Reactions of Tetrakis(dimethylamide)−Titanium, −Zirconium and −Hafnium with Silanes: Synthesis of Unusual Amide Hydride Complexes and Mechanistic Studies of Titanium−Silicon−Nitride (Ti−Si−N) Formation
2001-07-20T00:00:00Z (GMT) by
M(NMe2)4 (M = Ti, Zr, Hf) were found to react with H2SiR‘Ph (R‘ = H, Me, Ph) to yield H2, aminosilanes, and black solids. Unusual amide hydride complexes [(Me2N)3M(μ-H)(μ-NMe2)2]2M (M = Zr, 1; Hf, 2) were observed to be intermediates and characterized by single-crystal X-ray diffraction. [(Me2N)3M(μ-D)(μ-NMe2)2]2M (1-d2, 2-d2) were prepared through reactions of M(NMe2)4 with D2SiPh2. Reactions of (Me2N)3ZrSi(SiMe3)3 (5) with H2SiR‘Ph were found to give aminosilanes and (Me2N)2Zr(H)Si(SiMe3)3 (6). These reactions are reversible through unusual equilibria such as (Me2N)3ZrSi(SiMe3)3 (5) + H2SiPh2 ⇄ (Me2N)2Zr(H)Si(SiMe3)3 (6) + HSi(NMe2)Ph2. The deuteride ligand in (Me2N)2Zr(D)Si(SiMe3)3 (6-d1) undergoes H−D exchange with H2SiR‘Ph (R‘ = Me, H) to give 6 and HDSiR‘Ph. The reaction of Ti(NMe2)4 with SiH4 in chemical vapor deposition at 450 °C yielded thin Ti−Si−N ternary films containing TiN and Si3N4. Ti(NMe2)4 reacts with SiH4 at 23 °C to give H2, HSi(NMe2)3, and a black solid. HNMe2 was not detected in this reaction. The reaction mixture, upon heating, gave TiN and Si3N4 powders. Analyses and reactivities of the black solid revealed that it contained −H and unreacted −NMe2 ligands but no silicon-containing ligand. Ab initio quantum chemical calculations of the reactions of Ti(NR2)4 (R = Me, H) with SiH4 indicated that the formation of aminosilanes and HTi(NR2)3 was favored. These calculations also showed that HTi(NH2)3 (3b) reacted with SiH4 or H3Si−NH2 in the following step to give H2Ti(NH2)2 (4b) and aminosilanes. The results in the current studies indicated that the role of SiH4 in its reaction with Ti(NMe2)4 was mainly to remove amide ligands as HSi(NMe2)3. The removal of amide ligands is incomplete, and the reaction thus yielded “Ti(H)(NMe2)” as the black solid. Subsequent heating of the black solid and HSi(NMe2)3 may then yield TiN and Si3N4, respectively, as the Ti−Si−N materials.
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