Skeletal Ni electrode-catalyzed C-O cleavage of diaryl ethers entails direct elimination via benzyne intermediates

Abstract

Diaryl ethers undergo electrocatalytic hydrogenolysis (ECH) over skeletal Ni cathodes in a mild, aqueous process that achieves direct C-O cleavage without initial benzene ring saturation. Mechanistic studies find that aryl phenyl ethers with a single para or meta functional group (methyl, methoxy, or hydroxy) are selectively cleaved to the substituted benzene and phenol, in contrast to recently reported homogeneous catalytic cleavage processes. Ortho positioning of substituents reverses this C-O bond selectivity, except for the 2-phenoxyphenol case. Together with isotope labeling and co-solvent studies, these results point to two distinct cleavage mechanisms: (a) dual-ring coordination and C-H activation, leading to vicinal elimination to form phenol and a surface-bound aryne intermediate which is then hydrogenated and released as the arene; and (b) surface binding in keto form by the phenolic ring of the hydroxy-substituted substrates, followed by direct displacement of the departing phenol. Notably, acetone inhibits the well-known reduction of phenol to cyclohexanol, affording control of product ring saturation. A byproduct of this work is the discovery that the ECH treatment completely defluorinates substrates bearing aromatic C-F and C-CF3 groupings.

Thermal, photonic, and electrocatalysis in lignin depolymerization research

“…As a result, acetone selectively inhibits phenol monomer reduction, allowing intentional control over the choice of saturated or aromatic monomers. 38 Multimetallic catalysts are well-known for their ability to ne-tune catalytic performance due to their versatility in compositional, electronic, and geometric properties. 39 Various metal elements have been extensively studied for their potential in constructing multimetallic catalysts, which nd applications in both electrocatalytic and thermocatalytic reactions.…”

“…Zhou et al achieved direct C–O cleavage without initial benzene ring saturation by using electrocatalytic hydrogenation (ECH) over skeletal Ni cathodes in a mild, aqueous process. 38 Two distinct cleavage mechanisms were identified: (a) dual-ring coordination and C–H activation: This mechanism involves the activation of two adjacent rings, leading to vicinal elimination to form phenol and a surface-bound aryne intermediate. The aryne intermediate is subsequently hydrogenated and released as the arene.…”

Comparative life cycle assessment of corn stover conversion by decentralized biomass pyrolysis-electrocatalytic hydrogenation versus ethanol fermentation

“…11 Research and development has been conducted to support the commercialization of biomass fast pyrolysis to produce bio-oil. 12 The Py-ECH system combines localized fast pyrolysis and subsequent electrocatalytic hydrogenation (ECH) [13][14][15][16][17][18][19][20][21] with centralized petroleum renery-style hydroprocessing to produce "drop-in" liquid hydrocarbon fuels. While fast pyrolysis deconstructs the biomass to liquid bio-oil, solid biochar, and non-condensable gases, ECH employs mild conditions to hydrogenate and upgrade the energy content of the bio-oil so that it is stable for storage and transport to a central renery.…”

Isolation, Reactivity, and Tunable Properties of a Strained Antiaromatic Osmacycle

“…Highly strained rings such as cyclic alkynes and cyclic allenes have long fascinated chemists due to their unusual structures, enhanced reactivity, and wide applicability. − However, the realization of these transient species still challenges synthetic chemists on account of the considerable angle strain they possess. For instance, benzyne, 1,2-cyclohexadiene, and isobenzene have been employed as in situ -generated intermediates − and their presence was confirmed by infrared spectroscopy at low temperatures. − The introduction of a metal fragment is an effective strategy to stabilization of such highly strained rings. − To date, metallacyclopentynes, , metallacycloallenes, − metallacyclocumulenes, − metallabenzynes, − metallaisobenzenes, − and metallapentalynes − have been prepared and characterized. Usually, strained metallacycles react easily with air or water.…”