Zirconium-Catalyzed Carboalumination of α-Olefins and Chain Growth of Aluminum Alkyls: Kinetics and Mechanism
Zirconium-Catalyzed Carboalumination of α-Olefins and Chain Growth of Aluminum Alkyls: Kinetics and Mechanism
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DOI：
10.1021/ja104032w
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发表时间：
2011-04-13
影响因子：
15
通讯作者：
Norton, Jack R.
中科院分区：
文献类型：
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作者：
Camara, James M.;Petros, Robby A.;Norton, Jack R.
提出了zr催化α -烯烃碳铝化反应和zr催化乙烯生成烷基铝链的micelis - menten动力学机制。研究了[(EBI)Zr(mu-Me)(2)AlMe2][B(C6F5)(4)]催化下的碳铝化反应和链生长动力学。在[烯烃]和[催化剂]中均为一级反应，在[AlR3]中为反一级反应。用Dixon图量化了各种Zr/Al杂金属化合物与相应的锆甲基阳离子之间的平衡位置，在苯中40℃时，催化剂种类[rac-(EBI)Zr(mu-Me)(2)AlMe2][B(C6F5)(4)], [Cp2Zr(mu-Me)(2)AlMe2] [B(C6F5)(4)]和[Me2C(Cp)(2)Zr(mu-Me)(2)AlMe2] [B(C6F5)(4)]分别得到K = 1.1(3) × 10(-4) M, 4.7(5) × 10(-4) M和7.6(7)× 10(-4) M。这些平衡常数与[Cp2Zr(mu-Me)(2)AlMe2] [B(C6F5)(4)]体系的溶液行为一致，其中所有相关的物质都是通过H-1 NMR观察到的。基于动力学和/或H-1 NMR EXSY实验，对涉及单桥Zr/Al加成物的Zr催化烯烃碳铝化的替代机制进行了否定。
A mechanism based on Michaelis-Menten kinetics with corn petitive inhibition is proposed for both the Zr-catalyzed carboalumination of alpha-olefins and the Zr-catalyzed chain growth of aluminum alkyls from ethylene. AlMe3 binds to the active catalyst in a rapidly maintained equilibrium to form a Zr/Al heterobimetallic, which inhibits polymerization and transfers chains from Zr to Al. The kinetics of both carboalumination and chain growth have been studied when catalyzed by [(EBI)Zr(mu-Me)(2)AlMe2][B(C6F5)(4)]. In accord with the proposed mechanism, both reactions are first-order in [olefin] and [catalyst] and inverse first-order in [AlR3]. The position of the equilibria between various Zr/Al heterobimetallics and the corresponding zirconium methyl cations has been quantified by use of a Dixon plot, yielding K = 1.1(3) x 10(-4) M, 4.7(5) x 10(-4) M, and 7.6(7) x 10(-4) M at 40 degrees C in benzene for the catalyst species [rac-(EBI)Zr(mu-Me)(2)AlMe2][B(C6F5)(4)], [Cp2Zr(mu-Me)(2)AlMe2] [B(C6F5)(4)], and [Me2C(Cp)(2)Zr(mu-Me)(2)AlMe2] [B(C6F5)(4)] respectively. These equilibrium constants are consistent with the solution behavior observed for the [Cp2Zr(mu-Me)(2)AlMe2] [B(C6F5)(4)] system, where all relevant species are observable by H-1 NMR. Alternative mechanisms for the Zr-catalyzed carboalumination of olefins involving singly bridged Zr/Al adducts have been discounted on the basis of kinetics and/or H-1 NMR EXSY experiments.