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Aryl-aryl bond formation one century after the discovery of the Ullmann reaction.

Using molecules as electronic components is a powerful new direction in the science and technology of nanometre-scale systems1. Experiments to date have examined a multitude of molecules conducting in parallel2,3, or, in some cases, transport through single molecules. The latter includes molecules probed in a two-terminal geometry using mechanically controlled break junctions4,5 or scanning probes6,7 as well as three-terminal single-molecule transistors made from carbon nanotubes8, C60 molecules9, and conjugated molecules diluted in a less-conducting molecular layer10. The ultimate limit would be a device where electrons hop on to, and off from, a single atom between two contacts. Here we describe transistors incorporating a transition-metal complex designed so that electron transport occurs through well-defined charge states of a single atom. We examine two related molecules containing a Co ion bonded to polypyridyl ligands, attached to insulating tethers of different lengths. Changing the length of the insulating tether alters the coupling of the ion to the electrodes, enabling the fabrication of devices that exhibit either single-electron phenomena, such as Coulomb blockade, or the Kondo effect.

Coulomb blockade and the Kondo effect in single-atom transistors

Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aube rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.

Organic Azides: An Exploding Diversity of a Unique Class of Compounds

Starting from the early 1990’s, the chemistry of polyvalent iodine organic compounds has experienced an explosive development. This surging interest in iodine compounds is mainly due to the very useful oxidizing properties of polyvalent organic iodine reagents, combined with their benign environmental character and commercial availability. Iodine(III) and iodine(V) derivatives are now routinely used in organic synthesis as reagents for various selective oxidative transformations of complex organic molecules. Several areas of hypervalent organoiodine chemistry have recently attracted especially active interest and research activity. These areas, in particular, include the synthetic applications of 2-iodoxybenzoic acid (IBX) and similar oxidizing reagents based on the iodine(V) derivatives, the development and synthetic use of polymer-supported and recyclable polyvalent iodine reagents, the catalytic applications of organoiodine compounds, and structural studies of complexes and supramolecular assemblies of polyvalent iodine compounds.

The chemistry of polyvalent iodine has previously been covered in four books1–4 and several comprehensive review papers.5–17 Numerous reviews on specific classes of polyvalent iodine compounds and their synthetic applications have recently been published.18–61 Most notable are the specialized reviews on [hydroxy(tosyloxy)iodo]benzene,41 the chemistry and synthetic applications of iodonium salts,29,36,38,42,43,46,47,54,55 the chemistry of iodonium ylides,56–58 the chemistry of iminoiodanes,28 hypervalent iodine fluorides,27 electrophilic perfluoroalkylations,44 perfluoroorgano hypervalent iodine compounds,61 the chemistry of benziodoxoles,24,45 polymer-supported hypervalent iodine reagents,30 hypervalent iodine-mediated ring contraction reactions,21 application of hypervalent iodine in the synthesis of heterocycles,25,40 application of hypervalent iodine in the oxidation of phenolic compounds,32,34,50–53,60 oxidation of carbonyl compounds with organohypervalent iodine reagents,37 application of hypervalent iodine in (hetero)biaryl coupling reactions,31 phosphorolytic reactivity of o-iodosylcarboxylates,33 coordination of hypervalent iodine,19 transition metal catalyzed reactions of hypervalent iodine compounds,18 radical reactions of hypervalent iodine,35,39 stereoselective reactions of hypervalent iodine electrophiles,48 catalytic applications of organoiodine compounds,20,49 and synthetic applications of pentavalent iodine reagents.22,23,26,59

The main purpose of the present review is to summarize the data that appeared in the literature following publication of our previous reviews in 1996 and 2002. In addition, a brief introductory discussion of the most important earlier works is provided in each section. The review is organized according to the classes of organic polyvalent iodine compounds with emphasis on their synthetic application. Literature coverage is through July 2008.

Chemistry of Polyvalent Iodine

Helicates as Versatile Supramolecular Complexes.

Arylthio amidation, etherification, and lactonization of alkenes promoted by oxidation of bis(4-methoxyphenyl)disulfide with ammonium peroxydisulfate

Enantiomerically pure 2,5,6a-trisubstituted perhydrofuro[2,3- b ]furans were obtained by the cyclization of bis-alkenylketones, promoted by camphorselenenyl sulfate produced in situ by oxidation of camphor diselenide with ammonium persulfate in a mixture of water and acetonitrile at room temperature. The cyclization reaction proceeded through a double selenohydroxylation of the two double bonds and produced a mixture of the two diastereoisomers trans - and cis -2,5-bis[(camphorseleno)methyl] perhydrofuro[2,3- b ]furans. These were separated by medium pressure liquid chromatography and then deselenenylated with triphenyltin hydride and AIBN.

Synthesis of enantiomerically pure perhydrofuro[2,3-b]furans.

Electrophilic 2-Thienylselenenylation of Thiophene. Preparation of Oligo(seleno-2,5-thienylenes)

The 100 MHz n.m.r. spectrum of the title compound partially oriented in the nematic phase has been obtained and interpreted. The values of the direct dipolar couplings have been discussed in terms of models which take into account the possibilities of internal rotation rates either faster or slower than the molecular reorientation in the liquid crystals. It is concluded that the molecule exists in the conformations O-cis–cis(70–80%) and O-cis–trans(20–30%), whilst the proportion of the O-trans-trans rotamer is negligible.

Conformational analysis in heteroaromatic carbonyl compounds. Part II. Nuclear magnetic resonance investigation of thiophen-2,5-dicarbaldehyde in liquid crystals

The conformational behaviour of the radical anions of several bi- and ter-aryls has been investigated by e.s.r. spectroscopy. Comparison with their diamagnetic precursors shows that the addition of the unpaired electron to the π-system greatly increases the conformational rigidity of these compounds. This result is accounted for by INDO MO calculations, and can be rationalized in terms of the occupancy by the unpaired electron of the lowest vacant orbital of neutral bi- and ter-aryls which has a strong bonding character in the interannular regions.

Marcello Tiecco

Papers

Arylthio amidation, etherification, and lactonization of alkenes promoted by oxidation of bis(4-methoxyphenyl)disulfide with ammonium peroxydisulfate

Synthesis of enantiomerically pure perhydrofuro[2,3-b]furans.

Electrophilic 2-Thienylselenenylation of Thiophene. Preparation of Oligo(seleno-2,5-thienylenes)

Conformational analysis in heteroaromatic carbonyl compounds. Part II. Nuclear magnetic resonance investigation of thiophen-2,5-dicarbaldehyde in liquid crystals

Rotational isomerism in the radical anions of bi- and ter-aryls containing the thiophen ring