Coordination of ethylene to a zwitterionic Rh(III) half-sandwich complex : influence of ambiphilic Ligands on reactivity

The reactivity of Rh(III) half-sandwich complex Cp*RhMe2(κ P -μ Al-MePMe2CH2AlMe2) 2 (Cp* = η 5 - pentamethylcyclopentadienyl) with ethylene was investigated. Coordination of ethylene (or ethylene-d4) gave a mixture of products including as principal species zwitterionic complexes Cp*Rh+Me(C2H4)(PMe2CH2AlMe3 - ) 4 (or 4-d4) and [Cp*Rh+Me(C2H4)(PMe2CH2AlMe3 - )][AlMe3] (4’), after the abstraction of a Rh-methyl group by the pendant Lewis acid, and base free Cp*RhMe2(PMe2CH2AlMe2) (5). Heating this complex at 50 °C results in the generation of propene (or propene-d3,4), methane (or methane-d1), and trace amounts of butene, as organic materials, as well as previously characterized [Cp*RhMe(μ 2 -η 2 (P,C)-PMe2CH2)]2 (10) and rhodium(I) species. Two different pathways for the reactivity of the zwitterionic π-complex were investigated by density functional theory (DFT). It is likely that propene is formed by β-hydride elimination from a cationic Rh-propyl fragment that is generated either by insertion of ethylene into a Rh-C bond or by a nucleophilic attack of the methyl-aluminate fragment on coordinated ethylene. After releasing propene, the neutral complex Cp*RhHMe(PMe2CH2AlMe2) 11 is most likely responsible for the reductive elimination of methane

On the concept of frustrated Lewis pairs

In this concept article, we consider the notion of ‘frustrated Lewis pairs’ (FLPs). While the original use of the term referred to steric inhibition of dative bond formation in a Lewis pair, work in the intervening decade demonstrates the limitation of this simplistic view. Analogies to known transition metal chemistry and the applications in other areas of chemistry are considered. In the light of these findings, we present reflections on the criteria for a definition of the term ‘frustrated Lewis pair’. Segregation of the Lewis acid and base and the kinetic nature of FLP reactivity are discussed. We are led to the conclusion that, while an all-inclusive definition of FLP is challenging, the notion of ‘FLP chemistry’ is more readily recognized

Metal-free reduction of CO2

Even if carbon dioxide is now considered a major pollutant and the main source of global warming, it remains the feedstock used by Nature to generate organic compounds. There is considerable interest to find chemical processes that could replace fossil fuels by CO2 to generate industrially relevant carbon containing molecules. Mostly relying on frustrated Lewis pair technology and on the nucleophilic activation of CO2 or reducing agents by organic Lewis bases, novel catalytic opportunities have emerged to affect the metal-free catalytic reduction of carbon dioxide

Aluminum complexes bearing fonctionalized trisamido ligands and their reactivity in the polymerization of ε-caprolactone and rac-lactide

The addition of 1 and 2 equivalents of AlMe3 to cis,cis-C6H9(NHCH2C6H4-o-R)3 (R = PPh2 (3) and SPh (4)) gives complexes [cis,cis-C6H9(NCH2C6H4-o-R-κN)2(NHCH2C6H4-o-R-κN)]AlMe (R = PPh2 (7) and SPh (8)) and [cis,cis-C6H9(NCH2C6H4-o-R)3-κ5μ2N]Al2Me3 (R = PPh2 (5) and SPh (6)), respectively. The bimetallic complexes are active in the polymerization of ε-caprolactone and rac-lactide whereas the monometallic complexes are not, although no cooperative behaviour is observed between the two aluminium atoms of 5 and 6. The polycaprolactone samples, which were characterized using 1H NMR, MALDI-TOF, and SEC, show the presence of residual ligands 3 or 4 bound to the polymer and the in situ NMR studies confirm that the insertion occurs in an Al–N bond

(η4-Cyclo­octa-1,5-diene)diiodidoplatinum(II)

The monoclinic title complex, [PtI2(C8H12)], characterized by a twisted cyclo­octa­diene ring, is similar to its Cl and Br ortho­rhom­bic homologues. The observed Pt—I bond distances of 2.6094 (5) and 2.6130 (5) Å are in the expected range for PtI2 complexes. The C=C double bonds in the mol­ecule differ significantly [1.373 (10) and 1.403 (10) Å]. As expected for a platinum(II) complex, the PtII atom is in a square-planar environment (ΣPtα= 359.71°)

Mono-boratabenzene and phospholyl zirconocene(IV) derivatives : towards mixed heterocycles zirconocene complexes

In hopes of extending the existing knowledge on the chemistry of phospholyl and boratabenzene complexes of zirconium, which have shown potential notably as polymerization catalysts, this study aims at exploring the synthesis of mono boratabenzene and mono phospholyl zirconium complexes and at studying their reactivity towards the formation of mixed (boratabenzene)(phospholyl)zirconium complexes. Several derivatives of (η5-phospholyl)Zr(NMe2)xCl3−x and (η6-boratabenzene-NMe2)Zr(NMe2)xCl3−x were synthesized and used as precursors for the formation of mixed (boratabenzene)(phospholyl)zirconium complexes

Quelques résultats sur la modélisation et la couverture de portefeuilles exposés au risque de longévité

Ce mémoire vise à tarifer des produits dérivés ayant comme sous-jacent les taux de survie d'une cohorte. Pour ce faire, les taux de mortalité sont modélisés, pour être ensuite transformé en taux de survie. L'étape suivante est de construire un portefeuille constitué de 4 000 femmes Canadiennes âgées de 65 ans. Les simulations de Monte-Carlo sont ensuite utilisées afin de simuler les décès de ces femmes. Ces décès sont ensuite utiliser pour calculer l'espérance des flux monétaires futurs. Le principe est ensuite appliqué à un portefeuille de femmes canadiennes âgées entre 65 et 69 ans. L'objectif étant d'ajouter du réalisme à l'étude

Lewis acidity quantification and catalytic activity of Ti, Zr and Al-supported mesoporous silica

Water-tolerant supported Lewis acids are actively sought after, in particular to address the challenging direct amidation reaction. To this aim, a versatile and easy synthesis of large pore silica materials with supported Ti-, Al-, Zr-Lewis acids, using acetyl acetonate as a metal-stabilizing agent, was accomplished. The formation of bulk metal oxides was not observed, even at high concentrations of metal species. The Lewis acidity was demonstrated using quantitative and qualitative titration techniques using a series of Hammett indicators, such as butter yellow, phenylazodiphenylphosphine and dicinnamalacetone. The optimal concentration of metals corresponding to the highest Lewis acidity of solids was found to be 4% for Al-SBA-15, 12–15% for Ti-SBA-15 and 7% for Zr-SBA-15 materials. The water-tolerance of the supported metal centers was explored by a pyridine adsorption-FTIR study before and after water addition. The metalated materials were used as water-tolerant heterogeneous catalysts for the amidation of electron-poor and bulky amines, such as substituted anilines and morpholine, obtaining 59–99% yield of the corresponding amides