REACTIONS OF CO-2(CO)(8) WITH RC(2)R' ALKYNES .2. SYNTHESIS OF CO-2(CO)(6)(RC(2)R') COMPLEXES - OLIGOMERIZATION OR CYCLOTRIMERIZATION REACTIONS OF SUBSTITUTED ACETYLENES

The reactions of Co-2(CO)(8) with asymmetrically substituted alkynes lead to complexes Co-2(CO)(6)(RC(2)R') (1). These catalyze the cyclotrimerization of alkynes to substituted benzenes. Here we report on the synthesis and characterization of some new complexes 1 and on their reactivity with an excess of alkynes in relatively mild conditions; the characterization of new intermediate Co-2(CO)(4)(RC(2)R')(3) flyover derivatives (complexes 2) and the synthesis of some symmetrically and asymmetrically substituted benzenes is reported and commented. In some instances alkyne oligomers instead of cyclotrimers were obtained; the reactions are strongly dependent on the type of catalyst, on the conditions adopted and on the steric and electronic effects of the substituents on the alkynes, as shown also by a comparison of our results with those of analogous reactions on other cobalt and nickel derivatives.