Cobalt-carbonyl acetylene complex

Fig. 15. The oloso distorted octahedral structure of the cobalt carbonyl acetylene complex Co4(CO)ioC2Et2 (50).

While there is no direct evidence for this, they have succeeded in isolating an analogous cobalt carbonyl-acetylene complex (Sternberg et al., 43). 

Ferrocene was the first organometallic guest incorporated and numerous spectroscopic and electrochemical studies have been performed on ferrocene, substituted ferrocene, and related metallocene (e.g. cobaltocene) inclusion complexes (444-469]. Half-sandwich cyclopentadienyl- and benzene-metal carbonyl complexes have also been studied quite extensively [470-479] as have // -allyl metal (palladium) complexes [480], diene metal (rhodium) complexes [481-484], acetylene cobalt carbonyl cluster complexes [485], and complexes with metal carbonyls, e.g. Fe(CO)5, Mn2(CO)io, and CoNO(CO)3 [485a]. 

A more complex carbonylation process is involved in the formation of bisbutenolides (bifurandiones) from cobalt carbonyl-catalyzed carbonylation of alkynes112 117 (Scheme 68). The trans derivative (53) is formed in good yield from acetylene,112 but yields from substituted acetylenes (e.g., propyne)... 

The RCCo3(CO)9 catalysts in these reactions, however, only appear to be sources of simpler cobalt carbonyl species through their thermolysis, and it is the latter which cause the acetylene trimerization through well-established routes (73). Indeed, in some cases acetylene-derived cobalt carbonyl complexes are obtained (72) ... 

Acetylenic molecules are versatile ligands in organometallic chemistry [152— 154]. Examples of acetylene-metal reactions include facile complexations of one triple bond with Co2(CO)s [155-157] and two triple bonds with CpCo(CO)2 (Scheme 31) [158,159]. The hb-PYs contain numerous triple bonds and should be readily metallized through their complexations with the cobalt carbonyls. Upon admixing hb-P20 and the cobalt carbonyls in THF at room temperature, the solution color changed from yellow to brown, accompanied by CO gas evolution. The mixtures remained homogenous towards... 

Scheme 31 Upper panel-. Complex formation between acetylenes and cobalt carbonyls. Lower panel Formation of polymer complexes 81 and 82 via metal complexation and transformation of the complexes into soft ferromagnetic materials 83 and 84 by pyrolytic ceramization...

Acrylonitrile and related compounds displace all the carbonyl groups from nickel carbonyl to form [(RCH CHCN)2Ni], in which the nitrile bonds through the olefinic double bond 222, 418). The bis(acrylonitrile) complex catalyzes many reactions, including the conversion of acrylonitrile and acetylene to heptatrienenitrile and the polymerization of acetylene to cyclooctatetraene 418). Cobalt carbonyl gave a brown-red amorphous material with acrylonitrile, which had i cn absorptions typical of uncoordinated nitrile groups, but interestingly, the presence of C=N groups was also indicated 419). In acidic methanol, cobalt carbonyl converts a,j8-unsaturated nitriles to saturated aldehydes 459). 

The third compound was made by a Pauson-Khand reaction using the same starting material = the first. The only difference between these two target molecules is the position of the double bor. In the Nazarov reaction, it goes into the thermodynamically most favourable position but in 1-Pauson-Khand reaction it goes where the alkyne was. So we simply react the cyclic ether wci acetylene cobalt carbonyl complex. The cis stereochemistry is inevitable. 

Similarly, acetylene or any acetylene of the formula RC CH is polymerized by the acetylene-cobalt carbonyl complex III at room temperature complexes derived from acetylenes with no hydrogen atom (RC=CR) do not catalyze these polymerizations (16). 

The conditions for the synthesis must differ, as the electronic configuration of each metal changes, but the intermediate in each case probably is a complex in which acetylene and carbon monoxide are each linked to two metal atoms. Cobalt and iron compounds having both acetylene and carbonyl bridges have already been synthesized 27). The report of the preparation of a dimeric nickel hydrocarbonyl, [NiH(CO)a]2 by Behrens 28) may well lead to the isolation of a siipilar acetylene complex with nickel. 

Acetylene and monosubstituted acetylenes appear to give some of the 7T-(penteno-4-lactonyl)cobalt tricarbonyl complexes on reaction with alkylcobalt or acylcobalt tetracarbonyls also but other products are formed too. These other products have not been characterized but are thought to be linear, low molecular weight polymers of the acetylene or of the acetylene and carbon monoxide with an acyl group at one end of the polymer chain and a cobalt carbonyl group at the other. The formation of cyclic products from the more-substituted compounds and cyclic and linear ones from the less-substituted compounds is explainable because substitution is known to improve many cyclization reactions. 

Cobalt, nickel, iron, ruthenium, and rhodium carbonyls as well as palladium complexes are catalysts for hydrocarboxylation reactions and therefore reactions of olefins and acetylenes with CO and water, and also other carbonylation reactions. Analogously to hydroformylation reactions, better catalytic properties are shown by metal hydrido carbonyls having strong acidic properties. As in hydroformylation reactions, phosphine-carbonyl complexes of these metals are particularly active. Solvents for such reactions are alcohols, ketones, esters, pyridine, and acidic aqueous solutions. Stoichiometric carbonylation reaction by means of [Ni(CO)4] proceeds at atmospheric pressure at 308-353 K. In the presence of catalytic amounts of nickel carbonyl, this reaction is carried out at 390-490 K and 3 MPa. In the case of carbonylation which utilizes catalytic amounts of cobalt carbonyl, higher temperatures (up to 530 K) and higher pressures (3-90 MPa) are applied. Alkoxylcarbonylation reactions generally proceed under more drastic conditions than corresponding hydrocarboxylation reactions. 

Substitution of carbon monoxide ligands by one acetylene is the first step in the reaction of alkynes with metal carbonyk. This is well-established in the case of cobalt carbonyls by the isolation of substitution-type complexes of formula RC R Co CCO) (1) and RC2R Co (CO)j (2). Three different types of alkyne-substituted iron carbonyls have been isolated from iron carbonyls particularly with acetylenes having bulky substituents (3). They have recently been shown to be intermediates in the formation of complexes with more complicated organic ligands as well as of cyclic organic products. 

Scheme 3.17 Alkyne cobalt carbonyl complexes of aspirin 40, diphenyl acetylene 41 and 2-propyn-l-ol 42.

An interesting series of cobalt carbonyl derivatives are the deep violet trinuclear derivatives of general formula YCCo3(CO)9. These were first prepared by treatment of the acetylene complexes Co2(CO)6(RC2H) with... 

Ganesh and Nicholas demonstrated that the cobalt carbonyl complexes of the acetylenic aldehydes 77 undergo facile reaction with alkoxyallyborane to provide the homoallyUc alcohols 78. Oxidative deprotection of the cobalt carbonyl complexes using ceric ammonium nitrate readily furnishes the free homoallylic alcohols 79 (Scheme 25.10). ... 

The treatment of organocobalt carbonyl complexes formed from acetylene and cobalt carbonyl with phosphines also gives organocobaltcarbonylphos-phine complexes, e.g., Co2(CO)4(C6H5C=CC6Hs)[P(C6H5)3]2 (312). 

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