Complexes of the platinum metals. Part 24. The role of dioxygen in the reactions of trifluoroacetic acid with the rhodium and iridium nitrosyls [M(NO)(PPh3)3]

Abstract

The role of dioxygen in the conversion of the nitrosyls [M(NO)(PPh₃)₃](M = Rh or Ir) to the nitrosyl trifluoroacetates [M (O₂CCF₃)₂(NO)(PPh₃)₂] by trifluoroacetic acid, CF₃CO₂H, under aerobic conditions has been investigated by n.m.r. spectroscopy and gas uptake/evolution measurements. The rhodium reaction has been shown to proceed rapidly to completion in the presence of air with the consumption of a stoicheiometric amount of dioxygen (one mole per mole of complex) but occur only slowly and inefficiently under anaerobic conditions. In contrast, the corresponding iridium reaction occurs quite readily under anaerobic conditions. Mechanisms are proposed for these reactions and a similar dioxygen dependence in the reaction of [Pt(PPh₃)₄] with acetic acid is discussed.