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

• Published in: Inorganica Chimica Acta 2021-09, Vol.524, p.1, Article 120429
• Main Authors: Blanco, Christian O., Llovera, Ligia, Herrera, Alberto, Dorta, Romano, Agrifoglio, Giuseppe, Venuti, Doménico, Landaeta, Vanessa R., Pastrán, Jesús
• Format: Article
• Language: English
• Subjects: Aldehydes; Benzaldehyde; Benzyl alcohol; C2 and C1 bis-(+)-camphopyrazole ligands; Chemical analysis; Coordination compounds; Formic acid; Hydrogenation; Infrared analysis; Infrared spectroscopy; Isopropanol; Ligands; NMR spectroscopy; Potassium carbonate; Ruthenium; Ruthenium (II); Symmetry; Systems analysis; Transfer hydrogenation; Triethylamine
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2021.120429

[Display omitted] •The synthesis of two new chiral bis-(+)-camphopyrazole ligands is reported.•Five piano-stool ruthenium(II) complexes with camphopyrazole ligands were obtained.•The Ru(II) complexes catalyze the transfer hydrogenation of aldehydes from iPrOH.•The system in iPrOH/K2CO3 affords moderate yields of the desired alcohol product.•The TH in isopropanol is more selective than using HCOOH/NEt3 as hydrogen source. Ruthenium (II) piano-stool complexes with bis-(+)-camphopyrazole ligands of C2 and C1 symmetry were prepared in good yields (66–98%). New C2-C1 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 C2 symmetry ligands showed higher yields than those with C1 symmetry ligands in all of the evaluated systems.