Catalytic reactions carbon monoxide addition

Soderberg and coworkers have developed a palladium-phosphine-catalyzed reductive iV-het-eroannuladon of 2-nitrostyrenes forming indoles in good yields For example, reaction of 6-bromo-2-nitrostyrene with carbon monoxide in the presence of a catalytic amount of palladium diacetate (6 mol% and triphenylphosphine 124 mol% in acetonitrile at 30 gives 4-bromoindole in 86% yield fEq 10 62 Several functional groups, such as esters, ethers, bromides, tnflates, and additional nitro groups, have been shown to be compatible with the reaction conditions... 

The catalytic steam-reforming process of methanol on Cu/ZnO/Ab03 catalyst primarily produces hydrogen and carbon dioxide. In addition, the minor quantities of carbon monoxide are also produced. This mechanism is explained in terms of parallel reactions [11]. 

It is generally assumed that the Lewis acid in 3 decreases the charge on the metal, i.e., increases its electrophilicity. The removal of charge from the nickel allows additional electron donors to coordinate to the nickel atom, and reaction with, for example, 2 moles of carbon monoxide or 1 mole of 1,5-cyclooctadiene (COD) gives the insoluble, catalytically inactive and presumably ionic complexes 7 and 8. In contrast, 7r-allyl-nickel halides (1) add only 1 mole of carbon monoxide while they do not react with COD (52). 

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. 

The product is exclusively carbon monoxide, and good turnover numbers are found in preparative-scale electrolysis. Analysis of the reaction orders in CO2 and AH suggests the mechanism depicted in Scheme 4.6. After generation of the iron(O) complex, the first step in the catalytic reaction is the formation of an adduct with one molecule of CO2. Only one form of the resulting complex is shown in the scheme. Other forms may result from the attack of CO2 on the porphyrin, since all the electronic density is not necessarily concentrated on the iron atom [an iron(I) anion radical and an iron(II) di-anion mesomeric forms may mix to some extent with the form shown in the scheme, in which all the electronic density is located on iron]. Addition of a weak Bronsted acid stabilizes the iron(II) carbene-like structure of the adduct, which then produces the carbon monoxide complex after elimination of a water molecule. The formation of carbon monoxide, which is the only electrolysis product, also appears in the cyclic voltammogram. The anodic peak 2a, corresponding to the reoxidation of iron(II) into iron(III) is indeed shifted toward a more negative value, 2a, as it is when CO is added to the solution. 

Abstract The transition metal mediated conversion of alkynes, alkenes, and carbon monoxide in a formal [2 + 2+1] cycloaddition process, commonly known as the Pauson-Khand reaction (PKR), is an elegant method for the construction of cyclopentenone scaffolds. During the last decade, significant improvements have been achieved in this area. For instance, catalytic PKR variants are nowadays possible with different metal sources. In addition, new asymmetric approaches were established and the reaction has been applied as a key step in various total syntheses. Recent work has also focused on the development of CO-free conditions, incorporating transfer carbonylation reactions. This review attempts to cover the most important developments in this area. 

Two molecules of carbon monoxide were successively incorporated into an epoxide in the presence of a cobalt catalyst and a phase transfer agent [29]. When styrene oxide was treated with carbon monoxide (0.1 MPa), excess methyl iodide, NaOH (0.50 M), and catalytic amounts of Co2(CO)8 and hexadecyltrimethylammonium bromide in benzene, 3-hydroxy-4-phenyl-2(5H)-furanone was produced in 65% yield (Scheme 7). A possible reaction mechanism was proposed as shown in Scheme 8 Addition of an in situ... 

High-pressure in-situ NMR spectroscopy have been reported about reactions of carbon monoxide with cobalt complexes of the type, [Co(CO)3L]2. For L=P(n-C4H9)3, high pressures of carbon monoxide cause CO addition and disproportionation of the catalyst to produce a catalytically inactive cobalt(I) salt with the composition [Co(CO)3L2]+[Co(CO)4] . Salt formation is favoured by polar solvents [13],... 

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. 

In addition to the successful reductive carbonylation systems utilizing the rhodium or palladium catalysts described above, a nonnoble metal system has been developed (27). When methyl acetate or dimethyl ether was treated with carbon monoxide and hydrogen in the presence of an iodide compound, a trivalent phosphorous or nitrogen promoter, and a nickel-molybdenum or nickel-tungsten catalyst, EDA was formed. The catalytst is generated in the reaction mixture by addition of appropriate metallic complexes, such as 5 1 combination of bis(triphenylphosphine)-nickel dicarbonyl to molybdenum carbonyl. These same catalyst systems have proven effective as a rhodium replacement in methyl acetate carbonylations (28). Though the rates of EDA formation are slower than with the noble metals, the major advantage is the relative inexpense of catalytic materials. Chemistry virtually identical to noble-metal catalysis probably occurs since reaction profiles are very similar by products include acetic anhydride, acetaldehyde, and methane, with ethanol in trace quantities. 

Beyer and coworkers later extended these reactions to platinum clusters Ptn and have demonstrated that similar reaction sequences for the oxidation of carbon monoxide can occur with larger clusters [70]. In addition, they were able to demonstrate poisoning effects as a function of surface coverage and cluster size. A related sequence for Pt anions was proposed by Shi and Ervin who employed molecular oxygen rather than N2O as the oxidant [71]. Further, the group of Bohme has screened the mononuclear cations of almost the entire transition metal block for this particular kind of oxidation catalysis [72,73]. Another catalytic system has been proposed by Waters et al. in which a dimolybdate anion cluster brings about the oxidation of methanol to formaldehyde with nitromethane, however, a rather unusual terminal oxidant was employed [74]. 

Catalytic reduction of olefins by heavy metal catalysts probably involves metal hydride addition reactions also. If this is correct, the observed inhibition of the reduction by carbon monoxide, phosphines, sulfur compounds, and other materials with unshared electrons is exactly what would be expected if a vacant orbital on the hydride is required before addition can take place. 

An attempt was also made to produce 0-iodo acyl iodides by the reaction of iodine, carbon monoxide and olefins in the presence of palladium or platinum chloride. This is, in effect, an attempt to make Dr. Tsuji s reaction catalytic rather than stoichiometric. No carbonyl insertion occurred at 1 atm. of carbon monoxide. However, it was found that iodination of the olefin was catalyzed by platinum olefin complexes and that an additional increase in catalytic activity accompanied the presence of carbon monoxide. There has been much speculation at this conference concerning the possibility of affecting catalytic activity by changing the ligands in the coordination sphere of the catalyst. This would appear to be such a case. 

The combination of the formation of palladium(II) complexes in the oxidative addition of unsaturated halides onto palladium(O), and the palladium(II) mediated ring closure of olefins allows for the elimination of the oxidant. The ring closure of the methallyl-aniline derivative shown in 3.67. in the presence of /J-bromostyrcnc and a catalytic amount of palladium led to the ring closed - coupled product.84 The ring closure might also be accompanied by other follow-up reactions. 2-Methallyl-anilines were converted for example to indolylacetic acid derivatives in the presence of carbon monoxide.85... 

Evidence was presented that cobalt precursors under the reaction conditions are transformed into cobalt carbonyls.31 Additives such as Lewis bases accelerate the formation of the catalyst.11 [CoH(CO)4] the key catalytic species was shown by infrared (IR) spectroscopy to be formed under hydroformylation conditions32 and was isolated in the reaction of [Co(CO)4]2 and hydrogen.33 [CoH(CO)4] dissociates carbon monoxide to create [CoH(CO)3] [Eq. (7.2)], which is capable of olefin com-plexation because of a ligand vacancy ... 

The mechanism for the reaction is believed to be as shown in Eq. 15.170 (start with CH3OH, lower right, and end with CHjCOOH, lower left).180 The reaction can be initiated with any rhodium salt, e.g., RhCl3, and a source of iodine, the two combining with CO to produce the active catalyst, IRItfCO y. The methyl iodide arises from the reaction of methanol and hydrogen iodide. Note that the catalytic loop involves oxidative addition, insertion, and reductive elimination, with a net production of acetic acid from the insertion of carbon monoxide into methanol. The rhodium shuttles between the +1 and +3 oxidation states. The cataylst is so efficient that the reaction will proceed at atmospheric pressure, although in practice the system is... 

In a separate investigation MargeHs and Roginekii1107 carried nut catalytic oxidation of ethylene at 350° over vanadium pentoxidc. reportedly similar to metallic silver in catalytic properties. TVv asoertainod that carbon dioxide was formed faster from, ethylene oxide, or from acetaldehyde under comparable conditions, than from ethylene itself. Further, they noted the formation of carbon monoxide, and determined that its rate of formation was considerably greater than that of carbon dioxide, increasing still more in the presence of adtk-d ethylene oxide. The addition of ethylene oxide also appeared to depro both ethylene oxide and acetaldehyde formation. They concluded that reactions leading to carbon dioxide and water did not proceed by wav of ethylene oxide, but by way of some other intermediates, and tlmt-this process could occur either on the catalyst surface or in the gas phase. 

In 1977, Murai and co-workers described the catalytic addition of hydrosilane and carbon monoxide to an internal olefin to give enol silyl ethers in which one molecule of CO is incorporated.103-105 During the time period covered by this review, the transition metal-catalyzed reaction of HSiR3/ CO has been reported for many substrates. The catalytic system provides a facile route to a number of materials that are valuable in organic synthesis. The hydrosilane/CO system is very interesting, as different products can be obtained depending on substrate, catalyst, and reaction conditions employed. 

The synthesis of succinic acid derivatives, /3-alkoxy esters, and a,j3-unsaturated esters from olefins by palladium catalyzed carbonylation reactions in alcohol have been reported (24, 25, 26, 27), but full experimental details of the syntheses are incomplete and in most cases the yields of yS-alkoxy ester and diester products are low. A similar reaction employing stoichiometric amounts of palladium (II) has also been reported (28). In order to explore the scope of this reaction for the syntheses of yS-alkoxy esters and succinic acid derivatives, representative cyclic and acyclic olefins were carbonylated under these same conditions (Table I). The reactions were carried out in methanol at room temperature using catalytic amounts of palladium (II) chloride and stoichiometric amounts of copper (II) chloride under 2 atm of carbon monoxide. The methoxypalladation reaction of 1-pentene affords a good conversion (55% ) of olefin to methyl 3-methoxyhexanoate, the product of Markov-nikov addition. In the carbonylation of other 1-olefins, f3-methoxy methyl esters were obtained in high yields however, substitution of a methyl group on the double bond reduced the yield of ester markedly. For example, the carbonylation of 2-methyl-l-butene afforded < 10% yield of methyl 3-methyl-3-methoxypentanoate. This suggests that unsubstituted 1-olefins may be preferentially carbonylated in the presence of substituted 1-olefins or internal olefins. The reactivities of the olefins fall in the order RCH =CHo ]> ci -RCH=CHR > trans-RCH =CHR >... 

The [2+2+1] cycloaddition of an alkene, an alkyne and carbon monoxide is commonly known as the Pauson-Khand reaction. This transformation has been adopted many times in the synthesis of complex natural products and related compounds, which contain a cyclopentenone moiety, for example, prostaglandins. Two independent reports of this reaction appeared almost simultaneously in late 2002 by Iqbal and co-workers25 and Fisher and co-workers26, respectively. They not only used very similar substrate systems in their studies, but they also reached very similar conclusions Toluene was found to be the preferred solvent in this reaction, even though it is a very poor microwave absorber. A reaction time between 5 and 10 min, using dicob alto ctacar-bonyl or dicobalthexacarbonyl as the carbon monoxide source, and a temperature of 100-120°C resulted in high yields of the products. Fisher and co-workers used 20 mol% Co2(CO)8 and cyclohexylamine as an additive (Scheme 5.12), since this system had been used previously in order to allow a catalytic reaction. Iqbal and co-workers did not use cyclohexylamine, but instead used 1 equiv. of the carbon monoxide (Co2(CO)6) source. In both reports, the products were formed in 40-70% yield. 

Reaction (78) regenerates Mel from methanol and HI. Using a high-pressure IR cell at 0.6 MPa, complex (95) was found to be the main species present under catalytic conditions, and the oxidative addition of Mel was therefore assumed to be the rate determining step. The water-gas shift reaction (equation 70) also occurs during the process, causing a limited loss of carbon monoxide. A review of the cobalt-, rhodium- and iridium-catalyzed carbonylation of methanol to acetic acid is available.415... 

---