Cobalt linear chains

Both the linkages to form planes and their stacking are different depending on the kinds of A and M metals. The trigonal planar [MN3]6- unit was also observed in Ca6FeN5.18 The existence of double metal nitrides has not yet been reported for cobalt. Cobalt is between iron and nickel in the periodic table. It is an open question whether the double metal nitride with cobalt has a linear chain or a trigonal planar coordination. 

In addition to the above one-dimensional structures, a strip-like cobalt phosphate structure has been isolated. The strip consists of two corner-shared chains fused together forming the architecture shown in Fig. 7.5a-c [18]. The one-dimensional linear chains are connected via a three-coordinated oxygen atom, giving rise to such an arrangement. This type of structure could be a key intermediate in the formation of framework solids from the basic one-dimensional chains. 

The other heptanuclear cobalt(II) cage in the literature involves o-mercaptophenolate ligands. [Co7Na2(l,2-OSC6H4)g(DMF)i2] is formed from reaction of CoBr(PPh3)3 with sodium mer-captophenolate in DMF. The structure consists of an almost linear chain of five tetrahedrally coordinated Co and two sodium centers, with two further Co centers attached at the end of the chain. The room-temperature magnetic moment is a little lower than would be expected for seven cobalt(II) centers. 

An interesting method for producing copolyesters has been proposed. Soft drink bottles were washed, cut into flakes, and a catalyst was added, namely cobalt(II) acetate tetrahydrate. In this way, glycolysis of PET occurred and a monomeric compound, bis(2-hydroxyethyl terephthalate) (BHET), was obtained in good yield. Copolyesters were synthesized by the melt reaction of BHET with L-lactic acid (LA) oligomers in the presence of a catalyst made of tin(II) chloride dihydrate and p-toluenesulfonic acid monohydrate [86]. SEC fractions of the BHET-LA copolyester were collected and analyzed by MALDI. MS peaks were assigned to linear BHET-LA chains and to cycles. The authors noted that cycles elute at later times with respect to linear chains. The latter phenomenon is well understood [4]. 

The structures of frans-[CoCl2(3,5-X2py)2], X=C1, Br, are characterized (Fig. 11) by short XB interactions which develop in the ab plane, giving rise to original tetrameric motifs [49]. Magnetic interactions between cobalt ions are characteristic of linear cobalt chloride chain compounds, albeit the XB interactitMis limit here the magnetic interactions between the chains. 

The dicyanamido-bridged polymer [LCuCo(dca)2] crystallizes from a solution containing [CuL], cobalt nitrate, and sodium dicyanamide. Its crystal structure consists of linear chains, which result from connecting the [CuCo] nodes through single 5-dca bridges (one end of the dca bridge is coordinated into the apical position of the copper ion from a node, and the other one to the cobalt ion from the next node) (Fig. 16). 

The mixture of carbon monoxide and hydrogen is enriched with hydrogen from the water gas catalytic (Bosch) process, ie, water gas shift reaction, and passed over a cobalt—thoria catalyst to form straight-chain, ie, linear, paraffins, olefins, and alcohols in what is known as the Fisher-Tropsch synthesis. 

Use of less sterically hindered examples of 5 in combination with MAO allows for active catalysts for the linear (head-to-head) dimerisation of a-olefins such as 1-butene, 1-hexene, 1-decene and Chevron Phillips C20-24 a-olefin mixture (Scheme 4) [47], The mechanism for dimerisation is thought to involve an initial 1,2-insertion into an iron-hydride bond followed by a 2,1-insertion of the second alkene and then chain transfer to give the dimers. Structurally related cobalt systems have also been shown to promote dimerisation albeit with lower activities [62], Oligomerisation of the a-olefms propene, 1-butene and 1-hexene has additionally been achieved with the CF3-containing iron and cobalt systems 5j and 6j yielding highly linear dimers [23],... 

Figure 7.3 gives an overview of the reactions involved in the hydroformylation of internal alkenes to linear products. It has been suggested that cobalt, once attached to an alkene, runs along the chain until an irreversible insertion of CO occurs. Thus, the alkene does not dissociate from the cobalt hydride during the isomerisation process. There is no experimental support for a clear-cut proof for this mechanism. In alkene polymerisation reactions this type of chain running has been actually observed. 

Cobalt was the first catalyst used in commercial applications of the oxo-synthesis. In order to stabilize the HCo(CO)4 catalyst, high pressures are necessary with a maximum n/i ratio of 80/20. In the Shell process,324,325,393 cobalt catalysts modified with alkylphosphines e.g. ( )3 ( 4 9) are more selective towards linear products but exhibit high hydrogenation activity and are therefore mainly used for the direct synthesis of long chain alcohols. 

Hydrocarboxymethylation of Long-Chain Alkenes. An industrial process to carry out hydrocarboxymethylation of olefins to produce methyl esters particularly in the Ci2-Ci4 range for use as a surfactant feedstock was developed by Huels.183 A promoted cobalt catalyst in the form of fatty acid salts (preferably those formed in the reaction) is used. With high promoter catalyst ratio (5 1-15 1) at 180-190°C and pressure of 150-200 atm, the rate of alkene isomerization (double-bond migration) exceeds the rate of hydrocarboxymethylation. As a result, even internal olefins give linear products (the yield of normal products is about 75% at 50-80 % conversion). Secondary transformations of aldehydes (product of olefin hydro-formylation) lead to byproducts (ethers and esters) in small amounts. 

As a preliminary step in the manufacture of unsaturated polyester thermoset plastic one uses low molecular weight linear polyester (Mr 10,000) obtained by a polycondensation of polyglycols with saturated and unsaturated dicarboxylic acids. The precondensate can then be dissolved and stored in the stabilized comonomer, e.g. styrene, with which it will be crosslinked later. The crosslinking polymerization reaction between the polyester chains and the styrene bridges is initiated with the help of organic peroxides which are added dispersed in plasticizers. The reaction begins at 60-90 °C and then proceeds exothermally. In addition to this a cold hardening reaction can also be carried out. For this reaction cold accelerators are necessary, e.g. tertiary amines or cobalt naphthenate. 

The original reaction used cobalt as the catalyst, and the commercial process requires high temperatures (150 - 180°C) and pressures (>200 bar). It produces a mixture, roughly 3 1 of both linear and branched-chain aldehydes, as well as alcohols. These products are formally the consequence of anti-Markovnikov and Markovni-... 

An interesting variation on this is practised by Shell. In recent years, probably also helped by the sharp rise in the world oil price, there has been renewed interest in the F-T route to high quality diesel fuel. The Shell F-T plant in Malaysia which came on stream in 1993 uses multitubular fixed bed reactors to produce long chain hydrocarbon waxes by a LTFT process (over a promoted cobalt catalyst). These waxes are then selectively cracked over zeolites to give the desired shorter chain molecules suitable as diesel fuel. Since F-T hydrocarbons are predominantly linear they are not suitable for petrol engines, but are ideal for diesel. 

Thus, Blanchard and coworkers have shown the dependence of chain length of linear paraffins, formed over cobalt catalysts, from the pore size of the... 

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