Oxygen transfer reactivity mediated by nickel perfluoroalkyl complexes using molecular oxygen as a terminal oxidant

Abstract

Nickel perfluoroethyl and perfluoropropyl complexes supported by naphthyridine-type ligands show drastically different aerobic reactivity from their trifluoromethyl analogs resulting in facile oxygen transfer to perfluoroalkyl groups or oxygenation of external...

Photoinduced Carbon−Heteroatom Cross‐Coupling Catalyzed by Nickel Naphthyridine Complexes

“…The lability of ligand L1 and its ability of to easily change coordination mode between bidentate and monodentate allows to support various coordination geometries in Ni complexes in different oxidation states. [17,19] Our attempts to detect Ni I or Ni III intermediates or organic radicals during the reaction or by low-temperature irradiation in the absence or in the presence of aryl bromides resulted in no detectable signal in EPR spectra, suggesting that if such species are formed, they are highly unstable under these conditions, highlighting the important role of stabilizing macrocyclic or perfluoroalkyl ligands to enable convenient spectroscopic detection of paramagnetic Ni I or Ni III intermediates. [14,17]…”

“…[17] Analogous cobalt(III) perfluoroethyl naphthyridine complexes were found active in catalytic perfluoroethylation of arenes using Acid Togni-C 2 F 5 reagent. [18] These initial results indicated that naphthyridine and its substituted analogs represent simple and versatile bidentate ligand scaffolds [19] that support photoactive first-row transition metal complexes. We decided to further study naphthyridine light-promoted catalytic reactivity that can potentially be expanded to other types of catalytic processes.…”

Appended Lewis Acids Enable Dioxygen Reactivity and Catalytic Oxidations with Ni(II)

“…Part of this discrepancy is due to a redox mismatch between O 2 and Ni(II): most known Ni−O 2 adducts require prior reduction to the Ni(I) state 28−30 or the use of already reduced O 2 units (H 2 O 2 and base). 31−35 Additional strategies to induce reactivity between Ni II and O 2 include incorporation of (1) auxiliary ligands that undergo a chemical reaction upon O 2 addition (e.g., thioether/thiolate oxygenation, 26,36−43 C−C reductive elimination, 15,16,19,20 radical pathways 14 ), (2) ligand sets that impart highly reduced Ni centers, providing a driving force for electron transfer, 18,25,44−46 and (3) redox-active ligands to store reducing equivalents. 47 Incorporation of directed secondary sphere interactions provides a complementary synthetic strategy to enhance binding of otherwise inert substrates to metal sites, a design principle routinely exploited by metalloenzymes.…”

“…Despite the requirement of nickel to mediate biological reactivity with O 2 and reactive oxygen species (ROS), there are surprisingly few examples of aerobic oxidation of synthetic Ni II complexes, − which contrasts with most other 3d late-metals (e.g., Fe, Co, Cu). Part of this discrepancy is due to a redox mismatch between O 2 and Ni­(II): most known Ni–O 2 adducts require prior reduction to the Ni­(I) state − or the use of already reduced O 2 units (H 2 O 2 and base). − Additional strategies to induce reactivity between Ni II and O 2 include incorporation of (1) auxiliary ligands that undergo a chemical reaction upon O 2 addition (e.g., thioether/thiolate oxygenation, ,− C–C reductive elimination, ,,, radical pathways), (2) ligand sets that impart highly reduced Ni centers, providing a driving force for electron transfer, ,,− and (3) redox-active ligands to store reducing equivalents .…”

“…Despite the requirement of nickel to mediate biological reactivity with O 2 and reactive oxygen species (ROS), there are surprisingly few examples of aerobic oxidation of synthetic Ni II complexes, − which contrasts with most other 3d late-metals (e.g., Fe, Co, Cu). Part of this discrepancy is due to a redox mismatch between O 2 and Ni­(II): most known Ni–O 2 adducts require prior reduction to the Ni­(I) state − or the use of already reduced O 2 units (H 2 O 2 and base). − Additional strategies to induce reactivity between Ni II and O 2 include incorporation of (1) auxiliary ligands that undergo a chemical reaction upon O 2 addition (e.g., thioether/thiolate oxygenation, ,− C–C reductive elimination, ,,, radical pathways), (2) ligand sets that impart highly reduced Ni centers, providing a driving force for electron transfer, ,,− and (3) redox-active ligands to store reducing equivalents . Incorporation of directed secondary sphere interactions provides a complementary synthetic strategy to enhance binding of otherwise inert substrates to metal sites, a design principle routinely exploited by metalloenzymes. − Although secondary coordination sphere hydrogen bonding interactions have been extensively explored for dioxygen activation, − reactivity of O 2 with complexes bearing appended borane Lewis acids is underexplored and unknown with Ni.…”