Reactivity of sterically unencumbered transient nitrilium phosphanylide complexes towards 1-piperidinocarbonitrile: A case study

The thermal decomposition of the 7-phosphanorbornadiene complexes 6a,b in x ylene at 120 degreesC in the presence of two equivalents of 1-piperidinocar bonitrile yielded the 2H-1,3,2-azaphosphole complexes 11a,b and the 2H-1,4, 2-azaphosphole complexes 12a-c in ratios of 7:4 (11a:12a) and 1:5 (11b:12b) . Remarkably, the two atropisomers 12b and 12c were obtained (ratio: 5:1) i n the case of the P-phenyl-substituted 2H-1,4,2-azaphosphole complex. Inter estingly, the product ratios of both reactions were approximately the same if neat 1-piperidinocarbonitrile was used as the solvent. The reaction of c omplexes 6a,b with (CuCl)-Cl-I and 1-piperidinocarbonitrile, with exclusion of light, also furnished the 2H-1,3,2-azaphosphole complexes 11a,b as the main products. In the case of complex 6a, a by-product was detected by 31P NMR spectroscopy but could not be isolated. Complexes 11a,b, 12a and 13 wer e purified by column chromatography at low temperature and characterized by NMR and MS spectroscopic means and elemental analysis, whereas only a 1:1 mixture of 12b and 12c could be characterized.