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

Abstract

A series of vanadium compounds supported by tetradentate amino-bis(phenolate) ligands were screened for catalytic reactivity in the reaction of propylene oxide (PO) with carbon dioxide, [VO(OMe)(O2NOBuMeMeth)] (1), [VO(OMe)(ON2OBuMe)] (2), [VO(OMe)(O2NNBuBuPy)] (3), and [VO(OMe)(O2NOBuBuFurf)] (4) (where (O2NOBuMeMeth) = MeOCH2CH2N(CH2ArO-)2, Ar = 3,5-C6H2-Me, tBu]; (ON2OBuMe) = -OArCH2NMeCH2 CH2NMeCH2ArO-, Ar = 3,5-C6H2-Me, tBu; (O2NNBuBuPy) = C5H4NCH2N(CH2ArO-)2, Ar = 3,5-C6H2-tBu2; (O2NOBuBuFurf) = C4H3OCH2N(CH2ArO-)2, Ar = 3,5-C6H2-tBu2). They showed similar reactivities but reaction rates were greater for 2, which was studied in more detail. TOF for conversion of PO over 500 h-1 were observed. Activation energies were determined experimentally via 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.