Synthesis and Characterization of Tetrahedral Ru3O Clusters with Intrinsic Framework Chirality:  A Chiral Probe of the Intact Cluster Catalysis Concept

To bring evidence for or against the hypothesis of catalytic hydrogenation by intact trinuclear arene ruthenium clusters containing an oxo cap, cationic Ru3O clusters with three different arene ligands (intrinsically chiral tetrahedra) have been synthesized as racemic mixtures. By introduction of a chiral auxiliary substituent at one of the three different arene ligands, the separation of the two diastereomers was possible. The chiral Ru3O framework was evidenced by X-ray crystallography, by circular dichroism in the UV and IR regions, and by chiral shift reagents in the NMR spectra. The catalytic hydrogenation of the prochiral substrate methyl 2-acetamidoacrylate using a chiral Ru3O cluster showed no asymmetric induction, suggesting that the catalytically active species is not the intact Ru3O cluster.