Ruthenium–benzocrownether complexes: Synthesis, structures, catalysis and immobilisation in ionic liquids

A facile pathway to [RuCl2(η6-benzocrownether)]2 complexes is described and crystal structures of the complexes [RuCl2(η6-benzo-15-crown-5)]2 and [RuCl2(η6-dibenzo-18-crown-6)]2 are reported. The complexes were derivatised with (1S,2R)-2-amino-1,2-diphenylethanol and evaluated in the enantioselective transfer-hydrogenation of acetophenone. The effect of complexation of different alkaline metals (Na, K, Cs) within the crown on the selectivity and reaction rate was studied. Interaction of a sulfonated phosphine ligand with the crown was probed by NOESY-NMR and utilisation of the crownether to serve as an anchor for catalyst immobilisation was investigated.

Graphical abstractA facile route to dimeric benzocrownether complexes of the type [RuCl2(η6-benzocrownether)]2 is reported. These compounds are valuable precursors to catalysts and have been evaluated in the asymmetric transfer-hydrogenation of acetophenone by derivatisation with a chiral amino-alcohol ligand. The effect of complexed alkaline cations in the crownether has been investigated. In view of biphasic catalysis, the crown-moiety may also be utilised to tune the solubility properties of the resulting complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide