Reactivity of a Nickel(II) Bis(amidate) Complex withmeta‐Chloroperbenzoic Acid: Formation of a Potent Oxidizing Species

Abstract

Herein, we report the formation of a highly reactive nickel-oxygen species that has been trapped following reaction of a Ni(II) precursor bearing a macrocyclic bis(amidate) ligand with meta-chloroperbenzoic acid (HmCPBA). This compound is only detectable at temperatures below 250 K and is much more reactive toward organic substrates (i.e., C-H bonds, C=C bonds, and sulfides) than previously reported well-defined nickel-oxygen species. Remarkably, this species is formed by heterolytic O-O bond cleavage of a Ni-HmCPBA precursor, which is concluded from experimental and computational data. On the basis of spectroscopy and DFT calculations, this reactive species is proposed to be a Ni(III) -oxyl compound.

Rapid Hydrogen and Oxygen Atom Transfer by a High-Valent Nickel–Oxygen Species

“…Interestingly, 3 was kinetically competent in the reactions with alkanes bearing C-H bonds as strong as those of cyclohexane (bond dissociation energy, BDE, of 99. (O•)(L)] species previously reported by us, 16 albeit the reactivity of 3 is substantially greater ( Table 2). Analysis of the final oxidation products for the reaction of 3 with triphenylmethane indicated the formation of 1.4 TON of products consisting mainly of triphenylchloromethane together with small amounts of triphenylmethanol.…”

“…32 Remarkably, the reaction of 3 with thioanisole was too rapid to extract accurate kinetic data at -30ºC using our conventional UV/Vis absorption spectrophotometer. Overall, the data indicate that 3 is a highly active oxidizing species with 16 Similarly to the reaction with alkanes, analysis of the oxidized products after reaction of 3 with alkenes and sulfides proved that, indeed, this species mediated an oxygen-atom transfer reaction (Table S2). Thus, 1,2-epoxyoctane was formed in the reaction of 1-octene with 3 in 20% yield (with respect to nickel), while no epoxide product was detected in a blank experiment in the absence of nickel.…”

“…Preparation and handling of air-sensitive materials were carried out in a N 2 drybox (MBraun ULK 1000) with O 2 and H 2 O concentrations < 1 ppm [Ni II (L)] (1) was synthesized as previously reported. 16 Mass spectra were performed by electrospray ionization in a high-resolution mass spectrometer Bruker micrOTOF QII (Q-TOF) with a quadrupole analyzer with positive and negative ionization modes. UV/Vis absorption spectra were performed by a diode array spectrophotometer Agilent Cary 60 and low temperature control was maintained with a cryostat from Unisoku Scientific Instruments.…”

“…, by reaction of a nickel(II) precursor (1) with peracids at low temperature, 16 in which a macrocyclic tetradentate ligand (L) based on a 2,6-pyridinedicarboxamidate unit supported the metal center (Scheme 1). The [Ni…”

Tuning the Reactivity of Terminal Nickel(III)–Oxygen Adducts for C–H Bond Activation

“…9 To date, the most powerful high-valent nickel oxidant, reported by Company, was a putative formally Ni IV species, obtained from the reaction of a macrocyclic Ni II complex with m -CPBA. 10 Overall, the Ray/Company species lacked sufficient stability to allow exhaustive characterization. Other terminal Ni III -OX complexes displayed no particular oxidizing power towards C–H bonds.…”