Portrait of Dr Ewan Clark

Dr Ewan Clark

Senior Lecturer in Chemistry

About

Dr Ewan Clark completed his MSci at the University of Cambridge in 2004, working with Dr Alex Hopkins on the synthetic organic applications of silyl anions. He remained in Cambridge for his PhD, this time with Professor Jeremy Rawson (now at the University of Windsor), working on developing new, modular synthetic routes to sulphur/nitrogen heterocyclic systems and their co-ordination chemistry with first row transition metals. 

After submitting his thesis in 2008, Ewan moved to Newcastle University for a post-doctoral position with Dr Keith Izod where he worked on low-valent, heavy tetrelynes (the Ge(II) and Sn(II) analogues of more conventional carbenes) and their stabilisation by donor-functionalised phosphanide ligands. In 2011 he took up a second post-doctoral position with Dr Michael Ingleson at the University of Manchester to study the incorporation of novel main group borocation and carbocation Lewis acids into Frustrated Lewis Pairs for small molecule and sigma-bond activation. Ewan joined the School of Physical Sciences at Kent in 2014, taking the position of Lecturer in Chemistry.

Research interests

Dr Ewan Clark’s research interests lie in uncovering and exploiting the properties, both chemical and material, of main group elements with unconventional oxidation states or charges. In particular, the majority of conventional open shell (ie radical) chemistry or chemistry involving well-defined redox cycles is performed using transition metals whose multiple stable oxidation states and core-like valence orbitals predispose them for these functions. Nevertheless, this chemistry is not unique to the transition metals and opening up the analogous p-block chemistry will develop not only new and complementary applications, but also show hitherto unobserved properties.

The group expertise lies in the synthesis and handling of highly reactive compounds using inert atmosphere techniques and their characterisation in both solid state and solution by diffraction and spectroscopic methods.  These studies are then coupled with computational studies to derive complete structure-property relationships which in turn allow both a deeper understanding of the fundamental behaviour of the systems and form an iterative feedback loop to design and deliver compounds with tailored properties.  Current research topics are focused towards phosphorus chemistry and include the following.

Pnictogen radicals

Stable, neutral main-group radicals have been known for many years, dating back to 1900 when Gomberg first isolated and identified the C(III) radical which now bears his name. Since then, many more classes have been discovered but these are primarily derived from the top right of the periodic table, using the lighter elements.  As the periodic table is descended, the number of radicals falls off dramatically, and there are only a handful of structurally characterised phosphorus radicals known.  Incorporating heavier elements into radical systems has a dramatic effect on their properties, as the more radially diffuse orbitals of the heavier element allow a greater array of interactions in the solid state or in aggregated species.  Work is focused on developing new P(II) and P(IV) radicals, and their heavier congeners, both as materials in their own right and for use as ligands to transition metals to generate clusters with combined metal-radical magnetic properties.

Isoelectronic applications of cationic fragments for fluorescent materials

The isoelectronic analogy is a potent tool in synthetic chemistry as it allows many properties to be conserved (shape chief among them) while allowing the tailoring of others when developing derivatives. The [RP(III)]+ fragment is isoelectronic to [R2B], a ubiquitous moiety in fluorescent materials used to both tailor band gaps and impart structural rigidity and thus increase fluorescence quantum yields. The incorporation of a heavier element is predicted to decrease the bandgap relative to the analogous boron system, and thus give red-shifted emission and absorption spectra, crucial for applications in biomedical imaging and in light-harvesting for optoelectronic purposes, while the positive charge will result in different solubility profiles and solid-state aggregation which will diversify options in device manufacture techniques.

Main group redox catalysis

The stable oxidation state of many main group elements is inextricably tied to the co-ordination environment and geometry, with, for instance, bulky substituents destabilising phosphines with respect to phosphoranes (eg tBu3P is so strained and predisposed to oxidation that it ignites in air, while the less constricted Ph3P oxidises so slowly that it may be conveniently stored on the bench) Careful ligand design allows us to enforce geometries intermediate between those favoured by P(III) and P(V) and thus facilitate redox shuffling between the two states.  In this way, phosphorus may be induced to behave in a manner analogous to a transition metal and work is underway to exploit this in the development of new, metal-free hydrogenation catalysts.

Teaching

Ewan has taught a wide range of inorganic and physical courses over the years, and has extensive experience in both laboratory demonstration and one-on-one training in advanced synthetic techniques.

Publications

Article

  • Beqiri, D., Cascos- JiménezV., Roberts-Watts, J., Clark, E., Bousquet, E., Bristowe, N. and McCabe, E. (2019). Tuning octahedral tilts and the polar nature of A-site deficient perovskites. Chemical Communications [Online] 55:2609-2612. Available at: http://dx.doi.org/10.1039/C8CC10126D.
    Herein we highlight the ability to tune the structural chemistry of A-site deficient perovskite materials Ln1/3NbO3. Computational studies explore the balance between proper and hybrid-improper mechanisms for polar behaviour in these systems.
  • Pearce, K., Borys, A., Clark, E. and Shepherd, H. (2018). Exploring the reactivity of donor-stabilised phosphenium cations: Lewis acid catalysed reduction of chlorophosphanes by silanes. Inorganic Chemistry [Online] 57:11530-11536. Available at: http://dx.doi.org/10.1021/acs.inorgchem.8b01578.
    Phosphane-stabilised phosphenium cations react with silanes to effect either reduction to primary or secondary
    phosphanes, or formation of P-P bonded species depending upon counter-anion. This operates for in situ generated phosphenium
    cations, allowing catalytic reduction of P(III)-Cl bonds in the absence of strong reducing agents. Anion and substituent dependence
    studies have allowed insight into the competing mechanisms involved.
  • BalónováB., Martir, D., Clark, E., Shepherd, H., Zysman-Colman, E. and Blight, B. (2018). Influencing the Optoelectronic Properties of a Heteroleptic Iridium Complex by Second-Sphere H-Bonding Interactions. Inorganic Chemistry [Online] 57:8581-8587. Available at: https://doi.org/10.1021/acs.inorgchem.8b01326.
    The use of a new second-sphere coordination methodology for emission color tuning of iridium complexes is presented. We demonstrate that a complimentary H-bonding guest molecule binding through contiguous triple H-bonding interactions can induce a shift in the emission of the iridium complex from green to blue without the need to alter the ligand structure around the metal centre, while simultaneously increasing the photoluminescence quantum yield in solution. The association constant for this host-guest interaction was determined to be Ka = 4.3 x 103 M-1 in a solution of 2% dimethylsulfoxide in chloroform by UV-Vis titration analysis and the impact of the hydrogen bonding interaction further probed by photoluminescence, electrochemical, and computational methods. Our findings suggest that directed self-assemblies are an effective approach to influencing emission properties of phosphorescent iridium (III) complexes.
  • White, L., Tyuleva, S., Wilson, B., Shepherd, H., Ng, K., Holder, S., Clark, E. and Hiscock, J. (2018). Towards the prediction of global solution state properties for hydrogen bonded, self-associating amphiphiles. Chemistry - A European Journal [Online] 24:7761-7773. Available at: https://doi.org/10.1002/chem.201801280.
    Through this extensive structure-property study we show
    that critical micelle concentration correlates with self-associative
    hydrogen bond complex formation constant, when combined with
    outputs from low level, widely accessible, computational models.
    Herein, we bring together a series of 39 structurally related
    molecules obtained through stepwise variation of a hydrogen bond
    donor-acceptor amphiphilic salt. The self-associative and
    corresponding global properties for this family of compounds have
    been studied in the gas, solid and solution states. Within the solution
    state we have shown the type of self-associated structure present to
    be solvent dependent. In DMSO, this class of compound show a
    preference for hydrogen bonded dimer formation, however moving
    into aqueous solutions the same compounds are found to form
    larger self-associated aggregates. This observation has allowed us
    the unique opportunity to investigate and begin to predict selfassociation
    events at both the molecular and extended aggregate
    level.
  • Hiscock, J., Bustone, G. and Clark, E. (2017). Decontamination and Remediation of the Sulfur Mustard Simulant CEES with “Off-the-Shelf” Reagents in Solution and Gel States: A Proof-of-Concept Study. ChemistryOpen [Online] 6:497-500. Available at: https://doi.org/10.1002/open.201700063.
    The decontamination and remediation of sulfur mustard chemical warfare agents remains an ongoing challenge. Herein, we report the use of “off-the-shelf” metal salts alongside commercially available peroxides to catalyze the degradation of the simulant 2-chloroethyl ethyl sulfide (CEES) in solution and encapsulated within a supramolecular gel.
  • Clark, E. and Borys, A. (2017). Adducts of Donor—Functionalized Ar3P with the Soft Lewis—Acid I2: Probing Simultaneous Lewis Acidity and Basicity at Internally Solvated P(III) Centers. Inorganic Chemistry [Online] 56:4622-4634. Available at: http://dx.doi.org/10.1021/acs.inorgchem.7b00278.
    The enhancement of donor strength of ortho—functionalized triarylphosphanes is shown to occur via different mechanisms for O- and N- donor substituents, with internal solvation of the phosphorus center observed for N—- donors. Nevertheless, the steric congestion
    about the P— center is shown to significantly oppose the increase in donor ability, leading to donation weaker than that expected. A series of mono- and bis-aryl -substituted Ar3PI2 adducts—[(Ph3—-?n (o-OMe-C6H4) n PI2, Ph3—-?n (o-NMe2-C6H4) n PI2, Ph3—-?n (o-CH2NMe2-C6H4) n PI2 (n =—1——,21, 2—)]) have been synthesized via the 1:1 reaction of donor-functionalized phosphanes with diiodine. These soft Lewis acid/base adducts exhibit apparent internal solvation of the donor phosphorus by the pendant donor moieties, giving rise to five- or six-coordinate phosphorus atoms acting as both Lewis base and Lewis acid; the first neutral six-coordinate simultaneous P(III) Lewis acid and Lewis base adduct is reported. Single -crystal X-ray diffraction studies reveal unexpectedly weak donor strength for one of the phosphanes, indicating significant steric hindrance as a consequence of internal solvation. Crystallographic interrogation of the corresponding iodophosphonium salts [Ar3PI]X (X = I3, BArF) shows that the cationic complexes experience a still greater influence of the steric bulk of the donor moieties than their neutral precursors. The steric and electronic contributions to bonding have been analyzed through computational studies, determining the factors governing the basicity of these donor—functionalized phosphanes, and show that enhancement of P-centered donor strength occurs by conjugation of lone pairs through the arene rings for oxygen substituents, and via internal solvation for the nitrogen donors.
  • Lawrence, E., Clark, E., Curless, L., Courtney, J., Blagg, R., Ingleson, M. and Wildgoose, G. (2016). Metal-free electrocatalytic hydrogen oxidation using frustrated Lewis pairs and carbon-based Lewis acids. Chemical Science [Online] 7:2537-2543. Available at: http://dx.doi.org/10.1039/C5SC04564A.
    Whilst hydrogen is a potentially clean fuel for energy storage and utilisation technologies, its conversion to electricity comes at a high energetic cost. This demands the use of rare and expensive precious metal electrocatalysts. Electrochemical-frustrated Lewis pairs offer a metal-free, CO tolerant pathway to the electrocatalysis of hydrogen oxidation. They function by combining the hydrogen-activating ability of frustrated Lewis pairs (FLPs) with electrochemical oxidation of the resultant hydride. Here we present an electrochemical–FLP approach that utilises two different Lewis acids – a carbon-based N-methylacridinium cation that possesses excellent electrochemical attributes, and a borane that exhibits fast hydrogen cleavage kinetics and functions as a “hydride shuttle”. This synergistic interaction provides a system that is electrocatalytic with respect to the carbon-based Lewis acid, decreases the required potential for hydrogen oxidation by 1 V, and can be recycled multiple times.
  • Clark, E., Borys, A. and Pearce, K. (2016). Donor-substituted phosphanes – surprisingly weak Lewis donors for phosphenium cation stabilisation. Dalton Transactions [Online]. Available at: http://dx.doi.org/10.1039/C6DT03478K.
    Paradoxically, N- and O- donor substituted tri-arylphosphanes are shown to be weaker donors than PPh3 when binding the soft Lewis acid moiety [PPh2]+. This arises from internal solvation and rehybridisation at phosphorus, precluding chelation and increasing steric demand, in direct contrast to coordination modes observed for metal complexes.
  • Dunsford, J., Clark, E. and Ingleson, M. (2015). Direct C(sp2)-C(sp3) cross-coupling of diaryl zinc reagents with benzylic, primary, secondary, and tertiary alkyl halides. Angewandte Chemie International Edition [Online] 54:5688-5692. Available at: http://www.dx.doi.org/10.1002/anie.201411403.
    The direct C(sp2)-C(sp3) cross-coupling of diaryl zinc reagents with benzylic, primary, secondary, and tertiary alkyl halides proceeded in the absence of coordinating ethereal solvents at ambient temperature without the addition of a catalyst. The C(sp2)-C(sp3) cross-coupling showed excellent functional-group tolerance, and products were isolated in high yields, generally without the requirement for purification by chromatography. This process represents an expedient, operationally simple method for the construction of new C(sp2)-C(sp3) bonds. Zinc and you'll miss it! Direct C(sp2)-C(sp3) cross-coupling of diaryl zinc reagents with alkyl halides proceeded rapidly at ambient temperature without a coordinating ethereal solvent or an added catalyst (see scheme). This versatile, operationally simple approach to C(sp2)-C(sp3) bond formation enables the expedient construction of a diverse array of carbon-based structural motifs. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Crossley, D., Cade, I., Clark, E., Escande, A., Humphries, M., King, S., Vitorica-Yrezabal, I., Ingleson, M. and Turner, M. (2015). Enhancing electron affinity and tuning band gap in donor–acceptor organic semiconductors by benzothiadiazole directed C–H borylation. Chemical Science [Online] 6:5144-5151. Available at: http://doi.org/10.1039/c5sc01800e.
  • Dunsford, J., Clark, E. and Ingleson, M. (2015). Highly nucleophilic dipropanolamine chelated boron reagents for aryl-transmetallation to iron complexes. Dalton Transactions [Online] 44:20577-20583. Available at: http://doi.org/10.1039/c5dt03835a.
    New aryl- and heteroarylboronate esters chelated by dipropanolamine are synthesised directly from boronic acids. The corresponding anionic borates are readily accessible by deprotonation and demonstrate an increase in hydrocarbyl nucleophilicity in comparison to other common borates. The new borates proved competent for magnesium or zinc additive-free, direct boron-to-iron hydrocarbyl transmetallations with well-defined iron(II) (pre)catalysts. The application of the new borate reagents in representative Csp2–Csp3 cross-coupling led to almost exclusive homocoupling unless coupling is performed in the presence of a zinc additive.
  • Curless, L., Clark, E., Cid, J., Del Grosso, A. and Ingleson, M. (2015). Complete reductive cleavage of CO facilitated by highly electrophilic borocations. Chemical Communications [Online] 51:10903-10906. Available at: http://www.dx.doi.org/10.1039/c5cc03504j.
    The addition of CO to [((R3N)BH2)2(?-H)][B(C6F5)4] leads to formation of trimethylboroxine ((MeBO)3) and [(R3N)2BH2][B(C6F5)4]. When R = Et, [(Et3N)H2B(?-O)B(CH3)NEt3][B(C6F5)4], is isolated and demonstrated to be an intermediate in the formation of (MeBO)3. © 2015 The Royal Society of Chemistry.
  • Clark, E., Hayward, J., Leontowicz, B., Anwar, M., Pilkington, M. and Rawson, J. (2015). Copper-promoted aerial oxidation of benzothiadiazines: Access to benzothiadiazine S-oxide heterocycles. Dalton Transactions [Online] 44:2071-2074. Available at: http://www.dx.doi.org/10.1039/c4dt03467h.
    CuII-promoted aerial oxidation of a series of benzothiadiazines (1) under ambient conditions affords the first structurally characterised examples of thiadiazine S-oxides (2). The isolation of the homoleptic CuII 3-(2?-pyridyl)benzothiadiazide-S-oxide complex provides insight into the reaction mechanism.
  • Clark, E., Anwar, M., Leontowicz, B., Beldjoudi, Y., Hayward, J., Chan, W., Gavey, E., Pilkington, M., Zysman-Colman, E. and Rawson, J. (2014). Synthesis and characterisation of first row transition metal complexes of functionalized 1,2,4-benzothiadiazines. Dalton Transactions [Online] 43:12996-13005. Available at: http://www.dx.doi.org/10.1039/c4dt01413h.
    Reaction of the novel ligand 3-(2?-pyridyl)-benzo-1,2,4-thiadiazine (L) with the transition metal chloride salts MCl2·xH2O (MII = Mn, Fe, Co, Cu and Zn) in a 2 : 1 mole ratio afforded the mononuclear octahedral (high spin) complexes L2MCl2 (1a–1e respectively) in which L binds in a chelate fashion via N(2) and the pyridyl N atoms. In the case of CuCl2 the intermediate 1 : 1 four-coordinate complex LCuCl2 (2) was also isolated which adopts a polymeric structure with pseudo-square planar molecules linked via long CuS contacts (dCuS = 2.938(1) Å) in the apical position. In the presence of non-interacting ions, 3 : 1 complexes are isolated, exemplified by the reaction of L with Fe(CF3SO3)2 in a 3 : 1 ratio which affords the low spin complex [L3Fe][CF3SO3]2 (3). Reaction of L with VCl3 in a 2 : 1 mole ratio under aerobic conditions afforded the vanadyl complex [L2V([double bond, length as m-dash]O)Cl][Cl] (4).
  • Clark, E., Hayward, J., Leontowicz, B., Eisler, D. and Rawson, J. (2014). Syntheses of, and structural studies on, benzo-fused 1,2,4-thiadiazines. CrystEngComm [Online] 16:1755-1762. Available at: http://www.dx.doi.org/10.1039/c3ce42205d.
    The syntheses of nine benzo-fused-1,2,4-thiadizines are reported. The use of microwave synthesis has been shown to afford high yields and short reaction times in several key reaction steps. The molecular geometries of these heterocycles are discussed and their solid state packing motifs reveal a strong tendency for the N–H group to form hydrogen bonded chains.
  • Clark, E. and Ingleson, M. (2014). N-Methylacridinium Salts: Carbon Lewis Acids in Frustrated Lewis Pairs for ?-Bond Activation and Catalytic Reductions. Angewandte Chemie International Edition [Online] 53:11306-11309. Available at: http://www.dx.doi.org/10.1002/anie.201406122.
    N-methylacridinium salts are Lewis acids with high hydride ion affinity but low oxophilicity. The cation forms a Lewis adduct with 4-(N,N-dimethylamino)pyridine but a frustrated Lewis pair (FLP) with the weaker base 2,6-lutidine which activates H2, even in the presence of H2O. Anion effects dominate reactivity, with both solubility and rate of H2 cleavage showing marked anion dependency. With the optimal anion, a N-methylacridinium salt catalyzes the reductive transfer hydrogenation and hydrosilylation of aldimines through amine–boranes and silanes, respectively. Furthermore, the same salt is active for the catalytic dehydrosilylation of alcohols (primary, secondary, tertiary, and ArOH) by silanes with no observable over-reduction to the alkanes.
  • Izod, K., Clark, E., Foster, P., Percival, R., Riddlestone, I., Clegg, W. and Harrington, R. (2013). Light-induced rearrangement of thioether-substituted phosphanide ligands : Scope and limitations of a remarkable isomerization. Chemistry - A European Journal [Online] 19:6094-6107. Available at: http://www.dx.doi.org/10.1002/chem.201203918.
    Treatment of the thioether-substituted secondary phosphanes R 2PH(C6H4-2-SR1) [R 2=(Me3Si)2CH, R1=Me (1 PH), iPr (2PH), Ph (3PH); R2=tBu, R1=Me (4PH); R2=Ph, R1=Me (5 PH)] with nBuLi yields the corresponding lithium phosphanides, which were isolated as their THF (1-5Pa) and tmeda (1-5Pb) adducts. Solid-state structures were obtained for the adducts [R 2P(C6H4-2-SR1)]Li(L)n [R2=(Me3Si)2CH, R1=nPr, (L) n=tmeda (2Pb); R2=(Me3Si) 2CH, R1=Ph, (L)n=tmeda (3Pb); R 2=Ph, R1=Me, (L)n=(THF)1.33 (5 Pa); R2=Ph, R1=Me, (L)n=([12]crown- 4)2 (5Pc)]. Treatment of 1PH with either PhCH2Na or PhCH2K yields the heavier alkali metal complexes [{(Me3Si)2CH}P(C6H 4-2-SMe)]M(THF)n [M=Na (1Pd), K (1 Pe)]. With the exception of 2Pa and 2Pb, photolysis of these complexes with white light proceeds rapidly to give the thiolate species [R2P(R1)(C6H 4-2-S)]M(L)n [M=Li, L=THF (1Sa, 3 Sa-5Sa); M=Li, L=tmeda (1Sb, 3 Sb-5Sb); M=Na, L=THF (1Sd); M=K, L=THF (1 Se)] as the sole products. The compounds 3Sa and 4 Sa may be desolvated to give the cyclic oligomers [[{(Me 3Si)2CH}P(Ph)(C6H4-2-S)]Li] 6 ((3S)6) and [[tBuP(Me)(C6H 4-2-S)]Li]8 ((4S)8), respectively. A mechanistic study reveals that the phosphanide-thiolate rearrangement proceeds by intramolecular nucleophilic attack of the phosphanide center at the carbon atom of the substituent at sulfur. For 2Pa/2Pb, competing intramolecular β-deprotonation of the n-propyl substituent results in the elimination of propene and the formation of the phosphanide-thiolate dianion [{(Me3Si)2CH}P(C6H4-2-S)] 2-. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Clark, E. and Ingleson, M. (2013). [(acridine)BCl2]+: A borenium cation that is a strong boron- and carbon-based Lewis acid. Organometallics [Online] 32:6712-6717. Available at: http://www.dx.doi.org/10.1021/om400463r.
    [(acridine)BCl2][AlCl4] was synthesized by halide abstraction from (acridine)BCl3 with AlCl3. The hydride ion affinity of the C9 position in [(acridine)BCl2]+ was calculated to be 14 kcal mol–1 greater than that at boron. [(acridine)BCl2][AlCl4] reacts with 1 equiv of acridine to form the strained boronium cation [(acridine)2BCl2][AlCl4] and with P(mesityl)3 by photoinduced one-electron transfer to form the 9,9?-biacridane moiety by radical coupling. A stable frustrated Lewis pair (FLP) was formed on combining [(acridine)BCl2][AlCl4] and 2,4,6-tri-tert-butylpyridine (TBP), which heterolytically activated H2 at 100 °C. The ultimate location of the hydride from H2 activation was the C9 position of acridine and not boron. Carbon Lewis acid based reactivity also occurred when thieno[3,2-b]thiophene was added to the [(acridine)BCl2][AlCl4]/TBP FLP or to [(acridine)2BCl2][AlCl4], with arylation of acridine at C9 observed for both.
  • Curless, L., Clark, E., Dunsford, J. and Ingleson, M. (2013). E-H (E = R3Si or H) bond activation by B(C6F 5)3 and heteroarenes; Competitive dehydrosilylation, hydrosilylation and hydrogenation. Chemical Communications [Online] 50:5270-5272. Available at: http://www.dx.doi.org/10.1039/c3cc47372d.
    In the presence of B(C6F5)3 five-membered heteroarenes undergo dehydrosilylation and hydrosilylation with silanes. The former, favoured on addition of a weak base, produces H2 as a by-product making the process catalytic in B(C6F5) 3 but also enabling competitive heteroarene hydrogenation. © the Partner Organisations 2014.
  • Howe, K., Clark, E., Bowen, J. and Kendall, K. (2013). A novel water-based cathode ink formulation. International Journal of Hydrogen Energy [Online] 38:1731-1736. Available at: http://www.dx.doi.org/10.1016/j.ijhydene.2012.08.105.
    A new cathode ink for a solid oxide fuel cell has been developed (patent pending: UK Patent Application Number 1107672.6). A novel, water-based formulation was created and tested against the standard, in-house, acetone-based ink recipe. Poly(N-VinylPyrrolidone) (PVP) was selected as a suitable dispersant and Poly(Vinyl Alcohol) (PVA) as the binder and a range of chain lengths and quantities was tested. The PVA content was adjusted to optimise adhesion of the two layers, as some delamination was observed with the first attempt. Various PVP chain lengths and quantities were tested to determine the effect on ink dispersion, and hence cathode structure and porosity. The electrical performance was tested and found to be favourably comparable with the in-house recipe, giving a marginally higher peak power density of 0.48 W/cm2.Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
  • Clark, E., Del Grosso, A. and Ingleson, M. (2013). The hydride-ion affinity of borenium cations and their propensity to activate H2 in frustrated Lewis pairs. Chemistry - A European Journal [Online] 19:2462-2466. Available at: http://www.dx.doi.org/10.1002/chem.201203318.
    A range of frustrated Lewis pairs (FLPs) containing borenium cations have been synthesised. The catechol (Cat)-ligated borenium cation [CatB(PtBu3)]+ has a lower hydride-ion affinity (HIA) than B(C6F5)3. This resulted in H2 activation being energetically unfavourable in a FLP with the strong base PtBu3. However, ligand disproportionation of CatBH(PtBu3) at 100?°C enabled trapping of H2 activation products. DFT calculations at the M06-2X/6-311G(d,p)/PCM (CH2Cl2) level revealed that replacing catechol with chlorides significantly increases the chloride-ion affinity (CIA) and HIA. Dichloro–borenium cations, [Cl2B(amine)]+, were calculated to have considerably greater HIA than B(C6F5)3. Control reactions confirmed that the HIA calculations can be used to successfully predict hydride-transfer reactivity between borenium cations and neutral boranes. The borenium cations [Y(Cl)B(2,6-lutidine)]+ (Y=Cl or Ph) form FLPs with P(mesityl)3 that undergo slow deprotonation of an ortho-methyl of lutidine at 20?°C to form the four-membered boracycles [(CH2{NC5H3Me})B(Cl)Y] and [HPMes3]+. When equimolar [Y(Cl)B(2,6-lutidine)]+/P(mesityl)3 was heated under H2 (4?atm), heterolytic cleavage of dihydrogen was competitive with boracycle formation.
  • Lawson, J., Clark, E., Cade, I., Solomon, S. and Ingleson, M. (2013). Haloboration of internal alkynes with boronium and borenium cations as a route to tetrasubstituted alkenes. Angewandte Chemie International Edition [Online] 52:7518-7522. Available at: http://www.dx.doi.org/10.1002/anie.201302609.
    Hail boration! 2-Dimethylaminopyridine-ligated dihaloborocations [X 2B(2-DMAP)]+ with a strained four-membered boracycle were used for the haloboration of terminal and dialkyl internal alkynes (see scheme). Esterification then provided vinyl boronate esters as useful precursors to tetrasubstituted alkenes. Following mechanistic studies, the scope of the haloboration was expanded simply by variation of the amine. Pin=2,3-dimethyl-2, 3-butanedioxy. © 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of Creative Commons the Attribution Non-Commercial NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
  • Solomon, S., Del Grosso, A., Clark, E., Bagutski, V., McDouall, J. and Ingleson, M. (2012). Reactivity of Lewis acid activated diaza- and dithiaboroles in electrophilic arene borylation. Organometallics [Online] 31:1908-1916. Available at: http://www.dx.doi.org/10.1021/om201228e.
    Hydride abstraction from N,N�-bis(adamantyl)-1-hydrido-1,3,2- benzodiazaborole with catalytic [Ph 3C][closo-CB 11H 6Br 6] resulted in a low yield of arene borylation and a major product derived from migration of both adamantyl groups to the arene backbone. In contrast, the related aryl-substituted diazaborole N,N�-(2,6-diisopropylphenyl)-1-bromo-1,3,2-diazaborole did not borylate benzene or toluene, being resistant to halide abstraction even with strong halide acceptors: e.g., [Et 3Si][closo-CB 11H 6Br 6]. The reactivity disparity arises from greater steric shielding of the boron p z orbital in the 2,6-diisopropylphenyl- substituted diazaboroles. Boron electrophiles derived from 1-chloro-1,3,2- benzodithiaborole ((CatS 2)BCl) are active for arene borylation, displaying reactivity between that of catecholato- and dichloro-boron electrophiles. [(CatS 2)B(NEt 3)][AlCl 4] is significantly less prone to nucleophile-induced transfer of halide from [AlCl 4] to boron compared to catecholato and dichloro borocations, enabling it to borylate arenes containing nucleophilic -NMe 2 moieties in high conversion (e.g., N,N,4-trimethylaniline and 1,8-bis(dimethylamino) naphthalene). Calculations indicate that the magnitude of positive charge at boron is a key factor in determining the propensity of chloride transfer from [AlCl 4] to boron on addition of a nucleophile. © 2012 American Chemical Society.
  • Izod, K., Clark, E., Clegg, W. and Harrington, R. (2012). Hypervalent sulfur-functionalized diphosphagermylene and diphosphastannylene compounds. Organometallics [Online] 31:246-255. Available at: http://www.dx.doi.org/10.1021/om2008327.
    The reaction between either GeCl 2(1,4-dioxane) or SnCl 2 and 2 equiv of the lithium phosphide [{(Me 3Si) 2CH}P(C 6H 4-2-SMe)]Li(tmeda) gives the corresponding diphosphatetrylenes [{(Me 3Si) 2CH}P(C 6H 4-2-SMe)] 2E [E = Ge (10), Sn (11)] in good yields. Both 10 and 11 crystallize as discrete monomers in which the Ge and Sn atoms are coordinated by both P and S atoms. Although 10 and 11 crystallize as racemic mixtures of the RR and SS diastereomers, variable-temperature NMR experiments suggest that, in solution, these compounds are in dynamic equilibrium with small amounts of the corresponding RS and SR diastereomers. DFT calculations reveal that the lowest-energy minima for both 10 and 11 possess rac stereochemistry; two higher-energy minima were located for each of 10 and 11, both of which have meso stereochemistry. The two calculated meso diastereomers differ in the location of the sulfur and phosphorus substituents within the pseudo-trigonalbipyramidal structures. Both 10 and 11 decompose on exposure to light, generating the diphosphine {(Me 3Si) 2CH}(C 6H 4-2-SMe)P-P(C 6H 4-2-SMe){CH(SiMe 3) 2} (14) as the major product. © 2011 American Chemical Society.
  • Del Grosso, A., Clark, E., Montoute, N. and Ingleson, M. (2012). Tricationic analogues of boroxines and polyborate anions. Chemical Communications [Online] 48:7589-7591. Available at: http://www.dx.doi.org/10.1039/c2cc32605a.
    Addition of E 2O (E = Me 3Si or H) to [(pyridyl)BX 2][AlX 4] (X = Cl or Br) and subsequent heating produced the unprecedented trications [(2,6-lutidine) 4B 5O 6] 3+ and [(pyridine) 4B 3O 3] 3+. © 2012 The Royal Society of Chemistry.
  • Izod, K., Clark, E. and Stewart, J. (2011). Edge-versus vertex-inversion at trigonal pyramidal ge(II) centers-a new aromatic anchimerically assisted edge-inversion mechanism. Inorganic Chemistry [Online] 50:3651-3661. Available at: http://www.dx.doi.org/10.1021/ic200012v.
    Theoretical calculations reveal that the model phosphagermylenes {(Me)P(C6H4-2-CH2NMe2)}GeX [X = F (1F), Cl (1Cl), Br (1Br), H (1H), Me (1Me)], which are chiral at both the phosphorus and pyramidal germanium(II) centers, may be subject to multiple inversion pathways which result in interconversion between enantiomers/diastereomers. Inversion via a classical vertex-inversion process (through a trigonal planar transition state) is observed for the phosphorus center in all compounds and for the germanium center in 1H, although this latter process has a very high barrier to inversion (221.6 kJ mol?1); the barriers to vertex-inversion at phosphorus increase with decreasing electronegativity of the substituent X. Transition states corresponding to edge-inversion at germanium (via a T-shaped transition state) were located for all five compounds; for each compound two different arrangements of the substituent atoms [N and X axial (1XN?X) or P and X axial (1XP?X)] are possible, and two distinct transition states were located for each of these arrangements. In the first of these (1XN?XPlanar and 1XP?XPlanar), inversion at germanium is accompanied by simultaneous planarization at phosphorus; these transition states are stabilized by p??p? interactions between the phosphorus lone pair and the vacant pz-orbital at germanium. In the alternative transition states (1XN?XFolded and 1XP?XFolded), the phosphorus atoms remain pyramidal and inversion at germanium is accompanied by folding of the phosphide ligand such that there are short contacts between germanium and one of the ipso-carbon atoms of the aromatic ring. These transition states appear to be stabilized by donation of electron density from the ?-system of the aromatic rings into the vacant pz-orbital at germanium. The barriers to inversion via 1XP?XPlanar and 1XP?XFolded are rather high, whereas the barriers to inversion via 1XN?XPlanar and 1XN?XFolded are similar to those for inversion at phosphorus, clearly suggesting that the most important factor in stabilizing these transition states is the ?-withdrawing ability of the substituents, rather than ?-donation of lone pairs or donation of ?-electron density from the aromatic rings into the vacant pz-orbital at germanium.
  • Izod, K., Stewart, J., Clark, E., Clegg, W. and Harrington, R. (2010). Germanium(II) and tin(II) complexes of a sterically demanding phosphanide ligand. Inorganic Chemistry [Online] 49:4698-4707. Available at: http://www.dx.doi.org/10.1021/ic1003534.
    The reaction between PhPCl2 and 1 equiv of RLi, followed by in situ reduction with LiAlH4 and an aqueous workup yields the secondary phosphane PhRPH [R = (Me3Si)2CH]. Treatment of PhRPH with n-BuLi in diethyl ether generates the lithium phosphanide (RPhP)Li(Et 2O)n [15(Et2O)], which may be crystallized as the tetrahydrofuran (THF) adduct (RPhP)Li(THF)3 [15(THF)]. Compound 15(Et2O) reacts with 1 equiv of either NaO-tBu or KO-tBu to give the corresponding sodium and potassium phosphanides (RPhP)Na(Et2O) n (16) and (RPhP)K(Et2O)n (17), which may be crystallized as the amine adducts [(RPhP)Na(tmeda)]2 [16(tmeda)] and [(RPhP)K(pmdeta)]2 [17(pmdeta)], respectively. The reaction between 2 equiv of 17 and GeCl2(1,4-dioxane) gives the dimeric compound [(RPhP)2Ge]2'Et2O (18'Et2O). In contrast, the reaction between 2 equiv of 15 and SnCl2 preferentially gives the ate complex (RPhP)3SnLi(THF) (19) in low yield; 19 is obtained in quantitative yield from the reaction between SnCl2 and 3 equiv of 15. Crystallization of 19 from n-hexane/THF yields the separated ion pair complex [(RPhP)3Sn][Li(THF)4] (19a); exposure of 19a to vacuum for short periods leads to complete conversion to 19. Treatment of GeCl2(1,4-dioxane) with 3 equiv of 15 yields the contact ion pair (RPhP)3GeLi(THF) (20), after crystallization from n-hexane/THF. Compounds 15(THF), 16(tmeda), 17(pmdeta), 18'Et2O, 19a, and 20 have been characterized by elemental analyses, multielement NMR spectroscopy, and X-ray crystallography. While 15(THF) is monomeric, both 16(tmeda) and 17(pmdeta) are dimeric in the solid state. The diphosphagermylene 18'Et2O adopts a dimeric structure in the solid state with a syn,syn-arrangement of the phosphanide ligands, and this structure appears to be preserved in solution. The ate complex 19a crystallizes as a separated ion pair, whereas the analogous ate complex 20 crystallizes as a discrete molecular species. The structures of 19 and 20 are retained in non-donor solvents, while dissolution in THF yields the separated ion pairs 19a and [(RPhP)3Ge][Li(THF)4] (20a). © 2010 American Chemical Society.
  • Clark, E., Melen, R. and Rawson, J. (2010). Oxygen, sulfur, selenium, tellurium and polonium. Annual Reports on the Progress of Chemistry Section A [Online] 106:119-135. Available at: http://www.dx.doi.org/10.1039/b918371j.
    This Chapter reviews the 2009 literature regarding the Group 16 elements, with an emphasis on the synthesis of new metal clusters, heterocycles, reactivity trends and materials properties. © 2010 The Royal Society of Chemistry.
  • Izod, K., Stewart, J., Clark, E., McFarlane, W., Allen, B., Clegg, W. and Harrington, R. (2009). Dynamic behavior of intramolecularly base-stabilized phosphatetrylenes: insights into the inversion processes of trigonal pyramidal geramanium(II) and tin(II) centers. Organometallics [Online] 28:3327-3337. Available at: http://www.dx.doi.org/10.1021/om8011757.
    The reaction between SnCl2 and either 1 or 2 equiv of the lithium salt [{(Me3Si)2CH}(C6H 4-2-CH2NMe2)P]Li gives the heteroleptic compound [{(Me3Si)2CH}(C6H4-2- CH2NMe2)P]SnCl (7) and the homoleptic, intramolecularly base-stabilized diphosphastannylene [{(Me3Si)2CH}(C 6H4-2-CH2NMe2)P]2Sn (8), respectively, in good yields. The solid state structure of 8 shows that the tin(II) center is three-coordinate, bound by the N and P atoms of a chelating phosphide ligand and the P atom of a second phosphide ligand. Both 7 and 8 are highly dynamic in solution. Variable-temperature NMR spectra suggest that compound 7 and its germanium analogue 5 are subject to two distinct dynamic processes in polar solvents, which are attributed to the formation of adducts between either 5 or 7 and the free phosphine {(Me3Si) 2CH}(C6H4-2-CH2NMe2)PH (9) and interconversion between diastereomers of these adducts. Adduct formation is observed only in polar solvents and may be associated with the formation of weakly bound [[{(Me3Si)2CH}(C6H 4-2-CH2NMe2)P]E(L)]+ ··· Cl- ion pairs in solution. The dynamic behavior of 8 has been studied by multielement and variable-temperature NMR experiments; at high temperatures there is rapid equilibrium between diastereomers, but at low temperatures a single diastereomer predominates and exchange between the chelating and terminal phosphide ligands is frozen out. DFT calculations on the model compound {(Me)(C6H4-2-CH 2NMe2)P}SnCl (7a) suggest that epimerization occurs either through a vertex-inversion process at phosphorus [Einv) 65.3 kJ mol-1] or an edge-inversion process at tin [Einv) 141.0 kJ mol-1], of which the former is clearly favored. DFT calculations on the model complex {(Me)(C6H4-2-CH2NMe 2)P}2Sn (8a) indicate that the lowest energy dynamic process involves exchange between the chelating and terminal phosphide ligands via a pseudotrigonal bipyramidal intermediate [E)-12.6 kJ mol-1]. Inversion at tin in 8a (via an unusual hybrid edge/vertex-inversion process) is calculated to have a barrier of 206.3 kJ mol-1, whereas the barriers to vertex-inversion at phosphorus are 59.4 and 51.0 kJ mol-1 for the chelating and terminal phosphorus atoms, respectively.

Thesis

  • White, L. (2018). Symbiotic Supramolecular Chemistry - The Development of Smart Soaps.
    Supramolecular chemistry is continually being explored, applied and expanded in many countries all over
    the world. The complexity of this area of science means that it is continually researched.
    This study has demonstrated the importance of the self-assembly between surfactants structures
    and supramolecular aggregation. Within this thesis the design, synthesis, characterization and binding
    properties of five amphiphilic molecules are discussed. These molecules were investigated in the gaseous
    phase, solid and solution states by a variety of complementary analytical techniques with the results
    demonstrating that the anionic monomers have a propensity to self-associate into a variety of aggregated
    species.
    A selection of 1H and DOSY NMR experiments were conducted in DMSO-d6, providing evidence
    that these molecules tend to form dimeric rather than larger aggregated species. The presence of
    hydrogen bonding was further confirmed by 1H NMR self-association studies, showing a down field
    change in chemical shift due to both the urea NH. The data when fitted to dimerization/Equal K (EK)
    binding model showed that the dimerization constant increases in line with the increase of aromatic
    substituents. By direct observation it was established that the sulfonate-anion molecules self-associated
    through intermolecular hydrogen bonds to form aggregated species of either irregular or spherical shape
    in solution. The size and type of these species was both concentration, and solute dependent. CMC values
    and dimerization constants correlated well with the computationally derived Emax and Emin values, giving
    preliminary evidence that self-association properties may be predicted by low level computational
    modelling methods. This innovative, cohesive branch of supramolecular chemistry will revolutionise the
    study and scope of non-covalent interactions beyond the molecule.
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