 Thermal decarboxylation of copper benzoates, in the presence of an aryl halide, was found to produce (both symmetric and unsymmetric) biaryls through aryl-Cu intermediates.This monometallic copper system required drastic conditions for complete cross-coupling, and had various intrinsic limitations, both of which prevented development of a catalytic, preparatory version of this reaction.It was not until 2009 that Liu and Shang "et al."