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Issue 31, 2018
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Uranium(iii) complexes supported by hydrobis(mercaptoimidazolyl)borates: synthesis and oxidation chemistry

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Abstract

The reaction of [UI3(thf)4] with the sodium or lithium salts of hydrobis(2-mercapto-1-methylimidazolyl)borate ligands ([H(R)B(timMe)2]) in a 1 : 2 ratio, in tetrahydrofuran, gave the U(III) complexes [UI{κ3-H,S,S′-H(R)B(timMe)2}2(thf)2] (R = H (1), Ph (2)) in good yields. Crystals of [UI{κ3-H,S,S′-H(Ph)B(timMe)2}2(thf)2] (2) were obtained by recrystallization from a tetrahydrofuran/acetonitrile solution, and the ion-separated uranium complex [U{κ3-H,S,S′-H(Ph)B(timMe)2}2(CH3CN)3][I] (3-I) was obtained by dissolution of 2 in acetonitrile followed by recrystallization. One-electron oxidation of 2 with AgBPh4 or I2 resulted in the formation of the cationic U(IV) complexes [U{κ3-H,S,S′-H(Ph)B(timMe)2}3][X] (X = BPh4 (6-BPh4), I (6-I)), due to a ligand redistribution process. These complexes are the first examples of homoleptic poly(azolyl)borate U(IV) complexes. Treatment of complex 2 with azobenzene led to the isolation of crystals of the U(IV) compound [UI{κ3-H(Ph)B(timMe)2}22-timMe)] (7). Treatment of 2 with pyridine-N oxide (pyNO) led to the formation of the uranyl complex [UO22-S,S′-H(Ph)B(timMe)2}2] (8) and of complex 6-I, while from the reaction of [U{κ3-H(Ph)B(timMe)2}2(thf)3][BPh4] (5) with pyNO, the oxo-bridged U(IV) complex [{U{κ3-H(Ph)B(timMe)2}2(pyNO)}2(μ-O)][BPh4]2 (9) was also obtained. In the U(III) and U(IV) complexes, the bis(azolyl)borate ligands bind to the uranium center in a κ3-H,S,S′ coordination mode, while in the U(VI) complex the ligands bind to the metal in a κ2-S,S′ mode. The presence of U⋯H–B interactions in the solid-state, for the nine-coordinate complexes 1, 2, 3, 6 and 7 and for the eight-coordinate complex 9, was supported by IR spectroscopy and/or X-ray diffraction analysis.

Graphical abstract: Uranium(iii) complexes supported by hydrobis(mercaptoimidazolyl)borates: synthesis and oxidation chemistry

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Supplementary files

Article information


Submitted
25 Mar 2018
Accepted
02 May 2018
First published
03 May 2018

Dalton Trans., 2018,47, 10601-10612
Article type
Paper

Uranium(III) complexes supported by hydrobis(mercaptoimidazolyl)borates: synthesis and oxidation chemistry

L. Maria, I. C. Santos and I. Santos, Dalton Trans., 2018, 47, 10601
DOI: 10.1039/C8DT01149D

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