Towards the Strongest Neutral Organic Superbases Based on Intramolecular H-bonds

Abstract

Abstract. Utilizing several different trialkylarsine oxides and substituted pyridine N-oxides as a hydrogen bond acceptors in tri-substituted guanidines we designed several very basic superbases possessing intramolecular hydrogen bonds (IHB-superbases), with proton affinity in the gas phase that comes very close to that of paradigmatic P4-tBu Schwesinger superbase and with pKa in acetonitrile up to 36 units.

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

“…The values of HOMA for the aromatic and nonaromatic compounds are close to 1 and 0, respectively . It is worth mentioning that nowadays the DFT B3LPY computational method is being used as a reliable, straightforward and fast method for a variety of calculations such as basicity and acidity . This method has been utilized here for performing the computations.…”

Step Forward to Stronger Neutral Organic Superbases: Fused Troponimines

“…The deprotonation of the reactant is usually the most crucial step in many organic reactions, which sometimes require very strong superbases. Neutral organic superbases (NOS) are organic molecules that have higher basicity than that of 1,8-bis­(dimethylamino)­naphthalene (DMAN) with gas basicity (GB) of 239 kcal mol –1 and proton affinity (PA) of 245.3 kcal mol –1 . , The NOS are commonly categorized into amidines, guanidines, − phosphazenes, , phosphines, , aromatization-assisted cyclo-organic compounds like cyclopropeneimines and troponimines, − and compounds where above-mentioned subgroups are combined into one molecule, which are usually called hybrid superbases. Superbases, where basic substituents are brought into close proximity by substitution of aromatic backbone, are termed proton sponges.…”

“…It is worth mentioning that bis- N , N ′-(1,3-dialkyl-4,5-dimethyl-1 H -imidazol-2­(3 H )-ylidene) guanidines (p K (BH + ) of 24.9–28.5 in tetrahydrofuran (THF)) and biscyclopropeniminylguanidine (p K (BH + ) of 35.6 in THF) superbases as the most basic phosphorous-free NOS synthesized so far. In some recent theoretical studies, it was shown that in mixed CPI/guanidine systems where multiple intramolecular H-bonds (IMHB) stabilize conjugate acid PA values of up to 306.0 kcal mol –1 could be achieved. , Recently, we have demonstrated that troponimines (TI) possess the same capability as CPI, but resulting in higher GB/PA values . It should be mentioned that NOS design was not limited to theoretical investigations only; however, many theoretically designed NOS have been synthesized and are nowadays being used as promotors of chemical reactions. − Aromatization, therefore, is considered to be the main driving force in high-basicity trait of new NOS systems.…”

“…In some recent theoretical studies, it was shown that in mixed CPI/guanidine systems where multiple intramolecular H-bonds (IMHB) stabilize conjugate acid PA values of up to 306.0 kcal mol −1 could be achieved. 12,24 Recently, we have demonstrated that troponimines (TI) possess the same capability as CPI, but resulting in higher GB/PA values. 25 It should be mentioned that NOS design was not limited to theoretical investigations only; however, many theoretically designed NOS have been synthesized and are nowadays being used as promotors of chemical reactions.…”

Design of Robust Organosuperbases and Anion Receptors by Combination of Azine Heterocycle Skeleton and Phosphazene Motif

“…Diverse potential applications of the superbases in different fields such as the catalytic applications has always been an impetus in chemistry. During the recent years, a lot of experimental and theoretical studies have been reported on design of the strong organosuperbases and new proton sponges . This is not surprising due to two reasons including: 1) acid‐base chemistry is one of the main research fields in chemistry, 2) the advantages of the organosuperbases are based on their better solubility in the organic solvents, moderate conditions of reaction and their excellent stability .…”