Rhodium compounds, catalysis hydroformylation

Rhodium complexes with chiral dithiolato and dithiother ligands have been studied in rhodium-catalyzed asymmetric hydroformylation. In all instances, enantioselectivities were low.391-393 Catalysis with compounds containing thiolate ligands has been reviewed.394... 

A set of core-functionalized dendrimers was synthesized by Van Leeuwen et al. and one compound was applied in continuous catalysis. [45] The dendritic dppf, Xantphos and triphenylphosphine derivatives (Figures 4.22, 4.30 and 4.31) were active in rhodium-catalyzed hydroformylation and hydrogenation reactions (performed batch-wise). Dendritic effects were observed which are discussed in paragraph 4.5. The dendritic rhodium-dppf complex was applied in a continuous hydrogenation reaction of dimethyl itaconate. 

Today, iridium compounds find so many varied applications in contemporary homogeneous catalysis it is difficult to recall that, until the late 1970s, rhodium was one of only two metals considered likely to serve as useful catalysts, at that time typically for hydrogenation or hydroformylation. Indeed, catalyst/solvent combinations such as [IrCl(PPh3)3]/MeOH, which were modeled directly on what was previously successful for rhodium, failed for iridium. Although iridium was still considered potentially to be useful, this was only for the demonstration of stoichiometric reactions related to proposed catalytic cycles. Iridium tends to form stronger metal-ligand bonds (e.g., Cp(CO)Rh-CO, 46 kcal mol-1 Cp(CO)Ir-CO, 57 kcal mol ), and consequently compounds which act as reactive intermediates for rhodium can sometimes be isolated in the case of iridium. 

Optically active aldehydes are important precursors for biologically active compounds, and much effort has been applied to their asymmetric synthesis. Asymmetric hydroformylation has attracted much attention as a potential route to enantiomerically pure aldehyde because this method starts from inexpensive olefins and synthesis gas (CO/H2). Although rhodium-catalyzed hydrogenation has been one of the most important applications of homogeneous catalysis in industry, rhodium-mediated hydroformylation has also been extensively studied as a route to aldehydes. 

Hydroformylation - [CARBON MONOXIDE] (Vol 5) - [OXO PROCESS] (Vol 17) -of allyl alcohol [ALLYL ALCOHOL AND MONOALLYL DERIVATIVES] (Vol 2) -catalysts for [CATALYSIS] (Vol 5) -C-19 dicarboxylic acids from [DICARBOXYLIC ACIDS] (Vol 8) -of ethylene [ETHYLENE] (Vol 9) -of ethylene [PROPYL ALCOHOLS - N-PROPYLALCOLHOL] (Vol 20) -of maleate and fumarate esters [MALEIC ANHYDRIDE, MALEIC ACID AND FUMARIC ACID] (Vol 15) -phosphine catalyst [PHOSPHORUS COMPOUNDS] (Vol 18) -platinum-group metal catalysts for [PLATINUM-GROUP METALS] (Vol 19) -rhodium catalysis [PLATINUM-GROUP METALS, COMPOUNDS] (Vol 19) -ruthenium cmpds or catalyst [PLATINUM-GROUP METALS, COMPOUNDS] (Vol 19) -use of coordination compounds [COORDINATION COMPOUNDS] (Vol 7)... 

For hydroformylation over cobalt and rhodium zeolites the active species have not been defined. However, in the case of RhNaY the in situ formation of a rhodium carbonyl cluster has been identified (226) by infrared spectroscopy. Interestingly, this cluster appears to be different from known compounds such as Rh4(CO)12 and Rh6(CO)16. This does suggest that alternative carbonyl clusters may possibly be formed in zeolites due to the spatial restrictions of the intracrystalline cavities. The mechanism of hydroformylation in these zeolites is probably similar to that known for homogeneous catalysis. 

Although ruthenium is significantly less expensive than rhodium and although its use has been recommended since 1960 (7) for the oxo synthesis, complexes of this metal have not been developed as catalysts. However, many papers and patents have referred to the results obtained employing various ruthenium complexes. The purpose of this article is to analyze the work done involving ruthenium compounds, restricting the scope only to the hydroformylation reaction and not to the carbonylation reaction, which would demand to too lengthy an article. In this review we examine successively mononuclear ruthenium complexes, ruthenium clusters as precursors, photochemical activation, and supported catalysis. 

Among the most significant developments in the field of catalysis in recent years have been the discovery and elucidation of various new, and often novel, catalytic reactions of transition metal ions and coordination compounds 13, 34). Examples of such reactions are the hydrogenation of olefins catalyzed by complexes of ruthenium (36), rhodium (61), cobalt (52), platinum (3, 26, 81), and other metals the hydroformylation of olefins catalyzed by complexes of cobalt or rhodium (Oxo process) (6, 46, 62) the dimerization of ethylene (i, 23) and polymerization of dienes (15, 64, 65) catalyzed by complexes of rhodium double-bond migration in olefins catalyzed by complexes of rhodium (24,42), palladium (42), cobalt (67), platinum (3, 5, 26, 81), and other metals (27) the oxidation of olefins to aldehydes, ketones, and vinyl esters, catalyzed by palladium chloride (Wacker process) (47, 48, 49,... 

Using phosphite-modified rhodium catalysts, otherwise unreactive alkenes, such as 2-methyl-l-hexene, limonene and cyclohexene, are hydroformylated under mild conditions. " 2-Methyl-1-hexene, for example, yields almost exclusively 3-methylheptaldehyde, which is in contrast to the result of cobalt catalysis where a compound with a quaternary carbon is formed (Scheme 12). 

Enhanced catalytic activity has also been observed for the hydroformylation of oct-l-ene and dec-l-ene with water-soluble phosphine-caltK[4]arene—rhodium complexes (Figure 32). " These organometallic compounds behave, not only as homogeneous metal catalysts but also as inverse phase-transfer catalysts, that is, they perform a dual functional catalysis. The olefin is believed to be included in the hydrophobic cavity and to simultaneously interact with a catalytic transition metal center coordinated to the phosphine moieties. 

ExxonMobil Biphasic carbonylation catalysis using conventional rhodium catalysts in Lewis-acidic ionic liquids, the electrochemical oxidation of sulfur compounds in naphtha, the use of supported ionic liquids, catalytic hydroformylation, hydrogenations, aldol condensations, and even ionic liquid synthesis... 

Carbon dioxide is a ubiquitous and environmentally benign compound. Several attempts have been made to use it as medium or as support for individual steps of the hydroformylation. The acidic properties of CO2 in solution have been advantageously employed to remove homogeneous catalysts with basic properties from the neutral organic reaction products (see Section A Posteriori Separation of Products and Catalysts ). BASF claimed supercritical carbon dioxide (SCCO2) for the extraction of the so-called heavy ends from low-boiling hydroformylation products and rhodium catalyst [55]. In recent years, also implementations of reactions in compressed carbon dioxide in supercritical or near-critical conditions have attracted particular attention [56]. A first review on the application of supercritical fluids (SFCs) in homogeneous catalysis was authored by Jessop, Ikariya, and Noyori in 1999 [57]. Later on, Leitner and Abraham [58,59] provided updates with special focus on the use of compressed carbon dioxide. 

Biphasic catalysis in the presence of water-soluble catalysts has been the most significant development in recent years. After the report of Kuntz on the synthesis of sulfonated triarylphosphine TPPTS (Figure 14.1) and its successful industrial application in Rh-catalyzed hydroformylation of propene, great attention has been focused on the scientific study and industrial application of water-soluble catalysts, especially on water-soluble phosphines [6, 7], phosphites, and other phosphide compounds as well as their rhodium complexes [8]. Among them, TPPTS is the most widely studied and applied. Other important phosphine hgands will he introduced later. 

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