Rapid C-H Bond Activation by a Monocopper(III)-Hydroxide Complex
Donoghue, P.; Tehranchi, J.; Cramer, C. J.; Sarangi, R.; Solomon, E. I.; Tolman, W. B.
J. Am. Chem. Soc. 2011, 133, 17602 (doi:10.1021/ja117882h).
One electron oxidation of the tetragonal Cu(II) complex [Bu4N][LCuOH] at -80o 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-1s-1 at -80o C, ΔH‡ = 5.4(2) kcal mol-1, ΔS‡ = -30(2) eu) and with very large kinetic isotope effects (cf. kH/kD = 44 at -70o C). The findings suggest that a Cu(III)-OH moiety is a viable reactant in oxidation catalysis.