Redox-ligand sustains controlled generation of CF₃ radicals by well-defined copper complex

Abstract

Cooperative catalysis involving copper(ii) complex bearing redox ligands allows generation of CF˙3 radicals through ligand-based SET while metallic oxidation state is preserved.

Circumventing Intrinsic Metal Reactivity: Radical Generation with Redox‐Active Ligands

“…UV/Vis spectroscopy is an efficient tool for the monitoring of such electron transfer reactions as the original complex 1 displays an intense intervalence charge transfer band (IVCT) at λ =880 nm, due to the presence of two redox‐active iminosemiquinone ligands (Figure , blue trace). Similar to earlier findings, no reaction was found to occur between 1 and TEMPO. Upon reaction of complex 1 with the CF 3 + source, one would expect the formation of Ni(L SQ )(L BQ ) + complex 4 , where one of the SQ ligands has been oxidized upon ligand‐based SET to a BQ ligand, as is observed in the case of the copper complex .…”

“…We have recently reported the use of a copper complex Cu(L SQ ) 2 bearing non‐innocent redox iminosemiquinone (SQ) ligands for the controlled generation of CF 3 . radicals and their application to the trifluoromethylation of heteroaromatics and silyl enol ethers, and the hydrotrifluoromethylation of alkynes . The redox iminosemiquinone ligand used in this system was shown to sustain the SET occurring between an electrophilic CF 3 + source and the complex, thereby being oxidized to the iminobenzoquinone (BQ) form while the oxidation state of the metal center is preserved.…”

C−N Bond Formation from a Masked High‐Valent Copper Complex Stabilized by Redox Non‐Innocent Ligands

“…However, when adding up to 5equivalents of TEMPO (2,2,6,6-tetramethylpiperidine-Noxyl radical), the N-arylation product was isolated in 74 % yield, thus suggesting that the reaction does not involve substrate-based radicals.Besides, 2 alone does not react with TEMPO, [11] thus ruling out the possibility of an initial electron transfer between TEMPO and 2.M ass spectrometry performed on the reaction mixture allowed the observation of as pecies corresponding to [(L BQ ) 2 Cu(CF 3 )(Ph)] (see the Supporting Information). However, when adding up to 5equivalents of TEMPO (2,2,6,6-tetramethylpiperidine-Noxyl radical), the N-arylation product was isolated in 74 % yield, thus suggesting that the reaction does not involve substrate-based radicals.Besides, 2 alone does not react with TEMPO, [11] thus ruling out the possibility of an initial electron transfer between TEMPO and 2.M ass spectrometry performed on the reaction mixture allowed the observation of as pecies corresponding to [(L BQ ) 2 Cu(CF 3 )(Ph)] (see the Supporting Information).…”

“…[7d] Focusing on the wellestablished family of amidophenolate and related ligands, [8] we have recently reported [9] (Scheme 1) that oxidation of the copper(II) complex 1 [10] with an electrophilic source of CF 3 + [S-(trifluoromethyl)-dibenzothiophenium triflate;T DTT] affords the complex 2 in which the copper oxidation state has been preserved as copper(II) while the 2e À oxidation is sustained by the ligands (see the Supporting Information for computational data). [11] We reasoned that the propensity of these ligands to promote ligand-based (as opposed to metal-based) redox events could be interfaced with the reactivity of metallic highvalent oxidation states.I nterestingly,r edox non-innocent ligands have already been used in ar elated but opposite strategy aiming at preparing masked palladium(0) complexes. [11] We reasoned that the propensity of these ligands to promote ligand-based (as opposed to metal-based) redox events could be interfaced with the reactivity of metallic highvalent oxidation states.I nterestingly,r edox non-innocent ligands have already been used in ar elated but opposite strategy aiming at preparing masked palladium(0) complexes.…”

Bond Activations Assisted by Redox Active Ligand Scaffolds

“…In 2016, Desage‐El‐Murr, Fensterbank and co‐workers reacted complex 35 (Figure ) with an electrophilic CF 3 + source in the presence of TEMPO, a radical acceptor, and perceived the formation of TEMPO‐CF 3 and [Cu II (L ISQ )(L IBQ )] + . This observation indicated towards the generation of a CF 3 · from CF 3 + .…”