Alternative energy input for transfer hydrogenation using iridium NHC based catalysts in glycerol as hydrogen donor and solvent

摘要

Four Ir(I) and Ir(III) N-heterocyclic carbene(NHC) based complexes with 3,4,5-trimethoxybenzyl N-substituents have been obtained and fully characterized. The newcomplexes have been used as catalysts in the reduction of aldehydesand ketones with glycerol, and their activities have been comparedto those shown by other Ir(III) NHC-complexes previouslyreported. The reactions were carried out under oil bath heating,and a detailed comparative study has been carried out usingmicrowave (MW) and ultrasound (US) activation. The new Ir(III)complexes proved to be most efficient in the reduction of ketones,while the Ir(I) complexes are more active in the reduction ofaldehydes. The use of ultrasound has a tremendous impact inshortening reaction times, and good results have been obtained inthe reduction of aldehydes. In some experiments transmision electron microscopy (TEM) and UV−vis analysis showed thepresence of iridium-containing nanoparticles after MW or US activation.