Oxygen transfer to manganese–salen complexes: an electrospray tandem mass spectrometric study

Abstract

Electrospray ionisation in combination with tandem mass spectrometric techniques has been employed to study the formation of oxomanganese–salen complexes upon oxidation of [(salen)Mn^III]⁺ salts with iodosylbenzene [H₂salen = N,N′-bis(saliclyidene)ethylenediamine]. Two species were characterised as the principal oxidation products: the oxomanganese(V) complex [(salen)MnO]⁺, the actual oxygen-transfer agent in epoxidation reactions, and the dimeric, μ-oxo bridged [PhIO(salen)Mn–O–Mn(salen)OIPh]²⁺ with two terminal iodosylbenzene ligands, which acts as a reservoir species. For the first time, the coordination chemistry of iodosylbenzene with regard to the manganese–salen system was studied in detail. In addition, the mechanism of oxygen transfer by PhIO to the metal centre was studied by collision-induced dissociation (CID) of [(salen)MnOIPh]⁺. An alternative way to generate oxomanganese–salen complexes was found in the ligation of tertiary amine N-oxides to the manganese centre and subsequent fission of the N–O bond in the gas phase by CID. The electrospray-MS technique presents a convenient approach for the study of the coordination chemistry of highly reactive solution-phase species.