Redox Couple Involving NOx in Aerobic Pd-Catalyzed Oxidation of sp3‑C−H Bonds: Direct Evidence for Pd−NO3−/NO2− Interactions Involved in Oxidation and Reductive Elimination

TY - JOUR

T1 - Redox Couple Involving NOx in Aerobic Pd-Catalyzed Oxidation of sp3‑C−H Bonds: Direct Evidence for Pd−NO3−/NO2− Interactions Involved in Oxidation and Reductive Elimination

AU - Wenzel, Margot Nina

AU - Owens, Philippa Kate

AU - Bray, Joshua Thomas William

AU - Lynam, Jason Martin

AU - Aguiar, Pedro M.

AU - Reed, Christopher Paul

AU - Lee, James D

AU - Hamilton, Jacqueline Fiona

AU - Whitwood, Adrian C.

AU - Fairlamb, Ian James Stewart

N1 - © 2017 American Chemical Society. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details.

PY - 2017/1/25

Y1 - 2017/1/25

N2 - NaNO3 is used in oxidative Pd-catalyzed processes as a complementary co-catalyst to common oxidants, e.g., CuII salts, in C−H bond activation and Wacker oxidation processes. NaNO3 and NaNO2 (with air or O2) assist the sp3-C−H bond acetoxylation of substrates bearing an Ndirectinggroup. It has been proposed previously that a redox couple is operative. The role played by NOx anions is examined in this investigation. Evidence for an NOx anion interaction at PdII is presented. Palladacyclic complexes containing NOx anions 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 acetoxylationproduct, the transfer of which can only occur by interaction of 18O 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 NO2 gases 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 NO2 complexes are rapidly oxidized to the corresponding NO3 adducts on exposure to NO2(g). The investigation shows that NOx anions act as participating ligands at PdII in aerobic sp3-C−H bond acetoxylation processes and are involved in redox processes.

AB - NaNO3 is used in oxidative Pd-catalyzed processes as a complementary co-catalyst to common oxidants, e.g., CuII salts, in C−H bond activation and Wacker oxidation processes. NaNO3 and NaNO2 (with air or O2) assist the sp3-C−H bond acetoxylation of substrates bearing an Ndirectinggroup. It has been proposed previously that a redox couple is operative. The role played by NOx anions is examined in this investigation. Evidence for an NOx anion interaction at PdII is presented. Palladacyclic complexes containing NOx anions 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 acetoxylationproduct, the transfer of which can only occur by interaction of 18O 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 NO2 gases 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 NO2 complexes are rapidly oxidized to the corresponding NO3 adducts on exposure to NO2(g). The investigation shows that NOx anions act as participating ligands at PdII in aerobic sp3-C−H bond acetoxylation processes and are involved in redox processes.

UR - http://www.scopus.com/inward/record.url?scp=85014201745&partnerID=8YFLogxK

U2 - 10.1021/jacs.6b10853

DO - 10.1021/jacs.6b10853

M3 - Article

SN - 0002-7863

VL - 139

SP - 1177

EP - 1190

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

IS - 3

ER -