Nature of previously reported thermally unstable products derived from the reaction of [Co2(CO)8] with PhSSPh, EtSSEt or PhSeSePh and of the reactions of these products with alkynes or isocyanides

Thermally unstable red complexes previously isolated from the reaction of [Co2(CO)8] with REER (E = S, R = Ph or Et; E = Se, R = Ph) and assigned the structure [Co3(µ3-ER)(CO)9] have been reformulated as the trinuclear complexes [Co3(µ3-E)R(CO)8] (E = S, R = Ph 1a or Et 1b; E = Se, R = Ph 1c) on the basis of their spectroscopic properties and the nature of their reactions with alkynes and isocyanides. Thus the complexes [Co3(µ3-E)R(CO)8] 1a–1c react with PhCCH to give [Co3(µ3-E){PhCCHC(O)R}(CO)7] 2a–2c respectively (E = S, R = Ph 2a or Et 2b; E = Se, R = Ph 2c). It is proposed that 2a–2c are formed via migration of the R group in 1a–1c from the metal to a carbonyl carbon atom to give an acyl group. Subsequent insertion of PhCCH into the metal–acyl group bond is followed by co-ordination of the acyl oxygen to give a five-membered metallacyclic ring. The reaction of ButNC with 1a–1c gave the complexes [Co3(µ3-E)(µ-ButNCR)(CO)7] 3a–3c respectively (E = S, R = Ph 3a or Et 3b; E = Se, R = Ph 3c) and a similar reaction pathway is proposed. The structures of complexes 2a and 3a have been determined by single-crystal X-ray diffraction studies.