Halide-Dependent Mechanisms of Reductive Elimination from Gold(III)

Two unique organometallic halide series (Ph₃P)­Au­(4-Me-C₆H₄)­(CF₃)­(X) and (Cy₃P)­Au­(4-F-C₆H₄)­(CF₃)­(X) (X = I, Br, Cl, F) have been synthesized. The PPh₃-supported complexes can undergo both C_aryl–X and C_aryl–CF₃ reductive elimination. Mechanistic studies of thermolysis at 122 °C reveal a dramatic reactivity and kinetic selectivity dependence on halide ligand. For X = I or F, zero-order kinetic behavior is observed, while for X = Cl or Br, kinetic studies implicate product catalysis. The selectivity for C_aryl–CF₃ bond formation increases in the order X = I < Br < Cl < F, with exclusively C_aryl–I bond formation when X = I, and exclusively C_aryl–CF₃ bond formation when X = F. Thermodynamic measurements show that Au­(III)–X bond dissociation energies increase in the order X = I < Br < Cl, and that ground state Au­(III)–X bond strength ultimately dictates selectivities for C_aryl–X and C_aryl–CF₃ reductive elimination.