Soper Jake D, Kryatov Sergey V, Rybak-Akimova Elena V, Nocera Daniel G
Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge Massachusetts 02139-4207, USA.
J Am Chem Soc. 2007 Apr 25;129(16):5069-75. doi: 10.1021/ja0683032. Epub 2007 Mar 31.
Hangman metalloporphyrin complexes poise an acid-base group over a redox-active metal center and in doing so allow the "pull" effect of the secondary coordination environment of the heme cofactor of hydroperoxidase enzymes to be modeled. Stopped-flow investigations have been performed to decipher the influence of a proton-donor group on O-O bond activation. Low-temperature reactions of tetramesitylporphyrin (TMP) and Hangman iron complexes containing acid (HPX-CO2H) and methyl ester (HPX-CO2Me) functional groups with peroxyacids generate high-valent Fe=O active sites. Reactions of peroxyacids with (TMP)FeIII(OH) and methyl ester Hangman (HPX-CO2Me)FeIII(OH) give both O-O heterolysis and homolysis products, Compound I (Cpd I) and Compound II (Cpd II), respectively. However, only the former is observed when the hanging group is the acid, (HPX-CO2H)FeIII(OH), because odd-electron homolytic O-O bond cleavage is inhibited. This proton-controlled, 2e- (heterolysis) vs 1e- (homolysis) redox specificity sheds light on the exceptional catalytic performance of the Hangman metalloporphyrin complexes and provides tangible benchmarks for using proton-coupled multielectron reactions to catalyze O-O bond-breaking and bond-making reactions.
绞刑架型金属卟啉配合物在氧化还原活性金属中心上方平衡一个酸碱基团，这样做可以模拟氢过氧化物酶血红素辅因子二级配位环境的“拉动”效应。已进行了停流研究以解读质子供体基团对O - O键活化的影响。四甲基卟啉（TMP）以及含有酸（HPX - CO₂H）和甲酯（HPX - CO₂Me）官能团的绞刑架型铁配合物与过氧酸的低温反应会生成高价Fe = O活性位点。过氧酸与（TMP）FeIII（OH）和甲酯绞刑架型（HPX - CO₂Me）FeIII（OH）的反应分别产生O - O异裂和均裂产物，即化合物I（Cpd I）和化合物II（Cpd II）。然而，当悬挂基团为酸（HPX - CO₂H）FeIII（OH）时，仅观察到前者，因为奇电子均裂O - O键断裂受到抑制。这种质子控制的、2电子（异裂）对1电子（均裂）的氧化还原特异性揭示了绞刑架型金属卟啉配合物卓越的催化性能，并为利用质子耦合多电子反应催化O - O键断裂和键形成反应提供了切实的基准。
