A Phosphorus Bisylide: Exploring a New Class of Superbases with Two Interacting Carbon Atoms as Basicity Centers

Herein we present the first superbase MHPN with two interacting P-ylide entities. Unlike classical proton sponges, this novel compound class has carbon atoms as basicity centers which are forced into close proximity by a naphthalene scaffold. The bisylide exhibits an experimental pK_BH⁺  value of 33.3±0.2 on the MeCN scale and a calculated gas-phase proton affinity of 277.9 kcal mol^-1 (M062X/6-311+G**//M062X/6-31G*+ZPVE method) exceeding that of the corresponding monoylide by nearly 15 kcal mol^-1 . The origin of the unexpectedly high basicity of the new bisylide was investigated by NMR spectroscopic methods, single-crystal X-ray diffraction as well as theoretical calculations and can be partly attributed to the rapid exchange of the "acidic" proton between the two basic carbon atoms after protonation.