In the search for highly reactive oxidants we have identified high‐valent metal–fluorides as a potential potent oxidant. The high‐valent Ni–F complex [NiIII(F)(L)] (2, L=N,N′‐(2,6‐dimethylphenyl)‐2,6‐pyridinedicarboxamidate) was prepared from [NiII(F)(L)]− (1) by oxidation with selectfluor. Complexes 1 and 2 were characterized by using 1H/19F NMR, UV‐vis, and EPR spectroscopies, mass spectrometry, and X‐ray crystallography. Complex 2 was found to be a highly reactive oxidant in the oxidation of hydrocarbons. Kinetic data and products analysis demonstrate a hydrogen atom transfer mechanism of oxidation. The rate constant determined for the oxidation of 9,10‐dihydroanthracene (k2=29 m−1 s−1) compared favorably with the most reactive high‐valent metallo‐oxidants. Complex 2 displayed reaction rates 2000–4500‐fold enhanced with respect to [NiIII(Cl)(L)] and also displayed high kinetic isotope effect values. Oxidative hydrocarbon and phosphine fluorination was achieved. Our results provide an interesting direction in designing catalysts for hydrocarbon oxidation and fluorination

Au III -oxygen adducts have been implicated as intermediates in homogeneous and heterogeneous Au oxidation catalysis, but their reactivity is under-explored. Complex 1, ([Au III (OH)-(terpy)](ClO 4 ) 2 , (terpy = 2,2′:6′,2-terpyridine), readily oxidized substrates bearing C−H and O−H bonds. Kinetic analysis revealed that the oxidation occurred through a hydrogen atom transfer (HAT) mechanism. Stable radicals were detected and quantified as products of almost quantitative HAT oxidation of alcohols by 1. Our findings highlight the possible role of Au III -oxygen adducts in oxidation catalysis and the capability of late transition metal−oxygen adducts to perform proton coupled electron transfer.

Oxygenases have been postulated to utilize d 4 Fe IV and d 8 Cu III oxidants in proton-coupled electron transfer (PCET) hydrocarbon oxidation. In order to explore the influence the metal ion and d-electron count can hold over the PCET reactivity, two metastable high-valent metal−oxygen adducts, [Ni III (OAc)(L)] (1b) and [Cu III (OAc)(L)] (2b), L = N,N′-(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamidate, were prepared from their low-valent precursors [Ni II (OAc)-(L)] − (1a) and [Cu II (OAc)(L)] − (2a).The complexes 1a/ b−2a/b were characterized using nuclear magnetic resonance, Fourier transform infrared, electron paramagnetic resonance, Xray diffraction, and absorption spectroscopies and mass spectrometry. Both complexes were capable of activating substrates through a concerted PCET mechanism (hydrogen atom transfer, HAT, or concerted proton and electron transfer, CPET). The reactivity of 1b and 2b toward a series of para-substituted 2,6-di-tert-butylphenols (p-X-2,6-DTBP; X = OCH 3 , C(CH 3 ) 3 , CH 3 , H, Br, CN, NO 2 ) was studied, showing similar rates of reaction for both complexes. In the oxidation of xanthene, the d 8 Cu III oxidant displayed a small increase in the rate constant compared to that of the d 7 Ni III oxidant. The d 8 Cu III oxidant was capable of oxidizing a large family of hydrocarbon substrates with bond dissociation enthalpy (BDE C−H ) values up to 90 kcal/mol. It was previously observed that exchanging the ancillary anionic donor ligand in such complexes resulted in a 20-fold enhancement in the rate constant, an observation that is further enforced by comparison of 1b and 2b to the literature precedents. In contrast, we observed only minor differences in the rate constants upon comparing 1b to 2b. It was thus concluded that in this case the metal ion has a minor impact, while the ancillary donor ligand yields more kinetic control over HAT/CPET oxidation.

In exploring terminal nickel‐oxo complexes, postulated to be the active oxidant in natural and non‐natural oxidation reactions, we report the synthesis of the pseudo‐trigonal bipyramidal NiII complexes (K)[NiII(LPh)(DMF)] (1[DMF]) and (NMe4)2[NiII(LPh)(OAc)] (1[OAc]) (LPh=2,2’,2’’‐nitrilo‐tris‐(N‐phenylacetamide); DMF=N,N‐dimethylformamide; −OAc=acetate). Both complexes were characterized using NMR, FTIR, ESI‐MS, and X‐ray crystallography, showing the LPh ligand to bind in a tetradentate fashion, together with an ancillary donor. The reaction of 1[OAc] with peroxyphenyl acetic acid (PPAA) resulted in the formation of [(LPh)NiIII−O−H⋅⋅⋅OAc]2−, 2, that displays many of the characteristics of a terminal Ni=O species. 2 was characterized by UV‐Vis, EPR, and XAS spectroscopies and ESI‐MS. 2 decayed to yield a NiII‐phenolate complex 3 (through aromatic electrophilic substitution) that was characterized by NMR, FTIR, ESI‐MS, and X‐ray crystallography. 2 was capable of hydroxylation of hydrocarbons and epoxidation of olefins, as well as oxygen atom transfer oxidation of phosphines at exceptional rates. While the oxo‐wall remains standing, this complex represents an excellent example of a masked metal‐oxide that displays all of the properties expected of the ever elusive terminal M=O beyond the oxo‐wall.