Karunananda Malkanthi K, Vázquez Francisco X, Alp E Ercan, Bi Wenli, Chattopadhyay Soma, Shibata Tomohiro, Mankad Neal P
Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607, USA.
Dalton Trans. 2014 Sep 28;43(36):13661-71. doi: 10.1039/c4dt01841a.
Complexes of the type (NHC)M-Fp (NHC = N-heterocyclic carbene, M = Cu or ZnCl, Fp = FeCp(CO)2) have been used recently as replacements for noble metal C-H functionalization catalysts and for small molecule activation studies. The promising reactivity of these systems has been linked to the use of the late metal electrophiles Cu and Zn in place of early metal electrophiles, and also to the ability of the M-Fe pairs to cooperate during catalytically relevant multielectron redox processes such as bimetallic oxidative addition and bimetallic reductive elimination. Using Mössbauer spectroscopy and metal K-edge XANES analysis, a detailed electronic structure description of these complexes is presented. One unusual feature of the late-metal M-Fp interactions is the presence of significant M → Fe π-backdonation in addition to Fe → M σ-donation; this π-backdonation is absent in early metal analogues and is apparent from analysis of Mössbauer data and Fe K-edge data. Multi-edge XANES analysis of C-I bimetallic oxidative addition at a Cu-Fe reaction center reveals little change in metal effective nuclear charges during the two-electron redox process. IR spectroscopy indicates that the supporting carbonyl ligands participate to a large extent in the redox process.
最近，(NHC)M-Fp类型的配合物（NHC = N-杂环卡宾，M = Cu或ZnCl，Fp = FeCp(CO)₂）已被用作贵金属C-H官能化催化剂的替代品以及用于小分子活化研究。这些体系具有的良好反应活性与使用后期金属亲电试剂Cu和Zn取代早期金属亲电试剂有关，还与M-Fe对在催化相关的多电子氧化还原过程（如双金属氧化加成和双金属还原消除）中协同作用的能力有关。利用穆斯堡尔光谱和金属K边X射线吸收近边结构（XANES）分析，对这些配合物进行了详细的电子结构描述。后期金属M-Fp相互作用的一个不寻常特征是，除了Fe→M的σ给予外，还存在显著的M→Fe π反馈；这种π反馈在早期金属类似物中不存在，并且从穆斯堡尔数据和Fe K边数据的分析中可以明显看出。对Cu-Fe反应中心处C-I双金属氧化加成的多边缘XANES分析表明，在双电子氧化还原过程中金属有效核电荷几乎没有变化。红外光谱表明，配位羰基配体在很大程度上参与了氧化还原过程。
