Bimolecular Substitution in Octahedral Transition Metal Ions, and the Concept of Amphiphilicity

Abstract

THE problem of assigning mechanisms to certain octahedral substitution reactions has been complicated by two principal ambiguities. If the reacting complex has acidic protons on the non-participating groups, second-order kinetics resulting from substitution by basic anions may indicate either an S_N² or an S_N¹CB mechanism, and, in general, it is difficult to distinguish the two. With non-basic substituting anions or systems without extractable protons, first order kinetics may indicate either an S_N¹ mechanism or substitution involving preliminary bimolecular solvent intervention. The compound cis-bis-pyridino-bis-o-phenanthroline ruthenium II perehlorate, cis-[Ru phen₂ py₂] (ClO₄)₂, has no extractable protons, and therefore should give a unique answer to the first ambiguity; and it was hoped that dry solvent acetone would not engage in preliminary bimolecular substitution.