Ylide‐Functionalized Phosphines: Strong Donor Ligands for Homogeneous Catalysis

Phosphines are important ligands in homogenous catalysis and have been crucial for many advances, such as in cross‐coupling, hydrofunctionalization, or hydrogenation reactions. Herein we report the synthesis and application of a novel class of phosphines bearing ylide substituents. These phosphines are easily accessible via different synthetic routes from commercially available starting materials. Owing to the extra donation from the ylide group to the phosphorus center the ligands are unusually electron‐rich and can thus function as strong electron donors. The donor capacity surpasses that of commonly used phosphines and carbenes and can easily be tuned by changing the substitution pattern at the ylidic carbon atom. The huge potential of ylide‐functionalized phosphines in catalysis is demonstrated by their use in gold catalysis. Excellent performance at low catalyst loadings under mild reaction conditions is thus seen in different types of transformations.     

Preparation of cellulose nanofibers using green and sustainable chemistry

1. Download : Download high-res image (293KB)
2. Download : Download full-size image

     

Polarized fluorescence and absorption spectroscopy of 1,32-dihydroxy-dotriacontane-bis-rhodamine 101 ester. A new and lipid bilayer-spanning probe

We report on the properties of 1,32-dihydroxy-dotriacontane-bis-rhodamine 101 ester (Rh101C₃₂Rh101) in lipid bilayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and in liquid solvents. The results are compared with those of rhodamine 101 octadecanyl ester (Rh101C₁₈). Both molecules are solubilized in the lipid bilayer and the Rh101 moieties are anchored in the lipid-water interface, so that the electronic transition dipole moments (S ₀ S ₁) are oriented preferentially in the plane of the bilayer. At low concentrations of the dyes in lipid bilayers of DOPC, the fluorescence relaxation is single exponential with a lifetime of =4.9±0.2 ns. The relative fluorescence quantum yield of _C32/_C18 0.95 in DOPC vesicles. These results strongly suggest that only a small fraction of the Rh101C₃₂Rh101 molecules are quenched, by, for example, intra- or intermolecular dimers in the ground state at mole fractions of less than 0.1% in the lipid bilayers. For Rh101C₃₂Rh101 in lipid vesicles, the steady-state and time-resolved fluorescence anisotropies are compatible with efficient intramolecular electronic energy transfer. It is concluded that nearly every Rh101C₃₂Rh101 molecule is spanning across the lipid bilayer of DOPC.     

Glycosidase-substrate interactions analysis by STD-NMR spectroscopy: study of alpha-L-fucosidase

Saturation transfer difference-nuclear magnetic resonance (STD-NMR) is a recently developed method used to study the interaction between large proteins and small ligands. It has been successfully employed for various interactions including those between oligosaccharides or glycomimetics, and binding proteins such as lectins and antibodies. We have demonstrated that this method can be used to directly study the interaction between glycosidases and their substrates. We chose to study alpha-l-fucosidases, which, despite their wide distribution among living organisms and their biological significance, have not been studied with regard to their reaction mechanism. We were able for the first time to show direct evidences for the minimum structural requirements for a compound to interact with these enzymes. These findings will be useful for the design of new inhibitors and to optimize the synthetic properties (transglycosylation) of alpha-l-fucosidases.     

Comparison ofW ±+jet andZ 0+jet production at hadron colliders

We analyse the lowest-order QCD production mechanisms forp \(\bar p\) →W ^±+jet andp \(\bar p\) →Z ⁰+jet to find possible differences in jet properties for the two processes.     

Random walks on the hexagon

This paper gives several examples of how flow graphs can be used to determine the probability distribution of certain random variables. All the examples deal with random walks on the hexagon. Ideas for further such examples are listed at the end of the paper.     

A nonsymmetric matrix with integer eigenvalues

A nonsymmetric N?×?N matrix with elements as certain simple functions of N distinct real or complex numbers r ₁, r ₂, …, r_N is presented. The matrix is special due to its eigenvalues???the consecutive integers 0,1,2, …, N?1. Theorems are given establishing explicit expressions of the right and left eigenvectors and formulas for recursive calculation of the right eigenvectors. A special case of the matrix has appeared in sampling theory where its right eigenvectors, if properly normalized, give the inclusion probabilities of the conditional Poisson sampling design.     

Transition Metal-Free Synthesis of meta-Bromo- and meta-Trifluoromethylanilines from Cyclopentanones by a Cascade Reaction

Anilines are key constituents in biologically active compounds and often obtained from transition metal-catalyzed coupling of an aryl halide with an amine. In this work, we report a transition metal-free method for the synthesis of meta-bromo- and meta-trifluoromethylanilines starting from 3-tribromomethylcyclopentanone or 3-(2-bromo-2-chloro-1,1,1-trifluoroethyl)cyclopentanone, respectively. The scope of the transformation is shown by application of primary, secondary and aromatic amines. The reaction proceeds in acceptable to high yields (20–81 %), and allows for the synthesis of anilines with substitution patterns otherwise difficult to access.