The acid-base chemistry of some ruthenium ethyne-1,2-diyl complexes, [{Ru(CO) 2 (η-C 5 H 4 R)} 2 (μ 2 -C≡C)] (R=H, Me) has been investigated. Initial protonation of [{Ru(CO) 2 {η-C 5 H 4 R}} 2 (μ 2 -C≡C)] gave the unexpected complex cation, crystallised as the BF 4 salt, [{Ru(CO) 2 (η-C 5 H 4 R}} 3 (μ 3 -C≡C)][BF 4 ] (R=Me structurally characterised). This synthesis proved to be unreliable but subsequent, careful protonation experiments gave excellent yields of the protonated ethyne-1,2-diyl complexes, [{Ru(CO) 2 {η-C 5 H 4 R)} 2 (μ 2 -η 1 :η 2 -C≡CH)](BF 4 ) (R=Me structurally characterised) which could be deprotonated in high yield to return the starting ethyne-1,2-diyl complexes.