Synthesis, characterization and catalytic activities of rhenium carbonyl complexes bearing pyridine-alkoxide ligands

Thermal treatment of Re2(CO)10 with pyridine-alkoxide ligands PyC(CH2)4OH (LaH) and PyCR1R2OH (R1 = CH3, R2 = C6H5 (LbH); R1 = H, R2 = C6H5 (LcH); R1 = H, R2 = 4-CH3C6H4 (LdH); R1 = H, R2 = 4-OMeC6H4 (LeH); R1 = H, R2 = 4-ClC6H4 (LfH); R1 = H, R2 = 4-CF3C6H4 (LgH)) respectively in refluxing xylene generated a series of dirhenium carbonyl complexes [PyC(CH2)4O]2 [Re(CO)3]2 (1a) and (PyCR1R2O)2 [Re(CO)3]2 (R1 = CH3, R2 = C6H5 (1b); R1 = H, R2 = C6H5 (1c); R1 = H, R2 = 4-CH3C6H4 (1d); R1 = H, R2 = 4-OMeC6H4 (1e); R1 = H, R2 = 4-ClC6H4 (1f); R1 = H, R2 = 4-CF3C6H4 (1g)). Complexes 1a−1g were characterized by NMR spectroscopy, elemental analyses and FT-IR spectroscopy. Furthermore, the molecular structures of complexes 1a, 1d and 1g were determined by single crystal X-ray diffraction analysis. In the presence of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxyl) as co-oxidant and molecular oxygen (ambient air) as terminal oxidant, these dirhenium carbonyl complexes showed moderate catalytic activity for aerobic oxidation of secondary alcohols.