Reactivity of co-ordinated ligands. Part XX. Preparation and reactions of cyclo-octadiene complexes of iron, ruthenium, and osmium

The complexes tricarbonyl(η-cyclo-octa-1,5-diene)ruthenium, (I), and tricarbonyl(η-cyclo-octa-1,3-diene)osmium, (II), have been prepared and their reactivities examined and compared to those of the corresponding iron complexes. On reaction with Ph3CBF4 hydride-ion abstraction occurs to give cyclo-octadienylium complexes [(C8H11)M(CO)3]+. These react with anionic nucleophiles to give neutral complexes, some of which contain η-allyl groups and metal–carbon σ-bonds. Catalytic isomerisations of cyclo-octa-1,5-diene have been studied as well as those of the diene complexes, a novel ring contraction being observed in one case. Substitution of a carbonyl ligand by PPh3 has been observed for the η-allyl complexes of iron and ruthenium, and a carbonylation reaction to give bicyclo[4.2.1] non-2-en-9-one is also described.