Issue 12, 2024

Strain-based design, direct macrocyclization, and metal complexation of thiazole-containing calix[3]pyrrole analogues

Abstract

The coordination chemistry of ring-contracted porphyrinoids, such as subporphyrins and calix[3]pyrroles, has been largely unexplored owing to the synthetic difficulty of their free-base analogues. Here, we report strain-based molecular design and high-yield synthesis of thiazole-containing calix[3]pyrrole analogues for metal complexation. The artificial force induced reaction and StrainViz analysis methods were used to perform a conformational search and evaluate/visualize the ring strain. The results indicated that the thiazole-containing analogues are less strained than the parent calix[3]pyrrole, while incorporation of imidazole or oxazole unexpectedly leads to an increase in the total strain. Calix[1]furan[2]thiazole was obtained in 60% yield by the direct macrocyclization between α-bromoketone and bis(thioamide), whereas the meso-N(sp2)-bridged analogue, which was calculated to be 5.1 kcal mol−1 more strained, was only obtained in a 2% yield. Calix[1]furan[2]thiazole was converted to calix[1]pyrrole[2]thiazole to investigate metal complexation. Through the reaction with Et2Zn, calix[1]pyrrole[2]thiazole bound a Zn(II) ion in a tridentate fashion adopting a cone conformation, giving a water/air stable organozinc complex that catalyzes polymerization of lactide. Conversely, Ag(I) and Pd(II) ions coordinated to the partial cone conformation of calix[1]pyrrole[2]thiazole in a bidentate fashion. Strain-based molecular design expands the synthetic access to contracted porphyrinoids and provides the opportunity to take advantage of their rich coordination chemistry.

Graphical abstract: Strain-based design, direct macrocyclization, and metal complexation of thiazole-containing calix[3]pyrrole analogues

Supplementary files

Article information

Article type
Research Article
Submitted
17 Mar 2024
Accepted
03 May 2024
First published
03 May 2024
This article is Open Access
Creative Commons BY-NC license

Inorg. Chem. Front., 2024,11, 3548-3554

Strain-based design, direct macrocyclization, and metal complexation of thiazole-containing calix[3]pyrrole analogues

K. Watanabe, K. Shibata, T. Ichino, Y. Ide, T. Yoneda, S. Maeda and Y. Inokuma, Inorg. Chem. Front., 2024, 11, 3548 DOI: 10.1039/D4QI00684D

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