Neil Burford

University of Victoria, Victoria, British Columbia, Canada

Are you Neil Burford?

Claim your profile

Publications (193)982.03 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Triflate salts of trications [(bipy)2E]3+ ([6E][OTf]3) and [(tbbipy)2E]3+ ([6’E][OTf]3) (bipy = 2,2’-bipyridine, tbbipy = 4, 4’-di-tbutyl-2,2’-bipyridine; E = P, As, Sb, Bi) have been synthesized and comprehensively characterized. The unique molecular and electronic structures of this new class of complexes involving pnictogen Lewis acids has been assessed in the solid, solution and gas phases to reveal systematic variations in metric parameters, ligand lability and charge concentration. While the Lewis acidity of E3+ has the trend E = Bi < Sb < As < P as determined by gas-phase calculations and 1H NMR spectroscopy, the Lewis acidity of [6E]3+ has the trend E = P < As < Sb < Bi according to gas-phase calculations. Derivatives of [6’E][OTf]3 (E = P, As) are latent sources of E(OTf)3 as demonstrated by their reactions with dmap, which give the corresponding derivatives of [(dmap)3E][OTf]3. The highly oxidizing nature of P(OTf)3 and As(OTf)3 is evidenced in reactions of [6’E][OTf]3 (E = P, As) with phosphines, which give EI-containing monocations [(R3P)2E]1+ and oxidatively coupled dications [R3PPR3]2+, illustrating new P-P and P-As bond forming strategies. Cations [6’E]3+ (E = P, As) are C-H bond activating agents that dehydrogenate 1,4-cyclohexadiene, with higher activity observed for E = P. Combinations of [6’E]3+ and tBu3P activate H2 and D2 under mild conditions, evidencing frustrated Lewis pair activity. Oxidation of [6’P][OTf]3 with SO2Cl2 gives [(tbbipy)2PCl2][OTf]3, containing a PV-trication, but there is no evidence of the analogous reaction with [6’As][OTf]3. The observations highlight new directions in the chemistry of highly charged cations and reveal a rich reactivity for p-block triflates E(OTf)3, which can be accessed through derivatives of [6E][OTf]3 and [6’E][OTf]3.
    Chemical Science 08/2015; DOI:10.1039/C5SC02423D · 9.21 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Reactions of triarylphosphines with fluoroantimony(III) triflates give phosphine antimony(III) complexes, which undergo spontaneous reductive elimination of fluorophosphonium cations. The resulting phosphine antimony(I) complexes catenate to give the first examples of cationic antimony bicyclic compounds, [(R3 P)4 Sb6 ](4+) , featuring a bicyclo[3.1.0]hexastibine framework stabilized by four phosphine ligands. The unprecedented 14-electron redox process illustrates the generality of the reductive catenation method. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Angewandte Chemie International Edition 06/2015; 54(27). DOI:10.1002/anie.201503074 · 11.26 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Reactions of triarylphosphines with fluoroantimony(III) triflates give phosphine antimony(III) complexes, which undergo spontaneous reductive elimination of fluorophosphonium cations. The resulting phosphine antimony(I) complexes catenate to give the first examples of cationic antimony bicyclic compounds, [(R3P)4Sb6]4+, featuring a bicyclo[3.1.0]hexastibine framework stabilized by four phosphine ligands. The unprecedented 14-electron redox process illustrates the generality of the reductive catenation method.
    Angewandte Chemie 06/2015; 127(27). DOI:10.1002/ange.201503074
  • [Show abstract] [Hide abstract]
    ABSTRACT: The coordination chemistry of the stiboranes Ph4 Sb(OTf) (1 a, OTf = OSO2 CF3 ) and Ph3 Sb(OTf)2 (3) with Lewis bases has been investigated. The significant steric encumbrance of the Sb center in 1 a precludes interaction with most ligands, but the relatively low steric demands of 4-methylpyridine-N-oxide (OPyrMe) and OPMe3 enabled the characterization of [Ph4 Sb(OPyrMe)][OTf] (2 a) and [Ph4 Sb(OPMe3 )][OTf] (2 b), rare examples of structurally characterized complexes of stibonium acceptors. In contrast, 3 was found to engage a variety of Lewis bases, forming stable isolable complexes of the form [Ph3 Sb(donor)2 ][OTf]2 [donor=OPMe3 (6 a), OPCy3 (6 b, Cy=cyclohexyl), OPPh3 (6 c), OPyrMe (6 d)], [Ph3 Sb(dmap)2 (OTf)][OTf] (6 e, dmap=4-(dimethylamino)pyridine) and [Ph3 Sb(donor)(OTf)][OTf] [donor=1,10-phenanthroline (7 a) or 2,2'-bipy (7 b, bipy=bipyridine)]. These compounds exhibit significant structural diversity in the solid-state, and undergo ligand exchange reactions in line with their assignment as coordination complexes. Compound 3 did not form stable complexes with phosphine donors, with reactions instead leading to redox processes yielding SbPh3 and products of phosphine oxidation. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Chemistry - A European Journal 04/2015; 21(21). DOI:10.1002/chem.201406469 · 5.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Reductive elimination of [R3PPR3]2+, [11(R)]2+, from the highly electrophilic SbIII centres in [(R3P)3Sb]3+, [8(R)]3+, gives SbI containing cations [(R3P)Sb]1+, [9(R)]1+, which assemble into frameworks identified as cyclo-tetra(stibinophosphonium) tetracations, [(R3P)4Sb4]4+, [10(R)]4+. A phosphine catalyzed mechanism is proposed for conversion of fluoroantimony complexes [(R3P)2SbF]2+, [7(R)]2+, to [10(R)]4+, and the characterization of key intermediates is presented. The results constitute evidence of a novel ligand activation pathway for phosphines in the coordination sphere of hard, electron deficient acceptors. Characterization of the associated reactants and products supports earlier, albeit less definitive, detection of analogous phosphine ligand activation in CuIII and TlIII complexes, illustrating that these prototypical ligands can behave simultaneously as reducing agents and σ donors for a variety of hard acceptors. The reactivity of the parent cyclo-tetra(stibinophosphonium) tetracation, [10(Me)]4+, is directed by high charge concentration and strong polarization of the P-Sb bonds. The former explains the observed facility for reductive elimination to yield elemental antimony and the latter enabled activation of P-Cl and P-H bonds to give phosphinophosphonium cations, [Me3PPR’2]1+, including the first example of an H-phosphinophosphonium, [(Me3P)P(H)R’]1+, and 2-phosphino-1,3-diphosphonium cations, [(Me3P)2PR’]2+. Exchange of a phosphine ligand in [10(Me)]4+ with [nacnac]1- gives [(Me3P)3Sb4(nacnac)]3+, [15(Me)]3+, and with dmap gives [(Me3P)3Sb4(dmap)]4+, [16]4+. The lability of P-Sb or Sb-Sb interactions in [10(Me)]4+ has also been illustrated by characterization of heteroleptically substituted derivatives featuring PMe3 and PEt3 ligands.
    Chemical Science 02/2015; 6(4). DOI:10.1039/C4SC03939D · 9.21 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Three series of phosphine chalcogenide complexes of the antimony(III) halides SbX3 (X = F, Cl, Br, or I) have been synthesized and characterized by spectroscopic and crystallographic methods. Complexes of the generic formulae (Cy3PO)SbX3 (X = F (1a), Cl (1b), or Br (1c)), (Cy3PO)2SbX3 (X = F (2a), Cl (2b), or Br (2c)), and (Cy3PS)SbX3 (X = Cl (3b), Br (3c), or I (3d)) were synthesized via the treatment of solutions of SbX3 with OPCy3 and SPCy3, respectively. Derivatives of (Cy3PO)SbX3 were characterized by single crystal X-ray diffraction for 1a and 1b and crystallize as dimers through symmetry related intermolecular Sb–X interactions, providing the first structurally characterized examples of this class of complex. Derivatives of (Cy3PS)SbX3 (3b–3c) adopt analogous dimeric structures in the solid state. The solid-state structure of (Cy3PO)2SbCl3 (2b) is consistent with the previously reported structures of bis-phosphine oxide complexes of antimony(III), with a square pyramidal Sb center and cis-configured OPCy3 ligands. The phosphine chalcogenide complexes of SbX3 display configurations that are consistent with the perceived trans-labilizing properties of the ligands/substituents.
    Canadian Journal of Chemistry 01/2015; 93(3):1-5. DOI:10.1139/cjc-2014-0386 · 1.06 Impact Factor
  • Saurabh S. Chitnis · Neil Burford
    [Show abstract] [Hide abstract]
    ABSTRACT: An overview of the synthesis, structures and reaction chemistry of coordination complexes featuring an acceptor with at least one lone pair and at least one phosphine donor is presented. One or more examples of complexes have been structurally-characterized for the majority of p-block elements but few are known for most elements. The unusual condition of a p-block element centre accommodating a lone pair of electrons and offering a low energy LUMO gives the element centre the potential to behave as both a Lewis acid and a Lewis Base. The structural diversity and reactivity of the phosphine complexes highlights new directions in main group chemistry and by comparison with transition metal coordination chemistry, the featured complexes demonstrate significant configurational and stereochemical flexibility. Ligand exchange, oxidation and reduction chemistry at the lone pair acceptor centre reveals unusual reactivity and an interesting class of ligands and inorganic reagents, with new possibilities for catalysis or small molecule activation.
    Dalton Transactions 10/2014; 46(7). DOI:10.1039/C4DT02789B · 4.20 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The cyclo-diphosphinophosphonium salt [(PtBu)3Me][OTf] (2) has been shown to be highly reactive towards Lewis bases, exhibiting diverse reactivity towards phosphines, 4-(dimethylamino)pyridine (dmap) and chlorophosphines, providing approaches to new open-chain and cyclic catena-phosphorus frameworks. Reaction of 2 with R3P (R = Me or nPr) or dmap led to the ring-opened adducts [R3P-PtBu-PtBu-P(Me)tBu][OTf] (R = Me (4a), nPr (4b)) and [(dmap)-PtBu-PtBu-P(Me)tBu][OTf] (6), respectively. The complicated 31P NMR spectra of the three compounds were simulated, evidencing the presence of two diastereomeric forms of 4a, and single diastereomers of 4b and 6. This ring-opening reactivity of the cation in 2 parallels the reactivity of isolobal epoxides with nucleophiles under acidic conditions. Compound 2 was also shown to react with a 2:1 mixture of Me2PCl and TMSOTf to form the unexpected cyclo-1,2-diphosphino-3,4-diphosphonium salt [(Me2P)2(PtBu)2][OTf]2 (8), which is postulated to result from two consecutive ring-opening and ring closing steps. In contrast, reaction with MePCl2 furnished [(MeP)(PtBu)2P(Me)tBu][OTf] (9), consistent with insertion of a 'MeP' moiety into the cationic phosphorus framework of 2. The importance of ring strain on the reactivity of the cation in 2 was illustrated by comparative studies of the corresponding cyclo-tetraphosphorus cation in [(PtBu)4Me][OTf] (10), which exhibits no reactivity under analogous conditions.
    Journal of the American Chemical Society 09/2014; 136(42). DOI:10.1021/ja507741s · 12.11 Impact Factor
  • Saurabh S Chitnis · Marc J Whalen · Neil Burford
    [Show abstract] [Hide abstract]
    ABSTRACT: We report a comprehensive and systematic experimental and computational assessment of the P-P bond in prototypical molecules that represent a rare series of known compounds. The data presented compliments the existing solid-state structural data and previous computational studies to provide a thorough thermodynamic and electronic understanding of the P-P bond. Comparison of homolytic and heterolytic bond dissociation for tricoordinate-tricoordinate, tricoordinate-tetracoordinate and tetracoordinate-tetracoordinate P-P bonds frameworks 1-6 provides fundamental insights into covalent bonding. For all types of P-P bond discussed, homolytic dissociation is favoured over heterolytic dissociation, although the distinction is small for 21+ and 61+. The presence of a single cationic charge in a molecule substantially strengthens the P-P bond (relative to analogous neutral frameworks) such that it is comparable with the C-C bond in alkanes. Nevertheless, P-P distances are remarkably independent of molecular charge or coordination number, and trends in values of d(PC) and νsymm(PC) imply that a molecular cationic charge is distributed over the alkyl substituents. In the gas phase, the diphosphonium dication 32+ has similar energy to two [PMe3]+ radical cations, so that it is the lattice enthalpy of 3[OTf]2 in the solid-state that enables isolation, highlighting that values from gas-phase calculations are poor guides for synthetic planning for ionic compounds. There are no relationships or correlations between bond lengths, strengths and vibrational frequencies.
    Journal of the American Chemical Society 08/2014; 136(35). DOI:10.1021/ja507413s · 12.11 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Pniktanderivate können die Rolle von sowohl 2 e‐Donoren (Lewis‐Basen) als auch 2 e‐Akzeptoren (Lewis‐Säuren) übernehmen. Als prototypische Liganden in der Koordinationschemie von Übergangsmetallen bilden Amine und Phosphane auch Komplexe mit Lewis‐Säuren des p‐Blocks, die verschiedene Pniktogen‐zentrierte Akzeptoren umfassen. Die Lewis‐Acidität von Pniktogenzentren kann durch eine kationische Ladung verstärkt werden, was in den letzten Jahren zur Entwicklung von Verbindungen mit koordinativen Pn‐Pn‐ und Pn‐Pn′‐Wechselwirkungen genutzt wurde. Diese Verbindungen bieten die außergewöhnliche Möglichkeit zur homoatomaren Koordinationsbindung und ermöglichen die Entwicklung von Komplexen mit einem freien Elektronenpaar am Akzeptorzentrum. Dieser Aufsatz weist neue Richtungen für die systematische Erweiterung der Koordinationschemie von der Übergangsreihe zum p‐Block. GermanKoordinations‐ oder Donor‐Akzeptor‐Bindungen bilden die Grundlage der Übergangsmetallchemie, sie treten aber auch zwischen Nichtmetallen auf. Dieser Aufsatz betrachtet koordinative Wechselwirkungen zwischen Pniktogenen (Pn) und zeigt deren strukturelle Vielfältigkeit. Verbindungen, die Pn‐Pn‐ oder Pn′‐Pn‐Bindungen enthalten, werden geordnet nach dem als kationischer Akzeptor wirkenden Pniktogenelement behandelt.
    Angewandte Chemie 06/2014; 126(24). DOI:10.1002/ange.201307658
  • [Show abstract] [Hide abstract]
    ABSTRACT: The coordination of Me2E(OTf)2 (E = Si, Ge, Sn) acceptors by dmap or 2,2'-bipy furnishes two series of complexes which exhibit distinct structural trends that correlate with the covalent radii of the tetrael elements, and which contrast complexes of these ligands with EX4 (X = Cl or Br).
    Chemical Communications 06/2014; 50(59). DOI:10.1039/c4cc01109k · 6.83 Impact Factor
  • Alasdair P M Robertson · Paul A Gray · Neil Burford
    [Show abstract] [Hide abstract]
    ABSTRACT: Pnictine derivatives can behave as both 2e(-) donors (Lewis bases) and 2e(-) acceptors (Lewis acids). As prototypical ligands in the coordination chemistry of transition metals, amines and phosphines also form complexes with p-block Lewis acids, including a variety of pnictogen-centered acceptors. The inherent Lewis acidity of pnictogen centers can be enhanced by the introduction of a cationic charge, and this feature has been exploited in recent years in the development of compounds resulting from coordinate Pn-Pn and Pn-Pn' interactions. These compounds offer the unusual opportunity for homoatomic coordinate bonding and the development of complexes that possess a lone pair of electrons at the acceptor center. This Review presents new directions in the systematic extension of coordination chemistry from the transition series into the p-block.
    Angewandte Chemie International Edition in English 06/2014; 53(24). DOI:10.1002/anie.201307658 · 13.45 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Complexes of the generic formula [Cln(PR3)mSb]((3-n)+) (n = 1, 2, 3, or 4 and m = 1 or 2) have been prepared featuring [ClSb](2+), [Cl2Sb](1+), Cl3Sb, or [Cl4Sb](1-) as acceptors with one or two phosphine ligands {PMe3, PPh3, PCy3 (Cy = C6H11)}. The solid-state structures of the complexes reveal foundational features that define the coordination chemistry of a lone pair bearing stibine acceptor site. The experimental observations are interpreted with dispersion-corrected density functional theory calculations to develop an understanding of the bonding and structural diversity.
    Inorganic Chemistry 04/2014; 53(10). DOI:10.1021/ic500723y · 4.76 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The syntheses of salts containing ligand-stabilized Ph3Sb2+ and Ph3Bi2+ dications have been realized by in situ formation of Ph3Pn(OTf)2 (Pn=Sb or Bi) and subsequent reaction with OPPh3, dmap and bipy. The solid-state structures demonstrate diversity imposed by the steric demands and nature of the ligands. The synthetic method has the potential for broad application enabling widespread development of the coordination chemistry for PnV acceptors.
    Angewandte Chemie 03/2014; 126(13). DOI:10.1002/ange.201310613
  • [Show abstract] [Hide abstract]
    ABSTRACT: The syntheses of salts containing ligand-stabilized Ph3Sb 2+ and Ph3Bi2+ dications have been realized by in situ formation of Ph3Pn(OTf)2 (Pn=Sb or Bi) and subsequent reaction with OPPh3, dmap and bipy. The solid-state structures demonstrate diversity imposed by the steric demands and nature of the ligands. The synthetic method has the potential for broad application enabling widespread development of the coordination chemistry for PnV acceptors. A coordinated effort: The synthesis and characterization of OPPh 3, dmap (4-(dimethylamino)pyridine), and bipy (2,2′-bipyridine) complexes of SbV and BiV are reported. The solid-state structures demonstrate structural diversity driven by the steric demands and the nature of the ligands.
    Angewandte Chemie International Edition 03/2014; 53(13). DOI:10.1002/anie.201310613 · 11.26 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The transfer of a Ph2P+-moiety provided by Ph2PCl and chloronium-addition with PCl5 or PhICl2 to the cyclo-phosphanes (t-BuP)(n) (n = 3 (4), 4 (5)) were investigated. The reactions strongly depend on the presence of GaCl3 or Me3SiOTf as a halide abstracting reagent. The reaction of 4 with Ph2PCl and GaCl3 quantitatively yields cation [Ph2P(t-BuP)(3)](+) (6(+)) as a GaCl4--salt. Using Me3SiOTf as a halide abstracting reagent leads to the ring expansion of (t-BuP) 3 (4) to tetrameric (t-BuP) 4 (5) and cation 6(+) is only formed as a minor product. Chloronium addition employing the PCl5/GaCl3 or PhICl2/Me3SiOTf systems as Cl--sources to 4 gives complex reaction mixtures. In contrast, the Cl--addition to 5 gives cation [Cl(t-BuP)(4)](+) (8(+)) quantitatively when the system PCl5/GaCl3 is used. Utilising PhICl2 in the presence of Me3SiOTf gives t-BuPCl2 as the main product.
    Australian Journal of Chemistry 05/2013; 66(10):1155. DOI:10.1071/CH13141 · 1.56 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The reaction of CH3OSO2CF3 (MeOTf) with BiBr3 in tetrahydrofuran (THF) yields (THF)2BiBr2(OTf) (1), which is converted to (dmpe)BiBr2(OTf) (2Br) upon displacement of the THF ligands with bis(dimethylphosphino)ethane (dmpe). The chloride derivatives (dmpe)BiCl2(OTf) (2Cl) and (dmpe)BiCl(OTf)2 (3) are obtained from the reaction of BiCl3 and dmpe with 1 and 2 equiv of Me3SiOSO2CF3 (TMSOTf), respectively. The complexes readily decompose in solution to give elemental bismuth and a mixture of products. The solid-state structures reveal dimeric units bridged by both triflate O-S-O interactions and weak Bi-X-Bi interactions (X = Cl, Br). Comparison of the solid-state structures illustrates that both cis and trans configurations of halides are possible in complexes of the form L2BiX2(OTf), depending upon the denticity of the ligand. The experimentally observed configurations are consistent with minima calculated at the MP2 level for the triflate-free cations in the gas phase. Examination of the MP2-calculated electronic structure of 3 reveals the presence of low-lying π-type orbitals that may result in Z-type ligand activity. However, the attempted coordination of 3 with the electron-rich metal center in K2PdCl4, via metal-to-ligand back-donation, leads instead to halide abstraction, giving [(dmpe)2Pd][(CH3CN)2Bi2Cl6(OTf)2] (8). The anion in 8 consists of two octahedral bismuth environments bridged along one edge by two triflate anions. The results illustrate new coordination chemistry for bismuth.
    Inorganic Chemistry 05/2013; 52(12). DOI:10.1021/ic400875a · 4.76 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Square deal: Reactions of SbF3 with Me3 SiOSO2 CF3 produce Sb(3+) and [Sb-F](2+) cations which form complexes with two or three Me3 P ligands. Subsequent reductive elimination of diphosphonium or fluorophosphonium cations from the complexes give the folded square cyclo-[(Me3 P)4 Sb4 ][OTf]4 . Formation of the tetracation framework reveals new redox chemistry for Sb.
    Angewandte Chemie International Edition 04/2013; 52(18). DOI:10.1002/anie.201210012 · 11.26 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Gasantrieb: Die sequenzielle Abstraktion von Fluoridionen aus SbF3 in Gegenwart von 2,2′‐Bipyridin führt in hohen Ausbeuten zu einer Komplexreihe mit [SbF2]+‐, [SbF]2+‐ und [Sb]3+‐Akzeptoren (siehe Bild). Das thermodynamisch günstige schnelle Entfernen von gasförmigem Me3SiF könnte einen allgemeinen Ansatz auf dem Gebiet der Koordinationschemie von Hauptgruppenzentren und zur Erhöhung ihrer Lewis‐Acidität darstellen.
    Angewandte Chemie 02/2013; 125(7). DOI:10.1002/ange.201207529
  • [Show abstract] [Hide abstract]
    ABSTRACT: Gas driven: A high-yield approach to sequential fluoride ion abstraction from SbF(3) in the presence of 2,2'-bipyridine gives a series of complexes containing [SbF(2) ](+) , [SbF](2+) , and [Sb](3+) acceptors. The thermodynamically favorable rapid elimination of gaseous Me(3) SiF provides a potentially general approach to enhance the Lewis acidity and coordination chemistry of p-block centers.
    Angewandte Chemie International Edition 01/2013; 52(7). DOI:10.1002/anie.201207529 · 11.26 Impact Factor

Publication Stats

3k Citations
982.03 Total Impact Points


  • 2011–2015
    • University of Victoria
      • Department of Chemistry
      Victoria, British Columbia, Canada
    • University of Delaware
      • Department of Chemistry and Biochemistry
      Ньюарк, Delaware, United States
  • 1989–2014
    • Dalhousie University
      • Department of Chemistry
      Halifax, Nova Scotia, Canada
  • 1994–2011
    • University of Louisville
      • Department of Chemistry
      Louisville, Kentucky, United States
  • 1986–1994
    • University of New Brunswick
      • Department of Chemistry
      Fredericton, New Brunswick, Canada
  • 1987
    • Durham University
      • Department of Chemistry
      Durham, England, United Kingdom