Substitutional Reactivity of Dodecacarbonyltrimetal Complexes of Iron and Osmium

The kinetics of the substitution reactions of Fe₃(CO)₁₂and Os₃(CO)₁₂have been investigated for L = PPh₃, pbu₃, P(OPh)₃, and P(OMe)₃in hydrocarbon solution. The substitution of the iron cluster leads to both substitution and fragmentation products with a very small dependence on the entering ligand, typical of a CO dissociative interchange mechanism. Substitution of Fe₃(CO)₁₁PPh₃leads only to fragmentation at a rate which is faster than substitution on Fe₃(CO)₁₂. Substitution on Os₃(CO)₁₂occurs in an entering ligand independent reaction to Os₃(CO)₉L₃. The reactivities of these clusters are compared to the ruthenium analogue and to the mononuclear complexes M(CO)₅.