Structural and kinetic insights into the mechanism for ring opening metathesis polymerization of norbornene with [RuCl2(PPh3)2(piperidine)] as initiator complex

• The induction period for ROMP with the title complex is elucidated by DFT studies.
• The PPh3 molecules are lost when leading to the active carbene-complex.
• The O-ester group from the metal-carbene moiety stabilizes a 14-electron Ru-piperidine species.
• An electronic trans-synergism effect is operative throughout the ROMP mechanism.
• A kinetic profile is depicted.

This investigation combines theoretical results and experimental data to elucidate the main kinetic and mechanism for the ring opening metathesis polymerization of norbornene by means of the [RuCl2(PPh3)2(piperidine)] complex as catalyst initiator. Structural species were defined and a kinetic profile of the entire reaction is depicted. The determined mechanism showed an associative reaction between the [RuCl2(PPh3)2(piperidine)] complex initiator and ethyl diazoacetate as the first step, resulting in a metal-carbene species. This species loses one triphenylphosphine molecule (PPh3) and the global rate-determining step is associated with a removal of the second PPh3 molecule due to an electronic trans-synergism between piperidine and this PPh3 molecule. Entropic factors are crucial to the spontaneity observed for the dissociation of both PPh3 ligands. The step following the rate-determining one is associated with the binding of a norbornene molecule and a similar trans-synergism between this monomer and piperidine activates the catalysis. This electronic effect maintains the system in a very important conformation along the catalytic chain.

The mechanism for ROMP of norbornene with an alternative in-situ generated Ru-carbene species was elucidated by the combination of theoretical and experimental data. An associative reaction with ethyl diazoacetate promotes a total loss of phosphines. The catalysis occurs via an electronic trans-synergism between the piperidine and the monomer.Figure optionsDownload high-quality image (170 K)Download as PowerPoint slide