1,2,3-(NH)-triazoles: Its metal-free synthesis and application as ligands in transition metal catalysis

Abstract

An intermolecular cross-double-Michael addition between nitro and carbonyl activated olefins has been successfully developed through Lewis base catalysis. The reaction tolerates a large substrate scope with a variety of beta-alkyl nitroalkenes and unsaturated ketones/esters being suitable, producing the allylic nitro compounds in good to excellent yields. This Lewis base approach was further expanded to a three component metal free cascade reaction for the synthesis of 4,5-disubstituted-1,2,3-(NH)-triazoles. More than 25 new (NH)-triazoles were prepared in good to excellent yields under mild reaction conditions. In addition, the availability of the C-4 vinyl group allows for the easy conversion into other triazole derivatives. The synthesized (NH)-triazoles were subsequently developed as promising ligands for Rh(I) and Au(I) metal cations. The 4,5-disubstituted-1,2,3-( NH)-triazoles were applied to coordinate with Rh(I) metal cation, forming a new class of air and moisture stable triazole-bridged complexes in near quantitative yields. Furthermore, the X-ray crystallography studies revealed that the C-4 substituted groups effectively controlled the triazole binding site, resulting in different coordination patterns. In addition a series of 1,2,3-triazole-bound cationic Au(I) catalysts have been synthesized, and their structures were characterized by X-ray crystallography. Variable-temperature NMR studies revealed a dynamic triazole-Au cation coordination in solution. Reaction profiles clearly indicate these new catalysts to possess much better thermal stability than literature-reported Au catalysts, including IPrAu˙NTf 2