Oxorhenium(V) complexes with 1H-benzimidazole-2-carboxylic acid – Synthesis, structural characterization and catalytic application in epoxidation reactions

Depending on the experimental conditions three novel oxorhenium(V) complexes incorporating 1H-benzimidazole-2-carboxylic acid (2-bimH) cis-Cl,Cl-[ReOCl2(2-bim)(PPh3)] (1), cis-Br,Br-[ReOBr2(2-bim)(PPh3)] (2) and [ReOCl(2-bim)2] (3) were synthesized. The reported complexes were characterized by spectroscopic methods (IR, 1H, 13C, 31P NMR, UV–Vis, ESI+-MS), cyclic voltammetry and single crystal X-ray diffraction analysis. To elucidate the structural, spectroscopic and bonding properties, calculations at the DFT level were undertaken. The catalytic competencies of compounds 1–3 were investigated in the epoxidation of cyclooctene with tert-butyl hydroperoxide (TBHP) as oxidant. The studies revealed higher catalytic activities for complexes based on one 1H-benzimidazole-2-carboxylic acid (compounds 1 and 2) and phosphine as ancillary ligand, with the yield of cyclooctane-oxide varying between 60% and 64% (50 °C, 24 h).

The [ReOX2(2-bim)(PPh3)] (X = Cl, Br) and [ReOCl(2-bim)2] complexes have been prepared in the reactions of 1H-benzimidazole-2-carboxylic acid with [ReOX3(PPh3)2] and [ReOCl3(OPPh3)(SMe2)], respectively, and characterized by IR, 1H, 13C and 31P NMR, UV–Vis spectroscopy. The crystal and molecular structures of the complexes have been determined by X-ray crystallography. Electronic structures of the complexes have been calculated using the density functional theory (DFT) method. Spin-allowed electronic transitions have been calculated using the time-dependent DFT method and the UV–Vis spectra have been discussed on this basis. The catalytic properties of the complexes have been determined with olefin epoxidation.Figure optionsDownload as PowerPoint slide