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Transition metal complexes copper

The preparation of a series of transition metal complexes (Co. Ni. Pd. Pt, Ir. Au. Cu. Ag) with ambident anion (70) and phosphines as ligands has been reported recently (885). According to the infrared and NMR spectra the thiazoline-2-thione anion is bounded through the exocyclic sulfur atom to the metal. The copper and silver complexes have been found to be dimeric. [Pg.386]

Acetonitrile also is used as a catalyst and as an ingredient in transition-metal complex catalysts (35,36). There are many uses for it in the photographic industry and for the extraction and refining of copper and by-product ammonium sulfate (37—39). It also is used for dyeing textiles and in coating compositions (40,41). It is an effective stabilizer for chlorinated solvents, particularly in the presence of aluminum, and it has some appflcation in... [Pg.219]

A unique method to generate the pyridine ring employed a transition metal-mediated 6-endo-dig cyclization of A-propargylamine derivative 120. The reaction proceeds in 5-12 h with yields of 22-74%. Gold (HI) salts are required to catalyze the reaction, but copper salts are sufficient with reactive ketones. A proposed reaction mechanism involves activation of the alkyne by transition metal complexation. This lowers the activation energy for the enamine addition to the alkyne that generates 121. The transition metal also behaves as a Lewis acid and facilitates formation of 120 from 118 and 119. Subsequent aromatization of 121 affords pyridine 122. [Pg.319]

Catalytic, enantioselective cyclopropanation enjoys the unique distinction of being the first example of asymmetric catalysis with a transition metal complex. The landmark 1966 report by Nozaki et al. [1] of decomposition of ethyl diazoacetate 3 with a chiral copper (II) salicylamine complex 1 (Scheme 3.1) in the presence of styrene gave birth to a field of endeavor which still today represents one of the major enterprises in chemistry. In view of the enormous growth in the field of asymmetric catalysis over the past four decades, it is somewhat ironic that significant advances in cyclopropanation have only emerged in the past ten years. [Pg.85]

Azo compounds o-am ino-o -hydroxy diary 1 transition metal complexes, 6,57 bidentate dyes, 6,42 o,o -diaminodiaryI cobalt complexes, 6,58,60 o,o -dihydroxydiaryl copper complexes. 6.55,57 pK 6,47... [Pg.88]

Although the number of applications of olefin metathesis to transition metal complexes is small compared to the number of applications in organic synthesis, this field is becoming increasingly important. Spectacular examples are the double RCM reactions of copper phenanthroline complexes as a synthetic route to catenanes [113] or a recently reported approach to steric shielding of rhenium complex terminated sp-carbon chains [114]. [Pg.258]

Metal-Catalyzed. Cyclopropanation. Carbene addition reactions can be catalyzed by several transition metal complexes. Most of the synthetic work has been done using copper or rhodium complexes and we focus on these. The copper-catalyzed decomposition of diazo compounds is a useful reaction for formation of substituted cyclopropanes.188 The reaction has been carried out with several copper salts,189 and both Cu(I) and Cu(II) triflate are useful.190 Several Cu(II)salen complexes, such as the (V-f-butyl derivative, which is called Cu(TBS)2, have become popular catalysts.191... [Pg.921]

Copper catalyzes the decomposition of sulphonyl azides in benzene very slowly. When methanesulphonyl azide was boiled under reflux in benzene solution in the presence of an excess of freshly reduced copper powder, some decomposition occurred to give methanesulphonamide and azide was recovered 78>. Transition metal complexes have been found to exert a marked effect upon the yields of products and isomer ratios formed in the thermal decomposition of methanesulphonyl azide in methyl benzoate and in benzotrifluoride 36>. These results will be discussed in detail in the section on the properties of sulphonyl nitrenes and singlet and triplet behaviour. A sulphonyl nitrene-iron complex has recently been isolated 37> and more on this species will be reported soon. [Pg.16]

Another situation is observed when salts or transition metal complexes are added to an alcohol (primary or secondary) or alkylamine subjected to oxidation in this case, a prolonged retardation of the initiated oxidation occurs, owing to repeated chain termination. This was discovered for the first time in the study of cyclohexanol oxidation in the presence of copper salt [49]. Copper and manganese ions also exert an inhibiting effect on the initiated oxidation of 1,2-cyclohexadiene [12], aliphatic amines [19], and 1,2-disubstituted ethenes [13]. This is accounted for, first, by the dual redox nature of the peroxyl radicals H02, >C(0H)02 and >C(NHR)02 , and, second, for the ability of ions and complexes of transition metals to accept and release an electron when they are in an higher- and lower-valence state. [Pg.586]

As mentioned above, in contrast to classic antioxidant vitamins E and C, flavonoids are able to inhibit free radical formation as free radical scavengers and the chelators of transition metals. As far as chelators are concerned their inhibitory activity is a consequence of the formation of transition metal complexes incapable of catalyzing the formation of hydroxyl radicals by the Fenton reaction. In addition, as shown below, some of these complexes, for example, iron- and copper-rutin complexes, may acquire additional antioxidant activity. [Pg.858]

The NO/NO+ and NO/NO- self-exchange rates are quite slow (42). Therefore, the kinetics of nitric oxide electron transfer reactions are strongly affected by transition metal complexes, particularly by those that are labile and redox active which can serve to promote these reactions. Although iron is the most important metal target for nitric oxide in mammalian biology, other metal centers might also react with NO. For example, both cobalt (in the form of cobalamin) (43,44) and copper (in the form of different types of copper proteins) (45) have been identified as potential NO targets. In addition, a substantial fraction of the bacterial nitrite reductases (which catalyze reduction of NO2 to NO) are copper enzymes (46). The interactions of NO with such metal centers continue to be rich for further exploration. [Pg.220]

Certain transition metal complexes catalyze the decomposition of diazo compounds. The metal-bonded carbene intermediates behave differently from the free species generated via photolysis or thermolysis of the corresponding carbene precursor. The first catalytic asymmetric cyclopropanation reaction was reported in 1966 when Nozaki et al.93 showed that the cyclopropane compound trans- 182 was obtained as the major product from the cyclopropanation of styrene with diazoacetate with an ee value of 6% (Scheme 5-56). This reaction was effected by a copper(II) complex 181 that bears a salicyladimine ligand. [Pg.314]

The transition metal-catalyzed cyclopropanation of alkenes is one of the most efficient methods for the preparation of cyclopropanes. In 1959 Dull and Abend reported [617] their finding that treatment of ketene diethylacetal with diazomethane in the presence of catalytic amounts of copper(I) bromide leads to the formation of cyclopropanone diethylacetal. The same year Wittig described the cyclopropanation of cyclohexene with diazomethane and zinc(II) iodide [494]. Since then many variations and improvements of this reaction have been reported. Today a large number of transition metal complexes are known which react with diazoalkanes or other carbene precursors to yield intermediates capable of cyclopropanating olefins (Figure 3.32). However, from the commonly used catalysts of this type (rhodium(II) or palladium(II) carboxylates, copper salts) no carbene complexes have yet been identified spectroscopically. [Pg.105]

Because of the high nucleophilicity and reactivity of diazoalkanes, catalytic decomposition occurs readily, not only with a wide range of transition metal complexes but also with Brpnsted or Lewis acids. Well-established catalysts for diazodecomposition include zinc halides [638,639], palladium(II) acetate [640-642], rhodium(II) carboxylates [626,643] and copper(I) triflate [636]. Copper(II)... [Pg.114]


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See also in sourсe #XX -- [ Pg.217 ]

See also in sourсe #XX -- [ Pg.15 , Pg.171 , Pg.172 , Pg.173 , Pg.174 , Pg.175 , Pg.547 ]




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