Molecular structures and dynamic behaviour of two isomers of [Ru3(µ-H)(µ3-Me2NC4H4)(CO)9] formed from 1-dimethylaminobut-2-yne and containing η2-alkene-1,3-diyl and η2-alkene-1,2-diyl ligands respectively

Abstract

Single-crystal X-ray structures of the isomeric compounds [Ru₃(µ-H)(µ₃-MeCCCHNMe₂)(CO)₉](1) and [Ru₃(µ-H)(µ₃-MeCCHCNMe₂)(CO)₉](2), both prepared from [Ru₃(CO)₁₂] and the aminoalkyne MeCCCH₂NMe₂, have been determined. Isomer (1) formally contains the µ₃-η²-alkyne MeCCCHN⁺ 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.