Reactions of the cobaltaborane 2,4-{(η5-C5Me5)Co}2B3H7 with metal fragments.: Synthesis and characterization of nido-1-{(η5-C5Me5)Co}-2-{(CO)3Fe}B3H7 and arachno-(η5-C5Me5)(CO)CoB3H7

The reactions of nido-2,4-(Cp*Co)(2)B3H7, 1, Cp* = (eta(5)-C5Me5), with Fe-2(CO)(9) and Co-2(CO)(8) generate seven skeletal electron pair (sep) nido-1-{Cp*Co}-2-((CO)(3)Fe)B3H7, 2, by metal fragment substitution and seven sep arachno-Cp*(CO)CoB3H7, 3, by metal fragment degradation. Both compounds are characterized spectroscopically in solution and with single-crystal X-ray diffraction in the solid state. On the basis of the results and related chemistry, the suggested reaction pathway involves M(CO)(4), M = Fe and Co, coordination to a Co-H-B edge of 1 followed by loss of Cp*Co(CO) which leads to 2. We postulate that the cobalt analogue of 2, which would be an odd-electron species, readily loses a cobalt carbonyl fragment to form 3.