The interaction of RuCl₂L(η⁶-arene) complexes with terminal alkynes provides a general route to arene ruthenium-carbene complexes. The activation of HC≡CR (R=alkyl, aryl, SiMe3) by arene ruthenium(II) complexes in alcohol produces alkoxy-alkylcarbene complexes, via electrophilic vinylidene-ruthenium intermediates. Comparative electrochemical studies of arene ruthenium(II) and isoelectronic cyclopentadienyl ruthenium(II) complexes demonstrate that the electron deficiency of the [(arene)(L)(Cl)Ru]⁺ fragments can explain the high reactivity of the corresponding vinylidene intermediates toward nucleophilic additions. Arene ruthenium complexes readily promote the dehydration of prop-2-yn-1-ol derivatives HC≡C-C(R)(R’)OH to give alkoxy-alkenyl carbene and polyenyl carbene ruthenium derivatives. Analogous alkenylcarbene complexes can be produced by activation of alkenylacetylenes HC≡C-C(R)=CH₂. These reactions occur via allenylidene intermediates (Ru=C=C=CR₂, which have been isolated and characterized in several cases [R,R’=Ph,Fc]. The reaction of diynes HC≡C-C≡C-CR₂OY(Y=H, SiMe₃) with arene ruthenium complexes in the presence of various nucleophiles opens the route to new carbene and cumulenyl carbene complexes: in methanol, the reaction leads to methoxy-butatrienyl carbine complexes which reacts with water to give 3-oxo-1,4-pentadienyl complexes, whereas in ethanol, i-propanol or diphenylamine 3-alkenyl-allenylidene ruthenium complexes are obtained selectively. The formation of these compounds can be explained by the initial formation of the metallacumulene Ru⁺=(C=)₄CR₂ which is the site of a nucleophilic addition at either carbon C(1) or carbon C(3). In the presence of a basic amine HNiPr₂, the activation of the diyne leads to a different reaction and the formation of diynylruthenium derivatives.