Synthesis and structures of tantalum chloride and tantalum aryloxide compounds bearing bidentate and tridentate pyrrole-amine ligands

A series of mononuclear tantalum derivatives containing substituted pyrrole-amine ligands are synthesized. Reacting TaCl5 with one equivalent of Li[C4H2N-2,5-(CH2NMe2)(2)] in toluene affords TaCl4[C4H2N-2,5-(CH2NMe2)(2)] (1), whereas TaCl4[C4H3N-2-(CH2NEt2)] (2) is generated between the combination of TaCl5 and Li[C4H3N-2-(CH2NEt2)] in moderate yield. Similarly, while subjecting Li[C4H2N-2-(CH2NMe2)-5-((CH2NHBu)-Bu-t)] with TaCl5 in diethyl ether, it affords TaCl3[C4H2N-2-(CH2NMe2)-5-((CH2NBu)-Bu-t)] (3) at moderate yield. Interestingly, the mixing of TaCl4[C4H2N-2,5-(CH2NMe2)(2)] (1) with excess Li[O-Ph-2,6-Pr-i(2)] in tetrahydrofuran generates the tantalum aryloxide compound, Ta(O-Ph-2,6-Pr-i(2))Cl-3[C4H2N-2,5-(CH2NMe2)(2)] (4). Single crystal X-ray diffraction analysis reveals that compound 4 is hepta-coordinated possessing a distorted pentagonal bipyramidal geometry. All the compounds are characterized by proton nuclear magnetic resonance and carbon-13 nuclear magnetic resonance spectroscopy, and we highlight the structural variation of tantalum derivatives with bi- or tridentate (symmetric and asymmetric) pyrrole precursors.