Bimetallic Photoredox Catalysis: Visible Light-Promoted Aerobic Hydroxylation of Arylboronic Acids with a Dirhodium(II) Catalyst

Abstract

We report the use of a rhodium(II) dimer in visible light photoredox catalysis for the aerobic oxidation of arylboronic acids to phenols under mild conditions. Spectroscopic and computational studies indicate that the catalyst Rh 2 (bpy) 2 (OAc) 4 (1) undergoes metal−metal to ligand charge transfer upon visible light irradiation, which is responsible for catalytic activity. Further reactivity studies demonstrate that 1 is a general photoredox catalyst for diverse oxidation reactions.

Catalyst/Additive Free Oxidation of Benzyl Bromides to Benzaldehydes

“…Interestingly, the oxidation of benzyl bromide moiety to carbonyl was found along with the intended hydroxylation of boronic acid and afforded the aldehyde as the major product. [19] After careful examination of the reaction condition, it was found that the reaction proceeded without the catalyst under visible light and O 2 . We then elaborated the optimization of the solvent using 3 a as a substrate (Table 1).…”

“…As previously mentioned, research involving visible light mediated aerobic oxidation has been an emerging field because of the simplicity of light source and environmental benign usage of molecular oxygen as the terminal oxidant, [17–18] the present study was actually initiated from a discovery during our previous study of visible light promoted hydroxylation of aryl boronic acid with a dirhodium (II) catalyst (Scheme 2). Interestingly, the oxidation of benzyl bromide moiety to carbonyl was found along with the intended hydroxylation of boronic acid and afforded the aldehyde as the major product [19] . After careful examination of the reaction condition, it was found that the reaction proceeded without the catalyst under visible light and O 2 .…”

Direct Synthesis of Phenols from Phenylboronic Acids in Aqueous Media Catalyzed by a Cu(0)‐Nanoparticles Biohybrid

“…Recently several groups have reported the development of monohydroxylation or arylboronic acid by application of green oxidant or green solvents. [36][37][38] The application of metal nanoparticles as nanocatalysts has been demonstrated as an alternative to classic catalysts, improving the catalytic efficiency and permitting chemical reactions in more environmental benign conditions. [39][40][41] In this term, in our research group in the last years a new kind strategy based on the synthesis of novel nanobiohybrids consists in the in-situ generation of metal nanoparticles into a protein network have been pioneer established.…”

“…can be designed. Recently several groups have reported the development of monohydroxylation or arylboronic acid by application of green oxidant or green solvents …”

Iron‐Catalyzed Halogen Exchange of Trifluoromethyl Arenes**

“…SiF4 166 kcal/mol, BF3 170 kcal/mol). [8] However, additional catalysts are necessary in order to avoid high temperatures and long reaction times.…”