Synthesis, reactivity investigation, and X-ray diffraction structures of new platinum(II) compounds containing redox-active diphosphine ligands

Substitution of the 1,5-cyclooctadiene (cod) ligand in PtCl₂(cod) (1) by the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) yields PtCl₂(bpcd) (2). Knoevenagel condensation of 2 with 9-anthracenecarboxaldehyde leads to the functionalization of the bpcd ligand and formation of the corresponding 2-(9-anthracenylidene)-4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (abpcd) substituted compound PtCl₂(abpcd) (3), which is also obtained from the direct reaction of 1 with the abpcd ligand in near quantitative yield. The reaction of 3 with disodium maleonitriledithiolate (Na₂mnt) affords the chelating dithiolate compound Pt(mnt)(abpcd) (4). Compounds 2-4 have been fully characterized in solution by IR and NMR spectroscopies (¹H and ³¹P), and their molecular structures established by X-ray crystallography. The electrochemical properties of 2-4 have examined by cyclic voltammetry, and the nature of the HOMO and LUMO levels in these systems has been established by MO calculations at the extended Hückel level, the results of which are discussed with respect to electrochemical data and related diphosphine derivatives.