Synthesis and characterization of trianionic pincer-type complexes of tantalum(V) including solid (X-ray) and solution (NMR) state assignment of an intraligand N–H—F hydrogen bonding interaction

Abstract

Tanatalum(V) complexes ligated with a trianionic ONO3− pincer-type ligand were synthesized and characterized. Using the ONO trianionic pincer ligand precursor 2,2′-(azanediylbis(3-methyl-6,1-phenylene))bis(1,1,1,3,3,3-hexafluoropropan-2-ol) [CF3-ONO]H3 (1) and various sources of Ta(V), the following pincer complexes were synthesized: (I) anionic trichloride complex {[CF3-ONO]TaCl3}{HNEt3}·(HNEt3Cl)x (2), (II) diamido-amine complex [CF3-ONO]Ta(NMe2)2(HNMe2) (3-NHMe2) and its amine free version [CF3-ONO]Ta(NMe2)2 (3), (III) the neutral trichloride [CF3-ONHO]TaCl3 (4), (IV) the neutral dichloride [CF3-ONO]TaCl2(THF) (5), and (V) the dibenzyl complex [CF3-ONO]TaBn2 (6). Characterization methods include the complete assignment (where possible) for 1H, 13C, 19F, and 15N NMR spectra for complexes 2–6, and single crystal X-ray diffraction characterization for complexes 2, 3, and 4. Interesting aspects regarding the interplay of the ligand in its dianionic form versus its trianionic form, and an unusual H⋯F hydrogen bonding interaction within complex 4 were discovered from these synthetic pursuits.