Cobalt divalent, complexes

In contrast with the Schiff base salen, salicylaldehyde oxime (79) (salox) complexes of Co have received comparatively little attention, but a series of bis-bidentate divalent complexes of the form iraiis-Co(sa 1 ox)2( D M SO)2 have been reported.343 The heterocyclic bidentate oxime violurate (lH,3H-pyrimidine-2,4,5,6-tetrone 5-oximate, Hvi) (80) and its /V-methyl (mvi) and /V,/V -dimethyl (dmvi) derivatives form high-spin divalent [Co(vi)]+ and Co(vi)2 complexes, whereas [Co(vi)3] is low spin.344 The mixed-ligand Co(dmvi)2(phen) complex is also low spin. The crystal structure of m-Co(pxo)2Br2 (pxo = 2-acetylpyridine-l-oxide oxime) is isostructural with the Ni11 relative.345 The dichloro complex also adopts a cis configuration. The tridentate dioximes 2,6-diformyl-4-methylphenol dioxime and 2,6-diacetyl-4-methylphenol dioxime (Hdampo) form binuclear complexes of the type (81a) and (81b) respectively.346 Cobalt oxide nanoparticles were prepared by... 

Fungicidal activity of cobalt(II) and other divalent metals of tsc compounds have been observed, and is usually greater than for the free ligand.495 Broad antimicrobial activity has been reported for the cobalt(II) complex of acetophenone-4-(2 -carboxy-5 -sulfophenyl)-3-thio-semicarbazone.496... 

A high CO pressure would shift equilibrium (4.3) to the left and the catalytic reaction would become slower. In this complex CO is a far better ligand than an alkene. On the other hand the reaction uses CO as a substrate, so it cannot be omitted. Furthermore, low pressures of CO may lead to decomposition of the cobalt carbonyl complexes to metallic cobalt and CO, which is also undesirable. Finally, the product alcohol may stabilize divalent cobalt species which are not active as a catalyst ... 

In 1974, Hush and Woolsey reported that treating the cobalt(II) corrole species discussed above with pyridine induced little in the way of spectral changes. These authors took this as an indication that the divalent cobalt corrole complex in question shows little or no tendency towards axial coordination. In 1978, however, Murakami, et al. reported a different result, stating that one pyridine molecule does in fact coordinate axially to the cobalt center of an anionic Co(II) corrole. 

In the present work and in (5), evidence is reported that similar complexes are formed with divalent cobalt. All complexes described, with the exception of ammonia, are reversible. 

Rate constants have been obtained for the aquation of a series of pentaammine(carboxylato)cobalt(III) complexes [Co(NH3)5L] in UCIO4-HCIO4 media. " In many cases the values of fc<>bs are not proportional to [H ]. The data have been used to calculate association constants of protonated forms of the complexes and the corresponding rate constants for aquation. Association constants (Xml) of ion pairs formed by a series of divalent metal ions and also lanthanum(III) ions with [Co(NH3)sOOCC02] have been determined from spectrophotometric UV absorbance data at 50 and Rate constants for aquation of the... 

Table 1.13.1 contains values of equilibrium ion pair constants of some positively charged cobalt(III) complex cations and univalent anions, including also the divalent 804 " anion, for comparison. 

Metal ion complexation rates have been studied by the T-jump method. ° Divalent nickel and cobalt have coordination numbers of 6, so they can form complexes ML with monodentate ligands L with n = 1—6 or with bidentate ligands, n = 1-3. The ligands are Bronsted bases, and only the conjugate base form undergoes coordination with the metal ion. The complex formation reaction is then... 

Despite the above similarities, many differences between the members of this triad are also to be noted. Reduction of a trivalent compound, which yields a divalent compound in the case of cobalt, rarely does so for the heavier elements where the metal, univalent compounds, or hydrido complexes are the more usual products. Rhodium forms the quite stable, yellow [Rh(H20)6] " ion when hydrous Rh203 is dissolved in mineral acid, and it occurs in the solid state in salts such as the perchlorate, sulfate and alums. [Ir(H20)6] + is less readily obtained but has been shown to occur in solutions of in cone HCIO4. 

The 1,1-dithio complexes of cobalt have been studied extensively (1). Most of the literature is concerned with Co(III) compounds, as the complexes with divalent cobalt are extremely air-sensitive and have only been synthesized in acidic solution under rigorously deoxygenated conditions. The recent complexes of cobalt with 1,1-dithio ligands are listed in Table III, together with some of their physical properties. 

Triphenylformazan behaves as a bidentate ligand forming 2 1 complexes (217) with divalent copper, nickel, and cobalt.377 Formazan metal complexes can be compared to complexes of azo dyes or beta diketones due to structural similarity.301,302 In general, formazan metal complexes have low stability toward acids. However, when electron-donating substituents are added to the aromatic ring, a considerable enhancement in stability is observed. Cationic complexes of type 218 are also known. The complexation of formazan with metal cation can be accompanied by oxidation to the tetrazolium salt and the formation of a complex... 

Until recently, the hydroformylation using palladium had been scarcely explored as the activity of palladium stayed behind that of more active platinum complexes. The initiating reagents are often very similar to those of platinum, i.e., divalent palladium salts, which under the reaction conditions presumably form monohydrido complexes of palladium(II). A common precursor is (39). The mechanism for palladium catalysts is, therefore, thought to be the same as that for platinum. New cationic complexes of palladium that are highly active as hydroformylation catalysts were discovered by Drent and co-workers at Shell and commercial applications may be expected, involving replacement of cobalt catalysts. 

Typically, the synthesis of the precursor iron(II) and cobalt(II) halide complexes proceeds by treatment of an anhydrous or hydrated divalent iron or cobalt halide (e.g. MX2 jcH20 or MX2 X = Cl or Br) with 1 (and also 2-4) in... 

As we have seen earlier that the trivalent metal complexes are normally bound still more firmly due to the formation of four rings (unlike three rings with divalent metal complexes) and stable in strongly acidic solutions, for instance cobalt (Co2+) EDTA complex is fairly stable in concentrated hydrochloric acid ( 11.5 N). 

Narang, K. K. et al., Synth. React, lnorg. Met.-Org. Chem., 1996, 26(4), 573 The explosive properties of a series of 5 amminecobalt(III) azides were examined in detail. Compounds were hexaamminecobalt triazide, pentaammineazidocobalt diazide, cis- and fram-tetraamminediazidocobalt azide, triamminecobalt triazide [1], A variety of hydrazine complexed azides and chloroazides of divalent metals have been prepared. Those of iron, manganese and copper could not be isolated cobalt, nickel, cadmium and zinc gave products stable at room temperature but more or less explosive on heating [2],... 

The perchlorate salts of the complexes with divalent cobalt, nickel, and particularly iron (analogous to IV, p. S-15) are potentially explosive, and storage for more than 4 weeks is not advised. 

The tetranuclear and trinuclear clusters will only be observed at low pressures [8], but all other species are very common under hydroformylation conditions. Complex 4 is an ionic complex that is formed in polar solvents [9] and even hexa-solvated, divalent cobalt species may form as the cation. Under practical conditions both the dimers and the hydrides are observed, thus depending on the hydrogen pressure there will be more or less of the hydride present. 

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