Facile cyclometalation reactions of Cp-zirconium complexes with weakly Lewis acidic pendent boron functionalities.
Facile cyclometalation reactions of Cp-zirconium complexes with weakly Lewis acidic pendent boron functionalities.
复制标题
具有弱路易斯酸性硼官能团的 Cp-锆配合物的容易的环金属化反应。
作者：
M. Emmert;G. Kehr;R. Fröhlich;G. Erker
通过B ACHTUNGTRENNUNG（C6 F5）3或功能上相关的主族元素刘易斯酸（例如MAO）从第4族茂金属二甲基络合物中夺取甲基阴离子是均相茂金属齐格勒-纳塔烯烃聚合催化剂中最重要的活化途径。寻找这种反应的分子内版本似乎很诱人。最简单的方法是通过饱和烃系链将合适的刘易斯酸官能团连接到金属茂或相关的第4族金属络合物体系的α（Cp）环上。我们和其他人以前已经表明，这样的双官能系统是很容易获得的烯基官能化的二氯化二茂锆硼氢化。在第4族金属中心具有活性s-烃基配体的相关络合物的化学被证明更具挑战性。先前报道的典型实例包括络合物1和3（参见方案1）。前者被证明是不稳定的关于“自我攻击”的强亲电硼烷对相邻的Cp环。这种亲电芳香取代序列导致清洁形成稳定的两性离子产物2与苯的释放。据报道，双官能配合物3通过一系列烷基夺取反应最终形成4。这些实施例均含有强亲电性B ACHTUNGTRENNUNG（C6 F5）2基团。我们现在已经发现，即使是具有弱得多的9-硼双环ACHTUNGTRENNUNG [3.3.1]壬烷（9 BBN）亲电试剂与Cp环系统连接的系统也显示出相关的反应性。在此，我们希望描述一些选择的代表性实例，主要来自ZrCp 3系列，其显示了这样的连续反应如何在双官能烷基4金属络合物处发生，甚至当弱刘易斯酸性硼烷官能团通过低聚亚甲基系链连接到Cp环时。[Zr ACHTUNGTRENNUNG（烯丙基-Cp）ACHTUNGTRENNUNG（CH 3）ACHTUNGTRENNUNG（Cp 2）]（7）的合成沿着我们先前开发的用于制备母体[Zr ACHTUNGTRENNUNG（CH 3）ACHTUNGTRENNUNG（Cp 3）]络合物的途径。我们已经表明，在合成的早期阶段引入[Zr]-CH 3官能团是有利的。因此，我们用K ACHTUNGTRENNUNG（烯丙基-Cp）试剂6处理起始材料[Zr ACHTUNGTRENNUNG（CH 3）（Cl）ACHTUNGTRENNUNG（Cp 2）]（5）（参见方案2）。从甲苯中处理反应混合物，最终得到官能化的三（Zr）Zr产物7，产率为55%。对配合物7进行了光谱表征（在CD 2Cl 2中的1H NMR：d=0.28/16.3（H/C; [Zr]-CH 3），5.64（s，10 H; Cp），5.25/5.66（AA'BB'，各2 H; C5 H4）、3.19（CH 2）、5.02/ 5.07 ppm（= CH 2）和通过X射线晶体结构分析（单晶由甲苯/庚烷混合物获得[a] Dipl.化学M.埃默特，G博士。凯尔博士Frchlich，Prof. Dr. G. Erker Organisch-Chemisches Institut der Universit t M nster Corrensstr. 40，48149 M nster（德国）传真：（+49）251 -83-36503电子邮件：erker@uni-muenster.de []本作者负责X射线晶体结构分析。本文的支持信息可在WWW上http：//dx.doi.org/10.1002/chem.200900981下获得，并且包含化合物7-18的实验细节和表征。CCDC 721637（10）、-721638（7）和-721639（12）包含本文的补充晶体学数据。这些数据可以通过www.ccdc.cam.ac.uk/data_request/cif从剑桥晶体数据中心免费获得。方案1.
Methyl anion abstraction from group 4 metallocene dimethyl complexes by B ACHTUNGTRENNUNG(C6F5)3 or functionally related maingroup element Lewis acids (e.g. MAO) represents the most important activation pathway in homogeneous metallocene Ziegler–Natta olefin polymerization catalysis. It seemed tempting to search for intramolecular versions of this reaction. The simplest approach would be to attach a suitable Lewis acid functionality to the cyclopentadienyl (Cp) ring of a metallocene or related group 4 metal complex system by means of a saturated hydrocarbon tether. We and others have previously shown that such bifunctional systems are readily obtained by hydroboration of alkenyl-functionalized zirconocene dichlorides. The chemistry of related complexes with active s-hydrocarbyl ligands at the group 4 metal center proved to be more challenging. Typical previously reported examples include complexes 1 and 3 (see Scheme 1). The former turned out to be unstable with regard to “self attack” of the strongly electrophilic borane on the adjacent Cp ring. This electrophilic aromatic substitution sequence resulted in the clean formation of the stable zwitterionic product 2 with liberation of benzene. The bifunctional complex 3 was reported to react by a sequence of alkyl abstraction reactions to eventually form 4. These examples all contained the strongly electrophilic B ACHTUNGTRENNUNG(C6F5)2 group. We have now found that even systems featuring the much weaker 9-borabicycloACHTUNGTRENNUNG[3.3.1]nonane (9BBN) electrophile tethered to a Cp ring system show related reactivities. Herein we wish to describe some selected representative examples, mostly from the ZrCp3 series, that show how general such consecutive reactions take place at bifunctional alkyl group 4 metal complexes, even when a weakly Lewis acidic borane functionality is attached to a Cp ring by an oligomethylene tether. [Zr ACHTUNGTRENNUNG(allyl-Cp)ACHTUNGTRENNUNG(CH3)ACHTUNGTRENNUNG(Cp2)] (7) was synthesized along the pathway that we previously developed for the preparation of the parent [Zr ACHTUNGTRENNUNG(CH3)ACHTUNGTRENNUNG(Cp3)] complex. We have shown that it is advantageous to introduce the [Zr]-CH3 functionality at an early stage in the synthesis. Consequently, we treated the starting material [Zr ACHTUNGTRENNUNG(CH3)(Cl) ACHTUNGTRENNUNG(Cp2)] (5) with the K ACHTUNGTRENNUNG(allyl-Cp) reagent 6 (see Scheme 2). Workup of the reaction mixture from toluene eventually gave the functionalized tris(cyclopentadienyl)Zr product 7 in 55% yield. Complex 7 was characterized spectroscopically (H NMR in CD2Cl2: d=0.28/16.3 ( H/C; [Zr]-CH3), 5.64 (s, 10H; Cp), 5.25/5.66 (AA’BB’, 2H each; C5H4), 3.19 (CH2), 5.02/ 5.07 ppm (=CH2) and by X-ray crystal structure analysis (single crystals were obtained from a toluene/heptane mix[a] Dipl.-Chem. M. Emmert, Dr. G. Kehr, Dr. R. Frchlich, Prof. Dr. G. Erker Organisch-Chemisches Institut der Universit t M nster Corrensstr. 40, 48149 M nster (Germany) Fax: (+49)251-83-36503 E-mail : erker@uni-muenster.de [] This author was responsible for X-ray crystal structure analyses. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200900981, and contains experimental details and characterization of the compounds 7–18. CCDC721637 (10), -721638 (7), and -721639 (12) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Scheme 1.