Unusual Formation of 21-Oxacorrole from 21-Oxaporphyrin Induced by Phosphoryl Chloride

Expanded Porphyrin Contraction: From [22]Triphyrin(6.6.0) to [22]Triphyrin(6.5.0)

An expanded triphyrin containing a bipyrrole moiety and annulene links, namely tetraphenyl-[22]triphyrin(6.5.0), 2, has been synthesized. The synthesis proceeded by a postsynthetic transformation of tetraphenyl-[22]triphyrin(6.6.0), 1, in a metal-free unexpected and unprecedented ring contraction during column chromatography on alumina. The observed transformation, located at the hydrocarbon chain linking the pyrrole units, formally corresponds to a subtraction of one carbon atom from an annulene circuit. In contrast to the flexible substrate 1, the product 2 is conformationally rigid, and capable of chloride anion binding in its protonated form.

Synthesis, Structural, Spectral, and Electrochemical Studies of Selenabenziporphyrin and Its Pd(II) Complex

A new nonaromatic selenabenziporphyrin was synthesized by (3 + 1) condensation of m-benzitripyrrane and 2,5-bis[( p-tolyl)hydroxymethyl] selenophene under mild trifluoroacetic acid-catalyzed reaction conditions. The selenabenziporphyrin was characterized by high-resolution mass spectrometry, one- and two-dimensional NMR spectroscopy, and X-ray crystallography. The crystal structure revealed that the macrocycle was planar with moderately tilted m-phenylene ring and that the phenylene ring completely blocks the macrocyclic π-delocalization. The selenabenziporphyrin exhibits one broad absorption band at 645 nm along with one sharp band at 415 nm, and electrochemical studies revealed that the macrocycle was electron-deficient. The selenabenziporphyrin readily forms organometallic Pd(II) complex when treated with PdCl₂ in CH₃CN/CHCl₃ at reflux followed by recrystallization. The X-ray structure revealed that the Pd(II) ion was coordinated with two pyrrole "N"s, selenophene "Se", and m-phenylene ring "C" in square-planar fashion, and the complex retained its nonaromatic nature. The Pd(II) complex exhibits ill-defined absorption bands, and it was more electron-deficient than free-base selenabenziporphyrin macrocycle. Time-dependent density functional theory studies supported the experimental observations.

Two Macrocycles in One Shot: Synthesis, Spectroscopy, Photophysics, and Tautomerism of 23-Oxahemiporphycene and 21-Oxacorrole-5-carbaldehyde

The synthesis of 23-oxahemiporphycene, the first monooxa analogue of hemiporphycene, a structural isomer of porphyrin, is reported. Its generation under McMurry reaction conditions is surprisingly accompanied by the appearance of a formyl derivative of oxacorrole, 21-oxacorrole-5-carbaldehyde. A mechanism for the formation of the latter is proposed, relying on pinacol rearrangement of titanium pinacolate. The structures of the most stable tautomeric forms are established for both compounds based on IR and NMR spectra combined with DFT calculations. Spectral and photophysical characteristics are compared with those of structurally similar macrocycles. Replacement of one nitrogen by oxygen in hemiporphycene has only a minor impact. In contrast, for corrole it leads to the enhancement of stability and to strongly reduced rates of nonradiative deactivation of the lowest excited singlet state. This is explained by the planarity of oxacorroles, achieved by removing one of the inner hydrogen atoms from the inner cavity. Unusual crystal packing is observed for the protonated form of 23-oxahemiporphycene, which exhibits a π-π stacked columnar alignment of positively charged macrocycle units.

Heterocorroles: corrole analogues containing heteroatom(s) in the core or at a meso-position

Corroles are 18 π aromatic macrocyclic systems having one direct pyrrole–pyrrole linkage leading to a contracted cavity compared to porphyrins. Corroles exhibit contrasting coordination chemistry and properties compared to porphyrins. Structural modification of corroles by introducing a heteroatom in their aromatic conjugation circuit i.e., either in the core or at a meso position leads to a new class of corrinoids called heterocorroles. The core modification strategy includes replacing one or two core nitrogen atom(s) with O, S or C atoms and meso-modification involves replacing the meso-carbon atom at the 10-position with NH, NR, O, S, Se or Si atoms. This review article presents an overview of the progress in heterocorrole chemistry including their syntheses, key structural aspects and properties.

This review article presents an overview of the progress in heterocorrole chemistry including their syntheses, key structural aspects and properties.

Synthesis of Corroles and Their Heteroanalogs

Corroles have come a long way from being a curiosity to being a mainstream research topic. They are now regularly synthesized in numerous research laboratories worldwide with diverse specific aims in mind. In this review we present a comprehensive description of corroles' synthesis, developed both before and after 1999. To aid the investigator in developing synthetic strategies, some of the sections culminate in tables containing comparisons of various methodologies leading to meso-substituted corroles. The remaining challenges are delineated. In the second part of this review, we also describe the syntheses of isocorroles and heteroanalogs of corroles such as triazacorroles (corrolazines), 10-heterocorroles, 21-heterocorroles, 22-heterocorroles, N-confused corroles, as well as norcorroles. The review is complemented with a short outlook.

Cationic nickel porphyrinoids with unexpected reactivity

Nickel(II) complexes of ring-contracted 9-methylisocorroles were prepared by templated macrocyclisation and act as the first porphyrinoid catalysts for C–C cross-coupling.

Cationic nickel(ii) complexes of two ring-contracted porphyrinoid ligands distantly related to the corrins were prepared by metal templated macrocyclisation. The compounds show reversible electron transfer processes and were found to be the first porphyrinoid-based catalysts for C–C cross-coupling.

Core chemistry and skeletal rearrangements of porphyrinoids and metalloporphyrinoids

Porphyrin core alteration allows for the exploration of porphyrin-like or porphyrin-unlike coordination chemistry and provides an insight into reactions inside particularly shaped macrocyclic architecture including metal-mediated structural transformations.