Inversion of configuration at the metal in diastereomeric imido alkylidene monoaryloxide monopyrrolide complexes of molybdenum.

The two diastereomers of Mo(NAr)(CHCMe(2)Ph)(2,5-dimethylpyrrolide)(1), (S(M)R(1))-2 and (R(M)R(1))-2, respectively, where 1 is an enantiomerically pure (R) phenoxide and Ar = 2,6-diisopropylphenyl, form adducts with PMe(3). One of these ((R(M)R(1))-2(PMe(3))) has been isolated. An X-ray structure reveals that PMe(3) has added trans to the pyrrolide; it is a model for where an olefin would attack the metal. Trimethylphosphine will catalyze slow interconversion of (S(M)R(1))-2 and (R(M)R(1))-2 via formation of weak PMe(3) adducts. Reactions between (S(M)R(1))-2 or (R(M)R(1))-2 and ethylene yield Mo(NAr)(CH(2))(Me(2)Pyr)(1) species in which the configuration at Mo is inverted by ethylene at a rate of the order of the NMR time scale at 22 degrees C via formation of metallacyclobutane intermediates with imido and aryloxide ligands in axial positions. A reactant olefin is proposed to approach Mo and the product olefin to leave Mo trans to the pyrrolide.