Copper complexes 1,4-addition with

It has so far been known that the allyiic alkylation of unsymmetrical substrates catalyzed by copper complexes proceeds with a high S sr2 regioselectivity contrary to the palladium-catalyzed reactions. However, the corresponding enantioselective version of this reaction has been less developed, in sharp contrast to the copper-promoted asymmetric Michael addition to a,/ -unsaturated systems. 

After considering the matter of copper complexation with INH, Krivis and Rabb [536] suggested that a 1 1 cuprous complex was more likely than a cupric complex. They pointed out that the copper complex formed with INH followed the reduction of Cu(II) to Cu(I), so that 1 1 cuprous complexes were formed upon addition of Cu(II) to solutions containing INH. Krivis and Rabb also suggested that the formation of Cu(I) complexes of thiosemicarbazones accounted for the synergistic effect of copper with the antitubercular agent... 

The Reppe process is a method that was developed in the 1940s and typical manufacturers include BASF, Ashland, and Invista. Cu-Bi catalyst supported on silica is used to prepare the 1,4-butynediol by reacting formaldehyde and acetylene at 0.5 MPa and 90-110 C (Eq. (10.2)). The copper used in the reaction is converted to copper(I) acetylide, and the copper complex reacts with the additional acetylene to form the active catalyst. The role of bismuth is to inhibit the formation of water-soluble acetylene polymers (i.e., cuprenes) from the oligomeric acetylene complexes on the catalyst [5a]. The hydrogenation of 1,4-butynediol is accom-pUshed through the use of Raney Ni catalyst to produce 1,4-butanediol (Eq. (10.3)). The total yield of 1,4-butanediol production is 91% from acetylene [5b]. Since acetylene is a highly explosive compound, careful process control is necessary. 

More detailed mechanistic studies have been conducted with isolated ligated copper complexes, along with kinetic studies on reactions catalyzed by complexes of diamine ligands. These studies have shown that copper(I) amidate and imidate complexes are competent to be intermediates in the catalytic coupling of aryl halide with amides and imi-des. These studies also implied that two-coordinate anionic cuprate complexes undergo oxidative addition of the aryl halide more slowly than do related three-coordinate, neutral copper complexes containing a bidentate dative ligand. This conclusion is shown clearly by the formation of coupled product from iodotoluene and the species that equilibrates between the ionic and three-coordinate neutral species (Equation 19.119) and the lack of... 

Fortunately, in the presence of excess copper(II)nitrate, the elimination reaction is an order of magnitude slower than the desired Diels-Alder reaction with cyclopentadiene, so that upon addition of an excess of cyclopentadiene and copper(II)nitrate, 4.51 is converted smoothly into copper complex 4.53. Removal of the copper ions by treatment with an aqueous EDTA solution afforded in 71% yield crude Diels-Alder adduct 4.54. Catalysis of the Diels-Alder reaction by nickel(II)nitrate is also... 

Hydantoin itself can be detected ia small concentrations ia the presence of other NH-containing compounds by paper chromatography followed by detection with a mercury acetate—diphenylcarba2one spray reagent. A variety of analytical reactions has been developed for 5,5-disubstituted hydantoias, due to their medicinal iaterest. These reactions are best exemplified by reference to the assays used for 5,5-diphenylhydantoiQ (73—78), most of which are based on their cycHc ureide stmcture. Identity tests iaclude the foUowiag (/) the Zwikker reaction, consisting of the formation of a colored complex on treatment with cobalt(II) salts ia the presence of an amine (2) formation of colored copper complexes and (3) precipitation on addition of silver(I) species, due to formation of iasoluble salts at N. ... 

Hydrogenation. Gas-phase catalytic hydrogenation of succinic anhydride yields y-butyrolactone [96-48-0] (GBL), tetrahydrofiiran [109-99-9] (THF), 1,4-butanediol (BDO), or a mixture of these products, depending on the experimental conditions. Catalysts mentioned in the Hterature include copper chromites with various additives (72), copper—zinc oxides with promoters (73—75), and mthenium (76). The same products are obtained by hquid-phase hydrogenation catalysts used include Pd with various modifiers on various carriers (77—80), Ru on C (81) or Ru complexes (82,83), Rh on C (79), Cu—Co—Mn oxides (84), Co—Ni—Re oxides (85), Cu—Ti oxides (86), Ca—Mo—Ni on diatomaceous earth (87), and Mo—Ba—Re oxides (88). Chemical reduction of succinic anhydride to GBL or THF can be performed with 2-propanol in the presence of Zr02 catalyst (89,90). 

Organometallic complexes of copper, silver, and gold are ideal precursors for carbene complexes along with some C- and N-coordinated species. Their reactivity pattern, in particular in oxidative addition reactions, was the most comprehensively studied. 

The proposed reaction mechanism involves intermolecular nucleophilic addition of the amido ligand to the olefin to produce a zwitterionic intermediate, followed by proton transfer to form a new copper amido complex. Reaction with additional amine (presnmably via coordination to Cn) yields the hydroamination prodnct and regenerates the original copper catalyst (Scheme 2.15). In addition to the NHC complexes 94 and 95, copper amido complexes with the chelating diphosphine l,2-bis-(di-tert-bntylphosphino)-ethane also catalyse the reaction [81, 82]. 

In addition, the same group has used copper complexes of these ligands as efficient catalysts for enantioselective Cu-catalysed aza-Diels-Alder reactions of A-sulfonyl imines with Danishefsky s dienes, providing the corresponding six-membered heterocycles with enantioselectivities of up to 80% ee. ... 

The selectivity of the aldol addition can be rationalized in terms of a Zimmer -man-Traxler transition-state model with TS-2-50 having the lowest energy and leading to dr-values of >95 5 for 2-51 and 2-52 [18]. The chiral copper complex, responsible for the enantioselective 1,4-addition of the dialkyl zinc derivative in the first anionic transformation, seems to have no influence on the aldol addition. To facilitate the ee-determination of the domino Michael/aldol products and to show that 2-51 and 2-52 are l -epimers, the mixture of the two compounds was oxidized to the corresponding diketones 2-53. 

The mixture is then chilled in an ice bath for at least 3 hours, and the olive-brown precipitate of the sparingly soluble copper complex of imidazole derivatives is filtered. The product is washed with about 500 ml. of cold water, suspended while moist (Note 4) in 11. of water, and rendered just acid to litmus by the addition of concentrated hydrochloric acid (about 40 ml.). Hydrogen sulfide is then passed into the suspension, with frequent shaking, until precipitation of the copper is complete (2-3 hours). The precipitate is filtered and extracted with 500 ml. of hot water in two or three portions. The clear, light brown to reddish brown filtrate and washings are boiled for 15 minutes, and then 60 g. (0.26 mole) of picric acid is added with stirring heating is continued until solution is complete. 

The reduction of a solution of a trialkylphosphine copper(I) iodide complex (CuIPR ) with preformed lithium naphthalide (LiNp) in THF or DME under argon was found to give a more reactive copper species, which will undergo oxidative addition with a variety of organic substrates at room... 

This work was initiated in 1988 when Villacorta et al.71a reported the asymmetric conjugate addition of a Grignard reagent to 2-cyclohexenone. This study showed that 1,4-adducts with 4-14% ee were obtained in the presence of aminotroponeimine copper complex.713 Enhanced results (74% ee) were obtained by adding HMPA or silyl halides.71b Several other copper complexes were also used for inducing asymmetric conjugate addition reactions. Moderate results were obtained in most cases when THF was used as the solvent and HMPA as the additive. 

The presence of residual unbound transition-metal ions on a dyed substrate is a potential health hazard. Various eco standards quote maximum permissible residual metal levels. These values are a measure of the amount of free metal ions extracted by a perspiration solution [53]. Histidine (5.67) is an essential amino acid that is naturally present as a component of perspiration. It is recognised to play a part in the desorption of metal-complex dyes in perspiration fastness problems and in the fading of such chromogens by the combined effects of perspiration and sunlight. The absorption of histidine by cellophane film from aqueous solution was measured as a function of time of immersion at various pH values. On addition of histidine to an aqueous solution of a copper-complex azo reactive dye, copper-histidine coordination bonds were formed and the stability constants of the species present were determined [54]. Variations of absorption spectra with pH that accompanied coordination of histidine with copper-complex azo dyes in solution were attributable to replacement of the dihydroxyazo dye molecule by the histidine ligand [55]. 

---