The novel cyclodimerization of phenylacetylene at a ruthenium(II) centre. The synthesis and X-ray structural characterization of the first metallacyclopentatriene, [(η-C5H5)Ru(C4Ph2H2)Br], and its facile conversion into metallacyclopentadienes

Abstract

Cyclodimerization of two molecules of phenylacetylene at the ruthenium(II) centre in [(η-C₅H₅)Ru(η-C₈H₁₂= cyclo-octa-1,5-diene) gives the novel ruthenacyclopentatriene [(η-C₄H₅)Ru(C₄Ph₂H₂)Br] characterized by ¹H and ¹³C n.m.r. spectroscopy and by X-ray analysis; the triene undergoes facile ‘oxidative addition’ with donor ligands L (e.g. morpholine, trimethyl phosphite, dimethylphenylphosphine) in a bimolecular reaction involving an associative mode of activation to give the ruthenacyclopentadienes [(η-C₅H₅)Ru(L)(C₄Ph₂H₂)Br].