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.