Molecular s-block Assemblies for Redox-active Bond Activation and Catalysis: Repurposing the s-block as 3d-elements

通过催化调节反应的能量需求，在解决大量商品、制药和精细化工过程的动力学可行性方面发挥着至关重要的作用。按照目前的催化剂利用率水平，每年可获得约1,900亿美元。据估计，到2025年，这一价值将升至2270亿美元。同样清楚的是，一个真正的循环和可持续经济的未来繁荣将需要投资于我们对催化科学的基本方法。因此，创新的催化模式，更广泛地说，化学合成，将继续是推动科学技术进步的主要动力，并将成为新应用的种子玉米，以实现在新冠肺炎大流行病后实现绿色复苏的目标。尤其是均相催化，仍然以铂族金属(铂族金属，如Rh，Ir，Pd，Pt)为主。然而，由于成本高、供应脆弱和毒性相对较高，这些要素的持续和不断扩大的实施受到了威胁。这些因素激发了当代人们对确定替代催化载体的关注，这些催化载体来自地球上更丰富的更轻的过渡金属和主要的元素组(S和P-块)。然而，要实现这一目标，需要全球做出巨大努力，设计出创新的手段，有效地利用这一广泛的、高度不同的化学物质。尤其是镁和钙的地质可获得性，确保了这些元素的价格比PGMS低几个数量级，同时它们的吸引力因其通常无害的环境影响和生物兼容性而得到强调。虽然这些体系现在包含了广泛的多键异官能化和交叉偶联催化剂，但每个键的活化过程无一例外地发生在定义的两个电子步骤中，并通过保持极其稳定的Ae(II)氧化态进行。尽管Ae(II)阳离子的半径和极化率的调整引起了显著的可变性，但后一种特征排除了任何可能的氧化还原活性和可调的HOMO-LUMO能量，这些能量来自催化PGM的可用的nd价轨道流形。这一建议建立在申请人最近的发现(J.Am化学。SoC。2021,143,17851)，通过还原传统的分子镁(II)双苯胺，容易获得包括低氧化态的镁-镁键合单元和两个钠离子的异双金属组件。{Mg_2Na_2}组装的电子结构和化学结构不仅取决于形式上的镁(I)中心的存在，而且取决于镁-镁键与钠离子的协同作用。在这个建议中，我们提出了一项联合的合成和计算研究，以利用这一一般设计原则，并获得一类形式上低氧化状态的第1族/第2族异双金属化合物。生成的化合物将拥有狭窄且可操纵的前沿轨道能量，这将允许史无前例地进入表现出可逆氧化还原行为的S阻断系统。这些化合物将有助于探索它们对H2、CO、CO2和N2等小分子的反应活性，而它们潜在的氧化还原活性将使催化流形的构建成为可能，这些催化流形与来自过渡金属的d轨道构型的催化流形具有更高的共性，而不是孤立的第1和2族中心。

The moderation of a reaction's energy demands through catalysis plays a vital role in addressing the kinetic viability of a vast array of commodity, pharmaceutical and fine chemical processes. The current level of catalyst utilisation enables ca. $190 billion p.a. of domestic revenue for the UK, a value that it is estimated will rise to $227 bn by 2025. It is also clear that the future prosperity of a truly circular and sustainable economy will require investment in our fundamental approaches to catalytic science. Innovative modes of catalysis and, more generally, chemical synthesis, therefore, will continue to be primary drivers for the advancement of science and technology and a seed corn for new applications to meet the objectives for a green recovery in the aftermath of the COVID-19 pandemic. Homogeneous catalysis, in particular, continues to be dominated by platinum group metals (PGMs, e.g. Rh, Ir, Pd, Pt). The continued and growing implementation of these elements, however, is threatened by a combination of high cost, vulnerable supply and their relatively high toxicity. These factors have stimulated a contemporary focus on the identification of alternative catalytic vectors resulting from systems derived from the more earth abundant lighter transition metals and main group (s- and p-blocks) of elements. The fulfilment of this objective, however, requires a massive global effort to devise innovative means to productively harness this broad palette of highly disparate chemistry. The geological availability of, in particular, magnesium and calcium ensures that these elements are orders of magnitude less expensive than PGMs, while their appeal is underscored by their generally benign environmental impact and biocompatibility. Although these systems now encompass a wide range of multiple bond heterofunctionalization and cross coupling catalyses, without exception the individual bond activation processes occur in defined two electron steps and through the maintenance of the extremely stable Ae(II) oxidation state. Although significant variability arises with adjustments to the radii and polarizability of the Ae(II) cations, this latter feature precludes any possibility of the redox activity and tuneable HOMO-LUMO energies that arise from the available manifold of nd valence orbitals of catalytic PGMs.This proposal builds on the applicants' recent discovery (J. Am. Chem. Soc. 2021, 143, 17851) that a heterobimetallic assembly comprising a low oxidation state Mg-Mg bonded unit and two sodium cations is readily accessible by reduction of a conventional molecular Mg(II) bis-anilide. The electronic structure and chemistry of the {Mg2Na2} assembly is dependent not only on the presence of the formally Mg(I) centres but also on the cooperative interaction of the Mg-Mg bond with the sodium cations. In this proposal, we present a joint synthetic and computational study to exploit this general design principle and access a family of formally low oxidation state group 1 / group 2 heterobimetallics. The resultant compounds will possess narrow and manipulable frontier orbital energies that will allow unprecedented access to s-block systems that display reversible redox behaviour. These compounds will facilitate an exploration of their reactivity toward small molecules such as H2, CO, CO2 and N2, while their potential redox activity will enable the construction of catalytic manifolds, which display a higher degree of commonality with those derived from the nd orbital configurations of transition metals than those of isolated group 1 and 2 centres.