Heteroatom-Containing Porphyrin Analogues

Abstract

The heteroatom-containing porphyrin analogues or core-modified porphyrins that resulted from the replacement of one or two pyrrole rings with other five-membered heterocycles such as furan, thiophene, selenophene, tellurophene, indene, phosphole, and silole are highly promising macrocycles and exhibit quite different physicochemical properties compared to regular azaporphyrins. The properties of heteroporphyrins depend on the nature and number of different heterocycle(s) present in place of pyrrole ring(s). The heteroporphyrins provide unique and unprecedented coordination environments for metals. Unlike regular porphyrins, the monoheteroporphyrins are known to stabilize metals in unusual oxidation states such as Cu and Ni in +1 oxidation states. The diheteroporphyrins, which are neutral macrocycles without ionizable protons, also showed interesting coordination chemistry. Thus, significant progress has been made in last few decades on core-modified porphyrins in terms of their synthesis, their use in building multiporphyrin arrays for light-harvesting applications, their use as ligands to form interesting metal complexes, and also their use for several other studies. The synthetic methods available in the literature allow one to prepare mono- and diheteroporphyrins and their functionalized derivatives, which were used extensively to prepare several covalent and noncovalent heteroporphyrin-based multiporphyrin arrays. The methods are also developed to synthesize different hetero analogues of porphyrin derivatives such as heterocorroles, heterochlorins, heterocarbaporphyrinoids, heteroatom-substituted confused porphyrins, and so on. This Review summarizes the key developments that have occurred in heteroporphyrin chemistry over the last four decades.

Homocarbaporphyrinoids: The m‐o‐m and p‐o‐p Terphenyl Embedded Expanded Porphyrin Analogues and Their RhI Complexes

“…Porphyrins are widely studied functional pigments, which have been well explored in the literature . Analogues, such as isomeric, contracted, expanded, fused, and bridged porphyrinoids, have been synthesized and investigated for various applications . Among the analogues, the expanded porphyrins have received much attention due to their structural diversity, electronic properties, coordination chemistry, and reactivities, which are entirely different from porphyrins .…”

Polycyclic Aromatic Hydrocarbon‐/Heterocycle‐Embedded Porphyrinoids

“…The electronic properties of the porphyrins can be altered by introducing appropriate substituents at the β ‐pyrrole carbons or at the meso ‐carbons. However, one of the best ways to alter the electronic properties is by modifying the porphyrin core by replacing one or two pyrrole rings with other five membered heterocycles such as thiophene, furan, selenophene, tellurophene and the resulted porphyrins are known as core‐modified porphyrins or heteroporphyrins 2 . The heteroporphyrins exhibit very different physicochemical and coordination properties from regular porphyrins and are known to stabilize metals in unusual oxidation states .…”

Synthesis of [14]Oxatriphyrins(2.1.1) and Their Transformation into Ethane‐Bridged Oxatripyrrins by Boron Complexation

“…We and others have developed the chemistry of [14]triphyrin(2.1.1), which has a relatively planar structure with 14π-electron aromaticity and can be isolated as a free base. [18,19] It should be noted that core-modification of porphyrin is a powerful approach to customizing the properties of porphyrins [20][21][22] and can be applied to contracted porphyrins as [14]oxatriphyrins(2.1.1) with dichloro(phenyl)borane resulted in the formation of boron complexes with a reduced olefin bridge. Additionally, [14]triphyrins(2.1.1) exhibit rich redox properties based on the flexible macrocyclic aromaticity, which is advantageous for catalysis.…”