Noninnocent Ligand in Rhodium(III)-Complex-Catalyzed C–H Bond Amination with Tosyl Azide

Abstract

Six-coordinate rhodium(III) complexes coordinated by a planar trianionic ligand (L) are synthesized. One of the axial positions is occupied by chloride (Cl), bromide (Br), or iodide (I), and another axial position is coordinated by a solvent molecule such as acetonitrile (AN), water (HO), tetrahydrofuran (THF), or pyridine (PY) to complete an octahedral rhodium(III) center; [Rh(L)(X)(Y)] (1; X = Cl, Br, or I, Y = AN, HO, THF, or PY). Coordination of the AN, HO, and THF ligands to the metal center is rather weak, so that these solvent molecules are easily replaced by PY to give [Rh(L)(Cl)(PY)]. In the electrochemical measurements, all complexes have two reversible redox couples based on the ligand-centered oxidation L to L and to L, as reflected by the very similar redox potentials regardless of the different axial ligands. The rhodium(III) complexes catalyze C-H bond amination of xanthene with tosyl azide (TsN). Because the yields of the aminated product are nearly the same among the complexes, replacement of the axial solvent ligands with TsN readily occurs to give a nitrene-radical-bound rhodium(III) complex, [Rh(L)(NTs)(X)], as an active oxidant, which is generated by one-electron transfer from the trianionic L to the nitrene nitrogen atom. Generation of such a diradical intermediate was substantiated by the direct reaction of 1 with TsN in the absence of the substrate (xanthene). In this case, a rhodium(III) iminosemiquinone complex, 2, was generated by the intramolecular reaction between the nitrene-radical moiety and the radical moiety of the ligand L.

Radical‐Type Reactivity and Catalysis by Single‐Electron Transfer to or from Redox‐Active Ligands

“…The catalyst used consisted of a diamagnetic Rh III complex bearing a redox‐active ONNO‐type ligand, which switches from fully reduced trianionic to dianionic ligand radical R upon generation of the nitrene substrate radical bound to Rh III . Follow‐up work on this system established that the ligand may be considered chemically non‐innocent due to a fragmentation reaction occurring with the tosyl azide in the absence of xanthene substrate, forming R′ , which is also active for the same C−H amination catalytic reaction (Scheme ) …”

“…[52] The catalystu sed consisted of ad iamagneticR h III complex bearingaredox-active ONNO-type ligand, which switches from fully reduced trianionic to dianionic ligand radical R upon generation of the nitrene substrate radicalb ound to Rh III .F ollow-upw ork on this system established that the ligand mayb ec onsidered chemically non-innocentd ue to a fragmentation reaction occurring with the tosyl azide in the absence of xanthene substrate, forming R',w hichi sa lso active for the same CÀHa mination catalytic reaction (Scheme 8). [53] The Desage El-Murr group described the catalytic aziridination of cyclic and acyclica lkenes, non-conjugated dienes and styrenes using tosyliminoiodinane as nitrenes ource and Cu II (L ISQ ) 2 as catalyst. This copper-complex S has ad oublet ground-state due to antiferromagnetic coupling of one of the Scheme5.Selectedexamples of outer-sphere ligand-to-substrate single-electron transfer to CF 3 + .…”

Hydroxylation of Unactivated C(sp3)–H Bonds with m-Chloroperbenzoic Acid Catalyzed by an Iron(III) Complex Supported by a Trianionic Planar Tetradentate Ligand

“…We have recently developed a planar trianionic ligand having redox-noninnocent character, L 3– ( L H 3 = 2,4-di- tert -butyl-6-({(1 E ,2 E )-3-[(3,5-di- tert -butyl-2-hydroxyphenyl)­amino]-2-nitroallylidene}­amino)­phenol; Figure a), which was used for the synthesis of late-transition-metal [copper­(II), nickel­(II), palladium­(II), and rhodium­(III)] complexes. − In this study, we have synthesized and characterized an iron complex of L 3– [(NEt 4 )­[Fe III ( L 3 )­(Cl)] ( 1 )] and found its prominent catalyst ability in the hydroxylation of alkanes including those having only primary C–H bonds with m -chloroperbenzoic acid ( m -CPBA) under very mild conditions.…”

“…CCDC 2020480 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre,12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033. Department of Molecular Chemistry, Division of Applied Chemistry, Graduate School of Engineering, Osaka University, Osaka 565-0871, Japan; orcid.org/0000-0002-5209-266X; Email: y-morimoto@ chem.eng.osaka-u.ac.jp Shinobu Itoh − Department of Molecular Chemistry, Division of Applied Chemistry, Graduate School of Engineering, Osaka University, Osaka 565-0871, Japan; orcid.org/0000-0002-3711-2378; Email: shinobu@chem.eng.osaka-u.ac.jp…”

Merging Two Functions in a Single Rh Catalyst System: Bimodular Conjugate for Light-Induced Oxidative Coupling

“…This internal redox process often enables key elementary steps to operate readily, such as oxidative addition (OA), reductive elimination (RE), or hydrogen atom transfer, which would be otherwise challenging (Scheme A). Oxidative inducement of the reductive elimination process, in particular, has been of great interest as it constitutes a product-releasing step, which is often rate-limiting in a catalytic cycle. , This mechanistic consideration has been more pronounced for the first row metal complexes where the frontier orbitals of certain ligands are in similar levels to those of metals. , …”