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Electronic Support Effects of Tunable Mixed Metal Oxides on Immobilized Palladium N‐Heterocyclic Carbene Complexes
European Journal of Inorganic Chemistry ( IF 2.2 ) Pub Date : 2018-05-13 , DOI: 10.1002/ejic.201800220
Matthew T. Finn 1 , Courtney M. Donahue 2 , Anastasia V. Blake 2 , Nan An 1 , Scott R. Daly 2 , Adelina M. Voutchkova-Kostal 1
Affiliation  

Electronic effects of supports on site‐isolated organometallic complexes are poorly understood, despite indication that such effects impact stability and reactivity of immobilized complexes. Here we report X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption near edge structure (XANES) spectroscopy studies of surface‐immobilized PdII N‐heterocyclic carbene complexes on Mg‐Al mixed metal oxides (MMOs) using silane‐modified ligands. XPS revealed a ca. 1 eV increase in Pd binding energy as a result of immobilization on MMOs, suggesting that the PdII complex becomes more electropositive when appended to the surface. For MMOs doped with Fe, Ni, Co and Zn, analysis of Cl K‐edge and Pd L2‐ and L3‐edge showed increasing pre‐edge energies that followed the order Fe = Ni < Zn = Cr < undoped Mg‐Al MMO. The Pd L3 pre‐edge energies correlated to the calculated oxygen partial charge of the MMO, as estimated using the Sanderson electronegativity model. Transmission electron microscope images collected on the immobilized Pd complexes revealed nanoparticles on three of the five MMOs, whose presence can be related to the Pd XPS and XANES energies. These findings suggest that electronic differences associated with the MMO supports impact the stability of appended PdII complexes with respect to reduction to Pd0.

中文翻译:

可调谐混合金属氧化物对固定化钯N-杂环碳烯络合物的电子支持作用

尽管对支持物对固定的有机金属配合物的电子效应有影响,但这种影响会影响固定化配合物的稳定性和反应性,但人们对其了解很少。在此我们报告使用硅烷改性的配体对Mg-Al混合金属氧化物(MMO)上的表面固定的Pd II N-杂环卡宾配合物进行X射线光电子能谱(XPS)和X射线吸收近边缘结构(XANES)光谱研究。XPS揭示了一个 由于固定在MMO上,Pd结合能增加了1 eV,这表明当Pd II复合物附着在表面上时,其电正性更高。对于掺杂有Fe,Ni,Co和Zn的MMO,分析Cl K-edge和Pd L 2-和L 3边缘显示的前边缘能量不断增加,依次为Fe = Ni <Zn = Cr <未掺杂的Mg-Al MMO。Pd L 3前缘能量与MMO的计算出的氧偏电荷相关,这是使用Sanderson电负性模型估算得出的。在固定的Pd络合物上收集的透射电子显微镜图像显示了五个MMO中的三个的纳米颗粒,其存在可能与Pd XPS和XANES能量有关。这些发现表明,与MMO相关的电子差异会影响附加的Pd II复合物相对于Pd 0还原的稳定性。
更新日期:2018-05-24
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