Regioselective Cis Insertion of DMAD into Au–P Bonds: Effect of Auxiliary Ligands on the Reaction Mechanism

Abstract

The cis insertion of dimethyl acetylenedicarboxylate (DMAD, 2) into the Au–P bond of Au(SAr)(PAr′3) (1) occurs selectively at room temperature to give adduct 3, whose X-ray crystallographic analysis exhibits the predominant character of an alkenylphosphorus zwitterion complex. The first-order kinetics with respect to 1 and 2 and the large negative value of ΔS⧧ indicate that the reaction proceeds through the coordination of 2 to 1 followed by a concerted inner-sphere nucleophilic attack of PPh3 on the coordinated triple bond. In contrast, Au(Cl)(PPh3) (4) does not react with 2 even at 60 °C. However, the tricoordinated 16-electron complex Au(Cl)(PPh3)2 (5) quite successfully reacts with 2 to produce insertion product 6, demonstrating that two PPh3 ligands are required for the reaction.