Copper aryl complexes

A distorted butterfly CU4 unit with Cu-Cu distances less than 240 pm is found for (4-methyl-2-cupriobenzyl)dimethylamine tetramers . Copper aryl complexes stabilized by the amine nitrogen lone pair are prepared from CuBr and the appropriate aryllithium reagent in ether in 40-60% yields... 

Evans et al. reported that the bis(imine)-copper (II) complex 25, prepared from chiral bis(imine) ligand and Cu(OTf)2, is also an effective chiral Lewis acid catalyst [34] (Scheme 1.44, Table 1.18). By tuning the aryl imine moiety, the bis(2,6-dichlor-ophenylimine) derivative was found to be suitable. Although the endojexo selectivity for 3-alkenoyloxazolidinones is low, significant improvement is achieved with the thiazolidine-2-thione analogs, for which both dienophile reactivity and endojexo selectivity are enhanced. 

According to these conclusions, it is possible to propose a catalytic cycle (Fig. 20) involving no radical species, but a copper(I) complex with the classical oxidative addition, nucleophilic substitution and reductive elimination resulting lastly in the arylated nucleophile. 

In this case the decisive redox process, which would be specifically inhibited by the hydroquinone, would be the formation of the copper(I) complex corresponding to a monoelectronic transfer from copper(O) to the aryl halide. 

Examples of silver(l) alkyl and alkenyl (including aryl) complexes have been known from as early as 1941 6-9 however, the number of examples is fairly limited with respect to that of the heavier congeners, copper(l) and gold(l). Such a phenomenon can readily be attributed to the relatively low stability of this class of complexes, both photochemically and thermally. Simple homoleptic alkyl and alkenyl complexes of silver(i) are known to be very unstable under ambient temperature and light, and successful isolation of this class is fairly limited and mainly confined to those involving perfluoroorganics.10 The structures and the metal-carbon bond-dissociation energies for... 

EPR data have been reported for 5-aryl tetrazolate salts of copper(II) values are in the range 2.12-2.15 and the gL and gy values are similar to those recorded for copper(II) complexes of other N donors. Related cobalt and nickel complexes gave complex or unresolved spectra (119). EPR data have been analyzed for the complex salts [Mn(l,5-pmtta)6][C104]2 and [Cu(l,5-pmtta) ][C104]2 (n — 4 and 6). For the copper complexes, copper and nitrogen hyperfine splittings were observed (118). 

Hydrosilylation of acetophenone to give silyl ether (M R = Me) can also be achieved using copper(I) complexes with the chiral phosphine ligands (-)-DIOP (87) or (+)-NORPHOS (88). The enantioselectiv-ity is rather low, but a nonphosphine auxiliary, PYTHIA (89) with a Rh(COD)Ch catalyst using neat diphenylsilane reduces aryl ketones to (R)-l-phenylethyl alcohol silyl ethers in high yield and with high enantiomeric excess (Scheme 18). " ... 

Copper(I) complexes catalyse a variety of organic reactions which are of synthetic and industrial importance.305 In such processes that involve halide abstraction from aryl or alkyl halides, the abstraction step by a Cu(I) catalyst is believed to be the rate-determining step. In order to circumvent the property of facile disproportionation of Cu, various methods of stabilising Cu(I) and influencing reaction rates were considered.306 A kinetics study of ligand (L) effects on the reactivity of Cu(I)L complexes towards C13CC02 was undertaken. The results indicated that the rate of the chlorine abstraction reaction was affected by several factors. These were the redox potential of the Cu(II/I)L couple, the hybridisation on Cu(I) in the Cu(I)L complex, steric hindrance, and electron density on the central Cu(I) cation at the binding site of the chlorine atom to be abstracted. The volume of activation,... 

Cationic copper(II) complex 37 derived from a chiral bis(imine) ligand has also been shown to be an effective catalyst for reactions between cyclopentadiene and acylated thiazolidine-2-thione dienophiles, albeit with slightly lower se-lectivities than for the bis(oxazoline) complex 31 (Scheme 30) [93]. The bis(2,6-dichlorophenylimine) was found to be optimal among a number of electron-rich and -poor aryl imines screened. The reaction exhibits a positive non-linear effect which suggests that the minor ligand enantiomer can be sequestered by the formation of a catalytically less active (l ,l )/(S,S)Cu(II) dimer. 

Several copper-catalyzed 7 -arylation reactions of imidazole have been published. The coupling of arylboronic acids with imidazole in the presence of binuclear bis-p,-hydroxy copper (11) complexes in air has been carried out at ambient temperature without the need for base <04TL7659>. A variety of A -arylimidazoles were prepared in excellent yields through the cross-coupling of arylboronic acids with imidazole in methanol or water with copper(I) chloride <04CC188>. Copper(II) oxide-coated nanoparticles were used catalytically in the Ullmann coupling of imidazole with various aryl chlorides with cesium carbonate in dimethyl sulfoxide <04CC778>. 

Lipshutz and coworkers have developed copper hydride complexes with diphosphine ligands that catalyze the asymmetric hydrosilylation of aryl ketones at low temperatures (-50 to -78 °C) [68]. Nolan and coworkers discovered that copper complexes with NHC ligands are very efficient catalysts for the hydrosilylation of ketones, including hindered ketones such as di-cyclohexyl ketone and di-tert-butyl ketone [69]. 

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