Coordination Chemistry of Phosphonite Ligands

Transition metal complexes of phosphines (PR₃), phosphinites (PR₂XR), phosphonites (PR(XR)₂), and phosphites (P(XR)₃) are very useful due to their ability to catalyze a variety of important chemical reactions.  While the coordination chemistry of phosphines, phosphinites, and phosphites has been studied in detail, that of the phosphonites has not.  The phosphonites are expected to have properties intermediate between those of the phosphinites and the phosphites, and thus a knowledge of their coordination chemistry could lead to new applications of their complexes as catalysts. 

In this study, a variety of phosphonites were synthesized by reacting PRCl₂ (R= phenyl, 2-thienyl) with diols.  Complexes of the phosphonites with (CO)₄Mo and PdCl₂  were synthesized and  characterized using NMR spectroscopy and X-ray crystallography when suitable crystals could be obtained.  The equilibrium and rate constants for the cis-trans isomerizations of some of the (CO)₄Mo(phosphonite)₂ complexes, which were catalyzed by mercuric chloride, have also been determined.