Synthesis, mechanism and ethylene polymerization catalysis of Ge(iv), Sn(ii) and Zr(iv) complexes derived from substituted β-diketiminates

Abstract

Insertion of LiCH(SiMe₃)₂ into the CN bond of the appropriate nitriles RCN afforded dimeric β-diketiminato lithium complexes [Li{N(SiMe₃)C(R)C(H)C(R′)N(SiMe₃)}]₂ (1a, R = R′ = NMe₂; 1b, R = Bu^t, R′ = o-C₅H₄N). Lithium salt 1a was used as a precursor to react with SnCl₂ and GeCl₄, respectively, and complexes [ClSn{N(SiMe₃)C(NMe₂)C(H)C(NMe₂)N(SiMe₃)}] (2) and [Cl₂Ge{NC(NMe₂)C(H)C(NMe₂)N(GeCl₃)}] (3) were obtained in good yields. By β-diketiminato lithium 1b ligand transfer, the cyclo-1,3-diazasilane heterocyclic complex (4) was prepared using 1b and ZrCl₄. Unexpectedly, the chelating β-diketiminato backbone in 3 acts as a dianionic ligand, whereas in 4, the ligand acts as a neutral cyclo-1,3-diazasilane heterocyclic ring to coordinate with the Zr center. The X-ray structures of 2–4 are presented, and reaction pathways for each complex are proposed. Upon activation with methylaluminoxane, complex 4 exhibits good activity for ethylene polymerization.