engleski

Computational design of organic superbases possessing the guanidine functionalities

Design and synthesis of novel, neutral organic superbases represents a highly important area of organic chemistry nowadays. Important advantages of organic superbases are their use as homogeneous catalysts in organic reactions as recyclable environmentally friendly reagents. Many efforts have been put into development of basic fragments, which can be put together to enhance basicity of such systems. The systems widely explored are ‘proton sponges’ (PS), in which the two basic centers are brought to the close proximity by rigid framework. Strong lone-pair repulsion in these systems, in conjuction with stabilization by strong intramolecular hydrogen bonding (IMHB) upon protonation are the key factors for their extraordinary basicity. Here we report on the systematic DFT study of guanidines suitably positioned on polycyclic frameworks (by B3LYP/6-31G* and M052X/6-31G* methods, followed by single point energy estimations at B3LYP/6-311+G** and M052X/6-311+G** levels) which led to development of a series of novel superbases possessing the (1, 3-dimethylimidazolidin-2-ylidene)amino moiety with extremely high basicities, both in gas phase and in acetonitrile. Obtained absolute proton affinity (APA) and gas phase basicity (GB) values are amongst the highest of all the aliphatic proton sponges known.

computational chemistry; basicity

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