Palladium and cobalt complexes

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. 

Industrially performed catalytic oxidation reactions often suffer from drawbacks such as poor conversion and selectivity due to overoxidation, corrosive reaction media, lack of solvent and catalyst recycling, and negative environmental impact due to evaporation of the solvents. In order to provide a methodology that addresses these problems, ionic liquids have been investigated as reaction media. For example, the aerobic oxidation of benzyl alcohol and alkylbenzene to benzaldehyde and benzoic acids was performed in l-butyl-2,3-dimethylimidazolium tetrafluoroborate ([C4dmim][BF ]) using palladium and cobalt complexes respectively [34, 35]. 

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... 

As a guide for going through this review it can be helpful to consider briefly the electrochemical and chemical behavior of the most common transition metal complexes i.e., nickel, palladium and cobalt, used in the various reactions collected here. Additional data can be found in [1]. 

Chatt, J., Duncanson, L.A., Gatehouse, B.M., Lewis, J., Nyholm, R.S., Tobe, M.L., Todd, RF. and Venanzi, L.M. (1959) Infrared spectra and structure of some simple and bridged nitro-complexes of platinum, palladium and cobalt. J. Chem. Soc.,... 

Some metal complexes of metals other than nickel are known to catalyze the hydrocyanation of alkenes, among the best being those of palladium and cobalt. ... 

Originally devised as a method for the conversion of amino acids or amino acid esters to aldehydes. The Akabori reaction has been modihed for use in the determination of C-terminal amino acids by performing the reaction in the presence of hydrazine and for the production of derivatives useful for mass spectrometric identihcation. See Ambach, E. and Beck, W., Metal-complexes with biologically important ligands. 35. Nickel, cobalt, palladium, and platinum complexes with Schiff-bases of... 

C2H,N, Acetonitrile, cobalt, copper, and ruthenium complexes, 26 356, 359 molybdenum, palladium, and tungsten complexes, 26 128-133 osmium complex, 26 290, 292 ruthenium(II) complexes, 26 69-72 C2H4, Ethene, molybdenum complex, 26 102-105... 

Not only palladium, but many more non-metallocene late (and early) transition metal catalysts for the coordination polymerization of ethene and 1-olefins were reported [11]. Among the most significant findings in this area are the disclosures of novel highly active and versatile catalysts based on (i) bidentate diimine [N,N] nickel and palladium complexes [12], (ii) tridentate 2,6-bis(imino)pyridyl [N,N,N] iron and cobalt complexes [13], and (iii) bidentate salicyl imine [N,O] nickel complexes [14]. 

Third, n-allyl complexes are formed by palladium and cobalt analogous complexes of nickel and platinum are less stable, while ruthenium, rhodium, and iridium are not yet known to form them. In catalytic reactions the deuteration of cyclic paraffins over palladium has provided definite evidence for the existence of rr-bonded multiply unsaturated intermediates, while 7r-allylic species probably participate in the hydrogenation of 1,3-butadiene over palladium and cobalt, and of 1,2-cyclo-decadiene and 1,2-cyclononadiene over palladium. Here negative evidence is valuable platinum, for example does not form 7T-allylic complexes readily and the hydrogenation of 1,3-butadiene using platinum does not require the postulate that 7r-allylic intermediates are involved. Since both fields here are fairly well studied it is unlikely that this use of negative evidence will lead to contradiction in the light of future work. 

PC8HM, Phosphine, dimethylphenyl-, 22 133 iridium complex, 21 97 PC 2H27, Phosphine, tributyl-, chromium complexes, 23 38 PC18H1S, Phosphine, triphenyl-, 21 78 23 38 cobalt complexes, 23 24-25 cobalt, iridium, and rhodium complexes, 22 171, 173, 174 iridium complex, 21 104 palladium complex, 22 169 palladium and platinum complexes, 21 10 ruthenium complex, 21 29 PNOC 2Hl2, Phosphinic amide, diphenyl-, lanthanoid complexes, 23 180 PNAH.2, Propionitrilc, 3,3, 3 -phosphinidy-netri-,... 

Most of the catalysts employed in the chemical technologies are heterogeneous. The chemical reaction takes place on surfaces, and the reactants are introduced as gases or liquids. Homogeneous catalysts, which are frequently metalloorganic molecules or clusters of molecules, also find wide and important applications in the chemical technologies [24]. Some of the important homogeneously catalyzed processes are listed in Table 7.44. Carbonylation, which involves the addition of CO and H2 to a C olefin to produce a + 1 acid, aldehyde, or alcohol, uses rhodium and cobalt complexes. Cobalt, copper, and palladium ions are used for the oxidation of ethylene to acetaldehyde and to acetic acid. Cobalt(II) acetate is used mostly for alkane oxidation to acids, especially butane. The air oxidation of cyclohexane to cyclohexanone and cyclohexanol is also carried out mostly with cobalt salts. Further oxidation to adipic acid uses copper(II) and vanadium(V) salts as catalysts. The... 

NdC4jHj9, Neodymium, tris(2,6-dwert-butyl-4-methylphenoxo)-, 27 167 O3PC3H, Trimethyl phosphite, cobalt and rhodium complexes, 28 283,284 iron complexes, 28 171, 29 158 nickel complex, 28 101 O3PCJH15, Triethyl phosphite, iron complexes, 28 171, 29 159 nickel complex, 28 101 nickel, palladium, and platinum complexes, 28 104-106 03PC,H2i, Isopropyl phosphite, nickel complex, 28 101... 

The metal-catalyzed cross-coupling of aryl-, heteroaryl-, and alkenyhnagnesium derivatives is a broad-scope transformation that has found many synthetic applications C(sp )-C(sp ) couplings are by far the most common. Catalysts by nickel, palladium, and iron complexes is most widespread, but the emerging fields of cobalt and manganese catalysis can also provide useful alternatives. 

To commercialize LT-PE will require an understanding of how the kind of polyethylene and its microstructure affects its properties and applications. Interestingly, LT-PE can be divided into two types depending on whether the microstructure is linear or branched. Highly linear polyethylenes (including oligomers) are commonly produced by iron and cobalt complex pre-catalysts [22-31,41], whereas branched polyethylenes are formed by nickel and palladium complex pre-catalysts [17-21, 42], The microstmctural differences in LT-PE are caused by their characteristic mechanistic pathways of polymerization. 

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