Abstract Displacement of piperidine from Ru(COD)(piperidine)- trans-(H)Cl (I) by 1,4-diaza-1,3-dienes (DAD: RNCR′CR′NR) gives the complexes cis-Ru(COD)(DAD)-(H)Cl (III). With relatively bulky DAD ligands the complexes III are unstable and are converted into compounds IV, which are also formed from III on heating. Complexes III are not accessible from Ru(COD)(DAD)Cl 2(V). If the analogous starting material involving a cycloheptatriene Ib in place of the COD ligand is used, a piperidide anion is preserved as ligand instead of a hydride. In the room temperature 1H NMR spectra of rigid asymmetric III all twelve hydrogen atoms of the COD ligand can be seen separately. A full assignment has been made by use of 2D-H/H-correlated spectra. The highest field resonance (1.2 ppm) is assigned to an olefinic H atom, shielded by the DAD chelate. Complexes III catalyse the isomerization of terminal alkenes to a cis/ trans mixture ( 20 80 ) of internal alkenes. During the catalytic hydrosilylation of 1-alkenes this isomerization is a competing side reaction. Thermal decomposition of III gives free 1,3-COD; the decomposition under hydrogen gives cyclooctane stoichiometrically. In catalytic experiments III is found to catalyse the isomerization of 1,5-COD to 1,3-COD via 1,4-COD. Under hydrogen pressure (20 bar), III catalyses the hydrogenation of 1-hexene and cyclohexene. Four different ways in which one, two, or three ‘vacant sites’ can be generated starting from III are discussed.