Dynamic Mechanically Interlocked Rotaxane and Catenane Catalysts for Isoselective Ring Opening Polymerisation

聚合物由许多重复的小分子组成的长链组成，称为单体。聚合物材料在现代生活中必不可少，在服装、电子和医药等领域有着广泛的应用，因为它们所需的物理和化学性能可以通过仔细选择单体来设计。然而，许多聚合物材料是由不可再生的单体生产的，并且是不可生物降解的，这引起了对其未来制造和处置的严重环境问题。因此，公众和学术界对开发更具环境可持续性的可生物降解聚合物的路线越来越感兴趣。聚合物生产需要催化剂，最常见的是含有金属，以影响单体单元的调节连接以形成聚合物链。催化剂中金属的环境由其周围原子的排列决定，在指定催化剂性能和选择性方面起着关键作用。这种控制对于形成具有明确特性的材料至关重要，例如强度和耐温性，这对任何特定的应用都至关重要。最近的研究表明，将金属引入复杂的分子结构中会显着影响其催化行为。机械互锁的分子由两个组分组成，这两个组分彼此不可分离，但不直接连接，例如类似于链中的链接。以这种方式结合的组分被称为通过机械键连接。互锁组件的强制接近允许它们之间的强大相互作用，这在非互锁结构中是观察不到的。此外，互锁结构的组分的独特三维空间布置可以被设计成形成单体单元结合到其中的主体腔，通过将其置于明确限定的反应环境中来增加其对聚合的潜在反应性。这种互锁催化剂模拟酶的空间限定的活性位点。事实上，一系列互锁结构已被证明是催化活性的，与非互锁催化剂类似物相比，对各种有机反应显示出增强的选择性。尽管如此，除了一个例外，机械键合还没有被用于聚合催化。本项目旨在建立在这些初步结果的基础上，探索机械联锁催化剂的结构与聚合物性能之间的关系，以开发一系列用于形成可持续聚合物的此类催化剂。许多常规催化剂的特征在于多个催化组分，通常通过将两个金属原子结合在刚性框架中，或通过向混合物中添加第二助催化剂。该项目将试图展示一种前所未有的开发机械结合催化剂的策略，其中所有必要的组分都包含在一个分子中。这种独特的方法利用互锁系统的空间限制将催化剂的组件保持在非常接近的位置，而不使用通常在双中心催化剂中发现的刚性框架。此外，对互锁部件的相对接近度的控制可以使得催化能够选择性地打开和关闭，或者使得催化剂的反应性能够按需改变，例如通过屏蔽和暴露催化剂框架上的不同反应性位点。可转换性将允许“设计者聚合物”，促进对聚合物组成和性质的精确控制，以产生源自可再生和可生物降解单体来源的高度期望的聚合物材料。该项目属于EPSRC未来制造，催化和合成超分子化学研究领域的福尔斯。

Polymers consist of long chains comprised from many repeating smaller molecules, known as monomers. Essential in modern life, polymeric materials have extensive applications such as clothing, electronics and medicine, as their desired physical and chemical properties can be engineered by careful monomer selection. However, many polymeric materials are produced from non-renewable monomers and are non-biodegradable, raising serious environmental concerns over their future manufacture and disposal. Consequently, there is mounting public and academic interest in developing more environmentally sustainable routes to biodegradable polymers.Polymer production requires catalysts, most commonly containing metals, to affect regulated linking of the monomer units to form the polymer chain. The environment of the metal in the catalyst, dictated by the arrangement of atoms surrounding it, plays a key role in specifying catalyst performance and selectivity. Such control is essential to form materials with well-defined properties, such as strength and temperature resistance, crucial for any given application.Recent studies demonstrated that incorporating a metal into complex molecular architectures dramatically influences its catalytic behaviour. Mechanically interlocked molecules consist of two components, which are inseparable from each other, but not directly connected e.g. akin to links in a chain. Components bound in this manner are said to be linked by a mechanical bond. The forced proximity of interlocked components allows for powerful interactions between them which are not observed in non-interlocked structures. Furthermore, the unique three-dimensional spatial arrangement of the components of the interlocked structure can be designed to form a host cavity into which a monomer unit binds, increasing its potential reactivity to polymerisation by placing it in a well-defined reactive environment. Such an interlocked catalyst mimics the spatially defined active sites of enzymes. Indeed, a range of interlocked structures have been shown to be catalytically active, displaying enhanced selectivity for various organic reactions compared to non-interlocked catalyst analogues. Despite this, with one exception, mechanical bonding has not been exploited for polymerisation catalysis.This project seeks to build upon on those preliminary results, exploring the relationship between the structure of mechanically interlocked catalysts and polymer properties in order to develop a family of such catalysts for the formation of sustainable polymers. Many conventional catalysts feature multiple catalytic components, typically either by binding two metal atoms in a rigid framework, or through the addition of a second co-catalyst to the mixture. This project will seek to demonstrate an unprecedented strategy of developing mechanically bound catalysts where all requisite components are incorporated in a single molecule. This unique approach uses the spatial constraints of interlocked systems to hold the components of the catalyst in close proximity, without using the rigid frameworks often found in two-centred catalysts. In addition, control over the relative proximity of the interlocked components may enable catalysis to be switched on-and-off selectively or for the reactivity of the catalyst to be modified on-demand, for instance by shielding and exposing different reactive sites on a catalyst framework. Switchability will allow for 'designer polymers', facilitating exquisite control over polymer constitution and properties to produce highly desirable polymeric materials derived from renewable and biodegradable monomer sources. This project falls within the EPSRC Manufacturing the Future, Catalysis and Synthetic Supramolecular Chemistry research areas.