Chloro(η5-dihydropentalenyl)bis(triphenylphosphine)ruthenium(II): synthesis, structural characterization and catalytic activity in the dimerization of phenylacetylene

Reactions between HRuCl(PPh3)3 and 1,3- or 1,5-cyclooctadiene yield the 1,2-dihydropentalenyl complex (η5-C8H9)Ru(PPh3)2Cl through a series of steps including olefin insertion and electrocyclization. The reaction is accompanied by the loss of two equivalents of hydrogen. The product crystallizes in the monoclinic space group (No. 2). (η5-C8H9)Ru(PPh3)2Cl catalyzes the dimerization of phenylacetylene to a ≈2:1 mixture of Z:E 1,4-diphenyl-1-buten-3-yne. Comparison of the catalytic activity of (η5-C8H9)Ru(PPh3)2Cl with (η5-C5H5)Ru(PPh3)2Cl, (η5-C5Me5)Ru(PPh3)H3 and {η5-HB(pz)3}Ru(PPh3)2Cl suggests that the more electron-rich η5 ligands favor formation of the Z isomer.