The Ru=Ru double-bonded p-alkynecomplexes [Ru,(p-CO)(p-RC,R)(q-C5H5),] ( R = Ph or CF,) react in heptane or xylene at reflux with alkynes R'CECR' (R' = C0,Me or CF,) to link up to four molecules of alkyne; the structures of the complexes [ R U , ( C O ) { ~-C , ( C F , ) , ) ( ~-C ~H ~) ~] (two isomers) and [Ru,{p-C,(CF,),(CO,Me),}(q-C,H,),],which contains a C, ring with a C, 'tail', have been established by X-ray diffraction.

The Ru=Ru double-bonded p-alkyne complexes [ R u ~( ~-C O ) ( ~-R C ~R ) ( ~-C ~H ~) ~] react slowly or not at all with ethene and alkynes even under forcing conditions, but in the presence of acid C-H activation of ethene and alkyne-linking occur rapidly at room temperature to give di-p-vinyl complexes [ R u ~( C O ) ( ~-C R = C H R ) ( ~-C H = C H ~) ( ~-C ~H ~) ~] and metallacyclopentadiene complexes [Ru2(CO)( p-C4R4)(q-C5H5)2] respectively; the acid catalysis is shown to proceed via the formation of a Ru-Ru triple-bonded p-vinyl cation [ R ~~( p -c O ) ( p -c R = c H R ) ( q -c ~H ~) ~] + .