Synthesis and reactivity of aluminium-transition metal complexes

该项目属于EPSRC物理科学-催化研究领域。铝是一种储量丰富的金属，长期以来一直用于合成和工业化学。在这样的应用中，铝作为路易斯酸，考虑到首选状态，Al（III）是亲电的。例子包括Friedel Crafts反应和Zeigler Natta催化剂。2018年，Hicks等人报道了第一个亲核铝的例子。这种铝基配合物表现为亲核试剂，与亲电试剂如MeI反应，代表了典型铝反应性的完全逆转。铝-过渡金属配合物的例子是已知的，并且是由阴离子过渡金属与亲电Al（III）反应形成的。然而，由于缺乏可用的过渡金属试剂，这种方法受到限制。随着铝基络合物的发现，人们可以尝试相反的方法来形成铝-过渡金属键，使用铝作为亲核伙伴与带正电的金属物质反应。铝基化合物与金卤化物结合，合成了一种具有铝-金键的配合物。令人着迷的是，铝基的强给电子能力导致了亲核金配合物，其中金在形式上处于Au(I)氧化态。这种金络合物的独特之处在于金具有亲核试剂的性质。它被证明与二氧化碳反应，二氧化碳插入铝-金键，金攻击亲电碳。以同样的方式，它也与二二丙基碳二亚胺反应。这个项目的目的是进一步探索这种令人兴奋的新化学。目的是合成一系列含铝过渡金属键的配合物。目的是利用过渡金属卤化物前体的过渡金属方法合成晚期过渡金属铝体系。这种方法非常新颖，因为它逆转了铝的传统反应性，并将允许使用双金属系统，而这些系统以前在合成上过于具有挑战性。从合成的角度来看，灵感来自于类似的硼基（-BR2）和胆酰体系，它们在硼或镓上具有孤对。近年来，已经合成了大量的金属硼和金属镓，因此铝基也有望成功。据预测，新物种也将能够在过渡金属中心充当亲核试剂，就像金的例子一样。改变金属伴侣将允许调整反应性，因此对亲电试剂和小分子的反应性可以进行研究。这项工作的影响将是在合成中引入新的试剂，并提供一种新的双金属系统，用于小分子的激活，这是由于金属的电子性质不同而产生的。该项目与EPSRC催化和合成配位化学研究领域密切相关。鉴于金对二氧化碳和碳二亚胺的反应性，催化应用的潜力是广泛的。希望这种反应性可以扩大，不同的金属伴侣能够激活许多小分子和亲电试剂。过渡金属形成亲核试剂的潜力为催化体系开辟了新的可能性。急剧改变过渡金属电子性质的能力与催化极为相关，催化基本上是基于金属中心氧化态的变化。该项目旨在研究未开发的杂双金属铝系统的化学性质，从而产生非常规的反应性和小分子活化的新模式。其应用主要与催化和合成化学有关。

This project falls within the EPSRC Physical Sciences - catalysis research area. Aluminium is a highly abundant metal and has long been utilised in synthetic and industrial chemistry. In such applications, aluminium acts as a Lewis acid, given that the preferred state, Al(III) is electrophilic. Examples include the Friedel Crafts reaction and Zeigler Natta catalyst. In 2018, the first example of nucleophilic aluminium was reported by Hicks et al. This aluminyl complex was shown to behave as a nucleophile, reacting with electrophiles such as MeI, representing a complete reversal of typical aluminium reactivity. Examples of aluminium-transition metal complexes are known, and are formed by reacting an anionic transition metal with electrophilic Al(III) species. However, this approach is limited due to the lack of available transition metal reagents. Following the discovery of the aluminyl complex, it became possible to try the opposite approach to aliminium-transition metal bond formation, using the aluminium as the nucleophilic partner reacting with positively charged metal species. The aluminyl species was used, with a gold halide partner, to synthesis a complex featuring an aluminium-gold bond. Fascinatingly, the strong electron donating ability of the aluminyl resulted in a nucleophilic gold complex, in which gold is formally in the Au(I) oxidation state. This gold complex is unique in that gold behaves as a nucleophile. It was shown to react with CO2, which inserts into the aluminium-gold bond, with gold attacking the electrophilic carbon. In the same fashion, it also reacts with diisipropylcarbodiimide. It is the aim of this project to further explore this exciting new chemistry. The objective is to synthesise a range of complexes containing aluminium-transition metal bonds. It is intended to use the transmetallation approach with transition metal-halide precursors to synthesise late transition metal-aluminium systems. This method is highly novel, as it reverses the traditional reactivity of aluminium and will allow access to bimetallic systems that have previously been too synthetically challenging to make. From a synthetic point of view, inspiration comes from the analogous boryl (-BR2) and gallyl systems, which feature a lone pair on boron or gallium. In recent years, a multitude of boron-metal and gallium-metal species have been synthesised and so success with the aluminyl is also expected. It is predicted that the new species will also be capable of acting as nucleophiles at the transition metal centre, as with the gold example. Varying the metal partner will allow the reactivity to be tuned, and so the reactivity towards electrophiles and small molecules can be investigated. The impact of this work will be to introduce new reagents into synthesis and provide a new bimetallic system for small molecule activation, arising from differences in electronic properties of the metals. This project works very closely within the EPSRC research areas of catalysis and synthetic coordination chemistry. The potential for catalytic applications is widespread, given the reactivity of the gold species towards CO2 and carbodiimides. It is hoped that this reactivity can be expanded, with different metal partners being able to activate many small molecules and electrophiles. The potential to form nucleophiles from transition metals opens up new possibilities for catalytic systems. The ability to drastically alter the electronic properties of transition metals is extremely relevant to catalysis, which is fundamentally based on changes in oxidation state at a metal centre. This project seeks to investigate the unexplored chemistry of heterobimetallic aluminium systems, leading to unconventional reactivity and new modes of small molecule activation. The applications are largely related to catalysis and also synthetic chemistry.