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 [Co-2(CO)(8)] with REER (E = S, R = Ph or Et; E = Se, R = Ph) and assigned the structure [Co-3(mu(3)-ER)(CO)(9)] have been reformulated as the trinuclear complexes [Co-3(mu(3)-E)R(CO)(8)] (E = S, R = Ph la 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 [Co-3(mu(3)-E)R(CO)(8)] la-lc react with PhC=CH to give [Co-3(mu(3)-E){PhCCHC(O)R}(CO)(7)] 2a-2c respectively (E = S, R = Ph 2a or Pt 2b; E = Se, R = Ph 2c). It is proposed that 2a-2c are formed via migration of the R group in la-le from the metal to a carbonyl carbon atom to give an acyl group. Subsequent insertion of PhC=CH 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 (BuN)-N-t=C with 1a-1c gave the complexes [Co-3(mu(3)-E)(mu-(BuN)-N-t=CR)(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.