C–H Bond activation and C–C bond formation in the reaction of 2,5-dimethylthiophene with TpMe2Ir compounds

Abstract

The bulky 2,5-dimethylthiophene (2,5-Me₂T) reacts at 60 °C with Tp^Me2Ir(C₂H₄)₂ to give a mixture of two Tp^Me2Ir(III) hydride products, 3 and 4, that contain in addition a thienyl (3) or a thienyl-derived ligand (4). For the generation of 3 only sp² C–H activation is needed, but the formation of 4 requires also the activation of an sp³ C–H bond and the formation of a new C–C bond (between vinyl and thienyl fragments). In the presence of 2,5-Me₂T, compound 4 reacts further to produce a complex thiophenic structure (5, characterized by X-ray methods) that derives formally from two molecules of 2,5-Me₂T and a vinyl fragment. Compounds 3–5 can be readily protonated by [H(OEt₂)₂][BAr′₄] (Ar′ = 3,5-C₆H₃(CF₃)₂), with initial generation of carbene ligands (in the case of 3 and 5) as a consequence of H⁺ attack at the β-carbon of the Ir–thienyl unit. Free, substituted thiophenes, derived from the original 2,5-Me₂T, may be isolated in this way.