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]

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)A. 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.

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