Dicobalt octacarbonyl catalyst preparation

The hypothesis that the cobalt carbonyl radicals are the carriers of catalytic activity was disproved by a high pressure photochemistry experiment /32/, in which the Co(CO), radical was prepared under hydroformylation conditions by photolysis of dicobalt octacarbonyl in hydrocarbon solvents. The catalytic reaction was not enhanced by the irradiation, as would be expected if the radicals were the active catalyst. On the contrary, the Co(C0)4 radicals were found to inhibit the hydroformylation. They initiate the decomposition of the real active catalyst, HCo(C0)4, in a radical chain process /32, 33/. 

It has been observed that rapid isomerization accompanies the cobalt carbonyl-catalyzed hydrosilation of olefins (18). The reaction of equimolar amounts of a trisubstituted silane and dicobalt octacarbonyl has been shown to result in the formation of cobalt hydrocarbonyl (cf. Section IV). A very effective isomerization catalyst may be prepared by treatment of a solution of Co2(CO)8 in olefin ( 0.01 M) with a silicon hydride in sufficient quantity to slightly exceed the cobalt carbonyl concentration. 

When 3,4-di-O-acetyl-D-xylal (5), prepared by a modification of the procedure of Helferich and coworkers, was allowed to react with a mixture of carbon monoxide and hydrogen at a pressure of about 4000 Ib./in. and at a temperature of about 130° for about 90 minutes, in the presence of preformed dicobalt octacarbonyl in benzene as the catalyst, a mixture of two inseparable, partially acetylated hexitols was obtained in over 90% yield. Deacetylation of the latter with sodium methoxide in methanol yielded, in almost equimolar proportions, the chromatographically separable hexitols, l,5-anhydro-4-deoxy-L- yio-hexitol (6) and l,5-anhydro-4-deoxy-D-arahino-hexitol (7). Whenever the mixture of products was contaminated by the precursor aldehydo compounds, a prior reduction of these with sodium borohydride greatly facilitated the isolation of (6) and (7) in pure form. 

Tributylphosphine sulfide has been used as a co-catalyst with dicobalt octacarbonyl for the Pawson-Khand reaction. Thermolysis of a mixture of cadmium chloride and trioctylphosphine sulfide at 250 °C has been used as a route to the formation of nanocrystalline cadmium sulfide." A complex of triphenylphosphine sulfide with a silver-tungsten-iodine acceptor has been characterised by X-ray studies. Ferrocenylphosphine chalcogenides have attracted considerable interest as ligands. Complexes of the monophosphino-phosphine sulfide (269) with rhodium have been characterised." The disulfide (270) forms complexes with both gold(i) and gold(iii) acceptors," and a silver(i) complex of the diselenide (271) has been prepared. ... 

Chiral pyridine addition to cobalt catalysts derived from dicobalt octacarbonyl has a positive influence on cherno- and regioselectivity, but not on stereoselectivity. Thus, no asymmetric induction is observed with Co ( + )-(.S )-3-.vtx-butylpyridine in the hydroformylation of styrene23. Again no induction is observed with chiral cobalt clustersl08. Cobalt is also used in catalytic systems of the type Co(An)n(alkene)m(CO)pLq [An = coordinating or noncoordinat-ing anions, e.g., BPhJ with various chiral ligands [L = ZR4R5R6 (Z = As, N, P, Sb)]166. Low catalytic activities and inductions are observed with supported catalysts of cobalt on silica gel or alumina [in situ preparation from salt, modified with phosphanes, e.g., (+)- or (—)-Diop]89. 

CoSe2 nanomaterials have also been prepared as catalysts for nitrogen doped carbons as low cost materials. The carbon supports were synthesised by pyrolysis of vulcan, which was coated with carbon and nitrogen precursors with formaldehyde and ethylene diamine or 1,6-diaminohexane being the carbon and nitrogen sources respectively. To load the CoSca layer dicobalt octacarbonyl and nitrogen doped carbon were mixed with 200 ml dehydrated jylene. The carbonyl sol was then refluxed for 2 h at 140 °C in a four neck flask with nitrogen protection. 

Experiments at atmospheric pressure of carbon monoxide have shown that complex 24 converts rapidly first into 23 and diethyl malonate and in a much slower reaction, complex 23 converts further into octacarbonyl dicobalt and an other mole of diethyl malonate. In both reactions, the formation of highly reactive ethoxycarbo-nylketene was assumed by coupling of the ethoxycarbonyl carbene ligand with carbon monoxide, whose intermediate is scavenged by ethanol [76]. Reactions of complex 24 with in the presence of excess ethanol result in diethyl malonate with natural isotopic distribution of[77]. The combination of these steps led to an effective one-pot procedure for the preparation of various malonic acid derivatives by catalytic carbonylation of ethyl diazoacetate in the presence of a few mol% octacarbonyl dicobalt catalyst precursor [76]. Two new example procedures illustrate the usefulness of the method. 

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