24 F. P. DwYER 



This mechanism, which is similar to that proposed by Wilhams (1956b) 

 for the haemin catalysed oxidation of cysteine by molecular oxygen, is 

 applicable also to the remarkable reaction first discovered by Blau (1889). 

 The oxidized forms of the tris complexes of Fe, Ru and Os with phenanthroline, 

 bipyridine and terpyridine undergo spontaneous reduction when the pH 

 of the aqueous solutions is raised. Hydroxyl radical has been detected (Uri, 

 1952). This may reoxidize the complexes if the pH is lowered soon enough, 

 or decompose to ozone (Blau, 1898) or hydrogen peroxide (Brandt, Dwyer 





II2. II2* 



Fig. 5 



and Gyarfas, 1954). The polarization of the carbon atom (Fig. 6) may be 

 sufficient to lead to dissociation of a proton, as happens with simple hydrated 

 cations, and the electron then is captured from the attached OH group. 

 Reaction mechanisms of this kind could well be applied to oxidation- 

 reduction reactions in the cytochrome systems, but may have applications to 

 many synthetic processes involving activated — CH — and — CH2 groups, 

 as discussed previously. 



Undue attention seems to have been paid in metal porphyrins to the 



formal oxidation state of the metal in relation to possible oxidation states as 



H^ /^OH H^ deduced from simple compounds or salts. As a result, 



jf 1 ► r "jj + OH there has been much hesitation in invoking otherwise 



II 1^ feasible reaction mechanisms involving, for instance, 



formal Fe(IV), Fe(V) or Mg(I). In such strongly 

 interacting systems both the metal and the ligand are 

 in unique electronic states because of their combination. The relevant fact 

 is the number of electrons that can be added to or detached from the complex 

 unit. The source or fate of the electrons is immaterial. Often this informa- 

 tion can be obtained by electrolytic methods or simple chemical reagents. 



REDOX POTENTIALS OF RUTHENIUM COMPLEXES 



Simple model metal-complex systems offer much promise in elucidating 

 problems in metal-porphyrin chemistry (Williams, 1956a, b). This is 

 especially so when considering redox potentials. Much useful information on 

 the effect of substituents has been obtained from the iron /m(phenanthroline) 

 and bipyridine complexes. In general, the results parallel those obtained 

 with various porphyrins (Martell and Calvin, 1952). Electron attracting 

 substituents (NO2, Br, CI) render oxidation of the complexes more difficult 

 (potentials are more positive than in the unsubstituted complexes), whilst 



