Bimolecular Reductive Elimination of Ethane from Pyridine(diimine) Iron Methyl Complexes: Mechanism, Electronic Structure, and Entry into [2+2] Cycloaddition Catalysis
Bimolecular Reductive Elimination of Ethane from Pyridine(diimine) Iron Methyl Complexes: Mechanism, Electronic Structure, and Entry into [2+2] Cycloaddition Catalysis
复制标题
吡啶（二亚胺）甲基铁配合物双分子还原消除乙烷：机理、电子结构和进入[2 2]环加成催化
DOI：
10.1021/jacs.2c10547
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发表时间：
2023
影响因子：
15
通讯作者：
DeBeer, Serena
中科院分区：
文献类型：
--
作者：
Kovel, Carli B.;Darmon, Jonathan M.;Stieber, S. Chantal;Pombar, Gisselle;Pabst, Tyler P.;Theis, Bastian;Turner, Zoë R.;Üngör, Ökten;Shatruk, Michael;DeBeer, Serena
介绍了双分子还原消除法在烯烃-二烯环加成铁催化剂活化中的应用。该方法的关键是合成，表征，电子结构的确定，以及具有不同空间性质和电子基态的吡啶（二亚胺）铁甲基配合物家族的最终溶液稳定性。芳基取代的（MePDI）FeCH3和（EtPDI）FeCH3（RPDI = 2,6-(2,6- r2 - c6h3n = = CMe)2C5H3N）和烷基取代的例子（CyAPDI）FeCH3（CyAPDI = 2,6-(C6H11N = CMe)2C5H3N）的分子结构从平面和= 3/2基态明显扭曲。含有2,6-二异丙基芳基取代基的n -芳基衍生物（iPrPDI）FeCH3具有理想的平面几何形状，并表现出从= 1/2到= 3/2的自旋交叉行为。在23℃N2气氛下，（MePDI） fech3和（EtPDI） fech3分别通过乙烷还原消除生成铁二氮预催化剂[(MePDI)Fe(N2)]2（μ-N2）和[(EtPDI)Fe(N2)]2(μ-N2)，而（iPrPDI） fech3对C - C键的形成表现为惰性。相反，在这三种甲基铁配合物上加成丁二烯都能诱导乙烷生成，并生成相应的丁二烯铁配合物（RPDI）Fe(η - 4- c4h6) (R = Me, Et,iPr)，这是已知的烯烃和二烯[2+2]环加成的预催化剂。动力学、交叉实验和结构研究与磁测量和Mössbauer光谱相结合，阐明了铁配合物的电子和位阻特征，使这种不寻常的还原消除和预催化剂活化途径成为可能。在室温下，铁中心之间的甲基转金属速度快，不受空间环境或自旋状态的影响，而中间二聚体与n2或丁二烯进行了空间控制的速率决定反应，得到具有催化活性的铁化合物。
The application of bimolecular reductive elimination to the activation of iron catalysts for alkene–diene cycloaddition is described. Key to this approach was the synthesis, characterization, electronic structure determination, and ultimately solution stability of a family of pyridine(diimine) iron methyl complexes with diverse steric properties and electronic ground states. Both the aryl-substituted, (MePDI)FeCH3and (EtPDI)FeCH3(RPDI = 2,6-(2,6-R2-C6H3N═CMe)2C5H3N), and the alkyl-substituted examples, (CyAPDI)FeCH3(CyAPDI = 2,6-(C6H11N═CMe)2C5H3N), have molecular structures significantly distorted from planarity andS= 3/2 ground states. The relatedN-arylated derivative bearing 2,6-di-isopropyl aryl substituents, (iPrPDI)FeCH3, has an idealized planar geometry and exhibits spin crossover behavior fromS= 1/2 toS= 3/2 states. At 23 °C under an N2atmosphere, both (MePDI)FeCH3and (EtPDI)FeCH3underwent reductive elimination of ethane to form the iron dinitrogen precatalysts, [(MePDI)Fe(N2)]2(μ-N2) and [(EtPDI)Fe(N2)]2(μ-N2), respectively, while (iPrPDI)FeCH3proved inert to C–C bond formation. By contrast, addition of butadiene to all three iron methyl complexes induced ethane formation and generated the corresponding iron butadiene complexes, (RPDI)Fe(η4-C4H6) (R = Me, Et,iPr), known precatalysts for the [2+2] cycloaddition of olefins and dienes. Kinetic, crossover experiments, and structural studies were combined with magnetic measurements and Mössbauer spectroscopy to elucidate the electronic and steric features of the iron complexes that enable this unusual reductive elimination and precatalyst activation pathway. Transmetalation of methyl groups between iron centers was fast at ambient temperature and independent of steric environment or spin state, while the intermediate dimer underwent the sterically controlled rate-determining reaction with either N2or butadiene to access a catalytically active iron compound.