Platinum(II) Diimine Complexes with Halide/Pseudohalide Ligands and Dangling Trialkylamine or Ammonium Groups

A series of platinum(II) complexes with the formulas Pt(diimine)(pip(2)NCNH(2))(L)(2+) [pip(2)NCNH(2)(+) = 2,6-bis(piperidiniummethyl)phenyl cation; L = Cl, Br, I, NCS, OCN, and NO(2); diimine = 1,10-phenanthroline (phen), 5-nitro-1,10-phenanthroline (NO(2)phen), and 5,5'-ditrifluoromethyl-2,2'-bipyridine (dtfmbpy)] were prepared by the treatment of Pt(pip(2)NCN)Cl with a silver(I) salt followed by the addition of the diimine and halide/pseudohalide under acidic conditions. Crystallographic data as well as (1)H NMR spectra establish that the metal center is bonded to a bidentate phenanthroline and a monodentate halide/pseudohalide. The pip(2)NCNH(2)(+) ligand with protonated piperidyl groups is monodentate and bonded to the platinum through the phenyl ring. Structural and spectroscopic data indicate that the halide/pseudohalide group (L(-)) and the metal center in Pt(phen)(pip(2)NCNH(2))(L)(2+) behave as Brønsted bases, forming intramolecular NH···L/NH···Pt interactions involving the piperidinium groups. A close examination of the 10 structures reported here reveals linear correlations between N-H···Pt/L angles and H···Pt/L distances. In most cases, the N-H bond is directed toward the Pt-L bond, thereby giving the appearance that the proton bridges the Pt and L groups. In contrast to observations for Pt(tpy)(pip(2)NCN)(+) (tpy = 2,2';6',2"-terpyridine), the electrochemical oxidation of deprotonated adducts, Pt(diimine)(L)(pip(2)NCN), is chemically and electrochemically irreversible.