Kinetic trapping of a cobalt(ii) metallocage using a carbazole-containing expanded carbaporphyrinoid ligand

Weinan Zhou; Tridib Sarma; Yonghuan Su; Chuanhu Lei; Jonathan L Sessler

doi:10.1039/d1sc06514a

Kinetic trapping of a cobalt(ii) metallocage using a carbazole-containing expanded carbaporphyrinoid ligand

Chem Sci. 2021 Dec 20;13(3):692-697. doi: 10.1039/d1sc06514a. eCollection 2022 Jan 19.

Authors

Weinan Zhou^{1

2}, Tridib Sarma³, Yonghuan Su², Chuanhu Lei², Jonathan L Sessler⁴

Affiliations

¹ School of Materials Science and Engineering, Shanghai University Shanghai 200444 China.
² Center for Supramolecular Chemistry and Catalysis and Department of Chemistry, College of Science, Shanghai University Shanghai 200444 China chlei@shu.edu.cn.
³ Department of Chemistry, Cotton University Guwahati 781001 Assam India.
⁴ Department of Chemistry, The University of Texas at Austin 105 East 24th Street, Stop A5300 Austin Texas 78712-1224 USA sessler@cm.utexas.edu.

Abstract

The meso-unsubstituted expanded porphyrinoid 3, incorporating two carbazole moieties, acts as an effective ligand for Co(ii) and permits the isolation and X-ray diffraction-based characterization of a 6 : 3 metal-to-ligand metallocage complex that converts spontaneously to the constituent 2 : 1 metal-to-ligand metalloring species in chloroform solution. The discrete metalloring is formed directly when the Co(ii) complex is crystallized from supersaturated solutions, whereas crystallization from more dilute solutions favors the metallocage. Studies with two other test cations, Pd(ii) and Zn(ii), revealed exclusive formation of the monomeric metalloring complexes with no evidence of higher order species being formed. Structural, electrochemical and UV-vis-NIR absorption spectral studies provide support for the conclusion that the Pd(ii) complex is less distorted and more effectively conjugated than its Co(ii) and Zn(ii) congeners, an inference further supported by TD-DFT calculations. The findings reported here underscore how expanded porphyrins can support coordination modes, including bimetallic complexes and self-assembled cage structures, that are not necessarily easy to access using more traditional ligand systems.