Macrocyclic Copper(II) Complexes as Catalysts for Electrochemically Mediated Atom Transfer.

Copper-catalyzed electrochemical atom transfer radical addition (ATRA) is a new method for the creation of new C-C bonds under mild conditions. In this work, we have explored the reactivity of an analogous series of N macrocyclic Cu complexes as ATRA precatalysts, which are primed by reduction to their monovalent oxidation state. These complexes were fully characterized structurally, spectroscopically, and electrochemically. A spectrum of radical activation reactivity was found across the series [Cu(Mecyclen)(NCMe)] (Mecyclen = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane), [Cu(Mecyclam)(NCMe)] (Mecyclam = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), and [Cu(Mepyclen)(NCMe)] (Mepyclen = 3,7-dimethyl-3,7-diaza-1,5(2,6)-dipyridinacyclo-octaphane). The rate of radical production by [Cu(Mepyclen)(NCMe)] was modest, but rapid radical capture to form the organocopper complex [Cu(Mepyclen)(CHCN)] led to a dramatic acceleration in catalysis, greater than seen in any comparable Cu complex, but this led to rapid radical self-termination instead of radical addition.