New Chiral Molybdenum Catalysts for Asymmetric Olefin Metathesis that Contain 3,3‘-Disubstituted Octahydrobinaphtholate or 2,6-Dichlorophenylimido Ligands

Abstract

Optically pure (R)-5,5‘,6,6‘,7,7‘,8,8‘-octahydro-1,1‘-bi-2-naphthol was derivatized with mesityl and benzhydryl groups in the 3 and 3‘ positions to give R-H2Mes2Bitet and R-H2Benz2Bitet, respectively. Addition of R-K2Benz2Bitet to Mo(NAr)(CHCMe2Ph)(OTf)2(dme) yielded Mo(NAr)(CHCMe2Ph)(R-Benz2Bitet)(THF) (7), while addition of R-K2Mes2Bitet to Mo(NAr)(CHCMe2Ph)(OTf)2(dme) in THF gave Mo(NAr)(CHCMe2Ph)(R-Mes2Bitet)(THF) (8). Four complexes that contained the 2,6-dichlorophenylimido ligand were prepared by similar procedures, namely, Mo(NArCl)(CHCMe3)(S-Biphen)(THF) (9), Mo(NArCl)(CHCMe3)(R-Trip2BINO)(THF) (10), Mo(NArCl)(CHCMe3)(R-Mes2Bitet)(THF) (11), and Mo(NArCl)(CHCMe3)(R-Benz2Bitet)(THF) (12). X-ray studies of 8, 9, and 12 revealed them to be typical distorted trigonal bipyramids with THF and one biphenolate oxygen occupying axial positions. In 9 and 12 the alkylidene orientation was found to be syn, while in 8 the alkylidene orientation was found to be anti. Catalysts 7, 8, 9, 10, 11, and 12 were all efficient in terms of both conversion and % ee for two standard desymmetrization reactions to form dihydrofurans.