Yttrium Alkyl Complexes with Triamino−Amide Ligands

Two new monoanionic tetradentate triamino−amide ligands, [(Me2NCH2CH2)2N-B-N(t-Bu)]- (B = (CH2)2, L1; SiMe2, L2) were prepared. Reaction of L1H with Y(CH2SiMe3)3(THF)2
yielded L1Y(CH2SiMe3)2 (1), which was structurally characterized. Compound 1 decomposes
at ambient temperature via metalation of one of the NMe2 methyl groups to give {[(CH2)MeN(CH2)2][Me2N(CH2)2]N(CH2)2N(t-Bu)}Y(CH2SiMe3) (2). Attempts to prepare L2Y(CH2SiMe3)2 resulted in very rapid ligand metalation. Both 1 and 2 react with [PhNMe2H][B(C6F5)4] to generate the cation [(L1)YCH2SiMe3]+. The combination of 1 and [Ph3C][B(C6F5)4]
is active in catalytic ethene polymerization, but with a short catalyst lifetime. The metalated
complex 2 reacts with ethene and with pyridine by stoichiometric insertion into the Y−CH2N
bond, and the latter product was structurally characterized. In L1Y(X)(CH2SiMe3) complexes,
the Y−amine distance trans to X is very sensitive to the nature of X, suggesting the presence
of a trans influence.