Phosphorus-sulfur bond cleavage at a mixed-metal centre; Reaction of [(OC)₃Co(μ-PhCCH)Mo(CO)₂(η⁵-C ₅H₅)] with PPh₂(SPh)

The bimetallic cobalt-molybdenum complex [(OC)₄CoMo(CO)₃(η⁵-C₅H ₅)] reacted with phenylacetylene in benzene to give the bimetallic alkyne-bridged complex [(OC)₃Co(μ-PhCCH)Mo(CO)₂(η⁵-C ₅H₅)] 1 as the major product and the trimetallic alkylidyne-capped complex [Co₂Mo(μ₃-CCH₂Ph) (CO)₈(η⁵-C₅H₅)] 2 as the minor product. Reaction of 1 with PPh₂(SPh) resulted in substitution of a carbonyl group on the cobalt atom to give [{(PhS)Ph₂P}(OC)₂Co(μ-PhCCH)Mo(CO) ₂(η⁵-C₅H₅)] 3. Thermolysis of 3 in refluxing toluene afforded, as the major product, the complex [η⁵-C₅H₅)(OC)Mo(μ-PPh ₂CH=CPh)(μ-SPh)Co(CO)₂] 4, in which the unsymmetrical alkyne in 3 has been incorporated into a four- membered metallacycle, Mo-PPh₂-CH-CPh, such that the phenyl substituent is positioned on the carbon atom remote from the phosphide group. The related complex [(η⁵-C₅H₅)(OC)Mo(μ-PPh ₂CH=CPh)(μ-SPh)Co(CO)(PPh₃)] 5, in which one of the carbonyl groups on the cobalt atom in 4 has been substituted by a triphenylphosphine ligand, has also been isolated as a minor product from this reaction. Conversion of 4 into 5 has been achieved separately by reaction of 4 with PPh₃. Similarly, reaction of PPh₂(SPh) with 4 yields a related compound [(η⁵-C₅H₅)(OC)Mo(μ-PPh ₂CH=CPh)(μ-SPh)Co(CO){PPh₂(SPh)}] 6, in which the same carbonyl group on the cobalt atom has been substituted by PPh₂(SPh). Single-crystal X-ray diffraction studies have been performed on complexes 2,4 and 6.