Selective, Nickel-Catalyzed Hydrogenolysis of Aryl Ethers

TLDR

Selective hydrogenolysis of aromatic C–O bonds in aryl ethers remains an unsolved challenge, and existing heterogeneous catalytic methods require high temperature and pressure, yielding mixed products from competing aliphatic C–O bond hydrogenolysis and arene hydrogenation. The study aims to achieve selective hydrogenolysis of aromatic C–O bonds in alkyl aryl and diaryl ethers to produce only arenes and alcohols. A soluble nickel carbene complex catalyzes the reaction at 1 bar H₂ and 80–120 °C, with substrate reactivity ranking Ar–OAr ≫ Ar–OMe > ArCH₂–OMe. Hydrogenolysis of lignin model compounds demonstrates the method’s potential to convert refractory aryl‑ether biopolymers into hydrocarbons.

Abstract

Selective hydrogenolysis of the aromatic carbon-oxygen (C-O) bonds in aryl ethers is an unsolved synthetic problem important for the generation of fuels and chemical feedstocks from biomass and for the liquefaction of coal. Currently, the hydrogenolysis of aromatic C-O bonds requires heterogeneous catalysts that operate at high temperature and pressure and lead to a mixture of products from competing hydrogenolysis of aliphatic C-O bonds and hydrogenation of the arene. Here, we report hydrogenolyses of aromatic C-O bonds in alkyl aryl and diaryl ethers that form exclusively arenes and alcohols. This process is catalyzed by a soluble nickel carbene complex under just 1 bar of hydrogen at temperatures of 80 to 120°C; the relative reactivity of ether substrates scale as Ar-OAr>>Ar-OMe>ArCH(2)-OMe (Ar, Aryl; Me, Methyl). Hydrogenolysis of lignin model compounds highlights the potential of this approach for the conversion of refractory aryl ether biopolymers to hydrocarbons.