New azido-substituted tantalum compounds: syntheses and DFT examination of nitrogen-rich mono-, di-, and trinuclear tantalum(v) compounds

Abstract

The syntheses of new tantalum compounds containing an ancillary azido ligand(s) are described. The tantalum compound with the composition Ta(NMe₂)₄(N₃) has been synthesized in high yield from the reaction of TaCl(NMe₂)₄ with NaN₃ in THF. The solid-state structure reveals a dimeric architecture based on Ta₂(NMe₂)₈(μ-N₃)₂ (1), where the eight-membered dimetallocyclic ring possesses a chair-like conformation with bridging azido ligands binding the two Ta(NMe₂)₄ moieties. Solution molecular weight measurements and electronic structure calculations predict 1 to exist as a monomer at room temperature. 1 reacts with the formamidine ⁱPrNC(H)NHⁱPr to furnish fac-Ta(NMe₂)₃(η¹-N₃)[ⁱPrNC(H)NⁱPr] (2) and Me₂NH; compound 2 has been characterized by IR and ¹H NMR spectroscopy and X-ray diffraction analysis. Treatment of 1 with p-toluidine affords the trinuclear compound Ta₃(NMe₂)₅(μ-NMe₂)(μ-NC₆H₄Me-4)₂(NC₆H₄Me-4)(μ-N₃)₂(η¹-N₃) (3). Compound 3 contains three non-bonded tantalum atoms that are ligated by edge-bridging imido, amido, and azido ligands. The molecular structure of 3 has been determined by X-ray crystallography, and the unprecedented presence of terminal and bridging imido, amido, and azido ligands in a single tantalum compound confirmed. The bonding in 3 has been examined by DFT, and these data are discussed relative to the crystallographic structure. Compounds 1–3 represent the first structurally characterized examples of heteroleptic tantalum compounds that possess an all-nitrogen coordination sphere with at least one azido ligand.