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

摘要

The reaction of [UI3(thf)(4)] with the sodium or lithium salts of hydrobis(2-mercapto-1-methylimidazolyl)borate ligands ([H(R)B(tim(Me))(2)](-)) in a 1:2 ratio, in tetrahydrofuran, gave the U(iii) complexes [UI{(3)-H,S,S-H(R)B(tim(Me))(2)}(2)(thf)(2)] (R = H (1), Ph (2)) in good yields. Crystals of [UI{(3)-H,S,S-H(Ph)B(tim(Me))(2)}(2)(thf)(2)] (2) were obtained by recrystallization from a tetrahydrofuran/acetonitrile solution, and the ion-separated uranium complex [U{(3)-H,S,S-H(Ph)B(tim(Me))(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 I-2 resulted in the formation of the cationic U(iv) complexes [U{(3)-H,S,S-H(Ph)B(tim(Me))(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{(3)-H(Ph)B(tim(Me))(2)}(2)((2)-tim(Me))] (7). Treatment of 2 with pyridine-N oxide (pyNO) led to the formation of the uranyl complex [UO2{(2)-S,S-H(Ph)B(tim(Me))(2)}(2)] (8) and of complex 6-I, while from the reaction of [U{(3)-H(Ph)B(tim(Me))(2)}(2)(thf)(3)][BPh4] (5) with pyNO, the oxo-bridged U(iv) complex [{U{(3)-H(Ph)B(tim(Me))(2)}(2)(pyNO)}(2)(-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 (3)-H,S,S coordination mode, while in the U(vi) complex the ligands bind to the metal in a (2)-S,S mode. The presence of UH-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.