Metal-Organic Layers for Synergistic Lewis Acid and Photoredox Catalysis

Article abstract of DOI:10.1021/jacs.9b12593

We report the design of a new multifunctional metal-organic layer (MOL), Hf₁₂-Ir-OTf, comprising triflate (OTf)-capped Hf₁₂ secondary building units (SBUs) and photosensitizing Ir(DBB)[dF(CF₃)ppy]₂⁺ [DBB-Ir-F, DBB = 4,4′-di(4-benzoato)-2,2′-bipyridine; dF(CF₃)ppy = 2-(2,4-difluorophenyl)-5-(trifluoromethyl)pyridine] bridging ligands. Hf₁₂-Ir-OTf effectively catalyzed dehydrogenative cross-couplings of heteroarenes with ethers, amines, and unactivated alkanes with turnover numbers of 930, 790, and 950, respectively. Hf₁₂-Ir-OTf also competently catalyzed late-stage functionalization of bioactive and drug molecules such as caffeine, Fasudil, and Metyrapone. The superior catalytic performance of Hf₁₂-Ir-OTf over a mixture of photoredox catalyst and stoichiometric amounts of Br?nsted acids or substoichiometric amounts (20 mol %) of Lewis acids is attributed to the close proximity (1.2 nm) between photoredox and Lewis acid catalysts in Hf₁₂-Ir-OTf, which not only facilitates the reaction between the carbon radical and the activated heteroarene but also accelerates the electron transfer from the nitrogen radical intermediate to the Ir(IV) species in the catalytic cycle.