Cooperative Noble Base Metal Catalysis

在英国，化工行业是英国经济的关键贡献者。它每年为国家经济增加近200亿GB的价值，年营业额约600亿GB，维持着50多万个就业岗位。在这一部门，大多数化学品的制造涉及使用催化剂，这种催化剂通常以地壳中最稀有的元素为基础，如贵金属(Pd、Rh或Ir)。这些特权金属的有限供应，加上它们巨大的环境足迹(例如，获得1公斤纯金属Rh产生近32吨二氧化碳)阻碍了真正可持续工艺的发展。这推动了化学家们发现以廉价、丰富和无害的贱金属(如镍、钴和铁)为基础的催化剂。然而，BM中心的反应往往通过单电子事件进行，导致难以控制和维持催化剂的功能，从而阻碍了可持续、高效和可预测的催化剂的开发。在所有用于控制贱金属化学的策略中，我们被金属-配体的化学合作所吸引，在这种合作中，参与者配体参与成键和断裂事件。基于此，我们驯服双电子催化循环并利用BM开发可预测的催化方法的战略将利用低价铝基配体。因此，我们的目标将是提供能够(1)将基质结合到高度亲电的Al中心和(2)使用亲核贱金属中心激活它们的双亲Al-BM单元。使用铝作为结合部位并不是一个随机的选择：这种第13族元素不仅是良性的，而且是地壳中含量最丰富的金属。此外，在其+1氧化态表现出有趣的性质作为配体，成为一个强大的西格玛供体与一个空的和可访问的p轨道。这些性质最近在贵金属催化领域得到了开发。尽管如此，Al(I)与另一种富含地球的金属配对的异双金属配合物仍未得到充分开发，目前仅限于小分子的化学计量比活化。然而，在这些例子中，Al-BM键的完整性丢失。这是它们在催化过程中实施的主要挑战，因为配体的解离导致它们的协同激活能力被破坏，导致催化失活。为了克服这个问题，实现刚性和稳定的结构和Al-BM键，我们将建立一个合理的设计策略，以获得定制的Al-BM络合物，这些络合物将通过精心选择配体主干、锚臂和贱金属中心(Co、Ni、Fe)来构建。这些络合物将使用基于化学计量比到催化的策略的自下而上的方法进行研究：利用从化学计量比活化研究中收集的知识，以催化方式向Al-BM单元注入贵金属将是触手可及的。与贵金属催化相比，Coop-NBM的实施将代表着一种更环保、更便宜的有机分子功能化替代方案，从而实现具有工业应用潜力的环境友好方法。总体而言，这项研究计划的重要性在于它有可能提供基于地球上最丰富的元素(如铝和铁)的催化剂。贱金属与低价铝配体相结合的催化使用仍然是一个未知的领域，是建立一个新的化学空间的绝佳机会，这可能导致目前由贵金属催化进行的无数有机转化的环境足迹大幅减少。这肯定会让英国在开发可持续技术方面占据中心舞台，这些技术旨在让贵金属退出化学工业的主力地位。

In the UK, the chemicals sector is a key contributor to the UK economy. It adds close to £20 billions of value to the country's economy every year and has an annual turnover of approximately £60 billion, sustaining more than half a million jobs. Within this sector, the manufacture of most chemicals involves the use of a catalyst, which is usually based on the rarest elements on the Earth's crust, such as noble metals (Pd, Rh or Ir). The limited supply of these group of privileged metals, together with their huge environmental footprint (e.g. obtaining 1 kg of pure metallic Rh produces near 32t of carbon dioxide) blocks the development of truly sustainable processes. This is pushing chemists towards the discovery of catalysts based on inexpensive, abundant, and benign base metals (e.g. Ni, Co and Fe). However, reactivity on BM centres often proceeds through one-electron events, resulting in difficulties controlling and maintaining the catalyst function, thus preventing the development of sustainable, efficient, and predictable catalysts. Among all the strategies employed to control the chemistry of base metals, we were attracted by chemical metal-ligand cooperation, in which actor ligands participate in bond-forming and breaking events. Based on this, our strategy to tame two-electron catalytic cycles and develop predictable catalytic methods with BM will exploit low-valent aluminium-based ligands. Thus, our aim will be furnishing ambiphilic Al-BM units that are capable of (1) binding substrates to the highly electrophilic Al centre and (2) activate them using a nucleophilic base metal centre. Using Al as binding site is not a random choice: this group 13 element is not only benign, but the most abundant metal in the Earth's crust. Furthermore, in its +1 oxidation state presents interesting properties as ligand, becoming a powerful sigma-donor with an empty and accessible p-orbital. These properties have been recently exploited in the field of noble metal catalysis. Nonetheless, heterobimetallic complexes in which Al(I) is paired with another earth-abundant metal remain under-explored and currently limited to stoichiometric activation of small molecules. In these examples, however, the integrity of the Al-BM bond is lost. This represents a major challenge for their implementation in catalytic processes, as ligand dissociation leads to disruption of their cooperative activation ability, resulting in catalytic deactivation. To overcome this issue and achieve rigid and stable structures and Al-BM bonds, we will establish a rational design strategy to obtain bespoke Al-BM complexes that will be built by a delicate selection of ligand backbone, anchor arms, and base metal centre (Co, Ni, Fe). These complexes will be studied using a bottom-up approach based on a stoichiometric-to-catalytic strategy: employing the knowledge gathered from stoichiometric activation studies, infusing nobility to Al-BM units in a catalytic fashion will be within reach. The implementation of Coop-NBM will represent a greener and cheaper alternative to functionalise organic molecules compared to noble metal catalysis, allowing the achievement of environmentally friendly approaches with potential to be applied at industry.Overall, the importance of this research proposal lies in its potential to provide catalysts based on the most abundant elements of our planet, e.g. Al and Fe. Catalytic use of base metals combined with subvalent Al ligands remains an uncharted territory and an exceptional opportunity to establish a new chemical space that could lead to a dramatic reduction of the environmental footprint of countless organic transformations currently performed by noble metal catalysis. This will certainly make the UK take centre stage in the development of sustainable technologies aiming at retiring noble metals as workhorses of chemical industry.