Metal-cyanide exchange

Moderate yields of aromatic nitriles can be prepared by a process which consists formally of a metal-cyanide exchange reaction [106] but the mechanism of which differs fundamentally from that of metal-halogen exchange ... 

Polynuclear transition metal cyanides such as the well-known Prussian blue and its analogues with osmium and ruthenium have been intensely studied Prussian blue films on electrodes are formed as microcrystalline materials by the electrochemical reduction of FeFe(CN)g in aqueous solutionThey show two reversible redox reactions, and due to the intense color of the single oxidation states, they appear to be candidates for electrochromic displays Ion exchange properties in the reduced state are limited to certain ions having similar ionic radii. Thus, the reversible... 

The cyanide exchange on [M(CN)4]2 with M = Pt, Pd, and Ni is a rare case in which mechanistic comparisons between 3d, 4d, and 5d transition-metal complexes. Surprisingly, the behavior of these metal square-planar centers leads to mechanistic diversity involving pentacoordinated species or transition states as well as protonated complexes. The reactivities of these species are strongly pH-dependent, covering 15 orders of magnitude in reaction rates.85... 

Carbon-13 NMR was utilized to study different aspects of the reactivity of the metal complexes as a function of certain structural features in the selected oxocyano complexes of Mo(IV), W(IV), Tc(V), Re(V), and Os(VI) as depicted in Scheme 1 and illustrated in Figs. 1-4. The NMR spectral properties were similar to those obtained from 13C NMR in general, i.e., very sharp lines indicative of fairly long relaxation times in the order of a few seconds. The large quadrupolar moment ofTc-99 (7 = 9/2, 100% abundance) led to a very broad bound 13C signal (Fig. 5), thus excluding the quantitative study of the cyanide exchange by 13C NMR. However, 16N NMR was successfully used instead. 

In summary, it is clear from the above-discussed aspects that it was possible by multinuclear NMR (oxygen-17, nitrogen-15, carbon-13, and technetium-99) to successfully study the very slow cyanide exchange and the slow intermolecular oxygen exchange in these oxocy-ano complexes and correlate them both with the proton-transfer kinetics. Furthermore, the interdependence between the proton transfer and the actual dynamic inversion of the metal center was clearly demonstrated. 

Conventional polyether polyol technology involves alkoxylation of the starters with PO and EO using an alkali metal hydroxide catalyst such as potassium hydroxide. The catalyst can be neutralized and the neutral salt can be left in the final polyol, or optionally the catalyst can be extracted by washing with water or by deposition on an ion exchange medium. In recent years, a new catalyst technology has become widely adopted within the polyols industry, using zinc hexacyano-cobaltate (double metal cyanide catalyst, or DMC), which runs at very high... 

The complications which result from the hydrolysis of alkali metal cyanides in aqueous media may be avoided by the use of non-aqueous solvents. The one most often employed is liquid ammonia, in which derivatives of some of the lanthanides and of titanium(III) may be obtained from the metal halides and cyanide.13 By addition of potassium as reductant, complexes of cobalt(O), nickel(O), titanium(II) and titanium(III) may be prepared and a complex of zirconium(0) has been obtained in a remarkable disproportion of zirconium(III) into zirconium(IV) and zirconium(0).14 Other solvents which have been shown to be suitable for halide-cyanide exchange reactions include ethanol, methanol, tetrahydrofuran, dimethyl sulfoxide and dimethylformamide. With their aid, species of different stoichiometry from those isolated from aqueous media can sometimes be made [Hg(CN)3], for example, is obtained as its cesium salt form CsF, KCN and Hg(CN)2 in ethanol.15... 

Table 4 The Distribution of Anionic Metal Cyanide Complexes Between Anion-exchange Resins and an Aqueous Cyanide Solution as a Function of Solution pHa...

In the extraction process, the aurocyanide complex plus other metal cyanide complexes that are common in cyanide leach liquors (e.g. Fe(CN) 4-, Fe(CN)63-, Zn(CN)42-, Ni(CN)42-, Cu(CN)43-and Co(CN)63-) load onto the resin by simple ion exchange ... 

Lui et al. [109] have described an automated system for determination of total and labile cyanide in water samples. The stable metal-cyanide complexes such as Fe(CN)63 are photo-dissociated in an acidic medium with an on-line Pyrex glass reaction coil irradiated by an intense mercury lamp. The released cyanide is separated from most interferences in the sample matrix and is collected in a dilute sodium hydroxide solution by gas diffusion using a hydrophobic porous membrane separator. The cyanide ion is then separated from remaining interferences such as sulphide by ion exchange chromatography and is detected by an amperometric detector. The characteristics of the automated system were studied with solutions of free cyanide and metal-cyanide complexes. The results of cyanide determination for a number of wastewater samples obtained with this method were compared with those obtained with the standard method. The sample throughput of the system is eight samples per hour and the detection limit for total cyanide is 0.1 pg L 1. 

The thermal reaction between sulfonates and alkali metal cyanides (equation 16) or potassium hexa-cyanoferrate is more of historical value7 The finely powdered, dry and thoroughly mixed starting materials (equation 17) are heated up to 4(X) °C. For more efficient heat exchange the addition of mineral oil, sand, iron turnings or iron oxide is recommended. In spite of the quite forcing reaction conditions, yields of up to 80% are given in certain cases. ... 

Imidazoles, metallation of and metal-halogen exchange in 85H(23)417. Imidazoles, synthesis from cyanides 84T1093. 

Prussian blue analogs are here defined as polynuclear transition metal cyanides of the composition M [M (CN)6]i xHzO a retallizing with a cubic unit cell. They are easily obtained as sparsely soluble precipitates by mixing solutions of a cyano complex M (CN)e with an appropriate salt of The compounds prepared by using the hexacyanometalate in the form of the most common potassium salt invariably contain different amounts of potassium, which in some cases can be exchanged by cesium... 

Lithio-benzothiophenes can be generated, and reacted with electrophiles, if the temperature is kept low. ° Direct deprotonation of benzothiophenes follows the usual pattern for flve-membered heterocycles and takes place adjacent to the heteroatom,"" and in concord with this pattern, metal-halogen exchange processes favour a 2- over a 3-halogen the sequence below shows how this can be utilised to develop substituted benzothiophenes. 2-Lithiated reagents react with electrophiles for example with p-toluenesulfonyl cyanide, 2-cyano derivatives are produced and similarly, 2-trimethylstannylbenzofuran and -benzothiophene and benzofuran-2- and benzothiophene-2-boronic acids can be prepared. 

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