Selective co-oligomerization of 1,3-butadiene and carbon dioxide with immobilzed catalysts

Recent results on the heterogeneously catalyzed co-oligomerization of 1,3-butadiene and carbon dioxide are presented. Optimized preparation methods for the reaction of Pd(eta(3)-C3H5)(eta(5)-C5H5) 2 with [(i-Pr)(2)P-CH2]-polystyrene derivative PS-P yield palladium catalysts immobilized on polystyrene support (PS-01, PS-02, PS-03). Consequently, 'leaching' is reduced and catalysts may be re-used several times after a simple separation and cleaning procedure. Additionally, a similar immobilization of palladium complex units on silica is reported. The correlation of the formation of 2-[(E)-ethylidene]-6-heptene-5-olide 1 with process parameters such as temperature, kind of catalyst, and solvent, is presented and discussed in detail. Analytical methods (CP-MAS-NMR, XPS, SEM) were used to determine PS-02 before and after use. XPS data indicate an initial Pd-0 oxidation state. Used PS-02 possesses a changed coordination sphere around the anchored palladium centres which agrees to its different catalytic behaviour. (C) 1999 Elsevier Science B.V. All rights reserved.