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 (SAr = {SC₆H₃-2,6-(Tripp)₂}; Tripp = 2,4,6-iPr-C₆H₂). Treatment of U^IVCl₄ with 2 equiv of KSAr in Et₂O afforded both [U^IV(SAr)₂(Cl)₂] (1) and the Et₂O adduct, [U^IV(SAr)₂(Cl)₂(Et₂O)₂] (1·EtO) in poor yield. The reaction between [U^IV(BH₄)₄] and 1 equiv of KSAr in toluene gave several crystals of the double salt, [U^IV(μ-SAr)(BH₄)₂(μ-BH₄)(μ³-BH₄)K]₂ (2), and exposing the crude reaction mixture to Et₂O gave the disulfide dimer, (SAr)₂. The reaction between [U^IV(BH₄)₄] and 1 equiv of HSAr in hot toluene gave [U^III(H₃B·SAr κS,H,H)(BH₄)₂] (3) which proved resistant to further substitution using either HSAr or KSAr. Two U(III) mono-terphenylthiolates, [U^III(SAr)(BH₄)₂] (4a) and [{U^III(SAr)(BH₄)}₂{μ-B₂H₆}] (4b), were isolated as a mixture from the reaction between [U^III(BH₃)₃(toluene)] and 1 equiv of KSAr, while using 2 equiv of KSAr gave the bis-terphenylthiolate complex [U^III(SAr)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.