Imidazoporphyrins as supramolecular tectons: synthesis and self-assembly of zinc 2-(4-pyridyl)-1H-imidazo[4,5-b]porphyrinate

Inna A. Abdulaeva (1, 2) , Kirill P. Birin (2) , Anna A. Sinelshchikova (2) , Mikhail S. Grigoriev (2) , Konstantin A. Lyssenko , Yulia G. Gorbunova (2, 3) , Aslan Yu. Tsivadze (2, 3) , Alla Bessmertnykh-Lemeune (1)

1 ICMUB - Institut de Chimie Moléculaire de l'Université de Bourgogne [Dijon]
2 A.N. Frumkin Institute of Physical Chemistry and Electrochemistry
3 IGIC - N. S. Kurnakov Institute of General and Inorganic Chemistry

5,10,15,20-Tetramesityl-2-(4-pyridyl)-1H-imidazo[4,5-b]porphyrin (PyPor) bearing a pyridine donor site connected to the tetrapyrrolic macrocycle by a rigid imidazole linker was prepared in high yield by the condensation of the corresponding 2,3-dioxochlorin and 4-formylpyridine in the presence of ammonium acetate. After the insertion of a metal ion capable of metal–ligand axial coordination, namely Zn(II), this compound afforded self-complementary porphyrin PyPorZn which was suitable for self-assembly. In the crystals, this complex exists as a zigzag coordination polymer formed through the axial coordination of the pyridine nitrogen atom to the zinc ion of the neighbouring porphyrin molecule. The Zn atoms adopt a distorted tetragonal pyramidal environment and the pyridine rings significantly deviate from the orthogonal orientation to the mean N4 plane of the adjacent macrocycle (the Cpara–NPy–Zn angle is equal to 148°). This distortion was analysed by using DFT calculations of a zinc 5,10,15,20-tetraphenylporphyrinate–pyridine complex (TPPZn–Py). The energy and the geometry of TPPZn–Py were calculated by varying the tilt of the pyridine ligand. The change of the Cpara–NPy–Zn angle from 180° to 150° induces a small increase (within 1.5 kcal mol−1) of the total energy of the complex. Such a small increase can be easily compensated by the intermolecular CH⋯H and CH⋯π interactions in the crystals. The self-assembly of PyPorZn in non-coordinating solvents was also investigated by NMR and UV-vis spectroscopy. In contrast to the nickel complex PyPorNi, the zinc complex exists in 10−4 M solution in toluene and chloroform as a mixture of short linear oligomers. These oligomers dissociate affording monomer species upon heating, dilution or addition of a substituting ligand.

Domaines: Chimie de coordination; Chimie organique

Inna A. Abdulaeva, Kirill P. Birin, Anna A. Sinelshchikova, Mikhail S. Grigoriev, Konstantin A. Lyssenko, et al.. Imidazoporphyrins as supramolecular tectons: synthesis and self-assembly of zinc 2-(4-pyridyl)-1H-imidazo[4,5-b]porphyrinate. CrystEngComm, 2019, 21 (9), pp.1488-1498. ⟨10.1039/C8CE01992D⟩. ⟨hal-02379619⟩