Syntheses of Molybdenum and Tungsten Imido Alkylidene Complexes that Contain a Bidentate Oxo/Thiolato Ligand

3,3′,5,5′-Tetra-tert-butyl-2′-sulfanyl1,1′-biphenyl]-2-ol (H₂^tBu₄OS]) was prepared in 24 % yield overall from the analogous biphenol using standard techniques. Addition of H₂^tBu₄OS] to Mo(NAr)(CHCMe₂Ph)(2,5-dimethylpyrrolide)₂ led to formation of Mo(NAr)(CHCMe₂Ph)^tBu₄OS], which was trapped with PMe₃ to give Mo(NAr)(CHCMe₂Ph)^tBu₄OS](PMe₃) ( 1 (PMe₃)). An X-ray crystallographic study of 1 (PMe₃) revealed that two structurally distinct square pyramidal molecules are present in which the alkylidene ligand occupies the apical position in each. Both 1 (PMe₃)_A and 1 (PMe₃)_B are disordered. Mo(NAd)(CHCMe₂Ph)(^tBu₄OS)(PMe₃) ( 2 (PMe₃); Ad=1-adamantyl) and W(NAr)(CHCMe₂Ph)(^tBu₄OS)(PMe₃) ( 3 (PMe₃)) were prepared using analogous approaches. 1 (PMe₃) reacts with ethylene (1 atm) in benzene within 45 minutes to give an ethylene complex Mo(NAr)(^tBu₄OS)(C₂H₄) ( 4 ) that is isolable and relatively stable toward loss of ethylene below 60 °C. An X-ray study shows that the bond distances and angles for the ethylene ligand in 4 are like those found for bisalkoxide ethylene complexes of the same general type. Complex 1 (PMe₃) in the presence of one equivalent of B(C₆F₅)₃ catalyzes the homocoupling of 1-decene, allyltrimethylsilane, and allylboronic acid pinacol ester at ambient temperature. 1 (PMe₃), 2 (PMe₃), and 3 (PMe₃) all catalyze the ROMP of rac-endo,exo-5,6-dicarbomethoxynorbornene (rac-DCMNBE) in the presence of B(C₆F₅)₃, but the polyDCMNBE that is formed has a random structure.