Mechanistic Aspects of Submol% Copper-Catalyzed C-N Cross-Coupling

摘要

Carbonnitrogen bond formation can be catalyzed by copper in very low concentrations (approximate to 100ppm), with mechanistic features that are distinct from those in the high-concentration regime. The reaction was studied by initial rate kinetics, competitive Hammett studies, and DFT calculations. The deprotonation of the model nucleophile, pyrrole, is limited by mass transfer with the heterogeneous base. The positive reaction order in dimethylethylenediamine was explained by this reagent working not only as a ligand to Cu, but also as a facilitator for mass transfer. The selectivity-determining step in the competitive Hammett study is oxidative addition. Alternative mechanisms for this step, such as single-electron transfer, atom transfer, or sigma-bond metathesis, can be excluded based on the observed Hammett behavior and DFT calculations.