Advances in the use of metal-free tetrapyrrolic macrocycles as catalysts

This review provides an overview of recent progress made in the field of catalysis using metal-free tetrapyrrolic macrocycles, focusing on calix[4]pyrroles, porphyrins and corroles, which are structurally related to porphyrins. Calix[4]pyrroles are versatile receptors in supramolecular chemistry while porphyrins are considered as 'pigment of life' due to their role in vital biological processes. Beyond their natural functions, synthetic porphyrins have been applied in various fields, including organometallic catalysis, dye-sensitized solar cells, sensing, artificial olfactory systems, photodynamic therapy (PDT), anticancer drugs, biochemical probes, and electrochemical devices. Relevant examples of these two pyrrolic macrocycles as metal-free organocatalysts, photocatalysts, and electrocatalysts are presented here. The effect of macrocyclic structural modifications such as their functionalization with different substituents, distortion from planarity, conformational flexibility and rigidity towards catalytic activity are presented, highlighting the potential of these two macrocycles as metal-free catalysts.