N-15 NUCLEAR-MAGNETIC-RESONANCE STUDY OF 2-COORDINATE PHOSPHORUS CATIONS - SIGN-DETERMINATION OF COUPLING-CONSTANTS - APPLICATION OF 2-DIMENSIONAL (2D) HETERONUCLEAR SHIFT CORRELATIONS

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 C-13, N-15 (natural abundance), Si-29 and P-31 NMR spectroscopy. N-15 chemical shifts and coupling constants 1J((PN)-P-31-N-15) 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 N-15 nuclear shielding is considerably reduced (ca. 70 to 100 ppm as compared with 5 to 14) and there is a crude linear relationship between delta-N-15 and delta-P-31 values. Changes in the delta-N-15 values of 1 to 4 do not reflect P - N (pp)pi-interactions. A positive sign has been determined for the coupling constants (1J(PN))-P-31-N-15 [reduced coupling constants 1K((PN)-P-31-N-15) < O] for the phosphenium cations and for all other P(Ill)-N compounds studied. This was achieved by applying various one- and two-dimensional heteronuclear double resonance techniques. The experiments also gave signs of the coupling constants 2J((PNC)-P-31-C-13), 2J((PNSi)-P-31-Si-29), 3J((PNCC)-P-31-C-13), 3J((PNSiC)-P-31-C-13), 4J((PNCCH)-P-31-H-1) and 4J((PNSiCH)-P-31-H-1). Negative contributions to (1K(PN))-P-31-N-15, arising from the lone pair of electrons at phosphorus, are more noticeable in the case of the phosphenium cations.