When less is more: Ligand and solvent effects in Ni2+ Lewis acid transfer hydrogenation coupled with aldol condensation

The coupling of furfural with aliphatic alcohols can yield precursor molecules for the production of high-performance detergents. In the present work, we use Ni-based homogeneous catalysts for this transformation and specifically examine ligand, solvent and base effects. We show that chloride and phosphine-ligated Ni catalysts exhibit long induction periods, while Ni catalysts with O ligands do not. We use operando X-ray absorption spectroscopy to attribute this induction to the requirement for the P and Cl ligand substitution during reaction. Solvent effect experiments demonstrate that hydrocarbon solvents, such as toluene and cyclohexane show the highest performance, while tert‑butanol is least optimal. Potassium carbonate as a base shows highest rates, while amine bases require higher temperatures and excess furfural to achieve equivalent product yields.