Electrocatalytic Atom Transfer Radical Addition with Turbocharged Organocopper(II) Complexes.

The utility and scope of Cu-catalyzed halogen atom transfer chemistry have been exploited in the fields of atom transfer radical polymerization and atom transfer radical addition, where the metal plays a key role in radical formation and minimizing unwanted side reactions. We have shown that electrochemistry can be employed to modulate the reactivity of the Cu catalyst between its active (Cu) and dormant (Cu) states in a variety of ligand systems. In this work, a macrocyclic pyridinophane ligand (L1) was utilized, which can break the C-Br bond of BrCHCN to release CHCN radicals when in complex with Cu. Moreover, the [Cu(L1)] complex can capture the CHCN radical to form a new species [Cu(L1)(CHCN)] that, on reduction, exhibits halogen atom transfer reactivity 3 orders of magnitude greater than its parent complex [Cu(L1)]. This unprecedented rate acceleration has been identified by electrochemistry, successfully reproduced by simulation, and exploited in a Cu-catalyzed bulk electrosynthesis where [Cu(L1)(CHCN)] participates as a radical donor in the atom transfer radical addition of BrCHCN to a selection of styrenes. The formation of these turbocharged catalysts during electrosynthesis offers a new approach to the Cu-catalyzed organic reaction methodology.