Ruthenium (II) complexes with C2- and C1-symmetric bis-(+)-camphopyrazole ligands and their evaluation in catalytic transfer hydrogenation of aldehydes

Ruthenium (II) piano-stool complexes with bis-(+)-camphopyrazole ligands of C-2 and C-1 symmetry were prepared in good yields (66 98%). New C-2-C-1 ligands and complexes were characterized by multinuclear NMR spectroscopy, FT-IR and elemental analysis. The catalytic performance of the Ru(II)-bis-(+)-camphopyrazole complexes in the transfer hydrogenation of benzaldehyde and valeraldehyde using isopropanol/potassium carbonate and formic acid/triethylamine mixtures as hydrogen donors, was evaluated, resulting in moderate yields (>54%) for the reduction to the desired primary alcohols. The system with isopropanol as hydrogen source proved to be more selective than the analogous system using the azeotropic formic acid/triethylamine mixture, allowing benzyl alcohol to be obtained in quantitative yield (>99%) for a particular catalyst precursor. Furthermore, complexes with C-2 symmetry ligands showed higher yields than those with C-1 symmetry ligands in all of the evaluated systems.

Automated summary

The synthesis of ruthenium (II) piano-stool complexes with bis-(+)-camphopyrazole ligands and their catalytic performance in the transfer hydrogenation of benzaldehyde and valeraldehyde were evaluated. The complexes showed moderate yields and selectivity when using isopropanol and formic acid as hydrogen donors, with C-2 symmetry ligands outperforming C-1 symmetry ligands in all evaluated systems.