A "Beheaded" TAML Activator: A Compromised Catalyst that Emphasizes the Linearity between Catalytic Activity and pKa
A "Beheaded" TAML Activator: A Compromised Catalyst that Emphasizes the Linearity between Catalytic Activity and pKa
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DOI：
10.1021/acs.inorgchem.6b01988
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发表时间：
2016-12-05
影响因子：
4.6
通讯作者：
Collins, Terrence J.
中科院分区：
文献类型：
--
作者：
Mills, Matthew R.;Weitz, Andrew C.;Collins, Terrence J.
新型四氨基大环配体（TAML）活化剂[Fe-III{（Me 2CNCOCMe 2NCO）（2）CMe 2} OH 2]（-）（4）在pH 2-13范围内的水溶液中的pH值表明其具有两个不等价的轴向H2O配体的假八面体几何结构，并揭示了（i）由于（ii）旁边的四个供电子甲基，水的第一pK（a）预期基本漂移至11.38。其违反直觉地增强了对酸诱导的铁（III）从大循环中排出的抗性。4在pH 7-12范围内对H2 O2氧化橙子Ⅱ（S）的催化活性明显低于以前报道的TAML活化剂，尽管它遵循共同的速率定律（v/[Fe-III] = k（I）k（II）[H2 O2] [S]/（k（I）[H2 O2] + k（II）[S]）和典型的pH曲线。在pH 7和25 ℃下，速率常数k（I）和k（II）分别等于0.63 +/- 0.02和1.19 +/- 0.03 M-1 s（-1）。随着pK（a）、k（I）和k（II）的这些新值分别建立新的上限和下限，速率常数k（I）和k（II）与plc值的所有关系log k = log k（0）+ α X pK（a）建立为log k（0）= 13 +/- 2和20 +/- 4和α = -1.1 +/- 0.2和-1.8 +/- k（I）和k（II）分别为0.4。因此，TAML活化剂在四代催化剂中的反应性可通过其pK（a）值预测。
Studies of the new tetra-amido macrocyclic ligand (TAML) activator [Fe-III{(Me2CNCOCMe2NCO)(2)CMe2}OH2](-) (4) in water in the pH range of 2-13 suggest its pseudo-octahedral geometry with two nonequivalent axial H2O ligands and revealed (i) the anticipated basic drift of the first pK(a) of water to 11.38 due to four electron-donating methyl groups alongside (ii) its counterintuitive enhanced resistance to acid induced iron(III) ejection from the macro cycle. The catalytic activity of 4 in the oxidation of Orange II (S) by H2O2, in the pH range of 7-12 is significantly lower than that of previously reported TAML activators, though it follows the common rate law (v/[Fe-III] = k(I)k(II)[H2O2] [S]/(k(I)[H2O2] + k(II)[S]) and typical pH profiles for k(I) and k(II). At pH 7 and 25 C the rate constants k(I) and k(II) equal 0.63 +/- 0.02 and 1.19 +/- 0.03 M-1 s(-1), respectively. With these new values for pK(a), k(I) and k(II) establishing new high and low limits, respectively, the rate constants k(I) and k(II) were correlated with plc values of all relations log k = log k(0) + alpha X pK(a) were established with log k(0) = 13 +/- 2 and 20 +/- 4 and alpha = -1.1 +/- 0.2 and -1.8 +/- 0.4 for k(I) and k(II), respectively. Thus, the reactivity of TAML activators across four generations of catalysts is predictable through their pK(a) values.