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A new class of tantalum-based peroxocarbonate ionic liquid ([P4,4,4,4]3[Ta(η2-O2)3(CO4)]) has been generated through the reaction of pressurized CO2with [P4,4,4,4]3[Ta(O)3(η2-O2)] in the presence of H2O2during the reaction process. The newly formed species has been verified by NMR, FT-IR, HRMS and density functional theory (DFT) calculations. The CO2-induced monomeric peroxocarbonate anion-based ionic liquid is more advantageous than the monomeric peroxotantalate analogue for the epoxidation of olefins under very mild conditions. Interestingly, the transformation between peroxotantalate and peroxocarbonate species is completely reversible, and CO2can actually act as a trigger agent for epoxidation reaction. The further mechanism studies by DFT calculation reveal that peroxo η2-O2(site a) affords higher reactivity towards the CC bond than that of peroxocarbonate–CO4(site b). These quantitative illustrations of the relationship between structural properties and kinetic consequences enable rational design for an efficient and environmental IL catalyst for the epoxidation of olefins.

Catalytic HDexchange reactions were studied with [Rudtbpmpη2H2H2] 1 as catalyst. Under mild reaction conditions 25–75 °C a wide range of arenes and olefins undergo HD exchange with [D6]benzene. A preference for protons at sp2carbons was observed with conversions up to >90  and significant regioselectivity in certain cases. For more reaction insights NMRbased kinetic studies were performed with naphthalene as substrate, revealing an activation energy of 15.8 kcal mol–1for the HD exchange at the βposition. Furthermore, the key steps of the reaction mechanism were investigated by means of DFT calculations for both model complexes PMe2donor sites and real catalysts PtBu2donor sites. The calculations resulted in Gibbs free activation energies in the range of 10–16 kcal mol–1, indicating HD exchange at the βposition of naphthalene to be clearly favoured over the αposition, which is in full accordance with the experimental observations.© WileyVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008

Nickel(I) Complexes with 1,1′‐Bis(phosphino)ferrocenes as Ligands

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The synthesis and characterisation of nonclassical ruthenium hydride complexes containing bidentate PP and tridentate PCP and PNP pincer‐type ligands are described. The mononuclear and dinuclear ruthenium complexes presented have been synthesised in moderate to high yields by the direct hydrogenation route (one‐pot synthesis) or in a two‐step procedure. In both cases [Ru(cod)(metallyl)2] served as a readily available precursor. The influences of the coordination geometry and the ligand framework on the structure, binding, and chemical properties of the MH2fragments were studied by X‐ray crystal structure analysis, spectroscopic methods, and reactivity towards N2, D2, and deuterated solvents.

The oxidation of cycloalkanes or alkylarenes with molecular oxygen and acetaldehyde as sacrificial co‐reductant occurs efficiently in compressed (supercritical) carbon dioxide (scCO2) under mild multiphase conditions. No catalyst is required and high‐pressure ATR‐FTIR online measurements show that a radical reaction pathway is heterogeneously initiated by the stainless steel of the reactor walls. For secondary carbon atoms, high ketone to alcohol ratios are observed (3.5–7.9), most probably due to fast consecutive oxidation of alcoholic intermediates. Since CC scission reactions are detected only to a very small extent, tertiary carbon atoms are transformed into the corresponding alcohols with high selectivity. Detailed analysis of the product distributions and other mechanistic evidence suggest that acetaldehyde acts not only as the sacrificial oxygen acceptor, but also as an efficient H‐atom donor for peroxo and oxo radicals and as a crucial reductant for hydroperoxo intermediates. In comparison to other inert gases such as compressed N2or Ar, the use of carbon dioxide was shown to increase the yields of alkane oxygenates under identical reaction conditions.

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The reaction of oxalic amidines R¹N=C(NHR²)−C(NHR²)=NR¹ (oxamH2) with 2 equiv. (allyl)2M or (acac)2M (M: Ni, Pd) results in the formation of dinuclear complexes [(T)M(oxam)M(T)] containing dianionic bridging oxalamidinate and η³-allyl or acac as terminal ligands T. The complexes were characterized by elemental analyses, mass spectrometry, and ¹H and ¹³C NMR spectroscopy. In addition, the solid-state structures of 1 (M: Ni; T: η³-allyl; R¹ = p-tolyl; R² = mesityl), 2 (M: Ni; T: η³-allyl; R¹ = R² = mesityl), 9 (M: Pd; T: acac; R¹ = phenyl; R² = p-tolyl), and 10 (M: Pd; T: acac; R¹ = R² = p-tolyl) were determined by X-ray single-crystal diffraction analyses. All complexes contain the metal ions in a square-planar environment. Furthermore, in the η³-allyl complexes two isomers are found in which the two allyl groups are oriented in syn and anti positions. Trinuclear complexes of the composition [(T)M(oxam)M¹(oxam)M(T)] (M¹: Zn; M: Ni or Pd) are obtained by treating Et2Zn with 2 equiv. of an oxalic amidine in toluene, followed by addition of 2 equiv. M(acac)2 or Pd(allyl)2. The synthesis and solid-state X-ray analysis of the tetranuclear complex [(T)M(oxam)M¹(oxam)M¹(oxam)M(T)] (16: M = M¹: Zn; oxam: R¹ = p-tolyl; R² = mesityl) is also described. A number of Ni^II complexes oligomerize or polymerize ethylene upon activation with MAO or Et3Al. The catalyses can be adjusted by the bulkiness of the nitrogen substituents, the nature of the cocatalyst, and the nuclearity of the complexes. The most active and selective polymerization catalyst is the heterotrinuclear NiZnNi complex 12 which contains two tetramesityloxalamidinato bridges and acac as terminal ligands T. Complex 12 can be activated by using only 2 equiv. Et3Al per Ni. Initial efforts show that the palladium complexes are catalysts for the Heck coupling.

Tetrameric Lithium Tris(N, N‐dimethylamino)silylamide: Synthesis, Structure, and Reactivity

Vom 13. bis 16. Oktober vergangenen Jahres fand in Bruchsal das von der Dechema organisierte Symposium „Green Solvents for Catalysis ‐ Environmentally Benign Reaction Media”︁ statt. Die wissenschaftliche Koordination lag in den Händen von Walter Leitner (RWTH Aachen und MPl für Kohlenforschung, Mülheim/Ruhr), Kenneth R. Seddon (Queen's University, Belfast) und Peter Wasserscheid (RWTH Aachen). Zehn Hauptvorträge, 19 Kurzvorträge und 71 Poster bildeten ein anregendes Forum für den wissenschaftlichen Austausch zwischen 220 Wissenschaftlern aus 24 Nationen.

The oxidation of cyclooctane (1) to cyclooctanone (3) with molecular oxygen and acetaldehyde (2) as a co-reductant occurs efficiently in the presence of compressed CO₂. Up to 20% yields of 3 are obtained under optimised multiphase conditions.

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