Monocationic Bis-Alkyl and Bis-Allyl Yttrium Complexes: Synthesis, 89Y NMR Characterization, Ethylene or Isoprene Polymerization, and Modeling

Monocationic complexes of yttrium with various bis-alkyl and bis-allyl ligands Y­(CH2SiMe2Ph)2(THF)4]­[B­(C6F5)4], [Y­(CH2C6H4NMe2)2(THF)2]­[B­(C6F5)4], and [Y­[1,3-(SiMe3)2C3H3]2(THF)2]­[B­(C6F5)4] have been prepared by protonolysis of the corresponding homoleptic tris-alkyl or -allyl complexes using the anilinium borate salt [PhNMe2H]­[B­(C6F5)4]. The resulting ion-pair complexes have been isolated and characterized by different techniques such as elemental analysis, 1H, 13C, and 89Y NMR, and EXAFS for the allyl cationic complex [Y­[1,3-(SiMe3)2C3H3]2(THF)2]­[B­(C6F5)4]. More specifically, a 1H-coupled 89Y INEPT sequence has been developed in order to quantify the metal/alkyl ligand stoichiometry of both synthesized neutral tris-alkyl and cationic bis-alkyl yttrium complexes. The activity of the cationic complexes toward ethylene and isoprene homopolymerization has been assessed. In presence of TiBA, polyethylene was produced with activities ranging from 6 to 26 kgPE molY–1 h–1 bar–1. The molar mass of the yielded polymers shows a bimodal distribution. Under similar conditions, polyisoprene was produced up to full conversion of the monomer. The microstructure of the yielded polyisoprene displayed mainly cis-1,4-units (ca. 60–70%) and 3,4-units (ca. 20–30%). Only a few percent of trans-1,4 units was revealed.