Singh Priya, Lee Yuri, Mayfield Jaycee R, Singh Reena, Denler Melissa C, Jones Shannon D, Day Victor W, Nordlander Ebbe, Jackson Timothy A
The University of Kansas, Department of Chemistry and Center for Environmentally Beneficial Catalysis, 1567 Irving Hill Road, Lawrence, Kansas 66045, United States.
Lund University, Chemical Physics, Department of Chemistry, P.O. Box 124, SE-221 00 Lund, Sweden.
Inorg Chem. 2023 Nov 13;62(45):18357-18374. doi: 10.1021/acs.inorgchem.3c00600. Epub 2023 Jun 14.
A series of manganese(II) and oxomanganese(IV) complexes supported by neutral, pentadentate ligands with varied equatorial ligand-field strength (N3pyQ, N2py2I, and N4py) were synthesized and then characterized using structural and spectroscopic methods. On the basis of electronic absorption spectroscopy, the [Mn(O)(N4py)] complex has the weakest equatorial ligand field among a set of similar Mn-oxo species. In contrast, [Mn(O)(N2py2I)] shows the strongest equatorial ligand-field strength for this same series. We examined the influence of these changes in electronic structure on the reactivity of the oxomanganese(IV) complexes using hydrocarbons and thioanisole as substrates. The [Mn(O)(N3pyQ)] complex, which contains one quinoline and three pyridine donors in the equatorial plane, ranks among the fastest Mn-oxo complexes in C-H bond and thioanisole oxidation. While a weak equatorial ligand field has been associated with high reactivity, the [Mn(O)(N4py)] complex is only a modest oxidant. Buried volume plots suggest that steric factors dampen the reactivity of this complex. Trends in reactivity were examined using density functional theory (DFT)-computed bond dissociation free energies (BDFEs) of the MnO-H and Mn ═ O bonds. We observe an excellent correlation between Mn═O BDFEs and rates of thioanisole oxidation, but more scatter is observed between hydrocarbon oxidation rates and the MnO-H BDFEs.
合成了一系列由具有不同赤道配体场强度的中性五齿配体（N3pyQ、N2py2I和N4py）支撑的锰（II）和氧锰（IV）配合物，然后使用结构和光谱方法对其进行了表征。基于电子吸收光谱，[Mn(O)(N4py)]配合物在一组类似的锰氧物种中具有最弱的赤道配体场。相比之下，[Mn(O)(N2py2I)]在同一系列中显示出最强的赤道配体场强度。我们以烃类和苯甲硫醚为底物，研究了这些电子结构变化对氧锰（IV）配合物反应活性的影响。[Mn(O)(N3pyQ)]配合物在赤道平面上含有一个喹啉和三个吡啶供体，在C-H键和苯甲硫醚氧化反应中是最快的锰氧配合物之一。虽然弱赤道配体场与高反应活性相关，但[Mn(O)(N4py)]配合物只是一种中等强度的氧化剂。埋藏体积图表明，空间因素会抑制该配合物的反应活性。使用密度泛函理论（DFT）计算的MnO-H和Mn═O键的键解离自由能（BDFE）研究了反应活性趋势。我们观察到Mn═O BDFE与苯甲硫醚氧化速率之间具有良好的相关性，但在烃类氧化速率与MnO-H BDFE之间观察到更多的离散性。
