Conformational analysis of X 3PNP(O)X 2 and (X 3PNPX 3) + for X = H, F, Cl, CH 3 by the pcilo method

Abstract

Conformational energy maps have been calculated, using the PCILO method, for X 3PNP(O)X 2 and (X 3PNPX 3) + for X = H, F, Cl, CH 3 as a function of the PNP angle. In H 3PNP(O)H 2 the global energy minimum corresponds to the eclipsed conformation of the H 3P and P(O)H 2 fragments for all PNP angles, while in Cl 3PNP(O)Cl 2, the global minimum always has Cl 3P and P(O)C1 2 staggered: the global minimum in F 3PNP(O)F 2 corresponds to eclipsed F 3P and P(O)F 2 fragments at low PNP angles and staggered fragments at high PNP angles: in (CH 3)) 3PNPO(CH 3) 2 the global minimum conformation is very sensitive to ∠ PNP. Subordinate energy minima occur for all X 3PNP(O)X 2, species: in particular, there are two local conformational minima for Cl 3PNP(O)Cl 2 at the optimum value of ∠ PNP, and the relative energies of the three stable conformations are in good agreement with those derivable from the 31P NMR spectrum of this compound. In (X 3PNPX 3) + the global minimum, usually the sole minimum on the conformational energy surface, is always close to the eclipsed conformation: free rotation of the X 3P groups relative to one another is approached in each (X 3PNPX 3) + ion as ∠PNP approaches 180°. The conformations of the transition states for the equilibria between energy minima are reported with their relative energies, for X 3PNP(O)X 2 (X = H, F. Cl, CH 3) and for (Cl 3PNPCl 3) +