Benzoylguanidines as Anion‐Responsive Systems

Abstract

A series of benzoylguanidinium salts was prepared and the changes in UV/Vis spectra, triggered by the presence of anions, were investigated. All compounds undergo deprotonation with basic anions like dihydrogenphosphate and acetate in acetonitrile. The most pronounced spectral changes were obtained by deprotonation of N1‐benzoyl‐N3‐(p‐nitrophenyl) guanidinium chloride which shows the naked‐eye visible color change from colorless to yellow. Measured pKa(BH+) in acetonitrile ranges from 12–16, which is comparable to the pyridinium cations. The proton transfer equilibria were also tested in acetonitrile/water mixture where all but the most acidic derivatives showed pKa(BH+) of 4–6 units which corresponds to apparent association constants of 104–106 dm3 mol−1. UV/Vis spectra of neutral and protonated forms were modelled by the TD‐DFT approach using CAM‐B3LYP and PBE0 functionals and compared to CC2 results. In the case of CAM‐B3LYP, a parameter ω, defining amount of long‐range exchange correction, was varied to achieve the best agreement with the experimental spectra. The optimized ω parameters are 0.10 a0−1 for neutral benzoylguanidines and 0.20 a0−1 for neutral nitrobenzoyl and protonated systems. The larger ω parameter in the latter is ascribed to more pronounced charge transfer character of the HOMO‐LUMO transition – the one responsible for the lowest energy absorption band.

Fluorescent Guanidinium-Azacarbazole for Oxoanion Binding in Water

“…We designed GADAC to have a preorganized structure that presents four hydrogen bond donating groups to an oxoaniontwo from a guanidinium group, one from a carbazole N–H, and one from a 2-aminopyridine N–H (Scheme ). An intramolecular hydrogen bond between the guanidinium group and a second pyridino nitrogen is intended to restrict aryl C–N bond rotation and maintain planarity. − The two pyridino groups are intended to lower the p K a values of the guanidinium and amino groups and, thereby, enhance their ability to donate hydrogen bonds to oxoanions. − …”

“…5−12 For example, the installation of an adjacent amide or pyrrole moiety can increase the affinity of a guanidinium-containing compound for oxoanions. 15,16 Likewise, decreasing the pK a value of a guanidino group can enhance affinity 17 because hydrogen bond donors and acceptors with more closely matched pK a values form stronger hydrogen bonds. 18−20 In that regard, a common strategy has been to employ an N-acylguanidinium group, which has a pK a of 8.3 compared to that of 13.7 for an N-alkylguanidinium group.…”

“…Early oxoanion binders were macrocycles that showed a higher affinity for inorganic phosphate than did their acyclic counterparts . Since then, organic chemists have refined the number and display of guanidino groups, tuned their p K a values, and added other hydrogen bond donors within a variety of scaffolds. − For example, the installation of an adjacent amide or pyrrole moiety can increase the affinity of a guanidinium-containing compound for oxoanions. , Likewise, decreasing the p K a value of a guanidino group can enhance affinity because hydrogen bond donors and acceptors with more closely matched p K a values form stronger hydrogen bonds. − In that regard, a common strategy has been to employ an N -acylguanidinium group, which has a p K a of 8.3 compared to that of 13.7 for an N -alkylguanidinium group. ,− …”

“Backdoor Induction” of Chirality: Trans‐1,2‐cyclohexanediamine as Key Building Block for Asymmetric Hydrogenation Catalysts

“…We also checked whether the change in long range correction parameters (ω‐values) will additionally improve the simulated spectra. Namely, it has been shown that for some systems calculations with an “optimized” ω‐value give better agreement of the calculated spectra than the default one . For this purpose, we used ω‐values of 0.20, 0.15 and 0.10 |a 0 –1 |.…”

Mechanistic DFT Study of 1,3-Dipolar Cycloadditions of Azides with Guanidine

“…Guanidines are organic compounds that possess very interesting physico-chemical properties, such as very high basicity [1,2] and biological activity [3]. Their chemical behavior is extensively studied and guanidines have found applications in various fields, such as catalysis [4], coordination chemistry [5], supramolecular chemistry [6], medicinal chemistry [7,8] and chemical sensoring [9,10]. Whereas this versatile functional group undergoes numerous chemical reactions, guanidines are rarely involved in cycloaddition reactions [11], either in Diels-Alder or dipolar cycloadditions.…”