Antony Chesney

CHIRAL FERROCENYL-OXAZOLINES INCORPORATING THIOETHER UNITS : EFFECTIVE LIGANDS FOR PALLADIUM-CATALYSED ALLYLIC SUBSTITUTION

Abstract The syntheses of novel ferrocene-based chiral oxazolines 17, 18 and 26 are reported. The application of these compounds as catalysts for asymmetric palladium-catalysed allylic substitution reactions has been investigated. These reactions afford the substitution products in both high yield and high enantiomeric excess. The solution electrochemical redox-behaviour of 17, 18 and 26 in the presence of palladium ions establishes that palladium coordination to the oxazoline results in a significant anodic shift in the redox potential of the ferrocene ligand. The X-ray crystal structure of the ferrocene-hydroxy amide derivative 16 is also reported.

Chiral oxazolines linked to tetrathiafulvalene (TTF): Redox-active ligands for asymmetric synthesis

Abstract The syntheses of novel tetrathiafulvalene substituted chiral oxazolines 14 and 18 are reported. The application of these compounds as catalysts for asymmetric palladium-catalysed allylic substitution reactions has been investigated along with the solution electrochemical redox behaviour of 14a in the presence of palladium ions.

Voltammetric metal cation sensors based on ferrocene derivatives with oxazoline and imine substituents

Ferrocene derivatives la, lb and 2 containing oxazoline substituents act as efficient voltammetric sensors of Mg2+ and Ca2+ ions in acetonitrile solution in concentrations as low as 10 mol%: a new redox peak appears in the cyclic voltammogram, positively shifted by 310-360 mV for 1a and 1b, and by 160-190 mV for 2, compared to E-1/2 of the free ligand. For the bisferrocenyldiimine derivative 3 the shift is 150-160 mV. Compounds la, lb and 3 are also responsive to Cu2+ ions (shifts of 250, 320 and 160 mV, respectively) and compound 3 is responsive to Zn2+ ions (150 mV shift) with no interference from a large excess of several other metal salts. UV-vis spectrophotometric studies and H-1-NMR titration experiments confirm that the oxazoline or imine groups are the sites of metal complexation.

Electron acceptors of the fluorene series: Part 12. 9-(Metalloceneylidene)nitrofluorene derivatives of Fc–NF, NF–Fc–NF, and NF–Rc–NF types, and the vinylogues Fc–π–NF: synthesis, characterisation, intramolecular charge transfer, redox properties and X-ray structures for three fluorene–ferrocene derivatives

Reaction of ferrocenecarboxaldehyde 13 and its vinylogue, (E,E)-1-ferrocenyl-4-formyl-1,3-butadiene (16), with nitrofluorenes as CH-acids, results in push–pull compounds of the type Fc– –fluorene (8a –g, 12a–e). Similar reaction with bifunctional ferrocene and ruthenocene dicarboxaldehydes results, depending on the fluorene structure, in the products of mono- or di-condensation, OHCFcCHfluorene (11d,e) or fluoreneCHFcCHfluorene and fluoreneCHRcCHfluorene (9a –c, 10a–c). Intramolecular charge transfer (ICT) in compounds 8 results in lowering the rotation barrier around the CHfluorene double bond and easy E – Z isomerisation in solution. Cyclic voltammetry (CV) experiments show a reversible single-electron oxidation of FcCHfluorenes (8) yielding the cation and two reversible single-electron reduction waves yielding the radical anion and dianion (for 8a –e) which merge into one two-electron reduction wave for 8f–h. ICT was also manifested in the electron absorption spectra of 8– 12 ,a nd energies of ICT (as well as reduction potentials in CV) were found to display excellent correlation (r 0.99) with Hammett-type substituents constants ( p − ) in the fluorene moiety. Compounds 8–12 show solvatochromism [8a: ICT= 604.5 nm (acetonitrile), 622.5 nm (1,2-dichloroethane)], with, however, no quantitative regularities for 10 solvents of different polarity. Bathochromic shifts of 40–83 nm and an increase in the intensity of ICT bands were observed with lengthening of the -bridge between ferrocene and fluorene moieties (812) whereas substitution of the ferrocene unit in 9 by the ruthenocene unit (10) resulted to a hypsochromic shift of ca. 100 nm due to decreasing donor ability of the latter metallocene fragment. Acceptor 8a was found to sensitise the photoconductivity of poly-N-(2,3-epoxypropyl)carbazole showing moderate holographic response of the materials. Molecular and crystal structures for ferrocene derivatives 8a, 8g ,a nd11d were determined by single-crystal X-ray diffraction. Tetranitro derivative 8a shows substantial distortion, caused by steric repulsion between the nitro groups in positions 4 and 5, which precludes the formation of stacks, and pairs of fluorene moieties contact face-to-face (interplanar distance 3.8 A ). In di- and trinitro derivatives 8g and 11d the fluorene moieties are more planar and their crystal packing motifs are similar: fluorene moieties form good stacks, parallel to the x-axis in 8g and the y-axis in 11d, with interplanar separations between fluorene moieties of 3.35–3.36 A for 8g and alternate separations of 3.52 and 3.55 A for 11d.

Selected highlights in the application of ion-exchangers. as supports for reagents in organic synthesis

The development of cleaner and more efficient synthetic routes to minimise environmental damage has been approached in many ways. Amongst these are: improved catalytic methods, solvent free reactions, reactions employing water as the solvent, the application of supercritical fluids, new asymmetric methods to minimise the production of unwanted isomers and atom-efficient synthesis. In all of these cases, the focus is to reduce the amount of materials required to perform the desired synthetic step, to obtain products requiring the minimum amount of expensive and/or complex purification steps, and therefore to reduce waste. The use of supported reagents to achieve a variety of useful organic transformations, whilst achieving at least some of these objectives, is the object of this review.

Push-pull fluorene acceptors with ferrocene donor moiety

Abstract We report on synthesis of a series of new push-pull compounds of the type A-X-D, where A is polynitrofluorene acceptor moiety, D is donor ferrocene moiety and X is various kind of bridges between them. Electronic absorption spectra (λ ICT max ≈450–700 nm) and second order polarisabilities (EFISH, μβ(0) = 100-2400×10 −48 esu) of these compounds are reported.

Synthesis and Trapping of Transient 1, 2-Diselones To Yield 1, 4-Diselenin Derivatives: Calculated Structures of 1, 2-Diselones, 1, 2-Diselenetes and Their Sulfur Analogues

Two conceptually different routes to transient 1,2-diselones are reported: 1) via ring fragmentation of the 1,4,2-diselenazine system 6, and 2) by the tributylphosphane-induced depolymerisation of the shelf-stable organoselenium polymer 15. Evidence for the intermediacy of 1,2-diselone species 7 and 16 is provided in both cases by in situ trapping with dimethyl acetylenedicarboxylate (DMAD) to yield 1,4-diselenin derivatives. The route via 15 is especially expedient and trapping of 16 is efficient. Subsequent reactions of adduct 17 afford [1,2-ethanediylbis(diphenylphosphane)] [5,6-bis(methoxycarbonyl)-1,4-diselenin-2,3-dithiolato]nickel(IV) (20). Theoretical calculations at Hartree-Fock (HF) and Moller-Plesset electron-correlated levels (MP2) suggest that the cyclic 1,2-diselenete structure 7c is significantly more stable than the acyclic 1,2-diselone structure 7a. For the bicyclic system 16, the difference in energy between the cyclic and acyclic structures is considerably reduced due to the conformational rigidity imposed by the fused 1,3-dithiole ring. In contrast, the acyclic structures of the 1,2-dithione analogues 13a and 25a are computed to be more stable than their corresponding cyclic 1,2-dithiete structures 13c and 25c.

Synthesis and nitrosation reactions of π-extended 1,3-dithiol-2-ylidene systems

New 1,3-dithiol-2-ylidene derivatives, notably π-extended systems, have been synthesised by Wittig reactions of phosphorane and phosphonate ester derivatives of 1,3-dithiole with activated ketones and α,β-unsaturated ketones. Nitrosation reactions of a range of these π-extended systems, results in the formation of nitroalkenes, via unstable nitrosoalkene intermediates, which, in general, could not be isolated. The X-ray crystal structure of 1-(4,5-dicarbomethoxy-1,3-dithiol-2-ylidene)-1-cyano-1-phenyl-methane reveals a small degree of intramolecular electron transfer from the dithiole ring to the conjugated cyano group.

New π-electron donor systems based on acenaphtho[1,2-b][1,4]dithiine

Syntheses of the acenaphtho[1,2-b][1,4]dithiine derivatives 12, 25 and 29 are reported. Cyclic voltammetric studies reveal that these compounds undergo reversible single-electron oxidations at < 1.0 V, vs. Ag/AgCl. Lithiation of compound 12 with BuLi (2 equiv.) followed by addition of either methyl iodide or ethyl chloroformate yielded the unstable ring-opened acetylene derivatives 22a and 22b, respectively. A new synthesis of 1,2-diselenine derivative 33 is reported. Compound 25 formed 1 : 1 charge-transfer complexes with 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) and with 2,5-dibromo-TCNQ, both of which were electrical insulators. The X-ray crystal structures of compound 25, a charge-transfer complex 25:Br2TCNQ (1:1 stoichiometry) and compound 33 are reported. In the structure of 25:Br2TCNQ, molecules of 25 and Br2TCNQ form mixed stacks. The folding of the donor along the S ⋯ S vector in the complex is 17°(cf. 48° in pure 25) and the conformation of 25 is discussed in the light of previous studies on 1,4-dithiine derivatives. An interesting feature of the crystal structure of 33 is the formation of pseudo-dimers with two short intermolecular Se ⋯ Se contacts.

SELENIUM-NITROGEN BOND FORMATION BY RING EXPANSION : SYNTHESIS OF THE 1,4,2-DISELENAZINE RING SYSTEM, FRAGMENTATION TO A 1,2-DISELENETE AND REACTIONS TO YIELD 1,4-DISELENIN DERIVATIVES

1,3-Diselenolium cation salt 1 reacts with ammonia and iodine to afford the novel 1,4,2-diselenazine system 6 (40% yield) which fragments to yield dimethylcyanamide 8 and diselenin 9, presumably via intermediate 1,2-diselenete 7, which is trapped with dimethyl acetylenedicarboxylate to yield the cycloadduct 10.