Mechanistic studies on metal-catalyzed carbon-nitrogen bond forming reactions

Abstract

Mechanistic studies on copper and palladium-catalyzed C-N bond forming reactions are described. To understand the mechanistic details of these processes, several principles of physical organic chemistry have been employed. Chapter 1. We have investigated the mechanism of the copper-catalyzed N-arylation of amides using aryl iodides, i.e., the Goldberg reaction. The focus of the work has been directed towards amides since this reaction remains the most versatile in the presence of Cu(I)/1,2- cliamine catalyst systems. The results provide insights into the role of 1,2-diamines in modulating the coordination environment around Cu(I). The catalyst is more efficient at high concentrations of 1,2-diamine and high concentrations of amide, as revealed by a nonlinear dependence of the rate on 1,2-diamine concentration. Extended premixing times between the Cu(I) precatalyst and the amide lead to an extensive induction period which can be attenuated by replacing the Cu(I) precatalyst with a Cu(II) precatalyst. Evidence for the reduction of the Cu(II) precatalyst through the oxidation of the amide is also presented. Furthermore, we demonstrate that a 1,2-diamine ligated Cu(I)-amidate may potentially serve as the reactive species that undergoes aryl halide activation. This was established through both its chemical and kinetic competency in the stoichiometric N-arylation process. This behavior has important consequences for new catalyst development since these results show the significance of both the diamine and amide in modulating the overall reactivity of the system. Chapter 2.

(cont.) A systematic mechanistic analysis of Pd(OAc)₂/ monophosphino- biaryl-catalyzed C-N bond forming reactions with aryl chlorides has been performed. The results provide insights into the relationship between the steady-state concentration of active Pd and the size and substitution pattern of the monophosphinobiaryl ligands. These insights into the nature of catalyst activation help highlight the importance of establishing a high concentration of active catalyst. The catalyst derived from the bulkiest ligand in the series, the tri-i-propyl ligand 13, exhibits both accelerated rate and the increased stability required for practical application of this reaction.