Cobalt complexes with alkali metals

The cobalt complex is usually formed in a hot acetate-acetic acid medium. After the formation of the cobalt colour, hydrochloric acid or nitric acid is added to decompose the complexes of most of the other heavy metals present. Iron, copper, cerium(IV), chromium(III and VI), nickel, vanadyl vanadium, and copper interfere when present in appreciable quantities. Excess of the reagent minimises the interference of iron(II) iron(III) can be removed by diethyl ether extraction from a hydrochloric acid solution. Most of the interferences can be eliminated by treatment with potassium bromate, followed by the addition of an alkali fluoride. Cobalt may also be isolated by dithizone extraction from a basic medium after copper has been removed (if necessary) from acidic solution. An alumina column may also be used to adsorb the cobalt nitroso-R-chelate anion in the presence of perchloric acid, the other elements are eluted with warm 1M nitric acid, and finally the cobalt complex with 1M sulphuric acid, and the absorbance measured at 500 nm. 

Scheme 7.8 Preparation of the half-sandwich type cyclopentadienylcobalt(I) complexes 32 and 33 from cobaltocene and their degradation with alkali metals M (Li or K) in the presence of THF or tmeda to give the anionic olefin cobalt(-I) complexes 34-37 (the coordination of THF and tmeda to the cations M+ is omitted for clarity)...

Reactions of the (Tj5-C5Hs)cobaIt-olefin complexes (26) prepared according to Eqs. (25) and (26) with alkali metals (Li, Na, K) in the presence of olefins lead to the elimination of the second C5H5 ligand from the cobalt (Scheme 5). Complexes 27a and 27b, or the mixed complex 27c are obtained in high yields [Eq. (28)]. The syntheses of the pure complexes 27a and 27b do not, of course, require the isolation of intermediates 26a and 26b. As mentioned previously, synthesis is readily achieved from cobaltocene (24) by reaction with either stoichiometric amounts or excess alkali metal in the presence of COD or ethylene [Eq. (24)]. The alkali metal cyclopentadienides which are formed are easily separated from the cobalt complexes and can be used for the synthesis of cobaltocene (51) [Scheme 5 Eq. (29)]. 

Within this context, the present article concentrates on transition metal cluster complexes of cobalt, iron and manganese with mixed chalcogen/carbonyl ligand spheres obtained by reaction of simple binary metal carbonyls with alkali-metal sulfides, alkali-metal thiolates or transition-metal thiolate complexes and their selenium or tellurium counterparts. 

Alkali metal boratabenzenes may be liberated from bis (boratabenzene) cobalt complexes 7 and 13 by reductive degradation with elemental Li, sodium amalgam, or Na/K alloy (60), or alternatively by degradation with cyanides (61). The latter method has been developed in detail (Scheme 4). It produces spectroscopically pure ( H-NMR control) solutions of the products 26 the excess alkali metal cyanide and the undefined cyanocobalt compounds produced are essentially insoluble in acetonitrile. 

CO2 molecule, or Mg + and CO2 play the role of oxide acceptor to form water, carbonate, and MgC03, respectively [38]. The reactions of the iron carboxylate with these Lewis acids are thought to be fast and not rate determining. For the cobalt and nickel macrocyclic catalysts, CO2 is the ultimate oxide acceptor with formation of bicarbonate salts in addition to CO, but it is not clear what the precise pathway is for decomposition of the carboxylate to CO [33]. The influence of alkali metal ions on CO2 binding for these complexes was discussed earlier [15]. It appears the interactions between bound CO2 and these ions are fast and reversible, and one would presume that reactions between protons and bound CO2 are rapid as well. 

Rubidium metal alloys with the other alkali metals, the alkaline-earth metals, antimony, bismuth, gold, and mercury. Rubidium forms double halide salts with antimony, bismuth, cadmium, cobalt, copper, iron, lead, manganese, mercury, nickel, thorium, and zinc. These complexes are generally water insoluble and not hygroscopic. The soluble rubidium compounds are acetate, bromide, carbonate, chloride, chromate, fluoride, formate, hydroxide, iodide,... 

Alkali metal 1-methyl- and 1-phenyl-borinates are also available from bis(borinato)cobalt complexes (see below) on treatment with sodium or potassium cyanide in an aprotic solvent like acetonitrile. Cobalt cyanide precipitates and the alkali borinate remains in solution. After addition of thallium(I) chloride to some complexes, thallium 1-methyl- or 1-phenyl-borinate could be isolated as pale yellow solids, the only main group borinates isolated hitherto. They are insoluble in most organic solvents but readily soluble in pyridine and DMSO. The solids are stable on treatment with water and aqueous potassium hydride, but are decomposed by acids <78JOM(153)265). 

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... 

Therefore, melts-solvents of the first kind are of interest in the following scientific aspects determination of the acid-base product of the ionic solvent and estimation of the upper limit of acidity of these solvents (such as nitrates, sulfates). The decrease of stability of the solvent acid can be used for the stepwise decomposition of acidic solutions of cations and synthesis of complex oxide compounds and composites by coprecipitation [53-56], It is possible to obtain complex oxides containing alkali metals by precipitation of multivalent metal oxides with the alkali metal oxide as a strong Lux base, as was reported by Hong et al., who used 0.59LiNO3-0.41LiOH mixed melt to obtain electrochemically active lithium cobaltate, LiCo02 [57]. 

All the simple carbonyl hydrides (Table IY) may be readily prepared by acidification of alkali metal salts derived from the simple carbonyls. Only the carbonyl hydrides of Mn, Re, Co, and Fe are well characterized. They form highly toxic volatile liquids and are unstable thermally and with respect to oxidation. Pentacarbonylmanganese hydride is stable to light and air for several hours at room temperature (173), while the very unstable cobalt and iron complexes decompose spontaneously at — 20°C (167, 251). It may be noted that solutions of these carbonyl hydrides in inert solvents undergo spontaneous decomposition much more slowly than the pure substances. 

Formation of these extractable complexes involves coordination bonds with the metal cation, i.e., the sharing of electrons from the complexing agent to complete previously unfilled orbits of the cation. The alkalies and alkaline earths are not easily capable of forming such compounds because they have no empty electron orbits, and hence cannot be readily extracted with organic solvents immiscible with water. On the other hand, elements of the transition groups, such as the rare earths, uranium and the other actinides, iron, nickel, and cobalt, form coordination compounds with ease and are readily extracted by organic solvents immiscible with water. 

---