Unsymmetrical Ru-NHC catalysts: a key for the selective tandem Ring Opening-Ring Closing alkene Metathesis (RO-RCM) of cycloocteneElectronic supplementary information (ESI) available: Synthesis procedures, characterizations, catalytic reactivity test, X-ray crystal structure analysis. See DOI: 10.1039/c1dt11643f

Dissymmetry for selectivity: NHC ligand with two different pendant group allows the selective formation of cyclic oligomers in place of polymers opening new strategy to generate macrocycles. Dissymmetric NHC ligands on G-II type catalysts allow the selective formation of cyclic oligomers in place of polymers.