期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 139, 期 48, 页码 17667-17676出版社
AMER CHEMICAL SOC
DOI: 10.1021/jacs.7b10537
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资金
- Office of Science, of the U.S. Department of Energy [DE-AC02-05CH11231]
- National Science Foundation
- NIH [S10-RR027172]
Recent interest in the valorization of lignin has led to reactions involving the cleavage of strong aromatic C-O bonds. However, few experimental mechanistic studies of these reactions have been published. We report detailed mechanistic analysis of the hydrogenolysis of diaryl ethers catalyzed by the combination of Ni(COD)(2) (COD = 1,5-cyclooctadiene) and an N-heterocyclic carbene (NHC). Experiments on the catalytic reaction indicated that NaOt-Bu was necessary for catalysis, but kinetic analysis showed that the base is not involved in the rate-limiting C-O bond cleavage. The resting state of the catalyst is an NHC-Ni(eta(6)-arene) complex. Substitution of the coordinated solvent with diaryl ether allowed isolation of a diaryl ether-bound Ni complex. Rate-limiting C-O bond cleavage occurs to generate a three-coordinate product of oxidative addition, a metallacyclic version of which has been prepared independently. Stoichiometric studies show that arene and phenol products are released following reaction with H-2. NaOt-Bu was found to deprotonate the phenol product and to prevent formation of inactive Ni-I dimers.
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