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

The deprotonation of amidine 2-[Ph2P(O)]C6H4NHC(But)=N(2,6-Me2C6H3) (1) with BunLi affords lithium amidinate {2-[Ph2P(O)]C6H4NLiC(But)=N(2,6-Me2C6H3)}2 (2) having a dimeric structure, as demonstrated by X-ray diffraction. New amidinate dihalide complexes {2-[Ph2P(O)]C6H4NC(But)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%).