10,000 publications from this institution
The iridium-catalyzed silylation of aromatic C–H bonds has become a synthetically valuable reaction because it forms aryl silanes with high sterically derived regioselectivity with silane reagents that are produced and consumed on large scales. Many groups, including our own, have reported iridium complexes of phenanthroline or bipyridine ligands as catalysts for this reaction. Yet, little is known about the mechanism by which the iridium-catalyzed silylation of arenes occurs. Indeed, no iridium-silyl complexes have been prepared that react with C-H bonds to form C-Si bonds in a fashion that is chemically and kinetically competent to be part of the catalytic cycle. In this manuscript, we report the synthesis and reactivity of iridium-silyl compelexes of the 2,9-Me 2 Phen ligand that generates the most active known catalyst for the silylation of aromatic C-H bonds. We show by experiment and computation that the most stable and most reactive silyl complex of this ligand contains two silyl and one hydride ligands and by kinetic analysis of the catalytic reaction determine the rate-limiting step for arenes with varying electronic properties. Computational studies indicate that the steric encumberance of the phenanthroline ligand controls the number of silyl ligands bound to iridium and that the difference in the number of silyl ligands leads to large differences to the rates of the reaction. These studies provide insight into the origins of the high activity of the catalyst containing the 2,9-Me 2 Phen ligand.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Click to increase image sizeClick to decrease image size Acknowledgements The authors are grateful to Ms Fumiko Kanuchi, Ms Chihiro Jin and Professor Toshiyuki Uryu for fruitful collaborations.
Sum frequency generation (SFG) vibrational spectroscopy is highly surface sensitive because the second-order nonlinear optical process is only allowed in media without inversion symmetry, such as interfaces. As an all-optical technique, SFG can be employed to study molecular compositions and structures at solid/liquid and at solid/high pressure gas interfaces. This paper discusses the applications of SFG in our laboratory to study the reaction intermediates of catalytic reactions on metal surfaces under high-pressure conditions, the surface composition and structure of polymers, and the interfacial properties of proteins on liquid/solid interfaces. [DOI: 10.1380/ejssnt.2004.106]
The growth of passive films on a series of iron‐nickel‐chromium alloys, , in borate buffer solution was studied ellipsometrically as a function of applied potential and temperature. The kinetic film growth data were found to fit both the logarithmic and inverse logarithmic growth laws with the former providing a more rational representation of the growth behavior. For alloys containing 0, 5, and 10%Cr, the film growth rate constants were found to be essentially independent of applied potential. However, the 16Cr and 30Cr alloys show considerably lower film growth rates at low potentials (< 400 mVSCE), but at higher potentials the growth rates approach those for the low chromium content alloys. The steady‐state film thicknesses were found to vary linearly with potential, and again the two high chromium alloys exhibit anomalous behavior in that the potential dependence changes abruptly at ∼=350 mVSCE. This phenomenon has been interpreted in terms of changes in the composition of the passive film due to dissolution of chromium at high anodic overpotentials.
The evolution of a model for understanding asymmetric allylic alkylations catalyzed by palladium with the use of ligands derived from chiral diamines and 2-diphenylphosphinobenzoic acid provides a basis for attacking the problem of regio- and enantioselective alkylations proceeding through the intermediacy of 1-monosubstituted allyl complexes. The model predicted that in the kinetic ionization of an achiral precursor the major enantiomer of the product resulting from attack at the more substituted terminus would be the mirror image of that obtained under Curtin−Hammett conditions. Experimentally, the ee was rationally varied from 66% of one enantiomer to 83% of the mirror image using the same ligand. Nonpolar solvents and the absence of counterions that coordinate to palladium favor the kinetic product. More polar solvents and counterions that coordinate well to palladium favor Curtin−Hammett conditions. For maximum regio- and enantioselectivity, the chiral racemic 3-substituted-1-alkene is the preferred substrate.
A stoichiometric model of metabolism was developed to describe the balance of metabolic reactions during steady-state growth of Escherichia coli on glucose (or metabolic intermediates) and mineral salts. The model incorporates 153 reversible and 147 irreversible reactions and 289 metabolites from several metabolic data bases for the biosynthesis of the macromolecular precursors, coenzymes, and prosthetic groups necessary for synthesis of all cellular macromolecules. Correlations describing how the cellular composition changes with growth rate were developed from experimental data and were used to calculate the drain of precursors to macromolecules, coenzymes, and prosthetic groups from the metabolic network for the synthesis of those macromolecules at a specific growth rate. Energy requirements for macromolecular polymerization and proofreading, transport of metabolites, and maintenance of transmembrane gradients were included in the model rather than a lumped maintenance energy term. The underdetermined set of equations was solved using the Simplex algorithm, employing realistic objective functions and constraints; the drain of precursors, coenzymes, and prosthetic groups and the energy requirements for the synthesis of macromolecules served as the primary set of constraints. The model accurately predicted experimentally determined metabolic fluxes for aerobic growth on acetate or acetate plus glucose. In addition, the model predicted the genetic and metabolic regulation that must occur for growth under different conditions, such as the opening of the glyoxylate shunt during growth on acetate and the branching of the tricarboxylic acid cycle under anaerobic growth. Sensitivity analyses were performed to determine the flexibility of pathways and the effects of different rates and growth conditions on the distribution of fluxes. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 398–421, 1997.
Abstract Reported herein is an iridium‐catalyzed, regioselective silylation of the aromatic CH bonds of benzylamines and the benzylic CH bonds of 2, N ‐dialkylanilines. In this process, (hydrido)silyl amines, generated in situ by dehydrogenative coupling of benzylamine or aniline with diethylsilane, undergo selective silylation at the CH bond γ to the amino group. The products of this silylation are suitable for subsequent oxidation, halogenation, and cross‐coupling reactions to deliver benzylamine and arylamine derivatives.
Abstract Because the range of biological mechanisms responsible for the inactivation of viruses in man-made and natural water systems is poorly understood, the involvement of the free-living ciliated protozoan, Tetrahymena thermophila, in viral inactivation was investigated. The ciliate was found to remove the bacteriophage MS2 when the phage and ciliate were co-incubated in a simple salt solution. MS2 was enumerated as plaque forming units (pfus). MS2 removal was achieved only by living and not formalin-fixed ciliates, and was blocked by treatments that impaired the formation of food vacuoles. These treatments were cytochalasin B and low temperature. When fluorescently labelled with SYBR gold prior to co-incubation, MS2 were seen inside Tetrahymena within vesicles that had the shape and size of food vacuoles. The number of pfus associated with Tetrahymena was low. This suggests that the engulfment of the phage into food vacuoles led to the inactivation of MS2, which is frequently used as a surrogate for poliovirus in environmental microbiology. In the future, a broader understanding of the capacity of ciliates to inactivate viruses could lead to methods for improving water quality through the manipulation of ciliate populations and activities.
