Abstract: Process for preparing bridged, stereorigid, stereomerically pure dialkoxide metallocenes, diaryl oxide metallocenes and preferably diphenoxide metallocenes of the general formula Q(Cp)(Cp?)M(OR3)2 in which Cp=a cyclopentadienyl, an indenyl or a fluorenyl radical; Cp?=one of the Cp groups; Q=a single- or multimembered bridge (R1—Z—R2)b between Cp and Cp?, in which R1 and R2 may be the same or different and are each a hydrogen atom, a C1-C10-alkyl group, a C6-C10-aryl group, and Z is carbon, silicon or germanium where b=1, 2 or 3; M=a transition metal of group 4, especially Zr and Hf and Ti; O=oxygen; R3=a C1-C10-alkyl group, a C6-C10-aryl group, where the alkyl group may be branched or unbranched and may be substituted by aryl groups, and the aryl group may contain further substituents, which is characterized in that, in the first stage, a bridged, stereorigid metallocene dihalide in the form of a rac/meso mixture, having the general formula Q(Cp)(Cp?)M(X)2 is reacted with an alkylating reagent of the general

Abstract: The present invention relates to catalytic compositions for esterification, transesterification and polycondensation reactions, a process for the catalysis of said reactions employing such catalytic compositions and polyesters or resins obtainable by this process.