2 6 6 tetramethyl 3 5 heptanedionate terbium tris 2 2 6 6 tetramethyl 3 5 heptanedionate dysprosium tris 2 2 6 6 tetramethyl 3 5 heptanedionate holmium tris 2 2 6 6 tetramethyl 3 5 heptanedionate erbium tris 2 2 6 6 tetramethyl 3 5 heptanedionate thulium tris 2 2 6 6 tetramethyl 3 5 heptanedionate ytterbium tris 2 2 6 6 tetramethyl 3 5 heptanedionate and lutetium tris 2 2 6 6 tetramethyl 3 5 heptanedionate catalysts used in the invention can be either in solid form or in solution for example dissolved in one of the starting materials it is also possible to use mixtures of two or more catalysts the concentration of catalyst present is from 0 01 ppm to 10 000 ppm preferably from 0 1 ppm to 5000 ppm more preferably from 1 ppm to 1000 ppm based on the total mass of the organic carbonate and aliphatic polyol the reaction temperature of the transesterification reaction of at least one organic carbonate with at least one aliphatic polyol in the presence of at least one catalyst according to the invention for the preparation of aliphatic oligocarbonate polyols having a number average molecular weight of from 500 to 5000 is from 40 u00b0 c to 250 u00b0 c preferably from 60 u00b0 c to 230 u00b0 c more preferably from 80 u00b0 c to 210 u00b0 c examples of organic carbonates which can be used include aryl alkyl and alkylene carbonates such compounds are.