School of Chemistry and Chemical Engineering, Key Laboratory of Mesoscopic Chemistry of Ministry of Education, Institute of Theoretical and Computational Chemistry, Nanjing University, Nanjing 210093, PR China.
Inorg Chem. 2010 Apr 5;49(7):3361-9. doi: 10.1021/ic902418v.
Density functional theory calculations have been performed to investigate the molecular mechanism of the hydrogenation reactions of 1,1-diphenylethylene and myrcene catalyzed by the actual calcium hydride catalyst, CaH(dipp-nacnac)(thf) (dipp-nacnac = CH{(CMe)(2,6-iPr(2)-C(6)H(3)N)}(2)). The hydrogenation reactions of these two alkenes proceed via a similar pathway, which includes three steps. First, the hydride migrates from the calcium center to one olefinic carbon in the substrate. Then, the hydride transfer product can easily transform into a key ion-pair intermediate. This intermediate provides an intramolecular frustrated Lewis pair, in which the calcium center acts as a Lewis acid, and one olefinic carbon acts as a Lewis base. Next, the H-H bond is heterolytically cleaved by this frustrated Lewis pair through a concerted Lewis acid-Lewis base mechanism, producing the hydrogenation product and regenerating the catalyst. For these two reactions, the rate-limiting step is the hydride transfer step, with free energy barriers of 29.2 kcal for both substrates. In addition, our calculations indicate that the hydrogenation reaction of 1,1-diphenylethylene catalyzed by the analogous strontium hydride complex may readily occur, but the similar magnesium-mediated hydrogenation reaction is less likely to take place under similar conditions as adopted by the calcium hydride catalyst. The results can give satisfactory descriptions of experimental facts observed for these two hydrogenation reactions. The hydrogenation mechanism proposed here is different from that of the late transition metal-catalyzed alkene hydrogenation or the organolanthanide-catalyzed alkene hydrogenation.
运用密度泛函理论计算研究了实际氢化钙催化剂 CaH(dipp-nacnac)(thf)（dipp-nacnac=CH{(CMe)(2,6-iPr(2)-C(6)H(3)N)}(2)）催化下 1,1-二苯基乙烯和桃金娘烯的加氢反应的分子机理。这两种烯烃的加氢反应通过相似的途径进行，包括三个步骤。首先，氢化物从钙中心迁移到底物中的一个烯属碳上。然后，氢化物转移产物可以很容易地转化为关键的离子对中间体。这种中间体提供了一个分子内受阻路易斯对，其中钙中心充当路易斯酸，一个烯属碳充当路易斯碱。接下来，H-H 键通过受阻路易斯对通过协同路易斯酸-路易斯碱机制异裂，生成加氢产物并再生催化剂。对于这两个反应，速控步骤是氢化物转移步骤，对于两种底物，自由能垒均为 29.2 kcal/mol。此外，我们的计算表明，类似的锶氢化物配合物催化的 1,1-二苯基乙烯加氢反应可能很容易发生，但类似的镁介导的加氢反应在类似的条件下不太可能发生，如氢化钙催化剂所采用的条件。这些结果可以对这两种加氢反应的实验事实给出满意的描述。所提出的加氢机理与后期过渡金属催化的烯烃加氢或有机镧系金属催化的烯烃加氢不同。
