Die Sammlung Simone Collinet. Simone Breton als leidenschaftliche Sammlerin des Surrealismus

A series of highly active yttrium phosphasalen initiators for the heteroselective ring-opening polymerization of <i>rac</i>-lactide are reported. The initiators are yttrium alkoxide complexes ligated by iminophosphorane analogues of the popular “salen” ligand, termed “phosphasalens”. A series of novel phosphasalens have been synthesized, with varying substituents on the phenoxide rings and ethylene, propylene, <i>rac</i>-cyclohexylene, <i>R</i>,<i>R</i>-cyclohexylene, phenylene, and 2,2-dimethylpropylene groups linking the iminophosphorane moieties. Changing the substituents on the phosphasalen ligands results in changes to the rates of polymerization (<i>k</i>_obs) and to the PLA heterotacticity (<i>P</i>_s = 0.87). Generally, the initiators have high rates, excellent polymerization control, and a tolerance to low loadings

The word as a unit of meaning. The role of context in words meaning

A unit of meaning is a word plus all those words within its contextual context that are needed to disambiguate this word to make it monosemous. A lot of research were made to study the influence of the context. They testify that there is usually in each word a hard core of relatively stable meaning and can be modified by the context within certain limits

Branched Redox-Active Complexes for the Study of Novel Charge Transport Processes

The syntheses and electrochemical/optical properties of some branched and linear 1,1′-substituted ferrocene complexes for molecular electronics are described. Metal centers were extended (and where relevant, connected) by arylethynyl spacers functionalized with <i>m-</i>pyridyl, <i>tert-</i>butylthiol (S^<i>t</i>Bu), and trimethylsilyl (TMS) moieties. Such systems provide two well-defined molecular pathways for electron transfer and hold interesting prospects for the study of new charge transport processes, such as quantum interference, local gating, and correlated hopping events

Catalytic Transformation of Levulinic Acid to 2‑Methyltetrahydrofuran Using Ruthenium–<i>N</i>‑Triphos Complexes

A series of pre- or in situ-formed ruthenium complexes were assessed for the stepwise catalytic hydrogenation of levulinic acid (LA) to 2-methyltetrahydrofuran (2-MTHF) via γ-valerolactone (γVL) and 1,4-pentanediol (1,4-PDO). Two different catalytic systems based on the branched triphosphine ligands Triphos (CH₃C­(CH₂PPh₂)₃) and <i>N</i>-triphos (N­(CH₂PPh₂)₃) were investigated. The most active catalyst was the preformed ruthenium species [RuH₂(PPh₃)­{N­(CH₂PPh₂)₃-κ³<i>P</i>}] (<b>5</b>), which gave near quantitative conversion of LA to 1,4-PDO when no acidic additives were present, and 87% 2-MTHF when used in conjunction with HN­(Tf)₂. Various acidic additives were assessed to promote the final transformation of 1,4-PDO to 2-MTHF; however, only HN­(Tf)₂ was found to be effective, and NH₄PF₆ and <i>para</i>-toluenesulfonic acid (<i>p</i>-TsOH) were found to be detrimental. Mechanistic investigations were carried out to explain the observed catalytic trends and importantly showed that PPh₃ dissociation from <b>5</b> resulted in its improved catalytic reactivity. The presence of acidic additives removes catalytically necessary hydride ligands and may also compete with the substrate for binding to the catalytic metal center, explaining why only an acid with a noncoordinating conjugate base was effective. Crystals suitable for X-ray diffraction experiments were grown for two complexes: [Ru­(NCMe)₃{N­(CH₂PPh₂)₃-κ³<i>P</i>}] (<b>14</b>) and [Ru₂(μ-Cl)₃{N­(CH₂PPh₂)₃-κ³<i>P</i>}₂]­[BPh₄] (<b>16</b>)

8‑Quinolinolato Gallium Complexes: Iso-selective Initiators for <i>rac</i>-Lactide Polymerization

The synthesis and characterization of a series of 8-quinolinolato gallium complexes is presented, and the complexes are analogous to a series of aluminum complexes previously reported. The complexes have been shown to be active initiators for the ring-opening polymerization of <i>rac</i>-lactide. High degrees of polymerization control are demonstrated, as exemplified by the linear evolution of molecular weight as the polymerization progresses, narrow polydispersity indices, and molecular weights corresponding to those predicted on the basis of initiator concentration. Some of the initiators show iso-selective polymerization of <i>rac</i>-lactide, with <i>P</i>_i = 0.70. The polymerization rates have been monitored, and the pseudo first-order rate constants are compared to those of analogous aluminum compounds. The 8-quinolinolato gallium initiators show rates approximately 3 times higher than those of the series of aluminum compounds, while maintaining equivalently high iso-selectivity (<i>P</i>_i = 0.70) and polymerization control

Scandium and Yttrium Phosphasalen Complexes as Initiators for Ring-Opening Polymerization of Cyclic Esters

The synthesis and characterization of novel scandium and yttrium phosphasalen complexes is reported, where phosphasalen refers to two different bis­(iminophosphorane) derivatives of the more ubiquitous salen ligands. The activity of the complexes as initiators for the ring-opening polymerization of cyclic esters is presented. The scandium complexes are inactive for lactide polymerization but slow and controlled initiators for ε-caprolactone polymerization. The lack of activity toward lactide exhibited by these compounds is probed, and a rare example of single-monomer insertion product, unable to undergo further reactions with lactide, is identified. In contrast, the analogous yttrium phosphasalen complex is a very active initiator for the ring-opening polymerization of <i>rac</i>-lactide (<i>k</i>_obs = 1.5 × 10^–3 s^–1 at 1:500 [yttrium initiator]:[<i>rac</i>-lactide], 1 M overall concentration of lactide in THF at 298 K). In addition to being a very fast initiator, the yttrium complex also maintains excellent levels of polymerization control and a high degree of isoselectivity, with the probability of isotactic enchainment being <i>P</i>_i = 0.78 at 298 K

Synthesis, Characterization, and Reactivity of Ruthenium Hydride Complexes of N‑Centered Triphosphine Ligands

The reactivity of the novel tridentate phosphine ligand N­(CH₂PCyp₂)₃ (N-triphos^Cyp, <b>2</b>; Cyp = cyclopentyl) with various ruthenium complexes was investigated and compared that of to the less sterically bulky and less electron donating phenyl derivative N­(CH₂PPh₂)₃ (N-triphos^Ph, <b>1</b>). One of these complexes was subsequently investigated for reactivity toward levulinic acid, a potentially important biorenewable feedstock. Reaction of ligands <b>1</b> and <b>2</b> with the precursors [Ru­(COD)­(methylallyl)₂] (COD = 1,5-cycloocatadiene) and [RuH₂(PPh₃)₄] gave the tridentate coordination complexes [Ru­(tmm)­{N­(CH₂PR₂)₃-κ³<i>P</i>}] (R = Ph (<b>3</b>), Cyp (<b>4</b>); tmm = trimethylenemethane) and [RuH₂(PPh₃)­{N­(CH₂PR₂)₃-κ³<i>P</i>}] (R = Ph (<b>5</b>), Cyp (<b>6</b>)), respectively. Ligands <b>1</b> and <b>2</b> displayed different reactivities with [Ru₃(CO)₁₂]. Ligand <b>1</b> gave the tridentate dicarbonyl complex [Ru­(CO)₂{N­(CH₂PPh₂)₃-κ³<i>P</i>}] (<b>7</b>), while <b>2</b> gave the bidentate, tricarbonyl [Ru­(CO)₃{N­(CH₂PCyp₂)₃-κ²<i>P</i>}] (<b>8</b>). This was attributed to the greater electron-donating characteristics of <b>2</b>, requiring further stabilization on coordination to the electron-rich Ru(0) center by more CO ligands. Complex <b>7</b> was activated via oxidation using AgOTf and O₂, giving the Ru­(II) complexes [Ru­(CO)₂(OTf)­{N­(CH₂PPh₂)₃-κ³<i>P</i>}]­(OTf) (<b>9</b>) and [Ru­(CO₃)­(CO)­{N­(CH₂PPh₂)₃-κ³<i>P</i>}] (<b>11</b>), respectively. Hydrogenation of these complexes under hydrogen pressures of 3–15 bar gave the monohydride and dihydride complexes [RuH­(CO)₂{N­(CH₂PPh₂)₃-κ³<i>P</i>}] (<b>10</b>) and [RuH₂(CO)­{N­(CH₂PPh₂)₃-κ³<i>P</i>}] (<b>12</b>), respectively. Complex <b>12</b> was found to be unreactive toward levulinic acid (LA) unless activated by reaction with NH₄PF₆ in acetonitrile, forming [RuH­(CO)­(MeCN)­{N­(CH₂PPh₂)₃-κ³<i>P</i>}]­(PF₆) (<b>13</b>), which reacted cleanly with LA to form [Ru­(CO)­{N­(CH₂PPh₂)₃-κ³<i>P</i>}­{CH₃CO­(CH₂)₂CO₂H-κ²<i>O</i>}]­(PF₆) (<b>14</b>). Complexes <b>3</b>, <b>5</b>, <b>7</b>, <b>8</b>, <b>11</b>, and <b>12</b> were characterized by single-crystal X-ray crystallography

Lanthanide(III) Complexes of Rhodamine–DO3A Conjugates as Agents for Dual-Modal Imaging

Two novel dual-modal MRI/optical probes based on a rhodamine–DO3A conjugate have been prepared. The bis­(aqua)­gadolinium­(III) complex <b>Gd.L1</b> and mono­(aqua)­gadolinium­(III) complex <b>Gd.L2</b> behave as dual-modal imaging probes (<i>r</i>₁ = 8.5 and 3.8 mM^–1 s^–1 for <b>Gd.L1</b> and <b>Gd.L2</b>, respectively; λ_ex = 560 nm and λ_em = 580 nm for both complexes). The rhodamine fragment is pH-sensitive, and upon lowering of the pH, an increase in fluorescence intensity is observed as the spirolactam ring opens to give the highly fluorescent form of the molecule. The ligands are bimodal when coordinated to Tb­(III) ions, inducing fluorescence from both the lanthanide center and the rhodamine fluorophore, on two independent time frames. Confocal imaging experiments were carried out to establish the localization of <b>Gd.L2</b> in HEK293 cells and primary mouse islet cells (∼70% insulin-containing β cells). Colocalization with MitoTracker Green demonstrated <b>Gd.L2</b>’s ability to distinguish between tumor and healthy cells, with compartmentalization believed to be in the mitochondria. <b>Gd.L2</b> was also evaluated as an MRI probe for imaging of tumors in BALB/c nude mice bearing M21 xenografts. A 36.5% decrease in <i>T</i>₁ within the tumor was observed 30 min post injection, showing that <b>Gd.L2</b> is preferentially up taken in the tumor. <b>Gd.L2</b> is the first small-molecule MR/fluorescent dual-modal imaging agent to display an off–on pH switch upon its preferential uptake within the more acidic microenvironment of tumor cells

The Unusual Redox Properties of Fluoroferrocenes Revealed through a Comprehensive Study of the Haloferrocenes

We report the synthesis and full characterization of the entire haloferrocene (FcX) and 1,1′-dihaloferrocene (fcX₂) series (X = I, Br, Cl, F; Fc = ferrocenyl, fc = ferrocene-1,1′-diyl). Finalization of this simple, yet intriguing set of compounds has been delayed by synthetic challenges associated with the incorporation of fluorine substituents. Successful preparation of fluoroferrocene (<b>FcF</b>) and 1,1′-difluoroferrocene (<b>fcF</b>_<b>2</b>) were ultimately achieved using reactions between the appropriate lithiated ferrocene species and <i>N-</i>fluorobenzenesulfonimide (NFSI). The crude reaction products, in addition to those resulting from analogous preparations of chloroferrocene (<b>FcCl</b>) and 1,1′-dichloroferrocene (<b>fcCl</b>_<b>2</b>), were utilized as model systems to probe the limits of a previously reported “oxidative purification” methodology. From this investigation and careful solution voltammetry studies, we find that the fluorinated derivatives exhibit the <i>lowest</i> redox potentials of each of the FcX and fcX₂ series. This counterintuitive result is discussed with reference to the spectroscopic, structural, and first-principles calculations of these and related materials

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jig nFEB 03 2008Used I and SupUsed I and SupNot UsedJIGGER, TOMMY NOGGIN, between the jigs and the reelsChecked by Adrian Young on Tue 09 Jun 2015; Checked by Cathy Wiseman on Mon 03 Aug 201