Reaction of iminopropadienones with amines--formation of zwitterionic intermediates, ketenes, and ketenimines

Five aryliminopropadienones 4a- d have been synthesized by flash vacuum thermolysis (FVT) by using two different precursors in each case. These compounds were deposited at 50 K at a pressure of ca. 10(-6) mbar together with three different nucleophiles, namely, trimethylamine (TMA), dimethylamine (DMA), and diethylamine (DEA), in order to study their reactions as neat solids during warm-up by FTIR spectroscopy. The reaction with TMA showed that a zwitterionic species (5 and/or 6) was formed in all the cases. With DMA and DEA, an alpha-oxoketenimine and/or an imidoylketene (7 and 8 or 9 and 10) was formed as the final product. In addition, several bands were observed, which can be assigned to zwitterionic intermediates (11 or 12). Optimized structures and vibrational spectra for all products were calculated at the B3LYP/6-31G(d) level of theory by using the polarizable continuum model (epsilon = 5).