Neodymium dihalide complexes with a tridentate amidinate phosphine oxide ligand: synthesis, structure, and catalytic activity in isoprene polymerization

Resumo

The deprotonation of amidine 2-[Ph₂P(O)]C₆H₄NHC(Bu^t)=N(2,6-Me₂C₆H₃) (1) with BunLi affords lithium amidinate {2-[Ph₂P(O)]C₆H₄NLiC(Bu^t)=N(2,6-Me₂C₆H₃)}2 (2) having a dimeric structure, as demonstrated by X-ray diffraction. New amidinate dihalide complexes {2-[Ph₂P(O)]C₆H₄NC(Bu^t)N(2,6-Me₂C₆H₃)}NdHal₂(THF)₂ (Hal = I (3), Cl (4)) were synthesized by exchange reactions of lithium and potassium amidinates with anhydrous neodymium halides NdHal₃(THF)_n (Hal = I, n = 3.5; Cl, n = 0). The X-ray diffraction studies showed that the new compounds are monomeric and the amidinate ligand is tridentate. Chloride complex 4 involved in the three- and four-component catalyst systems 4–AlR₃–[Ph3C] [B(C₆F₅)₄] (1: 10: 1; AlR₃ = AlBuⁱ 3, AlMe₃), 4–AlR₃–PrⁱOH (1: 10: 10; AlR₃ = AlBuⁱ₃, AlMe₃), and 4–AlR₃–[Ph₃C][B(C₆F₅)₄]–PrⁱOH (1: 10: 1: 10; AlR₃ = AlBuⁱ₃, AlMe₃) exhibits activity in stereospecific isoprene polymerization and allows the preparation of high-molecular-weight polyisoprene samples with exceptionally high cis-1,4-unit content (up to 99.4%).