title: Mechanism of Ni-catalyzed selective C-O bond activation in cross-coupling of aryl esters.
abstract: Ni-catalyzed selective C-O bond activation opens a door for the cross-coupling of aryl esters. The present study reports a thorough theoretical analysis of Ni-catalyzed cross-coupling between aryl esters and arylboronic acids, with an emphasis on explaining the cause for the surprising selectivity in C-O activation. The overall catalytic cycle is found to include three basic steps: oxidative addition, transmetalation, and reductive elimination. Oxidative addition of Ar-OAc to Ni(0) in the presence of PCy(3) ligand proceeds through the monophosphine pathway (instead of the alternative two-phosphine pathway) with a relatively low barrier of +22.9 kcal/mol. Transmetalation proceeds via a base-assisted mechanism with a barrier of +31.2 kcal/mol. Reductive elimination is the most facile step in the whole catalytic cycle. Comparatively, oxidative addition of ArO-Ac to Ni(0) is a more facile process (barrier = +14.2 kcal/mol) than oxidative addition of Ar-OAc to Ni(0). However, the former process is associated with a fairly low reverse barrier, and its product does not transmetalate easily (barrier = +33.1 kcal/mol). By comparison, the latter process is an irreversible reaction, and its product transmetalates more readily. These results explain why only the cross-coupling products from the Ar-OAc activation (but not from the ArO-Ac activation) were observed in experiments.
authors.affiliation: Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing 100084, China.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Li
authors.forename: Song-Lin
authors.initials: SL
authors.lastname: Zhang
authors.forename: Yao
authors.initials: Y
authors.lastname: Fu
authors.forename: Qing-Xiang
authors.initials: QX
authors.lastname: Guo
authors.forename: Lei
authors.initials: L
authors.lastname: Liu
mesh_terms: D000468:Alkalies / Q000737:chemistry; D001897:Boronic Acids / Q000138:chemical synthesis / Q000737:chemistry*; D002384:Catalysis; D003198:Computer Simulation; D004952:Esters / Q000138:chemical synthesis / Q000737:chemistry*; D006841:Hydrocarbons, Aromatic / Q000138:chemical synthesis / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D009532:Nickel / Q000737:chemistry*; D010084:Oxidation-Reduction; D010720:Phosphines / Q000138:chemical synthesis / Q000737:chemistry; D011789:Quantum Theory
chemical_list: D000468:Alkalies; D001897:Boronic Acids; D004952:Esters; D006841:Hydrocarbons, Aromatic; D010720:Phosphines; D009532:Nickel; C044646:phosphine