The Preparation, Structures, and Reactions of Two-Coordinate Phosphorus Cations

Abstract

The synthesis of a variety of two-coordinate phosphorus cations (phosphenium ions) has been achieved via halide ion abstractions from precursor halophosphines. At least one dialkylamino group is necessary for the detection or isolation of a phosphenium ion, thus implying the importance of thermodynamic stabilization of these species by N→P conjugation. The structure of the salt, [(ipr2N) 2p] +[ AlCl4 ]-,has been determined by X-ray crystallography. Significant features of the structure are the rather short N-P bond lengths (1. 613 A), the near planarity of the (C2N2)2p skeleton, and the trigonal planar geometries at both nitrogen centers. Other phosphenium ions have been characterized primarily on the basis of 31p NMR chemical shifts which fall in the range +260 to +510 ppm. Many of the phosphenium ions exhibit fluxional behavior at ambient temperature. Dynamic NMR studies and molecular orbital calculations have established that the stereochemical non-rigidity is due rotation around the N-P bonds. The versatility of phosphenium ions as reagents has been demonstrated by the fact that they react with both electron pair donors such as phosphines and electron pair acceptors such as metal carbonyls. © 1980 IUPAC