PHOSPHORUS - SULFUR BOND CLEAVAGE AT A MIXED-METAL CENTRE; REACTION OF [(OC)(3)CO(MU-PHCCH)MO(CO)(2)(ETA(5)-C5H(5))] WITH PPH(2)(SPH)

The bimetallic cobalt-molybdenum complex [(OC)(4)CoMo(CO)(3)(eta(5)C(5)H(5))] reacted with phenylacetylene in benzene to give the bimetallic alkyne-bridged complex [(OC)(3)Co(mu-PhCCH)Mo(CO)(2)(eta(5)-C5H5)] 1 as the major product and the trimetallic alkylidyne-capped complex [Co2Mo(mu(3)-CCH(2)Ph)(CO)(8)(eta(5)-C5H5)] 2 as the minor product. Reaction of 1 with PPh(2)(SPh) resulted in substitution of a carbonyl group on the cobalt atom to give [{(PhS)Ph(2)P}(OC)(2)Co(mu-PhCCH)Mo(CO)(2)(eta(5)-C5H5)] 3. Thermolysis of 3 in refluxing toluene afforded, as the major product, the complex [(eta(5)-C5H5)(OC)Mo(mu-PPH2CH=CPh)(mu-SPh)Co(CO)(2)] 4, in which the unsymmetrical alkyne in 3 has been incorporated into a four-membered membered metallacycle, Mo-PPh(2)-CH-CPh, such that the phenyl substituent is positioned on the carbon atom remote from the phosphide group. The related complex [(eta(5)C(5)H(5))(OC)Mo(mu-PPh(2)CH=CPh)(mu-SPh)Co(CO)(PPh(3))] 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 PPh(3). Similarly, reaction of PPh(2)(SPh) with 4 yields a related compound [(eta(5)-C5H5)(OC)Mo(mu-PPh(2)CH=CPh) (mu-SPh)Co(CO){PPh(2)(SPh)}] 6, in which the same carbonyl group on the cobalt atom has been substituted by PPh(2)(SPh). Single-crystal X-ray diffraction studies have been performed on complexes 2, 4 and 6.