The Guerbet Reaction Network – a Ball‐in‐a‐Maze‐Game or: Why Ru‐MACHO‐BH is Poor in Coupling two Ethanol to n‐Butanol

Abstract

Invited for this month's cover is the group of Marcel A. Liauw at the RWTH Aachen University (Germany). The cover picture shows a playable version of the homogeneously catalyzed Guerbet‐coupling from ethanol to n‐butanol. The 2D ball‐in‐a‐maze‐game is shown here because the reaction steps are either performed in presence of a redox catalyst (top‐down) or in presence of a base (left‐right). Both axes can be moved independently from each other and substances are connected with humps in the height of the activation barrier. Playing the game repeatedly for a defined time and writing down the outcomes (see blackboard) yields the composition of the reaction mixture at a given time. Alas, the highly active redox catalyst Ru‐MACHO shows unsatisfying yields and selectivities of n‐butanol. But why? Read the full text of their Full Paper at 10.1002/cmtd.202000056.

Low-temperature selective ethanol upgrading to primary or secondary alcohols by homogeneous catalysis

“…Likewise, consistent with Liauw's results 39 , with Ru-2 we found poor coupling of ethanol to 1-butanol. On the contrary, 830 ppm of Ru-2 catalyzed 2-butanol production with a yield of 8% and an 86% selectivity towards secondary alcohols (Entry 5).…”

“…These complexes are robust catalysts for a wide range of sustainable chemical transformations under mild reaction conditions [33][34][35][36][37][38] . However, in support of the ndings made by Wass 11 , Liauw recently suggested that consumption of ethoxide additive, via formation of NaOAc by ethyl acetate saponi cation, is a major reason for low yields of ethanol upgrading to 1butanol catalyzed by Ru-2 39 . Indeed, NaOEt is often used for Guerbet reactions promoting the aldol condensation of acetaldehyde and selective formation of 1-butanol and higher primary alcohols 10,11,13 .…”