Regioselective Cis Insertion of DMAD into Au–P Bonds: Effect of Auxiliary Ligands on the Reaction Mechanism
摘要:
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 Delta S-double dagger 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 degrees 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.