Zirconium-mediated metathesis of imines: a study of the scope, longevity, and mechanism of a complicated catalytic system.
Zirconium-mediated metathesis of imines: a study of the scope, longevity, and mechanism of a complicated catalytic system.
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DOI：
10.1021/ja992869r
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发表时间：
2000-02
影响因子：
15
通讯作者：
Rebecca L. Zuckerman;S. Krska;Robert G. Bergman
中科院分区：
文献类型：
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作者：
Rebecca L. Zuckerman;S. Krska;Robert G. Bergman
通过使用立体要求高的配体来动态稳定亚硝基二茂配合物，或者通过添加二苯基乙炔来产生更热动力学稳定的静息状态，我们开发了过渡金属催化的亚胺复分解反应，其机理类似于由金属羰基配合物催化的烯烃复分解反应。以5 mol %的Cp*Cp(THF)Zr=N(t)Bu为催化剂前驱体，在PhCH=NPh和p-TolCH=N-p- tol之间的复分解反应中，在105℃的C(6)D(6)中生成了两种混合亚胺p-TolCH=NPh和PhCH=N-p- tol的1:1:1:1平衡混合物。TON = 1.77 h(-1))。以氮杂金属环丁烯Cp(2)Zr(N(Tol)C（Ph)=C(Ph)）为催化剂前驱体，在相同的反应条件下，经过4天（t(1/2) 170 m）共得到410次反应；TON = 4.3 h(-1))。通过监测亚胺和可观察到的含金属中间体的浓度，对金属环丁烯催化的PhCH=N-p-Tol和p-F-C(6)H(4)CH=N-p-F-C(6)H(4)的转化进行了广泛的动力学和平衡分析。采用数值积分方法将这些数据拟合为涉及配位不饱和（16电子）亚胺配合物作为关键中间体的详细机制。不同有机亚胺之间的反应范围的检查揭示了特征选择性似乎是独特的锆介导体系。几种原位生成具有催化活性的“CpCp’zr =NAr”（Cp’= Cp或Cp*）的锆新统配合物是不同n -芳基亚胺之间的有效交换剂。n -烷基醛胺被发现与n -芳基醛胺完全不反应，涉及两种n -烷基亚胺（TolCH=NPr和PhCH=NMe）的复分解反应产生缓慢或不稳定的结果，取决于所使用的催化剂。在n -芳基酮胺和n -芳基醛二胺之间观察到复分解，但对于n -芳基酮胺底物，催化剂的静息状态是由氯胺酮底物α位置的正式C-H活化产生的锆新世漆胺配合物。
By kinetically stabilizing imidozirconocene complexes through the use of a sterically demanding ligand, or by generating a more thermodynamically stable resting state with addition of diphenylacetylene, we have developed transition metal-catalyzed imine metathesis reactions that are mechanistically analogous to olefin metathesis reactions catalyzed by metal carbene complexes. When 5 mol % of Cp*Cp(THF)Zr=N(t)Bu is used as the catalyst precursor in the metathesis reaction between PhCH=NPh and p-TolCH=N-p-Tol, a 1:1:1:1 equilibrium mixture with the two mixed imines p-TolCH=NPh and PhCH=N-p-Tol is generated in C(6)D(6) at 105 degrees C. The catalyst was still active after 20 days with an estimated 847 turnovers (t(1/2) 170 m; TON = 1.77 h(-1)). When the azametallacyclobutene Cp(2)Zr(N(Tol)C(Ph)=C(Ph)) is used as the catalyst precursor under similar reaction conditions, a total of 410 turnovers are obtained after 4 days (t(1/2) 170 m; TON = 4.3 h(-1)). An extensive kinetic and equilibrium analysis of the metallacyclobutene-catalyzed metathesis of PhCH=N-p-Tol and p-F-C(6)H(4)CH=N-p-F-C(6)H(4) was carried out by monitoring the concentrations of imines and observable metal-containing intermediates over time. Numerical integration methods were used to fit these data to a detailed mechanism involving coordinatively unsaturated (16-electron) imido complexes as critical intermediates. Examination of the scope of reaction between different organic imines revealed characteristic selectivity that appears to be unique to the zirconium-mediated system. Several zirconocene complexes that could generate the catalytically active "CpCp'Zr=NAr" (Cp' = Cp or Cp*) species in situ were found to be effective agents in the metathetical exchange between different N-aryl imines. N-Alkyl aldimines were found to be completely unreactive toward metathesis with N-aryl aldimines, and metathesis reactions involving the two N-alkyl imines TolCH=NPr and PhCH=NMe gave slow or erratic results, depending on the catalyst used. Metathesis was observed between N-aryl ketimines and N-aryl aldimines, but for N-aryl ketimine substrates, the catalyst resting state consists of zirconocene enamido complexes, generated by the formal C-H activation of the alpha position of the ketimine substrates.