The Quest for Double Vicinal C–H Bond Activation on the (η ⁵:η ⁵-Fulvalene)diiridium Platform: Syntheses and Structures of (η ⁵:η ⁵-Fulvalene)Ir₂(ortho-μ-C₆H₄)(CO)₂ (Ir–Ir) and Related Complexes

Abstract

The fulvalene diiridium platform was scrutinized for its potential to effect double vicinal C–H activation of C₆H₆ and C₆H₁₂, respectively. For this purpose, an improved preparation of Fv[Ir(CO)₂]₂ was developed, and the syntheses of the new complexes FvIr(CO)₂Ir(CO)(η ²-C₆F₆), Fv[Ir(CO)(η ²-C₆F₆)]₂, Fv[Ir(CH₂=CH₂)₂]₂ (X-ray), Fv[Ir(PMe₃)(H)₂]₂ (X-ray), and (2,2′,3,3′-tetra-tert-butylFv)[Ir(CO)₂]₂ were accomplished. When irradiated in C₆H₆, these molecules succeeded to varying degrees, and best for (2,2′,3,3′-tetra-tert-butylFv)[Ir(CO)₂]₂, in the double metalation of the aromatic ring to engender ligating Ir₂(ortho-μ-C₆H₄)(CO)₂ (Ir–Ir) moieties, in addition to their precursor mono(phenyliridium hydride) constructs. A competing photochemical pathway is evident by the formation of diastereomers of Fv (or 2,2’,3,3’-tetra-tert-butylFv) [Ir(CO)(Ph)(H)]₂ and the resulting dehydrogenated ligated [Ir(CO)(Ph)]₂ (Ir–Ir). The structures of FvIr₂(ortho-µ-C₆H₄)(CO)₂ (Ir–Ir) and trans-Fv[Ir(CO)(Ph)]₂ (Ir–Ir) were corroborated by X-ray analyses. Efforts to realize C–H bond activations with C₆H₁₂ generally failed or fared very poorly, with the exception of the tert-butylFv system, which enabled single, but not further, insertion to give (2,2′,3,3′-tetra-tert-butylFv)[Ir(CO)(Cy)(H)][Ir(CO)₂] in 34% yield. To explore the relevant chemistry of phenyl- and alkyliridium species attached to Fv, several such derivatives were made by independent routes, adding knowledge to the fundamental behavior of this category of molecules. Where appropriate and for comparative purposes, similar reactions were performed on the corresponding Cp- and 1,2-di-tert-butylCpIr(CO)₂ relatives.

Key words

benzyne - C–H activation - dinuclear complexes - iridium - photochemistry

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