Oxygenated cobalt dioxygen carriers

The general features of oxygenation equilibria and autoxidation involving cobalt-based lacunar cyclidene dioxygen carriers have been extensively studied by Busch and coworkers with special reference to dioxygen affinities and their correlation with structural features Lacunar systems have considerable activities for reversible dioxygen binding in their cavities under ambient conditions. 

It has long been known that, when bound to cobalt(II), the pyridine-based chelate ligands 2,2 -bipyridine (bipy), 1,10-phenanthroline (phen), and 2,2 6, 2"-terpyridine (terpy) form complexes that react with dioxygen in aqueous solution (32-34). The mixed-ligand complexes [Co(terpy)(bipy)]2+ and [Co(terpy)(phen)]2+ can act as oxygen carriers in aqueous solutions at pH values as low as 3.0 (34b), and the superoxo species thus formed are apparently dinuclear. In addition, the dinuclear bipyridine complex [(bipy)2Coin(/ 2-0 )(/ 2-02 )CoIn(bipy)2 ]3+ has been shown to catalyze the oxidation of 2,6-di-ter -butylphenol to the feri-butyl-substituted diphenoquinone and quinone (35). 

McLendon G, MarteU AE (1976) Inorganic oxygen carriers as models for biological systems. Coord Chem Rev 19 1-8 McLendon G, Harris W, MarteU AE (1976) Dioxygen compl-exation by cobalt amino acid and peptide complexes. 1. Stoichiometry and equilibria. J Am Chem Soc 98 8379-8386... 

The syntheses of two complexes are described here the cobalt(II) lacunar cyclidene complex in which R =—(CH2)e— and = R = —CH3, and the iron(II) complex in which R =m-xylylene, R = —CH2C6H5, and R = —CgHs- The former is the most studied example of a lacunar cyclidene oxygen carrier, and the latter represents the first nonporphyrin iron complex capable of forming a stable dioxygen adduct at room temperature. 

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