Metallacycloheptatrienes of Iridium(III): Synthesis and Reactivity

Abstract

The Ir(I)−butadiene complex TpMe2Ir(η4-CH2_C(Me)C(Me)_CH2) (1) (TpMe2 = hydrotris(3,5-dimethylpyrazolyl)borate) reacts with ≥3 equiv of DMAD (RC CR, R = CO2Me) in CH2Cl2 at 60 °C, in the presence of adventitious water, with formation of the iridacycloheptatriene (2), by the oxidative coupling of three molecules of DMAD in the metal coordination sphere. In a related process, TpMe2IrPh2(N2) (4) gives two benzoannelated iridacycloheptatrienes, the symmetrical species (5) and the unsymmetrical one (6). The water ligand in these complexes is labile, and derivatives substituted with CO, PMe3, and NCMe have been obtained. 2, 5, and 6 react, at 25 °C, with oxo-transfer oxidizing reagents such as tBuOOH with formation of the keto-metallabicyclic products 7−9, which result from the selective oxo attack to the γ,δ-C_C double bond, irrespective of this being of the benzo or the (R)C_C(R) type. In the latter case, further oxidation takes place with tBuOOH, at ambient temperature, with formation of an iridabenzene (11) and an iridanaphthalene (12) (with five and three electron-withdrawing CO2Me substituents, respectively) in which the carboxylate MeO2CCO2- ligand completes the metal coordination sphere. Interestingly, substitution of this group by OH- or MeO- allows the formation of Jackson−Meisenheimer complexes, reflecting the inherent aromaticity of these electron-deficient metalloaromatics. Finally, the hydrogenation of the iridacycloheptatrienes has been studied. All new compounds have been fully characterized by microanalysis, IR and NMR spectroscopies, and, in some cases, single-crystal X-ray diffraction studies.