Characterization and chemical reactivity of room-temperature-stable Mn^III–alkylperoxo complexes

Abstract

A pair of room-temperature-stable MnIII–alkylperoxo complexes were characterized and shown to oxidize PPh3. Thermal decomposition studies provide evidence of both homolysis and heterolysis of the MnIII–alkylperoxo O–O bond.

Mimicking Elementary Reactions of Manganese Lipoxygenase Using Mn-hydroxo and Mn-alkylperoxo Complexes

“…In a previous study, we reported that the Mn III -hydroxo complex [Mn III (OH)( 6Me dpaq)] + could be generated via the oxidation of the Mn II -aqua complex [Mn II (H 2 O)( 6Me dpaq)](OTf) using 0.5 equiv. iodosobenzene (PhIO) [ 30 ]. Because a number of Mn III -hydroxo complexes can be generated by aerobic oxidation of their Mn II analogues [ 17 , 18 , 20 , 24 , 43 , 44 , 45 ], we explored the reaction of [Mn II (H 2 O)( 6Me dpaq)](OTf) with O 2 .…”

“…When dissolved in MeCN, the [Mn II (H 2 O)( 6Me dpaq)](OTf) complex shows a weak electronic absorption shoulder, stretching from approximately 600 to 490 nm ( Figure 1 ). The exposure of a MeCN solution of this complex to O 2 results in the eventual growth of a more intense band near 510 nm that is attributed to [Mn III (OH)( 6Me dpaq)] + [ 30 ]. This reaction is very slow, with approximately 75% conversion to the Mn III -hydroxo complex achieved after 48 h ( Figure 1 ).…”

“…Acetonitrile, diethyl ether, and methanol were dried and degassed using a PureSolv Micro solvent purification system. The H 6Me dpaq ligand and the [Mn II (OH 2 )( 6Me dpaq)](OTf), [Mn III (OH)( 6Me dpaq)](OTf), and [Mn III (OO t Bu)( 6Me dpaq)](OTf) complexes were synthesized according to a previously reported procedure (OTf − = trifluoromethanesulfonate) [ 30 ]. All synthetic experiments were performed under dinitrogen atmosphere in a glovebox unless otherwise noted.…”

“…Our lab reported Mn III -alkylperoxo complexes supported by the dpaq and dpaq 2Me ligands; however, the instability of these complexes, and the requirement of a large excess of t BuOOH to achieve their formation, made studies of reactivity unfeasible [ 29 ]. More recently, we reported that a derivative of the dpaq ligand, with 6-Me-pyridyl groups, is able to support Mn III -alkylperoxo complexes that are stable at room temperature and can be formed by adding an equivalent of an alkylhydroperoxide to the corresponding Mn III -hydroxo complex [Mn III (OH)( 6Me dpaq)] + ( Scheme 2 ) [ 30 ]. The observation that a set of thermally stable Mn III -hydroxo and Mn III -alkylperoxo complexes could be generated using the same supporting ligand presents a unique opportunity to model multiple steps in the proposed mechanism of MnLOX.…”

Oxidative versus basic asynchronous hydrogen atom transfer reactions of Mn(iii)-hydroxo and Mn(iii)-aqua complexes

“…Mechanisms of hydrogen atom transfer (HAT) reactions from organic substrates (SH) to metal-oxygen complexes, such as metal-oxo, metal-hydroxo, [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] metal-(hydro)peroxo [40][41][42][43][44] and metal-superoxo, [45][46][47][48][49][50][51][52][53][54] have been investigated extensively, as summarized in Scheme 1. HAT proceeds via the transfer of both a proton and an electron which can be transferred simul-spectrum of "asynchronicity", in which the transition state for the HAT reaction can contain either more PT or more ET character (Scheme 1).…”