Singh Roushan Prakash, Mankad Neal P
Department of Chemistry, University of Illinois Chicago, Chicago, Illinois 60607, United States.
JACS Au. 2025 May 8;5(5):2076-2088. doi: 10.1021/jacsau.5c00352. eCollection 2025 May 26.
Promoting societally important small molecule activation processes with earth-abundant metals is foundational for a sustainable chemistry future. In this context, mapping new reaction pathways that would enable abundant main-group elements to mimic the behaviors of - and -block elements is facilitated by exploring unusual oxidation states. The most abundant metal on earth, aluminum, has been well studied in the Lewis acidic +III and Lewis basic +I oxidation states but rarely in the potentially biphilic +II oxidation state until recently, when a renaissance of Al-(II) chemistry emerged from a range of research groups. In this Perspective, we review the chemistry of mononuclear Al radicals, including both Al-centered radicals (i.e., Al-(II) compounds) and redox non-innocent systems (i.e., formally Al-(II) species that are physically Al-(III) with ligand-centered radicals), with an emphasis on small molecule reactivity. We also provide a meta-analysis of the Al-(II) literature to summarize how different design strategies (e.g., redox non-innocence, strained coordination geometries) have been shown to impart biphilic character to Al radicals and tune their behavior, thus allowing Al radicals to mimic the chemistry of certain - and -block metal ions such as Ti-(III) and Sm-(II). We expect these molecular design concepts to inform future Al-(II) studies as the chemistry of this unusual oxidation state of Al continues to grow.
利用地球上储量丰富的金属促进具有重要社会意义的小分子活化过程是可持续化学未来的基础。在这种背景下，通过探索不寻常的氧化态有助于绘制新的反应途径，使储量丰富的主族元素能够模拟过渡金属和后过渡金属元素的行为。地球上含量最丰富的金属铝，在路易斯酸性 +III 和路易斯碱性 +I 氧化态下已有深入研究，但直到最近，在潜在的双亲性 +II 氧化态下的研究还很少，当时一系列研究小组兴起了铝（II）化学的复兴。在这篇展望文章中，我们综述了单核铝自由基的化学，包括以铝为中心的自由基（即 Al-(II) 化合物）和氧化还原非无辜体系（即形式上为 Al-(II) 物种但实际上是 Al-(III) 且带有以配体为中心的自由基），重点是小分子反应性。我们还对铝（II）文献进行了荟萃分析，以总结不同的设计策略（例如氧化还原非无辜性、应变配位几何结构）如何被证明赋予铝自由基双亲性特征并调节其行为，从而使铝自由基能够模拟某些过渡金属和后过渡金属离子（如 Ti-(III) 和 Sm-(II)）的化学性质。随着铝这种不寻常氧化态的化学不断发展，我们期望这些分子设计概念为未来的铝（II）研究提供参考。
