A practical ruthenium based catalytic system bearing a switchable selectivity between the dimerization and cyclotrimerization reactions of alkynes

In this study, a practical and inexpensive switchable catalytic system (cyclotrimerization vs. dimerization), [RuCl2(p-cymene)](2)/PR3 has been developed for the catalytic dimerization of terminal alkynes. Bulky and basic phosphine derivatives, PCy3 and P(Pri-)(3), were used with [RuCl2(p-cymene)](2) and excess of terminal alkyne to in situ formation of vinylidenic intermediates which are active towards dimerization reactions. Effect of phosphine/ruthenium ratio has been investigated. A solvent study was carried out and toluene was found to be the most versatile solvent for both cyclotrimerization and dimerization reactions. A set of aryl and alkyl acetylenes were chosen as substrates to investigate the effect of the nature of the substrates on alkyne dimerization reactions catalyzed by [RuCl2(p-cymene)](2)/PR3. In conclusion, we have shown that [RuCl2(p-cymene)](2)/PCy3 can be used as a practical and inexpensive catalytic system which has a switchable selectivity towards cyclotrimerization and dimerization reactions. Best results in means of regioselectivity and yield were observed by using arylacetylene derivatives in these reactions. This catalytic system emerges as an economical method for the transformation of arylacetylenes to corresponding enyne and arene derivatives in excellent yields and selectivity. (C) 2012 Elsevier B.V. All rights reserved.