σ-Bond Metathesis between M–X and RC(O)X′ (M = Pt, Pd; X, X′ = Cl, Br, I): Facile Determination of the Relative ΔG Values of the Oxidative Additions of RC(O)X to an M(0) Complex, Evidence by Density Functional Theory Calculations, and Synthetic Applications

Abstract

The novel utility of the ligand exchange reaction between M–X and RC(O)X′ (X, X′ = halogen; R = aryl, alkyl) is described. The relative ΔGs (ΔΔGs) of the oxidative additions of acid halides RC(O)X to M(PPh3)2Ln (M = Pt, Pd) were determined using the halogen-exchange reactions between X of trans-M(X)[C(O)R](PPh3)2 and X′ of RC(O)X′. Experimental thermodynamics data are reasonably consistent with those obtained by density functional theory (DFT) calculations. Activation parameters obtained by experiments as well as a systematic DFT study supported the fact that reactions occurred through slightly distorted quadrangular pentacoordinated σ-bond metatheses, in which the Cl atom underwent a more indirect course than the Br atom. Moreover, exchange reactions were employed as the accessible prototype for the conversion of halogen ligands of nickel triad complexes into heavier halogen ligands.