Abstract
We report the syntheses, electronic properties, and molecular structures of a series of polychalcogenido-bridged dinuclear uranium species. These complexes are supported by the sterically encumbering but highly flexible, single N-anchored tris(aryloxide) chelator (AdArO)3N3−. Reaction of an appropriate uranium precursor, either the U(III) starting material, [((AdArO)3N)U(DME)], or the dinuclear mono-chalcogenido-bridged uranium(IV/IV) compounds [{((AdArO)3N)U(DME)}2(μ-E)] (E = S, Se), with elemental sulfur or selenium, yields new complexes with a variety of bridging chalcogenide entities μ-Emn− (E = S, m = 2, n = 1 or 2 and E = Se, m = 2, 4; n = 2). Activation of the heavy chalcogens typically requires either a coordinatively unsaturated, strongly-reducing metal complex or a compound with a metal–metal bond. Since uranium complexes in the +IV oxidation state, are generally considered rather unreactive, the observed reaction of the here employed uranium(IV)/(IV) species with elemental chalcogens is fairly remarkable.
Highlights
From a basic research point of view, complexes containing the hard uranium ion and so sulfur, selenium, and tellurium ligands are fundamentally important to advance understanding of covalency in the metal ligand bond that is essential for the development of lanthanide/ actinide separation methodologies.[34,35,36]
N-anchored tris(aryloxide) ligands, we recently reported a series of chalcogen-bridged compounds containing purely inorganic chalcogenido ligands, [{((tBu,tBuArO)3tacn)UIV}2(m-E)] and [{((AdArO)3N)UIV(DME)}2(m-E)] (E 1⁄4 S, Se), that can be synthesized from the uranium(III) starting materials [((tBu,tBuArO)3tacn) UIII] and [((AdArO)3N)UIII(DME)] with stoichiometric amounts of elemental sulfur or selenium, respectively.[14]
We could show that complexes of the N-anchored ligand system, [{((AdArO)3N)UIV(DME)}2(m-E)] (E 1⁄4 O, S, Se), react with CO2 and even the heterocumulene analogues CS2 and COS to form dinuclear U(IV/IV) mixed-carbonate complexes.[20,21,40]
Summary
Actinide chalcogenido complexes containing the group 16 congeners sulfur, selenium, and tellurium have been known for three decades.[1,2,3,4,5,6,7,8,9,10,11,12,13] only recently elemental chalcogen activation and chalcogen atom transfer reactions with actinide complexes have been developed.[14,15,16,17,18,19,20,21,22] This renewed interest in actinide reactivity with the chalcogens and chalcogenides can – to some extent – be attributed to the importance of solid-state materials that are obtained from controlled pyrolysis of inorganic or organometallic chalcogenolates.[23]. Since the uranium(IV) oxidation state, as well as the heavy chalcogens, are considered to be rather unreactive, and the requirements for elemental chalcogen activation usually are either a coordinatively unsaturated, strongly-reducing metal complex or a compound with a metal–metal bond.[32] Hayton et al were able to perform the remarkable twoelectron oxidation of the terminal monooxo uranium(IV) complex [Cp*2Co][(R2N)3U(O)] (R 1⁄4 SiMe3) with the elemental chalcogens to form sulfur and selenium substituted uranyl analogues [O]U]E]2+ (E 1⁄4 S, Se).[22] the choice of an appropriate ligand appears to play a key role, since even iodine can oxidize U(IV) to U(V) under the right conditions.[42] The bridging Se2À ligand in the uranium(IV) starting complex [{((AdArO)3N)UIV(DME)}2(m-Se)] (2) apparently is very electronrich and capable of reducing another selenium atom without involving the two uranium(IV) centers in any further redox chemistry.
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