The molecular structure and NMR properties of P-phosphinoylmethyl aminophosphonium salts

Abstract

The molecular structures of two aminophosphonium salts (bromide and tetrafluoroborate) have been determined by X-ray analysis. They have similar conformations and hydrogen bond (HB) networks: the N H acid proton is bonded to the anion and, in the case of the fluoroborate, to the oxygen atom of the phosphine oxide, forming a pseudo six-membered ring closed by a weak N H¢ ¢ ¢O intramolecular hydrogen bond (IMHB). These compounds have been studied by multinuclear NMR in solution, including the 15N-labeled derivatives, to determine a complete set of coupling constants. A coupling of j1:5j Hz between the 15N and the 31P nuclei, separated by three bonds, was observed experimentally for the bromide in CDCl3 solution, which appears to be a classical 3JN-P across the covalent bonds and not a 3hJN-P across the IMHB.