C-N cross coupling with Cu and light

Abstract

Carbon-nitrogen bond-forming reactions of amines with aryl halides to generate arylamines (anilines), mediated by a stoichiometric copper reagent at elevated temp. (>180 °C), were first described by Ullmann in 1903. Advances in catalytic Ullmann C-N cross-couplings make this and related C-N bond-forming processes powerful tools for org. synthesis. Gaining insight into the mechanisms by which Ullmann couplings proceed, as well as demonstrating new pathways for accomplishing this important bond construction, is an important objective. In this talk I will describe the first examples of photoinduced Ullmann CN coupling reactions. These reactions arise from fundamental studies of a new class of highly emissive copper complexes supported by phosphine and amide ligands. Model studies suggested to us that the excited states of these complexes likely feature substantial aminyl radical character. As such they offered promise to engage in C-N cross coupling reactions that proceed via single electron transfer (SET) from the copper complex excited state to an aryl halide coupling partner. In close collaboration with Professor Gregory Fu and his group at Caltech, stoichiometric and catalytic C-N cross couplings using copper have now been realized at room temp. and even at -40 °C. An array of data are consistent with an SET mechanism, representing the most substantial exptl. support to date for the viability of this pathway for Ullmann C-N couplings.