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

The bulky 2,5-dimethylthiophene (2,5-Me2T) reacts at 60 degrees C with Tp(Me2)Ir(C2H4)(2) to give a mixture of two Tp(Me2)Ir(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 sp(2) C-H activation is needed, but the formation of 4 requires also the activation of an sp(3) 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 beta-carbon of the Ir-thienyl unit. Free, substituted thiophenes, derived from the original 2,5-Me2T, may be isolated in this way.