Basicity characterization of novel designed phosphorus containing cyclic structures by a computational approach

DFT calculations were carried-out for some of novel designed structures with basicity and superbasicity potentials. In this research, two series of cyclic phosphorus-containing compound were designed inspiring from 1,3,5,7-tetraazaadamantane and 1,4-diazabicyclo[2,2,2]octane. The proton affinity (PA) in the gas phase was calculated for each of the structures 1–14. Most of the designed structures were found to have higher basicity than that of 1,8-bis(dimethylamino) naphthalene (DMAN) as the threshold of superbasicity (3, 4, 7, 10–14). The effect of heteroatom and substituents type in the ring as well as of internal bond angles on the proton affinity were evaluated. It was found that the structure 14 possesses highest PA value of 1198.27 kJ mol⁻¹ in the gas phase. According to the obtained results, the PA values were significantly amplified by substitution with electron releasing groups on the molecular framework. Also, the limitations created by the ring for the electron donation of the substitutents in the neighborhood of the main phosphazene group are discussed.