Substituent Effect on the Catalytic Activity of Ruthenium(II) Complexes Bearing a Pyridyl-Supported Pyrazolyl-Imidazolyl Ligand for Transfer Hydrogenation of Ketones

Abstract

Air-and moisture-stable ruthenium(II) complexes bearing a multisubstituted pyrazolyl-imidazolyl-pyridine ligand were synthesized and structurally characterized by NMR and X-ray single-crystal crystallographic analyses. The substituents on the imidazolyl moiety of the NNN ligand exhibited a remarkable impact on the catalytic activity of the corresponding Ru(II) complexes for transfer hydrogenation of ketones in refluxing 2propanol, following the order NHTs > Me > H > NO 2 , to tune the catalytic activity. The highest final TOF value of 345 600 h −1 was reached by means of 0.05 mol % of the Ru(II)-NHTs-substituted NNN complex as the catalyst. The corresponding structurally confirmed RuH complexes are proposed as the catalytically active species.

Catalytic reduction of 1,4‐benzoquinone to hydroquinone via [FeFe]‐hydrogenase model complexes under mild conditions

“…and the electrochemical data are presented in Table . According to previous reports, the first reduction event is assigned to Fe I –Fe I /Fe I –Fe 0 and the oxidation process can be assigned to Fe I –Fe I /Fe II –Fe I oxidation . Complex 1 has a quasi‐reversible reduction peak at −1.73 V (Fe I –Fe I /Fe I –Fe 0 ) and its first oxidation peak (Fe I –Fe I /Fe II –Fe I ) at 0.79 V. The reduction peak of 1 is shifted negatively by 30 mV as compared to a typical di‐iron complex (μ‐pdt)Fe 2 (CO) 6 .…”

“…According to previous reports, the first reduction event is assigned to Fe I -Fe I /Fe I -Fe 0 [FeFe]-hydrogenase model complexes catalyze BQ to HQ www.soci.org and the oxidation process can be assigned to Fe I -Fe I /Fe II -Fe I oxidation. [27][28][29][30][31] Complex 1 has a quasi-reversible reduction peak at −1.73 V (Fe I -Fe I /Fe I -Fe 0 ) and its first oxidation peak (Fe I -Fe I / Fe II -Fe I ) at 0.79 V. The reduction peak of 1 is shifted negatively by 30 mV as compared to a typical di-iron complex (μ-pdt) Fe 2 (CO) 6 . The CV curve of 2 displayed an irreversible reduction event at −2.01 V, which was shifted positively by 280 mV compared to the first reduction peak of 1.…”

Two MnII, CuII complexes derived from 3,5‐bis(1‐imidazoly) pyridine: Synthesis, DNA binding, Molecular docking and cytotoxicity studies

“…Crystal data and structure refinement details are summarized in the Table and selected bond lengths and angles are given in Table . The structures of the complex 1–2 are stable in the solution state according to some similar ligands in some literatures …”

Ruthenium NNN complexes with a 2‐hydroxypyridylmethylene fragment for transfer hydrogenation of ketones

“…Although these complexes show high activity, they are not as good as the catalyst of Kunda's group . Yu's group developed various excellent NNN ruthenium catalysts with a pyrazole or benzotriazole heterocyclic ring (Figure d,e), with TOF values up to 3.5 × 10 5 h −1 …”

“…[32] Yu's group developed various excellent NNN ruthenium catalysts with a pyrazole or benzotriazole heterocyclic ring (Figure 1d,e), with TOF values up to 3.5 × 10 5 h −1 . [47,48] In the work reported in this paper, pyrazole or benzotriazole ring and 2-hydroxypyridylmethylene derivative were combined, and two NNN tridentate ligands L 2 and L 4 were synthesized and introduced to ruthenium centers.…”