Photoredox radical coupling

Addition Reactions.- The photoelectron transfer process of the iminium salt (38) with the 3-butenoate anion results in the formation of the allylated product (39). The reaction involves decarboxylation of the 3-butenoate followed by a radical coupling reaction. The photoaddition of halogenated alkenes to the tetraraza phenanthrene (40) yields products (41) of (2+2)-addition. The Eu(III)/Eu(II) photoredox system has been studied with regards to its reactivity toweu ds a-methylstyrene. Irradiation of the system at > 280 nm in methanol yielded the products (42) and(43). ... 

Both donor and acceptor molecules are indispensable for the accomplishment of the photoredox reaction and the electrochemical potentials of the donor (D/D +) and acceptor (A/A" ) couples should lie within the semiconductor band gap. Oxidation reactions, photocatalysed by Ti02, are usually performed in the presence of easily reducible molecular oxygen as an electron acceptor, thereby generating a superoxide radical ion (02 ) and subsequently hydroxyl radicals. The resulting holes on the semiconductor surface can oxidize many compounds (Scheme 6.292), including alcohols, hydroxyl anion and even water.1522,1523... 

The coupling of the Co(CO)4 radicals which are produced in the primary photochemical step seems to be the product-forming step of this photolysis. The trinuclear complexes (OC)4Co J-Mll-Co (CO)4 wih M = Zn, Cd, Hg [65] and (NC)5Co -HgI -Co (CN)5 [62] undergo similar photoredox reactions upon oct MMCT excitation. 

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