Tantalum, easy as Pi: understanding differences in metal-imido bonding towards improving Ta/Nb separations

Alexander B. Weberg, Subhajyoti Chaudhuri, Thibault Cheisson, Christian Uruburo, Ekaterina Lapsheva, Pragati Pandey, Michael R. Gau, Patrick J. Carroll, George C. Schatz*, Eric J. Schelter*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


The separation and purification of niobium and tantalum, which co-occur in natural sources, is difficult due to their similar physical and chemical properties. The current industrial method for separating Ta/Nb mixtures uses an energy-intensive process with caustic and toxic conditions. It is of interest to develop alternative, fundamental methodologies for the purification of these technologically important metals that improve upon their environmental impact. Herein, we introduce new Ta/Nb imido compounds: M(tBuN)(TriNOx) (1-M) bound by the TriNOx3− ligand and demonstrate a fundamental, proof-of-concept Ta/Nb separation based on differences in the imido reactivities. Despite the nearly identical structures of 1-M, density functional theory (DFT)-computed electronic structures of 1-M indicate enhanced basic character of the imido group in 1-Ta as compared to 1-Nb. Accordingly, the rate of CO2 insertion into the M = Nimido bond of 1-Ta to form a carbamate complex (2-Ta) was selective compared to the analogous, unobserved reaction with 1-Nb. Differences in solubility between the imido and carbamate complexes allowed for separation of the carbamate complex, and led to an efficient Ta/Nb separation (STa/Nb = 404 ± 150) dependent on the kinetic differences in nucleophilicities between the imido moieties in 1-Ta and 1-Nb.

Original languageEnglish (US)
Pages (from-to)6796-6805
Number of pages10
JournalChemical Science
Issue number23
StatePublished - May 12 2022

ASJC Scopus subject areas

  • General Chemistry


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