Tungsten complexes cyanides

Tungsten Complexes Containing Carbonyl, Isocyanide, and Cyanide Ligands Trmgsten Complexes Containing Hydrocarbon Ligands... 

In this reaction scheme, the formation of the pentacyano complex is a relatively fast reaction, with rate constants of about 116 and 2.9 Af" sec" for the molybdenum (20°C) and tungsten (25°C) complexes, respectively, whereas the formation of the octacyano complex from the pentacyano complex is a relative slow reaction, with a half-life of several minutes at a cyanide ion concentration of 1 Af for both the molybdenum and the tungsten complexes. The formation of the octacyano complex from the pentacyano complex is third order in the cyanide ion concentration 155,156). This suggests that the rate-determining step is the reaction of the heptacyano complex with cyanide ions. It seems, however, that the pentacyano complex is a necessary intermediate in the synthesis of the octacyano complex. This proposed reaction scheme makes it possible for the first time to explain why the octacyano complex of rhenium(V), which is also a d species, is still unknown in spite of several attempts (and claims of success) by different groups in the past (see Section IIA) to synthesize this complex The reactive complexes [Re0(H20)(CN)4]" and [ReO(OH)(CN)4] do not exist at a pH > 8, at which there are enough free cyanide ions since the values of [Re0(H20)(CN)4]" are only 1.4 and 4.2. The formation ofthe intermediate [ReOtCNlg] (see Scheme 6) is thus not possible. Thus one cannot proceed beyond the tetracyano complex in this way. 

Simple cyanides of tungsten have not been isolated, but two well-defined series of complex cyanides are known, one containing tetra-... 

TUNGSTEN COMPLEXES CONTAINING CARBONYL, ISOCYANIDE, AND CYANIDE LIGANDS... 

A series of similar reactions, in which a tungsten complex of an alkyne (103) can undergo reaction with a cyanide, has been reported The reaction yields cyclic products (104) usually involving five- or seven-membered rings. 

The reaction is believed to be a direct addition, and not involve the cleavage of the cyanide bond by tungsten complexes reported earlier. ... 

The dinuclear tungsten complex W2(OBu )6 reacts with acetylenes and cyanides to give metathesis products of W = W, C = C, and CsN bonds/ " ... 

This is by far the most stable and best-known oxidation state for chromium and is characterized by thousands of compounds, most of them prepared from aqueous solutions. By contrast, unless stabilized by M-M bonding, molybdenum(III) compounds are sparse and hardly any are known for tungsten(III). Thus Mo, but not W, has an aquo ion [Mo(H20)g] +, which gives rise to complexes [MoXg] " (X = F, Cl, Br, NCS). Direct action of acetylacetone on the hexachloromolybdate(III) ion produces the sublimable (Mo(acac)3] which, however, unlike its chromium analogue, is oxidized by air to Mo products. A black cyanide,... 

Tungsten(II) complexes carboxylic acid, 441 cyanides synthesis, 9... 

Fig. 9 Photocurrent quantum efficiency of tungsten ( ) and molybdenum (S) cyanide-complexed Ti02 electrodes compared with that of untreated Ti02( a)...

The reactions of the molybdenum(IV) and tungsten(IV) complexes with cyanide ions proceed via the same scheme as those of other mono-dentate ligands (see Scheme 3) with the formation of the pentacyano complex (155,156). This very fast reaction is followed by a much slower reaction with the production of the octacyano complex in the presence of an excess of cyanide ions. 

Tc—X bonds and the lability of X-ligands, but it has not been investigated, unlike tungsten cyanide complexes and unlike the Cl exchange between gaseous HCl and organic HCl solvates. The equilibrium in dichloromethane has been studied by Thomas and coworkers. ... 

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