Rapid C–H Bond Activation by a Monocopper(III)–Hydroxide Complex

One-electron oxidation of the tetragonal Cu(II) complex [Bu4N][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(OH2). 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. kH/kD = 44 at −70 °C). The findings suggest that a Cu(III)–OH moiety is a viable reactant in oxidation catalysis.