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

Abstract

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−1s−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.

The reactivity of the active metal oxo and hydroxo intermediates and their implications in oxidations

“…Tolman and co-workers synthesized a LCu III -OH complex generated by one electron oxidation of corresponding LCu II -OH (L: N,N 0 -bis(2,6-diisopropylephenyl)-2,6-pyridinedicarboxamide). 37 The synthetic Cu III -OH complex can react with dihydroanthracene (DHA) to yield a dominant anthracene product with the reduced Cu(II) complex (Scheme 22), and the kinetic studies revealed that the reaction occurs via a hydrogen atom transfer pathway with a very large KIE value (44 at 203 K).…”

Transition Metal Complexes and the Activation of Dioxygen

“…In a different approach, monocopper-hydroxide complexes 99 (R ¼ iPr or Me) were shown to undergo 1-electron oxidation at low potential (for R ¼ iPr, À0.076 V versus ferrocenium/ferrocene (Fc + /Fc) in acetone) to yield highly colored reactive intermediates ( Figure 47) [323,324]. These intermediates were identified as Cu(III)-hydroxide species 100 on the basis of DFT calculations and X-ray absorption spectroscopy for the system with R ¼ iPr [323].…”

“…These intermediates were identified as Cu(III)-hydroxide species 100 on the basis of DFT calculations and X-ray absorption spectroscopy for the system with R ¼ iPr [323].…”

On the Cu(III)/Cu(II) Redox Chemistry of Cu-Peptide Complexes to Assist Catalyst Design

“…The second characteristic set of ligands is {NH 2 ,2×N -,N im }. In this series (10)(11)(12)(13)(14), the slope approximates the 59 mV/logβ(Cu II ) unit value, which, in turn, means a nearly unchanged logβ Cu(III) . We found that complex 13 from this group was twice as active in water oxidation electrocatalysis as 9.…”

“…The feasibility of this option could be judged from the reactivity of the prepared species toward substrate C-H bonds. [11,12] Utilization of suitable tridentate pyridine-or piperidine-2,6-dicarboxamide-type supporting ligands provided LCu(III)-OH complexes from the LCu (II)-OH 2 precursors with 1e -oxidant, highlighting a new avenue to reactive high-valent copper species (Scheme 1b). [13,14] These substances possess hydroxide as a fourth equatorial ligand and their reactivity against C-H compounds exhibiting different bond dissociation energies (BDEs) extends to tetrahydrofurane and cyclohexane.…”