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

Cyclic and non-cyclic bis(am ino)phosphenium cations (1 to 4) together w ith their precursors (bis(am ino)phosphorus chlorides 5 to 8) and som e other bis(am ino)phosphorus com pounds (9 to 14) have been studied by l3C, 15N (natural abundance), 29Si and 3IP N M R spectroscopy. 15N chem ical shifts and coupling constants ' / ( 31P 15N ) o f phosphenium cations have been deter­ m ined for the first time. N M R data o f 1 to 4 are com pared w ith those o f a bis(am ino)carbene and various bis(am ino)stannylenes. In the phosphenium cations 1 to 4 the l5N nuclear shield­ ing is considerably reduced (ca. 70 to 100 ppm as com pared w ith 5 to 14) and there is a crude linear relationship between <515N and <531P values. Changes in the <5I5N values o f 1 to 4 do not reflect P N (pp)ft interactions. A positive sign has been determ ined for the coupling constants ,/ ( 31P ,5N ) [reduced coupling constants 'K (31P I5N ) < O] for the phosphenium cations and for all other P (I I I ) -N com pounds studied. This w as achieved by applying various oneand twodim ensional heteronuclear double resonance techniques. The experim ents also gave signs o f the coupling constants V (31P N 13C), 27(3'P N 29Si), 3/ ( 31P N C 13C), 37(31P N S i13C), 4/ ( 31PN C C 'H ) and 4y(31P N SiC 'H ). N egative contributions to 'K (31P I5N ), arising from the lone pair o f elec­ trons at phosphorus, are m ore noticeable in the case o f the phosphenium cations.