Highly Reactive Manganese(IV)-Oxo Porphyrins Showing Temperature-Dependent Reversed Electronic Effect in C–H Bond Activation Reactions

Abstract

We report that Mn(IV)-oxo porphyrin complexes, Mn IV (O)(TMP) (1) and Mn IV (O)(TDCPP) (2), are capable of activating the C−H bonds of hydrocarbons, including unactivated alkanes such as cyclohexane, via an oxygen non-rebound mechanism. Interestingly, 1 with an electron-rich porphyrin is more reactive than 2 with an electron-deficient porphyrin at a high temperature (e.g., 0 °C). However, at a low temperature (e.g., −40 °C), the reactivity of 1 and 2 is reversed, showing that 2 is more reactive than 1. To the best of our knowledge, the present study reports the first example of highly reactive Mn(IV)-oxo porphyrins and their temperature-dependent reactivity in C−H bond activation reactions.

Capturing Manganese Oxide Intermediates in Electrochemical Water Oxidation at Neutral pH by In Situ Raman Spectroscopy

“…Moreover, as the peak of the target high‐valent Mn‐oxo species can overlap with the Raman bands of the electrolyte, it is crucial to select a suitable electrolyte for the analysis. Based on previous studies of high‐valent Mn‐oxo species, [46–54] the stretching vibrational Raman band of Mn‐oxo was expected to be in the region of 707–803 cm −1 and 957–997 cm −1 , as demonstrated in Figure 1 b. In the case of phosphate and sulfate electrolytes, the peaks at 988 and 979 cm −1 are overlapping with the target region for Mn‐oxo species and are assigned to the symmetric stretching vibrational mode of PO 3 in HPO 4 2− and SO 4 2− , respectively [55, 56] .…”

“…Interestingly, a prominent spectral change was observed in the region of 700 to 800 cm −1 , in which the vibration bands of high‐valent Mn‐oxo moieties are generally observed [46–54] . Notably, upon increasing the applied potential, a new broad peak centered at 760 cm −1 appeared, which is indicated by the red dotted area in Figure 3 a.…”

Capturing Manganese Oxide Intermediates in Electrochemical Water Oxidation at Neutral pH by In Situ Raman Spectroscopy

“…Moreover,a st he peak of the target high-valent Mn-oxo species can overlap with the Raman bands of the electrolyte,it is crucial to select asuitable electrolyte for the analysis.B ased on previous studies of high-valent Mn-oxo species, [46][47][48][49][50][51][52][53][54] the stretching vibrational Raman band of Mn-oxo was expected to be in the region of 707-803 cm À1 and 957-997 cm À1 ,a s demonstrated in Figure 1b.I nt he case of phosphate and sulfate electrolytes,t he peaks at 988 and 979 cm À1 are overlapping with the target region for Mn-oxo species and are assigned to the symmetric stretching vibrational mode of PO 3 in HPO 4…”

“…[79,80] Interestingly,aprominent spectral change was observed in the region of 700 to 800 cm À1 ,inwhich the vibration bands of high-valent Mn-oxo moieties are generally observed. [46][47][48][49][50][51][52][53][54] Notably,u pon increasing the applied potential, an ew broad peak centered at 760 cm À1 appeared, which is indicated by the red dotted area in Figure 3a.T he peak at 760 cm À1 was confirmed multiple times,p roducing consistent and reliable results (Supporting Information, Figure S5). In addition, the in situ Raman analyses on bare FTO substrate strongly support the peak at 760 cm À1 to the Mn-oxo species generated during OER because no peak was newly observed in case of the bare FTO(Supporting Information, Figure S6).…”

Spectroscopic capture of a low-spin Mn(IV)-oxo species in Ni–Mn3O4 nanoparticles during water oxidation catalysis

“…From the previously studied molecular complexes, reported Raman peak positions for stretching vibrational mode of Mn(IV)-oxo species are between 707 and 803 cm −1 (refs. 46 – 48 ), while those of Mn(V)-oxo species are between 957 and 997 cm −1 (refs. 49 – 51 ).…”