Cedeño D L, Weitz E
Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, USA.
J Am Chem Soc. 2001 Dec 26;123(51):12857-65. doi: 10.1021/ja011643x.
The bond dissociation enthalpy for the Cr-C(2)Cl(4) bond in gas-phase Cr(CO)(5)(C(2)Cl(4)) has been determined to be 12.8 +/- 1.6 kcal/mol using transient infrared spectroscopy. The results of a density functional theory-based energy decomposition analysis are used to quantify the metal-olefin bonding interactions in terms of the bonding description provided by the Dewar-Chatt-Duncanson model (sigma donation and back-bonding). The bond energy decomposition analysis reveals that metal-olefin bond strengths can be strongly influenced by the Pauli repulsion energy and by the energy necessary to deform the olefin and the metal-centered moiety from their equilibrium geometries to their geometry in the final complex. Further, a comparison between the metal-olefin bond strengths and the magnitude of the electronic interactions demonstrates that the energy associated with these deformations is the determining factor in the trends in bond enthalpies in the series of complexes Cr(CO)(5)(C(2)X(4)) (X = H, F, Cl). Though deformation of the Cr(CO)(5) moiety contributes to the overall deformation energy, the major contribution involves deformation of the olefin. This occurs as a consequence of rehybridization of the olefin as a result of metal-olefin back-bonding. The results are discussed in terms of the Dewar-Chatt-Duncanson model, which provides the accepted qualitative description of bonding in organometallic olefin complexes.
利用瞬态红外光谱法测定了气相中Cr(CO)₅(C₂Cl₄) 中Cr-C(2)Cl(4) 键的键解离焓为12.8±1.6千卡/摩尔。基于密度泛函理论的能量分解分析结果，用于根据Dewar-Chatt-Duncanson模型（σ给予和反馈键）提供的键合描述来量化金属-烯烃键合相互作用。键能分解分析表明，金属-烯烃键强度可能会受到泡利排斥能以及使烯烃和以金属为中心的部分从其平衡几何构型变形到最终配合物中的几何构型所需能量的强烈影响。此外，金属-烯烃键强度与电子相互作用大小之间的比较表明，与这些变形相关的能量是配合物系列Cr(CO)₅(C₂X₄)（X = H、F、Cl）中键焓趋势的决定因素。虽然Cr(CO)₅部分的变形对整体变形能有贡献，但主要贡献涉及烯烃的变形。这是由于金属-烯烃反馈键导致烯烃重新杂化的结果。根据Dewar-Chatt-Duncanson模型对结果进行了讨论，该模型提供了有机金属烯烃配合物中键合的公认定性描述。
