Nanoheterogeneous ruthenium-containing catalysts based on dendrimers in the hydrogenation of aromatic compounds under two-phase conditions

Dendrimer-Stabilized Ru Nanoparticles Immobilized in Organo-Silica Materials for Hydrogenation of Phenols

“…As one can observe, change in the carrier, from a microporous to a mesoporous one, results in a sufficient decrease of Ru content, that can be attributed both to larger pore diameter of G2-dendr-meso-SiO 2 and to decrease in the nitrogen donor coordination centers for G2-dendrimer vs. G3-dendrimer. Herein, mean particle size predictably increases (Table 1, Entries 1 and 2), being equal to 0.97 nm for microporous G3-dendr-SiO 2 -Ru, that is typical for heterogeneous Ru catalysts, based on the PPI dendrimers of 3rd generation [57,58,83], and 1.28 nm for G2-dendr-meso-SiO 2 -Ru.…”

“…Herein substrate concentration was 1 mg or 1 µL per 1 µL of water, depending on the physical state of the former under ambient conditions, as in our previous works, dealing with two-phase Ru-catalyzed hydrogenation [57,58]. The use of water, in particular in a weight ratio to substrate of 1:1, promotes Ru catalysis, reaching a 10-1000-fold improvement in the reaction rate, which has already been proved by a series of works [57,100,101].…”

“…Earlier we proposed an approach for synthesis of efficient heterogeneous catalysts, suggesting preliminary cross-linking of poly(propylene imine) (PPI) or poly(amido amine) (PAMAM) dendrimers by various bifunctional agents, followed by metal nanoparticles impregnation (Scheme 1) [56][57][58][59][60][61]. The presence of amino and/or amido groups in such types of organic ligands provides effective complexation with metal ions, as well as immobilization of metal nanoparticles within a polymeric network.…”

“…The presence of amino and/or amido groups in such types of organic ligands provides effective complexation with metal ions, as well as immobilization of metal nanoparticles within a polymeric network. Thus, Ru catalysts, synthesized in such a way, demonstrated activity in hydrogenation of phenols and aromatics, essentially superior to conventional heterogeneous catalysts, at TOF values, exceeding 10,000 h −1 in some cases [57,58]. The main disadvantages of such materials are low porosity and exposure to hydrolysis under reaction conditions [57,62].…”

“…Scheme 1. (a) Approach for synthesis of nanoheterogeneous catalysts, based on dendrimer cross-linked networks [56][57][58][59]61]; (b) representative structure for Ru nanocatalysts, based on PPI dendrimers of the 3rd generation, cross-linked with hexamethylene diisocyanate (HMDI).…”