Control of the conformational dynamics of meso-meso vinylene-bridged Zn(II) porphyrin dimers through diamine coordination.

Two meso-meso vinylene-bridged Zn(II) porphyrin dimers and were analyzed in terms of the control of their conformational dynamics induced by the rotation around the double bond bridge. The dihedral angles between the two porphyrin rings were modulated through coordination with α,ω-diaminoalkanes of varying chain lengths.

Excited-state electronic couplings in a 1,3-butadiyne-bridged Zn(II)porphyrin dimer and trimer.

Electronic couplings in a 1,3-butadiyne-bridged Zn(ii) porphyrin dimer D and trimer T have been probed by measuring their excited-state properties at ensemble and single molecular levels. While single chromophore-like, strongly interacting behaviors are revealed for D, the coupling in T is indicated to be not so strong.

Direct arylation of meso-formyl porphyrin.

Palladium-catalyzed direct arylation of meso-formyl Ni(II) porphyrin with aryl bromides provided ß-monoarylated meso-formyl porphyrins. In spite of the existence of the meso-formyl group, the reactions proceeded regioselectively at the ß-position adjacent to the formyl group. ß-Arylated formyl porphyrin was converted to a tetraline-fused porphyrin by reduction and subsequent acid-catalyzed cyclization and to a meso-meso vinylene-bridged diporphyrin by McMurry coupling (see scheme).

Direct meso-alkynylation of porphyrins doubly assisted by pyridyl coordination.

Direct meso-alkynylation of ß,ß'-dipyridylporphyrin with various alkynyllithium reagents has been achieved, in which the ß,ß'-dipyridyl groups play an important role in facilitating the nucleophilic addition of the reagents through double coordination. This method enabled the synthesis of a meso-ethynylene-bridged diporphyrin.

Solvent- and temperature-dependent conformational changes between Hückel antiaromatic and Möbius aromatic species in meso-trifluoromethyl substituted [28]hexaphyrins.

We investigated the photophysical properties of figure-eight-like meso-hexakis(trifluoromethyl) [26]- and [28]hexaphyrins(1.1.1.1.1.1) denoted as TFM26H and TFM28H, respectively, using steady-state and time-resolved spectroscopy along with theoretical calculations to explore their electronic and magnetic natures depending on their molecular aromaticity. TFM26H exhibited a well-resolved absorption feature and intense fluorescence, both of which were neither solvent- nor temperature-dependent. These optical properties were in agreement with its Hückel's [4n + 2] aromaticity as observed in typical aromatic porphyrinoids. The S(1)-state lifetime of ~50 ps for TFM26H in solution was shorter than those in planar aromatic hexaphyrins (>100 ps) presumably due to nonplanar figure-eight geometry of TFM26H. However, TFM28H exhibited remarkable changes in solvent- and temperature-dependent absorption spectra as well as excited-state lifetimes indicating that a dynamic equilibrium occurs between the two conformational species. With the help of quantum mechanical geometry optimization and vertical excitation energy calculations, we found that the figure-eight double-sided conformer observed in the solid-state and single-sided distorted one could be the best candidates for the two conformers, which should be Hückel antiaromatic and Möbius aromatic species, respectively, based on their optical characteristics, molecular orbital structures, and excited-state lifetimes. Conformational dynamics between these two conformers of TFM28H was scrutinized in detail by temperature-dependent (1)H NMR spectra in various solvents, which showed that the conformational equilibrium was quite sensitive to solvents and that a conformational change faster than the NMR time-scale occurs even at 173 K.

Rhodium-catalyzed asymmetric conjugate alkynylation of nitroalkenes.

Asymmetric addition of (triisopropylsilyl)acetylene to nitroalkenes took place in the presence of a rhodium/chiral bisphosphine catalyst to give beta-alkynylated nitroalkanes in high yields with high enantioselectivity.

Rhodium-catalyzed asymmetric conjugate alkynylation of enones with alkynylsilanols.

Asymmetric conjugate alkynylation of alpha,beta-unsaturated ketones with (triisopropylsilyl)ethynylsilanols giving beta-alkynylketones took place in high yields with high enantioselectivity in the presence of chiral rhodium catalysts.

Facile formation of a benzopyrane-fused [28]hexaphyrin that exhibits distinct Möbius aromaticity.

A benzopyrane-fused [28]hexaphyrin, 2, was prepared by simple heating of [26]hexaphyrin 1 in acetic acid. Fused [28]hexaphyrin 2 features a molecular twist, a distinct diatropic ring current, a large HOMA value, a large negative NICS value, and a large two-photon absorption (TPA) cross section even at room temperature, all of which support the Möbius aromaticity of 2. To the best of our knowledge, 2 is the first macrocycle that acquires distinct Möbius aromaticity without any assistance from metal coordination, temperature control, or protonation.

Synthesis of a pyridine-fused porphyrinoid: oxopyridochlorin.

The treatment of 3,5-dibenzoylporphyrins with ammonium acetate provided novel oxopyridochlorins as the first examples of pyridine-fused porphyrinoids, which displayed absorption bands reaching into the near IR region and an ability to sensitize singlet oxygen effectively.