Relationship between reversible oxygenation and catalytic properties of amino acid cobalt complexes

The relationship between oxygenation properties and corresponding catalytic performance of 13 natural amino acid-cobalt (II) complexes were identified. The results indicate that for those complexes with reversible oxygenation properties, the shorter the time spent for completing a reversible oxygenation cycle is, the better their reversible oxygenation and the worse the property of their catalysis are. As a contrast, longer cycle time for completing a reversible oxygenation cycle attest to worse performance of reversible oxygenation but better property of catalysis. In particular, the results of glutamic cobalt (II) complexes confirms that when the ratio of Co(II) and ligand is 1:3, the reversible oxygenation property is good, while the catalytic reaction yields a low conversion rate of cyclohexene. On the other hand, the complex with Co(II):ligand 1:1 led to a high conversion rate of cyclohexene. With the help of the preliminary structural study and theoretical calculation, we suppose that the difference between reversible oxygenation property and catalytic property are mainly due to the coordinating ability of amino acid ligands. The strong coordinating ability of amino acid ligands is favorably to the high spin to low spin transform for reversibly absorbing O₂. While the less favorably for vinyl replacement exhibited poor catalytic properties, and vice versa.