C-H bond cleavage with reductants: re-investigating the reactivity of monomeric Mn(III/IV)-oxo complexes and the role of oxo ligand basicity.
C-H bond cleavage with reductants: re-investigating the reactivity of monomeric Mn(III/IV)-oxo complexes and the role of oxo ligand basicity.
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DOI：
10.1021/ja8100825
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发表时间：
2009-03-04
影响因子：
15
通讯作者：
Borovik AS
中科院分区：
文献类型：
--
作者：
Parsell TH;Yang MY;Borovik AS
结构相似的 MnIII 和 MnIV 配合物的热力学性质已被重新研究，以了解它们与具有 CH 键的底物的反应性。该配合物具有通式 [MnH3buea(O)]n-，其中 [H3buea]3- 是三足配体，三[(N'-叔丁基脲基)-N-亚乙基]氨基。这些配合物是独特的，因为 Mn-oxo 单元周围有分子内氢键（H 键）网络。早期报告中 MnIII/IV (O) 对的氧化还原电位分配不正确：与 DMSO 中的 Cp2Fe+/Cp2Fe 相比，校正值为 -1.0 V，而在相同条件下 MnIV/V(O) 过程为 -0.076。 MnIII(O)配合物中的氧代配体是碱性的，pKa为28.3； MnIV(O)配合物中末端氧代配体的碱度估计为~15。这些值用于重新评估相应 MnII/III-OH 配合物的 OH 键解离能 (BDEOH)：[MnIIIH3buea(OH)]- 和 [MnIIH3buea(OH)]2- 的 BDEsOH 值分别为 89 和 77 kcal/mol。两种 Mn(O) 配合物均与 9,10-二氢蒽 (DHA) 反应，以接近定量的产率产生蒽。基于配合物的低氧化还原电位，这是令人惊讶的，表明氧代配体的碱性是观察到的反应性的主要贡献者。与热力学结果相反，比较动力学研究发现 MnIII(O) 配合物的反应速度比 MnIV(O) 配合物快近 20 倍。通过 Eyring 分析确定的活化参数发现，两个系统之间的活化熵显着不同（ΔΔS‡ = -35 eu，其中 ΔΔS‡ = ΔS‡(MnIV(O)) - ΔS‡(MnIII(O))。这种不寻常的动力学行为可以在导致不同机制的氧代配体的碱性背景下进行解释：对于 [MnIIIH3buea(O)]2- 质子提出了转移电子转移机制，而 [MnIVH3buea(O)]- 可能是氢原子转移途径。
The thermodynamic properties of structurally similar MnIII and MnIV complexes have been re-investigated to understand their reactivity with substrates having C—H bonds. The complexes have the general formula, [MnH3buea(O)]n-, where [H3buea]3- is the tripodal ligand, tris[(N’-tert-butylureaylato)-N-ethylene]aminato. These complexes are unique because of the intramolecular hydrogen-bonding (H-bond) network surrounding the Mn—oxo units. The redox potentials for the MnIII/IV (O) couple was incorrectly assigned in earlier reports: the corrected values is -1.0 V vs Cp2Fe+/Cp2Fe in DMSO, while the MnIV/V(O) process is −0.076 under the same conditions. The oxo ligand in the MnIII(O) complexes is basic with a pKa of 28.3; the basicity of the terminal oxo ligand in the MnIV(O) complex is estimated to be ∼15. These values were used to re-evaluate the O—H bond dissociation energy (BDEOH) of the corresponding MnII/III—OH complexes: BDEsOH values of 89 and 77 kcal/mol were determined for [MnIIIH3buea(OH)]- and [MnIIH3buea(OH)]2-, respectively. Both Mn(O) complexes react with 9,10-dihydroanthracene (DHA) to produce anthracene in nearly quantitative yields. This is surprising based on the low redox potiental of the complexes, suggesting the basicity of the oxo ligand is a major contributor to the observed reactivity. In contrast to the thermodynamic results, a comparative kinetic investigation found that the MnIII(O) complex reacts nearly 20 times faster than the MnIV(O) complex. Activation parameters, determined from an Eyring analysis, found that the entropy of activation is significantly different between the two systems (ΔΔS‡ = -35 eu, where ΔΔS‡ = ΔS‡(MnIV(O)) - ΔS‡(MnIII(O)). This unusual kinetic behavior can be explained in the context of the basicity of the oxo ligands that leads to different mechanisms: for [MnIIIH3buea(O)]2- a proton transfer-electron transfer mechanism is proposed, whereas for [MnIVH3buea(O)]- a hydrogen-atom transfer pathway is likely.
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DOI：
10.1142/9781848160699_0001
发表时间：
2000-01-01
期刊：
BIOMIMETIC OXIDATIONS CATALYZED BY TRANSITION METAL COMPLEXES
影响因子：
--
作者：
Mayer, JM
通讯作者：
Mayer, JM
DOI：
10.1073/pnas.0709471104
发表时间：
2007-12-04
影响因子：
11.1
作者：
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通讯作者：
Nam, Wonwoo
影响因子：
15
作者：
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通讯作者：
Borovik, AS
影响因子：
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作者：
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影响因子：
15
作者：
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