title: Key mechanistic features of Ni-catalyzed C-H/C-O biaryl coupling of azoles and naphthalen-2-yl pivalates.
abstract: The mechanism of the Ni-dcype-catalyzed C-H/C-O coupling of benzoxazole and naphthalen-2-yl pivalate was studied. Special attention was devoted to the base effect in the C-O oxidative addition and C-H activation steps as well as the C-H substrate effect in the C-H activation step. No base effect in the C(aryl)-O oxidative addition to Ni-dcype was found, but the nature of the base and C-H substrate plays a crucial role in the following C-H activation. In the absence of base, the azole C-H activation initiated by the C-O oxidative addition product Ni(dcype)(Naph)(PivO), 1B, proceeds via ΔG = 34.7 kcal/mol barrier. Addition of Cs2CO3 base to the reaction mixture forms the Ni(dcype)(Naph)[PivOCs·CsCO3], 3_Cs_clus, cluster complex rather than undergoing PivO(-) → CsCO3(-) ligand exchange. Coordination of azole to the resulting 3_Cs_clus complex forms intermediate with a weak Cs-heteroatom(azole) bond, the existence of which increases acidity of the activated C-H bond and reduces C-H activation barrier. This conclusion from computation is consistent with experiments showing that the addition of Cs2CO3 to the reaction mixture of 1B and benzoxazole increases yield of C-H/C-O coupling from 32% to 67% and makes the reaction faster by 3-fold. This emerging mechanistic knowledge was validated by further exploring base and C-H substrate effects via replacing Cs2CO3 with K2CO3 and benzoxazole (1a) with 1H-benzo[d]imidazole (1b) or quinazoline (1c). We proposed the modified catalytic cycle for the Ni(cod)(dcype)-catalyzed C-H/C-O coupling of benzoxazole and naphthalen-2-yl pivalate.
authors.affiliation: Cherry L. Emerson Center for Scientific Computation, Emory University , 1515 Dickey Drive, Atlanta, Georgia 30322, United States.
authors.forename: Huiying
authors.initials: H
authors.lastname: Xu
authors.forename: Kei
authors.initials: K
authors.lastname: Muto
authors.forename: Junichiro
authors.initials: J
authors.lastname: Yamaguchi
authors.forename: Cunyuan
authors.initials: C
authors.lastname: Zhao
authors.forename: Kenichiro
authors.initials: K
authors.lastname: Itami
authors.forename: Djamaladdin G
authors.initials: DG
authors.lastname: Musaev
mesh_terms: D001583:Benzoxazoles / Q000737:chemistry*; D002384:Catalysis; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D009281:Naphthalenes / Q000737:chemistry*; D009532:Nickel / Q000737:chemistry*
chemical_list: D001583:Benzoxazoles; D008024:Ligands; D009281:Naphthalenes; C031721:naphthalene; D009532:Nickel