One-electron reduction process

The terdentate cyclometalated complexes [Ir(L)(L )]2+ and [Ir(L )2]1, L = 2,6-bis(7 -methyl-4 -phenyl-2 -quinoyl)pyridine (233), L = monoanion of L (234), luminesce at 77 K in MeOH/EtOH (lmax = 592 nm, r =20 ps) and at room temperature in deoxygenated acetonitrile (imax 620 nm, r = 325 ns).405 Both compounds undergo four reversible, ligand-centered, one-electron reduction processes. 

The first attempt to construct a dendrimer with an electroactive Ru-polypyridi-ne core was based on the reaction of Ru(bpy)2Cl2 with a branched polyether-substituted phenanthroline ligand (11) [27]. In the potential window +2/-2V, this compound shows a one-electron oxidation process and three distinct one-electron reduction processes that, by comparison with the behavior of the... 

This conclusion is partly true because superoxide is unable to abstract hydrogen atom even from the most active bisallylic positions of unsaturated compounds, while perhydroxyl radical abstracts H atom from linoleic, linolenic, and arachidonic fatty acids with the rate constants of 1-3 x 1031 mol-1 s-1 [24], However, the superoxide damaging activity does not originate from hydrogen atom abstraction reactions but from one-electron reduction processes, leading to the formation of hydroxyl radicals, peroxynitrite, etc, and in these reactions perhydroxyl cannot compete with superoxide. 

Unlike in CV, pairs of current measurements are made on each period of the square wave. These are at time forward late in the forward pulse, named /forward, and frevere in the reverse pulse, named Iteveix- Both tformad and Reverse are much greater than the time for fully charging the electrode capacitance, so that only the Faradaic current is recorded. With calculation of /net, the difference between /forward and /reverse, SWV presents three types of peak-shaped I-E relations. Figure 65 displays the SWV of a reversible one-electron reduction process. 

Cr(III) complexes, in particular those of the above discussed polypyridine ligands phen, bipy, terpy usually possess a considerably distorted octahedral geometry.23,24 As illustrated in Figure 14, [Cr(terpy)2]3 + displays four successive reversible one-electron reduction processes.25... 

As briefly alluded to, there are different classes of redox-active ligands in addition to the above mentioned ones. For example, we have seen in Chapter 5, Section 8, that azo-groups (in particular, 2-(phenylazo)pyr-imidine) are able to undergo two separate one-electron reduction processes. Conjugated polynitriles (mnt, tcne, tcnq) also constitute an important class of redox-active molecules and the electrochemical behaviour of their metal complexes has been reviewed.107 The same holds as far as alkyldithiocarbamates (Rdtc) and their metal complexes are concerned,108 or nitrosyl complexes in their possible NO+[NO fNO redox sequence.109 Thus, we would like to conclude the present Chapter by discussing a few less known redox non-innocent ligands. 

The intrinsic instability of organocopper] 11) compounds is most probably associated with the redox properties of copper. Decomposition of organocopper] 11) compounds can occur by two different routes (i) formation of an organocopper]I) compound and an organic radical R" that can undergo further reactions, which formally represents a one-electron reduction process, and (ii) direct formation of R-R and Cu]0), which is formally a two-electron reduction process (reductive elimination cf Eqns. 1 and 2 in Scheme 1.3). 

Anion radicals can also be produced electrolytically at a cathode. There are many advantages to this technique. Perhaps the most important is that the potential may be adjusted so that only the desired one-electron reduction process occurs. The rate of reduction can also be conveniently measured by electrolysis. The electrolyte employed must not be more easily reduced or oxidized than the compound under study. It must be unreactive toward all the species generated in the system and it must allow passage of current in aprotic, relatively nonpolar media. In acetonitrile or A.A-dimethylformamide, tetraalkylammonium perchlorates fill this role reasonably well.25 They are less satisfactory in ether solvents. 

Bipyridinium-type units (also known as viologens) are well-known electron acceptors64 extensively used in chemical and electrochemical redox processes,65 since they can undergo two reversible one-electron reduction processes. Because of these peculiar properties such units can be profitably used to functionalize the periphery of dendrimers, but examples of dendrimers containing a bipyridinium-type unit as a core are also reported.66... 

The [Co(mnt)2f ( = 1, 2, 3) redox series was reexamined with the aid of ESR by Vlcek and Vlcek.101 Upon chemical or electrochemical oxidation of [Co(mnt)2]2-, an initial spin-triplet monomer [Co(mnt)2] formed. Slow dimerization led to the final oxidation product [Co(mnt)2]2 , which in the solid state or in noncoordinating solvents was diamagnetic. Solution spectra in DMSO showed an ESR signal due to [Co(mnt)2] THF solution spectra were identical but indicated three times less monomer concentration. A THF solution of [Co(mnt)2]2- underwent a reversible one-electron reduction process localized on the metal to yield a green solution of a Co1 complex, [Co(mnt)2]3-, with no ESR signal. 

The biochemical importance of flavin coenzymes ap-pears to be their versatility in mediating a variety of redox processes, including electron transfer and the activation of molecular oxygen for oxygenation reactions. An especially important manifestation of their redox versatility is their ability to serve as the switch point from the two-electron processes, which predominate in cytosolic carbon metabo-lism, to the one-electron transfer processes, which predomi-nate in membrane-associated terminal electron-transfer pathways. In mammalian cells, for example, the end products of the aerobic metabolism of glucose are C02 and NADH (see chapter 13). The terminal electron-transfer pathway is a membrane-bound system of cytochromes, nonheme iron proteins, and copper-heme proteins—all one-electron acceptors that transfer electrons ultimately to 02 to produce H20 and NAD+ with the concomitant production of ATP from ADP and P . The interaction of NADH with this pathway is mediated by NADH dehydrogenase, a flavoprotein that couples the two-electron oxidation of NADH with the one-electron reductive processes of the membrane. 

In the nitrogen and boron analogs depicted in Scheme 3-52, two methyl groups provide a sufficient shielding at the NR2 centers (R = Me), while two mesityl groups are needed for protection of the BR2 centers (R = 2,4,6-trimethyl phenyl). Electrochemical studies of l,4-bis(dimesitylboryl)benzene have shown two well-separated one-electron reduction processes, with the formation of the corresponding anion radicals and dianions, respectively (Fiedler et al. 1996). According to UV/vis/near-IR and ESR spectroscopic data... 

A metal-induced one-electron reduction is frequently used to generate radical species. Termination of the radical reactions is due to a one-electron reduction process to give anions and therefore constitutes a non-chain process. As featured in Scheme 6.32, in many cases the multicomponent processes described here are a combination of radical and anionic bond-forming reactions. 

We present here a brief account of the specific dimerization, and other related, reactions undergone by a variety of purine and pyrimidine derivatives, and a number of related compound s, during the course of their electrochemical reduction at the surface of a mercury electrode. A characteristic feature of these reactions is the transfer of an electron to the compound, accompanied, or preceded, by its protonation. The resultant free radicals, generated by a one-electron reduction process, rapidly dimerize to products in which each of the monomeric components possesses an additional electron and an additional proton, relative to the parent monomer1 7). (See Scheme 1)... 

The increased interest to study of one-electron reduction process of nitroimida-zoles is caused, in particular, by their use as radiosensitizers [53, 395, 913, 919, 930, 939-947],... 

Extensive studies of the redox chemistry of [ Co3(CO)9 2 n-C(C=C)mC ] (m = 0, 271 1, 286) have been made independently by the groups of Robinson439 and Osella481,482 and the electrochemical behavior of the C2 and C4 complexes has been compared with that of Co2(CO)6 2(p-r 2-PhC2C2Ph).482,483 Two distinct one-electron reduction processes are found, of which the first shifts to more negative potentials as the carbon chain is lengthened. This is consistent with effective electronic communication between the redox centers. This is attenuated when a Co2(CO)6 group is attached to the carbon chain. All scans contain a wave due to the [Co(CO)4] anion formed by chemical decomposition. 

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