Out-Basicity of 1,8-bis(dimethylamino)naphthalene: the experimental and theoretical challenge

摘要: A possibility of non-conventional two-step protonation 1,8-bis(dimethylamino)naphthalene (proton sponge) is discussed. Unlike the generally accepted mechanism, involving relatively slow direct penetration a proton into cleft between peri-NMe2 groups, it consists rapid addition to out-inverted NMe2 group with subsequent slower rotational transfer inter-nitrogen space produce stable chelated cation. The following approaches were employed during work: (1) competitive hydrogen bond formation in specially designed alcohol which OH might chelate either sponge 1-NMe2 or another basic center (N,N-dimethylaniline) known basicity; (2) measuring basicity naphtho[1,8-b,c]diazabicyclo[3.3.3]undecane considered be close analogue capable exclusively out-protonation; (3) X-ray, spectral and DFT studies structure, energy stereodynamics compounds obtained, including their conformers. For first time, pKa value an organic base perfectly flat nitrogen atom reported. final conclusion made that both pathways protonation, traditional non-conventional, contribute parallel still undefined ratio. estimated out-basicity at least 5.5 orders magnitude lower than directly measured in-basicity.