Reaction landscape of a pentadentate N5-ligated MnII complex with O2˙− and H2O2 includes conversion of a peroxomanganese(iii) adduct to a bis(μ-oxo)dimanganese(iii,iv) species

Abstract

Herein we describe the chemical reactivity of the mononuclear [MnII(N4py)(OTf)](OTf) (1) complex with hydrogen peroxide and superoxide. Treatment of 1 with one equivalent superoxide at −40 °C in MeCN formed the peroxomanganese(III) adduct, [MnIII(O2)(N4py)]+ (2) in ~30% yield. Complex 2 decayed over time and the formation of the bis(μ-oxo)dimanganese(III,IV) complex, [MnIIIMnIV(μ-O)2(N4py)2]3+ (3) was observed. When 2 was formed in higher yields (~60%) using excess superoxide, the [MnIII(O2)(N4py)]+ species thermally decayed to MnII species and 3 was formed in no greater than 10% yield. Treatment of [MnIII(O2)(N4py)]+ with 1 resulted in the formation of 3 in ~90% yield, relative to the concentration of [MnIII(O2)(N4py)]+. This reaction mimics the observed chemistry of Mn-ribonucleotide reductase, as it features the conversion of two MnII species to an oxo-bridged MnIIIMnIV compound using O2− as oxidant. Complex 3 was independently prepared through treatment of 1 with H2O2 and base at −40 °C. The geometric and electronic structures of 3 were probed using electronic absorption, electron paramagnetic resonance (EPR), magnetic circular dichroism (MCD), variable-temperature, variable-field MCD (VTVH-MCD), and X-ray absorption (XAS) spectroscopies. Complex 3 was structurally characterized by X-ray diffraction (XRD), which revealed the N4py ligand bound in an unusual tetradentate fashion.

Geometric and electronic structure of a peroxomanganese(iii) complex supported by a scorpionate ligand

“…The Mn K-edge X-ray absorption data of [Mn II (Tp Ph2 )(DMF) 3 ](OTf) shows a rising edge at 6547.5 eV, characteristic of a Mn II species, 62,63 as well as a pre-edge feature at 6540.6 eV (ESI, Figure S6). The Fourier transform of the extended X-ray absorption fine structure (EXAFS) data of [Mn II (Tp Ph2 )(DMF) 3 ](OTf) exhibits a primary peak at R′ = 1.7 Å which was best fit with a shell of 3 O atoms at 2.16 Å and a shell of 3 N atoms at 2.28 Å (Figure 8, Table 6).…”

Mimicking Class I b Mn2‐Ribonucleotide Reductase: A MnII2 Complex and Its Reaction with Superoxide

“…[4a, 6c] Jackson and co-workers recently reported the formation of a bis(μ-oxo)Mn III Mn IV species using O 2 • − as an oxidant from mononuclear Mn II precursors. [7] Initially, a mononuclear Mn III -peroxide adduct was formed, which subsequently reacted with the mononuclear Mn II precursor forming the bis(μ-oxo)Mn III Mn IV species. To the best of our knowledge, however, a Mn II Mn III -peroxide complex has not been previously reported.…”

“…[13,7] Previously reported Mn III -peroxide complexes [Mn III (O 2 )(TMC)] + (TMC=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), [Mn III (O 2 )(13-TMC)] + (13-TMC=1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclotridecane), and [Mn III (O 2 )-(Tp iPr )] + (Tp iPr =tris(3,5-diisopropylpyrazolyl)borate), all exhibited an absorption band at around 460 nm attributed to peroxide-to-metal charge transfer [14] and a broader band in the 560–620 nm range, derived from d – d transitions. [14] In addition, Mn III -peroxides supported by other polydentate amine ligands exhibited a prominent band at λ max =430–445 nm and a weaker band at λ max =590–610 nm.…”

Mimicking Class I b Mn2‐Ribonucleotide Reductase: A MnII2 Complex and Its Reaction with Superoxide

“…[4] Aseries of mononuclear Mn III -peroxide and hydroperoxide species have been reported. [7] Initially,am ononuclear Mn III -peroxide adduct was formed, which subsequently reacted with the mononuclear Mn II precursor forming the bis(m-oxo)Mn III Mn IV species. [7] Initially,am ononuclear Mn III -peroxide adduct was formed, which subsequently reacted with the mononuclear Mn II precursor forming the bis(m-oxo)Mn III Mn IV species.…”

“…At higher concentrations of 1,l ower yields of 2 were obtained ( Supporting Information, Figure S3). [13,7] [14] and abroader band in the 560-620 nm range,d erived from d-d transitions. [12] We noted that the electronic absorption features for 2 were characteristic of Mn III -peroxide complexes.…”