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 (H 2 O) ( 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 C 6 H 5 OMe > C 6 H 5 NO 2 > C 6 H 5 COMe > C 6 H 5 Cl > C 6 H 5 Me. 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 (B 2 (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 -C n H 2 n +1 )(OAc) ( n = 7, 8, respectively).