Metal alkenes hydroformylation

Although most of the reports that have appeared since 1980 on hydroformylation of alkenes focus on rhodium catalysts, alkene hydroformylation catalyzed by Ptn complexes in the presence of Sn11 halides has been the object of great interest and platinum can be considered as the second metal in hydroformylation.77-79... 

Amidocarbonylation converts aldehydes into amido-substituted amino acids, which have many important industrial applications ranging from pharmaceuticals to detergents and metal-chelating agents.588 Two catalyst systems have been developed, a cobalt-based system and, more recently a palladium-based system. In the cobalt system, alkenes can be used as the starting material, thus conducting alkene-hydroformylation, formation of hemi-amidal and carbonylation in one pot as... 

Figure 1.13 Generation of rhodium-based supramolecularcatalysts by assembly of pyridine/hydroxypyridine pairs (a) Self-assembly modes of pyridine-based phosphines, (b) Alkene hydroformylation with supramolecular rhodium-diphosphine catalysts (c) CAChe minimized 3D structure ofthe rhodium-diphosphine complex (other ligands from the metal omitted for clarity).

A number of metals catalyze the hydroformylation reaction, of which rhodium is by far the most active, Rh >> Co > Ir, Ru > Os > Pt. Platinum and ruthenium are mainly of academic interest, although L2PtCl(SnCl3) complexes with chiral ligands find use in asymmetric alkene hydroformylations.59 In most cases, and certainly in industrial processes, cobalt has now been replaced by rhodium. 

The metal complexes most often studied as polymer-bound catalysts have been Rh(I) complexes, such as analogues of Wilkinson s complex. The catalytic activity of a bound metal complex is nearly the same as that of the soluble analogue. Rhodium complexes are active for alkene hydrogenation, alkene hydroformylation, and, in the presence of CH3I cocatalyst, methanol carbonylation, etc. Polymer supports thus allow the chemistry of homogeneous catalysis to take place with the benefits of an insoluble, easily separated catalyst . ... 

The inertness of SC-CO2 is also useful for metal-catalyzed hydroformylations and hydrogenations of alkenes to the corresponding aldehydes. Selective hydroformylations were obtained with Co catalysts. [26] They profit from the good miscibility in SC-CO2 (Scheme... 

Other Metal Catalysts. - Hydroformylation catalysts containing Co and Rh have been known for many years and these metals are the only catalysts used industrially. Recently two catalyst systems have been developed that have certain advantages over the conventional catalysts. Pt/Sn chloride complexes show very high selectivity to n-aldehyde. and Reppe-type systems which hydroformylate alkenes in the presence of CO/H2O rather than CO/H2. ... 

The discovery of hydroformylation by Otto Roelen was made while investigating the influence of alkenes on the Fischer-Tropsch reaction using a heterogeneous cobalt oxide catalyst supported on silica. Later it was concluded that hydroformylation is actually a homogeneous process catalyzed by ECo(CO) formed in situ. Many metals catalyze hydroformylation, but the most active catalysts contain cobalt, rhodium, palladium, and platinum as the central metal. The discussion in this chapter centers on the most utilized catalysts ECo(CO), ECo(CO)3PR3, ERh(CO)3(PR3)j, and HRhfCOljfdiphosphine). 

Most molecular metd clusters are metal carbonyls, and the CO ligands help to stabilize the metal frames. Consequently, it is logical to suppose that reactions involving CO might be good candidates for cluster catalysis. This supposition is, at least partially, borne out by the observations. Metal carbonyl clusters in solution are catalysts or catalyst precursors for alkene hydroformylation (Eq. 4.7) and the water-gas shift reaction (Eq. 4.8). [109, 110]... 

The following reactions of olefins have also been studied formation of dialkyl adducts (517) from vinyl monomers and dienes with lithium metal and alkyl bromides in THF alkylsulphonium salts (518) from thioethers and protonated alkenes hydroformylation of styrene and a-methylstyrene in the presence of bis-(iV-a-methylbenzylsalicylaldiminato)cobalt(n) to give 2-phenylpropanal (optical purity 1.9%) and 3-phenylbutanal (optical purity 2.9%) various electron-rich olefins of the type (519) with primary amines... 

The rates of olefin hydrogenation and isomerization by Group VIII metal-phosphine complexes are increased by the presence of hydroperoxides and/or oxygen. A similar rate enhancement is observed in the hydroformylation of alkenes catalysed by [RhCl(CO)(PPh3)2]. The addition of small amounts of cyclohexenyl hydroperoxide is considered to effect the unusual transformation of [RhCl(CO)(PPh3)2] to cw-[RhCl(CO)2(PPh3)], which appears to be a very active alkene hydroformylation and isomerization catalyst. Asymmetric induction in hydroformylation reactions has been achieved. ... 

Thus the answer to the first question posed in the introduction is clear no totally new catalytic activities or selectivities have been observed as a consequence of the use of molecular metal clusters as catalyst precursors. Indeed, in general the catalytic activity of metal clusters does appear to be rather low in reactions for which comparisons with mononuclear counterparts have been possible, e.g., alkene hydroformylation. 

Arsine complexes are especially stable for b-class metals such as Rh, Pd and Pt, and such complexes have found considerable industrial use in hydrogenation or hydroformylation of alkenes. 

The reverse reaction (formation of metal alkyls by addition of alkenes to M-H) is the basis of several important catalytic reactions such as alkene hydrogenation, hydroformylation, hydroboration, and isomerization. A good example of decomposition by y3-elimination is the first-order intramolecular reaction ... 

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