Computational study on transamination of alkylamides with NH3 ...

ARTICLE IN PRESSY.S. Won et al. / Journal of Crystal Growth 311 (2009) 3587–3591 35892p+Dimethylamine2t42.4 ‡TS42.427.6Intermediate2i28.9 ‡ 56.5TBTDMT0.0Fig. 2. Calculated energetics of the b-hydride elimination of TBTDMT to generate Ta(MeNCH 2 )(NMe 2 )[(N(t-Bu)]. Energies are reported in kcal/mol.3t-a9.43p-aTSTBTDMT+ NH 312.1 ‡+0.0TBTDMT•NH 3 - 2.7 - 3.0Dimethylamine3t-b23t-b1TS231.2TS119.83i-b31.53p-bTBTDMT+ NH 30.022.5TBTDMT•NH 3Intermediate -0.3- 2.72.4+t-butylamineFig. 3. Calculated energetics of the transamination of a dimethylamido ligand (a) and tert-butylamido ligand (b) of TBTDMT with NH 3 . Energies are reported in kcal/mol.Table 1Calculated rate constants for selected individual steps in the decomposition ofTBTDMT at different temperatures.Entry ReactionsaE a ln A a k(s 1 )(kcal/mol)25 1C 3001C 6001C1 TBTDMT-2t 36.7 18.4 2.7 10 19 9.5 10 8 0.42 TBTDMT NH 3 -3t-a 13.2 30.1 2.5 10 3 1.2 10 8 5.6 10 93 TBTDMT NH 3 -3t-b1 23.7 30.2 5.1 10 5 1.2 10 4 1.4 10 74 3i-b-3t-b2 32.2 33.4 7.6 10 10 1.6 10 2 2.8 10 6a E aand A are the activation energy and pre-exponential factor in theArrhenius form, k=A exp( E a /RT), obtained from the plot of the calculated rateconstant vs. temperature.order of magnitude even at an elevated temperature of 600 1C. Incontrast, the dimethylamido ligand exchange was calculated to bekinetically competent for film growth, while tert-butylimidoligand exchange was significantly slower due to its relativelyhigher barrier (Fig. 3b).These calculations are consistent with a switch to a transaminationpathway lowering the growth temperature when TBTDETwas used in the presence of NH 3 (growth at 300–375 1C, comparedto 500–650 1C with TBTDET as a single-source precursor) andexplains the efficient removal of carbon-containing ligands in thepresence of NH 3 compared to the facilitated carbon incorporationin the deposited films via a self-decomposition pathway (Fig. 2)[2–4,24–26]. Similar reactions are likely to be involved in the use