Corrole Dimers Research Articles

A Triply Linked Copper(III) Dicarbacorrole Dimer.

A triply linked dicarbacorrole dimer (7) was synthesized from a new meso-meso singly linked dicarbacorrole dimer precursor (6) via an oxidative fusion reaction by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) in the presence of trifluoromethanesulfonic acid (TfOH). Single crystal X-ray structure of 7 adopts a flat conformation with a length as ca. 15.946 Å and a width as 6.903 Å, which can be regarded as a short carbaporphyrinoid tape. Two coordinated Cu ions keeps the +3 oxidation state in 7, as confirmed by NMR spectroscopy, single crystal X-ray diffraction and X-ray photoelectron spectroscopy (XPS). This is in sharp contrast to the Osuka's triply linked tetrapyrrolic corrole dimers, where the inner 3NH form is not stable and thus can only act as a divalent ligand. Due to the non-aromatic nature of dicarbacorrole macrocycle, the largely decreased HOMO-LUMO gap and red-shifted absorption of 7 are best ascribed to the strong electronic interaction between two dipyrromethene-type chromophores. To our knowledge, this is the first fully fused carbaporphyrinoid dimer with β-β, meso-meso, β-β triply linkages prepared to date.

Can Corrole Dimers Be Good Photosensitizers to Kill Bacteria?

Corroles possess key photophysical and photochemical properties to be exploited as therapeutic agents in antimicrobial photodynamic therapy (aPDT). Herein, we present for the first time the antimicrobial efficiency of three corrole dimers and of the corresponding precursor against the Gram(+) bacterium Staphylococcus aureus. Additionally, to explore future clinical applications, the cytotoxicity of the most promising derivatives towards Vero cells was evaluated. The aPDT assays performed under white light irradiation (50 mW/cm2; light dose 450 J/cm2) and at a corrole concentration of 15 µM showed that some dimers were able to reduce 99.9999% of S. aureus strain (decrease of 5 log10 CFU/mL) and their photodynamic efficiency was dependent on position, type of linkage, and aggregation behavior. Under the same light conditions, the corrole precursor 1 demonstrated notable photodynamic efficiency, achieving total photoinactivation (>8.0 log10 CFU/mL reduction) after the same period of irradiation (light dose 450 J/cm2). No cytotoxicity was observed when Vero cells were exposed to corrole 1 and dimer 3 for 24 h according to ISO guidelines (ISO 10993-5) for in vitro cytotoxicity of medical devices. The results show that corrole dimers, dependent on their structures, can be considered good photosensitizers to kill Staphylococcus aureus.

Control of the dual emission behaviour of μ-oxo-bridged Si(iv) corrole dimers by substituent bulkiness

μ-Oxo-bridged Si(iv) corrole dimers show dual emission behavior. Their conformational relaxation can be controlled by substituent bulkiness.

Comparing Isoelectronic, Quadruple-Bonded Metalloporphyrin and Metallocorrole Dimers: Scalar-Relativistic DFT Calculations Predict a >1 eV Range for Ionization Potential and Electron Affinity.

A scalar-relativistic DFT study of isoelectronic, quadruple-bonded Group 6 metalloporphyrins (M = Mo, W) and Group 7 metallocorroles (M = Tc, Re) has uncovered dramatic differences in ionization potential (IP) and electron affinity (EA) among the compounds. Thus, both the IPs and EAs of the corrole derivatives are 1 eV or more higher than those of the porphyrin derivatives. These differences largely reflect the much lower orbital energies of the δ- and δ*-orbitals of the corrole dimers relative to those of the porphyrin dimers, which in turn reflect the higher (+III as opposed to +II) oxidation states of the metals in the former compounds. Significant differences have also been determined between Mo and W porphyrin dimers and between Tc and Re corrole dimers. These differences are thought to largely reflect greater relativistic destabilization of the 5d orbitals of W and Re relative to the 4d orbitals of Mo and Tc. The calculated differences in IP and EA should translate to major differences in electrochemical redox potentials-a prediction that in our opinion is well worth confirming.

Development of the Peripheral Functionalization Chemistry of meso-Free Corroles.

In contrast to the extensive development of the meso-functionalization of porphyrins, that of corroles had rarely been explored until the development of practical synthetic methods for meso-free corroles in 2015. The ready availability of meso-free corroles opened up meso-functionalization chemistry of corroles, giving rise to successful synthesis of various meso-substituted corroles such as meso-halogen, meso-nitro, meso-amino, meso-oxo, and meso-iminocorroles as well as meso-meso-linked corrole dimers and corrole tapes. In some cases, 2NH corroles exist as stable or transient radical species. The impact of meso-functionalization on the structures, electronic properties, optical characteristics, and aromaticity of corroles are highlighted in this Minireview.

Rhenium Corrole Dimers: Electrochemical Insights into the Nature of the Metal-Metal Quadruple Bond.

The interaction of free-base triarylcorroles with Re2(CO)10 in 1,2-dichlorobenzene in the presence of 2,6-lutidine at 180 °C under strict anerobic conditions afforded approximately 10% yields of rhenium corrole dimers. The compounds exhibited diamagnetic 1H NMR spectra consistent with a metal–metal quadruple bond with a σ2π4δ2 orbital occupancy. One of the compounds proved amenable to single-crystal X-ray structure determination, yielding a metal–metal distance of ∼2.24 Å, essentially identical to that in triple-bonded osmium corrole dimers. On the other hand, the electrochemical properties of Re and Os corrole dimers proved to be radically different. Thus, the reduction potentials of the Re corrole dimers are some 800 mV upshifted relative to those of their Os counterparts. Stated differently, the Re corrole dimers are dramatically easier to reduce, reflecting electron addition to δ* versus π* molecular orbitals for Re and Os corrole dimers, respectively. The data also imply electrochemical HOMO-LUMO gaps of only 1.0–1.1 V for rhenium corrole dimers, compared with values of 1.85–1.90 V for their Os counterparts. These HOMO–LUMO gaps rank among the first such values reported for quadruple-bonded transition-metal dimers for any type of supporting ligand, porphyrin-type or not.

Chiral Interlocked Corrole Dimers Directly Linked at Inner Carbon Atoms of Confused Pyrrole Rings

A facile synthetic strategy towards conformationally stable chiral chromophores based on dimeric porphyrinoids has been established. A peculiar class of face-to-face intramolecularly interlocked corrole dimers were formed by the oxidative C-C coupling linked at the inner carbon sites upon simple treatment of copper(II) ions. Their intrinsic electronic structures were modulated by the peripheral corrole ring annulations, which lead to distinct optical properties and redox profiles. The stereogenic carbon centers implemented in the confused corrole skeleton provided a rationale for designing novel chiral materials.

Pyrene Appended Free‐base, Phosphorus(V) and Gallium(III) Corroles and Their β,β′‐Linked Corrole Dimers: Synthesis, Photophysical and Electrochemical Properties

AbstractPyrene appended free‐base, phosphorus(V) and gallium (III) corrole conjugates were synthesized and characterized. Efficient β‐β′ dimerization of corroles was achieved by oxidation with p‐chloranil in moderate yield from their respective metallated corroles. The weak ground state electronic coupling between pyrene and corrole units was established by photophysical and electrochemical investigations. The fluorescence spectral studies showed a red shifted emission maximum for dimer with respect to their monomeric counterpart due to possible π‐conjugation and supported by the density functional theory (DFT). The electrochemical investigation revealed multiple oxidation associated with the corrole and pyrene centers.

Stable meso-meso-Linked 2NH-Corrole Radical Dimers as a Key Intermediate to Corrole Tape.

While oxidation of 5,5',15,15'-tetramesityl-10-10'-linked 3NH-corrole dimer with DDQ gave the corresponding triply linked 2NH-corrole tape, the use of an equimolar amount of p-chloranil as a milder oxidant resulted in the formation of a 10-10'-linked neutral 2NH-corrole radical dimer as a stable product. The stability of this peculiar product is ascribed largely to strong antiferromagnetic interaction of the two spins. Further oxidation of this diradical produced corrole tape, suggesting its involvement as a reaction intermediate to the corrole tape. Oxidation of 10-10'-linked bis-pyridine-coordinated CoIII corrole dimer with DDQ produced a cobalt corrole radical dimer and a doubly linked corrole dimer both as stable compounds bearing pyridine and cyanide axial ligands. This type of oxidative transformation involving neutral diradical intermediates is a unique reaction mechanism specific for corrole dimers.

Stable meso–meso‐Linked 2NH‐Corrole Radical Dimers as a Key Intermediate to Corrole Tape

AbstractWhile oxidation of 5,5′,15,15′‐tetramesityl‐10‐10′‐linked 3NH‐corrole dimer with DDQ gave the corresponding triply linked 2NH‐corrole tape, the use of an equimolar amount of p‐chloranil as a milder oxidant resulted in the formation of a 10‐10′‐linked neutral 2NH‐corrole radical dimer as a stable product. The stability of this peculiar product is ascribed largely to strong antiferromagnetic interaction of the two spins. Further oxidation of this diradical produced corrole tape, suggesting its involvement as a reaction intermediate to the corrole tape. Oxidation of 10‐10′‐linked bis‐pyridine‐coordinated CoIII corrole dimer with DDQ produced a cobalt corrole radical dimer and a doubly linked corrole dimer both as stable compounds bearing pyridine and cyanide axial ligands. This type of oxidative transformation involving neutral diradical intermediates is a unique reaction mechanism specific for corrole dimers.

Relativistic Effects on a Metal-Metal Bond: Osmium Corrole Dimers.

A series of metal-metal bonded osmium corrole dimers, {Os[T pXPC]}2, were synthesized in reasonably good yields (35-46%) via the interaction of the corresponding free-base meso-tris( p-X-phenyl)corroles (H3[T pXPC], X = CF3, H, CH3, and OCH3), Os3(CO)12, and potassium carbonate in 1,2,4-trichlorobenzene under an inert atmosphere at 180 °C over several hours. The complexes are only the second class of Os corroles reported to date (the first being OsVIN corroles) and also the second class of metal-metal bonded metallocorrole dimers (the other being Ru corrole dimers). Comparison of the X-ray structures, redox potentials, and optical spectra of analogous Ru and Os corrole dimers, along with scalar-relativistic DFT calculations, has provided an experimentally calibrated account of relativistic effects in these complexes. Three of the Os corrole dimers (X = CF3, H, and OCH3) were analyzed with single-crystal X-ray diffraction analysis, revealing inversion-related corrole rings with eclipsed Os-N bonds and Os-Os distances of ∼2.24 Å that are ∼0.06 Å longer than the Ru-Ru distances in the analogous Ru corrole dimers. Interestingly, a comparison of scalar-relativistic and nonrelativistic DFT calculations indicates that this difference in metal-metal bond distance does not, in fact, reflect a differential relativistic effect. For a given corrole ligand, the Ru and Os corrole dimers exhibit nearly identical oxidation potentials but dramatically different reduction potentials, with the Os values ∼0.5 V lower relative to Ru, suggesting that whereas oxidation occurs in a ligand-centered manner, reduction is substantially metal-centered, which indeed was confirmed by scalar-relativistic calculations. The calculations further indicate that approximately a third of the ∼0.5 V difference in reduction potentials can be ascribed to relativity. The somewhat muted value of this relativistic effect appears to be related to the finding that reduction of an Os corrole dimer is not exclusively metal-based but that a significant amount of spin density is delocalized over to the corrole ligand; in contrast, reduction of an Ru corrole dimer occurs exclusively on the Ru-Ru linkage. For isoelectronic complexes, the Ru and Os corrole dimers exhibit substantially different UV-vis spectra. A key difference is a strong near-UV feature of the Os series, which in energy terms is blue-shifted by ∼0.55 V relative to the analogous feature of the Ru series. TDDFT calculations suggest that this difference may be related to higher-energy Os(5d)-based LUMOs in the Os case relative to analogous MOs for Ru.

Singly, Doubly, and Triply Linked Corrole Oligomers: Synthesis, Structures, and Linking Position Dependent Properties.

Direct covalent connections of porphyrinoids have been demonstrated as an effective way to expand their π-electronic networks and perturb their optical and electrochemical properties. Covalent connections are also useful for studies on the precise electronic interaction between two porphyrinoid units. However, the chemistry of covalently linked corrole oligomers lags far behind that of the porphyrin counterparts in spite of the importance of corrole as a ring-contracted porphyrinoid. The lower symmetry of corroles naturally leads to many possible corrole dimers, which have been found to display different optical and electrochemical properties depending on the linking position. In this review, we summarize the synthesis, structures, and properties of corrole oligomers such as singly linked oligomers and fused dimers as well as their metal complexes with a particular focus on their linking position dependent electronic properties.

Stable Face-to-Face Singlet Diradicaloids: Triply Linked Corrole Dimer Gallium(III) Complexes with Two μ-Hydroxo-Bridges.

In known singlet diradicaloid molecules, two inherent radicals are interacted antiferromagnetically as a result of delicate energetic balances between closed-shell and open-shell states. Reported herein is that gallium(III) metalations of triply linked corrole dimers provide face-to-face dimers, with two μ-hydroxo-bridges, and they display curved π-planes nearing each other at about 3.24 Å. Based on ESR and SQUID measurements, and theoretical calculations, the dimers have been assigned as singlet diradicaloids that consist of two monoradicals each delocalized on the triply linked corrole dimer planes. Therefore, it is concluded that the dimers have unusual open-shell states stabilized by large through-space spin-exchange interactions.

Stable Face‐to‐Face Singlet Diradicaloids: Triply Linked Corrole Dimer Gallium(III) Complexes with Two μ‐Hydroxo‐Bridges

AbstractIn known singlet diradicaloid molecules, two inherent radicals are interacted antiferromagnetically as a result of delicate energetic balances between closed‐shell and open‐shell states. Reported herein is that gallium(III) metalations of triply linked corrole dimers provide face‐to‐face dimers, with two μ‐hydroxo‐bridges, and they display curved π‐planes nearing each other at about 3.24 Å. Based on ESR and SQUID measurements, and theoretical calculations, the dimers have been assigned as singlet diradicaloids that consist of two monoradicals each delocalized on the triply linked corrole dimer planes. Therefore, it is concluded that the dimers have unusual open‐shell states stabilized by large through‐space spin‐exchange interactions.

Meso‐Cumulenic 2H‐Corroles from meso‐Ethynyl‐3H‐corroles

AbstractAlkynyl‐substituted 3H‐corrole 9 a was converted to [3]cumulenic 2H‐corrole 10 a by treatment with trimethylsilyl chloride (TMSCl), and 1,3‐butadiyne‐bridged 3H‐corrole dimer 11 b was transformed into [5]cumulene‐bridged 2H‐corrole dimer 12 b by oxidation with PbO2. Both 10 a and 12 b were metalated to form ZnII complexes 10 a‐Zn and 12 b‐Zn. The structures of 10 a‐Zn and 12 b‐Zn show planar conformations with bond‐length alternations that are analogous to those of tetraaryl [n]cumulenes. The cumulenic corrole dimers 12 b and 12 b‐Zn display large NIR absorption bands in the range of 700–1400 nm (maximum ϵ≈1.0×105 m−1 cm−1) owing to the effective π‐conjugation between the two corrole units through the [5]cumulene bridge.

Meso-Cumulenic 2H-Corroles from meso-Ethynyl-3H-corroles.

Alkynyl-substituted 3H-corrole 9 a was converted to [3]cumulenic 2H-corrole 10 a by treatment with trimethylsilyl chloride (TMSCl), and 1,3-butadiyne-bridged 3H-corrole dimer 11 b was transformed into [5]cumulene-bridged 2H-corrole dimer 12 b by oxidation with PbO2 . Both 10 a and 12 b were metalated to form ZnII complexes 10 a-Zn and 12 b-Zn. The structures of 10 a-Zn and 12 b-Zn show planar conformations with bond-length alternations that are analogous to those of tetraaryl [n]cumulenes. The cumulenic corrole dimers 12 b and 12 b-Zn display large NIR absorption bands in the range of 700-1400 nm (maximum ϵ≈1.0×105 m-1 cm-1 ) owing to the effective π-conjugation between the two corrole units through the [5]cumulene bridge.

Different Antiferromagnetic Coupling between 5,5′‐ and 10,10′‐Linked Iron(III) Corrole Dimers

Two FeIII corroles were connected through a single meso–meso linkage at different positions, that is, 5,5′‐linkage and 10,10′‐linkage, which led to the observations of position‐dependent antiferromagnetic interactions between the two iron(III) corrole units. The iron(III) centers were found to exhibit an intermediate‐spin state, S = 3/2, under ambient conditions on the basis of 1H NMR spectra, Curie plots, Mössbauer spectroscopy, and super‐conducting quantum interference device (SQUID) measurements. In previous reports, the X‐ray structure of dipyridine tris(pentafluorophenyl)corrolato iron(III) was assigned as a six‐coordinate species, but the 10,10′‐linked and 5,5′‐linked dimers preferred five‐coordinate geometry in the solid state. In addition, a mixed five‐coordinate/six‐coordinate dimer was also obtained, implying a susceptibility of the coordination mode to the crystal packing force. By summarizing the results, it can be concluded that pyridinate–iron(III) tris(pentafluorophenyl)corroles can be better described as five‐coordinate, intermediate‐spin (S = 3/2) species under ambient conditions in toluene, whereas a dominant contribution of six‐coordinate low‐spin (S = 1/2) iron(III) complex appears when coordinated with stronger axial ligands such as imidazole at low temperature. Complementary to these interpretations, the 10,10′‐linked dimer exhibited a larger antiferromagnetic interaction between the two iron(III) corroles (J = –2.04 cm–1) than that of the 5,5′‐dimer (J = –0.64 cm–1).

Ruthenium-Ruthenium-Bonded [Bis{corrolato-ruthenium(III)}]n (n=0, +1, -1) Complexes: Model Compounds for the Photosynthetic Special Pair.

We present herein the synthesis of three new bis(corrolato-ruthenium(III)) complexes containing unsupported Ru-Ru bonds and their characterization in different redox states. The 1 H NMR spectra of the bis(corrolato-ruthenium(III)) complexes displayed "normal" chemical shifts and the compounds proved to be EPR-silent. Crystallographic characterization of the dimers indicated Ru-Ru distances of 2.175 Å, consistent with a triple bond between the two ruthenium centers. All of the synthesized complexes undergo two successive reversible oxidations and a single reversible reduction. A combination of UV/Vis/NIR/EPR spectroelectrochemical studies and DFT calculations established the redox state distributions in these ruthenium-ruthenium-bonded dimers. Whereas reduction of the dimers is metal-based and leads to metal-metal-bonded mixed-valent RuII -RuIII species, one-electron oxidation largely retains the RuIII -RuIII situation with the generation of metal-bound corrolato radicals. The present study thus concerns the first UV/Vis/NIR/EPR spectroelectrochemical characterization and DFT calculations of ruthenium-ruthenium-bonded rotationally ordered corrole dimers. The mean plane separation between the two corrole units in these dimers is around 3.543 Å, which is in close agreement to that in the "special pair" in chlorophyll. Oxidation of these ruthenium-ruthenium-bonded dimers gives rise to two new electronic absorption bands in the NIR region (similar to those of the special pair), which have apparently not been mentioned/observed in earlier reports on ruthenium-ruthenium-bonded corrole dimers. These bands mainly originate from inter-corrole transitions.

Triply Linked Corrole Dimers.

The oxidation of 10-10' singly linked corrole dimers with DDQ at low concentration in CHCl3 afforded meso-meso, β-β, β-β triply linked 2H-corrole dimers (with two inner NH groups in each corrole unit), which exhibited characteristic (1) H NMR and absorption spectra attributable to their nonaromatic electronic networks. These 2H-corrole dimers were reduced with NaBH4 to aromatic 3H-corrole dimers, which were unstable and easily oxidized back to the 2H-corrole dimers upon exposure to air. Bis(zinc(II)) complexes of the 2H-corrole dimers were synthesized and characterized as rare examples of nonaromatic zinc(II) corrole complexes.

Triply Linked Corrole Dimers

AbstractThe oxidation of 10–10′ singly linked corrole dimers with DDQ at low concentration in CHCl3 afforded meso–meso, β–β, β–β triply linked 2H‐corrole dimers (with two inner NH groups in each corrole unit), which exhibited characteristic 1H NMR and absorption spectra attributable to their nonaromatic electronic networks. These 2H‐corrole dimers were reduced with NaBH4 to aromatic 3H‐corrole dimers, which were unstable and easily oxidized back to the 2H‐corrole dimers upon exposure to air. Bis(zinc(II)) complexes of the 2H‐corrole dimers were synthesized and characterized as rare examples of nonaromatic zinc(II) corrole complexes.