Synthesis and Electrochemistry of a Ferrocene Conjugate of a Pd(II) Diimine Catecholate Complex and Its Charge-Transfer Properties in the One-Electron-Oxidized Form

A new Pd complex Pd(tBu2bpy)(FcC) 2Fc (FcC = 4-ferrocenylcatecholato, tBu2bpy = 4,4′-di-tert-butyl-2,2′-dipyridyl) was synthesized and characterized using 1H and 13C NMR spectroscopy, and ESI-MS. Electrochemical analysis of 2Fc using cyclic voltammetry in CH2Cl2/nBu4NPF6 revealed two well-defined, quasi-reversible waves assigned to the sequential oxidation of the Pd(tBu2bpy)(C) and ferrocene (Fc) moieties. The potential splitting between the waves (519 mV) indicated that there was an electronic interaction between both moieties. The one-electron-oxidized species of 2Fc was investigated using DFT calculations and UV–vis–NIR spectroscopy, and its charge-transfer property was compared with that of Pt(tBu2bpy)(FcC) 1Fc, FcV (4-ferrocenylveratrole), and FcA (4-ferrocenylcatechol bis(acetate)). 2Fc+ was Fc+-centered, rather than semiquinone-ligand centered, and exhibited an ICT transition band from to the catecholate to the Fc+ moiety in the NIR region. The electronic coupling (HAB) value of 2Fc+ (790 cm−1) was placed between FcV+ (660 cm−1) and 1Fc+ (1050 cm−1). Electronic interactions between the organometallic center and the non-innocent moiety were modulated by substitution of the metal ion (M2+ = Pt2+, Pd2+) in this series.