15N Nucelar Magnetic Resonance Study of Two-Coordinate Phosphorus Cations - Sign-Determination of Coupling Constants – Application of Two-Dimensional (2D) Heteronuclear Shift Correlations

Abstract

Cyclic and non-cyclic bis(amino)phosphenium cations (1 to 4) together with their precursors (bis(amino)phosphorus chlorides 5 to 8) and some other bis(amino)phosphorus compounds (9 to 14) have been studied by 13C, 15N (natural abundance), 29Si and 31P NMR spectroscopy. 15N chemical shifts and coupling constants 1J(31P15N) of phosphenium cations have been determined for the first time. NMR data of 1 to 4 are compared with those of a bis(amino)carbene and various bis(amino)stannylenes. In the phosphenium cations 1 to 4 the 15N nuclear shielding is considerably reduced (ca. 70 to 100 ppm as compared with 5 to 14) and there is a crude linear relationship between δ15N and δ31P values. Changes in the δ15N values of 1 to 4 do not reflect P-N (pp)π interactions. A positive sign has been determined for the coupling constants 1J(31Ρ15Ν) [reduced coupling constants 1K(31P15N) < O] for the phosphenium cations and for all other P(III)-N compounds studied. This was achieved by applying various one- and twodimensional heteronuclear double resonance techniques. The experiments also gave signs of the coupling constants 2J(31PN13C), 2J(31PN29Si), 3J(31PNC13C), 3J(31PNSi13C), 4J(31PNCC1H) and 4J(31PNSiC1H). Negative contributions to 1K(31P15N), arising from the lone pair of electrons at phosphorus, are more noticeable in the case of the phosphenium cations.