Uranium Tetrakis-Aryloxide Derivatives Supported by Tetraazacyclododecane: Synthesis of Air-Stable, Coordinatively-Unsaturated U(IV) and U(V) Complexes

We present the synthesis, characterization, and one-electron oxidation of two uranium­(IV) complexes, coordinated to the cyclen-anchored tetrakis­(aryloxide) ligands tetrakis-hydroxybenzyl-1,4,7,10 tetraazacyclododecane, (^R,RArOH)₄cyclen; R = ^<i>t</i>Bu, Me. The new uranium­(IV) and (V) complexes exhibit an eight-coordinate, tetragonal ligand environment, effecting exceptional stability of the coordinatively unsaturated uranium compounds. Cyclic voltammetry studies reveal redox events ranging from tri- to hexavalent species, covering an electrochemical window of ∼4 V

Molecular and Electronic Structures of Eight-Coordinate Uranium Bipyridine Complexes: A Rare Example of a Bipy^2– Ligand Coordinated to a U⁴⁺ Ion

Reaction of trivalent [((^{Ad,<i>t</i>Bu}ArO)₃tacn)­U] (<b>1</b>) with 2,2′-bipyridine (bipy) yields [((^{Ad,<i>t</i>Bu}ArO)₃tacn)­U­(bipy)] (<b>2</b>) and subsequent reduction of <b>2</b> with KC₈ in the presence of Kryptofix222 furnishes [K­(2.2.2-crypt)]­[((^{Ad,<i>t</i>Bu}ArO)₃tacn)­U­(bipy)] (<b>3</b>). Alternatively, complex <b>3</b> can be synthesized from <b>1</b> by addition of [K­(bipy)] in the presence of the cryptand. New complexes <b>2</b> and <b>3</b> are characterized by a variety of spectroscopic, electrochemical, and magnetochemical methods, single-crystal X-ray diffraction, computational methods, and CHN elemental analysis. Structural analyses reveal a bipyridine radical (bipy^•–) ligand in <b>2</b> and a dianionic (bipy^2–) species in <b>3</b>. Complex <b>3</b> represents a rare example of an isolated and unambiguously characterized bipy^2– ligand coordinated to a uranium ion. The electronic structure assignments are supported by UV/vis/NIR and EPR spectroscopy, as well as SQUID magnetometry. The results of CASSCF calculations indicate multiconfigurational ground states for complexes <b>2</b> and <b>3</b>. The electronic ground state for <b>2</b> consists of an open-shell doublet U⁴⁺(bipy^•–) state (91%) and a closed-shell doublet U⁵⁺(bipy^2–) state (9%). The almost degenerate multiconfigurational ground state for <b>3</b> was found to be composed of an open-shell singlet and pure triplet state 0.06 eV higher in energy, both resulting from the U⁴⁺(5f²) (bipy^2–) configuration

Molecular and Electronic Structures of Eight-Coordinate Uranium Bipyridine Complexes: A Rare Example of a Bipy^2– Ligand Coordinated to a U⁴⁺ Ion

Reaction of trivalent [((^{Ad,<i>t</i>Bu}ArO)₃tacn)­U] (<b>1</b>) with 2,2′-bipyridine (bipy) yields [((^{Ad,<i>t</i>Bu}ArO)₃tacn)­U­(bipy)] (<b>2</b>) and subsequent reduction of <b>2</b> with KC₈ in the presence of Kryptofix222 furnishes [K­(2.2.2-crypt)]­[((^{Ad,<i>t</i>Bu}ArO)₃tacn)­U­(bipy)] (<b>3</b>). Alternatively, complex <b>3</b> can be synthesized from <b>1</b> by addition of [K­(bipy)] in the presence of the cryptand. New complexes <b>2</b> and <b>3</b> are characterized by a variety of spectroscopic, electrochemical, and magnetochemical methods, single-crystal X-ray diffraction, computational methods, and CHN elemental analysis. Structural analyses reveal a bipyridine radical (bipy^•–) ligand in <b>2</b> and a dianionic (bipy^2–) species in <b>3</b>. Complex <b>3</b> represents a rare example of an isolated and unambiguously characterized bipy^2– ligand coordinated to a uranium ion. The electronic structure assignments are supported by UV/vis/NIR and EPR spectroscopy, as well as SQUID magnetometry. The results of CASSCF calculations indicate multiconfigurational ground states for complexes <b>2</b> and <b>3</b>. The electronic ground state for <b>2</b> consists of an open-shell doublet U⁴⁺(bipy^•–) state (91%) and a closed-shell doublet U⁵⁺(bipy^2–) state (9%). The almost degenerate multiconfigurational ground state for <b>3</b> was found to be composed of an open-shell singlet and pure triplet state 0.06 eV higher in energy, both resulting from the U⁴⁺(5f²) (bipy^2–) configuration

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We recently reported the formation of a bridging carbonate complex [{((^AdArO)₃N)­U}₂(μ–η¹:κ²-CO₃)] via reductive cleavage of CO₂, yielding a μ-oxo bridged complex, followed by the insertion of another molecule of CO₂. In a similar strategy, we were able to isolate and characterize a series of mixed carbonate complexes U–CO₂E–U, U–CS₂E–U, and even U–OC­(S)­Se–U, by reacting bridged chalcogenide complexes [{((^AdArO)₃N)­U}₂(μ-E)] (E = S, Se) with CO₂, CS₂, and COS. These chalcogenido mixed-carbonate complexes represent the first of their kind

Reactivity of U–E–U (E = S, Se) Toward CO₂, CS₂, and COS: New Mixed-Carbonate Complexes of the Types U–CO₂E–U (E = S, Se), U–CS₂E–U (E = O, Se), and U–COSSe–U

We recently reported the formation of a bridging carbonate complex [{((^AdArO)₃N)­U}₂(μ–η¹:κ²-CO₃)] via reductive cleavage of CO₂, yielding a μ-oxo bridged complex, followed by the insertion of another molecule of CO₂. In a similar strategy, we were able to isolate and characterize a series of mixed carbonate complexes U–CO₂E–U, U–CS₂E–U, and even U–OC­(S)­Se–U, by reacting bridged chalcogenide complexes [{((^AdArO)₃N)­U}₂(μ-E)] (E = S, Se) with CO₂, CS₂, and COS. These chalcogenido mixed-carbonate complexes represent the first of their kind

Coordination-Induced Spin-State Change in Manganese(V) Complexes: The Electronic Structure of Manganese(V) Nitrides

This work illustrates that manganese­(V) nitrido complexes are able to undergo a coordination-induced spin-state change by altering the ligand field from trigonal to tetragonal symmetry. For the reversible coordination of acetonitrile to trigonal [(TIMEN^xyl)­Mn­(N)]²⁺ (<b>1</b>; high-spin <i>S</i> = 1; with TIMEN^xyl = tris­[2-(3-xylylimidazol-2-ylidene)­ethyl]-amine), a temperature-dependent coordination-induced spin-state switch is established. Starting from the manganese­(V) nitrido complex <b>1</b>, the synthesis and characterization of a series of octahedral, low-spin (<i>S</i> = 0) manganese­(V) nitrido complexes of the type [(TIMEN^xyl)­Mn­(N)­(L)]^<i>n</i>+ (L = MeCN (<b>2</b>), ^<i>t</i>BuNC (<b>3</b>), CN^– (<b>4</b>), NCS^– (<b>5</b>), F^– (<b>6</b>), μ-{Ag­(CN)₂}⁻ (<b>7</b>), with <i>n</i> = 1, 2) is described. These represent the first examples of d² transition metal complexes showing a coordination-induced spin-state change. Spectroscopic, as well as ligand-field theory and density functional theory studies suggest a transition from a 2 + 2 + 1 orbital splitting in the trigonal case to a 1 + 2 + 1 + 1 splitting in tetragonal symmetry as the origin of the coordination-induced spin-state change

Uranium(IV) Halide (F⁻, Cl⁻, Br⁻, and I⁻) Monoarene Complexes

The syntheses of four nearly isostructural uranium­(IV) monoarene complexes, supported by the arene anchored tris­(aryloxide) chelate, [(^Ad,MeArO)₃mes]^3–, are reported. Oxidation of the uranium­(III) precursor [((^Ad,MeArO)₃mes)­U], <b>1</b>, in the presence of tetrahydrofuran (THF) results in THF coordination and distortion of the equatorial coordination sphere to afford the uranium­(IV) η⁶-arene complexes, [((^Ad,MeArO)₃mes)­U­(X)­(THF)], <b>2–X–THF</b>, (where X = F, Cl, Br, or I) as their THF adducts. The solvate-free trigonally ligated [((^Ad,MeArO)₃mes)­U­(F)], <b>2–F</b>, was prepared and isolated in the absence of coordinating solvents for comparison

Reactivity of U–E–U (E = S, Se) Toward CO₂, CS₂, and COS: New Mixed-Carbonate Complexes of the Types U–CO₂E–U (E = S, Se), U–CS₂E–U (E = O, Se), and U–COSSe–U

We recently reported the formation of a bridging carbonate complex [{((^AdArO)₃N)­U}₂(μ–η¹:κ²-CO₃)] via reductive cleavage of CO₂, yielding a μ-oxo bridged complex, followed by the insertion of another molecule of CO₂. In a similar strategy, we were able to isolate and characterize a series of mixed carbonate complexes U–CO₂E–U, U–CS₂E–U, and even U–OC­(S)­Se–U, by reacting bridged chalcogenide complexes [{((^AdArO)₃N)­U}₂(μ-E)] (E = S, Se) with CO₂, CS₂, and COS. These chalcogenido mixed-carbonate complexes represent the first of their kind

Reactivity of U–E–U (E = S, Se) Toward CO₂, CS₂, and COS: New Mixed-Carbonate Complexes of the Types U–CO₂E–U (E = S, Se), U–CS₂E–U (E = O, Se), and U–COSSe–U

We recently reported the formation of a bridging carbonate complex [{((^AdArO)₃N)­U}₂(μ–η¹:κ²-CO₃)] via reductive cleavage of CO₂, yielding a μ-oxo bridged complex, followed by the insertion of another molecule of CO₂. In a similar strategy, we were able to isolate and characterize a series of mixed carbonate complexes U–CO₂E–U, U–CS₂E–U, and even U–OC­(S)­Se–U, by reacting bridged chalcogenide complexes [{((^AdArO)₃N)­U}₂(μ-E)] (E = S, Se) with CO₂, CS₂, and COS. These chalcogenido mixed-carbonate complexes represent the first of their kind

Ruthenium Carbonyl Complexes Bearing Bis(pyrazol-1-yl)carboxylato Ligands

The syntheses of the two dicarbonyl complexes [Ru­(bdmpza)­Cl­(CO)₂] (<b>3</b>) and [Ru­(2,2-bdmpzp)­Cl­(CO)₂] (<b>4</b>), bearing a bis­(3,5-dimethylpyrazol-1-yl)­acetato (bdmpza) or a 2,2-bis­(3,5-dimethylpyrazol-1-yl)­propionato (2,2-bdmpzp) scorpionate ligand, are described. Both complexes are obtained by reacting the polymer [RuCl₂(CO)₂]_<i>n</i> with either K­[bdmpza] or K­[2,2-bdmpzp]. Reaction of the acid Hbdmpza with [Ru₃(CO)₁₂] results in the formation of two structural isomers of a hydrido complex, [Ru­(bdmpza)­H­(CO)₂] (<b>5a</b>,<b>b</b>). Under aerobic conditions conversion of [Ru­(bdmpza)­H­(CO)₂] (<b>5a</b>,<b>b</b>) to form the Ru­(I) dimer [Ru­(bdmpza)­(CO)­(μ-CO)]₂ (<b>6</b>) seems to be hindered in comparison to the case for the η⁵-C₅H₅ (Cp) analogues. Dimer <b>6</b> is obtained via a reaction of Hbdmpza with <i>catena</i>-[Ru­(OAc)­(CO)₂]_<i>n</i> instead. The molecular structures of <b>3</b>, <b>4</b>, and <b>6</b> have been obtained by single-crystal X-ray structure determinations. The precatalytic properties of the two dicarbonyl complexes <b>3</b> and <b>4</b> toward the catalytic oxidation of cyclohexene with different oxidizing agents are discussed as well