Hydroformylation and Related Carbonylation

The hydroformylation reaction or 0x0 process is an important industrial synthetic tool. Starting from an alkene and using syngas, aldehydes with one or more carbon atoms are obtained. In almost all industrial processes for the hydroformylation of alkenes, rhodium or cobalt complexes are used as catalysts [33]. A number of studies on ruthenium complex-catalyzed hydroformylation have been reported [34]. One of the reasons for the extensive studies on ruthenium complex catalysts is that, although the rhodium catalysts used in industry are highly active, they are very expensive, and hence the development of a less-expensive catalytic system is required. Since inexpensive ruthenium catalysts can achieve high selectivity for desired u-alde-hydes or n-alcohols, if the catalytic activity can be improved to be comparable with that of rhodium catalysts, it is possible that a ruthenium-catalyzed 0x0 process would be realized. 

The ruthenium complex-catalyzed hydroformylation of 1-alkene was first examined by Wilkinson s group. Ru(CO)3(PPh3)2/phosphine catalysts were found to have moderate catalytic activity [35-37]. Ru3(CO)i2 [38] and anionic hydridocluster complexes such as [NEt4][Ru3H(CO)ii] [39] have also been shown to have catalytic activity. In molten phosphonium salt, Ru3(CO)i2/2,2 -bipyridine has high catalytic activity [40]. The Ru3(CO)i2/l,10-phenanthroline catalyst in N,N-dimethylacetamide (DMAC) shows excellent activity and selectivity for u-aldehydes (Eq. 11.10) [41]. 

The hydroformylation of alkene proceeds under ultra-violet (UV) irradiation (200 W, Hg-Xe lamp) with a Ru(CO)3(PPh3)2, Ru(CO)4(PPh3) or Ru3(CO)i2 catalyst system at a low pressure of CO at ambient temperature. In the reaction of propylene, the n/i ratio was 3.9 (Eq. 11.11) [42]. 

A bimetallic system of Ru3(CO)i2/Co2(CO)g shows high catalytic activity for the hydroformylation of cydohexene. Synergistic effects may play an important role in the insertion of alkene into a hydrido-metal bond [43], 

The bimetallic catalyst system Ru3(CO)i2/Co2(CO)g catalyzes the reaction of terminal acetylenes with methyl iodide and 1 atm of CO under phase-transfer conditions to give y-oxocarboxylic add (Eq. 11.12) [44]. 

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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. 

E. 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]. 

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. 

Fig. 22. Catalytic performances of ZnO- and carbon-supported Rh, bimetallic RhCo, and Co carbonyl clusters [RhsICO),, Rh4, Co,(CO),2] for propene hydroformylation (C3H / CO/H2 ratio 1 1 I, total pressure 0.8 atm at I52°C). For specific rates, open circles relate to carbon-supported and filled circles to ZnO-supported catalysts. For n-isomer selectivities, open squares relate to carbon-supported and filled squares relate to ZnO-supported catalysts.

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. 

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. 

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