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Zirconium catalysis of the asymmetric carboalumination of olefins and the chain growth of aluminum alkyls.

机译：烯烃不对称碳铝的锆催化和烷基铝的链增长。

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摘要

A mechanism based on the competitive inhibition of Michaelis-Menten kinetics has been proposed for the Zr-catalyzed carboalumination of alpha-olefins and the Zr-catalyzed chain growth of aluminum alkyls. In this mechanism AlMe 3 plays two roles. First, it binds to the active catalyst in a rapidly maintained equilibrium to form a Zr/Al heterobimetallic that controls the reactivity of the system by inhibiting polymerization. Second, it acts as a fast transmetallating agent to transfer chains from the active Zr center.;New enantiopure catalysts for the asymmetric carboalumination of olefins have been developed. In the methylalumination of allylbenzene, only modest ee's are observed. The catalysts may be activated for ethylalumination by stirring with AlEt3 and then subsequently adding [Ph3C][B(C 6F5)4] to produce an active green solution. Ethylalumination of allylbenzene proceeds smoothly without side products and in most cases with greater selectivity than the corresponding methylalumination. The greatest enantioselectivity is observed with 4-substituted Me2Si-bridged (bis)indenyl zirconocenes.;The proposed mechanism has been verified by studying the kinetics of both carboalumination and catalyzed chain growth. Both reactions have been shown to be first-order in [olefin] and [catalyst], and inverse first-order in [AlR3], in accordance with the proposed mechanism and rate law. The rapidly maintained equilibrium between Zr/Al heterobimetallic and free zirconium alkyl cation may be quantified by use of a Dixon plot, yielding equilibrium dissociation constants of 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°C in benzene for the catalyst species [rac -(EBI)Zr(micro-Me)2AlMe2+[B(C 6F5)4-], [Cp2Zr(micro-Me) 2AlMe2+][B(C6F5) 4-], and [Me2C(Cp)2Zr(micro-Me) 2AlMe2+][B(C6F5) 4-] respectively. These equilibrium constants are consistent with the observed solution behavior seen for the [Cp2Zr(micro-Me) 2AlMe2+][B(C6F5) 4-] system, for which all the relevant species are observable by 1H NMR. Alternative mechanisms for the Zr-catalyzed carboalumination of olefins involving singly-bridged Zr/Al adducts may be discounted based on kinetics or 1H NMR EXSY experiments.
机译：已经提出了基于竞争性抑制Michaelis-Menten动力学的机理用于Zr催化的α-烯烃碳铝化和Zr催化的烷基铝链增长。在这种机制中，AlMe 3扮演着两个角色。首先，它以快速维持的平衡与活性催化剂结合形成Zr / Al异双金属，通过抑制聚合反应来控制体系的反应性。其次，它是一种快速的金属转移剂，用于从活性Zr中心转移链。;已开发出用于烯烃不对称碳铝化的新型对映体纯催化剂。在烯丙基苯的甲基铝化中，仅观察到适度的ee。可以通过与AlEt3搅拌，然后将[Ph3C] [B（C 6F5）4]加入以生成活性绿色溶液，来活化催化剂进行乙基铝化。烯丙基苯的乙基铝化反应平稳进行，没有副产物，并且在大多数情况下，其选择性都比相应的甲基铝化更高。用4-取代的Me2Si-桥联的（双）茚基锆茂合金观察到最大的对映选择性。通过研究碳铝化和催化链增长的动力学，证实了所提出的机理。根据提出的机理和速率定律，两个反应在[烯烃]和[催化剂]中均显示为一级，在[AlR3]中为逆一级。 Zr / Al杂双金属和游离锆烷基阳离子之间快速维持的平衡可以通过Dixon图来定量，得出平衡解离常数K = 1.1（3）x 10-4 M，4.7（5）x 10-4 M ，并在40°C于7.6（7）x 10-4 M在苯中的催化剂种类[rac-（EBI）Zr（micro-Me）2AlMe2 + [B（C 6F5）4-]，[Cp2Zr（micro-Me） ）2AlMe2 +] [B（C6F5）4-]和[Me2C（Cp）2Zr（micro-Me）2AlMe2 +] [B（C6F5）4-]。这些平衡常数与[Cp2Zr（micro-Me）2AlMe2 +] [B（C6F5）4-]体系中观察到的溶液行为一致，该体系的所有相关物种均可通过1H NMR观察到。基于动力学或1 H NMR EXSY实验，可以不考虑Zr催化的涉及单桥Zr / Al加合物的烯烃碳铝化的其他机理。

著录项

  • 作者

    Camara, James M.;

  • 作者单位

    Columbia University.;

  • 授予单位 Columbia University.;
  • 学科 Chemistry Inorganic.;Chemistry Polymer.;Chemistry Organic.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 127 p.
  • 总页数 127
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

  • 入库时间 2022-08-17 11:38:24

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