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首页> 外文期刊>Organometallics >Mechanistic Investigation of Cycloreversion/Cycloaddition Reactions between Zirconocene Metallacycle Complexes and Unsaturated Organic Substrates
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Mechanistic Investigation of Cycloreversion/Cycloaddition Reactions between Zirconocene Metallacycle Complexes and Unsaturated Organic Substrates

机译：锆茂金属茂配合物与不饱和有机底物之间的回旋/加成反应机理研究

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摘要

Treatment of the diazametallacycle Cp2Zr(N(t-Bu)C=N(SiMe3)N(SiMe3? (4a) with diphe- nylacetylene resulted in the formation of the azametallacyclobutene Cp2Zr(N(t-Bu)C(Ph)= C(Ph? (6a) and Me3SiN=C=NSiMe3 in high yield. A kinetic study using UV -vis spectroscopy was carried out on the transfonnation. Saturation kinetic behavior was observed for the system, which is supportive of a mechanism that involves a reversible formal [2 + 2] retrocycloaddition of 4a to generate the transient imido species Cp2Zr=N-t-Bu (7a) and Me3- SiN=C=NSiMe3. Trapping 7a with diphenylacetylene in an overall [2 + 2] cycloaddition reaction affords zirconacycle 6a. The study of cycloreversion/cycloaddition reactions between diazametallacycle complexes and diphenylacetylene was extended to other zirconocene systems. Detailed kinetic studies were performed for the exchange reactions between the diazametallacycle complexes Cp2Zr(N(2,6-Me2Ph)C=N(SiMe3)N(SiMe3? (8a) and Cp2Zr- (N(2,6-Me2Ph)C=N(t-Bu)N(t-Bu? (8b) with diphenylacetylene (5a) to give the corresponding azametallacyclobutene complex Cp2Zr(N(2,6-Me2Ph)C(Ph)=C(Ph? (6c) and extruded car- bodiimides (Me3SiN=C=NSiMe3 for 8a and (t-Bu)N=C=N(t-Bu) for 8b). For both systems, the reactions were found to be first order in metallacycle and zero order in alkyne. Treatment of the diazametallacycle complexes Cp2Zr(N(2,6-i-Pr2Ph)C=N(Cyc)N(Cyc? (9a) and Cp2Zr- (N(2,6-i-Pr2Ph)C=N(i-Pr2)N(i-Pr2? (9b) with alkyne 5a resulted in the formation of the six- membered zirconacycles lOa,b, respectively, upon heating at 75 °C. The products lOa,b are generated from the overall insertion of alkyne 5a into the nitrogen-carbon bond of the zirconium-containing diazacyclobutane. Complex lOa has been characterized by an X-ray crystallographic study. When the azacyclobutene Cp2Zr(N(2,6-i-Pr2Ph)C(Ph)=C(Ph? (6e) was treated with CycN=C=NCyc or (i-Pr)N=C=N(i-Pr), the same six-membered zirconacycle complexes lOa,b were obtained. Kinetic analysis of the reaction of6e and (i-Pr)N=C=N(i- Pr) to yield lOb supports an associative process wherein alkyne 5a directly inserts into the zirconium -carbon bond of 6e. The diazametallacycle complex 4a underwent a stoichiometric metathetical exchange with symmetrical carbodiimides RN=C=NR (R = p-Tol, m-Tol, i-Pr, Cyc) to generate new cyclic zirconocene complexes and Me3SiN=C=NSiMe3. Kinetic studies were carried out on the exchange reaction between 4a and (m-Tol)N=C=N(m-Tol) to form 4e and Me3SiN=C=NSiMe3. The experimental rate data obtained are consistent with a dissociative mechanism. Additionally, the saturation rate constant derived for this system from the data is the same (within experimental error) as the saturation rate constant obtained from the kinetic study of4a and diphenylacetylene to form 6a and Me3SiN=C=NSiMe3. These findings provide additional support for a dissociative mechanistic pathway in the exchange reactions, since the rate constant in the formal [2 + 2] retrocycloaddition reaction to generate imidozirconocene species Cp2Zr=N-t-Bu (7a) and Me3SiN=C=NSiMe3 should be the same for both reactions.
机译：用二苯乙炔处理二氮杂金属环Cp2Zr（N（t-Bu）C = N（SiMe3）N（SiMe3？（4a））导致形成氮杂金属环丁烯Cp2Zr（N（t-Bu）C（Ph）= C （Ph？（6a）和Me3SiN = C = NSiMe3高收率。对紫外光进行了动力学研究，采用紫外可见光谱。观察到该系统的饱和动力学行为，这支持了涉及可逆机制的机理。正式的[2 + 2] 4a逆向加成生成瞬态亚胺基物种Cp2Zr = Nt-Bu（7a）和Me3-SiN = C = NSiMe3。在整个[2 + 2]环加成反应中用二苯乙炔捕获7a得到了氧化锆环6a。将二氮杂金属环配合物与二苯乙炔之间的环还原/环加成反应的研究扩展到其他锆茂体系，并对二氮杂金属环配合物Cp2Zr（N（2,6-Me2Ph）C = N（SiMe3）N（ SiMe3？（8a）和Cp2Zr-（N（2,6-Me2Ph）C = N（t-Bu）N（t-Bu？（8b），含二苯乙炔（5a），得到相应的氮杂金属环环丁烯络合物Cp2Zr（N（2,6-Me2Ph）C（Ph）= C（Ph？ （6c）和挤出的碳二亚胺（对于8a，Me3SiN = C = NSiMe3，对于8b，（t-Bu）N = C = N（t-Bu））。对于这两个系统，发现在金属环烷中反应是一级，在炔烃中是零级。二氮杂金属环配合物Cp2Zr（N（2,6-i-Pr2Ph）C = N（Cyc）N（Cyc？（9a）和Cp2Zr-（N（2,6-i-Pr2Ph）C = N（i- Pr2）N（i-Pr2α（9b）与炔烃5a的混合物在75°C加热时分别形成六元氧化锆环10a，b。产物10a，b是由炔烃的整体插入而产生的通过X射线晶体学研究对配合物10a进行了表征，当氮杂环丁烯Cp2Zr（N（2,6-i-Pr2Ph）C（Ph）= C（Ph用CycN ＝ C ＝ NCyc或（i-Pr）N ＝ C ＝ N（i-Pr）处理α（6e），得到相同的六元氧化锆环配合物10a，b。生成10b的i-Pr）N = C = N（i-Pr）支持了缔合过程，其中炔烃5a直接插入6e的锆-碳键中。二氮杂金属环配合物4a与对称碳二亚胺进行了化学计量的易位交换RN = C = NR（R = p-Tol，m-Tol，i-Pr，Cyc）生成新环状锆茂配合物，Me3SiN = C = NSiMe3。动力学研究了4a与（m-Tol）N = C = N（m-Tol）之间形成4e和Me3SiN = C = NSiMe3的交换反应。获得的实验速率数据与解离机理一致。此外，从该数据得出的该系统的饱和速率常数与实验研究中的饱和速率常数相同（在实验误差范围内），该饱和速率常数是从4a和联苯乙炔形成6a的动力学研究中获得的，Me3SiN = C = NSiMe3。这些发现为交换反应中的离解机制途径提供了额外的支持，因为在正式的[2 + 2]逆向加成反应中生成咪唑并新世物种Cp2Zr = Nt-Bu（7a）和Me3SiN = C = NSiMe3的速率常数应为两种反应都一样。

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