A direct comparison between neutral active sites and their corresponding cationic analogues is enabled by protonation of neutral bis(imino)phenoxy complexes, active for ethylene polymerization. The additional imine motif compared to parent salicylaldiminato catalysts does not influence the microstructure of the products in ethylene polymerization, but allows for the incorporation of a proton right next to the active center in an N···H+···O bridge yielding cationic complexes. These show an increased Ni-O bond length and a drastically reduced electron density on the Ni atom. In pressure reactor experiments, two different catalysts that produce linear HDPE or undergo extensive chain walking, respectively, in their neutral version, both produce short chain oligomers when the catalyst is charged cationically. A mechanistic analysis by DFT methods reveals an increased propensity for β-hydride elimination compared to ethylene insertion chain growth for the cationic complexes. This results from a higher relative stability of β-agostic species vs olefin-coordinated species.

The Impact of Charge in a Ni(II) Polymerization Catalyst

Voccia M.;Falivene L.;Caporaso L.
;
2021-01-01

Abstract

A direct comparison between neutral active sites and their corresponding cationic analogues is enabled by protonation of neutral bis(imino)phenoxy complexes, active for ethylene polymerization. The additional imine motif compared to parent salicylaldiminato catalysts does not influence the microstructure of the products in ethylene polymerization, but allows for the incorporation of a proton right next to the active center in an N···H+···O bridge yielding cationic complexes. These show an increased Ni-O bond length and a drastically reduced electron density on the Ni atom. In pressure reactor experiments, two different catalysts that produce linear HDPE or undergo extensive chain walking, respectively, in their neutral version, both produce short chain oligomers when the catalyst is charged cationically. A mechanistic analysis by DFT methods reveals an increased propensity for β-hydride elimination compared to ethylene insertion chain growth for the cationic complexes. This results from a higher relative stability of β-agostic species vs olefin-coordinated species.
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11386/4776784
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 10
  • ???jsp.display-item.citation.isi??? 10
social impact