Andrew J. P. White

Imperial College London, Londinium, England, United Kingdom

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Publications (719)3118.18 Total impact

  • Michael S. Inkpen · Andrew J.P. White · Tim Albrecht · Nicholas J. Long
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    ABSTRACT: Trans-RuCl2(PP3)2 (1a) (PP3 = tris[2-(diphenylphosphino)ethyl]phosphine) was prepared by reaction of RuCl2(PPh3)3 with 2 eq. PP3. Through coordination of two potentially tetradentate ligands in a bidentate arrangement, four uncoordinated phosphine moieties remain readily available for subsequent reaction. This is demonstrated through their facile oxidation with hydrogen peroxide, providing trans-RuCl2(PP[P=O]2)2 (1b) (PP[P=O]2 = bis[2-(diphenylphosphine oxide)ethyl][2-(diphenylphosphino)ethyl]phosphine). Whilst chloride abstraction reactions from 1a appear slow (typical for trans dichlorides), cis-RuCl2(PP3) is shown to react rapidly with ethynylferrocene under ‘Dixneuf’ conditions (CH2Cl2, NaPF6, NEt3), providing the tri(hetero)metallic butenynyl complex [(PP3)Ru(η3–FcC3CHFc)]PF6 (2, Fc = ferrocenyl). The pendant groups of 1a-b offer great potential for future coordination studies (for example, to prepare mixed transition metal/lanthanide materials), whereby the facile synthetic route to 2 suggests a path towards examination of complex mixed-valence systems comprising multiple redox-active centres.
    No preview · Article · Jan 2016 · Journal of Organometallic Chemistry
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    ABSTRACT: A series of imino- and amino-pyridine ligands based on dihydrobenzofurobenzofuran (BFBF) and methanodibenzodioxocine (DBDOC) backbones have been synthesized. These ligands form exclusively dinuclear complexes with metals such as iron(II) and copper(II). The structures for complexes 15, 16, 18, 19, 20, 21, 23, and 24 were determined by X-ray crystallography. The complexes show large distances for the metal nuclei and different geometries depending on the nature of the metal. An octahedral geometry was observed for the iron(II) complexes, while copper (II) complex 24 showed a distorted trigonal bipyramidal geometry. The iron (II) complexes showed activity as catalysts in the cycloaddition of CO2 to epoxides, obtaining moderate yields of cyclic carbonates.
    No preview · Article · Jan 2016 · Dalton Transactions
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    ABSTRACT: In a continued effort to improve the suitability of ionic liquids in applications operating at raised temperatures, novel spirocyclic 'azoniaspiro' salts (with cations derived from five-, six-, seven- and eight-membered rings) are prepared and characterised. The structural and thermal properties of these salts are compared against those of established analogues. The stable geometries and ion pairing behaviour of these species are investigated via a combined experimental/computational approach, employing X-ray crystallography and Density Functional Theory (DFT) methods. Subsequently, the thermal stabilities of these organic salts are characterised and compared using a broad range of techniques. Hyphenated Thermogravimetry-Mass Spectrometry investigations enable complex mechanisms underlying thermal decomposition to be elucidated. Lastly, transition state structures are optimised, corresponding to plausible decomposition mechanisms of the azoniaspiro salt, 6-azoniaspiro[6.5]dodecanium chloride, and one prototypical monocyclic species 1-butyl-1-methylpiperidinium chloride, using DFT. The observed improved thermal stabilities of the azoniaspiro salts, and their potential higher-temperature stable-liquid ranges, render them promising candidates for future ionic liquid applications.
    Full-text · Article · Dec 2015 · Physical Chemistry Chemical Physics
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    ABSTRACT: The synthesis of three new dizinc(II) complexes bearing a macrocyclic [2 + 2] Schiff base ligand is reported. The bis(anilido)tetraimine macrocycle reacts with diethylzinc to form a bis(ethyl)dizinc(II) complex, [L(Et)Zn2Et2] (1). The reaction of complex 1 with isopropyl alcohol is reported, forming a bis(isopropyl alkoxide)dizinc complex, [L(Et)Zn2((i)PrO)2] (2). Furthermore, complex 1, with 2 equiv of alcohol, is applied as an initiator for racemic lactide ring-opening polymerization. It shows moderately high activity, resulting in a pseudo-first-order rate coefficient of 9.8 × 10(-3) min(-1), with [LA] = 1 M and [initiator] = 5 mM at 25 °C and in a tetrahydrofuran solvent. Polymerization occurs with good control, as evidenced by the linear fit to a plot of molecular weight versus conversion, the narrow dispersities, and the limited transesterification. The same initiating system is inactive for the ring-opening copolymerization of carbon dioxide (CO2) and cyclohexene oxide at 80 °C and 1 bar of CO2 pressure. However, stoichiometric reactions between complex 2 and CO2, at 1 bar pressure, result in the reversible formation of new dizinc carbonate species, [L(Et)Zn2((i)PrO)((i)PrOCO2)] (3a) and [L(Et)Zn2((i)PrOCO2)2] (3b), and the reaction was studied using density functional theory calculations. All of the new complexes, 1-3b, are fully characterized, including NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction.
    No preview · Article · Dec 2015 · Inorganic Chemistry
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    ABSTRACT: A ligand-accelerated effect is observed in the cyclization of propargylic amides catalyzed by bis(pyridyl)silver(I) complexes, with an unexpected reversal of electronic demand to the analogous NH addition reaction. The catalyst was found to be effective for internal alkyne substrates, offering exclusive selectivity for the 5-exo-dig product. Differences in selectivity profile between gold- and silver-catalyzed processes are highlighted and discussed.
    No preview · Article · Nov 2015 · Advanced Synthesis & Catalysis
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    ABSTRACT: A series of four dizinc complexes coordinated by salen or salan ligands, derived from ortho-vanillin and bearing (±)-trans-1,2-diaminocyclohexane (L1) or 2,2-dimethyl-1,3-propanediamine (L2) backbones, is reported. The complexes are characterized using a combination of X-ray crystallography, multinuclear NMR, DOSY, and MALDI-TOF spectroscopies, and elemental analysis. The stability of the dinuclear complexes depends on the ligand structure, with the most stable complexes having imine substituents. The complexes are tested as catalysts for the ring-opening copolymerization (ROCOP) of CO2/cyclohexene oxide (CHO) and phthalic anhydride (PA)/CHO. All complexes are active, and the structure/activity relationships reveal that the complex having both L2 and imine substituents displays the highest activity. In the ROCOP of CO2/CHO its activity is equivalent to other metal salen catalysts (TOF = 44 h(-1) at a catalyst loading of 0.1 mol %, 30 bar of CO2, and 80 °C), while for the ROCOP of PA/CHO, its activity is slightly higher than other metal salen catalysts (TOF = 198 h(-1) at a catalyst loading of 1 mol % and 100 °C). Poly(ester-block-carbonate) polymers are also afforded using the most active catalyst by the one-pot terpolymerization of PA/CHO/CO2.
    No preview · Article · Nov 2015 · Inorganic Chemistry
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    ABSTRACT: We report the synthesis and full characterization of the entire haloferrocene (FcX) and 1,1′-dihaloferrocene (fcX2) series (X = I, Br, Cl, F; Fc = ferrocenyl, fc = ferrocene-1,1′-diyl). Finalization of this simple, yet intriguing set of compounds has been delayed by synthetic challenges associated with the incorporation of fluorine substituents. Successful preparation of fluoroferrocene (FcF) and 1,1′-difluoroferrocene (fcF2) were ultimately achieved using reactions between the appropriate lithiated ferrocene species and N-fluorobenzenesulfonimide (NFSI). The crude reaction products, in addition to those resulting from analogous preparations of chloroferrocene (FcCl) and 1,1′-dichloroferrocene (fcCl2), were utilized as model systems to probe the limits of a previously reported "oxidative purification" methodology. From this investigation and careful solution voltammetry studies, we find that the fluorinated derivatives exhibit the lowest redox potentials of each of the FcX and fcX2 series. This counterintuitive result is discussed with reference to the spectroscopic, structural, and first-principles calculations of these and related materials.
    Full-text · Article · Nov 2015 · Organometallics
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    ABSTRACT: A series of iso-structural complexes [(SIPr)AgX] (X = Cl, Br, I, OTf; SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolidene) were synthesised, including the first example of a N-heterocyclic carbene silver(i) complex containing an O-bound triflate. Bond Energy Dissociation and Natural Orbitals for Chemical Valence bond analyses (BEDA & ETS-NOCV) revealing a significant NHC → M σ-back-donation, which influences the stability and sigma-donicity of these complexes.
    No preview · Article · Oct 2015 · Chemical Communications
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    ABSTRACT: Addition of fluoroarenes, fluoroalkanes or benzofuran to [{(2,6-(i)Pr2C6H3NCMe)2CH}Al] results in facile oxidative addition of either a C-F or C-O bond to the Al(i) centre.
    No preview · Article · Sep 2015 · Chemical Communications
  • Adi E. Nako · Wenyi Chen · Andrew J. P. White · Mark R. Crimmin
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    ABSTRACT: The scope of the catalytic dehydrocoupling of primary and secondary amines with phenylsilanes has been investigated using [Y{N(SiMe3)2}3] and a four-coordinate analogue bearing a cyclometalated phosphonium methylide ligand. Inclusion of the phosphorus-based ligand on yttrium results in increased substrate scope in comparison to the tris(amide) analogue. While reversible C-H bond activation of the cyclometalated ligand was observed in stoichiometric experiments, D-labeling experiments and DFT calculations suggest that reversible ligand activation is not involved in silazane formation under catalytic conditions. We suggest that the extended reaction scope with the four-coordinate yttrium phosphonium methylide complex relative to the three-coordinate yttrium (tris)amide complex is a result of differences in the ease of amine inhibition of catalysis.
    No preview · Article · Sep 2015 · Organometallics
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    ABSTRACT: The electronic and redox properties of a series of cyclometalated Pd complexes with oxidation states of +2, +3 and +4 were examined using a range of currently available spectroscopic and electrochemical techniques. Changes in metal-ligand bond lengths were established by X-ray crystallography and correctly predicted by DFT calculations, from which the frontier orbitals and partial atomic charges can be obtained. X-ray absorption spectroscopy (XAS) revealed interesting XANES features that suggest a synergistic relationship between metal-ligand interactions. The electrochemical study of the Pd(ii) dimer was found to contain two sequential oxidative potentials indicative of a weak metal-metal interaction.
    Full-text · Article · Sep 2015 · Dalton Transactions
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    ABSTRACT: Unsaturated silicon compounds are valuable building blocks for the synthesis of molecules with novel silicon-based structural motifs with potential applications in materials chemistry. The difficulties associated with the transfer of the Si=Si moiety to promising substrates can be explained by the lack of suitably functionalized derivatives. Herein we report the synthesis and full characterization of the first homoleptic trisilaallyl chloride R2Si = Si(R)–Si(Cl)R2 (R = 2, 4,6-triisopropylphenyl) by an unprecedented nucleophilic substitution at a central silicon atom under retention of an adjacent Si=Si double bond. Attempts to reductively generate the corresponding allylic anion led to the cleavage of the Si–Si single bond and isolation of the Et2O solvate of the corresponding disilenide.
    No preview · Article · Aug 2015 · Zeitschrift für anorganische Chemie
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    ABSTRACT: The detection of carbon monoxide in solution and air has been achieved using simple, inexpensive systems based on the vinyl complexes [M(CHCHR)Cl(CO)(BTD)(PPh3 )2 ] (R=aryl, BTD=2,1,3-benzothiadiazole). Depending on the nature of the vinyl group, chromogenic and fluorogenic responses signalled the presence of this odourless, tasteless, invisible, and toxic gas. Solutions of the complexes in CHCl3 underwent rapid change between easily differentiated colours when exposed to air samples containing CO. More significantly, the adsorption of the complexes on silica produced colorimetric probes for the naked-eye detection of CO in the gas phase. Structural data for key species before and after the addition of CO were obtained by means of single X-ray diffraction studies. In all cases, the ruthenium and osmium vinyl complexes studied showed a highly selective response to CO with exceptionally low detection limits. Naked-eye detection of CO at concentrations as low as 5 ppb in air was achieved with the onset of toxic levels (i.e., 100 ppm), thus resulting in a remarkably clear colour change. Moreover, complexes bearing pyrenyl, naphthyl, and phenanthrenyl moieties were fluorescent, and greater sensitivities were achieved (through turn-on emission fluorescence) in the presence of CO both in solution and air. This behaviour was explored computationally using time-dependent density functional theory (TDDFT) experiments. In addition, the systems were shown to be selective for CO over all other gases tested, including water vapour and common organic solvents. Supporting the metal complexes on cellulose strips for use in an existing optoelectronic device allows numerical readings for the CO concentration to be obtained and provision of an alarm system. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    No preview · Article · Aug 2015 · Chemistry - A European Journal
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    Mark Richard Crimmin · Olga Ekkert · Andrew J P White · Harold Toms
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    ABSTRACT: We report the addition of M–H bonds (M = Al, Zn, Mg) to a Rh(III) intermediate generated from the reductive elimination of triethylsilane from [Cp*Rh(H)2(SiEt3)2]. A series of new heterobimetallic complexes possessing Rh–M bonds have been isolated and characterised by a number of spectroscopic (1H, 29Si, 13C, 103Rh NMR, infrared, and X-ray diffraction) and computational techniques (NBO and QTAIM analysis). Experimental and computational data are consistent with cleavage of the M–H bond upon addition to rhodium with formation of new Rh–M and Rh–H bonds. Upon photolysis the Al analogue of this series undergoes a further elimination reaction producing triethylsilane and a highly unusual Rh2Al2H4 containing cluster proposed to contain an Al(I) bridging ligand.
    Preview · Article · Jul 2015 · Chemical Science
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    ABSTRACT: The stereospecific intramolecular hydroamination of alkynyl trichloroacetimidates catalyzed by bis(pyridyl)silver(I) complexes to form 1,3-oxazolines and oxazines has been investigated in greater detail. The rate of the reaction is profoundly influenced by the electronic character of the pyridyl ligand; leading to optimized conditions whereby reactions can be completed at ambient temperature with catalyst loadings as low as 1 mol%, while maintaining stereoselectivity towards the (Z)-isomer. Further investigations into establishing the role of the ligand, and the synthesis of (E)-isomer, are also presented.
    No preview · Article · Jul 2015 · Advanced Synthesis & Catalysis
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    ABSTRACT: A series of multimetallic copper(II) complexes have been re-investigated for methane oxidation with H2O2. The preparation and properties of trinuclear copper(II) complexes of the form [Cu3(triazole)n(OH2)12-n] (n = 8,10) are reported. While these complexes are trimeric in the solid-state, 1H NMR studies suggest that facile ligand dissociation occurs in solution. The oxidation of cyclohexane with H2O2 catalyzed by [Cu3(triazole)n(OH2)12-n] (n = 8, 10) is compared against a literature known oxo-centered tetrameric cluster (Angew. Chem., Int. Ed. 2005, 44, 4345) and these catalysts display moderate activities. The series have also been investigated in methane oxidation at 30 bar and 40 oC. Analytical techniques including a solvent suppression 1H NMR method have been applied to quantify the liquid- and gas-phase products. The multi-metallic copper(II) complexes and copper(II) nitrate control samples produce only methanol and CO2. While TONs for methanol production range from 1.4-4.6 in all cases approximately 50 times the amount of CO2 is produced relative to methanol. We conclude that selectivity is a determining factor in methane oxidation under these conditions and should be considered in future studies.
    Full-text · Article · Jun 2015 · Catalysis Science & Technology

  • No preview · Article · Jun 2015 · Catalysis Science & Technology
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    Mark Richard Crimmin · Andrew J P White · Adi E Nako
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    ABSTRACT: A series of bis(σ-B–H) complexes of copper(I) have been prepared by displacement of arene solvent from a β-diketiminate copper(I) complex by four-coordinate boranes, H3B–L (L = NMe3, lutidine). In the presence of the same copper arene complex, the secondary amine-borane H3B–NMe2H undergoes dehydrogenation. We provide evidence for formation of a heterogenous catalyst from decomposition of the solution species.
    Preview · Article · Jun 2015 · Dalton Transactions
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    ABSTRACT: Investigation of atropisomeric [(diphosphine)Au2Cl2] complexes in the title reaction reveals an over-riding electronic effect, e.g. more-electron-rich phosphines promote greater enantioselectivity.
    No preview · Article · Jun 2015 · ChemInform
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    Christian B Nielsen · Andrew J P White · Iain McCulloch
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    ABSTRACT: The 4,7-dithieno-2,1,3-benzothiadiazole (DTBT) moiety and its fluorinated counterpart are important π-conjugated building blocks in the field of organic electronics. Here we present a combined experimental and theoretical investigation into fundamental properties relating to these two molecular entities and discuss the potential impact on extended π-conjugated materials and their electronic properties. While the fluorinated derivative, in the solid state, packs with a cofacial overlap smaller than that of DTBT, we report experimental evidence of stronger optical absorption as well as stronger intra- and intermolecular contacts upon fluorination.
    Preview · Article · Apr 2015 · The Journal of Organic Chemistry

Publication Stats

17k Citations
3,118.18 Total Impact Points

Institutions

  • 1992-2015
    • Imperial College London
      • Department of Chemistry
      Londinium, England, United Kingdom
  • 2012
    • University College London
      • Department of Chemistry
      Londinium, England, United Kingdom
  • 2010
    • University of Sunderland
      Sunderland, England, United Kingdom
  • 2002-2010
    • Università degli Studi di Messina
      • Dipartimento di Scienze Chimiche
      Messina, Sicily, Italy
  • 1999-2010
    • Universidad de Extremadura
      • Faculty of Veterinary
      Ara Pacis Augustalis, Extremadura, Spain
    • Universidad de Burgos
      • Department of Chemistry
      Burgos, Castille and León, Spain
  • 2009
    • University of Bristol
      • School of Chemistry
      Bristol, England, United Kingdom
  • 2004
    • Università degli Studi di Siena
      Siena, Tuscany, Italy
  • 1997-2004
    • Imperial Valley College
      IPL, California, United States
  • 2000-2003
    • University of California, Los Angeles
      • Department of Chemistry and Biochemistry
      Los Ángeles, California, United States
  • 1996-2001
    • Northwestern University
      • Department of Chemistry
      Evanston, Illinois, United States
  • 1997-2000
    • University of Bologna
      Bolonia, Emilia-Romagna, Italy
  • 1996-1999
    • University of Birmingham
      • School of Chemistry
      Birmingham, England, United Kingdom
  • 1998
    • University of Ljubljana
      • Faculty of Chemistry and Chemical Technology
      Lubliano, Ljubljana, Slovenia