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

Abstract

The complexes [RuCl(Cy)(NH2Ph)2]Cl (1), [RuCl2(Cy)(NH2Bz)] (2), and [RuCl2(Cy)(NHBz2)] (3) were obtained under the same conditions from [RuCl2(Cy)]2; Cy = η6‐p‐cymene, Ph = phenyl, and Bz = benzyl. X‐ray crystallography showed the additional NH2Ph ligand in 1, differing from the neutral mono‐amine complexes 2 and 3. The number of amines in the complexes does not show clear correlations with s‐donor character or steric hindrance of the amines. Different reactivities were observed for ROMP of norbornene (NBE), measured from batch reactions and by kinetic studies using Raman and 1H NMR spectroscopy, with semiquantitative conversions: with 1 up to 30 °C and around 40% with 2 and 3. DFT calculations confirmed the proposal that the reactions occur with the release of an amine in complex 1 through a dissociative mechanism, while complexes 2 and 3 react through an associative mechanism with loss of amines. The presence of the amine in the propagation species of 1 indicates the participation of the amine as an auxiliary ligand. All carbene species are of the η2‐p‐cymene type, and the catalytic cycle occurs with a 14‐16‐14 electron counting mechanism.