2-Chloro-1,3,2-diazaphospholenes: A crystal structural study

A series of 2-chloro-1,3,2-diazaphospholenes with different substitution patterns has been prepared from 1,4-diazabutadienes according to a general synthetic methodology. Subsequent chloride abstraction with Lewis acids affords the corresponding 1,3,2-diazaphospholenium salts. All products have been characterised spectroscopically and by single-crystal X-ray diffraction studies. A detailed analysis of trends in the structural parameters supports the interpretation that the unusual P–Cl bond lengthening in the diazaphospholenes is attributable to n(N)/σ*(P-Cl) hyperconjugation.