Transition Metal-Free Hydrosilylation and Hydroboration of Unsaturated Carbon-Heteroatom Bonds

Abstract

The hydrosilylation or hydroboration of unsaturated C-O and C-N bonds yields valuable reagents and intermediates for organic synthesis. Traditionally, these reactions have been carried out by transition metal catalysts which are generally expensive and toxic, or stoichiometric reagents which produce a significant amount of waste. As such, transition metal-free catalytic alternatives have steadily gained popularity as a more sustainable alternative. This thesis presents the use of cheap and readily available simple alkali metal bases such as KOtBu and nBuLi as powerful catalysts for the reduction of carbonyls and imines. Notably, aldehydes can be selectively obtained through the reduction of tertiary amides and esters, and amines can be produced from nitriles using a similar method. These conversions have previously been relegated to the domain of late transition metal catalysts. Variation of the silane or borane was found to be highly influential in adjusting the chemoselectivity. For example, in the conversion of amides to aldehydes, use of (EtO)3SiH resulted in overreduction to the amine product, whereas (EtO)2MeSiH allowed for selective reduction to the aldehyde equivalent. In this work, we discuss our investigations into the scope and selectivity of this straightforward yet effective system. Additionally, we introduce a new approach for achieving long-term precise control of reaction conditions at low temperatures.