Anthony G. Avent

Antifungal alkyl pyrones of Trichoderma harzianum

Two strains of Trichoderma harzianum were both found to produce the volatile metabolites 6-n-pentyl-2H-pyran-2-one and 6-n-pentenyl-2H-pyran-2-one. The pentyl analogue, the major product, demonstrated potent inhibitory properties to a wide range of fungi and considerably reduced the rate of damping off in lettuce seedlings by Rhizoctonia solani during in vitro testing.

Evidence for hydrogen bonding in solutions of 1-ethyl-3-methylimidazolium halides, and its implications for room-temperature halogenoaluminate(III) ionic liquids

Multinuclear NMR spectroscopy and conductivity measurements showed that the 1-ethyl-3-methyl-imidazolium cation, [emim]+, not only forms strong hydrogen bonds (using all three ring protons H2, H4 and H5) with halide ions in polar molecular solvents (e.g. ethanenitrile) and ionic liquids, but that it exists in a quasi-molecular state, [emim]X, in non-polar solvents (e.g. trichloro- and dichloro-methane), showing a conventional aromatic stacking phenomenon.

Synthesis and characterisation of bis(amino)silylene–nickel(0), –palladium(II), –platinum(0), –platinum(II) and copper(I) complexes

Abstract The bis(amino)silylene Si[(NCH2tBu)2C6H4-1,2] ( SiNN) behaved as a ligand in displacing COD or PPh3 from [Ni(COD)2], [Pt(PPh3)4] or [CuI(PPh3)3], yielding the crystalline d10 complexes [Ni(SiNN)4] (crystallised from Et2O as the 1:1-adduct 2), [Pt(PPh3)(SiNN)3] (5) or [CuI(PPh3)2(SiNN)] (6). Under the same conditions (in C6H6 at ambient temperature), SiNN and [MCl2(PPh3)2] yielded the crystalline (i) d8 complex trans-[M{SiNN(Cl)}2(SiNN)2] [M=Pt (3), Pd (4)] or (ii) the d10 complexes [Ni(PPh3)4−n(SiNN)n] (n=4 (2) or 3 (1), depending on stoichiometry; with Cl2SiNN as co-product). The X-ray structures of 2, 4, 5 and 6 are presented; those of 1 and 3 appeared in a preliminary communication. Compound 3 was shown to undergo three fluxional processes in CDCl3 solution, as shown by detailed variable temperature NMR spectroscopic experiments. These involved in order of increasing energy (a) two conformers of 3, (b) one of these and the cis-isomer, and (c) Si→Si 1,3-shifts of Cl−. These results are placed into the context of related published silylenemetal chemistry.

FORMATION OF C70PH10 AND C70PH8 FROM THE ELECTROPHILE C70CL10

In the presence of ferric chloride, benzene readily undergoes electrophilic substitution by C70Cl10 to give both yellow C70Ph10 and orange-red C70Ph8, each of which is luminescent. Their structures have been characterised by 1H and 13C NMR spectroscopy [including nOe and two-dimensional (COSY) analysis], and by UV, IR, and mass spectrometry. C70Ph10 is not formed directly from C70Cl10, but rather by further phenylation of the intermediate C70Ph8. The adjacent phenyl groups of C70Ph10 are sterically prevented from rotating at room temperature.

Hydrolysis of the diterpenoid glycoside, stevioside

Abstract The minor products from the acid-catalysed hydrolysis of the diterpenoid glycoside, stevioside have been identified and the location of the deuterium has been established when the hydrolysis is carried out in the presence of deuterium bromide.

Kinetic stability of heteroleptic (β-diketiminato) heavier alkaline-earth (Ca, Sr, Ba) amides

The potential of the heteroleptic heavier alkaline-earth hexamethyldisilazides [{HC(C(Me)2N-2,6-iPr2C6H3)2}Ae{N(SiMe3)2}(THF)](Ae = Ca, Sr, Ba) as kinetically-stable reagents for further protolytic reaction chemistry has been assessed. Only the previously reported calcium complex was found to be stable to solution dismutation and dynamic ligand exchange. The barium complex was isolated in sufficient purity to enable characterisation by an X-ray analysis. Reactions of the kinetically robust calcium complex with cyclohexylamine and tert-butylamine resulted in displacement of THF and formation of solvated structures, which could be characterised by 1H NMR spectroscopy. Attempts to isolate these solvated complexes were unsuccessful due to redistribution to the homoleptic complex [{HC(C(Me)2N-2,6-iPr2C6H3)2}2Ca]. In contrast, the more acidic amine [H2NCH2CH2OMe] was cleanly deprotonated resulting in the isolation of the first well defined primary amido derivative of a heavier alkaline-earth element, [{HC(C(Me)2N-2,6-iPr2C6H3)2}Ca{NHCH2CH2OMe}]2, which retains its dimeric constitution in solution and is stable to further intermolecular ligand exchange. Reactions of [{HC(C(Me)2N-2,6-iPr2C6H3)2}Ca{N(SiMe3)2}(THF)] with a variety of ortho-disubstituted anilines also resulted in immediate protonation of the hexamethyldisilazide ligand. Only the most sterically demanding 2,6-diisopropylphenyl anilide derivative possessed sufficient kinetic stability to allow isolation of the heteroleptic complex. The crystal structure of [{HC(C(Me)2N-2,6-iPr2C6H3)2}Ca{N(H)-2,6-iPrC6H3}(THF)] was shown to exist as a mononuclear, pseudo-five-coordinate complex in which the coordinative unsaturation of the calcium centre is relieved by a Ca...H-C agostic-type interaction to one of the ortho isopropyl groups of the anilide ligand. This interaction is not maintained in solution however and the complex slowly redistributes to the homoleptic beta-diketiminato species and ill-defined polymeric calcium anilido products.

13 C NMR spectroscopy of C76, C78, C84 and mixtures of C86–C102; anomalous chromatographic behaviour of C82, and evidence for C70H12

Using high pressure liquid chromatography, the fullerenes C76, C78. C84, and C86–C102 have been separated (in some cases partially) from soot produced by the arc-discharge procedure. The 13C NMR spectrum for C76 confirms that reported previously, whilst the spectrum for C78 indicates the presence of C2v, D3, C2v, isomers in the approximate relative yields (there is a small batch dependence) of 52 : 30 : 18%. The spectrum for the D3 isomer (confirmed from two separate batches) differs from that given in the literature with respect to the location of one peak. The relative peak heights in the C8413C NMR spectrum are similar to those reported for samples produced under different conditions. The stabilities of the component isomers must therefore be similar and so produced in a similar ratio irrespective of conditions; this indicates them to be the D2and a O2d isomers. The spectrum also contains over 70 minor peaks due to other isomers of C84. Eleven of the peaks are more intense than the others, consistent with the presence of the D3d and D6h isomers, predicted to be of relatively high stability. Two fractions (giving yellow solutions in hexane) eluted after C84: the first was separated into two components, shown by mass spectrometry to consist of minor amounts of C86–C92, and mainly C90 and C92 with lesser amounts of C94–C,102, respectively. The 13C NMR spectrum of the C94–C102 component indicated the presence of a fullerene isomer of high symmetry. The second yellow fraction consisted largely of C82 together with traces of fullerenes up to C108, but the quantity was insufficient for the 13C NMR spectrum to be obtained. The retention time of C82 is inconsistent with values for the other fullerenes indicating that it consists of the C3v isomer, predicted to be polar. C90 eluted with two different retention times suggesting that the second fraction is also a polar isomer. One sample of C84 contained a coeluent, identified by mass spectrometry as C70H12; proposals are made concerning its possible origin, structure, and stability relative to other hydrogenated derivatives.

Synthetic and structural experiments on yttrium, cerium and magnesium trimethylsilylmethyls and their reaction products with nitriles; with a note on two cerium β-diketiminates

The yttrium, cerium and magnesium bis(trimethylsilyl)methyls [Ln{CH(SiMe3)2}3] [Ln = Y (1), Ce (2)], and the known compound Mg[CH(SiMe3)2]2 (C) and [Mg(μ-Br){CH(SiMe3)2}(OEt2)]2 (D) formed the crystalline nitrile adducts [1(NCBut)2] (5), [2(NCPh)] (6), [C(NCR)2] [R = But (8), Ph (9), C6H3Me2-2,6 (10)] and [Mg(μ-Br){CH(SiMe3)2}(NCR)]2 [R = But (11), Ph (12), C6H3Me2-2,6 (13)], rather than β-diketiminato–metal insertion products. The β-diketiminato–cerium complex [Ce{(N(SiMe3)C(C6H4But-4))2CH}{N(SiMe3)2}2] (16) was obtained from [Ce{N(SiMe3)2}3] and the β-diketimine H[{N(SiMe3)C(C6H4But-4)}2CH]]. The cerium alkyl 2 and [Ln{CH(SiMe3)(SiMe2OMe)}3] [Ln = Y (3), Ce (4)] were obtained from the appropriate lithium alkyl precursor and [Ce(OC6H2But2-2,6-Me-4)3] or LnCl3, respectively. Heating complex 3 with benzonitrile in toluene afforded 2,2-dimethyl-4,6-diphenyl-5-trimethylsilyl-1,3-diaza-2-silahexa-1,3-diene (7), a member of a new class of heterocycles. The X-ray structures of the crystalline compounds 1–7, D, [Mg{CH(SiMe3)2}2(OEt2)2], the known [Ce(Cl){(N(SiMe3)C(Ph))2CH}2] (E) and 16 are reported. The cerium alkyl 2 (like 1) has one close Ce⋯C contact for each ligand, attributed to a γ-C–Ce agostic interaction. The Ln alkyls 3 and 4 have a trigonal prismatic arrangement of the chelating ligands (each of the same chirality at Cα) around the metal. In an arene solution at 313 K 3 exists as two isomers, as evident from detailed NMR spectroscopic experiments.

Studies toward the synthesis of natural and unnatural dienediynes 1. Approaches to a functionalised bicyclic ring system

The synthesis of a functionalised bicyclic ring system related to the naturally occurring dienediynes, NCS and Kedarcidin Chromophores is presented. Key steps involve: conjugate addition of an enediyne to a functionalised enone and intramolecular boron mediated aldol reaction.

Stereospecific synthesis of 4-fluoroglutamic acids

Abstract A stereospecific route to 4-fluoroglutamic acids from pyroglutamic acid has been devised and variable temperature 1 H-nmr spectroscopic studies have explained apparent inconsistencies in the stereochemical outcome of steps in a synthesis of 4-fluoroglutamic acids from hydroxyprolines.