Azolium-Linked Cyclophanes:  A Comprehensive Examination of Conformations by ¹H NMR Spectroscopy and Structural Studies

Abstract

The synthesis and characterization of a series of azolium-linked cyclophanes are reported. The cyclophanes consist of two azolium groups (17 examples) or three imidazolium groups (1 example) linked to two benzenoid units (benzene, naphthalene, p-xylene, mesitylene, 1,2,3,4- and 1,2,4,5-tetramethylbenzene, 2,6-pyridine, and p-tert-butylphenol) via methylene groups. Cyclophanes containing ortho-, meta-, and para-substitution patterns in the benzenoid units were examined. The conformations of the cyclophanes were examined in solution by variable-temperature NMR studies and in the solid state by crystallographic studies. The p-cyclophanes and mesitylene-based m- and o/m-cyclophanes are rigid on the NMR time scale, as indicated by sharp (1)H NMR spectra at all accessible temperatures. The non-mesitylene-based m-cyclophanes and the o-cyclophanes are fluxional on the NMR time scale at high temperatures, but in most cases, specific conformations can be "frozen out" at low temperatures. Many structures deduced from solution studies were consistent with those in the solid state.

Synthesis and Characterisation of Mono‐ and Bidentate Alkoxybenzimidazolin‐2‐ylidene Palladium Complexes: Interesting Solution Behaviour and Application in Catalysis

“…The results of the single-crystal X-ray studies of 2b (Figure S1), and 4-8 (see Figures 5,6,7,8,9, and 10; Tables 1, 2, 3, and 4) support the proposed formulations, with 2b, 6, 7, and 8 solvated in some manner. Compound 2b crystallised with one molecule of CHCl 3 per formula unit.…”

“…The bidentate NHCs consist of benzimidazolin-2-ylidene units that are linked by one o-xylyene group, and generally bind to the metal centre in a rigid fashion. [6,7] The benzimidazolin-2-ylidene units possess bulky substituents on the nitrogen atoms and electron donating butoxy groups on the arene ring, the latter which also serve to increase the solubility of the complexes in common organic solvents. We have previously reported the use of similar electron-rich benzimidazolin-2-ylidenes as ligands in a range of palladium complexes of mono-and bidentate NHC ligands possessing phosphane or pyridine ancillary ligands, [8,9] and are interested in extending this investigation by studying the differences in catalytic activity between the bis(NHC)PdX 2 and (NHC)Pd(allyl)X systems.…”

Metal Complex Derivatives of Azole: a Study on Their Synthesis, Characterization, and Antibacterial and Antifungal Activities

“…Therefore, the intracellular concentration of this metal is tightly regulated by zinc transporters, which could be removing zinc from the fungal cells. 57,58 In general, complex (15) showed the highest antifungal effects and inhibited the growth of all tested Candida species and also A. fumigatus. Singh et al 16 reported .…”

Azolium-Linked Cyclophanes: Effects of Structure, Solvent, and Counteranions on Solution Conformation Behavior

“…process (anti→anti exchange) was more facile than the benzene ring flip process (anti→syn exchange), and rate constants and activation energies for each process were estimated from the variable temperature NMR data (See the first entry in Table 1). 7 The benzimidazolium cyclophane 5.2Br displayed behavior similar to that of 3.2Br, including broad signals at room temperature, corresponding to the benzylic protons, that coalesced at higher temperatures. In general, the "non-alkylated" cyclophanes 3.2Br-5.2Br were very soluble in water, displayed low solubility in DMSO and methanol, and were insoluble in organic solvents of medium polarity such as acetone, chloroform and dichloromethane.…”