Photoreactions assisted

To this category belong, e.g., homogeneous photocatalytic systems based on soluble metal complexes or organic dyes as photocatalysts. Instructive examples are photoreactions assisted by heteropolyacids (HPAs), transition meal complexes with carbonyl, phosphine or some other ligands, and metal porphyrins. 

Ronald E. Hester is Professor of Chemistry in the University of York. He was for short periods a research fellow in Cambridge and an assistant professor at Cornell before being appointed to a lectureship in chemistry in York in 1965. He has been a full professor in York since 1983. His more than 300 publications are mainly in the area of vibrational spectroscopy, latterly focusing on time-resolved studies of photoreaction intermediates and on biomolecular systems in solution. He is active in environmental chemistry and is a founder member and former chairman of the Environment Group of the Royal Society of Chemistry and editor of Industry and the Environment in Perspective (RSC, 1983) and Understanding Our Environment (RSC, 1986). As a member of the Council of the UK Science and Engineering Research Council and several of its sub-committees, panels and boards, he has been heavily involved in national science policy and administration. He was, from 1991-93, a member of the UK Department of the Environment Advisory Committee on Hazardous Substances and is currently a member of the Publications and Information Board of the Royal Society of Chemistry. 

Neither the primary photoreaction itself (either to I700 or to a pre-I700) nor any of the subsequent thermal steps which have so far been accessible to experiment are subject to a rate-determining H/D effect, although the change from H20 to D20 does exert some slight influence in terms of solvent assistance. 

The 1,4-photoaddition of aliphatic amines with benzene via photoinduced electron transfer was first reported by Bryce-Smith more than 30 years ago [375-378], In the photoreaction of triethylamine with benzene, the proton transfer from the radical cation of triethylamine to the radical anion of benzene is proposed as a probable pathway (Scheme 113). In the case of tertiary amines, the photoaddition is accelerated by the addition of methanol or acetic acid as a proton source. Similar photoaddition of diethyl ether to benzene takes place assisted by trifluoroacetic acid, where methanol is not affective [379], In these photoreactions, a-hydrogen next to the heteroatom moves to the radical anion of benzene as a proton, followed by radical ccoupling to give 1,4-addition products. Similar photoaddition of amines to the benzene ring has been reported by Ohashi et al. [380,381],... 

Ho, J.-H. and Ho, T.-I. (2002) Novel photoreaction of N-alkyl(p-metho-xyphenyl) arylarn i ries assisted by protic acids. Chemical Communications, 270-271. 

From the results above, it can be observed that as in the unpromoted PC oxidation, in the Fe-assisted PC oxidation of phenol all aromatic intermediates are detected in small amounts from the time when the photoreaction is initiated. One can notice as well that there is a rapid reduction in the TOC... 

All observations lead to the conclusion that the oxidation of o-DHB follows a similar pattern than phenol oxidation in both unpromoted PC and Fe-assisted PC with all intermediates, aromatic species, and carboxylic acids being detected as soon as the photoreaction is initiated. This shows that some of the o-DHB molecules are quickly oxidized to CO2, as suggested by the early decrease in TOC. Likewise, some o-DHB molecules are partially oxidized to carboxylic acids. These results demonstrate that the oxidation of o-DHB can also be represented with a series-parallel reaction scheme. 

Chelate coordination-assisted SET reactivity as described in Eq. (12) may be invoked in some remarkable insertion reactions of alkylaluminium porphyrins [139] and are not restricted to the main group organometallics. Photoreactions of low-spin d systems with a filled fag sub-shell such as Co(III) [140] or Pt(IV) [141] with chelating 7r-acceptor ligands also involve CT absorptions and apparent radical pair formation (spin-trapping, CIDNP [141]) before typical followup reactions such as C-alkylation [38,95,140] occur. 

When unsymmetrical disilanes are used as substrates, more bulky silyl groups are predominantly added to the dicyanoethenes. A key step of this photoreaction is also the reaction of the radical anion of the dicyanoethene with silyl radicals which are generated by solvent-assisted cleavage of the radical cations of disilanes (Scheme 41) [125],... 

Mizuno and his co-workers reported the photosilylation of electron-deficient alkenes by use of hexamethyldisilane and unsymmetrical disilanes. The photoreaction of l,l-dicyano-2-phenylethene and disilanes in acetonitrile in the presence of phenanthrene affords sily-lated dicyanoethanes in good yields. A key intermediate in this process is the silyl radical, generated by solvent (nucleophile)-assisted cleavage of the radical cation of disilanes. Silyl radical attack at the radical... 

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