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

Abstract

This paper describes the synthesis, structural characterization, and solution behavior of some xylyllinked imidazolium and benzimidazolium cyclophanes decorated with alkyl or alkoxy groups. The addition of alkyl/alkoxy chains to the cyclophanes allows for studies in chlorinated solvents, whereas previous solution studies of azolium cyclophanes have generally required highly polar solvents. The azolium cyclophanes may exist in a syn/syn conformation (azolium rings mutually syn, arene rings mutually syn) or a syn/anti conformation (azolium rings mutually syn, arene rings mutually anti). The preferred conformation is significantly affected by (i) binding of bromide (ionpairing) to the protons on the imidazolium or benzimidazolium rings, which occurs in solutions of bromide salts of the cyclophanes in chlorinated solvents, and (ii) the addition of alkoxy groups to the benzimidazolium cyclophanes. These structural modifications have also led to cyclophanes that adopt conformations not previously identified for similar azolium cyclophane analogues. Detailed 1 H NMR studies for one cyclophane identified binding of bromide at two independent sites within the cyclophane.3

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

“…Microanalyses were performed by the Microanalytical Laboratory at the Research School of Chemistry, Australian National University, Canberra. 5,6-Dibutoxybenzimidazole [10] and [{Pd(η 3 -C 3 H 5 )Cl(μ-Cl)} 2 ] [32] were prepared according to established procedures.…”

“…[10] 1,3-Dibenzyl-5,6-dibutoxybenzimidazolium chloride (2a) was prepared in excellent yield (94 %) by alkylation of 1a with benzyl chloride, while 1,3-dibenzhydryl-5,6-dibutoxybenzimidazolium chloride (2b) was prepared in more modest yield (37 %) in one pot from 5,6-dibutoxybenzimidazole, diphenylchloromethane and NaOH. The bis(benzimidazolium) salts 3a and 3b were prepared in high yields (78 % and 83 %, respectively) by the reaction of α,αЈ-dibromo-o-xylene with 1a and 1b, respectively.…”

Synthesis and Characterisation of (Alkoxybenzimidazolin‐2‐ylidene)palladium Complexes: The Effect of Ancillary Ligands on the Behaviour of Precatalysts

“…The N-methylbenzimidazoles 1a and 1b were prepared from the appropriate dibutoxybenzimidazole, [10] and were subsequently alkylated by using an excess of methyl iodide to give the benzimidazolium salts 2a and 2b in excellent yields. These salts, which serve as ligand precursors, were not hygroscopic and showed excellent solubility in a range of common organic solvents (e.g.…”

“…5,6-Dibutoxy-1-methylbenzimidazole (1a): 5,6-Dibutoxybenzimidazole [10] (3.5 g, 13 mmol) was added to a suspension of NaH (0.38 g, 16 mmol) in thf (80 mL), and the mixture was stirred for 1 h. Methyl iodide (0.85 mL, 13 mmol) was added dropwise, and the mixture was stirred at room temperature for 1 h, then heated at 40°C for 20 h. The mixture was filtered through Celite, and the filtrate was concentrated in vacuo. The residue was dissolved in diethyl ether and washed with water (3 ϫ 30 mL), then dried (MgSO 4 ).…”

Review on supermolecules as chemical drugs

“…In the researches of macrocyclic compound cyclophanes, imidazolium or benzimidazolium cyclophanes became the highlight. For example, bis-imidazolium 149 and tetraimidazolium 150 have gained large success in host-guest researches and mimicking enzyme catalysis [24][25][26][277][278][279][280] , and the onium cations in macrocycles as the host molecules of supramolecular drugs inevitably play important roles in the research and development of supramolecular drugs.…”