Heterocycle-appended porphyrins: synthesis and challenges

Porphyrin and their versatile metal complexes represent a special class of coordination compounds possessing unique physical-chemical properties. The achievements in the development of the synthetic approaches for the modification of the porphyrin macrocycle allowed the preparation of a variety of functional derivatives for diverse applications. Among a broad diversity of synthetically available metalloporphyrins meso-substituted tetrapyrroles are comprehensively investigated. However, beta-substituted porphyrins could be considered as the most suitable models for mimicking the key roles of naturally occurring dyes in vital processes. The introduction of various substituents to the beta-positions of the macrocycle opens an access to the tuning of the electronic and, in turn, physical-chemical properties of the obtained complexes. The present review summarizes the synthetic aspects of beta-functionalized tetrapyrrolic compounds - heterocycle-appended porphyrins - and their physical-chemical properties. The observed synthetic methodologies are divided onto several parts depending on the type of heterocycle appended to the porphyrin beta,beta'-positions. The first five parts of the synthetic aspects chapter are devoted to the methods of the annulation of nitrogen-containing heterocycles. Strategies for the preparation of porphyrins bearing annulated sulfur-heterocycles are observed separately. A concluding chapter of the review comprises the most interesting and promising physical-chemical properties of these compounds and related challenges of their practical applications in different fields. (C) 2019 Published by Elsevier B.V.