Uranium(III) and Uranium(IV) <i>meta</i>-Terphenylthiolate Complexes

We report the synthesis and characterization of crystalline <i>m</i>-terphenylthiolate uranium complexes supported by the bulky ligand system, SAr^<i>i</i>Pr6 (SAr^<i>i</i>Pr6 = {SC₆H₃-2,6-(Tripp)₂}; Tripp = 2,4,6-<i>i</i>Pr-C₆H₂). Treatment of U^IVCl₄ with 2 equiv of KSAr^<i>i</i>Pr6 in Et₂O afforded both [U^IV(SAr^<i>i</i>Pr6)₂(Cl)₂] (<b>1</b>) and the Et₂O adduct, [U^IV(SAr^<i>i</i>Pr6)₂(Cl)₂(Et₂O)₂] (<b>1·Et</b>_<b>2</b><b>O</b>) in poor yield. The reaction between [U^IV(BH₄)₄] and 1 equiv of KSAr^<i>i</i>Pr6 in toluene gave several crystals of the double salt, [U^IV(μ-SAr^<i>i</i>Pr6)(BH₄)₂(μ-BH₄)(μ³-BH₄)K]₂ (<b>2</b>), and exposing the crude reaction mixture to Et₂O gave the disulfide dimer, (SAr^<i>i</i>Pr6)₂. The reaction between [U^IV(BH₄)₄] and 1 equiv of HSAr^<i>i</i>Pr6 in hot toluene gave [U^III(H₃B·SAr^<i>i</i>Pr6 κ<i>S</i>,<i>H</i>,<i>H</i>)(BH₄)₂] (<b>3</b>) which proved resistant to further substitution using either HSAr^<i>i</i>Pr6 or KSAr^<i>i</i>Pr6. Two U(III) <i>mono</i>-terphenylthiolates, [U^III(SAr^<i>i</i>Pr6)(BH₄)₂] (<b>4a</b>) and [{U^III(SAr^<i>i</i>Pr6)(BH₄)}₂{μ-B₂H₆}] (<b>4b</b>), were isolated as a mixture from the reaction between [U^III(BH₃)₃(toluene)] and 1 equiv of KSAr^<i>i</i>Pr6, while using 2 equiv of KSAr^<i>i</i>Pr6 gave the <i>bis</i>-terphenylthiolate complex [U^III(SAr^<i>i</i>Pr6)₂(BH₄)] (<b>5</b>). Complex <b>4b</b> is a rare example of a <i>nido</i>-metalloborane. Complexes <b>1</b>-<b>5</b> have been characterized variously by single-crystal and powder X-ray diffraction, multinuclear NMR spectroscopy, infrared spectroscopy, UV-Vis-NIR spectroscopy, SQUID magnetometry, and elemental analyses as appropriate. Quantum chemical calculations have been employed to interpret the nature of the U-S bonding interactions across these complexes.