Cobalt tris complexes

When, however, the ligand molecule or ion has two atoms, each of which has a lone pair of electrons, then the molecule has two donor atoms and it may be possible to form two coordinate bonds with the same metal ion such a ligand is said to be bidentate and may be exemplified by consideration of the tris(ethylenediamine)cobalt(III) complex, [Co(en)3]3+. In this six-coordinate octahedral complex of cobalt(III), each of the bidentate ethylenediamine molecules is bound to the metal ion through the lone pair electrons of the two nitrogen atoms. This results in the formation of three five-membered rings, each including the metal ion the process of ring formation is called chelation. 

An additional study on the reaction of molecular oxygen with an NHC complex is depicted in Scheme 10.3 [13]. The tri-NHC cobalt complex 9 is obtained by reaction of T1MEN > 8 (TIMEN = tris[2-(3-alkylimidazol-2-ylidene)ethyl]amine) with... 

In the complex [Co(NH3)6]Cl3, the cation is [Co(NH3)6]3+, and it is named first. The coordinated ammonia molecules are named as ammine, with the number of them being indicated by the prefix hexa. Therefore, the name for the compound is hexaamminecobalt(III) chloride. There are no spaces in the name of the cation. [Co(NH3)5C1]C12 has five NH3 molecules and one CN coordinated to Co3+. Following the rules just listed leads to the name pentaamminechlorocobalt(III) chloride. Potassium hexacyanoferrate(III) is K3[Fe(CN)6j. Reinecke s salt, NH4[Cr(NCS)4(NH3)2], would be named as ammonium diamminetetrathiocyanatochro mate (III). In Magnus s green salt, [Pt(NH3)4][PtCl4], both cation and anion are complexes. The name of the complex is tetraammineplatinum(II) tetrachloroplatinate(II). The compound [Co(en)3](N03)3 is named as tris(ethylenediamine)cobalt(III) nitrate. 

Table VII lists three precursor complexes of the type tris(phenolato)cobalt(III) and four compounds containing only one coordinated phenolate (146, 152). In the cyclic voltammograms of [Com(LBu2)] and [Com(LBuMet)] three reversible, ligand-centered, one-electron oxidation waves are observed. On the time scale of a Cou-lometric experiment, only the monocations [Com(LBu2 )]+ and [Com(LBuMet )]+ are stable and were spectroscopically characterized. In contrast, [Conl( L,Bu2)(acac)]+ undergoes a reversible one-electron oxidation yielding the dication [Com(T/Bu2 )(acac)]2+, which is fairly stable in solution.

John Gildard has resolved the complex tris(ethylenediamine)cobalt(III) into the D and l form, and by forming diastereoisomers he has treated these separately with pseudonoma bacterium. The results have been very, interesting indeed. 

The resolution of racemic amino acid mixtures via coordination to a metal ion has been a popular field of study. [Cu(L-aa)2] complexes can be used to resolve DL-Asp, dl-G1u and DL-His.58,59 (—)-[Co(EDTA)] has been used to resolve DL-His having first resolved the racemic [Co(EDTA)] ion using the L-histidinium cation.60 Schiff base complexes of both Co111 and Ni11 have also been used to resolve amino acids.61,62 A more esoteric finding is that the bacterium Enterobacter cloacae prefers to metabolize the A-( —) isomer of/ac-[Co(GlyO)3] rather than the A-(+) form,63 an observation reminiscent of that made by Bailar using tris(ethylenediamine)cobalt(III) salts. 

Bis(acetylacetonato)cobalt(II) and tris(acetylacetonato)cobalt(III) have both been found to possess fungicidal activity on treated cotton and linen fabrics.49 Both complexes have octahedral coordination about the metal, the cobalt(II) complex achieving this by forming a linear tetranuclear species (18). The latter complex is the somewhat more effective fungicide. 

The following procedure is based on the reaction of an aqueous solution of cobalt(II) chloride with the equivalent amount of (2-aminoethyl)carbamic acid, followed by oxidation with hydrogen peroxide and the subsequent formation of bis(ethylene-diamine)cobalt(III) ions. The bis(ethylenediamine)cobalt(lII) species are converted to the carbonato complex by reaction with lithium hydroxide and carbon dioxide. During the entire preparation a vigorous stream of carbon dioxide is bubbled through the reaction mixture. This procedure appears to be essential in order to minimize the formation of tris(ethylenediamine)cobalt(III) chloride as a by-product. However, the formation of a negligible amount of the tris salt cannot be avoided. The crude salts have a purity suitable for preparative purposes. The pure salts are obtained by recrystallization from aqueous solution. 

The catalytic action of CDTA complexes of Fe(III), Ni(II), Cu(II), Cr(in), and Mn(II) on the oxidation of L-ascorbic acid with tris(oxalato)cobaltate has been investigated. The rate is proportional to the concentration of the complex. Fe(III)-CDTA is the best catalyst for the reaction.76... 

Reaction of Cytochrome cimu with Tris(oxalato)cobalt(III) The cytochrome c protein was also used as reductant in a study of the redox reaction with tris (oxalato)cobalt(III).284 Selection of the anionic cobalt(III) species, [Conl(ox)3]3 was prompted, in part, because it was surmised that it would form a sufficiently stable precursor complex with the positively charged cyt c so that the equilibrium constant for precursor complex formation (K) would be of a magnitude that would permit it to be separated in the kinetic analysis of an intermolecular electron transfer process from the actual electron transfer kinetic step (kET).2S5 The reaction scheme for oxidation of cyt c11 may be outlined ... 

Phenylbiguanide, C6H6NHC(NH)NHC(NH)NH2, combines with trivalent cobalt, as does biguanide itself, to form complex tris(phenylbiguanido) cobalt (III), its hydroxide, and tris(phenylbiguanide)cobalt salts.1 All of these resem-... 

Tris(phenylbiguanido)cobalt(III) hydroxide, [Co(C6-H5C2N6H5) 3]-3H20 or [Co(C6H6C2N6H6) 3] (OH) 3, forms rose-red crystals which melt with decomposition near 200° and are insoluble in water and alcohol. The compound absorbs carbon dioxide from the atmosphere and liberates ammonia from solutions of ammonium salts on boiling. Boiling water and alkali have no action upon the complex base, but concentrated acids decompose it. The anhydrous material may be obtained by heating the hydrate to 145 to 150° for 24 hours, but it readily absorbs water on exposure to air. The substance is preserved in an atmosphere free from carbon dioxide. 

Hydrated tris(phenylbiguanide)cobalt(III) chloride forms needle-shaped, red crystals which are soluble in water and alcohol but insoluble in ether and acetone. When heated to 110° for 15 hours, the hydrate loses the whole of its water to form the red anhydrous salt. The solution of the complex chloride gives colored precipitates with a number of complex anions such as hexacyanoferrate(II), hexacyano-ferrate(III), nitroprusside, hexacyanocobaltate(III), and chloroplatinate. 

Tris (ethylenediamine) cobalt (III) chloride was first prepared by Werner.1 Resolution was effected through the chloride d-tartrate which was obtained by allowing the chloride (1 mol) to react with silver d-tartrate (1 mol). The correct ratio of chloride ion to tartrate ion is important and this has meant that it was necessary to isolate the pure solid chloride, the synthesis of which has been described by Work.2 In the present method the less soluble diastereo-isomer is isolated directly and the expensive and unstable silver d-tartrate is replaced by barium d-tartrate. The addition of activated carbon ensures rapid oxidation of the initial cobalt (II) complex and eliminates small amounts of by-products of the reaction. 

The first example of facile reversible trans-to-cis isomerization of the azo group through a combination of photoirradiation and a redox cycle has been achieved in an azobenzene-attached tris(bipyridine)cobalt system [56-58]. This combination makes possible both forward and backward isomerization in response to irradiation from a single light source (Scheme 1). The Co11 complex, 70-2BF4, with trans-azobenzene moieties affords the cis form in... 

The crude trihydrido-tris(triphenylphosphine)cobalt(III) prepared above will pick up nitrogen directly to form the nitrogen complex. 

Scheme 4 Synthesis and oxygenation of Tris-carbene cobalt complex...

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