Volatility and High Thermal Stability in Tantalum Complexes Containing Imido, Amidinate, and Halide or Dialkylamide Ligands

Abstract

Treatment of Ta(NtBu)Cl(3)(py)(2) with 2 equiv of Li(iPrNCMeNiPr) or Li(tBuNCMeNtBu) afforded Ta(NtBu)(iPrNCMeNiPr)(2)Cl and Ta(NtBu)(tBuNCMeNtBu)(2)Cl in 63% and 61% yields, respectively. Treatment of Ta(NtBu)(iPrNCMeNiPr)(2)Cl or Ta(NtBu)(tBuNCMeNtBu)(2)Cl with LiNRR' afforded Ta(NtBu)(iPrNCMeNiPr)(2)(NRR') and Ta(NtBu)(tBuNCMeNtBu)(2)(NRR') in 79-92% yields (R, R' = Me, Et). Treatment of Ta(NtBu)(tBuNCMeNtBu)(2)Cl with AgBF(4) afforded Ta(NtBu)(tBuNCMeNtBu)(2)F in 54% yield, while treatment of Ta(NtBu)(tBuNCMeNtBu)(2)Cl with BBr(3) afforded Ta(NtBu)(tBuNCMe-NtBu)(2)Br in 68% yield. X-ray crystal structures of Ta(NtBu)(tBuNCMeNtBu)(2)F and Ta(NtBu)(tBuNCMeNtBu)(2)Br revealed that the amidinate ligands exhibit eta(2)-coordination, and that the imido and halide ligands are cis to each other within the distorted octahedral structures. NMR studies indicated that the other complexes have analogous structures. Additionally, variable temperature NMR studies revealed that some of the complexes undergo amidinate rearrangement. The enthalpies, entropies, and free energies of activation for these rearrangements were calculated for Ta(NtBu)(tBuNCMeNtBu)(2)X (X = F, Cl, Br). When X = F, DeltaH(double dagger) = 9.1 +/- 0.4 kcal/mol, DeltaS(double dagger) = -20.5 +/- 1.6 cal/mol x K, and DeltaG(double dagger)(298 K) = 15.3 +/- 0.7 kcal/mol. For X = Cl, DeltaH(double dagger) = 12.4 +/- 0.3 kcal/mol, DeltaS(double dagger) = -20.2 +/- 0.8 cal/mol x K, and DeltaG(double dagger)(298 K) = 18.4 +/- 0.3 kcal/mol. When X = Br, DeltaH(double dagger) = 12.5 +/- 0.5 kcal/mol, DeltaS(double dagger) = -21.7 +/- 1.5 cal/mol x K, and DeltaG(double dagger)(298 K) = 19.0 +/- 0.7 kcal/mol. All of the complexes are volatile, and they sublime between 120 and 203 degrees C. In addition, Ta(NtBu)(iPrNCMeNiPr)(2)NMe(2) has a decomposition point that is 65-160 degrees C higher than widely used film growth precursors and is therefore a promising candidate for use in chemical vapor deposition and atomic layer deposition film growth techniques.