Jung Jieun, Liu Shuo, Ohkubo Kei, Abu-Omar Mahdi M, Fukuzumi Shunichi
†Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA and SENTAN, Japan Science and Technology Agency (JST), Suita, Osaka 565-0871, Japan.
‡Department of Bioinspired Science, Ewha Womans University, Seoul 120-750, Korea.
Inorg Chem. 2015 May 4;54(9):4285-91. doi: 10.1021/ic503012s. Epub 2015 Apr 13.
Electron transfer from octamethylferrocene (Me8Fc) to the manganese(V) imidocorrole complex (tpfc)Mn(V)(NAr) [tpfc = 5,10,15-tris(pentafluorophenyl)corrole; Ar = 2,6-Cl2C6H3] proceeds efficiently to give an octamethylferrocenium ion (Me8Fc(+)) and (tpfc)Mn(IV)(NAr) in acetonitrile (MeCN) at 298 K. Upon the addition of trifluoroacetic acid (TFA), further reduction of (tpfc)Mn(IV)(NAr) by Me8Fc gives (tpfc)Mn(III) and ArNH2 in deaerated MeCN. TFA also results in hydrolysis of (tpfc)Mn(V)(NAr) with residual water to produce a protonated manganese(V) oxocorrole complex ((tpfc)Mn(V)(OH)) in deaerated MeCN. (tpfc)Mn(V)(OH) is rapidly reduced by 2 equiv of Me8Fc in the presence of TFA to give (tpfc)Mn(III) in deaerated MeCN. In the presence of dioxygen (O2), (tpfc)Mn(III) catalyzes the two-electron reduction of O2 by Me8Fc with TFA in MeCN to produce H2O2 and Me8Fc(+). The rate of formation of Me8Fc(+) in the catalytic reduction of O2 follows zeroth-order kinetics with respect to the concentrations of Me8Fc and TFA, whereas the rate increases linearly with increasing concentrations of (tpfc)Mn(V)(NAr) and O2. These kinetic dependencies are consistent with the rate-determining step being electron transfer from (tpfc)Mn(III) to O2, followed by further proton-coupled electron transfer from Me8Fc to produce H2O2 and (tpfc)Mn(IV). Rapid electron transfer from Me8Fc to (tpfc)Mn(IV) regenerates (tpfc)Mn(III), completing the catalytic cycle. Thus, catalytic two-electron reduction of O2 by Me8Fc with (tpfc)Mn(V)(NAr) as a catalyst precursor proceeds via a Mn(III)/Mn(IV) redox cycle.
在298 K的乙腈（MeCN）中，八甲基二茂铁（Me8Fc）向锰（V）亚氨基卟啉配合物（tpfc）Mn（V）（NAr）[tpfc = 5,10,15 - 三（五氟苯基）卟啉；Ar = 2,6 - Cl2C6H3]的电子转移有效地进行，生成八甲基二茂铁鎓离子（Me8Fc(+)）和(tpfc)Mn(IV)(NAr)。加入三氟乙酸（TFA）后，在除气的MeCN中，Me8Fc进一步将(tpfc)Mn(IV)(NAr)还原为(tpfc)Mn(III)和ArNH2。TFA还会导致(tpfc)Mn(V)(NAr)与残留水发生水解反应，在除气的MeCN中生成质子化的锰（V）氧代卟啉配合物((tpfc)Mn(V)(OH))。在TFA存在下，(tpfc)Mn(V)(OH)会被2当量的Me8Fc迅速还原，在除气的MeCN中生成(tpfc)Mn(III)。在氧气（O2）存在下，(tpfc)Mn(III)催化Me8Fc与TFA在MeCN中对O2进行双电子还原，生成H2O2和Me8Fc(+)。在O2的催化还原中，Me8Fc(+)的生成速率相对于Me8Fc和TFA的浓度遵循零级动力学，而速率随(tpfc)Mn(V)(NAr)和O2浓度的增加呈线性增加。这些动力学依赖性与速率决定步骤是从(tpfc)Mn(III)到O2的电子转移，随后是从Me8Fc进行进一步的质子耦合电子转移以生成H2O2和(tpfc)Mn(IV)一致。Me8Fc向(tpfc)Mn(IV)的快速电子转移使(tpfc)Mn(III)再生，完成催化循环。因此，以(tpfc)Mn(V)(NAr)作为催化剂前体，Me8Fc对O2的催化双电子还原通过Mn(III)/Mn(IV)氧化还原循环进行。
