Six-, Five-, and Four-Coordinate Ruthenium(II) Hydride Complexes Supported by N-Heterocyclic Carbene Ligands: Synthesis, Characterization, Fundamental Reactivity, and Catalytic Hydrogenation of Olefins, Aldehydes, and Ketones
Date: February 20, 2009
Creator: Lee, John P.; Ke, Zhuofeng; Ramírez, Magaly A.; Gunnoe, T. Brent; Cundari, Thomas R., 1964-; Boyle, Paul D. et al
Description: This article discusses six-, five-, and four-coordinate ruthenium(II) hydride complexes. The Ru(II) hydride complex (IMes)2Ru(Cl)(H)(CO) (1) {IMes = 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene} was synthesized from [Ru(CO)2Cl2]n and free IMes. Complex 1 rapidly reacts with CO to produce the cis-dicarbonyl Ru(II) complex (IMes)2Ru(Cl)(H)(CO)2 (2). The reaction of 1 with NaBAr'4 {Ar' = 3,5-(CF3)C6H3} produces the four-coordinate Ru(II) cationic complex [(IMes)2Ru(H)(CO)][BAr'4] (4), which can be trapped by two equivalents of tert-butylisonitrile to produce [(IMes)2Ru(H)(CO)(CNtBu)2][BAr'4] (5). Experimental and computational studies suggest that complex 4 is a diamagnetic system that adopts a sawhorse structure. The hydride ligand of complex 2 is readily displaced as dihydrogen upon reaction with HCI to produce (IMes)2Ru(CI)2(CO)2 (3). Both complex 1 and 4 were found to react with D2 (30 psi) at room temperature to produce the isotopomers (IMes)2Ru(CI)(D)(CO) (1-d1) and [(IMes)2Ru(D)(CO)][BAr'4] (4-d1), respectively, with the rate of formation of 4-d1 at least 28 times faster than the conversion of 1/D2 to 1-d1. In the presence of excess D2 complex 4 reversibly incorporates deuterium into the ortho methyl groups of the IMes ligands, whereas complex 1 does not show evidence of H/D exchange with the IMes ligands. Both 1 and 4 were found to catalyze the hydrogenation of olefins, ketones, and aldehydes.
Contributing Partner: UNT College of Arts and Sciences
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Unusual Electronic Features and Reactivity of the Dipyridylazaallyl Ligand: Characterizations of (smif)2M [M = Fe, Co, Co+, Ni; smif = {(2-py)CH}2N] and [(TMS)2NFe]2(smif)2
Date: February 19, 2009
Creator: Frazier, Brenda A.; Wolczanski, Peter T.; Lobkovsky, Emil B. & Cundari, Thomas R., 1964-
Description: This article discusses unusual electronic features and reactivity of the dipyridylazaallyl ligand. Application of the dipyridylazaallyl ligand (2-py)CHNCH(2-py) (smif) to a series of first-row transition metals afforded (smif)2Mn [n = 0, M = Fe (1), Co (2), Ni (3); n = +1, M = Co (2+)] and {(TMS)2NFe}2(smif)2 (42) via metathetical procedures. The Mössbauer spectrum of 1 (S = 0) and TDDFT calculations, including a UV-vis spectral simulation, reveal it to be covalent, strong-field system with ∆ₒ estimated as ~18 000 cm-1 and B ≈ 470 cm-1. (smif)2Ni (3) has S = 1 (SQUID), and calculations show that the unpaired spins reside in the dz2 and dх2-y2 orbitals. X-ray structural parameters suggest that low-spin d6 1 and 2+ are relatively symmetric D2d species, but 2 and 3 manifest a distortion in which one smif is canted in the plane perpendicular to the other. (smif)FeN(TMS)2 (4) is principally monomeric in solution, but reversibly dimerizes (Keq ≈ 10-4 M-1) via C-C bond formation in the azaallyl backbone to crystallize as {(TMS)2NFe}2(smif)2 (42). The azaallyl compounds possess extraordinary UV-vis absorptivities (Ɛ ≈ 18000-52000) at 580 ± 15nm and 406(25)nm that have been identified as intraligand bands with Cnb→smif π* character.
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Coinage Metal-Ethylene Complexes Supported by Tris(pyrazolyl)borates: A Computational Study
Date: February 18, 2009
Creator: Kazi, Abul B.; Dias, H. V. Rasika; Tekarli, Sammer M.; Morello, Glenn R. & Cundari, Thomas R., 1964-
Description: This article discusses coinage metal-ethylene complexes supported by tris(pyrazolyl)borates. Abstract: Data from computational and experimental sources have been combined to address the bonding and structure of [RB(3-(R1),5-(R2)Pz)3]M(C2H4) complexes, where M = Cu, Ag, Au. A k3 to k2 distortion of the scorpionate ligand was also studied. NMR properties were deemed to be the most useful in assessing the nature of the bonding in these complexes. Using computational recipes, 13C chemical shifts accurately reproduced quantitative experimental values and trends as a function of metal, ligand, and substituent. Au-ethylene complexes are found to be substantially "less π-complex" (T-shaped structure) in their bonding description versus Ag and Cu congeners, although the former are by no means entirely metallacyclopropane in their constitution. Combining the present calculations with prior contributions to coinage metal bonding leads the authors to propose that similarity of molecular structure among a congeneric series of coinage metal complexes reflects a principally ionic coinage metal-ligand bonding regime, while dissimilarity of structure within the series reflects a primarily covalent bonding regime.
Contributing Partner: UNT College of Arts and Sciences
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Metaphoric Analysis of a Shipyard Union Dispute: Theory and Method in the Cultural Analysis of Collective Action
Date: February 2009
Creator: Ignatow, Gabe
Description: This book chapter discusses the metaphoric analysis of a shipyard union dispute and the theory and method in the cultural analysis of collective action. Rather than treating grievances and political opportunities, given, and exogenous to organized movement groups, cultural analysts of social movements have recently focused on cognitive and linguistic processes by which factors relevant to collective behavior are themselves interpreted collectively.
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc78308/
Expression of genes associated with carbohydrate metabolism in cotton stems and roots
Date: January 22, 2009
Creator: Taliercio, Earl W.; Romano, Gabriela; Scheffler, Jodi & Ayre, Brian G.
Description: This article discusses the expression of genes associated with carbohydrate metabolism in cotton stems and roots. Abstract: Background: Cotton (Gossypium hirsutum L) is an important crop worldwide that provides fiber for the textile industry. Cotton is a perennial plant that stores starch in stems and roots to provide carbohydrates for growth in subsequent seasons. Domesticated cotton makes these reserves available to developing seeds which impacts seed yield. The goals of these analyses were to identify genes and physiology pathways that establish cotton stems and roots as physiological sinks and investigate the role these pathways play in cotton development during seed set. Results: Analysis of field-grown cotton plants indicated that starch levels peaked about the time of first anthesis and then declined similar to reports in greenhouse-grown cotton plants. Starch accumulated along the length of the stem and the shape and size of the starch grains from stems were easily distinguished from transient starch. Microarray analyses compared gene expression in tissues containing low levels of starch with tissues rapidly accumulating starch. Statistical analysis of differentially expressed genes indicated increased expression among genes associated with starch synthesis, starch degradation, hexose metabolism, raffinose synthesis and trehalose synthesis. The anticipated changes in these sugars ...
Contributing Partner: UNT College of Arts and Sciences
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Arylpalladium Phosphonate Complexes as Reactive Intermediates in Phosphorus-Carbon Bond Forming Reactions
Date: January 21, 2009
Creator: Kohler, Mark C.; Grimes, Thomas V.; Wang, Xiaoping; Cundari, Thomas R., 1964- & Stockland, Robert A., Jr.
Description: This article discusses arylpalladium phosphonate complexes as reactive intermediates in phosphorus-carbon bond forming reactions. Abstract: Phosphorus-carbon bond formation from discrete transition metal complexes have been investigated through a combination of synthetic, spectroscopic, crystallographic, and computational methods. Reactive intermediates of the type (diphosphine)Pd(aryl)P(O)(OEt)2) have been prepared, characterized, and studied as possible intermediates in metal-mediated coupling reactions. Several of the reactive intermediates were characterized crystallographically, and a discussion of the solid state structures is presented. In contrast to other carbon-heteroelement bond forming reactions, palladium complexes containing electron-donating substituents on the aromatic fragment exhibited faster rates of reductive elimination. Large bit angle diphosphine ligands induced rapid rates of elimination, while bipyridine and small bite angle diphosphine ligands resulted in much slower rates of elimination. An investigation of the effect of typical impurities on the elimination reaction was carried out. While excess diphosphine, pyridine, and acetonitrile had little effect on the observed rate, the addition of water slowed the phosphorus-carbon bond forming reaction. Coordination of water to the complex was observed spectroscopically and crystallographically. Computational studies were utilized to probe the reaction pathways for P-C bond formation via Pd catalysis.
Contributing Partner: UNT College of Arts and Sciences
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Effective carbon partitioning driven by exotic phloem-specific regulatory elements fused to the Arabidopsis thaliana AtSUC2 sucrose-proton symporter gene
Date: January 20, 2009
Creator: Srivastava, Avinash C.; Ganesan, Savita; Ismail, Ihab O. & Ayre, Brian G.
Description: This article discusses effective carbon partitioning. Abstract: Background: AtSUC2 (At1g22710) from Arabidopsis thaliana encodes a phloem-localized sucrose/proton symporter required for efficient photoassimilate transport from source tissues to sink tissues. AtSUC2 plays a key role in coordinating the demands of sink tissues with the output capacity of source leaves, and in maintaining phloem hydrostatic pressure during changes in plant-water balance. Expression and activity are regulated, both positively and negatively, by developmental (sink or source transition) and environmental cues, including light, diurnal changes, photoassimilate levels, turgor pressure, drought and osmotic stress, and hormones. Results: To assess the importance of this regulation to whole-plant growth and carbon partitioning, AtSUC2 cDNA was expressed from two exotic, phloem-specific promoters in a mutant background debilitated for AtSUC2 function. The first was a promoter element from Commelina Yellow Mottle Virus (CoYMV), and the second was the rolc promoter from Agrobacterium rhizogenes. CoYMVp::AtSUC2 cDNA restored growth and carbon partitioning to near wild-type levels, whereas plants harboring rolCp::AtSUC2 cDNA showed only partial complementation. Conclusion: Expressing AtSUC2 cDNA from exotic, phloem-specific promoters argues that strong, phloem-localized expression is sufficient for efficient transport. Expressing AtSUC2 from promoters that foster efficient phloem transport but are subject to regulatory cascades different from the ...
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Event-Driven Power-Law Relaxation in Weak Turbulence
Date: January 5, 2009
Creator: Silvestri, Ludovico; Fronzoni, Leone; Grigolini, Paolo & Allegrini, Paolo
Description: This article discusses event-driven power-law relaxation in weak turbulence. Abstract: We characterize the spectral properties of weak turbulence in a liquid crystal sample driven by an external electric field, as a function of the applied voltage, and we find a 1/f noise spectrum S(f) ∝ 1/fn within the whole range 0< ɳ <2. We theoretically explore the hypothesis that the system complexity is driven by non-Poisson events resetting the system through creation and annihilation of coherent structures, retaining no memory of previous history (crucial events). The authors study the time asymptotic regime by means of the density ψ(τ) of the time distances between two crucial events, yielding ɳ = 3 - μ, where μ is defined through the long-time form ψ(τ) ∝ 1/τµ, with 1 < µ < 3. The system regression to equilibrium after an abrupt voltage change experimentally confirms the theory, proving violations of the ordinary linear response theory for both ɳ > 1 and ɳ < 1.
Contributing Partner: UNT College of Arts and Sciences
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Annual Variation of Abundance and Composition in Forest Bird Assemblages on Navarino Island, Cape Horn Biosphere Reserve, Chile
Date: 2009
Creator: Ippi, Silvina; Anderson, Christopher B.; Rozzi, Ricardo, 1960- & Elphick, Chris S.
Description: This article discusses the annual variation of abundance and composition in forest bird assemblages on Navarino Island, Cape Horn Biosphere Reserve, Chile. Abstract: The structure and dynamics of avian communities in the temperate forests of southern South America have been generally studied during the breeding season (November - March), and reports about seasonal variations and migratory behavior of species are almost lacking. This study examined intra-annual variations on a monthly basis in bird species composition and abundance in the world's southernmost forested ecosystems, found in the Cape Horn Biosphere Reserve, Chile (55°S). Combining data obtained through point-count surveys, mist-netting, and checklist methods, the authors recorded a total of 34 bird species belonging to 20 families. Eighteen of these species were Passeriformes, and the most abundant year-round resident species were Thorn-tailed Rayadito (Aphrastura spinicauda) and Patagonian Sierra-Finch (Phrygilus patagonicus). The most abundant seasonal migrants species were White-crested Elaenia (Elaenia albiceps) and Southern House Wren (Troglodytes musculus). Point-count and mist-netting methods showed a reduction in species richness and abundance during winter, with one third of the bird assemblage absent. This proportion was lower than that documented for more northern Nothofagus forests. Additionally, the authors' data provided no evidence that intra-annual patterns of ...
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Dinámica estacional y patrones de distribución de la avifauna asociada a humedales subantárticos en la Reserva de Biosfera Cabo de Hornos (54-55°S), Chile
Date: 2009
Creator: Ibarra, J. Tomás; Rozzi, Ricardo, 1960-; Gilabert, Horacio; Anderson, Christopher B.; McGehee, Steven M. & Bonacic, Cristián
Description: This article discusses the seasonal dynamics and distribution patterns of birds associated to the sub-Antarctic wetlands in Cape Horn Biosphere Reserve (54-55°S), Chile. Abstract: Little is known about bird ecology in sub-Antarctic ecosystems of the Cape Horn Reserve (CHBR), Chile. The authors examined the role of altitude, seashore distance, lake size, season, and vegetation cover in affecting bird diversity and abundance on Navarino Island (54-55°S, 67°W) in the CHBR. The authors determined avian community composition, species richness and relative abundance for wetlands and their adjacent habitats on a seasonal basis. A total of 56 species belonging to 10 orders and 25 families were recorded, and significant seasonal changes for bird species (P = 0.001) and abundance (P < 0.01) were observed, with 33.9% residents, 48.2% winter migrants, and 17.9% with unknown migratory status. The distance of wetlands from the coastline was the main predictor variable for annual species richness (P < 0.01) and total avian abundance (P < 0.05). Wetlands far from the seashore and at higher altitudes had lower diversity and abundance, although the change in elevation was relatively slight (< 300 m). These data show the seasonal patterns and dynamics, as well as the major underlying mechanisms, for ...
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