Long-Lived Five-Coordinate Platinum(IV) Intermediates: Regiospecific C–C Coupling

Three different phosphine derivatives of doubly cyclometalated diphenypyridine complexes of Pt­(II), 1, were reacted with methyl iodide to give octahedral Pt­(IV) complexes, 2, as two isomers. Treatment of either isomer of complexes 2 with AgBF4, to abstract iodide, gave long-lived five-coordinate complexes 3, which could be trapped as pyridine adducts. Complexes 3 underwent a C–C coupling reaction, at a rate that depended on phosphine size, to give a methyl group attached to the original diphenylpyridine. Recylometalation was then performed, and the cycle of reactions was repeated to give a diphenylpyridine doubly methylated on only one phenyl, with complete regiospecificity. NMR was used to demonstrate the geometry of all complexes in solution, with multiple X-ray crystal structures confirming these assignments.