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Professor Bradley Williams

Biography

I have a synthesis chemistry research background with an industrial focus. My expertise includes research leadership and management, operational management and line management of technical and support staff, and project management. I have extensive experience with industry liaison and research contract negotiations, and with policy and strategy development and implementation. I founded and was the first Director of the Research Centre for Synthesis and Catalysis at the University of Johannesburg (UJ, South Africa), and also the Bioresource Processing Alliance at Callaghan Innovation (New Zealand). I raised funds to equip the Department of Chemistry at UJ with high capital value research/analytical equipment for improved strategic positioning and have contributed to quality control processes at Faculty and institutional levels. I have raised over $19M to fund research and major CAPEX.

Professional

MAJOR WORK EXPERIENCE

Academic

2016-present    Professor of Chemistry and Associate Head of School (Strategic Development), University of Technology Sydney, Australia

2012-2015         Appointment as Visiting Professor, University of Johannesburg, South Africa

2004-2011         Professor; University of Johannesburg

2001-2003         Associate Professor, University of Johannesburg

2000                    Senior Lecturer, University of Johannesburg

1998-1998         Lecturer, University of Johannesburg

1996-1997         Post-doctoral Research Fellow and Tutor, Imperial College, London, UK

Commercial

2014-Feb 2016     Deputy Dean: Faculty of Graduate Research, Senior Principal Scientist and Professor, Ferrier Research Institute of the Victoria University of Wellington, New Zealand

2012-2013         Group Manager: Integrated Bioactive Technologies at Callaghan Innovation, New Zealand

TERTIARY EDUCATION

1995:    Ph.D. (Organic Chemistry)

1992:     MSc. cum laude (Organic Chemistry)

PROFESSIONAL DISTINCTIONS

2014: New Zealand Institute of Chemistry’s prize for Industrial and Applied Chemistry

2012: Fellow of the New Zealand Institute of Chemistry

2012-2013: Director: Bioresource Processing Alliance

2009-present, Member of the Editorial Advisory Board of The Open Catalysis Journal

2009: University representative for Higher Education Quality Commission audit of Faculty of Science and also Senate representative for this audit

2006, member of the organising committee for the International Symposium on Homogeneous Catalysis

2003-present, referee of numerous research articles for various international journals, including leading journals such as Chem. Commun., Angew. Chem. and Organometallics.

2003-2006: University of Johannesburg’s representative working with CIPRO (South African patent office) and WIPO (World Intellectual Patent Organisation)

2001: Dean’s award for best researcher at senior lecturer level

1996: Foundation for Research and Development postdoctoral fellowship

1990: James Moir Medal of the South African Chemical Institute

1990-1995: postgraduate research fellowship, AECI Limited

1989-1995: various university and Foundation for Research and Development merit scholarships

Image of Bradley Williams
Associate Head of School (Strategic Development), School of Mathematical and Physical Sciences
BSc (Hons), Chemistry, Chemistry
 
Phone
+61 2 9514 2265

Research Interests

My research interests include

  • Carbohydrate chemistry (see Org. Lett. 2014, 16, 4543; Org. Biomol. Chem. 2012, 10, 5636) - this is synthetic methodology and aims to develop new types of chemistry;

  • Transition metal-catalysed carbonylation reactions (see Organometallics 2014, 33, 7023; ChemCatChem 2014, 6, 2801; Angew. Chem. Int. Ed. 2012, 51, 1648; ChemCatChem, 4, 206; Angew. Chem. 2008, 47, 560)

  • Lewis acid catalysed reactions and fundamental aspects (see Fuel Proc. Technol. 2012, 94, 74; Green Chem. 2010, 12, 1919; Tetrahedron, 2010, 66, 4573; J. Mol. Catal. A Chem. 2010, 317, 68; J. Org. Chem. 2009, 74, 9509)

  • Analytical method development (see Anal. Chem. 2015, 87, 9559; Talanta 2015, 144, 445; J. Agric. Food Chem. 2015, 63, 5985; J. Agric. Food Chem. 2014, 83, 6713; Anal. Chem. 2011, 83, 6713)
Can supervise: Yes
I am available to supervise in any of the project areas mentioned above.

I have taught

  • organic chemistry from first year level to Honours level;
  • advanced frontier molecular orbital theory of organic reactions;
  • pharmaceutical analytical chemsitry and the regulatory environment;
  • organometallic chemistry and homogeneous catalysis.

Conferences

Williams, D.B.G., Lombard, H., Van Niekerk, M. & Coetzee, P.P. 2002, 'Deprotection techniques for phosphine-borane complexes: Methods and extraction coefficients', Phosphorus, Sulfur and Silicon and Related Elements, pp. 2115-2116.
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Journal articles

Williams, D.B.G., Mason, J.M., Tristram, C.J. & Hinkley, S.F.R. 2015, 'Cellulose as a Source of Water Dispersible Renewable Film-Forming Materials', Macromolecules, vol. 48, no. 23, pp. 8497-8508.
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© 2015 American Chemical Society. Cellulose is found to be a good source of waterborne film-forming materials when modified with the correct type and level of functional groups. The modification of cellulose to incorporate high levels of levulinic functionality and other C 2 -C 6 alkyl esters is reported for the first time. The levulinyl-functionalized cellulose is readily modified to produce oxime or acylhydrazone derivatives, which is particularly useful to fine-tune the physical characteristics of the cellulose ester. This includes the glass transition temperature of the cellulose esters, their ability to produce fine uniform colloidal particles in aqueous media and ultimately provide the principle film-forming component of an architectural coating. The process has been demonstrated at the 500 g level suggesting ready scalability. Lewis acids and Lewis acid-assisted Brønsted acids are employed for the first time in such chemistry, and together with sulfur-based Brønsted acids are all found to be effective catalysts for the esterification of cellulose to produce mixed ester systems. The Lewis acid catalysts demonstrate exceptional activity and produce high molecular weight cellulose derivatives.
George, M.J., Marjanovic, L. & Williams, D.B.G. 2015, 'Solvent-Assisted Headspace Sampling Using Solid Phase Microextraction for the Analysis of Phenols in Water', Analytical Chemistry, vol. 87, no. 19, pp. 9559-9562.
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© 2015 American Chemical Society. Headspace analysis is used widely and relies on volatilization of analytes into the headspace above the matrix. We detail the dramatic influence that added solvent can have on headspace analysis of phenols, without the requirement for specialized headspace vials. The use of water-immiscible solvents is key and leads to a 1-3 orders of magnitude enhancement in the volatilization of these analytes and shorter fiber exposure times than are otherwise required.
George, M.J., Marjanovic, L. & Williams, D.B.G. 2015, 'Picogram-level quantification of some growth hormones in bovine urine using mixed-solvent bubble-in-drop single drop micro-extraction.', Talanta, vol. 144, pp. 445-450.
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Growth hormones are important biologically active compounds. However, they can cause deleterious effects if not used with care and their use in farmed animals is banned in the European Union. This study presents the development and application of a mixed-solvent "bubble-in-drop single drop micro-extraction" (BID-SDME) method for enrichment of stilbene hormones in bovine urine samples. The hormones are quantified using GC-MS showing good linearity with the coefficient of determination (R(2)) of 0.999 and 0.999 for hexestrol and diethylstilbestrol, respectively, in the concentration range 0.05-10 ng mL(-1). Excellent precision (RSD<10%) and accuracy (using a bovine urine certified reference material) were obtained. The observed detection capability (CC, or LOD) values were 0.01 ng mL(-1) (hexestrol), 0.03 ng mL(-1) (cis-diethylstilbestrol) and 0.02 ng mL(-1) (trans-diethylstilbestrol), respectively, while the decision limit (CC, or LOQ) values were 0.03 ng mL(-1), 0.08 ng mL(-1) and 0.07 ng mL(-1), which are comparable to or better than those reported in literature. Importantly, sample handling is significantly simplified by our method and enrichment values are greatly enhanced. The results show that a 3:1 chloroform/toluene mixture gave the highest extraction efficiency with a drop-bubble ratio of 2:1. We highlight the importance of solvent density on the success of the BID-SDME method.
Vyssotski, M., Bloor, S.J., Lagutin, K., Wong, H. & Williams, D.B. 2015, 'Efficient Separation and Analysis of Triacylglycerols: Quantitation of -Palmitate (OPO) in Oils and Infant Formulas.', Journal of agricultural and food chemistry, vol. 63, no. 26, pp. 5985-5992.
A high-efficiency, convenient, and reliable method for the separation of structurally similar triacylglycerols is detailed and applied in the quantitative analysis of 1,3-dioleoyl-2-palmitoylglycerol (OPO) in infant formulas and OPO oils. OPO is an important lipid component in "humanized" infant formula. A fast preparative isolation of an OPO-containing fraction from the crude complex mixture, by nonaqueous reversed phase HPLC, followed by Ag(+)-HPLC with detection at 205 nm allowed fine separation and detection of the desired fraction. OPO was quantitated independently of its regioisomer 1,2-dioleoyl-3-palmitoylglycerol (OOP) and isomers of stearoyl-linoleoyl-palmitoyl glycerol that might be present in infant formulas. For samples with low OPO content, an evaporative light-scattering detector (ELSD) was more preferable than UV detection, with a calculated LOD of 0.1 g of OPO injected and LOQ of 0.3 g. The method, which showed high reproducibility (RSD < 5%), was suitable for both high OPO content oils and low OPO products such as unenriched infant formula. A number of possible interference issues were considered and dealt with.
Traut-Johnstone, T., Kanyanda, S., Kriel, F.H., Viljoen, T., Kotze, P.D., van Zyl, W.E., Coates, J., Rees, D.J., Meyer, M., Hewer, R. & Williams, D.B. 2015, 'Heteroditopic P,N ligands in gold(I) complexes: synthesis, structure and cytotoxicity.', Journal of inorganic biochemistry, vol. 145, pp. 108-120.
New heteroditopic, bi- and multidentate imino- and aminophosphine ligands were synthesised and complexed to [AuCl(THT)] (THT=tetrahydrothiophene). X-ray crystallography confirmed Schiff base formation in three products, the successful reduction of the imino-group to the sp(3)-hybridised amine in several instances, and confirmed the formation of mono-gold(I) imino- and aminophosphine complexes for four Au-complexes. Cytotoxicity studies in cancerous and non-cancerous cell lines showed a marked increase in cytotoxicity upon ligand complexation to gold(I). These findings were supported by results from the 60-cell line fingerprint screen of the Developmental Therapeutics Programme of the National Institutes of Health for two promising compounds. The cytotoxicity of some of these ligands and gold(I)complexes is due to the induction of apoptosis. The ligands and gold(I)complexes demonstrated selective toxicity towards specific cell lines, with Jurkat T cells being more sensitive to the cytotoxic effects of these compounds, while the non-cancerous human cell line KMST6 proved more resistant when compared to the cancerous cell lines. Results from the NIH DTP 60 cell-line fingerprint screen support the observed enhancement of cytotoxicity upon gold(I) complexation. One gold(I)complex induced high levels of apoptosis at concentrations of 50 M in all the cell lines screened in this study, while some of the other compounds selectively induced apoptosis in the cell lines. These results point towards the potential for selective toxicity to cancerous cells through the induction of apoptosis.
Tristram, C.J., Mason, J.M., Williams, D.B.G. & Hinkley, S.F.R. 2015, 'Performance Improvement for Dye-sensitized Solar Cells with Cone-calix[4]arene Based Dyes', ChemSusChem.
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&copy; 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Invited for this months cover is the group of Jun-Min Liu and Cheng-Yong Su at Sun Yat-Sen University. The image shows that- cone-calix[4]arene-based dye flowers can develop in the field of dye-sensitized solar cells as sunflowers thrive under sunshine. The Full Paper itself is available at 10.1002/cssc.201402401 "The calix[4]arene dye flower itself is a beautiful, positive, and energetic plant." This and more about the story behind the research that inspired the cover image can be found on page{black small square}{black small square} (10.1002/cssc.201403048). View the Front Cover on page{black small square}{black small square} (10.1002/cssc.201403047).
Tristram, C.J., Ingham, B., Williams, D.B.G. & Hinkley, S.F.R. 2015, 'Determination of glass transitions in novel cellulose polymers by synchrotron wide-angle X-ray scattering', Materials Today Communications, vol. 2, pp. e49-e54.
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&copy; 2014 Elsevier Ltd. Synchrotron wide angle X-ray scattering (WAXS) was used to measure the glass-transition temperature (T g ) values for various cellulosic materials including a novel cellulose ester. WAXS patterns were obtained of films cast on silicon nitride windows. Two strong scattering peaks were observed that correlated with the intramolecular repeating anhydroglucose unit (d=10.6-14.3&Aring;) and an intermolecular packing spacing (d=4.4-4.5&Aring;). Real-time measurements were made during temperature cycling over a range of 80-160&deg;C at 5&deg;C/min. Significant shifts in position, width and area for the peak assigned to the intermolecular arrangement of the pseudo-linear cellulose mixed-ester chains were correlated with temperature. The calculated T g mid-points correlated well with T g values determined by differential scanning calorimetry (DSC). This application of temperature-dependent WAXS measurements shows promise for T g determination in samples where shallow second-order transitions are observed by DSC and where other techniques are not applicable.
Tristram, C.J., Mason, J.M., Williams, D.B.G. & Hinkley, S.F.R. 2015, 'Doubly renewable cellulose polymer for water-based coatings.', ChemSusChem, vol. 8, no. 1, pp. 63-66.
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A levulinoyl ester-containing cellulose polymer is introduced as a waterborne coating. Incorporation of the biomass-derived levulinic acid proceeds via an unexpected intermediate and provides the unusual feature of a cellulose derivative that is readily chemically modified. The levulinoyl-cellulose ester could be chemically manipulated, allowing it to be dispersed to generate a waterborne hydrocolloid latex. This was capable of film-formation at room temperature, and was formulated for use as a coating of high-renewable content.
Tristram, C.J., Mason, J.M., Williams, D.B.G. & Hinkley, S.F.R. 2015, 'Doubly Renewable Cellulose Polymer for Water-Based Coatings', ChemSusChem.
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&copy; 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Invited for this month's cover is the Industrial Formulations group at the Ferrier Research Institute, Victoria University of Wellington. The image depicts plant matter being converted into a novel cellulose ester and, in turn, into a paint formulation suitable for architectural coatings.
Tristram, C.J., Mason, J.M., Williams, D.B.G. & Hinkley, S.F.R. 2015, 'Doubly renewable cellulose polymer for water-based coatings', ChemSusChem.
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Traut-Johnstone, T., Kriel, F.H., Hewer, R. & Williams, D.B. 2014, '4-(3-Azaniumylpropyl)morpholin-4-ium chloride hydrogen oxalate: an unusual example of a dication with different counter-anions.', Acta crystallographica. Section C, Structural chemistry, vol. 70, no. Pt 12, pp. 1121-1124.
The mixed organic-inorganic title salt, C7H18N2O(2+)C2HO4(-)Cl(-), forms an assembly of ionic components which are stabilized through a series of hydrogen bonds and charge-assisted intermolecular interactions. The title assembly crystallizes in the monoclinic C2/c space group with Z = 8. The asymmetric unit consists of a 4-(3-azaniumylpropyl)morpholin-4-ium dication, a hydrogen oxalate counter-anion and an inorganic chloride counter-anion. The organic cations and anions are connected through a network of N-HO, O-HO and C-HO hydrogen bonds, forming several intermolecular rings that can be described by the graph-set notations R3(3)(13), R2(1)(5), R1(2)(5), R2(1)(6), R2(3)(6), R2(2)(8) and R3(3)(9). The 4-(3-azaniumylpropyl)morpholin-4-ium dications are interconnected through N-HO hydrogen bonds, forming C(9) chains that run diagonally along the ab face. Furthermore, the hydrogen oxalate anions are interconnected via O-HO hydrogen bonds, forming head-to-tail C(5) chains along the crystallographic b axis. The two types of chains are linked through additional N-HO and O-HO hydrogen bonds, and the hydrogen oxalate chains are sandwiched by the 4-(3-azaniumylpropyl)morpholin-4-ium chains, forming organic layers that are separated by the chloride anions. Finally, the layered three-dimensional structure is stabilized via intermolecular N-HCl and C-HCl interactions.
Tshivhase, M. & Williams, D.B.G. 2014, 'Color-coded ligands: Tracking the catalyst using highly pigmented porphyrazine ligands in biphasic reactions', Organometallics, vol. 33, no. 24, pp. 7023-7026.
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&copy; 2014 American Chemical Society. We demonstrate the concept that highly colored imidazolium porphyrazine ligands and complexes may be useful for visualizing the location of a catalyst and/or ligand. This was analytically demonstrated by the application of UV-vis spectrophotometry to detect the ligand and ICP-OES spectroscopy for quantification of the Pd in the biphasic systems. In the first instance, a toluene/water system was used, in which the complex and ligand preferred the organic phase. Water-soluble substrates were made to react under these conditions by employing the complexes as catalysts in Heck and Suzuki C-C bond forming reactions. In the second instance, an ionic liquid containing biphasic mixture was used, in which the ligand/catalyst was retained in the ionic liquid. Catalyst recycling experiments were met with limited success.
Simelane, S.B., Kinfe, H.H., Muller, A. & Williams, D.B. 2014, 'Aluminum triflate catalyzed tandem reactions of D-galactal: toward chiral benzopyrans, chromenes, and chromans.', Organic letters, vol. 16, no. 17, pp. 4543-4545.
3,4,6-Tri-O-acetyl-D-galactal is selectively converted into 1-O-aryl-2-deoxy derivatives or chiral bridged benzopyrans under Al(OTf)3 catalysis, depending on reaction conditions. The benzopyrans react with Al(OTf)3/acetic anhydride in ring-opening reactions in the absence or presence of acetic acid to selectively produce chiral chromenes or chromans, respectively, in high yields.
Makume, B.F., Bredenkamp, T. & Williams, D.B.G. 2014, 'Substrate requirements for palladium-aluminium triflate co-catalysed hydromethoxycarbonylation reactions of alkynes bearing oxygen atoms', ChemCatChem.
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The palladium diacetate-aluminium triflate combination is an effective catalyst for the hydromethoxycarbonylation reaction of isolated alkenes and alkynes. However, its application in the hydromethoxycarbonylation of oxygen atom-bearing alkynes is non-trivial: the position relative to the alkyne (e.g., allylic, homoallylic) and nature of the oxygen atom determine the success of the transformation. We detail the minimum structural requirements for a successful outcome with ether-containing alkyne substrates and hydroxyl-containing analogues. In general, the oxygen atom has a detrimental effect on the outcome of the hydromethoxycarbonylation reaction, which can be overcome in many instances. The presence of the oxygen atom(s) causes decreases in the rate of the reaction compared to aliphatic alkynes and the closer the oxygen atom is to the triple bond, the more pronounced the effect. The chemistry is demonstrated on complex substrates derived from 5 and 6-carbon sugars in optimised reactions. &copy; 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Williams, D.B., George, M.J. & Marjanovic, L. 2014, 'Rapid detection of atrazine and metolachlor in farm soils: gas chromatography-mass spectrometry-based analysis using the bubble-in-drop single drop microextraction enrichment method.', Journal of agricultural and food chemistry, vol. 62, no. 31, pp. 7676-7681.
Tracking of metolachlor and atrazine herbicides in agricultural soils, from spraying through to harvest, was conducted using our recently reported "bubble-in-drop single-drop microextraction" method. The method showed good linearity (R(2) = 0.999 and 0.999) in the concentration range of 0.01-1.0 ng/mL with LOD values of 0.01 and 0.02 ng/mL for atrazine and metolachlor, respectively. Sonication methods were poor at releasing these herbicides from the soil matrixes, while hot water extraction readily liberated them, providing an efficient accessible alternative to sonication techniques. Good recoveries of 97% and 105% were shown for atrazine and metolachlor, respectively, from the soil. The spiking protocol was also investigated, resulting in a traceless spiking method. We demonstrate a very sensitive technique by which to assess, for example, the length of residence of pesticides in given soils and thus risk of exposure.
Evans, S.J., Renison, C.A., Williams, D.B.G. & Muller, A. 2013, 'P,P-Bis[4-(dimethylamino)phenyl]-N,N-bis(propan-2-yl)phosphinic amide', Acta Crystallographica Section E: Structure Reports Online, vol. 69, no. 2.
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The molecular structure of the title compound, C 22 H 3 4N3OP, adopts a distorted tetrahedral geometry at the P atom, with the most noticeable distortion being for the O - P - N angle [117.53 (10)&deg;]. An effective cone angle of 187&deg; was calculated for the compound. In the crystal, weak C - HO interactions create infinite chains along [100] , whereas C - H interactions propagating in [001] generate a herringbone motif.
Evans, S.J., Renison, C.A., Williams, D.B.G. & Muller, A. 2013, 'Rac-[2-(Dicyclohexylphosphanyl)phenyl](phenyl)phosphinic diisopropylamide-borane hemihydrate', Acta Crystallographica Section E: Structure Reports Online, vol. 69, no. 2.
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In the title compound, C 30 H48BNOP20.5H 2 O, the water molecule is disordered about an inversion centre. Both phosphorus atoms shows distortions in their tetrahedral environments with the cyclohexyl substituents disordered over two orientations in a 0.851 (3):0.149 (3) occupancy ratio. The crystal structure is assembled via O - HO interactions between pairs of phosphininc amide molecules and water molecules, creating hydrogen-bonded dimers with graph-set R 2 4 (8) along [001]. Weak C - HO interactions are also observed.
Williams, D.B.G., Simelane, S.B. & Kinfe, H.H. 2012, 'Aluminium triflate catalysed O-glycosidation: Temperature-switched selective Ferrier rearrangement or direct addition with alcohols', Organic and Biomolecular Chemistry, vol. 10, no. 29, pp. 5636-5642.
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A temperature-controlled mechanism switch between the Al(OTf) 3 -catalysed direct addition of alcohols or the Ferrier rearrangement reactions in some glycals is presented. The scope and limitations are investigated as are the influence of the stereochemistry and nature of the protecting groups on the glycal substrate. &copy; 2012 The Royal Society of Chemistry.
Mokhadinyana, M., Desset, S.L., Williams, D.B. & Cole-Hamilton, D.J. 2012, 'Cooperative ligand effects in phase-switching homogeneous catalysts.', Angewandte Chemie (International ed. in English), vol. 51, no. 7, pp. 1648-1652.
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Williams, D.B.G. & Bredenkamp, T. 2012, 'Pd/Al(OTf) 3 Catalyzed Methoxycarbonylation: On the Importance of Counterions and the Acid Source', ChemCatChem, vol. 4, no. 2, pp. 206-208.
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Williams, D.B.G., Sibiya, M.S. & Van Heerden, P.S. 2012, 'Efficient hydroalkoxylation of alkenes to generate octane-boosting ethers using recyclable metal triflates and highly active metal triflate/ Brønsted acid-assisted catalysts', Fuel Processing Technology, vol. 94, no. 1, pp. 75-79.
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gem-Disubstituted alkenes are directly and readily etherified with alcohols using Al(OTf) 3 and Zr(OTf) 4 as recyclable Lewis acid catalysts. In contrast, primary or secondary alkene analogues were inert under these conditions, enabling excellent chemoselectivity. Lanthanide triflates are inactive as catalysts for such reactions, as is phosphoric acid. But a combination of these two otherwise inactive entities led to an 'assisted acidity' scenario that saw significant unmatched catalyst activity. All catalysts of this study are recyclable a number of times without loss of activity. &copy; 2011 Elsevier B.V. All rights reserved.
Traut, T., Kriel, F.H., Zyl, W.E.V. & Williams, D.B.G. 2011, 'Chlorido{N-[2-(diphenylphosphanyl)benzyl]-1-(pyridin-2-yl) methanamine-P}gold(I)', Acta Crystallographica Section E: Structure Reports Online, vol. 67, no. 11.
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In the title compound, [AuCl(C 25 H 23 N 2 P)], the Au I atom is in a typical almost linear coordination environment defined by phosphane P and Cl atoms [bond angle = 175.48 (4)&deg;]. Helical supra-molecular chains along the b axis and mediated by N - HCl hydrogen bonds feature in the crystal packing. &copy; Traut et al. 2011.
Williams, D.B.G. & Mbatha, G.B. 2011, 'The synthesis and characterisation of carbohydrate-functionalised porphyrazines', Dyes and Pigments, vol. 88, no. 1, pp. 65-74.
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A synthetic pathway to the incorporation of mono- and disaccharide carbohydrate moieties into porphyrazine systems was demonstrated. A range of selectively protected monosaccharide precursors was coupled to a small variety of phthalonitriles; the intermediates were co-macrocyclised to form hybrid porphyrazines in Linstead macrocyclisation reactions. Demetallisation of Mg-porphyrazine products was readily effected to afford the free-base pigments, which were subsequently converted into their zinc or nickel complexes. Some porphyrazines were deprotected of their isopropylidene groups (on the carbohydrate moieties) under acidic conditions to reveal polar OH groups. The extraction coefficients of the porphyrazines between 2-octanol and phosphate buffered saline solution were measured. Comparison of the partition coefficients of the carbohydrate-substituted porphyrazines and their deprotected counterparts revealed that structural alteration offers a way to significantly increase the hydrophilicity of substituted porphyrazines. &copy; 2010 Elsevier Ltd. All rights reserved.
Williams, D.B.G., Kotze, P.D.R., Ferreira, A.C. & Holzapfel, C.W. 2011, 'Phosphine-Borane complexes: In situ deprotection and application as ligands in the Rh- or Pd-Catalysed hydroformylation reaction', Journal of the Iranian Chemical Society, vol. 8, no. 1, pp. 240-246.
Triarylphosphine-borane complexes are directly useful in the Rh-catalysed hydroformylation reaction of 1-octene (or Pdcatalysed hydroformylation of 1-pentene). Mild reaction conditions provide similar yields and selectivities of the anticipated aldehyde products to reactions making use of the corresponding free phosphines as ligands. The mono- or bidentate P-B adducts undergo in situ CO-mediated deprotection the produce the free phosphine ligands. The results demonstrate that phosphine-borane complexes may be directly applied to carbonylation reactions without a prior deprotection step, with little to no change in the reaction outcome.
Williams, D.B., George, M.J., Meyer, R. & Marjanovic, L. 2011, 'Bubbles in solvent microextraction: the influence of intentionally introduced bubbles on extraction efficiency.', Analytical chemistry, vol. 83, no. 17, pp. 6713-6716.
Significant improvements to microdrop extractions of triazine pesticides are realized by the intentional incorporation of an air bubble into the solvent microdroplet used in this microextraction technique. The increase is attributed partly to greater droplet surface area resulting from the air bubble being incorporated into the solvent droplet as opposed to it sitting thereon and partly to thin film phenomena. The method is useful at nanogram/liter levels (LOD 0.002-0.012 g/L, LOQ 0.007-0.039 g/L), is precise (7-12% at 10 g/L concentration level), and is validated against certified reference materials containing 0.5 and 5.0 g/L analyte. It tolerates water and fruit juice as matrixes without serious matrix effects. This new development brings a simple, inexpensive, and efficient preconcentration technique to bear which rivals solid phase microextraction methods.
Williams, D.B.G., Shaw, M.L. & Hughes, T. 2011, 'Recyclable Pd(OAc)2/ligand/Al(OTf)3 catalyst for the homogeneous methoxycarbonylation and hydrocarboxylation reactions of phenylacetylene', Organometallics, vol. 30, no. 18, pp. 4968-4973.
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The Pd-catalyzed methoxycarbonylation reaction of phenylacetylene was studied making use of various promoters, including aluminum triflate and several other acid-type promoters of this reaction. The influence of the ligand (bidentate-type ligands and monodentate analogues) was found to be determinative of the success of the reaction. The catalyst was found to be recyclable through 10 catalytic runs. The unique results when using BINAP, relating to the selectivity for the branched product and the stability of the catalyst produced, led to a study on the sulfonated analogue thereof, with the intention of performing hydrocarboxylation reactions to directly prepare the carboxylic acid. The product obtained accordingly may be varied between the methyl ester or its carboxylic acid equivalent, depending on the solvent medium and the ligand employed. &copy; 2011 American Chemical Society.
Pongrácz, P., Petcz, G., Shaw, M., Williams, D.B.G. & Kollár, L. 2010, 'Platinum complexes of 2-diphenylphosphinobenzaldehyde-derived P-alkene ligands and their application in the hydroformylation of styrene', Journal of Organometallic Chemistry, vol. 695, no. 22, pp. 2381-2384.
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Neutral complexes of the formula PtCl 2 L 2 (where L = diethyl 2-diphenylphosphino-benzylidene-malonate (1), diisopropyl 2-diphenylphosphino-benzylidene-malonate (2), di-tert-butyl 2-diphenylphosphino- benzylidene-malonate (3), methyl E-2-(2-diphenylphosphinophenyl)-acrylate (4), tert-butyl E-2-(2-diphenylphosphinophenyl)acrylate (5)) were prepared. These complexes proved to be excellent precursors to active catalysts for the hydroformylation of styrene. The platinum-containing catalytic systems prepared from malonate-based ligands 1 and 2 provided the highest activity. Chemoselectivities of up to 87% were obtained, while the two aldehyde regioisomers were formed in almost equimolar ratio. The in situ studies by using lower ligand to Pt ratios resulted in slight decrease in both regio- and chemoselectivities. 31 P NMR studies on the PtCl 2 L 2 complexes revealed that the formation of trans isomers is highly preferred in the case of benzylidene malonate-type ligands with two ester functionalities (1-3) probably due to steric hindrance. A mixture of cis/trans geometrical isomers (on the Pt) with a predominance of the trans isomer was formed when acrylate-type ligands with one ester functionality (4 and 5) were used. &copy; 2010 Elsevier B.V. All rights reserved.
Williams, D.B.G. & Lawton, M. 2010, 'Drying of organic solvents: Quantitative evaluation of the efficiency of several desiccants', Journal of Organic Chemistry, vol. 75, no. 24, pp. 8351-8354.
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Various commonly used organic solvents were dried with several different drying agents. A glovebox-bound coulometric Karl Fischer apparatus with a two-compartment measuring cell was used to determine the efficiency of the drying process. Recommendations are made relating to optimum drying agents/conditions that can be used to rapidly and reliably generate solvents with low residual water content by means of commonly available materials found in most synthesis laboratories. The practical method provides for safer handling and drying of solvents than methods calling for the use of reactive metals, metal hydrides, or solvent distillation. &copy; 2010 American Chemical Society.
Williams, D.B.G., Cullen, A., Fourie, A., Henning, H., Lawton, M., Mommsen, W., Nangu, P., Parker, J. & Renison, A. 2010, 'Mild water-promoted selective deacetalisatison of acyclic acetals', Green Chemistry, vol. 12, no. 11, pp. 1919-1921.
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Various aliphatic and aromatic dimethyl and diethyl acetals and ketals were found to hydrolyse in essentially quantitative yield when heated to 80 &deg;C in neat water or aqueous medium without a catalyst or any other additive, while cyclic acetals were stable under these conditions. Selective deprotection is possible when both types of acetal are present. &copy; The Royal Society of Chemistry 2010.
Williams, D.B.G. & Lawton, M. 2010, 'Metal triflates: On the question of Lewis versus Brønsted acidity in retinyl carbocation formation', Journal of Molecular Catalysis A: Chemical, vol. 317, no. 1-2, pp. 68-71.
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Al(OTf) 3 generates blue carbocations from retinyl acetate. The mechanism appears to be exclusively water-derived induced Br&oslash;nsted acidity causing loss of acetic acid, not Lewis-mediated acetate abstraction. Dry DCM (1 ppm water) avoided water interference. The hindered base 2,6-di-tert-butylpyridine, used to distinguish between Lewis- and Br&oslash;nsted acidity, was also probed. The results implicate a possible mechanism for similar transformations involving carbocations. &copy; 2009 Elsevier B.V. All rights reserved.
Williams, D.B.G., Simelane, S.B., Lawton, M. & Kinfe, H.H. 2010, 'Efficient tetrahydropyranyl and tetrahydrofuranyl protection/deprotection of alcohols and phenols with Al(OTf)3 as catalyst', Tetrahedron, vol. 66, no. 25, pp. 4573-4576.
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A simple and efficient method for the conversion of alcohols and phenols into their corresponding THP and THF ethers at room temperature has been developed using 1 mol % aluminium triflate as catalyst. The deprotection reaction in the presence of methanol using Al(OTf) 3 was equally successful and could be performed at ambient temperature in high yields. &copy; 2010 Elsevier Ltd. All rights reserved.
Williams, D.B.G., Caddy, J., Blann, K., Grové, J.J.C. & Holzapfel, C.W. 2009, 'Chiral cyclobutanols and cyclopentane dimers via samarium(II) iodide induced keto-olefin cyclisations of carbohydrate-derived unsaturated ketones', Synthesis, no. 12, pp. 2009-2014.
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Some pentose and hexose sugars were converted into unsaturated ketone derivatives, which themselves served as substrates for 4-exo-trig radical cyclisation reactions mediated by SmI 2 . Depending on the order of addition of reagents, the keto-olefins could also be made to undergo a surprising tandem 5-endo-trig cyclisation/dimerisation reaction to a cyclopentane dimer or a cyclobutane monomer. &copy; Georg Thieme Verlag Stuttgart.
Petocz, G., Rangits, G., Shaw, M., Bod, H.D., Williams, D.B.G. & Kollár, L. 2009, 'Platinum complexes of malonate-derived monodentate phosphines and their application in the highly chemo- and regioselective hydroformylation of styrene', Journal of Organometallic Chemistry, vol. 694, no. 2, pp. 219-222.
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Neutral complexes of the formula PtCl 2 L 2 (where L = diethyl 2-diphenylphosphino-malonate (1), diethyl 2-methyl-2-diphenylphosphinomalonate (2), dibenzyl 2-diphenylphosphinomalonate (3), 1,3-dihydroxy-2-methyl-2-diphenylphosphinopropane (4)) were prepared. These proved to be precursors to active catalysts for the hydroformylation of styrene. The platinum-containing catalytic systems prepared from ligand 4 provided the highest activity, while the platinum compounds prepared from other ligands all showed similar levels of reactivity to each other. The matching of high chemo- and regioselectivities were observed in most cases. Surprisingly, the complexes were practically inactive in imidazolium-type ionic liquids. 31 P NMR studies on the PtCl 2 L 2 complexes revealed that the stereoselectivity of the cis/trans geometrical isomers is strongly dependent on the structure of the ligand. &copy; 2008 Elsevier B.V. All rights reserved.
Williams, D.B.G., Evans, S.J., De Bod, H., Mokhadinyana, M.S. & Hughes, T. 2009, 'Directed ortho metallation chemistry and phosphine synthesis: New ligands for the suzuki-miyaura reaction', Synthesis, no. 18, pp. 3106-3112.
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We describe the use of the phosphinic amide moiety as an effective directed ortho metallation group for the incorporation of various phosphino groups onto a benzene ring to generate phosphine ligands. These ligands were used to generate active palladium catalysts for the Suzuki-Miyaura reaction in which deactivated aryl bromides and some aryl chlorides were used as substrates. Surprisingly and interestingly, the (2-alkylphenyl)phosphine derivatives were found to be especially active. The stereoelectronic and electronic features of the ligands were probed by use of selenium oxidation products and Vaska's rhodium complexes, respectively. Some unusual features were observed, specifically relating to the inductive effects of the alkyl side chains in relation to the electronwithdrawing phosphinic amide functions. The two probes were also compared, and the results were related to the catalytic data obtained from the Suzuki reactions. Quite unexpectedly, the ligands generate catalysts with good activity despite their being relatively electronpoor. This low electron density, resulting from the phosphinic amide functionality, renders them stable to oxidation and hydrolysis for over six months while exposed to air. Additionally, the use of the phosphinic amide directing group is unusual and rare, and has not, to our knowledge, been noted before in the preparation of phosphine ligands.
Williams, D.B.G. & Netshiozwi, T.E. 2009, 'Synthesis and characterisation of severely hindered P-OR compounds', Tetrahedron, vol. 65, no. 48, pp. 9973-9982.
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P-Cl substrates were converted into their P-OR analogues from hindered alcohols using an amine base. Where the system was severely hindered, more forcing conditions were required that necessitated the presence of a metal alkoxide nucleophile before successful reactions were observed. In some instances, the products were thermally unstable and reverted to alkenes by elimination reactions, while others were sensitive to moisture. Here, hydrolysis products prevailed if moisture was not rigorously excluded. Details are presented to obtain the P(III) and P(V) esters, diesters and half esters. &copy; 2009 Elsevier Ltd. All rights reserved.
Williams, D.B. & Cullen, A. 2009, 'Al(OTf)(3)-mediated epoxide ring-opening reactions: toward piperazine-derived physiologically active products.', The Journal of organic chemistry, vol. 74, no. 24, pp. 9509-9512.
Al(OTf)(3) is a good catalyst for the ring opening of epoxides, forming beta-amino alcohols bearing the piperazine motif. Two different strategies were examined, where the glycidyl ether resided on one-half of the molecule or the other, allowing insight into a best-case approach for the ring-opening step. Each half of the molecule contained an heteroatom that could be used either to attach the glycidyl moiety or as the nucleophile in the ring-opening reaction, for the same set of reagents, allowing this approach.
Williams, D.B.G., Sibiya, M.S., van Heerden, P.S., Kirk, M. & Harris, R. 2009, 'Verkade super base-catalysed transesterification of propylene carbonate with methanol to co-produce dimethyl carbonate and propylene glycol', Journal of Molecular Catalysis A: Chemical, vol. 304, no. 1-2, pp. 147-152.
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The co-generation of dimethyl carbonate (potential fuels additive, environmentally friendly replacement for more toxic methylating agents, etc.) and propylene glycol via the transesterification reaction of propylene carbonate and methanol was studied using base catalysis. Verkade super bases (proazaphosphatranes) proved especially effective at low catalyst loadings (0.5%) for the rapid transesterification of propylene carbonate with methanol under mild conditions and with high product selectivity (typically > 99.5%). These bases neatly avoid the use of alkoxide catalysts which generate by-products in their neutralisation. The kinetics of the reactions were studied using data obtained from in situ NMR reaction monitoring. The influences of several reaction optimisation parameters are also dealt with. &copy; 2009 Elsevier B.V. All rights reserved.
Williams, D.B., Shaw, M.L., Green, M.J. & Holzapfel, C.W. 2008, 'Aluminum triflate as a highly active and efficient nonprotic cocatalyst in the palladium-catalyzed methoxycarbonylation reaction.', Angewandte Chemie (International ed. in English), vol. 47, no. 3, pp. 560-563.
Williams, D.B.G. & Pretorius, M. 2008, 'Synthesis and evaluation of phosphine-N ligands in transition metal-catalysed C{single bond}C bond forming reactions', Journal of Molecular Catalysis A: Chemical, vol. 284, no. 1-2, pp. 77-84.
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A series of phosphino-imine and the corresponding phosphino-amine P,NR ligands (R = alkyl, aryl) was synthesised from the commercially available starting material 2-(diphenylphosphino)benzaldehyde, including P,N bi-, tri- and tetradentate imine ligands, their secondary amine analogues, and also the methylated tertiary amine equivalents. As an extension, some P,NPPh 2 and P,NPCy 2 derivatives were also prepared from the same starting material. All of these ligands were successfully applied in catalytic reactions (Heck, cross-coupling and hydroformylation), and benchmarked against traditional ligands with satisfying results. While providing catalyst systems that were stable and generally acceptably active in comparison with the benchmarks, the Pd-ligand catalyst systems of this study were found to be especially active in Stille reactions. &copy; 2008 Elsevier B.V. All rights reserved.
Williams, D.B.G. & Lawton, M.C. 2008, 'Highly atom efficient aluminium triflate catalysed acetal formation', Green Chemistry, vol. 10, no. 9, pp. 914-917.
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Aromatic and aliphatic acetals are formed in excellent yields under solventless conditions at room temperature within 30 minutes by treating aldehydes and ketones with 0.5 mol% Al(OTf) 3 as a recyclable catalyst in the presence of only 1.2 equivalents of an orthoester as reagent. &copy; The Royal Society of Chemistry.
Maumela, M.C., Blann, K., De Bod, H., Dixon, J.T., Gabrielli, W.F. & Williams, D.B.G. 2007, 'Efficient synthesis of novel N-substituted bulky diphosphinoamines', Synthesis, no. 24, pp. 3863-3867.
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A convenient procedure for the facile preparation of electron-rich bulky diphosphinoamines from alkylamines and chlorodiphenylphosphine has been developed. The choice of solvent proved to be critical to the successful synthesis of the diphosphinoamine (PNP) products. &copy; Georg Thieme Verlag Stuttgart.
Williams, D.B.G. & Shaw, M.L. 2007, 'P-alkene bidentate ligands: an unusual ligand effect in Pd-catalysed Suzuki reactions', Tetrahedron, vol. 63, no. 7, pp. 1624-1629.
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The versatile reagent bis(diphenylphosphino)benzaldehyde was used to prepare a variety of electronically and sterically varied ligands using Wittig or aldol methodology in high yields. Pd-catalysed Suzuki reactions were evaluated using these ligands. The influence of the functional group on the alkene, which is in direct conjugation with the phosphorus centre of the ligand, was visible in the activity profiles of the reactions. In general, the activity and stability of the Pd-ligand system increased as electron deficiency and steric bulk increased at the alkene. Furthermore, the ligands could be used at decreased catalyst loadings with improved yields and did not themselves participate in the reactions as substrates. &copy; 2007 Elsevier Ltd. All rights reserved.
Williams, D.B.G., Ajam, M. & Ranwell, A. 2007, 'High rate and highly selective vinyl acetate hydroformylation in ionic liquids as solvent or cosolvent', Organometallics, vol. 26, no. 18, pp. 4692-4695.
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The hydroformylation of vinyl acetate to form 2-acetoxypropanal (an important intermediate in the synthesis of the environmentally friendly solvent ethyl lactate) catalyzed by Rh(CO 2 (acac) using phosphite or phosphine ligands was investigated in ionic liquids as reaction media (neat and as blends) or as additives to organic solvents. The ionic liquid had a significant effect on the selectivity of the hydroformylation of vinyl acetate, with very high TOFs being realized and selectivities of over 99% being obtained for the desired branched product at > 95% selectivity for aldehyde products in reactions up to 0.3 mol scale. This effect could be obtained for relatively low volumes of the ionic liquid in an organic solvent, and combinations of benefits were observed by blending ionic liquids. It was also shown that the ionic liquid/catalyst could be recycled without loss of activity. &copy; 2007 American Chemical Society.
Williams, D.B.G., Traut, T., Kriel, F.H. & van Zyl, W.E. 2007, 'Bidentate amino- and iminophosphine ligands in mono- and dinuclear gold(I) complexes: Synthesis, structures and AuCl displacement by AuC6F5', Inorganic Chemistry Communications, vol. 10, no. 5, pp. 538-542.
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Bidentate imino- and aminophosphine ligands were prepared by firstly a Schiff-base condensation reaction between 2-(diphenylphosphino)benzaldehyde and the corresponding primary amines to afford the imino derivatives and secondly reduction of the imines with NaBH 4 to the aminophosphine ligands in satisfactory yields. The ligands readily reacted with chlorogold(I) compounds to produce new mononuclear iminophosphine- and dinuclear aminophosphine chlorogold(I) complexes. Further, reaction of the dinuclear chlorogold complex with C 6 F 5 Au(tht) (tht = tetrahydrothiophene) led to the displacement of one AuCl moiety by AuC 6 F 5 forming a digold(I) mixed halogen/organometallic complex. Both digold(I) complexes displayed intramolecular AuAu interactions, whilst the di(chlorogold) complex also showed an intermolecular Au Au interaction, as determined by X-ray crystallography. The displacement of only one of the two AuCl groups presumably relates to the strength of the Au-P bond (inert) vs. the weakness of the Au-N bond (labile), the latter being more easily broken. &copy; 2007 Elsevier B.V. All rights reserved.
Williams, D.B.G. & Lawton, M. 2006, 'Aluminium triflate: an efficient recyclable Lewis acid catalyst for the aminolysis of epoxides', Tetrahedron Letters, vol. 47, no. 37, pp. 6557-6560.
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Epoxides are powerful starting materials for a range of useful materials and can be converted into, amongst others, amino alcohols. In this work, a range of epoxides was ring-opened using various alkyl- and arylamines under the action of aluminium triflate as a catalyst. This catalyst was found to be highly active, producing the desired amino alcohol products in high yields with low catalyst loadings. Additionally, it was shown that the aluminium triflate catalyst is recyclable by simple extraction into water and may be re-used several times. &copy; 2006 Elsevier Ltd. All rights reserved.
Bradley, D., Williams, G., Ajam, M. & Ranwell, A. 2006, 'Highly selective metathesis of 1-octene in ionic liquids', Organometallics, vol. 25, no. 12, pp. 3088-3090.
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The self-metathesis of 1-octene to form 7-tetradecene catalyzed by ruthenium carbene complexes at low concentrations (0.02 mol %) was investigated in ionic liquids as reaction media and as additives. The study showed that the ionic liquid has a significant effect on the selectivity of the metathesis of 1-octene, with conversion to product of greater than 95% being obtained and selectivities of over 98% being realized. The outcomes of the reactions compared well with those performed under solventless conditions, showing improved conversions and selectivittes. &copy; 2006 American Chemical Society.
Williams, D.B., Caddy, J. & Blann, K. 2005, 'Highly functionalised cyclobutanols via samarium(II) iodide-induced pinacol cyclisations of carbohydrate-derived 1,4-diketones.', Carbohydrate research, vol. 340, no. 7, pp. 1301-1309.
D-Ribofuranose and D-arabinofuranose derivatives were converted in a few steps into their 1,4-diketone derivatives, which were pinacol cyclised under the action of SmI2 to form the corresponding chiral cyclobutanediol products. These products can potentially be applied to the synthesis of anti-viral agents, some of whose structures incorporate chiral cyclobutanediol moieties.
Bradley, D., Williams, G. & Lawton, M. 2005, 'Aluminium triflate: A remarkable Lewis acid catalyst for the ring opening of epoxides by alcohols', Organic and Biomolecular Chemistry, vol. 3, no. 18, pp. 3269-3272.
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Al(OTf) 3 was found to be an extremely effective catalyst (at ppm levels) for ring opening reactions of epoxides using a range of alcohols. &copy; The Royal Society of Chemistry 2005.
Pretorias, M., Williams, D.B.G., Roodt, A. & Muller, A. 2004, 'Dichloro({N-[2-(diphenylphosphino-P)benzyl]-benzylamino} diphenylphosphine-P)palladium(II) toluene solvate', Acta Crystallographica Section E: Structure Reports Online, vol. 60, no. 10.
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The title compound, [PdCl 2 (C 38 H 33 NP 2 )]C 7 H 8 , crystallizes with an accompanying toluene solvent molecule. Important geometrical parameters are Pd-P = 2.2556 (8) and 2.2749 (8) &Aring;, Pd-Cl = 2.3521 (9) and 2.3338 (8) &Aring;, P-Pd-P = 96.31 (3)&deg;, and Cl-Pd-Cl = 89.59 (3)&deg;. &copy; 2004 International Union of Crystallography Printed in Great Britain - all rights reserved.
De Bod, H., Williams, D.B.G., Roodt, A. & Muller, A. 2004, '(N,N-diethylamino)(2-hydroxyphenyl)phenylphosphine oxide', Acta Crystallographica Section E: Structure Reports Online, vol. 60, no. 7.
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The title compound, C 16 H 20 NO 2 P [O=P(C 6 H 5 )(C 6 H 4 OH)(Et 2 N) or P(Ph)(PhOH)(Et 2 N)], crystallizes as a 21:79 racemic mixture of the R and S isomers in the asymmetric unit and is stabilized by strong intramolecular hydrogen bonds with HO = 1.97 (4) and 1.84 (5) A. The Tolman cone angle is calculated to be 199&deg;. &copy; 2004 International Union of Crystallography Printed in Great Britain - all rights reserved.
Pretorius, M., Williams, D.B.G., Roodt, A. & Muller, A. 2004, '[2-(Anilinomethyl)phenyl]diphenyl phosphine and {2-[(N-methylanilino)- methyl]phenyl}diphenylphosphine', Acta Crystallographica Section C: Crystal Structure Communications, vol. 60, no. 6.
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The properties of two isomers C 25 H 22 NP and C 26 H 24 NP along with Tolman angles were compared. It was observed that the two compounds were isomorphous, having individual molecules in the centrosymmetric space group C2/c (Z=8). It was also observed that the calculation of the Tolman cone angle was helpful in determining ligand steric behaviour at a metal centre. The results show that the Tolman angle was important for monodentate or monocoordinated ligands.
Williams, D.B.G. & Blann, K. 2004, 'Highly functionalised cyclobutanols by samarium(II) iodide induced radical cyclisations of carbohydrate-derived unsaturated ketones', European Journal of Organic Chemistry, no. 15, pp. 3286-3291.
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Certain carbohydrates have been found to be excellent precursors for the samarium diiodide-mediated 4-exo-trig cyclisation reaction of their keto-olefin derivatives, which were readily prepared in a few easy steps. The cyclisation was found to be stereoselective, affording cis products, the diastereoselective excesses of which were influenced by the nature of the protecting group employed at C5-O of the furanose sugar. The major chiral cyclobutane product of the cyclisation step was converted into an advanced intermediate for the synthesis of a nucleoside anti-viral analogue. &copy; Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
Williams, D.B.G. & Evans, S.J. 2004, 'Use of palladium-mediated allylic substitution reactions in the synthesis of 2,5-disubstituted-2,5-dihydrofurans', Tetrahedron Letters, vol. 45, no. 39, pp. 7189-7192.
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2,5-Disubstituted-2,5-dihydrofurans were synthesised in both one- and two-pot reactions starting from 2,5-diacetoxy-2,5-dihydrofuran. These palladium-mediated allylic substitution reactions were useful in preparing symmetrical or unsymmetrical products by employing the same nucleophile twice or two different nucleophiles, respectively. &copy; 2004 Elsevier Ltd. All rights reserved.
Williams, D.B.G., Caddy, J. & Blann, K. 2003, 'Fragmentation and cleavage reactions mediated by samarium iodide. Part 2: - and -elimination reactions of c-x substrates', Organic Preparations and Procedures International, vol. 35, no. 3, pp. 307-360.
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Caddy, J., Williams, D.B.G., Roodt, A. & Muller, A. 2003, '(1R*,5S*,6S*,7R*)-6,7-Dihydroxy-6-hydroxymethyl-2- oxabicyclo[3.2.0]-heptan-3-one', Acta Crystallographica Section E: Structure Reports Online, vol. 59, no. 8.
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The crystal structure analysis of the title compound, C 7 H 10 O 5 , shows that a four-five lactonization instead of a four-six self condensation took place during the reaction sequence. The structure is stabilized by strong hydrogen-bonding interactions that serve to form a layer structure. The absolute configuration was assigned based on the chemical synthesis from a starting material of known chirality. &copy; 2003 International Union of Crystallography Printed in Great Britain - all rights reserved.
Blann, K., Williams, D.B.G., Roodtt, A. & Muller, A. 2003, '(1R*,5R*,6S*,7R*)-6,7-Dihydroxy-6-hydroxy-methyl-2- oxabicyclo[3.2.0]heptan-3-one', Acta Crystallographica Section E: Structure Reports Online, vol. 59, no. 10.
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The title compound C 7 H 10 O 5 , crystallizes in the space group P3 1 ] as individual molecules on a three old screw axis, and is stabilized by strong intermolecular hydrogen bonds between the methylene alcohol [O-H O 1.75 (5) &Aring;] and the two secondary alcohol moieties [O-H O 1.81 (3) and 1.91 (3) &Aring;]. &copy; 2003 International Union of Crystallography Printed in Great Britain - all rights reserved.
Bradley, D.M., Mapitse, R., Thomson, N.M. & Hayes, C.J. 2002, 'Enantioselective synthesis of the excitatory amino acid (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid.', The Journal of organic chemistry, vol. 67, no. 22, pp. 7613-7617.
An enantioselective synthesis of the alpha,alpha-dialkyl-alpha-amino acid (1S,3R)-ACPD has been achieved using an alkylidene carbene 1,5-CH insertion reaction as a key step. The ketone cyclization precursor was synthesized from Garner's aldehyde in high yield via a Wittig homologation and subsequent catalytic hydrogenation. Treatment of the ketone with 1.2 equiv of lithio(trimethylsilyl)diazomethane in THF resulted in the formation of the corresponding cyclopentene-containing CH-insertion product in 62-69% yield in high enantiomeric excess. Subsequent functional group manipulation allowed the synthesis of the amino acid (1S,3R)-ACPD to be completed.
Williams, D.B.G., Lombard, H., Van Niekerk, M., Coetzee, P.P. & Holzapfel, C.W. 2002, 'Deprotection techniques for phosphine-borane complexes: Methods and extraction coefficients', Phosphorus, Sulfur and Silicon and the Related Elements, vol. 177, no. 12, pp. 2799-2803.
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Triarylphosphine-, diarylalkylphosphine-, and trialkylphosphine-borane complexes were deprotected using various amines and acids. After deprotection, the resulting borane species were extracted from the free phosphines using various solvent systems. The aqueous layers were analyzed for borane making use of inductively coupled plasma optical emission spectroscopy; and extraction coefficients were then calculated from the analytical data.
Williams, D.B.G., Blann, K., Caddy, J. & Holzapfel, C.W. 2002, 'Aryl -ketoesters as precursors for -butyrolactone dimers in samarium(II) iodide-mediated reactions', Synthetic Communications, vol. 32, no. 24, pp. 3755-3762.
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Various aryl -ketoesters were transformed into corresponding substituted -lactone dimers in good yield upon reaction with SmI 2 .
Williams, D.B.G., Lombard, H. & Holzapfel, C.W. 2001, 'A comparative study of some Pd-catalysed Heck reactions in polar- and aqueous biphasic media', Synthetic Communications, vol. 31, no. 13, pp. 2077-2081.
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A comparative study of some Pd-catalysed reactions was carried out making use of various ligands and catalyst precursors in polar polar/aqueous biphasic media, the results of which assist in the judicious selection of the appropriate reaction conditions for such Heck reactions.
Williams, D.B.G., Blann, K. & Holzapfel, C.W. 2001, 'Observations on the samarium diiodide-promoted C-C fragmentation/ring expansion chemistry of some aliphatic 1,4-diketones', Journal of the Chemical Society. Perkin Transactions 1, no. 3, pp. 219-220.
The observations on the samarium diiodide-promoted C-C fragmentation/ring expansion chemistry of some aliphatic 1,4-diketones were presented. It was found that some photochemical electron transfer, as well as SmI 2 -mediated transformations were carried out on non-aromatic substrates. It was shown that given the otherwise identical molecule, the ability of the SmI 2 HMPA complex to chelate the 1,4-dicarbonyl moiety in the one case and not in the other is the primary factor that determines the fragmentation reaction.
Williams, D.B.G., Blann, K. & Caddy, J. 2001, 'Fragmentation and cleavage reactions mediated by smi2. Part 1: X-y, x-x and c-c substrates', Organic Preparations and Procedures International, vol. 33, no. 6, pp. 565-602.
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Bradley, D., Williams, G., Blann, K. & Holzapfel, C.W. 2001, 'Aryl -ketoesters as precursors for -butyrolactones in samarium(II) iodide-mediated reactions', Synthetic Communications, vol. 31, no. 2, pp. 203-209.
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Various aryl -ketoesters were transformed into the corresponding substituted -lactones in good yield upon reaction with SmI 2 .
Billing, D.G., Holzapfel, C.W., Blann, K. & Williams, D.B.G. 2000, 'Meso-2,2'-Diphenyl-3,3',4,4'-tetrahydro-2,2'-bifuran-5,5'(2H,2'H)-dione', Acta Crystallographica Section C: Crystal Structure Communications, vol. 56, no. 11, pp. e522-e523.
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&copy; International Union of Crystallography 2000. The crystal structure of the title compound, C 20 H 18 O 4 , contains a crystallographic inversion center. The C-C bond linking the two halves of the molecule is slightly elongated at 1.577 (3) &Aring;.
Bellec, N., Montalban, A.G., Williams, D.B.G., Cook, A.S., Anderson, M.E., Feng, X., Barrett, A.G.M. & Hoffman, B.M. 2000, 'Porphyrazinediols: Synthesis, characterization, and complexation to group IVB metallocenes', Journal of Organic Chemistry, vol. 65, no. 6, pp. 1774-1779.
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The first metalated porphyrazinediols 11 have been prepared from (L)- (+)-dimethyl tartrate via conversion into the corresponding dispoke or 2,3- dimethoxy-2,3-butanediyl protected 2,3-dihydroxymaleonitrile, Linstead macrocyclization, transmetalation, and deprotection. Their stability is very dependent on the nature of the metal ion in the cavity of the porphyrazine. Reaction of these porphyrazinediols with metallocene dichlorides led to new solitaire porphyrazines 12 while DDQ oxidation followed by trapping with diaminomaleonitrile afforded new porphyrazine dinitriles 14.
Hachiya, S.I., Cook, A.S., Williams, D.B.G., Montalban, A.G., Barrett, A.G.M. & Hoffman, B.M. 2000, 'Synthesis, characterization and reactions of enantiomerically pure 'winged' spirane porphyrazines', Tetrahedron, vol. 56, no. 35, pp. 6565-6569.
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A series of enantiomerically pure porphyrazineoctaol derivatives have been prepared from L-(+)-dimethyl tartrate via conversion into the corresponding dispoke protected dihydroxymaleonitrile, Linstead macrocyclization and transmetallation. The derived chloromanganese(III) complexes catalyzed the epoxidation of styrene with sodium hypochlorite as the oxygen atom source but with modest enantioselectivities ( < 25%). (C) 2000 Elsevier Science Ltd. All rights reserved.
Bradley, D., Williams, G., Blann, K. & Holzapfel, C.W. 2000, 'Samarium(II) iodide promoted fragmentation and sequential reactions of aromatic 1,4-diketones', Journal of Organic Chemistry, vol. 65, no. 9, pp. 2834-2836.
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Braithwaite, D.H., Holzapfel, C.W. & Williams, D.B.G. 1999, 'Stereoselective thallium-induced ring contraction of glycals', Journal of Chemical Research - Part S, no. 2, pp. 108-109.
Various glycals, treated with TI(NO 3 ) 3 3H 2 O under mild conditions in an acetonitrile-methanol solvent mixture, underwent ring contraction in a stereoselective fashion, affording stable acetal products.
Holzapfel, C.W., Portwig, M. & Williams, D.B.G. 1999, 'Carbohydrates as spiroketal precursors', South African Journal of Chemistry, vol. 52, no. 4, pp. 165-167.
The preparation of some chiral spiroketals from carbohydrate precursors is described. The reversibility of the Lewis acid-catalysed ketalisation reaction ensured the dominance of the anomeric effect in determining the stereochemical outcome of the spiroketalisation step. In this way, enantiomerically pure products could be obtained from readily available starting materials.
Braithwaite, D.H., Holzapfel, C.W. & Williams, D.B.G. 1998, 'Carbohydrate-derived allylic stannanes', South African Journal of Chemistry, vol. 51, no. 4, pp. 162-164.
The preparation of tri(n-butyl)tin derivatives of various carbohydrates is described. Glycal derivatives were converted into the corresponding stannanes upon treatment with Bu 3 SnH under photochemical activation. This reaction was found to be regioselective but not stereoselective. Upon treating the glycals with Bu 3 Sn(Bu)Cu(CN)Li 2 as a nucleophile, the corresponding stannanes were obtained in an enantiomerically pure form. Preliminary results indicate that these stannanes may be converted into enantiopure C-glycosides by radical substitution of the tributyltin function.
Van Heerden, F.R., Huyser, J.J., Williams, D.B.G. & Holzapfel, C.W. 1998, 'Palladium-catalysed substitution reactions of geminal allylic diacetates', Tetrahedron Letters, vol. 39, no. 29, pp. 5281-5284.
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The Pd(0)-catalysed substitution of allylic 1,1-diacetates by both carbon and oxygen nucleophiles is described. The products isolated resulted from either single or double substitution reactions.
Andersen, K., Anderson, M., Andersen, O.P., Baum, S., Baumann, T.F., Beall, L.S., Broderick, W.E., Cook, A.S., Eichhorn, D.M., Goldberg, D., Hope, H., Jarrell, W., Lange, S.J., McCubbin, Q.J., Mani, N.S., Miller, T., Garrido Montalban, A., Rodriguez-Morgade, M.S., Lee, S., Nie, H. & Olmstead, M.M. 1998, 'Star porphyrazines and related multimetallic macrocycles', Journal of Heterocyclic Chemistry, vol. 35, no. 5, pp. 1013-1042.
Forsyth, T.P., Bradley G Williams, D., Montalban, A.G., Stern, C.L., Barrett, A.G.M. & Hoffman, B.M. 1998, 'A facile and regioselective synthesis of trans-heterofunctionalized porphyrazine derivatives', Journal of Organic Chemistry, vol. 63, no. 2, pp. 331-336.
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New methodology was developed for the selective synthesis of regiochemically defined porphyrazines of the form M[pz(A 2 ;B 2 )] (shown in Chart 1) where A and B represent peripheral functionalization attached to the -positions of the pyrroles. Specifically, phthalonitriles or derivatives thereof with sterically bulky groups in positions 3 and 6, in particular 4,7- bis(isopropyloxy)-1,3-diiminoisoindoline (3) act as a 'trans director' when macrocyclized with heteroatom-appended maleonitriles under Linstead conditions, the result being preferential formation of the trans- M[pz(A 2 ;B 2 )] pigment where A = SR, NMe 2 , OR, as well as R (shown in Chart 2). Linstead crossover macrocyclization of 3 with 4, 11, 15, and 18 gave pigments 10, 14, 17, and 19, respectively. These pigments were characterized by 1 H NMR, 13 C NMR, UV-visible spectroscopy, mass spectrometry, microanalysis, and 17 was characterized by single-crystal X-ray analysis.
Cook, A.S., Williams, D.B.G., White, A.J.P., Williams, D.J., Lange, S.J., Barrett, A.G.M. & Huffman, B.M. 1997, 'Enantiomerically Pure "Winged" Spirane Porphyrazinoctaols', Angewandte Chemie (International Edition in English), vol. 36, no. 7, pp. 760-761.
Grové, J.J.C., Holzapfel, C.W. & Williams, D.B.G. 1996, 'One-pot SmI2-promoted transformation of carbohydrate derivatives into cyclopentanols', Tetrahedron Letters, vol. 37, no. 32, pp. 5817-5820.
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Selectively functionalised carbohydrate derivatives underwent SmI 2 -promoted Grob-fragmentation reactions. This was followed by an in situ, stereocontrolled SmI 2 -mediated cyclisation to afford the corresponding cyclopentanols.
Grové, J.J.C., Holzapfel, C.W. & Williams, D.B.G. 1996, 'Stereoselective SmI2-mediated conversion of carbohydrates into cyclopentanols', Tetrahedron Letters, vol. 37, no. 8, pp. 1305-1308.
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Carbohydrate derivatives were employed as precursors in the synthesis of stereodefined cyclopentanols. This rapid conversion was effected by a zinc-assisted Grob-fragmentation, followed by a stereocontrolled SmI 2 -mediated cyclisation.
Holzapfel, C.W., Bradley, D. & Williams, G. 1995, 'A facile route to 3a,8a-dihydrofuro[2,3-b]benzofurans', Tetrahedron, vol. 51, no. 31, pp. 8555-8564.
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Consecutive employment of palladium-catalysis and samanum(II)iodide-induced radical chemistry allows access to analogues of the ABC enol ether tricycle of aflatoxin B 1 (1). The Pd-assisted coupling of tubutylstannyl ethers of various 2-iodophenols with 2,5-diacetoxy-2,5-dihydrofuran (4) provided products that could be cyclised into 3a,8a-dihydrofuro [2,3-b]benzofurans using SmI 2 . Elimination of an acetatosamarium species provides the requisite unsaturation situ . &copy; 1995 Elsevier Science Ltd All rights reserved.
Holzapfel, C.W., Bradley, D. & Williams, G. 1994, 'Heck reactions of some cyclic enol ethers: Intramolecular trapping of migratory palladium', Synthetic Communications, vol. 24, no. 15, pp. 2139-2146.
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The palladium&#8212;catalysed annulation of a number of enol ethers by o&#8212;chloromercuriophenol results in bridged tricyclic systems. &copy; 1994, Taylor & Francis Group, LLC. All rights reserved.