Gunter Ebeling

Carbonylation of alkynols catalyzed by Pd(II)/2-PyPPh2 dissolved in organic solvents and in ionic liquids: a facile entry to α-methylene γ- and δ-lactones

Abstract The carbonylation of terminal 3-alkyn-1-ols and 1-alkyn-4-ols by Pd(OAc) 2 associated with 2-(diphenylphosphino)pyridine (2-PyPPh 2 ) dissolved in organic solvents or in 1- n -butyl-3-methyl imidazolium ionic liquids affords quantitatively and selectively exo -α-methylene γ- and δ-lactones, respectively. In the case of the reactions performed in ionic liquids (biphasic conditions), the lactones were isolated by simple distillation and the ionic catalyst solution can be reused.

The Formation of Imidazolium Salt Intimate (Contact) Ion Pairs in Solution

1-n-Butyl-2,3-dimethylimidazolium (BMMI) ionic liquids (ILs) associated with different anions undergo H/D exchange preferentially at 2-Me group of the imidazolium in deuterated solvents. This process is mainly related to the existence of ion pairs rather than the anion basicity. The H/D exchange occurs in solvents (CDCl3 and MeCN for instance) in which intimate contact ion pairs are present and the anion possesses a labile H in its structure, such as hydrogen carbonate and prolinate. In D2 O, separated ion pairs are formed and the H/D exchange does not occur. A plausible catalytic cycle is that the IL behaves as a neutral base in the course of all H/D exchange processes. NMR experiments, density functional calculations, and molecular dynamics simulations corroborate these hypotheses.

Surface composition/organization of ionic liquids with Au nanoparticles revealed by high-sensitivity low-energy ion scattering

High-sensitivity low-energy ion scattering (HS-LEIS) analysis was used to elucidate the outermost layer of both functionalized and non-functionalized imidazolium ionic liquids (ILs). The IL outermost layer is composed of all atoms of both cations and anions. The HS-LEIS analyses also allow for quantitative measurement of the thickness of IL overlayers on Au nanoparticles prepared by sputter deposition, which was shown to be a monolayer of ions, as predicted by density functional theory calculations.

Charge-tagged N-heterocyclic carbenes

The interception, formation and characterization of the first stable, long lived charge-tagged N-heterocyclic carbenes of the general type 4x+ (x = 1–3) and analogues is reported. Via ESI(+)-MS of solutions of bromine salts of doubly, triply and quadruply charged imidazolium ion IL (3.Brn, n = 2–4), the isolated 4x+ as well as charged aggregates [3.Br(n−x)]x+ likely to be participating in the [3.Br(n−x)]x+ ⇌ 4x+ + HBr solution equilibrium could be transferred and characterized in the gas phase. Mimicking the solution equilibrium, the gaseous [3.Br(n−x)]x+ were found to dissociate nearly exclusively viaHBr loss during thermal activationvia collisions to form gaseous 4x+, which were found to add to acrolein and acetone.

Ruthenium‐Catalyzed Hydroformylation of Alkenes by using Carbon Dioxide as the Carbon Monoxide Source in the Presence of Ionic Liquids

The reaction of [BMI⋅Cl] (BMI=1‐butyl‐3‐methylimidazolium) or [BMMI⋅Cl] (BMMI=3‐butyl‐1,2‐dimethylimidazolium) with Ru3(CO)12 generates Ru–hydride–carbonyl–carbene species in situ that are efficient catalysts for a reverse water gas shift/hydroformylation/hydrogenation cascade reaction. The addition of H3PO4 increased the catalytic activity of the first step (i.e., the hydrogenation of CO2 to CO). Under the optimized reaction conditions [120 °C and 6.0 MPa CO2/H2 (1:1) for 17 h], cyclohexene and 2,2‐disubstituted alkenes were easily functionalized to alcohols through sequential hydroformylation/carbonyl reduction.

Intrinsic Mobility of Gaseous Cationic and Anionic Aggregates of Ionic Liquids

Travelling-wave ion mobility mass spectrometry was used to measure the intrinsic mobility of a series of gaseous supra-cation and supra-anion aggregates of several ionic liquids. Close mobilities were observed in a T-wave cell filled with helium at ca. 0.8 mbar for [(DAI)(n+1)(X)(n)](+) (DAI is the 1,3-dialkylimidazolium cation and X is the anion) as compared to the respective anions [(DAI)(n)(X)(n+1)](-) for n=0 to 9. The anomalous behavior reported before in the condensed phase seems therefore to be related to the unique structural organization of pure ionic liquids that provides both polar and non-polar regions with directionality in which the anionic species are more retained than the cationic species in the salt network.

A palladium complex containing a new C2-symmetric bidentate non-racemic oxalamidine ligand: synthesis and catalytic properties

Abstract Non-racemic (S,S,S,S)-(-)-2,2′-bis-(4,5-diphenyl-1, 3-imidazoline) 1 has been prepared in good yields from the reaction of (S,S)-(-)1,2-diphenylethylenediamine with diethyl oxalimidate. The reaction of 1 with sodium tetrachloropalladate yields [ PdCl 2 ( 1 )] complex 2, whose structure has been ascertained by means of X-ray diffraction analysis. Complex 2 catalyzes the hydro-arylation of norbornene in good catalytic activity but with poor enantioselectivity.

The retro-chloropalladation reaction of heterosubstituted alkynes

Abstract The bridge-splitting reaction of dimeric palladacycles of the type {Pd[κ1-C, κ1-N-C(R)C(Cl)CH2NMe2](μ-Cl)}2 (R=Ph, Me, CH2CH2OH), derived from the chloropalladation of propargyl amines (RCCCH2NMe2), with pyridine (Py), triphenylphosphine (PPh3) and tert-butylisonitrile (tBuNC) affords the monomeric compounds [PdC(R)CCH2NMe2(Cl)L] (L=Py, PPh3, tBuNC). These monomeric compounds are not stable in solution and undergo retro-chloropalladation reactions yielding the propargyl amines and [PdCl(L)-μ-Cl]2. This process is strongly dependent upon the nature of the incoming nucleophile (L), the R group on the metallated ligand and the temperature. The retro-halopalladation reaction is almost instantaneous in the case of the reaction of the bromo derivative [PdC(Ph)C(Br)CH2NMe2-μ-Br]2 and pyridine at room temperature. These results can be rationalized in terms of the stability of the PdC bond of the intermediate monomeric compound [PdC(R)C(X)CH2NMe2(X)L], that is directly related to the nature of its substituents R (Ph, Me and CH2CH2OH), of ligands which are both cis and trans to it (Py, CNtBu, PPh3, Cl and Br) and the temperature.

A chiral spiro-oxime ligand and its organopalladium(II) coordination chemistry

Abstract The reaction of (±)-1,6-Bisoximo[4.4]nonane 1 (prepared quantitatively from the reaction of hydroxylamine hydrochloride and (±)-spiro[4.4]-1,6-nonanedione) with cyclopalladated compounds [Pd(o-C6H4CH(R)NMe2)-μ-Cl]2 (RH, Me) in the presence of KPF6 yields monocationic dimeric complexes of the type [ Pd ( o-C 6 H 4 CH ( R ) NMe 2 ) - (μ - 1 ) - μ -Cl ] PF 6 containing the bisoxime bridging two palladium centers. The structures of the oxime ligand 1 and the dimeric palladium complex (RH) 2 were determined by means of X-ray diffraction analysis.

Carbon Dioxide Transformation in Imidazolium Salts: Hydroaminomethylation Catalyzed by Ru‐Complexes

The catalytic species generated by dissolving Ru3 (CO)12 in the ionic liquids 1-n-butyl-3-methyl-imidazolium chloride or 1-n-butyl-2,3-dimethyl-imidazolium chloride are efficient multifunctional catalysts for: (a) reverse water-gas shift, (b) hydroformylation of alkenes, and (c) reductive amination of aldehydes. Thus the reaction of alkenes with primary or secondary amines (alkene/amine, 1:1) under CO2 /H2 (1:1) affords the hydroaminomethylations products in high alkene conversions (up to 99 %) and selectivities (up to 96 %). The reaction proceeds under relatively mild reaction conditions (120 °C, 60 bar=6 MPa) and affords selectively secondary and tertiary amines. The presence of amine strongly reduces the alkene hydrogenation competitive pathway usually observed in the hydroformylation of terminal alkenes by Ru complexes. The catalytic system is also highly active for the reductive amination of aldehydes and ketones yielding amines in high yields (>90 %).