Organometallic Reactivity of Metal-Centered Radicals

该奖项是由宾夕法尼亚大学化学系Bradford B.Wayland博士在无机化学、生物无机化学和金属有机化学项目中颁发的，用于支持金属促进的烯烃聚合机理的研究。将追求三个目标。首先，金属有机物种(M-R)将与以金属为中心的自由基和有机自由基形成平衡，从而为评估有机-金属键均解的热力学参数提供了一种直接的方法。其次，将研究链转移催化(CTC)的细节，它控制聚合物的相对分子质量并引入端基烯烃官能团。一系列具有最低配体空间需求和不同M-H键焓的持久性金属配合物将被设计用于不同类别的烯烃单体的CTC中。将确定影响金属自由基物种在快速氢自由基提取和M-H与烯烃快速加成中的有效性的因素。最后，研究了有机金属络合物在引发和控制烯烃活性自由基聚合(LRP)中的作用。LRP是一种生产低多分散性均聚物和需要自由基引发的烯烃嵌段共聚物的方法。有机钴四硫基卟啉配合物引发和控制了丙烯酸酯的LRP反应，并为建立促进LRP过程的金属络合物设计的指导标准提供了原型。配体和聚合物自由基的空间需求将被用来阻止金属中心自由基和聚合物自由基达到β-氢提取的过渡态，金属中心自由基的持久自由基效应有望抑制聚合物自由基的双分子终止。几个系列的持久性金属化合物将在合成不同类别的烯烃方面进行有效性测试。为了解决环境问题以及产品分离和催化剂回收的实际考虑，将合成一系列水溶性和聚合物负载型催化剂。聚烯烃是重要的工业产品。这项研究将开发一种合理的方法来合成各种聚烯烃，并可能导致新的结构定义的嵌段共聚物，具有未知的材料性能。参与这项研究的学生不仅将学习涉及无机化学和有机化学的复杂方法，还将了解与能源相关的研究、聚合物化学、催化和材料科学中的主要问题和挑战。

This award in the Inorganic, Bioinorganic, and Organometallic Chemistry program supports research on the mechanism of metal-promoted olefin polymerization by Dr. Bradford B. Wayland, Chemistry Department, University of Pennsylvania. Three goals will be pursued. First, organometallic species (M-R) will be formed in equilibrium with metal-centered and organic radicals to enable a direct method for evaluating thermodynamic parameters for organo-metal bond homolysis. Second, the details of chain transfer catalysis (CTC), which controls polymer molecular weight and introduces end group alkene functionality, will be studied. A series of persistent metalloradical complexes with minimum ligand steric demands and varying M-H bond enthalpies will be designed for application in CTC for different classes of olefin monomers. Factors responsible for the effectiveness of metallo-radical species in fast hydrogen radical abstraction and rapid addition of M-H to olefins will be determined. Finally, the role of organometallic complexes in initiating and controlling living radical polymerization (LRP) of olefins will be investigated. LRP is an approach to producing low polydispersity homopolymers and block copolymers of olefins that requires radical initiation. Organocobalt tetramesityl porphyrin complexes initiate and control LRP of acrylates and provide a prototype for establishing guideline criteria for the design of metal complexes that promote LRP processes. Ligand and polymeric radical steric demands will be used to prevent metal-centered radicals and polymeric radicals from achieving the transition state for beta-hydrogen abstraction and the persistent radical effect of metal-centered radicals is expected to suppress bimolecular termination of polymeric radicals. Several series of persistent metalloradicals will be tested for effectiveness in the synthesis of different classes of olefins. A series of water soluble and polymer supported catalysts will be synthesized to address environmental issues and the practical considerations of product separation and catalyst recovery.Polyolefins are important commercial products. This research will develop a rational approach to the synthesis of various polyolefins and potentially result in new structurally defined block copolymers with unexplored material properties. Students involved in the study will learn not only sophisticated methods involving inorganic and organic chemistry, but will be introduced to major issues and challenges in energy-related research, polymer chemistry, catalysis and materials science.