Uranium(III) and uranium(IV) meta-terphenyl thiolate complexes

We report the synthesis and characterization of crystalline uranium(IV) and uranium(III) complexes supported by the bulky hexa-iso-propyl-m-terphenylthiolate ligand system, SAriPr6 (SAriPr6 = {SC6H3-2,6-(Tripp)2}; Tripp = 2,4,6-iPr-C6H2). These constitute the first examples of m-terphenylthiolate complexes of uranium in any oxidation state and highlight the supporting role of U···arene interactions in the isolation of heteroleptic complexes with this ligand set, and demonstrate the diverse reactivity of [UIV(BH4)4]. Treatment of UIVCl4 with two equivalents of KSAriPr6 in Et2O afforded [UIV(SAriPr6)2(Cl)2] (1) in poor yield along with several crystals of the Et2O adduct, [UIV(SAriPr6)2(Cl)2(Et2O)2] (1·Et2O). While the reaction between [UIV(BH4)4] and one equivalent of KSAriPr6 in toluene gave several crystals of the poorly soluble double salt, [UIV(μ-SAriPr6)(BH4)2(μ-BH4)(μ3-BH4)K]2 (2), exposing the crude reaction mixture to Et2O gave the oxidized disulfide ligand dimer, (SAriPr6)2 as the sole identifiable product. The reaction between [UIV(BH4)4] and one equivalent of HSAriPr6 in hot toluene gave [UIII(H3B·SAriPr6 κS,H,H)(BH4)2] (3) – the net product of thermolytic reduction of the uranium and deprotonation of the arylthiol. Complex 3 proved resistant to further substitution using either HSAriPr6 or KSAriPr6. Both U(III) mono-arylthiolates, [UIII(SAriPr6)(BH4)2] (4a) and [{UIII(SAriPr6)(BH4)}2{μ-B2H6}] (4b) were isolated as a mixture from the reaction between [UIII(BH3)3(toluene)] and one equivalent of KSAriPr6. Complex 4b is a rare example of a nido-mettaloborane. When two equivalents of KSAriPr6 were reacted with [UIII(BH3)3(toluene)], the bis-arylthiolate complex [UIII(SAriPr6)2(BH4)] (5) was isolated in good yield. Complexes 1–5 have been characterized variously by single-crystal X-ray diffraction, multi-nuclear NMR spectroscopy, infra-red spectroscopy, UV-Vis-NIR spectroscopy, SQUID magnetometry, elemental analyses as appropriate. Quantum chemical calculations have been employed to interpret the nature of the U–S bonding interactions across these U(III) and U(IV) complexes.