Hypervalent, Low-Coordinate Phosphorus(Ⅲ) Centers in Complexes of the Phosphadiazonium Cation with Chelate Ligands

摘要

Trifluoromethylsulfonyloxy-(2,4,6-tri-tert-butylphenylimino)phosphine, Mes~*NPOTf (Mes~* = 2,4,6-tri-tert-butylphenyl, OTf = trifluoromethanesulfonate, triflate) reacts quantitatively with the multifunctional ligands 2,2′-bipyridine (2,2′-BIPY), N,N,N′,N′-tetramethylethylenediamine (TMEDA), 1,2-bis(diethylphos-phino)ethane (DEPE), 1,2-bis(diphenylphosphino)ethane (DIPHOS), and N,N,N′,N″,N″-pentamethyldieth-ylenetriamine (PMDETA) to give the Lewis acid-base complexes [Mes~*NP(2,2′-BIPY)][OTf], [Mes*NP(TMEDA)][OTf], [Mes~*NP(DIPHOS)][OTf], [Mes~*NP(DEPE)][OTf], and [Mes~*NP(PMDETA)][OTf], respectively. Single-crystal X-ray diffraction studies indicate that the closest contact of the ligand donor atoms occurs at phosphorus in all cases, affecting significant displacement of the OTf anion. The resulting cations [Mes~*NP(L)]~+ are best described as complexes of a neutral chelating ligand on a phosphadiazonium Lewis acceptor, and 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. More importantly, the new complexes represent rare examples of systems containing hypervalent, low-coordinate phosphorus(Ⅲ) centers.