Acidic and basic properties of the hydroxycarbonyl complex [IrCl2(CO2H)(CO)(PMe2Ph)2]

Abstract

The hydroxycarbonyl compound [IrCl₂(CO₂H)(CO)(PMe₂Ph)₂](1), formed by the rapid reaction of water with the dicarbonyl cation [IrCl₂(CO)₂(PMe₂Ph)₂]⁺, behaves both as an acid and as a base. The base-catalysed decarboxylation to give [Ir(H)Cl₂(CO)(PMe₂Ph)₂] occurs via the compound [IrCl(CO)(PMe₂Ph)₂], but low-temperature ³¹P and ¹H n.m.r. experiments have failed to identify any intermediate such as [IrCl₂(CO₂)(CO)(PMe₂Ph)₂]^– or [IrCl(CO₂)(CO)(PMe₂Ph)₂]. The decarboxylation of such species very rapidly follows deprotonation of the hydroxycarbonyl even at –90 °C. Treatment of (1) with HBF₄·Et₂O leads to dehydroxylation with no observable intermediates whereas CF₃CO₂H reacts initially to give a new species which only gives [IrCl₂(CO)₂(PMe₂Ph)₂]⁺ with an excess of acid present. This cation exists in solution in two forms. Acetic acid, in contrast, leads to decarboxylation.