronic effects such as the trans influence of ligands on bond lengths and relative energies. Parameters and results for model octahedral complexes of Ru, Os, Rh, and Ir are determined and discussed. The model is then applied to the study of reactive intermediates involved in asymmetric hydrogenation catalyzed by iridium complexes with chiral phosphinooxazolines (PHOX) ligands. The new force field explores and capitalizes on the separation of electronic and steric effects on the stability of different diastereomers and reproduces DFT results which are consistent with experimental observations.