Elizabeth P. Wildman’s research while affiliated with University of Manchester and other places

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Publications (21)


Author Correction: Thorium–phosphorus triamidoamine complexes containing Th–P single- and multiple-bond interactions
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May 2023

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31 Reads

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1 Citation

Elizabeth P. Wildman

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Stephen T. Liddle
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Synthesis of the compounds reported in this study. a Treatment of 1 with sodium azide produces the thorium-azide 2, which when reduced in toluene with potassium graphite gives the known thorium-benzyl 3. When the same reduction is conducted in benzene the thorium-imidos 4M are isolated, and these complexes can alternatively be prepared by deprotonation of the thorium-amide 5. Notably, when the deprotonation of 5 is conducted in toluene an imido/toluene-amide-benzyl equilibrium is established. Attempts to trap the thorium-nitride intermediate resulted in the isolation of the cyclic amine 7. b Treatment of the potassium-amide 8 with a thorium separated ion pair gives the thorium-methoxide 9 whereas use of a less sterically demanding thorium-iodide gives the isolable thorium-amide 10
Molecular structures of 4K, 5, 6 and 10 with selective labelling. a the parent imido dimer 4K. b the parent amide 5. c the borane-capped azide 6. d the amide-heterocycle 10. The data for these complexes were collected at 150 K, displacement ellipsoids are presented at 40% probability and non-imido hydrogen atoms and minor disorder components are omitted for clarity
Computed reaction profile for the reduction of 2 by potassium in toluene. This pathway accounts for the reduction of the azide to nitride then subsequent protonation from toluene solvent to give a parent imido which reacts further with toluene to give parent amide 5 along with benzyl 3 and potassium-azide in-line with experimental findings. The iso-propyl groups of the silyl substituents are omitted for clarity. In this reaction scheme potassium rather than potassium graphite was used to give a tractable calculation
Views of the potassium-azide stabilising interactions. These are both in the first transition state of Figs. 3 and 5 at 1.3 kcal/mol as the azide is activated and extrudes N2. These frontier orbitals alternatively highlight the interaction of the azide unit with vacant sp-hybrid orbitals of the two potassium ions following electron transfer from the latter into the π*-orbitals of the former. The iso-propyl groups of the silyl substituents are omitted for clarity
Computed reaction profile for the reduction of 2 by potassium in benzene. This pathway accounts for the reduction of the azide to nitride then subsequent protonation from benzene solvent to give a parent imido, which dimerises in-line with experimental findings. The iso-propyl groups of the silyl substituents are omitted for clarity. In this reaction scheme potassium rather than potassium graphite was used to give a tractable calculation

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Thorium-nitrogen multiple bonds provide evidence for pushing-from-below for early actinides

September 2019

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250 Reads

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34 Citations

Although the chemistry of uranium-ligand multiple bonding is burgeoning, analogous complexes involving other actinides such as thorium remain rare and there are not yet any terminal thorium nitrides outside of cryogenic matrix isolation conditions. Here, we report evidence that reduction of a thorium-azide produces a transient Th≡N triple bond, but this activates C-H bonds to produce isolable parent imido derivatives or it can be trapped in an N-heterocycle amine. Computational studies on these thorium-nitrogen multiple bonds consistently evidences a σ > π energy ordering. This suggests pushing-from-below for thorium, where 6p-orbitals principally interact with filled f-orbitals raising the σ-bond energy. Previously this was dismissed for thorium, being the preserve of uranium-nitrides or the uranyl dication. Recognising that pushing-from-below perhaps occurs with thorium as well as uranium, and with imido ligands as well as nitrides, suggests this phenomenon may be more widespread than previously thought.


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Electron‐Precise Actinide‐Pnictide (An‐Pn) Bonds Spanning Non‐Metal, Metalloid, and Metal Combinations (An = U, Th; Pn = P, As, Sb, Bi)

December 2017

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59 Reads

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62 Citations

We report the synthesis and characterisation of the compounds [An(TrenDMBS){Pn(SiMe3)2}] and [An(TrenTIPS){Pn(SiMe3)2}] [TrenDMBS = N(CH2CH2NSiMe2But)3, An = U, Pn = P, As, Sb, Bi; An = Th, Pn = P, As; TrenTIPS = N(CH2CH2NSiPri3)3, An = U, Pn = P, As, Sb; An = Th, Pn = P, As, Sb]. The U-Sb and Th-Sb moieties are unprecedented examples of any kind of An-Sb molecular bond, and the U-Bi bond is the first electron-precise one. The Th-Bi combination was too unstable to isolate, underscoring the fragility of these linkages. However, the U-Bi complex is the heaviest electron-precise pairing of two elements involving an actinide on a macroscopic scale under ambient conditions, and this is exceeded only by An-An pairings prepared under cryogenic matrix isolation conditions. Thermolysis and photolysis experiments suggest that the U-Pn bonds degrade by hemolytic bond cleavage, whereas the more redox robust thorium compounds engage in an acid-base/dehydrocoupling route.


Figure 1 of 1
Electron‐Precise Actinide‐Pnictide (An‐Pn) Bonds Spanning Non‐Metal, Metalloid, and Metal Combinations (An = U, Th; Pn = P, As, Sb, Bi)

December 2017

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65 Reads

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14 Citations

Angewandte Chemie

We report the synthesis and characterisation of the compounds [An(TrenDMBS){Pn(SiMe3)2}] and [An(TrenTIPS){Pn(SiMe3)2}] [TrenDMBS = N(CH2CH2NSiMe2But)3, An = U, Pn = P, As, Sb, Bi; An = Th, Pn = P, As; TrenTIPS = N(CH2CH2NSiPri3)3, An = U, Pn = P, As, Sb; An = Th, Pn = P, As, Sb]. The U-Sb and Th-Sb moieties are unprecedented examples of any kind of An-Sb molecular bond, and the U-Bi bond is the first electron-precise one. The Th-Bi combination was too unstable to isolate, underscoring the fragility of these linkages. However, the U-Bi complex is the heaviest electron-precise pairing of two elements involving an actinide on a macroscopic scale under ambient conditions, and this is exceeded only by An-An pairings prepared under cryogenic matrix isolation conditions. Thermolysis and photolysis experiments suggest that the U-Pn bonds degrade by hemolytic bond cleavage, whereas the more redox robust thorium compounds engage in an acid-base/dehydrocoupling route.


A Suite of Sterically-Demanding Hybrid Alkyl/Cyclopentadienyl Ligands

October 2017

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25 Reads

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3 Citations

Organometallics

The hybrid alkyl/cyclopentadienyl “constrained-geometry” proligands (Me3Si)2CH{SiMe2(C5H5)}, (Me3Si)2CH{SiMe2(C5Me4H)} and (Me3Si)2CH{SiMe2(C5H4-3-SiMe3)} were synthesized by the reaction of the bromosilane (Me3Si)2CH(SiMe2Br) with the corresponding lithium cyclopentadienides. Metalation of these proligands with an excess of MeK gives access to the corresponding dipotassium salts [(Me3Si)2C{SiMe2(C5H4)}]K2(OEt2)0.5, [(Me3Si)2C{SiMe2(C5Me4)}]K2(OEt2), and [[(Me3Si)2C{SiMe2(C5H3-3-SiMe3)}]K2(C6H6)]2·2C6H6 after recrystallization. Similarly, the reaction between the phosphine–borane-substituted chlorosilane (Me3Si)CH{PMe2(BH3)}(SiMe2Cl) and [C5Me4H]Li gives the proligand (Me3Si)CH{PMe2(BH3)}{SiMe2(C5Me4H)}, which reacts with 2 equiv of PhCH2K to give the dipotassium salt [(Me3Si)C{PMe2(BH3)}{SiMe2(C5Me4)}]K2(THF). X-ray crystallography revealed that the dipotassium salts of these hybrid ligands crystallize as zigzag polymers or three-dimensional networks. The suitability of the dipotassium salts as ligand transfer reagents for the synthesis of lanthanide complexes was probed through the synthesis of the lanthanum(III) complex [(Me3Si)2C{SiMe2(C5Me4)}]La(I)(THF)2, in which the dianionic ligand chelates the lanthanum center.



Table 1 : Selected computed DFT,NBO, and QTAIM data for Zr2, Zr3 À , U3 À ,and Th3 À .
Figure 2. Kohn-Shamf rontier molecular orbitals representing the principal components of the Zr=Pdouble-bondi nteractioni nZr3 À. Left:HOMO (164, À0.511 eV). Right:HOMOÀ1( 163, À0.849 eV). 
Terminal Parent Phosphanide and Phosphinidene Complexes of Zirconium(IV)

May 2017

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76 Reads

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35 Citations

The reaction of [Zr(TrenDMBS)(Cl)] [Zr1, TrenDMBS = N(CH2CH2NSiMe2But)3] with NaPH2 gave the terminal parent phosphanide complex [Zr(TrenDMBS)(PH2)] [Zr2, Zr-P = 2.685(2) Å]. Treatment of Zr2 with one equivalent of KCH2C6H5 and two equivalents of benzo-15-crown-5 ether (B15C5) afforded an unprecedented example outside of matrix isolation of a structurally authenticated transition metal terminal parent phosphinidene complex [Zr(TrenDMBS)(PH)][K(B15C5)2] [Zr3, Zr=P = 2.469(2) Å]. DFT calculations reveal a polarized-covalent Zr=P double bond, with a Mayer bond order of 1.48, and together with NMR and IR spectroscopic data also suggest an agostic-type Zr···HP interaction [∠ZrPH = 66.7°] which is unexpectedly similar to that found in cryogenic spectroscopically observed phosphinidene species. Surprisingly, computational data suggest that the Zr=P linkage reported here is as polarized, and thus as covalent, as essentially isostructural U=P and Th=P analogues.


Table 1 : Selected computed DFT,NBO, and QTAIM data for Zr2, Zr3 À , U3 À ,and Th3 À .
Figure 2. Kohn-Shamf rontier molecular orbitals representing the principal components of the Zr=Pdouble-bondi nteractioni nZr3 À. Left:HOMO (164, À0.511 eV). Right:HOMOÀ1( 163, À0.849 eV). 
Terminal Parent Phosphanide and Phosphinidene Complexes of Zirconium(IV)

May 2017

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48 Reads

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9 Citations

Angewandte Chemie

The reaction of [Zr(TrenDMBS)(Cl)] [Zr1, TrenDMBS = N(CH2CH2NSiMe2But)3] with NaPH2 gave the terminal parent phosphanide complex [Zr(TrenDMBS)(PH2)] [Zr2, Zr-P = 2.685(2) Å]. Treatment of Zr2 with one equivalent of KCH2C6H5 and two equivalents of benzo-15-crown-5 ether (B15C5) afforded an unprecedented example outside of matrix isolation of a structurally authenticated transition metal terminal parent phosphinidene complex [Zr(TrenDMBS)(PH)][K(B15C5)2] [Zr3, Zr=P = 2.469(2) Å]. DFT calculations reveal a polarized-covalent Zr=P double bond, with a Mayer bond order of 1.48, and together with NMR and IR spectroscopic data also suggest an agostic-type Zr···HP interaction [∠ZrPH = 66.7°] which is unexpectedly similar to that found in cryogenic spectroscopically observed phosphinidene species. Surprisingly, computational data suggest that the Zr=P linkage reported here is as polarized, and thus as covalent, as essentially isostructural U=P and Th=P analogues.


Table 2 | Comparison of computed NBO data for a selection of structurally related actinide-pnictide complexes. 
Figure 2 | Molecular structure of 2 at 150 K with displacement ellipsoids set to 40%. Non-arsenic-bound hydrogen atoms and minor disorder components are omitted for clarity. 
Figure 3 | Molecular structure of 3 at 150 K with displacement ellipsoids set to 40%. Non-arsenic-bound hydrogen atoms and minor disorder components are omitted for clarity. 
Triamidoamine thorium-arsenic complexes with parent arsenide, arsinidiide and arsenido structural motifs

March 2017

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71 Reads

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54 Citations

Despite a major expansion of uranium–ligand multiple bond chemistry in recent years, analogous complexes involving other actinides (An) remain scarce. For thorium, under ambient conditions only a few multiple bonds to carbon, nitrogen, phosphorus and chalcogenides are reported, and none to arsenic are known; indeed only two complexes with thorium–arsenic single bonds have been structurally authenticated, reflecting the challenges of stabilizing polar linkages at the large thorium ion. Here, we report thorium parent–arsenide (ThAsH2), –arsinidiides (ThAs(H)K and ThAs(H)Th) and arsenido (ThAsTh) linkages stabilized by a bulky triamidoamine ligand. The ThAs(H)K and ThAsTh linkages exhibit polarized-covalent thorium–arsenic multiple bonding interactions, hitherto restricted to cryogenic matrix isolation experiments, and the AnAs(H)An and AnAsAn linkages reported here have no precedent in f-block chemistry. 7s, 6d and 5f orbital contributions to the Th–As bonds are suggested by quantum chemical calculations, and their compositions unexpectedly appear to be tensioned differently compared to phosphorus congeners.



Citations (9)


... The original extended-Hückel theory study of PFB by Tatsumi and Hoffmann 10 , and subsequent related theoretical work 11-13,24 did not quantify PFB, and by extension ITI, in terms of energy across different types of compounds. Furthermore, the delocalized nature of the valence canonical MOs has made it difficult to assess the contributions of actinide 6p AOs in larger systems, such that PFB has been evaluated indirectly, for instance via calculations excluding or including 6p in frozen cores 13,16,18,24 . ...

Reference:

Actinide inverse trans influence versus cooperative pushing from below and multi-center bonding
Thorium-nitrogen multiple bonds provide evidence for pushing-from-below for early actinides

... [18] Apart from these observations, no systematic study on the stability of uranium phosphine complexes has been reported so far. While the nature of the bond of uranium with anionic Pbased ligands, such as phosphide, phosphinidiides and phosphinidenes has been studied in more detail in the last years, [28][29][30][31][32] bonding analyses of uranium-phosphine bonds have not been reported to the best of the authors knowledge. ...

Electron‐Precise Actinide‐Pnictide (An‐Pn) Bonds Spanning Non‐Metal, Metalloid, and Metal Combinations (An = U, Th; Pn = P, As, Sb, Bi)

... U nexpected properties, structures, and reactivities emerge in heavy elements because their high nuclear charge accelerates surrounding electrons to relativistic speeds, altering orbital shapes and energies and the nature of chemical bonds 1 . This in turn, leads to abrupt changes in behavior between neighboring elements 2-8 and a breakdown of simple descriptions of electronic structure that can be used to explain emerging properties 1,[9][10][11][12][13][14][15][16][17] . Examples of these discontinuities include the large volume expansion between α-Pu and α-Am, and the corresponding localization of 5f electrons that leads to superconductivity in α-Am at low temperatures 18 , as well as the diminishment of redox activity that occurs at this same juncture in the actinide series 19 . ...

Electron‐Precise Actinide‐Pnictide (An‐Pn) Bonds Spanning Non‐Metal, Metalloid, and Metal Combinations (An = U, Th; Pn = P, As, Sb, Bi)

Angewandte Chemie

... 163 The hybrid alkyl/cyclopentadienyl ''constrained-geometry'' proligand (149) was synthesized from in-situ generated [(Me 3 Si)CH(PMe 2 (BH 3 ))]Li and Me 2 SiCl 2 followed by the reaction with Cp * Li; (149) was isolated from the reaction mixture as one regioisomer. 164 New geminally bonded intramolecular donor-acceptor systems (150) and (151) ...

A Suite of Sterically-Demanding Hybrid Alkyl/Cyclopentadienyl Ligands
  • Citing Article
  • October 2017

Organometallics

... [6] However, due to the reactive triplet ground state, unsaturated valence shell, and relatively large size of heavier Pn ions, previous studies were mainly restricted to spectroscopic species, [7] or a small number of bridging PnH stabilised by transition metals. [8] Structurally authenticated molecules with terminal (i.e. the PnR group is bound to only one metal) PnH groups are sparse across the whole Periodic Table, with a handful of terminal parent phosphinidene (M=PH) compounds known for p-, [9] d-, [10] and f-blocks. [11] Terminal arsinidene (M=AsR) congeners have emerged for p- [12] and f-block [13] derivatives recently, but M=AsH remains unknown for the d-block; indeed, only five M=AsR d-block complexes have been crystallographically characterised in the past 28 years. ...

Terminal Parent Phosphanide and Phosphinidene Complexes of Zirconium(IV)

Angewandte Chemie

... 119,120 Liddle also presented a follow-up paper on the analogous Zr complex (33), which reacts in a similar way to the uranium and thorium analogues (forming the respective phosphanide and phosphinidene compounds, 34 and 35, Scheme 23c). 121 We can draw links to possible onward organic Scheme 22. Schrock and Co-workers Have Undertaken a Systematic Study on the Coordination Chemistry of Molybdenum and Tungsten Amides, Phosphides, and Arsenides Scheme 23. (a, b) Liddle's Studies on the Phosphanide and Phosphinidene Chemistry of the Actinides; a (c) Studies on the Analogous Zr Complex a Na(12c4) 2 cations omitted for clarity, and 12-crown-4 (12c4) and benzo-15-crown-5 abbreviated for clarity (b15c5). ...

Terminal Parent Phosphanide and Phosphinidene Complexes of Zirconium(IV)

... We previously reported parent phosphanide [61][62][63] , arsenide [63][64][65][66] , phosphinidene [61][62][63]67 , arsinidene [63][64][65] , phosphido 62,67 and arsenido [64][65][66] complexes of uranium and thorium supported by {N(CH 2 CH 2 NR) 3 } 3− triamidoamine ligands (Tren R ; R = SiPr i 3 , tri-isopropylsilyl, TIPS, or SiCy 3 , tri-cyclohexylsilyl, TCHS). Studying parent complexes is desirable because a H substituent is the simplest, most electronically innocent substituent to have, and from a main group perspective provides fundamental, metal-stabilized parent fragments for study. ...

Triamidoamine thorium-arsenic complexes with parent arsenide, arsinidiide and arsenido structural motifs

... We previously reported parent phosphanide 61-63 , arsenide 63-66 , phosphinidene [61][62][63]67 , arsinidene 63-65 , phosphido 62,67 and arsenido 64-66 complexes of uranium and thorium supported by {N(CH 2 CH 2 NR) 3 } 3− triamidoamine ligands (Tren R ; R = SiPr i 3 , tri-isopropylsilyl, TIPS, or SiCy 3 , tri-cyclohexylsilyl, TCHS). Studying parent complexes is desirable because a H substituent is the simplest, most electronically innocent substituent to have, and from a main group perspective provides fundamental, metal-stabilized parent fragments for study. ...

Thorium–phosphorus triamidoamine complexes containing Th–P single- and multiple-bond interactions

... [1][2][3] This is due to a combination of: (i) three amide centres that are covalent σ-and dative π-donors; (ii) the presence of a tertiary amine that can modulate the strength of its dative σ-donation to a coordinated An-ion as required by the metal and also engage in inverse-trans-influence (ITI) binding; (iii) being a quadridentate ligand that maximises kinetic and thermodynamic stability of the resulting An-complexes; (iv) varied N-silyl substitution patterns that can systematically tune the steric and electronic properties of the Tren R scaffold, including producing a well-defined pocket at the coordinated An-metal with which to stabilise novel linkages or reactivity. It is therefore the case that Tren R -ligands have supported novel Anligand multiple bonds, [4][5][6][7][8][9][10][11][12][13][14][15] An-metal bonds, [16][17][18][19][20][21] novel main group moieties, [22][23][24][25][26][27][28][29][30][31] uranyl activation, [32,33] small molecule activation, [34][35][36][37][38][39][40][41][42][43] single-molecule magnetism and electronic communication, [44,45] novel photochemistry, [46] insight into fundamental f-block phenomena such as disproportionation, the ITI, pushing-from-below, [47][48][49][50][51] and NMR chemical shift anisotropy covalency studies. [52,53] The above advances have all been achieved utilising a relatively small range of silyl Tren R ligands, including trimethylsilyl (Tren TMS ), dimethyl-tert-butyl-silyl (Tren DMBS ), tri-iso-propylsilyl (Tren TIPS ), tricyclohexyl-silyl (Tren TCHS ), and triphenyl-silyl (Tren TPS ). ...

Uranium-halide and -azide derivatives of the sterically demanding triamidoamine ligand TrenTPS [TrenTPS=(N(CH2CH2NSiPh3)3)3-]
  • Citing Article
  • July 2016

Polyhedron