Journal
MOLECULAR CATALYSIS
Volume 528, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.mcat.2022.112457
Keywords
Catalytic epoxidation; (R)-carvone; Homogeneous catalysis; Gallium nitrate; Hydrogen peroxide; Metal-ligand cooperation
Categories
Funding
- CNPq [312288/2019-0, 422290/2016-5, 404843/2018-2]
- FAPESP [2018/01258-5, 2021/12342-0]
- Sustainable Technologies Unit of UFABC
- Ministry of Science and Higher Education of the Russian Federation
- FCT, Portugal [UIDB/00100/2020, LA/P/0056/2020]
- European Unions Horizon 2020 research and innovation program [860762]
- Coordenaao de Aperfeioamento de Pessoal de Nivel Superior-Brasil (CAPES) [001]
- Marie Curie Actions (MSCA) [860762] Funding Source: Marie Curie Actions (MSCA)
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In this study, the catalytic epoxidation of (R)-carvone by the Ga(NO3)3/H2O2 system was explored, along with the investigation of metal-ligand cooperation using 17 different ligands. The results show that different ligands exhibit different selectivities and efficiencies in the epoxidation reaction.
In this work, the catalytic epoxidation of (R)-carvone by the Ga (NO3)(3)/H2O2 system was studied alongside the metal-ligand cooperation by exploring 17 different ligands. It was observed that the acidic ligands such as acetic acid mostly favor the epoxidation of the endocyclic double bond of (R)-carvone (22% yield, 1 h), while nitrogen heterocycles direct the epoxidation to the exocyclic double bond, especially the ones that are unsubstituted or have electron-donating groups, such as pyrazine (28% yield, 5 h), 4-dimethylaminopyridine (28% yield, 8 h), and 1-methyimidazole (43% yield, 8 h). Pyrazinecaboxylic acid favored the epoxidation of the exocyclic double bond (25%, 3 h). EPR analysis of both Ga(NO3)3/H2O2 and Ga(NO3)3/PCA/H2O2 systems indicates the presence of hydroxyl radicals in the reaction medium, although these do not determine the epoxidation rate that is likely regulated by the interaction of Ga-peroxo complexes with (R)-carvone. This study contributes to widening the application of the cooperating ligand concept in molecular catalysis toward further development of more se-lective and efficient epoxidation reactions catalyzed by non-transition metal centers.
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