Formation and Reactivity of a Fleeting Ni^III Bisphenoxyl Diradical Species

Abstract

Cytochrome P450s and Galactose Oxidases exploit redox active ligands to form reactive high valent intermediates for oxidation reactions. This strategy works well for the late 3d metals where accessing high valent states is rather challenging. Herein, we report the oxidation of Ni II (salenwith mCPBA (meta-chloroperoxybenzoic acid) to form a fleeting Ni III bisphenoxyl diradical species, in CH 3 CN and CH 2 Cl 2 at À 40 °C. Electrochemical and spectroscopic analyses using UV/Vis, EPR, and resonance Raman spectroscopies revealed oxidation events both on the ligand and the metal centre to yield a Ni III bisphenoxyl diradical species. DFT calculations found the electronic structure of the ligand and the dconfiguration of the metal center to be consistent with a Ni III bisphenoxyl diradical species. This three electron oxidized species can perform hydrogen atom abstraction and oxygen atom transfer reactions.

Mn(II) Polypyridyl Complexes: Precursors to High Valent Mn(V)=O Species and Inhibitors of Cancer Cell Proliferation

“…[35] The significant background reaction due to excess oxidant constraints the quantitative analysis of the oxidized product, while for the quantitative purpose, APCI mass spectrometry data has been recorded (Figures S22 and S23). [37,38] As monitored by UV/Vis spectroscopy, the rate of consumption of 1 a/2 a scales linearly with substrate concentration, suggesting that even in the presence of abundant mCPBA, 1 a/2 a is involved in their oxidation.…”

Synthesis, Characterization, and Study of Catalytic Activity of Chiral Cu(II) and Ni(II) Salen Complexes in the α-Amino Acid C-α Alkylation Reaction

“…As for their physical description, the resulting metal complexes were all air-stable brown solids. While complexes 3, 5-7, 9, 10 and 12-14 were synthesized for the first time in the context of the current study, 1, 2, 4, 8 and 11 had been synthesized previously [20,[23][24][25][26].…”

“…The research group led by Klein reported studies devoted to the realization of an unprecedented high valent Ni III bisphenoxyl diradical species [20]. Moreover, Ni(II) salen complexes were used as highly active Ni catalysts for the reductive amination of ketones by ammonia [21,22].…”

“…It should be noted that 1, 4, 8, 9 and 11 compounds were previously synthesized [20,[23][24][25][26], but were never evaluated before as catalysts in the phase transfer alkylation with the N-2-Cl-benzylidenealanine and N-4-Cl-benzylidenealanine isopropyl esters (Scheme 1).…”

Altering the Localization of an Unpaired Spin in a Formal Ni(V) Species

“…aminium radical cation [N(C 6 H 3 Br 2 ) 3 * ] + to form [1 II -L ** ]. [15] Very recently, we reported the action of excess of mCPBA on 1 leading to the formation of Ni(III) bisphenoxyl diradical species, [1 III -L ** ] (Scheme 1a) both in CH 3 CN and CH 2 Cl 2 at 233 K. [16] It has been demonstrated in the literature that the site of oxidation from metal to the ligand (i. e., [1 II -L * ] and [1 III -L]) can be shuffled depending upon the conditions employed. [13] In the present study, we examined the conditions that cause the shift in equilibria in [1 III -L ** ].…”