Yttrium Alkyl and Benzyl Complexes with Amino−Amidinate Monoanionic Ancillary Ligands

The sequential reaction of YCl 3 (THF) 3.5 with [ t -BuC(N i -Pr) 2 ]Li (Li[ A ]) and 2 equiv of LiCH(SiMe 3 ) 2 gave the mono(amidinate) dialkyl yttrium complex [ t -BuC(N i -Pr) 2 ]Y[CH(SiMe 3 ) 2 ] 2 (μ-Cl)Li(THF) 3 ( 1 ), which was structurally characterized. Use of the potentially tridentate amidinate−amine ligands [PhC(NSiMe 3 )N(CH 2 ) n NMe 2 ] - ( n = 2, B; 3, C ) yielded the salt-free dialkyl complexes [PhC(NSiMe 3 )N(CH 2 ) n NMe 2 ]Y[CH(SiMe 3 ) 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(NSiMe 3 )N(CH 2 ) 2 NMe 2 ] 2 Y(R) 2 (R = CH 2 Ph, 3a; CH 2 SiMe 3, 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 complex, [PhC(NSiMe 3 )N(CH 2 ) 3 NMe 2 ] 2 YCH 2 Ph ( 4 ). In this compound only one of the two dimethylamino functionalities is coordinated to the metal center.