Current State-of-Art in the Guerbet-Type β-Alkylation of Secondary Alcohols with Primary Alcohols Catalyzed by Complexes Based on 3d Metals

Development of greener, sustainable, and atom-economical methods for the formation of Carbon–Carbon bonds leading to versatile fuels and value-added chemicals has been an area of recent global research. For example, the methodology for C–C bond formation proves to be useful for the valorization of ethanol to butanol which acts as an alternative fuel. This methodology can be further applied in natural product synthesis including but not limited to synthesis of several cholesterol and flavan derivatives. This greatly negates the typical disadvantages of classical coupling of alkyl halides that generally are accompanied by the formation of hazardous waste. Transition metal-catalyzed Guerbet-type coupling of alcohols is a promising route to new C–C bonds as they are greener and atom-economical with water as the sole by-product. Typically, these reactions follow the sequence of catalytic dehydrogenation to carbonyl compounds, aldol condensation and a tandem catalytic hydrogenation of the resulting α,β-unsaturated carbonyl compound. Barring the large library of precious metal (Ru, Ir, Rh, and Pd) based homogeneous catalytic systems that accomplish the β-alkylation of alcohols, there are only a few reports on corresponding homogeneous catalytic systems derived from 3d metals and are mainly based on Mn, Fe, Co, Cr, and Ni. In this chapter, an attempt has been made to shed light on the current state-of-art in the 3d-metal catalyzed β-alkylation of secondary alcohols with primary alcohols from a synthetic and mechanistic point-of-view.