Cobalt complex derivative

Love and coworkers have reported a series of dinuclear cobalt complexes derived from a rigid binucleating macrocycle H4L 18 as shown in Fig. 26 (150). The synthesis of the dicobalt complex [Co2(L18)] (36) was achieved by an anaerobic transamination reaction between H4L18 and [Co(thf) N(SiMe3)2 2] in THF. The unsaturated species 36 forms a bis(pyridine) adduct, 36 py2 (py — pyridine), which has a cleft-like structure reminiscent of pacman diporphyrin complexes (151,152). Both cobalt ions are square pyramidal, with Col and Co2 displaced out of the N4-basal planes by 0.17 and 0.18 A, respectively. The apical sites are occupied by pyridine nitrogen atoms that are exo and endo to the cleft. Interestingly the endo pyridine is canted and reflects the... 

Because such alkylation proceeds by S l mechanism, even cobalt complexes derived from unreactive (in an SN2 sense) halides can be formed. The cobalt complexes are air-stable compounds, but are affected by direct daylight. The incorporated Co—C bond is weak and, therefore, photolysis of 33 sets free the anomeric radical 11. In the presence of olefins 12 this radical adds to the double bond, followed by subsequent combination to give the insertion product 35 (Scheme 9). 

Cobalt complexes derived from Schiff bases 388 catalyzed the hydroxyacylation of electron-deficient alkenes (Fig. 90) [431, 432]. Thus, methyl acrylate 387 reacted with aliphatic aldehydes 386 in the presence of 5 mol% of the in situ generated catalyst, molecular oxygen, and acetic anhydride to 2-acyloxy-4-oxoesters 389 in 56-77% yield. When acetic anhydride was omitted, the yields of products were lower and mixtures of the free hydroxy compounds and acylated compounds resulting from Tishchenko reactions were obtained. Electron-rich alkenes did not undergo the transformation, since the addition of the acyl radical is much slower. The acylcobalt species inserts oxygen instead and acts as an epoxidation catalyst. 

Table 8 shows cobalt complexes derived from organic isothiocyanates. 

On the other hand, another cooperative catalysis approach was developed by Oh and Kim with a highly diastereo- and enantioselective domino aldol-cyclisation reaction occurring between aldehydes and methyl a-isocyanoacetate. The process employed a combination of a chiral cobalt complex derived from brucine amino diol and an achiral thiourea. The reaction was applicable to a range of aliphatic, aromatic and heteroaromatic aldehydes, providing the corresponding chiral oxazolines in good yields and diastereoselectivities of up to >90% de combined with good to excellent enantioselectivities of up to 98% ee, as shown in Scheme 7.12. 

Another class of metal complex dyes is derived from the formazan stmcture. These dyes are appHed to wool and nylon from a neutral or weakly acidic dyebath analogous to the 2 1 premetallized OjO -dihydroxyazo complexes. The bluish-gray dye Cl Acid Black 180 [11103-91-6] (61) (Cl 13710) is a 2 1 cobalt complex of the formazan type. 

Other, closely related, nicotinic acid derivatives and the unsubstituted system itself have also been studied and undergo similar reactions. Moreover, the approach may be extended to 2,2 -bipyridyls. Newkome and his collaborators have used the 2,2 -bipyridyl unit 19) as an electrophile in which ortho-hr ommes served as leaving groups. They have also used halomethyl systems and formed the macrocycles from these systems . A compound derived from the latter starting material 20) is reported to form a cobalt complex, in which both nitrogens and only one of the oxygen atoms participate in the binding . The two precursor units are shown below as 79 and 20, respectively. 

The second structural type found for organometallic cobalt porphyrins contains an organic fragment bridged between the cobalt and one pyrrolic nitrogen. Cobalt complexes of N-alkyl- or N-arylporphyrins arc well established (but will not be specifically addressed here). The bridged complexes are derivatives of these where the N-alkyl group also forms a cr-bond to cobalt. They are also related to the axially... 

Finally, the tris(pyrazolyl)hydroborato ligand system has also provided an interesting example in which a crystallographic site is disordered between a vacancy and a chain of three atoms. Thus, the x-ray structure of the cobalt complex [TpAnt]CoNCS (Ant = 9-anthryl) revealed the presence of the cocrystallized thallium derivative... 

The metal ion, e.g. Fe or Co, when in its lower oxidation state can share electron charge with the oxygen molecule adduct. Several iron and cobalt prophyrin derivatives and cobalt-Schiff bases show the necessary reversibility and rates for successful application [e.g. 23]. a, a, a", a" -weso-tetrakis[(o-piralamidophenyl)-po phinato] Co (II) has been complexed with 1-methylimidazole to make a complex (CoPIm) which, when mixed with polybutyl methacrylate gave oxygen permeabilities on the order of 10-9 sec-cm/(cm2-s-cmHg) with a selectivity of about 5 over nitrogen [23]. 

Organocobalt complexes catalyze the cyelocotrimerization of acetylenes and nitriles, which affords pyridine and benzene derivatives (100). (Cyclo-pentadienyl)cobalt complexes such as CoCp(COD) favor pyridine formation (100), and modification of the Cp ligand has considerable influence on the activity of the catalyst and the chemo- and regioselectivity of the catalytic process (101). 

Subtle differences in the behavior of azoarenes toward cobalt carbonyl derivatives are observed in regard to metal-complex formation. Azobenzene is transformed by dicobalt octacarbonyl in processes of orthometallation and carbonyl insertion into 2-phenylindazolin-3-one (see Section IV,D,2). In contrast, cyclopentadienylcobalt dicarbonyl effects N—N bond cleavage, and carbonylation of the isolable complex 88a provides 1 -phenylbenzimid-azolin-2-one (Scheme 106).171... 

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