Expanded Mercaptocalixarenes: A New Kind of Macrocyclic Ligands for Stabilization of Polynuclear Thiolate Clusters

Abstract

The syntheses and properties of expanded 4‐tert‐butyl‐mercaptocalix[4]arenes, in which the methylene linkers are replaced by −CH2NRCH2− or −CH2NRCH2− and −CH2NRCH2CH2CH2NRCH2− units, are described. The new macrocycles were obtained in a step‐wise manner, utilizing fully protected, i. e. S‐alkylated, derivatives of the oxidation‐sensitive thiophenols in the cyclisation steps. Reductive cleavage of the macrobicyclic or macrotricyclic intermediates (6, 7, 11) afforded the free thiophenols (H48, H49, and H412) in preparative yields as their hydrochloride salts. The protected proligands can exist in two conformations, resembling the “cone” and “1,3‐alternate” conformations found for the parent calix[4]arenes. The free macrocycles do not show conformational isomerism, but are readily oxidized forming intramolecular disulfide linkages. Preliminary complexation experiments show that these expanded mercaptocalixarenes can serve as supporting ligands for tetranuclear thiolato clusters.

Mixed Thioether/Amine‐Functionalized Expanded Calixarenes, Related Macropolycycles, and Metal Complexes thereof

“…Precursor 1 was prepared as described in the literature [11] . Compounds 5 and 6 were available from previous studies [10d,12] . All reagents and solvents were commercial grade and used without further purification.…”

Fifty Years of Inorganic Biomimetic Chemistry: From the Complexation of Single Metal Cations to Polynuclear Metal Complexes by Multidentate Thiolate Ligands

“…We recently reported on the tetraazatetrathiacalix [4]arene L21H 4 , which derives from calix [4]arene by substitution of the amine bridges for the methylene bridges, and can be considered as an expanded calixarene. [89] We showed that this macrocycle could form a tetranuclear Co (II) complex [Co 4 (L21)(μ 4 -Cl)(μ-OAc) 2 ]Cl (44), obtained in 59 % yield after crystallisation, by reaction of L21H 4 •4HCl with a slight excess of Co(OAc) 2 •4H 2 O in the presence of the stoichiometric amount of lithium acetate (Figure 32). An X-ray crystal structure determination showed that L21 4À adopted a C 2 -symmetric cone conformation in the complex, the four cobalt dications and a μ 4 -bridging chloride anion closing the small opening of the calixarene.…”

“…(Left) Preparation of the tetranuclear Co (II) complex 44 from the tetraazatetrathiacalix [4]arene L21H 4 (L=OAc À ); (right) ORTEP side view of the X-ray crystal structure of 44 (protons omitted for clarity). [89] (Reproduced from Ref. [89] Copyright (2022), with permission from Wiley-VCH GmbH).…”

“…[89] (Reproduced from Ref. [89] Copyright (2022), with permission from Wiley-VCH GmbH). be indicative of some increased π-π-(or charge transfer) interactions between the aromatic rings of the electron rich amino thiophenolato macrocycle and the electron poor azobenzene-carboxylato ligand.…”