Carbonylative catalysis

Styrene, a-ethyl-asymmetric hydroformylation catalysts, platinum complexes, 6, 266 asymmetric hydrogenation catalysts, rhodium complexes, 6, 250 Styrene, a-methyl-asymmetric carbonylation catalysis by palladium complexes, 6, 293 carbonylation... 

The antibiotic activity of certain (3-lactams depends largely on their interaction with two different groups of bacterial enzymes. (3-Lactams, like the penicillins and cephalosporins, inhibit the DD-peptidases/transpeptidases that are responsible for the final step of bacterial cell wall biosynthesis.63 Unfortunately, they are themselves destroyed by the [3-lactamases,64 which thereby provide much of the resistance to these antibiotics. Class A, C, and D [3-lactamases and DD-peptidases all have a conserved serine residue in the active site whose hydroxyl group is the primary nucleophile that attacks the substrate carbonyl. Catalysis in both cases involves a double-displacement reaction with the transient formation of an acyl-enzyme intermediate. The major distinction between [3-lactamases and their evolutionary parents the DD-peptidase residues is the lifetime of the acyl-enzyme it is short in (3-lactamases and long in the DD-peptidases.65-67... 

However, when a less active olefin (e.g., diisobutylene or cyclohexene) or a liganded system (Bu3P/Co = 2/1,80 atm CO/H2, 190°C) was used, the hydrido species, e.g., HCo(CO)3PBu3, predominated throughout the reaction. The author concluded that in slower systems, initial interaction of the olefin with the hydrido species HCo(CO)3L could be the ratedetermining step. These results are complementary to those discussed (vide supra) for the rhodium carbonyl catalysis. 

Keywords Carbonylation Catalysis Rhodium Iridium Mechanism... 

The commercialisation of an iridium-based process is the most significant new development in methanol carbonylation catalysis in recent years. Originally discovered by Monsanto, iridium catalysts were considered uncompetitive relative to rhodium on the basis of lower activity, as often found for third row transition metals. The key breakthrough for achieving high catalytic rates for an iridium catalyst was the identification of effective promoters. Recent mechanistic studies have provided detailed insight into how the promoters influence the subtle balance between neutral and anionic iridium complexes in the catalytic cycle, thereby enhancing catalytic turnover. 

In this chapter we will discuss some aspects of the carbonylation catalysis with the use of palladium catalysts. We will focus on the formation of polyketones consisting of alternating molecules of alkenes and carbon monoxide on the one hand, and esters that may form under the same conditions with the use of similar catalysts from alkenes, CO, and alcohols, on the other hand. As the potential production of polyketone and methyl propanoate obtained from ethene/CO have received a lot of industrial attention we will concentrate on these two products (for a recent monograph on this chemistry see reference [1]). The elementary reactions involved are the same formation of an initiating species, insertion reactions of CO and ethene, and a termination reaction. Multiple alternating (1 1) insertions will lead to polymers or oligomers whereas a stoichiometry of 1 1 1 for CO, ethene, and alcohol leads to an ester. 

In the present review we shall describe recent developments in the catalysis of reactions by dicobalt octacarbonyl. Although many of the reactions to be described do not necessarily involve dicobalt octacarbonyl directly in the catalytic cycle, but some derivative, there are several reasons for choosing this compound as a starting point. The most important reason being that dicobalt octacarbonyl is a reasonably stable, commercially available, fairly well characterized compound which easily gives active catalytic intermediates. Although by no means unique in their catalytic properties, the cobalt carbonyls do provide a particularly active and versatile example of metal carbonyl catalysis. Their catalytic reactions are also by far the most investigated and best understood. 

Although the homogeneous catalyst systems have been successfully applied in commercial practice, some intrinsic problems associated with catalyst separation remain. This has led to considerable interest in the development of a suitable heterogeneous analog. Rhodium compounds have been heterogenenized on substrates such as carbon (197), alumina (198, 199), and synthetic polymers (200). More recently, zeolites have also attracted quite some attention as a support material for carbonylation catalysis, as is discussed later. 

Carbonylation catalysis encompasses a large and important area of chemistry. Unlike many other catalytic reactions,... 

The most significant advances in carbonylation catalysis in the next several years will undoubtedly occur in the area of novel ligand systems, new solvents, and asymmetric induction, which will be briefly covered here see Asymmetric Synthesis by Homogeneous Catalysis). 

The production of carboxylic acids via carbonylation catalysis is the second most important industrial homogeneous group of processes. Reppe developed most of the basic carbonylation chemistry in the 1930s and 1940s. The first commercial carbonylation process was the stoichiometric Ni(CO)4-based hydroxycarbonylation of acetylene to give acrylic acid (see Section 3.5 for details). This discovery has since evolved into a trae Ni-catalyzed process, used mainly by BASF. The introduction of rhodium catalysts in the 1970s revolutionized carboxylic acid production, particularly for acetic acid, much in the same way that Rh/PPhs catalysts changed the importance of hydroformylation catalysis. 

In a very elegant mechanistic study by Ojima et al., involving the amidocarbonylation of three structurally related cyclic amides having methallyl side chains (utilizing cobalt carbonyl catalysis) they have demonstrated [23] that coordination of the amide carbonyl to the cobalt metal is essential for amidocarbonylation, whereas lactame formation is not. A general mechanism of amidocarbonylation, featuring the very unique hydrolysis (alcoholysis) of the acyl-cobalt bond by water (or alcohol) generated in situ, is reproduced in Scheme 1 [23]. 

Krafft, M. E., Bonaga, L. V., Hirosawa, C. Practical cobalt carbonyl catalysis in the thermal Pauson--Khand reaction efficiency enhancement using Lewis bases. J. Org. Chem. 2001,66, 3004-3020. 

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). 

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