Cobaltous acetylacetonates

The first term on the right-hand side denotes the rate of dioxygen reaction with styrene (see Chapter 4) and the second term is the rate of catalytic free radical generation via the reaction of styrene with dioxygen catalyzed by cobaltous stearate or cobaltous acetylacetonate. The rate constants were found to be ki = 7.45 x 10-6 L mol-1 s-1, k2 = 6.30 x 10 2 L2 mol 2 s 1 (cobaltous acetylacetonate), and k2 = 0.31L2 mol-2 s 2 (cobaltous stearate) (T = 388 K, solvent = PhCl [169]). The mechanism with intermediate complex formation was proposed. 

Nickel or Cobalt acetylacetonate Metathesis Poly(dicyclopentadiene) in cyclohexane Nippon Zeon Co., Ltd 27 (1996)... 

MacKenzie Chemical Works cobaltic acetylacetonate stirred flask, absorbed 0.3 mole 02/mole peroxide. 

The liquid-phase oxidation of acrolein (AL), the reaction products, their routes of formation, reaction in the absence or presence of catalysts such as acetylacetonates (acac) and naphthenates (nap) of transition metals and the influence of reaction factors were discussed in an earlier paper (22). The coordinating state of cobalt acetylacetonate in the earlier stage of the reaction depends on the method of addition to the reaction system (25, 26). The catalyst, Co(acac)2-H20-acrolein, which was synthesized by mixing a solution of Co(acac)2 in benzene with a saturated aqueous solution, decreases the induction period of oxygen uptake and increases the rate of oxygen absorption. The acrolein of the catalyst coordinated with its cobalt through the lone pair of electrons of the aldehyde oxygen. Therefore, it is believed that the coordination of acrolein with a catalyst is necessary to initiate the oxidation reaction (10). 

Visible light spectra were obtained using a Hitachi Model EPI-2 spectrometer. The absorption spectra of a reaction mixture formed, when cobaltous or cobaltic acetylacetonate was used as a catalyst, were measured to detect the state of the catalyst quantitatively. The spectrum of the reaction solution had a maximum absorption at 500 to 600m//, and a strong absorption in the ultraviolet region. The concentration of the catalyst in the oxidation solution was suitable for measuring the absorption spectra. The variation of the spectra with time was measured during the oxidation. 

Figure 2. Visible light spectra of cobalt acetylacetonate catalysts in benzene...

Under the same conditions, cobalt acetylacetonate afforded a mixture of four products the mono-, di-, and triacetylated chelates (XVII, XVIII, and XIX), along with the starting material. In contrast to the chromium chelates, the mixture of cobalt complexes was cleanly separated by chromatography. The identity of each of these products was established by an NMR spectrum. The presence of uncoordinated carbonyl groups was revealed by infrared absorption at 1675 cm.-1... 

The partially resolved cobalt acetylacetonate was found to be optically stable in solution or in the solid state for long periods. However, slow crystallization of this substance always produced racemic crystals (14). Several of the optically active substituted cobalt chelates exhibited the same strange phenomenon. Removal of the solvent from solutions of optically active cobalt acetylacetonate with a slow stream of air yielded a solid which showed little apparent crystalline character under a polarizing microscope but dissolved to form a solution of about the same specific rotation as the starting solution. 

Careful stepwise crystallization of cobalt acetylacetonate from solutions of the partially resolved chelate produced surprising results (14). A typical experiment is summarized in Table VI. The molecular rotation of the filtrates steadily increased as each crystal crop was removed until no solute remained in solution— at this time all optical activity had, of course, been lost. All crystal crops were racemic It seems that the racemate is being preferentially crystallized from solution and at the same time a surface racemization is taking place to make up the deficient enantiomorph as the d, l crystals are formed. 

Manganous acetylacetonate Manganic acetylacetonate Ferrous acetylacetonate Ferric acetylacetonate Cobaltic acetylacetonate Rhodium chloride Nickel acetylacetonate Potassium platinous chloride Tetrammine copper (II) sulfate Potassium gold cyanide... 

The polymerization of butadiene to 1.2 polymers with anionic Ziegler type catalysts has been studied by Natta and co-workers (46). They have shown that isotactic 1.2-polybutadiene can be produced by the use of catalysts which are made up of components which have basic oxygen and nitrogen structures such as triethylaluminum with cobalt acetylacetonate or with chromium acetylacetonate. Natta and co-workers have shown that either syndiotactic or isotactic structures are produced depending on the ratio of aluminum to chromium. Syndiotactic structures are obtained at low aluminum to chromium ratios while isotactic polybutadiene is obtained at high ratios. The basic catalyst component is characteristic of syndiotactic catalysts. Natta, Porri, Zanini and Fiore (47) have also produced 1.2 polybutadiene using... 

The stereoselective preparation of rfl .v-2-hydroxymethyl-5-subslituted tetrahydrofurans from 4-pentenols is possible by oxidative cyclization catalyzed by cobalt(ll) salts. Both cobalt(II) trifluoroacetate and cobalt acetylacetonate have been employed for the cyclization, but better yields are obtained with Co(modp)2 (l)45. 

The extraordinary behavior of cobalt in coordinate catalysis is also evident from Figure 1. Nickel and cobalt acetylacetonate in the presence... 

The asymmetric conjugate addition of diethylzinc with chalcone was also catalyzed by nickel and cobalt complex (Eq. (12.31)) [71]. A catalytic process was achieved by using a combination of 17 mol% of an aminoalcohol 34 and nickel acetylacetonate in the reaction of diethylzinc and chalcone to provide the product in 90% ee [72, 73]. Proline-derived chiral diamine 35 was also effective, giving 82% ee [74]. Camphor-derived tridentate aminoalcohol 36 also catalyzes the conjugate addition reaction of diethylzinc in the presence of nickel acetylacetonate to afford the product in 83% ee [75]. Similarly, the ligand 37-cobalt acetylacetonate complex catalyzes the reaction to afford the product in 83% ee [76]. 

A set of three Co-doped precursors (with 1, 2 and 5 wt% Co) were prepared by dissolving the required amount of cobalt acetylacetonate in isobutanol prior to the operation of refluxing with isobutanol and 85% H3PO4. The subsequent filtration, washing and doping procedures were identical to that employed for the undoped precursor. These doped catalysts were then activated for 25h at 400°C under the same reaction mixture and flow conditions as described previously. 

Materials. Phenyl isocyanate (Eastman Kodak) and 2-butanol were fractionally distilled under reduced pressure prior to use. Dioxane was purified by first refluxing with sodium metal, then distilling under reduced pressure. Triphenyl phosphine, dibutyl-tin dilaurate (DBTDL) and cobalt acetylacetonates were used as-received from Eastman Kodak and M T companies, respectively. 

Another supporting evidence for complex formation as a prerequisite to synergism was obtained from the study of the catalysis of phenyl isocyanate-butanol reaction by soluble organic cobalt compounds in presence and absence of DABCO catalyst. The results obtained are presented in Figures 4 and 5. It is evident that the combination of DABCO catalyst with divalent cobalt compounds shows synergistic effects while the trivalent cobalt acetylacetonate shows relatively low activity. The explanation of these observations is the structure of these compounds. 

Efforts to introduce larger acyl groups, such as propionyl and butyryl, into the 3-position of chromium and cobalt acetylacetonates failed, probably because steric hindrance by the 2- and 4-methyl groups allowed the chelate ring to be degraded rather than substituted. On the other hand, the increased stability of the rhodium(III) acetylacetonate permitted the synthesis of monobenzoyl, dibenzoyl, and monobutyryl acetylacetonates under Friedel-Crafts reaction conditions (56). 

In the case of cobalt acetylacetonate, Co(Acac)2, peroxidation is probably helped by the coordination of an acrolein molecule resulting in a complex capable of having two trans and cis configurations [37], viz. 

The reduction of cobalt acetylacetonate with triakylaluminium leads to species composed of zerovalent cobalt and unreduced cobalt species. The exact composition depends upon the Al/Co ratio and the activation process. When we used a catalyst corresponding to a Al/Co = 1, activaded with hydrogen at 180°C, we obtained an increase of the selectivity of the hydrogenation of 2-pentyl-2-nonenal into 2-pentyl-2-nonenol. 

The catalysts were prepared by reducing the cobalt acetylacetonate dissolved in benzene, under a inert atmosphere of argon, using a known quantity of triethylaluminium (as a function of the desired Al/Co ratio). The solution immediatly became black and the metallic particles formed were able to be stabilized by butadiene at 0°C. The solvent employed during the hydrogenation reaction was dodecane or propylene carbonate. The benzene was then evaporated under a controlled atmosphere and the degradation products were then removed and analyzed, the temperature being increased up to 200°C. The catalyst thus obtained was used "in situ". 

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