Shvo catalyst

The Shvo catalyst, named after Youval Shvo, is an organoruthenium compound that is used for transfer hydrogenation. Related derivatives are known where p-tolyl replaces some of the phenyl groups. The compound is of academic interest as an early example of a catalyst for transfer hydrogenation that operates by an 'outer sphere mechanism.'Shvo's catalyst represents a subset of homogeneous hydrogenation catalysts that involves both metal and ligand in its mechanism. The Shvo catalyst, named after Youval Shvo, is an organoruthenium compound that is used for transfer hydrogenation. Related derivatives are known where p-tolyl replaces some of the phenyl groups. The compound is of academic interest as an early example of a catalyst for transfer hydrogenation that operates by an 'outer sphere mechanism.'Shvo's catalyst represents a subset of homogeneous hydrogenation catalysts that involves both metal and ligand in its mechanism. The complex was originally prepared by the reaction of diphenylacetylene and triruthenium dodecacarbonyl. This synthetic route is efficient, despite the complicated pathway, which includes formation of cyclopentadienone-like ligands. Related syntheses use the preformed cyclopentadienone. A related iron analogue is also known, see Knölker complex. The compound contains a pair of equivalent Ru centres that are bridged by a strong hydrogen bond and a bridging hydride. In solution, the complex dissociates unsymmetrically: The hydride (η5-C5Ph4OH)RuH(CO)2 transfers H2, especially to polar substrates such as ketones and iminium cations. The cyclopentadienone species (η6-C5Ph4O)Ru(CO)2 abstracts H2 from substrates. In the early 1980s, while studying transfer dehydrogenation reactions catalyzed by triruthenium dodecacarbonyl, it was noted by Youval Shvo that both rate of reaction and catalytic turnover were drastically improved through the use of diphenylacetylene as hydrogen acceptor. A series of judicious experiments demonstrated that under the reaction conditions, diphenylacetylene was reacting with the complex to form cyclopentadienone ligands in situ. The complexes with cyclopentadienone were shown to be the source of the improved outcomes. In 1986, Shvo and others reported that they had characterized this new class of ruthenium complexes which were catalytically active in the hydrogenation and dehydrogenation of numerous functional groups. Shvo's catalyst is typically synthesized using tetracyclone and triruthenium dodecacarbonyl, which are refluxed together in a dry aromatic solvent such as toluene for at least 2 days. After forming the monomeric species, the bridged hydrogen dimer is formed by refluxing in the presence of a hydrogen donor, such as isopropanol. When in solution, Shvo's catalyst dissociates into two unequal halves: one contains both hydrogen atoms from the dimer, and the other becomes coordinatively unsaturated. The hydrogen-containing complex performs hydrogenation through addition of both H+ and H- to the double bond, while the unsaturated complex abstracts hydrogen from a suitable donor or from H2 gas itself. Together, the components work in tandem to efficiently transfer H2 from one molecule to another, bringing about the redox reaction. In the presence of a suitable hydrogen donor or hydrogen gas, Shvo's catalyst is useful for the reduction of several polar functional groups. In 2011 this catalyst was demonstrated to be effective at hydrogenating bio-oil in order to improve its quality as a fuel and promoting the hydrolysis of complex carbohydrates into monomeric sugars.