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The intermolecular α-arylation of esters by palladium-catalyzed coupling of aryl bromides with zinc enolates of esters is reported. Reactions of three different types of zinc enolates have been developed. α-Arylation of esters occurs in high yields with isolated Reformatsky reagents, with Reformatsky reagents generated from α-bromo esters and activated zinc, and with zinc enolates generated by quenching alkali metal enolates of esters with zinc chloride. The use of zinc enolates, instead of alkali metal enolates, greatly expands the scope of the arylation of esters. The reactions occur at room temperature or at 70 °C with bromoarenes containing cyano, nitro, ester, keto, fluoro, enolizable hydrogen, hydroxyl, or amino functionality and with bromopyridines. The scope of esters encompasses acyclic acetates, propionates, and isobutyrates, α-alkoxyesters, and lactones. The arylation of zinc enolates of esters was conducted with catalysts bearing the hindered pentaphenylferrocenyl di-tert-butylphosphine (Q-phos) or the highly reactive dimeric Pd(I) complex {[P(t-Bu)3]PdBr}2.

The paper gives several fundamental results on strong structural stability of nonlinear resistive <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</tex> -ports. A nonlinear resistive <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</tex> -port consists of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n_{R}</tex> (coupled) internal resistors and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</tex> external ports. Intersection of the internal resistor constitutive relations and the Kirchhoff space is called the configuration space. The projected image of the configuration space onto the port space is called the constitutive relation of the composite <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</tex> -port. Strong structural stability means qualitative persistence of the constitutive relation of composite <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</tex> -port under small perturbations of internal resistor constitutive relations. Theorem I asserts that a nonlinear resistive <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</tex> -port is strongly structurally stable if and only if (i) Kirchhoff space is transversal to the internal resistor constitutive relations, and (ii) the projection map of the configuration space onto port space is a nice immersion. There is, however, an underlying assumption for this fact to be true; there are no port-only loops and no port-only cut sets (Condition P). Theorem 2 says that there are "many" strongly structurally stable <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</tex> -ports, Theorem 3 gives a strong structural stabilization result via network perturbation, and Theorem 4 and Theorem 5 give results for special class of internal resistor constitutive relations.

Nanodiamond imaging is a new molecular imaging modality that takes advantage of nitrogen-vacancy (NV) defects in nanodiamonds to image the distribution of nanodiamonds within a living organism with high sensitivity and high resolution. Nanodiamond is a nontoxic material that is easily conjugated to biomolecules, such that the distribution of nanodiamond within a living organism can be used to elicit physiological information. Unlike the tracers used in other molecular imaging modalities such as positron emission tomography (PET) and single photon emission computed tomography (SPECT), nanodiamonds are stable and thus allow longitudinal imaging of the same organism over a long time span. Unlike fluorescence-based molecular imaging that has a resolution degraded by photon scattering, the resolution of nanodiamond imaging is defined by the strength of a magnetic gradient. <br/> To form an image, a magnetic field-free region is created, such as exists halfway between two identical magnets with north poles facing each other. Optical excitation pumps the NVs into a bright fluorescence state, and microwaves transfer them to a dark state, but only for those NVs within the field-free region and resonant with the microwaves. By rastering the field-free region across the sample, the changes in fluorescence yield the nanodiamond concentration. Images of nanodiamond phantoms within chicken breast have been recorded with a prototype system. By modifying the nanodiamond particles and enhancing the imaging system, it should be possible to approach 100 &mu;m resolution and to increase the sensitivity to a 10 nanomolar carbon concentration per root Hz in a mm³ voxel.

Pendent metals bound to heterocubanes are key components of well-known active sites in enzymes that mediate difficult chemical transformations. Investigations into the specific role of these metal ions, sometimes referred to as "danglers," have been hindered by a paucity of rational synthetic routes to appropriate model structures. To generate pendent metal ions bonded to an oxo cubane through a carboxylate bridge, the cubane Co4(μ3-O)4(OAc)4(t-Bupy)4 (OAc = acetate, t-Bupy = 4-tert-butylpyridine) was exposed to various metal acetate complexes. Reaction with Cu(OAc)2 gave the structur-ally characterized (by X-ray diffraction) dicopper dangler Cu2Co4(μ4-O)2(μ3-O)2(OAc)6(Cl)2(t-Bupy)4. In contrast, the anal-ogous reaction with Mn(OAc)2 produced the MnIV-containing cubane cation [MnCo3(μ3-O)4(OAc)4(t-Bupy)4]+ by way of a metal-metal exchange that gives Co(OAc)2 and [CoIII(μ-OH)(OAc)]n oligomers as byproducts. Additionally, reaction of the formally CoIV cubane complex [Co4(μ3-O)4(OAc)4(t-Bupy)4][PF6] with Mn(OAc)2 gave the corresponding Mn-containing cubane in 80% yield. A kinetic and mechanistic examination of the related metal-metal exchange reaction between Co4(μ3-O)4(OBz)4(py)4 (OBz = benzoate) and [Mn(acac)2(py)2][PF6] by UV-vis spectroscopy provided support for a pro-cess involving rate-determining association of the reactants and electron transfer through a μ-oxo bridge in the adduct intermediate. The rates of exchange correlate with the donor strength of the cubane pyridine and benzoate ligand sub-stituents; more electron-donating pyridine ligands accelerate metal-metal exchange, while both electron donating and withdrawing benzoate ligands can accelerate exchange. These experiments suggest that the basicity of the cubane oxo ligands promotes metal-metal exchange reactivity. The redox potentials of the Mn and cubane starting materials, and isotopic labeling studies, suggest an inner-sphere electron transfer mechanism in a dangler intermediate.

Hydrated and anhydrous rhodium oxides, Rh/sub 2/O/sub 3/ 5H/sub 2/O and Rh/sub 2/O/sub 3/ crystallites, were used as catalysts for the hydrogenation of CO at 6 atm and in the range of 250 to 350/sup 0/C. The anhydrous oxide reduced to metallic rhodium rapidly, while the hydrated oxide was quite stable under the reaction conditions. The hydrated oxide produces a high concentration of oxygenated hydrocarbons, mostly acetaldehyde in addition to C/sub 2/ to C/sub 5/ alkenes and methane, in contrast to the unsupported metal which is a mediocre methanation catalyst. The activation energy for the formation of all of the products is 26 +- 2 kcal/mole indicating that they are likely to be produced from a common precursor intermediate, C/sub x/H/sub y/. The addition of ethylene to CO and H/sub 2/ results in the conversion of the olefin to propionaldehyde. This carbonylation reaction was not observed on the rhodium metal. The slower rates of hydrogenation on the oxide and its ability to insert CO into the C/sub t/H/sub y/ intermediates appear to be responsible for the changed product distribution in the CO/H/sub 2/ reaction. Electron spectroscopy studies indicate the presence of patches of oxide and metal both participate in themore » reaction and control the production distribution.« less

A micro-mechanistic understanding of bone fracture that encompasses how cracks interact with the underlying microstructure and defines their local failure mode is lacking, despite extensive research n the response of bone to a variety of factors like aging, loading, and/or disease.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTBase-Free Silylene Complexes without .pi.-Donor Stabilization. Molecular Structure of [Cp*(PMe3)2Ru:SiMe2][B(C6F5)4]Steven K. Grumbine, T. Don Tilley, Frederick P. Arnold, and Arnold L. RheingoldCite this: J. Am. Chem. Soc. 1994, 116, 12, 5495–5496Publication Date (Print):June 1, 1994Publication History Published online1 May 2002Published inissue 1 June 1994https://doi.org/10.1021/ja00091a074RIGHTS & PERMISSIONSArticle Views387Altmetric-Citations100LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (265 KB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information Get e-Alerts

The National Study of Physician Organizations and the Management of Chronic Illness (NSPO) examined relationships among physician organization characteristics and the implementation of care management processes (CMP) aimed at improving outcomes and reducing costs for the treatment of four chronic diseases: asthma, congestive heart failure (CHF), depression, and diabetes. To that end, NSPO conducted this national survey of medical groups and independent practice associations (IPA) with 20 or more physicians. An IPA is defined as an organization through which physicians contract with managed care plans. Examples of CMPs include evidence-based clinical practice guidelines, protocols and pathways, case and care management systems, and disease management, demand management, and health promotion programs. Interviews were conducted with the medical director, president, or chief executive officer of each surveyed physician organization. The survey collected data on (1) practice type, size, age, location, and ownership, (2) governance, management, and use of computerized data systems, (3) revenue and overall financial position, (4) physician compensation models, (5) relationships with health plans and degree of risk assumption, and (6) care management and clinical practice -- particularly in regard to asthma, CHF, depression, and diabetes.

The ansa complex Me2Si(C5Me4)2ScMe (2) was isolated in 45% yield from the reaction of Me2Si(C5Me4)2ScCH2CH(CH2CH3)2 (1) with methane. The rate of the C−H bond activation of methane by 2 was found to be 2 orders of magnitude greater than that by Cp*2ScMe. Compound 2 is a catalyst for the addition of methane across the double bond of secondary terminal olefins.