Bis(pyrazole)- and bis(pyrazolyl)-palladium complexes as phenylacetylene polymerization catalysts

Two types of pyrazole-based palladium complexes were used to catalyze the polymerization of phenylacetylene. Catalysts with electron-withdrawing linkers, [{1,3-(3,5-R(2)pzCO)(2)C6H4}Pd2Cl2(mu-Cl)(2)] (R = 'Bu (1), Ph (2), Me (3), [{2,6-(3,5-R(2)pzCO)(2)C5H3N)}PdCl2] (R = 'Bu (4), Me (5)), show high conversion; whilst those with simple pyrazole ligands, [(3,5-R(2)pz)(2)PdCl2)] (R = H (6), Me (7), 'Bu (8)), [(3,5-'Bu(2)pz)(2)PdCl(Me)] (9), have much lower conversions. Conversion greatly improved when 9 was used to catalyze the co-polymerization of sulfur dioxide and phenylacetylene. Both types of catalysts produce predominantly trans-cisoidal polyphenylacetylene. (C) 2007 Elsevier Ltd. All rights reserved.