C-2-symmetric ansa-lanthanidocene complexes. Synthesis via silylamine elimination and beta-SiH agostic rigidity

The synthesis as well as the spectroscopic and structural characterization of a new class of C-2-symmetric. mononuclear metallocene complexes of the l anthanide elements is described. Heteroleptic lanthanidocene silylamide com plexes have been obtained ate-complex-free according to silylamine eliminat ion reactions of complexes Ln[N(SiHMe2)(2)](3)(THF)(x) (x = 1, Ln = Sc; x = 2, Ln = Y, La, Nd, Lu) and linked, substituted cyclopentadiene and indene systems, The molecular structure of [Me2Si(C5Me4)(2)]La[N(SiHMe2)(2)] (95% isolated yield) has been determined by X-ray crystallography. Brintzinger-t ype, indenyl-derived metallocene complexes have been isolated in racemic yi elds as high as 72%. TR and multinuclear NMR spectroscopy (H-1, C-13, Si-29 , Y-89) reveals the presence of an unprecedented strong diagostic interacti on between the electron-deficient metal centers and the SiH moiety of the b is(dimethylsilyl)amide ligand: Sill stretching vibrations as low as 1759 cm (-1) and (1)J(Si.H) coupling constants as low as 133 Hz indicate a distinct weakening of the SiH bonding. X-ray structure analyses of the compounds ra c-[Me2Si(2-Me-Benz-Ind)(2)]Ln[N(SiHMe2)(2)] (Ln = Y, Lu) and rac-[Me2Si(2-M e-C9H5)(2)]Ln[N(SiHMe2)(2)] (Ln = Y, Lu) show that the structural features of both the chelating ancillary ligands and such agostically fused metallac ycles depend on the type of the ligand and the size of the metal: bite angl es Omega of approximately "U-shaped" ansa-ligands as large as 68.2(2)degree s and Ln-Si and Ln-H contacts as close as 3.028(1) and 2.37(3) Angstrom, re spectively, have been detected, the latter forcing very large Si-N-Si angle s up to 160.1(2)degrees. The isolation of reaction intermediates such as Y[ N(SiHMe2)(2)](3)(THF) and partly exchanged [Me2Si(2-Me-4-Ph-Ind)(2)H]Y[N(Si HMe2)(2)](2) provides mechanistic details of this peculiar silylamine elimi nation reaction. Additionally the pK(a) values of various protonated ligand s including new 9-(SiHMe2)-fluorene, 3-(SiHMe2)-indene, and 3-(SiHMe2)-2-Me -indene determined according to the method of Fraser give evidence of a the rmodynamically controlled ligand exchange.