POSS‐Based Nitrogen‐Doped Hierarchically Porous Carbon as Metal‐Free Oxidation Catalyst

Abstract

Carbon materials have emerged in recent years as alternative metal‐free catalysts for various reactions. Pyrolysis of polyhedral oligomeric silsesquioxane (POSS)‐based hybrid porous polymers (HPP), results in nitrogen‐doped hierarchically porous carbons (N‐HPC). HPP is easily synthesized from octaphenyl‐POSS and 2,4,6‐trichloro‐1,3,5‐triazine via Friedel‐Crafts reaction and exhibits high porosity with BET surface area (SBET) of 1071 m2/g and pore volume of 0.99 cm3/g. Remarkably, HPP acts as a “dual template” after pyrolysis, bestowing the materials simultaneously with enhanced micro‐ and meso‐porosity. After silica etching, N‐HPC materials possess a hierarchically micro‐ and mesoporous structure with SBET of up to 1536 m2/g and pore volume of 1.00 cm3/g. Moreover, N‐HPC show to be catalytically active in the oxidative coupling of amines to imines using oxygen (1 bar) as the primary oxidant under neat conditions. The remarkable O2‐activation ability of these novel metal‐free materials could be certainly expanded to other transformations.

Phenazine Radical Cations as Efficient Homogeneous and Heterogeneous Catalysts for the Cross‐Dehydrogenative Aza‐Henry Reaction

“…A common approach to obtain such sites at the catalyst surface is the doping with heteroatoms, specially nitrogen, [29 -39] either by chemical modification of a pre-existing material, or by calcination of pre-organized precursors such as organic polymers, [40] metal-organic frameworks (MOFs), [41] and covalently linked porous polymers (CPP). [42] The latter material class, also known as (micro)porous organic polymers (POPs or MOPs) or covalent organic frameworks (COFs), have gained a lot of attention on their own right, due to their tunable properties and their myriad of potential applications, [43 -45] including gas capture and separation, [46][47][48][49][50][51] and catalysis. [52 -55] The synthesis of these modular materials has been achieved through cross-linking of functional building blocks using different methodologies including Friedel-Crafts arylation, [42,56,57] Suzuki, [58] Sonogashira, [59] and Buchwald-Hartwig cross-couplings, [60] and Yamamoto polymerization, [61] among others.…”

“…Notable examples are the reports from the Miyake group on their use as catalysts for photoinduced atom transfer radical polymerization, [64,65] and the use the nonfunctionalized 5,10-dihydrophenazine (in stoichiometric amounts) as oxidant and proton-transfer reagent for aldehyde esterification. [53] Inspired by our previous works on the preparation of hybrid porous polymers based on polyhedral oligomeric silsesquioxane (POSS), [42] and the aforementioned pyrazine and phenazine radical-cation oxidation catalysts, [63] we designed and synthesized a novel type of covalently linked porous polymers exhibiting tetrakis(phenyl) silane moieties as structural elements cross-linked by phenazine groups (Scheme 1,C).…”

“…Thermogravimetric analysis (TGA) reveals that the catalyst shows high thermal stability with T d (5 % mass loss) at approximately 350°C, comparable to other silicon-centered porous materials (Figure 2,c). [42] Field emission scanning electron microscopy (FE-SEM) of 2 shows that the solid consists of a nanostructured interlinking irregular particles of lamellar shape (Figure 2,d). In contrast to the conventional amorphous porous polymers, the Xray diffraction (XRD) pattern of 2 shows two broad reflexes centered at 12.7°and 19.4°, equivalent to dspacing distances of 6.2 and 4.4 Å, respectively (Figure 2,e).…”

“…The catalytic activity of heterogeneous organocatalysts depends on two main factors, the porosity (since a high surface area and pore volume enhances substrate adsorption and transport), [15–21,28] and the presence of active sites (which can adsorb/coordinate and activate the reactants and stabilize reaction intermediates). A common approach to obtain such sites at the catalyst surface is the doping with heteroatoms, specially nitrogen, [29–39] either by chemical modification of a pre‐existing material, or by calcination of pre‐organized precursors such as organic polymers, [40] metal‐organic frameworks (MOFs), [41] and covalently linked porous polymers (CPP) [42] . The latter material class, also known as (micro)porous organic polymers (POPs or MOPs) or covalent organic frameworks (COFs), have gained a lot of attention on their own right, due to their tunable properties and their myriad of potential applications, [43–45] including gas capture and separation, [46–51] and catalysis [52–55] .…”

A POSS‐Phosphazene Based Porous Material for Adsorption of Metal Ions from Water

“…As a result,t hey are being used actively as functional monomersf or the creationo fp orous structures. [35] Severalm ethods including Heck [36,37] andF riedel-Crafts reactions [38,39] have been reported for the chemical transformation of POSS to hybrid porousm aterials.…”