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.