Homoselenacalix[n]arenes

Abstract

A novel family of homoselenacalix[n]arenes (n = 3-8), with bridging CH(2)SeCH(2) groups connecting the aryl subunits, has been synthesized via two different approaches employing nucleophilic Se species. The macrocycles are adequately characterized, including single-crystal X-ray structures for the homoselenacalix[4]- and homoselenacalix[6]arene homologues. The combined features of a calixarene-like macrocyclic scaffold and the presence of multiple selenium atoms create appealing (biomimetic) supramolecular opportunities.

Homothiacalix[4]arenes: Synthetic Exploration and Solid‐State Structures

“…Our interest in (homohetera)calixarenes previously led us to discover a new class of homocalixarene macrocycles, containing CH 2 SeCH 2 bridging units, with a ring size varying from three to eight monomeric building blocks. [9] A precursor enabling high solubility for all homoselenacalix[n]arenes (n = 3-8) was chosen in this previous study. Therefore, we envisaged to use the same building block, 1,3-bis(bromomethyl)-5-tert-butyl-2-methoxybenzene (1), as an electrophile and its corresponding dithiol derivative 2 as the nucleophilic component (see Scheme 1).…”

“…This substitution pattern also allows direct comparison with the related homooxa-and homoselenacalixarenes. [5,9] Results and Discussion Synthesis and characterization: In 1981, Tashiro and Yamato described the occurrence of a cyclic tetramer, [8b] which can be regarded as an octahomotetrathiacalix [4]arene (p-tert-butyloctahomotetrathiacalix [4]arene tetramethyl ether 4), [11] as a side product (7 %) during the synthesis of dithiacyclophane 3 (56 %) by a cyclocondensation reaction of 1,3-bis(-chloromethyl)-5-tert-butyl-2-methoxybenzene and its corresponding dithiol derivative 2 with KOH base in EtOH/benzene (see Scheme 1). Gheorghiou and co-workers only obtained metacyclophane 3 (38 %), starting from precursors 1 and 2 under similar conditions.…”

“…The same observations were previously made for the homoselenacalix [4]arene homologue. [9] To gain further insight into the conformational behavior of homothiacalix [4]arene 4 in solution, variable-temperature (VT) 1 H NMR spectra were recorded. No signal splitting was observed for temperatures down to 230 K, while further shielding of the methoxy pro- Studies on the effect of intra-and extraannular aryl substituents on the macrocyclization outcome for homoselenacalix [4]arenes indicated that the methoxy groups on the inner rim played a crucial role for the selective formation of the cyclic tetramer.…”

“…They are expanded analogues of calixarenes in which CH 2 XCH 2 bridges (X = O, NR, S, Se) partly or completely replace the methylene bridges between the aromatic units of the classical carbon-bridged calix[n]arenes or the heteroatoms of regular heteracalixarenes. [2][3][4][5][6][7][8][9] The dimethylenehetera linkages impose an increased cavity size, as well as conformational mobility, and provide additional (potentially cooperative) binding sites through the heteroatoms. These features are beneficial for supramolecular binding of a suitable guest in an induced-fit fashion.…”

Homodiselenacalix[4]arenes: Molecules with Unique Channelled Crystal Structures

“…[2] However,t hese are still rarelye ncountereda mong organic compounds. [3,12] The main driving forces for the formationof supramolecular organic frameworks are the geometrical constraints on the buildingb locks, which favour ap articular molecular conformation achieved through an et of different supramolecular interactions, such as hydrogen andh alogen bondinga nd p-p stacking.I nt he case of soft supramolecular frameworks, these can switch when triggered by externals timuli,w hich causesr eorganisation of the molecules in the crystal unit.…”