The indenyl complexes [RuX(η 5 -C 9 H 7 )(dppm)] (dppm ) bis(diphenylphosphino)methane, X ) H, D) react with phenylacetylene to give the products of syn addition [Ru{(E)-CHdCXPh}(η 5 -C 9 H 7 )(dppm)] in toluene, in the temperature range 40-80 °C. The indenyl complexes [RuH(η 5 -C 9 H 7 )LL′] (L ) L′ ) PMe 2 Ph; L ) PPh 3 , L′ ) PMe 2 Ph; L ) PPh 3 , L′ ) PMe 3 ; LL′ ) dppe) and [RuH(η 5 -Me 3 C 9 H 4 )(CO)(PPh 3 )] and the cyclopentadienyl complex [RuH(η 5 -C 5 H 5 )(dppm)] do not react with PhCtCH, even under more forcing conditions. The complexes [RuH(η 5 -C 9 H 7 )LL′] (LL′ ) dppe; LL′ ) dppm; L ) L′ ) PMe 2 Ph; L ) PPh 3 , L′ ) PMe 3 ; L ) PPh 3 , L′ ) PMe 2 Ph) and the indenyl-substituted complexes [RuH(η 5 -Me 3 C 9 H 4 )(CO)(PR 3 )] (PR 3 ) PPh 3 , P i Pr 3 ) react with dimethyl acetylenedicarboxylate to give the alkenyl derivatives [Ru{(E)-C(CO 2 Me)dCH(CO 2 Me)}(η 5 -C 9 H 7 )LL′] and [Ru{(E)-C(CO 2 -Me)dCH(CO 2 Me)}(η 5 -Me 3 C 9 H 4 )(CO)(PR 3 )], respectively, in diethyl ether under reflux. The reaction of [RuH(η 5 -C 9 H 7 )LL′] with methyl propiolate yields the R-metalated alkenyl complexes [Ru{C(CO 2 Me)dCH 2 }(η 5 -C 9 H 7 )LL′] (LL′ ) dppe, dppm; L ) L′ ) PMe 2 Ph; L ) PPh 3 , L′ ) PMe 3 ) in refluxing diethyl ether. A kinetic study has been carried out for the reaction of the complexes [RuX(η 5 -C 9 H 7 )(dppm)] with phenylacetylene in toluene, by 1 H and 31 P{ 1 H} NMR spectroscopy. The reactions are first order with respect to the ruthenium complex and to the alkyne. The hydride and the deuteride complexes react at the same rate; intermediates are not detectable neither by kinetic studies nor by spectroscopy. The activation parameters, from rate measurements in the range 40-60 °C, are as follows: ∆H q ) 17 ( 2 kcal mol -1 , ∆S q ) -21 ( 4 cal mol -1 K -1 . An associative mechanism is proposed for the reaction, which involves the formation of an intermediate from the ruthenium complex and the alkyne under rate-determining steady-state conditions, followed by fast hydride migration and product formation. Due to the lack of reactivity of the analogous cyclopentadienyl complex [RuH(η 5 -C 5 H 5 )(dppm)], the reaction represents a case of indenyl effect. On the other hand, the indenyl and the cyclopentadienyl complexes react at comparable rates with the activated alkyne methyl propiolate.