Ruthenium-Catalyzed Reactions for Organic Synthesis.

Reactions of synthesis gas

Under specific scenarios, the catalytic hydrogenation of CO2 with renewable hydrogen is considered a suitable route for the chemical recycling of this environmentally harmful and chemically refractory molecule into added-value energy carriers and chemicals. The hydrogenation of CO2 into C1 products, such as methane and methanol, can be achieved with high selectivities towards the corresponding hydrogenation product. More challenging, however, is the selective production of high (C2+) hydrocarbons and oxygenates. These products are desired as energy vectors, owing to their higher volumetric energy density and compatibility with the current fuel infrastructure than C1 compounds, and as entry platform chemicals for existing value chains. The major challenge is the optimal integration of catalytic functionalities for both reductive and chain-growth steps. This Minireview summarizes the progress achieved towards the hydrogenation of CO2 to C2+ hydrocarbons and oxygenates, covering both solid and molecular catalysts and processes in the gas and liquid phases. Mechanistic aspects are discussed with emphasis on intrinsic kinetic limitations, in some cases inevitably linked to thermodynamic bounds through the concomitant reverse water–gas-shift reaction, which should be considered in the development of advanced catalysts and processes.

Carbon Dioxide Hydrogenation into Higher Hydrocarbons and Oxygenates: Thermodynamic and Kinetic Bounds and Progress with Heterogeneous and Homogeneous Catalysis.

Publisher Summary This chapter focuses on the nature of the transformations at the metal center, especially with regard to oxidation state and formation of the initial alkyl-, alkoxy-, or carboalkoxy-metal bond from saturated precursors, and discusses the mechanistic aspects of transition-metal-catalyzed alcohol carbonylations. Prerequisite to any catalytic activity is the ability of the metal center to interact effectively with alcohols or alcohol-derived precursors. There are several ways in which this can occur, and most of these are observed or postulated in at least one catalytic scheme. In order to understand the specific reactivities, though, the reader should be familiar with some fundamental aspects of organo-transition-metal chemistry. Homologation reactions, which are believed to usually proceed by way of aldehyde intermediates, are also discussed in the chapter but only as they pertain to the incorporation of the CO into the metal-carbon bonds. A frequent theme in alcohol carbonylations by transition metals is the use of a halide or pseudo-halide promoters or cocatalysts. Despite major problems of corrosion associated with its use, iodide is almost always found to be most effective in this capacity. This is because the halide serves several purposes, for each of which iodide is ideally suited.

R.A. Head

Papers

The catalytic hydrocarbonylation of alcohols - a review