C−H Bond Activation of Thiophenes by Ir Complexes of the Hydrotris(3,5-dimethylpyrazolyl)borate Ligand, Tp Me2

The bis(ethylene) derivative Tp Me2 Ir(C 2 H 4 ) 2 ( 1 ) reacts with thiophene, 2-methylthiophene, and 3-methylthiophene with formation of Tp Me2 Ir(2-thienyl) 2 (SC 4 H 3 R) (R = H, 4; R = Me, 7, 8 ) species in which the two thienyl moieties are the result of the α-C−H bond activation of the thiophenes. PMe 3 and CO adducts of formulation Tp Me2 Ir(2-thienyl) 2 (L) are readily synthesized from the corresponding S -bonded thiophene derivatives. The structure of the CO complex Tp Me2 Ir(2-SC 4 H 3 ) 2 (CO) ( 6 ) has been confirmed by a single-crystal X-ray analysis. NMR spectroscopic studies are in accord with these adducts existing in solution as mixtures of three rotameric species that arise from restricted rotation around the Ir−thienyl bonds. Hydrogenation of complexes 4, 7, and 8 under relatively mild conditions gives the corresponding Tp Me2 IrH 2 (SC 4 H 3 R) dihydrides. These last mentioned species experience interesting Ir−H and C−H(thienyl) deuteration exchanges with C 6 D 6 as well as a complex decomposition reaction that gives mainly dimeric species with an unusual C, S -μ 2 -η 1 -η 1 bridging ligand. Mechanistic proposals for these two processes are presented. Monothienyl Ir(III) species are also accessible; for example the complex Tp Me2 IrH(2-SC 4 H 3 )(SC 4 H 4 ) ( 19 ) can be obtained from Tp Me2 IrH 2 (C 2 H 4 ) and thiophene. Finally, the thermal activation of SC 4 H 4, 2- and 3-SC 4 H 3 Me, and 2,5-SC 4 H 2 Me 2 by the 2,3-dimethylbutadiene−Ir(I) complex Tp Me2 (η 4 -CH 2 C(Me)C(Me)CH 2 ) has been investigated. Thiophene and the monomethylthiophenes give the complexes 4, 7, and 8, whereas for 2,5-SC 4 H 2 Me 2, the reaction takes a different course and affords a hydride-thienyl derivative along with the E and Z isomers of a thienyl-substituted olefin.