Metal–Organic Framework Stabilizes a Low-Coordinate Iridium Complex for Catalytic Methane Borylation

Abstract

Catalytic borylation has recently been suggested as a potential strategy to convert abundant methane to fine chemicals. However, synthetic utility of methane borylation necessitates significant improvement of catalytic activities over original phenanthroline- and diphosphine-Ir complexes. Herein, we report the use of metal–organic frameworks (MOFs) to stabilize low-coordinate Ir complexes for highly active methane borylation to afford the monoborylated product. The mono­(phosphine)-Ir based MOF, Zr-P1-Ir, significantly outperformed other Ir catalysts in methane borylation to afford CH3Bpin with a turnover number of 127 at 110 °C. Density functional theory calculations indicated a significant reduction of activation barrier for the rate limiting oxidative addition of methane to the four-coordinate (P1)­IrIII(Bpin)3 catalyst to form the six-coordinate (P1)­IrV(Bpin)3(CH3)­(H) intermediate, thus avoiding the formation of sterically encumbered seven-coordinate IrV intermediates as found in other Ir catalysts based on chelating phenanthroline, bipyridine, and diphosphine ligands. MOF thus stabilizes the homogeneously inaccessible, low-coordinate (P1)­Ir­(boryl)3 catalyst to provide a unique strategy to significantly lower the activation barrier for methane borylation. This MOF-based catalyst design holds promise in addressing challenging catalytic reactions involving highly inert substrates.

Isolating reactive metal-based species in Metal–Organic Frameworks – viable strategies and opportunities

“…Site-isolation of ligand binding sites in UiO-derivatives, which can be enhanced by mixed-linker approaches (to the detriment of structure determination by SCXRD), has been employed to prepare novel catalysts that negate the dimerization and ligand disproportionation reactions that encumber such species in solution. 120 In a salient study, Lin et al 133,134 This deviation from linearity can lower the crystallographic symmetry of the metal coordinating site and favour structure determination. Dincȃ et al employed a novel strategy to incorporate a 'scorpionate'-type N,N,N-chelation site into a Zr framework.…”

“…The CuI can be removed by treatment with acid, generating a chelating site for post-synthetic metalation with the more reactive [Cu(NCCH 3 ) 4 ]BF 4 . Another tripodal ligand, 4 0 ,4 000 ,4 00000 -phosphanetriyltris([1,1 0 -biphenyl]-4carboxylic acid), has been used by Lin et al to prepare a Zr(IV) based MOF Zr-P1 featuring free phosphine donors which undergo post-synthetic metalation with Rh(I) 136 and Ir(I) 134,136 complexes. Phosphines are featured extensively in homogeneous catalysts due to their strong and tuneable coordinating ability; however, homogeneous systems can suffer from ligand disproportionation and nanoparticle formation.…”

Self-assembly of a cobalt(II)-based metal–organic framework as an effective water-splitting heterogeneous catalyst for light-driven hydrogen production

“…Among the organic dye molecules Eosin Y, RhB and fluorescein (Fl), Fl showed the highest H 2 production as photosensitizer under the same conditions. The H 2 production experiments were next carried out under the irradiation of a solution containing Fl, 1 and TEA as a three-component photocatalysis system at 298 K (Feng et al, 2019;Zhang et al, 2019Zhang et al, , 2020. A xenon lamp (500 W) was utilized as the light source using a = 400 nm filter to eliminate the effect of ultraviolet light.…”

“…Metal-organic frameworks (MOFs), as a kind of porous materials, have been the subject of much research, not only owing to their high porosity and the high surface area of the structures which makes them useful for potential applications in gas storage and separation (Lorzing et al, 2019;Wang et al, 2019b), drug delivery (Orellana-Tavra et al, 2020) and molecular recognition (Zhu et al, 2017;Mizutani et al, 2020), but also for the tunability and tailorability of their coordination modes and the numerous possible modifications with functional groups making them useful in catalysis (Zhou et al, 2016;Ji et al, 2019;Song et al, 2019;Feng et al, 2019;Wu et al, 2019), fluorescent sensing (Mi et al, 2019;Yang et al, 2019c;Pratik & Cramer, 2019) and magnetic materials (Lan et al, 2019;Gu et al, 2018;Li et al, 2019). The self-assembly of MOFs with various organic linkers and metal ions or clusters endows these materials with active sites and designable backbones, displaying the combined advantages of homogeneous and heterogeneous properties as catalysts, such as high activity and selectivity on one hand, and recovery and high controllability on the other hand.…”

Electroactive Metal–Organic Frameworks as Emitters for Self‐Enhanced Electrochemiluminescence in Aqueous Medium

“…One effective approach to overcome this obstacle is to introduce the conductive substance into a single MOF nanostructure by incorporating metal nanoparticles or carbon-based nanomaterials into the framework, and coordinating functional molecular components on the framework. [5] Alternatively, by taking advantage of their synthetic tunability and structural regularity, MOFs can be constructed with electroactive linkers, such as metal-porphyrin and ruthenium complexes. [6] In particular, it is highly desirable that the MOFs are endowed with high electronic conductivity and strong catalytic activity when the electro-active mixed ligands are co-assembled into MOF structures, [7] providing the great potentials for electrochemical related applications.…”