Roberto Fernando de Souza

The use of new ionic liquids in two-phase catalytic hydrogenation reaction by rhodium complexes

Abstract The reaction of 1-n-butyl-3-methylimidazolium chloride (BMIC) with sodium tetrafluoroborate or sodium hexafluorophosphate produced the room temperature-, air- and water-stable molten salts (BMI+)(BF4−) (1) and (BMI+)(PF6−) (2), respectively, in almost quantitative yield. The rhodium complexes RhCl(PPh3)3 and [Rh(cod)2][BF4] are completely soluble in these ionic liquids and they are able to catalyse the hydrogenation of cyclohexene at 10 atm and 25°C in a typical two-phase catalysis with turnovers up to 6000.

Water-induced accelerated ion diffusion: voltammetric studies in 1-methyl-3-[2,6-(S)-dimethylocten-2-yl]imidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate and hexafluorophosphate ionic liquids

The electrochemical properties of the room temperature ionic liquids 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM+BF4−), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM+PF6−) and 1-methyl-3-[2,6-(S)-dimethylocten-2-yl]imidazolium tetrafluoroborate (MDIM+BF4−) as solvents have been studied using micro-samples, with a volume of 10 μL, of the ionic liquids under vacuum conditions and under conditions with controlled gas and moisture supplies. The impact of water—absorbed into the ionic liquid in a controlled manner from the gas phase—on the voltammetry of dissolved redox systems and on the accessible potential window of the ionic liquids was investigated. The diffusion coefficients for three representative redox systems, the oxidation of neutral N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), the reduction of cationic methyl viologen (MV2+) and reduction of anionic hexacyanoferrate(III), Fe(CN)63−, have been determined as a function of the water content of the ionic liquids. Water is shown to have a much more dramatic acceleration effect on the diffusion of the ionic compounds compared to its effect on neutral species in ionic liquids. A model based on nanoscale structural features of wet ionic liquid materials is proposed. The novel methodology, which employs redox-active compounds dissolved or partitioned in microdroplets of ionic liquid, uses conditions suitable for the study of ionic liquids for applications in electrochemical gas phase reactors and gas sensor systems.

Room temperature dialkylimidazolium ionic liquid-based fuel cells

The non-Bronsted acid–base room temperature imidazolium ionic liquids, such as 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMI.BF4), are out-standing electrolytes for fuel cells. A 67% overall cell efficiency is achieved using these liquids as supporting electrolytes for a commercially available alkaline fuel cells (AFC) at room temperature operating with air and hydrogen at atmospheric pressure.

Enlarged electrochemical window in dialkyl-imidazolium cation based room-temperature air and water-stable molten salts

The electrochemical windows of the ionic liquids 1-n-butyl-3-methyl imidazolium tetrafluoroborate (BMI+)(BF4−) and 1-butyl-3-methyl imidazolium hexafluorophosphate (BMI+)(PF6−) have been investigated at platinum, vitreous carbon, tungsten and gold electrodes. The lowest current densities and widest electrochemical windows were found on tungsten and vitreous carbon 6.10 and 5.45 V for (BMI+)(BF4−) and >7.10 and 6.35 V for (BMI+)(PF6−), respectively.

C-H-π Interactions in 1-n-Butyl-3-methylimidazolium Tetraphenylborate Molten Salt: Solid and Solution Structures

The crystal structure of 1-n-butyl-3-methylimidazolium tetraphenylborate molten salt (1) shows C-H-pi interactions between the hydrogens of the imidazolium cation and the phenyl rings of the tetraphenylborate anion. The imidazolium ring is surrounded by three tetraphenylborate anions that are connected with the same cation by C-H-pi (phenyl rings) interactions. The nearest inter-ion interaction is found between the N-CH-N proton of the cation and the B-phenyl centroid (2.349 A) with a nearly T-shaped geometry. The inter-ionic solution structure of 1 has been investigated by the detection of inter-ionic contacts in 1H NOESY NMR spectra between the protons of the cation and the anion. The 1H-NMR spectra of molten salt 1 is almost independent of its concentration in [D6]DMSO solution, the imidazolium proton chemical shifts are in the expected region and there are no observable NOE effects between the protons of the cation with those of the anion, indicating that 1 behaves in [D6]DMSO as a solvent-separated ion pair. In CDCl3 the 1H-NMR spectra of 1 are concentration dependent and all the imidazolium protons are shielded as compared with those observed in [D6]DMSO. Moreover, the 1H NOESY NMR spectra show all the peaks affected by the interaction between the protons of the imidazolium cation and those of the anion, indicating that in CDCl3 1 possesses a contact ion pair structure. The NCHN proton of the cation exhibits the greatest shielding (up to -4.5 ppm). an indication of the existence of C-H-pi interactions, even in solution. The calculated distance of this proton to the phenyl centroid is 2.3 A for a C-H -pi angle of 180 degrees. The apparent volumes for the cation and anion, calculated from the measured 13C-NMR relaxation times, increase from 38 and 140 A3 in [D6]DMSO to 360 and 600 A3 in CDCl3, respectively; this indicates the formation of floating aggregates of the type (1)(n) in CDCl3 via weak hydrogen bonds, with increasing concentration.

Asymmetric hydrogenation of 2-arylacrylic acids catalyzed by immobilized Ru-BINAP complex in 1-n-butyl-3-methylimidazolium tetrafluoroborate molten salt

Abstract The [RuCl2-(S)-BINAP]2.NEt3 catalyst precursor dissolved in 1-n-butyl-3-methylimidazolium tetrafluoroborate molten salt is able to hydrogenate 2-arylacrylic acids (aryl=Ph or 6-MeO-naphthyl) with enantioselectivities similar or higher than those obtained in homogeneous media. Moreover, the hydrogenated products can be quantitatively separated from the reaction mixture and the recovered ionic liquid catalyst solution can be reused several times without any significant changes in the catalytic activity or selectivity.

Ionic liquid-phase asymmetric catalytic hydrogenation: hydrogen concentration effects on enantioselectivity

Abstract Molecular hydrogen is almost four times more soluble in the ionic liquid 1- n -butyl-3-methylimidazolium tetrafluoroborate (BMI·BF 4 ) than in its hexafluorophosphate (BMI·PF 6 ) analogue at the same pressure. The Henry coefficient solubility constant for the solution BMI·BF 4 /H 2 is K =3.0×10 −3 mol L −1 atm −1 and 8.8×10 −4 mol L −1 atm −1 for BMI·PF 6 /H 2 , at room temperature. The asymmetric hydrogenation of ( Z )-α-acetamido cinnamic acid and kinetic resolution of (±)-methyl-3-hydroxy-2-methylenebutanoate by (−)-1,2-bis((2 R ,5 R )-2,5-diethylphospholano)benzene(cyclooctadiene)rhodium(I) trifluoromethanesulfonate and dichloro[( S )-(−)-2,2′-bis(di- p -tolylphosphino)-1,1′-binaphthyl]ruthenium(II) complexes immobilised in BMI·PF 6 and BMI·BF 4 were investigated. Remarkable effects in the conversion and enantioselectivity of these reactions were observed as a function of molecular hydrogen concentration in the ionic phase rather than pressure in the gas phase.

Ionic liquid modified electrodes. Unusual partitioning and diffusion effects of Fe(CN)64−/3− in droplet and thin layer deposits of 1-methyl-3-(2,6-(S)-dimethylocten-2-yl)-imidazolium tetrafluoroborate

Room temperature ionic liquids exhibit unusual and, for electrochemical applications, promising properties such as ionic conductivity and non-volatility. Microdroplet and thin film deposits of an ionic liquid, 1-methyl-3-(2,6-(S)-dimethylocten-2-yl)-imidazolium tetrafluoroborate (MDIM+BF4−) on electrode surfaces are studied in order to assess the ability of aqueous ions to partition into the ionic liquid. Two complementary methodologies, deposition of ionic liquid onto a 4.9 mm diameter basal plane pyrolytic graphite electrode followed by voltammetric analysis and casting of an ionic liquid film onto a random array of 7 μm diameter carbon microelectrodes (RAMTM electrode) followed by chronoamperometry, are employed. The ability of hydrophilic ions to partition from the water phase into the ionic liquid phase is unexpected and is shown to depend strongly on (i) the type of ion, (ii) specific interaction of the ion with the ionic liquid, and (iii) the concentration of the supporting electrolyte. Voltammetric responses obtained for the reduction of Fe(CN)63− partitioned into microdroplet and thin film deposits of MDIM+BF4− indicate selective uptake of ferricyanide into the ionic liquid phase. Chronoamperometric experiments at RAMTM electrodes are used to quantify both the concentration of Fe(CN)63− in the ionic liquid and the diffusion coefficient.

Selective two-phase catalytic ethylene dimerization by NiII complexes/AlEtCl2 dissolved in organoaluminate ionic liquids

Abstract Nickel(II) complexes dissolved in methyl-1-butyl-3-imidazolium chloride/AlCl 3 molten salt in the presence of AlEtCl 2 and aromatic solvents catalyse the dimerization of ethylene into butenes in a typical two-phase catalytic reaction. The nature of the nickel catalyst precursor has a strong influence on the reactions activity and selectivity. Thus, ethylene dimers and trimers were obtained in the presence of NiF 2 and NiCl 2 (PCy 3 ) 2 , whereas only butenes were formed using the complex [Ni(MeCN) 6 ] [BF 4 ] 2 as a catalyst precursor. In this latter case but-1-ene was formed with a selectivity of 83% and turnover frequencies of up to 1731 h -1 . Moreover, the conversion and selectivity to but-1-ene increase with increasing ethylene pressure. The use of aromatic co-solvents is also essential for the ethylene dimerization, since other hydrocarbons induce the formation of higher ethylene oligomers. Copyright

Two-phase catalytic hydrogenation of olefins by Ru(II) and Co(II) complexes dissolved in 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid

Abstract The interaction of RuCl 2 (PPh 3 ) 3 and 1-n-butyl-3-methylimidazolium tetrafluoroborate molten salt yields an air and water stable solution that is able to hydrogenate olefins with turnover frequencies up to 537 h −1 in a typical two-phase catalytic reaction. The complex K 3 Co(CN) 5 also affords a catalytic system with the ionic liquid that catalyzes the reduction of butadiene into but-1-ene with 100% conversion and selectivity.