Department of Chemistry and Center for Metals in Biocatalysis, University of Minnesota, 207 Pleasant St. SE, Minneapolis, Minnesota 55455, USA.
Inorg Chem. 2013 Apr 1;52(7):3976-84. doi: 10.1021/ic3027896. Epub 2013 Mar 15.
Complexes 1-OH and 1-F are related complexes that share similar X-Fe(III)-O-Fe(IV)═O core structures with a total spin S of ½, which arises from antiferromagnetic coupling of an S = 5/2 Fe(III)-X site and an S = 2 Fe(IV)═O site. EXAFS analysis shows that 1-F has a nearly linear Fe(III)-O-Fe(IV) core compared to that of 1-OH, which has an Fe-O-Fe angle of ~130° due to the presence of a hydrogen bond between the hydroxo and oxo groups. Both complexes are at least 1000-fold more reactive at C-H bond cleavage than 2, a related complex with a OH-Fe(IV)-O-Fe(IV)═O core having individual S = 1 Fe(IV) units. Interestingly, 1-F is 10-fold more reactive than 1-OH. This raises an interesting question about what gives rise to the reactivity difference. DFT calculations comparing 1-OH and 1-F strongly suggest that the H-bond in 1-OH does not significantly change the electrophilicity of the reactive Fe(IV)═O unit and that the lower reactivity of 1-OH arises from the additional activation barrier required to break its H-bond in the course of H-atom transfer by the oxoiron(IV) moiety.
1-OH 和 1-F 是相关的配合物，它们具有相似的 X-Fe(III)-O-Fe(IV)=O 核心结构，总自旋 S 为 ½，这是由 S = 5/2 Fe(III)-X 位和 S = 2 Fe(IV)=O 位的反铁磁耦合产生的。EXAFS 分析表明，与 1-OH 相比，1-F 具有近乎线性的 Fe(III)-O-Fe(IV)核心，这是由于羟基和氧之间存在氢键，导致 Fe-O-Fe 角约为 130°。与具有 OH-Fe(IV)-O-Fe(IV)=O 核心且具有单个 S = 1 Fe(IV)单元的相关配合物 2 相比，这两种配合物在 C-H 键断裂方面的反应性至少高 1000 倍。有趣的是，1-F 的反应性比 1-OH 高 10 倍。这提出了一个有趣的问题，即是什么导致了反应性的差异。比较 1-OH 和 1-F 的 DFT 计算强烈表明，1-OH 中的氢键不会显著改变反应性 Fe(IV)=O 单元的亲电性，1-OH 的低反应性是由于在 oxoiron(IV) 部分进行 H 原子转移过程中打破其氢键所需的额外活化能。
