Uranium(III) and Uranium(IV) meta-Terphenylthiolate Complexes

We report the synthesis and characterization of crystalline m-terphenylthiolate uranium complexes supported by the bulky ligand system, SAr^iPr6 (SAr^iPr6 = {SC₆H₃-2,6-(Tripp)₂}; Tripp = 2,4,6-iPr-C₆H₂). Treatment of U^IVCl₄ with 2 equiv of KSAr^iPr6 in Et₂O afforded both [U^IV(SAr^iPr6)₂(Cl)₂] (1) and the Et₂O adduct, [U^IV(SAr^iPr6)₂(Cl)₂(Et₂O)₂] (1·Et₂O) in poor yield. The reaction between [U^IV(BH₄)₄] and 1 equiv of KSAr^iPr6 in toluene gave several crystals of the double salt, [U^IV(μ-SAr^iPr6)(BH₄)₂(μ-BH₄)(μ³-BH₄)K]₂ (2), and exposing the crude reaction mixture to Et₂O gave the disulfide dimer, (SAr^iPr6)₂. The reaction between [U^IV(BH₄)₄] and 1 equiv of HSAr^iPr6 in hot toluene gave [U^III(H₃B·SAr^iPr6 κS,H,H)(BH₄)₂] (3) which proved resistant to further substitution using either HSAr^iPr6 or KSAr^iPr6. Two U(III) mono-terphenylthiolates, [U^III(SAr^iPr6)(BH₄)₂] (4a) and [{U^III(SAr^iPr6)(BH₄)}₂{μ-B₂H₆}] (4b), were isolated as a mixture from the reaction between [U^III(BH₃)₃(toluene)] and 1 equiv of KSAr^iPr6, while using 2 equiv of KSAr^iPr6 gave the bis-terphenylthiolate complex [U^III(SAr^iPr6)₂(BH₄)] (5). Complex 4b is a rare example of a nido-metalloborane. Complexes 1–5 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.