Reactivity of the p-Cymene-Ruthenium Complex with Two Phenylamines for Metathesis Polymerization of Norbornene Compared to the Reactivity of Complexes with a Single Benzylamine or Dibenzylamine

The complexes [RuCl(Cy)(NH₂Ph)₂]Cl (1), [RuCl₂(Cy)(NH₂Bz)] (2), and [RuCl₂(Cy)(NHBz₂)] (3) were synthesized under identical conditions from [RuCl₂(Cy)]₂, where Cy=η⁶-p-cymene, Ph=phenyl, and Bz=benzyl. X-ray crystallography revealed an additional NH₂Ph ligand in 1, distinguishing it from the neutral mono-amine complexes 2 and 3. The number of amines in these complexes did not correlate clearly with the σ-donor character or steric hindrance of the amines. Different reactivities were observed for the ROMP of norbornene (NBE), as measured by batch reactions and kinetic studies using Raman and ¹H NMR spectroscopy. Semiquantitative conversions reached up to 90 % with complex 1 and around 40 % with complexes 2 and 3. DFT calculations supported the hypothesis that the reaction for complex 1 involves the release of an amine through a dissociative mechanism, whereas complexes 2 and 3 react through an associative mechanism involving amine loss. The presence of an amine in the propagation species of complex 1 suggests the participation of the amine as an ancillary ligand. All carbene species are of the η²-p-cymene type, and the catalytic cycle follows a 14–16-14 electron counting mechanism.