1,8,1',8'-Tetrakis(dimethylamino)-2,2'-dinaphthylmethanols: double in/out proton sponges with low-barrier hydrogen-bond switching.

Previously unknown bis[1,8-bis(dimethylamino)naphth-2-yl]phenylmethanol (5) and bis[1,8-bis(dimethylamino)naphth-2-yl]methanol (6) have been obtained and studied by combination of X-ray, NMR, and IR techniques at variable temperature. It has been established that both proton sponge units in the solid tertiary alcohol 5 exist in nonconventional in/out form, one of which is fixed by intramolecular O-H...N hydrogen bonding. In solution, a fast interconversion of two isoenergetic hydrogen chelates occurs which can be frozen below 183 K. Unlike this, the secondary alcohol 6 in the solid at 100 K adopts the in/out-in/in conformation and at 293 K demonstrates a kind of dynamic behavior which can be described as temperature-driven dimer-induced rechelation. In solution under ambient conditions 6 exists as an equilibrating mixture of chelated and unchelated monomeric forms in a approximately 1:1.8 molar ratio.