The reactivity of the 'P2N' ligand 2-(diphenylphosphino)-N-[2-(diphenylphosphino)benzylidene]-benzeneamine towards sulfur and acid

The reaction of 2-(diphenylphosphino)-N-[2-(diphenylphosphino)benzylidene]benzeneamine (PNCHP) with sulfur in a 1:1 molar ratio shows the phosphorus atom nearest the imine nitrogen to be preferentially oxidised. The overall product distribution, determined by synthesising each component independently, is: 50% 2-(diphenylphosphinothioyl)-N-[2-(diphenylphosphino)- benzylidene]benzeneamine (SPNCHP), 7% 2-(diphenylphosphino)-N-[2-(diphenylphosphinothioyl)benzylidene]benzeneamine (PNCHPS) and 27% 2-(diphenylphosphinothioyl)-N-[2-(diphenylphosphinothioyl)benzylidene]benzeneamine SPNCHPS (27%) with 16% of the reactant, PNCHP, remaining. The structures of PNCHP and SPNCHP have been determined by single-crystal X-ray diffraction. The PNCHP molecule has an approximate centre of symmetry with the two phosphorus atoms adopting a trans orientation with respect to each other. The two phosphorus atoms in SPNCHP also adopt a trans arrangement to minimise non-bonded steric interactions. The -CH=N- 'bridge' linking the two phenyl rings is not coplanar with its associated phenyl ring. The single crystal X-ray structure of the solvate, SPNCHP . CH2Cl2, shows that the extent of this non-planarity is influenced by the presence of a CH2Cl2, solvent of crystallisation. Reaction of PNCHP with the strong acids, HClO4 and HBF4 results in protonation of the imine nitrogen followed by nucleophilic attack on the imine carbon by the phosphorus nearest the imine nitrogen to form the phosphonium salt [PNHCHP]X (X = ClO4 and BF4, the structures of which have been determined by X-ray crystallography, A new P-C bond is formed thus producing a five-membered heterocyclic ring. (C) 2000 Elsevier Science B.V. All rights reserved.