Scandium and neodymium dichloride complexes with Ph3EO ligands (E = C, Si): synthesis, structure, and catalytic activity in isoprene polymerization

Abstract

The reaction of equimolar amounts of ScCl₃ and [Ph₃EOLi] (E = C, Si) afforded the monomeric dichloride complexes Ph₃EOScCl₂(THF)₃ (E = C (1), Si (2)) in 78 and 81% yields, respectively. The reaction of NdCl₃ with [Ph₃COLi] gave the dimeric dichloride ate complex [Ph₃CONd(THF){(μ-Cl)₂Li(THF)₂}μ-Cl]₂ (3). Under similar conditions, the reaction of NdCl₃ with [Ph₃SiOLi] afforded the dimeric neodymium monochloride complex [(Ph₃SiO)₂Nd(THF)₂(μ-Cl)]₂ (4) regardless of the ratio of the reagents. Complexes 1–4 involved in the two- and three-component catalytic systems (1–4)—[Ph₃C][B(C₆F₅)₄] (1: 1) and (1–4)—AlBuⁱ₃—[Ph₃C][B(C₆F₅)₄] (1: 10: 1) initiate the polymerization of isoprene (IP) at room temperature and provide the 14–100% monomer-to-polymer conversion ([IP]/[Ln] = 1000) within 1 to 24 h. The synthesized polymer samples have predominantly a trans-1,4 structure (59.1–80.6%), a low number-average molecular weight (M_n = 0.71–12.71 · 10³), and a relatively broad molecular weight distribution (M_w/M_n = = 1.90–4.01). The reaction of complex 1 with [Ph₃C][B(C₆F₅)₄] (1: 1) gave the cationic dichloride complex [ScCl₂(THF)₄]⁺[B(C₆F₅)₄]⁻ (5). Complex 5 initiates the isoprene polymerization, resulting in the quantitative monomer-to-polymer conversion within 1 h. The synthesized polyisoprene contains 59.1% of trans-1,4 units and has M_n = 4.78 · 10³ and a narrow molecular weight distribution (M_w/M_n = 1.65).