Design of superbasic guanidines: The role of multiple intramolecular hydrogen bonds

摘要

New organic superbases have been designed using the concept of multiple intramolecular hydrogen bonds. Substituents capable of forming strong intramolecular H-bonds were selected on the basis of the energy of stabilization that occurs upon the formation of a complex between N,N′,N″- trimethylguanidine and small model molecules. The proton affinities and the corresponding pK_a values in acetonitrile of the new superbases are examined by Density Functional Theory (DFT). It is shown that N,N′,N″-substitution of guanidine with appropriate substituents results in new organic superbases with gas phase proton affinities between 286 and 293 kcal mol~(-1), thus being 15 to 20 kcal mol~(-1) more basic than parental superbase N,N′,N″-tris[(3-dimethylamino)propyl]- guanidine (tris-DMPG), whereas estimated pK_a values in acetonitrile range between 29.5 and 33.2.