Date: May 1993
Creator: Cundari, Thomas R., 1964- & Gordon, Mark S.
Description: This article discusses small molecule elimination from group IVB (Ti, Zr, Hf) amido complexes. An ab initio quantum chemical analysis of HX (X = H, CH₃, Cl, NH₂, SiH₃) elimination by group IVB (Ti, Zr, Hf) amidos (H₂(X)M - NH₂ → H₂M = NH + HX), of interest in the context of CVD precursor design, is reported. Several deductions may be drawn from the calculations. First, in the transition state (TS) for HX elimination, electropositive and electroneutral X give rise to metal-transannular hydrogen (Ht) distances only slightly longer than normal metal-terminal hydride bonds lengths, while electronegative X groups yield substantially longer MHt distances. Second, the HX elimination barrier (∆Hǂelim) is lower when HX is polarized Hδ- • Hδ+ (X = SiH₃) or nonpolar (X = H). Third, a plot of calculated ∆Hǂelim versus MHt distances in the TS. Fourth, analysis of the electronic structure along the intrinsic reaction coordinate (IRC) supports the importance of N-H•••M agostic interactions preceding N-H scission. Fifth, the IRC shows the MHt distance decreasing as Ht is transferred from N to X, reaching a minimum when the transfer is roughly half complete, and then increasing once more is HX is eliminated. These results point to the ...
Contributing Partner: UNT College of Arts and Sciences