Controlled hydrolysis of aryltellurium trichlorides using 2-pyrrolidinones: isolation and structural characterization of monomeric aryltellurium(IV) monohydroxides

Abstract

The 2-pyrrolidinone (Pyrr)-assisted hydrolysis of aryltellurium trichlorides, provided their first-step hydrolysis products as 1 : 1 molecular adducts, ArTeCl₂OH.Pyrr (Ar = 1-C₁₀H₇, Npl, 1; 2,4,6-Me₃C₆H₂, Mes, 2). The hydroxo ligand occupies an equatorial position in the ψ-trigonal bipyramidal geometry around Te(IV) and is involved in a strong H-bonding interaction with the amido O of the base. As NplTeBr₃ did not react with 2-pyrrolidinone under similar conditions, the bromo analogue of 1, NplTeBr₂OH.Pyrr (3), was prepared by a metathetical reaction with NaBr. Both 1 and 2 undergo electrophilic substitution with acetone and pinacolone to afford Ar(RCOCH₂)TeCl₂ (R = Me, t-Bu), but do not react with iodoacetic acid, suggesting that the hydroxo ligand acts as a nucleophile rather than a base. The Te–OH bond in 1 is also cleaved by CH₃COCl to give the parent trihalide NplTeCl₃, while reaction with BrCH₂COBr results in NplTeBr₃ (4) as the ultimate tellurium containing product. The reaction of NplTeCl₃ with N-Methyl protected 2-pyrrolidinone (PyrrMe), under similar conditions, gave an ionic complex [(PyrrMe)₂H] [NplTeCl₄] (5), but did not react with N-acyl protected 2-pyrrolidinone, PyrrCOCH₂Br. However, the latter added oxidatively to elemental tellurium to give (PyrrCOCH₂)₂TeBr₂ (6). In the crystal lattice of 5, discreet five-coordinate square pyramidal CTeX₄ units are present, while in the case of 4 the same units are realized via intermolecular Te⋯Br interactions in a one-dimensional supramolecular architecture. N-(2-pyrrolidinone)amidomethyl ligands in 6 adopt a rare, if not the first, 1,6-(C,O) mode of chelation in preference to 1,4-(C,O) mode often observed in similar Te(IV) compounds.