Photocatalytic function of the B₁₂ complex with the cyclometalated iridium(iii) complex as a photosensitizer under visible light irradiation

Abstract

A visible light induced three-component catalytic system with the cobalamin derivative (B) as a catalyst, the cyclometalated iridium(iii) complex (Irdfppy, Irppy, Irpbt and [Ir{dF(CF)ppy}(dtbpy)]PF) as a photosensitizer and triethanolamine as an electron source under N was developed. This catalytic system showed a much higher catalytic efficiency than the previous catalytic system using [Ru(ii)(bpy)]Cl as the photosensitizer for the dechlorination reaction of 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT). Noteworthy is the fact that the remarkable high turnover number (over ten thousand) based on B, which ranks at the top among the reported studies, was obtained when Irdfppy was used as a photosensitizer. This photocatalytic system was also successfully applied to the B enzyme-mimic reaction, i.e., the 1,2-migration of the phenyl group of 2-bromomethyl-2-phenylmalonate. The plausible reaction mechanism was proposed, which involved two quenching pathways, an oxidative quenching pathway and a reductive quenching pathway, to be responsible for the initial electron transfer of the excited-state photosensitizers during the DDT dechlorination reaction. Transient photoluminescence experiments revealed that the oxidative quenching of the photosensitizer dominated over the reductive quenching pathway.

Visible Light‐Driven, One‐pot Amide Synthesis Catalyzed by the B12 Model Complex under Aerobic Conditions

“…The cobalt complex, Co(III)(DO)(DOH)Br 2 (Chart S1a), which is a well‐known functional model compound of B 12 , showed only a 10 % yield of 1 a (entry 7 in Table ). Its low reactivity may be due to its low stability under aerobic conditions with light irradiation, while the robust B 12 complex showed a high efficiency during the reaction . Subsequently, the catalytic reaction was carried out using a solar simulator to show the application of sunlight for the reaction and 1 a was produced in 95 % yield (entry 8 in Table ).…”

Visible-Light Reductive Cyclization of Nonactivated Alkyl Chlorides

“…The heterogeneous and hybrid B 12 -TiO 2 catalyst has been employed in hydrogenation and reductive dimerization of styrenes, 72 dehalogenation and ring expansion reactions of alkyl bromides 73,74 and dechlorination of benzotrichloride. 75 Remarkably, under anaerobic conditions, B 12 -TiO 2 reacts with benzotrichloride to form the corresponding 1,2-dichlorostilbenes. On the other hand, when the reaction is carried out under aerobic conditions, methyl benzoate is obtained quantitatively.…”

Learning from B12 enzymes: biomimetic and bioinspired catalysts for eco-friendly organic synthesis

“…The conductive band electron of TiO 2 ( E red = −0.5 V vs NHE in neutral water) could reduce 1 to form Co(I) species upon irradiation with ultraviolet (UV) light. We also reported a visible-light-driven system with a molecular photosensitizer such as Ru(bpy) 3 2+ [ 39 – 40 102 – 103 ], cyclometalated iridium(III) complexes [ 104 ], and organic red dyes [ 105 – 107 ].…”

“…The recycled use of 1 and [Ru(bpy) 3 ]Cl 2 was also achieved using an ionic liquid as the reaction medium [ 103 ]. Recently, we have found that cyclometalated iridium(III) complexes such as Irdfppy [ 112 ] are superior to [Ru(bpy) 3 ]Cl 2 in terms of their photosensitization abilities in visible-light-driven B 12 catalytic systems ( Scheme 9 ) [ 104 ]. This was probably due to the gradual decomposition of [Ru(bpy) 3 ]Cl 2 under visible light irradiation.…”

“…The above-mentioned visible-light-driven system composed of 1 , and Irdfppy system was used for radical-mediated isomerization reactions. Visible-light irradiation of diethyl 2-bromomethyl-2-phenylmalonate produced the phenyl-migrated product ( Scheme 10 ) [ 104 ]. The product distribution highly depended on the solvents.…”