Aminorhenium carbon dioxide complexes: formal oxidation of a carbon monoxide ligand with peroxy-acids or bromine/hydroxide

The electron-rich aminorhenium complexes η5:η1-C5H4CH2CH2NR(CH3)Re(CO)2 (3a–d; R=methyl, benzyl, n-butyl, n-butyl-OH) are easily oxidized with peroxy-acids to give the corresponding η2-CO2 complexes η5: η1- C5H4CH2CH2NR(CH3)Re(CO)(η2-CO2) (4a–d) in excellent yield. The resultant η2-CO2 complex is predominantly the anti-isomer. The structures of η2-CO2 complex η5:η1-C5H4CH2CH2N(CH3)(n- C4H8OH)Re(CO)(η2-CO2) (4d-anti) and the corresponding CO complex 3d have been confirmed by X-ray crystallography. The η2-CO2 complexes 4a–4d are stable at ambient temperature under air. In addition to peroxy-acid oxidation, bromination of the aminorhenium dicarbonyl complexes followed by base treatment also provided the corresponding η2-CO2 complexes. The reaction mechanism for the formation of CO2 complex from the corresponding dicarbonyl is discussed briefly.