Cooperative dihydrogen activation with unsupported uranium-metal bonds and characterization of a terminal U(iv) hydride.

Cooperative chemistry between two or more metal centres can show enhanced reactivity compared to the monometallic fragments. Given the paucity of actinide-metal bonds, especially those with group 13, we targeted uranium(iii)-aluminum(i) and -gallium(i) complexes as we envisioned the low-valent oxidation state of both metals would lead to novel, cooperative reactivity. Herein, we report the molecular structure of [(C5Me5)2(MesO)U-E(C5Me5)], E = Al, Ga, Mes = 2,4,6-Me3C6H2, and their reactivity with dihydrogen. The reaction of H2 with the U(iii)-Al(i) complex affords a trihydroaluminate complex, [(C5Me5)2(MesO)U(µ2-(H)3)-Al(C5Me5)] through a formal three-electron metal-based reduction, with concomitant formation of a terminal U(iv) hydride, [(C5Me5)2(MesO)U(H)]. Noteworthy is that neither U(iii) complexes nor [(C5Me5)Al]4 are capable of reducing dihydrogen on their own. To make the terminal hydride in higher yields, the reaction of [(C5Me5)2(MesO)U(THF)] with half an equivalent of diethylzinc generates [(C5Me5)2(MesO)U(CH2CH3)] or treatment of [(C5Me5)2U(i)(Me)] with KOMes forms [(C5Me5)2(MesO)U(CH3)], which followed by hydrogenation with either complex cleanly affords [(C5Me5)2(MesO)U(H)]. All complexes have been characterized by spectroscopic and structural methods and are rare examples of cooperative chemistry in f element chemistry, dihydrogen activation, and stable, terminal ethyl and hydride compounds with an f element.

Iron(II) complexes supported by pyrazolyl-substituted cyclopentadienyl ligands: synthesis and reactivity.

The preparation of bis(pyrazolyl)cyclopentadienyl iron complexes is described. Isopropyl substitution promotes solubility of the iron chloride complex that serves as a precursor to several derivatives through ligand exchange. Modification of the cyclopentadienyl substituent to replace a pyrazolyl unit with a phenyl group favors formation of a substituted ferrocene complex.

Deep eutectic solvents comprising creatine and citric acid and their hydrated mixtures.

We report the phase diagram for the binary creatine-citric acid mixture which features a stable and broad eutectic region. Combinations containing 10-60 mol% creatine yield a deep eutectic solvent with a glass transition temperature at 270 K. Addition of up to 70 mol% water to the binary mixture affords retention of the eutectic nature and a handle to vary solvent viscosity and polarity.

Crystal structure of [Th3(Cp*)3(O)(OH)3]2Cl2(N3)6: a discrete mol-ecular capsule built from multinuclear organothorium cluster cations.

An unusually large and structurally complex charge-neutral polynuclear cluster, hexa-µ2-azido-di-µ3-chlorido-hexa-µ2-hydroxido-di-µ3-oxido-hexa-kis-(penta-methyl-cyclo-penta-dien-yl)hexa-thorium-diethyl ether-tetra-hydro-furan (1/0.56/1.44), [Th3(C10H15)6Cl3(N3)6(OH)6O2]·0.56C4H10O·1.44C4H8O or [Th3(Cp*)3(O)(OH)3]2Cl2(N3)6·0.56C4H10O·1.44C4H8O (Cp* = [penta-methyl-cyclo-penta-dien-yl])-, has been crystallized as a mixed tetra-hydro-furan/diethyl ether solvate and structurally characterized. The mol-ecule contains a number of unusual features, the most notable being a finite yet exceptionally long cyclic metal-azido chain. These rare features are the consequence of both sterically protecting Cp* ligands and highly bridging oxide and hydroxide ligands in the same system and illustrate the inter-esting new possibilities that can arise from combining organometallic and solvothermal f-block element chemistry.

Divergent uranium- versus phosphorus-based reduction of Me3SiN3 with steric modification of phosphido ligands.

We describe an example of a two-electron metal- and ligand-based reduction of Me3SiN3 using uranium(iv) complexes with varying steric properties. Reaction of (C5Me5)2U(CH3)[P(SiMe3)(Ph)] with Me3SiN3 produces the imidophosphorane complex, (C5Me5)2U(CH3)[N[double bond, length as m-dash]P(SiMe3)2(Ph)] through oxidation of phosphorus. However, a similar reaction with a more sterically encumbering phosphido ligand, (C5Me5)2U(CH3)[P(SiMe3)(Mes)] forms the U(iv) complex, (C5Me5)2U[κ 2-(N,N)-N(SiMe3)P(Mes)N(SiMe3)]. In probing the mechanism of this reaction, a U(vi) bis(imido) complex, (C5Me5)2U([double bond, length as m-dash]NSiMe3){[double bond, length as m-dash]N[P(SiMe3)(Mes)]} was isolated. DFT calculations show an intramolecular reductive cycloaddition reaction leads to the formation of the U(iv) bis(amido)phosphane from the U(vi) bis(imido) complex. This is a rare example of the isolation of a reaction intermediate in f element chemistry.

Site-Specific Metal Chelation Facilitates the Unveiling of Hidden Coordination Sites in an FeII/FeIII-Seamed Pyrogallol[4]arene Nanocapsule.

Under suitable conditions, C-alkylpyrogallol[4]arenes (PgCs) arrange into spherical metal-organic nanocapsules (MONCs) upon coordination to appropriate metal ions. Herein we present the synthesis and structural characterization of a novel FeII/FeIII-seamed MONC, as well as studies related to its electrochemical and magnetic behaviors. Unlike other MONCs that are assembled through 24 metal ions, this nanocapsule comprises 32 Fe ions, uncovering 8 additional coordination sites situated between the constituent PgC subunits. The FeII ions are likely formed by the reducing ability of DMF used in the synthesis, representing a novel synthetic route toward polynuclear mixed-valence MONCs.

Oxidation State Distributions Provide Insight into Parameters Directing the Assembly of Metal-Organic Nanocapsules.

Two structurally analogous Mn-seamed C-alkylpyrogallol[4]arene (PgC n)-based metal-organic nanocapsules (MONCs) have been synthesized under similar reaction conditions and characterized by crystallographic, electrochemical, and magnetic susceptibility techniques. Both MONCs contain 24 Mn centers, but, somewhat surprisingly, marked differences in oxidation state distribution are observed upon analysis. One MONC contains exclusively MnII ions, while the other is a mixed-valence MnII/ MnIII assembly. We propose that these disparate oxidation state distributions arise from slight differences in pH achieved during synthesis, a factor that may lead to many spectacular new MONCs (and associated host-guest chemistries).

Structure and properties of [(4,6-tBu2C6H2O)2Se]2An(THF)2, An = U, Np, and their reaction with p-benzoquinone.

The synthesis and characterization of U(iv) and Np(iv) selenium bis(phenolate) complexes are reported. The reaction of two equivalents of the U(iv) complex with p-benzoquinone results in the formation of a U(v)-U(v) species with a bridging reduced quinone. This represents a rare example of high-valent uranium chemistry as well as a rare example of a neptunium aryloxide complex.

Influence of Substituents on the Electronic Structure of Mono- and Bis(phosphido) Thorium(IV) Complexes.

A series of metallocene thorium complexes with mono- and bis(phosphido) ligands have been investigated with varying hues: (C5Me5)2Th(Cl)[P(Mes)2] (Mes = mesityl = 2,4,6-(CH3)3C6H2; dark red-purple), (C5Me5)2Th[P(Mes)(CH3)]2 (dark red-purple), (C5Me5)2Th(CH3)[P(Mes)2] (dark red-purple), (C5Me5)2Th(CH3)[P(Mes)(SiMe3)] (orange), (C5Me5)2Th(Cl)[P(Mes)(SiMe3)] (orange), (C5Me5)2Th[P(Mes)(SiMe3)]2 (orange), and (C5Me5)2Th[PH(Mes)]2 (pale yellow). While all of these complexes bear a mesityl group on phosphorus, the electronic structure observed differs depending on the other substituent (mesityl, methyl, trimethylsilyl, or hydrogen). This sparked an investigation of the electronic structure of these complexes using 31P NMR and electronic absorption spectroscopy in concert with time-dependent density functional theory calculations.

Four-electron reduction chemistry using a uranium(iii) phosphido complex.

The first uranium(iii) phosphido complex is reported. The reaction of (C5Me5)2UI(THF) with KP[(C6H2Me3-2,4,6)(SiMe3)] affords (C5Me5)2U[P(C6H2Me3-2,4,6)(SiMe3)](THF), 1. The reactivity of 1 was explored with two equivalents of N3SiMe3 and N3Ad, Ad = adamantyl, both of which produce U(vi) bis(imido) complexes via four-electron reduction of the azides.

In situ redox reactions facilitate the assembly of a mixed-valence metal-organic nanocapsule.

C-alkylpyrogallol[4]arenes (PgCs) have been studied for their ability to form metal-organic nanocapsules (MONCs) through coordination to appropriate metal ions. Here we present the synthesis and characterization of an MnII/MnIII-seamed MONC in addition to its electrochemical and magnetic behavior. This MONC assembles from 24 manganese ions and 6 PgCs, while an additional metal ion is located on the capsule interior, anchored through the introduction of bridging nitrite ions. The latter originate from an in situ redox reaction that occurs during the self-assembly process, thus representing a new route to otherwise unobtainable nanocapsules.

Formation of Methane versus Benzene in the Reactions of (C5 Me5 )2 Th(CH3 )2 with [CH3 PPh3 ]X (X=Cl, Br, I) Yielding Thorium-Carbene or Thorium-Ylide Complexes.

The reaction of (C5 Me5 )2 Th(CH3 )2 with the phosphonium salts [CH3 PPh3 ]X (X=Cl, Br, I) was investigated. When X=Br and I, two equivalents of methane are liberated to afford (C5 Me5 )2 Th[CHPPh3 ]X, rare terminal phosphorano-stabilized carbenes with thorium. These complexes feature the shortest thorium-carbon bonds (≈2.30 Å) reported to date, and electronic structure calculations show some degree of multiple bonding. However, when X=Cl, only one equivalent of methane is lost with concomitant formation of benzene from an unstable phosphorus(V) intermediate, yielding (C5 Me5 )2 Th[κ2 -(C,C')-(CH2 )(CH2 )PPh2 ]Cl. Density functional theory (DFT) investigations of the reaction energy profiles for [CH3 PPh3 ]X, X=Cl and I showed that in the case of iodide, thermodynamics prevents the production of benzene and favors formation of the carbene.

Uranium(iii) and thorium(iv) alkyl complexes as potential starting materials.

The synthesis and characterisation of a rare U(iii) alkyl complex, U[η4-Me2NC(H)C6H5]3, using the dimethylbenzylamine (DMBA) ligand has been accomplished. While attempting to prepare the U(iv) compound, reduction to the U(iii) complex occurred. In the analogous Th(iv) system, C-H bond activation of a methyl group of one dimethylamine was observed yielding Th[η4-Me2NC(H)C6H5]2[η5-(CH2)MeNC(H)C6H5] with a dianionic DMBA ligand. The utility of these complexes as starting materials has been analyzed using a bulky dithiocarboxylate ligand to yield tetravalent actinide species.

Copper(i) clusters with bulky dithiocarboxylate, thiolate, and selenolate ligands.

The coordination chemistry of copper has interest due to its use in biological systems as well as for photochemical and medicinal properties. We report the coordination chemistry of copper(i) complexes using terphenyl-based dithiocarboxylate, thiolate, and selenolate ligands. The number of metal ions of the resulting complexes can be tuned by varying the steric properties of the terphenyl ligands, changing the starting material, as well as adding PEt3. In addition, the steric crowding of the terphenyl ligand leads to varying reactivity. For example, while the reaction of carbon disulfide with [Cu(2,6-(Ph)2C6H3)]2 results in an insertion into the copper-carbon bond, no reaction occurs with [Cu(2,4,6-(Mes)2C6H3)], Mes = 2,4,6-Me3C6H2, or [Et3PCu(2,4,6-(Mes)2C6H2)2C6H3]. The synthesis and characterization of new copper(i) complexes using NMR and IR spectroscopy, as well as X-ray crystallography is described.