Complexes of N-Confused Porphyrin Derivatives as Ortho-Metallating Ligands. Synthesis, Structure, Redox Properties, and Chirality.

A family of transition metal complexes of meso-aryl-2-aza-21-carbaporphyrin (N-confused porphyrin, NCP) derivatives acting as ortho-metallating ligands for ruthenium(II), rhodium(III), and iridium(III) is synthesized and characterized by XRD, spectroscopic, and electrochemical methods. The chirality of these systems is shown by the separation of the enantiomers and analyzed by circular dichroism and DFT. A preliminary catalytic study indicates the activity of the iridium(III) ortho-metallated complexes in the N-heterocyclization of primary amines with diols.

Bispalladium(II) Complexes of di-p-Pyrirubyrin Derivatives as Promising Near-Infrared Photoacoustic Dyes.

The insertion of palladium(II) into di-p-pyrirubyrin results in mutually convertible bimetallic complexes. Post-synthetic functionalization of one of them yielded bispalladium(II) dioxo-di-p-pyrirubyrin and, after demetallation, dioxo-di-p-pyrirubyrin, introducing for the first time the α,ß'-pyridin-2-one unit into the macrocyclic frame. Bispalladium(II) di-p-pyrirubyrin 6, bispalladium(II) dioxo-di-p-pyrirubyrin 9, and dioxo-di-p-pyrirubyrin 10 absorb and emit light around 1000 nm and are characterized by high photostability. Thus, they are promising candidates for near-infrared photoacoustic dyes, ideally targeting (9) the wavelength of Yb-based fiber lasers. The incorporation of an α,ß'-pyridine moiety into expanded porphyrins opens a highly interesting area of research due to the attractive optical and coordination properties of the resulting molecules.

Organometallic chemistry confined within a porphyrin-like framework.

The world of modified porphyrins changed forever when an N-confused porphyrin (NCP), a porphyrin isomer, was first published in 1994. The replacement of one inner nitrogen with a carbon atom revolutionised the chemistry that one is able to perform within the coordination cavity. One could explore new pathways in the organometallic chemistry of porphyrins by forcing a carbon fragment from the ring or an inner substituent to sit close to an inserted metal ion. Since the NCP discovery, a series of modifications became available to tune the coordination properties of the cavity, introducing a fascinating realm of carbaporphyrins. The review surveys all possible carbatetraphyrins(1.1.1.1) and their spectacular coordination and organometallic chemistry.

Manganese(III) porphyrin-catalyzed regioselective dual functionalization of C(sp3)-H bonds: the transformation of arylalkanes to 1,4-diketones.

The first, direct way from arylalkanes to 1,4-dicarbonyl compounds has been shown. It makes obtaining these useful products more accessible and cheaper. Our method is based on a one-pot reaction with excellent regioselectivity, mild conditions, and water as the main solvent. A plausible reaction mechanism has also been proposed.

Organoboron Complexes in Edge-Sharing Macrocycles: The Triphyrin(2.1.1)-Tetraphyrin(1.1.1.1) Hybrid.

The formation of a precisely designed environment predefined for stabilizing electron-deficient atoms, such as boron(III), is an important approach for optimizing the properties of a chromophore. A triphyrin(2.1.1) motif built on the extended π-system of a tetraphyrin(1.1.1.1) skeleton creates a new coordination environment, with a CNN set of donors confined in a limited space predefined for binding small cations. The entrapment of boron(III) in the triphyrin(2.1.1) sector, with formation of a direct B-C bond, significantly changes the optical response and the global aromatic character of the compound, leading to an extension of the π-delocalisation.

Inversion Triggered by Protonation-A Rubyrin with Embedded α,ß'-Pyridine Moieties.

Incorporation of α,ß'-pyridine into a [26]hexaphyrin(1.1.0.1.1.0) frame resulted in formation of 29,33-diaza-A,D-di-p-benzi[26]hexaphyrin (A,D-di-p-pyrirubyrin), which acquires a strictly planar conformation with two nitrogen pyridine atoms directed to the center of the macrocyclic core. The mode of α,ß'-pyridine incorporation results in efficient 26-electron π-conjugation, as shown by the clear spectroscopic and structural aromatic features. The formation of the trication and tetracation through protonation is accompanied by a conformational flip of one or two pyridinium moieties to result in N-confused or doubly N-confused conformers of the original macrocyclic frame.

Rhodium-Induced Reversible C-C Bond Cleavage: Transformations of Rhodium(III) 22-Alkyl-m-benziporphyrins.

The structurally prearranged carbaporphyrins 22-methyl- and 22-ethyl-m-benziporphyrins provide the platform stabilizing aromatic rhodium(III) 22-(µ-methylene-m-benziporphyrin) and rhodium(III) 22-(µ-ethylidene-m-benziporphyrin). An intramolecular conversion facilitated by the m-phenylene reactivity and observed for both aromatic complexes efficiently leads to rhodium(III) 21-(µ-methylene)-21-carbaporphyrin and rhodium(III) 21-(µ-ethylidene)-21-carbaporphyrin. The distinctive macrocyclic environment of rhodium(III) 21-carbaporphyrin created an opportunity to trap unique organometallic transformations of inner core substituents affording the fulvene-like bond pattern or the rearrangement to 21-vinyl substituent. The one-electron reduction of the rhodium(III) carbaporphyrin anion π-radical with a (dxy )2 (dxz )2 (dyz )2 -(P.- ) electronic configuration is demonstrated. The further process of reduction of paramagnetic species triggers the ethyl migration from carbon(22) to rhodium(III), affording the diamagnetic rhodium(III) meta-benziporphyrin containing the apically coordinated σ-ethyl ligand providing an example of reversible C(sp2 )-C(sp3 ) bond cleavage.

Gold(III) Triggered Transformations of 22-Methyl-m-benziporphyrin Involving an Effective Contraction of Benzene to Cyclopentadiene.

A structurally prearranged carbaporphyrin, 22-methyl-m-benziporphyrin, provided the perfect macrocyclic platform to form gold(III) 22-methyl-m-benziporphyrin, which facilitates the specific m-benzene ring contraction yielding gold(III) 21-methyl 21-carbaporphyrin with remarkably high yield.

meso-N-Pyrrole as a Versatile Substituent Influencing the Optical Properties of Porphyrin.

A meso-N-pyrrole porphyrin converts into a π-extended porphyrin forming an indolizine-3-one motif. The indolizine-3-one frame opens a lactam subunit preserving a six-membered, heterocyclic structure fused with the main macrocycle. The optical properties of formed derivatives follow the structural modifications giving the absorbance and emission eventually modulated by the NH-centered modifications of the fused unit.

A Rhodium-Mediated Contraction of Benzene to Cyclopentadiene: Transformations of Rhodium(III) m-Benziporphyrin.

The contraction of benzene is one of an exclusive group of reactions where the cleavage of aromatic structure is of fundamental importance. Rhodium(III) m-benziporphyrin undergoes an unprecedented transformation of the built-in m-phenylene in which a perimeter carbon atom is extruded to form rhodium(III) 21-carbaporphyrin, stabilizing the formyl-unit-substituted rhodacyclopropane motif.

A fused meso-aminoporphyrin: a switchable near-IR chromophore.

An aryl amine attached to the meso position of a porphyrin controls the π-delocalization using a redox process or a protonation/deprotonation centered at the meso-nitrogen. An easily accessible modulated motif affords a switchable near-IR chromophore as reflected by significant changes in absorption and fluorescence spectra.

Synthesis and switching the aromatic character of oxatriphyrins(2.1.1).

Triangularly shaped, contracted porphyrinoids belong to a group of molecules where the geometry significantly modifies the observed electronic properties. The need for a controllable, effective, and widely applicable approach to triphyrins drives extensive research towards macrocyclic materials that act as potential controlling motifs by switching their aromaticity. Two isomeric thiophene-fused triphyrins(2.1.1) were synthesized by applying an innovative approach. Spectroscopic techniques (NMR, UV/Vis) show that both macrocycles are aromatic and quantitatively convert into anti-aromatic structures after reduction with a zinc amalgam. The reduced forms were stabilized through boron(III) coordination, thereby allowing the observation of anti-aromatic 16 π delocalization within a contracted porphyrin.