Intermolecular C–H Bond Activation of Alkanes and Arenes by NCN Pincer Iridium(III) Acetate Complexes Containing Bis(oxazolinyl)phenyl Ligands

Carbon–hydrogen bond activation of arenes by the pincer Ir­(III) acetate complex (phebox)­Ir­(OAc)2(H2O) (1; phebox = bis­(oxazolinyl)­phenyl) proceeded at 100 °C to give the corresponding aryl Ir­(III) complexes (phebox)­Ir­(Ar)­(OAc) in high yields. Reactions of the monosubstituted arenes anisole, toluene, chlorobenzene, acetophenone, and nitrobenzene resulted in the formation of meta- and para-substituted aryl complexes in high yields. Competitive experiments between two monosubstituted arenes exhibited relative reaction rates in the order C6H5OMe > C6H5NO2 > C6H5COMe > C6H5Cl > C6H5Me. The kinetic isotope effects of C–H bond activation of benzene and nitrobenzene were determined to be 2.9 ± 0.1 and 2.0 ± 0.4, respectively. The Ir complex 1 underwent catalytic borylation of arenes with bis­(pinacolato)­diboron (B2(pin)2) or pinacolborane (HB­(pin)), giving the corresponding borylated products. The Ir complex 1 was also reactive toward alkane C–H bond activation, demonstrated by the reactions with n-heptane and n-octane at 160 °C that cleanly afforded the corresponding alkyl complexes (phebox)­Ir­(n-CnH2n+1)­(OAc) (n = 7, 8, respectively).