Cobalt . acetylacetonate complexes

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]. 

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. 

Numerous d cobalt(III) complexes are known and have been studied extensively. Most of these complexes are octahedral in shape. Tetrahedral, planar and square antiprismatic complexes of cobalt(lII) are also known, but there are very few. The most common ligands are ammonia, ethylenediamine and water. Halide ions, nitro (NO2) groups, hydroxide (OH ), cyanide (CN ), and isothiocyanate (NCS ) ions also form Co(lII) complexes readily. Numerous complexes have been synthesized with several other ions and neutral molecular hgands, including carbonate, oxalate, trifluoroacetate and neutral ligands, such as pyridine, acetylacetone, ethylenediaminetetraacetic acid (EDTA), dimethylformamide, tetrahydrofuran, and trialkyl or arylphosphines. Also, several polynuclear bridging complexes of amido (NHO, imido (NH ), hydroxo (OH ), and peroxo (02 ) functional groups are known. Some typical Co(lll) complexes are tabulated below ... 

Photoreduction of cobalt(III) complexes in nonaqueous solvent systems has been little studied because of the limited solubility of cobalt(III) complexes and their tendency to photooxidize the solvent. Irradiation with 365-mjj. light of cis- or trans-Co(en)2C 2 + and Co(en)2Cl(DMSO)2+ in dimethylsulfoxide (DMSO) leads rapidly to production of a green tetrahedral cobalt(II) product apparently with concurrent solvent oxidation.53,71 Irradiation with 365-mjx light of the molecular Co(acac)3 in benzene rapidly gives a red precipitate which may be the cobalt(II) acetylacetonate.53... 

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... 

Friedel—Crafts acetylation can be achieved, but the introduction of one acetyl group deactivates the remaining chelate rings so that mixtures of mono-, di- and tri-acetyl products are formed in the case of chiomium(III) and cobalt(III) complexes, but only mono- and di-acetyl products from rhodium(III) acetylacetonate. 

Hexaammineplatinum(IV) salts also undergo imine-forming reactions with acetylacetone (equation 49).172 A cobalt(III) acetylacetone complex can be formed as a result of intramolecular addition of cobalt-bound hydroxide ion to acetylacetone. The cobalt-bound oxygen atoms are retained in the new chelate ring (equation 50).173... 

A linear dependence of log on log rf was found [175] in the case of a one-electron reduction of cobalt(III) complexes with acetylacetone (AcAc) in several aprotic solvents, but the behavior in protolytic solvents was different. 

There are now numerous, metal-linked oligomeric (and polymeric) systems that fall into this category. For example, the acetylacetonates of manganese(II), nickel(II) and zinc(II) have long been known to be trimeric while the cobalt(II) complex is tetrameric, with three (3-diketonate oxygen atoms bridging adjacent metal centres in a linear array in each case. Other more recent examples include systems built... 

It is apparent that the coordination geometry at the cobalt atom is distorted octahedral. The cyclopentadienyl rings of the phosphinoferrocene fragment are staggered and tilted towards the cobalt atom (by 4.4° in the acetylacetonate complex and by 5.0° in the dithiocarbamate complex). 

E8.24 The ratio of cobalt to acetylacetone in the complex is 3 1. Converting the given mass percents of Co and C to moles of Co and C, we find that for every one mole of Co in the product we have 15 moles of C moles of Co = 0.28 mol moles of C = 4.2 mol. Considering that every acac" ligand has five carbon atoms, it is obvious that for each mole of Co we have three moles of acac, This ratio is consistent with the formula Co(acac)j. (Consult Section 7.1 for more detail on the acetylacetonate ligand and cobalt coordination complexes.)... 

Since a halide free, non-corrosive catalyst for DMC production would be a further process improvement, alternative catalytic systems have been investigated. Cobalt(II) complexes with N,0 ligands, such as carboxylates, acetylacetonates and Schiff bases, have been shown to produce DMC with a good reaction rate and selectivity [74]. 

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. 

Iron(III) and cobalt(II) complexes of these polymeric ligands were found to be effective catalysts for the oxidation of cyclohexane and ethylbenzene with H2Oz or 02 in biphasic media. The authors proposed that the oxidation takes place inside polymer micelles which can be regarded as microreactors. However, no recycle experiments were performed to ascertain the stability of these catalysts. A priori one would expect acetylacetonate ligands to undergo facile degradation under oxidizing conditions. 

Certain organometallic compounds can be used to mediate controlled/ living radical polymerization due to their liable and reversibly-cleavable metal-carbon bond. For example, organocobalt complex, such as tetramesitylporphyrinato Co(II) complex [Co(TMP)], has been used to mediate the CRP of aciylates. The first successful cobalt-mediated CRP of VAc was reported by Debuigne and Jerome et. al. using cobalt(ll) acetylacetonate complex Co(acac)2 (Scheme 2) ... 

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. 

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