Musso Janis V, Benedikter Mathis J, Wang Dongren, Frey Wolfgang, Altmann Hagen J, Buchmeiser Michael R
Institute of Polymer Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
Institute of Organic Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
Chemistry. 2020 Jul 17;26(40):8709-8713. doi: 10.1002/chem.202000840. Epub 2020 Jun 25.
The first reversible N-heterocyclic carbene (NHC) induced α-H abstraction in tungsten(VI) imido-dialkyl dialkoxide complexes is reported. Treatment of W(NAr)(CH Ph) (OtBu) (Ar=2,6-dichlorophenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl) with different NHCs leads to the formation of complexes of the type W(NAr)(CHPh)(NHC)(CH Ph)(OtBu) in excellent isolated yields of up to 96 %. The highly unusual release of the tert-butoxide ligand as tBuOH in the course of the reaction was observed. The formed alkylidene complexes and tBuOH are in an equilibrium with the NHC and the dialkyl complexes. Reaction kinetics were monitored by H NMR spectroscopy. A correlation between the steric and electronic properties of the NHC and the reaction rates was observed. Kinetics of a deuterium-labeled complex in comparison to its non-deuterated counterpart revealed the presence of a strong primary kinetic isotope effect (KIE) of 4.2, indicating that α-H abstraction is the rate-determining step (RDS) of the reaction.
首次报道了在钨（VI）亚胺基二烷基二烷氧基配合物中，可逆的N-杂环卡宾（NHC）诱导的α-H夺取反应。用不同的NHC处理W（NAr）（CH₂Ph）（OtBu）₂（Ar = 2,6-二氯苯基、2,6-二甲基苯基、2,6-二异丙基苯基），可得到W（NAr）（CHPh）（NHC）（CH₂Ph）（OtBu）型配合物，分离产率高达96%，非常优异。在反应过程中观察到叔丁醇盐配体以tBuOH形式异常释放。生成的亚烷基配合物和tBuOH与NHC和二烷基配合物处于平衡状态。通过¹H NMR光谱监测反应动力学。观察到NHC的空间和电子性质与反应速率之间存在相关性。与未氘代的对应物相比，氘代配合物的动力学显示出4.2 的强一级动力学同位素效应（KIE），表明α-H夺取是反应的速率决定步骤（RDS）。
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