Low-spin 1,1'-diphosphametallocenates of chromium and iron.

We report two anionic diphosphametallocenates, [K(2.2.2-crypt)][M(PC4Me4)2] (M = Cr, 2-Cr; Fe, 2-Fe). Both are low-spin (S = ½) by EPR spectroscopy and SQUID magnetometry. This contrasts the high-spin (S = 3/2) ferrocenate, [K(2.2.2-crypt)][Fe(C5H2-1,2,4-tBu)2] (4-Fe). Quantum chemical calculations suggest this is due to significant differences in ligand field splitting of the d-orbitals which also explain structural features in the 2-M complexes.

Actinide 2-metallabiphenylenes that satisfy Hückel's rule.

Aromaticity and antiaromaticity, as defined by Hückel's rule, are key ideas in organic chemistry, and are both exemplified in biphenylene1-3-a molecule that consists of two benzene rings joined by a four-membered ring at its core. Biphenylene analogues in which one of the benzene rings has been replaced by a different (4n + 2) π-electron system have so far been associated only with organic compounds4,5. In addition, efforts to prepare a zirconabiphenylene compound resulted in the isolation of a bis(alkyne) zirconocene complex instead6. Here we report the synthesis and characterization of, to our knowledge, the first 2-metallabiphenylene compounds. Single-crystal X-ray diffraction studies reveal that these complexes have nearly planar, 11-membered metallatricycles with metrical parameters that compare well with those reported for biphenylene. Nuclear magnetic resonance spectroscopy, in addition to nucleus-independent chemical shift calculations, provides evidence that these complexes contain an antiaromatic cyclobutadiene ring and an aromatic benzene ring. Furthermore, spectroscopic evidence, Kohn-Sham molecular orbital compositions and natural bond orbital calculations suggest covalency and delocalization of the uranium f2 electrons with the carbon-containing ligand.

A sulphur and uranium fiesta! Synthesis, structure, and characterization of neutral terminal uranium(vi) monosulphide, uranium(vi) η2-disulphide, and uranium(iv) phosphine sulphide complexes.

Three new uranium species (C5Me5)2U([double bond, length as m-dash]N-2,6-iPr2-C6H3)([double bond, length as m-dash]S), (C5Me5)2U([double bond, length as m-dash]N-2,6-iPr2-C6H3)(η2-S2), and (C5Me5)2U([double bond, length as m-dash]N-2,6-iPr2-C6H3)(S[double bond, length as m-dash]PMe3) were synthesized and fully characterized by a combination of NMR, IR, and UV/vis-NIR spectroscopies, elemental analysis, and cyclic voltammetry. The solid state structures of (C5Me5)2U([double bond, length as m-dash]N-2,6-iPr2-C6H3)([double bond, length as m-dash]S) and (C5Me5)2U([double bond, length as m-dash]N-2,6-iPr2-C6H3)(η2-S2) were also determined. The compound (C5Me5)2U([double bond, length as m-dash]N-2,6-iPr2-C6H3)([double bond, length as m-dash]S) is the first neutral uranium complex with a terminal sulphido ligand, and (C5Me5)2U([double bond, length as m-dash]N-2,6-iPr2-C6H3)(S[double bond, length as m-dash]PMe3) is the first uranium compound with a coordinated phosphine sulphide ligand. The phosphine sulphide adduct, (C5Me5)2U([double bond, length as m-dash]N-2,6-iPr2-C6H3)(S[double bond, length as m-dash]PMe3), can be synthesized either by reaction of the uranium(iv) complex (C5Me5)2U([double bond, length as m-dash]N-2,6-iPr2-C6H3)(thf) with S[double bond, length as m-dash]PMe3 or by the reaction of the uranium(vi) terminal sulphido complex (C5Me5)2U([double bond, length as m-dash]N-2,6-iPr2-C6H3)([double bond, length as m-dash]S) with PMe3.

Synthesis, Characterization, and Density Functional Theory Analysis of Uranium and Thorium Complexes Containing Nitrogen-Rich 5-Methyltetrazolate Ligands.

Two nitrogen-rich, isostructural complexes of uranium and thorium, (C5Me5)2U[η(2)-(N,N')-tetrazolate]2 (7) and (C5Me5)2Th[η(2)-(N,N')-tetrazolate]2 (8), containing 5-methyltetrazolate, have been synthesized and structurally characterized by single-crystal X-ray diffraction, electrochemical methods, UV-visible-near-IR spectroscopy, and variable-temperature (1)H NMR spectroscopy. Density functional theory (DFT) calculations yield favorable free energies of formation (approximately -375 kJ/mol) and optimized structures in good agreement with the experimental crystal structures. Additionally, calculated NMR chemical shifts of 7 and 8 are in good agreement with the variable-temperature (1)H NMR experiments. Time-dependent DFT calculations of both complexes yield UV-visible spectroscopic features that are consistent with experiment and provide assignments of the corresponding electronic transitions. The electronic transitions in the UV-visible spectroscopic region are attributed to C5Me5 ligand-to-metal charge transfer. The low-lying molecular orbitals of the tetrazolate ligands (∼2 eV below the HOMO) do not contribute appreciably to experimentally observed electronic transitions. The combined experimental and theoretical analysis of these new nitrogen-rich uranium and thorium complexes indicates the tetrazolate ligand behaves primarily as a σ-donor.

New Twists and Turns for Actinide Chemistry: Organometallic Infinite Coordination Polymers of Thorium Diazide.

Two organometallic 1D infinite coordination polymers and two organometallic monometallic complexes of thorium diazide have been synthesized and characterized. Steric control of these self-assembled arrays, which are dense in thorium and nitrogen, has also been demonstrated: infinite chains can be circumvented by using steric bulk either at the metallocene or with a donor ligand in the wedge.

Phenylsilane as a safe, versatile alternative to hydrogen for the synthesis of actinide hydrides.

The thorium and uranium dihydride dimer complexes [(C5Me5)2An(H)(µ-H)]2 (An = Th, U) have been easily prepared using phenylsilane, which is an efficient and safer alternative to hydrogen gas. The synthetic utility of this new hydriding method has been demonstrated by the preparation of a variety of organometallic complexes, including, for the first time, (C5Me5)2U(SMe)2, (C5Me5)2Th(C4Ph4), (C5Me5)2U(C4Ph4), (C5Me5)2ThS5, and (C5Me5)2U(bipy) using [(C5Me5)2An(H)(µ-H)]2 (An = Th, U) as multi-electron reductants.

Syntheses, structures, and (1)H, (13)C{(1)H} and (119)Sn{(1)H} NMR chemical shifts of a family of trimethyltin alkoxide, amide, halide and cyclopentadienyl compounds.

The synthesis and full characterization, including Nuclear Magnetic Resonance (NMR) data ((1)H, (13)C{(1)H} and (119)Sn{(1)H}), for a series of Me3SnX (X = O-2,6-(t)Bu2C6H3 (), (Me3Sn)N(2,6-(i)Pr2C6H3) (), NH-2,4,6-(t)Bu3C6H2 (), N(SiMe3)2 (), NEt2, C5Me5 (), Cl, Br, I, and SnMe3) compounds in benzene-d6, toluene-d8, dichloromethane-d2, chloroform-d1, acetonitrile-d3, and tetrahydrofuran-d8 are reported. The X-ray crystal structures of Me3Sn(O-2,6-(t)Bu2C6H3) (), Me3Sn(O-2,6-(i)Pr2C6H3) (), and (Me3Sn)(NH-2,4,6-(t)Bu3C6H2) () are also presented. These compiled data complement existing literature data and ease the characterization of these compounds by routine NMR experiments.

A rare tetranuclear thorium(IV) µ4 -oxo cluster and dinuclear thorium(IV) complex assembled by carbon-oxygen bond activation of 1,2-dimethoxyethane (DME).

The synthesis and X-ray crystal structure of two new multinuclear thorium complexes are reported. The tetranuclear µ4 -oxo cluster complex Th4 (µ4 -O)(µ-Cl)2 I6 [κ(2) (O,O')-µ-O(CH2 )2 OCH3 ]6 and the dinuclear complex Th2 I5 [κ(2) (O,O')-µ-O(CH2 )2 OCH3 ]3 (DME) (DME=dimethoxyethane) are formed by CO bond activation of 1,2-dimethoxyethane (DME) mediated by thorium iodide complexes.

Thorium-mediated ring-opening of tetrahydrofuran and the development of a new thorium starting material: preparation and chemistry of ThI4(DME)2.

The thorium(IV) tetraiodide complex ThI(4)(DME)(2) (3) (DME = 1,2-dimethoxyethane) has been prepared in high yield by reacting the corresponding chloride complex ThCl(4)(DME)(2) with an excess of trimethylsilyl iodide (Me(3)SiI) in toluene. This new route avoids the use of thorium metal as a reagent. ThI(4)(DME)(2) (3) exhibits excellent thermal stability compared to ThI(4)(THF)(4) (1), which undergoes rapid ring-opening of THF at ambient temperature to yield the iodobutoxide complex ThI(3)[O(CH(2))(4)I](THF)(3) (2). Subsequent ligand-exchange between 2 and DME affords ThI(3)[O(CH(2))(4)I](DME)(2) (11), which can be converted to 3 with Me(3)SiI. Salt metathesis between 2 and K(L(Me)) (L(Me) = (2,6-(i)Pr(2)C(6)H(3))NC(Me)CHC(Me)N(2,6-(i)Pr(2)C(6)H(3))) cleanly gives (L(Me))ThI(2)[O(CH(2))(4)I](THF) (10), which is a rare example of a thorium ß-diketiminate complex. Complexes 2, 10, and 11 represent the first reported examples of THF ring-opening mediated by thorium. The synthetic utility of ThI(4)(DME)(2) (3) is demonstrated by preparation of thorium(IV) alkoxide, amide, and organometallic compounds.

Molecular quadrangle formation from a diuranium µ-η6,η6-toluene complex.

A new inverted sandwich of a µ-η(6),η(6)-toluene diuranium complex reacted with quinoxaline to form a tetranuclear macrocycle with ferrocene diamide uranium(IV) vertices and reduced quinoxaline edges.

Uranium azide photolysis results in C-H bond activation and provides evidence for a terminal uranium nitride.

Uranium nitride [U[triple bond]N](x) is an alternative nuclear fuel that has great potential in the expanding future of nuclear power; however, very little is known about the U[triple bond]N functionality. We show, for the first time, that a terminal uranium nitride complex can be generated by photolysis of an azide (U-N=N=N) precursor. The transient U[triple bond]N fragment is reactive and undergoes insertion into a ligand C-H bond to generate new N-H and N-C bonds. The mechanism of this unprecedented reaction has been evaluated through computational and spectroscopic studies, which reveal that the photochemical azide activation pathway can be shut down through coordination of the terminal azide ligand to the Lewis acid B(C(6)F(5))(3). These studies demonstrate that photochemistry can be a powerful tool for inducing redox transformations for organometallic actinide complexes, and that the terminal uranium nitride fragment is reactive, cleaving strong C-H bonds.

Organometallic uranium(IV) fluoride complexes: preparation using protonolysis chemistry and reactivity with trimethylsilyl reagents.

Reaction of the uranium alkyl complex (C(5)Me(5))(2)UMe(2) (1) with Et(3)N.3HF in toluene in the presence of a donor ligand (pyridine or trimethylphosphine oxide) results in gas evolution and the formation of the uranium(IV) difluoride complexes (C(5)Me(5))(2)UF(2)(L) (L = NC(5)H(5) (2), Me(3)P=O (3)). Similarly, reaction of (C(5)Me(5))(2)U[kappa(2)-(C,N)-CH(2)Si(CH(3))(2)N(SiMe(3))] (5) with Et(3)N.3HF in toluene gives the uranium(IV) amide-fluoride complex (C(5)Me(5))(2)U[N(SiMe(3))(2)](F) (6). The fluoride complex (C(5)Me(5))(2)UF(2)(NC(5)H(5)) (2) shows versatile reaction chemistry with a variety of trimethylsilyl reagents and demonstrates that the U-F bond provides an attractive synthetic strategy for accessing new functional groups that are not available from alkoxide or chloride complexes.

Comparative study of f-element electronic structure across a series of multimetallic actinide and lanthanoid-actinide complexes possessing redox-active bridging ligands.

A comparative examination of the electronic interactions across a series of trimetallic actinide and mixed lanthanide-actinide and lanthanum-actinide complexes is presented. Using reduced, radical terpyridyl ligands as conduits in a bridging framework to promote intramolecular metal-metal communication, studies containing structural, electrochemical, and X-ray absorption spectroscopy are reported for (C(5)Me(5))(2)An[-N horizontal lineC(Bn)(tpy-M{C(5)Me(4)R}(2))](2) (where An = Th(IV), U(IV); Bn = CH(2)C(6)H(5); M = La(III), Sm(III), Yb(III), U(III); R = H, Me, Et) to reveal effects dependent on the identities of the metal ions and R-groups. The electrochemical results show differences in redox energetics at the peripheral "M" site between complexes and significant wave splitting of the metal- and ligand-based processes indicating substantial electronic interactions between multiple redox sites across the actinide-containing bridge. Most striking is the appearance of strong electronic coupling for the trimetallic Yb(III)-U(IV)-Yb(III), Sm(III)-U(IV)-Sm(III), and La(III)-U(IV)-La(III) complexes, [8](-), [9b](-), and [10b](-), respectively, whose calculated comproportionation constant K(c) is slightly larger than that reported for the benchmark Creutz-Taube ion. X-ray absorption studies for monometallic metallocene complexes of U(III), U(IV), and U(V) reveal small but detectable energy differences in the "white-line" feature of the uranium L(III)-edges consistent with these variations in nominal oxidation state. The sum of these data provides evidence of 5f/6d-orbital participation in bonding and electronic delocalization in these multimetallic f-element complexes. An improved, high-yielding synthesis of 4'-cyano-2,2':6',2''-terpyridine is also reported.

Convenient access to the anhydrous thorium tetrachloride complexes ThCl(4)(DME)(2), ThCl(4)(1,4-dioxane)(2) and ThCl(4)(THF)(3.5) using commercially available and inexpensive starting materials.

Anhydrous thorium tetrachloride complexes ThCl(4)(DME)(2), ThCl(4)(1,4-dioxane)(2), and ThCl(4)(THF)(3.5) have been easily accessed from inexpensive, commercially available reagents under mild conditions and serve as excellent precursors to a variety of thorium(iv) halide, alkoxide, amide and organometallic compounds.

Actinide redox-active ligand complexes: reversible intramolecular electron-transfer in U(dpp-BIAN)2/U(dpp-BIAN)2(THF).

Actinide complexes of the redox-active ligand (dpp-BIAN)(2-) (dpp-BIAN = 1,2-bis(2,6-diisopropylphenylimino)acenaphthylene), U(dpp-BIAN)(2) (1), U(dpp-BIAN)(2)(THF) (1-THF), and Th(dpp-BIAN)(2)(THF) (2-THF), have been prepared. Solid-state magnetic and single-crystal X-ray data for complex 1 indicate a ground-state U(IV)-pi*(4) configuration, whereas a (dpp-BIAN)(2-)-to-uranium electron transfer occurs for 1-THF, resulting in a U(III)-pi*(3) ground configuration. The solid-state magnetic data also indicate that interconversion between the two forms of the complex is possible, limited only by the ability of tetrahydrofuran (THF) vapor to penetrate the solid upon cooling of the sample. In contrast to those in the solid state, spectroscopic data acquired in THF indicate only the presence of the U(IV)-pi*(4) form for 1-THF in solution, evidenced by electronic absorption spectra and by measurement of the solution magnetic moment in THF-d(8) using the Evans method. Also reported is the electrochemistry of the complexes collected in CH(2)Cl(2), CF(3)C(6)H(5), and THF. As expected from the solution spectroscopic data, only small differences are observed in half-wave potentials of ligand-based processes in the presence of THF, consistent with the solution U(IV)-pi*(4) configuration of the complexes in all cases. Density functional theory calculations were undertaken for complexes 1 and 1-THF to determine if intrinsic energetic or structural factors underlie the observed charge-transfer process. While the calculated optimized geometries agree well with experimental results, it was not possible to arrive at a convergent solution for 1-THF in the U(III)-pi*(3) configuration. However, perturbations in the orbital energies in 1 versus 1-THF for the U(IV)-pi*(4) configuration do point to a diminished highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap in 1-THF, consistent with the solid-state magnetic data. These results represent the first example of a stable and well-defined, reversible intramolecular electron transfer in an actinide complex with redox-active ligands.

Pentavalent uranium chemistry: synthetic pursuit of a rare oxidation state.

This feature article presents a comprehensive overview of pentavalent uranium systems in non-aqueous solution with a focus on the various synthetic avenues employed to access this unusual and very important oxidation state. Selected characterization data and theoretical aspects are also included. The purpose is to provide a perspective on this rapidly evolving field and identify new possibilities for future developments in pentavalent uranium chemistry.

Cation-cation interactions, magnetic communication, and reactivity of the pentavalent uranium ion [U(NtBu)2]+.

Communication is important: The dimeric bis(imido) uranium complex [{U(NtBu)(2)(I)(tBu(2)bpy)}(2)] (see picture; U green, N blue, I red) has cation-cation interactions between [U(NR)(2)](+) ions. This f(1)-f(1) system also displays f orbital communication between uranium(V) centers at low temperatures, and can be oxidized to generate uranium(VI) bis(imido) complexes.

Selenate and tellurate complexes of pentavalent uranium.

Oxidation of (C(5)Me(5))(2)U([double bond, length as m-dash]N-2,6-(i)Pr(2)-C(6)H(3))(THF) with PhE-EPh yields the corresponding U(V)-chalcogenate complexes (C(5)Me(5))(2)U([double bond, length as m-dash]N-2,6-(i)Pr(2)-C(6)H(3))(EPh) (E = S, Se, Te) in excellent (>90%) isolated yields.

Challenging the metallocene dominance in actinide chemistry with a soft PNP pincer ligand: new uranium structures and reactivity patterns.

A soft embrace for U: Replacement of C(5)Me(5) by the soft PNP pincer ligand is a successful strategy to promote new reactivities and support new structures for the actinide series (see picture, py-O = pyridine-N-oxide). The specific electronic and steric properties of the PNP ligand enable access to previously unreported structures not available for the C(5)Me(5) ligand set and support not only low-valent uranium but also the high-valent uranium(VI) ion.