N-Heterocyclic Carbene Based Zirconium Complexes For Use In Lactones Ring Opening Polymerization

A catalytic process for the production of polyesters based on lactide, comprising the step of employing a compound of formula (I) as a catalyst

• wherein
• M is Zr or Hf;
• R1 is selected from halogen, C1-C10 Alkyl, C1-C10 alkoxy, aryl, benzyl (Bn), aryloxy, benzyloxy or amide of the formula N(R7)(R8),
• R2 is optional and is a coordinative solvent,
• X is a halogen, C1-C10 Alkyl, C1-C10 alkoxy, aryl, benzyl (Bn), aryloxy, benzyloxy or amide of the formula N(R7)(R8),
• R3 and R4 are independently from each other selected from the group consisting of hydrogen, C1-C10 alkyl, and C5-C10 cycloalkyl, the alkyl groups being optionally substituted by halogen;
• C1-C10 alkoxy, unsubstituted phenyl or substituted phenyl,
• R5 and R6 are independently from each other selected from the group consisting of hydrogen, C1-C10 alkyl, C5-C10 cycloalkyl, the alkyl groups being optionally substituted by halogen;
• unsubstituted phenyl or substituted phenyl,
• R5 and R6 are optionally linked together to form an unsaturated or saturated 5 to 6 membered ring, wherein the cycle may have one or more chiral centers,
• R7 and R8 are independently from each other selected from the group consisting of C1-C10 alkyl, C5-C10 cycloalkyl, unsubstituted phenyl or substituted phenyl (with substituents being halogen, C1-C10 alkyl or nitro).