Molybdenum imido alkylidene complexes containing biphen ligands that have silyl groups attached through the 6 and 6′ methyl group carbon atoms

Two new biphenolate ligands were prepared starting from 3,3'-di-tert-butyl-5,5',6,6'-tetramethyl-2,2'-dimethoxy-1,1'-biphenyl via deprotonation of the 6 and 6' methyl group with KO-t-Bu/n-BuLi, reaction with dichlorodimethylsilane or chlorotrimethylsilane, and deprotection with boron tribromide. Molybdenum imido alkylidene complexes were prepared by treating Mo(NAr)(CHCMe2Ph)(OTf)(2)(DME) with the dipotassium salt of each biphenolate. X-ray crystallographic studies of syn-Mo(NAr)(CHCMe2Ph)[(rac)-Me(2)SiBiphen] and syn-Mo(NAr)(CHCMe2Ph)[(rac)-TMS(2)Biphen] revealed a significantly different geometry of the biphenolate ligands compared to previously structurally characterized four-coordinate biphenolate molybdenum imido alkylidene complexes. The enantiopure complexes were shown to catalyze asymmetric olefin metathesis with an enantioselectivity comparable to that of Mo(NAr)(CHCMe2Ph)[(S)-Biphen].