Metals in Hydroformylation

There are very many investigations in the literature concerning the evaluation of different metals and associated organic ligands in hydroformylation. In 2013, Franke and Seller [1] provided a concise summary about the applicability of alternative metals in hydroformylation. In the same year, another survey was assembled by a joint French/Italian cooperation [2]. In order to avoid a full repetition, only some basic conclusions will be mentioned here, which are not in the focus of the reviews cited above. 

In the early (mainly patent) literature, besides Co and Rh, Ni, Ir, and other metals of the VIII group, also Cr, Mo, W, Cu, Mn, and even Ca, Mg, and Zn were suggested or claimed for hydroformylation [3]. However, several of them do not exhibit any activity. 

Hydrcformylation Fundamentals, Processes, and Applications in Organic Synthes, First Edition. 

Noteworthy, the instability of HCo(CO)4 under the formation of Co2(CO)g can be attributed in part to the fast intermolecular elimination of H2- In this manner, also the formation of alkanes can be explained as a key step in the hydrogenation of olefins. On the other hand, the acidic properties of HCofCO) allow the convenient separation of product and catalyst after hydroformylation by conversion into water-soluble Co salts ( decobalting ) [10]. 

Strong acidic metal hydrido complexes such as HCofCO) or complexes with Lewis acid properties, such as Rh2Cl2(CO)4, [Ru(MeCN)3(triphos)](CF3S03)2, [Pt(H20)2(dppe)](CF3S03)2, [Pd(H20)2(dppe)](CF3S03)2, or [Ir(MeCN)3(tri-phos)] (CF3S03)3, are able to act in alcohols as acetahzation catalysts, which means they can mediate the transformation of the newly formed aldehydes into acetals (see Section 5.3). 

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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... 

Ungvary F (2004) Application of transition metals in hydroformylation annual survey. CCHRAM 248(9-10) 867-880... 

Bearing in mind the greater atomic radius of Rh, it becomes apparent why an unmodified rhodium catalyst generates a greater amount of branched aldehydes in comparison to the cobalt congener. For example, in the hydroformylation of 1-pentene, an Hb ratio of only 1.6 1 was found, while with the cobalt complex a ratio of 4 1 resulted. A similar correlation has been qualitatively deduced from reactions mediated by the metal clusters Rug(CO)j 2> 0 3(00)22, and 4(00)22. Because of the larger atomic radii of the metals, in hydroformylation these catalysts produce more branched aldehydes than observed in the reaction with Co2(CO)g. Unfortunately, most of these results were achieved under different reaction conditions or are difficult to interpret because of low reaction rates and are therefore not strictly comparable. 

Iron is one of the most abundant metals on earth. It occurs in 6wt% in the lithosphere and can be easily obtained from the corresponding ores. Because of the widespread occurrence and broad availability of iron, catalysts made from this material can be exceptionally cheap. Several attempts are described in the literature to use iron as a catalytically active metal in hydroformylation and related reactions. Unfortunately, up to now relevant catalysts have shown extremely low reactivity and the results do not suggest a suitable application. Two main approaches can be distinguished ... 

Annual reviews have appeared of organoruthenium and -osmium chemistry in 1988, organoiron chemistry in 1989, and transition metals in hydroformylation, oxidation and reduction in 1989. The latest in an annual series of reviews on the mechanisms of inorganic reactions also contains much relevant material. 9 An analysis of the structural systemadcs of 1292 complexes with PK13 ligands has appeared. ... 

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