The synthesis and characterization of amido silyl complexes of tantalum(V) free of π-anionic ligands are reported. The amido silyl chloride complexes (Me 2 N) 3 Ta(SiR 3 )Cl [SiR 3 ) Si(SiMe 3 ) 3 (1a), SiPh 2 Bu t (2)] were prepared from (Me 2 N) 3 TaCl 2 and the corresponding silyllithium reagents Li(THF) 3 Si(SiMe 3 ) 3 and Li(THF) 3 SiPh 2 Bu t . The amido silyl complexes (Me 2 N) 4 Ta-(SiR 3 ) [SiR 3 ) Si(SiMe 3 ) 3 (3), SiPh 2 Bu t (4)] were synthesized by the reactions of (Me 2 N) 4 -TaCl with Li(THF) 3 SiR 3 . Complex 3 was found to react with 1 equiv of O 2 to give an oxidation product (Me 2 N) 3 Ta(η 2 -ONMe 2 )[OSi(SiMe 3 ) 3 ] (5), and the structure of 5 was confirmed by X-ray crystallography. The spectroscopic data and crystal structure determination reveal that the coordination geometry around Ta metal in 1a and 2-4 is trigonal bipyramid with silyl ligands in an equatorial position.Early-transition-metal amido complexes have attracted much attention in recent years in part because of their important applications as precursors in chemical vapor deposition of microelectronic metal nitride (MN x ) and M-Si-N ternary films as diffusion barriers in Sibased microelectronic devices. 1,2 In particular, M-Si-N ternary films, which are often amorphous, have shown better diffusion barrier properties than, e.g., TiN films that are usually polycrystalline and thus have grain boundaries for diffusion. 1c,d,2 Although numerous well-

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A series of early-transition-metal silyl complexes free of anionic π-ligands such as cyclopentadienyl (Cp = η5-C5H5) have been synthesized. These Cp-free complexes (Me2N)3MSi(SiMe3)3 [M = Zr (1), Hf (2)], (Me2N)3TiSiPh2But (3), (Me2N)3ZrSiPh2But·0.5THF (4), (Me2N)3HfSiPh2But·nTHF [n = 0.5 (5a), 1 (5b)], and (Me2N)2[(Me3Si)2N]ZrSiR3 [SiR3 = Si(SiMe3)3 (7), SiPh2But (8)] were prepared by metathetic reactions of chloro triamido complexes (Me2N)3MCl (M = Ti, Zr, Hf) or (Me2N)2[(Me3Si)2N]ZrCl (6) with silyllithium reagents Li(THF)3Si(SiMe3)3 or Li(THF)3SiPh2But. The structures of 1, 3, 4, 5b, and 8 have been determined by X-ray crystallography and show that 1, 3, and 8 adopt a distorted tetrahedral coordination geometry while 4 and 5b have a distorted trigonal bipyramidal geometry around the metal. The unit cell parameters are as follows. 1:  space group R3c, a = 15.505(2) Å, c = 19.308(4) Å, V = 4019.9(13) Å3, Z = 6. 3:  space group P21, a = 8.633(5) Å, b = 14.790(7) Å, c = 9.388(4) Å, β = 92.44(4)°, V = 1197.6(10) Å3, Z = 2. 4:  space group P bca, a = 16.538(9) Å, b = 17.282(7) Å, c = 18.566(8) Å, V = 5306(4) Å3, Z = 8. 5b:  space group P na21, a = 17.463(6) Å, b = 9.453(3) Å, c = 17.800(6) Å, V = 2938(2) Å3, Z = 4. 8:  space group P ca21, a = 19.775(5) Å, b = 10.182(2) Å, c = 15.752(5) Å, V = 3172(2) Å3, Z = 4. The M−Si bond distances for 1, 3, 4, 5b, and 8 are 2.781(2), 2.635(2), 2.803(2), 2.807(4), and 2.860(2) Å, respectively. The Zr−Si bond in 8, to our knowledge, is the longest reported Zr−Si bond.