1,4-Dialkyl-1,4-diazabutadienes: Their reactions with aluminum and indium halides

Reactions of 1,4-bis[(S) methylbenzyl]-1,4-diazabutadiene (1), 1,4-bis[(R) 1′-chlorobutan-2′-yl]-1,4-diazabutadiene (2), 1,4-bis[(S,S) 1′-chloro-1′-phenyl-propan-2′-yl]-1,4-diazabutadiene (3), and 1,4-di-tert-butyl-1,4-diazabutadiene (4) with aluminum and indium halides were performed. Reaction of 1,4-diazabutadienes 1-4 with two equivalents of aluminum halides in toluene afforded ionic aluminum coordination compounds (5-10) which in THF solution are transformed into 1,3-dialkyl-2-methaneiminealkyl imidazolium heterocycles (11-14) by condensation of two 1,4-diazabutadienes and elimination of amine hydrochloride. Equimolar reactions of 1-4 with InCl₃ in dry acetonitrile at -78 °C afforded the neutral and diamagnetic InCl ₃ coordination compounds (15-18), which are stable in the solid state under dry conditions, but in THF solution are slowly transformed into the corresponding 1,3-dialkyl-imidazolium heterocycles 19-22. The X-ray diffraction analyses of compounds 2, 3, 10, 11, 14 and 17 are described. Quantum mechanical calculations were performed in order to find the minimum energy conformers of 1,4-diazabutadienes, 1,3-dialkyl-2-methaneiminealkyl imidazolium and 1,3-dialkyl-imidazolium derivatives as well as the aluminum and indium coordination compounds.