Systematic Kinetic Studies of Associative and Dissociative Reactions of Substituted Metal Carbonyl Clusters: The Intimate Mechanisms

Abstract

Systematic kinetic studies¹ of associative reactions² of metal carbonyl clusters can provide reactivity profiles that are as usefully characteristic of the clusters as their crystal structures. A given cluster can be quantitatively characterized by its sensitivity to the electronic and steric nature of a series of P-donor nucleophiles,² by is standard or “intrinsic” reactivity (I.R.) towards nucleophilic attack,² and by the distribution between substitution and fragmentation products formed as a consequence of nucleophilic attack.³ Thus the electronic and steric profiles for associative reactions of Ru₃(CO)₁₁L show that bond-making in the transition states decreases along the series L = P(OEt)₃ > CO > P-n-Bu₃ and this correlates with increasing intrinsic reactivities of the clusters. This must result from a balance between opposing steric and electronic effects but the exact way in which these operate is not yet clear.