Copper complexes cyanates

Fig. 13. Response of the active site copper complex to chemical and physical perturbations. (A) Absorption spectra for the lAGO Cu(II) complex in the absence (—L) and presence (+L) of a coordinating anion, cyanate (OCN ). (B) Absorption spectra for lAGO Cu(II) complex at ambient (300 K, RT) and cryogenic temperatures (200 K, LT).

Copper has been demonstrated to mediate cyanation of aryl bromides and iodides through the activation of C-CN bonds (Scheme 20). Phenylacetonitrile [64], malononitrUe [65], and even acetonitrile as a reaction solvent [66] have been reported to serve as cyanating agents. 2-Phenylpyridines [67] and indoles [68] are directly cyanated by copper-mediated cyanation reaction using phenylacetonitrile, which is supposedly oxidized first at its benzylic position to give benzoyl cyanide, which further reacts with copper complexes to generate a cyanocopper species responsible for the cyanation event. Nevertheless, detailed mechanisms of these cyanation reactions remain elusive. 

Vinylic copper reagents react with CICN to give vinyl cyanides, though BrCN and ICN give the vinylic halide instead." Vinylic cyanides have also been prepared by the reaction between vinylic lithium compounds and phenyl cyanate PhOCN." Alkyl cyanides (RCN) have been prepared, in varying yields, by treatment of sodium trialkylcyanoborates with NaCN and lead tetraacetate." Vinyl bromides reacted with KCN, in the presence of a nickel complex and zinc metal to give the vinyl nitrile. Vinyl triflates react with LiCN, in the presence of a palladium catalyst, to give the vinyl nitrile." ... 

In the case of amine nucleophiles, the products from the reaction with co-ordinated cyanates are carbamates or ureas (Fig. 4-34), and this provides a particularly convenient method for the preparation of carbamate complexes. An example of this behaviour is seen in the reaction of 3,5-dimethylpyrazole with cyanate in the presence of copper(n) salts (Fig. 4-35). Similar reactions are observed with co-ordinated thiocyanates and other heterocumulene s. 

The blue complex is stable in the presence of a moderate excess of acetic acid the reaction can therefore be applied to the detection of cyanates in alkaline solution. The solution to be tested is added to the copper-pyridine-chloroform mixture, acetic acid added slowly and the solution shaken vigorously after each addition. As soon as the solution is neutral, the chloroform will assume a blue colour. 

Note that copper is univalent in the complex. The cyanogen, which is formed, partly reacts to form cyanate and cyanide ions ... 

The first mechanism is. in fact, reminiscent of the well-known copper-catalyzed dimerization of acetylene viny(acetylene being the main by-product of this process. This side reaction can, however, be inhibited to some extent by the use of cobalt salts as additives [IS]. The cyanation of acetylene and of alkenyl halides is also promoted by Co and Ni cyanides and Pd catalysis. A reducing reagent, such as Zn or NaBll4, has been used in conjunction with cobalt cyanide complexes, and the formation of. succinonitrile has been reported to result from the basebase-catalyzed hydrocyanation of acrylonitrile. 

Cobaltaie(l -), dodecacarbonylirontri-, tetraethylammonium, 27 188 Cobaltate(l -), dodecacarbonylirontri-, (triphenylphosphine)gold(l -(-), 27 188 -------, dodecacarbonylrutheniumtri-, tetraethylammonium, 26 358 Copper, (acetonitrile)dodecacarbonyltrico-balt ruthenium-, 26 359 Crystal growth, 26 377 Cyanate, tungsten complex, 26 42 Cycloheptatriene, molybdenum complex, 27 4... 

For example the oxidation of cuprocyanide complexes (Cu(CN) " , = 2, 3, 4) results in the formation of copper oxides (red and black) at values of pH > 12. At lower pH (7-11) the formation of azulmin (HCN polymer) occurs along with cyanate. At pH of 5-7 the oxalate ammonium ions and white oximide can be produced. The current efficiencies for direct oxidation of several metal cyanides, e.g. Cu(I), Cd(II) and Zn(II) are low. 

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