COMPUTER SIMULATION OF PHOSPHORANE STRUCTURES

Abstract

Abstract Parametrization of a molecular mechanics program to include terms specific for five-coordinate phosphorus compounds results in computer simulated structures of phosphoranes which compare favorably with structures obtained by x-ray diffraction. The principal new feature peculiar to five coordination is a term which measures the effect of electron pair repulsion modified by the ligand electronegativity for the two sets of bonds around phosphorus and takes into account the trigonal bipyramid and square pyramid as structural possibilities. The structures treated are HPF4, (CH3) n PF5–n (n = 0, 1, 2, 3), the catechol derivative, (C6H4O2)2PCH3, the dioxaphospholane [(CF3)2CO]2P[C(CH3)2CH2C(CH3)2]C6H4Br, the ephedrine derivative, (OCHPhCH(CH3)NCH3)2PH, and (PhO)5P. The good agreement between geometries obtained by computer simulation and x-ray diffraction suggests that application to phosphorus reaction mechanisms should result in a quantitative structuring of reaction intermediates and transition states.