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.