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The nature of the indenyl effect

机译：茚基效应的性质

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The #eta#~5-to-#eta#~3 coordination shift of cyclopentadienyl (Cp=C_5C_5~-) and indenyl(Ind=C_9H_7~-)ligands in molybdenocene complexes,[(#eta#~5-Cp')-(##eta~5-Cp)Mo(CO)_2]~(2+)(Cp'=Cp or Ind),driven by a two-electron reduction of those species,was studied and compared by means of molecular orbital calaclations (B3LYP HF/DFT hybrid functional,DZP basis sets).The results obtained,in terms of optimized geometries,relative energies,and bond analysis parameters,compare well with the experimental data,and verify the well-known indenyl effect,that is,a significantly more facile #eta#~5-to-#eta#~3 rearrangement for the indenyl ligand when compared to cyclopentadienyl.However,the study of the folding of free Cp and Ind,combined with thd (#eta#~(5/3)-Cp')-M bond analysis,shows that the observed difference is not the result of an intrinsic characteristic of the indenyl ligand,such as the traditionally accepted aromaticity gain in the benzene ring formed in #eta#~3-Ind complexes.Instead,it is directly related to the Cp'-M bond strength.While the difference in the energy required to fold the two free ligands is negligible(<=1 kcalmol~(-1) for folding angles up to 20deg),the (#eta#~5-Cp)-M;however,the opposite situation is found for the #eta#~5 complexes and a stabilization of the #eta#~3 intermediates of transition states yielding smaller activation energies and faster reaction rates for processes in which that is the rate-determining step.
机译：茂金属茂配合物中环戊二烯基（Cp = C_5C_5〜-）和茚基（Ind = C_9H_7〜-）配体的＃eta＃〜5至＃eta＃〜3配位移位[（＃eta＃〜5-Cp'）通过分子轨道研究和比较了由这些物质的双电子还原驱动的-（## eta〜5-Cp）Mo（CO）_2]〜（2 +）（Cp'= Cp或Ind） （B3LYP HF / DFT杂化功能，DZP基集）。获得的结果在优化的几何形状，相对能量和键分析参数方面均与实验数据相符，并验证了众所周知的茚基效应，即，与环戊二烯基相比，茚基配体的＃eta＃〜5-to-＃eta＃〜3重排明显更容易。但是，结合Cd（＃eta＃〜（ 5/3）-Cp'）-M键分析表明，观察到的差异不是茚基配体固有特征的结果，例如＃eta＃〜3-苯环中传统上公认的芳香性增加Ind complexs。相反，它是dir与Cp'-M键的强度密切相关。折叠两个游离配体所需的能量差异可以忽略不计（对于小于20度的折叠角，<= 1 kcalmol〜（-1）），（＃eta＃〜 5-Cp）-M;但是，发现＃eta＃〜5配合物的相反情况和过渡状态的＃eta＃〜3中间体的稳定化产生了较小的活化能和更快的反应速率，其中速率确定步骤。

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