Low valent main group compounds in small molecule activation

Weetman, Catherine; (2021) Low valent main group compounds in small molecule activation. In: Encyclopedia of Inorganic and Bioinorganic Chemistry. Wiley, Hoboken, NJ. ISBN 9781119951438 (https://doi.org/10.1002/9781119951438.eibc2779)

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Since the discovery that main group elements can mimic transition metals, efforts have focussed on harnessing main group elements' abilities to break strong bonds to enable new sustainable methodologies. In this regard, use of small molecules, such as those found in greenhouse gases, is a prime target for incorporation into catalytic cycles to produce value-added products. Initial challenges in main group chemistry focussed on the ability to isolate these highly reactive low-oxidation state species, whilst also maintaining the reactive sites. An array of low valent compounds have been successfully isolated (i.e., multiple bonds, tetrylenes, anions, and cations), through careful ligand design, and have challenged traditional bonding models and preconceptions of the main group elements. Current advances have highlighted how reactive these low-valent sites are with the ability to activate strong bonds, such as those found in small molecules (e.g., H2, CO, CO2, etc.). This represents the first step in a redox-based catalytic cycle, as the low-valent main group center undergoes oxidative addition reactions. Current challenges remain in reductive elimination, and thus functionalization of the small molecule, but examples of low-valent main group elements in catalysis are starting to emerge and represent a bright future for main group chemistry. This article highlights the achievements of low valent main group elements, with a focus on group 2, 13, and 14 elements, in small molecule activation as well as the fundamental concepts that have aided the development of this rapidly advancing field.