From 3D to 2D: Multifunctional metal-organic layers for organic synthesis

Recently, in Journal of the American Chemical Society, Quan et al. presented a novel bifunctional metal-organic layer (MOL) that hierarchically integrated organic photosensitizer eosin Y and 2,2′:6′,2″-terpyridine ligated iron triflate. Under blue light irradiation, self-supporting two-dimensional MOL efficiently catalyzed trifluoromethylative difunctionalization alkenes, including bulky bioactive molecules. This work highlights bright future low-dimensional molecular materials synthesis. Metal-organic frameworks (MOFs) have attracted significant interest as platform for development multifunctional catalytic systems.1Zhang T. Lin W. artificial photosynthesis photocatalysis.Chem. Soc. Rev. 2014; 43: 5982-5993Crossref PubMed Google Scholar, 2Li B. Wen H.-M. Cui Y. Zhou Qian G. Chen Emerging Multifunctional Metal-Organic Framework Materials.Adv. Mater. 2016; 28: 8819-8860Crossref Scopus (949) 3Huang Y.-B. Liang J. Wang X.-S. Cao R. framework catalysts: synergistic catalysis tandem reactions.Chem. 2017; 46: 126-157Crossref 4Feng X. Song Transforming Hydroxide-Containing Metal–Organic Nodes Transition Metal Catalysis.Trends Chem. 2020; 2: 965-979Abstract Full Text PDF (6) Scholar The versatile tunable MOF structures allow rational incorporation different functionalities into single or transformations. However, efficiency systems based on three-dimensional (3D) is limited by slow diffusion substrates products through their micro- meso-porous structures. As result, catalysts not yet been pursued synthesis valuable fine chemicals with complicated skeletons pharmaceutical intermediates. (2D) version MOFs, layers (MOLs) free access to all sites transformations lift constraints substrate size limitation 3D MOFs. al., first time, demonstrated dyes transition metal could be afford system photoredox (Figure 1A).5Quan Shi Jiang C. Bifunctional Layer Organic Dyes Iron Centers Synergistic Photoredox Catalysis.J. Am. 2021; 143: 3075-3080Crossref (19) Compared widely studied Ir- Ru-based photosensitizers, present promising alternatives due abundance, relatively low costs, environmental friendliness.6Nicewicz D.A. Nguyen T.M. Recent Applications Catalysts Synthesis.ACS Catal. 4: 355-360Crossref (628) Scholar,7Crisenza G.E.M. Melchiorre P. Chemistry glows green catalysis.Nat. Commun. 11: 803Crossref (104) Through capping ligand exchange, successfully loaded carboxylate-containing ( EY ) onto Hf6 secondary building units (SBUs) Hf6-4′-(4-carboxyphenyl)[2,2′:6′,2″-terpyridine]-5,5″-dicarboxylate (referred hereafter Hf6-TPY) MOL. Subsequent metalation Fe(OTf)2 at terpyridine produced Hf-EY-Fe MOL, which was shown synergistically catalyze wide range several sterically molecules turnover numbers (TONs) high 1,840. readily recovered from reaction mixtures reused four times without any loss activity. It difficult install MOFs symmetry steric bulk. Earlier works mostly relied physical trapping absorption porous entrapped can undergo self-quenching leach In Quan’s work, Hf6-TPY synthesized solvothermally between HfCl4 H3TPY adopted 2D network structure built SBUs TPY bridging ligands,8Cao L. Z. Peng F. Huang Yan Zhang al.Self-Supporting Layers Single-Site Solid Catalysts.Angew. Int. Ed. Engl. 55: 4962-4966Crossref (230) formate groups above below monolayer. provide labile installation metathesis group generated EY-functionalized Hf-EY, 10 mol% loading relative SBU. Hf-EY further metalated Hf-EY-Fe, formula Hf6(μ3-O)4(μ3-OH)4(HCO2)5.9(EY)0.1[TPY-Fe(OTf)2]2. morphologies electronic properties were carefully examined show precise both photosensitizers TPY-Fe(OTf)2 proximity facilitates electron mass transfer two active sites. extensively homogeneous catalysis, but most these studies used higher loadings over traditional noble photosensitizers. Higher are needed rapid photo-decomposition intramolecular or/and intermolecular pathways. proposed immobilization surface suppress photo-degradation taking advantage site-isolation effect lower catalyst compared systems. Upon LED only 0.05–0.1 aminotrifluoromethylation, hydroxytrifluoromethylation, chlorotrifluoromethylation alkenes TONs up 800, 850, 1,840, respectively. These activities much than those EY-based photocatalysts 1B). authors also broad scope reactions, 26 examples good excellent isolated yields. thus showed tremendous potential photocatalytic CF3-containing small-molecule drugs.9Müller K. Faeh Diederich Fluorine pharmaceuticals: looking beyond intuition.Science. 2007; 317: 1881-1886Crossref (4582) Moreover, recycled losses convincingly application late-stage functionalization molecules, CF3-functionalization olefin-containing Nootkatone Rotenone well vinyl derivatives estrone, Fmoc-phenylalanine, adapalene, dehydrocholic acid, centers 1C). CF3-functionalized 56%–80% exhibit Van der Waals sizes ranging 1.4 2.2 nm, they do easily diffuse channels Control experiments photosensitizing efficiency, < 20% yields large substrates. other MOLs crucial role Fe process. Based radical capture luminescence quenching experiments, mechanism synergy photoexcited oxidizes [FeII] [FeIII], resulting anion reduces CF3 agent deliver open-shell trifluoromethyl (⋅CF3). ⋅CF3 then reacts an alkene generate carbon radical, subsequently oxidized nearby [FeIII] nucleophiles product. attributed results site isolation stabilization enhanced electron/mass transfer. summary, this approach precisely incorporate material Several outstanding questions remain monolayered MOLs, structural diversity, chemical robustness, difficulty characterization comparison We anticipate issues addressed more research efforts MOLs. With clear advantages reactions,10Feng Dimensional Reduction Lewis Acidic Frameworks Multicomponent Reactions.J. 8184-8192Crossref (15) we envision discovery applications practical near future.