Excited-State Aromaticity of Gold(III) Hexaphyrins and Metalation Effect Investigated by Time-Resolved Electronic and Vibrational Spectroscopy.

Expanded porphyrins with appropriate metalation provide an excellent opportunity to study excited-state aromaticity. The coordinated metal allows the excited-state aromaticity in the triplet state to be detected through the heavy-atom effect, but other metalation effects on the excited-state aromaticity were ambiguous. Herein, the excited-state aromaticity of gold(III) hexaphyrins through the relaxation dynamics was revealed via electronic and vibrational spectroscopy.

π-Ruthenium Complexes of Hexaphyrins(1.1.1.1.1.1): A Triple-Decker Complex Bearing Two Ruthenoarene Units.

Ruthenium(II) π-coordination onto [28]hexaphyrins(1.1.1.

Internally Bridged Hückel Aromatic [46]Decaphyrins: (Doubly-Twisted-Annuleno)Doubly-Twisted-Annulene Variants.

Internally 3,3'-biphenyl-, 2,2',5,5'-bithiophene-, and 2,5-thieno[3,2-b]thiophene-bridged [46]decaphyrins were prepared. In addition to the global 46π-conjugated circuits, the internal core-modified [32]heptaphyrin- and [30]hexaphyrin moieties in 2,2',5,5'-bithiophene- and 2,5-thieno[3,2-b]thiophene-bridged [46]decaphyrins also possess doubly twisted topologies (|L |=2) and are regarded as (doubly-twisted-annuleno)doubly-twisted-annulene variants. All these decaphyrins display distinct Hückel aromaticity owing to the global 46π-electronic networks but the contributions of the local half circuits were almost negligible due to the perpendicular orientation of the bridges.

Quadruply Twisted Hückel-Aromatic Dodecaphyrin.

Molecular topology of π-conjugated circuits becomes increasingly important in the chemistry of aromatic and antiaromatic compounds. meso-Pentafluorophenyl-substituted 5,35-(1,4-phenylene)bridged [56]dodecaphyrin was synthesized by condensation of 1,4-phenylene-bridged dicarbinol dimer and 5,10,15-tris-(pentafluorophenyl)tetrapyrrane followed by oxidation with DDQ and was oxidized to its [54]- and [52]congeners in a stepwise manner. Metalation of the [52]dodecaphyrin with Pd (dba) gave two bis-Pd complexes that are isomers of metalation sites: anti and syn with regard to the 1,4-phenylene bridge.

A Stable Antiaromatic 5,20-Dibenzoyl [28]Hexaphyrin(1.1.1.1.1.1): Core Au Metalation and Subsequent Peripheral B Metalation.

5,20-Dibenzoyl [28]hexaphyrin(1.1.1.

Near-Infrared S Fluorescence from Deprotonated Möbius Aromatic [32]Heptaphyrin.

This study revealed S fluorescence from deprotonated meso-pentafluorophenyl-substituted Möbius aromatic [32]heptaphyrin(1.1.1.

Internally 2,5-Thienylene-Bridged [46]Decaphyrin: (Annuleno)annulene Network Consisting of Möbius Aromatic Thia[28]hexaphyrins and Strong Hückel Aromaticity of its Protonated Form.

Internally 1,3-phenylene- and 2,5-thienylene-bridged [46]decaphyrins 2 and 3 have been synthesized. While 2 shows modest aromatic character derived from the global 46π-conjugated circuit, 3 displays larger aromatic character owing to the contribution of an (annuleno)annulene-type network consisting of two twisted Möbius aromatic thia[28]hexaphyrin segments in addition to the global 46π-network. Upon protonation, these [46]decaphyrins underwent large structural changes to acquire strong aromaticity.

[62]Tetradecaphyrin and Its Mono- and Bis-Zn(II) Complexes.

A coiled structure of meso-pentafluorophenyl-substituted [62]tetradecaphyrin 1 was revealed by X-ray structural analysis. Synthetic protocols were devised to form mono- and bis-Zn(II) complexes, 1 Zn and 1 Zn2 , selectively. The former displayed a trigonal-bipyramidal pentacoordinated Zn(II) ion as a rare case and a cyclic voltammogram exhibiting eleven reversible redox waves.

Multifaceted [36]octaphyrin(1.1.1.1.1.1.1.1): deprotonation-induced switching among nonaromatic, Möbius aromatic, and Hückel antiaromatic species.

Deprotonation of nonaromatic octakis-(pentafluorophenyl)-substituted [36]octaphyrin(1.1.1.

Conformational Fixation of a Rectangular Antiaromatic [28]Hexaphyrin Using Rationally Installed Peripheral Straps.

A rectangular [28]hexaphyrin bearing outer straps at the long side has been synthesized by SN Ar reaction of [26]hexaphyrin with allyl alcohol, intramolecular olefin metathesis by using Hoveyda-Grubbs second-generation catalyst, and reduction with NaBH4 . The peripheral straps enforce a rectangular conformation for the [28]hexaphyrin, which shows Hückel antiaromatic character, as confirmed by its planar X-ray structure, a strong paratropic ring current, characteristic UV/Vis/NIR absorption features, small electrochemical HOMO-LUMO gap, and very fast S1 decay.

Group 9 Metal Complexes of meso-Aryl-Substituted Rubyrin.

Invited for the cover of this issue are Takanori Soya and Atsuhiro Osuka at Kyoto University. The image depicts Group 9 metal (Co, Rh, and Ir) complexes of meso-aryl-substituted rubyrin and a meteorite approaching to the atmosphere. A large amount of Iridium is often contained in meteorites.

Group 9 Metal Complexes of meso-Aryl-Substituted Rubyrin.

The metalation of meso-tetrakis(pentafluorophenyl)-substituted [26]rubyrin has been explored with Group 9 metal salts (Rh(I) , Co(II) , Ir(III) ), affording a Hückel aromatic [26]rubyrin-bis-Rh(I) complex with a highly curved gable-like structure, a Hückel antiaromatic [24]rubyrin-bis-Co(II) complex that displays intramolecular antiferromagnetic coupling between the two Co(II) ions (J=-4.5 cm(-1) ), and two Cp*-capped Ir(III) complexes; in one, the iridium metal sits on the [26]rubyrin frame with two IrN bonds, whereas the other has an additional IrC bond, although both Ir(III) complexes display moderate aromatic character. This work demonstrates characteristic metalation abilities of this [26]rubyrin toward Group 9 metals.

Stable [48]-, [50]-, and [52]dodecaphyrins(1.1.0.1.1.0.1.1.0.1.1.0): the largest Hückel aromatic molecules.

[52]Dodecaphyrin(1.1.0.

A Möbius aromatic [28]hexaphyrin bearing a diethylamine group: a rigid but smooth conjugation circuit.

The reaction of [26]hexaphyrin with triethylamine in the presence of BF3 ⋅OEt2 and O2 furnished a diastereomeric mixture of a diethylamine-bearing [28]hexaphyrin as a rare example of a Möbius aromatic metal-free expanded porphyrin. The Möbius aromaticity of these molecules is large, as indicated by their large diatropic ring currents, which are even preserved at 100 °C, owing to their internally multiply bridged robust structure with a smooth conjugation network. These molecules were reduced with NaBH4 to give an antiaromatic [28]hexaphyrin, and were oxidized with MnO2 to give aromatic [26]hexaphyrins, both through a Möbius-to-Hückel topology switch induced by a CN bond cleavage.

Ni(II) metalations of [40]- and [42]nonaphyrins(1.1.1.1.1.1.1.1.1): the largest doubly twisted Hückel antiaromatic molecule.

Ni(II) metalation of [42]nonaphyrin gave two Hückel aromatic [42]nonaphyrin Ni(II) complexes that possess different doubly twisted figure-eight conformations. While these complexes are conformers, the activation barriers for conformational interconversion were found to be exceptionally high. However, one-way isomerization from the higher-energy conformer to the lower-energy conformer can be induced upon treatment with trifluoroacetic acid (TFA).