Titelbild: Enantiospecific C?H Activation Using Ruthenium Nanocatalysts (Angew. Chem. 36/2015)

The activation of C H bonds has revolutionized modern synthetic chemistry. However, no general strategy for enantiospecific C H activation has been developed to date. We herein report an enantiospecific C H activation reaction followed by deuterium incorporation at stereogenic centers. Mechanistic studies suggest that the selectivity for the α‐position of the directing heteroatom results from a four‐membered dimetallacycle as the key intermediate. This work paves the way to novel molecular chemistry on nanoparticles.     

2H NMR calculations on polynuclear transition metal complexes: on the influence of local symmetry and other factors

It is now well-known that (2)H solid-state NMR techniques can bring a better understanding of the interaction of deuterium with metal atoms in organometallic mononuclear complexes, clusters or nanoparticles. In that context, we have recently obtained experimental quadrupolar coupling constants and asymmetry parameters characteristic of deuterium atoms involved in various bonding situations in ruthenium clusters, namely D(4)Ru(4)(CO)(12), D(2)Ru(6)(CO)(18) and other related compounds [Gutmann et al., J. Am. Chem. Soc., 2010, 132, 11759], which are model compounds for edge-bridging (μ-H) and face-capping (μ(3)-H) coordination types on ruthenium surfaces. The present work is in line with density functional theory (DFT) calculations of the electric field gradient (EFG) tensors in deuterated organometallic ruthenium complexes. The comparison of quadrupolar coupling constants shows an excellent agreement between calculated and observed values. This confirms that DFT is a method of choice for the analysis of deuterium NMR spectra. Such calculations are achieved on a large number of ruthenium clusters in order to obtain quadrupolar coupling constants characteristic of a given coordination type: terminal-D, η(2)-D(2), μ-D, μ(3)-D as well as μ(4)-D and μ(6)-D (i.e. interstitial deuterides). Given the dependence of such NMR parameters mainly on local symmetry, these results are expected to remain valid for large assemblies of ruthenium atoms, such as organometallic ruthenium nanoparticles.     

DFT study of the ring opening polymerization of ε-caprolactone by grafted lanthanide complexes: 1--Effect of the grafting mode on the reactivity of borohydride complexes

The influence of the grafting mode of a borohydride lanthanum complex on a silica surface on the energetic (kinetic and thermodynamic parameters) of the Ring Opening Polymerization (ROP) reaction of ε-caprolactone has been studied in the framework of density functional theory (DFT). For all considered grafted catalysts (monografted, bigrafted, or bigrafted after breaking of a Si-O-Si bridge), it is shown that lanthanum borohydride grafted complexes are efficient in lactone polymerization. Moreover, the reaction pathways (leading to a -CH(2) OBH(2) chain end) are predicted to be energetically similar for the three grafting modes, indicating that all grafted modes can account for the activity for silica treated at 700 °C. The catalytic activity of the grafted complexes is also very similar to that of the homogeneous complexes.     

Silo clogging reduction by the presence of an obstacle

We present experimental results on the effect that inserting an obstacle just above the outlet of a silo has on the clogging process. We find that, if the obstacle position is properly selected, the probability that the granular flow is arrested can be reduced by a factor of 100. This dramatic effect occurs without any remarkable modification of the flow rate or the packing fraction above the outlet, which are discarded as the cause of the change in the clogging probability. Hence, inspired by previous results of pedestrian crowd dynamics, we propose that the physical mechanism behind the clogging reduction is a pressure decrease in the region of arch formation.     

Polymerization of rac‐Lactide Using Achiral Iron Complexes: Access to Thermally Stable Stereocomplexes

Enantiopure poly(lactic acid) (PLA) can form stereocomplexes when enantiomeric PLA chains are mixed in equivalent amounts. Such materials provide interesting features that might be suitable for numerous applications. Despite several advantages, the main drawback of PLA is its narrow window of processing, thus limiting its use for industrial applications. Reported herein are achiral iron complexes, that are highly active, productive, and stereoselective under mild reaction conditions for the ring‐opening polymerization of lactide. The corresponding catalytic systems enable the production of stereoblock polymers with high molecular weights, allowing the formation of thermally stable and industrially relevant stereocomplexes.     

Exploring microsolvation of the anesthetic propofol

Propofol (2,6-diisopropylphenol) is a broadly used general anesthetic. By combining spectroscopic techniques such as 1- and 2-color REMPI, UV/UV hole burning, infrared ion-dip spectroscopy (IRIDS) obtained under cooled and isolated conditions with high-level ab initio calculations, detailed information on the molecular structure of propofol and on its interactions with water can be obtained. Four isomers are found for the bare propofol, while only three are detected for the monohydrated species and two for propofol·(H(2)O)(2). The isopropyl groups do not completely block the OH solvation site, but reduce considerably the strength of the hydrogen bonds between propofol and water. Such results may explain the high mobility of propofol in the GABA(A) active site, where it cannot form a strong hydrogen bond with the tyrosine residue.     

Shell interactions for Dirac operators

The self-adjointness of H+V$H+V$ is studied, where H=−iα⋅∇+mβ$H=-i\alpha \cdot \mathrm{\nabla }+m\beta$ is the free Dirac operator in R³${\mathbb{R}}^3$ and V is a measure-valued potential. The potentials V under consideration are given by singular measures with respect to the Lebesgue measure, with special attention to surface measures of bounded regular domains. The existence of non-trivial eigenfunctions with zero eigenvalue naturally appears in our approach, which is based on well known estimates for the trace operator defined on classical Sobolev spaces and some algebraic identities of the Cauchy operator associated to H.     

Assessing the stable carbon isotopic composition of intercellular CO2 in a CAM plant using gas chromatography-combustion-isotope ratio mass spectrometry

Most of the literature focused on internal CO(2) (Ci) determinations in plants has used indirect methods based on gas-exchange estimations. We have developed a new method based on the capture of internal air gas samples and their analysis by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). This method provided a direct measure of intercellular CO(2) concentrations combined with stable carbon isotopic composition in O. ficus-indica plants. Plants were grown at both ambient and elevated CO(2) concentration. During the day period, when the stomata are closed, the Ci was high and was very (13)C-enriched in both ambient and elevated CO(2)-grown plants, reflecting Rubisco's fractionation (this plant enzyme has been shown to discriminate by 29 per thousand, in vitro, against (13)CO(2)). Other enzyme fractionations involved in C metabolism in plants, such as carbonic anhydrase, could also be playing an important role in the diurnal delta(13)C enrichment of the Ci. During the night, when stomata are open, Ci concentrations were higher in elevated (and the corresponding delta(13)C values were more (13)C-depleted) than in ambient CO(2)-grown plants.