(CO),(p3-CO)(p3-CC (0) CH3)]-(l), an acyl-substituted al-h (cola 1 kylidyne cluster that readily adds Hz or CO to form CH or CC bonds with the apical carbon atom. In either case, the p,-bonding arrangement of the capping CC (0) CH3 group is replaced by one in which the oxygen atom of the acyl participates in bonding to the metal framework. Thus the ketonic group plays a role in determining the chemistry of this anionic alkylidyne cluster by ...