The chemistry of gold with unsaturated organics: coordination, activation and catalysis

The aim was to understand gold‟s reactivity with unsaturated organic bonds. We focused on the role of supporting ligands, activating agents and the organic substrates employed in such reactions. Gold tetrafluorophthalimidates have been isolated, with coordination found to be surprisingly strong; no [N(CO)2C6F4]- displacement with ζ- and π-donors were observed. B(C6F5)3 and norbornene addition to [(Ph3P)Au{N(CO)2C6F4}] leads to a [Au(nbe)3]+ cation paired with a new, non-coordinating phthalimido-diborate anion. Aryl-N substituents of [(Ph3P)Au{nacnac}] influences its differing solid state structures; examples of κ1- and (the first example of) asymmetric κ2-coordination was observed. In solution these complexes show intricate fluxional behaviour. Attempts at oxidation to synthesise a gold(III)-oxo complex were unsuccessful. In situ generated Au+ cations can selectively activate benzylic C-H and C-C bonds of methylarenes and dimesitylmethane under mild conditions. Mechanistic and kinetic studies with hexamethylbenzene have identified a C-H activation step of and the formation of a benzyl cation intermediate. Zwitterionic and heterobimetallic gold(I) complexes containing a (o-sulfophenyl)- diphenylphosphine ligand were formed, with the supporting Cl- and R2S ligands on gold(I) found to be non-labile, resulting in the complexes being catalytically inert. The incorporation of anions to [(C6F5)4Au2Ag2]n clusters gave structural and photoluminescent data, which evidently show that the emission colours of these powders are dependent on the extent of aurophilic bonding between cluster units. Dechlorination of [(C6F5)2AuCl]2 in the presence of olefins were prone to reductive elimination to yield „naked‟ gold(I)-(η2)olefin complexes. Repeating the reaction with benzene, toluene and xylenes appeared to give the unstable and unidentified gold(I)-arene analogues. 1H NMR monitoring of gold(III)-catalysed hydroarylation reactions revealed that silver salts do not act as a simple chloride scavengers, but identification of the gold species in solution was unsuccessful. In addition, a family of highly electrophilic fluorosulfonium and fluorobismuthium compounds were synthesised. These complexes decomposed at room temperature by intermolecular fluorination of the aryl substituents. N.B.: CIF files were attached to this thesis at the time of its submission. Please refer to the author for further details

The synthesis and characterization of Cu2ZnSnS4 thin films from melt reactions using xanthate precursors

Kesterite, Cu2ZnSnS4 (CZTS), is a promising absorber layer for use in photovoltaic cells. We report the use of copper, zinc and tin xanthates in melt reactions to produce Cu2ZnSnS4 (CZTS) thin films. The phase of the as-produced CZTS is dependent on decomposition temperature. X-ray diffraction patterns and Raman spectra show that films annealed between 375 and 475 °C are tetragonal, while at temperatures <375 °C hexagonal material was obtained. The electrical parameters of the CZTS films have also been determined. The conduction of all films was p-type, while the other parameters differ for the hexagonal and tetragonal materials: resistivity (27.1 vs 1.23 Ω cm), carrier concentration (2.65 × 10+15 vs 4.55 × 10+17 cm−3) and mobility (87.1 vs 11.1 cm2 V−1 s−1). The Hall coefficients were 2.36 × 103 versus 13.7 cm3 C−1

Towards eco-friendly crop protection: natural deep eutectic solvents and defensive secondary metabolites

Plant science

Synthesis and structures of gold perfluorophthalimido complexes

Compounds of the new tetrafluorophthalimido anion, [C6F4(CO)2N]-, are readily accessible by treatment of tetrafluorophthalimide with either LiNPri2 or mixtures of NEt3 and Me3ECl (E = Si or Sn), to give C6F4(CO)2N-X (X = Li 3, SiMe34, and SnMe35). The reaction of the trimethylsilyl derivative 4 with AgF leads cleanly to the ion pair complex [Ag(NCMe)2][Ag(N(CO)2C6F4)2] (6·2MeCN), which contains a linear [Ag{N(CO)2C6F4}2]- anion and a tetracoordinate Ag+ cation. Compound 6 reacts with iodine to give the N-iodo compound C6F4(CO)2NI 7, which crystallises as an acetonitrile adduct. Treatment of 6 with LAuCl affords LAu{N(CO)2C6F4} (L = Ph3P 8a, Cy3P 8b, or THT 9), whereas the reaction with AuCl in acetonitrile affords the heterobinuclear compound [Ag(MeCN)2][Au{N(CO)2C6F4}2]·MeCN (10·3MeCN). The tetrafluorophthalimido ligand is not readily displaced by donor ligands; however, the addition of B(C6F5)3(Et2O) to a diethyl ether solution of 8a leads to the salt [Au(PPh3)2][N{COB(C6F5)3}2C6F4)] 11. The analogous reaction of (THT)Au{N(CO)2C6F4} with B(C6F5)3 in toluene in the presence of excess norbornene (nb) gives [Au(nb)3][N{COB(C6F5)3}2C6F4)] 12. Compounds 11 and 12 contain a new non-coordinating phthalimido-bridged diborate anion with O-bonded boron atoms. The crystal structures of compounds 2–11 are reported

Reactivity of "ligand-free" Au:C-H and C-C activation versus π coordination

[(Me S)Au] cations, generated from (Me S)AuCl and AgSbF in dichloromethane at 0-20 °C, serve as sources of solvated Au (alongside unreactive [Au(SMe ) ] ), which reacts with the methyl-substituted arenes C Me H (n = 0-2) with C-H bond cleavage to give the sulfonium salts [C Me H CH SMe ] . There was no evidence for arene π coordination to Au or for the formation of σ-bonded Au-benzyl species. Surprisingly, the reaction of Au with CH Ar leads to C-C bond cleavage (Ar = 2,4,6-C H Me ). The reactions are highly selective for benzylic C-H and C-C bonds, whereas metalation of the arene ring is not observed. © 2011 American Chemical Society

Ultrafast charge dynamics in dispersions of monolayer MoS2 nanosheets

Ultrafast charge dynamics in dispersions of MoS2 nanosheets in N-methyl-2-pyrrolidone are reported. Samples were prepared by the ultrasonication-assisted exfoliation of MoS2 powder, resulting in nanosheets that were predominantly monolayer and had an average sheet size of 32.4 ± 0.1 nm. These dispersions were characterized using absorption and photoluminescence spectroscopy, transient photoluminescence measurements, and atomic force microscopy before the ultrafast charge dynamics were studied via transient absorption spectroscopy. The transient absorption spectra exhibited bleach peaks and photoinduced absorption peaks in spectral regions corresponding to both the A and B excitons of MoS2. The growth and decay of the features in the B exciton region were determined largely by the dynamics of the exciton population, while the features in the A exciton region depend on the dynamics of both excitons and trions