Selective reduction of aromatic nitro compounds affording aromatic amines under CO/H 2O conditions catalyzed by phosphine-added rhodium and ruthenium carbonyl complexes

Abstract

High catalytic activities for the selective reduction of aromatic nitro compounds to the corresponding amines under the mild reaction conditions of room temperature and 1 atm of CO were found to be exhibited by chelatephosphine (dppe, dppm, etc.; dppe: 1,2-bis(diphenylphosphino)ethane, dppm: bis(diphenylphosphino)methane)-added rhodium and ruthenium carbonyl complexes in a 5 N NAOH aqueous solution. The reduction proceeded not only with high catalytic activities, but also with remarkably high nitro group selectivities; for example, 1-nitroanthraquinone afforded 1-aminoanthraquinone without other unsaturated groups (such as CO) being reduced. PR 3-added Rh(CO) 2(acac) complexes (PR 3: PEtPh 2, PEt 2Ph, PEt 3, etc.; acac: acetylacetonato) in diglyme in a 5 N NaOH aqueous solution were also found to show significant catalytic activities for the reduction of aromatic nitro compounds under mild CO/H 2O conditions. Both electronic and steric factors of phosphine ligands are important in making this reaction proceed at such remarkable rates.