1,8-Bis(dimethylaminomethyl)naphthaiene: a new proton sponge

Abstract

1,8-bis(dimethylaminomethyl)naphthalene (DMAMN), which exhibits the features of a proton sponge, has been synthesized. ¹H NMR, infrared and X-ray diffraction studies on protonated DMAMN indicate the formation of intramolecular NHN ⁺ hydrogen bonds which are a little weaker than those in protonated 1,8-bis(dimethylamino)naphthalene (DMAN). This is particularly apparent in the IR spectra of solid salts (appearance of an absorption above 2000 cm^–1). One should emphasize that in CH₃CN solution the intensity of the broad continuum for DMAMN·H⁺ is larger than that for DMAN·H ⁺. In the latter case a π-electron conjugation contributes, which in intramolecular hydrogen bonds reduces the transition moment of the protonic stretching vibrations. The structure of DMAMN nitrate was determined by X-ray diffraction. Crystals of DMAMN·HNO₃ are monoclinic, space group P2¹/c with a= 10.938(3), b= 11.829(3), c= 12.497(3)Åβ= 90.40(3)° and Z= 4. The intramolecular [NHN]⁺ hydrogen bond length is 2.642(3)Å.