ADDITION OF CARBOXYLIC-ACIDS TO ALKYNES CATALYZED BY RUTHENIUM COMPLEXES

The addition of carboxylic acids to alkynes has been found to be catalyzed by Ru3(CO)12 as well as by dimeric ruthenium carboxylate complexes of general structure [Ru(RCOO)(CO)2(L)]2. The reaction yields vinyl esters. It was found to be general with respect to both the acid and the alkyne. A rearranged regioisomer vinyl ester is also formed in the reactions with phenylacetylenes. A stereospecific kinetically controlled syn-addition of the carboxylic acid to the triple bond has been observed. Regioselectivity with asymmetrical alkynes is poor. Observation of an order of reaction of 1/2 with respect to [Ru(PhCOO)(CO)2(PhCOOH)]2, the catalyst, indicates that the active catalytic species are mononuclear ruthenium complexes. A stoichiometric reaction modelled on the catalytic reaction was monitored by infrared spectroscopy and finally quenched with PPh3. The quenching products were identified as new mononuclear ruthenium complexes, and these identifications greatly facilitated understanding of the mechanism leading to a suggested catalytic cycle.