Simple Alkyls and Aryls

Ruthenium and osmium form some remarkably stable alkyls and aryls compounds, often in unusually high oxidation states. 

Like rhodium and iridium, ruthenium forms a (thermally unstable above 0°C) hexamethylate anion 

Alkyldene and alkylidyne compounds have also been made [200]. 

Osmium forms a number of compounds in the +4, +5 and +6 states. OsAr4 (Ar = Ph, o-tolyl, cyclohexyl) has tetrahedral coordination of osmium (e.g. Os—C 1.994 A in Os(QH5)4). The tetraphenyl and tetra(cyclohexyl) compounds are air sensitive, but the o-tolyl is very inert (stable to O2, CO, NO) presumably owing to the orf/io-methyls shielding the osmium the latter can be oxidized to paramagnetic Os(o-tolyl)4 (with little change in the Os-C bond length). Osmium(IV) tetraaryls undergo a reductive elimination in the presence of PR3 (R, e.g. Me, OMe, OEt) by an associative mechanism [198]. 

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Thiophene [110-02-1] and a number of its derivatives are significant in fine chemical industries as intermediates to many products for pharmaceutical, agrochemical, dyestuffs, and electronic appHcations. This article concentrates on the industrial, commercial, and economic aspects of the production and apphcations of thiophene and thiophene derivatives and details the main synthetic schemes to the parent ring system and simple alkyl and aryl derivatives. Functionalization of the ring and the synthesis of some functional derivatives that result, not from the parent ring system, but by direct ring cyclization reactions are also considered. Many good reviews on the chemistry of thiophene and thiophene derivatives are available (1 7). 

Cesium forms simple alkyl and aryl compounds that are similar to those of the other alkah metals (6). They are colorless, sohd, amorphous, nonvolatile, and insoluble, except by decomposition, in most solvents except diethylzinc. As a result of exceptional reactivity, cesium aryls should be effective in alkylations wherever other alkaline alkyls or Grignard reagents have failed (see Grignard reactions). Cesium reacts with hydrocarbons in which the activity of a C—H link is increased by attachment to the carbon atom of doubly linked or aromatic radicals. A brown, sohd addition product is formed when cesium reacts with ethylene, and a very reactive dark red powder, triphenylmethylcesium [76-83-5] (C H )2CCs, is formed by the reaction of cesium amalgam and a solution of triphenylmethyl chloride in anhydrous ether. 

Data taken from <71pmhi3i297), which contains references to the original literature. Simple alkyl- and aryl-imidazoles. iV-Unsubstituted compounds are IV-acylated prior to injection. 

Studies of die structures of cuprate species were initiated to elucidate die niedi-anisnis by wbidi tliey interact witli substrates and to understand dieit special reactivities. tn die early days tliese investigaiions were restricted to solution studies by spectroscopic tediniques. It was not until 1982 dial tlie dtst example of a cuprate species - [iCu Pbi-jiLiiTHFj))] - was stiuctutally diatacterlzed by X-tay crystal stiucture deterniination [ 100] ivide infra). It sbotild be noted tliat most of diese studies, reviewed previously [29, 45, 101], were limited to "simple" alkyl and aryl derivatives. 

Simple alkyls and aryls AuR are generally unstable but coordinative saturation ensures the stability of adducts Au(PR3)R ... 

Cycloaddition reactions of the simple alkyl and aryl aldehydes 65 with (E)-l-methoxy-1,3-butadiene (18b) under high pressure conditions afforded adducts 66 and 67 in reasonable to good yields [2g, 23]. A marked preference for the c applying pressure enforces cnJo-addition (Scheme 5.5). Using mild Lewis-acid catalysts [24], such as Eu(fod)3, Yb(fod)3, or Eu(hfc)3, in combination with pressure, allows good results to be obtained with the added advantage of reducing the pressure to 10 kbar [25] (Scheme 5.5). 

Undoubtedly, the uniform structural and spectral behavior of the trigonal-planar jt-radicals (t-Bu2MeSi)E (E = Si, Ge, Sn) 43-45 both in the solid state and in solution should be ascribed to the immediate impact of the bulky electropositive silyl substituents. In contrast, it is well known that simple alkyl and aryl substituents cause a highly pronounced pyramidalization at the radical centers, where the unpaired electron typically occupies the orbital with a high s-contribution (o-radicals)7 ... 

Simple alkyl and aryl cr-bonded complexes are conveniently prepared by reaction of an alkylating reagent with a halocobalt(II) precursor. All-alkyl systems are rare, but the penta-methylcobaltate(II) anion is known.197 More typically, the coordination sphere of the metal contains additional co-ligands, particularly with P, S, or N donors. Some examples that reflect the style of reactions extant appear below. 

The method was first applied to the preparation of a number of simple alkyl and aryl C-l glycals,71 but since then the scope of this approach have been extended with the preparation of a small library of significant C-l glycals including steroidal, and glycerolipidic residues endowed with potential biological activity.72... 

A range of l,3-oxazolidin-4-ones (93) have been prepared by cyclocondensation of cyanohydrins, R R C(OH)CN, with aldehydes or ketones, R COR, under anhydrous strong acid conditions. The R groups used are mainly simple alkyl and aryl moieties, and the mechanism is discussed. 

The contention that disulfides are the major products of reaction when thiols are oxidized in aqueous alkaline solution has been amply confirmed by the present investigation. Thus, in the absence and in the presence of various metal ions (Table I) and in the oxidation of various simple alkyl and aryl thiols (Table III) disulfide has always been produced quantitatively. Under these circumstances, experiments have been designed to investigate the kinetics and mechanism of the reaction as a basis for further detailed studies. 

Homopolymers of simple alkyl and aryl isocyanides (Mv.p.osm > 1000-4000) are insoluble in all common solvents. This statement, however, requires elaboration of the fact that trichloroacetic acid successfully disperses these polymers. Observations with poly(cr-toluyl isocyanide) are informative, since the polymer is canary yellow in color, and turns to dark brown in trichloroacetic acid—acting in the manner of an acid-base indicator dye. Dilution with water of the trichloroacetic acid solution of poly(aqueous alkali produces the original yellow color. It appears that the polyisocyanide is dispersed in trichloroacetic acid as a pro-tonated species. Conductimetric experiments on poly(a-phenylethyl isocyanide) in dichloroacetic acid confirm this view (25). 

Simple alkyl and aryl derivatives of nickel(II) with monodentate phosphines are, in general, too unstable to be isolated in the solid state as pure compounds. However, it has been found that a considerable stabilization occurs when the carbon cr-bonded to nickel(II) is part of either an alkynic group, a fluorinated or chlorinated group, or an orf/io-substituted phenyl group. 

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