Hydroformylation and related carbonylation reactions

Hydroformylation and Related Carbonylation Reactions.—Reviews on the synthesis of commercially important organic intermediates via rhodium-catalysed hydroformylation reactions, carbonylations with triarylphosphine-palladium catalysts, diene carbonylations, and heterogenized rhodium catalysts for methanol carbonylation have been published. 

Carbonylation of propene in hexane-MeOH-HgO gives mainly PrC02Me when catalysed by [Ru Fe3 n(CO)i2]+CuCl2 [activity n=2 n=l]. [Ru-(TPP)(PPh3)2l is an efficient catalyst for the decarbonylation of aldehydes cleavage of the aldehyde C-H bond may be involved since non-aromatic substrates give a mixture of products, e.g., heptanal gives n-hexane (65%), iso- 

Yoshida, T. Okano, K. Saito, and S. Otsuka, Inorg. Chim. Acta, 1980, 44, LI 35. 

Starchevskii, M. N. Vargaftik, and 1.1. Moiseev, Izv. Akad. Nauk SSSR, Ser. Khim., 

The carbonylation of nitrobenzene to phenyl isocyanate is catalysed by [RhCl(CO)2]2 + L (L=MoCl6 or py.H+Cl- ), [RhH(CO)(PPh3)3], = and PdCl2-pyMe+ Carbonylation of allylic substrates has also been studied in detail rhodium phosphine complexes [e.g., RhCl(PPh3)s] are particularly useful for the synthesis of AT-alkyl-2-pyrrolidones [reactions (6)], whereas the carbonylations of allylic alcohols to vinylacetate esters [reaction (7)] are best carried out with [PdCl2(PAr3)a]10MCl2 (M=Sn or Ge).  

Hydroformylation and related carbonylation reactions Treatment of olefins with carbon monoxide and hydrogen under pressure and in the presence of dicobalt octacarbonyl gives mainly aldehydes or ketones. Alcohols and paraffins are formed as by-products. The hydroformylation of olefins to aldehydes is of considerable industrial importance. The prediction that cobalt tetracarbonyl hydride was a catalyst in these reactions [93, 94] has been amply verified for example the stoicheio-metric hydroformylation of 1-pentene by HCo(CO)4 proceeds at room temperature giving isomeric alddiydes [95]. It has been shown that HCo(CO)4 is formed under the hig pressure (100 atm. 1 1 H2 CO) and temperature (100-300°) conditions used in hydroformylation reactions [95, 96]. 

Recent investigation of the chemistry of alkyl and acyl cobalt carbonyl complexes by Heck and co-workers provides considerable insight into the detailed mechanisms in hydroformylation reactions. They have shown that the following equilibria occur  

On the basis of kinetic studies [97] and from the observation that ethyl-cobalt tetracarbonyl decomposes reversibly to ethylene and HCo(CO)4 [97], it appears that there are the equilibria. 

On the basis of these equilibria the following formal mechanism for hydroformylation of ethylene has been proposed  

The formation of alcohols during hydroformylation reactions may become the major reaction at higher temperatures [101,102], 

As was mentioned earlier (p 189), an important property of transition metal a-alkyls is their ability to rmdergo insertion reactions, especially with carbon monoxide, when acyl complexes are formed. Frequently such carbonylation reactions are reversible. Studies on the decarbonylation of acetylmanganese pentacarbonyl labelled with in the acetyl-CO group indicate that this carbonyl group is retained in the molecule as a carbon monoxide ligand  

Similar carbonylations can be effected by treatment of transition metal 7-alkyls with ligands other than carbon monoxide, e.g. triphenyl phosphine, phosphites, primary amines or iodide ion  

The above experiments, together with kinetic and infrared studies indicate that carbonylation and decarbonylation are intramolecular processes. Two main mechanisms for the carbonylation can be envisaged— carbonyl insertion (a) or methyl migration (b)  

Infrared studies using tracers are in agreement with the methyl migration mechanism (b) for both the carbonylation and decarbonylation processes. A similar mechanism has been proposed for the conversion of tr w-MeCOMn(CO)4PPh3 into cw-MeMn(CO)4PPh3  

Many other a-alkyl complexes behave similarly, although the ease of carbonylation (or decarbonylation of the acyl derivatives) varies quite widely with the nature of the complex. Thus F3CCOG (CO)4 decarbonyl-ates at 30 C whereas F3CCOG)(CO)3PPh3 does not begin to lose carbon monoxide below about 130 C. 

---

The importance of these and related processes in hydroformylation and other carbonylation reactions has been underscored by several reviewers 62,115,118) and will not be reiterated here. 

The hydroformylation of alkenes generally has been considered to be an industrial reaction unavailable to a laboratory scale process. Usually bench chemists are neither willing nor able to carry out such a reaction, particularly at the high pressures (200 bar) necessary for the hydrocarbonylation reactions utilizing a cobalt catalyst. (Most of the previous literature reports pressures in atmospheres or pounds per square inch. All pressures in this chapter are reported in bars (SI) the relationship is 14.696 p.s.i. = 1 atm = 101 325 Pa = 1.013 25 bar.) However, hydroformylation reactions with rhodium require much lower pressures and related carbonylation reactions can be carried out at 1-10 bar. Furthermore, pressure equipment is available from a variety of suppliers and costs less than a routine IR instrument. Provided a suitable pressure room is available, even the high pressure reactions can be carried out safely and easily. The hydroformylation of cyclohexene to cyclohexanecarbaldehyde using a rhodium catalyst is an Organic Syntheses preparation (see Section 4.5.2.5). 

Hydroformylation, the Water-gas Shift Reaction, Fisdier-Tropsch, and Related Carbonylation Reactions... 

Metal-catalyzed reactions of CO with organic molecules have been under investigation since the late 1930s and early 1940s, when Roelen (/) discovered the hydroformylation reaction and Reppe (2) the acrylic acid synthesis and other related carbonylation reactions. These early studies of the carbonyla-tions of unsaturated hydrocarbons led to extremely useful syntheses of a variety of oxygenated products. Some of the reactions, however, suffered from the serious problem that they produced isomeric mixtures of products. For example, the cobalt-catalyzed hydroformylation of propylene gave mixtures of n-butyraldehyde and isobutyraldehyde. 

Several excellent comprehensive reviews that include the hydroformylation reaction and related reactions of carbon monoxide have appeared in the past decade.1-2 Because of the industrial importance of these reactions, much of the literature is process oriented and has focused on the carbonylation of simple alkenes derived from petroleum feedstock. 

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-... 

New functionalizing reactions with carbon monoxide to give carbonyl compounds, in addition to hydroformylation, have been developing rapidly during the past ten years, but mainly for laboratory-scale synthesis. Industrial applications of carbon monoxide in the synthesis of fine chemicals have been until now rare. In this section, applications of the carbonylation of benzyl-, aryl-, and related vinyl-and allyl-X compounds are discussed [1]. Emphasis is given especially to a fundamental understanding and to technically interesting developments. 

Research in the Organic Chemistry Section involved the structure of coal, the chemistry and separation of the complex mixtures of organic molecules from CH, metal carbonyls, and homogeneous catalysis. The chemistry and structure of carbonyls and related compounds were determined, and the kinetics and mechanisms of the hydroformylation reactions was elucidated. The section was directed by Dr. Milton Orchin until 1953 and subsequently by Dr. Irving Wender. Dr. Heinz Sternberg made valuable contributions to this research. 

It is generally agreed that Roelen s discovery of the hydroformylation reactiont was the birth of the transition metal-catalyzed carbonylation. Initially, Co catalysts were most extensively used, but the Rh-based processes have since been developed as a superior methods. Although Pd may have been tested along with several other metals, such as Fe, Ru, and Ni, it has never been shown to be very useful in the hydroformylation reaction, sometimes called the oxo process. A publication in 1963 by Tsuji et al. on a related but clearly different reaction of alkenes with CO and alcohols in the presence of a Pd catalyst producing esters was one of the earliesL if not the earliesL reports describing a successful and potentially useful Pd-catalyzed carbonylation reaction. This was soon followed by the discovery of another Pd-catalyzed carbonylation reaction of allylic electrophiles with CO and alcohols ° (Scheme 7). 

The steps in the hydroformylation reaction are closely related to those that occur in the Fischer-Tropsch process, which is the reductive conversion of carbon monoxide to alkanes and occurs by a repetitive series of carbonylation, migration, and reduction... 

Since 1985, several thousands of publications have appeared on complexes that are active as catalysts in the addition of carbon monoxide in reactions such as carbonylation of alcohols, hydroformylation, isocyanate formation, polyketone formation, etc. It will therefore be impossible within the scope of this chapter to review all these reports. In many instances we will refer to recent review articles and discuss only the results of the last few years. Second, we will focus on those reports that have made use explicitly of coordination complexes, rather than in situ prepared catalysts. Work not containing identified complexes but related to publications discussing well-defined complexes is often mentioned by their reference only. Metal salts used as precursors on inorganic supports are often less well defined and most reports on these will not be mentioned. 

Rhodium cationic and zwitteiionic complexes proved to be superior catalysts for the hydroformylation of vinylsilanes, producing either a- or ff-silyl aldehydes depending on the reaction conditions [162], On the other hand, carbonylation of vinylsilanes in the reaction related to hydrocarboxylation and hydroesterification afforded P- and a-silyl esters in high yields (eq. (14) [163]). 

In a first approximation, the new methods correspond to the conventional solvent techniques of supported catalysts (cf Section 3.1.1.3), liquid biphasic catalysis (cf Section 3.1.1.1), and thermomorphic ( smart ) catalysts. One major difference relates to the number of reaction phases and the mass transfer between them. Owing to their miscibility with reaction gases, the use of an SCF will reduce the number of phases and potential mass transfer barriers in processes such as hydrogenation, carbonylations, oxidation, etc. For example, hydroformylation in a conventional liquid biphasic system is in fact a three-phase reaction (g/1/1), whereas it is a two-phase process (sc/1) if an SCF is used. The resulting elimination of mass transfer limitations can lead to increased reaction rates and selectiv-ities and can also facilitate continuous flow processes. Most importantly, however, the techniques summarized in Table 2 can provide entirely new solutions to catalyst immobilization which are not available with the established set of liquid solvents. 

---