The true catalyst in hydrogen transfer reactions with alcohol donors in the presence of RuCl2(PPh3)3 is ruthenium(0) nanoparticles

Abstract

The widespread soluble complex RuCl₂(PPh₃)₃ is evidently not the true catalyst in numerous hydrogen transfer reactions where it has been utilized. In the presence of alcohol donors, particularly under boiling conditions, the complex is swiftly reduced to Ru(0) and forms nanosized clusters which are the genuine catalysts. The so formed nanoparticles are not stable and they slowly agglomerate into larger non-active assemblies which are observable by the naked eye. Both the formation and the agglomeration of these nanoparticles are enhanced in the presence of a base such as NaOH. Conversely, addition of stabilizers, such as surface active agents or active carbon, inhibits the agglomeration process and elongates the life time of the catalyst although the observed activity is reduced. The presence of nanoparticles and their unique role in the catalysis of hydrogen transfer reactions between alcohols and ketones were corroborated by TEM imaging, NMR diffusion measurements, XPS and UV-vis spectroscopy and by kinetic studies.