Chemistry Department, College of Science, Shiraz University, Shiraz, Iran.
J Phys Chem A. 2011 Oct 27;115(42):11796-809. doi: 10.1021/jp205254r. Epub 2011 Sep 29.
We report the results of density functional theory (DFT) calculations of ethylene adsorption over the most stable pure and bimetallic clusters of Fe(n)Cu(m) (2 ≤ m+n ≤ 4), in two adsorption modes of π and di-σ. Our results show that the quality of interaction of ethylene with iron center in bimetallic clusters of iron-copper is characteristically different from what is found over pure iron. Over the range of our studies for dimers, trimers, and tetramers, whether for π or di-σ mode, alloying iron clusters results in a substantial improvement in adsorption of ethylene over cluster and exhibits a notable increase in binding and interaction energies compared with pure iron clusters. One of the interesting features of this adsorption is that ethylene never orients toward di-σ mode for Cu-Cu or Fe-Cu bonds, and π orientation is strongly preferred. Ethylene adsorption in di-σ coordination is accompanied by the sever restructuring, larger deformation energy, and the larger interaction energy. In the next part, we answer this question of how electronic perturbations induced by copper atoms can enhance the activity of iron toward ethylene. This interpretation is done within the framework of natural bond orbital (NBO) and natural resonance theory (NRT) analyses. Different reaction pathways detected by NRT analysis (donor-acceptor, metallacyclic, and carbanion) reveal interesting aspects of differences between the nature of metal-alkene coordination in bimetallic and purely metallic clusters.
我们报告了密度泛函理论（DFT）计算的乙烯吸附在最稳定的纯和双金属团簇 Fe(n)Cu(m)（2 ≤ m+n ≤ 4）上的结果，在π和双σ两种吸附模式下。我们的结果表明，乙烯与铁中心在铁铜双金属簇中的相互作用质量与纯铁中的情况明显不同。在我们对二聚体、三聚体和四聚体的研究范围内，无论是π还是双σ模式，合金化铁簇都会导致乙烯对簇的吸附得到实质性改善，并表现出与纯铁簇相比显著增加的结合和相互作用能。这种吸附的一个有趣特征是，乙烯从不或倾向于在 Cu-Cu 或 Fe-Cu 键上采用双σ模式，而π模式则是强烈优先的。在双σ配位中，乙烯的吸附伴随着严重的重构、更大的变形能和更大的相互作用能。在接下来的部分中，我们将回答铜原子诱导的电子微扰如何增强铁对乙烯的活性的问题。这种解释是在自然键轨道（NBO）和自然共振理论（NRT）分析的框架内进行的。NRT 分析检测到的不同反应途径（供体-受体、金属环和碳负离子）揭示了双金属和纯金属簇中金属-烯烃配位性质差异的有趣方面。
