Hydrogenation of imines with Ru complexes

A process for the reduction by hydrogenation, using molecular H2, of a C5-C20 substrate of formula

• wherein Ra and Rc represent, independently from each other, a hydrogen atom or a C1-C15 hydrocarbon group optionally comprising one to three oxygen atoms and/or one to two nitrogen atoms and/or one sulphur or halogen atom;
• Rb represents a C1-C15 hydrocarbon group optionally comprising one to three oxygen atoms and/or one to two nitrogen atoms and/or one sulphur or halogen atom, a hydrogen atom, a SO2Rb′, a ORb″ or a PORb′2 group wherein Rb′ represents a C1-C6 alkyl group or a phenyl or tolyl group and Rb′ represents a hydrogen atom, a C1-C6 alkyl group or a phenyl or tolyl group;
• or Ra and Rc represent, when taken together, a C1-C10 alkanediyl or alkenediyl group;
• provided that at least one Ra, Rb, or Rc is not a hydrogen atom;
• into the corresponding amine, wherein said process is carried out in the presence of at least one catalyst or pre-catalyst of formula
• [Ru(PP)(NN)n(RCOO)2](1) or [Ru(P)2(NN)n(RCOO)2] (1′)
• wherein n is 0 or 1;
• PP represents a C5-C50 bidentate ligand wherein the coordinating groups are two phosphino groups;
• P represents a C3-C50 monodentate ligand;
• NN represents a C2-C20 bidentate ligand wherein the coordinating atoms are two nitrogen atoms;
• and
• each R represents, simultaneously or independently, a hydrogen atom, a C1-C12 linear hydrocarbon group, or a branched or cyclic C3-C12 hydrocarbon group and said hydrocarbon group comprises optionally one to five heteroatoms selected amongst halogen, oxygen and nitrogen atoms;
• and
• wherein the process is performed in the absence of a base additive.