PMO‐Immobilized Au^I–NHC Complexes: Heterogeneous Catalysts for Sustainable Processes

Abstract

A stable periodic mesoporous organosilica (PMO) with accessible sulfonic acid functionalities is prepared via a one-pot-synthesis and is used as solid support for highly active catalysts, consisting of gold(I)-N-heterocyclic carbene (NHC) complexes. The gold complexes are successfully immobilized on the nanoporous hybrid material via a straightforward acid-base reaction with the corresponding [Au(OH)(NHC)] synthon. This catalyst design strategy results in a boomerang-type catalyst, allowing the active species to detach from the surface to perform the catalysis and then to recombine with the solid after all the starting material is consumed. This boomerang behavior is assessed in the hydration of alkynes. The tested catalysts were found to be active in the latter reaction, and after an acidic work-up, the IPr*-based gold catalyst can be recovered and then reused several times without any loss in efficiency.

From Deep Eutectic Solvents to Nitrogen‐rich Ordered Mesoporous Carbons: A Powerful Host for the Immobilization of Palladium Nanoparticles in the Aerobic Oxidation of Alcohols

“…Based on the positive hot‐filtration test, most likely the catalytic reaction was caused by the leached soluble (homogeneous) Pd species. But according to high observed recyclability and durability of the present catalyst system, it seems that the Pd catalyst is indeed working in a boomerang‐type catalyst that means active species re‐incorporate with solid surface after separation from catalyst surface and quite reaction catalysis so that all the starting material is consumed [97–102] . To put in nut shells, such catalysts can be recovered and reused repeatedly several times without any loss in efficiency.…”

“…But according to high observed recyclability and durability of the present catalyst system, it seems that the Pd catalyst is indeed working in a boomerang-type catalyst that means active species re-incorporate with solid surface after separation from catalyst surface and quite reaction catalysis so that all the starting material is consumed. [97][98][99][100][101][102] To put in nut shells, such catalysts can be recovered and reused repeatedly several times without any loss in efficiency. However, to be sure that boomerang or release and catch system is operative, the recycling experiment in the aerobic oxidation of benzyl alcohol under optimal reaction conditions described in entry 1 in Table 2, have been investigated at incomplete conversion level (after 2 h in each run).…”

Functionalized Periodic Mesoporous Organosilicas: Tunable Hydrophobic Solid Acids for Biomass Conversion

“…Sulfonic acids were also grafted along with other functionalities and used for chemical transformations, with propylsulfonic acid-anchored isocyanurate bridging periodic mesoporous organosilica synthesized for the one-pot synthesis of bis -(indolyl)methane [131]. In addition, sulfonic-acid-grafted PMO materials were used in conjunction with metal or metal complexes, such as gold(I)- N -heterocyclic carbene, which was successfully immobilized and explored for hydration of diphenylacetylene [132]. A sulfated zirconia-doped sulfonic acid PMO material was also reported, which offered tunable Brønsted and Lewis acidity and was explored for the cascade synthesis of ethyl levulinate synthesis from glucose and ethanol (Scheme 10).…”

Recent advanced development of metal-loaded mesoporous organosilicas as catalytic nanoreactors

“…46 ). 240 The catalytic activities of PMO-SO 3 -Au(IPr), cPMO-SO 3 -Au(IPr) and cPMO-SO 3 -Au(IPr*) were evaluated by the hydration of diphenylacetylene in a mixture of dioxane and water. 10 mol% of PMO-SO 3 -Au(IPr) was used in the hydration of diphenylacetylene, and the yield reached 91% after reaction for 5 h. When PMO-SO 3 H was used, no catalytic activity was observed.…”

“…When 7.5 mol% of cPMO-SO 3 -Au(IPr) and cPMO-SO 3 -Au(IPr*) were used, the yields of the product reached >99% after reaction for 3 h. In addition, for the reusability of catalysts, an acid work-up was necessary after each cycle in order to reactivate the catalyst and obtain high yields in the subsequent cycles. 240 …”