Benjamin C. Hui

Bio: Benjamin C. Hui is an academic researcher. The author has contributed to research in topics: Catalysis & Dimethylacetamide. The author has an hindex of 3, co-authored 6 publications receiving 52 citations.

Synthesis and catalytic properties of some carbonyltriphenylphosphineruthenium(II) complexes

Abstract: The preparation of [HRuCl(CO)2(PPh3)2], [RuCl2(CO)2(PPh3)2], [RuCl2(CO)(PPh3)2], and [RuCl2(CO)(PPh3)2L] complexes (L =NN′-dimethylformamide, NN′-dimethylacetamide, or dimethyl sulphoxide) from [RuCl2(PPh3)3] is reported. Analogous bromo-complexes were also synthesised. The solvent molecules (L) are co-ordinated to the metal through oxygen, and are removed by recrystallisation from methylene chloride-methanol. Under mild conditions the carbonyl complexes show low activity for homogeneous olefin hydrogenation and are ineffective for hydroformylation, but the five-co-ordinate complex [RuCl2(CO)(PPh3)2] is efficient as an olefin isomerisation catalyst.

Catalytic Activation of Molecular Hydrogen by Ruthenium Chloride Complexes in N,N-Dimethylacetamide Solution

Abstract: N, N-Dimethylacetamide solutions of "RuCl3•3H2O", which is a mixture of Ru (IV) and Ru(III), react with hydrogen under mild conditions in stepwise stoichiometric processes to give finally univalent...

Catalytic Hydrogenation of Unsaturated Carboxylic Adds Using N,N-Dimethylacetamide Solutions of Ruthenium(I) Chlorides

Abstract: N,N-Dimethylacetamide solutions of dimeric ruthenium(I) chlorides catalyze homogeneously the hydrogenation of ethylene and unsaturated carboxylic acids under mild conditions. Kinetic and mechanistic studies show that the catalysis involves a monomeric Ru(I) complex which forms reversibly a steady state concentration of a Ru(III)H2 species; this reacts with olefinic substrate to yield saturated product by two successive single hydrogen atom transfers with regeneration of the Ru(I) catalyst. The overall hydrogen addition to fumaric acid is cis. Hydrogenation of maleic acid is accompanied by an efficient isomerization to fumaric acid.

Catalytic activation of molecular hydrogen by ruthenium chloride complexes in n,n-dimethylacetamide solution

Abstract: N, N-Dimethylacetamide solutions of "RuCl3•3H2O", which is a mixture of Ru (IV) and Ru(III), react with hydrogen under mild conditions in stepwise stoichiometric processes to give finally univalent...

Homogeneous catalytic hydrogenation of supercritical carbon dioxide

Abstract: THE use of carbon dioxide as a starting material for the synthesis of organic compounds has long been a goal for synthetic chemists. The hydogenation of carbon dioxide to formic acid, methanol and other organic substances is particularly attractive, but has remained difficult. This route to formic acid has been described recently, based on the use of organometallic rhodium catalysts in dimethyl sulphoxideII and aqueous2 solvents. We report here the efficient production of formic acid in a supercritical mixture of carbon dioxide and hydrogen containing a catalytic ruthenium() phosphine complex. The use of a supercritical phase, in which hydrogen is highly miscible, leads to a very high initial rate of reaction up to 1,400 moles of formic acid per mole of catalyst per hour. The same reaction under identical conditions but in liquid organic solvents is much slower. Our results suggest that supercritical fluids represent a promising medium for homogeneous catalysis.

Hydrogenation Reactions Catalyzed by Transition Metal Complexes

Abstract: Publisher Summary This chapter focuses on the hydrogenation reactions catalyzed by transition metal complexes, with the aim of developing catalysts for selective hydrogenation under mild conditions. Olefin hydrogenations—for example—are important industrial processes, and selectivity is critical to the success of such processes. Greater product selectivity has an important impact on energy and resource utilization in terms of reduced process energy requirements for product separation and purification, and in terms of low-value byproducts. The advances in asymmetric hydrogenation—a stereospecific selectivity—have been notable, and an understanding of the detailed pathways is just beginning to emerge, although much remains to be done, and matching of substrates with the most suitable chiral catalyst still remains an empirical art. The chapter demonstrates the degree of understanding that can be attained for a homogeneous hydrogenation catalyst at the molecular level. Enantiomeric products are used widely in the pharmaceutical industry and as food additives, and the production of either the natural or nonnatural amino acids is at least one advantage shown by the organometallic catalysts compared to enzyme systems. The incorporation of an effective rhodium catalyst into a protein begins to bring closer together analogies between the two areas. Interest is growing in chiral catalysts based on less expensive metals, such as cobalt, and a wider range of chiral ligands–including naturally occurring ones, is being exploited.

The dehydrogenation of ammonia–borane catalysed by dicarbonylruthenacyclic(II) complexes

Abstract: The reactivity of ruthenacyclic compounds towards ammonia–borane's dehydrogenation was investigated by considering both hydrolytic and anhydrous conditions. The study shows that the highly soluble μ-chlorido dicarbonylruthenium(II) dimeric complex derived from 4-tert-butyl,2-(p-tolyl)pyridine promotes, with an activation energy Ea of 22.8 kcal mol−1, the complete hydrolytic dehydrogenation of NH3BH3 within minutes at ca. 40 °C. The release of 3 eq. of H2 entails the formation of boric acid derivatives and the partly reversible protonolysis of the catalyst, which produces free 2-arylpyridine ligand and a series of isomers of “Ru(CO)2(H)(Cl)”. Under anhydrous conditions, hydrogen gas release was found to be slower and the dehydrogenation of NH3BH3 results in the formation of conventional amino–borane derivatives with concomitant protonolysis of the catalyst and release of isomers of “Ru(CO)2(H)(Cl)”. The mechanism of the protonolysis of the ruthenacycle was investigated with state-of-the-art DFT-D methods. It was found to proceed by the concerted direct attack of the catalyst by NH3BH3 leading either to the formation of a coordinatively unsaturated “Ru(CO)2(H)(Cl)” species. The key role of “Ru(CO)2(H)(Cl)” species in the dehydrogenation of ammonia–borane was established by trapping and quenching experiments and inferred from a comparison of the catalytic activity of a series of dicarbonylruthenium(II) complexes.