Development of copper complexes containing quinoline derivatives as photoredox catalysts for atra reactions

Abstract

The photocatalytic for C-C and C-S bond formations by ATRA reaction is an attractive topic in green organic synthesis. In the first part of this dissertation, a series of aminoquinoline-methylpyridine conjugates (1Q, 2Q, and 3Q) was synthesized, characterized, and used as a ligand for complexing Cu(II) ion. The ligand containing one aminoquinoline unit and two methylpyridine (1Q), gave the complex with the highest catalytic activity for haloalkylation of alkenes. The reaction proceeds well with high chemo- regio- and stereoselectivity for over 20 examples of alkenes. The mechanistic study is consistent with the visible-light-induced homolysis (VLIH) of Cu(II)-X bond to Cu(I) complexes which subsequently reduces the alkyl halide via a single electron transfer (SET) to form the Cu(II) bound radical. A base additive or AIBN which acts as a halogen atom transfer (XAT) reagent promotes the ATRA product yields of haloform substrate by preventing acid poisoning of the catalyst. In the second part, the Cu(II) complexes of C5 substituted-1Q derivatives, including a heavy atom (1Q-I), electron-withdrawing group (1Q-CN), and electron-donating group (1Q-OMe) were prepared and studied for photocatalytic chlorosulfonylation of olefins (C-S bond formation). The substituents showed little effect to the product yields thus the more readily synthesized ligand 1Q was further optimized. The reactions effectively provided a broad scope of olefin substrates (40 examples) in the absence or presence of base under blue LED or white light. The reactions on alkynes also gave only E-selective products. This is the first time for observation of exclusive formation of E-isomer in the reaction catalyzed by a homoleptic copper complex. To tune photophysical properties, the extended conjugation at the C5 position of the quinoline ring, ligands 1Q-Ph and 1Q-DMAP were prepared. The preliminary study of these ligands showed an improvement in the catalytic activity in comparison with Cu(II)·1Q complex.