CO insertion reaction

CO insertion reactions. The catalytic hydrogenation mechanism presented was based on detection of species 64 and HC1 during hydrogenation of ethylene, Eq. (92). Species 65 then catalyzes the reaction by pathways outlined in Eq. (5). 

Owing in part to its great commercial importance, the CO insertion reaction is perhaps the most thoroughly studied metal carbonyl reaction other than substition (11-13). As shown in equation 3a, the currently... 

The simple second-order kinetics of equation 5a apply for Mn(CO)5(0113) when L=CO at subatraospheric pressures. It is under this set of conditions that we have studied the Lewis acid promoted CO insertion reaction, see Figure 2. 

Prior to our studies it was recognized that ion pairing with anionic metal carbonyls could promote CO insertion and related reactions (14-16). Both kinetic and non-kinetic evidence suggests the importance of ion pairs in these types of reactions (14,17). For example, a small cation was found to greatly accelerate the CO insertion reaction relative to the same reaction with a large cation, equation 6 (14). 

Investigations in our laboratory by Rebecca Stimson have demonstrated that it is possible to combine the borane reduction of a metal acyl with the Lewis acid promoted CO insertion reaction which has been discussed earlier in this paper (29). In this reaction, which is presumed to proceed by equation 17, the... 

The study of alkene insertions in complexes containing diphosphine ligands turned out to be more complicated than the study of the CO insertion reactions [13], When one attempts to carry out insertion reactions on acetylpalladium complexes decarbonylation takes place. When the reaction is carried out under a pressure of CO the observed rate of alkene insertion depends on the CO pressure due to the competition between CO and ethene coordination. Also, after insertion of the alkene into the acetyl species (3-elimination occurs, except for norbomene or norbomadiene as the alkene. In this instance, as was already reported by Sen [8,27] a syn addition takes place and in this strained skeleton no (3-elimination can take place. Therefore most studies on the alkene insertion and isolation of the intermediates concern the insertion of norbomenes [21,32], The main product observed for norbomene insertion into an acetyl palladium bond is the exo species (see Figure 12.8). 

Thus, the migratory CO insertion reaction on the iridium center, which is the rate-determining step of the iridium catalytic cycle, is accelerated by T ligand dissociation. These results tend to rationalize the seminal and inspired observations of Forster at Monsanto Co. [25]. 

Kinetic and Mechanistic Studies of Stoichiometric Reaction Steps 3.3.2.1 Migratory CO Insertion Reactions of Metal Alkyls... 

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... 

RCH2OH + Co2(CO)7 (72) A known reaction of cobalt hydrocarbonyl suggests that the cobalt-carbon bond may be preferred. It has been reported that, under rather vigorous conditions, acetaldehyde or formaldehyde react with CO and a cobalt catalyst to give o -hydroxy acids or esters in alcohol solution (7). The intermediate with the carbon-cobalt bond probably is undergoing a CO insertion reaction, folllwed by a hydrolysis or... 

The CO insertion reactions shown are likely to involve the coordinatively saturated (tetracarbonyl) complexes, and are expected to be reversible. The coordinatively unsaturated tricarbonyl and saturated tetracarbonyl complexes are presumed to be in equilibrium, the position lying predominantly toward the coordinatively saturated species. Glycolaldehyde is postulated as the ethylene glycol presursor, as will be further described below. 

The glycolaldehyde shown in (51) results from a CO insertion reaction followed by reductive elimination, and is presumed to be a precursor of ethylene glycol. Since ethylene glycol is, however, at most a trace product of this catalytic system, step (51) appears to be essentially inoperative. Methyl formate, a major primary product of this system under some conditions, is also presumed to be formed by a CO insertion process, (53). Methanol may be formed by a reductive elimination (hydrogenolysis) of either a hydroxymethyl ligand, (52), or of a methoxy ligand, (54). 

Unlike common five and six membered heterocycles, purines rarely undergo coupling reactions including the insertion of an olefin or carbon monoxide. This behaviour is not well understood since Heck and CO insertion reactions are known to proceed on similar systems. 

A classic example of a CO insertion reaction (called migratory insertion for reasons to be explained later) is found in Ihe work of Noack and Calderazzo.153... 

The validity of this mechanism has been demonstrated for a number of CO insertion reactions. Thus when chemists use the term CO insertion, they usually mean alkyl migration. Several things to keep in mind when considering a reaction of this type are (I) it involves ligands which are cis to one another. (2) in the course of the reaction a vacant coordination becomes available, and (3) the reverse reaction cannot occur unless a ligand is first eliminated. 

The precise origin of the stereoselectivity in these reactions is not known at present. The acyl mechanism has generally been assumed, rather than the alkoxycarbonyl one (see Section 61.2.5.8) and it seems reasonable that asymmetric induction must have taken place prior to or during the CO insertion reaction. A review of asymmetric carbonylation is available.579... 

Simple alkyls or aryls have also been made many such as Fe(CO)2-(PMe3)2MeX122 (17-E-XXI) have been widely studied because of the importance of the CO insertion reaction which gives Fe(CO)2(PMe3)2(COMe)X and is used in catalysis. Another important subgroup is that of compounds of the type (porph)FeR123 which have been cited before. 

Whereas the CO insertion reaction has been investigated extensively in organometallic chemistry and homogeneous catalysis, there are only few first-principles investigations available for this reaction on transition metal surfaces (32,33,60). 

The dependence of product selectivity on CO partial pressure can be ratkmal-tzed in terms of stcric crowding in the aJkyl-lo-acyl transition state, that is, in the CO insertion reaction (cycles A and B of Scheme 3). Increasing the carbon monoxide partial pressure, however, has a detrimental effect on the overall rate of the hydroformylaiiun reaction. 

In the particular case of metal carbonyls (e.g.. Mo(CO)s L), a CO insertion reaction would be the initial step leading to the carbene [5]. 

SCF and CAS SCF calculations on mono and bimetallic transition metal hydride complexes are reported. The importance of including the non dynamical correlation elTects for the study of the cis-trans isomerism in dihydrido complexes and for the study of the CO insertion reaction into the metal hydride bond is stressed. The metal to metal hydrogen transfer in a class of bimetallic d — d hydride complexes is analyzed and the feasibility of the transfer discussed as a function of the coordination pattern around the two metal centers. 

The CO insertion reaction into the metal hydride bond is in fact a member of the class of ligand insertion reactions to which much theoretical work has been devoted (28,29-35). Some years ago we analyzed the ethylene insertion into the rhodium hydride bond of a Rh(III) hexacoordinated complex (. We later focused our attention on the CO insertion reaction into the Mn-H bond ofHMn(CO)5 (37-39) and very recently we have undertaken the study of the CO2 insertion reaction into the Cr-H bond of HCr(CO)5 (C. Bo and A. Dedieu, Inorg. Chem., in press). We will concentrate here on the CO insertion reaction and compare it to the two other insertion reactions. The study of the reaction (1) was carried out at both the SCF and... 

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