Trans Influence of Ligands on the Oxidation of Gold(I) Complexes

Gold­(I) complexes are considered active species toward oxidative addition; current understanding indicates a different mechanism in contrast to other late transition metals, but a rational understanding of the reactivity profile is lacking. Herein, we propose that the accessibility of the gold­(I) center to tri- or tetra-coordination is critical in the oxidative process involving a tri- or tetra-coordinate gold­(I) with the oxidizing reagent as one of the ligands as an intermediate. A computational study of the geometry of (Phen)­R3PAu­(I)­NTf2 complexes shows that the accessibility of such tricoordinate species shows a good correlation with the “trans influence” of phosphine ligands: the weak σ-donating phosphine ligands promote tricoordination of gold­(I) complexes. The oxidative addition to the asymmetric tricoordinate (Phen)­R3PAu­(I)­NTf2 complexes with alkynyl hypervalent iodine reagents was built. The kinetic profile of the oxidative addition exhibits a good relationship to the Hammett substituent parameter (ρ = 3.75, R2 = 0.934), in which the gold­(I) complexes bearing less σ-donating phosphine ligands increase the rate of oxidative addition. The positive ρ indicates a high sensitivity of the oxidative addition to the trans influence. The reactivity profile of oxidative addition to a linear bis­(pyridine)­gold­(I) complex further supports that the oxidative addition to gold­(I) complexes is promoted by ligands with small trans influence.