Chalcogeno-urea Ligands on a Phosphadiazonium Lewis Acceptor: A New Synthetic Approach to Ch-P Bonds (Ch = O, S, Se)

The isolation and characterization of the first intermolecular chalcogeno-urea complexes of iminophosphines are described. Trifluoromethylsulfonyloxy(2,4,6-tri-tert-butylphenylimino)phosphine, Mes*NPOTf, reacts quantitatively with chalcogenoimidazolines (ChIm, Ch = O, S, Se) and 1,3-dimethyldiphenylurea (OU) to give Lewis acid-base complexes, [Mes*NP·ChIm]OTf and [Mes*NP·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 [Mes*NP·L]^+ are best described as complexes of a neutral ligand on a phosphadiazonium Lewis acceptor. As such, the complex ions [Mes*NP·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.