C-H Bond Activation by an Isolated Dinuclear U(III)/U(IV) Nitride

Synthetic studies of bimetallic uranium nitride complexes with the N(SiMe3)(2) ligand have generated a new nitride complex of U(III), which is highly reactive toward C-H bonds and H-2. Treatment of the previously reported U(IV)/U(IV) nitride complex [Na(DME)(3)][((Me3Si)(2)N)(2)U(mu-N)(mu-kappa(2):CN-CH2SiMe2NSiMe3)U(N(SiMe3)(2))(2)] (DME = 1,2-dimethoxyethane), 1, with 2 equiv of HNEt3BPh3 yielded the cationic U(IV)/U(IV) nitride complex, [{((Me3Si)(2)N)(2)U(THF)}(2)(mu-N)][BPh4] (THF = tetrahydrofuran), 3, by successive protonolysis of one N(SiMe3)(2) ligand and the uranium-methylene bond. Reduction of 3 with KC8 afforded a rare example of a U(III) nitride, namely, the U(III)/U(IV) complex, [{((Me3Si2N)(2)U(THF)}(2)(mu-N)], 4. Complex 4 is highly reactive and undergoes 1,2-addition of the C-H bond of the N(SiMe3)(2) ligand across the uranium-nitride moiety to give the U(III)/U(IV) inside cyclometalate complex, [{((Me3Si)(2)N)(2)(THF)U(mu-NH)(mu-kappa(2):C,N - CH2SiMe2NSiMe3)U(N(SiMe3)(2)))(THF)], 5. Complex 4 also reacts with toluene at -80 degrees C to yield an inverse sandwich imide complex arising from C-H bond activation of toluene, [{((Me3SO2N)(2)U(THF)}(2)(mu-N)][{((Me3SO2N)(3)U(mu-NH)U(N(SiMe3)(2))](2)(C7H8)], 6. Complex 4 effects the heterolytic cleavage of the C-H of phenylacetylene to yield the imide acetylide [{((Me3Si)(2)N)(2)U(THF)[(2)(mu-N)][((Me3Si)(2)N)(2)U(eta(1)-CCPh)(mu(2)-NH)(mu(2)-eta(2): eta(1)-CCPh)U(N(SiMe3)(2))(2)], 7. Complex 4 also reacts with H-2 to produce an imide hydride U(III)/U(IV) complex, [{((Me3SO2N)(2)U(THF)}(2)(mu-NH)(mu-H)], 9. These data demonstrate that nitride complexes of U(III) are accessible with amide ligands and show the high reactivity of molecular U(III) nitrides in C-H bond activation

Molecular Complex of Tb in the +4 Oxidation State

Lanthanides (Ln) usually occur in the +3, or more recently the +2, oxidation states. The only example of an isolated molecular Ln(4+) so far remains Ce4+. Here we show that the +4 oxidation state is also accessible in a molecular compound of terbium as demonstrated by oxidation of the tetrakis(siloxide)terbium(III) ate complex, [KTb(OSi((OBu)-Bu-t)(3))(4)], 1-Tb, with the tris(4-bromophenyl) amminium oxidant, [N(C6H4Br)(3)] [SbCl6], to afford the Tb4+ complex [Tb(OSi((OBu)-Bu-t)(3))(4)], 2-Tb. The solid state structures of 1-Tb and 2-Tb were determined by X-ray crystallography, and the presence of Tb4+ was unambiguously confirmed by electron paramagnetic resonance and magnetometry. Complex 2-Tb displays a similar voltammogram to the Ce4+ analogue but with redox events that are about 1 V more positive

Synthesis and crystallographic characterization of di-phenyl-amide rare-earth metal complexes Ln(NPh2)3(THF)2 and [(Ph2N)2 Ln(μ-NPh2)]2.

Studies of the coordination chemistry between the di-phenyl-amide ligand, NPh2, and the smaller rare-earth Ln III ions, Ln = Y, Dy, and Er, led to the structural characterization by single-crystal X-ray diffraction crystallography of both solvated and unsolvated complexes, namely, tris-(di-phenyl-amido-κN)bis-(tetrahydro-furan-κO)yttrium(III), Y(NPh2)3(THF)2 or [Y(C12H10N)3(C4H8O)2], 1-Y, and the erbium(III) (Er), 1-Er, analogue, and bis-[μ-1κN:2(η6)-di-phenyl-amido]-bis-[bis-(di-phenyl-amido-κN)yttrium(III)], [(Ph2N)2Y(μ-NPh2)]2 or [Y2(C12H10N)6], 2-Y, and the dysprosium(III) (Dy), 2-Dy, analogue. The THF ligands of 1-Er are modeled with disorder across two positions with occupancies of 0.627 (12):0.323 (12) and 0.633 (7):0.367 (7). Also structurally characterized was the tetra-metallic ErIII bridging oxide hydrolysis product, bis-(μ-di-phenyl-amido-κ2 N:N)bis-[μ-1κN:2(η6)-di-phenyl-amido]-tetra-kis-(di-phenyl-amido-κN)di-μ3-oxido-tetra-erbium(III) benzene disolvate, {[(Ph2N)Er(μ-NPh2)]4(μ-O)2}·(C6H6)2 or [Er4(C12H10N)8O2]·2C6H6, 3-Er. The 3-Er structure was refined as a three-component twin with occupancies 0.7375:0.2010:0.0615

Single metal four-electron reduction by U(II) and masked "U(II)" compounds

International audienceThe redox chemistry of uranium is dominated by single electron transfer reactions while single metal four-electron transfers remain unknown in f-element chemistry. Here we show that the oxo bridged diuranium(iii) complex [K(2.2.2-cryptand)](2)[{((Me3Si)(2)N)(3)U}(2)(mu-O)], 1, effects the two-electron reduction of diphenylacetylene and the four-electron reduction of azobenzene through a masked U(ii) intermediate affording a stable metallacyclopropene complex of uranium(iv), [K(2.2.2-cryptand)][U(eta(2)-C2Ph2){N(SiMe3)(2)}(3)], 3, and a bis(imido)uranium(vi) complex [K(2.2.2-cryptand)][U(NPh)(2){N(SiMe3)(2)}(3)], 4, respectively. The same reactivity is observed for the previously reported U(ii) complex [K(2.2.2-cryptand)][U{N(SiMe3)(2)}(3)], 2. Computational studies indicate that the four-electron reduction of azobenzene occurs at a single U(ii) centre via two consecutive two-electron transfers and involves the formation of a U(iv) hydrazide intermediate. The isolation of the cis-hydrazide intermediate [K(2.2.2-cryptand)][U(N2Ph2){N(SiMe3)(2)}(3)], 5, corroborated the mechanism proposed for the formation of the U(vi) bis(imido) complex. The reduction of azobenzene by U(ii) provided the first example of a "clear-cut" single metal four-electron transfer in f-element chemistry

Tuning the structure, reactivity and magnetic communication of nitride-bridged uranium complexes with the ancillary ligands

Molecular uranium nitride complexes were prepared to relate their small molecule reactivity to the nature of the U & xe001;N & xe001;U bonding imposed by the supporting ligand. The U4+-U4+ nitride complexes, [NBu4][{(((BuO)-Bu-t)(3)SiO)(3)U}(2)(mu-N)], [NBu4]-1, and [NBu4][((Me3Si)(2)N)(3)U}(2)(mu-N)], 2, were synthesised by reacting NBu4N3 with the U3+ complexes, [U(OSi((OBu)-Bu-t)(3))(2)(mu-OSi((OBu)-Bu-t)(3))](2) and [U(N(SiMe3)(2))(3)], respectively. Oxidation of 2 with AgBPh4 gave the U4+-U5+ analogue, [((Me3Si)(2)N)(3)U}(2)(mu-N)], 4. The previously reported methylene-bridged U4+-U4+ nitride [Na(dme)(3)][((Me3Si)(2))(2)U(mu-N)(mu-kappa(2)-C,N-CH2SiMe2NSiMe3)U(N(SiMe3)(2))(2)] (dme = 1,2-dimethoxyethane), [Na(dme)(3)]-3, provided a versatile precursor for the synthesis of the mixed-ligand U4+-U4+ nitride complex, [Na(dme)(3)][((Me3Si)(2)N)(3)U(mu-N)U(N(SiMe3)(2))(OSi((OBu)-Bu-t)(3))], 5. The reactivity of the 1-5 complexes was assessed with CO2, CO, and H-2. Complex [NBu4]-1 displays similar reactivity to the previously reported heterobimetallic complex, [Cs{(((BuO)-Bu-t)(3)SiO)(3)U}(2)(mu-N)], [Cs]-1, whereas the amide complexes 2 and 4 are unreactive with these substrates. The mixed-ligand complexes 3 and 5 react with CO and CO2 but not H-2. The nitride complexes [NBu4]-1, 2, 4, and 5 along with their small molecule activation products were structurally characterized. Magnetic data measured for the all-siloxide complexes [NBu4]-1 and [Cs]-1 show uncoupled uranium centers, while strong antiferromagnetic coupling was found in complexes containing amide ligands, namely 2 and 5 (with maxima in the chi versus T plot of 90 K and 55 K). Computational analysis indicates that the U(mu-N) bond order decreases with the introduction of oxygen-based ligands effectively increasing the nucleophilicity of the bridging nitride

Delivery of a Masked Uranium(II) by an Oxide-Bridged Diuranium(III) Complex

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Stabilization of the Oxidation State plus IV in Siloxide-Supported Terbium Compounds

The synthesis of lanthanides other than cerium in the oxidation state +IV has remained a desirable but unmet target until recently, when two examples of Tb-IV with saturated coordination spheres were isolated. Here we report the third example of an isolated molecular complex of terbium(IV), where the supporting siloxide ligands do not saturate the coordination sphere. The fully characterized six-coordinate complex [Tb-IV(OSiPh3)(4)(MeCN)(2)], 2-Tb-Ph, shows high stability and the labile MeCN ligands can be replaced by phosphinoxide ligands. Computational studies suggest that the stability is due to a strong pi(O-Tb) interaction which is stronger than in the previously reported Tb-IV complexes. Cyclic-voltammetry experiments demonstrate that non-binding counterions contribute to the stability of Tb-IV in solution by destabilizing the +III oxidation state, while alkali ions promote Tb-IV/Tb-III electron transfer

Accessing the plus IV Oxidation State in Molecular Complexes of Praseodymium

Out of the 14 lanthanide (Ln) ions, molecular complexes of Ln(IV) were known only for cerium and more recently terbium. Here we demonstrate that the +IV oxidation state is also accessible for the large praseodymium (Pr) cation. The oxidation of the tetrakis(triphenysiloxide) Pr(III) ate complex, [KPr(OSiPh3)(4)(THF)(3)], 1-Pr-Ph, with [N(C6H4Br)(3)][SbCl6], affords the Pr(IV) complex [Pr(OSiPh3)(4)(MeCN)(2)], 2-Pr-Ph, which is stable once isolated. The solid state structure, UV-visible spectroscopy, magnetometry, and cyclic voltammetry data along with the DFT computations of the 2-Pr-Ph complex unambiguously confirm the presence of Pr(IV)

Reactivity of Complexes of 4f^<i>n</i>5d¹ and 4f^<i>n</i>+1 Ln²⁺ Ions with Cyclooctatetraene

The Ln²⁺ complexes [K­(2.2.2-cryptand)]­[Cp′₃Ln] (Ln = La, Ce, Pr, Nd, Sm, Eu, Dy, Tm, Yb; Cp′ = C₅H₄SiMe₃) were reacted with 1,3,5,7-cyclooctatetraene, C₈H₈, to determine if the reactivity of the complexes of 4f^<i>n</i>+1 ions differed from that of 4f^<i>n</i>5d¹ ions. Crystallographically characterizable (C₈H₈)^2– complexes were obtained only for the larger metals in the lanthanide series, and two types of products were obtained: [K­(2.2.2-cryptand)]­[Cp′₂Ln­(C₈H₈)] (Ln = La, Ce) and [K­(2.2.2-cryptand)]­[Ln­(C₈H₈)₂] (Ln = Ce, Pr, Nd, Sm). The expected co-products of the two-electron reduction of C₈H₈ by 2 equiv of [K­(2.2.2-cryptand)]­[Cp′₃Ln], namely, the tetrakis­(cyclopentadienyl) complexes, [K­(2.2.2-cryptand)]­[Cp′₄Ln], were crystallographically characterized for six metals (Ln = Ce, Pr, Nd, Sm, Dy, Tm)