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Photocatalysis in coordination cages using supramolecular arrays of chromophores

使用发色团超分子阵列在配位笼中进行光催化

基本信息

批准号：
EP/R03382X/1
负责人：
Mike Ward
金额：
$ 60.39万
依托单位：
University of Warwick
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2018
资助国家：
英国
起止时间：
2018 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FR03382X%2F1
关键词：
Photocatalysis coordination cages using supramolecular

项目摘要

The use of light to cause chemical reactions is well established and, from a renewable energy perspective, of fundamental importance. A recently-developed way in which this can be made to happen is via 'photo-redox catalysis'. A metal complex catalyst, or an organic catalyst, absorbs light to enter an high-energy excited state which persists for hundreds / thousands of nanoseconds; this can then donate an electron to (or accept an electron from) a substrate, generating a radical anion (or cation) which then undergoes the desired reaction. In the last 10 years this use of the photophysical properties of simple light-absorbing species with appropriate excited states has become a well-established tool in synthetic chemistry.In this project we wish to take this principle to a much higher level by using coordination cages - hollow, pseudo-spherical metal/ligand assemblies with large central cavities that can accommodate small molecule 'guests' - as multi-component catalysts. The cages contain large numbers of metal and ligand components built into their superstructure in a regular array surrounding the central cavity. They can be prepared in such a way that they contain large numbers of metal complex catalysts or organic catalyst units in the superstructure. In the largest cages of the type that we will prepare, 24 individual aromatic luminescent units can be incorporated into a single cage-like assembly surrounding a central cavity which a 'guest' molecule will bind. Having 24 potential photo-redox catalysts surrounding a single reactive species could would be almost impossible to achieve in any other way.The aim is to see if, when a potential substrate (reactant) is bound inside the central cavity of one of the cages, it undergoes a photo-redox catalytic transformation far more effectively than when it is free in solution where it has to collide randomly with the catalyst in the short space of time that the catalyst excited state exists. Binding the substrate in the cage cavity removes the requirement for chance collisions of separate species in solution by holding the guest very close to a high local concentration of catalyst units, such that electron transfer will be very fast and hence the catalysis should be much faster and more efficient. In addition, because the cage cavities show size- and shape-selectivity for the guests that they bind, the cage-based catalysts should show much higher selectivity for specific substrates allowing one substrate from a mixture to be selected, bound, transformed and ejected form the cavity whilst others are unaffected. Success here will result in a new generation of photo-redox catalysts, based on supramolecular host/guest principles, that are far more effective than the current ones.In addition, the exciting possibility exists that - given a single molecule of a substrate surrounded by a large number of potential electron-donors - two electrons could be transferred essentially simultaneously to a single guest to give a doubly-reduced product. This is extremely difficult to achieve normally because of the unlikelihood of one substrate molecule colliding with two one-electron catalyst molecules while they are both in their short-lived excited state; an analogy would be like trying to hit a flying clay target with two rifle bullets simultaneously. However the very high local concentration of large numbers of chromophores around each bound guest makes this much more statistically likely, such that two-electron photocatalysis may become a reality in a wide range of cage/guest systems. This is of fundamental importance for solar energy harvesting as many of the important reactions involved in either water splitting to generate H2 fuel, or fixation of CO2 to generate methanol as a fuel, require simultaneous transfer of two electrons: use of coordination cages as multi-electron photo-redox catalysts could make this a reality.

利用光来引起化学反应是公认的，并且从可再生能源的角度来看，具有根本的重要性。最近开发的一种方法是通过“光氧化还原催化”。金属络合物催化剂或有机催化剂吸收光进入高能激发态，持续数百/数千纳秒;然后可以向基底提供电子（或接受电子），产生自由基阴离子（或阳离子），然后进行所需的反应。在过去的10年中，这种利用简单的光吸收物种与适当的激发态的物理性质已经成为合成化学中一个成熟的工具。在这个项目中，我们希望通过使用配位笼-中空的，伪球形的金属/配体组件，具有大的中心空腔，可以容纳小分子的“客人”-作为多组分催化剂，将这一原则提高到一个更高的水平。笼包含大量的金属和配体成分，以围绕中心腔的规则阵列构建到它们的超结构中。它们可以以这样的方式制备，即它们在超结构中含有大量的金属络合物催化剂或有机催化剂单元。在我们将制备的最大笼型中，24个单独的芳香族发光单元可以结合到一个单一的笼状组装体中，该组装体围绕着一个中心空腔，一个“客体”分子将结合在该空腔中。在单一活性物质周围有24个潜在的光氧化还原催化剂几乎不可能以任何其他方式实现。（反应物）被束缚在其中一个笼的中心空腔内，它经历了一个照片-氧化还原催化转化比当它在溶液中游离时有效得多，在溶液中它必须在短的催化剂激发态存在的时间。将基底结合在笼腔中通过使客体非常接近催化剂单元的高局部浓度而消除了溶液中单独物质的偶然碰撞的要求，使得电子转移将非常快，因此催化应该更快和更有效。此外，由于笼型空腔对它们结合的客体显示出尺寸和形状选择性，因此笼型催化剂对特定底物应显示出高得多的选择性，从而允许从混合物中选择、结合、转化一种底物并从空腔中排出，而其他底物不受影响。这方面的成功将导致基于超分子主体/客体原理的新一代光氧化还原催化剂的产生，这种催化剂比目前的催化剂有效得多。此外，令人兴奋的可能性存在：给定被大量潜在电子供体包围的底物的单个分子，两个电子可以基本上同时转移到单个客体，得到双重还原产物。这在正常情况下是极难实现的，因为当两个单电子催化剂分子都处于短暂的激发态时，一个底物分子不可能与两个单电子催化剂分子碰撞;类比就像试图同时用两颗步枪子弹击中飞行的粘土靶。然而，每个结合客体周围大量发色团的局部浓度非常高，使得这种情况在统计上更有可能发生，因此双电子光催化可能在广泛的笼/客体系统中成为现实。这对于太阳能收集具有根本重要性，因为水分解产生H2燃料或CO2固定产生甲醇作为燃料的许多重要反应都需要同时转移两个电子：使用配位笼作为多电子光氧化还原催化剂可以使这成为现实。