Redox Routes

The carbonyl ligands in M(S2C2R2)2(CO)2 are readily substituted by sources of O2-, S2, and Se2 (Fig. 15) (198, 199). Furthermore, phenoxides, arylthio-lates, and arylselenoates (198, 204, 205) also displace one or both of the carbonyl ligands, the determining factor apparently being the steric crowding around the M(IV) center. 

Some insights into the details of dithiolene-transfer reactions are provided by a study of the reaction of CpCo(S2C6H4) with Mo(CO)3 sources [e.g., Mo-(CO)3(py)3/BF3 py = pyridine]. The product is the trimetallic species Mo(CO)2[CpCo(S2C6H4)]2 (Fig. 16) (206). Structurally elated complexes have been prepared from [Ni(S2Q.,H4)2 and sources of Cp Ru+ (207). 

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Chelate Polymers Give New Redox Route. Chem. Eng. News, April 2, 1962, p. 48. 

Chemical differences between imide and sulfide ligand types, however, are substantive and dictate synthetic tactics. In ionic form, N-anions are considerably more basic than sulfur anions [e.g. in DMSO PhNH2, = 30.6 PhSH, 10.3) and, when coordinated to weak-field iron, the former remain more reactive than the latter. Furthermore, redox transformations coupled to weak-field iron are much more accessible with sulfur than nitrogen. As a result, imide ligation is introduced in Scheme 5.9 by protolysis rather than the salt-metathesis or redox routes typical in Fe-S chemistry. Protolysis requires iron precursors with reactive ligands as latent bases the relative instability of these complexes forces the incorporation of imide (or equivalent N-anions) early in the synthetic sequence. 

Synthesis by Substitution Routes. Many of the limitations inherent in the redox route described above can be avoided by preparation of technetium-99m radiopharmaeeutieals by a substitution route, i.e. the classical substitution of ligands onto a pre-reduced and isolated technetium center. Substitution routes allow control over the oxidation state and ligand environment of the technetium product, and permit the synthesis of complexes containing different ligands. By substitution routes it should be possible to prepare series of complexes in which some ligands are held fixed while others are varied in a systematic fashion to affect biological specificity. 

C O were observed with no peaks of C O2, COO and C O2 with respect to the formation of the C-labelled reaction products. They proposed that the WGSR on the carburized 4.8 and 8.5 wt% M0/AI2O3 catalysts preceded the redox route based on the dissociation of CO and H2O as well as the dissociation-association mechanism. 

A new one-step electrochemical redox route for the synthesis of high quality graphene-PEDOT nanocomposite film based on simultaneous... 

The application of the electron localizability approach allows for studying details of the atomic interactions in intermetalhc clathrates. This may contribute to the understanding of structural features which cannot be achieved within the Zintl— Klemm concept. Another, from chemical point important, outcome of the electron localizabUity approach is the electron-locahzabihty-based oxidation number (ELIBON [77]) which is the real-space equivalent of the traditional oxidation numbers. Apphcation of oxidation numbers on intermetaUic clathrates allows for new ways of understanding of experimentally observed clathrate compositions and for novel redox routes for their preparation. 

Interestingly, Birch and Russell reported that during the early stages of photolysis of hrevianamide A into brevianamides C and D with white light, traces of hrevianamide B could be detected in the mixture. A mechanism for this transformation was postulated as shown in Scheme 3. However, the absolute stereochemistry of the hrevianamide B produced under these conditions was not determined. As will become clear below, the absolute stereochemistry of the hrevianamide B produced from hrevianamide A, either via the photochemical route, or via the chemical redox route through deoxybrevianamide A as described above, must be as depicted in Schemes 1 and 3 giving (-)-brevianamide B. 

Regarding the mechanism, several authors have proposed a redox route for soot oxidation, which utilizes some form of oxygen from the support in a typical reduction/oxidation mechanism where the catalyst undergoes a partial reduction. An alternative redox route involves oxygen from the support and gas phase, which reacts with soot to form adsorbed GOg in the form of surface carbon oxygen complexes (like adsorbed carbonates). Decomposition of carbonate is then stimulated by gas-phase oxygen, which also reoxidizes the support, as illustrated below ... 

MnCeOx catalysts with different Mn-to-Ce atomie ratio (Mn/Ce) ranging between 0.33 and 2 were prepared via the ""redox route, eonsisting in the titration of a KMn04 solution at ca. 60°C under stirring with an aqueous solution of Ce(N03)3 and Mn(N03>2 precursors at constant pH (8.0+0.2) [1-5], The following main redox reactions ... 

In this connection it is of interest to Investigate methods for stabilizing secondary catalytic systems. In our opinion the electrochemical method is of practical importance [31]. The contacting solution is in this case placed in an electrochemical system. An external emf secures a specific potential at the metal-complex catalyst which changes through a secondary redox route. The design of the electrochemical system must accordingly satisfy the requirements of the catalytic and electrode processes. 

Redox Routes in Compressed and Heated Fluids Hydrothermal, Solvothermal and Supercritical Fluid Methods... 

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