Protonation as a driving force for pentacoordination of phosphorus

Abstract

CND0/2 calculations are reported on four caged phosphorus compounds, Y-P(OCH,CH,),X (X = N, CH; Y = 0, OH', H'). Structures with and without a transannular bond between P and X were taken into account; the influence of this bond on the stability of the compounds was examined. For X = N and Y = Hf the lowest-energy structure corresponds with the geometry found by X-ray analysis. If X = CH, formation of a transannular bond proves to be unlikely, as expected. The calculations predict the formation of a P-N bond upon protonation of the phosphate (X = N, Y = 0). The net atomic charges in the protonated phosphite were used to calculate its NMR coupling constant, lJpH, which correlates well with the value found experimentally. A . R. Gregory and M. Paddon-Row, J. Am. Chem. SOC. 98,7521 (1976). L. J. VandeGriend, J . G. Verkade, J . F. M. Pennings and H . M. Buck, J. Am. Chem. SOC. 99, 2459 (1977).