Selective C(sp²)‐H Amination Catalyzed by High‐Valent Cobalt(III)/(IV)‐bpy Complex Immobilized on Silica Nanoparticles

Abstract

High‐valent cobaltIV‐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 CoIV species prepared by electrooxidation of CoIII(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 CoIII(bpy)3 into silica support and the electrochemical generation of CoIV 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.

Electrochemical Insight into Mechanisms and Metallocyclic Intermediates of C−H Functionalization

“…Cobalt‐catalyzed C−H activations are very attractive; however, their mechanism has not been fully established, although they were suggested to occur via cobalt(II/III/I) (for example, [65–68] ) or cobalt(III/IV/II) catalytic cycles [8,69] . Interestingly, the mechanism through cobalt(II/III/I) transitions is proposed in works on classical organic synthesis, [65–68] and the cobalt(III/IV/II) pathway is proposed in electrochemical studies [8,69] .…”

Synthetic Tuning of CoII-Doped Silica Nanoarchitecture Towards Electrochemical Sensing Ability

“…Stöber and water-in-oil microemulsion (w/o) techniques provide a facile approach for encapsulation of charged metal complexes into silica nanoparticles [2,9,[14][15][16][38][39][40]. The use of the both techniques results in the synthesis of the hybrid silica nanoparticles.…”

“…However, successful doping or deposition of d-metal complexes without significant changes in the ligand environment can be performed only for kinetically inert complexes, which are exemplified in literature by tris-dipyridyles of Co III and Ru II [16,[38][39][40]. The labile d-metal complexes, including those of Ni II and Co II , can also be doped into silica nanoparticles, although their ligand environment scarcely remains unchanged after the doping [14,15].…”

“…The water-in-oil microemulsion (w/o) and Stöber procedures are most widely applied for doping of hydrophilic dopants such as d-metal salts or complexes into silica spheres [14][15][16][38][39][40]. As it was previously reported, the choice of w/o or Stöber procedure for doping of metal ions into silica nanoparticles has a great impact on both content of the dopants and their electrochemical and catalytic activity [14][15][16]. Thus, the present work is aimed at highlighting a role of the synthetic procedure and nature of the precursor on the structure of the Co II -dopants and nanoarchitecture of Co II -doped silica nanoparticles.…”

“…Silica nanoparticles provide a good platform for uploading of metal ions and complexes through different synthetic approaches, including doping into silica matrix or deposition at a surface of nanoparticles [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. Such hybrid silica nanoparticles uploaded by transition d-metal ions exhibit electrochemical behavior controlled by both inner-sphere environments of the metal ions and nano-architecture of the nanoparticles [ 14 , 15 , 17 , 18 ].…”