In Situ Formation of Frustrated Lewis Pairs in a Water‐Tolerant Metal‐Organic Framework for the Transformation of CO₂

Abstract

Frustrated Lewis pairs (FLPs) consist of sterically hindered Lewis acids and Lewis bases,w hichp rovide high catalytic activity towards non-metal-mediated activation of "inert" small molecules,i ncluding CO 2 among others.O ne critical issue of homogeneous FLPs,h owever,i st heir instability upon recycling,leading to catalytic deactivation. Herein, we provide as olution to this issue by incorporating ab ulky Lewis acid-functionalized ligand into aw ater-tolerant metalorganic framework (MOF), named SION-105,and employing Lewis basic diamine substrates for the in situ formation of FLPs within the MOF.U sing CO 2 as aC 1-feedstock, this combination allows for the efficient transformation of avariety of diamine substrates into benzimidazoles. SION-105 can be easily recycled by washing with MeOH and reused multiple times without losing its identity and catalytic activity,h ighlighting the advantage of the MOF approach in FLP chemistry.During the last decade,intensive efforts have been devoted to tackle the enormous emissions of CO 2 into the atmosphere; these include the development and promotion of renewable energy sources,i mprovements in energy efficiency, the reduction of carbon emissions,t he development of efficient carbon capture and storage technologies,a nd the transformation of the emitted CO 2 into valuable products. [1,2] To date,t he last approach has attracted al ot of attention, since using CO 2 feedstocks could help to close the carbon cycle and reduce petrochemical consumption. Thec hallenge,h owever, is that CO 2 is arelatively unreactive molecule. [3] In recent years,frustrated Lewis pairs (FLPs), comprising Lewis acids and bases sterically hindered in such aw ay that the acid-base adduct is not formed as in classical Lewis pairs, exhibit outstanding ability for CO 2 non-metal-mediated activation due to their unquenched reactivity. [4][5][6][7] One of the challenges of FLP chemistry,i st heir high sensitivity towards moisture,a lthough recent studies showed that careful tuning of the steric environment of the acidic center, as well as regulation of basicity of the basic center, affords moisturetolerant systems. [8][9][10] Indeed, the current research tendency toward FLPs already shifts from the early proof-of-concept investigations to practical applications,with FLPs being facile and powerful tools in chemical conversion. [9,[11][12][13] FLPs have been found to be applicable for the conversion of CO 2 to CO, methanol, methane,a nd formamides among others. [14][15][16] Moreover,C O 2 can be used as aC 1-building block for the synthesis of more complicated value-added products,such as the conversion of o-phenylenediamine and CO 2 into benzimidazole using silanes as reducing agents,w hich proceeds through an FLP-mediated pathway,w ith B(C 6 F 5 ) 3 as ac atalyst. [17] It is worth noting that the majority of industrial chemical processes deploy heterogeneous catalytic systems,a st he comparative stability and facile separation of the products from the catalyst facilitates scale-up and continuous product...

A Highly Water-Stable meta-Carborane-Based Copper Metal–Organic Framework for Efficient High-Temperature Butanol Separation

“…Due to their designable structure and the resultant diverse chemical and physical properties, MOFs are useful for a variety of applications. [19][20][21][22][23][24][25][26][27][28][29][30] Hitherto, in the context of biobutanol recovery, hydrophobic zeolitic imidazolate frameworks (ZIFs), ZIF-8 and ZIF-71 were principally investigated for their adsorptive ABE separation as they have a low affinity for water compared to other hydrophilic ZIFs like ZIF-90. [31][32][33][34][35][36][37][38][39][40][41] To improve the hydrolytic and thermal stability, as well as the hydrophobicity of MOFs, ligands based on carboranes can be introduced within their structures.…”

Interfacial Frustrated Lewis Pairs of CeO2 Activate CO2 for Selective Tandem Transformation of Olefins and CO2 into Cyclic Carbonates

“…14 FLP sites within metal organic frameworks with B-based ligands as Lewis acids catalyzed the conversion of diamines into benzimidazoles by using CO 2 as a C1 feedstock. 15 To date, most homogeneous and heterogeneous FLPs have activated CO 2 through the respective interactions between Lewis basic sites/C and Lewis acidic sites/one O atom of CO 2 . 14,16−18 Recently, FLPs constructed on defective CeO 2 (lattice O as the Lewis base and two neighboring adjacent Ce 3+ ions as Lewis acids, Figure 1) have been reported for hydrogen activation.…”

CO2 Methanation via Amino Alcohol Relay Molecules Employing a Ruthenium Nanoparticle/Metal Organic Framework Catalyst

“…[30,31] Recently, we synthesized a MOF, named SION-105, based on Eu III and a tricarboxylate ligand with Lewis acidic boron centers, which functions as a heteroge- neous catalyst for the synthesis of benzimidazoles, using CO 2 as a C1 building block. [32] The three-coordinate B center of the (tris(p-carboxylic acid) tridurylborane, H 3 tctb) ligand of SION-105 is protected by bulky duryl groups, precluding irreversible binding with Lewis bases, such as water, thus, providing exceptional stability and moisture tolerance. At the same time, B remains accessible for the activation of CO 2 as a Lewis acid site.…”

“…At the same time, B remains accessible for the activation of CO 2 as a Lewis acid site. [32] The Eu III centers might also act as Lewis acidic sites enhancing the catalytic activity. [33] The catalyst was prepared from SION-105 via an impregnation-reduction process using RuCl 3 as the NP precursor.…”

“…[40] Moreover, XPS analysis revealed more oxidized Ru species are present in Ru/C and Ru/Al 2 O 3 ( Figure S5), which probably decrease their catalytic performance. Compared to SION-105, [32] the powder X-ray diffraction (XRD) profile of Ru/SION-105 displayed no additional peaks attributable to very small Ru NPs ( Figure S6). Thermogravimetric analysis (TGA) was used to examine the structural stability of the SION-105 support and the Ru/ SION-105 catalysts.…”