LAUSR

Abstract Synthetic LMoO2 compounds have long been of keen interest both as structural and functional models for molybdoenzymes and in their own right as catalysts for a variety of oxygen atom-transfer (OAT) reactions. Investigations of their use as catalysts for stereoselective OAT transformations, however, are little known. In this study chiral diimine-salen molybdenum complexes, L*MoO2, are evaluated for their potential to catalyze oxidative kinetic resolution of racemic monophosphines by pyridine N-oxide. A set of six L*MoO2 complexes incorporating chiral salen-type Schiff base ligands derived from 1,2-diaminocyclohexane (7-10) and 1,1’-diaminobinapthylene (12) has been prepared and characterized. Compounds 7-10 and 12 are active catalysts for the oxidation of racemic PMePhtBu by pyridine N-oxide, affording low to moderate enantioselectivities (0 - 35 % ee) of the phosphine oxide OPMePhtBu. Key structure/reactivity features of the catalysts for these reactions include: the presence of a p-NO2 substituent on the salen-unit increases the catalyst activity; and increasing the steric bulk of the ortho-salen-substituent increases enantioselectivity. DFT computational analysis has identified a viable reaction pathway that features a stereochemically-defining O-transfer transition state involving phosphine attack on the chiral LMoO2 complex, which accounts for the experimental stereoselectivity and catalyst activity.