New Volatile Tantalum Imido Precursors with Carboxamide Ligands

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