Cooperative Noble Base Metal Catalysis

在英国，化学品行业是英国经济的主要贡献者。它每年为该国经济增加近200亿英镑的价值，年营业额约为600亿英镑，维持了50多万个就业岗位。在这一部门内，大多数化学品的制造都涉及使用催化剂，这种催化剂通常以地壳上最稀有的元素为基础，如贵金属（钯、铑或铱）。这些特权金属的有限供应，以及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。这促使化学家们发现基于廉价、丰富和良性贱金属（如Ni、Co和Fe）的催化剂。然而，BM中心上的反应性通常通过单电子事件进行，导致难以控制和维持催化剂功能，从而阻止可持续的、高效的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，我们被化学金属-配体合作所吸引，其中作用配体参与成键和断裂事件。基于此，我们的策略驯服双电子催化循环和开发可预测的催化方法与BM将利用低价铝基配体。因此，我们的目标将是提供两亲性Al-BM单元，其能够（1）将底物结合到高度亲电的Al中心，以及（2）使用亲核的贱金属中心活化它们。使用Al作为结合位点不是一个随机的选择：这种第13族元素不仅是良性的，而且是地壳中最丰富的金属。此外，在其+1氧化态呈现出有趣的性质作为配体，成为一个强大的σ-供体与空的和可访问的p-轨道。这些性质最近已在贵金属催化领域中被开发。尽管如此，其中Al（I）与另一种地球上丰富的金属配对的杂原子络合物仍然未被开发，并且目前仅限于小分子的化学计量活化。然而，在这些实施例中，丧失了Al-BM键的完整性。这代表了它们在催化过程中实施的主要挑战，因为配体解离导致它们的协同活化能力的破坏，导致催化失活。为了克服这个问题，并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配合物，将建立一个微妙的选择配体骨架，锚臂，和贱金属中心（钴，镍，铁）。这些复合物将使用自下而上的方法进行研究，基于化学计量的催化策略：采用从化学计量活化研究中收集的知识，以催化方式将贵族注入Al-BM单元将触手可及。与贵金属催化剂相比，Coop-NBM的实施将代表一种更环保、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。总的来说，这项研究提案的重要性在于它有可能提供基于地球上最丰富的元素（例如Al和Fe）的催化剂。与低价Al配体结合的贱金属的催化使用仍然是一个未知的领域，并且是建立一个新的化学空间的绝佳机会，该空间可以导致目前通过贵金属催化进行的无数有机转化的环境足迹的显著减少。这肯定会使英国在可持续技术的发展中占据中心地位，旨在淘汰贵金属作为化学工业的主力。

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.