Alkenes hydrogenation, homogeneous catalysis

The reaction between alkenes and synthesis gas (syngas), an equimolar mixture of carbon monoxide and hydrogen, to form aldehydes was discovered in 1938 by Otto Roelen [1,2]. Originally called oxo-reaction , hydroformyla-tion is the term used today. This reflects the formal addition of formaldehyde to the olefinic double bond. Commercially, homogeneous metal complexes based on cobalt and rhodium are used as catalysts. With more than 10 million metric tons of oxo products per year, this reaction represents the most important use of homogeneous catalysis in the chemical industry. 

Breit, B. and Seiche. W. (2003) Hydrogen bonding as a constniction element for bidentate donor ligands in homogeneous catalysis Regioselective hydroformylation of terminal alkenes, J.Ahi. Chem. Soc.. 125. 6608-6609. 

Aqueous biphasic catalysis is also used in homogeneous hydrogenations.117-119 In new examples Ru clusters with the widely used TPPTN [tris(3-sulfonatophenyl) phosphine] ligand120 and Rh complexes with novel carboxylated phosphines121 were applied in alkene hydrogenation, whereas Ru catalysts were used in the hydro-genation of aromatics. Aerobic oxidation of terminal alkenes to methyl ketones was carried out in a biphasic liquid-liquid system by stable, recyclable, water-soluble Pd(II) complexes with sulfonated bidentate diamine ligands.124... 

Hydrogen activation precedes the coordination of the alkene. Reviews on hydrogen activation in relation to homogeneous catalysis are available.43,44 General reviews on homogeneous hydrogenation are listed at the end of Section 61.2.2. 

We have already alluded to the diversity of oxidation states, the dominance of oxo chemistry and the cluster carbonyls. Brief mention should be made too of the tendency of osmium (shared also by ruthenium and, to some extent, rhodium and iridium) to form polymeric species, often with oxo, nitrido or carboxylato bridges. Although it does have some activity in homogeneous catalysis (e.g. of m-hydroxylation, hydroxyamination or animation of alkenes, see p. 558, and occasionally for isomerization or hydrogenation of alkenes, see p. 571), osmium complexes are perhaps too substitution-inert for homogeneous catalysis to become a major feature of the chemistry of the element. The spectroscopic properties of some of the substituted heterocyclic nitrogen-donor complexes may yet make osmium an important element for photodissociation energy research. 

However, in 1972, one year before Manassen s and Joo s first publications, Parshall working at Dupont in Delaware reported that the hydrogenation and alkoxycarbonylation of alkenes could be catalysed by PtCL when dissolved in tetraalkylammonium chloride/tin dichloride at temperatures of less than 100°C/5] It was even noted that the product could be separated by decantation or distillation. Parshall recognised the separation problem associated with homogeneous catalysis and in this paper states, An approach that seems under utilised is the use of molten salts as stable, non-volatile solvents from which organic products are readily separated by distillation. .. or decantation . An even earlier report by a group working for the U S. 

Asymmetric Synthesis by Homogeneous Catalysis Coordination Organometallic Chemistry Principles Hydrobo-ration Catalysis Hydrogenation Isomerization of Alkenes Mechanisms of Reaction of Organometallic Complexes Silicon Organosilicon Chemistry. 

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