Aluminum Amidinates: Insights into Alkyne Hydroboration.

The mechanism of the aluminum-mediated hydroboration of terminal alkynes was investigated using a series of novel aluminum amidinate hydride and alkyl complexes bearing symmetric and asymmetric ligands. The new aluminum complexes were fully characterized and found to facilitate the formation of the (E)-vinylboronate hydroboration product, with rates and orders of reaction linked to complex size and stability. Kinetic analysis and stoichiometric reactions were used to elucidate the mechanism, which we propose to proceed via the initial formation of an Al-borane adduct. Additionally, the most unstable complex was found to promote decomposition of the pinacolborane substrate to borane (BH3), which can then proceed to catalyze the reaction. This mechanism is in contrast to previously reported aluminum hydride-catalyzed hydroboration reactions, which are proposed to proceed via the initial formation of an aluminum acetylide, or by hydroalumination to form a vinylboronate ester as the first step in the catalytic cycle

Functionalisation of Carbon-Fluorine Bonds with Main Group Reagents

Synthetic approaches to produce reactive chemical building blocks from fluorinated molecules by the functionalization of carbon–fluorine bonds with main group reagents are reviewed. The reaction types can be categorized as: (i) the formal 1,2-addition of C–F bonds across Si–Si, B–B, or Mg–Mg bonds; (ii) the oxidative addition of C–F bonds to Si(II), Ge(II), and Al(I) centres; and (iii) the dehydrogenative coupling of C–F bonds with Al–H or B–H bonds. Many of the advances have emerged between 2015–2016 and are largely focused upon aromatic substrates that contain sp2 C–F bonds

Recent advances in low oxidation state aluminium chemistry

Documenting the synthesis and isolation of novel low oxidation state aluminium (Al) compounds, which until recently has seen relatively slow progress over the 30 years since such species were first isolated

Metal-Size Influence in Iso-Selective Lactide Polymerization

Iso-selective initiators for the ring-opening polymerization (ROP) of rac-lactide are rare outside of Group 13. We describe the first examples of highly iso-selective lutetium initiators. The phosphasalen lutetium ethoxide complex shows excellent iso-selectivity, with a Pi value of 0.81–0.84 at 298 K, excellent rates, and high degrees of polymerization control. Conversely, the corresponding La derivative exhibits moderate heteroselectivity (Ps=0.74, 298 K). Thus, the choice of metal center is shown to be crucial in determining the level and mode of stereocontrol. The relative order of rates for the series of complexes is inversely related to metallic covalent radius: that is, La>Y>Lu

How message framing affects consumer attitudes in food crises

Purpose - The purpose of this paper is to explore the relationship between consumer risk perceptions and behaviour when information about food risks is framed in a positive or negative way. Design/methodology/approach - Using food consumption scenarios in an on-line experiment consumers perceived risk and risk tolerance is examined when messages are framed in three different news-type stories. Findings - As anticipated, message framing emerged as a significant predictor of perceived risk and the higher an individual’s self-reported tolerance of risk, the more risk they were willing to accept. Research limitations/implications - The use of hypothetical scenarios and relatively small convenience sample size could be improved by further research. Practical implications - Through simple adjustments to wording, food crises of confidence may be reduced and the implications for communication management strategies are discussed. Originality/value - Originality stems from being one of the first papers to use Framing and Prospect Theory in a food crisis situation, in which both risk and framing are operationalised in different ways and the risk was not specified by the researcher. Also, unlike previous research identical numerical facts were framed in a positive, negative or neutral light by changing the wording

Colonial Organization of Mine Labour in Charcas 1 (Present-Day Bolivia) and Its Consequences 2 (Sixteenth to the Seventeenth Centuries)

This article analyses the changes in the organization of labour during the sixteenth and seventeenth centuries in colonial Charcas, present-day Bolivia, focusing on the role that different colonial authorities played in this process and its consequences. The Spanish took advantage of the pre-Hispanic organization of labour from the beginning of their conquest. However, in a colonial context, labour relations changed significantly, and the architect of those alterations was Viceroy Francisco de Toledo. We examine the transformations in mine labour carried out by the Spanish colonial polity; these had a significant effect not only on mining, but also on all labour relations in the southern colonial Andes.Fil: Gil Montero, Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Instituto de Geografía, Historia y Ciencias Sociales. Universidad Nacional del Centro de la Provincia de Buenos Aires. Instituto de Geografía, Historia y Ciencias Sociales; ArgentinaFil: Zagalsky, Paula Cecilia. Universidad Nacional de Jujuy; Argentina. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Functionalisation of Carbon–Fluorine Bonds with Main Group Reagents

Synthetic approaches to produce reactive chemical building blocks from fluorinated molecules by the functionalization of carbon–fluorine bonds with main group reagents are reviewed. The reaction types can be categorized as: (i) the formal 1,2-addition of C–F bonds across Si–Si, B–B, or Mg–Mg bonds; (ii) the oxidative addition of C–F bonds to Si(II), Ge(II), and Al(I) centres; and (iii) the dehydrogenative coupling of C–F bonds with Al–H or B–H bonds. Many of the advances have emerged between 2015–2016 and are largely focused upon aromatic substrates that contain sp2 C–F bonds

Reversible Alkene Binding and Allylic C-H Activation with an Aluminum(I) Complex

The monomeric molecular aluminium(I) complex 1 [{(ArNCMe)2CH}Al] (Ar = 2,6-di-iso-propylphenyl) reacts with a series of terminal and strained alkenes including ethylene, propylene, allylbenzene and norbornene to form alkene bound products. Remarkably all these reactions are reversible under mild conditions (298–353 K) with alkene binding being disfavoured at higher temperatures due to the positive reaction entropy. Van't Hoff analyses have allowed quantification of the binding events with Image ID:c8sc04865g-t1.gif. Calculations and single crystal X-ray diffraction studies are consistent with the alkene bound species being metallocyclopropane complexes. Alkene binding involves a reversible redox process with changes from the +1 to +3 aluminium oxidation state. Under more forcing conditions the metallocyclopropane complexes undergo non-reversible allylic C–H bond activation to generate aluminium(III) allyl hydride complexes. This represents a rare example of redox-based main group reactivity in which reversible substrate binding is followed by a further productive bond breaking event. Analysis of the mechanism reveals a reaction network in which alkene dissociation and reformation of 1 is required for allylic C–H activation, a realisation that has important implications for the long-term goal of developing redox-based catalytic cycles with main group compounds