Modelling of an Aza-Michael Reaction from Crystalline Naphthalene Derivatives Containing Peri-Peri Interactions: Very Long N-C Bonds?

The separation between a pair of peri-located dimethylamino and ethene-2,2-dinitrile groups in a naphthalene molecule, which models the progress of a Michael reaction, can be controlled by the installation of a short ethylene bridge or the introduction of repulsive interactions at the opposite set of peri positions. Introduction of a dimethylammonium substituent produced a hydrated chloride salt in which the Me2N···C(H)=C(CN)2 separation between reactive groups decreases, reversibly, from 2.167 A at 200 K to 1.749 A at 100 K, with the maximum rate of change in the range 128-140 K, which was studied by variable temperature X-ray crystallography and  solid state NMR. From these and other crystallographic data a correlation between Me2N···C bond formation and alkene bond breaking was constructed for the first step of an aza-Michael reaction.