Reactions of 1,4-diphenylbut-1-en-3-yne and 1,4-diferrocenylbuta-1,3-diyne with Ru3(CO)10(μ-dppm). Unusual structures of the clusters Ru3(CO)5(η-CO)(η-dppm){μ3-C4Ph2(CH=CHPh)2} (two isomers) and Ru3(CO)5(η-CO)(η-dppm){μ3-C4Fc2(CH≡CFc)2}