The first reaction step in the thermolysis of zirconium and hafnium tetraalkyl complexes has been studied with ab initio molecular orbital calculations in comparison with that of the titanium tetraalkyl complexes (Wu, Y.-D.; Peng Z.-H.; Xue, Z. J. Am. Chem. Soc. 1996, 118, 9772). Several clear differences in geometry and reactivity between TiR4 and ZrR4 (HfR4) are predicted:  (1) While TiMe4 is in a staggered conformation, ZrMe4 and HfMe4 are predicted to be in an eclipsed conformation; (2) the activation energy for the unimolecular methane elimination through intramolecular hydrogen abstraction is in the order TiMe4 ≪ ZrMe4 < HfMe4; (3) the activation energy for the bimolecular methane elimination through intermolecular hydrogen abstraction for the three systems is much lower than that of the unimolecular mechanism and is in the order ZrMe4 < HfMe4 < TiMe4; (4) unimolecular α-hydrogen abstraction for Ti(n-Pr)Me3 and Ti(CH2CMe3)4 is more favorable than γ-hydrogen abstraction. However, the opposite is predicted for the Zr and Hf complexes. Chemical vapor deposition of ZrC from Zr(CH2CMe3)4 and Zr(CD2CMe3)4 has been studied. The major volatile products are neopentane and isobutene, which are in a ratio of about 2.3 in both reactions. In the case of Zr(CD2CMe3)4, the molar ratios of neopentane-d 2/neopentane-d 3 and isobutene-d 2/isobutene-d 0 are about 4.9 and 1.52, respectively. These support a mechanism in which γ-hydrogen abstraction is the first step of thermolysis.

M(NMe(2))(4) (M = Ti, Zr, Hf) were found to react with H(2)SiR'Ph (R' = H, Me, Ph) to yield H(2), aminosilanes, and black solids. Unusual amide hydride complexes [(Me(2)N)(3)M(mu-H)(mu-NMe(2))(2)](2)M (M = Zr, 1; Hf, 2) were observed to be intermediates and characterized by single-crystal X-ray diffraction. [(Me(2)N)(3)M(mu-D)(mu-NMe(2))(2)](2)M (1-d(2), 2-d(2)) were prepared through reactions of M(NMe(2))(4) with D(2)SiPh(2). Reactions of (Me(2)N)(3)ZrSi(SiMe(3))(3) (5) with H(2)SiR'Ph were found to give aminosilanes and (Me(2)N)(2)Zr(H)Si(SiMe(3))(3) (6). These reactions are reversible through unusual equilibria such as (Me(2)N)(3)ZrSi(SiMe(3))(3) (5) + H(2)SiPh(2) right arrow over left arrow (Me(2)N)(2)Zr(H)Si(SiMe(3))(3) (6) + HSi(NMe(2))Ph(2). The deuteride ligand in (Me(2)N)(2)Zr(D)Si(SiMe(3))(3) (6-d(1)) undergoes H-D exchange with H(2)SiR'Ph (R' = Me, H) to give 6 and HDSiR'Ph. The reaction of Ti(NMe(2))(4) with SiH(4) in chemical vapor deposition at 450 degrees C yielded thin Ti-Si-N ternary films containing TiN and Si(3)N(4). Ti(NMe(2))(4) reacts with SiH(4) at 23 degrees C to give H(2), HSi(NMe(2))(3), and a black solid. HNMe(2) was not detected in this reaction. The reaction mixture, upon heating, gave TiN and Si(3)N(4) powders. Analyses and reactivities of the black solid revealed that it contained -H and unreacted -NMe(2) ligands but no silicon-containing ligand. Ab initio quantum chemical calculations of the reactions of Ti(NR(2))(4) (R = Me, H) with SiH(4) indicated that the formation of aminosilanes and HTi(NR(2))(3) was favored. These calculations also showed that HTi(NH(2))(3) (3b) reacted with SiH(4) or H(3)Si-NH(2) in the following step to give H(2)Ti(NH(2))(2) (4b) and aminosilanes. The results in the current studies indicated that the role of SiH(4) in its reaction with Ti(NMe(2))(4) was mainly to remove amide ligands as HSi(NMe(2))(3). The removal of amide ligands is incomplete, and the reaction thus yielded "=Ti(H)(NMe(2))" as the black solid. Subsequent heating of the black solid and HSi(NMe(2))(3) may then yield TiN and Si(3)N(4), respectively, as the Ti-Si-N materials.