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.

Homogeneous catalytic hydrogenation of supercritical carbon dioxide

The syntheses of cycloruthenated compounds by several methods, and especially by the C–H activation pathway, have been reviewed. Many ruthenium-containing starting materials lead to these interesting organometallic compounds, which have found various applications in different fields of chemistry. Their reactivity highlights both thevariety of reactions that were found to occur at the Ru–C bonds as well as the inertness of the organometallic moiety when these species are exposed to strongly oxidizing molecules or to reactive halogenation reagents. Their use as catalyst precursors showed them to be particularly efficient for hydrogenation reactions, either by H2 or by hydride transfer. Physicochemical characteristics of cycloruthenated complexes include: (i) a cathodic shift of the electrochemical potentials corresponding to various redox couples, (ii) a bathochromic shift of UV/Vis absorption bands, (iii) valuable luminescence properties. Dinuclear cycloruthenated complexes display specific properties connected to interactions between the metals, such as strong electronic coupling, evidenced by intervalence bands of mixed-valence species, or efficient energy transfer.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Cycloruthenated Compounds – Synthesis and Applications

The field of asymmetric catalysis has progressed rapidly since the early 1980s, as judged by the increasing number of reports each year and the greater frequency with which enantioselective catalysts are employed in industry.1-3 This intense research effort has greatly expanded the variety of reactions that can be performed with good substrate generality and in a highly enantioselective fashion. Despite this remarkable success, most asymmetric catalysts do not meet the criteria required to be attractive to industry, such as high turnover frequency, long catalyst lifetimes, tolerance of air and moisture, and high enantioselectivity. Therefore, new catalysts will need to be developed. The approach to developing new catalysts has not changed greatly since the early days of asymmetric catalysis. In general, chemists rely on their intuition to design and optimize new catalysts. Research in asymmetric catalysis has been driven by the need to develop and optimize enantioselective processes. As a result, investigations into the reaction mechanisms have received less emphasis, and our understanding is not well developed. Further contributing to this deficiency is the complexity exhibited by many catalytic systems. Thus, the era of rationally designed catalysts may be in the distant future. Emerging strategies to develop asymmetric catalysts based on combinatorial methods hold great promise.4-29 Several research groups have successfully synthesized families of ligands and catalysts for use in asymmetric catalysis, while others have used † University of Pennsylvania. ‡ Merck Research Laboratories. 3297 Chem. Rev. 2003, 103, 3297−3344

Use of achiral and meso ligands to convey asymmetry in enantioselective catalysis

Silica Hybrid Gel Catalysts Containing Group(VIII) Transition Metal Complexes: Preparation, Structural, and Catalytic Properties in the Synthesis ofN,N-Dimethylformamide and Methyl Formate from Supercritical Carbon Dioxide

Organometallic intramolecular-coordination compounds containing a phosphorus donor ligand

Dissociation of dichlorotris(triphenylphosphine(ruthenium(II) in benzene and in N,N-dimethylacetamide solution

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.

Synthesis and catalytic properties of some carbonyltriphenylphosphineruthenium(II) complexes

Stoicheiometric hydrogenation of olefins using HRuCl(PPh3)3 in the absence of hydrogen results in formation of the dimer [(Ph3P)ClRu(o-C6H4PPh2)]2; this complex reacts with H2, and HCl, to yield in solution the catalytically important bisphosphine complexes RuXCl(PPh3)2(X = H, Cl).

Larry D. Markham

Papers

Dissociation of dichlorotris(triphenylphosphine(ruthenium(II) in benzene and in N,N-dimethylacetamide solution

Synthesis and catalytic properties of some carbonyltriphenylphosphineruthenium(II) complexes

Stoicheiometric hydrogenation of olefins using HRuCl(PPh3)3 and formation of an ortho-metallated ruthenium(II) complex

Dissociation of dichlorotris(triphenylphosphine(ruthenium(II) in benzene and in N,N-dimethylacetamide solution

Synthesis and catalytic properties of some carbonyltriphenylphosphineruthenium(ii) complexes