Add time:08/26/2019         Source:sciencedirect.com

The phosphorus/nickel ratio for 30 P-ligands and Ni(CO)4 as the catalytic system was varied over three orders of magnitude, and the effect upon the oligomerisation of 3-methyl-1-butyn-3-ol to yield dimers to tetramers was examined. With a catalytically effective ligand association, the formation of cyclooctatetraenes, which are the main products without a P-ligand, is inhibited in favour of the 1,3,5-trisubstituted benzene and a linear trimer.Bulky phosphites are very effective ligands for oligomerisation to the symmetric cyclic trimer.A plot of characteristics of the product distribution versus steric and electronic parameters of the ligands indicates that alkyl- and arylphosphines possess properties in the catalytic system different from alkyl- and arylphosphites as well as phenylphosphinites, so that regression analysis requires a cross-term of both parameters.The interpretation of characteristic alterations in the ligand concentration control maps is in agreement with the proposed mechanisms for the oligomerisation of alkynes by nickel complexes given in the literature.The steric influence of the phosphines on the ratio of the 1,2,4- to the 1,3,5-trisubstituted benzene is evident from experimental data; it increases from mono to di-association of the ligands.

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