Homogeneous telomerization of1,3-butadiene with alcohols in the presence of palladium catalysts modified by hybrid chelate ligands

1,3-Butadiene telomerization with methanol and higher alcohols was investigated in the presence of different palladium(0) and palladium(II) complexes based on hybrid chelate ligands. When (PO)-O-boolean AND Ligands were used, the resulting palladium complexes displayed poor activity and low selectivity to telomers, also in the presence of alkoxide promoters. Even worse performances were found when ionic palladium(II) or neutral palladium(0) and palladium(II) complexes based on (NN)-N-boolean AND chelate ligands were employed in combination with alkoxide promoters. Better results were obtained by using ionic palladium(II) complexes with (PNN)-N-boolean AND-N-boolean AND ligands in combination with an alkoxide promoter. Very promising results were achieved when the telomerization reaction was catalyzed by palladium(0) complexes obtained in situ from Pd(dba), and (PN)-N-boolean AND ligands. The data are discussed and interpreted in terms of different capability of the chelate Ligands, depending on their size and donor power, to give palladium complexes with metal sites at low oxidation state characterized at the same time by a sufficient stability and coordinative unsaturation to promote high catalytic activity and selectivity. (C) 1999 Elsevier Science B.V. All rights reserved.