Hydrogenation photoassisted

Successive hydrogen transfers within 60, followed by coordination of olefin and then H2 (an unsaturate route), constitute the catalytic cycle, while isomerization is effected through HFe(CO)3(7r-allyl) formed from 59. Loss of H2 from 60 was also considered to be photoinduced, and several hydrides, including neutral and cationic dihydrides of iridium(III) (385, 450, 451), ruthenium(II) (452) and a bis(7j-cyclopentadienyltungsten) dihydride (453), have been shown to undergo such reductive elimination of hydrogen. Photoassisted oxidative addition of H2 has also been dem-... 

Kakuta N, Park KH, Finlayson MF, Ueno A, Bard AJ, Campion A, Fox MA, Webber SE, White JM (1985) Photoassisted hydrogen production using visible light and coprecipitated ZnS-CdS without a noble metal. J Phys Chem 89 732-734... 

T., and Haruta, M. (1995) Photoassisted hydrogen production from a water-efhanol solution a comparison of activities of Au-TiOj and Pt-Ti02. Journal of Photochemistry and Photobiology A Chemistry, 89 (2), 177-189. 

Photoassisted catalytic hydrogenation reactions invariably involve promoted loss of a ligand and generation of coordinatively unsaturated species. Examples in the literature are becoming increasingly common. 

Pierotti, C., Deal, C., and Derr, E. Activity coefficient and molecular structure, Ind. Chem. Eng. Fundam., 51 95-101, 1959. Pignatello, J.J. Dark and photoassisted Fe -catalyzed degradation of chlorophenoxy herbicides by hydrogen peroxide. Environ. 

Giordano N, Antonucci V, Cavallaro S, Lembo R, Bart JCJ (1982) Photoassisted decomposition of water over modified rutile electrodes. Int J Hydrogen Energy 7 867-872... 

Abruna HD, Bard AJ (1981) Semiconductor electrodes. 40. Photoassisted hydrogen evolution at poly (benzyl viologen)-coated p-type silicon electrodes. J Am Chem Soc 103 6898-6901... 

MoO(TPP)Br] can be chemically reduced by superoxide to give [MoO(TPP)], via Mov and Mo superoxide complexes, which are stable at low temperatures.114 In the presence of superoxide, the substitution reaction of [MoO(TPP)Br] with MeOH to give [MoO(TPP)(OMe)] proceeds via an Mo species rather than via [MoO(TPP)(MeOH)]+, which is the pathway in the absence of superoxide.277 Photochemical reduction of [MoO(TPP)(OMe)] yields [MoO(TPP)], which reacts with 02 in MeOH to re-form [MoO(TPP)(OMe)j and produce H202, thus giving a catalytic route for the photoassisted reduction of molecular oxygen to hydrogen peroxide.278... 

Several authors (23,24) have reported photoassisted reactions between carbon and water yielding some hydrogen and C02. Photo-Kolbe reactions of carboxylates have also been demonstrated (25). However, neither addition of acetate to 0.08M nor an unintentional gross contamination of the 10M NaOH electrolyte with charred epoxy residue caused significant acceleration of hydrogen production in our experiments. The presence of carbon monolayers on SrTi03 shows the need for caution in evaluating photoreactions where the total product yield is on the order of one monolayer or less. 

Pignatello JJ. Dark and photoassisted Fe3 +-catalyzed degradation of chloro-phenoxy herbicides by hydrogen peroxide. Environ Sci Technol 1992 26 944-951. 

Doong R-A, Chang W-FI. Photoassisted iron compound catalytic degradation of organophosphorous pesticides with hydrogen peroxide. Chemosphere 1998 37 2563-2572. 

Pignatello JJ, Huang FQ. Degradation of polychlorinated dibenzo-/>-dioxin and dibenzofuran contaminants in 2,4,5-T by photoassisted iron-catalyzed hydrogen peroxide. Water Res 1993 27 1731-1736. 

Fig. 15.10. Scanning electron microscope picture of a photoassisted electrochemically Pt-deposited p-Si specimen at the surface. (Reprinted from C. U. Maier, Hydrogen Evolution on Platinum-Coated p-Silicon Photocathodes, Int. J. Hydrogen Energy21 836,1996. Reproduced with permission of the International Association for Hydrogen Energy.)...

Kruczynski L, Gesser HD. Factors affecting hydrogen evolution from hydrated Ti(OH)3 a model system for photoassisted hydrogen production on titania. Inorg Chim Acta 1983 72 161-3. 

Pujadas M. and Salvador P. (1989), EER and photocurrent transient investigation of the photoassisted evolntion of hydrogen at an electroplatinized TiOa singlecrystal—unphcations to water sphtting at Ti02 snspensions , J. Electrochem. Soc. 136,716-723. 

Photoreactions that involve transition metal ions, complexes or compounds can usually be classified as (photo)redox (simultaneous oxidation and reduction) processes. A representative non-photoassisted catalytic system is Fenton s reagent that produces HO radicals on reaction of ferrous ions (Fe2 +) and hydrogen peroxide (Scheme 6.287a). Its photochemical counterpart is the photo-Fenton process,1527 in which ferric (Fe3 + ) complexes in aqueous solutions (absorbing over 300 nm) are reduced to ferrous ions (Scheme 6.287b). 

Chromium hexacarbonyl, Cr(CO)s catalyzes the photoassisted hydrogenation of 1,3-dienes to alkenes. Hence, 2,3-dimethyl-1,3-butadiene gives 2,3-dimethyl-2-butene in quantitative yield by 1,4-addition of hydrogen ... 

---