Role of the (104) MgCl₂ Lateral Cut in Ziegler–Natta Catalysis: A Computational Investigation

Density functional theory (DFT) has been used for the study of ethylene polymerization in the Ziegler–Natta (ZN) olefin polymerization system for eight different alkoxy group containing titanium catalysts (<b>Cat-A–H</b>), Ti­(III)­Et­(OR)­(OR′) (where R = −CH₃, – Et, −<i>tert</i>-butyl, −cyclohexane, R′ = −CH₃, −Et, −<i>tert</i>-butyl, −cyclohexane). What is of significance is that the catalysts studied were all considered to be tethered to the (104) MgCl₂ surface, which has traditionally been considered a “dormant” surface in ZN catalysis systems, in contrast to the “more active” (110) MgCl₂ surface. Our calculations indicate that the binding of all the catalysts to the (104) surface is favorable, even after taking entropic effects into account. For purposes of comparison, ethylene polymerization has been investigated for the <b>Cat-C</b> (TiEt­(OEt)₂) and the <b>Cat-H</b> (TiEt­(Cl)­(OC₄H₈Cl)) (OC₄H₈Cl = the chlorobutoxy group) cases, for both the (i) (110) and the (ii) (104) MgCl₂ surfaces. It has been seen that for both (i) and (ii) the energy gap between insertion and the termination barriers (Δ<i>X</i>) was nearly the same for both the <b>Cat-C</b> and <b>Cat-H</b> cases, which shows that ethylene polymerization on the (104) MgCl₂ surface is likely to be a prominent occurrence in Z–N catalysis, when alkoxy groups are bound to the titanium center. Additionally, for the <b>Cat-C</b> and the <b>Cat-H</b> cases, the regio- and stereoselective behavior of the propylene monomer on the titanium species present on the (110) and the (104) MgCl₂ surfaces has also been investigated, and the results indicate that the (104) MgCl₂ surface is only slightly less effective than the (110). However, the calculations also indicate that for <b>Cat-H</b> the (104) MgCl₂ surface significantly improves the molecular weight of polypropylene in comparison to the (110) surface, further showcasing how the (104) surface (ignored until date) might be a major player in ZN catalysis. Given that a major portion of the MgCl₂ support is made up of (104) lateral cuts, the current findings are of considerable relevance

Ruthenium–NHC complex-catalyzed P( iii )-directed C–H borylation of arylphosphines

International audience(NHC)(arene)Ru(II) complexes with bidentate LX-type NHC-carboxylate ligands were efficiently synthesized and fully characterized including solid-state structures. The strong coordination of the NHC carboxylate ligand and the labile character of the arene ligand are highlighted. These unprecedented Ru(II) complexes demonstrated efficient catalytic activities in the selective P(III)-directed C–H borylation at the ortho position of arylphosphines, representing the first report of the use of a ruthenium–NHC based catalyst in C–H borylation

A Photocatalytic Approach for the Synthesis of L‐Shape Bicyclic NHC Ligands

International audienceL‐shape N ‐Heterocyclic Carbenes (NHCs) based on the imidazo[1,5‐ a ]pyridine (ImPy) scaffold have recently gained considerable interest as the true carbene ligand analogues of the popular dialkylbiarylphosphines, better known as Buchwald phosphines. Nevertheless, the substitution pattern of ImPy ligands is still rather limited due to synthetic access issues. We report herein an efficient and versatile visible light photocatalytic strategy to access L‐shape bifunctional ImPy ligands laterally‐functionalized by a phenol group. Mechanistic investigations supported by density functional theory (DFT) reveal that the excited state of the iridium photocatalyst undergoes either a reductive quenching (SET process) or an energy‐transfer quenching (EnT process) depending on the nature of the counterion of the 5‐bromoimidazo[1,5‐ a ]pyridinium substrate salt. Moreover, the bifunctional character of these new family of L‐shape ImPy ligands is demonstrated by the preparation of a gold(I) complex exhibiting a free OH function capable of intermolecular hydrogen bonding. This work highlights the advantage of visible light photocatalysis in the synthesis of advanced NHC ligand structures, a strategy that has not yet been considered despite its potential benefits in terms of versatility, diversity and practicability

Exploring Heteroaromatic Rings as a Replacement for the Labile Amide of Antiplasmodial Pantothenamides

Malaria-causing Plasmodium parasites are developing resistance to antimalarial drugs, providing the impetus for new antiplasmodials. Although pantothenamides show potent antiplasmodial activity, hydrolysis by pantetheinases/vanins present in blood rapidly inactivates them. We herein report the facile synthesis and biological activity of a small library of pantothenamide analogues in which the labile amide group is replaced with a heteroaromatic ring. Several of these analogues display nanomolar antiplasmodial activity against Plasmodium falciparum and/or Plasmodium knowlesi, and are stable in the presence of pantetheinase. Both a known triazole and a novel isoxazole derivative were further characterized and found to possess high selectivity indices, medium or high Caco-2 permeability, and medium or low microsomal clearance in vitro. Although they fail to suppress Plasmodium berghei proliferation in vivo, the pharmacokinetic and contact time data presented provide a benchmark for the compound profile likely required to achieve antiplasmodial activity in mice and should facilitate lead optimization.This work was financially supported by grants from the Australian National Health and Medical Research Council (to K.J.S. and K.A.; APP1129843) and the Canadian Institute of Health Research (to K.A.; grant no. 89784). The China Scholarship Council is thanked for providing a scholarship to J.G. The Australian Government provided scholarships for E.T.T. and V.M.H., whereas C.S. was funded by an NHMRC Overseas Biomedical Fellowship (1016357)

Platelet inhibition by nitrite is dependent on erythrocytes and deoxygenation.

Nitrite is a nitric oxide (NO) metabolite in tissues and blood, which can be converted to NO under hypoxia to facilitate tissue perfusion. Although nitrite is known to cause vasodilation following its reduction to NO, the effect of nitrite on platelet activity remains unclear. In this study, the effect of nitrite and nitrite+erythrocytes, with and without deoxygenation, on platelet activity was investigated.Platelet aggregation was studied in platelet-rich plasma (PRP) and PRP+erythrocytes by turbidimetric and impedance aggregometry, respectively. In PRP, DEANONOate inhibited platelet aggregation induced by ADP while nitrite had no effect on platelets. In PRP+erythrocytes, the inhibitory effect of DEANONOate on platelets decreased whereas nitrite at physiologic concentration (0.1 µM) inhibited platelet aggregation and ATP release. The effect of nitrite+erythrocytes on platelets was abrogated by C-PTIO (a membrane-impermeable NO scavenger), suggesting an NO-mediated action. Furthermore, deoxygenation enhanced the effect of nitrite as observed from a decrease of P-selectin expression and increase of the cGMP levels in platelets. The ADP-induced platelet aggregation in whole blood showed inverse correlations with the nitrite levels in whole blood and erythrocytes.Nitrite alone at physiological levels has no effect on platelets in plasma. Nitrite in the presence of erythrocytes inhibits platelets through its reduction to NO, which is promoted by deoxygenation. Nitrite may have role in modulating platelet activity in the circulation, especially during hypoxia

Iridium(I) complexes with bidentate NHC ligands as catalysts for dehydrogenative directed C-H silylation

International audienceA series of (NHC)(cod)Ir(I) complexes bearing NHC-carboxylate ligands were efficiently synthesized and fully characterized. Their solid-state structures confirmed the bidentate coordination mode of these LX-type NHC ligands. These unprecedented iridium(I) complexes demonstrated efficient catalytic activities in dehydrogenative directed C-H silylation of arenes, and allowed for excellent ortho-selectivity control with aromatic silylating agents

Nitrite+erythrocytes inhibited ATP release from platelets induced by ADP (A), collagen (B), and U46619 (C).

<p>PRP+erythrocytes (20% hematocrit) were incubated with 0.1 µM nitrite in the presence and absence of 200 µM C-PTIO for 5 min. The ATP release was induced by 20 µM ADP, 2.5 µg/mL collagen or 1 µM U46619. ^*<i>P</i><0.05 compared with PRP+erythrocytes and PRP+erythrocytes+nitrite+C-PTIO (ANOVA). All experiments were performed at 37°C. Data are means ± SEM (n = 5).</p

Nitrite+erythrocytes inhibited platelet aggregation.

<p>(A) ADP induced platelet aggregation in PRP+erythrocytes (20% hematocrit) in the concentration dependent manner. (B) Erythrocytes at 0, 1, 10 and 20% hematocrit did not have effect on ADP-induced platelet aggregation in the absence of nitrite. (C) Nitrite+erythrocytes (20% hematocrit) inhibited ADP-induced platelet aggregation. Nitrite was incubated in PRP or PRP+erythrocytes in the presence or absence of 200 µM C-PTIO for 5 min before induction of aggregation by ADP. ^*<i>P</i><0.05 compared with PRP and PRP+erythrocytes+C-PTIO (ANOVA). (D) The inhibitory effect of 0.1 µM nitrite was dependent on hematocrits. PRP and PRP+erythrocytes (1, 10, and 20% hematocrit) were incubated with 0.1 µM nitrite for 5 min before induction of platelet aggregation by 20 µM ADP. ADP-induced platelet aggregation in the absence of nitrite was shown in the control group. ^*<i>P</i><0.05 compared with PRP+nitrite at 0% hematocrit (ANOVA). (E) Nitrite+erythrocytes inhibited collagen-induced platelet aggregation. PRP or PRP+erythrocytes samples (20% hematocrit) were incubated with nitrite in the presence and absence of 200 µM C-PTIO for 5 min and then the aggregation was induced by 2.5 µg/mL collagen. ^*<i>P</i><0.05 compared with PRP and PRP+erythrocytes+C-PTIO (ANOVA). (F) Nitrite+erythrocytes inhibited U46619-induced platelet aggregation. 0.1 µM nitrite was incubated in PRP or PRP+erythrocytes (20% hematocrit) in the presence or absence of 200 µM C-PTIO for 5 min. Then, the aggregation was induced by 1 µM U46619. ^*<i>P</i><0.05 compared with PRP+erythrocytes and PRP+erythrocytes+C-PTIO (ANOVA). All experiments were performed at 37°C. Data are means ± SEM (n≥3).</p