η4-quinone, η5-semiquinone and η6-hydroquinone complexes of pentamethylcyclopentadienyl iridium.: X-ray molecular structure of [Cp*Ir(η4-1,4 benzoquinone)]

Treatment of hydroquinone with [Cp* Ir(solvent)(3)][BF4](2) (1) in acidic medium afforded the stable pi-bonded complex [Cp* Ir(eta(6)-hydroquinone)][BF4](2) (2) in high yield. Complex 2 can be easily deprotonated by a base to give the related [Cp* Ir(eta(5)-semiquinone)][BF4] (3) and [Cp* Ir(eta(4)-quinone)] (4) compounds identified by spectroscopic methods. Complex 4 reacts with an excess of HBF4 . Et2O to give the starting material 2 quantitatively. Interestingly, these chemical transformations occur with facile reversible changes of the oxidation state from Ir(III) to Ir(I). Further the X-ray molecular structure of 4 is reported. (C) 1998 Elsevier Science S.A.