Light-Induced Small Molecule Fixation by Diradicals

能量的化学储存构成了一个巨大的挑战，意味着强键（如N2、CO2等）向弱键的转变。理想情况下，按照光化学方法的蓝图，太阳的能量被直接用于按顺序切割这些键（“光激活”）。该领域大多数方法的共同特点是过渡金属，因为需要控制将能量“分割”成更小的“能量包”。然而，近年来在具有过渡金属样反应性和小前沿轨道能隙等电子结构的低价主基团化合物领域取得了很大进展。调查的动机是用地球上资源丰富且对环境无害的元素代替稀有和有毒的金属。具有极小的HOMO-LUMO能隙或甚至具有三重态基态（如双氧）的分子被称为双自由基（类）。他们在孤立中取得了巨大的进步。然而，双自由基的键活化化学研究却很少。尽管它们的电子结构与过渡金属和双氧类似，但它们的光致反应性，超越了瞬态双基态和酰基态，仍然是一个未知的领域。在这个项目中，我们将证明仅基于地球上丰富元素的双根碱类“拟金属”化合物可以光化学激活小分子，如二氮，并将其转化为增值产品。

The chemical storage of energy constitutes a grand challenge and implies the transformation of strong bonds, as in N2, CO2, etc., to weaker bonds. Ideally and in accordance with the blueprints of photochemical approaches, the sun’s energy is directly used to cleave these bonds (“photoactivation”) in a sequential manner. Common feature of most approaches in this field are transition metals due to the requirement to control “partitioning” of energy into smaller “energy packages”. However, recent years brought much progress in the field of low-valent main-group compounds with transition metal-like reactivity and electronic structures such as small frontier orbital energy gaps. Investigations are driven by the incentives to substitute rare and toxic metals with earth-abundant and environmentally benign elements. Molecules with exceedingly small HOMO–LUMO energy gaps or even a triplet ground state such as dioxygen are referred to as diradical(oid)s. Tremendous progress has been made in their isolation. Yet, the bond activation chemistry of diradicals has rarely been explored. Despite the analogy of their electronic structure with transition metals and dioxygen, their photoinduced reactivity, beyond transient diradical states and acenes, remains even unchartered territory. Within this project, we will demonstrate that diradicaloid, “metallomimetic” compounds based only on earth-abundant elements may photochemically activate small molecules such as dinitrogen, and convert them into value-added products.