Mao Minoura

Cobalt (Co) complexes of porphyrin derivatives possess distinctive redox properties, and hence, their development has attracted significant interest across a wide range of fields. Herein, we report the new examples of the Co complexes of 5,15‐diazaporphyrin (DAP) and 5‐monoazaporphyrin (MAP) derivatives bearing meso ‐aryl groups. These Co complexes were prepared by metal‐templated cyclization of Co–bis(dipyrrin) complexes, complexation of azaporphyrin freebases with a Co salt, and meso ‐N‐functionalization of the Co complexes of DAP and MAP with diphenyliodonium hexafluorophosphate or methyl triflate. The structures as well as the optical and redox properties of these new Co complexes were elucidated by X‐ray crystallography, spectroscopic and voltammetric measurements, and density functional theory calculations. The introduction of a positive charge to the DAP and MAP rings via meso ‐N‐functionalization considerably altered the frontier‐orbital energies, resulting in redshifts of the Q bands and anodic shifts of the ligand‐centered redox processes. The addition of axial ligands also had notable effects on the metal‐centered and ligand‐centered redox processes. All the Co ^II complexes catalyzed the intramolecular radical cyclization and 1,2‐H‐shift reactions of N ‐benzyl‐ N ‐Boc‐3‐diazopropane‐1‐amine in the presence of Cs ₂ CO ₃ to yield two kinds of products via the corresponding σ‐bonded alkyl Co‐azaporphyrin intermediates.

Fucoxanthin (C ₄₂ H ₅₈ O ₆ ) is a highly functionalized allenic epoxy xanthophyll containing hydroxy, acetoxy, ketone and conjugated polyene units. Although its constitution and stereochemistry had been established by chemical, spectroscopic and synthetic studies, its small-molecule single-crystal X-ray structure has remained unavailable. Moss reported in 1979 [ Pure Appl. Chem. (1979), 51 , 507–514] that an early X-ray study by G. M. Sheldrick had reached only a partial solution of the fucoxanthin structure and that refinement had stalled at R ≃ 25%. The first small-molecule single-crystal X-ray structure of fucoxanthin has now been determined as the diethyl ether monosolvate, C ₄₂ H ₅₈ O ₆ ·C ₄ H ₁₀ O, at 100 K in the space group P 1 using synchrotron radiation (λ = 0.4132 Å). The asymmetric unit contains two crystallographically independent fucoxanthin molecules and two diethyl ether molecules. The structure defines the relative stereochemistry, allene geometry, epoxide geometry, polyene bond-length alternation and solvate-assisted packing of fucoxanthin, and provides an independent small-molecule metrical reference for comparison with protein-bound fucoxanthin ligands.

Herein, we report the first examples of group-14 metal complexes of 5-monoazaporphyrins. Six-coordinate silicon(IV) and tin(IV) complexes of 10,15,20-triaryl-5-monoazaporphyrins (Ar3MAPMX2; M = Si or Sn, X = F, Cl, OH, or OCOPh) were prepared by metalation of the freebases of Ar3MAP (Ar3MAPH2) with the corresponding metal salts, followed by sequential axial-ligand exchange reactions. Furthermore, N-phenylation and N-ethynylation reactions of Ar3MAPSiF2 with the corresponding iodonium salts afforded 5,10,15,20-tetraaryl-MAP salts and 5-ethynyl-10,15,20-triaryl-MAP salts, respectively. We also established an environmentally benign method for synthesizing Ar3MAPH2 without a column-separation process. The structures, aromaticity, and optical and electrochemical properties of the SiIV and SnIV complexes of the MAP derivatives were investigated using X-ray crystallography, spectroscopic techniques, cyclic voltammetry, and DFT calculations. The SiIV and SnIV centers stabilized the HOMO and LUMO energy levels and weakened the diatropic ring-current effect of their MAP ligands. The positive charge generated by introducing substituents on the meso nitrogen considerably stabilized the frontier orbitals, resulting in a decrease in aromaticity. Time-resolved fluorescence spectroscopy of fluorescent SiIV complexes also provided valuable information on the effects of the meso-nitrogen atom and its substituents on the excited-state dynamics of MAP chromophores.

In contrast to the great advances of phthalocyanine‐based materials, the potential of 5,10,15‐triazaporphyrins has not been realized because of the lack of fundamental information about their structure‐property relationships. Here, we report new derivatives of dibenzo‐5,10,15‐triazaporphyrin (DBTriAP) with aryl or alkyl substituents at the meso and/or β positions. Freebases of DBTriAP were prepared by the condensation of two types of 1,9‐dibromodipyrrins with 1,3‐diiminoisoindoline and subsequent functionalization of the β‐pyrrolic carbons. Zinc(II) complexes of DBTriAP were obtained by complexation of the corresponding freebases with zinc(II) acetate. The optical and electrochemical properties of the DBTriAP derivatives were studied by steady‐state and transient ultraviolet/visible absorption/emission spectroscopy, magnetic circular dichroism spectroscopy, cyclic voltammetry (CV), and density functional theory (DFT) calculations. Replacing the β‐pyrrolic hydrogens of the 5‐mesityl‐DBTriAP derivatives with aryl groups resulted in substantial red shifts of the low‐energy absorption band because of the effective π‐delocalization and/or charge‐transfer interaction with the DBTriAP chromophore. The 2,3,17,18‐tetraethyl‐DBTriAP freebase exhibited split redox processes in its cyclic voltammogram, suggesting the rapid formation of a π‐stacked dimer radical cation facilitated by the highly planar structure. Most of the DBTriAP derivatives emitted red fluorescence with quantum yields of 0.07–0.31, indicating their potential as luminescent materials.

The first stable 1‐stannavinylidene‐NHC complex with bulky silyl substituents has been obtained from the retro‐dimerization of cyclic 1,3‐bis(stannylene) with an N‐heterocyclic carbene (NHC). To accomplish the retro‐dimerization of cyclic 1,3‐bis(stannylene), a suitably sized NHC is required. Both in the solid state and in solution, 1‐stannavinylidene‐NHC complex is characterized by the presence of a C = Sn π bond. When treated with SnCl₂, 1‐stannavinylidene‐NHC complex undergoes an addition reaction to afford the corresponding stable gem‐bis(chlorostannylene).

Metal–organic frameworks (MOFs) with high porosity usually suffer from problems associated with pore collapse upon activation. Preserving the porosity can thus be considered an important subject to be resolved with regard to the application of MOFs as industrial materials. Herein, we report the preservation of the porosity of phenothiazine-dioxide-based Cu-MOFs via the incorporation of substituents into the organic linkers.

The synthesis and full characterization of 1,4-dilithio-1,4-bis(triisopropylsilyl)-2,3-diphenylbuta-1,3-diene (1b) are reported. This molecule featuring extremely bulky silyl groups at the 1- and 4-positions serves as a precursor for the synthesis of 2,5-bis(triisopropylsilyl)-3,4-diphenyl-1-silacyclopenta-1,3-dienes (siloles) bearing various substituents at the silicon atom (SiR₂ = SiH₂ (4), SiH(OMe) (5), SiF₂ (6), SiBr₂ (7), SiBr(OMe) (8)). Importantly, compounds 6 and 7 reacted with lithium to afford 2,5-bis(triisopropylsilyl)-3,4-diphenyldilithiosilole (9). The solid-state molecular structure and solution NMR spectra reveal the formation of an aromatic ring system, as opposed to the precursors 6 and 7, with two Li cations coordinated by the silacycle in η⁵-fashions. The sterically bulky dilithiosilole 9 can be applied as an important starting material in the pursuit of low-valent silicon species without donor stabilization.

Porphyrinoids in the 20π‐electron state have been extensively studied from the fundamental viewpoint of investigating their structure–antiaromaticity relationships. However, most of the 20π porphyrinoids are highly distorted and unstable in air, which hinder the comprehensive analysis of paratropic ring‐current effects derived from planar π‐electron systems. Herein, we present the first examples of antiaromatic Sn(IV) complexes of 5,10,15,20‐tetraaryl‐5,15‐diazaporphyrinoids (SnX₂TADAPs), prepared by the complexation of the corresponding freebases with Sn(II) chloride under aerobic conditions and subsequent metathesis of the axial ligands, that show paratropic ring‐current effects. Notably, both neutral 20π‐electron derivatives and 19π‐electron radical cations of SnX₂TADAP are extremely stable in air owing to the intrinsic electronic effects of the central Sn(IV) unit and meso nitrogen atoms. NMR spectroscopy, cyclic voltammetry, and density functional theory calculations were performed to assess the ring‐current effects and orbital energies of a series of the 20π‐electron SnX₂TADAPs, and the results reveal that the paratropic ring‐current effects arising from the planar 20π‐electron DAP ring increases with a decrease in the HOMO–LUMO energy gap.

Highly stable selanyl halides, 1-ATQSeX (X = I (1), Br (2) and Cl (3)), were prepared. The structures of 1, 2, 6 (1-ATQSeX: X = Me) and 7 (1-ATQBr) were determined. QC calculations were performed on 1–3, 4 (X = F), 5 (X = H), 6, 7 and 8 (X = SeATQ-1). The O⋯Se distances in 1–4 from the sum of the vdW radii of the atoms (Δr(Se, O₁)) were less than −1 Å, in magnitude, which must be the driving force for the high stability. The O-*-Se interactions seem stronger in the order of 1 < 2 < 3 < 4. The intrinsic dynamic and static natures of O⋯Se and/or Se⋯X in 1–8 are elucidated by QTAIM dual functional analysis (QTAIM-DFA). The Se-*-I, Se-*-Br, Se-*-Cl and Se-*-F interactions in 1–4 are predicted to have the natures of covalent, TBP with CT, TBP with CT, and typical HB with covalency, respectively, whereas O-*-Ses in 1–4 are all predicted to have the nature of MC with CT. The Se-*-H, Se-*-C_Me and Se-*-Se interactions in 5, 6 and 8 are all predicted to have the covalent nature, while O-*-Ses in 5, 6 and 8 are all predicted to have the nature of typical HB with no covalency. The E(2) values of 1–6 and 8 are calculated with NBO analysis, and correlate excellently with Δr(Se, O₁), except for Se-*-F, for which E(2) is evaluated to be much larger. The E(2) values also correlate very well with C_ii ⁻¹ for all Se-*-X in 1–4, although data from 5, 6 and 8 deviated from the correlation, where C_ii is the diagonal element of the compliance (force) constant for the internal vibrations. The behaviour of the interactions is further examined based on the QTAIM-DFA parameters of θ and θ_p. The stabilizing effect is further confirmed by the calculations with the ν(CO) values analyzed carefully.

The reactivity of an isolable 2‐germapropadiene with acids, ketones, and amines was investigated. The reactions of 2‐germapropagiene 1 with hydrogen chloride and acetic acid afforded the corresponding dichlorogermane (2) and diacetoxygermane (3), respectively, indicating that the central germanium atom of 1 is electrophilic. The reaction of 1 with benzaldehyde proceeds via a formal [2+2] cycloaddition to afford the corresponding spiro compound (4). Moreover, 1 reacts smoothly with acetone to furnish germane 5, which contains a six‐membered ring involving two acetone molecules. Furthermore, 1 undergoes N−H bond insertion with methylamine or aniline to afford diamino germanes 7 and 8, respectively. The reaction of 1 with urea selectively afforded the corresponding N−H−insertion product (8).