Challenging metal-based transformations. From single-bond activation to catalysis and metallaquinonoids
D. Milstein
Department of Organic Chemistry, The Weizmann Institute
of Science, Rehovot, 76100 Israel
Abstract: 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.
*Plenary lecture presented at the XXth International
Conference on Organometallic Chemistry (ICOMC), Corfu, Greece, 7-12
July 2002. Other presentations are published in this issue,
pp. 421-494.
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