Cationic complexes cobalt

LCo(H20)6] ion, and bidentate /V-donor ligands such as cn, bipy and phen form octahedral cationic complexes [Co(L-L)3] , which are much more stable to oxidation than is the hexaammine [Co(NH3)6l . Acac yields the orange [Co(acac)2(H20)2] which has the tram octahedral structure and can be dehydrated to [Co(acac)2l which attains octahedral coordination by forming the tetrameric species shown in Fig. 26.3. This is comparable with the trimeric [Ni(acac>2]3 (p. 1157), like which it shows evidence of weak ferromagnetic interactions at very low temperatures. fCo(edta)(H20)] is ostensibly analogous to the 7-coordinate Mn and complexes with the same stoichiometry, but in fact the cobalt is only 6-coordinate, 1 of the oxygen atoms of the cdta being too far away from the cobalt (272 compared to 223 pm for the other edta donor atoms) to be considered as coordinated. 

A warmed alcoholic solution of cobalt(Il) nitrate and 2-formylpyridine S-methyldithiocarbazate, 6, yielded diamagnetic [Co(6-H)2]N03 [126]. However, cobalt(II) chloride, bromide and thiocyanate yielded complexes with cobalt(III) cations and cobalt(II) anions, [Co(9-H)2]2 [C0A4]. 

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. 

The kinetics of base hydrolysis of several complexes of the type [Co(NH3)3L3] have been examined in order to see whether the mechanism for these uncharged complexes is the same as that operating for base hydrolysis of the standard cationic complexes (75). A comparison of kinetic parameters - a small selection is given in Table II (76,77) - suggests that all cobalt(III)-nitro-amine complexes, charged and uncharged, undergo base hydrolysis by the SnICB (Dch) mechanism. 

Ammino-derivatives op Cobalt Salts—Cobaltous Salt Ammines—Cobaltic Salt Ammines—Mononuclear Cobalt-ammines containing One Atom of Cobalt in the Molecule—Cobaltic Salts with Trivalent Cation—Cobalt-ammines Containing Divalent Cation—Cobalt-ammines containing Monovalent Cation—Cobalt-ammines consisting of Non-dissociable Complex— Cobalt-ammines containing Monovalent Anion—Cobalt Salts containing Trivalent Anion—Polynuclear Cobalt-ammines containing Two or more Cobalt Atoms in the Molecule—Cobalt-ammines of Unknown Constitution— Ionisation Metamerism—Polymerisation Isomerism—Valency Isomerism —Co-ordination Position Isomerism—Isomerism due to Asymmetric Cobalt Atoms. 

The formation of the blue complex cobalt salt serves as a sensitive test for the detection of either cobaltous or mercuric ions with a sensitivity of ly Co or lOy of Hg in solution. Depending on the cation to be tested for, the test reagent consists of a concentrated solution of either mercuric chloride or cobaltous acetate containing alkali thiocyanate. The test may be carried out in one drop of liquid on a slide under a microscope (50-100X). Agitation of the drop with... 

The kinetics of the acid hydrolysis of dihydroxo-bridged cobalt(III) complexes have been studied for both cationic and anionic species. The stoichiometry of the hydrolysis reaction for cationic complexes can be expressed by Eq. (56). The equilibrium lies completely to the right at low pH (typically less than 3) and the reverse process in Eq. (56) can normally be disregarded. For all the systems studied to date the observed rate laws can be interpreted in terms of Scheme 4. 

This chapter includes those transition metal-pentadienyl cationic complexes that are quite stable, can be stored and handled easily, and are therefore useful as stoichiometric intermediates for organic synthesis. The dienyliron systems, which are readily available and inexpensive, have dominated this area of chemistry, and will occupy the larger part of the discussion. The chemistry of more expensive and less easily prepared dienylmetal complexes, such as those of manganese and cobalt, will be dealt with at the end of the chapter. 

There are marked differences between the carbonyl cations of cobalt and its congeners, rhodium and iridium. For instance, the heavier elements form square-planar carbonyl cations as well as higher coordinate complexes. This is paralleled by the isocyanide cations thus cobalt forms [Co(CNR)5]+ cations (191), whereas rhodium and iridium form [M(CNR)4]+ cations (191, 192, 194). 

The structure of the cationic complex [Co2(p,Tj2,772-HC2CH2PEt3)(CO)6]+ has been established by an X-ray diffraction study (Fig. 13).79 The main difference between this type of cationic derivative and the parent propargylium complexes is the absence of any anchimeric assistance from the cobalt to the carbocation center. The cobalt-carbon interaction is replaced by a direct interaction with the heteroatom of the nucleophile. This is reflected in the infrared spectra of the [Co2(/x,r72,T72-HC2CH2nuc)(CO)fi]+ species. The values of the carbonyl stretching bands lie in between those of [Co2(ju.,Tj2,Tj2-HC2CH2OH)(CO)6] and [Co2(m,t, t73-HC2CH2)(CO)6]+. 

The species shown in the system 8.13 are those present under reaction conditions. At lower temperatures and pressures, a wealth of different complexes are present, including dicobalt octacarbonyl and cationic complexes of cobalt that differ depending on what cobalt compound was initially charged [17,23-25]. 

Di-/Li-hydroxo-bis[bis(ethylenediamine)cobalt(III)] dithionate may be obtained analogously to the chromium(III) salt from cis- [aquabis(ethylenediamine)hydrox-ocobalt(III)] dithionate, either by heating at 110° or by refluxing in acetic anhydride. The formation of the bridged cation of cobalt(III) is much slower than that of chromium(III). In contrast to the chromium(III) complex there is no evidence that the bridged cobalt(III) complex can be formed by aqueous hydrolysis. 

Transition metal carbonyls such as Co2(CO)8 and CoH(CO)4, formed in the reaction of R3SiH with dimer (but also Fe(CO)5 and M3(CO)i2 (M = Fe, Ru, Os)) have been found to be active catalysts for the hydrosilylation of olefins, dienes, unsaturated nitriles, and esters as well as for hydrosilylation C=0 and C=N bonds [56]. Hydrosilylation of phenylthioacetylenes in the presence of this catalyst is extremely regioselective [57]. Cobalt(I) complexes, e. g., CoH(X)2L3 (X = H, N), could be prospective candidates for investigation of the effectiveness of alkene hydrosilylation by trialkoxysilanes as well as dehydro-genative silylation [58]. Direct evidence for the silyl migration mechanism operative in a catalytic hydrosilylation pathway was presented by Brookhart and Grant [59] using the electrophilic Co cationic complex. 

Protonation of (norbornadiene)cobalt complex 43 induces C-C bond cleavage of the norbornenyl ring to form cationic complex 44 [63,64]. Re-protonation of the reduced complex 45 induces a second cleavage of a non-strained cyclopen-tene ring to give an open r)5-pentadienyl complex 46. It is postulated that a three-center interaction of the highly electrophilic metal center with the a-electrons of the adjacent C-C bond is involved. 

See Footnote t in Section A, p. 166. The bath temperature should be kept below 40°. tThe liquor and the water extract contain the unipositive bis-mer-[N-(2-aminoethyl)-7-methyl-salicylideneiminato]cobalt(III) cation complex, Con,[o-OC6H4C(Me)=N(CH2)2NH2]2 +. To isolate its iodide salt, the aqueous solution is concentrated under vacuum to a volume of 10 mL. After some hours, a solid precipitates. It is collected by filtration, dried by suction, and is then extracted with dichloromethane. The liquor is evaporated to dryness under vacuum, which yields the complex in question (as the monohydrate 3.68 g, 6.8 mmoles, 49%). It can be converted to the desired product ([la)I) by treatment with Na[BH ]/Pd and EtI in alkaline methanol solution under conditions similar to those of the basic procedure. 

Tris(phenanthroline) complexes of ruthenium(II), cobalt(III), and rhodium(III) are octahedral, substitutionally inert complexes, and as a result of this coordina-tive saturation the complexes bind to double-helical DNA through a mixture of noncovalent interactions. Tris(phenanthroline) metal complexes bind to the double helix both by intercalation in the major groove and through hydrophobic association in the minor groove. " " Intercalation and minor groove-binding are, in fact, the two most common modes of noncovalent association of small molecules with nucleic acids. In addition, as with other small molecules, a nonspecific electrostatic interaction between the cationic complexes and the DNA polyanion serves to stabilize association. Overall binding of the tris(phenanthroline) complexes to DNA is moderate (log K = 4)." ... 

Cationic Complexes. Both Rh and Ir give cobalt-like ammines of the types [ML6]3 +, [MLsX]2+, and [ML4X2]+, of which [Rh(NH3)5Cl]Cl2 is a typical example. The salts are made in various ways, but usually by the interaction of aqueous solutions of RhCl3(aq) with the ligand. 

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