Crystallographic and NMR studies on species intermediate between haloalkoxyphosphoranes and alkoxyphosphonium halides

A series of the monocyclic organophosphorus compounds ([o-OC(CH3)2C6H4]PPh(CH2 Ph)X) bearing a halogen (X = F, Cl, and Br) or a tetrafluoroborate (X = BF4) were synthesized. The solid-state structures of the bromide, the tetrafluoroborate, and an analogous fluoride ([o-OC(CF3)2C6H4]PPh(CH2 Ph)F) were determined by single crystal X-ray crystallography. The geometry of the fluoride was almost an ideal trigonal bipyramid (TBP). On the other hand, the bromide and tetrafluoroborate were essentially phosphonium salts with phosphorane character to some extent for the former. In CD3 CN, the bromide, the chloride, and the tetrafluoroborate were found to exist as phosphonium salts. However, it was suggested that in CDCl3, the bromide and the chloride have structures rapidly equilibrating or averaged between the phosphorane and the phosphonium forms. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:523–530, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20717