The electronic structure of a β-diketiminate manganese hydride dimer
The electronic structure of a β-diketiminate manganese hydride dimer
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β-二酮亚胺氢化锰二聚体的电子结构
DOI：
10.1039/d0dt02842h
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发表时间：
2020
影响因子：
4
通讯作者：
Baik, Mu-Hyun
中科院分区：
文献类型：
--
作者：
Oh, Changjin;Siewe, Joëlle;Nguyen, Thao T.;Kawamura, Airi;Flores, Marco;Groy, Thomas L.;Anderson, John S.;Trovitch, Ryan J.;Baik, Mu-Hyun
用密度泛函理论研究了β-二酮酸配体[(2,6- ipr2phbdi)Mn(μ-H)]2负载的二聚体氢化锰催化剂的电子结构。从简单的电子计数规则可以预测锰中心之间的三键；然而，计算表明，在铁磁耦合和反铁磁耦合极值下，Mn-Mn的Mayer键阶分别为0.21和0.27。根据实验确定的−15±0.1 cm−1 （SQUID）和−10.2±0.7 cm−1 （EPR）的海森堡交换耦合常数，计算得到的J0值为−10.9 cm−1，证实了基态涉及高自旋Mn(II)-d5中心之间的反铁磁耦合。空间体积对键序的影响通过对β-二酮酸配体的最小空间要求版本的模型研究进行了检验，发现可以忽略不计。金属基轨道和β-二氯胺盐基轨道之间的混合被发现是导致金属-金属多键缺失的原因。桥接氢化物导致金属中心位置相对较近，而具有2p轨道的桥接原子导致Mn-Mn距离较长和更稳定的二聚体。桥接氢氧化物变体[(2,6- ipr2phbdi)Mn(μ-OH)]2的合成和表征为上述评价提供了实验支持。
The electronic structure of a dimeric manganese hydride catalyst supported by β-diketiminate ligands, [(2,6-iPr2PhBDI)Mn(μ-H)]2, was investigated with density functional theory. A triple bond between the manganese centres was anticipated from simple electron-counting rules; however, calculations revealed Mn–Mn Mayer bond orders of 0.21 and 0.27 for the ferromagnetically-coupled and antiferromagnetically-coupled extremes, respectively. In accordance with experimentally determined Heisenberg exchange coupling constants of −15 ± 0.1 cm−1 (SQUID) and −10.2 ± 0.7 cm−1 (EPR), the calculated J0 value of −10.9 cm−1 confirmed that the ground state involves antiferromagnetic coupling between high spin Mn(II)-d5 centres. The effect of steric bulk on the bond order was examined via a model study with the least sterically-demanding version of the β-diketiminate ligand and was found to be negligible. Mixing between metal- and β-diketiminate-based orbitals was found to be responsible for the absence of a metal–metal multiple bond. The bridging hydrides give rise to a relatively close positioning of the metal centres, while bridging atoms possessing 2p orbitals result in longer Mn–Mn distances and more stable dimers. The synthesis and characterization of the bridging hydroxide variant, [(2,6-iPr2PhBDI)Mn(μ-OH)]2, provides experimental support for these assessments.