Synthesis and theoretical investigation of a 1,8-bis(bis(diisopropylamino)cyclopropeniminyl)naphthalene proton sponge derivative.

We report herein the synthesis and characterization of a new proton sponge derivative, 1,8-bis(bis(diisopropylamino)cyclopropeniminyl)naphthalene 4 (DACN), as well as its bis-protonated counterpart 6. A crystal structure of 6 is presented, along with variable temperature (1)H NMR data on the BF4(-) salt (6⋅BF4). DFT calculations were performed to investigate the structure of the monoprotonated species 7 and to gain insight into the structural and electronic nature of all three species. The proton affinity (PA) of 4, calculated at the B3LYP/6-311G++(d,p)//B3LYP/6-31G(d,p) level, taking into account thermal corrections from the B3LYP/6-31G(d,p) method, was 282.3 kcal mol(-1), while its pKa was estimated at 27.0. NICS calculations were performed to examine the changes in aromaticity within these systems upon each successive protonation. Lastly, homodesmotic reaction schemes were used in order to estimate the factors contributing to the strong PA predicted for 4.