The Economical And Green Catalyst System For Novel Approaches Towards C-C Bond Formations

The aromatic C-H functionalization or direct arylation of aromatic C-H is one of the hottest research areas in the construction of biaryl motifs. The successful catalysts reported have focused on Pd, Ir, Rh, Ru, Cu and Ni etc. Herein, we first reported the iron-catalyzed direct arylation of unactivated arenes with aryl halides. At a relatively mild temperature, using DMEDA as ligand and LiHMDS as base, the aromatic C-H functionalization with various aryl halides including aryl iodides, aryl bromides and chlorides was achieved by cheap iron catalyst. The unactivated arenes include benzene, toluene, anisole and ferrocene. Moreover, aryl radical pathway was involved in the direct arylation.We first developed the organomolecule-catalyzed direct arylation of unactivated benzene with various aryl iodides to produce biaryls. The catalytical amount of DMEDA was essential for the success of the direct arylation of benzene in the presence of potassium tert-butoxide at 80℃. And further investigation on the reaction mechanism indicated that aryl radical was involved in this transformation.Furthermore, cobalt-catalyzed direct arylation of unactivated arenes with aryl halides was explored. Excellent yields were achieved using solely cobalt salt without adding extra ligands especially for aryl bromides and aryl iodides in the presence of LiHMDS base. And intramolecular direct arylation was achieved under the same reaction conditions.Oxidative coupling is one of most important coupling approaches to construct C-C bonds. The oxidants used in transition-metal-catalyzed oxidative coupling reactions were mainly focused on organic oxidants and inorganic oxidants, which would produce wastes and bring difficulties to isolation and purification. We employed green and cheap oxidant oxygen in the iron-catalyzed oxidative homo-coupling of aryl Grignard reagents to the facile synthesis of biaryls. The benefits of the above method are green oxidant O2, cheap and non-toxic iron catalyst and mild reaction conditions. Using the oxidative coupling methods, we explored the cobalt-catalyzed oxidative carbonylation of various aryl zinc reagents using oxygen as the oxidant to the facile synthesis of aryl ketones. High yields and excellent selectivity were achieved under very mild conditions without adding extra ligands.