Oxygen‐Atom Transfer by a Naked Manganese(V)–Oxo–Porphyrin Complex Reveals Axial Ligand Effect

Abstract

A ligand-free Manganese(V)-oxo-porphyrin complex generating a naked species in the gas phase and performing efficient oxygen-atom-transfer (OAT) to an array of sampled olefins was obtained. The naked Manganese(V)-oxo-porphyrin cation is obtained in the gas phase by electrospray ionization (ESI) of a solution prepared by controlled treatment of the porphynatomanganese(III) chloride with iodosylbenzene in methanol at -20°C. A high-resolution mass spectrum shows the isotropic peak cluster centered at 1043.0116, as expected for the neat addition of an oxygen atom to the reagent ion at 1027.0148. The overall ion population at 1043 is depleted of the reactive fraction by admitting β-pinene into the ion path leading to the cell

Biomimetic Oxidation Reactions of a Naked Manganese(V)–Oxo Porphyrin Complex

“…The ET process is consistent with the previously estimated lower limit of 8.1 eV for the IE of gaseous [(tpfpp)Mn IV O]. [18] The nature of the para-substituent in thioanisoles has an important effect on the reactivity, as evident from the increasing efficiency when the para-substituent becomes more electron releasing, with a concomitant bias toward the addition route. At variance with the amine reactions, a freeenergy correlation plot with s + values provides poor results, while a more meaningful correlation (r 2 = 0.976) is obtained for s constants of para-substituted thioanisoles.…”

“…Lack of H-atom reactivity has similarly been found with compounds with very weak CÀH or OÀH bonds, including 1,4-cyclohexadiene, [18] cyclobutyl-, and benzyl alcohol. Examples of HAT processes have been reported to be prominent processes by gaseous (non)metal oxides, including MnO + , [24] whose chemistry is dominated by radical-abstraction reactions.…”

“…The profiles of product ion abundances deriving from the routes of Equations (1) + C, start to appear with the most oxidizable compounds, namely tertiary aliphatic and aromatic amines, suggesting that ET products are thermochemically allowed for IE values 7.85 eV. [18] As to the iminium ion, formed only from tertiary aliphatic amines, L = NR 3 (R = CH 3 , C 2 H 5 ), it may well arise from deprotonation of the initial amine radical cation by the manganyl species, [(tpfpp)Mn . , which in turn may be readily oxidized to the iminium ion, [L À H] + [Eq.…”

“…0.5 mm) at À20 8C has been recently described. [18] The reaction mixture sampled by ESI and characterized by high resolution FT-ICR mass spectrometry exhibits an isotopic cluster centered at m/z 1043.0116, revealing the incorporation of one oxygen atom into the reactant species [(tpfpp)Mn III ] + (2) centered at m/z 1027.0148. Un-A C H T U N G T R E N N U N G fortunately, upon collision-induced dissociation (CID) experiments, aimed at revealing the structure of the oxomanganese complex, only trivial hydrogen fluoride losses are obtained.…”

“…This binding mode is consistent with the results of a CID experiment, in which the exclusive loss of the ligand 2Fpy has been found. [18] The notably different reactivity observed with the sampled olefins and with 2Fpy has allowed the isomeric population at nominal m/z 1043 to be resolved.…”