Hydrogenation of esters with Ru/tetradentate ligands complexes

A process for the reduction by molecular hydrogenation, of a substrate containing one or two ester or lactone functional groups into its corresponding alcohol or diol, the process comprising reducing said substrate with molecular hydrogen in the presence of a base and at least one catalyst or pre-catalyst in the form of a ruthenium complexes of formula 1 or 2

• [Ru(L4)Y2] (1)
• [Ru(L4)(X)n(Y)2-n](Z)n (2)
• wherein:
• L4 is a ligand of formula (4-A):
• R2 and R3, when taken separately, represent, simultaneously or independently, a linear, branched or cyclic C1 to C8 alkyl or alkenyl group optionally substituted, a C6 to C10 aromatic group optionally substituted, or an OR20′ or NR2′R3′ group, R2′ and R3′ being a C1 to C8 alkyl or alkenyl group;
• or the groups R2 and R3, when taken together, form a saturated or unsaturated ring optionally substituted, having 4 to 10 atoms and including the phosphorus atom to which the R2 and R3 groups are bonded ;
• R9, R10 and R11, taken separately, represent, simultaneously or independently, a hydrogen atom, a C1-C8 linear, branched or cyclic alkyl or alkenyl group optionally substituted or a C6 to C10 aromatic group optionally substituted;
• two adjacent or geminal R9, taken together, may form preferably C5 to C8, ring including the carbon atom to which the R9 groups are bonded;
• an R10 group and an R9 group, in α-position to the same N atom, can be bonded together to form a C4 - to C6 ring;
• two adjacent R11 groups can be bonded together to form a C6 to C10 aromatic ring optionally substituted or a C5 to C12 metallocediyl group optionally substituted and including the carbon atom to which the R11 groups are bonded;
• and
• k are, simultaneously or independently, equal to 0 or 1;
• each Y represents, simultaneously or independently, CO, a hydrogen or halogen atom, a hydroxyl group, or a C1-C6 alkoxy or carboxylic radical, or a BH4 or ALH4 group;
• X represents a C3-C30 mono-phosphine or a solvent;
• Z represents a non-coordinated anion;
• and
• n is 0, 1 or 2 and
• the substrate is a compound of formula (I)
• wherein Ra and Rb represent, simultaneously or independently, a linear, branched or cyclic C1-C30 aromatic, alkyl or alkenyl group optionally substituted;
• or
• Ra and Rb are bonded together and form a C4-C20 saturated or unsaturated group, optionally substituted;
• and
• wherein the substituents of Ra and Rb are a COORc, group, one, two or three halogen, ORc, NRc2 or Rc groups, in which Rc is a hydrogen atom, a halogenated C1- to C2 groups or a C1 to C10 cyclic, linear or branched alkyl, or alkenyl group.