Comparison of Basicity of the Diimine and Quinoid Group of 1,10-Phenanthroline-5,6-dione Ligated on Pt(II)

Abstract

Abstract A platinum(II) complex bearing 1,10-phenanthroline-5,6-dione (phenO2), [PtCl(phenO2-N,N′)(PPh3)]+ ([2]+) was newly prepared and characterized. An X-ray crystallographic study of [2](PF6) revealed that the phenO2 ligand coordinates to platinum with the N,N′-chelate form. The basicity of the quinoid part of phenO2 in [2]+ and of the diimine one in [Pt(phenO2-O,O′)(PPh3)2] with an O,O′-chelate ring (3) was evaluated in the absence and the presence of Li+ by means of UV–vis spectroscopy and cyclic voltammetry. The quinoid group in [2]+ practically had no ability to bind Li+, but induced on anodic potential shift of the phenO2 localized redox potential by 850 mV due to the strong interaction between the reduced form of [2]+ and Li+. Undeniably, a weak interaction of Li+ with the diimine moiety of free phenO2 (K = 3.6 M−1) is greatly enhanced in the interaction between Li+ and the diimine site in 3 because of the electron donation from the catecholato group of the complex.