Electronic structure and phosphorus shielding: transition between PN double and triple bonding in iminophosphines RO-P = NMes

The P-31 nuclear magnetic shielding tensors of five iminophosphines of the type RO-P=NMes* (R = organyl, silyl and organosulfonyloxy; Mes* = 2,4,6-tBu (3)C(6)H(2)) were characterized by means of solid-state P-31 cross-polariza tion magic angle spinning NMR studies and IGLO quantum chemical model calcu lations. The results revealed a systematic variation in the principal value s sigma(ii) (i = 1, 2, 3) of the shielding tensors which can be correlated with the transition from a formal PN double to a triple bond. According to the IGLO calculations, the principal axis 2 is in all compounds nearly orth ogonal on the local OPN plane, while the principal axis I deviates 5-15 deg rees from the PO bond and the axis 3 deviates 11-35 degrees from the PN bon d. (C) 1999 John Wiley & Sons, Ltd.