Search

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.

Aromaticity and antiaromaticity, as defined by Huckel’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 Biphenylene analogues in which one of the benzene rings has been replaced by a different (4n + 2) π-electron system have so far been associated only with organic compounds4,5.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. The synthesis of uranium- and thorium-containing metallabiphenylenes demonstrates the ability of the actinides to stabilize aromatic/antiaromatic structures where transition metals have failed.

Neutron radiography through Spectroscopic Imaging by Fast Neutrons (SIFaN) is described. The fast neutron tracking principle [1] has been extended to include neutron-induced fissions in actinide perovskites. The design and performance of a new SIFaN instrument, called SIFaN-perovskite (or SIFaN-P), are studied by a combination of MCNP and semi-analytical models. Hybrid organic-inorganic and actinide perovskites are considered and compared with gas and silicon for neutron detection and tracking. The Los Alamos LANSCE facility provides access to the initial SIFaN-P testing and demonstration.

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.

Two new uranium metallacyclopropenes, (C5Me4R)2U(η2-Ph2PC CPPh2) (R = Me, Et) were prepared by reducing the corresponding (C5Me4R)2UCl2 complexes with KC8 in the presence of 1,2-bis(diphenylphosphino)acetylene (Ph2P C C PPh2). Both compounds were fully characterized by a combination of elemental analysis and multinuclear NMR, UV–visible–NIR, and IR spectroscopies. Differences in the electronic spectra of these novel compounds and the known (C5Me5)2U(η2-Me3SiC CSiMe3) are discussed. Also presented is the solid-state structure of (C5Me4Et)2U(η2-Ph2PC CPPh2), which reveals significant distortions of the coordinated 1,2-bis(diphenylphosphino)acetylene (Ph2P C C PPh2) ligand.

The terminal actinide fluoride bonds in (C 5 Me 5 ) 2 ThF 2 (py) (py = pyridine) and (C 5 Me 5 ) 2 UF 2 (O=PR 3 ) (R = Me, Ph) react with two equivalents of Me 3 SiN 3 in toluene to form the polymeric thorium bis(azide), [(C 5 Me 5 ) 2 Th(N 3 ) 2 ] ∞ , and a new class of monometallic uranium bis(azide) complexes, (C 5 Me 5 ) 2 U(N 3 ) 2 (O=PR 3 ), respectively. Full characterization of the novel complexes (C 5 Me 5 ) 2 ThF 2 (py) and (C 5 Me 5 ) 2 UF 2 (O=PR 3 ) are reported, including the solid-state structures of (C 5 Me 5 ) 2 ThF 2 (py) and (C 5 Me 5 ) 2 U(N 3 ) 2 (O=PPh 3 ). Electronic absorption spectral data are also reported for (C 5 Me 5 ) 2 AnF 2 (py) (An = Th, U) and (C 5 Me 5 ) 2 U(N 3 ) 2 (O=PR 3 ) to confirm metal oxidation state and enable elucidation of the fluoride and azide ligand bonding in these complexes.

Trimethyltin fluoride (Me₃SnF) is a mild and selective reagent for the installation of actinide fluoride bonds as demonstrated by the room temperature synthesis of a variety of organometallic and inorganic thorium(IV), uranium(IV), and uranium(V) fluoride complexes ((1,2,4-tBu₃C₅H₂)₂ThF₂, (C₅Me₅)₂U(F)(O-2,6-iPr₂C₆H₃), U(F)(O-2,6-tBu₂C₆H₃)₃, U(F)[N(SiMe₃)₂]₃ (C₅Me₅)₂UF₂(L) (L = O=PMe₃, O=PPh₃, O=PCy₃), and (C₅Me₅)₂U(F)(=N-2,6-iPr₂C₆H₃)) from their corresponding chloride, bromide, and iodide analogues. From these reactions, the new (C₅Me₅)₂UF₂(L) (L = O=PPh₃, O=PCy₃) uranium fluoride complexes were isolated and characterized by NMR spectroscopy and X-ray crystallography.

The title compound, (E)-1-(2,6-diisopropylphenyl)-2-phenyldiazine (I), was synthesized and characterized using a combination of 1H, 13C, and 15N NMR spectroscopy, infrared and UV/Vis spectroscopy, X-ray crystallography, and GC mass spectrometry. The solid-state structure is also reported. The unsymmetric azobenzene crystallizes in the space group P21/c with unit cell parameters a = 8.001(7) A, b = 17.827(16) A, c = 11.129(10) A, β = 101.960(10)°, V = 1553(2) A3, Z = 4, D calc = 1.139 g/cm3. The synthesis of (E)-1-(2,6-diisopropylphenyl)-2-phenyldiazine (I) and its characterization using a combination of combination of 1H, 15N, and 13C NMR spectroscopy, infrared and UV/Vis spectroscopy, mass spectrometry, and X-ray crystallography is described in this report.

The thorium and uranium complexes (C5Me5)2AnMe2, [(C5Me5)2An(H)(μ-H)]2 (An = Th, U) and [(C5Me5)2U(H)]2 dehydrogenate dimethylamine borane (Me2NH·BH3) at room temperature. Upon mild heating at 45 °C, turnover frequencies (TOFs) of 400 h–1 are obtained, which is comparable to some of the fastest Me2NH·BH3 dehydrogenation catalysts known in the literature. A β-hydride elimination mechanism for dehydrogenation is proposed because of the observation of Me2N═BH2, Me2N═BMe2, and Me2N═BHMe in the 11B NMR spectra of catalytic and stoichiometric reactions. The similar catalytic metrics between the actinide dimethyl and hydride complexes with Me2NH·BH3 indicate that the actinide hydride complexes are the active catalysts in this chemistry.

A new uranium metallacyclocumulene, (C5Me5)2U(η4-1,2,3,4-PhC4Ph), was synthesized by both reaction of (C5Me5)2UCl2 with 1,4-diphenylbutadiyne in the presence of KC8 and by ligand exchange between (C5Me5)2U(η2-Me3SiC2SiMe3) and 1,4-diphenylbutadiyne. Full characterization of (C5Me5)2U(η4-1,2,3,4-PhC4Ph) is reported, including the solid-state structure. (C5Me5)2U(η4-1,2,3,4-PhC4Ph) displays an unusually detailed UV–visible spectrum, which is rare for uranium(IV) metallocene complexes.

The reaction of (C5Me5)2AnCl2 (An = Th, U) with 2.8 or 4 equivalents of LiNMe2, respectively, affords (C5Me5)2An(NMe2)2 in high yields. In addition to improved syntheses, the solid-state structures, voltammetric data, and UV-visible–NIR spectra for these classic actinide bis(dimethylamido) complexes are presented for the first time.

Aromaticity and antiaromaticity, as defined by Hückel's rule, are key ideas in organic chemistry, and are both exemplified in biphenylene

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.

This work demonstrates that the oxidation state and chemistry of uranium hydrides can be tuned with temperature and the stoichiometry of phenylsilane. The trivalent uranium hydride [(C5Me5)2U–H]x (5) was found to be comprised of an equilibrium mixture of U(III) hydrides in solution at ambient temperature. A single U(III) species can be selectively prepared by treating (C5Me5)2UMe2 (4) with 2 equiv of phenylsilane at 50 °C. The U(III) system is a potent reducing agent and displayed chemistry distinct from the U(IV) system [(C5Me5)2U(H)(μ-H)]2 (2), which was harnessed to prepare a variety of organometallic complexes, including (C5Me5)2U(dmpe)(H) (6), and the novel uranium(IV) metallacyclopentadiene complex (C5Me5)2U(C4Me4) (11).

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.

Calcium borohydride allows for the high-yielding synthesis of (C5Me5)2An(η3-H3BH)2 (An = Th, U) by reaction with (C5Me5)2AnCl2 (An = Th, U). While a preparative synthesis of (C5Me5)2U(η3-H3BH)2 has been previously reported in the literature using K(C5Me5) and U(BH4)4, the use of Ca(BH4)2 is higher yielding and mild. Full characterization of the novel compound (C5Me5)2Th(η3-H3BH)2 is presented.

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 panel of seventeen experts from academia, industry, and government laboratories share their thoughts on a variety of matters of importance to the readership of Organometallics. These include directions for the field and recent breakthroughs (illustrated with selected examples), the interface with green chemistry, the quest for reproducible experimental procedures, data and research integrity, laboratory safety, the preparation of coworkers for non-academic careers, and needs regarding instrumentation, infrastructure, shared facilities, and computational methods. A lively give and take is evident in the edited transcript, which continues a biennial tradition initiated in 2011.

The coordination behavior of the bulky β-diketiminate ligands N,N′-bis(2,6-diisopropylphenyl)pentane-2,4-diiminate (LMe) and N,N′-bis(2,6-diisopropylphenyl)-2,2–6,6-tetramethylheptane-3,5-diiminate (LtBu) toward ThX4(THF)4 (X = Br, I) and UCl4 has been investigated. The reaction between K[LMe] and ThX4(THF)4 (X = Br, I) afforded the mono(β-diketiminate)thorium(IV) halide complexes (LMe)ThX3(THF) (X = Br (7), I (8)). The same reaction carried out with the more sterically demanding K[LtBu] gave (LtBu)ThBr3(THF) (9) and (LtBu)ThI3 (11). All attempts to install two β-diketiminate ligands on thorium(IV) were unsuccessful, giving the mono(β-diketiminate)thorium(IV) halide complex and unreacted K[LMe] or K[LtBu]. However, complex 9 was shown to react with smaller anions such as K[C5H4Me] to give the mixed-ligand methylcyclopentadienyl β-diketiminate complex (LtBu)Th(C5H4Me)Br2 (10). Complexes 7–11 represent rare examples of thorium complexes featuring only one β-diketiminate ligand, and complexes 9–11 are the fi...

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.

Trifluoromethyltrimethylsilane, (CH3)3SiCF3, in the presence of CsF serves as an excellent CF3 group-transfer reagent, and reaction with Cp2TiF2 in THF gives the titanocene trifluoromethyl fluoride complex Cp2Ti(CF3)(F) (1; Cp = C5H5) in 60% isolated yield. Reaction of complex 1 with the trimethylsilyl reagents, (CH3)3SiX (X = OTf = OSO2CF3, Cl, Br, I, N3, and OSO2Ph), in a tetrahydrofuran or toluene solution affords the corresponding Ti–CF3 derivatives Cp2Ti(CF3)(X) (X = OTf (2), Cl (12), Br (13), I (14), N3 (15), and OSO2Ph (16)) in good isolated yields of 67–84%. These compounds have been characterized by a combination of reactivity studies, IR and 1H/13C{1H}/19F NMR spectroscopies, and single-crystal X-ray diffraction. The Ti–CF3 linkage in these complexes is remarkably robust, and although the α-C–F bonds are elongated, there is no evidence of an α-fluoride (Ti···F–CF2) between the electrophilic Ti(IV) metal center and any of the C–F bonds in the trifluoromethyl group in the solid-state or in solutio...

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.

Reaction of (C5Me5)2Lu(Me)(μ-Me)Li(THF)3 (2) with excess 12-crown-4 affords the new separated ion pair complex, [Li(12-crown-4)2][(C5Me5)2LuMe2] (3), in excellent yield. This complex reacts with 2,6-diisopropylaniline and phenylacetylene to give the methyl amide complex [Li(12-crown-4)2][(C5Me5)2Lu(Me)(NH-2,6-iPr2C6H3)] (4) and the bis(acetylide) complex [Li(12-crown-4)2][(C5Me5)2Lu(C≡C–Ph)2] (5), respectively. Attempts to promote methane loss from complexes 3 and 4 to generate a lutetium methylidene or imido complex, respectively, were unsuccessful. The ability of the bis(acetylide) complex 5 to act as a π-tweezer complex was also explored. Reaction between [Li(12-crown-4)2][(C5Me5)2Lu(C≡C–Ph)2] (5) and CuSPh gave only intractable lutetium products and the copper(I) species [Li(12-crown-4)2][Cu(C≡C–Ph)2] (8). The new lutetium complexes have been characterized by elemental analysis and NMR spectroscopy. Finally, the X-ray crystal structures of (C5Me5)2Lu(Me)(μ-Me)Li(THF)3 (2), [Li(12-crown-4)2][(C5Me5)2LuMe2] (3), [Li(12-crown-4)2][(C5Me5)2Lu(Me)(NH-2,6-iPr2C6H3)] (4), [Li(12-crown-4)2][(C5Me5)2Lu(C≡C–Ph)2] (5), and [Li(12-crown-4)2][Cu(C≡C–Ph)2] (8) are also reported.

The title compound (C5Me5)2Th[-N=C(Ph)(tpy)]2 (1) (Ph=C6H5, tpy=2,2′:6′,2″-terpyridine) was synthesized and characterized by NMR spectroscopy, elemental analysis, and X-ray crystallography. This system represents the first example of an actinide complex featuring ketimide ligands with both a phenyl group and a terpyridyl group. The complex crystallizes in the monoclinic space group P21/c with unit cell parameters a = 10.7037(6) A, b = 32.0735(16) A, c = 34.6506(18) A, β = 90.127(3)°, V = 11895.7(11) A3, Z = 8, D calc = 1.406 Mg/m3. The thorium(IV) complex adopts a pseudo-tetrahedral geometry, with the two ketimide ligands occupying the plane bisecting the metallocene unit. Structural comparisons of the title complex are made with related metallocene thorium(IV) bis(ketimide) derivatives. This report describes the synthesis of (C5Me5)2Th[-N=C(Ph)(tpy)]2 (Ph=C6H5, tpy=2,2′:6′,2″-terpyridine) and its characterization by NMR spectroscopy, elemental analysis, and X-ray crystallography.

The title compound (C5Me5)2U(OtBu)(SePh) (1) was synthesized and characterized by NMR spectroscopy, elemental analysis, and X-ray crystallography. This system represents a unique example of an actinide complex with two different group 16 elements coordinated to the metal center and the first mixed-ligand actinide alkoxide-selenide complex. The complex crystallizes in the orthorhombic space group Pbca with unit cell parameters a = 17.830(7) A, b = 14.973(6) A, c = 21.254(8) A, V = 5674(4) A3, Z = 8, D calc = 1.727 Mg/m3. The uranium(IV) mixed-ligand alkoxide-selenide complex adopts a pseudo-tetrahedral geometry, with the tert-butoxide and phenylselenide ligands occupying the plane bisecting the metallocene unit. Structural comparisons of the complex (C5Me5)2U(OtBu)(SePh) (1) are made with related selenide and alkoxide uranium(IV) complexes. Reaction of (C5Me5)2U(OtBu)2 with Me3Si-SePh affords the unusual alkoxide-selenide uranium(IV) complex (C5Me5)2U(OtBu)(SePh), which has been characterized by a combination of NMR spectroscopy, elemental analysis, and X-ray crystallography.

Reaction of the trivalent uranium complex (C5Me5)2U(O-2,6-iPr2C6H3)(THF) (1) with copper(I) chloride affords the corresponding tetravalent mixed-ligand aryloxide–chloride complex (C5Me5)2U(O-2,6-iPr2C6H3)(Cl) (2). The oxidative functionalization protocol cannot be extended to the synthesis of (C5Me5)2U(O–tBu)(Cl) (3) since the corresponding trivalent precursor is not stable. Salt metathesis between (C5Me5)2UCl2 and KOtBu is the method of choice for the preparation of the tetravalent alkoxide–chloride derivative (C5Me5)2U(O–tBu)(Cl) (3). The X-ray crystal structures of (C5Me5)2U(O-2,6-iPr2C6H3)(Cl) (2) and (C5Me5)2U(O–tBu)(Cl) (3) are reported and represent the first structurally characterized uranium(IV) metallocene aryloxide–chloride and alkoxide–chloride complexes, respectively. Both complexes adopt a pseudo-tetrahedral geometry, with a chloride and aryloxide/alkoxide ligand occupying the plane bisecting the metallocene unit.

The uranium(III) and uranium(IV) iodide complexes UI3(1,4-dioxane)1.5 and UI4(1,4-dioxane)2 have been easily prepared in high yield by reacting uranium turnings with a 1,4-dioxane solution of iodine under mild conditions. The two complexes exhibit outstanding thermal stability and are excellent precursors to a variety of uranium(III), uranium(IV), and uranium(VI) alkoxide, amide, organometallic, and halide compounds, including a safe, room-temperature synthesis of [UCl4(1,4-dioxane)]2, which is a useful synthetic alternative to UCl4.

The synthetic efficacy of thorium tetrachloride bis(dimethoxyethane), ThCl4(DME)2, is improved by adding 1,2-dimethoxyethane (DME) to the reaction mixture. The syntheses of the known metallocene dichlorides (C5Me5)2ThCl2 (1), (1,2,4-tBu3-C5H2)2ThCl2 (2), and (C5Me4Et)2ThCl2 (3) are used to demonstrate this finding. The full characterization and X-ray crystal structure of (C5Me4Et)2ThCl2 (3) is also reported.

A series of uranium(IV) mixed-ligand amide–halide/pseudohalide complexes (C5Me5)2U[N(SiMe3)2](X) (X = F (1), Cl (2), Br (3), I (4), N3 (5), NCO (6)), (C5Me5)2U(NPh2)(X) (X = Cl (7), N3 (8)), and (C5Me5)2U[N(Ph)(SiMe3)](X) (X = Cl (9), N3 (10)) have been prepared by one electron oxidation of the corresponding uranium(III) amide precursors using either copper halides, silver isocyanate, or triphenylphosphine gold(I)azide. Agostic U⋯H–C interactions and η3-(N,C,C′) coordination are observed for these complexes in both the solid-state and solution. There is a linear correlation between the chemical shift values of the C5Me5 ligand protons in the 1H NMR spectra and the UIV/UIII reduction potentials of the (C5Me5)2U[N(SiMe3)2](X) complexes, suggesting that there is a common origin, that is overall σ-/π-donation from the ancillary (X) ligand to the metal, contributing to both observables. Optical spectroscopy of the series of complexes 1–6 is dominated by the (C5Me5)2U[N(SiMe3)2] core, with small variations derived from the identity of the halide/pseudohalide. The considerable π-donating ability of the fluoride ligand is reflected in both the electrochemistry and UV-visible-NIR spectroscopic behavior of the fluoride complex (C5Me5)2U[N(SiMe3)2](F) (1). The syntheses of the new trivalent uranium amide complex, (C5Me5)2U[N(Ph)(SiMe3)](THF), and the two new weakly-coordinating electrolytes, [Pr4N][B{3,5-(CF3)2C6H3}4] and [Pr4N][B(C6F5)4], are also reported.

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.

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.

A safe gold-based oxidative functionalization protocol has been developed, which allows access to an assortment of uranium complexes bearing azido- and carbon-functional groups. Alkyl, alkynyl, and azido complexes are accessed in a single step from commercially available or easily prepared gold complexes. This methodology works for UIII UIV and UIV UV oxidation. A new high yielding synthetic preparation of (Ph3P)Au-N3 is also presented. These reactions proceed rapidly in high yields, and represent a new class of reaction for gold. This work shows that gold chemistry is not just unique for organic transformations and holds great promise for similarly advancing organometallic chemistry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The coordination behavior of the bis[2-(diisopropylphosphino)-4-methylphenyl]amido ligand (PNP) toward UI3(THF)4 and UCl4 has been investigated to access new uranium(III) and uranium(IV) halide complexes supported by one and two PNP ligands. The reaction between (PNP)K (6) and 1 equiv of UI3(THF)4 afforded the trivalent halide complex (PNP)UI2(4-tBu-pyridine)2 (7) in the presence of 4-tert-butylpyridine. The same reaction carried out with UCl4 and no donor ligand gave [(PNP)UCl3]2 (8), in which the uranium coordination sphere in the (PNP)UCl3 unit is completed by a bridging chloride ligand. When UCl4 is reacted with 1 equiv (PNP)K (6) in the presence of THF, trimethylphosphine oxide (TMPO), or triphenylphosphineoxide (TPPO), the tetravalent halide complexes (PNP)UCl3(THF) (9), (PNP)UCl3(TMPO)2 (10), and (PNP)UCl3(TPPO) (11), respectively, are formed in excellent yields. The bis(PNP) complexes of uranium(III), (PNP)2UI (12), and uranium(IV), (PNP)2UCl2 (13), were easily isolated from the analogous reactions between 2 equiv of 6 and UI3(THF)4 or UCl4, respectively. Complexes 12 and 13 represent the first examples of complexes featuring two PNP ligands coordinated to a single metal center. Complexes 7-13 have been characterized by single-crystal X-ray diffraction and 1H and 31P NMR spectroscopy. The X-ray structures demonstrate the ability of the PNP ligand to adopt new coordination modes upon coordination to uranium. The PNP ligand can adopt both pseudo-meridional and pseudo-facial geometries when it is kappa3-(P,N,P) coordinated, depending on the steric demand at the uranium metal center. Additionally, its hemilabile character was demonstrated with an unusual kappa2-(P,N) coordination mode that is maintained in both the solid-state and in solution. Comparison of the structures of the mono(PNP) and bis(PNP) complexes 7, 9, 11-13 with their respective C5Me5 analogues 1-4 undoubtedly show that a more sterically congested environment is provided by the PNP ligand. The electronic influence of replacing the C5Me5 ligands with PNP was investigated using electronic absorption spectroscopy and electrochemistry. For 12 and 13, a chemically reversible wave corresponding to the UIV/UIII redox transformation comparable to that for 3 and 4 was observed. However, a 350 mV shift of this couple to more negative potentials was observed on substitution of the bis(C5Me5) by the bis(PNP) framework, therefore pointing to a greater electronic density at the metal center in the PNP complexes. The UV-visible region of the electronic spectra for the mono(PNP) and bis(PNP) complexes appear to be dominated by PNP ligand-based transitions that are shifted to higher energy in the uranium complexes than in the simple ligand anion (6) spectrum, for both the UVI and UIII oxidation states. The near IR region in complexes 1-4 and 7, 9, 11-13 is dominated by f-f transitions derived from the 5f3 and 5f2 valence electronic configuration of the metal center. Though complexes of both ligand sets exhibit similar intensities in their f-f bands, a somewhat larger ligand-field splitting was observed for the PNP system, consistent with its higher electron donating ability.

Migratory insertion of diphenyldiazomethane into both metal-carbon bonds of the bis(alkyl) and bis(aryl) complexes (C(5)Me(5))(2)AnR(2) yields the first f-element bis(hydrazonato) complexes (C(5)Me(5))(2)An[eta(2)-(N,N')-R-N-N=CPh(2)](2) [An = Th, R = CH(3) (18), PhCH(2) (15), Ph (16); An = U, R = CH(3) (17), PhCH(2) (14)], which have been characterized by a combination of spectroscopy, electrochemistry, and X-ray crystallography. The two hydrazonato ligands adopt an eta(2)-coordination mode leading to 20-electron (for Th) and 22-electron (for U) complexes that have no transition-metal analogues. In fact, reaction of (C(5)H(5))(2)Zr(CH(3))(2) or (C(5)Me(5))(2)Hf(CH(3))(2) with diphenyldiazomethane is limited to the formation of the corresponding mono(hydrazonato) complex (C(5)R(5))(2)M[eta(2)-(N,N')-CH(3)-N-N=CPh(2)](CH(3)) (M = Zr, R = H or M = Hf, R = CH(3)). The difference in the reactivities of the group 4 metal complexes and the actinides was used as a unique platform for investigating in depth the role of 5f orbitals on the reactivity and bonding in actinide organometallic complexes. The electronic structure of the (C(5)H(5))(2)M[eta(2)-(N,N')-CH(3)-N-N=CH(2)](2) (M = Zr, Th, U) model complexes was studied using density functional theory (DFT) calculations and compared to experimental structural, electrochemical, and spectroscopic results. Whereas transition-metal bis(cyclopentadienyl) complexes are known to stabilize three ligands in the metallocene girdle to form saturated (C(5)H(5))(2)ML(3) species, in a bis(hydrazonato) system, a fourth ligand is coordinated to the metal center to give (C(5)H(5))(2)ML(4). DFT calculations have shown that 5f orbitals in the actinide complexes play a crucial role in stabilizing this fourth ligand by stabilizing both the sigma and pi electrons of the two eta(2)-coordinated hydrazonato ligands. In contrast, the stabilization of the hydrazonato ligands was found to be significantly less effective for the putative bis(hydrazonato) zirconium(IV) complex, yielding a higher energy structure. However, the difference in the reactivities of the group 4 metal and actinide complexes does not arise on thermodynamic grounds but is primarily of kinetic origin. Unfavorable steric factors have been ruled out as the sole influence to explain these different behaviors, and electronic factors were shown to govern the reactivity. For the actinides, both the C(5)H(5) and more realistic C(5)Me(5) ligands have been taken into account in computing the energy surface. The reaction profile for the C(5)Me(5) system differs from that with the C(5)H(5) ligand by a uniform shift of approximately 5 kcal/mol in the relative energies of the transition state and products. The insertion of a second diazoalkane molecule into the sole metal-carbon bond in the mono(hydrazonato) complexes involves a high energy barrier (approximately 20 kcal/mol) for the zirconium(IV) system, whereas the actinides can facilitate the approach of the diazoalkane by coordination (formation of an adduct) and its insertion into the An-C bond with a very low barrier on the potential energy surface.

Reaction of the trivalent uranium complexes (C5Me5)2UI(THF) (1), (C5Me5)2U[N(SiMe3)2] (3), (C5Me5)2U(NPh2)(THF) (4), and (C5Me5)2U(O-2,6-iPr2-C6H3)(THF) (5) with copper(I) iodide affords the corresponding tetravalent uranium diiodide, amide iodide, and aryloxide iodide complexes (C5Me5)2UI2 (2), (C5Me5)2U[N(SiMe3)2](I) (6), (C5Me5)2U(NPh2)(I) (7) and (C5Me5)2U(O-2,6-iPr2-C6H3)(I) (8), respectively. This protocol was also extended to the synthesis of the alkyl iodide complex (C5Me5)2U(CHPh2)(I) (10). The isolation of complex 10 from the in situ generated trivalent uranium alkyl complex (C5Me5)2U(CHPh2)(THF) (9) illustrates the synthetic value of this oxidation procedure in those situations where the uranium(III) metallocene complex cannot be isolated or is unstable. Overoxidation and ligand redistribution are not observed with this Cu-based UIII → UIV oxidation procedure. Attempted functionalization of the UIV amide iodide complex (C5Me5)2U[N(SiMe3)2](I) (6) with Me2Mg afforded the novel azametallacycle (C...

Reaction of two equivalents of [(C 5 [e 4 Et)2U(CH3)(Cl)] (6) or [(C 5 Me 5 ) 2 Th(CH 3 )(Br)] (7) with 1,4-dicyanobenzene leads to the formation of the novel 1,4-phenylenediketimide-bridged bimetallic organoactinide complexes [{(C5Me4Et)2(Cl)U}2(μ-{N=C-(CH3)-C 6 H 4 -(CH3)C=N})] (8) and [{(C 5 Me 5 -) 2 (Br)Th} 2 ,(μ-{N=C(CH 3 )-QH4-(CH 3 )CmN))] (9), respectively. These complexes were structurally characterized by single-crystal X-ray diffraction and NMR spectroscopy. Metal-metal interactions in these isovalent bimetallic systems were assessed by means of cyclic voltammetry, UV-visible/NIR absorption spectroscopy, and variable-temperature magnetic susceptibility. Although evidence for magnetic coupling between metal centers in the bimetallic U IV /U IV (5f 2 -5f 2 ) complex is ambiguous, the complex displays appreciable electronic communication between the metal centers through the π system of the dianionic diketimide bridging ligand, as judged by voltammetry. The transition intensities of the f-f bands for the bimetallic U IV /U IV system decrease substantially compared to the related monometallic ketimide chloride complex, [(C 5 Me 5 ) 2 U(Cl){-N= C(CH3)-(3,4,5-F 3 -C 6 H 2 ))] (11). Also reported herein are new synthetic routes to the actinide starting materials [(C5Me4Et)2U(CH3)(Cl)] (6) and [(C 5 Me 5 ) 2 Th(CH 3 )(Br)] (7) in addition to the syntheses and structures of the monometallic uranium complexes [(C 5 Me 4 Et) 2 UCl 2 ] (3), [(C 5 Me 4 Et) 2 U-(CH 3 ) 2 ) (4), [(C 5 Me 4 Et)2U(-N=C(CH3)-C 6 H 4 -C=N) 2 ) (10), and 11.

Ultrafast pump-probe spectroscopic studies have been performed on (C 5Me 5) 2U[- N=C(Ph)(CH 2Ph)] 2 and (C 5Me 5) 2Th[- N=C(Ph)(CH 2Ph)] 2 including, for the uranium complex, the first direct measurement of dynamics of electronic deactivation within a 5f-electron manifold. Evidence has been found for strong coupling between the electronic ground state and the f-electron manifold which dominates the dynamics of the excited states of the bis(ketimide) uranium complex. These also demonstrate strong singlet-f manifold coupling, which assists in the deactivation of the photoexcited state of the uranium complex, and provide information on intersystem crossing and internal conversion processes in both complexes.

4,4′-Di-tert-butyl-2,2′-bipyridyl (tBu2bpy) stabilizes the thermally sensitive [Lu(CH2SiMe3)3] unit, giving the isolable lutetium(III) (trimethylsilyl)methyl complex (tBu2bpy)Lu(CH2SiMe3)3 (4). This tris(alkyl) complex does not undergo alkane elimination, and it readily reacts with Ph3COH, H2N-2,6-iPr2-C6H3, H2N-2,4,6-tBu3-C6H2, and N,N′-dicyclohexylcarbodiimide (DCHCDI) to afford a variety of Lu(III) tris(alkoxide), tris(amide), mono(amide) bis(alkyl), and amidinate bis(alkyl) compounds. Reaction of the amide bis(alkyl) complex (tBu2bpy)Lu(NH-2,4,6-tBu3-C6H2)(CH2SiMe3)2 (7) with triphenylphosphine oxide gives (Ph3P═O)2Lu(NH-2,4,6-tBu3-C6H2)(CH2SiMe3)2 (9), showing that the bidentate tBu2bpy ligand can be displaced.

Lutetium alkyl complexes supported by a monoanionic, tridentate ligand system formed by the dearomatization and functionalization of a 2,2′:6′,2′′-terpyridine have been reacted with 2,4,6-triphenylaniline or the fluorinated anilines 4-F-C6H4NH2 and C6F5NH2 to give both terminal mono(amide) and bis(amide) lutetium(III) complexes, which have been fully characterized. Both [tBu3(2′-Me3SiCH2)tpy]Lu[NH(2,4,6-Ph3-C6H2)]2 (3) and [tBu3(2′-Me3SiCH2)tpy](C5Me5)Lu(NHC6F5) (7) have been structurally characterized. The fluorinated anilide complexes [tBu3(2′-Me3SiCH2)tpy](C5Me5)Lu(NHArF) (ArF = 4-F-C6H4 (6), C6F5 (7)) provide rare examples of lutetium organofluorine complexes, with 7 featuring an intramolecular F···H−C interaction that is present in both solid state and solution.

The thorium alkyl complex (C 5 Me 5 ) 2 Th(CH 3 ) 2 and 2-picoline react to give preferential sp 3 C-H bond activation in the presence of a more reactive sp 2 C-H bond, while the analogous uranium complex, (C 5 Me 5 ) 2 U(CH 3 ) 2 , reacts with only the ortho 2-picoline sp 2 C-H bond, as originally expected. Herein, we describe this competitive sp 3 versus sp 2 C-H bond activation chemistry with 2-picoline and (C 5 Me 5 ) 2 An(CH 3 ) 2 (An = Th, U) and provide experimental observations that suggest different mechanistic reaction pathways are operative for the uranium and thorium complexes. We also report the X-ray crystal structures for the thorium picolyl complex, (C5Me5)2Th(CH 3 )[η 2 -(N,C)-2-CH2-NC5H3], and the η 2 -pyridyl complexes (C5Me5)2Th(CH 3 )[η 2 -(N,C)-6-CH3-NC 5 H 3 ] and (C5Me5)2U(CH 3 )[η 2 -(N,C)-6-CH3-NC5H3].

Thorium(IV) is often considered to show similar chemistry to Group IV transition metals. However, studies in our laboratory have shown that this generalization is incorrect. This report presents direct comparisons where the Th(IV) metallocene complexes (C5Me5)2ThR2 (R = CH3, Ph, CH2Ph) undergo unique chemical reactivity with pyridine, 2-picoline, pyridine N-oxide, 2-picoline N-oxide, and benzonitrile, while the Group IV metal analogues (C5R5)2M(CH3)2 (R = H, CH3; M = Zr, Hf) do not. We also report revised high-yield syntheses for the zirconium and hafnium starting materials, (C5H5)2MR2 (M = Zr, Hf; R = CH3, Ph, CH2Ph), using Grignard reagents for alkylation in addition to the X-ray crystal structures of (C5H5)2Hf(Ph)2 and (C5H5)2Hf(CH2Ph)2.

Reaction of (C5Me5)Lu(CH2SiMe3)2(THF) with pyridine results in the activation of an ortho C−H bond to form the corresponding η2-(N,C)-pyridyl complex with elimination of SiMe4. This is a rare example of pyridine metalation at a lanthanide metal center in the absence of a bent metallocene framework. The η2-(N,C)-pyridyl coordination mode was confirmed by X-ray crystallographic analysis. The pyridyl complex adopts a distorted square-pyramid geometry with the C5Me5 unit residing in the apical position and the pyridyl ligand and remaining ligands residing in the basal plane. Isotopic labeling studies suggest that C−H bond activation is consistent with a σ-bond metathesis mechanism.