3.6.5 Cobalt Catalysts

Cobalt is present in various metalloenzymes like methylmalonyl coenzyme A mutase. It is also a key constituent of vitamin B₁₂ which plays an important role in normal functioning of the central nervous system. Cobalt exists mainly in two oxidation states. The standard electrode potential for Co(III)/Co(II) system is 1.82 V which shows that it is a very strong oxidant. Also, the existence of cobalt based redox systems in biological systems has intuited the exploration of similar bio-mimicking systems for redox reactions. Some of these reactions are illustrated below.

3.6.5.1 Oxidation Reactions

Epoxidation of alkenes can be achieved by using cobalt(II)-Schiff base complex in the presence of reducing agent such as aldehydes, β-ketoester, acetal and triphenylphosphine under molecular oxygen (Scheme 1). A series of cobalt(II) complexes have been designed and developed for this purpose. The reactions are general, efficient and effective at ambient temperature.

Scheme 1