title: Redox Couple Involving NOxin Aerobic Pd-Catalyzed Oxidation of sp3-C-H Bonds: Direct Evidence for Pd-NO3-/NO2-Interactions Involved in Oxidation and Reductive Elimination.
abstract: NaNO3is used in oxidative Pd-catalyzed processes as a complementary co-catalyst to common oxidants, e.g., CuIIsalts, in C-H bond activation and Wacker oxidation processes. NaNO3and NaNO2(with air or O2) assist the sp3-C-H bond acetoxylation of substrates bearing an N-directing group. It has been proposed previously that a redox couple is operative. The role played by NOxanions is examined in this investigation. Evidence for an NOxanion interaction at PdIIis presented. Palladacyclic complexes containing NOxanions are competent catalysts for acetoxylation of 8-methylquinoline, with and without exogenous NaNO3. The oxidation of 8-methylquinoline to the corresponding carboxylic acid has also been noted at PdII.18O-Labeling studies indicate that oxygen derived from nitrate appears in the acetoxylation product, the transfer of which can only occur by interaction of18O at Pd with a coordinating-acetate ligand. Nitrated organic intermediates are formed under catalytic conditions, which are converted to acetoxylation products, a process that occurs with (50 °C) and without Pd (110 °C). A catalytically competent palladacyclic dimer intermediate has been identified. Head-space analysis measurements show that NO and NO2gases are formed within minutes on heating catalytic mixtures to 110 °C from room temperature. Measurements by in situ infrared spectroscopy show that N2O is formed in sp3-C-H acetoxylation reactions at 80 °C. Studies confirm that cyclopalladated NO2complexes are rapidly oxidized to the corresponding NO3adducts on exposure to NO2(g). The investigation shows that NOxanions act as participating ligands at PdIIin aerobic sp3-C-H bond acetoxylation processes and are involved in redox processes.
authors.affiliation: Department of Chemistry, University of York , York YO10 5DD, United Kingdom.
authors.forename: Margot N
authors.initials: MN
authors.lastname: Wenzel
authors.affiliation: Department of Chemistry, University of York , York YO10 5DD, United Kingdom.
authors.forename: Philippa K
authors.initials: PK
authors.lastname: Owens
authors.affiliation: Department of Chemistry, University of York , York YO10 5DD, United Kingdom.
authors.forename: Joshua T W
authors.identifier: 0000-0003-2384-9675
authors.initials: JT
authors.lastname: Bray
authors.affiliation: Department of Chemistry, University of York , York YO10 5DD, United Kingdom.
authors.forename: Jason M
authors.initials: JM
authors.lastname: Lynam
authors.affiliation: Department of Chemistry, University of York , York YO10 5DD, United Kingdom.
authors.forename: Pedro M
authors.initials: PM
authors.lastname: Aguiar
authors.affiliation: Department of Chemistry, University of York , York YO10 5DD, United Kingdom.
authors.forename: Christopher
authors.initials: C
authors.lastname: Reed
authors.affiliation: Department of Chemistry, University of York , York YO10 5DD, United Kingdom.
authors.forename: James D
authors.initials: JD
authors.lastname: Lee
authors.affiliation: Department of Chemistry, University of York , York YO10 5DD, United Kingdom.
authors.forename: Jacqueline F
authors.initials: JF
authors.lastname: Hamilton
authors.affiliation: Department of Chemistry, University of York , York YO10 5DD, United Kingdom.
authors.forename: Adrian C
authors.initials: AC
authors.lastname: Whitwood
authors.affiliation: Department of Chemistry, University of York , York YO10 5DD, United Kingdom.
authors.forename: Ian J S
authors.identifier: 0000-0002-7555-2761
authors.initials: IJ
authors.lastname: Fairlamb