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Nickel-Mediated Hydrogenolysis of C–O Bonds of Aryl Ethers: What Is the Source of the Hydrogen?

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posted on 28.03.2012, 00:00 by Paul Kelley, Sibo Lin, Guy Edouard, Michael W. Day, Theodor Agapie
Mechanistic studies of the hydrogenolysis of aryl ethers by nickel were undertaken with (diphosphine)­aryl methyl ethers. A Ni(0) complex containing Ni–arene interactions adjacent to the aryl–O bond was isolated. Heating led to aryl–O bond activation and generation of a nickel aryl methoxide complex. Formal β-H elimination from this species produced a nickel aryl hydride which can undergo reductive elimination in the presence of formaldehyde to generate a carbon monoxide adduct of Ni(0). The reported complexes map out a plausible mechanism of aryl ether hydrogenolysis catalyzed by nickel. Investigations of a previously reported catalytic system using isotopically labeled substrates are consistent with the mechanism proposed in the stoichiometric system, involving β-H elimination from a nickel alkoxide rather than cleavage of the Ni–O bond by H2.

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