Cyclodextrins as first and second sphere ligands for Rh(I) complexes of lower-rim PTA derivatives for use as catalysts in aqueous phase hydrogenation

• Synthesis of new lower-rim functionalized PTA-based Rh complex
• Self-assembled formation of supramolecular complexes with modified CD
• Testing in Rh-catalysed hydrogenation of allylic and unsaturated alcohols in water

The rhodium complex [Rh(cod)Cl(N-tBuBzPTA)]PF6 (2) was obtained by reacting the appropriate Rh(I) precursor with the lower-rim PTA derivative [N-tBuBzPTA]PF6 (tBuBz = 4-tert-butylbenzyl; PTA = 1,3,5-triaza-7-phosphaadamantane). The solubility and stability in water of 2 were increased in the presence of native-β-cyclodextrin (β-CD). The interaction of 2 with mono-amino β-cyclodextrin (β-CDNH2, 2 equiv.) led to a supramolecular Rh assembly (3), identified by 31P, 1H and 2D T-ROESY NMR experiments. The catalytic activity of 3 was evaluated in the water-phase hydrogenation of unsaturated and allylic alcohols and preliminary results are presented here.

Supramolecular ligands obtained by inclusion of a PTA derivative within the hydrophobic cavity of a mono-amino-β-CD efficiently stabilized Rh-complexes in water. The resulting self-assemblies were effective catalysts in aqueous hydrogenation of unsaturated and allylic alcohols under mild conditions.Figure optionsDownload as PowerPoint slide