Hydroformylation transition metal catalysts

Silylformylation, defined as the addition of RsSi- and -CHO across various types of bonds using a silane R3SiH, CO, and a transition metal catalyst, was discovered by Murai and co-workers, who developed the Co2(CO)8-catalyzed silylformylation of aldehydes, epoxides, and cyclic ethers [26]. More recently, as described in detail in Section 5.3.1, below, alkynes and alkenes have been successfully developed as silylformylation substrates. These reactions represent a powerful variation on hydroformylation, in that a C-Si bond is produced instead of a C-H bond. Given that C-Si groups are subject to, among other reactions, oxidation to C-OH groups, silylformylation could represent an oxidative carbonylation of the type described in Scheme 5.1. 

Various transition metal catalysts, including those based on Rh, Pt, Pd, Co, and Ti, have been bound to polymer supports—mainly through the phosphenation reaction described by Eq. 9-65 for polystyrene but also including other polymers, such as silica and cellulose, and also through other reactions (e.g., alkylation of titanocene by chloromethylated polystyrene). Transition-metal polymer catalysts have been studied in hydrogenation, hydroformylation, and hydrosilation reactions [Chauvin et al., 1977 Mathur et al., 1980]. 

For catalytic application where a transition metal catalyst is dissolved in the ionic liquid or the ionic liquid itself acts as the catalyst two additional aspects are of interest. Firstly, the special solubility properties of the ionic liquid enables a biphasic reaction mode in many cases. Exploitation of the miscibility gap between the ionic catalyst phase and the products allows, in this case, the catalyst to be isolated effectively from the product and reused many times. Secondly, the non-volatile nature of ionic liquids enables a more effective product isolation by distillation. Again, the possibility arises to reuse the isolated ionic catalyst phase. In both cases, the total reactivity of the applied catalysts is increased and catalyst consumption relative to the generated product is reduced. For example, all these advantages have been convincingly demonstrated for the transition metal catalysed hydroformylation [17]. 

This chapter focuses on the application of transition metal catalysts and enzymes for the formation of carbon-carbon bonds. Transition metal-catalyzed carbon-carbon bond formations are not always very green but they often replace even less favorable conventional approaches. The key to making them really green is that they have to be easily separable and reusable. Several of these reactions, such as the hydroformylation, oligomerisation, carbonylation of alcohols and the metathesis, are therefore also treated in Chapter 1, Section 1.8 and Chapter 7, since their greener variations are performed in novel reaction media. 

This reaciion was discovered in the late 1930s by Otto Roelen of Ruhrehemie, who was working on Fischer-Tropsch4ype chemistry. He found that alkencs can be converted to aldehydes by treatment with CO and H2 in the presence of a cobalt catalyst at elevated temperatures and pressures 12—14]. Today, in terms of product volume, hydroformylation represents one of the largest industrial applications of soluble transition metal catalysts. 

The hydroformylation of olefins is the most widely used homogeneous catalytic process using CO gas. It involves the addition of one molecule of CO and H2 to an olefin in the presence of a transition metal catalyst, most frequently based on cobalt or rhodium, resulting in the formation of an aldehyde. Generally, it is believed that the activation of H2 in cobalt-catalysed hydroformylation occurs on the unsaturated species Co2(CO)7 or Co(acylXCO)3 formed by the following reactions ... 

After publication of details of the biphasic catalytic hydroformylation system in 1994 many applications of the same concept were found. A variety of fluorous triaryl phosphane ligands was synthesized to enable recycling of precious transition metal catalysts [10b, 18] (Scheme 3.3). 

S. Kanagasabapathy, Studies in Oxidative Carbonylation and Hydroformylation Reactions Using Transition Metal Catalysts, Ph. D. Thesis, University of Pune,... 

Besides styrene, many other alkenyl and allyl aromatics can be hydroformylated with chirally modified transition metal catalysts. Depending on the substitution pattern, problems of regio- and stereoselectivity here are similar to those of styrene or aliphatic alkenes. The results are compiled in Table 5. 

Polymer supported transition metal catalysts Asymmetric hydroformylation or oxidation reactions d... 

Transition metal catalysts encapsulated within the ligand-template nanoreactor G, P(Py)s [ZnJs, have been applied to catalyze industrially relevant processes such as hydroformylation and Heck reaction. Nanoreactor [G 3 Rh(CO)(acac)] encapsulates a Rh-species that contains only one tris(meta-pyridyl)phosphine ligand, P(m-Py)3, surrounded by three Zn-porphyrins or Zn-salphens. Under syngas pressure (H2/CO), rhodium species like Rh(CO)(acac)P(Py)3 transform into a complex of type HRh(CO)3P(Py)3, which is the active species for the hydroformylation reaction, hi this reaction terminal alkenes are converted into linear and/or branched aldehydes, and the ratio of these products strongly depends on the specific catalyst applied. Hydroformylation of 1-octene by encapsulated rhodium, [G 3 HRh(CO)3], resulted in a 10-fold rate enhancanent compared... 

A. W. Kleij, M. Lutz, A. L. Spek, P. W. N. M. van Leeuwen, J. N. H. Reek, Encapsulated transition metal catalysts comprising peripheral Zn(ll)salen building blocks template-control-led reactivity and selectivity in hydroformylation catalysis, Chem. Common., 2005, 3661. 

Hydroformylation, the addition of H and CHO to an olefinic double bond, is the oldest and largest industrial process that involves homogeneous transition-metal catalysts. The original catalyst was derived from Co2(CO)g. Later, phosphine modification of the system was introduced to afford better product selectivity and lower operating pressures. Still later, related Rh systems were introduced. ... 

Due to its highly metal functionalized Si-0 framework 2 can be seen as a model compound for Si-O-supported transition metal catalysts. In first experiments we have studied the catalytic activity of 2 in the hydroformylation of 1-hexene. The experiments were performed in toluene at a temperature of 120°C and a reaction time of 18 h. The initial CO/H2 pressure at room temperature was 70-80 bar. The use of a catalyst formulation of 2 and triphenylphosphane in a 1 8 stoichiometry led to complete conversion of 1-hexene to the corresponding aldehydes. NMR and GC analyses of the hydroformylation products showed a 3 1 mixture of 1-heptanal and 2-methylhexanal had been formed. Filtration of the reaction mixture led to the isolation of a brownish solid, which still showed catalytic activity. According to IR spectroscopic results it is supposed that the catalytically active species formed in situ is a substitution product of 2 and triphenylphosphine. However, the mechanistic pathway of this catalysis is not yet understood. Experiments leading to a further understanding are under investigation. 

In the first reported example of gas-phase SILP hydroformylation with a homogeneous transition-metal catalyst, the starting material was propene [11]. The well-studied suUbxantphos ligand 6 was used here to modify and immobilize the rhodium catalyst complex in [BM IM][PFg] and halogen-free [BMIM][7t-CgH j OSOj]... 

In addition, a number of reports on the indole synthesis utilizing a similar concept of the in sUu generation of the key reactive arylhydrazones, similar to 284, with the aid of transition metal catalysts recently appeared in the literature. Among them, the domino Rh-catalyzed hydroformylation [263] of alkenes leading to aldehydes followed by a subsequent hydrazone formation and Fischer indolization process, which was introduced by Eilbracht [264—267] and later investigated by Beller [268], represents an attractive and efficient 3 + 1 + 1 approach for a one-pot construction of complex indoles. 

Supramolecular chemistry has been a very popular research topic for three decades now. Most applications are foreseen in sensors and opto-electronical devices. Supramolecular catalysis often refers to the combination of a catalyst with a synthetic receptor molecule that preorganizes the substrate-catalyst complex and has also been proposed as an important possible application. The concept, which has proven to be powerful in enzymes, has mainly been demonstrated by chemists that investigated hydrolysis reactions. Zinc and copper in combination with cyclodextrins as the receptor dramatically enhance the rate ofhydrolysis. So far, the ample research devoted to transition metal catalysis has not been extended to supramolecular transition metal catalysis. A rare example of such a supramolecular transition metal catalyst was the results of the joined efforts of the groups of Nolte and Van Leeuwen [SO], They reported a basket-shaped molecule functionalized with a catalytically active rhodium complex that catalyzed hydrogenation reactions according to the principles of enzymes. The system showed substrate selectivity, Michaelis Menten kinetics and rate enhancement by cooperative binding of substrate molecules. The hydroformylation of allyl catachol substrates resulted in a complex mixture of products. 

Hydroformylation of olefins [Eq. (69)] requires the presence of a transition metal catalyst. It is less successful with conjugated dienes than with noncon-... 

Because of the technical success of rhodium based hydroformylations, it is understandable that since the 1970s the vast majority of academic and industrial investigations in this area dealt with the development of new rhodium catalysts. However, the worldwide demand of rhodium for chemical and technical processes and its enormous price stimulate the search for alternative transition-metal catalysts up to now [1]. A particular focus was given to ruthenium [2]. 

Ricinoleic acid contains a hydroxyl function at a stereogenic carbon atom. Such additional functional groups may interact with transition-metal catalysts causing directing effects or lead to their deactivation. In the hydroformylation of ethyl ricinoleate, the formed aldehydes are converted immediately into cyclic ethers by acetalization and subsequent dehydration (Scheme 6.87) [36]. 

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