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)­(pip2NCNH2)­(L)2+ [pip2NCNH2+ = 2,6-bis­(piperidiniummethyl)­phenyl
cation; L
= Cl, Br, I, NCS, OCN, and NO2; diimine = 1,10-phenanthroline
(phen), 5-nitro-1,10-phenanthroline (NO2phen), and 5,5′-ditrifluoromethyl-2,2′-bipyridine
(dtfmbpy)] were prepared by the treatment of Pt­(pip2NCN)­Cl
with a silver­(I) salt followed by the addition of the diimine and
halide/pseudohalide under acidic conditions. Crystallographic data
as well as 1H NMR spectra establish that the metal center
is bonded to a bidentate phenanthroline and a monodentate halide/pseudohalide.
The pip2NCNH2+ 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)­(pip2NCNH2)­(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)­(pip2NCN)+ (tpy = 2,2′;6′,2″-terpyridine),
the electrochemical oxidation of deprotonated adducts, Pt­(diimine)­(L)­(pip2NCN), is chemically and electrochemically irreversible.