Benzimidazolin-2-iminato Hafnium Complexes: Synthesis, Characterization, and Catalytic Addition of Alcohols to Carbodiimides

A series of asymmetric imidazolin-2-iminato and benzimidazolin-2-iminato hafnium(IV) complexes were synthesized and fully characterized including single-crystal X-ray diffraction. The asymmetric imidazolin-2-iminato hafnium complex exhibits a shorter Hf-N bond length as compared with the corresponding benzimidazolin-2-iminato hafnium complex. These complexes were successfully utilized as catalysts for the addition of alcohols to carbodiimides. The synthesis of several active intermediates and kinetics, thermodynamics, and stoichiometric reaction studies allowed us to propose a mechanism for the reaction. The X-ray crystal structure of the monomeric Hf(OtBu)4 is presented.