Visible Light Photocatalysis of Carbon–Carbon σ-Bond Anaerobic Oxidation of Ketones with Water by Cobalt(II) Porphyrins

Abstract

Co II (por) (por = porphyrinato dianion) reacted selectively with isopropyl ketones at the carbon (CO)−carbon (α) bond at room temperature to give high yields of Co III (por) acyls and the corresponding oxidized carbonyl compounds in up to 89% yields. Co III (por)OH is proposed to be the C−C bond activation (CCA) intermediate. The stoichiometric reaction is further developed into the photocatalytic CCA using both UV and visible light sources (λ 405 nm). Under ambient conditions, the photocatalytic C−C oxidation of 2,6dimethylcyclohexanone gives 2-heptanone in up to 24 turnovers in the presence of isopropyl alcohol as the H atom donor and H 2 O as the oxidant. Various isopropyl ketones successfully undergo photocatalysis.

C–O Bond Cleavage of Alcohols via Visible Light Activation of Cobalt Alkoxycarbonyls

“…Crystals of complex 9 were grown by slow diffusion of pentane into CHCl 3 , resulting in long thin red crystals with the complex adopting a square-pyramidal geometry (Figure ). This pentacoordinate form is commonly observed in similar porphyrin systems that contain acyl and vinyl substituents. The alkoxycarbonyl complex has a slightly shorter Co–C1 bond length in comparison to the acyl substituents (1.906 Å vs 1.922–1.926 Å) and comparable Co–N bond lengths.…”

“…While the synthesis and reactivity of the analogous alkyl cobalt porphyrin complexes have been studied, − including determining their Co–C bond dissociation energies, , much less is known about the acyl and alkoxycarbonyl complexes. Chan and co-workers reported isolable acyl Co­(por) complexes (por = porphyrinato dianion) as intermediates in a photochemical C–C bond activation of ketones . Only one alkoxycarbonyl derivative has been reported by Fu and co-workers for the initiation of living radical polymerization .…”

“…Chan and co-workers reported isolable acyl Co(por) complexes (por = porphyrinato dianion) as intermediates in a photochemical C−C bond activation of ketones. 20 Only one alkoxycarbonyl derivative has been reported by Fu and co-workers for the initiation of living radical polymerization. 21 Development of a general synthesis of alkoxycarbonyl porphyrin complexes would facilitate further structure and reactivity studies.…”

Kinetics and DFT Studies of Photoredox Carbon–Carbon Bond Cleavage Reactions by Molecular Vanadium Catalysts under Ambient Conditions

“…None of our attempts to crystallize 2c succeeded, although we do not anticipate any major differences be-tween 2c and the remaining complexes. Furthermore, 2a-f have been thoroughly characterized by other techniques including 1 H, 13 C, 51 V, and 19 F (where present) NMR spectroscopy, UV-visible spectroscopy, high-resolution mass spectrometry (HRMS), and elemental analyses.…”

“…[15][16][17][18] Consequently, despite its potential for facilitating novel synthetic pathways in late-stage organic transformations or valorizing neglected feedstocks such as lignin or recycled plastics, there have been few reports that present C-C activation of aliphatic sp 3 carbons, especially by visible light at ambient temperatures and pressures. [19][20][21] Our team has been active in creating the constituents of artificial photosynthetic constructs, including multielectron (photo)catalysts for both reduction and oxidation processes, with exclusive use of only earth-abundant elements. [22][23][24] For instance, we have employed nickel complexes in their reduced -ate forms for the electrocatalytic reduction of CHCl 3 and also the evolution of H 2 from seawater in separate studies.…”