And cobalt complex

The Auger depth profile obtained from a plasma polymerized acetylene film that was reacted with the same model rubber compound referred to earlier for 65 min is shown in Fig. 39 [45]. The sulfur profile is especially interesting, demonstrating a peak very near the surface, another peak just below the surface, and a third peak near the interface between the primer film and the substrate. Interestingly, the peak at the surface seems to be related to a peak in the zinc concentration while the peak just below the surface seems to be related to a peak in the cobalt concentration. These observations probably indicate the formation of zinc and cobalt complexes that are responsible for the insertion of polysulfidic pendant groups into the model rubber compound and the plasma polymer. Since zinc is located on the surface while cobalt is somewhat below the surface, it is likely that the cobalt complexes were formed first and zinc complexes were mostly formed in the later stages of the reaction, after the cobalt had been consumed. 

Chiral salen chromium and cobalt complexes have been shown by Jacobsen et al. to catalyze an enantioselective cycloaddition reaction of carbonyl compounds with dienes [22]. The cycloaddition reaction of different aldehydes 1 containing aromatic, aliphatic, and conjugated substituents with Danishefsky s diene 2a catalyzed by the chiral salen-chromium(III) complexes 14a,b proceeds in up to 98% yield and with moderate to high ee (Scheme 4.14). It was found that the presence of oven-dried powdered 4 A molecular sieves led to increased yield and enantioselectivity. The lowest ee (62% ee, catalyst 14b) was obtained for hexanal and the highest (93% ee, catalyst 14a) was obtained for cyclohexyl aldehyde. The mechanism of the cycloaddition reaction was investigated in terms of a traditional cycloaddition, or formation of the cycloaddition product via a Mukaiyama aldol-reaction path. In the presence of the chiral salen-chromium(III) catalyst system NMR spectroscopy of the crude reaction mixture of the reaction of benzaldehyde with Danishefsky s diene revealed the exclusive presence of the cycloaddition-pathway product. The Mukaiyama aldol condensation product was prepared independently and subjected to the conditions of the chiral salen-chromium(III)-catalyzed reactions. No detectable cycloaddition product could be observed. These results point towards a [2-i-4]-cydoaddition mechanism. 

The first reported chiral catalysts allowing the enantioselective addition of diethylzinc to aryl aldehydes in up to 60% cc were the palladium and cobalt complexes of 1,7,7-trimethylbicy-clo[2.2.1. ]heptane-2,3-dione dioxime (A,B)3. A number of other, even more effective catalysts, based on the camphor structure (C K, Table 26) have been developed. 

Although the actual reaction mechanism of hydrosilation is not very clear, it is very well established that the important variables include the catalyst type and concentration, structure of the olefinic compound, reaction temperature and the solvent. used 1,4, J). Chloroplatinic acid (H2PtCl6 6 H20) is the most frequently used catalyst, usually in the form of a solution in isopropyl alcohol mixed with a polar solvent, such as diglyme or tetrahydrofuran S2). Other catalysts include rhodium, palladium, ruthenium, nickel and cobalt complexes as well as various organic peroxides, UV and y radiation. The efficiency of the catalyst used usually depends on many factors, including ligands on the platinum, the type and nature of the silane (or siloxane) and the olefinic compound used. For example in the chloroplatinic acid catalyzed hydrosilation of olefinic compounds, the reactivity is often observed to be proportional to the electron density on the alkene. Steric hindrance usually decreases the rate of... 

Intermolecular cyclopropanation of olefins poses two stereochemical problems enantioface selection and diastereoselection (trans-cis selection). In general, for stereochemical reasons, the formation of /ra ,v-cyclopropane is kinetically more favored than that of cis-cyclopropane, and the asymmetric cyclopropanation so far developed is mostly /ram-selective, except for a few examples. Copper, rhodium, ruthenium, and cobalt complexes have mainly been used as the catalysts for asymmetric intermolecular cyclopropanation. 

Schiff Bases and Macrocyclic Nickel and Cobalt Complexes 487... 

The third class of metal catalysts includes nickel and cobalt complexes of Schiff bases and nitrogen macrocyclic ligands, which can form on electroreduction cobalt(I) and nickel(I) reactive intermediates for the activation of organic halides. 

Tris(0-ethyl dithiocarbonato)chromium(III) is obtained as a dark blue crystalline powder which decomposes at 100 to 140°. The indium(III) ethylxanthate complex forms small colorless crystals which decompose at 130 to 150°.16,17 The cobalt (III) ethylxanthate complex is isolated as a dark green crystalline powder whose decomposition temperature determined by use of a thermal balance is 135 to 137° (lit. value, 117° 2 118 to 119°8). These compounds decompose slowly in air and more rapidly when heated in solution. The tripositive chromium, indium, and cobalt complexes are insoluble in water but are soluble in many organic solvents (Table T). 

Thiapyran derivatives can be prepared from preformed organoiron and -cobalt complexes as in Scheme 160 the organocobalt complex (136) can be used as an intermediate in the synthesis of 1,2-dithia cyclopent-4-en-3-thione (See Scheme 122 in Section IV,H.)... 

The study just described is in accordance with the observation that electrochemical reduction of the (highly conjugated) phthalocyanine (5) complex of Mn(n) also gives no evidence for the formation of a Mn(i) species (in contrast to the corresponding iron and cobalt complexes which, on reduction, yield Fe(i) and Co(i) products) (Lever, Minor Wilshire, 1981). 

This chapter will concentrate on the electronic spin-state crossover observed in the iron and cobalt complexes formed with the HB(pz)3 and HC(pz)3 ligands and their various methyl derivatives. In the majority of cases, the spin-state crossover occurs in the solid state and, as a consequence, solid state studies will be covered first, followed by the more limited studies... 

Symmetrical premetallised 1 2 metal-dye complexes of unsulphonated monoazo structures with aluminium (5.57) or trivalent iron (5.58) have been patented recently for use as solvent dyes [36]. They contain a polar methoxypropylaminosulphone grouping in each diazo component and are marketed as alkylamine salts. It remains to be seen, however, whether a full colour gamut of bright aluminium and iron complex dyes can be discovered with light fastness performance equivalent to that of currently available chromium and cobalt complex dyes. 

Bis(aminomethylenemalonate) (163, R = H) formed nickel and cobalt complexes (1594) with metal acetate in methanol in 75% and 90% yields, respectively (85ZC28). 

Telfer, S. G. Bemardinelli, G. Williams, A. F. Iron and cobalt complexes of 5,5 -di(methylene-A-aminoacidyl)-2,2 -bipyridyl ligands Ligand design for diastereoselectivity and anion binding. J. Chem. Soc. Dalton Trans. 2003, 435 40. 

Enantiomer-differentiating co-polymerization of terminal epoxides is achieved by chiral chromium and cobalt complexes. Jacobsen etal. reported the co-polymerization of 1-hexene oxide with GO2 by using complex 35a. The reaction proceeds with kinetic resolution at 90% conversion, the unreacted epoxide is found to be enriched in the (i )-enantiomer of 90% ee. Detailed information about the resultant polymer, however, is not described. As discussed in the previous section, chiral cobalt-salen complex 34c co-polymerizes PO and GO2 (Table 3). When 34c with /r<3 / j--(li ,2i )-diaminocyclohexane backbone is applied to the co-polymerization, (A)-PO is consumed preferentially over (i )-enantiomer with a of 2.8 to give optically active PPG (Equation (8)). In a similar manner, a binary catalyst system, 34d/Bu4NGl, preferentially consumes (A)-PO over R)-PO with = 2.8-3.5. ... 

The application of perfluorous polyethers in biphasic catalysis was first described by Vogt (133), who also synthesized ligands based on hexafluor-opropene oxide oligomers to create metal complexes that are soluble in the perfluorous polyethers. The solvophobic properties of the fluorous solvent were successfully incorporated in the metal complexes catalytic oligomerization and polymerization reactions with nickel and cobalt complexes were demonstrated. 

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