Yttrium alkyl and benzyl complexes with amino-amidinate monoanionic ancillary ligands

The sequential reaction of YCl3(THF)(3.5) with [t-BuC(Ni-Pr)(2)]Li (Li[A]) and 2 equiv of LiCH-(SiMe3)(2) gave the mono(amidinate) dialkyl yttrium complex [t-BuC(Ni-Pr)(2)]Y[CH(SiMe3)(2)](2)-(mu-Cl)Li(THF)(3) (1), which was structurally characterized. Use of the potentially tridentate amidinate-amine ligands [PhC(NSiMe3)N(CH2)(n)NMe2](-) (n = 2, B; 3, C) yielded the salt-free dialkyl complexes [PhC(NSiMe3)N(CH2)(n)NMe2]Y[CH(SiMe3)(2)](2) (n = 2, 2a; 3, 2b). A structure determination of 2a showed the tridentate ligand to adopt an approximately meridional geometry. Attempts to prepare analogous benzyl or trimethysilylmethyl complexes with ligand B yielded the ate-complexes Li[PhC(NSiMe3)N(CH2)(2)NMe2](2)Y(R)(2) (R = CH2Ph, 3a; CH2SiMe3, 3b). A crystal structure of 3a showed that the Li ion is encapsulated by two amidinate and two amine nitrogens. The increased spacer length between the amidinate and amine functionalities in ligand C prevented encapsulation of the Li ion, but still produced a bis(amidinate) yttrium benzyl comp lex, [PhC(NSiMe3)N(CH2)(3)NMe2](2)YCH2Ph (4). In this compound only one of the two dimethylamino functionalities is coordinated to the metal center.