Platinum(II) Monomer and Dimer Complexes with a Bis(oxazolinyl)phenyl Pincer Ligand

A series of platinum(II) complexes with the formulas Pt(phebox)(L)(+) (phebox(-) = 1,3-bis(4,4'-dimethyl-2'-oxazolinyl)phenyl anion; L = pyridine (py), 4-phenylpyridine, quinoline, acridine) and Pt-2(phebox)(2)(mu-L')(2+) (L' = pyrazine, 4,4'-bipyridine, 1,2-bis(4-pyridyl)ethane) was prepared. Crystallographic data establish that the metal center is bonded to the tridentate phebox(-) and monodentate pyridyl ligands. The five-membered oxazoline rings favor a CH2-CMe2 twist conformation. Pt(phebox) Cl and Pt(phebox)(py)(+) undergo a ligand-based chemically reversible redox reaction, whereas the electrochemistry of the other complexes is chemically and electrochemically less reversible. In contrast to complexes with the 1,3-his(piperdylmethyl)phenyl anion ligand (pip(2)NCN(-)) or related pincer ligands, each of the phebox(-) complexes described here exhibits intense emission in room-temperature methylene chloride solution, which is assigned as originating from a lowest, predominantly phebox(-) ligand-centered excited state. In acetonitrile, the complexes undergo solvolysis resulting in displacement of the pyridyl ligands. The accumulated data demonstrate that subtle variations in the nature of the NCN and ancillary ligands of platinum(II) complexes provide access to at least five orbitally distinct emissive excited states.