/pdf/aryl-aryl-bond-formation-one-century-after-the-discovery-of-1jdyxlkwix.pdf

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.

Coupling of thieno[3,2-b]thiophen-2-ones with diazoalkanes

Reactivity of halogenated aromatic radical anions. electron spin resonance evidence for the dimerization of the 6-halogeno-2h,3h-benzo(b)thiophene-2,3-semidiones

Selenium radical anions are suggested to be the reactive intermediates in the reductive cleavage of aryl alkyl, vinyl alkyl or vinyl acyl selenides; the aryl and vinyl selenolate anions thus obtained have been used to synthetize several types of selenium containing compounds. Radical cations are suggested to intervene in the oxydeselenenylation of aryl alkyl selenides promoted by oxidizing agents in hydroxylated solvents. This process has been used to effect the conversions of alkenes and vinyl bromides into dialkoxyalkanes and α-alkoxy acetals, and of alkynes and methyl ketones into α-keto ketals and α-keto acetals which occur by treatment with persulphate ions and catalytic amounts of diphenyl diselenide.

Selenium Radical Ions in Organic Synthesis

The radical ion pairs of several dithiolactones have been studied by e.s.r. spectroscopy. The e.s.r. spectral shape is strongly temperature dependent owing to the intramolecular migration of the alkali counterion between the two carbonyl groups of the organic anion. In the case of asymmetric derivatives, two non-equivalent ion pairs have been unambiguously detected for the first time. The factors affecting their relative stability are described. The kinetics of the cation exchange has been investigated for some of the compounds examined, by analysing the line shape variations with temperature. It is emphasized that the activation parameters calculated on the usual assumption that the change of temperature influences only the rate of migration should be considered with some caution since parallel changes of the structure of the ion pairs may also occur. The effects of these variations on the measured parameters are discussed.

Intramolecular cation exchange in ion pairs. Part II. Isomeric radical ion pairs of dithiolactones

The radical anions of compounds containing the thiophen nucleus (I)–(IV) have been produced by reduction with Na–K alloy and their e.s.r. spectra have been investigated. The spin-density distribution has been interpreted in terms of sulphur p and d models.

Marcello Tiecco

Papers

Coupling of thieno[3,2-b]thiophen-2-ones with diazoalkanes

Reactivity of halogenated aromatic radical anions. electron spin resonance evidence for the dimerization of the 6-halogeno-2h,3h-benzo(b)thiophene-2,3-semidiones

Selenium Radical Ions in Organic Synthesis

Intramolecular cation exchange in ion pairs. Part II. Isomeric radical ion pairs of dithiolactones

Negative radicals of condensed thiophens