Contribution to the Mechanism of Copper-Catalyzed C-N and C-O Bond Formation

Copper(I) species associated with 1,10-phenanthroline are generated from copper(0) precursors by chemical oxidation by the aryl halides (via electron transfer) or from copper(II) precursors by chemical reduction by N- or O- nucleophiles in the presence of a base. The mechanism of cross-coupling reactions between ArX (X = I, Br, Cl) and N- or O-nucleophiles catalyzed by copper(I) ligated to 1,3-diketonate ligands (generated from 2-acetylcyclohexanone or 2,2,6,6-tetramethyl-3,5-heptanedione) is proposed on the basis of cyclic Voltammetry, H-1 NMR, ESI-MS, and DFT calculations. The key anionic complexes [(1,3-diketonate)Cu-I-ZR](-) (ZR = NHCy, OH, OPh) undergo oxidative additions to PhI via intermediate complexes formed by halogen bonding between PhI and the negatively charged N or O atom (Z) of [(1,3-diketonate)Cu-I-ZR](-). The reductive eliminations from the Cu-III complexes (1,3-diketonate)Cu-III(Ph)-ZR generated in the oxidative additions are always faster than the rds oxidative additions.