Deoxygenation, photochemical

The compounds Fe(Ti -C5H5)(CO)2Br (1.54 g, 6.0 mmol) and 1,2-ethane-diylbis(diphenylphosphine) (2.46 g, 6.2 mmol) are dissolved in anhydrous benzene (200 mL distilled from CaH2) and transferred into a standard quartz, water-cooled, deoxygenated photochemical vessel fitted with a magnetic stirrer. The concentration of Fe(-ri -C5H5)(CO)2Br must be 0.03 M. 

Photochemical reduction. A deoxygenated aqueous solution of FMN (50 pM) containing 2mM EDTA is irradiated with a longwave UV light immediately before use (Nickerson and Strauss, 1960 Strauss and Nickerson, 1961). The reduction of FMN is accompanied by the formation of H202, which might be undesirable in some experiments. 

In an interesting contrast to the photochemical behavior of the simpler sulfine system, the photolysis of thioketene S-oxides such as 25 in carbon tetrachloride leads to the corresponding thioketenes in excellent yield36. This photochemical deoxygenation is... 

Another methodology is the deoxygenation of nitroxides by (TMSlsSiH, shown in Reaction (22). Indeed, the reaction of this silane with TEMPO, in the presence of thermal or photochemical radical initiators, afforded the corresponding amine in quantitative yield, together with the siloxane (TMS)2Si (H)OTMS. 

Furoxans and benzofuroxans undergo thermal and photochemical ring cleavage, reactions with nucleophiles, Boulton-Katritzky rearrangement, reduction and deoxygenation, ring transformation, etc. (see also Section 5.05.6.2). 

Figure 3. Photochemical and thermal solubilization of hematite in deoxygenated hematite suspensions containing S(IV). (Reproduced from Ref. 42. Copyright 1985, American Chemical Society.)...

Photochemical deoxygenation of nitrobenzene to nitrosobenzene with cyanide ions 38,40) or by molecular complexation with boron trichloride have been reported. No experiments to elucidate the multiplicity of the reacting excited state have been described, however. 

The photocatalytic system is shown in Scheme 5, where BNAH is oxidized by the ZnP + moiety in the radical ion pair ZaP -Ceo (ki) produced upon photoirradiation of ZnP-Ceo, whereas HV " is reduced to HV by the Ceo" moiety of ZnP +-C6o ki). These individual electron-transfer processes compete, however, with the BET in the radical ion pair (/cbet)- This pathway was experimentally confirmed by photolysis of the ZnP-Ceo/BNAH/HV and ZnP-H2P-C6o/BNAH/HV + systems with visible light (433 nm) in deoxyge-nated PhCN [70], For instance. Fig. 4 depicts the steady-state photolysis in deoxy-genated PhCN, in which the HV absorption band (X ax = 402 and 615 nm) increases progressively with irradiation time. By contrast, no reaction occurs in the dark or in the absence of the photocatalyst (i.e., ZnP-Ceo or ZnP-H2P-C6o) under photoirradiation [70]. Once HV+ is generated in the photochemical reaction, it was found to be stable in deoxygenated PhCN. The stoichiometry of the reaction is established as given by Eq. (3), where BNAH acts as a two-electron donor to reduce two equivalents of HV [70] ... 

The fact that the ratio (55 45) of 1-methylcarbazole to 3-methylcarbazole was effectively the same when obtained either via the triethylphosphite (or trisdimethylaminophosphine) deoxygenation of 2-nitro-3 -methylbiphenyl or of 2-nitroso-3 -methylbiphenyl or via the thermal or photochemical decomposition of the corresponding azides is taken as strong circumstantial evidence that each process proceeds via a common intermediate-the nitrene. The electrophilic nature of such a nitrene was well illustrated by the formation of 275 and not 276 from the nitrene 277. ... 

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