Photocatalytic generation of nitrenes and radicals can be used to tune or even control their reactivity. Photocatalytic activation of sulfonyl azides leads to the elimination of N2 and the resulting reactive species initiate C-H activations and amide formation reactions. Here, we present reactive radicals that are generated from sulfonyl azides: sulfonyl nitrene radical anion, sulfonyl nitrene and sulfonyl amidyl radical, and test their gas phase reactivity in C-H activation reactions. The sulfonyl nitrene radical anion is the least reactive and its reactivity is governed by the proton coupled electron transfer mechanism. In contrast, sulfonyl nitrene and sulfonyl amidyl radicals react via hydrogen atom transfer pathways. These reactivities and detailed characterization of the radicals with vibrational spectroscopy and with DFT calculations provide information necessary for taking control over the reactivity of these intermediates.

• Klíčová slova
• amidyl radical, ion spectroscopy, nitrene, photocatalysis, reaction mechanisms,
• MeSH
• azidy * MeSH
• iminy * chemie   MeSH
• protony MeSH
• transport elektronů MeSH
• vodík chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• azidy * MeSH
• iminy * MeSH
• phenylnitrene MeSH Prohlížeč
• protony MeSH
• vodík MeSH

Iron(IV)-oxo intermediates in nature contain two unpaired electrons in the Fe-O antibonding orbitals, which are thought to contribute to their high reactivity. To challenge this hypothesis, we designed and synthesized closed-shell singlet iron(IV) oxo complex [(quinisox)Fe(O)]+ (1+ ; quinisox-H=(N-(2-(2-isoxazoline-3-yl)phenyl)quinoline-8-carboxamide). We identified the quinisox ligand by DFT computational screening out of over 450 candidates. After the ligand synthesis, we detected 1+ in the gas phase and confirmed its spin state by visible and infrared photodissociation spectroscopy (IRPD). The Fe-O stretching frequency in 1+ is 960.5 cm-1 , consistent with an Fe-O triple bond, which was also confirmed by multireference calculations. The unprecedented bond strength is accompanied by high gas-phase reactivity of 1+ in oxygen atom transfer (OAT) and in proton-coupled electron transfer reactions. This challenges the current view of the spin-state driven reactivity of the Fe-O complexes.

• Klíčová slova
• ion spectroscopy, iron oxo complexes, ligand design, spin state,
• Publikační typ
• časopisecké články MeSH

Terminal oxo complexes of late transition metals are frequently proposed reactive intermediates. However, they are scarcely known beyond Group 8. Using mass spectrometry, we prepared and characterized two such complexes: [(N4Py)CoIII (O)]+ (1) and [(N4Py)CoIV (O)]2+ (2). Infrared photodissociation spectroscopy revealed that the Co-O bond in 1 is rather strong, in accordance with its lack of chemical reactivity. On the contrary, 2 has a very weak Co-O bond characterized by a stretching frequency of ≤659 cm-1 . Accordingly, 2 can abstract hydrogen atoms from non-activated secondary alkanes. Previously, this reactivity has only been observed in the gas phase for small, coordinatively unsaturated metal complexes. Multireference ab-initio calculations suggest that 2, formally a cobalt(IV)-oxo complex, is best described as cobalt(III)-oxyl. Our results provide important data on changes to metal-oxo bonding behind the oxo wall and show that cobalt-oxo complexes are promising targets for developing highly active C-H oxidation catalysts.

• Klíčová slova
• C−H activation, cobalt-oxo complexes, helium tagging, ion spectroscopy, iron-oxo complexes, oxo wall,
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

The C-H activation of 2-phenylpyridine, catalyzed by copper(ii), palladium(ii) and ruthenium(ii) carboxylates, was studied in the gas phase. ESI-MS, infrared multiphoton dissociation spectroscopy and quantum chemical calculations were combined to investigate the intermediate species in the reaction. Collision induced dissociation (CID) experiments and DFT calculations allowed estimation of the energy required for this C-H activation step and the subsequent acetic acid loss. Hammett plots constructed from the CID experiments using different copper carboxylates as catalysts revealed that the use of stronger acids accelerates the C-H activation step. The reasoning can be traced from the associated transition structures that suggest a concerted mechanism and the key effect of the carbon-metal bond pre-formation. Carboxylates derived from stronger acids make the metal atom more electrophilic and therefore shift the reaction towards the formation of C-H activated products.

• Publikační typ
• časopisecké články MeSH

Electrospray ionization of methanolic solutions of p-hydroxyphenacyl derivatives HO-C(6)H(4)-C(O)-CH(2)-X (X = leaving group) provides abundant signals for the deprotonated species which are assigned to the corresponding phenolate anions (-)O-C(6)H(4)-C(O)-CH(2)-X. Upon collisional activation in the gas phase, these anions inter alia undergo loss of a neutral "C(8)H(6)O(2)" species concomitant with formation of the corresponding anions X(-). The energies required for the loss of the neutral roughly correlate with the gas phase acidities of the conjugate acids (HX). Extensive theoretical studies performed for X = CF(3)COO in order to reveal the energetically most favorable pathway for the formation of neutral "C(8)H(6)O(2)" suggest three different routes of similar energy demands, involving a spirocyclopropanone, epoxide formation, and a diradical, respectively.

• MeSH
• acetofenony chemie   MeSH
• anionty chemie   MeSH
• cyklopropany chemie   MeSH
• epoxidové sloučeniny chemie   MeSH
• hmotnostní spektrometrie s elektrosprejovou ionizací MeSH
• molekulární struktura MeSH
• roztoky chemie   MeSH
• spirosloučeniny chemie   MeSH
• teoretické modely MeSH
• vzácné plyny chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, N.I.H., Extramural MeSH
• Názvy látek
• acetofenony MeSH
• anionty MeSH
• cyklopropany MeSH
• epoxidové sloučeniny MeSH
• roztoky MeSH
• spirosloučeniny MeSH
• vzácné plyny MeSH