Mixed amido/imido/guanidinato complexes of tantalum: Effects of ligand substitution on thermal properties

Mixed amido/imido/guanidinato tantalum complexes [Ta(NR¹R ²){C(NR¹R²)(NR³)₂} ₂(NR⁴)] [R¹,R² = methyl, ethyl; R³ = cyclohexyl (cy), isopropyl; R⁴ = tert-butyl, n-propyl] have been synthesized by the insertion of carbodiimides into tantalum-amide bonds. All compounds have been characterized by means of NMR spectroscopy, mass spectrometry, and CHN analysis. Additionally, single crystal structures of five compounds (4: R¹ = Me, R² = Et, R ³ = iPr, R⁴ = tBu; 5: R¹, R² = Et, R³ = iPr, R⁴ = tBu; 6: R¹, R² = Me, R³ = cy, R⁴ = tBu; 8: R¹, R² = Et, R³ = cy, R⁴ = tBu; 9: R¹, R² = Et, R³ = iPr, R⁴ = nPr) have been determined and relevant structural issues are discussed. The thermal properties of all complexes have been investigated by TGA/DTA measurements. Thus, complexes originating from diisopropylcarbodiimide (iPr-cdi) are significantly more volatile than complexes derived from dicyclohexylcarbodiimide (cy-cdi). In contrast, variations of R¹, R², and R⁴ have only a small impact on the thermal behavior of the complexes. Finally, selected compounds have been pyrolyzed at 600°C, and the decomposition products studied by GC-MS and ¹H NMR spectroscopy.