Carboranyl diphosphenes: synthesis, structure and reactivity

Carboranyl-diphosphenes {1-P-2-[C(^tBu) = N(Ar)]-1,2-C₂B₁₀H₁₀}₂ [Ar = Dmp (6) or Ph (7); Dmp = 2,6-Me₂C₆H₃, Ph = C₆H₅] are prepared in good yields by the reduction of iminocarboranyldichlorophosphines 1-PCl₂-2-[C(^tBu) = N(Ar)]-1,2-C₂B₁₀H₁₀ [where Ar = Dmp (4) or Ph (5)] with potassium graphite (KC₈) in THF. Compounds 6 and 7 have similar dimeric structures in the solid state as confirmed by single-crystal X-ray analyses. Their solution structures are, however, different on the basis of ³¹P NMR studies, which could be ascribed to the steric effects of Dmp over Ph. As a result, 6 and 7 exhibit different coordination chemistry toward W(CO)₅(THF). On the other hand, they show similar properties with oxidizing agents, giving a variety of phosphorus(III) compounds. The results indicate that 6 dissociates into carboranyl phosphinidene in THF.