The structures and electronic properties of bulky electron-withdrawing phosphines

摘要

The crystal structures of the N-carbazolyl phosphines PPh(NC_(12)H_8)_2 and P(NC_(12)H_8)_3 have been determined.In the latter,large deviations from planarity are observed for one of the nitrogen atoms,which facilitate strong intermolecular C-H...pi and pi...pi interactions in the supramolecular structure.The compounds PPh_(3-n)(NC_(12)H_8)_n(n = 1-3)react with selenium to give the phosphine selenides SePPh_(3-n)(NC_(12)H_8)_n.From the ~(31)P{~1H} NMR spectra,the ~1J_(PSe)coupling constants for these compounds are inversely related to the sigma-basicity of the phosphines,which decreases with the increasing number of N-carbazolyl groups.The crystal structure of 0.65 SeP(NC_(12)H_8)_3 centre dot 0.35 P(NC_(12)H_8)_3 contrasts with that for P(NC_(12)H_8)_3 as all of the nitrogen atoms are planar and pi...pi interactions are absent.The electronic differences between phenyl and N-pyrrolyl phosphines are borne out by the reaction of the diphosphine Ph_2PCH_2P(NC_4H_4)_2 with sulphur,which gives exclusively Ph_2P(S)CH_2P(NC_4H_4)_2.