Cobalt complexes oximes

The benzyl ligand of benzylbis(dimethylglyoximato)pyridine cobalt complex has been selectively converted to 3,5-dibenzyl-l,2,4-oxadiazole by a reaction with alkyl nitrite in the presence of light (426). The reaction proceeds by the in situ formation of an oxime and a nitrile oxide (Scheme 1.44). 

There are some reports on the asymmetric catalytic hydrogenation of C=N double bonds. Rhodium phosphine complexes do not have high activity, and the stereoselectivity is low. - Homogeneous hydrogenation of oximes, Schiff s bases and cyclic imines " have been reported. A cyano cobalt complex has been used for the homogeneous catalytic hydrogenation of oximes and Schiff s bases but the degree of asymmetric induction is unknown. 

The analogous three-membered ring has been obtained with the cobalt complex containing the tridentate ligand 2-((2-pyridylmethyl)amino)-3-butanone oxime. It has been notified that intramolecular process forming the metallacycle 114 is quite rapid, whereas the carbon bonded to cobalt is inert toward intermolecular nucleophilic attack (Equation (18)). " ... 

Another type of oximes, amino-oxime ligands, has been developed by the condensation of biacetyl monooxime with 2-(aminomethyl)pyridine and 2-(2-aminoethyl)pyridine. This tridendate ligand led to different stereoisomers. The stability of the various possible isomers of cobalt complexes 147 and 148 has been calculated. The minimum strain energy is observed for a w< r-configuration for imino complexes [Co(L )2] and amino complex [Co(L - )(HL )] + (Figure 43). 

The relative reactivity of pairs of chloride and bromide complexes is often reported and discussed. Recent studies in this category which refer to such pairs of cobalt(in)-amine-halide complexes include those of aquation of cw-[Co(en)g(cyclohexylamine)X] +, of tra 5-[Co(cyclam)(N02)X]+, and of c/j-[Co(phen)2(N02)X]+, in all cases with X = Cl or Br. Similar reactivity comparisons have been made for cobalt(in)-oxime-halide complexes, including the series /ra 5-[Co(dmgH)2LX], with L = semicarbazide or thiosemi-carbazide, and traw-[Co(dmgH)2(tu)X] (in 20% ethanol). In these latter cases X = Cl, Br, or I. Several of these systems will be mentioned again later, in the section on effects of non-leaving ligands. 

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... 

In contrast with the role of cofactor B12 in methionine synthase (methyl group transfer to a thiol), functional Bi2 model complexes have provided a formidable challenge. Several oxime alkyl-cobalt (structural) B12 models when reacted with arene- and alkanethiolates lead only to... 

Huynk et al. [218] also used differential pulse cathodic stripping voltammetry for the determination of cobalt and nickel in seawater by dimetbylgly-oxime complexation. They report detection hmits of 0.002 pg/1 for cobalt and 0.005 xg/l for nickel. 

The preparation of oximes from olefins is a valuable approach for the synthesis of nitrogen-containing compounds such as amino acids and heterocycles. Okamoto and colleagues have reported that a catalytic reduction-nitrosation of styrenes 31 with ethyl nitrite and tetrahydroborate anion by the use of bis(dimethylglyoximato)cobalt(II) complex afford the corresponding acetophenone oximes 32 (Scheme 23). 

Nonsteroidal antiinflammatory drugs, interaction with lithium, 36 66 No-phonon transition, 35 324 Norbomadiene complexes with cobalt, 12 286 with copper, 12 328, 330, 331 with gold, 12 348, 349 with group VIB metals, 12 231 with group VnB metals, 12 241 with iron, 12 265 with palladium, 12 314 with platinum, 12 319 with rhodium, 12 300-302 with ruthenium, 12 278, 279 with silver, 12 340-342, 344, 346 Norbomylsiloxane, 42 226, 228 Notch receptor proteins, 46 473, 475 h (N)" oxime complexes, osmium, 37 260 h (N,0) oxime complexes, osmium, 37 260 (NPr ljiFeCfrdto),], magnetization versus temperature, 43 230... 

Oxime 85 with sodium cobalt nitrite Na3Co(N02)6 forms a poorly water soluble Cobalt(III) complex CoL3 that, by contrast to 85, is relatively stable to acids. 

The most common hydrox y oxime ligands are salicylaldoximes, complexes of which with copper(II), nickel(II) amd palladium(II), cobalt(II), iron(II), iron(HI) and manganese(II) have been investigated extensively including crystal and molecular structures13 of the first three. In an interesting study,71 the reactions of cobalt bis chelates of this type have been studied with aluminum isopropoxide. 

Using a quadridentate ligand derived from 1,3-propanediamine and 2,3-butanedione the cobalt-oxime complex (61) was prepared, and again in presence of the chiral base quinine (60) this was used to hydrogenate benzil according to equation (54) in an optical yield of 79%.277 These cobalt systems permitted only low turnover numbers to be achieved. 

When simple terminal alkenes are used as acceptors, the cyclic primary alkyl cobalt species are stable, and can often be isolated and purified by standard techniques.145 Scheme 32 shows some of the transformations that Pattenden has accomplished with the cyclic alkylcobalt complex (55).146 In addition to standard elimination to an alkene, the complexes can be converted to alcohols, halides, oximes, and phe-... 

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