New Volatile Tantalum Imido Precursors with Carboxamide Ligands

A series of Ta(V) ^t Bu-imido/N-alkoxy carboxamide complexes, TaCl₂(N ^t Bu)(pyridine)(edpa) (1), TaCl(N ^t Bu)(edpa)₂ (2), Ta(N ^t Bu)(edpa)₃ (3), TaCl₂(N ^t Bu)(pyridine)(mdpa) (4), and Ta(N ^t Bu)(mdpa)₃ (5), were successfully synthesized by metathesis reactions between Ta(N ^t Bu)Cl₃(py)₂ and several equivalents of Na(edpa) (edpaH = N-ethoxy-2,2-dimethylpropanamide) and Na(mdpa) (mdpaH = N-methoxy-2,2-dimethylpropanamide). Furthermore, complexes 3 and 5 were simply transformed to new dimeric structures [Ta(μ₂-O)(edpa)₃]₂ (6) and [Ta(μ₂-O)(mdpa)₃]₂ (7) with the elimination of the N ^t Bu imido group by air exposure. Compounds 1-7 were characterized by ¹H and ¹³C nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis (TGA), and single-crystal X-ray diffraction. Single-crystal X-ray diffraction analysis revealed that complexes 3 and 5 have a distorted pentagonal bipyramidal geometry around the central Ta atom, with three monoanionic bidentate N-alkoxy carboxamide ligands and one ^t Bu imido ligand saturating the coordination of tantalum ions. TGA revealed that complexes 3 and 5 had superior thermal characteristics and stability. These complexes could potentially be applied as precursors for tantalum oxide thin films.