51
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Arnold PL, Dutkiewicz MS, Zegke M, Walter O, Apostolidis C, Hollis E, Pécharman AF, Magnani N, Griveau JC, Colineau E, Caciuffo R, Zhang X, Schreckenbach G, Love JB. Subtle Interactions and Electron Transfer between UIII
, NpIII
, or PuIII
and Uranyl Mediated by the Oxo Group. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201607022] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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52
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Arnold PL, Dutkiewicz MS, Zegke M, Walter O, Apostolidis C, Hollis E, Pécharman AF, Magnani N, Griveau JC, Colineau E, Caciuffo R, Zhang X, Schreckenbach G, Love JB. Subtle Interactions and Electron Transfer between U(III) , Np(III) , or Pu(III) and Uranyl Mediated by the Oxo Group. Angew Chem Int Ed Engl 2016; 55:12797-801. [PMID: 27628291 DOI: 10.1002/anie.201607022] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Indexed: 11/08/2022]
Abstract
A dramatic difference in the ability of the reducing An(III) center in AnCp3 (An=U, Np, Pu; Cp=C5 H5 ) to oxo-bind and reduce the uranyl(VI) dication in the complex [(UO2 )(THF)(H2 L)] (L="Pacman" Schiff-base polypyrrolic macrocycle), is found and explained. These are the first selective functionalizations of the uranyl oxo by another actinide cation. At-first contradictory electronic structural data are explained by combining theory and experiment. Complete one-electron transfer from Cp3 U forms the U(IV) -uranyl(V) compound that behaves as a U(V) -localized single molecule magnet below 4 K. The extent of reduction by the Cp3 Np group upon oxo-coordination is much less, with a Np(III) -uranyl(VI) dative bond assigned. Solution NMR and NIR spectroscopy suggest Np(IV) U(V) but single-crystal X-ray diffraction and SQUID magnetometry suggest a Np(III) -U(VI) assignment. DFT-calculated Hirshfeld charge and spin density analyses suggest half an electron has transferred, and these explain the strongly shifted NMR spectra by spin density contributions at the hydrogen nuclei. The Pu(III) -U(VI) interaction is too weak to be observed in THF solvent, in agreement with calculated predictions.
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53
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Doidge ED, Carson I, Tasker PA, Ellis RJ, Morrison CA, Love JB. A Simple Primary Amide for the Selective Recovery of Gold from Secondary Resources. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201606113] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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54
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Doidge ED, Carson I, Tasker PA, Ellis RJ, Morrison CA, Love JB. A Simple Primary Amide for the Selective Recovery of Gold from Secondary Resources. Angew Chem Int Ed Engl 2016; 55:12436-9. [DOI: 10.1002/anie.201606113] [Citation(s) in RCA: 90] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Indexed: 11/10/2022]
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55
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Cokoja M, Reich RM, Wilhelm ME, Kaposi M, Schäffer J, Morris DS, Münchmeyer CJ, Anthofer MH, Markovits IIE, Kühn FE, Herrmann WA, Jess A, Love JB. Olefin Epoxidation in Aqueous Phase Using Ionic-Liquid Catalysts. CHEMSUSCHEM 2016; 9:1773-1776. [PMID: 27219852 DOI: 10.1002/cssc.201600373] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2016] [Indexed: 06/05/2023]
Abstract
Hydrophobic imidazolium-based ionic liquids (IL) act as catalysts for the epoxidation of unfunctionalized olefins in water using hydrogen peroxide as oxidant. Although the catalysts are insoluble in both the substrate and in water, surprisingly, they are very well soluble in aqueous H2 O2 solution, owing to perrhenate-H2 O2 interactions. Even more remarkably, the presence of the catalyst also boosts the solubility of substrate in water. This effect is crucially dependent on the cation design. Hence, the imidazolium perrhenates enable both the transfer of hydrophobic substrate into the aqueous phase, and serve as actual catalysts, which is unprecedented. At the end of the reaction and in absence of H2 O2 the IL catalyst forms a third phase next to the lipophilic product and water and can easily be recycled.
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56
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Warr RJ, Bell KJ, Gadzhieva A, Cabot R, Ellis RJ, Chartres J, Henderson DK, Lykourina E, Wilson AM, Love JB, Tasker PA, Schröder M. A Comparison of the Selectivity of Extraction of [PtCl6](2-) by Mono-, Bi-, and Tripodal Receptors That Address Its Outer Coordination Sphere. Inorg Chem 2016; 55:6247-60. [PMID: 27256829 DOI: 10.1021/acs.inorgchem.6b00848] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Extraction and binding studies of [PtCl6](2-) are reported for 24 mono-, bi-, and tripodal extractants containing tris(2-aminoethyl)amine (TREN) or tris(3-aminopropyl)amine (TRPN) scaffolds. These reagents are designed to recognize the outer coordination sphere of [PtCl6](2-) and to show selectivity over chloride anion under acidic conditions. Extraction from 0.6 M HCl involves protonation of the N-center in tertiary amines containing one, two, or three urea, amide, or sulfonamide hydrogen-bond donors to set up the following equilibrium: 2L(org) + 2H(+) + [PtCl6](2-) ⇌ [(LH)2PtCl6](org). All reagents show higher Pt loading than trioctylamine, which was used as a positive control to represent commercial trialkylamine reagents. The loading of [PtCl6](2-) depends on the number of pendant amides in the extractant and follows the order tripodal > bipodal > monopodal, with urea-containing extractants outperforming amide and sulfonamide analogues. A different series of reagents in which one, two, or three of the alkyl groups in tris-2-ethylhexylamine are replaced by 3-N'-hexylpropanamide groups all show a comparably high affinity for [PtCl6](2-) and high selectivity over chloride anion in extractions from aqueous acidic solutions. (1)H NMR titration of three extractants [LH·Cl] with [(Oct4N)2PtCl6] in CDCl3 provides evidence for high selectivity for [PtCl6](2-) over chloride for tri- and bipodal extractants, which show higher binding constants than a monopodal analogue.
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57
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Connolly EA, Leeland JW, Love JB. Mono- and Dinuclear Macrocyclic Calcium Complexes as Platforms for Mixed-Metal Complexes and Clusters. Inorg Chem 2016; 55:840-7. [PMID: 26709870 DOI: 10.1021/acs.inorgchem.5b02289] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Mono- and dinuclear calcium complexes of the Schiff-base macrocycles H4L have been prepared and characterized spectroscopically and crystallographically. In the formation of Ca(THF)2(H2L(1)), Ca2(THF)2(μ-THF)(L(1)), and Ca2(THF)4(L(2)), the ligand framework adopts a bowl-shaped conformation instead of the conventional wedge, Pacman-shaped structure as seen with the anthracenyl-hinged complex Ca2(py)5(L(3)). The mononuclear calcium complex Ca(THF)2(H2L(1)) reacts with various equivalents of LiN(SiMe3)2 to form calcium/alkali metal clusters and dinuclear transition metal complexes when reacted subsequently with transition metal salts. The dinuclear calcium complex Ca2(THF)2(μ-THF)(L(1)), when reacted with various equivalents of NaOH, is shown to act as a platform for the formation of calcium/alkali metal hydroxide clusters, displaying alternate wedged and bowl-shaped conformations.
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58
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Stevens CJ, Prescimone A, Tuna F, McInnes EJL, Parsons S, Morrison CA, Arnold PL, Love JB. Inter- versus Intramolecular Structural Manipulation of a Dichromium(II) Pacman Complex through Pressure Variation. Inorg Chem 2016; 55:214-20. [PMID: 26683991 DOI: 10.1021/acs.inorgchem.5b02151] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The effect of pressure on the intranuclear M···M separation and intermolecular secondary interactions in the dinuclear chromium Pacman complex [Cr2(L)](C6H6) was evaluated because this compound contains both a short Cr···Cr separation and an exogenously bound molecule of benzene in the solid state. The electronic structure of [Cr2(L)] was determined by electron paramagnetic resonance spectroscopy, SQUID magnetometry, and density functional theory calculations and shows a diamagnetic ground state through antiferromagnetic exchange, with no evidence for a Cr-Cr bond. Analysis of the solid-state structures of [Cr2(L)](C6H6) at pressures varying from ambient to 3.0 GPa shows little deformation in the Cr···Cr separation, i.e., no Cr-Cr bond formation, but instead a significantly increased interaction between the exogenous arene and the chromium iminopyrrolide environment. It is therefore apparent from this analysis that [Cr2(L)] would be best exploited as a rigid chemical synthon, with pressure regulation being used to mediate the approach and secondary interactions of possible substrates.
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59
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Healy MR, Roebuck JW, Doidge ED, Emeleus LC, Bailey PJ, Campbell J, Fischmann AJ, Love JB, Morrison CA, Sassi T, White DJ, Tasker PA. Contributions of inner and outer coordination sphere bonding in determining the strength of substituted phenolic pyrazoles as copper extractants. Dalton Trans 2016; 45:3055-62. [DOI: 10.1039/c5dt04055h] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Simple phenolic pyrazoles have strengths and selectivities comparable to oxime extractants which account for a quarter of the world's copper production.
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60
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Zheng XJ, Bell NL, Stevens CJ, Zhong YX, Schreckenbach G, Arnold PL, Love JB, Pan QJ. Relativistic DFT and experimental studies of mono- and bis-actinyl complexes of an expanded Schiff-base polypyrrole macrocycle. Dalton Trans 2016; 45:15910-15921. [DOI: 10.1039/c6dt01625a] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Relativistic DFT calculations present accurate geometries of complexes and redox properties, confirmed by the newly-developed experimental syntheses.
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61
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Carson I, MacRuary KJ, Doidge ED, Ellis RJ, Grant RA, Gordon RJ, Love JB, Morrison CA, Nichol GS, Tasker PA, Wilson AM. Anion Receptor Design: Exploiting Outer-Sphere Coordination Chemistry To Obtain High Selectivity for Chloridometalates over Chloride. Inorg Chem 2015; 54:8685-92. [DOI: 10.1021/acs.inorgchem.5b01317] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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62
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Healy MR, Carter E, Fallis IA, Forgan RS, Gordon RJ, Kamenetzky E, Love JB, Morrison CA, Murphy DM, Tasker PA. EPR/ENDOR and Computational Study of Outer Sphere Interactions in Copper Complexes of Phenolic Oximes. Inorg Chem 2015; 54:8465-73. [DOI: 10.1021/acs.inorgchem.5b01180] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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63
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Pankhurst JR, Cadenbach T, Betz D, Finn C, Love JB. Towards dipyrrins: oxidation and metalation of acyclic and macrocyclic Schiff-base dipyrromethanes. Dalton Trans 2015; 44:2066-70. [PMID: 25563854 DOI: 10.1039/c4dt03592e] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Oxidation of acyclic Schiff-base dipyrromethanes cleanly results in dipyrrins, whereas the macrocyclic 'Pacman' analogues either decompose or form new dinuclear copper(ii) complexes that are inert to ligand oxidation; the unhindered hydrogen substituent at the meso-carbon allows new structural motifs to form.
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64
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Arnold PL, Cadenbach T, Marr IH, Fyfe AA, Bell NL, Bellabarba R, Tooze RP, Love JB. Homo- and heteroleptic alkoxycarbene f-element complexes and their reactivity towards acidic N-H and C-H bonds. Dalton Trans 2015; 43:14346-58. [PMID: 24920060 DOI: 10.1039/c4dt01442a] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The reactivity of a series of organometallic rare earth and actinide complexes with hemilabile NHC-ligands towards substrates with acidic C-H and N-H bonds is described. The synthesis, characterisation and X-ray structures of the new heteroleptic mono- and bis(NHC) cyclopentadienyl complexes LnCp2(L) 1 (Ln = Sc, Y, Ce; L = alkoxy-tethered carbene [OCMe2CH2(1-C{NCHCHN(i)Pr})]), LnCp(L)2 (Ln = Y) , and the homoleptic tetrakis(NHC) complex Th(L)4 4 are described. The reactivity of these complexes, and of the homoleptic complexes Ln(L)3 (Ln = Sc 3, Ce), with E-H substrates is described, where EH = pyrrole C4H4NH, indole C8H6NH, diphenylacetone Ph2CC(O)Me, terminal alkynes RC≡CH (R = Me3Si, Ph), and cyclopentadiene C5H6. Complex 1-Y heterolytically cleaves and adds pyrrole and indole N-H across the metal carbene bond, whereas 1-Ce does not, although 3 and 4 form H-bonded adducts. Complexes 1-Y and 1-Sc form adducts with CpH without cleaving the acidic C-H bond, 1-Ce cleaves the Cp-H bond, but 2 reacts to form the very rare H(+)-[C5H5](-)-H(+) motif. Complex 1-Ce cleaves alkyne C-H bonds but the products rearrange upon formation, while complex 1-Y cleaves the C-H bond in diphenylacetone forming a product which rearranges to the Y-O bonded enolate product.
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65
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Arnold PL, Pécharman AF, Lord RM, Jones GM, Hollis E, Nichol GS, Maron L, Fang J, Davin T, Love JB. Control of oxo-group functionalization and reduction of the uranyl ion. Inorg Chem 2015; 54:3702-10. [PMID: 25799215 DOI: 10.1021/acs.inorgchem.5b00420] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Uranyl complexes of a large, compartmental N8-macrocycle adopt a rigid, "Pacman" geometry that stabilizes the U(V) oxidation state and promotes chemistry at a single uranyl oxo-group. We present here new and straightforward routes to singly reduced and oxo-silylated uranyl Pacman complexes and propose mechanisms that account for the product formation, and the byproduct distributions that are formed using alternative reagents. Uranyl(VI) Pacman complexes in which one oxo-group is functionalized by a single metal cation are activated toward single-electron reduction. As such, the addition of a second equivalent of a Lewis acidic metal complex such as MgN″2 (N″ = N(SiMe3)2) forms a uranyl(V) complex in which both oxo-groups are Mg functionalized as a result of Mg-N bond homolysis. In contrast, reactions with the less Lewis acidic complex [Zn(N″)Cl] favor the formation of weaker U-O-Zn dative interactions, leading to reductive silylation of the uranyl oxo-group in preference to metalation. Spectroscopic, crystallographic, and computational analysis of these reactions and of oxo-metalated products isolated by other routes have allowed us to propose mechanisms that account for pathways to metalation or silylation of the exo-oxo-group.
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66
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Zegke M, Nichol GS, Arnold PL, Love JB. Catalytic one-electron reduction of uranyl(VI) to Group 1 uranyl(V) complexes via Al(III) coordination. Chem Commun (Camb) 2015; 51:5876-9. [PMID: 25727815 DOI: 10.1039/c5cc00867k] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Reactions between the uranyl(VI) Pacman complex [(UO2)(py)(H2L)] of the Schiff-base polypyrrolic macrocycle L and Tebbe's reagent or DIBAL result in the first selective reductive functionalisation of the uranyl oxo by Al to form [(py)(R2AlOUO)(py)(H2L)] (R = Me or (i)Bu). The clean displacement of the oxo-coordinated Al(III) by Group 1 cations has enabled the development of a one-pot, DIBAL-catalysed reduction of the U(VI) uranyl complexes to a series of new, mono-oxo alkali-metal-functionalised uranyl(V) complexes [(py)3(MOUO)(py)(H2L)] (M = Li, Na, K).
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67
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Cadenbach T, Pankhurst JR, Hofmann TA, Curcio M, Arnold PL, Love JB. Macrocyclic Platforms for the Construction of Tetranuclear Oxo and Hydroxo Zinc Clusters. Organometallics 2015. [DOI: 10.1021/om501244n] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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68
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Arnold PL, Farnaby JH, Gardiner MG, Love JB. Uranium(III) Coordination Chemistry and Oxidation in a Flexible Small-Cavity Macrocycle. Organometallics 2015. [DOI: 10.1021/om5012193] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
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69
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Cokoja M, Markovits IIE, Anthofer MH, Poplata S, Pöthig A, Morris DS, Tasker PA, Herrmann WA, Kühn FE, Love JB. Catalytic epoxidation by perrhenate through the formation of organic-phase supramolecular ion pairs. Chem Commun (Camb) 2015; 51:3399-402. [DOI: 10.1039/c4cc10235e] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Organic-phase supramolecular ion pair (SIP) host–guest assemblies of perrhenate anions (ReO4−) with ammonium amide receptor cations are reported.
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70
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Love JB. Dalton Discussion 14 – Advancing the chemistry of the f-elements, 28–30 July 2014, Edinburgh. Dalton Trans 2015; 44:2515-6. [DOI: 10.1039/c4dt90197e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Welcome to this Dalton Transactions themed issue including papers from Dalton Discussion 14 – Advancing the chemistry of the f-elements.
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71
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Arnold PL, Stevens CJ, Farnaby JH, Gardiner MG, Nichol GS, Love JB. New Chemistry from an Old Reagent: Mono- and Dinuclear Macrocyclic Uranium(III) Complexes from [U(BH4)3(THF)2]. J Am Chem Soc 2014; 136:10218-21. [DOI: 10.1021/ja504835a] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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72
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Berben LA, Love JB. Metal-mediated transformations of small molecules. Chem Commun (Camb) 2014; 50:7221-2. [DOI: 10.1039/c4cc90123a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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73
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Arnold PL, Farnaby JH, White RC, Kaltsoyannis N, Gardiner MG, Love JB. Switchable π-coordination and C–H metallation in small-cavity macrocyclic uranium and thorium complexes. Chem Sci 2014. [DOI: 10.1039/c3sc52072b] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Actinide complexes of a small-cavity, dipyrrolide macrocycle exhibit unusual bent metallocene-type binding, or bis(arene)-type binding, or both at once in a di-uranium adduct.
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74
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Stevens C, Nichol GS, Arnold PL, Love JB. Isocyanide and Phosphine Oxide Coordination in Binuclear Chromium Pacman Complexes. Organometallics 2013; 32:6879-6882. [PMID: 24489428 PMCID: PMC3905932 DOI: 10.1021/om4009313] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2013] [Indexed: 01/13/2023]
Abstract
The new binuclear chromium Pacman complex [Cr2(L)] of the Schiff base pyrrole macrocycle H4L has been synthesized and structurally characterized. Addition of isocyanide, C≡NR (R = xylyl, tBu), or triphenylphosphine oxide donors to [Cr2(L)] gives contrasting chemistry with the formation of the new coordination compounds [Cr2(μ-CNR)(L)], in which the isocyanides bridge the two Cr(II) centers, and [Cr2(OPPh3)2(L)], a Cr(II) phosphine oxide adduct with the ligands exogenous to the cleft.
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75
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Wilson AM, Bailey PJ, Tasker PA, Turkington JR, Grant RA, Love JB. Solvent extraction: the coordination chemistry behind extractive metallurgy. Chem Soc Rev 2013; 43:123-34. [PMID: 24088789 DOI: 10.1039/c3cs60275c] [Citation(s) in RCA: 231] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The modes of action of the commercial solvent extractants used in extractive hydrometallurgy are classified according to whether the recovery process involves the transport of metal cations, M(n+), metalate anions, MXx(n-), or metal salts, MXx into a water-immiscible solvent. Well-established principles of coordination chemistry provide an explanation for the remarkable strengths and selectivities shown by most of these extractants. Reagents which achieve high selectivity when transporting metal cations or metal salts into a water-immiscible solvent usually operate in the inner coordination sphere of the metal and provide donor atom types or dispositions which favour the formation of particularly stable neutral complexes that have high solubility in the hydrocarbons commonly used in recovery processes. In the extraction of metalates, the structures of the neutral assemblies formed in the water-immiscible phase are usually not well defined and the cationic reagents can be assumed to operate in the outer coordination spheres. The formation of secondary bonds in the outer sphere using, for example, electrostatic or H-bonding interactions are favoured by the low polarity of the water-immiscible solvents.
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