Ring expansion of a Cp moiety upon CO insertion: Synthesis and characterization of [(η6-C6H5OCo)Co3(CO)9]

Reaction of [(CpV)2(B2H6)2], 1 (Cp = η5-C5H5) with four equivalents of [Co2(CO)8] or [Co4(CO)12] in hexane at 70 °C leads to the isolation of the tetranuclear carbonyl cluster, [(η6-C6H5OCo)Co3(CO)9], 2 in modest yield. The geometry of 2 is similar to that of [Co4(CO)12] where all the four Co atoms are arranged in a tetrahedral geometry. The apical cobalt atom in 2 is coordinated to C6H5O ring in a η6-fashion and the other three cobalt atoms are each coordinated to three carbonyl ligands. Compound 2 has been characterized in solution by IR, 1H, 13C NMR and mass spectrometry and the structural types were unequivocally established by crystallographic analysis.