New Volatile Tantalum Imido Precursors with Carboxamide Ligands.

Abstract

A series of Ta(V) tBu-imido/N-alkoxy carboxamide complexes, TaCl2(NtBu)(pyridine)(edpa) (1), TaCl(NtBu)(edpa)2 (2), Ta(NtBu)(edpa)3 (3), TaCl2(NtBu)(pyridine)(mdpa) (4), and Ta(NtBu)(mdpa)3 (5), were successfully synthesized by metathesis reactions between Ta(NtBu)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 NtBu 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 tBu 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.