Evaluation of Enantiomerically Pure Binaphthol-Based Molybdenum Catalysts for Asymmetric Olefin Metathesis Reactions that Contain 3,3‘-Diphenyl- or 3,3‘-Dimesityl-Substituted Binaphtholate Ligands. Generation and Decomposition of Unsubstituted Molybdacyclobutane Complexes

Abstract

Enantiomerically pure molybdenum imido alkylidene complexes were prepared that contain binaphtholate ligands substituted in the 3 and 3‘ positions with either phenyl (4; Mo(NAr)(CHCMe2Ph)[Ph](THF)) or 2,4,6-trimethylphenyl groups (5; Mo(NAr)(CHCMe2Ph)[Mes](THF); Ar = 2,6-i-Pr2C6H3). Compound 5 was found to be an anti trigonal bipyramidal complex in an X-ray study. Asymmetric metatheses employing complex 5 were found to proceed to high conversion and to give high product % ee, while reactions that employed complex 4 were found to give lower conversion and lower % ee. One ring-closing reaction with 5 was shown to take place at a rate that was proportional to catalyst and substrate. Molybdacyclobutane complexes were observed in solution during ring-closing reactions. The molybdacyclobutane complex generated by treating 5 with ethylene was found to be a trigonal bipyramidal species which decomposed to yield some propylene; the metal-containing product or products of decomposition could not be identified. Moly...