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3,3′,5,5′‐Tetra‐tert‐butyl‐2′‐sulfanyl[1,1′‐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)₂led to formation of Mo(NAr)(CHCMe₂Ph)[^tBu₄OS], which was trapped with PMe₃to give Mo(NAr)(CHCMe₂Ph)[^tBu₄OS](PMe₃) (1(PMe₃)). An X‐ray crystallographic study of1(PMe₃) revealed that two structurally distinct square pyramidal molecules are present in which the alkylidene ligand occupies the apical position in each. Both1(PMe₃)_Aand1(PMe₃)_Bare 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 in4are like those found for bisalkoxide ethylene complexes of the same general type. Complex1(PMe₃) in the presence of one equivalent of B(C₆F₅)₃catalyzes the homocoupling of 1‐decene, allyltrimethylsilane, and allylboronic acid pinacol ester at ambient temperature.1(PMe₃),2(PMe₃), and3(PMe₃) all catalyze the ROMP ofrac‐endo,exo‐5,6‐dicarbomethoxynorbornene (rac‐DCMNBE) in the presence of B(C₆F₅)₃, but the polyDCMNBE that is formed has a random structure.

We synthesized Mo(NC₆F₅)(CHCMe₂Ph)(TPPO)(PPhMe₂)Cl (TPPO= 2,3,5,6‐tetraphenylphenoxide), Mo(NC₆F₅)(CHCMe₂Ph)(TTBTO)(PPhMe₂)Cl (TTBTO= 2,6‐di(3′,5′‐di‐tert‐butylphenyl)phenoxide), and Mo(NC₆F₅)(CHCMe₂Ph)(TPPO)(PPhMe₂)(CF₃Pyr) (CF₃Pyr = 3,4‐bistrifluoromethylpyrrolide), in order to evaluate them as catalysts for the homocoupling of 3‐methyl‐1‐butene. They were compared with Mo(NC₆F₅)(CHCMe₂Ph)(HMTO)(PPhMe₂)Cl (HMTO= 2,6‐dimesitylphenoxide), Mo(NC₆F₅)(CHCMe₂Ph)(HIPTO)(PPhMe₂)Cl (HIPTO= 2,6‐di(2′,4′,6′‐triisopropylphenyl)phenoxide), and several other Mo and Ru catalysts. In the best cases turnover numbers (TONs) of 400 – 700 were observed for the homocoupling of 3‐methyl‐1‐butene in a closed vessel (ethylene not removed).