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

Insertion of LiCH(SiMe3)(2) into the CN bond of the appropriate nitriles RCN afforded dimeric beta-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 beta-diketiminato lithium 1b ligand transfer, the cyclo-1,3-diazasilane heterocyclic complex [N(R)C(BUt)C(H)C(o-C5H4N)NSiMe2]Zrcl(4) (4) was prepared using 1b and ZrCl4. Unexpectedly, the chelating beta-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 Xray 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.