Chalcogeno-urea ligands on a phosphadiazonium Lewis acceptor: a new synthetic approach to Ch-P bonds (Ch = O, S, Se).

Abstract

The isolation and characterization of the first intermolecular chalcogeno-urea complexes of iminophosphines are described. Trifluoromethylsulfonyloxy(2,4,6-tri-tert-butylphenylimino)phosphine, MesNPOTf, reacts quantitatively with chalcogenoimidazolines (ChIm, Ch = O, S, Se) and 1,3-dimethyldiphenylurea (OU) to give Lewis acid-base complexes, [MesNP.ChIm]OTf and [MesNP.OU]OTf. Single crystal X-ray diffraction studies indicate that the closest contact of the chalcogeno-urea donor occurs at phosphorus in all cases, representing compounds that contain examples of O-P, S-P, and Se-P coordinate bonds. In all complexes, coordination of the ligand causes significant displacement of the OTf anion, and the resulting cations [MesNP.L](+) are best described as complexes of a neutral ligand on a phosphadiazonium Lewis acceptor. As such, the complex ions [MesNP.L](+) are novel examples of cationic systems containing dicoordinate phosphorus centers. The complexes highlight the potential for electron-rich centers to behave as Lewis acids despite the presence of a lone pair of electrons at the acceptor site.