Ligands that Store and Release Electrons during Catalysis

摘要

Numerous (organometallic) transition-metal-catalyzed transformations involve elementary steps wherein two electrons are formally transferred from or to the metal (i.e., oxidative addition and reductive elimination). Such two-electron processes are widespread in the coordination sphere of noble transition metals (Pd, Rh, Pt, etc.), which explains their dominant role in homogeneous catalysis. In contrast, most of the cheaper (first-row) transition metals undergo one-electron transformations, which can be tremendously valuable in mediating radical-type reactions, but also limits their applicability in organic reactions that require two-electron oxidative addition or reductive elimination steps. The 2010 Nobel Prize for Chemistry indeed acknowledges the catalytic value of noble transition metals (Pd in C-C bond formation), but recent developments show that ligands serving as electron reservoirs offer valuable opportunities to expand the development of organometallic catalysis with first-row transition metals.