Reaction of R3PSe with I2; crystal structures of Ph3PSeI2, (Me2N)3PSeI2 and (Et2N)3PSeI2, the first crystallographically characterised charge-transfer complexes of tertiary phosphine selenides with diiodine

Abstract

The compounds Ph₃PSeI₂, (Me₂N)₃PSeI₂ and (Et₂N)₃PSeI₂ have been prepared and characterised by ³¹P-{H} NMR and infrared spectroscopy. Their single crystal structures have also been determined. Interesting variations in d(P–Se) and d(I–I) are noted upon changing R (Ph, Me₂N, Et₂N). The variation in d(P–Se) for R₃PSeI₂ compared to the parent tertiary phosphine selenide is also discussed with respect to the degree of retention of phosphorus selenium double-bond character upon co-ordination of I₂. The variations in d(P–Se) and d(I–I) are reflected in the infrared and ³¹P-{H} NMR spectra of the R₃PSeI₂ compounds when compared to R₃PSe (R = Ph, Me₂N or Et₂N). The P–Se–I geometries for all three compounds are bent [Ph₃PSeI₂, 106.0(1), (Me₂N)₃PSeI₂, 100.4(2) (average); (Et₂N)₃PSeI₂, 106.4(1)°] whereas the Se–I–I linkages are all essentially linear [173.69(6), 174.98(8) (average); 178.04(5)°]. These results are interpreted as a donation of electron density from the selenium atom to the σ*-antibonding orbital of the diiodine.