HOMOGENEOUS AND BIPHASIC OLIGOMERIZATION OF TERMINAL ALKYNES BY SOME WATER-SOLUBLE RHODIUM CATALYSTS

The catalytic activity of six water soluble rhodium compounds, RhCl3.3H2O 1, RhCl(Ph2PC6H4-3-SO3Na)3.4H2O2, (COD)RhCl(Ph2PC6H4-3-SO3Na)-H2O3, [(COD)Rh(mu-Ph2PC6H4-3-SO2-O)]2 4, [(CO)Rh(Ph2PC6H4-3-CO2H)(mu-SPh)]2 5, and [Rh3O(OAc)6-(H2O)3]OAc 6, for oligomerization of model hydrophilic and lipophilic terminal alkynes was investigated under homogeneous and under biphasic conditions. While propynoic acid 7 is converted by all six catalysts solely into trimellitic acid, 8, and trimesic acid, 9, phenylacetylenes 10 either dimerize, trimerize or give stereoregular polymers. The nature of the oligomerization products proved to depend on the catalyst, the medium and the reaction temperature. In acetonitrile, complex 4 transforms the various phenylacetylenes (except 4-nitrophenylacetylene, 10f ) mainly or entirely to the head-to-tail dimers, 13, which undergo thermal rearrangement to the head-to-head isomers, 14.