Alkenes, metal catalyzed hydroformylation

Alkenes, Rh-catalyzed hydroformylations, 7, 249 Alkene-vinylcyclobutanone, in [6+2]-cycloadditions, 10, 624 Alkene-vinylcyclopropanes, metal-catalyzed [5+21-... 

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... 

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). 

The first example of homogeneous transition metal catalysis in an ionic liquid was the platinum-catalyzed hydroformylation of ethene in tetraethylammonium trichlorostannate (mp. 78 °C), described by Parshall in 1972 (Scheme 5.2-1, a)) [1]. In 1987, Knifton reported the ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [Bu4P]Br, a salt that falls under the now accepted definition for an ionic liquid (see Scheme 5.2-1, b)) [2]. The first applications of room-temperature ionic liquids in homogeneous transition metal catalysis were described in 1990 by Chauvin et al. and by Wilkes et ak. Wilkes et al. used weekly acidic chloroaluminate melts and studied ethylene polymerization in them with Ziegler-Natta catalysts (Scheme 5.2-1, c)) [3]. Chauvin s group dissolved nickel catalysts in weakly acidic chloroaluminate melts and investigated the resulting ionic catalyst solutions for the dimerization of propene (Scheme 5.2-1, d)) [4]. 

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... 

Transition-metal-catalyzed carbonylations are of great importance in organic synthesis as a powerful tool to prepare a variety of carbony compounds. Among them, hydroformylation has been most extensively studied not only in the laboratory but also in industry. Industrial production of alkanals from 1-alkenes... 

During a study of the origin of oxygenates in Fischer-Tropsch synthesis in the presence of a cobalt catalyst, Roelen observed the formation of propanal and 3-penta-none when ethylene was added to the feed.1 The process now termed hydroformylation or oxo reaction is the metal-catalyzed transformation of alkenes with carbon monoxide and hydrogen to form aldehydes ... 

Despite some differences, the mechanism of rhodium-catalyzed hydroformylation is very similar to that of the cobalt-catalyzed process.39-42 Scheme 7.1 depicts the so-called associative route which is operative when the ligand is in excess. Rhodium metal and many Rh(I) compounds serve as precursor to form21,22—in the presence of triphenylphosphine, CO and H2—the active species [RhH(CO)(PPh3)3] (5). At high CO partial pressure and low catalyst concentration without added PPh3, the [RhH(CO)2(PPh3)] monotriphenylphosphine complex instead of 6 coordinates the alkene and participates in the so-called dissociative route.21,39... 

Alkenes and Dienes. Alkenes exhibit lower reactivity in metal-catalyzed carboxylation than in hydroformylation. The general reactivity pattern of different alkenes, however, is the same terminal linear alkenes are the most reactive substrates. Cycloalkenes are the least reactive, but strained compounds may react under very mild conditions 128... 

An example is the rhodium catalyzed hydroformylation reaction, which is an industrially important homogenous catalytic process [3]. In contrast, it is amazing that such an important transition-metal catalyzed C/C bond-forming process has been employed only rarely in organic synthesis [4]. Part of the reason stems from the difficulty in controlling stereoselectivity. Even though some recently developed chiral rhodium catalysts allow for enantio- and diastereoselective hydroformylation of certain specific classes of alkenes [5, 6], only little is known about the diastereoselective hydroformylation of acyclic olefins [7, 8]. 

Ruthenium is not an effective catalyst in many catalytic reactions however, it is becoming one of the most novel and promising metals with respect to organic synthesis. The recent discovery of C-H bond activation reactions [38] and alkene metathesis reactions [54] catalyzed by ruthenium complexes has had a significant impact on organic chemistry as well as other chemically related fields, such as natural product synthesis, polymer science, and material sciences. Similarly, carbonylation reactions catalyzed by ruthenium complexes have also been extensively developed. Compared with other transition-metal-catalyzed carbonylation reactions, ruthenium complexes are known to catalyze a few carbonylation reactions, such as hydroformylation or the reductive carbonylation of nitro compounds. In the last 10 years, a number of new carbonylation reactions have been discovered, as described in this chapter. We ex-... 

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. 

Metal enolates have played a Umited role in the metal-catalyzed isomerization of al-kenes . As illustrated in a comprehensive review by Bouwman and coworkers, ruthenium complex Ru(acac)3 (51) has been used to isomerize a wide range of substituted double bonds, including aUylic alcohols (131), to the corresponding ketones (132) (equation 38) . The isomerization of aUylic alcohols affords products that have useful applications in natural product synthesis and in bulk chemical processes. An elegant review by Fogg and dos Santos shows how these complexes can be used in tandem catalysis, where an alkene is subjected to an initial isomerization followed by a hydroformylation reaction ... 

As an introduction, it is of interest to report the special influence of the position of a functionality, taking as an example the phosphonation of 1-phosphanorbornadiene 1 [4]. This molecule has shown very good properties as a ligand for transition-metal catalyzed hydrogenation [5] and hydroformylation [6] of alkenes. 

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