Determination of the viscosity of the ionic liquids [bmim][PF6] and [bmim][TF2N] under high CO2 gas pressure using sapphire NMR tubes

The viscosities of the ionic liqs. [bmim][PF6] and [bmim][TF2N] (bmim = 1-methyl-3-butylimidazolium, TF2N = bis(trifluoromethylsulfonyl)imide) have been detd. under CO2 pressure at 298 K. The viscosity decreases from 381 to 23 cP for [bmim][PF6] without CO2 and for 2.17 m CO2 solns. (mole fraction XCO2 = 0.381, 55 bar CO2), resp. For [bmim][TF2N] the viscosity decreases from 54 cP for the ionic liq. to 21 cP for a 1.61 m soln. of CO2 (mole fraction XCO2 = 0.403, 55 bar CO2)

Homogeneous Catalytic Dehydrogenation of Formic Acid: Progress Towards a Hydrogen-Based Economy

One of the limiting factors to a hydrogen-based economy is associated with the problems storing hydrogen. Many different approaches are under evaluation and the optimum approach will not be the same for all applications, i.e., static, mobile, small and large scale needs, etc. In this article we focus on formic acid as a promising molecule for hydrogen storage that, under certain catalytic conditions, can be dehydrogenated to give highly pure hydrogen and carbon dioxide with only extremely low levels of carbon monoxide gas produced. We describe the various homogeneous catalysts available that usually operate in aqueous formic acid solutions. We also briefly describe the reverse reaction that would contribute to making the use of formic acid in hydrogen storage even more attractive

Hydrogen storage and delivery: immobilization of a highly active homogeneous catalyst for the decomposition of formic acid to hydrogen and carbon dioxide

The homogeneous catalytic system, based on water-soluble ruthenium(II)– TPPTS catalyst (TPPTS = meta-trisulfonated triphenylphosphine), selectively decomposes HCOOH into H2 and CO2 in aqueous solution. Although this reaction results in only two gas products, heterogeneous catalysts could be advantageous for recycling, especially for dilute formic acid solutions, or for mobile, portable applications. Several approaches have been used to immobilize/solidify the homogeneous ruthenium– TPPTS catalyst based on ion exchange, coordination and physical absorption. The activity of the various heterogeneous catalysts for the decomposition of formic acid has been determined. These heterogenized catalysts offer the advantage of easy catalyst separation/recycling in dilute formic acid, or for mobile, portable applications

Mechanistic Study of the N-Formylation of Amines with Carbon Dioxide and Hydrosilanes

N-formylation of amines with CO2 and hydrosilane reducing agents proceeds via fast and complex chemical equilibria, which hinder easy analysis of the reaction pathways. In situ reaction monitoring and kinetic studies reveal that three proposed pathways, via direct- and amine assisted formoxysilane formation (pathways 1 and 2, respectively) and via a silylcarbamate intermediate (pathway 3), are possible depending on the reaction conditions and the substrates. While pathway 1 is favored for non-nucleophilic amines in the absence of a catalyst, a base catalyst results in noninnocent behavior of the amine in the CO2 reduction step toward the formoxysilane intermediate. The reaction pathway is altered by strongly nucleophilic amines, which form stable adducts with CO2. Silylcarbamate intermediates form, which can be directly reduced to the N-formylated products by excess hydrosilane. Nevertheless, without excess hydrosilane, the silylcarbamate is an additional intermediate en route to formoxysilanes along pathway 2. Exchange NMR spectroscopy (EXSY) revealed extensive substituent exchange around the hydrosilane silicon center, which confirms its activation during the reaction and supports the proposed reaction mechanisms. Numerous side reactions were also identified, which help to establish the reaction equilibria in the N-formylation reactions

Amide bond formation via C(sp(3))-H bond functionalization and CO insertion

An efficient method for the synthesis of amides via Pd-catalyzed oxidative carbonylation of C(sp(3))-H bonds with CO and amines is described. The route efficiently provides substituted phenyl amides from alkanes

Ruthenium Nanoparticles Intercalated in Hectorite: A Reusable Hydrogenation Catalyst for Benzene and Toluene

The cationic organometallic aqua complexes formed by hydrolysis of [(C6H6)RuCl2]2 in water, mainly [(C6H6)Ru(H2O)3]2+, intercalate into sodium hectorite by ion exchange, replacing the sodium cations between the anionic silicate layers. The yellow hectorite thus obtained reacts in ethanol with molecular hydrogen (50 bar, 100°C) with decomposition of the organometallic aqua complexes to give a black material, in which ruthenium(0) nanoparticles (9-18nm) are intercalated between the anionic silicate layers, the charges of which being balanced by hydronium cations. The black ruthenium-modified hectorite efficiently catalyses the hydrogenation of benzene and toluene in ethanol (50 bar H2, 50°C), the turnover frequencies attaining 7000 catalytic cycles per hou

Intricacies of Cation-Anion Combinations in Imidazolium Salt-Catalyzed Cycloaddition of CO2 Into Epoxides

The cycloaddition of CO2 into epoxides catalyzed by imidazolium and related salts continues to attract attention due to the industrial importance of the cyclic carbonate products. The mechanism of the imidazolium-catalyzed transformation has been proposed to require the participation of the acidic C2 proton. However, other simple salts without acidic protons, such as N,N,N,N-tetrabutylammonium chloride, are also efficient catalysts for the reaction. Hence, we decided to investigate the role of the ring protons of imidazolium salts in this reaction. To this end, we systematically studied the catalytic activity of a series of methyl substituted imidazolium cations, in the presence of various halide anions, both by experiment and in silico. Our results demonstrate that, while stabilization of intermediates by C2, C4, or C5 protons in imidazolium salts takes place, it is the nucleophilicity of the anion that governs the overall activity, which is intimately related to the strength of the interactions between the cation and anion. Consequently, the reactivity of the halide anion strongly depends on the nature of the cation and cosolvents. This study completes the (known) mechanism and should facilitate the development of highly efficient catalysts