School of Chemistry - Research Publications

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Author: O'Hair, Richard × Author: White, Jonathan ×

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    Palladium-Mediated CO2 Extrusion Followed by Insertion of Allenes: Translating Mechanistic Studies to Develop a One-Pot Method for the Synthesis of Alkenes
    Yang, Y ; Spyrou, B ; White, JM ; Canty, AJ ; Donnelly, PS ; O'Hair, RAJ (AMER CHEMICAL SOC, 2022-07-11)
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    Electronic and Steric Effects on the Reactivity of Seleniranium Ions with Alkenes in the Gas Phase
    Brydon, SC ; Thomson, C ; O'Hair, RAJ ; White, JM (AMER CHEMICAL SOC, 2023-01-27)
    Gas phase ion-molecule reactions between seleniranium ions, R-c-SeCH2CH2+, and cis-cyclooctene were used to probe electronic and steric effects of substituents on kinetics and branching ratios. The second-order rate coefficients increased in the order p-OMeC6H4 < C6H5 < p-BrC6H4 < p-CF3C6H4 < m-NO2C6H4, giving a Hammett plot with R2 = 0.98 and ρ = +1.66. The two main pathways include direct transfer of the selenium moiety to the incoming alkene (π-ligand exchange) and the less favored ring-opening by attack at an iranium carbon to give a cis-bicyclic selenonium ion as supported by density functional theory (DFT) calculations. Branching ratios of each pathway indicated that electron-withdrawing groups directed more attack at carbon than selenium in agreement with previous solution-phase results. Increased steric bulk on selenium was investigated by changing the R group from a methyl to t-butyl, which not only shut down π-ligand exchange but also significantly reduced the overall reactivity. Finally, the reactivity of the iranium ion derived from Se-methylselenocysteine was investigated and shown to react faster and favor π-ligand exchange as the leaving group was changed from ethene to acrylic acid.
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    Synthesis and X-Ray Crystallographic Characterisation of Frustum-Shaped Ligated [Cu18H16(DPPE)6]2+ and [Cu16H14(DPPA)6]2+ Nanoclusters and Studies on Their H2 Evolution Reactions
    Li, J ; Ma, HZ ; Reid, GE ; Edwards, AJ ; Hong, Y ; White, JM ; Mulder, RJ ; O'Hair, RAJ (WILEY-V C H VERLAG GMBH, 2018-02-09)
    We report new structural motifs for Cu nanoclusters that conceptually represent seed crystals for large face-centred cubic (FCC) crystal growth. Kinetically controlled syntheses, high resolution mass spectrometry experiments for determination of the dication formulae and crystallographic characterisation were carried out for [Cu18 H16 (DPPE)6 ][BF4 ][Cl] (DPPE=bis(diphenylphosphino)ethane) and [Cu16 H14 (DPPA)6 ][(BF4 )2 ] (DPPA=bis(diphenylphosphino)amine) polyhydrido nanoclusters, which feature the unprecedented bifrustum and frustum metal-core architecture in metal nanoclusters. The Cu18 nanocluster contains two Cu9 frustum cupolae and the Cu16 nanocluster has one Cu9 frustum cupola and a Cu7 distorted hexagonal-shape base. Gas-phase experiments revealed that both Cu18 H16 and Cu16 H14 cores can spontaneously release H2 upon removal of one bisphosphine capping ligand.
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    Experimental and theoretical investigations into the manifestation of the γ-effect in 2-and 4-[2-silylethyl)]pyridines and pyridinium ions
    Karnezis, A ; Brydon, SC ; Molino, A ; Wilson, DJD ; O'Hair, RAJ ; White, JM (ELSEVIER SCIENCE SA, 2021-11-15)
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    Mobile Proton Triggered Radical Fragmentation of Nitroarginine Containing Peptides
    Leeming, MG ; White, JM ; O'Hair, RAJ ; Donald, WA (SPRINGER, 2014-03)
    Protonated nitroarginine, [R(NO2) + H](+), which contains the nitroguanidine 'explosophore,' undergoes homolytic N - N nitro-imine bond cleavage to expel NO2(•) and form a radical cation of arginine in high yield (100% relative abundance) upon low-energy collision-induced dissociation (CID). Other ionization states of nitroarginine, including [R(NO2) - H](-), and a fixed-charge derivative of nitroarginine do not expel NO2(•) (<1%), but instead dissociate via heterolytic bond cleavage with abundant losses of small molecules (N2O and H2N2O2) from the nitroguanidine group. The effects of proton mobility on the CID reactions of nitroarginine containing peptides was investigated for peptide derivatives of leucine enkephalin, including XYGGFLR(NO2), X = D, G, K, and R, by examining the different protonation states: [M - H](-); [M + H](+); and [M + 2H](2+). For [M + H](+) containing the less basic N-terminal residues (X = D, G) and all [M + 2H](2+), mobile proton fragmentation reactions that result in peptide sequence ions dominate. In contrast, for peptides containing the basic N-terminal residues (R and K), the CID spectra of both the [M - H](-) and [M + H](+) are dominated by the losses of small even-electron neutrals from the nitroarginine side-chain. The fraction of nitroguanidine directed fragmentation of the nitroarginine side chain that results in bond homolysis to form [XYGGFLR](+•) by expulsion of NO2(•) increases by more than 10 times as the protonation state changes from [M - H](-) (<10%) to [M + 2H](2+) (ca. 90%) and by about four times as the acidity of the [M + H](+) N-terminal residue increases from R (19.0%) to D (76.5%). These results indicate that protonated peptides containing nitroarginine can undergo non-canonical mobile proton triggered radical fragmentation.