When Does Carbonylation of Carbenes Yield Ketenes? A Theoretical Study with Implications for Synthesis
When Does Carbonylation of Carbenes Yield Ketenes? A Theoretical Study with Implications for Synthesis
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DOI：
10.1021/ja109812r
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发表时间：
2011-03-16
影响因子：
15
通讯作者：
Frenking, Gernot
中科院分区：
文献类型：
--
作者：
Goedecke, Catharina;Leibold, Michael;Frenking, Gernot
用密度泛函理论和从头算方法对32个不同类型的卡宾RR`C和相应的烯酮RR`C=C=O进行了量子化学计算。计算出的卡宾的单重态-三重态能隙Delta ES-T与乙烯酮的键解离能（BDE）表现出非常高的相关性。使用卡宾和CO的三重态作为相互作用片段的RR`C-CO键的能量分解分析支持Delta ES-T作为BDE的主导因素的分配，但也表明卡宾的特定相互作用有时可以补偿S/T间隙。相互作用能Δ E-int值的变化趋势主要取决于卡宾与CO之间的Pauli排斥作用。氨基取代烯酮的稳定性强烈依赖于氮孤对轨道与烯酮双键之间的不稳定共轭。不饱和N-杂环卡宾母体化合物NHC 1具有烯酮结构，CO作为势能面上的局部能量最小值。然而，化合物NHC 1-CO对于解离是热稳定的。饱和同系物NHC 2-CO只有很小的键离解能D-e = 3.2 kcal/mol。[3]二茂铁并吩型化合物FeNHC-CO的BDE为D-e = 16.0 kcal/mol。
Quantum-chemical calculations using DFT and ab initio methods have been carried out for 32 carbenes RR`C which comprise different classes of compounds and the associated ketenes RR`C=C=O. The calculated singlet-triplet gaps Delta ES-T of the carbenes exhibit a very high correlation with the bond dissociation energies (BDEs) of the ketenes. An energy decomposition analysis of the RR`C-CO bond using the triplet states of the carbene and CO as interacting fragments supports the assignment of Delta ES-T as the dominant factor for the BDE but also shows that the specific interactions of the carbene may sometimes compensate for the S/T gap. The trend of the interaction energy Delta E-int values is mainly determined by the Pauli repulsion between the carbene and CO. The stability of amino-substituted ketenes strongly depends on the destabilizing conjugation between the nitrogen lone-pair orbital and the ketene double bonds. There is a ketene structure of the unsaturated N-heterocyclic carbene parent compound NHC1 with CO as a local energy minimum on the potential-energy surface. However, the compound NHC1-CO is thermodynamically unstable toward dissociation. The saturated homologue NHC2-CO has only a very small bond dissociation energy of D-e = 3.2 kcal/mol. The [3]ferrocenophanetype compound FeNHC-CO has a BDE of D-e = 16.0 kcal/mol.