Chemistry of phosphido-bridged dimolybdenum complexes. Part 5. Synthesis and protonation of a phosphido-bridged dimolybdenum complex containing a terminal alkyne ligand: X-ray crystal structures of [Mo2(µ-PPh2)2(CO)(η-C2Me2)(η-C5H5)2] and [Mo2(µ-Co)(µ-PPh2){µ-Ph2PC(Me)CHMe}(η-C5H5)2][BF4]

Abstract

The reaction between the alkyne complex [Mo₂(µ-C₂Me₂)(CO)₄(η-C₅H₅)₂] and P₂Ph₄ in refluxing toluene affords a 42% yield of [Mo₂(µ-PPh₂)₂(CO)(η-C₂Me₂)(η-C₅H₅)₂]. An X-ray diffraction study has revealed that the but-2-yne ligand is co-ordinated to only one molybdenum atom, and that the molecule contains a planar Mo₂(µ-PPh₂)₂ unit with a formal Mo–Mo double bond of length 2.865(1)Å. Several other minor products are discussed in relation to the proposed mechanism of the reaction. Reaction of the terminal alkyne complex with HBF₄·OEt₂ causes a structural rearrangement in which the protonated but-2-yne is inserted into one of the Mo–P bonds to give a bridging Ph₂PC(Me)CHMe vinylphosphine ligand; the structure of the product has been confirmed by X-ray diffraction.