Silica-supported silver nanoparticles as an efficient catalyst for aromatic C-H alkylation and fluoroalkylation.

The efficient catalysis of oxidative alkylation and fluoroalkylation of aromatic C-H bonds is of paramount importance in the pharmaceutical and agrochemical industries, and requires the development of convenient Ag0-based nano-architectures with high catalytic activity and recyclability. We prepared Ag-doped silica nanoparticles (Ag0/+@SiO2) with a specific nano-architecture, where ultra-small sized silver cores are immersed in silica spheres, 40 nm in size. The nano-architecture provides an efficient electrochemical oxidation of Ag+@SiO2 without any external oxidant. In turn, Ag+@SiO2 5 mol% results in 100% conversion of arenes into their alkylated and fluoroalkylated derivatives in a single step at room temperature under nanoheterogeneous electrochemical conditions. Negligible oxidative leaching of silver from Ag0/+@SiO2 is recorded during the catalytic coupling of arenes with acetic, difluoroacetic and trifluoroacetic acids, which enables the good recyclability of the catalytic function of the Ag0/+@SiO2 nanostructure. The catalyst can be easily separated from the reaction mixture and reused a minimum of five times upon electrochemical regeneration. The use of the developed Ag0@SiO2 nano-architecture as a heterogeneous catalyst facilitates aromatic C-H bond substitution by alkyl and fluoroalkyl groups, which are privileged structural motifs in pharmaceuticals and agrochemicals.

A Ni(iii) complex stabilized by silica nanoparticles as an efficient nanoheterogeneous catalyst for oxidative C-H fluoroalkylation.

We have developed Ni(III)-doped silica nanoparticles ([(bpy)xNi(III)]@SiO2) as a recyclable, low-leaching, and efficient oxidative functionalization nanocatalyst for aromatic C-H bonds. The catalyst is obtained by doping the complex [(bpy)3Ni(II)] on silica nanoparticles along with its subsequent electrooxidation to [(bpy)xNi(III)] without an additional oxidant. The coupling reaction of arenes with perfluoroheptanoic acid occurs with 100% conversion of reactants in a single step at room temperature under nanoheterogeneous conditions. The catalyst content is only 1% with respect to the substrates under electrochemical regeneration conditions. The catalyst can be easily separated from the reaction mixture and reused a minimum of five times. The results emphasize immobilization on the silica support and the electrochemical regeneration of Ni(III) complexes as a facile route for developing an efficient nanocatalyst for oxidative functionalization.