Oxidation-Reduction Conversion of Transition Metals

One of more often observed transformations is reduction or oxidation of transition metals. Metal oxidation on reaction with a polymer will be discussed first. One of the typical processes is oxidative addition of metal(O) to a macroligand. For example, tezrato(triphenylphosphine)metal(0), M(PPh3)4 (M = Pt, Pd, Ni), is oxidized by halogenated polystyrene (PS) to a bivalent state as die functional groups on the polymer become metal ligands (scheme 6).  

Similar processes have been observed using metal(O) vapor deposition on polymers, metal dissolution in the presence of polymers, mechanochemical syntheses involving macromolecular ligands, etc. However, transition metal reduction is most often observed in these processes. Hence compounds of and are reduced relatively easily, as it was shown with PVA as a model compound. A graft copolymer of cellulose is reduced in a similar manner. The degree of reduction depends on the pH of reaction medium (maximum of 70% at pH 4.5-5.0), and if die resulting is fuUy bound to the polymer. 

It is known that Mo easily reduces to Mo +. Peptide complexes of Mo and Mo , which are formed as a result of M0O2CI2 or (NH4)2MoOCl5 reaction with 

The Cu complex again oxidizes to Cu + in air. It is interesting fliat oxidation of Cu bound to poly(l-vinylimidazole) is characterized by higher enthalpy and lower entropy compared to the low-molecular-weight imidazole complex. These differences are attributed to the changes in polymer hgand conformation as a result of Cu oxidation to Cu and is evidenced by viscosity measurements. It has been noted that copper ion doping in poly(ihioether) stabilizes the oxidation state of Cu and results in the formation of a Cu+-Cu + system with a potential of 1V in aqueous solution.  

An abnormal behavior was observed for Cr + macrocomplexes with polyether modified by amino groups Cr + oxidizes to Cr + on adding NaCl, and at—1.3 V the reverse reaction is observed. Such metal-containing polymers as woven fibers can serve as an electric muscle, elechic resistance systems, etc. Fe +- Fe + reversible reduction in sandwich complexes ofri -pentamethylbenzylferrocene with PVC or chloromethylated PS was used to fabricate redox electrodes.  

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