Alan R Kennedy

Karl-Franzens-Universität Graz, Gratz, Styria, Austria

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Publications (484)1804.47 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Reaction of the sodium monoamido-bisalkylzincate [(TMEDA)Na(TMP)(Bu(t))Zn(Bu(t))] (TMEDA is N,N,N',N'-tetramethylethylenediamine; TMP is 2,2,6,6-tetramethylpiperidide) and the related lithium zincate [(PMDETA)Li(TMP)Zn(Bu(t))2] (PMDETA is N,N,N',N'',N''-pentamethyldiethylenetriamine) with the sensitive bio-relevant scaffold N,N-dimethylphenylethylamine, DMPEA, afforded the crystalline complexes [(TMEDA)Na(TMP)(NMe2)Zn(Bu(t))] and [(PMDETA)Li(NMe2)Zn(Bu(t))2], respectively, both of which have been characterized by NMR spectroscopic and X-ray crystallographic studies. Made by reaction of a LiTMP-(TMP)Al(Bu(i))2 mixture with DMPEA, a third dimethylamino-containing crystalline complex, the aluminate [(THF)Li(TMP)(NMe2)Al(Bu(i))2] has been similarly characterized. All three complexes can be regarded as products of cleave and capture chemistry whereby metallation at the benzylic position of DMPEA has led to a β-elimination of an anionic Me2N fragment that has been captured by a charge balancing cationic heterobimetallic entity. While a metallated intermediate prior to the elimination has proved elusive in all of these reactions, DMPEA has been captured fully intact in the novel Lewis acid-Lewis base crystalline complex [DMPEA·Li(TMP)Zn(Me)2], which has also been characterized by the aforementioned techniques.
    Dalton Transactions 02/2015; DOI:10.1039/C5DT00247H · 4.10 Impact Factor
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    ABSTRACT: Reaction of ferrocene with 1 or 2 molar equiv of the synergistic-operative bimetallic sodium zincate base TMEDA·Na(μ-TMP)(μ-tBu)Zn(tBu) yields mainly mono- or dizincated complexes TMEDA·Na(μ-TMP)[μ-(C5H4)Fe(C5H5)]ZntBu (1) and [TMEDA·Na(μ-TMP)Zn(tBu)]2(C5H4)2Fe (2). Likewise, the separated pairing of Li(TMP) and (TMP)AliBu2 in the presence of THF can mono- or dimetalate ferrocene in a synergistic two-step lithiation/trans-metal-trapping protocol to give THF·Li(μ-TMP)[μ-(C5H4)Fe(C5H5)]Al(iBu)2 (4) or [THF·Li(μ-TMP)Al(iBu)2]2(C5H4)2Fe (5). In the absence of Lewis donating cosolvents, a 4-fold excess of the sodium zincate appears to produce an unprecedented 4-fold zincated ferrocene of formula Na4(TMP)4Zn4(tBu)4[(C5H3)2Fe] (3), whereas when donor solvent is withheld from the lithium/aluminum pairing, only dimetalation of ferrocene is possible. Tetrametalation seems to be inhibited by the in situ generation of TMP(H) via amido basicity, which then acts as a Lewis donor toward lithium, preventing inverse-crown formation and preferentially forming the Lewis acid-Lewis base adduct [TMP(H)·Li(μ-TMP)Al(iBu)2]2(C5H4)2Fe (6). With the exception of 3, all aforementioned complexes have been characterized by X-ray crystallography, while 1-6 have also been studied by solution NMR spectroscopic studies.
    Organometallics 02/2015; DOI:10.1021/om5012352 · 4.25 Impact Factor
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    ABSTRACT: A simple method to modify the primary face of cyclodextrins (CDs) is described. The 6I-O-yl radical of α-, β-, and γ-CDs regioselectively abstracts the H5II, located in the adjacent D-glucose unit, by an intramolecular 1,8-hydrogen-atom-transfer reaction through a geometrically restricted nine-membered transition state to give a stable 1,3,5-trioxocane ring. The reaction has been extended to the 1,4-diols of α- and β-CD to give the corresponding bis(trioxocane)s. The C2-symmetric bis(trioxocane) corresponding to the α-CD is a stable crystalline solid whose structure was confirmed by X-ray diffraction analysis. The calculated geometric parameters confirm that the primary face is severely distorted toward a narrower elliptical shape for this rim.
    Angewandte Chemie International Edition in English 01/2015; DOI:10.1002/anie.201412300 · 13.45 Impact Factor
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    ABSTRACT: Substrate-induced phases (SIPs) are polymorphic phases which are found in thin films of a material and are different from the single crystal or "bulk" structure of a material. In this work, we investigate the presence of a SIP in the family of [1]benzothieno[3,2-b]benzothiophene (BTBT) organic semiconductors and the effect of aging and solvent vapor annealing on the film structure. Through extensive X-ray structural investigations of spin coated films, we find a SIP with a significantly different structure to that found in single crystals of the same material forms; the SIP has a herringbone motif while single crystals display layered π-π stacking. Over time, the structure of the film is found to slowly convert to the single crystal structure. Solvent vapor annealing initiates the same structural evolution process but at a greatly increased rate, and near complete conversion can be achieved in a short period of time. As properties such as charge transport capability are determined by the molecular structure, this work highlights the importance of understanding and controlling the structure of organic semiconductor films and presents a simple method to control the film structure by solvent vapor annealing.
    ACS Applied Materials & Interfaces 01/2015; 7(3). DOI:10.1021/am5075908 · 5.90 Impact Factor
  • Organometallics 01/2015; DOI:10.1021/om501225g · 4.25 Impact Factor
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    ABSTRACT: Two thienoacene dimers based on the thieno[3,2-b]thiophene moiety were efficiently synthesized, characterized and evaluated as active hole-transporting layers in organic thin-film field-effect transistors. Both compounds behaved as active p-channel organic semi-conductors showing averaged hole mobility of up to 1.33 cm2 V−1 s−1.
    12/2014; 3(3). DOI:10.1039/C4TC02158D
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    ABSTRACT: Sensitive optical detection of nitroaromatic vapours with diketo-pyrrolopyrrole thin films is reported for the first time and the impact of thin film crystal structure and morphology on fluorescence quenching behaviour demonstrated.
    Chemical Communications 11/2014; DOI:10.1039/c4cc08468c · 6.38 Impact Factor
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    ABSTRACT: The regioselectivity of deprotonation reactions between arene substrates and basic metalating agents is usually governed by the electronic and/or coordinative characteristics of a directing group attached to the benzene ring. Generally, the reaction takes place in the ortho position, adjacent to the substituent. Here, we introduce a protocol by which the metalating agent, a disodium-monomagnesium alkyl-amide, forms a template that extends regioselectivity to more distant arene sites. Depending on the nature of the directing group, ortho-meta' or meta-meta' dimetalation is observed, in the latter case breaking the dogma of ortho metalation. This concept is elaborated through the characterization of both organometallic intermediates and electrophilically quenched products.
    Science 11/2014; 346(6211):834-7. DOI:10.1126/science.1259662 · 31.48 Impact Factor
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    ABSTRACT: The effect on catalyst performance of altering substituents at the 2-position of the Macmillan imidazolidinone has been examined. Condensation of L-phenylalanine N-methyl amide with acetophenone derivatives results in a series of imidazolidinones whose salts can be used to accelerate the Diels-Alder cycloaddition. Electron withdrawing groups significantly increases the overall rate of cycloaddition without compromise in selectivity. The most effective catalyst was shown to be efficient for a variety of substrates and the applicability of this catalyst to alternative secondary amine catalysed transformations is also discussed.
    Organic & Biomolecular Chemistry 10/2014; 13(1). DOI:10.1039/C4OB01916D · 3.49 Impact Factor
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    ABSTRACT: Proton transfer to the sulfa drug sulfadiazine [systematic name: 4-amino-N-(pyrimidin-2-yl)benzenesulfonamide] gave eight salt forms. These are the monohydrate and methanol hemisolvate forms of the chloride (2-{[(4-azaniumylphenyl)sulfonyl]azanidyl}pyrimidin-1-ium chloride monohydrate, C10H11N4O2S+·Cl−·H2O, (I), and 2-{[(4-azaniumylphenyl)sulfonyl]azanidyl}pyrimidin-1-ium chloride methanol hemisolvate, C10H11N4O2S+·Cl−·0.5CH3OH, (II)); a bromide monohydrate (2-{[(4-azaniumylphenyl)sulfonyl]azanidyl}pyrimidin-1-ium bromide monohydrate, C10H11N4O2S+·Br−·H2O, (III)), which has a disordered water channel; a species containing the unusual tetraiodide dianion [bis(2-{[(4-azaniumylphenyl)sulfonyl]azanidyl}pyrimidin-1-ium) tetraiodide, 2C10H11N4O2S+·I42−, (IV)], where the [I4]2− ion is located at a crystallographic inversion centre; a tetrafluoroborate monohydrate (2-{[(4-azaniumylphenyl)sulfonyl]azanidyl}pyrimidin-1-ium tetrafluoroborate monohydrate, C10H11N4O2S+·BF4−·H2O, (V)); a nitrate (2-{[(4-azaniumylphenyl)sulfonyl]azanidyl}pyrimidin-1-ium nitrate, C10H11N4O2S+·NO3−, (VI)); an ethanesulfonate {4-[(pyrimidin-2-yl)sulfamoyl]anilinium ethanesulfonate, C10H11N4O2S+·C2H5SO3−, (VII)}; and a dihydrate of the 4-hydroxybenzenesulfonate {4-[(pyrimidin-2-yl)sulfamoyl]anilinium 4-hydroxybenzenesulfonate dihydrate, C10H11N4O2S+·HOC6H4SO3−·2H2O, (VIII)}. All these structures feature alternate layers of cations and of anions where any solvent is associated with the anion layers. The two sulfonate salts are protonated at the aniline N atom and the amide N atom of sulfadiazine, a tautomeric form of the sulfadiazine cation that has not been crystallographically described before. All the other salt forms are instead protonated at the aniline group and on one N atom of the pyrimidine ring. Whilst all eight species are based upon hydrogen-bonded centrosymetric dimers with graph set R22(8), the two sulfonate structures also differ in that these dimers do not link into one-dimensional chains of cations through NH3-to-SO2 hydrogen-bonding interactions, whilst the other six species do. The chloride methanol hemisolvate and the tetraiodide are isostructural and a packing analysis of the cation positions shows that the chloride monohydrate structure is also closely related to these.
    09/2014; 70. DOI:10.1107/S2053229614018725
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    ABSTRACT: Vinyl cyclopropane rearrangement (VCPR) has been utilised to synthesise a difluorinated cyclopentene stereospecifically and under mild thermal conditions. Difluorocyclopropanation chemistry afforded ethyl 3-(1'(2'2'-difluoro-3'-phenyl)cyclopropyl) propenoate as all four stereoisomers (18a, 18b, 22a, 22b) (all racemic). The trans-E isomer (18a), prepared in 70 % yield over three steps, underwent near quantitative VCPR to difluorocyclopentene 23 (99 %). Rearrangements were monitored by (19) F NMR (100-180 °C). While cis/trans cyclopropane stereoisomerisation was facile, favouring trans-isomers by a modest margin, no E/Z alkene isomerisation was observed even at higher temperatures. Neither cis nor trans Z-alkenoates underwent VCPR, even up to much higher temperatures (180 °C). The cis-cyclopropanes underwent [3,3]-rearrangement to afford benzocycloheptadiene species. The reaction stereospecificity was explored by using electronic structure calculations, and UB3LYP/6-31G* methodology allowed the energy barriers for cyclopropane stereoisomerisation, diastereoisomeric VCPR and [3,3]-rearrangement to be ranked in agreement with experiment.
    Chemistry 09/2014; 20(44). DOI:10.1002/chem.201403737 · 5.70 Impact Factor
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    ABSTRACT: 1-lithio-2-butyl-1,2-dihydropyridines, typically formed as intermediates in the nucleophilic substitution (addition/elimination) of pyridine with (n- or t-) butyl lithium, have been isolated and comprehensively characterized. The linear substituted isomer is polymeric while the branched substituted isomer is a cyclotrimer. The lower oligomerization of the latter complex confers exceptional hexane solubility making it an excellent lithium hydride source in non-polar, aliphatic media.
    Chemical Communications 09/2014; 51(25). DOI:10.1039/C4CC06421F · 6.38 Impact Factor
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    ABSTRACT: The chemistry of the hydrotris(mercaptobenzothiazolyl)borate anion (Tbz) with metal salts (HgI2, SbI3, BiI3, CoCl2) is reported in an attempt to probe the stability of the of Tbz ligand once coordinated to hard and soft metals. Complexes of Tbz with bismuth, containing the [Bi(Tbz)I3](-) anion, are stable, but with the other metals this is not the case. Although simple complexes such as [Hg(Tbz)I] and [E(Tbz)I3](-) (E = Sb, Bi) can be isolated from the reaction mixtures, subsequent reactions lead to ligand modification or decomposition. In the presence of mercury and antimony we observe the formation of a hitherto unseen cationic pentacyclic heterocycle. With cobalt we observe a small quantity of a product which suggests a more complete decomposition. A simple benzothiazole (bz) adduct [Co(bz)2Cl2] has been identified, in which the Tbz ligand has disintegrated and the parent heterocycle, mercaptobenzothiazole, has been desulfurized. A rationale for these observations is given.
    Inorganic Chemistry 09/2014; 53(19). DOI:10.1021/ic5013236 · 4.79 Impact Factor
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    ABSTRACT: Using structurally defined potassium- tetra(alkyl)magnesiates, a new straightforward methodology to promote regioselective Mg-H exchange reactions of a wide range of aromatic and heteroaromatic substrates is disclosed. Contacted ion pair intermediates are likely to be involved, with K being the key to facilitate the magnesiation processes.
    Chemical Communications 09/2014; 50(85). DOI:10.1039/C4CC05305B · 6.38 Impact Factor
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    William J. Kerr, Alan R. Kennedy, Rory Moir, Marc Reid
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    ABSTRACT: Synthesis of a series of iridium(I) complexes of the type [(COD)Ir(IMes)(PPh3)]X (X = BF4, OTf, and BArF) has been established. Application of these species in mild hydrogen isotope exchange processes revealed more efficient catalysis and, further, a wider solvent scope when employing larger, more non-coordinating counterions.
    Organic & Biomolecular Chemistry 09/2014; 12(40). DOI:10.1039/C4OB01570C · 3.49 Impact Factor
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    ABSTRACT: Control over solid state structure is critical for effective performance in optoelectronic devices bearing if-conjugated charge mediating organic materials. A series of five structurally related N-benzyl-substituted diketopyrrolopyrroles (DPPs) differing solely in 2 out their 60 atoms were synthesized and crystal structures obtained. Systematic variation of the long axis aligned, pi-pi stacks has been identified within the single crystal structure series and intermolecular interaction energies and charge transfer integrals for the pi-pi stacks have been computed by means of density functional theory (M06-2X/6-311G(d)). The computed intermolecular interaction energies as well as charge transfer integrals were further investigated utilizing a series of systematically cropped dimer pairs, highlighting the crucial role of the benzyl/halo substitution on stabilization of these pi-pi dimers. Two of the DPPs, including a new polymorph of a previously reported structure exhibit twice the intermolecular interaction energy and comparable hole transfer integrals to Rubrene, one of the most efficient hole conducting materials known. The computed properties for all of the pi-pi dimer systems reported herein are consistent with trends predicted by a model system. As such these materials show great promise as charge mediators in organic electronic applications and may be exploited in systematic structure activity based investigations of charge transfer theory.
    Crystal Growth & Design 07/2014; 14(9). DOI:10.1021/cg5010165 · 4.56 Impact Factor
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    ABSTRACT: A general thermolysis reaction for the transformation of Group 1 TMP compounds (LiTMP, NaTMP, KTMP) to 1-aza-allylic TTHP derivatives is reported. TMEDA accelerates the reaction and produces the crystalline complexes [(TMEDA)LiTTHP] and [(TMEDANaTTHP)2]. Methane elimination during the transformational process was confirmed via TVA coupled to MS.
    Chemical Communications 07/2014; DOI:10.1039/C4CC04959D · 6.38 Impact Factor
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    ABSTRACT: A systematic study both in the solid- and solution-state, was carried out for a series of sodium magnesiates containing the utility amide ligand 1,1,1,3,3,3-hexamethyldisilazide (HMDS). The first complex considered is the donor-free bisamido monoalkyl polymeric complex [Na(μ-HMDS)2Mg((n)Bu)]∞. The reactivity of with common tertiary bidentate donors including N,N,N',N'-tetramethylethylenediamine (TMEDA) or its chiral relative (1R,2R)-tetramethylcyclohexyldiamine [(R,R)-TMCDA] is detailed. Surprisingly, the products of these reactions are not simple diamine adducts but are solvent separated sodium magnesiate systems [(TMEDA)2·Na](+)[Mg(HMDS)3](-) and [{(R,R)-TMCDA}2·Na](+)[Mg(HMDS)3](-). By concentrating on the likely equilibria which may give rise to formation of , a potential intermediate complexed ion pair [{(TMEDA)2·Na}(μ-(n)Bu)Mg(HMDS)2] was isolated. Additionally, the novel "inverse magnesiates" [{Na(μ-HMDS)}2Mg(μ-(n)Bu)2·(TMEDA)]∞ and [{Na(μ-HMDS)}2Mg(μ-(n)Bu)2·{(R,R)-TMCDA}]∞, were obtained by reacting solutions of composition "NaMg(HMDS)((n)Bu)2" (a likely by-product in the formation of from ), with TMEDA or (R,R)-TMCDA. The structure and nature of these bimetallic complexes have been determined using a combination of X-ray crystallographic studies and multinuclear NMR spectroscopy.
    Dalton Transactions 07/2014; 43(38). DOI:10.1039/c4dt00921e · 4.10 Impact Factor
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    ABSTRACT: Expanding the synthetic potential of Mg–Zn hybrid organyl reagents (generated via transmetallation reactions), this study uncovers a versatile approach, involving a sequence of direct Zn–I exchange and Pd catalysed cross-coupling reactions which grants access to a wide range of asymmetric bis(aryls). By combining X-ray crystallography with ESI-MS and non-deuterium NMR spectroscopic studies, new light is shed on the heterobimetallic constitution of the intriguing organometallic species [(THF)4MgCl2Zn(tBu)Cl] (1) and [{Mg2Cl3(THF)6}+{ZntBu3}−] (2), formed through transmetallation of tBuMgCl with n equivalent amounts of ZnCl2 (n = 1 and 3 respectively). Operating by cooperative effects, alkyl-rich hybrid 2 can effectively promote direct Zn–I exchange reactions with aromatic halides in short periods of time at room temperature in THF solution. The structural elucidation of key organometallic intermediates involved in some of these Zn–I exchanges, provides new reactivity insights into how these bimetallic systems operate. Thus, while the reaction of 2 with 3 equivalents of 2-iodoanisole (3b) gives magnesium dizincate [{Mg(THF)6}2+{Zn(o-C6H4-OMe)3}2−] (4) which demonstrates the 3-fold activation of the tBu groups attached to Zn in 2, using 2-iodobenzonitrile (3i), only two tBu groups react with the substrate, affording [(THF)4MgCl(NC-o-C6H4)ZnI(o-C6H4-CN)(THF)] (7). In 7 Mg and Zn are connected by an aryl bridge, suggesting that the formation of contacted ion-pair hybrids may have a deactivating effect on the outcome of the Zn–I exchange process. A wide range of homoleptic tris(aryl) zincate intermediates have been prepared in situ and used as precursors in Pd catalysed cross-coupling reactions, affording bis(aryls) 6a–s in excellent yields under mild reaction conditions without the need of any additive or polar cosolvent such as NMP or DMI.
    Chemical Science 06/2014; 5(9). DOI:10.1039/C4SC01263A · 8.60 Impact Factor
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    ABSTRACT: Previously it was reported that activation of (t)Bu2Zn by [(TMEDA)Na(μ-dpa)]2 led to tert-butylation of benzophenone at the challenging para-position, where the sodium amide functions as a metalloligand towards (t)Bu2Zn manifested in crystalline [{(TMEDA)Na(dpa)}2Zn(t)Bu2] (TMEDA is N,N,N',N'-tetramethylethylenediamine, dpa is 2,2'-dipyridylamide). Here we find altering the Lewis donor or alkali metal within the metalloligand dictates the reaction outcome, exhibiting a strong influence on alkylation yields and reaction selectivity. Varying the former led to the synthesis of three novel complexes, [(PMDETA)Na(dpa)]2, [(TMDAE)Na(dpa)]2, and [(H6-TREN)Na(dpa)], characterised through combined structural, spectroscopic and theoretical studies [where PMDETA is N,N,N',N'',N''-pentamethyldiethylenetriamine, TMDAE is N,N,N',N'-tetramethyldiaminoethylether and H6-TREN is N',N'-bis(2-aminoethyl)ethane-1,2-diamine]. Each new sodium amide can function as a metalloligand to generate a co-complex with (t)Bu2Zn. Reacting these new co-complexes with benzophenone proved solvent dependent with yields in THF much lower than those in hexane. Most interestingly, sub-stoichiometric amounts of the metalloligands [(TMEDA)Na(dpa)]2 and [(PMEDTA)Na(dpa)]2 with 1 : 1, (t)Bu2Zn-benzophenone mixtures produced good yields of the challenging 1,6-tert-butyl addition product in hexane (52% and 53% respectively). Although exchanging Na for Li gave similar reaction yields, the regioselectivity was significantly compromised; whereas the K system was completely unreactive. Replacing (t)Bu2Zn with (Me3SiCH2)2Zn shut down the alkylation of benzophenone; in contrast, (t)BuLi generates only the reduction product, benzhydrol. Zincation of the parent amine dpa(H) generated the crystalline product [Zn(dpa)2], as structurally elucidated through X-ray crystallography and theoretical calculations. Although the reaction mechanism for the alkylation of benzophenone remains unclear, incorporation of the radical scavenger TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl radical) into the reaction system completely inhibits benzophenone alkylation.
    Dalton Transactions 06/2014; 43(38). DOI:10.1039/c4dt00914b · 4.10 Impact Factor

Publication Stats

4k Citations
1,804.47 Total Impact Points

Institutions

  • 2015
    • Karl-Franzens-Universität Graz
      Gratz, Styria, Austria
  • 1996–2015
    • University of Strathclyde
      • Department of Pure and Applied Chemistry
      Glasgow, Scotland, United Kingdom
  • 2012–2013
    • Erciyes Üniversitesi
      • Department of Physics
      Kayseri, Kayseri, Turkey
    • Universidad Santiago de Cali
      Santiago de Cali, Valle del Cauca, Colombia
  • 2001–2012
    • Newcastle University
      • School of Chemistry
      Newcastle upon Tyne, ENG, United Kingdom
  • 2011
    • University of Bath
      • Department of Chemistry
      Bath, ENG, United Kingdom
  • 2010
    • Spanish National Research Council
      Madrid, Madrid, Spain
    • Kano University of Science & Technology
      Wudil, Kano, Nigeria
  • 2007–2009
    • Johannes Gutenberg-Universität Mainz
      • Institute of Inorganic and Analytical Chemistry
      Mainz, Rhineland-Palatinate, Germany
  • 2003–2008
    • Universidad de La Laguna
      • Department of Organic Chemistry
      San Cristóbal de La Laguna, Canary Islands, Spain
  • 2006
    • University of Notre Dame
      • Department of Chemistry and Biochemistry
      United States