Rapid Hydrogen and Oxygen Atom Transfer by a High-Valent Nickel-Oxygen Species.
Terminal high-valent metal-oxygen species are key reaction intermediates in the catalytic cycle of both enzymes (e.g., oxygenases) and synthetic oxidation catalysts. While tremendous efforts have been directed toward the characterization of the biologically relevant terminal manganese-oxygen and iron-oxygen species, the corresponding analogues based on late-transition metals such as cobalt, nickel or copper are relatively scarce. This scarcity is in part related to the "Oxo Wall" concept, which predicts that late transition metals cannot support a terminal oxido ligand in a tetragonal environment. Here, the nickel(II) complex (1) of the tetradentate macrocyclic ligand bearing a 2,6-pyridinedicarboxamidate unit is shown to be an effective catalyst in the chlorination and oxidation of C-H bonds with sodium hypochlorite as terminal oxidant in the presence of acetic acid (AcOH). Insight into the active species responsible for the observed reactivity was gained through the study of the reaction of 1 with ClO-at low temperature by UV-vis absorption, resonance Raman, EPR, ESI-MS, and XAS analyses. DFT calculations aided the assignment of the trapped chromophoric species (3) as a nickel-hypochlorite species. Despite the fact that the formal oxidation state of the nickel in 3 is +4, experimental and computational analysis indicate that 3 is best formulated as a NiIIIcomplex with one unpaired electron delocalized in the ligands surrounding the metal center. Most remarkably, 3 reacts rapidly with a range of substrates including those with strong aliphatic C-H bonds, indicating the direct involvement of 3 in the oxidation/chlorination reactions observed in the 1/ClO-/AcOH catalytic system.
Grup de Química Bioinspirada, Supramolecular i Catàlisi (QBIS-CAT), Institut de Química Computacional i Catàlisi (IQCC), Departament de Química, Facultat de Ciències, Universitat de Girona, C/ Maria Aurèlia Capmany 69 , E17003 Girona, Catalonia, Spain.
Teresa
T
Corona
Molecular Inorganic Chemistry, Stratingh Institute for Chemistry, Faculty of Mathematics and Natural Sciences, University of Groningen , Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Apparao
A
Draksharapu
Molecular Inorganic Chemistry, Stratingh Institute for Chemistry, Faculty of Mathematics and Natural Sciences, University of Groningen , Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Sandeep K
SK
Padamati
Grup de Química Bioinspirada, Supramolecular i Catàlisi (QBIS-CAT), Institut de Química Computacional i Catàlisi (IQCC), Departament de Química, Facultat de Ciències, Universitat de Girona, C/ Maria Aurèlia Capmany 69 , E17003 Girona, Catalonia, Spain.
Ilaria
I
Gamba
Grup de Química Bioinspirada, Supramolecular i Catàlisi (QBIS-CAT), Institut de Química Computacional i Catàlisi (IQCC), Departament de Química, Facultat de Ciències, Universitat de Girona, C/ Maria Aurèlia Capmany 69 , E17003 Girona, Catalonia, Spain.
Vlad
V
Martin-Diaconescu
Grup de Química Bioinspirada, Supramolecular i Catàlisi (QBIS-CAT), Institut de Química Computacional i Catàlisi (IQCC), Departament de Química, Facultat de Ciències, Universitat de Girona, C/ Maria Aurèlia Capmany 69 , E17003 Girona, Catalonia, Spain.
Ferran
F
Acuña-Parés
Molecular Inorganic Chemistry, Stratingh Institute for Chemistry, Faculty of Mathematics and Natural Sciences, University of Groningen , Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Wesley R
WR
Browne
Grup de Química Bioinspirada, Supramolecular i Catàlisi (QBIS-CAT), Institut de Química Computacional i Catàlisi (IQCC), Departament de Química, Facultat de Ciències, Universitat de Girona, C/ Maria Aurèlia Capmany 69 , E17003 Girona, Catalonia, Spain.
Anna
A
Company