Rapid C-H bond activation by a monocopper(III)-hydroxide complex

One-electron oxidation of the tetragonal Cu(II) complex [Bu ₄N][LCuOH] at -80 °C generated the reactive intermediate LCuOH, which was shown to be a Cu(III) complex on the basis of spectroscopy and theory (L = N,N′-bis(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamide). The complex LCuOH reacts with dihydroanthracene to yield anthracene and the Cu(II) complex LCu(OH ₂). Kinetic studies showed that the reaction occurs via H-atom abstraction via a second-order rate law at high rates (cf. k = 1.1(1) M ^-1 s ^-1 at -80 °C, ΔH ^‡ = 5.4(2) kcal mol ^-1, ΔS ^‡ = -30(2) eu) and with very large kinetic isotope effects (cf. k _H/k _D = 44 at -70 °C). The findings suggest that a Cu(III)-OH moiety is a viable reactant in oxidation catalysis.