Abstract
A series of new ferrocene- and ruthenocene-containing iridium(III) heteroleptic complexes of the type [(ppy)2Ir(RCOCHCOR′)], with ppy = 2-pyridylphenyl, R = Fc = FeII(η5-C5H4)(η5-C5H5) and R′ = CH3 (1) or Fc (2), as well as R = Rc = RuII(η5-C5H4)(η5-C5H5) and R′ = CH3 (3), Rc (4) or Fc (5) was synthesized via the reaction of appropriate metallocene-containing β-diketonato ligands with [(ppy)2(μ-Cl)Ir]2. The single crystal structure of 3 (monoclinic, P21/n, Z = 4) is described. Complexes 1–5 absorb light strongly in the region 280−480 nm the metallocenyl β-diketonato substituents quench phosphorescence in 1–5. Cyclic and square wave voltammetric studies in CH2Cl2/[N(nBu)4][B(C6F5)4] allowed observation of a reversible IrIII/IV redox couple as well as well-resolved ferrocenyl (Fc) and ruthenocenyl (Rc) one-electron transfer steps in 1−5. The sequence of redox events is in the order Fc oxidation, then IrIII oxidation and finally ruthenocene oxidation, all in one-electron transfer steps. Generation of IrIV quenched phosphorescence in 6, [(ppy)2Ir(H3CCOCHCOCH3)]. This study made it possible to predict the IrIII/IV formal reduction potential from Gordy scale group electronegativities, χR and/or ΣχR′ of β-diketonato pendent side groups as well as from DFT-calculated energies of the highest occupied molecular orbital of the species involved in the IrIII/IV oxidation at a 98% accuracy level.
Highlights
Despite the scarcity and high price of iridium, an important commercial use of this metal and its complexes is the CativaTM process for acetic acid generation by carbonylation of methanol [1,2].large scale commercial iridium-catalysed generation of hydrogen by water electrolysis is hindered by the scarceness and high cost of the metal
We report here the synthesis, spectroscopy and electrochemical characterization of new ferroceneand ruthenocene-containing iridium(III) heteroleptic complexes [(ppy)2 Ir(RCOCHCOR0 )], with R =
The metallocene-containing iridium(III) heteroleptic complexes [(ppy)2 Ir(RCOCHCOR0 )], 1–6, were prepared as shown in Scheme 1 via adaption of published methods [32] to be applicable to synthesis of the present new complexes
Summary
Despite the scarcity and high price of iridium, an important commercial use of this metal and its complexes is the CativaTM process for acetic acid generation by carbonylation of methanol [1,2]. Large scale commercial iridium-catalysed generation of hydrogen by water electrolysis is hindered by the scarceness and high cost of the metal. Ir(III) complexes containing a chelating β-diketonato ligand in addition to N- and C- bonding ligands have been extensively studied [7]. The extensively studied organic light emitting iridium complex, fac-tris(2-pyridylphenyl-N,C2 )iridium(III), [Ir(ppy)3 ], has C∧ N cyclometalate ligands [12]. This anionic ligand offers a strong Ir-C covalent interaction and, exhibits a highly stabilized ligand-field strength.
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