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

Abstract

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).