162 results on '"Nichol GS"'
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2. Controlled and sequential single-electron reduction of the uranyl dication.
- Author
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Obey TJN, Nichol GS, and Love JB
- Abstract
A flexible tripodal pyrrole-imine ligand (H
3 L) has been used to facilitate the controlled and sequential single-electron reductions of the uranyl dication from the U(VI) oxidation state to U(V) and further to U(IV), processes that are important to understanding the reduction of uranyl and its environmental remediation. The uranyl(VI) complexes UO2 (HL)(sol) (sol = THF, py) were straightforwardly accessed by the transamination reaction of H3 L with UO2 {N(SiMe3 )2 }2 (THF)2 and adopt 'hangman' structures in which one of the pyrrole-imine arms is pendant. While deprotonation of this arm by LiN(SiMe3 )2 causes no change in uranyl oxidation state, single-electron reduction of uranyl(VI) to uranyl(V) occurred on addition of two equivalents of KN(SiMe3 )2 to UO2 (HL)(sol). The potassium cations of this new [UV O2 (K2 L)]2 dimer were substituted by transmetalation with the appropriate metal chloride salt, forming the new uranyl(V) tetra-heterometallic complexes, [UV O2 Zn(L)(py)2 ]2 and [UV O2 Ln(Cl)(L)(py)2 ]2 (Ln = Y, Sm, Dy). The dimeric uranyl(V)-yttrium complex underwent further reduction and chloride abstraction to form the tetrametallic U(IV) complex [UIV O2 YIII (py)]2 , so highlighting the adaptability of this ligand to stabilise a variety of different uranium oxidation states.- Published
- 2024
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3. Heavy Heterodendralenes: Structure and Reactivity of Phosphabora[3]dendralenes.
- Author
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Zarkina VG, Nichol GS, and Cowley MJ
- Abstract
The incorporation of phosphorus and boron into [3]dendralenes provides access to heavy heterodendralenes, a new class of main-group precursor to "doped" polycyclic hydrocarbons. [ n ]Dendralenes are a core class of unsaturated hydrocarbons built from geminally connected polyenes; the resulting arrangement of conjugated C═C bonds enables [ n ]dendralenes to undergo reactions that allow rapid access to complex polycyclic compounds. The increasing technological and synthetic importance of main-group-containing polycyclic hydrocarbons and their analogues makes new routes to access such systems highly attractive. Here we report the preparation of the first heavy heterodendralenes in the form of phosphorus- and boron-containing [3]dendralenes, prepared by a ring-opening reaction of a 1,2-phosphaborete. We reveal the electronic effect of P/B incorporation and demonstrate that, like their hydrocarbon analogues, phosphabora[3]dendralenes undergo diene-transmissive cycloaddition chemistry.
- Published
- 2024
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4. Triptycene-like naphthopleiadene as a readily accessible scaffold for supramolecular and materials chemistry.
- Author
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Amin MK, Ye C, Pang S, Liu Y, Taylor D, Nichol GS, and McKeown NB
- Abstract
Triptycene derivatives are used extensively in supramolecular and materials chemistry, however, most are prepared using a multi-step synthesis involving the generation of a benzyne intermediate, which hinders production on a large scale. Inspired by the ease of the synthesis of resorcinarenes, we report the rapid and efficient preparation of triptycene-like 1,6,2',7'-tetrahydroxynaphthopleiadene directly from 2,7-dihydroxynaphthalene and phthalaldehyde. Structural characterisation confirms the novel bridged bicyclic framework, within which the planes of the single benzene ring and two naphthalene units are fixed at an angle of ∼120° relative to each other. Other combinations of aromatic 1,2-dialdehydes and 2,7-disubstituted naphthalenes also provided similar triptycene-like products. The low cost of the precursors and undemanding reaction conditions allow for rapid multigram synthesis of 1,6,2',7'-tetrahydroxynaphthopleiadene, which is shown to be a useful precursor for making the parent naphthopleiadene hydrocarbon. The great potential for the use of the naphthopleiadene scaffold in supramolecular and polymer chemistry is demonstrated by the preparation of a rigid novel cavitand, a microporous network polymer, and a solution-processable polymer of intrinsic microporosity., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)
- Published
- 2024
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5. Transition Metal-Free Catalytic C-H Zincation and Alumination.
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Kumar Bisai M, Łosiewicz J, Sotorrios L, Nichol GS, Dominey AP, Cowley MJ, Thomas SP, Macgregor SA, and Ingleson MJ
- Abstract
C-H metalation is the most efficient method to prepare aryl-zinc and -aluminium complexes that are ubiquitous nucleophiles. Virtually all C-H metalation routes to form Al/Zn organometallics require stoichiometric, strong Brønsted bases with no base-catalyzed reactions reported. Herein we present a catalytic in amine/ammonium salt (Et
3 N/[(Et3 N)H]+ ) C-H metalation process to form aryl-zinc and aryl-aluminium complexes. Key to this approach is coupling an endergonic C-H metalation step with a sufficiently exergonic dehydrocoupling step between the ammonium salt by-product of C-H metalation ([(Et3 N)H]+ ) and a Zn-H or Al-Me containing complex. This step, forming H2 /MeH, makes the overall cycle exergonic while generating more of the reactive metal electrophile. Mechanistic studies supported by DFT calculations revealed metal-specific dehydrocoupling pathways, with the divergent reactivity due to the different metal valency (which impacts the accessibility of amine-free cationic metal complexes) and steric environment. Notably, dehydrocoupling in the zinc system proceeds through a ligand-mediated pathway involving protonation of the β-diketiminate Cγ position. Given this process is applicable to two disparate metals (Zn and Al), other main group metals and ligand sets are expected to be amenable to this transition metal-free, catalytic C-H metalation., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)- Published
- 2024
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6. Catalytic Access to Diastereometrically Pure Four- and Five-Membered Silyl-Heterocycles Using Transborylation.
- Author
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Willcox DR, Cocco E, Nichol GS, Carlone A, and Thomas SP
- Abstract
Silyl-heterocycles offer a unique handle to expand and explore chemical space, reactivity, and functionality. The shortage of catalytic methods for the preparation of diverse and functionalized silyl-heterocycles however limits widespread exploration and exploitation. Herein the borane-catalyzed intramolecular 1,1-carboboration of silyl-alkynes has been developed for the synthesis of 2,3-dihydrosilolyl and silylcyclobut-2-enyl boronic esters. Successful, catalytic carboboration has been achieved on a variety of functionally diverse silyl-alkynes, using a borane catalyst and transborylation-enabled turnover. Mechanistic studies, including
13 C-labelling, computational studies, and single-turnover experiments, suggest a reaction pathway proceeding by 1,2-hydroboration, 1,1-carboboration, and transborylation to release the alkenyl boronic ester product and regenerate the borane catalyst., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)- Published
- 2024
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7. Structure-Property Relationships for Potential Inversion From Electron Acceptors Based on Thiophene-Fused Triptycene Quinones, 1,4-Diketones and Their Malononitrile Adducts.
- Author
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Warrington S, Montanaro S, Elsegood MRJ, Nichol GS, and Wright IA
- Abstract
The synthesis and properties of a series of 11,11,12,12-tetracyano-9,10-anthraquinodimethane (TCAQ) inspired electron acceptors based on thiophene-fused quinone and triptycene motifs is presented. This has yielded insights into structure-property relationships for establishing and modulating simultaneous two-electron reduction processes in TCAQ analogues. These new compounds were synthesised using a Friedel-Crafts acylation between triptycene and thiophene-3,4-dicarbonyl chloride. Isomeric para-quinones featuring a [c]-fused thiophene on one side and a β,β- or α,β-fused triptycene on the other were isolated alongside a thiophene-3,4-diketone which bears two triptycene fragments. Knoevenagel condensation of these products with malononitrile produced a quinoidal bis(dicyanomethylene), an oxo-dicyanomethylene and an acyclic bis(dicyanomethylene). This series of new electron accepting molecules has been studied using X-ray crystallography and the implications of their 3D structures on NMR and UV/vis absorbance spectroscopy and cyclic voltammetry results have been ascertained with conclusions underpinned by computational methods., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)
- Published
- 2024
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8. The Sensitivity of Structure to Ionic Radius and Reaction Stoichiometry: A Crystallographic Study of Metal Coordination and Hydrogen Bonding in Barbiturate Complexes of All Five Alkali Metals Li-Cs.
- Author
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Clegg W and Nichol GS
- Abstract
A systematic study has been conducted on barbiturate complexes of all five alkali metals, Li-Cs, prepared from metal carbonates or hydroxides in an aqueous solution without other potential ligands present, varying the stoichiometric ratio of metal ion to barbituric acid (BAH). Eight polymeric coordination compounds (two each for Na, K, and Rb and one each for Li and Cs) have been characterised by single-crystal X-ray diffraction. All contain some combination of barbiturate anion BA
- (necessarily in a 1:1 ratio with the metal cation M+ ), barbituric acid, and water. All organic species and water molecules are coordinated to the metal centres via oxygen atoms as either terminal or bridging ligands. Coordination numbers range from 4 (for the Li complex) to 8 (for the Cs complex). Extensive hydrogen bonding plays a significant role in all the crystal structures, almost all of which include pairs of N-H···O hydrogen bonds linking BA- and/or BAH components into ribbons extending in one dimension. Factors influencing the structure adopted by each compound include cation size and reaction stoichiometry as well as hydrogen bonding., Competing Interests: The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.- Published
- 2024
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9. Shape-Selective Supramolecular Capsules for Actinide Precipitation and Separation.
- Author
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O'Connell-Danes J, Ngwenya BT, Morrison CA, Nichol GS, Delmau LH, and Love JB
- Abstract
Improving actinide separations is key to reducing barriers to medical and industrial actinide isotope production and to addressing the challenges associated with the reprocessing of spent nuclear fuel. Here, we report the first example of a supramolecular anion recognition process that can achieve this goal. We have designed a preorganized triamidoarene receptor that induces quantitative precipitation of the early actinides Th(IV), Np(IV), and Pu(IV) from industrially relevant conditions through the formation of self-assembled hydrogen-bonded capsules. Selectivity over the later An(III) elements is shown through modulation of the nitric acid concentration, and no precipitation of actinyl or transition-metal ions occurs. The Np, Pu, and Am precipitates were characterized structurally by single-crystal X-ray diffraction and reveal shape specificity of the internal hydrogen-bonding array for the encapsulated hexanitratometalates. This work complements ion-exchange resins for 5f-element separations and illustrates the significant potential of supramolecular separation methods that target anionic actinide species., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)
- Published
- 2024
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10. NacNac-zinc-pyridonate mediated ε-caprolactone ROP.
- Author
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Hughes JWJ, Babula DJ, Stowers-Veitch F, Yuan K, Uzelac M, Nichol GS, Ingleson MJ, and Garden JA
- Abstract
Herein we report the synthesis, isolation and polymerisation activity of two new zinc compounds based on a 2,6-diisopropylphenyl (Dipp) β-diiminate (NacNac) ligand framework with zinc also ligated by an amidate (2-pyridonate or 6-methyl-2-pyridonate) unit. The compounds crystallised as either monomeric (6-Me-2-pyridonate derivative) or dimeric (2-pyridonate) species, although both were found to be monomeric in solution via
1 H DOSY NMR spectroscopy, which was supported by DFT calculations. These observations suggest that both complexes initiate ring-opening polymerisation (ROP) through a single-site monometallic mechanism. High molecular weight poly ε-caprolactone (PCL) was achieved via exogenous initiator-free ROP conditions with both catalysts. An increase in the 2-pyridonate initiator steric bulk (6-Me- vs. 6-H-) resulted in an improved catalytic activity, facilitating complete monomer conversion within 1 h at 60 °C. Pyridonate end-groups were observed by MALDI-ToF mass spectrometry, contrasting with previous observations forDipp NacNac-Zn acetate complexes (where no acetate end groups are observed), instead this more closely resembles the reactivity ofDipp NacNac-Zn alkoxide complexes in ROP (where RO end groups are observed). Additional major signals in the MALDI-ToF spectra were consistent with cyclic PCL species, which are attributed to back-biting ring-closing termination steps occuring in a process facilitated by the pyridonate unit being an effective leaving group. To the best of our knowledge, these complexes represent the first examples of pyridonate, and indeed amidate, initated ROP.- Published
- 2023
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11. Odd and Even Numbered Ferric Wheels.
- Author
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Cutler DJ, Canaj AB, Singh MK, Nichol GS, Gracia D, Nojiri H, Evangelisti M, Schnack J, and Brechin EK
- Abstract
The structurally related odd and even numbered wheels [Fe
III 11 ZnII 4 (tea)10 (teaH)1 (OMe)Cl8 ] (1) and [FeIII 12 ZnII 4 (tea)12 Cl8 ] (2) can be synthesized under ambient conditions by reacting FeIII and ZnII salts with triethanolamine (teaH3 ), the change in nuclearity being dictated by the solvents employed. An antiferromagnetic exchange between nearest neighbors, J = -10.0 cm-1 for 1 and J = -12.0 cm-1 for 2, leads to a frustrated S = 1/2 ground state in the former and an S = 0 ground state in the latter., (© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.)- Published
- 2023
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12. Borylation directed borylation of N -alkyl anilines using iodine activated pyrazaboles.
- Author
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Millet CRP, Noone E, Schellbach AV, Pahl J, Łosiewicz J, Nichol GS, and Ingleson MJ
- Abstract
Doubly electrophilic pyrazabole derivatives (pyrazabole = [H
2 B(μ-C3 N2 H3 )]2 ) combined with one equiv. of base effect the ortho -borylation of N -alkyl anilines. Initial studies found that the bis(trifluoromethane)sulfonimide ([NTf2 ]- ) pyrazabole derivative, [H(NTf2 )B(μ-C3 N2 H3 )]2 , is highly effective for ortho -borylation, with this process proceeding through N-H borylation and then ortho C-H borylation. The activation of pyrazabole by I2 was developed as a cheaper and simpler alternative to using HNTf2 as the activator. The addition of I2 forms mono or ditopic pyrazabole electrophiles dependent on stoichiometry. The ditopic electrophile [H(I)B(μ-C3 N2 H3 )]2 was also effective for the ortho -borylation of N -alkyl-anilines, with the primary C-H borylation products readily transformed into pinacol boronate esters (BPin) derivatives. Comparison of borylation reactions using the di-NTf2 -and the diiodo-pyrazabole congeners revealed that more forcing conditions are required with the latter. Furthermore, the presence of iodide leads to competitive formation of side products, including [HB(μ-C3 N2 H3 )3 BH]+ , which are not active for C-H borylation. Using [H(I)B(μ-C3 N2 H3 )]2 and 0.2 equiv. of [Et3 NH][NTf2 ] combines the higher yields of the NTf2 system with the ease of handling and lower cost of the iodide system generating an attractive process applicable to a range of N -alkyl-anilines. This methodology represents a metal free and transiently directed C-H borylation approach to form N -alkyl-2-BPin-aniline derivatives., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)- Published
- 2023
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13. Experimental Quantification of Halogen⋅⋅⋅Arene van der Waals Contacts.
- Author
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West AML, Dominelli-Whiteley N, Smolyar IV, Nichol GS, and Cockroft SL
- Abstract
Crystallographic and computational studies suggest the occurrence of favourable interactions between polarizable arenes and halogen atoms. However, the systematic experimental quantification of halogen⋅⋅⋅arene interactions in solution has been hindered by the large variance in the steric demands of the halogens. Here we have synthesized molecular balances to quantify halogen⋅⋅⋅arene contacts in 17 solvents and solvent mixtures using
1 H NMR spectroscopy. Calculations indicate that favourable halogen⋅⋅⋅arene interactions arise from London dispersion in the gas phase. In contrast, comparison of our experimental measurements with partitioned SAPT0 energies indicate that dispersion is sufficiently attenuated by the solvent that the halogen⋅⋅⋅arene interaction trend was instead aligned with increasing exchange repulsion as the halogen increased in size (ΔGX ⋅⋅⋅Ph =0 to +1.5 kJ mol-1 ). Halogen⋅⋅⋅arene contacts were slightly less disfavoured in solvents with higher solvophobicities and lower polarizabilities, but strikingly, were always less favoured than CH3 ⋅⋅⋅arene contacts (ΔGMe ⋅⋅⋅Ph =0 to -1.4 kJ mol-1 )., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)- Published
- 2023
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14. Tetra-, tetradeca- and octadecametallic clusters of Mn.
- Author
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Agapaki E, Canaj AB, Nichol GS, and Brechin EK
- Abstract
Reaction of equimolar amounts of MnBr
2 ·4H2 O and HL1 ((3,5-dimethyl-1 H -pyrazol-1-yl)methanol) in a basic MeCN solution leads to the formation of [MnII4(L1 )4 Br4 (H2 O)4 ] (1), whose metallic skeleton is a [MnII4] tetrahedron and cluster core a [MnII4(μ3 -O)4 ] cubane. Replacing MnBr2 ·4H2 O with Mn(O2 CMe)2 ·4H2 O affords [MnIII2MnII12O2 (L1 )4 (OAc)22 ] (2) which is best described as a series of edge-sharing [Mn4 ] tetrahedra that have self-assembled into a linear array in which each [Mn2 ] pair is 'twisted' with respect to its neighbours in a corkscrew-like manner. Employment of the triangle [MnIII3O(OAc)6 (py)3 ](ClO4 ) as a reactant instead of a MnII salt results in the formation of [MnIII14MnII4O14 (L1 )4 (HL1 )2 (OAc)18 (H2 O)2 ] (3) whose core is comprised of three vertex-sharing [MnIII4] butterflies flanked on either side by one [MnIII4] cubane and one [MnIII2MnII2] tetrahedron. Dc magnetic susceptibility and magnetisation measurements of polycrystalline samples of 1-3 reveal the predominance of antiferromagnetic exchange interactions. For [Mn4 ] (1) this leads to a diamagnetic ground state, while for [Mn18 ] (3) competing exchange interactions result in Single-Molecule Magnet (SMM) behaviour with Ueff = 22 K.- Published
- 2023
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15. Amides as modifiable directing groups in electrophilic borylation.
- Author
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Iqbal SA, Uzelac M, Nawaz I, Wang Z, Jones TH, Yuan K, Millet CRP, Nichol GS, Chotana GA, and Ingleson MJ
- Abstract
Amide directed C-H borylation using ≥two equiv. of BBr
3 forms borenium cations containing a R2 N(R')C[double bond, length as m-dash]O→B(Ar)Br unit which has significant Lewis acidity at the carbonyl carbon. This enables reduction of the amide unit to an amine using hydrosilanes. This approach can be applied sequentially in a one-pot electrophilic borylation-reduction process, which for phenyl-acetylamides generates ortho borylated compounds that can be directly oxidised to the 2-(2-aminoethyl)-phenol. Other substrates amenable to the C-H borylation-reduction sequence include mono and diamino-arenes and carbazoles. This represents a simple method to make borylated molecules that would be convoluted to access otherwise ( e.g. N -octyl-1-BPin-carbazole). Substituent variation is tolerated at boron as well as in the amide unit, with diarylborenium cations also amenable to reduction. This enables a double C-H borylation-reduction-hydrolysis sequence to access B,N-polycyclic aromatic hydrocarbons (PAHs), including an example where both the boron and nitrogen centres contain functionalisable handles (N-H and B-OH). This method is therefore a useful addition to the metal-free borylation toolbox for accessing useful intermediates (ArylBPin) and novel B,N-PAHs., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)- Published
- 2023
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16. Utilizing Raman Spectroscopy as a Tool for Solid- and Solution-Phase Analysis of Metalloorganic Cage Host-Guest Complexes.
- Author
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O'Connor HM, Tipping WJ, Vallejo J, Nichol GS, Faulds K, Graham D, Brechin EK, and Lusby PJ
- Abstract
The host-guest chemistry of coordination cages continues to promote significant interest, not least because confinement effects can be exploited for a range of applications, such as drug delivery, sensing, and catalysis. Often a fundamental analysis of noncovalent encapsulation is required to provide the necessary insight into the design of better functional systems. In this paper, we demonstrate the use of various techniques to probe the host-guest chemistry of a novel Pd
2 L4 cage, which we show is preorganized to selectively bind dicyanoarene guests with high affinity through hydrogen-bonding and other weak interactions. In addition, we exemplify the use of Raman spectroscopy as a tool for analyzing coordination cages, exploiting alkyne and nitrile reporter functional groups that are contained within the host and guest, respectively.- Published
- 2023
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17. Influence of alkali metal cations on the formation of the heterobimetallic actinide tert -butoxides [AnM 3 (O t Bu) 7 ] and [AnM 2 (O t Bu) 6 ] (An IV = Th, U; M I = Li, Na, K, Rb, Cs).
- Author
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Lichtenberg A, Zegke M, Nichol GS, Raauf A, and Mathur S
- Subjects
- Sodium chemistry, Lithium chemistry, Cations, Metals, Alkali chemistry, Uranium chemistry
- Abstract
Heterobimetallic tert -butoxides of alkali metal cations with tetravalent actinide centers exhibit two distinctive structural motifs, [AnM
2 (Ot Bu)6 ] and [AnM3 (Ot Bu)7 ] (AnIV = Th, U and MI = Li, Na, K, Rb, Cs), evidently governed by the size of the alkali metal ions. Both [AnM3 (Ot Bu)7 ] AnM3 (AnIV = U, MI = Li; AnIV = Th, MI = Li, Na) and [AnM2 (Ot Bu)6 ] AnM2 (AnIV = U, MI = Na-Cs; AnIV = Th, MI = K-Cs) compounds are obtained in nearly quantitative yields by reacting actinide and alkali metal silyl amides with an excess of tert -butyl alcohol. The AnM3 complexes form a cubane-type coordination motif, whereas the AnM2 complexes display a geometry resembling two face-shared bipyramids. The sodium derivatives of thorium and uranium (ThNa3 and UNa2) allow the determination of the structural transition threshold as a function of the ratio of the ionic radii ri (AnIV )/ ri (MI ). The AnM3 complexes are formed for ratios above 0.92 and the AnM2 type is formed for ratios below 0.87. All compounds are unambiguously characterized in both solution and solid states by NMR and IR spectroscopic studies and single crystal X-ray diffraction analyses, respectively.- Published
- 2023
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18. Synthesis of Electrophiles Derived from Dimeric Aminoboranes and Assessing Their Utility in the Borylation of π Nucleophiles.
- Author
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Millet CRP, Pahl J, Noone E, Yuan K, Nichol GS, Uzelac M, and Ingleson MJ
- Abstract
Dimeric aminoboranes, [H
2 BNR2 ]2 (R = Me or CH2 CH2 ) containing B2 N2 cores, can be activated by I2 , HNTf2 (NTf2 = [N(SO2 CF3 )2 ]), or [Ph3 C][B(C6 F5 )4 ] to form isolable H2 B(μ-NR2 )2 BHX (for X = I or NTf2 ). For X = [B(C6 F5 )4 ]- further reactivity, presumably between [H2 B(μ-NMe2 )2 BH][B(C6 F5 )4 ] and aminoborane, forms a B3 N3 -based monocation containing a three-center two electron B-(μ-H)-B moiety. The structures of H2 B(μ-NMe2 )2 BH(I) and [(μ-NMe2 )BH(NTf2 )]2 indicated a sterically crowded environment around boron, and this leads to the less common O-bound mode of NTf2 binding. While the iodide congener reacted very slowly with alkynes, the NTf2 analogues were more reactive, with hydroboration of internal alkynes forming (vinyl)2 BNR2 species and R2 NBH(NTf2 ) as the major products. Further studies indicated that the B2 N2 core is maintained during the first hydroboration, and that it is during subsequent steps that B2 N2 dissociation occurs. In the mono-boron systems, for example,i Pr2 NBH(NTf2 ), NTf2 is N-bound; thus, they have less steric crowding around boron relative to the B2 N2 systems. Notably, the monoboron systems are much less reactive in alkyne hydroboration than the B2 N2 -based bis-boranes, despite the former being three coordinate at boron while the latter are four coordinate at boron. Finally, these B2 N2 electrophiles are much more prone to dissociate into mono-borane species than pyrazabole [H2 B(μ-N2 C3 H3 )]2 analogues, making them less useful for the directed diborylation of a single substrate., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)- Published
- 2022
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19. Diastereoselective, Catalytic Access to Cross-Aldol Products Directly from Esters and Lactones.
- Author
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Moreno González A, Nicholson K, Llopis N, Nichol GS, Langer T, Baeza A, and Thomas SP
- Abstract
High oxidation-state carbonyl coupling partners including esters and lactones were reacted with enones to give aldol-type products directly using two-fold organoborane catalysis. This new retrosynthetic disconnection to aldol-type products is compatible with enolisable coupling partners, without self-condensation, and couples the high reactivity of secondary dialkylboranes with the stability of pinacolboronic esters. Excellent chemoselectivity, substrate scope (including those containing reducible functionalities and free alcohols) and diastereocontrol were achieved to access both the syn- and anti-aldol-type products. Mechanistic studies confirmed the two-fold catalytic role of the single secondary borane catalyst for boron enolate formation and formation of an aldehyde surrogate from the ester or lactone coupling partner., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)
- Published
- 2022
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20. Boron-Catalyzed, Diastereo- and Enantioselective Allylation of Ketones with Allenes.
- Author
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Nicholson K, Peng Y, Llopis N, Willcox DR, Nichol GS, Langer T, Baeza A, and Thomas SP
- Abstract
The diastereo- and enantioselective allylation of ketones remains a synthetic challenge, with transition metal catalysis offering the most applied methods. Here, a boron-catalyzed allylation of ketones with allenes is presented. Excellent yield, regioselectivity, and diastereoselectivity were found across functionalized substrates. The reaction was further developed to accommodate an enantioenriched boron catalyst and thus gave asymmetric ketone allylation in good yield, diastereoselectivity, and enantioselectivity. Mechanistic studies supported a hydroboration-allylation-transborylation pathway., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)
- Published
- 2022
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21. A graceful break-up: serendipitous self-assembly of a ferromagnetically coupled [NiII14] wheel.
- Author
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Agapaki E, Singh MK, Canaj AB, Nichol GS, Schnack J, and Brechin EK
- Subjects
- Magnetics, Magnets
- Abstract
The complex [NiII14(HL
2 )12 (HCOO)14 Cl14 (MeOH)(H2 O)] describes an aesthetically pleasing wheel displaying ferromagnetic nearest neighbour exchange.- Published
- 2022
- Full Text
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22. Iron-catalysed alkene and heteroarene H/D exchange by reversible protonation of iron-hydride intermediates.
- Author
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Britton L, Docherty JH, Sklyaruk J, Cooney J, Nichol GS, Dominey AP, and Thomas SP
- Abstract
C-H functionalisation reactions offer a sustainable method for molecular construction and diversification. These reactions however remain dominated by precious metal catalysis. While significant interest in iron-catalysed C-H activation reactions has emerged, the isolation, characterisation and mechanistic understanding of these processes remain lacking. Herein the iron-catalysed C(sp
2 )-H bond hydrogen/deuterium exchange reaction using CD3 OD is reported for both heterocycles and, for the first time, alkenes (38 examples). Isolation and characterisation, including by single-crystal X-ray diffraction, of the key iron-aryl and iron-alkenyl C-H metallation intermediates provided evidence for a reversible protonation of the active iron hydride catalyst. Good chemoselectivity was observed for both substrate classes. The developed procedure is orthogonal to previous iron-catalysed H/D exchange methods which used C6 D6 , D2 , or D2 O as the deuterium source, and uses only bench-stable reagents, including the iron(ii) pre-catalyst. Further, a new mechanism of iron-hydride formation is reported in which β-hydride elimination from an alcohol generates the iron hydride. The ability to produce, isolate and characterise the organometallic products arising from C-H activation presents a basis for future discovery and development., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)- Published
- 2022
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23. Dissecting Solvent Effects on Hydrogen Bonding.
- Author
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Meredith NY, Borsley S, Smolyar IV, Nichol GS, Baker CM, Ling KB, and Cockroft SL
- Subjects
- Hydrogen Bonding, Solvents chemistry, Thermodynamics, Amides
- Abstract
The experimental isolation of H-bond energetics from the typically dominant influence of the solvent remains challenging. Here we use synthetic molecular balances to quantify amine/amide H-bonds in competitive solvents. Over 200 conformational free energy differences were determined using 24 H-bonding balances in 9 solvents spanning a wide polarity range. The correlations between experimental interaction energies and gas-phase computed energies exhibited wild solvent-dependent variation. However, excellent correlations were found between the same computed energies and the experimental data following empirical dissection of solvent effects using Hunter's α/β solvation model. In addition to facilitating the direct comparison of experimental and computational data, changes in the fitted donor and acceptor constants reveal the energetics of secondary local interactions such as competing H-bonds., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)
- Published
- 2022
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24. Guest-induced magnetic exchange in paramagnetic [M 2 L 4 ] 4+ coordination cages.
- Author
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Singh MK, Etcheverry-Berríos A, Vallejo J, Sanz S, Martínez-Lillo J, Nichol GS, Lusby PJ, and Brechin EK
- Abstract
Paramagnetic complexes that possess magnetically switchable properties show promise in a number of applications. A significantly underdeveloped approach is the use of metallocages, whose magnetic properties can be modulated through host-guest chemistry. Here we show such an example that utilises a simple [Cu
II 2 L4 ]4+ lantern complex. Magnetic susceptibility and magnetisation data shows an absence of exchange in the presence of the diamagnetic guest triflate. However, replacement of the bound triflate by ReBr6 2- switches on antiferomagnetic exchange between the Cu and Re ions, leading to an S = 1/2 ground state for the non-covalent complex [ReBr6 2- ⊂CuII 2 L4 ]2+ . Comparison of this complex to a "control" palladium-cage host-guest complex, [ReBr6 2- ⊂PdII 2 L4 ]2+ , shows that the encapsulated ReBr6 2- anions retain the same magnetic anisotropy as in the free salt. Theoretically calculated spin-Hamiltonian parameters are in close agreement with experiment. Spin density analysis shows the mode of interaction between the CuII and ReIV centres is through the Re-Br⋯Cu pathway, primarily mediated through the Cu(dx )|Br2 2 sp |Re(dyz ) interaction. This is further supported by overlap integral calculations between singly occupied molecular orbitals (SOMOs) of the paramagnetic ions and natural bonding orbitals analysis where considerable donor-to-acceptor interactions are observed between hybrid 4s4p orbitals of the Br ions and the empty 4s and 4p orbitals of the Cu ions.- Published
- 2022
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25. A Lewis Base Nucleofugality Parameter, N F B , and Its Application in an Analysis of MIDA-Boronate Hydrolysis Kinetics.
- Author
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Taylor NP, Gonzalez JA, Nichol GS, García-Domínguez A, Leach AG, and Lloyd-Jones GC
- Subjects
- Hydrolysis, Kinetics, Boranes, Lewis Bases
- Abstract
The kinetics of quinuclidine displacement of BH
3 from a wide range of Lewis base borane adducts have been measured. Parameterization of these rates has enabled the development of a nucleofugality scale ( NF B ), shown to quantify and predict the leaving group ability of a range of other Lewis bases. Additivity observed across a number of series R'3- n Rn X (X = P, N; R' = aryl, alkyl) has allowed the formulation of related substituent parameters ( nf PB , nf AB ), providing a means of calculating NF B values for a range of Lewis bases that extends far beyond those experimentally derived. The utility of the nucleofugality parameter is explored by the correlation of the substituent parameter nf PB with the hydrolyses rates of a series of alkyl and aryl MIDA boronates under neutral conditions. This has allowed the identification of MIDA boronates with heteroatoms proximal to the reacting center, showing unusual kinetic lability or stability to hydrolysis.- Published
- 2022
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26. Enhanced N-directed electrophilic C-H borylation generates BN-[5]- and [6]helicenes with improved photophysical properties.
- Author
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Yuan K, Volland D, Kirschner S, Uzelac M, Nichol GS, Nowak-Król A, and Ingleson MJ
- Abstract
Helicenes are chiral polycyclic aromatic hydrocarbons (PAHs) of significant interest, e.g. in supramolecular chemistry, materials science and asymmetric catalysis. Herein an enhanced N-directed electrophilic C-H borylation methodology has been developed that provides access to azaborine containing helicenes (BN-helicenes). This borylation process proceeds via protonation of an aminoborane with bistriflimidic acid. DFT calculations reveal the borenium cation formed by protonation to be more electrophilic than the product derived from aminoborane activation with BBr
3 . The synthesised helicenes include BN-analogues of archetypal all carbon [5]- and [6]helicenes. The replacement of a CC with a BN unit (that has a longer bond) on the outer helix increases the strain in the BN congeners and the racemization half-life for a BN-[5]helicene relative to the all carbon [5]helicene. BN incorporation also increases the fluorescence efficiency of the helicenes, a direct effect of BN incorporation altering the distribution of the key frontier orbitals across the helical backbone relative to carbo-helicenes., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)- Published
- 2022
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27. An [FeIII30] molecular metal oxide.
- Author
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Dearle AE, Cutler DJ, Coletta M, Lee E, Dey S, Sanz S, Fraser HWL, Nichol GS, Rajaraman G, Schnack J, Cronin L, and Brechin EK
- Abstract
Dissolution of FeBr
3 in a mixture of acetonitrile and 3,4-lutidine in the presence of an amine results in the formation of an [Fe30 ] molecular metal oxide containing alternating layers of tetrahedral and octahedral FeIII ions. Mass spectrometry suggests the cluster is formed quickly and remains stable in solution, while magnetic measurements and DFT calculations reveal competing antiferromagnetic exchange interactions.- Published
- 2021
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28. Reversible Dissociation of a Dialumene*.
- Author
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Falconer RL, Byrne KM, Nichol GS, Krämer T, and Cowley MJ
- Abstract
Dialumenes are neutral Al
I compounds with Al=Al multiple bonds. We report the isolation of an amidophosphine-supported dialumene. Our X-ray crystallographic, spectroscopic, and computational DFT analyses reveal a long and extreme trans-bent Al=Al bond with a low dissociation energy and bond order. In solution, the dialumene can dissociate into monomeric AlI species. Reactivity studies reveal two modes of reaction: as dialumene or as aluminyl monomers., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)- Published
- 2021
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29. Formation of a hydride containing amido-zincate using pinacolborane.
- Author
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Uzelac M, Yuan K, Nichol GS, and Ingleson MJ
- Abstract
Amido-zincates containing hydrides are underexplored yet potentially useful complexes. Attempts to access this type of zincate through combining amido-organo zincates and pinacolborane (HBPin) via Zn-C/H-BPin exchange led instead to preferential formation of amide-BPin and/or [amide-BPin(Y)]
- (Y = Ph, amide, H), when the amide is hexamethyldisilazide or 2,2,6,6-tetramethylpiperidide and the hydrocarbyl group was phenyl or ethyl. In contrast, the use of a dipyridylamide (dpa) based arylzinc complex led to Zn-C/H-BPin metathesis being the major outcome. Independent synthesis and full characterisation of two Ln Li[(dpa)ZnPh2 ] (L = THF, n = 3; L = PMDETA, n = 1) complexes, 1 and 3, respectively, enabled reactivity studies that demonstrated that these species display zincate type reactivity (by comparison to the lower reactivity of the neutral complex (Me-dpa)ZnPh2 , 4, Me-dpa = 2,2'-dipyridyl- N -methylamine). This included 1 performing the rapid deprotonation of 4-ethynyltoluene and also phenyl transfer to α,α,α-trifluoroacetophenone in contrast to neutral complex 4. Complex 1 reacted with one equivalent of HBPin to give predominantly PhBPin ( ca. 90%) and a lithium amidophenylzincate containing a hydride unit, complex 7-A, as the major zinc containing product. Complex 7-A transfers hydride to an electrophile preferentially over phenyl, indicating it reacts as a hydridozincate. Attempts to react 1 with >1 equivalent of HBPin or with catecholborane led to more complex outcomes, which included significant borane and dpaZn substituent scrambling, two examples of which were crystallographically characterised. While this work provides proof of principle for Zn-C/H-BPin exchange as a route to form an amido-zincate containing a hydride, amido-organozincates that undergo more selective Zn-C/H-BPin exchange still are required.- Published
- 2021
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30. [(V IV O) 2 MII5] (M = Ni, Co) Anderson wheels.
- Author
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Fraser HWL, Payne EH, Sarkar A, Wilson LRB, Mitcov D, Nichol GS, Rajaraman G, Piligkos S, and Brechin EK
- Abstract
Heterometallic Anderson wheels of formula [(V
IV O)2 MII5(hmp)10 Cl2 ](ClO4 )2 ·2MeOH (M = Ni, 1; Co, 2) have been synthesised from the solvothermal reaction of M(ClO4 )2 ·6H2 O and VCl3 with hmpH (2-(hydroxymethyl)pyridine). The metallic skeleton describes a centred hexagon, with the two vanadyl ions sitting on opposing sides of the outer ring. Magnetic susceptibility and magnetisation measurements indicate the presence of both ferromagnetic and antiferromagnetic exchange interactions. Theoretical calculations based on density functional methods reproduce both the sign and strength of the exchange interactions found experimentally, and rationalise the parameters extracted.- Published
- 2021
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31. Aluminium-Catalyzed C(sp)-H Borylation of Alkynes.
- Author
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Willcox DR, De Rosa DM, Howley J, Levy A, Steven A, Nichol GS, Morrison CA, Cowley MJ, and Thomas SP
- Abstract
Historically used in stoichiometric hydroalumination chemistry, recent advances have transformed aluminium hydrides into versatile catalysts for the hydroboration of unsaturated multiple bonds. This catalytic ability is founded on the defining reactivity of aluminium hydrides with alkynes and alkenes: 1,2-hydroalumination of the unsaturated π-system. This manuscript reports the aluminium hydride catalyzed dehydroborylation of terminal alkynes. A tethered intramolecular amine ligand controls reactivity at the aluminium hydride centre, switching off hydroalumination and instead enabling selective reactions at the alkyne C-H σ-bond. Chemoselective C-H borylation was observed across a series of aryl- and alkyl-substituted alkynes (21 examples). On the basis of kinetic and density functional theory studies, a mechanism in which C-H borylation proceeds by σ-bond metathesis between pinacolborane (HBpin) and alkynyl aluminium intermediates is proposed., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)
- Published
- 2021
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32. The Phospha-Bora-Wittig Reaction.
- Author
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Borys AM, Rice EF, Nichol GS, and Cowley MJ
- Abstract
We report the phospha-bora-Wittig reaction for the direct preparation of phosphaalkenes from aldehydes, ketones, esters, or amides. The transient phosphaborene Mes*P═B-NR
2 reacts with carbonyl compounds to form 1,2,3-phosphaboraoxetanes, analogues of oxaphosphetane intermediates in the classical Wittig reaction. 1,2,3-Phosphaboraoxetanes undergo thermal or Lewis acid-promoted cycloreversion, yielding phosphaalkenes. Experimental and density functional theory studies reveal far-reaching similarities between classical and phospha-bora-Wittig reactions.- Published
- 2021
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33. [Fe 15 ]: a frustrated, centred tetrakis hexahedron.
- Author
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Cutler DJ, Singh MK, Nichol GS, Evangelisti M, Schnack J, Cronin L, and Brechin EK
- Abstract
The combination of two different Fe
III salts in a solvothermal reaction with triethanolamine results in the formation of a high symmetry [FeIII15] cluster whose structure conforms to a centred, tetrakis hexahedron.- Published
- 2021
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- View/download PDF
34. Simple Amides and Amines for the Synergistic Recovery of Rhodium from Hydrochloric Acid by Solvent Extraction.
- Author
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Carrick AI, Doidge ED, Bouch A, Nichol GS, Patrick J, Schofield ER, Morrison CA, and Love JB
- Subjects
- Amides, Amines, Hydrochloric Acid, Solvents, Rhodium
- Abstract
The separation and isolation of many of the platinum group metals (PGMs) is currently achieved commercially using solvent extraction processes. The extraction of rhodium is problematic however, as a variety of complexes of the form [RhCl
n (H2 O)6-n ](n-3)- are found in hydrochloric acid, making it difficult to design a reagent that can extract all the rhodium. In this work, the synergistic combination of a primary amine (2-ethylhexylamine, LA ) with a primary amide (3,5,5-trimethylhexanamide, L1 ) is shown to extract over 85 % of rhodium from 4 M hydrochloric acid. Two rhodium complexes are shown to reside in the organic phase, the ion-pair [HLA ]3 [RhCl6 ] and the amide complex [HLA ]2 [RhCl5 (L1 )]; in the latter complex, the amide is tautomerized to its enol form and coordinated to the rhodium centre through the nitrogen atom. This insight highlights the need for ligands that target specific metal complexes in the aqueous phase and provides an efficient synergistic solution for the solvent extraction of rhodium., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)- Published
- 2021
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35. Zinc catalysed electrophilic C-H borylation of heteroarenes.
- Author
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Grundy ME, Yuan K, Nichol GS, and Ingleson MJ
- Abstract
Cationic zinc Lewis acids catalyse the C-H borylation of heteroarenes using pinacol borane (HBPin) or catechol borane (HBCat). An electrophile derived from [IDippZnEt][B(C
6 F5 )4 ] (IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) combined with N , N -dimethyl- p -toluidine (DMT) proved the most active in terms of C-H borylation scope and yield. Using this combination weakly activated heteroarenes, such as thiophene, were amenable to catalytic C-H borylation using HBCat. Competition reactions show these IDipp-zinc cations are highly oxophilic but less hydridophilic (relative to B(C6 F5 )3 ), and that borylation proceeds via activation of the hydroborane (and not the heteroarene) by a zinc electrophile. Based on DFT calculations this activation is proposed to proceed by coordination of a hydroborane oxygen to the zinc centre to generate a boron electrophile that effects C-H borylation. Thus, Lewis acid binding to oxygen sites of hydroboranes represents an under-developed route to access reactive borenium-type electrophiles for C-H borylation., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)- Published
- 2021
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36. A [Mn 18 ] wheel-of-wheels.
- Author
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Coletta M, Tziotzi TG, Gray M, Nichol GS, Singh MK, Milios CJ, and Brechin EK
- Abstract
A [Mn18] wheel of wheels is obtained from the reaction of MnBr2·4H2O and LH3 in MeOH. The metallic skeleton reveals two asymmetric [MnIII6MnII2] square wheels connected into a larger wheel via two MnII ions. Magnetic susceptibility and magnetisation data reveal competing exchange interactions, supported by computational studies.
- Published
- 2021
- Full Text
- View/download PDF
37. Design of pure heterodinuclear lanthanoid cryptate complexes.
- Author
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Buch CD, Hansen SH, Mitcov D, Tram CM, Nichol GS, Brechin EK, and Piligkos S
- Abstract
Heterolanthanide complexes are difficult to synthesize owing to the similar chemistry of the lanthanide ions. Consequently, very few purely heterolanthanide complexes have been synthesized. This is despite the fact that such complexes hold interesting optical and magnetic properties. To fine-tune these properties, it is important that one can choose complexes with any given combination of lanthanides. Herein we report a synthetic procedure which yields pure heterodinuclear lanthanide cryptates LnLn*LX
3 (X = NO3 - or OTf- ) based on the cryptand H3 L = N[(CH2 )2 N[double bond, length as m-dash]CH-R-CH[double bond, length as m-dash]N-(CH2 )2 ]3 N (R = m -C6 H2 OH-2-Me-5). In the synthesis the choice of counter ion and solvent proves crucial in controlling the Ln-Ln* composition. Choosing the optimal solvent and counter ion afford pure heterodinuclear complexes with any given combination of Gd(iii)-Lu(iii) including Y(iii). To demonstrate the versatility of the synthesis all dinuclear combinations of Y(iii), Gd(iii), Yb(iii) and Lu(iii) were synthesized resulting in 10 novel complexes of the form LnLn*L(OTf)3 with LnLn* = YbGd 1 , YbY 2 , YbLu 3 , YbYb 4 , LuGd 5 , LuY 6 , LuLu 7 , YGd 8 , YY 9 and GdGd 10 . Through the use of1 H,13 C NMR and mass spectrometry the heterodinuclear nature of YbGd, YbY, YbLu, LuGd, LuY and YGd was confirmed. Crystal structures of LnLn*L(NO3 )3 reveal short Ln-Ln distances of ∼3.5 Å. Using SQUID magnetometry the exchange coupling between the lanthanide ions was found to be anti-ferromagnetic for GdGd and YbYb while ferromagnetic for YbGd., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)- Published
- 2021
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38. Instantaneous and Phosphine-Catalyzed Arene Binding and Reduction by U(III) Complexes.
- Author
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Arnold PL, Halliday CJV, Puig-Urrea L, and Nichol GS
- Abstract
Neutral arenes such as benzene have never been considered suitable ligands for electropositive actinide cations, yet we find that even simple U
III UX3 aryloxide complexes such as U(ODipp)3 bind and reduce arenes spontaneously at room temperature, forming inverse arene sandwich (IAS) complexes Xn U(μ-C6 D6 )UXm (X = ODipp, n =2, m =3; X = OBMes2 n=m=2 or 3) (ODipp = OC6 H3 i Pr2 -2,6; Mes = 2,4,6-Me3 -C6 H2 ). 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 UIII centers of U(ODipp)3 . Phosphines that are not considered suitable ligands for actinides can catalyze the formation of the IAS complexes. This enables otherwise inaccessible asymmetric and less congested IAS complexes to be isolated and the bonding in this series compared.- Published
- 2021
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39. Exploiting host-guest chemistry to manipulate magnetic interactions in metallosupramolecular M 4 L 6 tetrahedral cages.
- Author
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Scott AJ, Vallejo J, Sarkar A, Smythe L, Regincós Martí E, Nichol GS, Klooster WT, Coles SJ, Murrie M, Rajaraman G, Piligkos S, Lusby PJ, and Brechin EK
- Abstract
Reaction of Ni(OTf)
2 with the bisbidentate quaterpyridine ligand L results in the self-assembly of a tetrahedral, paramagnetic cage [NiII 4 L6 ]8+ . By selectively exchanging the bound triflate from [OTf⊂NiII 4 L6 ](OTf)7 ( 1 ), we have been able to prepare a series of host-guest complexes that feature an encapsulated paramagnetic tetrahalometallate ion inside this paramagnetic host giving [MII X4 ⊂NiII 4 L6 ](OTf)6 , where MII X4 2- = MnCl4 2- ( 2 ), CoCl4 2- ( 5 ), CoBr4 2- ( 6 ), NiCl4 2- ( 7 ), and CuBr4 2- ( 8 ) or [MIII X4 ⊂NiII 4 L6 ](OTf)7 , where MIII X4 - = FeCl4 - ( 3 ) and FeBr4 - ( 4 ). Triflate-to-tetrahalometallate exchange occurs in solution and can also be accomplished through single-crystal-to-single-crystal transformations. Host-guest complexes 1-8 all crystallise as homochiral racemates in monoclinic space groups, wherein the four {NiN6 } vertexes within a single Ni4 L6 unit possess the same Δ or Λ stereochemistry. Magnetic susceptibility and magnetisation data show that the magnetic exchange between metal ions in the host [NiII 4 ] complex, and between the host and the MX4 n - guest, are of comparable magnitude and antiferromagnetic in nature. Theoretically derived values for the magnetic exchange are in close agreement with experiment, revealing that large spin densities on the electronegative X-atoms of particular MX4 n - guest molecules lead to stronger host-guest magnetic exchange interactions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)- Published
- 2021
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40. Reversible Reductive Elimination in Aluminum(II) Dihydrides.
- Author
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Falconer RL, Nichol GS, Smolyar IV, Cockroft SL, and Cowley MJ
- Abstract
Oxidative addition and reductive elimination are defining reactions of transition-metal organometallic chemistry. In main-group chemistry, oxidative addition is now well-established but reductive elimination reactions are not yet general in the same way. Herein, we report dihydrodialanes supported by amidophosphine ligands. The ligand serves as a stereochemical reporter for reversible reductive elimination/oxidative addition chemistry involving Al
I and AlIII intermediates., (© 2020 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)- Published
- 2021
- Full Text
- View/download PDF
41. Phthalocyanine-polyoxotungstate lanthanide double deckers.
- Author
-
Sarwar S, Sanz S, van Leusen J, Nichol GS, Brechin EK, and Kögerler P
- Abstract
Acetate ligand metathesis results in the first hybrid [MIII(Pc)(PW11O39)]6- (M = Y, Dy, Tb) double-decker scaffolds, where a phthalocyanate (Pc2-) and one of the conceptually most simple polyoxotungstates, a monolacunary Keggin cluster, are interlinked via a single rare earth ion. Characterisation includes high-resolution mass spectrometry, synchrotron-based single-crystal X-ray diffraction, various spectroscopic and electrochemical methods, and magnetic studies revealing slow relaxation of the magnetisation for the Dy derivate.
- Published
- 2020
- Full Text
- View/download PDF
42. Combining alkali metals and zinc to harness heterometallic cooperativity in cyclic ester ring-opening polymerisation.
- Author
-
Gruszka W, Lykkeberg A, Nichol GS, Shaver MP, Buchard A, and Garden JA
- Abstract
Heterometallic cooperativity is an emerging strategy to elevate polymerisation catalyst performance. Here, we report the first heterotrimetallic Na/Zn
2 and K/Zn2 complexes supported by a ProPhenol ligand, which deliver "best of both" in cyclic ester ring-opening polymerisation, combining the outstanding activity (Na/K) and good control (Zn2 ) of homometallic analogues. Detailed NMR studies and density-functional theory calculations suggest that the Na/Zn2 and K/Zn2 complexes retain their heterometallic structures in the solution-state. To the best of our knowledge, the K/Zn2 analogue is the most active heterometallic catalyst reported for rac -lactide polymerisation ( kobs = 1.7 × 10-2 s-1 ), giving activities five times faster than the Na/Zn2 complex. These versatile catalysts also display outstanding performance in ε-caprolatone and δ-valerolactone ring-opening polymerisation. These studies provide underpinning methodologies for future heterometallic polymerisation catalyst design, both in cyclic ester polymerisation and other ring-opening (co)polymerisation reactions., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)- Published
- 2020
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43. Kinetic selection of Pd 4 L 2 metallocyclic and Pd 6 L 3 trigonal prismatic assemblies.
- Author
-
O'Connor HM, Coletta M, Etcheverry-Berríos A, Nichol GS, Brechin EK, and Lusby PJ
- Abstract
The self-assembly of Pd4L2 metallocylcic and Pd6L3 trigonal prismatic assemblies are described. The selection of one species over the other has been achieved by careful choice of ancilliary ligands, which switch the dynamics of the Pd-pyridine bonds such that a highly unusual and distorted smaller assembly can be kinetically trapped en route to the more energetically favourable larger species. Both assemblies provide promise as easy to access multicavity reaction vessels.
- Published
- 2020
- Full Text
- View/download PDF
44. Reconciling Electrostatic and n→π* Orbital Contributions in Carbonyl Interactions.
- Author
-
Muchowska KB, Pascoe DJ, Borsley S, Smolyar IV, Mati IK, Adam C, Nichol GS, Ling KB, and Cockroft SL
- Abstract
Interactions between carbonyl groups are prevalent in protein structures. Earlier investigations identified dominant electrostatic dipolar interactions, while others implicated lone pair n→π* orbital delocalisation. Here these observations are reconciled. A combined experimental and computational approach confirmed the dominance of electrostatic interactions in a new series of synthetic molecular balances, while also highlighting the distance-dependent observation of inductive polarisation manifested by n→π* orbital delocalisation. Computational fiSAPT energy decomposition and natural bonding orbital analyses correlated with experimental data to reveal the contexts in which short-range inductive polarisation augment electrostatic dipolar interactions. Thus, we provide a framework for reconciling the context dependency of the dominance of electrostatic interactions and the occurrence of n→π* orbital delocalisation in C=O⋅⋅⋅C=O interactions., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)
- Published
- 2020
- Full Text
- View/download PDF
45. Pressure-and temperature induced phase transitions, piezochromism, NLC behaviour and pressure controlled Jahn-Teller switching in a Cu-based framework.
- Author
-
McMonagle CJ, Comar P, Nichol GS, Allan DR, González J, Barreda-Argüeso JA, Rodríguez F, Valiente R, Turner GF, Brechin EK, and Moggach SA
- Abstract
In situ single-crystal diffraction and spectroscopic techniques have been used to study a previously unreported Cu-framework bis[1-(4-pyridyl)butane-1,3-dione]copper(ii) (CuPyr-I). CuPyr-I was found to exhibit high-pressure and low-temperature phase transitions, piezochromism, negative linear compressibility, and a pressure induced Jahn-Teller switch, where the switching pressure was hydrostatic media dependent., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)
- Published
- 2020
- Full Text
- View/download PDF
46. Characterization of the Zwitterionic Intermediate in 1,1-Carboboration of Alkynes.
- Author
-
Bismuto A, Nichol GS, Duarte F, Cowley MJ, and Thomas SP
- Abstract
The reaction of a Lewis acidic borane with an alkyne is a key step in a diverse range of main group transformations. Alkyne 1,1-carboboration, the Wrackmeyer reaction, is an archetypal transformation of this kind. 1,1-Carboboration has been proposed to proceed through a zwitterionic intermediate. We report the isolation and spectroscopic, structural and computational characterization of the zwitterionic intermediates generated by reaction of B(C
6 F5 )3 with alkynes. The stepwise reactivity of the zwitterion provides new mechanistic insight for 1,1-carboboration and wider B(C6 F5 )3 catalysis. Making use of intramolecular stabilization by a ferrocene substituent, we have characterized the zwitterionic intermediate in the solid state and diverted reactivity towards alkyne cyclotrimerization., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)- Published
- 2020
- Full Text
- View/download PDF
47. Total synthesis of brevianamide A.
- Author
-
Godfrey RC, Green NJ, Nichol GS, and Lawrence AL
- Subjects
- Alkaloids biosynthesis, Alkaloids chemistry, Biological Products chemistry, Cyclization, Molecular Structure, Penicillium metabolism, Piperazines chemistry, Spiro Compounds chemical synthesis, Spiro Compounds chemistry, Stereoisomerism, Alkaloids chemical synthesis, Biological Products chemical synthesis, Chemistry Techniques, Synthetic methods, Piperazines chemical synthesis
- Abstract
The fungal-derived bicyclo[2.2.2]diazaoctane alkaloids are of interest to the scientific community for their potent and varied biological activities. Within this large and diverse family of natural products, the insecticidal metabolite (+)-brevianamide A is particularly noteworthy for its synthetic intractability and inexplicable biogenesis. Despite five decades of research, this alkaloid has remained an elusive target for chemical synthesis due to insurmountable issues of reactivity and selectivity associated with all previously explored strategies. We herein report the chemical synthesis of (+)-brevianamide A (seven steps, 7.2% overall yield, 750 mg scale), which involves a bioinspired cascade transformation of the linearly fused (-)-dehydrobrevianamide E into the topologically complex bridged-spiro-fused structure of (+)-brevianamide A.
- Published
- 2020
- Full Text
- View/download PDF
48. An [Fe III 34 ] Molecular Metal Oxide.
- Author
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Dearle AE, Cutler DJ, Fraser HWL, Sanz S, Lee E, Dey S, Diaz-Ortega IF, Nichol GS, Nojiri H, Evangelisti M, Rajaraman G, Schnack J, Cronin L, and Brechin EK
- Abstract
The dissolution of anhydrous iron bromide in a mixture of pyridine and acetonitrile, in the presence of an organic amine, results in the formation of an [Fe
34 ] metal oxide molecule, structurally characterised by alternate layers of tetrahedral and octahedral FeIII ions connected by oxide and hydroxide ions. The outer shell of the complex is capped by a combination of pyridine molecules and bromide ions. Magnetic data, measured at temperatures as low as 0.4 K and fields up to 35 T, reveal competing antiferromagnetic exchange interactions; DFT calculations showing that the magnitudes of the coupling constants are highly dependent on both the Fe-O-Fe angles and Fe-O distances. The simplicity of the synthetic methodology, and the structural similarity between [Fe34 ], bulk iron oxides, previous FeIII -oxo cages, and polyoxometalates (POMs), hints that much larger molecular FeIII oxides can be made., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)- Published
- 2019
- Full Text
- View/download PDF
49. Inter-ligand intramolecular through-space anisotropic shielding in a series of manganese carbonyl phosphorous compounds.
- Author
-
Kurtz DA, Dhakal B, McDonald LT, Nichol GS, and Felton GAN
- Abstract
Eight novel manganese carbonyl complexes of the type [Mn(bpy-tBu)(CO)3PR3]+ (bpy-tBu = 4,4'-di-tert-butyl-2,2'-bipyridine; R = Cy, nBu, Me, p-tol, Ph, p-F-Ph, OEt, and OMe), have been synthesized and characterized by 1H NMR, FTIR, UV/Vis, HRMS and CV. X-ray crystallographic structures of [Mn(bpy-tBu)(CO)3(PCy3)]+ and [Mn(bpy-tBu)(CO)3(PPh3)]+ were obtained. The short Mn-P bond length allows for close proximity of the bipyridine ligand and the phosphine R groups, resulting in strong anisotropic shielding of certain bipyridine protons by aryl R groups (reordering the bipyridine 1H NMR pattern in the most extreme case). Electrochemical analysis of the compound series reveals that while each is a competent precatalyst for electrochemical carbon dioxide reduction (to carbon monoxide), the lability of the PR3 ligand results in similar catalytic performance amongst the series.
- Published
- 2019
- Full Text
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50. 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.
- Author
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Zegke M, Zhang X, Pidchenko I, Hlina JA, Lord RM, Purkis J, Nichol GS, Magnani N, Schreckenbach G, Vitova T, Love JB, and Arnold PL
- Abstract
The uranyl(vi) 'Pacman' complex [(UO
2 )(py)(H2 L)] A (L = polypyrrolic Schiff-base macrocycle) is reduced by Cp2 Ti(η2 -Me3 SiC[triple bond, length as m-dash]CSiMe3 ) and [Cp2 TiCl]2 to oxo-titanated uranyl(v) complexes [(py)(Cp2 TiIII OUO)(py)(H2 L)] 1 and [(ClCp2 TiIV OUO)(py)(H2 L)] 2 . Combination of ZrII and ZrIV synthons with A yields the first ZrIV -uranyl(v) complex, [(ClCp2 ZrOUO)(py)(H2 L)] 3 . Similarly, combinations of Ae0 and AeII synthons (Ae = alkaline earth) afford the mono-oxo metalated uranyl(v) complexes [(py)2 (ClMgOUO)(py)(H2 L)] 4 , [(py)2 (thf)2 (ICaOUO)(py) (H2 L)] 5 ; the zinc complexes [(py)2 (XZnOUO)(py)(H2 L)] (X = Cl 6 , I 7 ) are formed in a similar manner. In contrast, the direct reactions of Rb or Cs metal with A generate the first mono-rubidiated and mono-caesiated uranyl(v) complexes; monomeric [(py)3 (RbOUO)(py)(H2 L)] 8 and hexameric [(MOUO)(py)(H2 L)]6 (M = Rb 8b or Cs 9 ). In these uranyl(v) complexes, the pyrrole N-H atoms show strengthened hydrogen-bonding interactions with the endo -oxos, classified computationally as moderate-strength hydrogen bonds. Computational DFT MO (density functional theory molecular orbital) and EDA (energy decomposition analysis), uranium M4 edge HR-XANES (High Energy Resolution X-ray Absorption Near Edge Structure) and 3d4f RIXS (Resonant Inelastic X-ray Scattering) have been used (the latter two for the first time for uranyl(v) in 7 (ZnI)) to compare the covalent character in the UV -O and O-M bonds and show the 5f orbitals in uranyl(vi) complex A are unexpectedly more delocalised than in the uranyl(v) 7 (ZnI) complex. The Oexo -Zn bonds have a larger covalent contribution compared to the Mg-Oexo /Ca-Oexo bonds, and more covalency is found in the U-Oexo bond in 7 (ZnI), in agreement with the calculations., (This journal is © The Royal Society of Chemistry 2019.)- Published
- 2019
- Full Text
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