Complexes of the platinum metals. Part 30. Fragmentation reactions of rhodium and iridium trichloro-and tribromo-acetates

Abstract

The nitrosyl complexes [M(NO)(PPh₃)₃](M = Rh or Ir) react readily with trichloroacetic acid in acetone solution at ambient temperature to afford the dichloro-complexes [MCl₂(NO)(PPh₃)₂] in excellent yield. The rhodium-based reaction performed at ca. 0 °C and quickly worked-up affords the carboxylate complex [Rh(O₂CCCl₃)₂(NO)(PPh₃)₂] which is stable in pure acetone, but rapidly converts to the dichloride [RhCl₂(NO)(PPh₃)₂] when free trichloroacetic acid and triphenylphosphine are introduced to the solution. The complexes [MCl(CO)(PPh₃)₂], [MH(CO)(PPh₃)₃], mer-[IrH₃(PPh₃)₃], and [RhCl(PPh₃)₃] also react with trichloroacetic acid to form trichloroacetates which undergo similar ligand fragmentation reactions. Reaction pathways involving formation of CCl₃^–, Cl^–, :CCl₂, and CO₂ fragments are outlined; hydrolysis of dichlorocarbene affords carbonyl ligands. Similar reactions have been observed with tribromoacetic acid.