Toluene cobalt complex

The intermolecular Pauson-Khand reaction of the resulting S/P-cobalt complexes with norbornadiene was studied under thermal and A -oxide activation conditions. Thus, heating the diastereomerically pure complex (R = Ph, R = Cy) with ten equivalents of norbornadiene at 50 °C in toluene afforded the corresponding exo-cyclopentenone in a quantitative yield and with an enantio-selectivity of 99% ee. Under similar conditions, the analogous trimethylsilyl complex (R = TMS, R = Cy) afforded the expected product in a high yield but with a lower enantioselectivity of 57% ee. In order to increase this enantio-selectivity, these authors performed this reaction at room temperature in dichloromethane as the solvent and in the presence of NMO, which allowed an enantioselectivity of 97% ee to be reached. These authors assumed that the thermal activation promoted the isomerisation of the S/P ligand leading to a nonstereoselective process. 

The bis(boratabenzene)cobalt complexes 7 and 13 may also undergo substitution of a C5H5BR ligand. With Ni(CO)4 in refluxing toluene, the substitution products Co(CO)2(C5H5BR) 15 and 11 are formed (47,49). The cyanide degradation is another important example (Section V,B,2). 

Among various candidates, 1,2-dimethoxyethane (DME) in toluene was found to be the best promoter providing the cycloaddition products in high yields, but required a higher pressure of CO (7 atm). Water was less efficient under the same conditions, but provided the comparable yield at higher concentrations. Nevertheless, use of DME as the solvent instead is detrimental to the reaction under the conditions. Once again, one should notice that there must be a competition between the demetallation from the alkyne-cobalt complex and the catalytic cycle for the PKR products. 

Quite a range of P-lactams have been made by methodologies following disconnection a with carbamoyl radicals (aminoacyls) as intermediates. Pattenden and co-workers made carbamoyl cobalt salophen complexes and showed that on photolysis carbamoyl radicals were released and underwent 4-exo cyclisations [75-77]. For example, carbamyl chloride derivative 59 was converted to cobalt complex 60, which on photolysis yielded the cyclised cobalt-azetidinone complex 61. The free azetidinone 62 was released by heating the cobalt complex in toluene and was transformed into thienamycin in several subsequent steps (Scheme 15). 

Varieties of dinuclear cobalt complexes are known with two phosphido bridges. Those so far reported with the di-terf-butylphosphido ligand have two pseudotetrahedral 18-electron Co atoms linked by a metal-metal bond formally of order 2. Tetracarbonylbis(ii-di-terf-butylphosphido)-dicobalt( -t-1) can be prepared from the reaction of Co(CO)4l (generated in situ) with Li(r-Bu2P) in THE We describe here a simplified, high yield synthesis of this dimer via the interaction of Co2(CO)g with r-Bu2PH in toluene. The complex should prove to be a useful starting material for further reactivity studies. 

The complexes are thermally labile as shown by variable-temperature NMR spectroscopy. Upon heating in toluene at reflux for 3 h, the u-diphosphaallyl cobalt complex is irreversibly transformed into the 7r-allylic complex. This isomerization upon heating constitutes the first example of such interconversion in the diphosphaallyl systems. The synthesis of a- or rc-diphosphaallyl complexes can also be realized from the photochemical isomers of diphosphiranes, the 1,3-diphosphapropenes. In this case, the reaction occurs more readily under milder conditions than above, and the same diphosphaallyl complexes were obtained in 70-90% yield with the same selectivity as their parent diphosphiranes <93JOM(453)77>. 

The stable cobalt complex LI is prepared by cocondensing cobalt atoms and butadiene at liquid nitrogen temperature This technique is also used to prepare 7t-allyl complexes of the nickel triad metals, e.g., LII . Metal hydrides are intermediates in these reactions , as shown by the reaction of nickel hydrides with dienes to yield rt-allyl complexes . The 7i-allyl complex LIII may be prepared by adding HCl and butadiene to (PPh3)4Ni in toluene or THF at —78°C, then warming to RT . ... 

Figure 6. EPR spectra of oxygen-containing samples of [sCImCo(II)]2 diporphyrins. (A) Upper trace complex of 1 with 1 atm of O2 at 77° K bottom trace after sample was evacuated at --20°C and recorded at 77°K. (B) Room temperature spectrum of the dioxygen adduct of cobalt complex of 3 after addition of small amount of I2. This is a typical binuclear fx-superoxo dicobalt spectrum. All experiments were carried out in CH2CI2/toluene mixtures.

To the contrary, in toluene solution no reaction occurs and [Co(Salen)COOCH3] is recovered. These results point to [Co(Salen)COOCH3] being a key intermediate in the reaction scheme with the rate determining step being nucleophilic attack on the methoxycarbonyl moiety by an alcohol molecule. A similar pathway is anticipated for other cobalt complexes. 

The heptanuclear iron carbonyl cluster [Fe3(CO)u(/u-H)]2-Fe(DMF)4 (178) acted as an efficient catalyst in the reduction of carboxamides by l,2-bis(dimethylsilyl)benzene in toluene to the corresponding amines in high yields. Several tertiary and secondary amides including a sterically crowded amide were also reduced smoothly A review of the development of optically active cobalt complex catalysts for enan-tioselective synthetic reactions has addressed the applications of ketoiminatocobalt(II) complexes such as (5)-MPAC (179) and (5)-AMAC (180), transition-state models for borohydride reduction, halogen-free reduction by cobalt-carbene complexes. 

PPO is generally prepared by oxidative polymerization of 2,6-dimethylphenol in toluene solution in the presence of oxygen over an catalyst. Copper-amine catalysts are undoubtedly the most studied systems whereas other metal systems including manganese chloride (12), cobalt complex (13) have also shown to be effective in bench scale. Various amines including mono-dentate and biden-tate amines have been used as ligand for copper (I) complex which shows a wide range of activity as indicated in Table 2.4 (2,14-16). 

The relative catalytic activities of a series of cobaloximes and of aquo-cobalamine for homogeneous oxidation of formaldehyde have been qualitatively assessed. Vitamin Biaa is by far the most effective the rate law for the process is complicated. The effect of these catalysts on decomposition of the formic acid produced was also studied. Somewhat simpler cobalt complexes catalyse the oxidation of alkylbenzenes. Thus cobalt(ii) acetate in hydrochloric acid is a good catalyst for the oxidation of p-xylene or p-toluic acid to terephthalic acid. Co(acac>3 catalyses oxidation of toluene, and a cobalt stearate complex catalyses the oxidation of isopropylbenzene. ... 

Figure 4.13 Simulation of ESR spectrum of the above cobalt dithiolene complex in frozen toluene at 77 K.

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