Metallacyclobutadiene versus Metallatetrahedrane Structures for CI,MoC,H, Complexes

98 Organometallics 1988, 7, [98][99][100][101][102][103][104][105] portant difference in chemical reactivity between Fe-(TMM)L3 complexes (L = PR3 (3) and L = CO): a oneelectron transfer easily occurs from 3 on attempts of alkylation and the resulting 17-electron intermediate is stabilized by the basic phosphines L, whereas Fe-(TMM)(CO), is the site of electrophilic substitutions,15 but its one-electron abstraction is difficult to perform and immediately undergoes decomposition, presumably via initial cleavage of an Fe-CO bond. This illustrates the deciding role of the nature of the ligands to modulate the behavior of complexes within the same family. Cyclic voltammetry of 6a-c showed a reversible oneelectron oxidation at negative potential corresponding to the formation of Fe(o-xylylene)L,+ (69, and an irreversible wave between 0.50 and 0.70 V was observed Conclusion Our results present an easy access to electron-rich (q4-hydrocarbon)iron complexes via FeC12(PR3)n intermediates, magnesium, and halogenated substrates. This method avoids the preliminary preparation of unstable Grignard reagents and should offer a potential for organometallic syntheses. The nature and the number of ancillary PR3 groups play a determining role for the reactivity of FeC12(PR3) with o-BrMgCH2C6H4CH3, which leads to either a C-H activation or a C-C coupling reaction. The studied Fe(q4-TMM)L3 and Fe(q4-o-xylylene)L3 complexes show at the same time a high tendency to give an electron transfer and an unexpected stability of the resulting paramagnetic species. These two characteristics, which are indicative of the electron-rich nature of the complexes, appear to be modulated by the electron-donor capability of the phosphorus groups and also by the type of interaction between the hydrocarbon ligand and the' metal. Acknowledgment. We are grateful to C. Mountassir and Dr. S. Sinbandhit for helpful assistance and discussions. Registry No. la, 55853-16-2; lb, 95911-92-5; Id, 55059-43-3; 2,1871-57-4; 3a, 95911-86-7; 3a+(CF3SOf), 95911-88-9; 3a+(N0<), 111409-15-5; 3c+(CF3S03-), 111409-17-7; 4a, 612-12-4; 5,56812-61-4; 6a, 111409-13-3; 6a+, 111409-14-4; 6b, 95911-91-4; 6d, 95911-89-0; 7,952-80-7; 8b, 111409-18-8; 9b, 110074-88-9; MeC-(CH2PMe&, 77609-83-7 The bonding and energetics in the C13MoC3H3 metallacyclobutadiene are contrasted with those in the metallatetrahedrane. The complexes are found to be within 20 kcal/mol of one another, with the metallatetrahedrane being the lower in energy. The Mo-C bonds are essentially covalent in both structures, and the metallacyclobutadiene posseseefl resonance stabilization. Charge distribution in the carbon fragments reveals no cyclopropenium character in the C3H3 ring of the metallatetrahedrane. Bonding, energetics, and charge distributions are all discussed with an emphasis on structure and reactivity

Grassroots Agency: Participation and Conflict in Buenos Aires Shantytowns seen through the Pilot Plan for Villa 7 (1971–1975)

open access articleIn 1971, after more than a decade of national and municipal policies aimed at the top-down removal of shantytowns, the Buenos Aires City Council approved the Plan Piloto para la Relocalización de Villa 7 (Pilot Plan for the Relocation of Shantytown 7; 1971–1975, referred to as the Pilot Plan hereinafter). This particular plan, which resulted in the construction of the housing complex, Barrio Justo Suárez, endures in the collective memory of Argentines as a landmark project regarding grassroots participation in state housing initiatives addressed at shantytowns. Emerging from a context of a housing shortage for the growing urban poor and intense popular mobilizations during the transition to democracy, the authors of the Pilot Plan sought to empower shantytown residents in novel ways by: 1) maintaining the shantytown’s location as opposed to eradication schemes that relocated the residents elsewhere, 2) formally employing some of the residents for the stage of construction, as opposed to “self-help” housing projects in which the residents contributed with unpaid labor, and 3) including them in the urban and architectural design of the of the new housing. This paper will examine the context in which the Pilot Plan was conceived of as a way of re-assessing the roles of the state, the user, and housing-related professionals, often seen as antagonistic. The paper argues that residents’ fair participation and state intervention in housing schemes are not necessarily incompatible, and can function in specific social and political contexts through multiactor proposals backed by a political will that prioritizes grassroots agency

Elliptic flow of charged particles in Pb-Pb collisions at 2.76 TeV

We report the first measurement of charged particle elliptic flow in Pb-Pb collisions at 2.76 TeV with the ALICE detector at the CERN Large Hadron Collider. The measurement is performed in the central pseudorapidity region (|$\eta$|<0.8) and transverse momentum range 0.2< $p_{\rm T}$< 5.0 GeV/$c$. The elliptic flow signal v$_2$, measured using the 4-particle correlation method, averaged over transverse momentum and pseudorapidity is 0.087 $\pm$ 0.002 (stat) $\pm$ 0.004 (syst) in the 40-50% centrality class. The differential elliptic flow v$_2(p_{\rm T})$ reaches a maximum of 0.2 near $p_{\rm T}$ = 3 GeV/$c$. Compared to RHIC Au-Au collisions at 200 GeV, the elliptic flow increases by about 30%. Some hydrodynamic model predictions which include viscous corrections are in agreement with the observed increase.Comment: 10 pages, 4 captioned figures, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/389

Higher harmonic anisotropic flow measurements of charged particles in Pb-Pb collisions at 2.76 TeV

We report on the first measurement of the triangular $v_3$, quadrangular $v_4$, and pentagonal $v_5$ charged particle flow in Pb-Pb collisions at 2.76 TeV measured with the ALICE detector at the CERN Large Hadron Collider. We show that the triangular flow can be described in terms of the initial spatial anisotropy and its fluctuations, which provides strong constraints on its origin. In the most central events, where the elliptic flow $v_2$ and $v_3$ have similar magnitude, a double peaked structure in the two-particle azimuthal correlations is observed, which is often interpreted as a Mach cone response to fast partons. We show that this structure can be naturally explained from the measured anisotropic flow Fourier coefficients.Comment: 10 pages, 4 figures, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/387

Controversy and consensus on the management of elevated sperm DNA fragmentation in male infertility: A global survey, current guidelines, and expert recommendations

Purpose Sperm DNA fragmentation (SDF) has been associated with male infertility and poor outcomes of assisted reproductive technology (ART). The purpose of this study was to investigate global practices related to the management of elevated SDF in infertile men, summarize the relevant professional society recommendations, and provide expert recommendations for managing this condition. Materials and Methods An online global survey on clinical practices related to SDF was disseminated to reproductive clinicians, according to the CHERRIES checklist criteria. Management protocols for various conditions associated with SDF were captured and compared to the relevant recommendations in professional society guidelines and the appropriate available evidence. Expert recommendations and consensus on the management of infertile men with elevated SDF were then formulated and adapted using the Delphi method. Results A total of 436 experts from 55 different countries submitted responses. As an initial approach, 79.1% of reproductive experts recommend lifestyle modifications for infertile men with elevated SDF, and 76.9% prescribe empiric antioxidants. Regarding antioxidant duration, 39.3% recommend 4–6 months and 38.1% recommend 3 months. For men with unexplained or idiopathic infertility, and couples experiencing recurrent miscarriages associated with elevated SDF, most respondents refer to ART 6 months after failure of conservative and empiric medical management. Infertile men with clinical varicocele, normal conventional semen parameters, and elevated SDF are offered varicocele repair immediately after diagnosis by 31.4%, and after failure of antioxidants and conservative measures by 40.9%. Sperm selection techniques and testicular sperm extraction are also management options for couples undergoing ART. For most questions, heterogenous practices were demonstrated. Conclusions This paper presents the results of a large global survey on the management of infertile men with elevated SDF and reveals a lack of consensus among clinicians. Furthermore, it demonstrates the scarcity of professional society guidelines in this regard and attempts to highlight the relevant evidence. Expert recommendations are proposed to help guide clinicians

thyrsiflora

Lysimachia thyrsiflora Linnaeustufted yellow loosestrife;tufted loosestrife;water loosestrife;yellow loosestrife;swamp loosestrifelysimaque thyrsiflore;lysimaque à fleurs en thyrsethyrsifloraNorth of Fort McMurray Poplar Ck. L.In standing water on floating Carex mat.Typha spp., Carex spp