On the Lewis Acidity of the Oxoiron(IV) Unit in a Tetramethylcyclam Complex
On the Lewis Acidity of the Oxoiron(IV) Unit in a Tetramethylcyclam Complex
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四甲基环酰胺配合物中氧代铁 (IV) 单元的路易斯酸度
DOI：
10.1002/chem.201704977
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Que, Jr., Lawrence
中科院分区：
文献类型：
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作者：
Klein, Johannes E.;Draksharapu, Apparao;Shokri, Alireza;Cramer, Christopher J.;Que, Jr., Lawrence
对于+II和+III氧化态的六氧原子配合物，氧化态与刘易斯酸度之间的相关性已经很好地建立起来，其中较高的氧化态导致结合的H2O配体的pka较低。本文通过测定氧铁（IV）配合物[FeIV(O)(TMC)(OH2)]2+（1‐OH2； TMC=1,4,8,11‐四甲基环环素）的ph值来确定其刘易斯酸度。我们确定了1‐OH2的pkav为6.9±0.5，该值介于[FeIII(OH2)6]3+和[FeII(OH2)6]2+之间。这个中间值可以很容易地被高碱性氧化物配体的存在合理化，减轻了铁（IV）中心的刘易斯酸度。虽然氧配体在1‐OH2中只占据一个位置，与从非平面TMC配体的同面突出的所有四个甲基相反，其共轭基1‐oh1作为同义反互变异构体的混合物存在，它们通过氧配体和羟基配体之间的质子转移而相关。
The correlation between oxidation state and Lewis acidity is well established for hexaquairon complexes in the +II and +III oxidation state, in which the higher oxidation state leads to a lower pKafor the bound H2O ligand. This article addresses the Lewis acidity of the oxoiron(IV) complex [FeIV(O)(TMC)(OH2)]2+(1‐OH2; TMC=1,4,8,11‐tetramethylcyclam) by determining the pKaof the H2O ligand. We establish that1‐OH2has a pKaof 6.9±0.5, a value that falls in between those found for [FeIII(OH2)6]3+and [FeII(OH2)6]2+. This intermediate value can be readily rationalized by the presence of the highly basic oxide ligand that mitigates the Lewis acidity of the iron(IV) center. Although the oxo ligand occupies only one position in1‐OH2,antito all four methyl groups that protrude from the same face of the nonplanar TMC ligand, its conjugate base1‐OHexists as a mixture ofsynandantitautomers, which are related by proton transfer between the oxo and the hydroxo ligands.