Fernández Israel, Frenking Gernot
Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Strasse, 35043 Marburg, Germany.
Chemistry. 2007;13(20):5873-84. doi: 10.1002/chem.200601674.
The electronic structure and bonding situation in 21 metallabenzenes (metal=Os, Ru, Ir, Rh, Pt, and Pd) were investigated at the DFT level (BP86/TZ2P) by using an energy decomposition analysis (EDA) of the interaction energy between various fragments. The aim of the work is to estimate the strength of the pi bonding and the aromatic character of the metallacyclic compounds. Analysis of the electronic structure shows that the metallacyclic moiety has five occupied pi orbitals, two with b1 symmetry and three with a2 symmetry, which describe the pi-bonding interactions. The metallabenzenes are thus 10 pi-electron systems. This holds for 16-electron and for 18-electron complexes. The pi bonding in the metallabenzenes results mainly from the b1 contribution, but the a2 contribution is not negligible. Comparison of the pi-bonding strength in the metallacyclic compounds with acylic reference molecules indicates that metallabenzenes should be considered as aromatic compounds whose extra stabilization due to aromatic conjugation is weaker than in benzene. The calculated aromatic stabilization energies (ASEs) are between 8.7 kcal mol(-1) for 13 and 37.6 kcal mol(-1) for 16 which is nearly as aromatic as benzene (ASE=42.5 kcal mol(-1)). The classical metallabenzene model compounds 1 and 4 exhibit intermediate aromaticity with ASE values of 33.4 and 17.6 kcal mol(-1). The greater stability of the 5d complexes compared with the 4d species appears not to be related to the strength of pi conjugation. From the data reported here there is no apparent trend or pattern which indicates a correlation between aromatic stabilization and particular ligands, metals, coordination numbers or charge. The lower metal-C5H5 binding energy of the 4d complexes correlates rather with weaker sigma-orbital interactions.
通过对不同片段间相互作用能进行能量分解分析（EDA），在密度泛函理论（DFT）水平（BP86/TZ2P）下研究了21种金属苯（金属 = Os、Ru、Ir、Rh、Pt和Pd）的电子结构和键合情况。这项工作的目的是估算金属环化合物的π键强度和芳香性。电子结构分析表明，金属环部分有五个占据的π轨道，两个具有b1对称性，三个具有a2对称性，它们描述了π键相互作用。因此，金属苯是10π电子体系。这适用于16电子和18电子配合物。金属苯中的π键主要源于b1贡献，但a2贡献也不可忽略。将金属环化合物与非环参考分子的π键强度进行比较表明，金属苯应被视为芳香化合物，其因芳香共轭产生的额外稳定性比苯中的要弱。计算得到的芳香稳定化能（ASEs）在13时为8.7 kcal mol⁻¹，在16时为37.6 kcal mol⁻¹，几乎与苯一样具有芳香性（ASE = 42.5 kcal mol⁻¹）。经典的金属苯模型化合物1和4表现出中等芳香性，ASE值分别为33.4和17.6 kcal mol⁻¹。与4d物种相比，5d配合物的更大稳定性似乎与π共轭强度无关。从这里报告的数据来看，没有明显的趋势或模式表明芳香稳定化与特定配体、金属、配位数或电荷之间存在相关性。4d配合物较低的金属 - C5H5结合能与较弱的σ轨道相互作用有更大关联。
