Synthesis and structural analysis of 1,4‐bis[ n ‐( N,N ‐dimethylamino)phenyl]buta‐1,3‐diynes and charge‐transfer complexes with TCNE

n ‐( N,N ‐Dimethylamino)phenylethynes were satisfactorily prepared by a Wittig reaction between chloromethylene(triphenyl)phosphine ylide and the appropriate n ‐( N,N ‐dimethylamino)benzaldehyde, followed by dehydrochlorination with a strong base. The conjugate dimers 1,4‐bis[ n ‐( N,N ‐dimethylamino)phenyl]buta‐1,3‐diyne were obtained by oxidative dimerization with copper(I) chloride. X‐ray molecular structure analysis of the dimer 1,4‐bis[ 2 ‐( N,N ‐dimethylamino)phenyl]buta‐1,3‐diyne corroborated the resonance contribution of the o ‐dimethylamino substituent, which was confirmed in the solid state by the molecular crystalline packing. Both o ‐ and p ‐( N,N ‐dimethylamino) conjugate dimers develop 1:1 charge‐transfer complexes with TCNE and their structure was identified by NMR, IR and UV–visible spectroscopic data. Differential scanning calorimetric analyses of the 1,3‐diynes showed an irreversible transformation to a thermopolymer as a unimolecular reaction. Copyright © 2001 John Wiley & Sons, Ltd.