Catalytic Chemoselective Sulfimidation with an Electrophilic [Co^III(TAML)]⁻‐Nitrene Radical Complex**

Abstract

The cobaltspecies PPh 4 [Co III (TAML red)] is ac ompetent and stable catalystf or the sulfimidationo f(aryl)(alkyl)substituteds ulfides with iminoiodinanes, reaching turnover numbers up to 900 and turnover frequencies of 640 min À1 under mild and aerobic conditions. The sulfimidationp roceeds in ah ighly chemoselective manner,e ven in the presence of alkenes or weak CÀHb onds, as supported by interand intramolecular competition experiments. Functionalization of the sulfide substituent with various electron-donating and electron-withdrawing arenes and several alkyl, benzyl and vinyl fragments is tolerated, with up to quantitative product yields. Sulfimidation of phenyla llyl sulfide led to [2,3]-sigmatropic rearrangement of the initially formed sulfimide species to afford the corresponding N-allyl-S-phenylthiohydroxylamines as attractive products. Mechanistic studies suggestt hat the actual nitrenet ransfer to the sulfide proceeds via (previously characterized) electrophilicn itrene radicali ntermediatest hat afford the sulfimide productsv ia electronically asynchronous transition states, in which SET from the sulfide to the nitrener adicalc omplexp recedes NÀSbond formation in as ingle concerted process.

Silver‐Catalyzed Enantioselective Sulfimidation Mediated by Hydrogen Bonding Interactions

“…The decadic logarithm of the relative rates k X / k H reveals a good relation with the tabulated σ p values [31] of the substituents X. The slope of the linear function was determined as ρ =−0.52 (see the SI for more details) in agreement with a positive charge to be developed at the reactive center [32, 33] …”

Controlling Radical-Type Single-Electron Elementary Steps in Catalysis with Redox-Active Ligands and Substrates

“…Intrigued by the influence of the redox-active TAML on the selective formation of nitrene radicals at cobalt(III), the catalytic applicability and mechanisms of the neutral and anionic complexes in nitrene radical transfer to alkenes 104 and thioethers 105 was investigated. These reactions are typically sensitive to oxygen and water, as this often leads to decomposition of the catalytically active nitrene radical intermediates.…”

“…The nitrene radical intermediates are formed in a quantitative manner, which are involved in subsequent product forming transition states involving substantial positive charge development on the alkene or thioether substrate. Specifically, Hammett parameters for aziridination 104 (ρ • = 0.14, ρ + = −0.80, |ρ + /ρ • | = 5.71) and sulfimidation 105 (ρ • = 0.25, ρ + = −0.57, |ρ + /ρ • | = 2.28) with the PPh 4 [Co III (TAML red )] catalyst are consistent with (partial) electron transfer from the substrate to the nitrene radical complex and significant stabilization of a (transiently) formed substrate radical cation. These observations do not match the commonly observed radical-type addition pathway, for which much smaller |ρ + /ρ • | ratios are observed.…”

“…Computational (NEVPT2-CASSCF and DFT) studies are consistent with the data obtained from the Hammett analysis and were used to further study the role of the redox-active ligand and substrates during catalysis. The calculated mechanisms for aziridination 104 and sulfimidation 105 via [Co III (TAML sq )(N • Ns)] − (B) are depicted in Scheme 9 . Nitrene radical formation via ligand-to-substrate single-electron transfer is exergonic and is followed by C–N (aziridination, left) or S–N (sulfimidation, right) bond formation via electronically asynchronous transition states TS1 and TS3 ( vide infra ).…”

Advances in Stereoselective Iron(II)‐Catalyzed Synthesis of Sulfilimines with N‐Mesyloxycarbamates

“…[7,8] While the synthesis of racemic sulfilimines has been well-developed, asymmetric methodologies remain less common. To date, only a few stereoselective methods with Ag, [9] Co, [10] Cu, [11,12] Ru, [13 -15] Mn, [16,17] Rh [18] and Fe [19] catalysts have been reported. These methods are generally effective, but often rely on complex catalytic systems or hazardous reagents.…”