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

One-electron oxidation of the tetragonal Cu(II) complex [Bu4N][LCuOH] at -80 degrees 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 degrees C, Delta H-double dagger = 5.4(2). kcal mol(-1), Delta S-double dagger = -30(2) eu) and with very large kinetic isotope effects.(cf. k(H)/k(D) = 44 at -770 degrees C). The findings suggest that a Cu(III)-OH moiety is a viable reactant in oxidation catalysis.