Liam Balloch

University of Strathclyde, Glasgow, SCT, United Kingdom

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Publications (9)48.4 Total impact

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    ABSTRACT: Metal detector: a bowl-shaped nanomolecule (see picture; S yellow, C gray, Zn blue) containing an unprecedented 16-atom [ZnC(3)](4) "anti-crown" ring has been unearthed by isolating a dizincated 2-substituted thiophene intermediate that would normally be hidden in tandem functionalization methodology.
    Angewandte Chemie International Edition 06/2012; 51(28):6934-7. · 13.73 Impact Factor
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    ABSTRACT: Post-metallation derivatives of the sodium dialkyl(amido)zincate reagent (TMEDA)Na(μ-TMP)Zn((t)Bu)(2) (TMEDA is N,N,N',N'-tetramethylethylenediamine and TMP is 2,2,6,6-tetramethylpiperidide) have been of structural interest due to the insight they give into aromatic metallation mechanisms. Here, the aromatic substrate is formally replaced with [ZnO](2) to give tetra-tert-butyldi-μ(4)-oxido-bis(tetramethylethylenediamine-κ(2)N,N')bis(μ(2)-2,2,6,6-tetramethylpiperidin-1-ido-κ(2)N:N)disodiumtetrazinc hexane 0.59-solvate, [Na(2)Zn(4)(C(4)H(9))(4)(C(9)H(18)N)(2)O(2)(C(6)H(16)N(2))(2)]·0.59C(6)H(14). The crystallographically centrosymmetric complex retains many of the structural features of its parent monomer but has an unusual dimeric structure, with a central planar Zn-O-Zn-O ring joined to two orthogonal near-planar Zn-O-Na-N rings through the distorted tetrahedral geometries of the oxide ions.
    Acta Crystallographica Section C Crystal Structure Communications 07/2011; 67(Pt 7):m252-4. · 0.78 Impact Factor
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    ABSTRACT: More usually thought of as a base, the sodium zincate [(TMEDA)·Na(μ-TMP)(μ-(t)Bu)Zn((t)Bu)] 1 can undergo single electron transfer with TEMPO to give [(TMEDA)·Na(μ-TMP)(μ-TEMPO(-))Zn((t)Bu)] 2 and [(TMEDA)·Na(μ-TEMPO(-))(2)Zn((t)Bu)] 3; and with chalcone [PhCOCH=CHPh] gives [{(TMEDA)·Na(μ-TMP)Zn((t)Bu)}(2)(μ-OCPhCH=CHPhCHPhCH=CPh-μ-O)] which contains two chalcone units C-C coupled though their benzylic C atoms.
    Chemical Communications 06/2011; 48(10):1541-3. · 6.38 Impact Factor
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    ABSTRACT: Previously we reported that direct zincation of N,N-dimethylaniline by the mixed-metal zincate reagent 1 ((TMEDA)Na(TMP)(t-Bu)Zn(t-Bu)) surprisingly led to meta-metallation (zincation) of the aniline, as manifested in the crystalline complex 2 ((TMEDA)Na(TMP)(m-C(6)H(4)-NMe(2))Zn(t-Bu)), and that iodination of these isolated crystals produced the meta-isomer N,N-dimethyl-3-iodoaniline quantitatively. Completing the study here we find that treating the reaction solution with iodine produces a 72% conversion and results in a mixture of regioisomers of N,N-dimethyliodoaniline, with the meta-isomer still the major product (ortho:meta:para ratio, 6:73:21), as determined by NMR. In contrast to this bimetallic method, sodiation of N,N-dimethylaniline with n-BuNa produced the dimeric, ortho-sodiated complex 3 (((TMEDA)Na(o-C(6)H(4)-NMe(2)))(2)), as characterised by X-ray crystallography and NMR. No regioisomers were observed in the reaction solution. Introducing t-Bu(2)Zn to this reaction solution afforded a cocrystalline product in the solid-state, composed of the bis-anilide 4 ((TMEDA)Na(o-C(6)H(4)-NMe(2))(2)Zn(t-Bu)) and the Me(2)N-C cleavage product 5 ({(TMEDA)(2)Na}(+){(t-Bu(2)Zn)(2)(µ-NMe(2))}(-)), which was characterised by X-ray crystallography. NMR studies of the reaction mixture that produces 4 and 5 revealed one additional species, but the mixture as a whole contained only ortho-species and a trace amount of para-species as established by iodine quenching. In an indirect variation of the bimetallic reaction, TMP(H) was added at room temperature to the reaction mixture that afforded 4 and 5. This gave the crystalline product 6 ((TMEDA)Na(TMP)(o-C(6)H(4)-NMe(2))Zn(t-Bu)), the ortho-isomer of the meta-complex 2, as determined from X-ray crystallographic and NMR data. Monitoring the regioselectivity of the reaction by iodination revealed a 16.6:1.6:1.0 ortho:meta:para ratio. Interestingly, when the TMP(H) containing solution was heated under reflux for 18 hours more meta-isomer was produced (corresponding ratio 3.7:4.2:1.0). It is likely that this change has its origin in a retro reaction that produces the original base 1 as an intermediate. Theoretical calculations at the DFT level using the B3LYP method and the 6-311G** basis set were used to probe the energetics of both monometallic and bimetallic systems. In accord with the experimental results, it was found that ortho-metallation was favoured by sodiation; whereas meta- (closely followed by para-) metallation was favoured by direct sodium-mediated zincation.
    Beilstein Journal of Organic Chemistry 01/2011; 7:1234-48. · 2.80 Impact Factor
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    ABSTRACT: As a further contribution to alkali-metal-mediated metalation, a method for converting C−H bonds directly to C−Zn bonds without the need for an additional salt metathesis step, reactions of the sodium TMP-zincate [(TMEDA)Na(μ-TMP)(μ-tBu)Zn(tBu)] (1) with three different electron-rich aromatic substrates, have been investigated. Under ambient-temperature conditions, N,N-diethylbenzamide, N,N-diethyl-3-methoxybenzamide, and N,N-diethyl phenyl O-carbamate were zincated ortho to the substituent group (in between both substituents in the second case) in the crystalline products [(TMEDA)Na(μ-TMP){μ-2-[1-C(O)NEt2]C6H4}Zn(tBu)] (3), [(TMEDA)Na(μ-TMP){μ-2-(1-C(O)NEt2)(3-OMe)C6H3}Zn(tBu)] (4), and [(TMEDA)Na(μ-TMP){μ-2-(1-OC(O)NEt2)C6H4}Zn(tBu)] (6). X-ray crystallography established that, in each case, the deprotonated aromatic fragment is captured by the residue of the bimetallic base, giving rise to seven-membered (NaNZnCCCO) ring structures for 3 and 4 and an eight-membered (NaNZnCCOCO) ring structure for 6. The new zincated aromatics were also characterized by solution-state 1H and 13C NMR spectroscopy. Reactivity studies of 3, 4, and 6 were also performed with iodine. In each case, three molar equivalents of iodine in THF solution gave the ortho-iodo products N,N-diethyl-2-iodobenzamide (7), N,N-diethyl-2-iodo-3-methoxybenzamide (8), and N,N-diethyl-2-iodophenyl-O-carbamate (9) in quantitative, 71% and 75% yields as determined by NMR analysis, respectively.
    12/2010;
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    ABSTRACT: Breaking with convention, the reaction of the sodium zincate, [(TMEDA)Na(mu-TMP)(mu-(t)Bu)Zn((t)Bu)] with benzyl methyl ether (PhCH(2)OMe) produces exclusively an ortho-zincated intermediate [(TMEDA)Na(mu-TMP)(mu-C(6)H(4)CH(2)OMe)Zn((t)Bu)] instead of the expected "thermodynamic" alpha-metallated product.
    Chemical Communications 04/2010; 46(13):2319-21. · 6.38 Impact Factor
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    ABSTRACT: Treatment of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) with a group 1 metal (Li, Na, K, Rb, or Cs), resulted in the reduction of this important radical to the TEMPO(-) anion--the first examples of elemental-metal single electron reduction of the radical to its anionic form. The synthesis and characterization of seven alkali metal TEMPO(-) complexes are reported. A variety of structural motifs are encountered depending on the choice of metal and/or solvent. (THF)(2) x [Li(+)(TEMPO(-))](4) 1 crystallized from THF as a cyclic (Li(4)O(4)) molecule. Two Li centers are stabilized by coordination to a THF molecule; the others by intramolecular coordination to N(TEMPO) atoms. [(THF) x Na(+)(TEMPO(-))](4) 2 exists as a distorted cubane where each Na center is coordinated to a THF molecule. No appreciable Na-N(TEMPO) coordination is observed. [(THF)(2) x Na(+)(3)(TEMPO(-))(2)(OH)](2) 3 was serendipitously prepared and exists as a distorted bis(cubane). It is envisaged that 3 is formed from 2 by insertion of a (Na-OH)(2) double bridge into its framework. [Na(+)(4)(mu(3)-TEMPO(-))(2)(mu(2)-TEMPO(-))(2)(TMEDA)(2)] 4, adopts a four-runged ladder structure, whereby the two outer Na centers are coordinated to TMEDA, in addition to two mu(2)-O and a N atom. The inner metal atoms are bound to three mu(3)-O atoms and a N atom. [(THF) x K(+)(TEMPO(-))](4) 5 resembles the motif found for 2; however, presumably because of the larger size of the metal, K-N(TEMPO) interactions are present in 5. The asymmetric unit of [(TMEDA) x Rb(+)(2)(TEMPO(-))(2)](2) 6 comprises a Rb(4)O(4) cubane with half a molecule of TMEDA coordinated to each metal. From a supramolecular perspective, 6 exists as a polymeric array of cubane units connected by TMEDA bridges. Completing the series, [Cs(+)(TEMPO)](infinity) 7 crystallizes from hexane to form a donor-free polymeric complex. Complexes 1, 2, and 4-7 are soluble in D(8)-THF solution, and their NMR spectra are reported. The solution structures in donor solvent appear virtually identical.
    Inorganic Chemistry 06/2009; 48(14):6934-44. · 4.59 Impact Factor
  • Angewandte Chemie International Edition 01/2009; 48(46):8675-8. · 13.73 Impact Factor
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    ABSTRACT: The new mixed lithium−zinc enolate compounds [(TMEDA)2Li2Zn{OC(CH2)Mes}4] (2) and [{TMP(H)}2Li2Zn{OC(CH2)Mes}4] (3) were prepared by reaction of the sterically demanding ketone 2,4,6-trimethylacetophenone (1) with the all-amido homoleptic zincate [LiZn(TMP)3] (TMP = 2,2,6,6-tetramethylpiperidide). X-ray crystallographic studies revealed that these compounds adopt a trinuclear Li···Zn···Li chain arrangement with enolate O bridges. In contrast, the metalation of 1 with heteroleptic [(TMEDA)LiZn(TMP)Me2] afforded the dimeric lithium enolate [(TMEDA)2Li2{OC(CH2)Mes}2] (4) as a crystalline solid, which has been characterized in the solid state by X-ray crystallography, and Me2Zn·TMEDA and TMP(H) as coproducts, showing that the dimethylamido zincate behaves as an amide base. The homoleptic zinc enolate [(TMEDA)Zn{OC(CH2)Mes}2] (5) was obtained by reaction of 1 with the zinc amide Zn(TMP)2, and its structure was determined by X-ray crystallography. 5 adopts a rarely observed monomeric arrangement where the two enolate groups bind terminally to the zinc. New enolates 2−5 have also been characterized by 1H, 13C, and 7Li NMR spectroscopy in C6D6 solution. DFT studies of the metalation of 1 by Zn(TMP)2 and Et2Zn revealed that the former amide has a much greater kinetic basicity than the latter alkyl reagent.
    Organometallics. 10/2008; 27(22).