Coupling of alkynes promoted by Ru(CO)3(PPh3)2 and carbon dioxide:: syntheses and structures of (η4-C4R2R2′CO) Ru(CO)2(PPh3) (R = R′ = Ph; R = Ph, R′ = CCPh) and {Ph2C4(CCPh)2}Ru(CO)(PPh3)2

Dimerization of alkyne by Ru(CO)(3)(PPh3)(2) proceeded under carbon dioxide in refluxing toluene or C6H5 to afford a cyclopentadienone Ru(0) complex (R2C4R2'Co)Ru(Co)(2)(PPh3) (R = R' = Ph; R = Ph, R' = -C=CPh) and cyclobutadiene Ru(0) complex (R2C4R2')Ru(CO)(2)(PPh3) (R = Ph, RI = -C=CPh) in moderate yields, each compound being formed as mixtures of isomers, 2, band 3,4-diethynylated cyclobutadiene-l-one and 1,2-and 1,3-diethynylated cyclobutadiene, from MS, IR, C-13-, P-31-NMR and X-ray analyses. At higher temperatures, a carbonate Ru(II) complex Ru(CO3)(CO)(2)(PPh3)(2) was also obtained in 85% yield from the reaction in presence of diphenylacetylene. A cationic Ru(II) species supplied by (CO + CO32-) formed via a reductive disproportionation of CO2 is proposed as an intermediate in an earlier stage of the coupling reactions of the alkyne molecules. (C) 1999 Elsevier Science S.A. All rights reserved.