Cobalt complexes oxidation

Acyclic /V-alkylimines, asymmetric hydrogenation, 10, 56 Acyclic ( j3-allyl)cobalt complexes, oxidation reactions, 7, 58 Acyclic allylic esters, alkylation, 11, 76 Acyclic aromatic imines, asymmetric hydrogenation, 10, 56 Acyclic 1-buly l-( )5-pencadienyl) iron cations, preparation and reactivity, 6, 156... 

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

In its complex compounds, of which there are many thousands, Co almost invariably has a +3 oxidation number. Apparently, Co+s ion accompanied by six coordinating groups is particularly stable. Cobalt complexes are important in biochemistry. Some enzyme reactions go through a cobalt-complexing mechanism. Although only small traces are needed, cobalt is essential to the diet. 

In a more recent and improved approach to cyclopropa-radicicol (228) [ 110], also outlined in Scheme 48, the synthesis was achieved via ynolide 231 which was transformed to the stable cobalt complex 232. RCM of 232 mediated by catalyst C led to cyclization product 233 as a 2 1 mixture of isomers in 57% yield. Oxidative removal of cobalt from this mixture followed by cycloaddition of the resulting cycloalkyne 234 with the cyclic diene 235 led to the benzofused macrolactone 236, which was converted to cyclopropa-radicicol (228). 

Similar effects are observed in the iron complexes of Eqs. (9.13) and (9.14). The charge on the negatively charged ligands dominates the redox potential, and we observe stabilization of the iron(iii) state. The complexes are high-spin in both the oxidation states. The importance of the low-spin configuration (as in our discussion of the cobalt complexes) is seen with the complex ions [Fe(CN)6] and [Fe(CN)6] (Fq. 9.15), both of which are low-spin. 

It is noteworthy that, as early as 1929, Shibata and Tsuchida reported a kinetic resolution of rac-3,4-dihydroxyphenylalanine by selective oxidation of one enantiomer using a chiral cobalt complex [Co(en)3NH3Cl]Br2 as a catalyst [46,47]. Figure 12 shows a highly enantioselective addition of diisopropy-Izinc to 2-(ferf-butylethynyl)pyrimidine-5-carbaldehyde via an autocatalytic process in the presence of a chiral octahedral cobalt complex with ethylenedi-... 

The hexamine cobalt (II) complex is used as a coordinative catalyst, which can coordinate NO to form a nitrosyl ammine cobalt complex, and O2 to form a u -peroxo binuclear bridge complex with an oxidability equal to hydrogen peroxide, thus catalyze oxidation of NO by O2 in ammoniac aqueous solution. Experimental results under typical coal combusted flue gas treatment conditions on a laboratory packed absorber- regenerator setup show a NO removal of more than 85% can be maitained constant. 

Keywords Flue gas denitration, NO oxidation, ammine cobalt complex, activated carbon INTRODUCTION... 

Polarographic studies are reported on thioesters, mainly of the type (140) and (141), and on trichloroethylphosphonites. In the field of nucleotides and nucleosides it is found that ATP has a very high surface activity at the mercury electrode, which is strongly dependent upon complex formation with transition metals. The polarographic behaviour of cobalt complexes with triphenylphosphine and its oxide has been studied in order to estimate extraction efficiencies. 

We distinguish electrodes consisting of simple oxides, from those consisting of complex oxide systems. The latter include cations of different metals or cations of a given metal in different valence states. An example for the latter type is cobalt cobaltite C03O4 (a spinel structure) containing Co and Co ions. 

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. 

Bis(aryl)cobalt(II) compounds have been prepared by reaction of R MgX (where R = C6H6 Cl n = 2-4) with Co(PR3)2Cl2.203 They undergo both thermally and oxidatively induced decomposition, with the corresponding biphenyl a product. The reactions of alkyl-cobalt complexes have been reviewed recently, and include thermolysis, photolysis, oxidation, and reduction reactions.25 Homolysis of the Co—C bond is a feature of reactions. 

Under the conditions of the cobalt-mediated carbonylative A-oxide-promoted cocyclization (Pauson-Khand reaction) at room temperature, compound 547 provides exocyclic 1,3-diene 548 as the major product (>98%) together with only traces of the corresponding carbonylative product 549. Owing to the relative instability of the diene, it is more efficient to perform a one-pot cobalt cyclization/Diels-Alder process after A-oxide-promoted cyclization of the cobalt complexes. Compound 550 is obtained as a single diastereomer in 39% overall yield if MTAD is used as a dienophile (Scheme 90) <2003JOC2975>. 

The [Co(CN)5]3 complex is an effective catalyst for some reactions, particularly the isomerization of alkenes. Newer and more efficient catalysts have been developed for some of the processes, but the catalytic behavior of the pentacyanocobalt(II) ion is also significant from a historical perspective. In reactions such as that shown in Eq. (22.10), two Co2+ ions increase one unit in oxidation state, instead of the more common situation in which one metal ion increases by two units in oxidation state. The cobalt complex also reacts with CIT3I, Cl2, and H202, which are indicated as X-Y in the equation... 

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