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 I ) and dormant (Cu II ) 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 BrCH 2 CN to release • CH 2 CN radicals when in complex with Cu I . Moreover, the [Cu I (L1)] + complex can capture the • CH 2 CN radical to form a new species [Cu II (L1)(CH 2 CN)] + in situ that, on reduction, exhibits halogen atom transfer reactivity 3 orders of magnitude greater than its parent complex [Cu I (L1)] + . This unprecedented rate acceleration has been identified by electrochemistry, successfully reproduced by simulation, and exploited in a Cu-catalyzed bulk electrosynthesis where [Cu II (L1)(CH 2 CN)] + participates as a radical donor in the atom transfer radical addition of BrCH 2 CN to a selection of styrenes. The formation of these turbocharged catalysts in situ during electrosynthesis offers a new approach to the Cu-catalyzed organic reaction methodology.