Intramolecular redox reactions

The oxidation of 1-nitronaphthalene by ceric ammonium nitrate has been reported (16). The resulting 1-iiitronaphthoquinone condenses with 1,3-butadiene followed by air oxidation under alkaline conditions to form 1-nitroanthraquinone, or l-aminoanthraquinone is formed direcdy by an intramolecular redox reaction. 

A useful approach to the substitution of ring C—H positions lies in the activation of the heteroaromatic system by an A-oxide group, initiating a formal intramolecular redox reaction. 1-Methyllumazine 5-oxide reacts with acetic anhydride in a Katada rearrangement... 

Disiloxane, tetramesityl-, 3,206 Disproportionation iridium catalysts, 4,1159 Dissolution nuclear fuels, 6, 927 Distannene, 3,217 Distannoxane, 1,3-dichloro-, 3,207 Distibine, tetraphenyl-, 2,1008 Distibines, 2,1008 Disulfido ligands metal complexes, 2,531-540, 553 bonding, 2, 539 electron transfer, 2, 537 intramolecular redox reactions, 2,537 reactions, 2, 537... 

Thiocarbamate (tc, RHNCSO-) is a monodentate ambidentate ligand, and both oxygen- and sulfur-bonded forms are known for the simple pentaamminecobalt(III) complexes. These undergo redox reactions with chromium(II) ion in water via attack at the remote O or S atom of the S- and O-bound isomers respectively, with a structural trans effect suggested to direct the facile electron transfer in the former.1045 A cobalt-promoted synthesis utilizing the residual nucleophilicity of the coordinated hydroxide in [Co(NH3)5(OH)]2+ in reaction with MeNCS in (MeO)3PO solvent leads to the O-bonded monothiocarbamate, which isomerizes by an intramolecular mechanism to the S-bound isomer in water.1046... 

The model shown in Scheme 2 indicates that a change in the formal oxidation state of the metal is not necessarily required during the catalytic reaction. This raises a fundamental question. Does the metal ion have to possess specific redox properties in order to be an efficient catalyst A definite answer to this question cannot be given. Nevertheless, catalytic autoxidation reactions have been reported almost exclusively with metal ions which are susceptible to redox reactions under ambient conditions. This is a strong indication that intramolecular electron transfer occurs within the MS"+ and/or MS-O2 precursor complexes. Partial oxidation or reduction of the metal center obviously alters the electronic structure of the substrate and/or dioxygen. In a few cases, direct spectroscopic or other evidence was reported to prove such an internal charge transfer process. This electronic distortion is most likely necessary to activate the substrate and/or dioxygen before the actual electron transfer takes place. For a few systems where deviations from this pattern were found, the presence of trace amounts of catalytically active impurities are suspected to be the cause. In other words, the catalytic effect is due to the impurity and not to the bulk metal ion in these cases. 

In the absence of chloride ion, the Cu(I)/Cu(II) catalytic cycle could be initiated by an intramolecular redox reaction of the [Cu2(HA)2]2+ dimer to yield unsymmetrical products ... 

After formation of an O-coordinated ketyl radical anion and a cis coordinated tyrosin via hydrogen abstraction, a rapid intramolecular one-electron redox reaction occurs with release of the product aldehyde and formation of the fully reduced active site containing a Cu(I) ion, which then reacts with 02 to give H202 and the active enzyme. The above sequence represents Nature s mechanistic blueprint for coordination chemists. 

Illustrative examples of intramolecular oxidations of remote groups in nitroaromatic ions are the redox reactions occurring in ionized benzotriazoles and triazolopyridines bearing o-nitroaryl substituents on nitrogen85. Dissociative ionization apparently causes... 

Intramolecular redox reactions for bichromophoric compounds containing nitro and amino (or amino acid) groups have also been examined. For example4, irreversible... 

In biological systems, electron transfer kinetics are determined by many factors of different physical origin. This is especially true in the case of a bimolecular reaction, since the rate expression then involves the formation constant Kf of the transient bimolecular complex as well as the rate of the intracomplex transfer [4]. The elucidation of the factors that influence the value of Kf in redox reactions between two proteins, or between a protein and organic or inorganic complexes, has been the subject of many experimental studies, and some of them are presented in this volume. The complexation step is essential in ensuring specific recognition between physiological partners. However, it is not considered in the present chapter, which deals with the intramolecular or intracomplex steps which are the direct concern of electron transfer theories. 

Spectroscopic data further support an intramolecular redox reaction upon CO2 coordination to The vibrational spectrum... 

Redox reactions usually lead, however, to a marked change in the species, as reactions 4-6 indicate. Important reactions involve the oxidation of organic and metalloprotein substrates (reactions 5 and 6) by oxidizing complex ions. Here the substrate often has ligand properties, and the first step in the overall process appears to be complex formation between the metal and substrate species. Redox reactions will often then be phenomenologically associated with substitution. After complex formation, the redox reaction can occur in a variety of ways, of which a direct intramolecular electron transfer within the adduct is the most obvious. 

Spectrophotometry has been a popular means of monitoring redox reactions, with increasing use being made of flow, pulse radiolytic and laser photolytic techniques. The majority of redox reactions, even those with involved stoichiometry, have seeond-order characteristics. There is also an important group of reactions in which first-order intramolecular electron transfer is involved. Less straightforward kinetics may arise with redox reactions that involve metal complex or radical intermediates, or multi-electron transfer, as in the reduction of Cr(VI) to Cr(III). Reactants with different equivalences as in the noncomplementary reaction... 

Chromium(II) is a very effective and important reducing agent that has played a significant and historical role in the development of redox mechanisms (Chap. 5). It has a facile ability to take part in inner-sphere redox reactions (Prob. 9). The coordinated water of Cr(II) is easily replaced by the potential bridging group of the oxidant, and after intramolecular electron transfer, the Cr(III) carries the bridging group away with it and as it is an inert product, it can be easily identified. There have been many studies of the interaction of Cr(II) with Co(III) complexes (Tables 2.6 and 5.7) and with Cr(III) complexes (Table 5.8). Only a few reductions by Cr(II) are outer-sphere (Table 5.7). By contrast, Cr(edta) Ref. 69 and Cr(bpy)3 are very effective outer-sphere reductants (Table 5.7). 

Intramolecular redox reactions within metal-sulfido moieties provide an interesting route to 82 complexes. An example is the formation of [Mo202S2(S2)2] from Mo02S2 161). The following redox processes could be involved (see note added in proof). 

Electron-transfer and intramolecular redox reactions (related to 82 complexes). The redox behavior of 82 complexes is of particular interest because it can probably provide a foundation for understanding the course of reactions involved in relevant enzymes and catalysts (especially hydrodesulfurization catalysts). Intramolecular redox reactions related to type la 82 ligands can be summarized as follows ... 

E. Intramolecular Redox Assistance of Bimolecular Redox Reactions Conclusions... 

V,/V-Dimethylamino)benzonitrile (DMABN) and its derivatives, as a class of organic donor-acceptor compounds, exhibit dual fluorescence, one related to the local excited state ( B band) and the other ascribed to the twisted intramolecular charge transfer (TICT) state ( A band).17 As expected, compound 818 exhibits dual fluorescence, showing two fluorescence bands centered at 350 and 432 nm, which can be ascribed to the corresponding band (from the local excited state) and A band (from the TICT state), respectively. After oxidation of TTF unit in 8, the fluorescence intensity of A band decreases while that of band increases slightly. As expected, further reduction of TTF" + into neutral TTF unit leads to the restoration of the fluorescence spectrum of 8. Therefore, the dual fluorescence spectrum of 8 can be reversibly modulated by redox reactions of TTF unit in 8. 

In inorganic compounds or complexes with variable valence system, a redox reaction may be set up by intramolecular or intermolecular electron transfer processes (redox reactions). 

C, Photo-oxidation-reduction or Redox-reactions. A photo-oxidation-reduction process in solution may be intramolecular when the redox reaction occurs between the central metal atom and one of its ligands or intermolecular when the complex reacts with another species present in the solution. 

It is not necessary that the reaction should always lead to decomposition of the ligand. If the central ion can give a stable complex with one lower (or higher) oxidation number, the product of a intramolecular redox reaction may be a complex with a central metal ion of different oxidation number. 

Direct elimination of H2S and NH3 between NH4+ and WS42" can give WS3 chains, while an intramolecular redox reaction will produce HjS, NH3, S and WS2 layers. Scheme 1. Outlines the two slightly different pathways that may be simultaneously operative to deposit both WS3 and WS2 to form inorganic walls. 

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