Anion receptors with 1,3,5‐triazacyclohexane and 1,4,7,10‐tetraazacyclododecane scaffolds

Abstract

Fluoride, chloride, and bromide affinities of 1,3,5-triazacyclohexane (TACH) and 1,4,7,10-tetraazacyclododecane (Cyclen) were studied theoretically using ωB97XD and B3LYP functionals and 6-311++G(d,p) basis set. To enhance and modify the anion affinities of TACH and Cyclen, several anion receptors with-(CH 2) n OH and-(CH 2) n NH 2 (n = 1-3) substituents were designed and investigated. These anion receptors are attached to the halides (X −) via formation of NH … X and OH … X hydrogen bonds. The anion affinities calculated by ωB97XD were larger than those obtained by B3LYP indicating the dispersion contribution to the anion affinities. It was found that the anion affinities of these compounds depend on both the alkyl chain length and nature of the interaction, NH … X or OH … X. The ωB97XD-calculated fluoride affinities of TACH and Cyclen were 149.5 and 207.2 kJ mol −1 , respectively. By substitution of-(CH 2) n OH groups, anion receptors with F − affinities of 277 and 326 kJ mol −1 were obtained, which can be classified among the strongest organic anion receptors. The affinity of all TACH and Cyclen toward the halides was as F − > Cl − > Br − , while substitution of-(CH 2) 3 OH and-(CH 2) 3 NH 2 into Cyclen changed the trend to F − > Br − > Cl − .

Is It Possible to Achieve Organic Superbases beyond the Basicity Limit Using Tetrahedrane Scaffolds?

“…Protonation of tetrahedrane 1 opens its cage and the excess positive charge is delocalized throughout the resulting homocyclopropenyl cation 1H + . To assist in this delocalization, and subsequently enhance the basicity, we dressed 1 with cyclopropene and cycloheptatriene rings, which accommodate positive charge through the formation of the cationic aromatic rings, and with guanidino and permethylguanidino moieties typically used in the design or organic superbases, which can stabilize protonated structures through both the charge delocalization and inductive effect.…”

“…The structures of the bases and their protonated forms were optimized using the B3LYP DFT method and the highly flexible 6–311++G(d,p) basis set in line with our earlier reports . Frequency calculations were performed at the same level of theory to obtain the gas‐phase PA and GB values at 298 K and 1 atm.…”

“…Because of vast applications of organic bases and superbases in many branches of chemistry and chemical industry, considerable efforts have been made to design and synthesize compounds with a wide range of basicities Numerous classes of superbases, such as proton sponges, phosphazenes, imines, imidazolines, guanidines and bis‐gaundines, have been proposed. The principle strategy in the design of these systems is a stepwise extension of the molecular framework by the inclusion of substituents or structural motifs with the charge delocalization ability.…”

Design of Exceptional Strong Organosuperbases Based on Iminophosphorane and Azaphosphiridine Derivatives: Harnessing Ring Strain and Aromaticity to Engineer Neutral Superbases

“…Based on these factors, a wide variety of the superbase such as silylenes, germylenes, guanidines, imidazolines, guanidinophosphazenes, phosphorus ylides, amines, quinones, iminopolyenes, etc . have been reported in the scientific resources . Phosphazenes are a large family of the phosphorous superbases which have nowadays attracted much attention .…”

“…Aromaticity can stabilize the positive charge on the superbase's conjugate acid by delocalization and the basicity increases. The number of investigations using this factor to design the superbases is scarce . Lambert et al .…”