Magnetic circular dichroism and density functional theory studies of electronic structure and bonding in cobalt(II)-N-heterocyclic carbene complexes
Magnetic circular dichroism and density functional theory studies of electronic structure and bonding in cobalt(II)-N-heterocyclic carbene complexes
复制标题
DOI：
10.1039/c7dt01748k
复制
发表时间：
2017-10-21
影响因子：
4
通讯作者：
Neidig, Michael L.
中科院分区：
文献类型：
--
作者：
Iannuzzi, Theresa E.;Gao, Yafei;Neidig, Michael L.
简单钴盐和N-杂环卡宾（NHC）配体的组合在C-H官能化、氢化芳基化和交叉偶联催化中是高度有效的，尽管显示出对NHC配体的身份的强烈依赖性。此外，与NHC配体有效的反应往往是无效的膦配体，进一步激励的基本电子结构和良好定义的扭曲四面体Co（II）配合物的键合差异的评价。磁性圆二色性（MCD）研究表明，钴（II）-双膦比钴（II）-NHC配合物具有更大的配位场。对一组扩展的L2CoCl2配合物（L-2 = NHC、双膦和二胺）进行了理论密度泛函理论（DFT）计算，研究了NHC与双膦和二胺配体的电子结构和相对连接性质. Mayer键序和电荷分解分析表明，NHC配体是比双膦稍强的供体配体，但也导致Co-Cl键在反式影响中减弱。从MCD和DFT的研究，改变NHC的N-取代基的Co（II）-NHC配合物的配位场有一个更大的影响比饱和的骨干。总的来说，这些研究提供了详细的了解Co（II）配合物中的电子结构和键合效应与配体类型的催化中常用的探索。
The combination of simple cobalt salts and N-heterocyclic carbene (NHC) ligands has been highly effective in C-H functionalization, hydroarylation and cross-coupling catalysis, though displaying a strong dependence on the identity of the NHC ligand. In addition, reactions effective with NHC ligands are often ineffective with phosphine ligands, further motivating the evaluation of the fundamental electronic structure and bonding differences in well-defined distorted tetrahedral Co(II) complexes. Magnetic circular dichroism (MCD) studies indicate that Co(II)-bisphosphines have larger ligand fields than Co(II)-NHC complexes. Theoretical density functional theory (DFT) calculations were performed on an expanded set of L2CoCl2 complexes (L-2 = NHC, bisphosphine and diamine) to study the electronic structure and relative ligation properties of NHCs compared to bisphosphine and diamine ligands. Mayer bond order and charge decomposition analyses indicate that NHC ligands are slightly stronger donor ligands than bisphosphines but also result in a weakening of Co-Cl bonds in a trans-like influence. From MCD and DFT studies, changing the NHC N-substituent has a larger effect on the ligand field of Co(II)-NHC complexes than saturating the backbone. Overall, these studies provide detailed insight into the electronic structure and bonding effects in Co(II) complexes with ligand types commonly explored in catalysis.