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.