Conjugated photocatalysts

Photohydroalkylations are in most cases carbon-centered radical conjugate additions onto electron-deficient olefins [7]. Scheme 3.3 summarizes in detail the pathways for the photogeneration of radicals from R-H(Y) 1. In path a, a photocatalyst P (when excited) cleaves homolytically a suitable C—H bond, and the resultant radical adds to the olefin 2 to form the adduct radical 3. a,(3-Unsaturated nitriles, ketones, and esters... 

The mild conditions of photocatalysis appear well suited for the conjugate alkylation of sensitive substrates such as unsaturated aldehydes, in contrast to the high susceptibility of such substrates to 1,2 rather than 1,4 attack in thermal methods. In this case, y-butyrolactols (or lactones) have been synthesized. The organic solvent could in part be replaced by water, thus allowing the use of a hydrosoluble photocatalyst (disodium benzophenonedisulfonate (BPSS) or the sodium salt of 4-benzoylbenzoic acid). The BPSS photocatalyzed reaction of 2-hexenal in a methanol-water 1 1 mixture afforded lactol 11 (ca. l.b g, 57% yield) that was easily oxidized to the corresponding y-lactone (12, Scheme 2.5). ... 

Sato S, Arai T, Morikawa T, Utanura K, Suzuki TM, Tanaka H, Kajino T (2011) Selective CO2 conversion to formate conjugated with H2O oxidation utilizing semiconductor/complex hybrid photocatalysts. J Am Chem Soc 133 15240... 

In pollutant destruction, either Eq. (1) or Eq. (2) constitutes half the conjugate reaction pair the other half of the pair comprises the pollutant molecule or ion. Besides oxygen, any dissolved species with a reduction potential more positive than the conduction band of the photocatalyst can, in principle, consume electrons and complete the redox cycle. For example, with a toxic metal ion... 

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