Synthesis of Molybdenum(VI) Neopentylidene Neopentylidyne Complexes

Mo(C-t-Bu)(CH-t-Bu)(Cl)(PMe₂Ph)₂ (1) was prepared as off-white crystals in 26% yield through addition of 2.5 equiv of Mg(CH₂-t-Bu)₂ to Mo(O)[OC(CF₃)₃]₄ in diethyl ether followed by 3 equiv of PMe₂Ph and a workup that includes dichloromethane (the source of Cl). Compound 1 is largely a syn isomer initially that equilibrates to give approximately a 1:1 mixture of syn and anti isomers within 1-2 h. Compound 1 reacts with Li(3,5-dimethylpyrrolide) to give Mo(C-t-Bu)(CH-t-Bu)(η¹-Me₂Pyr)(PMe₂Ph)₂ (2a) as a pale yellow solid in 76% yield, and 2a reacts with Ph3SiOH to give a mixture of syn and anti Mo(C-t-Bu)(CH-t-Bu)(OSiPh3)(PMe₂Ph)₂ (3a) in 84% yield. All three compounds tend to lose PMe2Ph to give 14e monophosphine complexes with the formulas Mo(C-t-Bu)(CH-t-Bu)(X)(PMe₂Ph) (X = Cl, Me₂Pyr, or OSiPh₃), none of which could be isolated. X-ray studies show the structures of 1, 2a, and 3a to be analogous with τ values of 0.45, 0.53, and 0.69, respectively.