Cobalt carbonyl general reactions

Cationic cobalt(m) complexes have successfully been applied to the asymmetric carbonyl-ene reaction.15 The yield and enantioselectivity were dependent, to a large extent, upon the counterion, with SbF6- giving the best results (16, Equation (9)). The conditions were general for a variety of alkenes, but only glyoxaldehydes were used as the carbonyl component. 

Heck has studied the reaction of triphenylphospbine22-24 and trimethylol-propane phosphite25 with the substituted cobalt carbonyls listed in Tables 1-4. The general mechanism for the reaction of the acyl cobalt carbonyls shown in Table 1 in the presence of triphenylphosphine is... 

Oxidative addition of the carbon-carbon bond of cyclopropanes to zero-valent cobalt species is not in general a facile process. It is assumed that in this reaction the alkynyl part of the molecule works as an anchor for the cobalt carbonyl, which enables an efficient insertion of the cobalt moiety into the proximal carbon-carbon bond of the cyclopropane to proceed. It therefore became a matter of interest to see whether direct connection of the alkynyl part with the cyclopropanol is essential or not for this type of reaction. 

Ring enlargement to r/3-oxocyclobutenyl complexes, by carbonyl insertion into the three-membered ring, is generally observed in reactions of group 9 cobalt carbonyl anions with cyclopropenylium cations (equation 197)271 275. Formation of j/ -oxocyclobutenyl complexes also occurs with nitroso iron carbonyl anions270,275. These reactions are usually... 

Steric factors are important in reactions of this type. The substituted cobalt carbonyl hydrides HCo(CO)4-n(PPh3)n react with increasing difficulty as n increases (entries 32-34). Another general effect is that a hydridosilane HSiX3 will react more readily (and the product be more robust) as X becomes more electronegative (227,230). This seems to be valid for all oxidative addition processes. 

Industrially the straight chain isomer is generally the most desired product and hence the normal/iso product ratio obtained for a given catalyst is of importance. Further, the hydrogenation activities of catalysts vary considerably such that alcohols can in some cases be obtained in a single step (222). The first catalysts developed for this reaction were based on cobalt carbonyl and later cobalt carbonyl phosphine complexes. However, more recently attention has been focused on the intrinsically much more active rhodium catalysts (222, 223). A simplified mechanism for (223) cobalt- and rhodium-catalyzed hydroformylation has been proposed which involves the following steps ... 

The Co1 arene complex [Co(C6Me6)2]+ has a sandwich structure, with two ij6-bound arene ligands. The complex is paramagnetic, with two unpaired electrons.39 Alkyl cobalt(I) carbonyls, generally made by the reactions... 

Co(in) complexes promote similar reactions. When four of the six octahedral positions are occupied by amine ligands and two cis positions are available for further reactions, it is possible to study not only the hydrolysis itself, but the steric preferences of the complexes. In general, these compounds catalyze the hydrolysis of N-terminal amino acids from peptides, and the amino acid that is removed remains as part of the complex. The reactions apparently proceed by coordination of the free amine to cobalt, followed either by coordination of the carbonyl to cobalt and subsequent reaction with OH or H2O from the solution (path A in Figure 12-15) or reaction of the carbonyl carbon with coordinated hydroxide (path B). As a result, the N-terminal amino acid is removed from the peptide and left as part of the cobalt complex in which the a-amino nitrogen and the carbonyl oxygen are bonded to the cobalt. Esters and amides are also hydrolyzed by the same mechanism, with the relative importance of the two pathways dependent on the specific compoimds used. 

Cobalt is the catalyst most widely employed for hydrocarboxylations and hydroesterifications. The strong similarity to hydroformylation is shown in the catalyst and in the conditions of T and P. In general the three process rates are in the order hydrofor-mylation>hydrocarboxylation>hydroesterification. Like hydroformylation, the high P of CO required, the instability and toxicity of cobalt carbonyl or hydrocarbonyl and the difficulty of catalyst-product separation detract from the overall attractiveness of this reaction . 

The reaction of olefins with carbon monoxide and hydrogen in the presence of cobalt carbonyl catalysis affords inter alia aldehydes, ketones, and alcohols. These reactions are of considerable industrial importance. The industrial reactions were originally called the Fischer-Tropsch or Oxo syntheses but now are described under the general title of hydro-formylation reactions 3, 224). 

The Bronsted theory states that the acid/base character of a compound depends on its reaction partner and is therefore not an absolute. An indication that transition metal compounds can act as bases is provided by the long-known protonation reactions of transition metal complexes, generally of low oxidation state. An example is cobalt carbonyl hydride, the true catalyst in many carbonylation reactions ... 

This reaction can be carried out catalytically with respect to cobalt carbonyl anion, if the l-acylmethyl-w-allylcobalt tricarbonyl is prepared in situ from an alkyl or acyl halide, cobalt carbonyl anion, and a diene under carbon monoxide. This method is perhaps the most versatile and generally useful method now available for the preparation of acyidienes. 

Recently, cobalt carbonyl has been used in thiolative lactonization of alkynes with thiols with incorporation of two molecules of carbon monoxide which affords a,(3-xmsaturated y-thio y-lactones regioselectively in 50-70% yield, depending upon the type of thiol and acetylene used [44]. This reaction becomes relevant as sulphur compoimds are generally believed to be catalyst poison (Scheme 10.5). 

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. 

The kinetics of the acyl-alkyl equilibrium reactions with cobalt carbonyls has not been studied yet. It is generally assumed that an acylcobalt tricarbonyl complex is an intermediate of the reaction. 

Papers dealing with the general reactions of phosphorus group ligan s in the realm of the metal carbonyls are also represented in this report. Basolo and co-workers have examined the kinetics of CO substitution in a number of iridium carbonyl complexes and have found the first examples of a dissociative mechanism for CO substitution in the cobalt triad carbonyl complexes. Bridged diarsinidene complexes are also reported. ... 

Generally, pressures of 80 to 300 atm are applied at reaction temperatures above 100 °C, with the exception of the Shell process which has been successfully applied in the last few years [148]. In the Shell process cobalt carbonyls modified by phosphine ligands are used as catalysts. They exhibit a high thermal stability and allow operations at pressures of 3 to 35 atm even at such high temperatures as 180—200 °C. 

Brittelli has described a cheap and general one-pot synthesis of a,/3-unsaturated acids based on the Wadsworth-Emmons reaction (Scheme 44)." A straightforward and high yielding synthesis of /9-unsubstituted-a,/3-unsaturated acids which is suitable for large-scale preparations has been developed (Scheme 45)." a,/3-Unsaturated acids can be prepared in high yield by cobalt carbonyl-catalysed carbonylation of vinyl bromides under phase-transfer conditions." ... 

The investigations described so far indicate that reactions of metal carbonylates in general lead only to the coordination of two metal carbonyl groups to the 1,3,5-trisilacyclohexanes. From the chemistry of silylcobalt compounds it is known that silanes of the type R SiH (n = 1-3) cleave dinuclear Co2(CO)g, producing silyl-cobalt-carbonyl complexes [166, 167, 171]. 

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