Hydrogen autotransfer with alcohols for alkylations

Abstract

Despite the advancements enabled by organometallic complexes in organic synthesis, which have led to innovative transformations and tackled issues related to waste and atom economy, concerns persist regarding the cost of noble metals and ligands. Expanding on previous work, iron and ruthenium complexes with cyclopentadienone ligands, akin to Knölker catalysts, have demonstrated remarkable efficiency in bond reduction and alkylations using alcohols as pro-electrophiles. This review delves into novel alkylation methodologies involving hydrazides or ketones, inventive dehydrogenative coupling reactions yielding highly functionalized structures, and the optimization of metal-catalysed reactions through organometallic complex modifications. Metal-catalysed hydrogen auto-transfer, or hydrogen borrowing, offers a sustainable approach to forming C–C or C–N bonds from eco-friendly alcohols. While transitioning the diaminocyclopentadienone tricarbonyl ligand to first-row transition metals under mild conditions remains challenging, recent findings indicate that blue-light irradiation at room temperature can facilitate this transformation without external photosensitizers. Thus, while conventional studies without light remain demanding, the incorporation of light can enhance this research domain, where such catalysts may play a pivotal role. Moreover, further exploration of asymmetric catalysis is warranted. This review aims to benefit not only the community working with Knölker derivative catalysts but also organic chemists seeking potential applications and inorganic chemists interested in catalyst development, particularly in pursuit of catalysts for asymmetric syntheses. Additionally, the focus on sustainability makes it relevant for chemists dedicated to green chemistry.