Synthesis and Electrochemical Studies of Ruthenium(II) Dicarbonyl Bis(ferrocenyl-β-diketonates)

Abstract

The reaction of [Ru3(CO)12] (1) with six equiv. of FcC(O)CH2C(O)R (2a, R = Me; 2b, R = Fc; Fc = Fe(η5-C5H4)(η5-C5H5)) produced the RuII compounds [Ru(CO)2(FcC(O)CHC(O)R)2] (3a, R = Me; 3b, R = Fc) in moderate yields. IR studies and single-crystal X-ray analysis (3a) confirmed that the CO ligands are cis-oriented and that the respective β-diketonates O,O'-chelate-bonded setting-up an octahedral surrounding at RuII. Electrochemical (cyclic and square-wave voltammetry) and spectroelectrochemical (UV/Vis-NIR, IR) measurements were additionally carried out. Compounds 3a,b display two (3a: E1o' = 140; E2o' = 255 mV; ΔEo' = 115 mV for [3a]+/[3a]2+) or four (3b: E1o' = 80 mV, E2o' 190 mV (ΔEo' = 110 mV, [3b]+/[3b]2+), E3o' = 355 mV (ΔEo' = 165 mV, [3b]2+/[3b]3+), E4o' = 490 mV (ΔEo' = 135 mV, [3b]3+/[3b]4+)) electrochemical reversible one-electron redox processes indicating electrostatic interactions among the ferrocenyl groups as oxidation progresses, which was confirmed by UV/Vis-NIR and in situ IR spectroscopy. One ferrocenyl group on each β-diketonate ligand is by this means 1st oxidized before the 2nd ferrocenyl group of the same β-diketonate building block follows.