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  1. The title chlorin, 2 Ph H 2 , hydrogen-bonded to dimethylaminopyridine (DMAP), C 44 H 32 N 4 O 2 ·C 7 H 10 N 2 , and its corresponding zinc(II) complex, 2 Ph Zn , axially coordinated to ethylenediamine (EDA), [Zn(C 44 H 30 N 4 O 2 )]·C 2 H 8 N 2 , were isolated and crystallized by adventitious reduction of the corresponding osmate esters by DMAP and EDA, respectively. Known since 1996 and, inter alia , used for the preparation of a wide range of (planar and non-planar) chlorin analogues (so-called pyrrole-modified porphyrins), their conformational analyses in the solid state are important benchmarks. Both macrocycles are only modestly distorted from planarity and both are slightly more non-planar than the corresponding dimethoxy-derivative, but less planar than a free-base meso -pentafluorophenyl-based osmate ester. NSD analyses provide quantitative and qualitative analyses of the distortion modes. One origin of the non-planarity is presumably the avoidance of the eclipsed configuration of the two vic–cis diols on the pyrroline moiety; the resulting deformation of the pyrroline translates in some cases into the macrocycle. The structure of 2 Ph H 2 features voids making up ca 26% of the unit-cell volume filled withmore »highly disordered solvate molecules (chloroform and hexanes). 2 Ph Zn crystallized with a 13.6 (4)% occupied solvate methanol molecule.« less
    Free, publicly-accessible full text available April 1, 2023
  2. The title morpholinochlorin, C 46 H 16 F 20 N 4 O 3 , was crystallized from hexane/methylene chloride as its 0.44 methylene chloride solvate, C 46 H 16 F 20 N 4 O 3 ·0.44CH 2 Cl 2 . The morpholinochlorin was synthesized by stepwise oxygen insertion into a porphyrin using a `breaking and mending strategy': NaIO 4 -induced diol cleavage of the corresponding 2,3-dihydroxychlorin with in situ methanol-induced, acid-catalyzed intramolecular ring closure of the intermediate secochlorins bisaldehyde. Formally, one of the pyrrolic building blocks was thus replaced by a 2,3-dimethoxymorpholine moiety. Like other morpholinochlorins, the macrocycle of the title compound adopts a ruffled conformation, and the modulation of the porphyrinic π-system chromophore induces a red-shift of its optical spectrum compared to its corresponding chlorin analog. Packing in the crystal is governed by interactions involving the fluorine atoms of the pentafluorophenyl substituents, dominated by C—H...F interactions, and augmented by short fluorine...fluorine contacts, C—F...π interactions, and one severely slipped π-stacking interaction between two pentafluorophenyl rings. The solvate methylene chloride molecule is disordered over two independent positions around an inversion center with occupancies of two × 0.241 (5) and two × 0.199 (4), for a total site occupancy of 88%.
  3. Abstract

    To date, only two pigments have been identified in avian eggshells: rusty-brown protoporphyrin IX and blue-green biliverdin IXα. Most avian eggshell colours can be produced by a mixture of these two tetrapyrrolic pigments. However, tinamou (Tinamidae) eggshells display colours not easily rationalised by combination of these two pigments alone, suggesting the presence of other pigments. Here, through extraction, derivatization, spectroscopy, chromatography, and mass spectrometry, we identify two novel eggshell pigments: yellow–brown tetrapyrrolic bilirubin from the guacamole-green eggshells ofEudromia elegans,and red–orange tripyrrolic uroerythrin from the purplish-brown eggshells ofNothura maculosa. Both pigments are known porphyrin catabolites and are found in the eggshells in conjunction with biliverdin IXα. A colour mixing model using the new pigments and biliverdin reproduces the respective eggshell colours. These discoveries expand our understanding of how eggshell colour diversity is achieved. We suggest that the ability of these pigments to photo-degrade may have an adaptive value for the tinamous.

  4. Free, publicly-accessible full text available June 3, 2023
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  6. Bis(benzene-1,2-diolato-κ 2 O , O ′)bis(dimethyl sulfoxide-κ O )titanium(IV), [Ti(C 6 H 4 O 2 ) 2 (C 2 H 6 OS) 2 ], crystallizes with two crystallographically independent molecules in the space group P 2 1 / c emulating orthorhombic Pbca symmetry (β = 90.0445 (9)°]. The two molecules are related by pseudo-glide symmetry, broken by modulation of each one catecholate and dimethyl sulfoxide (DMSO) ligand. Twinning by pseudomerohedry was observed [twin ratio 0.5499 (7):0.4401 (7)]. Complex 3 was obtained by heating of diprotonated titanium tris-catecholate precursor 2 H in DMSO, by formal displacement of a catechol molecule by two DMSO molecules. Complex 3 is just the second heteroleptic, mono-nuclear, neutral bis-catecholate complex with TiO 6 metal coordination, the only other one being its bis-DMF analogue 6 . The two molecules of 3 exhibit a distorted octahedral geometry. The geometry and distortions from ideal symmetry of 3 are discussed and compared to 6 and to cationic tris-catecholate titanium complexes.
    Free, publicly-accessible full text available April 1, 2023
  7. Octaethyltrioxopyrrocorphins unexpectedly show macrocycle-aromatic properties, even though they contain the macrocyclic π-system of the non-aromatic pyrrocorphins (hexahydroporphyrins). Two of the four possible triketone regioisomers were first reported in 1969 by one-pot oxidation of octaethylporphyrin but remained essentially unexplored since. We detail here the targeted preparation of the remaining two triketone isomers and the optical and NMR spectroscopic properties of all isomers. All four regioisomers possess unique electronic properties, including broadly varying degrees of diatropicity that were experimentally determined using 1 H NMR spectroscopy and computationally verified. Structural patterns modulating the aromaticity were recognized. These differences highlight the regioisomerically differentiated influences of the three β-oxo-functionalities. We also present the solid state structure of the two most common isomers (in their free base form or as zinc complexes), allowing further conclusions to be made about the resonance structures present in these triketones. Remarkably, also, the halochromic properties of the triketones differ sharply from those of regular (hydro)porphyrins, providing further support for the proposed 16-membered, 18 π-electron aromatic ring-current. The work conceptually expands the understanding of tris-modified hydroporphyrinoid analogues and the factors that enable and control porphyrinoid aromaticity.
  8. The synthesis of a low-molecular weight, neutral, porphyrin meso-tetra(dioxan-2-yl)porphyrin of significant solubility in aqueous solution is described using 4 × 1 or 2 + 2-type approaches. The key intermediate dioxan-2-carbaldehyde is accessible in either racemic or in stereo-pure forms from commercially available starting materials in three steps, allowing also the preparation of chiral porphyrins.