Carbon oxides insertion reactions

Nickel tetracarbonyl is known to dissociate into the more reactive tricarbonyl readily [step (1)] and this species is known to react readily with a variety of halides by oxidative addition presumably as shown in steps (2) and (3). Subsequent loss of CO would give an equilibrium mixture of the four complexes shown in (3). Step (4) is the well-known carbon monoxide insertion reaction. The acylnickel complex formed in this step then may re-ductively eliminate acid halide [step (5)], which then alcoholizes [step (6)] or it may react directly with alcohol to form ester and a hydridonickel complex (7), which then reacts with CO and decomposes to nickel tricarbonyl and HC1 (8) ... 

A relatively small number of carbon monoxide insertion reactions are known for alkyl or aryl derivatives of nickel. The oxidative addition of benzoyl chloride to Ni(PPh3)4 at 0°C was reported to give the corresponding phenyl derivative of nickel(Il) [reaction (c)], thus implying that the reverse of the carbonyl insertion from an unstable... 

MMT. MMT photolyses rapidly by sunlight in the atmosphere with a very short half-life, i.e., less than 2 minutes (Ter Haar et al. 1975 Garrison et al. 1995). MMT is converted to a mixture of solid manganese oxides and carbonates. The organic portion of the solid consists of a complex mixture of acids, esters, and hydrocarbon polymers that results from the partial oxidation of the cyclopentadienyl ring, carbon monoxide insertion reactions and polymerization of multifunctional compounds (Ter Haar et al. 1975). 

A detailed study of the mechanism of the insertion reaction of monomer between the metal-carbon bond requires quantitative information on the kinetics of the process. For this information to be meaningful, studies should be carried out on a homogeneous system. Whereas olefins and compounds such as Zr(benzyl)4 and Cr(2-Me-allyl)3, etc. are very soluble in hydrocarbon solvents, the polymers formed are crystalline and therefore insoluble below the melting temperature of the polyolefine formed. It is therefore not possible to use olefins for kinetic studies. Two completely homogeneous systems have been identified that can be used to study the polymerization quantitatively. These are the polymerization of styrene by Zr(benzyl)4 in toluene (16, 25) and the polymerization of methyl methacrylate by Cr(allyl)3 and Cr(2-Me-allyl)3 (12)- The latter system is unusual since esters normally react with transition metal allyl compounds (10) but a-methyl esters such as methyl methacrylate do not (p. 270) and the only product of reaction is polymethylmethacrylate. Also it has been shown with both systems that polymerization occurs without a change in the oxidation state of the metal. 

Some distinctive features of the insertion reactions reported in Table VII can be summarized as follows First, carbon monoxide gives rise by insertion (5, 195a) to acyl bonds which are easily cleaved by water, alcohols, or compounds with mobile hydrogen. The metal is thus easily removed from the organic part and, being eliminated in its reduced state, can undergo a further oxidative addition, leading to a catalytic cycle. Thus, use of CO is very favorable for catalytic reactions. 

As mentioned above nonconjugated dienes give stable complexes where the two double bonds can form a chelate complex. A common pathway in palladium-catalyzed oxidation of nonconjugated dienes is that, after a first nucleophilic addition to one of the double bonds, the second double bond inserts into the palladium-carbon bond. The new (cr-alkyl)palladium complex produced can then undergo a /(-elimination or an oxidative cleavage reaction (Scheme 2). An early example of this type of reaction, although not catalytic, was reported by Tsuji and Takahashi (equation 2)12. 

Figure 15.8 a simple example is presented of a subsequent insertion of CO and methanolysis of the palladium acyl intermediate [14], This is not a very common reaction, because both the ligand requirements and the redox conditions for Wacker and carbonylation chemistry are not compatible. For insertion reactions one would use cis coordinating diphosphines or diimines, which makes the palladium centre more electron-rich and thus the nucleophilic attack in the Wacker part of the scheme will be slowed down. In addition, the oxidants present may lead to catalytic oxidation of carbon monoxide. 

We have explored two types of carbon-carbon bond forming reactions operated under almost neutral conditions. Both reactions are initiated by the formation of an H-Rh-Si species through oxidative addition of a hydrosilane to a low-valence rhodium complex. Aldol-type three-component couphngs are followed by the insertion of an a,yS-unsatu-rated carbonyl compound into a Rh-H bond, whereas silylformylation is accomplished by the insertion of an acetylenic moiety into a Rh-Si bond. 

Following our first report on the palladium-catalyzed reaction of vinyl triflates with olefins (Heck-type reaction), oxidative insertion of palladium(O) into the carbon-oxygen bond of easily available vinyl triflates ... 

Contrary to the ionic mechanism suggested by Tsuji, an insertion mechanism explains the facts much better. An external attack of carbon monoxide at the most positive carbon atom of propylene in a palladium chloride complex, as Tsuji proposed, would be expected to produce 3-chloro-2-methylpropionyl chloride rather than the observed product, 3-chlorobutyryl chloride. Since oxidation of propylene by Pd (II) ion gives acetone rather than propionalydehyde, a CO insertion reaction and elimination should produce the observed compound, 3-chlorobutyryl chloride... 

The oxidative addition is quite general with alkyl, allyl, benzyl, vinyl, and aryl halides as well as with acyl halides to afford the palladium (II) complex VII. The frans-bis( triphenylphosphine )alkylpalladium halides can also be carbonylated in an insertion reaction to give the corresponding acyl complexes, the stereochemistry of which (17, 18) proceeds with retention of configuration at the carbon bonded to palladium. The acyl complex also can be formed from the addition of the corresponding acid halide to tetrakis (triphenylphosphine) palladium (0). 

The oldest known276 reaction of a cycloproparene with an organometallic reagent is the oxidative addition of 11 to Fe2(CO)9 followed by carbon monoxide insertion to give a metallaindanone. This same reaction (equation 33) occurs with 95 (where C(l) is substi-... 

The reaction of Co(tc-Cp)(CO)2 and of [Co(7t-Cp)NO]2 with nitric oxide in the presence of norbornene has been reported. In both cases the species shown in Figure 14 may be isolated in high yield.125 The mechanism of these three component syntheses could well be related to that of the NO insertion reactions (Scheme 2) in that here NO insertion might occur into the metal-carbon tt-bond of a cobalt-norbornene intermediate. 

The processes going on inside this ceramic catalytic converter include the reactions shown in the insert. Fragments of unburned hydrocarbons and carbon monoxide and nitric oxide molecules are converted to less noxious substances, such as nitrogen and carbon dioxide, by reactions at the surface of the catalyst. 

Olefinic compounds will often insert into carbon-transition metal bonds as CO does, and this reaction is an important step in many catalytic syntheses. When this step is combined with an oxidative addition of an organic halide to a palladium(O) complex in the presence of a base, a very useful, catalytic olefinic substitution reaction results (26-29). The oxidative addition produces an organopalladium(II) halide, which then adds 1,2 to the olefinic reactant (insertion reaction). The adduct is unstable if there are hydrogens beta to the palladium group and elimination of a hydridopalladium salt occurs, forming a substituted olefinic product. The hydridopalladium salt then reforms the... 

The catalytic dicarbonylation of ethylene to dimethyl succinate can be carried out in 90% conversion.94 High reaction temperatures and low carbon monoxide pressures can lead to unsaturated esters as a result of a faster -hydride elimination from the intermediate (23) than carbon monoxide insertion. This later reaction path has been termed oxidative carboxylation. 

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