Homo- and copolymerization of norbornene using tridentate IzQO palladium catalysts with dimethylaminoethyl as a side arm

Abstract

Late-transition metal complexes containing N-heterocyclic carbenes (NHCs) are still limited in the field of olefin polymerization, especially in the copolymerization of olefins with polar monomers. In this contribution, a series of tridentate imidazo[1,5-a]quinolin-9-olate-1-ylidene (IzQO) palladium catalysts 4a–4d with dimethylaminoethyl as a side arm were synthesized by Rh(III)-catalyzed C–H bond activation and annulation reactions from the tridentate o-aryloxide-NHC palladium complex 3. In the presence of Me₂AlCl, these palladium complexes showed high activities (up to 2.74 × 10⁸ g of PNB (mol of Pd)⁻¹ h⁻¹) and high thermal stability (up to 140 °C) toward homo- and copolymerization of norbornene with n-butyl vinyl ether (BVE) and methyl 10-undecanoate (UA). It was demonstrated that the rigid annulated backbone significantly enhanced the activities of these complexes, but had little effect on the incorporation rate in the copolymerization of norbornene with BVE and UA. The electron-withdrawing groups at the annulated backbone showed a positive effect on the (co)polymerization activity. In addition, the obtained copolymers showed high co-monomer incorporation and good solubility. As far as we know, this is the first report on the copolymerization of norbornene with vinyl ether monomers using NHC-based palladium complexes.