Density functional theory studies on the reagent Ph3PBr2

We report density functional theory geometry optimizations at the B3LYP/6-311G(d, p) level of theory for the title reagent. Four stationary points on the molecular potential energy surface were located and characterized. Three of these stationary points are energy minima, one a saddle point. The minima correspond to the conventional Ph3PBr2 (three-fold Br - P - Br axis with twisted phenyl rings), the ion-pair [Ph3PBr](+) Br- and a four-coordinated Ph3PBr2 spoke structure that can best be described as charge transfer on account of the substantial charge transfer from the Ph3P fragment to Br-2 ( as determined by a standard Mulliken population analysis and other considerations). The particular saddle point found corresponds to a three-fold Br - P - Br structure with coplanar phenyl rings. Single point B3LYP/6-311+ g(3d, 2p) calculations were done at the stationary point geometries in order to investigate possible deficiencies in the basis set. Solvent effects for the three solvents water, dichloroethane and cyclohexane were modelled using the self consistent reaction field Onsager method at the single point B3LYP/6-311+ g( 3d, 2p) level of theory. In the gas phase, the charge transfer complex is the most stable of the four; in solution it is the least stable.