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DOI: 10.1039/A705201D (Paper) Reference Section for: J. Chem. Soc., Dalton Trans., 1997, 4823-4828

Structure of R3PCl2 compounds in the solid state and in solution: dependency of structure on R. Crystal structures of trigonal bipyramidal (C6F5)3PCl2, Ph2(C6F5)PCl2 and of ionic Prn3PCl2

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Stephen M. Godfrey, Charles A. McAuliffeRobin G.Pritchard, Robin G. Pritchard, Joanne M. Sheffield and Graeme M. Thompson

Abstract

A number of triorganophosphorus dichloride compounds R3PCl2, (R3 = substituted aryl, mixed aryl–alkyl or triaryl) have been synthesized from diethyl ether solution and characterised by analytical and 31P-{1H} NMR data in CDCl3 solution. The majority of the compounds are ionic, [R3PCl]Cl, in CDCl3 solution, in keeping with analogous species containing the heavier halogens [R3PX]X (X = Br or I), according to 31P-{1H} NMR studies. In contrast, the compounds R3PCl2 [R3 = (C6F5)3 or (C6F5)Ph2] have a molecular five-co-ordinate trigonal-bipyramidal structure both in CDCl3 solution and in the solid state. The crystal structures of these two compounds have been determined and represent the only crystallographic studies of trigonal-bipyramidal compounds of stoichiometry R3PCl2. The compound (C6F5)3PCl2 exhibits almost perfect trigonal-bipyramidal geometry, whereas (C6F5)Ph2PCl2 shows significant distortion. This may be due to the asymmetry of the equatorial groups around the phosphorus atom. Why R3PCl2 [R3 = (C6F5)3 or (C6F5)Ph2] adopt a trigonal-bipyramidal structure is reasoned to be due to the acidity of the parent tertiary phosphines, which favours this geometry for the dihalogen adducts, a phenomenon previously observed for dihalogen adducts of tertiary arsines. The crystal structure of Prn3PCl2, the first crystallographically characterised example of an ionic R3PCl2 compound which does not contain a solvent molecule, has been found to contain two Prn3PCl2 entities. The first consists of an ionic [Prn3PCl]+ unit weakly linked by a long Cl[hair space][hair space]· · ·[hair space][hair space]Cl contact to a Cl–, d(Cl[hair space][hair space]· · ·[hair space][hair space]Cl) 3.207(3) Å. The second shows a discrete [Prn3PCl]+ cation, the Cl– anion being associated with δ+ H atoms on a [Prn3PCl]+ moiety. This compound was prepared and crystallised from diethyl ether and its relation to the solvated complex [Ph3PCl[hair space][hair space]· · ·[hair space][hair space]Cl[hair space][hair space]· · ·[hair space][hair space]ClPPh3]Cl·CH2Cl2 is discussed.

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