Prying open a reactive site for allylic arylation by phosphine-ligated geminally diaurated aryl complexes

Gas-phase ion–molecule reaction experiments, theoretical kinetic modeling, and computational chemistry were used to examine the role of a second gold center in promoting allylic arylation. Geminally diaurated complexes [(L)_<i>n</i>Au₂Ph]⁺ are demonstrated to participate in C–C bond formation reactions with allyl halides, CH₂═CHCH₂X (X = Cl, Br, and I), given a favorable phosphine ligand architecture. Thus, while [(Ph₃P)₂Au₂Ph]⁺, <strong>1</strong>, is unreactive toward the allyl halides, [(dppm)Au₂Ph]⁺, <strong>2</strong> (where dppm = bis(diphenylphosphino)methane, (Ph₂P)₂CH₂), reacts via C–C bond coupling to produce [(dppm)Au₂X]⁺. The reaction kinetics (efficiencies) follows the expected leaving group ability, X = I (58%) > Br (2%) > Cl (0.02%). DFT calculations were carried out to examine the potential mechanism for the C–C bond coupling reactions of <strong>2</strong> with each of the three allyl halides. The most favorable mechanism for C–C bond coupling of <strong>2</strong> requires the active participation of both gold centers in a redox couple mechanism wherein the allylic halide oxidatively adds across the gold centers to form a Au^IAu^III complex with a weak Au···Au interaction, followed by intramolecular reductive elimination of allyl benzene from the Au^III center.