Adducts of phosphorus(V) chloride with pyridine bases

Abstract

Complex formation between PCl₅ and a variety of pyridine bases has been investigated in solution by means of ³¹P n.m.r. spectroscopy. Most unidentate pyridines form molecular 1 : 1 adducts co-ordinated via the pyridine nitrogen, although 2-cyanopyridine may be attached via the cyano-group. Complex formation appears to be inhibited by both steric and electronic effects, but steric hindrance seems to be more important. Some methyl-substituted pyridines are chlorinated by PCl₅, with formation of PC₃. Bidentate pyridines form ionic derivatives [PCl₄L][PCl₆](2 : 1), [PCl₄L]Cl (1 : 1), or mixtures of these, but the stable species in concentrated solution is the 2 :1 adduct. Some of the adducts have been isolared and characterised by a number of physical techniques. The solid-state structures appear to correspond with those in solution, except for derivatives of bidentate pyridines mentioned above.