Coupling of alkynes promoted by Ru(CO) 3(PPh 3) 2 and carbon dioxide: syntheses and structures of (η 4-C 4R 2R′ 2CO)Ru(CO) 2(PPh 3) (R=R′=Ph; R=Ph, R′=CCPh) and {Ph 2C 4(CCPh) 2}Ru(CO)(PPh 3) 2

Abstract

Dimerization of alkyne by Ru(CO) 3(PPh 3) 2 proceeded under carbon dioxide in refluxing toluene or C 6H 6 to afford a cyclopentadienone Ru(0) complex (R 2C 4R′ 2CO)Ru(CO) 2(PPh 3) (R=R′=Ph; R=Ph, R′=–CCPh) and cyclobutadiene Ru(0) complex (R 2C 4R′ 2)Ru(CO) 2(PPh 3) (R=Ph, R′=–CCPh) in moderate yields, each compound being formed as mixtures of isomers, 2,4-and 3,4-diethynylated cyclobutadiene-1-one and 1,2-and 1,3-diethynylated cyclobutadiene, from MS, IR, 13C-, 31P-NMR and X-ray analyses. At higher temperatures, a carbonate Ru(II) complex Ru(CO 3)(CO) 2(PPh 3) 2 was also obtained in 85% yield from the reaction in presence of diphenylacetylene. A cationic Ru(II) species supplied by (CO+CO 3 2−) formed via a reductive disproportionation of CO 2 is proposed as an intermediate in an earlier stage of the coupling reactions of the alkyne molecules.