Reaction mechanisms of metal–metal bonded carbonyls. Part VIII. Substitution reactions of cyclo-tris(tetracarbonylruthenium)(3Ru–Ru)

Abstract

Reactions of cyclo-tris(tetracarbonylruthenium)(3Ru–Ru), (I), with some phosphorus- and arsenic-donor ligands (L), mainly in decalin, have been studied over a range of temperature. Observed pseudo-first-order rate constants obey the rate equation k_obs=k₁+k₂[L] and activation parameters have been obtained. Values of log k₂ obey a moderately good linear free-energy relation when plotted against corresponding values of Δ(h.n.p.)(the relative half-neutralization potentials for titration of the nucleophiles with perchloric acid in nitromethane), but those for triphenyl- and tricyclohexyl-phosphine lie well below the line. The use of such relations, and of deviations from them, in indicating the relative contributions of bond making in reactions of a wide variety of metal carbonyl complexes is described and compared with other methods. Reactions of complex (I) appear to involve an exceptionally high degree of bond making. The relative strengths of carbonyl and phosphorus-donor ligands as nucleophiles in attacking vacant co-ordination sites in several complexes are also considered.