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RESEARCH PRODUCT

The oligomerisation of 3-hydroxy-1-alkynes with palladium(II) diketonates and phosphorus ligands as the catalytic system

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Abstract 3-Methylhex-1-yne-3-ol has been oligomerised by use of Pd(II) acetylacetonate with 31 different phosphorus ligands as catalyst, yielding a dimer (2,4-disubstituted but-1-en-3-yne) and a linear trimer (1,4,6-trisubstituted hexa-1,3-dien-5-yne) as the two main products. By input-output relations a variation of the diketonate and the P ligand, as weil as an alteration of the phosphorus/palladium ratio, has been connected with product ratios as dependent variables. Phosphines produced three association steps up to a cone angle of 170°; the third step representing a stop complex. For the first association the activity of the catalytic system and the portion of the 2,4-dimer increased with the donor character of the P ligands. Moreover the part of the 2,4-dimer was strongly favoured by an increasing cone angle of the ligand as well as by the volume of the substituents at the alkynol. The second association developed the more active systems with a modest steric effect of the ligands on product ratios. The trimerisation was favoured by π-acceptor ligands and by more electronegative substituents at the diketonate anion. The results served to support the hypothesis, that two mechanisms and ionic intermediates should be insolved.