Electronic and Steric Parameters of 76 N-Heterocyclic Carbenes in Ni(CO)3(NHC)
Electronic and Steric Parameters of 76 N-Heterocyclic Carbenes in Ni(CO)3(NHC)
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DOI：
10.1021/om900654g
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发表时间：
2009-11-23
期刊：
影响因子：
2.8
通讯作者：
Gusev, Dmitry G.
中科院分区：
文献类型：
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作者：
Gusev, Dmitry G.
我们报道了一组具有代表性的n-杂环碳（NHC）配体的电子给体和空间性质，并用DFT计算进行了量化。本研究提供了Ni(CO)(3)（NHC）的常规TEP数据(Tolman电子参数= nu(CO) (A(1)))，并对76个NHC配体按供体功率增加的顺序进行了排序。TEP数据揭示了NHC环尺寸、取代和环化对其影响的几个一般趋势。计算还提供了CO从Ni(CO)(3)（NHC）配合物中消除和16电子Ni(CO)(2)（NHC）物质形成的反应焓。该反应在很大程度上受空间控制，这允许定义一个新的NHC配体的空间描述符，r（“斥力”）= 10 x (7.568 - 0.003172TEP - 0.0446 δ H)，范围从最小的（ImNH(2)） 0.0到最大的（ImNAd(2)） 8.0。Ni(CO)(3)L和Os(H-2)Cl-2(CO)L-2配合物分别用L = NHC和PR3配体更容易消除CO和H-2。显然，即使是相对较小的NHC配体也有很高的空间要求，n -杂环碳的这种性质可能在配位化学和催化中起重要作用。
We report electron-donor and steric properties of a diverse group of representative N-heterocyclic carbene (NHC) ligands quantified with the help of DFT calculations. This study afforded the conventional TEP data (Tolman electronic parameter = nu(CO) (A(1)) of Ni(CO)(3)(NHC)), which allowed ranking 76 NHC ligands in order of increasing donor power, The TEP data reveal several general trends concerning the influence of NHC ring size, substitution, and annulation. The calculations also provided reaction enthalpies for CO elimination from the Ni(CO)(3)(NHC) complexes and formation of the 16-electron Ni(CO)(2)(NHC) species. This reaction is largely under steric control, which allowed defining a new steric descriptor for NHC ligands, r ("repulsiveness") = 10 x (7.568 - 0.003172TEP - 0.0446 Delta H), ranging from 0.0 for the smallest (ImNH(2)) to 8.0 for the most repulsive carbene (ImNAd(2)) of this work. Ni(CO)(3)L and Os(H-2)Cl-2(CO)L-2 complexes eliminate CO and H-2, respectively, more readily With L = NHC vs PR3 ligands. Apparently, even relatively small NHC ligands are very sterically demanding, and this property of N-heterocyclic carbenes may play a major role in coordination chemistry and catalysis.