Iridium-Pentahydride Referee for Competition of Activations between C–H and C–F Bonds and between C–H Bonds Located in Different Positions

Polyhydride IrH5(PiPr3)2 (1) activates an ortho-CH bond of acetophenone and an ortho-CF bond of 2,3,4,5,6-pentafluoroacetophenone to give IrH2{κ2-C,O-[C6H4C­(O)­CH3]}­(PiPr3)2 (2) and IrH2{κ2-C,O-[C6F4C­(O)­CH3]}­(PiPr3)2 (3). When the phenyl group contains ortho-CH and ortho-CF bonds, ortho-CH bond activation is kinetically favored. Thus, complexes IrH2{κ2-C,O-[C6H3FC­(O)­CH3]}­(PiPr3)2 (4) and IrH2{κ2-C,O-[C6H4C­(O)­C6H3F2]}­(PiPr3)2 (5) are obtained from the reactions of 1 with 2-fluoroacetophenone and 2,6-difluorobenzophenone. Complex 1 also activates an ortho-CH bond of the 4-fluorophenyl group of 2-(4-fluorophenyl)­pyridine. The reaction leads to IrH2{κ2-C,N-[C6H3F-py]}­(PiPr3)2 (6). Replacement of the hydrogen atom of one of the ortho-CH bonds with a fluorine accelerates orthometalation, while the ortho-CH and ortho-CF bonds compete for the metal center. Thus, 2-(2,4-difluorophenyl)­pyridine produces a 1:9 mixture of 6 and IrH2{κ2-C,N-[C6H2F2-py]}­(PiPr3)2 (7). Complex 1 activates in a competitive manner ortho-CH and ortho-CF bonds of 2,6-bis­(2,4-difluorophenyl)­pyridine to give mixtures of IrH­{κ3-C,N,C-[C6H2F2-py-C6H2F2]}­(PiPr3)2 (8) and IrH­{κ3-C,N,C′-[C6H2F2-py-C6H3F]}­(PiPr3)2 (9). H/D Isotopic exchange experiments indicate that these orthometalations are thermodynamically assisted by chelating effect resulting from coordination of carbonyl or pyridyl groups. However, the activation of other C­(sp2)–H bonds less sterically hindered is kinetically favored. The distribution of deuterium atoms in the orthometalated phenyl ring also shows kinetic preference for the activation of bonds located ortho to fluorine.