Molecular structures and dynamic behaviour of two isomers of [Ru₃(μ-H)-(μ₃-Me₂NC₄H ₄)(CO)₉] formed from 1-dimethylaminobut-2-yne and containing η²-alkene-1,3-diyl and η²-alkene-1,2-diyl ligands respectively

Single-crystal X-ray structures of the isomeric compounds [Ru₃(μ-H) (μ₃-MeC=CCH=NMe₂)(CO)₉] (1) and [Ru₃(μ-H)(μ₃-MeC=CHC=NMe₂)(CO) ₉] (2), both prepared from [Ru₃(CO)₁₂] and the aminoalkyne MeC≡CCH₂NMe₂, have been determined. Isomer (1) formally contains the μ₃-η²-alkyne MeC≡CCH=N⁺ Me₂ which requires the associated negative charge of the zwitterion to be located at the ruthenium atoms. ¹³C N.m.r. spectra reveal localised dynamic exchange of axial and equatorial CO ligands at Ru atoms and these processes together with a rotation of the μ₃-alkyne lead to a single ¹³CO n.m.r. signal at +90 °C. The isomer (2) formed by heating (1), contains two 1,3-related Ru-C σ bonds and a η²-alkene group. Although there is localised axial-equatorial CO exchange at two of the three Ru atoms, no μ₃ ligand rotation is observed in this case.