Oxidorhenium(V) Complexes with Phenolate‐ and Carboxylate‐Based Ligands: Structure and Catalytic Epoxidation

Several oxidorhenium(V) complexes with phenolate‐ and carboxylate‐based ligands were synthesized: [ReOCl(hpbi) 2 ] · THF, [ReOCl(hmpbta) 2 ], [ReOBr(hmpbta) 2 ], [ReOCl(hpbo) 2 ], [ReOCl(hpbt) 2 ] · 2MeCN, [ReO(OMe)(quin) 2 ], [ReO(OMe)(pic) 2 ], [ReO(OMe)(2,5‐dipic) 2 ] · C 5 H 5 N, [ReOCl(pic) 2 ], and [ReOCl(3‐ind) 2 ] [in which Hhpbi = 2‐(2‐hydroxyphenyl)‐1 H ‐benzimidazole, Hhmpbta = 2‐(2‐hydroxy‐5‐methylphenyl)benzotriazole, Hhpbo = 2‐(2‐hydroxyphenyl)‐2‐benzoxazole, Hhpbt = 2‐(2‐hydroxyphenyl)benzothiazole, Hquin = quinaldic acid, picH = picolinic acid, 2,5‐dipicH = 2,5‐pyridinedicarboxylic acid, and 3‐indH = indazole‐3‐carboxylic acid]. The compounds were characterized by spectroscopic methods and single‐crystal X‐ray diffraction analysis. Interestingly, the complex [ReO(OMe)(quin) 2 ] is a rare trans ‐N,N and trans ‐O,O isomer of [ReOX(N–O) 2 ] with two chelating quinoline‐2‐carboxylate ligands in the equatorial plane and a linear axial [O=Re–OMe] unit. The other disubstituted compounds were found to be the most common cis ‐N,N structure of [ReOX(N‐O) 2 ] with the oxygen atom of one of the chelating ligands in a trans position to the oxido ligand. All the complexes were tested in the epoxidation of cyclooctene with tert ‐butyl hydroperoxide (3 equiv.). The lowest conversion of only 3 % has been confirmed for [ReOCl(hpbi) 2 ]. All other complexes reached yields of cyclooctane oxide between 58 and 75 %.