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 com plex [t-BuC(Ni-Pr)(2)]Y[CH(SiMe3)(2)](2)-(mu-Cl)Li(THF)(3) (1), which was s tructurally characterized. Use of the potentially tridentate amidinate-amin e ligands [PhC(NSiMe3)N(CH2)(n)NMe2](-) (n = 2, B; 3, C) yielded the salt-f ree 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-compl exes 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 ami dinate and two amine nitrogens. The increased spacer length between the ami dinate 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 di methylamino functionalities is coordinated to the metal center.