Probing the evolution of an Ar-BINMOL-derived salen-Co(III) complex for asymmetric Henry reactions of aromatic aldehydes: salan-Cu(II) versus salen-Co(III) catalysis

A new type of chiral salen-Co catalyst that features aromatic p-walls and an active Co(III) center has been developed for enantioselective Henry/nitroaldol reactions on the basis of salen-Cu catalysis. The asymmetric Henry reaction of aromatic aldehydes and nitromethane catalyzed by an Ar-BINMOL derived salen-Co(III) complex was achieved with high yields (up to 93%) and excellent enantioselectivities (up to 98% ee). And more interestingly, it was supposed that either salan-Cu(II) or salen-Co(III) complex catalyzed Henry reaction was an ideal model reaction for providing direct evidence of noncovalent interaction due to the distinguishable ortho-substituted aromatic aldehydes from meta-or parasubstituted benzaldehydes in terms of enantioselectivities and yields.