Synthesis of Tantalum(V) Amido Silyl Complexes and the Unexpected Formation of (Me2N)3Ta(η2-ONMe2)[OSi(SiMe3)3] from the Reaction of (Me2N)4Ta[Si(SiMe3)3] with O2

The synthesis and characterization of amido silyl complexes of tantalum(V) free of π-anionic ligands are reported. The amido silyl chloride complexes (Me2N)3Ta(SiR3)Cl [SiR3 = Si(SiMe3)3 (1a), SiPh2But (2)] were prepared from (Me2N)3TaCl2 and the corresponding silyllithium reagents Li(THF)3Si(SiMe3)3 and Li(THF)3SiPh2But. The amido silyl complexes (Me2N)4Ta(SiR3) [SiR3 = Si(SiMe3)3 (3), SiPh2But (4)] were synthesized by the reactions of (Me2N)4TaCl with Li(THF)3SiR3. Complex 3 was found to react with 1 equiv of O2 to give an oxidation product (Me2N)3Ta(η2-ONMe2)[OSi(SiMe3)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.