Core-modified hexaphyrin: synthesis and characterization of 31,34-disilahexaphyrinoid

Condensation of 16-silatripyrrane with pentafluorobenzaldehyde under catalytic conditions followed by DDQ oxidation leads to 31,34-disilahexaphyrinoid--a four times reduced derivative of 31,34-disilahexaphyrin which contains two built-in silole units flanked by four tetrahedrally hybridized meso carbons. In the preferred folded macrocyclic conformation the silole rings remain perpendicular to each other. The steric hindrance of bulky substituents at silicon atoms and β-positions of siloles prevented aromatization. Only one meso diastereomer (5S, 15S, 20R, 30R) has been isolated and subsequently identified by 1D and 2D NMR techniques. The density functional theory (DFT) has been applied to model the molecular structure of 31,34-disilahexaphyrinoid consistent with constraints imposed by NOE experiments. The total energies calculated at the B3LYP/6-31G**//B3LYP/6-31G** level for four feasible meso diastereomers clearly demonstrated the energetic preference for the meso diastereomer (5S, 15S, 20R, 30R).     

Contracted and expanded meso-alkynyl porphyrinoids: from triphyrin to hexaphyrin

The boron trifluoride-catalyzed Rothemund condensation of triisopropylsilyl (TIPS) propynal 1 with 3,4-diethylpyrrole in dichloromethane, followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) generates a mixture of products, including [15]triphyrin(1.1.3) H3, corrole H(3)4, porphyrin H(2)2, [24]pentaphyrin(1.1.1.1.1) H(4)5, [28]hexaphyrin(1.1.1.1.1.1) H(4)6, and two linear tripyrromethenes H(2)7 and H(2)8. We report the spectroscopic characteristics of these unusual chromophores, together with the crystal structures of triphyrin H3 (and its zinc complex ZnCl3), porphyrin H(2)2 (and its metal complexes Zn2, Ni2 and Pt2), hexaphyrin H(4)6, and tripyrromethene nickel(II) complex Ni7. When the condensation is catalyzed with trifluoroacetic acid, rather than boron trifluoride, the triphyrin H3 become the main product (26% yield). This novel macrocycle is linked with a TIPS-substituted exocyclic double bond. This C=C bond makes an eta(2)-interaction with the zinc center in ZnCl3 with C-Zn distances of 2.863 and 3.025 A. The porphyrin H(2)2 is severely ruffled, and its absorption spectrum is red-shifted and broadened compared with the analogous compound without ethyl substituents. The hexaphyrin H(4)6 adopts a figure-of-eight conformation with virtual C(2) symmetry in the solid state and C(2) symmetry in solution on the NMR time scale. Oxidation with DDQ appears to convert this nonaromatic [28]hexaphyrin into an aromatic [26]hexaphyrin with a strongly red-shifted absorption spectrum, but the oxidized macrocyle is too unstable to isolate.     

Heterobismetal complexes of [26]hexaphyrin(1.1.1.1.1.1)

Au(III)Cu(III) and Au(III)Rh(I) heterobismetal complexes of meso-aryl-substituted [26]hexaphyrin were rationally prepared from a monometal Au(III) complex. The Au(III)Cu(III) complex is an aromatic molecule with a rectangular shape, while Au(III)Rh(I) complexes are out-of-plane macrocycles, being either aromatic or antiaromatic depending upon the number of conjugated pi electrons. The 26pi Au(III)Rh(I) complex was converted into an aromatic and planar 26pi Au(III)Rh(III) complex via double C-H bond activation upon refluxing in pyridine.     

Biscopper complexes of meso-aryl-substituted hexaphyrin: gable structures and varying antiferromagnetic coupling

The copper metalation into the hexaphyrins is accompanied by large structural changes to give four complexes exhibiting gable structures and varying antiferromagnetic couplings.     

Group 12 metal complexes of [26]hexaphyrin(1.1.1.1.1.1)

Metalation of meso-hexakis(pentafluorophenyl)-substituted [26]hexaphyrin(1.1.1.1.1.1) (1) has been explored with group 12 metal ions Zn(II), Cd(II), and Hg(II). Zn(II) and Cd(II) ions afforded dinuclear gable-shaped complexes 2 and 3 in good yields, while Hg(II) ion provided bis-Hg(II) and mono-Hg(II) planar complexes (4 and 5) via C-H bond cleavage.     

Synthesis and crystal structure of a meso-trialkynyl[28]hexaphyrin

A 5,15,25-trialkynyl [28]hexaphyrin(1.1.1.1.1.1) is the main product of the boron trifluoride-catalysed condensation of meso-anthryl dipyrromethane and triisopropylsilylpropynal; it absorbs strongly in the near-infrared, out to 1093 nm.     

Oxidation of hydroquinones with meso-hexakispentafluorophenyl [26]hexaphyrin(1.1.1.1.1.1)

Treatment of various hydroquinones and catechols with meso-pentafluorophenyl [26]hexaphyrin(1.1.1.1.1.1) provided the corresponding quinones quantitatively.     

Regioselective vicinal-dichlorination of meso-aryl [26]hexaphyrin(1.1.1.1.1.1)

Two synthetic methods are developed for halogenations of meso-hexakis(pentafluorophenyl)-substituted [26]hexaphyrin(1.1.1.1.1.1); one is regioselective trans-vicinal-dichlorination with sulfuryl chloride and the other is acid-assisted hydrohalogenation followed by oxidation with DDQ.     

Doubly N-confused hexaphyrin: a novel aromatic expanded porphyrin that complexes bis-metals in the core

Meso-hexakis(pentafluorophenyl)-substituted doubly N-confused hexaphyrins and their metal complexes were synthesized for the first time, and the structures were elucidated by X-ray single-crystal analyses. The free base form of oxidized hexaphyrin (5) had two preorganized N3O pockets in the macrocyclic core, where a hydrogen-bonding network was formed to keep the molecule planar (the mean plane deviation is 0.054 A). The formation of a planar bis-Cu(II) complex was confirmed by UV/vis, magnetic susceptibility measurements, and X-ray crystallography. The bis-Ni(II) complex (7), on the other hand, was distored from planarity, but it changed to the planar structure upon solvent (acetonitrile) coordination as judged by the observation of a sharp Soret-like band in absorption spectra and the X-ray structures of the complexes.     

A new reagent for the synthesis of [26]hexaphyrin: N-sulfonyl aldimine

The selective synthesis of [26]hexaphyrin(1.1.1.1.1.1) has been achieved by the reaction of meso-substituted tripyrrane and N-sulfonyl aldimine. The protocol is simple and requires only a catalytic amount of copper(II) triflate under mild reaction conditions.     

Copper(II) and oxovanadium(v) complexes of hexaphyrin(1.0.1.0.0.0)

The expanded porphyrin hexaphyrin(1.0.1.0.0.0) coordinates both early and late transition metals; a binuclear in-plane copper(ii) complex and an oxovanadium(v) derivative were prepared and characterized.     

Phosphonium ylides from nucleophilic addition of triphenylphosphine to [26]hexaphyrin(1.1.1.1.1.1)

[reaction: see text] Nucleophilic addition of triphenylphosphine to neutral meso-hexakis(pentafluorophenyl)-substituted [26]hexaphyrin(1.1.1.1.1.1) (1) provided a stable phosphonium ylide of [28]hexaphyrin (3), which was quantitatively oxidized to its 26pi-counterpart (4) that exhibited a planar and rectangular conformation and a diatropic ring current.     

Regioselective nucleophilic substitution reaction of meso-hexakis(pentafluorophenyl) substituted [26]hexaphyrin

Reaction of various alkoxides led to the selective replacement of the p-fluorine substituents of meso-hexakis(pentafluorophenyl) substituted [26]hexaphyrin. Reaction with isopropyl amine gave meso-hexakis(4-isopropylamino-2,3,5,6-tetrafluorophenyl) substituted [28]hexaphyrin.     

Reversible caterpillar-motion like isomerization in a N,N'-dimethyl hexaphyrin(1.1.1.1.1.1) induced by two-electron oxidation or reduction

Caterpillar-motion like rotational isomerization of meso-aryl substituted [26]- and [28]hexaphyrins has been revealed for the first time. Two-electron oxidation and reduction induce reversible interconversion between N,N'-dimethyl [26]- and [28]hexaphyrins with a rotational isomerization, in which the N-methylated pyrroles move from the corner in the former to the centre in the latter.     

Immobilization of a hexaphyrin(1.0.1.0.0.0) derivative onto a tentagel-amino resin and its use in uranyl cation detection

The synthesis of an isoamethyrin derivative containing two CH(2)CH(2)CO(2)CH(3) moieties in the beta-pyrrolic positions and its use in the colorimetric detection of the uranyl cation after immobilization onto a solid support is reported.     

Easy preparation of cobalt corrole and hexaphyrin and isolation of new oligopyrroles in the solvent-free condensation of pyrrole with pentafluorobenzaldehyde

[reaction: see text] Following the discovery that meso-substituted corroles are formed in solvent-free condensation of pyrrole with aldehydes, we demonstrate that a small variation in the methodology is suitable for facile synthesis of cobalt(III) corrole and hexaphyrin. These compounds, as well as three noncyclic products, were fully characterized by spectroscopy and X-ray crystallography.     

Highly selective Ir-catalyzed direct sixfold borylation of peripheral aromatic substituents on hexakisaryl-substituted [28]hexaphyrin(1.1.1.1.1.1)

Direct functionalization of aromatic substituents on [28]hexaphyrin was achieved by Ir-catalyzed borylation with the Smith-Miyaura-Hartwig protocol. High para selectivity was observed in the reaction on 2,6-dichlorophenyl and 2,6-dimethoxyphenyl substituents of [28]hexaphyrin. The reaction with [26]hexaphyrin resulted only in reduction of the substrate to provide [28]hexaphyrin without borylation, thus highlighting the importance of the oxidation state of substrates in this catalytic transformation. The borylated hexaphyrin can be used for Suzuki-Miyaura cross-coupling reaction.     

Deprotonation‐Induced Aromaticity Enhancement and New Conjugated Networks in meso‐Hexakis(pentafluorophenyl)[26]hexaphyrin

meso‐Hexakis(pentafluorophenyl)‐substituted neutral hexaphyrin with a 26π‐electronic circuit can be regarded as a real homolog of porphyrin with an 18π‐electronic circuit with respect to a quite flat molecular structure and strong aromaticity. We have investigated additional aromaticity enhancement of meso‐hexakis(pentafluorophenyl)[26]hexaphyrin(1.1.1.1.1.1) by deprotonation of the inner N? H groups in the macrocyclic molecular cavity to try to induce further structural planarization. Deprotonated mono‐ and dianions of [26]hexaphyrin display sharp B‐like bands, remarkably strong fluorescence, and long‐lived singlet and triplet excited‐states, which indicate enhanced aromaticity. Structural, spectroscopic, and computational studies have revealed that deprotonation induces structural deformations, which lead to a change in the main conjugated π‐electronic circuit and cause enhanced aromaticity.