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.

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.

Guest Encapsulation Alters the Thermodynamic Landscape of a Coordination Host.

The architecture of self-assembled host molecules can profoundly affect the properties of the encapsulated guests. For example, a rigid cage with small windows can efficiently protect its contents from the environment; in contrast, tube-shaped, flexible hosts with large openings and an easily accessible cavity are ideally suited for catalysis. Here, we report a "Janus" nature of a Pd6L4 coordination host previously reported to exist exclusively as a tube isomer (T). We show that upon encapsulating various tetrahedrally shaped guests, T can reconfigure into a cage-shaped host (C) in quantitative yield. Extracting the guest affords empty C, which is metastable and spontaneously relaxes to T, and the T⇄C interconversion can be repeated for multiple cycles. Reversible toggling between two vastly different isomers paves the way toward controlling functional properties of coordination hosts "on demand".

Disequilibrating azobenzenes by visible-light sensitization under confinement.

Photoisomerization of azobenzenes from their stable E isomer to the metastable Z state is the basis of numerous applications of these molecules. However, this reaction typically requires ultraviolet light, which limits applicability. In this study, we introduce disequilibration by sensitization under confinement (DESC), a supramolecular approach to induce the E-to-Z isomerization by using light of a desired color, including red. DESC relies on a combination of a macrocyclic host and a photosensitizer, which act together to selectively bind and sensitize E-azobenzenes for isomerization. The Z isomer lacks strong affinity for and is expelled from the host, which can then convert additional E-azobenzenes to the Z state. In this way, the host-photosensitizer complex converts photon energy into chemical energy in the form of out-of-equilibrium photostationary states, including ones that cannot be accessed through direct photoexcitation.

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.

Altering the Properties of Spiropyran Switches Using Coordination Cages with Different Symmetries.

Molecular confinement effects can profoundly alter the physicochemical properties of the confined species. A plethora of organic molecules were encapsulated within the cavities of supramolecular hosts, and the impact of the cavity size and polarity was widely investigated. However, the extent to which the properties of the confined guests can be affected by the symmetry of the cage─which dictates the shape of the cavity─remains to be understood. Here we show that cage symmetry has a dramatic effect on the equilibrium between two isomers of the encapsulated spiropyran guests. Working with two Pd-based coordination cages featuring similarly sized but differently shaped hydrophobic cavities, we found a highly selective stabilization of the isomer whose shape matches that of the cavity of the cage. A Td-symmetric cage stabilized the spiropyrans' colorless form and rendered them photochemically inert. In contrast, a D2h-symmetric cage favored the colored isomer, while maintaining reversible photoswitching between the two states of the encapsulated spiropyrans. We also show that the switching kinetics strongly depend on the substitution pattern on the spiropyran scaffold. This finding was used to fabricate a time-sensitive information storage medium with tunable lifetimes of the encoded messages.

Ternary host-guest complexes with rapid exchange kinetics and photoswitchable fluorescence.

Confinement within molecular cages can dramatically modify the physicochemical properties of the encapsulated guest molecules, but such host-guest complexes have mainly been studied in a static context. Combining confinement effects with fast guest exchange kinetics could pave the way toward stimuli-responsive supramolecular systems-and ultimately materials-whose desired properties could be tailored "on demand" rapidly and reversibly. Here, we demonstrate rapid guest exchange between inclusion complexes of an open-window coordination cage that can simultaneously accommodate two guest molecules. Working with two types of guests, anthracene derivatives and BODIPY dyes, we show that the former can substantially modify the optical properties of the latter upon noncovalent heterodimer formation. We also studied the light-induced covalent dimerization of encapsulated anthracenes and found large effects of confinement on reaction rates. By coupling the photodimerization with the rapid guest exchange, we developed a new way to modulate fluorescence using external irradiation.

Encapsulation within a coordination cage modulates the reactivity of redox-active dyes.

Confining molecules within well-defined nanosized spaces can profoundly alter their physicochemical characteristics. For example, the controlled aggregation of chromophores into discrete oligomers has been shown to tune their optical properties whereas encapsulation of reactive species within molecular hosts can increase their stability. The resazurin/resorufin pair has been widely used for detecting redox processes in biological settings; yet, how tight confinement affects the properties of these two dyes remains to be explored. Here, we show that a flexible PdII6L4 coordination cage can efficiently encapsulate both resorufin and resazurin in the form of dimers, dramatically modulating their optical properties. Furthermore, binding within the cage significantly decreases the reduction rate of resazurin to resorufin, and the rate of the subsequent reduction of resorufin to dihydroresorufin. During our studies, we also found that upon dilution, the PdII6L4 cage disassembles to afford PdII2L2 species, which lacks the ability to form inclusion complexes - a process that can be reversed upon the addition of the strongly binding resorufin/resazurin guests. We expect that the herein disclosed ability of a water-soluble cage to reversibly modulate the optical and chemical properties of a molecular redox probe will expand the versatility of synthetic fluorescent probes in biologically relevant environments.

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.

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.

Reversible switching of arylazopyrazole within a metal-organic cage.

Arylazopyrazoles represent a new family of molecular photoswitches characterized by a near-quantitative conversion between two states and long thermal half-lives of the metastable state. Here, we investigated the behavior of a model arylazopyrazole in the presence of a self-assembled cage based on Pd-imidazole coordination. Owing to its high water solubility, the cage can solubilize the E isomer of arylazopyrazole, which, by itself, is not soluble in water. NMR spectroscopy and X-ray crystallography have independently demonstrated that each cage can encapsulate two molecules of E-arylazopyrazole. UV-induced switching to the Z isomer was accompanied by the release of one of the two guests from the cage and the formation of a 1:1 cage/Z-arylazopyrazole inclusion complex. DFT calculations suggest that this process involves a dramatic change in the conformation of the cage. Back-isomerization was induced with green light and resulted in the initial 1:2 cage/E-arylazopyrazole complex. This back-isomerization reaction also proceeded in the dark, with a rate significantly higher than in the absence of the cage.

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.

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.

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.

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.

Incorporation of a p-Phenylene Unit into the Azuliporphyrinogens Frame-Oxidation and Ruthenium Cluster Coordination.

A porphyrinogen macrocycle incorporating two azulenes, phenylene and thiophene into the framework, joined by four C(sp3 ) atoms has been obtained as a mixture of six isomers. They were successfully separated and characterized spectroscopically. The identity of two of them was confirmed by X-ray crystallography. One isomer was tested in reaction with [Ru3 (CO)12 ] yielding exclusively π-complex with two clusters attached to azulenes. The partial oxidation of porphyrinogens yielded dication with two unmodified meso bridges. The stepwise oxidation followed by reaction with water as nucleophile afforded the dicationic species with two hydroxyl groups and a trication with one OH group. The hydroxy-dication can be reversibly transformed into hydroxy-trication by addition of HBF4 etherate.

Helicenophyrins: Expanded Carbaporphyrins Incorporating Aza[5]helicene and Heptacyclic S-Shaped Aza[5]helicene Motifs.

Incorporation of phenanthrene into a hexaphyrin(1.1.1.1.1.0) frame resulted in intramolecular ring fusion, thus giving rise to chiral helicenophyrins. These molecules contain helicene and porphyrin features by incorporating either an aza[5]helicene or heptacyclic S-shaped aza[5]helicene.