Building N-hydroxyphthalimide organocatalytic sites into a covalent organic framework for metal-free and selective oxidation of silanes

Abstract

A novel crystalline covalent organic framework COF-NHPI was built by a bottom-up strategy to guarantee highly ordered embedment of the N-hydroxyphthalimide (NHPI) units as nitroxyl radical organocatalytic sites. The COF-NHPI...

Porous Aromatic Framework Covalently Embedded with N‐Hydroxyphthalimide as Metal‐free Heterogeneous Catalyst for Highly Efficient and Selective Aerobic Oxidation

“…As shown in Scheme S1, all the verified reactions were completely suppressed by 1.0 equivalent of radical scavenge BHT (2,6‐di‐tert‐butyl‐4‐methylphenol) to result in minimal conversions (<3%), suggesting the radicals are involved in these reactions as key intermediates. More reliable evidence was provided by the electron paramagnetic resonance (EPR) spectrum of the in situ reaction mixture, showing a hyperfine splitting structure with a g ‐value of 2.0073 (Figure S8) [26,27] . Based on the previous researches and these results, the plausible mechanism of this heterogeneous PAF‐NHPI catalytic oxidation fueled by molecular oxygen was proposed [26,27,48,52–54] .…”

“…[26,27] Based on the previous researches and these results, the plausible mechanism of this heterogeneous PAF-NHPI catalytic oxidation fueled by molecular oxygen was proposed. [26,27,48,[52][53][54] In brief, as shown in Figure S9, with the assistance of the cocatalyst TBN or TBHP and heating under oxygen gas atmosphere, the NHPI sites on the porous PAF-NHPI frameworks are converted into the active phthalimide N-Oxyl (PINO) radical sites, generating the essential PAF-PINO heterogeneous catalyst. The PAF-PINO will abstract the hydrogen from the alcohols, aldehydes or hydrosilanes to form the corresponding carbon radical intermediates, or add to the alkene group to generate a carbon radical adduct species.…”

“…[25,28] Very recently, we have developed a bottom-up strategy to covalently functionalize the MOFs and COFs with NHPI catalytic sites, achieving prominent performance in heterogeneous catalytic oxidation of various alcohols and hydrosilanes due to their uniform pores and highly dense organocatalytic sites. [26,27] The remaining issue is that these well-known highly ordered porous materials are prone to erosion since they are constructed through fragile dynamic bonds.…”

“…With the urgent demands and requirements for green and sustainable industrial applications, the construction of heterogeneous catalysts from NHPI has attracted great attention and gradually sprouted recently. [25][26][27] Physical sorption and chemical grafting are the two main strategies used to immobilize NHPI on solid supports. The chemical grafting by covalent bonding is superior to the physical sorption in improving stability and reusability, but grafting on traditional porous material is still faced with the low-density and irregular distribution of catalytic sites as well as insufficient channel spaces.…”

TEMPO-immobilized metal–organic frameworks for efficient oxidative coupling of 2-aminophenols and aldehydes to benzoxazoles

“…[18][19][20][21] To bring reusability and recyclability to this reactive species, there has been recent interest in the immobilization of TEMPO radicals onto heterogeneous media. 15,[22][23][24][25][26] Metalorganic frameworks (MOFs) are three-dimensional organicinorganic hybrid heterogeneous materials that have been extensively used in various applications, including gas storage, molecular separation, and molecular shuttling, because of their permanent porosity. [27][28][29][30][31] MOFs exhibit structural diversity, not only in terms of their inorganic nodes but also their organic ligands, which can be functionalized with various useful organic molecules.…”