Synthesis and Structural Studies of Binuclear Platinum(II) Complexes with a Novel Phosphorus−Nitrogen−Phosphorus Ligand†

The new pyridinediphosphinite ligand PONOP (1) was synthesized in one step from 2,6-pyridinedimethanol and diphenylchlorophosphane. Reaction of 1 with PtCl 2 (PhCN) 2 led to the neutral homobimetallic complex [Pt 2 Cl 4 -(PONOP) 2 ] (2), where the benzonitriles have been substituted by the phosphorus atoms of 1. The X-ray structure of 2 revealed a metallamacrocycle where the pyridines remained free. Addition of 2 equiv of [Cu(MeCN) 4 ](BF 4 ) to 2 led to CuCl and to the binuclear dicationic complex [Pt 2 Cl 2 (PONOP) 2 ](BF4)2 (3), where chloro ligands have been substituted by pyridine groups. Conversely, reaction of 3 with chloride anions gave back complex 2. Solid-state (X-ray) and solution (NMR) studies indicated that after the transformation of 2 into 3, the platinum centers were brought much closer and the pyridinediphosphinite ligand was stiffened. The methylene NMR protons of 3 were strongly deshielded, and the corresponding proton-phosphorus coupling constants followed a Karplus-type relationship.