Electronic synergism in [RuCl2(PPh3)2(amine)] complexes differing the reactivity for ROMP of norbornene and norbornadiene

The reactivity of the new complex [RuCl2(PPh3)2(3,5-Me2piperidine)], complex 1, was investigated for ring opening metathesis polymerization (ROMP) of norbornene (NBE) and norbornadiene (NBD) in the presence of ethyl diazoacetate (EDA) in CHCl3. The aim is to observe the combination of PPh3 and an amine as ancillary ligands concerning the steric hindrance and the electronic perturbation in the properties of the N-bound site when replacing the amines. Thus, the results with 1 were compared to the results obtained when the amine is piperidine (complex 2). Reaction with 1 provides 70% yield of isolated polyNBE (Mn = 8.3 × 104 g/mol; PDI = 2.03), whereas 2 provides quantitative reaction (Mn = 1.2 × 105 g/mol; PDI = 1.90) with [NBE]/[Ru] = 5000, [EDA]/[Ru] = 48 and 1.1 μmol of Ru for 5 min at 25 °C. The resulting polymers showed c.a. 62% of trans-polyNBE, determined by 1H NMR, and Tg = 32 °C, determined by DSC and DMTA. For ROMP of NBD, 1 showed quantitative yield with PDI = 2.62 when [NBD]/[Ru] = 5000 for 20 min at 25 °C, whereas the reaction with 2 reached 55% with PDI = 2.16 in the same conditions. It is concluded that the presence of the two methyl groups in the piperidine ring provides an increase in the induction period to produce the Ru-carbene species justifying better polyNBE results with 2, and a greater amine⟶σRu⟶πmonomer synergism which contributed to the best activation of less tensioned olefin as NBD.

Graphical abstract. 3,5-Dimethylpiperidine and piperidine were evaluated as ancillary ligands in the reactivity of similar Ru complexes for ring opening metathesis polymerization. The methyl groups in the amine ring provided a best activation of norbornadiene. However, they delay the Ru-carbene production, with better polynorbornene results for the piperidine-complex.Figure optionsDownload full-size imageDownload high-quality image (27 K)Download as PowerPoint slideResearch highlights▶ Amines as ancillary ligands afforded successful ROMP of NBE and NBD. ▶ The amines provide different induction period for the Ru-carbene formation. ▶ The amine⟶σRu⟶πmonomer electronic synergism is the reason for catalyst efficiency.