Ligand-Directed Actinide Oxo-Bond Manipulation in Actinyl Thiacalix[4]arene Complexes.

Understanding the chemistry of the inert actinide oxo bond in actinyl ions AnO22+ is important for controlling actinide behavior in the environment, during separations, and in nuclear waste (An = U, Np, Pu). The thioether calixarene TC4A (4-tert-butyltetrathiacalix[4]arene) binds equatorially to [AnO2]n+ (An = U, Np) forming a conical pocket that differentiates the two trans-oxo groups. The 'ate' complexes, [A]2[UO2(TC4A)] (A = [Li(DME)2], HNEt3) and [HNEt3]2[NpO2(TC4A)], enable selective oxo chemistry.

4f-Orbital mixing increases the magnetic susceptibility of Cp'Eu.

Traditional models of lanthanide electronic structure suggest that bonding is predominantly ionic, and that covalent orbital mixing is not an important factor in determining magnetic properties. Here, 4f orbital mixing and its impact on the magnetic susceptibility of Cp'Eu (Cp' = CHSiMe) was analyzed experimentally using magnetometry and X-ray absorption spectroscopy (XAS) methods at the C K-, Eu M-, and L-edges. Pre-edge features in the experimental and TDDFT-calculated C K-edge XAS spectra provided unequivocal evidence of C 2p and Eu 4f orbital mixing in the π-antibonding orbital of a' symmetry.

α-Phenylthioaldehydes for the effective generation of acyl azolium and azolium enolate intermediates.

α-Phenylthioaldehydes are readily prepared using a simple multi-step procedure and herein are introduced as a new precursor for the NHC-catalysed generation of acyl azolium and azolium enolate intermediates that are of widespread synthetic interest and utility. Treatment of α-phenylthioaldehydes with an NHC precatalyst and base produces an efficient redox rearrangement a Breslow intermediate, elimination of thiophenolate, and subsequent rebound addition to the generated acyl azolium to give the corresponding thiol ester. In the presence of an external alcohol, competition between redox rearrangement and redox esterification can be controlled through judicious choice of the -aryl substituent within the NHC precatalyst and the base used in the reaction.

The effect of ancillary ligands on hydrocarbon C-H bond functionalization by uranyl photocatalysts.

The aqueous uranyl dication has long been known to facilitate the UV light-induced decomposition of aqueous VOCs (volatile organic compounds), the long-lived highly efficient, uranyl excited state. The lower-energy visible light excited uranyl ion is also able to cleave unactivated hydrocarbon C-H bonds, yet the development of this reactivity into controlled and catalytic C-H bond functionalization is still in its infancy, with almost all studies still focused on uranyl nitrate as the precatalyst. Here, hydrocarbon-soluble uranyl nitrate and chloride complexes supported by substituted phenanthroline (Phphen) ligands are compared to each other, and to the parent salts, as photocatalysts for the functionalization of cyclooctane by H atom abstraction.

Photocatalytic dechlorination of unactivated chlorocarbons including PVC using organolanthanide complexes.

Simple lanthanide cyclopentadienyl (Cp) complexes can photochemically cleave the sp carbon-chlorine bond of unactivated chlorinated hydrocarbons including polyvinyl chloride (PVC). The excited state lifetimes of these simple complexes are among the longest observed for cerium complexes (175 ns for [(Cp)Ce(μ-Cl)]) and the light absorption by the Cp ligand is efficient, so photocatalytic reactivity is enhanced for cerium and now also made possible for neighboring, normally photoinactive, lanthanide congeners.

Tris(carbene)borates; alternatives to cyclopentadienyls in organolanthanide chemistry.

The chemistry of the tris-carbene anion phenyltris(3-alkyl-imidazoline-2-yliden-1-yl)borate, [C3Me]- ligand, is initiated for f-block metal cations. Neutral, molecular complexes of the form are formed for cerium(III), while a separated ion pair forms for ytterbium(III). DFT/QTAIM computational analyses of the complexes and related tridentate tris(pyrazolyl)borate () - supported analogs demonstrates the anticipated strength of the σ donation and confirms greater covalency in the metal-carbon bonds of the [C3Me]- complexes in comparison with those in the TpMe,Me complexes.

Controlled monodefluorination and alkylation of C(sp)-F bonds by lanthanide photocatalysts: importance of metal-ligand cooperativity.

The controlled functionalization of a single fluorine in a CF group is difficult and rare. Photochemical C-F bond functionalization of the sp-C-H bond in trifluorotoluene, PhCF, is achieved using catalysts made from earth-abundant lanthanides, (Cp)Ln(2--3,5- Bu-CH)(1-C{N(CH)N(Pr)}) (Ln = La, Ce, Nd and Sm, Cp = CMeH). The Ce complex is the most effective at mediating hydrodefluorination and defluoroalkylative coupling of PhCF with alkenes; addition of magnesium dialkyls enables catalytic C-F bond cleavage and C-C bond formation by all the complexes.

Covalent bond shortening and distortion induced by pressurization of thorium, uranium, and neptunium tetrakis aryloxides.

Covalency involving the 5f orbitals is regularly invoked to explain the reactivity, structure and spectroscopic properties of the actinides, but the ionic versus covalent nature of metal-ligand bonding in actinide complexes remains controversial. The tetrakis 2,6-di-tert-butylphenoxide complexes of Th, U and Np form an isostructural series of crystal structures containing approximately tetrahedral MO cores. We show that up to 3 GPa the Th and U crystal structures show negative linear compressibility as the OMO angles distort.

Contrasting behaviour under pressure reveals the reasons for pyramidalization in tris(amido)uranium(III) and tris(arylthiolate) uranium(III) molecules.

A range of reasons has been suggested for why many low-coordinate complexes across the periodic table exhibit a geometry that is bent, rather a higher symmetry that would best separate the ligands. The dominating reason or reasons are still debated. Here we show that two pyramidal UX molecules, in which X is a bulky anionic ligand, show opposite behaviour upon pressurisation in the solid state.

A Combined Experimental and Theoretical Investigation of Arene-Supported Actinide and Ytterbium Tetraphenolate Complexes.

Modular tetraphenolate ligands tethered with a protective arene platform (-phenyl or -terphenyl) are used to support mononuclear An(IV) (An = Th, U) complexes with an exceptionally large and open axial coordination site at the metal. The base-free complexes and a series of neutral donor adducts were synthesized and characterized by spectroscopies and single-crystal X-ray diffraction. Anionic Th(IV) -ate complexes with an additional axial aryloxide ligand were also synthesized and characterized.

Actinide tetra-N-heterocyclic carbene 'sandwiches'.

Highly-symmetrical, thorium and uranium octakis-carbene 'sandwich' complexes have been prepared by 'sandwiching' the An(iv) cations between two anionic macrocyclic tetra-NHC ligands, one with sixteen atoms and the other with eighteen atoms. The complexes were characterized by a range of experimental methods and DFT calculations. X-ray crystallography confirms the geometry at the metal centre can be set by the size of the macrocyclic ring, leading to either square prismatic or square anti-prismatic shapes; the geometry of the latter is retained in solution, which also undergoes reversible, electrochemical one-electron oxidation or reduction for the uranium variant.

Instantaneous and Phosphine-Catalyzed Arene Binding and Reduction by U(III) Complexes.

Neutral arenes such as benzene have never been considered suitable ligands for electropositive actinide cations, yet we find that even simple U UX aryloxide complexes such as U(ODipp) bind and reduce arenes spontaneously at room temperature, forming inverse arene sandwich (IAS) complexes XU(μ-CD)UX (X = ODipp, =2, =3; X = OBMes n=m=2 or 3) (ODipp = OCHPr-2,6; Mes = 2,4,6-Me-CH). In some of these cases, further arene reduction has occured as a result of X ligand redistribution. These unexpected spontaneous reactions explain the anomalous spectra and reported lack of further reactivity of strongly reducing U centers of U(ODipp).

Selective oxo ligand functionalisation and substitution reactivity in an oxo/catecholate-bridged U/U Pacman complex.

The oxo- and catecholate-bridged U/U Pacman complex [{(py)UOU(μ-OCH)(py)}(L)] (L = a macrocyclic "Pacman" ligand; anthracenylene hinge between N-donor pockets, ethyl substituents on -carbon atom of each N-donor pocket) featuring a bent U-O-U oxo bridge readily reacts with small molecule substrates to undergo either oxo-atom functionalisation or substitution. Complex reacts with HO or MeOH to afford [{(py)U(μ-OH)U(μ-OCH)(py)}(L)] () and [{(py)U(μ-OH)(μ-OMe)U(μ-OCH)(py)}(L)] (), respectively, in which the bridging oxo ligand in is substituted for two bridging hydroxo ligands or one bridging hydroxo and one bridging methoxy ligand, respectively. Alternatively, reacts with either 0.

Heterotrimetallic {LnOVPt} complexes with antiferromagnetic Ln-V coupling and magnetic memory.

The new PtVO(SOCR)4 lantern complexes, 1 (R = CH3) and 2 (R = Ph) behave as neutral O-donor ligands to Ln(OR)3 with Ln = Ce, Nd. Four heterotrimetallic complexes with linear {LnOVPt} units were prepared: [Ln(ODtbp)3{PtVO(SOCR)4}] (Ln = Ce, 3Ce (R = CH3), 4Ce (R = Ph); Nd, 3Nd (R = CH3), 4Nd (R = Ph); ODtbp = 2,6-ditertbutylphenolate). Magnetic characterization confirms slow magnetic relaxation behaviour and suggests antiferromagnetic coupling across {Ln-O[double bond, length as m-dash]V} in all four complexes, with variations tunable as a function of Ln and R.

Quantum chemical topology and natural bond orbital analysis of M-O covalency in M(OCH) (M = Ti, Zr, Hf, Ce, Th, Pa, U, Np).

Covalency is complex yet central to our understanding of chemical bonding, particularly in the actinide series. Here we assess covalency in a series of isostructural d and f transition element compounds M(OCH) (M = Ti, Zr, Hf, Ce, Th, Pa, U, Np) using scalar relativistic hybrid density functional theory in conjunction with the Natural Bond Orbital (NBO), quantum theory of atoms in molecules (QTAIM) and interacting quantum atoms (IQA) approaches. The IQA exchange-correlation covalency metric is evaluated for the first time for actinides other than uranium, in order to assess its applicability in the 5f series.

Author Correction: Metallacyclic actinide catalysts for dinitrogen conversion to ammonia and secondary amines.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Metallacyclic actinide catalysts for dinitrogen conversion to ammonia and secondary amines.

Chemists have spent over a hundred years trying to make ambient temperature/pressure catalytic systems that can convert atmospheric dinitrogen into ammonia or directly into amines. A handful of successful d-block metal catalysts have been developed in recent years, but even binding of dinitrogen to an f-block metal cation is extremely rare. Here we report f-block complexes that can catalyse the reduction and functionalization of molecular dinitrogen, including the catalytic conversion of molecular dinitrogen to a secondary silylamine.

Differential uranyl(v) oxo-group bonding between the uranium and metal cations from groups 1, 2, 4, and 12; a high energy resolution X-ray absorption, computational, and synthetic study.

The uranyl(vi) 'Pacman' complex [(UO)(py)(HL)] (L = polypyrrolic Schiff-base macrocycle) is reduced by CpTi(η-MeSiC[triple bond, length as m-dash]CSiMe) and [CpTiCl] to oxo-titanated uranyl(v) complexes [(py)(CpTiOUO)(py)(HL)] and [(ClCpTiOUO)(py)(HL)] . Combination of Zr and Zr synthons with yields the first Zr-uranyl(v) complex, [(ClCpZrOUO)(py)(HL)] . Similarly, combinations of Ae and Ae synthons (Ae = alkaline earth) afford the mono-oxo metalated uranyl(v) complexes [(py)(ClMgOUO)(py)(HL)] , [(py)(thf)(ICaOUO)(py) (HL)] ; the zinc complexes [(py)(XZnOUO)(py)(HL)] (X = Cl , I ) are formed in a similar manner.

Dicerium letterbox-shaped tetraphenolates: f-block complexes designed for two-electron chemistry.

Rare examples of molecular, dinuclear CeIII and PrIII complexes with robust Ln-coordination are accessible by use of the tetraphenolate pTP as a supporting, chelating O-donor ligand platform, pTP = [{2-(OC6H2R2-2,4)2CH}-C6H4-1,4]4- that favours the higher formal oxidation states accessible to rare earths. Two classes of complexes have been made from the platforms; one metallacyclic 2 + 2 [Ln2(pTP)2] framework with a rigid, letterbox-shaped geometry and [Ln(aryloxide)4] core, and one more flexible [(LnX)2(pTP)] with one rare earth ion at either end of the platform. The LnIII letterbox complexes have two K+ counter-cations, one of which sits inside the letterbox, binding the two central arenes of the platform sufficiently strongly that it cannot be displaced by solvent molecules (THF and pyridine) or crown ethers.

Thermal and Photochemical Reduction and Functionalization Chemistry of the Uranyl Dication, [UO].

The uranyl ion, [UO], possesses rigorously , strongly covalent, and chemically robust U-oxo groups. However, through the use of anaerobic reaction techniques, both one- and two-electron reductive functionalization of the uranyl oxo groups has been discovered and developed. Prior to 2010, this unusual reactivity centered around the reductive silylation of the uranyl ion which entailed conversion of the oxo ligands into siloxy ligands and reductive metalation of the uranyl oxo with Group 1 and -block metals.

A Combined Experimental and Theoretical Study of the Versatile Reactivity of an Oxocerium(IV) Complex: Concerted Versus Reductive Addition.

A combined experimental and theoretical investigation on the cerium(IV) oxo complex [(L ) Ce(=O)(H O)]⋅MeC(O)NH (1; L =[Co(η -C H ){P(O)(OEt) } ] ) demonstrates that the intermediate spin-state nature of the ground state of the cerium complex is responsible for the versatility of its reactivity towards small molecules such as CO, CO , SO , and NO. CASSCF calculations together with magnetic susceptibility measurements indicate that the ground state of the cerium complex is of multiconfigurational character and comprised of 74 % of Ce and 26 % of Ce . The latter is found to be responsible for its reductive addition behavior towards CO, SO , and NO.

Correction: Waste not, want not: CO (re)cycling into block polymers.

Correction for 'Waste not, want not: CO (re)cycling into block polymers' by Sumesh K. Raman et al., Chem.

Waste not, want not: CO (re)cycling into block polymers.

A new way to combine two different polymerisation reactions, using a single catalyst, results in efficient block polymer synthesis. The selective polymerisation of mixtures of l-lactide-O-carboxyanhydride and cyclohexene oxide, using a di-zinc catalyst in a one-pot procedure, allows the preparation of poly(l-lactide-b-cyclohexene carbonate). The catalysis near quantitatively recycles the carbon dioxide released during polyester formation into the subsequent polycarbonate block, with an atom economy of up to of 91%.