Asymmetric Photocatalysis with Bis-cyclometalated Rhodium Complexes

• DOI: 10.1021/acs.accounts.9b00028
• Publication Date: 2019-03-06T18:48:23Z
• Authors: Xiaoqiang Huang; Eric Meggers
• Keywords: Stereocenter; Chirality

ConspectusAspects of sustainability are playing an increasingly important role for the development new synthetic methods. In this context, combination asymmetric catalysis, which is considered one most economic strategies to generate nonracemic chiral compounds, and visible light as abundant source energy induce or activate chemical reactions has recently gained much attention. Furthermore, photochemistry with catalysis provides opportunity mechanistically unique reaction schemes. However, such photocatalysis very challenging two main problems can be pinpointed undesirable photochemical background difficulties in controlling stereochemistry photochemically generated highly reactive intermediates.In Account, we present discuss using currently versatile photoactivatable catalysts, namely, bis-cyclometalated rhodium(III) complexes. The catalysts contain inert cyclometalating 5-(tert-butyl)-2-phenyl benzoxazole benzothiazole ligands together labile acetonitriles, overall chirality due a stereogenic metal center. rhodium complexes serve excellent Lewis acids substrates 2-acyl imidazoles N-acyl pyrazoles, which, upon replacement acetonitrile ligands, coordinate center 2-point fashion. These rhodium–substrate intermediates display photophysical properties often photoactive developed This excitation long-lived photoexcited states intrinsic acid reactivity opens door multitude visible-light-induced conversions.In first mode reactivity, function control radical enolates electron-deficient radicals, rhodium-coordinated enones electron-rich rhodium-bound radicals by photoinduced single electron transfer. their ground key while separate photoredox cycles initiate generations via transfer either additional compounds serving catalyst (secondary photocatalysis). second within cycle (primary photocatalysis) undergo stereocontrolled chemistry direct bond forming out excited state. multiple modes intertwining have been applied α- β-alkylations, β-aminations, β-C–H functionalization carbonyl [3 + 2] photocycloadditions between cyclopropanes alkenes alkynes, [2 alkenes, dearomative photocycloadditions, 3] vinyl azides.We anticipate that these schemes (photoactive) will spur photocatalysts catalysis.