Back to basics: identification of reaction intermediates in the mechanism of a classic ligand substitution reaction on Vaska's complex

Abstract

The mechanism of methylation of Vaska's complex trans-[ClIr(CO)(PPh₃)₂] by trimethylgallium was studied and the identification of the spectroscopically detected intermediates was achieved with the aid of computational methods. The reaction pathway, computed by means of density functional theory (M05-2X-D3/def2-SVP), involves the initial formation of a chloride-bridged adduct trans-[(Cl·GaMe₃)Ir(CO)(PPh₃)₂] to then proceeds to a transition state [(μ₂-Cl,C-ClMeGaMe₂)Ir(CO)(PPh₃)₂]. This transition state subsequently evolves to the methylated adduct [MeIr(CO)(PPh₃)₂·(GaMe₂Cl)] to finally release the alkylated product trans-[MeIr(CO)(PPh₃)₂] together with GaMe₂Cl.