Direct cathodic reductions

In this part of the chapter, the discussion is focused on the direct cathodic reduction of halogenated organic compounds, although the last section will address the increasingly active area of catalytic reductions of carbon-halogen bonds. 

Electro-generated and regenerated bis(bipyridine)rhodium(I) complexes were able to catalyze the selective non-enzymatically coupled electrochemical generation of NADH from NAD . The direct cathodic reduction even at very negative working potentials leads to the formation of large amounts of enzymatically inactive NAD dimers, while the indirect electrochemical reduction via the rhodium complex acting as... 

It is interesting to compare direct cathodic reduction with reduction of the same substance using solvated electrons. Thus, phosphine cations, which are formed in hexamethylphosphotriamide solutions of iodine, tosyl and mesyl chlorides (see above), and also N-tosylcarbazol during direct cathodic reduction (whose potential is by 2.5 and 0.8 V, respectively, more positive than the generation potential of solvated electrons) yield, unlike the reaction with solvated electrons, unexcited particles chemiluminescence is absent in this case Thus, investigation of... 

This electrochemical synthesis of carbamates is related to the direct cathodic reduction of CO, carboxylation of amine via carbonate anion yielding the carbamate anion and the alkylation of the carbamate anion. For the last step of the whole synthetic process, two possible routes are possible the N-aUcylation of the carbamate anion (yielding nitrogen-derived products and CO elimination) and the... 

An electrosynthetic approach to 2-nitroalcohols via activation of nitromethane by electrogenerated superoxide anion has been reported by Evans et al. [166-168]. Recently, the electrochemically induced Henry reaction has been performed via direct cathodic reduction of nitromethane (Scheme 16.28) [169, 170]. 

Scheme 16.28 Henry reaction performed via direct cathodic reduction of nitromethane (Reprinted from Ref. [170] with kind permission of John Wiley and Sons)...

It has been demonstrated by Bhadani and Parravano that pyridine anion radicals, formed by electrochemical reduction, are able to initiate the polymerization of 4-vinylpyridine, if the monomer is added to the yellow or blue pre-electrolyzed pyridine solution54. The yellow color is attributed to the Py and the blue one to the 4,4 -Bipy anion radicals. 4-Vinylpyridine, if present during the electrolysis undergoes direct cathodic reduction giving rise to anionic polymerization. 

DIRECT CATHODIC REDUCTIONS OF UNSATURATED ORGANIC MATERIALS... 

Ru and Fe complexes in which two bipy ligands saturate the hexacoordination at PVP or PVbipy chains are among the most conmuMi residues they were also obtained on the electrode stuface by direct cathodic reduction of the relevant monomer, as reported in the already cited Ref. [8]. 

In principle, the cathode represents the most advantageous source of reducing equivalents from various viewpoints. This regeneration method is reagent-free as the electrons are dehvered directly from the cathode to NAD(P)". Hence accumulation of by-products in the reaction mixture does not occur, leading to very dean overall processes. The direct cathodic reduction of NAD(P)", however, proceeds with poor selectivity yielding enzymatically inactive NAD(P)H isomers or dimers [7]. 

Imidazolonium cations allowed the synthesis of organic carbamates. For this, the activation of carbon dioxide has been conducted in O2/CO2 saturated ionic liquids, via electrochemically generated 02. The electron uptake occurred at a less negative potential than the one needed for the direct cathodic reduction of CO2. This kind of electrochemical activation has been applied to the C-N bond formation from amines and CO2 to yield organic carbamates [63]. 

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