Bonding in Cationic Phosphine Imines

Abstract

¹H NMR spectra of pyridinium salts bearing a phosphine imine substituent in the 2-position reveal the formation of contact ion pairs. The high anion sensitivity of protons next to the pyridinium nitrogen and the phosphorus shows that these heteroatoms are both cationic centres. Hence, the classical all-octet formula A provides a better description of the cation than the alternative formulae B - D.