Pyridine cobalt complex

In the context of pyridin synthesis from alkynes and nitriles homogeneously catalyzed by (cyclopentadienyl)cobalt complexes (Eq. 13), it was found that electron-withdrawing groups on the cyclopentadienyl ring significantly increase the activity [63]. During the screening of various cobalt half-sandwich complexes... 

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). 

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... 

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). 

Diethyl aluminium chloride Cobalt chloride-pyridine complex... 

Yamazaki and Wakatsuki [77JOM(139)157] have contributed quite considerably to our understanding of the course of the cobalt-catalyzed pyridine synthesis by isolating a number of phosphine-stabilized cpCo complexes that may be regarded as plausible intermediates in the following... 

Examples of coordination complexes of pyridine with metals are legion and only a few can be mentioned here. Pyridine is a ligand in square complexes of gold (AuEt2Br-py) and copper (Cupy2-Cl2). The cobalt complex CoCLrpy2 has an octahedral structure. Nickel and platinum can coordinate with four pyridine molecules (30). 

Alkali metal 1-methyl- and 1-phenyl-borinates are also available from bis(borinato)cobalt complexes (see below) on treatment with sodium or potassium cyanide in an aprotic solvent like acetonitrile. Cobalt cyanide precipitates and the alkali borinate remains in solution. After addition of thallium(I) chloride to some complexes, thallium 1-methyl- or 1-phenyl-borinate could be isolated as pale yellow solids, the only main group borinates isolated hitherto. They are insoluble in most organic solvents but readily soluble in pyridine and DMSO. The solids are stable on treatment with water and aqueous potassium hydride, but are decomposed by acids <78JOM(153)265). 

Involvement of two nucleophilic nitrogen atoms is thus typical for the amino heterocycles. The mutual disposition of the pyridine and amine nitrogen atoms allows the formation of chelate structures for the cobalt complexes of purine, 221 and 222. Structures with the N, iV -five-membered metal cycles were proven for the tri- and tetranuclear complexes of silver ) with 8-aminoquinoline (223) (92IC4370), and polymeric copper- and rhodium-acetate clusters (224). Another coordination mode can be found in the complexes of 4-amino-3,5-bis(pyridin-2-yl)-l,2,4-triazole, (225 or... 

Similarly, cobalt(ll)-pyridine (CoPy) complexes bound to copolymers of styrene and acrylic or methacrylic acid, cross-linked with divinylbenzene, catalyze the autoxidation of tetralin dispersed in water at 50°C and 1 bar.45 The rate of oxidation with the colloidal CoPy catalyst was twice as fast as with homogeneous CoPy and nine times as fast as with cobalt(II) acetate in acetic acid. 

The metal carboxylate insertion mechanism has also been demonstrated in the dicobaltoctacarbonyl-catalyzed carbomethoxylation of butadiene to methyl 3-pentenoate.66,72 The reaction of independently synthesized cobalt-carboxylate complex (19) with butadiene (Scheme 8) produced ii3-cobalt complex (20) via the insertion reaction. Reaction of (20) with cobalt hydride gives the product. The pyridine-CO catalyst promotes the reaction of methanol with dicobalt octacarbonyl to give (19) and HCo(CO)4. 

Pyridine ligands 186 are monodentate, forming complexes of the kind presented by 189. Pyridine is coordinated in the same way in copper acetate 194 [314] and iron rhodanide complexes [315], adducts of cobalt complex with fe(salicylidene)ethyle-nediamine 195 [316] and nickel chelate, formed by tridentate N,S-donor azomethine ligand 196 [317] ... 

At the same time, according to x-ray data for zinc chelate 909, the nitrogen atom is turned to the side of the metal. The distance Npy-Zn is 2.80 A, that allows us to consider the possible participation of the examined donor center in binding with the metal, leading to formation of a hexacoordinated structure (two-capped tetrahedron) [243]. In relation with this result, let s pay attention to the data reported in Refs. 244 and 248. The tetrahedral configuration without coordination of the nitrogen atom of pyridine is attributed to the cobalt complex 907 (X = NTs, M — Co), although this N atom is rotated to the side of the metal [244]. The pentacoordinated complex 910 is described in Ref. 248, in which only one pyridine substituent is coordinated (the distance Npy-Co is 2.45 A) ... 

Yamazaki et al. (91, 119) and Bonnemann el at. (120) have recently reported catalytic syntheses of substituted pyridines from acetylenes and nitriles. Various cobalt complexes serve as active catalysts, in particular, CpCo(PPh3)2 (91) or Co(C8Hi2) (C8Hi3) (120). Similar reactions of acetylenes with CS2 or RNCS also give new heterocycles (91) ... 

The same radical cyclization can be performed using a more simplified vitamin B12 model, such as Z w(dimethylglyoximato)(pyridine)Cobalt chloride Co3+ Cl -Py complex (B), as shown in eq. 11.3. Treatment of propargyl P-bromoethyl ether (3) with NaBH4 and a catalytic amount of the cobalt complex (B) provides fi-exo-methylene tetrahydrofuran via 5-exo-dig manner [2-7]. 

Donors have been added to the cobalt catalysts used to polymerize butadiene (20). Cobalt chloride-pyridine complexes gave a soluble catalyst with AlEt2Cl which was effective for cis polymerization of butadiene, but at the low concentrations of pyridine employed (Al/Co/py = 1000/1/1 to 4), there was no effect on the polymer structure. However, it was observed that the molecular weight fell as the ratio of pyridine to cobalt was increased. Isopropyl ether in the cobalt octoate-methylaluminum sesquichloride catalyst had a similar effect, although at the highest ether concentrations (typical ratios employed were Al/Co/iPr20 = 160/1/3.5 to 8), a reduction in cis content and polymerization... 

The chromium carbonyl linkers 1.40 (98) and 1.41 (99) were prepared from commercial triphenylphospine resin and respectively from pre-formed p-arene chromium carbenes and Fischer chromium amino carbenes. Their SP elaboration is followed by cleavage with pyridine at reflux for 2 h (1.40) and with iodine in DCM for 1 h at rt (1.41) both linkers produce the desired compounds in good yields. A similar cobalt carbonyl linker 1.42 (100) was prepared as a mixmre of mono- (1.42a) and bis- (1.42b) phosphine complex, either from pre-formed alkyne complexes on triphenylphosphine resin or by direct alkyne loading on the bisphosphine cobalt complex traceless cleavage was obtained after SP transformations by aerial oxidation (DCM, O2, hp, 72 h, rt) and modified alkynes were released with good yields and... 

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