21-Carba-23-selenaporphyrinoid Dyads-An Azepine Unit as a Merging Motif.

The oxidation of 10,15-diaryl-21-carba-23-selenaporphyrinoids resulted in the creation of dyads. The dimerization process follows a [5+2] cycloaddition path with the formation of an azepine unit. The arrays display two direct bonds between the peripheral carbocyclic carbon atoms of one carbaselenaporphyrinic subunit and the central carbon and nitrogen atoms of the second subunit. This results in a unique canted arrangement of two carbaporphyrinoid planes resembling an open seashell-like motif.

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.

Two-photon absorption of 28-hetero-2,7-naphthiporphyrins: expanded carbaporphyrinoid macrocycles.

The one- and two-photon absorption (1PA and 2PA) properties of three expanded aceneporphyrinoids, 28-thia-, 28-selena- and 28-tellura-2,7-naphthiporphyrin, have been studied. The open-aperture Z-scan technique was used to determine two-photon absorption cross-sections in the near infrared range using an amplified femtosecond laser system. The maximum values of the cross sections were found to be 99, 200 and 650 GM at 900 nm and 1, 13 and 31 GM at 1400 nm for the three investigated compounds, respectively. These results demonstrate enhanced 2PA properties compared with well-known porphyrin photosensitizers, such as Foscan®, showing the potential of porphyrin core modification for optimizing infrared nonlinear absorbers.

Dicarba[26]hexaporphyrinoids(1.1.1.1.1.1) with an Embedded Cyclopentene Moiety-Conformational Switching.

Invited for the cover of this issue is Lechoslaw Latos-Grazynski and co-workers at University of Wroclaw. The image depicts two essential conformations of 31,34-dicarba[26]hexachlorins: dumbbell and rectangular with regular or doubly inverted carbocyclic rings, respectively. Read the full text of the article at 10.1002/chem.202002603.

Dicarba[26]hexaporphyrinoids(1.1.1.1.1.1) with an Embedded Cyclopentene Moiety-Conformational Switching.

Incorporation of cyclopentene fragments into a skeleton of parental [26]hexaphyrin(1.1.1.1.1.1) afforded extended carbaporphyrinoids: 31,34-dicarbahexa[26]chlorin and its derivatives: the first externally substituted by ethoxy and 2,4,6-trimethylbenzylidene groups and the second one formed by selective oxidation of one cyclopentene ring. Macrocycles adopt dumbbell-shaped conformations with two meso hydrogen atoms located inside the macrocyclic cavity. Protonation of 31,34-dicarba[26]hexachlorins provided dications existing in dumbbell-shaped and rectangular conformations.

Chemistry inside a Porphyrin Skeleton: Platinacyclopentadiene from Tellurophene.

Platinum(II) binds to 21,23-ditelluraporphyrin forming a side-on complex, which can be easily transformed into an aromatic metallaporphyrin, that is, 21-platina-23-telluraporphyrin, with a platinacyclopentadiene unit built in the porphyrin skeleton in place of one pyrrole ring. The central platinum(II) ion with a CCNTe square-planar coordination sphere can be oxidized to platinum(IV) by chlorine, bromine, methyl iodide or allyl chloride to yield octahedral complexes. All platinatelluraporphyrins show dynamic behavior involving the platinum ion coordination sphere fluxionality and the porphyrin skeleton deformation, both in-plane and out-of-plane, as demonstrated by 1 H NMR spectroscopy.

Conformation-Dependent Response to the Protonation of Diphenanthrioctaphyrin(1.1.1.0.1.1.1.0): A Route to Pseudorotaxane-Like Structures.

Diphenanthrioctaphyrin(1.1.1.0.1.1.1.0), an expanded carbaporphyrinoid incorporating two phenanthrenylene moieties, exists as two separate, yet interconvertible, locked stereoisomers. These species demonstrate complex dynamic behavior upon protonation, consisting in multiple conformational rearrangements and anion-binding events. The formation of one of the final dicationic forms is accompanied by the inclusion of a complex anion(s) within the macrocyclic cavity yielding a pseudorotaxane-like host-guest complex. Protonation with trifluoroacetic or dichloroacetic acids followed by neutralization afforded a conformation-switching cycle, which involves six structurally different species. Analogous acidification with chiral 10-camphorsulfonic acid and subsequent neutralization generated one of the free base stereoisomers with enantiomeric excess. Therefore, it was shown that the simple acid-base chemistry of diphenanthrioctaphyrin can act as stimulus, inducing chirality into the system, allowing for the manipulation of the stereochemical information imprinted into the enantiomers of the macrocycle.

Kinetic versus Thermodynamic Control Over Multiple Conformations of Di-2,7-naphthihexaphyrin(1.1.1.1.1.1).

Di-2,7-naphthihexaphyrin(1.1.1.1.1.1), a non-aromatic carba-analogue of the hexaphyrin(1.1.1.1.1.1), incorporating two built-in 2,7-naphthylene moieties was synthesized as two separate, conformationally locked stereoisomers. Both conformers followed complex protonation pathways involving structurally different species, which can be targeted under kinetic and thermodynamic control. The neutralization of the ultimate dicationic product, accessible from both stereoisomers of the free base, allowed to realize the complex conformational switching cycle involving six structurally different species.

Expanded Carbaporphyrinoids.

This Review outlines the progress in the field of synthetic expanded carbaporphyrinoids. The evolution of this topic is demonstrated with expanded porphyrin-inspired systems with a variety of incorporated entities that introduce one or more carbon atoms into the cavity. The discussion starts with platyrins-the macrocycles that were identified as parent molecules of not only the expanded carbaporphyrinoids, but the carbaporphyrinoid class in general. After historic considerations, the plethora of expanded porphyrin-like macrocycles containing N-confused or neo-confused pyrrole motifs and different carbocyclic subunits are presented. Special emphasis is given to applications of expanded carbaporphyrinoids in different areas, including organometallic chemistry, switching systems, or aromaticity, concluding with the demonstration of a covalent cage based on an expanded carbaporphyrinoid.

C-H and C-M Activation, Aromaticity Tuning, and Co⋠⋠⋠Ru Interactions Confined in the Azuliporphyrin Framework.

Invited for the cover of this issue is Lechoslaw Latos-Grazynski and co-workers at University of Wroclaw. The image depicts cobalt(II) azuliporphyrin as a magical organometallic platform to perform other types of chemistry, that is, dioxygen activation, aromaticity control, and construction of intermetallic communication motifs. Read the full text of the article at 10.1002/chem.201903215.

Oxygenation of Phenanthriporphyrin and Copper(III) Phenanthriporphyrin: An Efficient Route to Phenanthribilinones.

Photooxidation of copper(III) 5,6-dimethoxyphenathriporphyrin and copper(III) 5,6-dioxophenanthriporphyrin, which contain phenanthrene or dioxophenathrene moieties built into the macrocyclic frameworks, resulted in the regioselective cleavage that afforded organometallic copper(III) complexes of open-chain phenanthribilinone-type acyclic ligands terminated by carbonyl groups. The copper(III) coordinates two carbon atoms of phenantherene (dioxophenanthrene) and two nitrogen atoms of pyrrole and pyrrolone units, preserving the donor sets of the paternal complexes. The primary dioxygen attack is located at the meso carbon atom adjacent to the phenanthrene moiety. Demetalation of copper(III) 21-benzoyl-phenanthribilin-1-one and copper(III) 21-benzoyl-dioxophenanthribilin-1-one yielded mainly two diastereomers [15Z, 20E] and [15Z, 20Z], which differ in the configurations at two Cα-Cmeso double bonds. The regioselectivity of the cleavage, detected in the course of experimental studies, has been substantiated by DFT investigations. The regioselective cleavage of 5,6-dimethoxyphenanthriporphyrin in reaction with basic iron(III) acetate was detected, providing the synthetically efficient methodology to produce 21-benzoyl-dioxophenanthribilin-1-one.

28-Hetero-2,7-Naphthiporphyrins: Horizontal Expansion of the m-Benziporphyrin Macrocycle.

Replacement of the m-phenylene moiety of m-benziporphyrins with the 2,7-naphthalenyl subunit yielded 28-hetero-2,7-naphthiporphyrins-macrocycles that can be considered as expanded carbaporphyrinoids. This group retains some features of parent m-benziporphyrins, but due to larger size and different shape of the macrocyclic cavity, their coordination properties are different. Upon reduction and conformational rearrangement the 28-thia- and 28-selena-2,7-naphthiporphyrin form organophosphorus(V) complexes.

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.

C-H and C-M Activation, Aromaticity Tuning, and Co⋠⋠⋠Ru Interactions Confined in the Azuliporphyrin Framework.

Taking advantage of the specific properties of azuliporphyrin and the reactivity of cobalt(II), activation of an azulene C(sp2 )-H bond occurred and organometallic complexes with Co-C bonding were formed. The system allowed for macrocyclic aromaticity tuning through metal coordination and oxidation. Thanks to the CoII -C and parallel tested CuII -C reactivity and the affinity of metal centers to dioxygen, oxygen atom insertion into the M-C bond could be investigated. Insertion starts with an oxygen molecule coordination and leads to monomeric and dimeric complexes of specific electronic structures. Formation of unique paramagnetic σ/π-hybrid bimetallic complexes enabled spectroscopic and theoretical investigations of peculiar CoII ⋅⋅⋅Ru0 interactions.

Shaping a Porphyrinoid Frame by Heteroatoms Extrusion: Formation of an Expanded [22]Triphyrin(6.6.0).

An aromatic expanded triphyrin, [22]triphyrin(6.6.0) 2, containing a pyrrole unit, a bipyrrole moiety, and annulene links, was obtained from a tellurium-containing precursor meso-tetraaryl-26,28-ditellurasapphyrin 1. The reaction path proceeds through an acid-promoted tellurium extrusion from 1 yielding directly 2, characterized in a dicationic form by X-ray crystallography. In solution the neutral macrocycle 2 reveals flexibility typical for annulenes and it exists as a mixture of conformers that differ by the configuration of the annulene fragments, as proven by 1 H NMR studies and analyzed by DFT methods. The conformation is controlled by protonation state, the nature of an interacting anion, solvent identity, and by interaction with water.

Diphenanthrioctaphyrin(1.1.1.0.1.1.1.0): Conformational Switching Controls the Stereochemical Dynamics of the Topologically Chiral System.

The analogue of octaphyrin(1.1.1.0.1.1.1.0) bearing two dimethoxyphenanthrene units was synthesized and characterized in solution and solid state. The macrocycle was demonstrated to exist as two locked conformers that can be easily separated and handled individually. The conversion of conformers was proven to be facilitated by the presence of hydrogen-bond acceptors, such as amines. The bis-boron(III) complex of diphenanthrioctaphyrin has been obtained, proving that the metalloid center acts as the topology selector stabilizing only one conformation of the macrocycle, irrespective of the stereoisomer used for the insertion. Both conformers of diphenanthrioctaphyrin, as well as the boron complex formed from them, have been separated into enantiomers using HPLC with a chiral stationary phase. All of these systems have shown strikingly different stereodynamic behavior.

A meso-Tetraaryl-21-carbaporphyrin: Incorporation of a Cyclopentadiene Unit into a Porphyrin Architecture.

Incorporation of a cyclopentadiene moiety into the meso-tetraarylporphyrin framework, using 1,3-bis(arylhydroxymethyl)ferrocene as a synthon, resulted in the rational synthesis of a meso-tetraaryl-21-carbaporphyrin. The molecular design preserves all essential virtues of the original tetrapyrrolic architecture of meso-tetraarylporphyrin, including the perfect match between the ionic radii of an inserted metal and the size of the macrocyclic (CNNN) core, and steric protection provided by thoughtfully chosen meso-aryl substituents. Its protonation of the inner core reveal an adjustable (trigonal versus tetrahedral) geometry.

Organocopper(III) Phenanthriporphyrin-Exocyclic Transformations.

5,6-Dimethoxyphenanthriporphyrin 1 and 5,6-dioxophenanthriporphyrin 2 act as suitable organometallic ligands for copper(III), adopting trianionic [CCNN] coordination cores. Under oxidizing conditions, in the presence of methanol, copper(III) phenanthriporphyrin 1-Cu undergoes transformation to copper(III) phenanthriporphodimethene with methoxy substituents attached to two trans meso positions. Addition of acids to 1-Cu yields two isomeric copper(III) isophenanthriporphyrins protonated on one of the meso carbon atoms. Protonation of copper(III) 5,6-dioxophenanthriporphyrin 2-Cu yields the aromatic diprotonated complex 2-Cu-H22+. In the presence of HBF4 2-Cu undergoes borylation at the carbonyl oxygen atoms, forming an aromatic exocyclic boron(III) complex.

Three-Stage Aromaticity Switching in Boron(III) and Phosphorus(V) N-Fused p-Benziporphyrin.

Insertion of PCl3 or PhBCl2 into 5,10,15,20-tetraaryl-p-benziporphyrin prompted an intramolecular fusion affording anti-aromatic phosphorus(V) and non-aromatic boron(III) complexes of two N-fused dihydro-p-benziporphyrin isomers. These macrocycles are classified as carbatriphyrin due to the common [CNN] coordination. A sequence of direct transformations, triggered by protonation or two-electron redox processes, afforded a set of three mutually convertible N-fused p-benziporphyrinoids, with distinct anti-aromatic, non-aromatic, and aromatic spectroscopic features.