Catalysis by rhodium(I) in nucleophilic substitutions at rhodium(III)

Abstract

The rates of halogen interchange in trans-[Rh(py)₄X₂]⁺(X = Cl or Br; py = pyridine) have been found to be markedly inhibited by oxygen and to be catalysed by both primary and secondary alcohols. No corresponding effect has been observed for the related ethylenediamine complexes trans-[Rh(en)₂X₂]⁺: in this case catalytic halogen interchanges are induced only by the presence of stronger reducing agents. The mechanisms of these catalytic reactions are discussed and evidence is presented which shows the active catalyst to be a Rh^I species which is formed via a Rh^III–H intermediate.