engleski

Exceptional superbasicity of bisguanidine proton sponges imposed by the bissecododecahedrane molecular scaffold: A computational study

Exceptional superbasicity of a series of bisguanidines with bissecododecahedrane molecular scaffold was found in the course of a computational study. 3-Syn, 13-syn-disubstituted bissecododecahedrane skeleton ensures that nitrogen lone pairs of electrons are in close proximity, and the rigid framework of the polycyclic cage guarantees acid-base properties similar to those of proton sponges. Amine functionalization with alkyl substituents, imines and guanidines, leads to high basicity. Based on DFT computations, bisguandine-bissecododecahedrane proton sponges with (1, 3-dimethylimidazolidin-2-ylidene)amino moiety are predicted to have very high basicities, both in gas phase and acetonitrile. This skeleton provides the highest proton affinity (PA) value among all the aliphatic proton sponges reported (289.4 kcal mol-1, while gas phase basicity is 284.3 kcal mol-1, at the B3LYP/6-311+G**//B3LYP/6-31G* level). In acetonitrile calculated PA is 319.4 kcal mol-1 and estimated pKa 38.5 units. Substitution of bissecododecahedrane with intrinsically more basic nitrogen functionalities increases PA of 315.1 kcal mol-1 and pKa to 46 units.

Guanidines / Basicity / Heterocycles / Dodecahedranes / Density functional calculationsguanidines / basicity / heterocycles / dodecahedranes / density functional calculations

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