Photoactive Chiral Metal–Organic Frameworks for Light-Driven Asymmetric α-Alkylation of Aldehydes

Abstract

Chiral metal-organic frameworks (MOFs) with porous and tunable nature show promise as heterogeneous asymmetric catalysts. Through incorporating the stereoselective organocatalyst L- or D-pyrrolidin-2-ylimidazole (PYI) and a triphenylamine photoredox group into a single framework, we have developed two enantiomeric MOFs, Zn-PYI1 and Zn-PYI2, to prompt the asymmetric α-alkylation of aliphatic aldehydes in a heterogeneous manner. The strong reductive excited state of the triphenylamaine moiety within these MOFs initiated a photoinduced electron transfer, rendering an active intermediate for the α-alkylation. The chiral PYI moieties acted as cooperative organocatalytic active sites to drive the asymmetric catalysis with significant stereoselectivity. Control experiments using the lanthanide-based metal-organic frameworks Ho-TCA and MOF-150, assembled from 4,4',4"-nitrilotribenzoic acid, as catalysts suggested that both the photosensitizer triphenylamine moiety and the chiral organocatalyst D-/L-PYI moiety were necessary for the light-driven α-alkylation reactions. Further investigations demonstrated that the integration of both photocatalyst and asymmetric organocatalyst into a single MOF makes the enantioselection superior to that of simply mixing the corresponding MOFs with the chiral adduct. The easy availability, excellent stereoselectivity, great separability, and individual components fixed with their well-defined porous and repeating structures make the MOF a versatile platform for a new type of tandem catalyst and cooperative catalyst.

Construction of Four Zn(II) Coordination Polymers Used as Catalysts for the Photodegradation of Organic Dyes in Water

“…Thirdly, the carboxylate groups of the ancillary ligands display µ 2 -η 1 :η 1 and µ 3 -η 1 :η 2 coordination modes in 1, µ 1 -η 1 :η 0 in 2, µ 1 -η 1 :η 1 (3) and µ 2 -η 1 :η 1 in 4. In 1, the OAc´anions work as the terminal ligands joining the seven Zn atoms to afford the heptanuclear [Zn 7 (µ 4 -O)(µ 3 -OAc) 2 (µ 2 -OAc) 8 ] unit. In 4, the ADB ligands serve as two-connectted nodes to link Zn 2 subunits forming 2D network, which may be due to the species of ancillary ligands.…”

“…In recent years, increasing attention on functional coordination polymers (CPs) has led to the fast development of this type of solid material, which are due to their intriguing aesthetic structures and topological features, as well as their potential applications in catalysis, adsorption, separation and so on [1][2][3][4][5][6][7][8][9][10][11][12]. Significant effort has been devoted to producing CPs with desired structures and properties using various approaches [13].…”

Oxidative cross-dehydrogenative coupling of amines and α-carbonyl aldehydes over heterogeneous Cu-MOF-74 catalyst: A ligand- and base-free approach

“…During the last few years, many MOFs have been explored as heterogeneous catalysts or catalyst supports in organic synthesis [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54]. One of the challenges in MOFs catalysis is to make crystals whose pore apertures are of a size suitable for the inclusion of large organic molecules.…”

Selective and Reusable Oxidation of Sulfides to Sulfoxides with Hydrogen Peroxide Catalyzed by Organic–Inorganic Polyoxometalate-Based Frameworks

“…In previous work, a heterogeneous catalyst was designed withthe incorporation of different catalytically active components into MOFs and then synthesized with a remarkable impact [7][8][9][10][11]. Several important studies on the MOF-based catalysis have currently been published [12][13][14][15][16][17][18].…”