Redox isomers

The intermediate is coordinatively unsaturated and susceptible to an electrophilic attack at the carbene anion ligand. Product formation occurs by electrophilic addition at the ligand and completion of the octahedral coordination. 

The overall reaction is an oxidative addition of HCl to a carbyne complex which is transformed to a carbene complex. 

Catalytically Active Species Generated by Charge Transfer Excitation 

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That the above redox isomer is formed instead of the FenRuin one, can be demonstrated by careful analysis of the MLCT band of the product, as well as by the properties of the intervalence (IV) band. However, it is well known that the [Run(NH >)r,LV,+ ions are generally much more reactive that the [Fen(CN)5L]" analogues toward oxidation by peroxydisulfate (126,128), as required by the lower redox potential at the ruthenium center. A careful mechanistic analysis showed that, although the FeinRun isomer is the thermodynamically stable product, it is not the kinetically accessible one. Then, the reaction evolves as follows ... 

The equilibrium between metal-quinone redox isomers has been found to be extremely sensitive to the properties of nitrogen-donor coligands. The redox isomers, reported in Ref. 159, can exist (5.14) in the cobalt complexes containing semiquino-late (SQ) and catecholate (Cat) ligands derived from 3,5-di-/-butyl-l,2-benzoquinone (3,5-DBBQ) ... 

A different rendering of the relevant core atoms of the dication [Fe, N2H2, S(thiolate) donors] shows that the dicationic diazene complex B and the N2 complex C are potential redox isomers or valence tautomers (Scheme 38). 

Co(tmphen)2]3[Fe(CN)6]2 2H2O. The characterization of this redox isomer by Mossbauer spectroscopy and magnetic measurements established that the molecules exist as [Co 3pe 2] in the entire temperature range from 2 to 300 K. 

According to this description, the release of CO should be accompanied by the generation of a CUO2CU moiety in the primary photochemical step. This fragment may contain Cu (02 ) Cu or its redox isomer Cu (0 )2Cu. Calculations have shown... 

A great variety of binary Mo-S complex anions is formed and can be isolated in reactions of the tetrathiomolybdate anion [MoS ] " with various suinde and polysulfide anions. The nature of the anionic products that can be isolated from these reactions depends on (a) the amount of excess sulfur used (and the types of ligands present in the reaction mixtures), (b) the type of counterion used in the isolation of the complex anions, and (c) the type of solvent employed in the synthetic procedure. In a recent article, we described a scheme that interrelates the various [Mo2(S),(S2)6-,] anions. In this scheme (Fig. 1), any of the six homologs can hypothetically be obtained from any other by either the addition of sulfur, or the abstraction of sulfur by triphenylphosphine. Experimentally, the correctness of this scheme has been verified by the successful synthesis of most of the [Mo2(S) (S2)6 ] complexes, or of their internal redox isomers. In the [Mo2(S), (82)6 series, the homologs with n = 4, 5, and 6 have been characterized structurally. Those with n = 2 and 3 have been characterized structurally as the internal-redox isomers, [(S4)Mo(S)(//-S)2(S)Mo S2)] (ref. 3) and... 

Kistner A, Habermann E (1992) Reductive cleavage of tetanus toxin and botulinum neurotoxin A by the thioredoxin system from brain. Evidence for two redox isomers of tetanus toxin. Naunyn. Schmiedebergs Arch. Pharmacol. 345 227-34... 

C.A. Bessel and D.R. Rolison, Topological Redox Isomers Surface Chemistry of Zeolite-encapsulated Co(salen) and [Fe(bpy)3]2+ Complexes. J. Phys. Chem. B, 1997, 101, 1148-1157. 

Electrochemical methods provide information on the coexistence of different topological redox isomers. Discrimination between different redox isomers can... 

Concentration profiles for the variation of the concentration of the different topological redox isomers with depth were estimated from chronoamperometric and chronocoulometric data. Application of methods described in Section 2.5 led researchers to establish that the electrochemical process represented by Equation (4.9) is controlled by electron diffusion with = 1 x 10 crnVscc (Domenech et al., 2009). Resulting curves are shown in Figure 4.20 for a three-isomer system. 

Peak splitting (see Figure 8.22) can be attributed to the superposition of processes due to iron species in different zeolite sites (topological redox isomers, see Chapter 4) and also to the occurrence of chloride-assisted reduction processes. 

The response of BTP Y in Bi N /MeCN is restricted to a unique reduction process near to -0.40 V, but it differs signihcantly in the presence of Et4N+. Here, two reduction processes at -0.22 and -0.36 V appear (Figure 11.2). As described in Chapter 4, this response can be associated to the presence of different boundary-associated topological redox isomers for which no signihcant comproportionation reaction occurs, namely. 

Bessel, C.A., and Rolison, D.R. 1997a. Topological redox isomers Surface chemistry of zeolite-encapsulated Cofsalcn) and fc(bpv),P complexes. Journal of Physical Chemistry B 101, 1148-1157. 

Domenech, A., Formentin, P, Garcia, 11,. and Sabater, M.J. 2002a. On the existence of different zeolite-associated topological redox isomers. Electrochemistry of Y zeolite-associated Mnfsalen )Ni complex. Journal of Physical Chemistry B 106, 574-582. 

Figure 2 The stabilized structure of the redox isomers of quinonoid compounds without or with the proton source in aprotic solvent.

C25H34CuN203S] CH3 fflu n temperature dependent equilibrium with Cu redox isomer toluene 2.0047 Cu 0.41 Cu 0.44 H(5) 0.36 99Ral... 

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