Cobalt metallacycles. Part 9. Some reactions of cobaltaindene, cobaltafluorene, cobaltaxanthen, and cobaltacyclopentane complexes

Abstract

The reactivity of the title compounds toward acetylenes, olefins, carbon monoxide, and isocyanides, as well as their behaviour on thermal decomposition, has been examined and compared with those of previously reported cobaltacyclopentadiene and cobaltacyclopentene. In most cases the unsaturated reactant is incorporated into the final organic product. The common first step in the reactant incorporation and the thermal decomposition is dissociation of ligating phosphine, the ease of which markedly depends on the nature of the metallacycle. Molecular orbital calculations on cobaltacyclopentadiene and cobaltacyclopentane have been carried out to interpret their reactivity. The calculated stabilization energy is found to be a good measure of the reactivity. A discussion of the metallaring expansion by insertion of ethylene is based on the concept of overlap populations between relevant carbon atoms.