New Volatile Tantalum Imido Precursors with Carboxamide Ligands

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