Coupling Reactions of Carbon Dioxide with Epoxides Catalyzed by Vanadium Aminophenolate Complexes.

A series of vanadium compounds supported by tetradentate aminobis(phenolate) ligands were screened for catalytic reactivity in the reaction of propylene oxide (PO) with CO2 : [VO(OMe)(O2 NOBuMeMeth )], [VO(OMe)(ON2 OBuMe )], [VO(OMe)(O2 NNBuBuPy )], and [VO(OMe)(O2 NOBuBuFurf )]. They showed similar reactivities, but reaction rates were higher for [VO(OMe)(ON2 OBuMe )], which was studied in more detail. Turnover frequencies for conversion of PO over 500 h-1 were observed. Activation energies were determined experimentally through in situ IR spectroscopy for propylene carbonate (48.2 kJ mol-1 ), styrene carbonate (45.6 kJ mol-1 ), and cyclohexene carbonate (54.7 kJ mol-1 ) formation.