Substituent influence of 2-pyridinecarboxylic acid framework in olefin epoxidation with oxidorhenium(V) complexes

In this project, we report the synthesis, full characterization, and catalytic activity in cyclooctene epoxidation reactions of five new oxidorhenium(V) complexes ( 1 ( ReOCl 2 (PPh 3 )( L1 ) ), 2 ( [ReOCl 2 (PPh 3 )( L2 )] ), 3 ( [ReOCl 2 (PPh 3 )( L3 )] ), 4 [ReOCl 2 (PPh 3 )( L4)] , and 5 ( [ReOCl 2 (PPh 3 )( L5 )]·OPPh 3 ) with 2-picolinic acid derivatives as bidentate ligands: 6-fluoropyridine-2-carboxylic acid (H L1 ), 6-chloropyridine-2-carboxylic acid (H L2 ), 6-bromopyridine-2-carboxylic acid (H L3 ), 5-bromopyridine-2-carboxylic acid (H L4 ), and 5-hydroxypyridine-2-carboxylic acid (H L5) . Variations of the ligand allow to investigate the impact of various halide substituents (F, Cl, and Br) and their position on the pyridine ring to assess their effect on catalytic activity. The chemical structures and purity of synthesized complexes 1–5 were confirmed using 1 H and 13 C NMR spectroscopy, infrared spectroscopy, mass spectrometry, and elemental analysis. Additionally , single crystals of complexes 1 , 2 , and 5 suitable for X-ray diffraction were obtained, and their solid-state structures confirmed . Among the tested complexes, complex 2 with the ligand 6-chloropyridine-2-carboxylic acid exhibited the highest catalytic activity in the cyclooctene epoxidation reaction, reaching the highest catalytic rate with a conversion of 75%. • Catalytic activity in cyclooctene epoxidation reactions of new rhenium(V) complexes. • Impact of various halide substituents on pyridine ring on their catalytic activity. • Ligand 6-chloropyridine-2-carboxylic acid influenced the highest catalytic activity.