Cobalt porphyrins: Synthesis and mechanistic insight overview on versatile applications

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Metal porphyrins are naturally occurring complexes (e.g. hemoglobin, myoglobin, cytochromes P450 and others) of great significance. Along with their natural presence, nowadays, they are also synthesized for various research purposes due to their extensive applications in several field viz. conversion reactions, energy storage, medicinal application (antioxidant, anti-inflammatory, anticancer, antiviral properties), photodynamic therapy, electronics, sensors, solar cells and many more applications. Out of several transition metal-based porphyrin complexes, cobalt porphyrins have shown a number of valuable properties and applications like self-assembling, antioxidant activities, photoelectrochemical oxidation of water, electrochemical H 2 evolution, oxygen reduction and evolution reactions (ORR and OER), reductive decomposition of carbon dioxide (CO 2 ), role in organic synthesis (i.e. cycloalkane oxidation, cyclopropanation of alkenes, and toluene's oxidation), dye degradation, and role in detection of 4-hydroxybenzoic acid. These applications of cobalt porphyrins have been mechanistically explained in this review indicating the potential efficiency and advantages of these complexes as promising catalysts. Potential roles in emerging photo-assisted electrocatalysis (CO 2 reduction, OER, and HER) and cascade CO 2 conversion catalysis have also been insightfully explored. This review also explores the detailed synthetic approaches for diverse classes of cobalt porphyrins' preparation and advancements on their monomeric and dimeric units. New emerging green synthetic routes for cobalt porphyrins synthesis have also been discussed and assessed. A significant works have been done on synthesis as well as application of cobalt porphyrins, but, there are limited reviews which could cover its wide arrays of applications and suitability for the further research advancements. Thus, this review provides a systematic approach on the synthesis of cobalt porphyrins, wide range of important applications and their mechanistic overviews.