Cobalt complexes dioximes

The first reported chiral catalysts allowing the enantioselective addition of diethylzinc to aryl aldehydes in up to 60% cc were the palladium and cobalt complexes of 1,7,7-trimethylbicy-clo[2.2.1. ]heptane-2,3-dione dioxime (A,B)3. A number of other, even more effective catalysts, based on the camphor structure (C K, Table 26) have been developed. 

Benzoquinone, 3,5-di-t-butyl-cobalt complexes, 2, 398 Benzoquinone dioximates metal complexes... 

There is one direct method of preparing primary diamines from alkoies, in which the alkene is treated with nitric oxide and a cobalt complex, and the intermediate worked up reductively. The two-stage reduction gives better stereoselectivity (Scheme 38). Typical yields from alkenes listed and cisurans se-lectivities (expected product first) are cyclopentene, 70%, 70 30 rr[Pg.484]

Cobalt complexes of this type were initially isolated by Boston and Rose [2] and independently by Umland and coworkers [38]. Boron-capped iron(II) and cobalt(III) tris-dioximates have been obtained by two main routes a direct template reaction on the metal ion and the... 

The singlet nature of most bands in the IR spectra of cobalt complexes confirmed the Cs symmetry of their molecules. The C=N stretching vibration bands were appreciably shifted and intensified compared with those of the initial dioximes. Only one band of this type was observed for cobalt(III) complexes, and its position and intensity were more affected than those of cobalt(II) clathrochelates. 

The linear trinuclear [NiDm3(ttnFe)2](PF6)2-0.5H2O complex contains two high-spin capping iron(III) ions with configuration 7.37 A apart. The Ni-N bond distance in the coordination polyhedron (2.035 A) is much higher than those in the square-planar Ni(HDm)2 bis-dimethylglioximate (1.85 A), and clathrochelate iron(III) and cobalt (III) dioximates (M-N ca 1.9 A) [80]. 

The quasi-reversible character of these redox reactions indicates that some geometrical changes are taking place without changing the clathrochelate framework. As in the case of trinuclear cobalt complexes, macrobicyclic nickel dioximates are characterized by a high oxidation state stabilization in comparison with other nickel complexes. For example, for Ni(HDm)2 bis-dioximate, two processes (oxidation and reduction) were observed for nickel(II) ion [80],... 

Nevertheless, if a comparison is made of the literature data on equilibrium measurements in dioxane-water solvent mixtures, more data are to be found which contradict the above conclusions than those which support them. In order to investigate this question, Gaizer et al [Ga 74b] determined the stability constants of the iodide mixed complexes obtained from three cobalt(III) dioxime parent complexes, in solvent mixtures with a dioxane content of 10-75%. The three dioximes were dimethylglyoxime, cyclohexanedione dioxime (Nioxime) and furil dioxime. The results are given in Table 8.4, together with the stoichiometric constants determined in solutions of ionic strengths of 0.1 m, and also the thermodynamic constants obtained with the activity coefficients calculated for the various solvent mixtures (with a knowledge of their relative permittivities). A comparison of the data obtained in the different solvent mixtures is possible only in the case of the... 

Alkoxycarbonylcarbenes, which are frequently used for cyclopropanation, have been reviewed by Marchand and Brockway.In conjunction with a copper complex of an asymmetric ligand, ethyl diazoacetate will condense with 2,5-dimethyl-hexa-2,4-diene to give optically active chrysanthemic ester.With a cobalt complex of (+ )-camphorquinone dioxime, enantioselectivities as high as 70 % could be obtained in the addition of diazoacetate to 1,1-disubstituted olefins. As would be expected, choice of both metal and chelate is critical in such asymmetric syntheses. ... 

Table 2 First-order rate constants and activation parameters for aquation of cobalt(jn)-dioxime-halide and -pseudohalide complexes rate constants at 50 °C in aqueous solution...

Complexes containing encapsulated metal ions (clathrochelates ) with the formula [M(dioxime)3(BR)2] are known with iron(II) 135, cobalt(ll) 136, cobalt(III) 137, and ruthenium(ll) 138 (Fig. 37) [205-220]. Generally, these macrobicyclic complexes are prepared by template synthesis from a mixture of... 

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... 

Cyclohexane-1,2-dione dioxime (nioxime) complexes of cobalt (II) and nickel (II) were concentrated from 10 ml seawater samples onto a hanging mercury drop electrode by controlled adsorption. Cobalt (II) and nickel (II) reduction currents were measured by differential pulse cathodic stripping voltammetry. Detection limits for cobalt and nickel were 6 pM and 0.45 mM, respectively. The results of detailed studies for optimising the analytical parameters, namely nioxime and buffer concentrations, pH, and adsorption potential are discussed. 

Donat and Bruland [217] conducted a direct determination of cobalt and nickel in seawater by differential pulse cathodic scanning voltammetry, preceded by absorptive collection of cyclohexane-1,2 dioxime complexes. 

Although square-planar configuration is customarily considered classical for v/c-dioximate of nickel(II), attempts have been made repeatedly over the years for preparing the above complexes in other configurations also. By employing weakly polar solvents and some other variations, success has been claimed in the preparation of mono(dioxime) complexes of nickel(II).42,43 The dichloro-bis(l,2-cyclohexanedione dioximato)nickel(II) has been shown to have an octahedral vie structure.44 Examples of tris(dioxime) complexes of transition metals in general45"18 and of bivalent atoms40,47 in particular are rare and structural details of only a tris(dioxime) complex of cobalt(III) are known.48 In a more recent publication,49 the crystal structure of tris(l,2-cyclohexanedione dioximo)nickel(II) sulfate dihydrate has been elucidated. 

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