Reactivity of Polymer-Co III Complexes

A Co(IH) complex is inert in ligand-substitution reactions, and its uniform structure is thus maintained even in an aqueous solution. The reaction mechanism of a Co(III) complex in solution is well known, so that a pendant-type polymer-Co(IU) complex, e.g. 17,19, is one of the most suitable compounds for a quantitative study of the effects of a polymer ligand on the reactivity of a metal complex. The reactivities of the polymer-Co(III) complexes are discussed here kinetically and compared with those of the monomeric Co(III) complexes in the following reactions electron-transfer reactions between the polymer complexes and Fe(II) [Eqs. (5) and (6)], and the ligand-substitution reaction of the polymer-Co(III) complex with hydroxy ions or water [Eqs. (7) and (8)J. One of the electron-transfer reactions proceeds via 

L = polymer-ligand, e.g. FVP = poly(4-vinylpyridine), PVI = poly(N-vinylimidazole) en = ethylenediamine, phen = phenantroline 

A polymer-Co(III) complex behaves as a poly(electrolyte) in an aqueous solution, and the reaction is expected to be sensitive to the charge of reactant species. Rate constants (fcpvp) for the reactions of the poly(4-vinylpyridine) (PVP)-Co(III) complexes, [CoaiIXen)2(PVP)Cl]Cl2 [Eqs. (5), (7), and (8)] and those (icPy) of the monomeric pyridine complex, [Co(lII)(en)2(Py)Cl]Cl2, were determined78-80.  

The reactivity ratios of the PVP complex and the pyridine complex (fcpvp/kpy) are summarized in Table 7. 

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