Selective C(sp(2))-H Amination Catalyzed by High-Valent Cobalt(III)/(IV)-bpy Complex Immobilized on Silica Nanoparticles

摘要

High-valent cobalt(IV)-bpy complex stabilized in silica matrix was detected as catalytically active form and intermediate in cobalt-mediated oxidative C-H/NH cross-coupling reaction. These Co-IV species prepared by electrooxidation of Co-III(bpy)(3)-doped silica nanoparticles (SNs) at relatively low anodic potentials have demonstrated high catalytic activity. Both size and architecture of the SNs are highlighted as the factors beyond the complex structure affecting its oxidation potential and catalytic efficiency. The factors have been optimized for the catalyst with high efficiency, easy separation and reusability for 7 times at least. The optimal nanocatalyst (1 mol%) provides 100 % conversion of reactants in a single step of ligand-directed coupling of H2NTs with arenes under electrochemical regeneration conditions. The results emphasize both synthetic route for efficient embedding of Co-III(bpy)(3) into silica support and the electrochemical generation of Co-IV complexes as a facile route for developing the efficient nanocatalyst of oxidative functionalization. The observed reactivity has the potential in development of Co-catalyzed coupling reactions.