Transfer hydrogenation of ketones catalyzed by complexes of ruthenium(II) with the heterotridentate [P,N,O] ligands (S)-2-[{2-(diphenylphosphanyl)benzylidene}amino]propan-1-ol, (S)-2-[{2-(diphenylphosphanyl)benzyl}amino]propan-1-ol or the [P,N,S] ligand (S)-2-(dimethylamino)-1-(diphenylphosphino)-3-(methylthio)propane

Abstract

Ruthenium complexes [mer-κ3-{(S)-Ph2PC6H4CH = NCH(CH3)CH2OH}PPh3RuCl2P,N,O] 1, [mer-κ3-{(S)-Ph2PC6H4CH2NHCH(CH3)CH2OH}PPh3RuCl2P,N,O] 2 and [{(S)-Ph2PCH2C(H)N(CH3)2CH2SCH3}PPh3RuCl2] 3 have been prepared and their activity in the catalytic transfer hydrogenation of ketones investigated. Using isopropanol-isopropoxide as the hydrogen donor, 1.OPPh3.toluene and 2.OPPh3.CH2Cl2 both showed low activity with average turnover frequency up to 1.1 per hour and enantiomeric excess up to 39.9% where 3 showed no activity. With dimethylamine borane as the hydrogen donor, 1.OPPh3.toluene and 3 proved active catalysts showing average activity up to 3.0 turnovers per hour and selectivity up to 46% ee. New structural information on [(HNMe2)2BH2]Cl, a side product in the reaction, is presented.