Cobalt pentacyano complex

In pentacyano complexes of cobalt(III) the net charge at the coordination center is considerably decreased by the strong coordinate bonds of the five cyano groups. Thus the EPA properties of cobalt(III) are considerably lower in this complex unit, but further stabilization may still be effected by a sixth EPD ligand of high donicity like ammonia. By the reaction... 

Wayne K. Wilmarth It is a pleasure to report the work carried out by Albert Haim and Robert Grassi dealing with substitution reactions of the pentacyano-cobalt(III) complexes. 

It has been known for some time, as a result of the work of Prof. Adamson and others, that cobalt (I I) forms a stable pentacyano complex in aqueous solution. However there have been some questions raised about the structure of this species particularly as to whether it is a truly pentacoordinated species or whether there is a loosely held water molecule. 

Haim, A. and W. K. Wilmarth Binuclear Complex Ions III. Formation of Peroxo and Cyano Bridged Complexes by Oxidation of the Pentacyano Complexes of Cobalt (II). J. Am. Chem. Soc. 83, 509 (1961). 

The mechanism is similar in form to that for other reactions of the hydrido-pentacyano-complex, including the reaction with [FeCCbOe] -, involving the formation of the cobalt(i) complex [Co(CN)5l ",... 

Reactions and catalytic properties 20 of rhodium complexes in solution (160) Reactions catalysed by pentacyano- 36 cobaltate(H) (114)... 

Among the complexes which may function in this way are pentacyano-cobaltate ion, iron pentacarbonyl, the platinum-tin complex, and iridium and rhodium carbonyl phosphines. It has been suggested that with tristriphenylphosphine Rh(I) chloride, a dihydride is formed and that concerted addition of the two hydrogen atoms to the coordinated olefin occurs (16). There are few examples of the homogeneous reduction of other functional groups besides C=C, C=C, and C=C—C=C penta-cyanocobaltate incidentally is specific in reducing diolefins to monoolefins. 

A slightly different aspect of catalysis of aquation of complexes is that of aquation of, for instance, azides by nitrous acid. This has already been mentioned in connection with the generation of intermediates of the type [Co(NH3)5] + in the first section of this chapter. A similar system is nitrous acid catalysed aquation of pyridiomethyl- or benzyl-pentacyano-cobaltate(iii), where aquation proceeds by S l attack at the ligand. ... 

The complex isolated from the reaction of crotyl bromide with pentacyano-cobaltate(II) undergoes the same reactions with hydrido complex and acid as that isolated from butadiene 2. Reduction of a- and y-methylallyl chlorides yields the same distribution of butene isomers as obtained from butadiene. Treatment of these isomeric chlorides with pentacyanocobaltate(II) in the absence of hydrogen yields equal quantities of butadiene and butenes. 

A Raman spectroscopic study of the hydrogenation of aqueous pentacyano-cobaltate(n) has been reported. In the presence of excess cyanide ion hydrogenation may be accompanied by the formation of some [Co(CN)e] . Also, the reaction of [CoCChOsJ and BH4- is not an efficient method for the preparation of the hydrido-complex since the major product has been characterized as the hexacyano-species. 

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