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The electrochemical reductive cleavage of the C–O bond in the lignin α-O-4 model compound benzyl phenyl ether (BPE) at room temperature was investigated using earth-abundant nickel as a catalyst in methanol. Experiments using a divided cell setup using either NiCl2·6H2O salt or pre-deposited Ni on a carbon paper cathode (Ni/CP) under an inert atmosphere revealed the essential role of freshly and uniformly deposited Ni0 on the electrode surface for the reductive, catalytic cleavage to yield phenol and toluene. To better understand the reaction mechanism, the surface morphology and composition of the Ni/CP electrode were investigated by SEM, XRD, and XPS. Additionally, the role of methanol as a proton donor was established, and electrochemical hydrogenation/hydrogenolysis (ECH) experiments of BPE with sterically hindered substituents revealed that the reaction mechanism shares similarities with Pd/C hydrogenation/hydrogenolysis chemistry. DFT calculations further supported this mechanistic route and were consistent with the experimental observations. Based on both experimental and calculation results, a mechanism including (1) the interaction of the benzylic side of BPE with the catalyst surface, (2) adsorbed hydrogen interacting with the benzylic carbon to induce C–O bond scission, and (3) proton transfer to the phenoxy anion from the methanol was proposed. [ABSTRACT FROM AUTHOR]

Current catalytic hydrogenolysis of lignin C–O bonds, which is crucial for lignin valorization, often requires a noble metal catalyst or/and harsh conditions such as elevated temperatures and high pressures. Herein, we report a highly selective electrochemical protocol to reductively cleave the benzylic C–O bond of the α-O-4 lignin model compound benzyl phenyl ether (BPE) at room temperature and ambient pressure. Nearly complete conversion of BPE to toluene and phenol in methanol was achieved in an undivided cell using Ni foam at both the anode and cathode, with yields of 97% and 30%, respectively. Using a divided cell, yields of 90% (toluene) and 84% (phenol) could be achieved using inexpensive carbon paper as the cathode when Ni(II) salts were added to the cathode chamber. Notably, other divalent metal salts did not lead to any product formation, suggesting a unique role of Ni ions in benzylic C–O bond cleavage. Further, a substrate scope study revealed the suitability of the method for a variety of substituted BPEs. This work provides an economical and environmentally friendly method for selective cleavage of C–O bonds in benzylic ethers as model compounds for lignin. [ABSTRACT FROM AUTHOR]