Challenging metal-based transformations. From single-bond activation to catalysis and metallaquinonoids

Catalytic reactions resulting from our C-X (X = H, C, O, N, halide) bond activation studies are described. Aryl chlorides can react with aluminum alkyls in preference to bromides. Using PCP-type Pd catalysts, Heck reaction with aryl iodides and bromides can proceed without involvement of Pd(0). Ru-catalyzed oxidative coupling of arenes with alkenes using O₂ was accomplished. Using specifically designed systems, the scope and mechanisms of C-C activation in solution was studied and compared to C-H activation. C-C activation by Rh(I), Ir(I), Ni(II), Pt(II), Ru(II), and Os(II) was observed. Metal insertion into a strong C-C bond can be kinetically and thermodynamically more favorable than the competing C-H activation. Selective, single-step oxidative addition of a strong C-C bond to a metal was observed and kinetically evaluated. Catalytic C-C hydrogenolysis was demonstrated. A combination of C-C activation and C-R formation (R = aryl, silyl) resulted in unusual methylene transfer chemistry. Selective activation of aryl-O and Me-O bonds was observed. New types of interactions between metals and arenes and unusual quinonoid complexes, including quinone methides, xylylenes, methylene arenium, and a metallaquinone, were discovered. C-H and C-C agostic complexes of cationic metals, proposed as intermediates in bond activation, were isolated. Stabilization and controlled release of biologically relevant, extremely unstable, simple quinone methides, was accomplished.