Reactions of a Dicarbenium Fulvalenyl Complex with Aromatic Nucleophiles and Synthesis of (μ-Alkyne)(fulvalenyl)tetracarbonyldimolybdenum Compounds:  A Structure−Reactivity Relationship

The compound [FvMo2(CO)4(μ-η3:η3-CH2C⋮CCH2)][BF4]2 (3) reacts with weak nucleophiles to give the related carbenium complexes [FvMo2(CO)4(μ-η2:η3-CH2C⋮CCH2Nu)][BF4] (Nu = −C6H4OH, −C6H4OMe), where attack occurs exclusively on one carbenium center (−CH2 +). Subsequent treatment by NaBH4 reduces the second carbenium center (−CH2 +) to yield the disubstituted alkyne fulvalenyl adducts. The difference in reactivity between 3 and the analogous dicarbenium Cp system [Cp2Mo2(CO)4(μ-η3:η3-CH2C⋮CCH2)][BF4]2 is attributed to the fulvalene effect.