Lanthanide borohydride complexes supported by diaminobis(phenoxide) ligands for the polymerization of epsilon-caprolactone and L- and rac-lactide

Reaction of Na2O2NN' [H2O2NN' = (2-C5H4N)CH2N[2-HO-3,5-C6H2(t)Bu2]2] with M(BH4)3(THF)3 afforded the dimeric, rare-earth borohydride compounds [M(O2NN')(mu-BH4)(THF)n]2 [M = Y(III), n = 0.5 (1-Y); M = NdIII, n = 1 (1-Nd); M = SmIII, n = 0 (1-Sm)]. For comparison the chloride analogues [M(O2NN')(mu-Cl)(THF)n]2 (2-M; M = La(III) or Sm(III), n = 0; M = Nd(III), n = 1) and the corresponding pyridine adducts [M(O2NN')(mu-X)(py)]2 [X = BH4 (3-M) or Cl (4-M); M = La(III), Nd(III), or Sm(III)] were prepared and structurally characterized for 4-La. Compounds 1-M initiated the ring-opening polymerization of epsilon-caprolactone. The best molecular weight control (suppression of chain transfer) for all three monomers was found for the samarium system 1-Sm. The most effective heterotactic enrichment (Pr) in the polymerization of rac-lactide was found for 1-Y (P(r) = 87%). Compound 1-Nd catalyzed the block copolymerization of epsilon-caprolactone and L- and rac-lactide provided that epsilon-caprolactone was added first. Attempted block polymerization by the addition of L-lactide first, or random copolymerization of a ca. 1:1 mixture of epsilon-caprolactone and L-lactide, gave only a poly(L-lactide) homopolymer.     

Behaviour of water-soluble dinuclear rhodium complexes in the hydroformylation reaction of oct-1-ene

The biphasic hydroformylation reaction of oct-1-ene, has been investigated by using the water-soluble dinuclear complex [Rh₂(μ-S^tBu)₂(CO)₂(TPPTS)₂] as precursor. Addition of ethanol as a cosolvent dramatically improved the yields but the good regioselectivity in linear aldehyde observed for neat oct-1-ene—water systems (97%) decreased to 83% (for 22% ethanol w/w). It is shown that the dinuclear framework cannot be maintained, that the mononuclear complex [RhH(CO)(TPPTS)₃] is formed, and that thiol and significant amounts of [Rh₂(μ-S^tBu)₂(CO)₄] move into the organic phase. This reaction from the dinuclear species requires the simultaneous presence of water and carbon monoxide. Introduction of the water-soluble thiol HS(CH₂)₃NMe₂ in the bridging positions affords the complex [Rh₂(μ-S(CH ₂)₃NHMe₂)₂(CO)₂(TPPTS)₂]Cl₂ which can be kept in the aqueous hase but has a low level of catalytic activity.     

Influence of methyl‐modified silyl groups on the properties of polymers and Si/B/N/C ceramics derived from N‐silylated borazine derivatives

Thermal silazane cleavage of dichloroboryldisilylamines (SiCl_mMe_3?m)N(SiMe₃)(BCl₂) (1: m = 1; 2: m = 2) at 196 °C leads to the borazine derivates [(SiCl_mMe_3?m)NB(Cl_nMe_1?n)]₃ (3: m = 1, n = 0.185; 4: m = 2, n = 0.111) characterized by NMR and IR spectroscopy and mass spectrometry. Single‐crystal X‐ray diffraction structure analyses reveal (BN)₃ units with unusual twisted boat conformations in both compounds. Additionally, more detailed studies are done to clear up the function of the by‐products (SiCl_mMe_3?m)N(SiClMe₂)(BClMe) formed during the cyclization step leading to asymmetrically boron substituted borazine derivatives. The single‐source precursors 3 and 4 were cross‐linked with methylamine producing polymers 3P and 4P, which were transformed into black amorphous materials with ceramic yields of 20.8 % and 50.3 %, respectively. Ceramic 4C (Si_1.00B_0.98 N_2.55 C_1.37O_0.05) was further investigated by ¹¹B and ²⁹Si magic angle spinning (MAS) NMR spectroscopy. A combined study of high‐temperature TG analyses and X‐ray powder diffraction analyses confirms the thermal stability of 4C up to 1670 °C. Copyright © 2012 John Wiley & Sons, Ltd.     

Phenyliodine(III) Diacetate/I2-Mediated Domino Approach for Pyrrolo[1,4]Thiazines and 1,4-Thiazines by a One-Pot Morin Rearrangement of N,S-Acetals

An efficient domino transformation using a phenyliodine(III) diacetate (PIDA)/I₂ combination towards Morin 1,4-thiazine compounds has been developed starting from N,S-acetals. The latter leads to “one-step” regioselective methylene insertion without the need for traditional sulfoxide intermediates in good yields. The reaction involves easily accessible N,S-acetals obtained from cost-effective basic ketones and cysteamine as starting materials. This process ultimately leads to 1,4-thiazines related to natural product and fused derivatives necessary for further QSAR study.     

In-house validation for analytical methods and quality control for risk evaluation of chlordecone in food

Chlordecone was used until 1993 as a pesticide in the banana plantation of Martinique and Guadeloupe (French Antilles) against the root borer. This organochlorine pesticide was lipophilic, remnant, and toxic for human beings with both acute and chronic effects. Chlordecone was strongly absorbed and stored in soil and weakly decomposed in environment. Surveys conducted in 2001 revealed its presence in soil, rivers, and domestic food products. Local food (fruits and vegetables, cattle, poultry, and fish) was growing on soils, widely contaminated by chlordecone, used in the past as banana plantations. In 2003, French Administration asked for a risk evaluation for the Antilles population. The French Agency for Food Safety, proposed a Provisional Tolerable Daily Intake of 0.0005?mg?kg^?1?b.w.?day^?1, and an Acute Reference Dose of 0.01?mg?kg^?1?b.w.?day^?1, based on a toxicological risk assessment. The French National Reference Laboratory for pesticides has carried out two analytical methods, one for food of animal origin and another for food of fruit and vegetable origin. These methods were validated in the reference laboratory and dispatched to 13 laboratories for a proficiency test before the launch of two studies on Martinique and Guadeloupe food. About 900 samples from Martinique were sent to the network of laboratories for analysis of chlordecone. Performance parameters obtained through the proficiency test were briefly reported. The quality control test proposed in this study was discussed to shed light on the true variability achievable by intra-laboratory and inter-laboratory analysis. The limits of conventional quality-control procedures were discussed, and a process was proposed in order to get better confidence in analytical results.     

Electrokinetic characterization of hybrid NOA 81-glass microchips: Application to protein microchip electrophoresis with indirect fluorescence detection

A low-cost and straightforward hybrid NOA (Norland optical adhesive) 81-glass microchip electrophoresis device was designed and developed for protein separation using indirect fluorescence detection. This new microchip was first characterized in terms of surface charge density via electroosmotic mobility measurement and stability over time. A systematic determination of the electroosmotic mobility (μ_eo) over a wide pH range (2–10) and at various ionic strengths (20–50 mM) was developed for the first time via the neutral marker approach in an original simple frontal methodology. The evolution of μ_eo was proved consistent with the silanol and thiol functions arising from the glass and the NOA materials, respectively. The repeatability and reproducibility of the measurements on different microchips (RSD < 14%) and within 15 days (less than 5% decrease) were successfully demonstrated. The microchip was then applied for the efficient electrophoretic separation of proteins in a zonal mode coupled with indirect fluorescence detection, which is, to our knowledge, the first proof of concept of capillary zone electrophoresis in this hybrid microsystem.     

An Effective Mass Theorem for the Bidimensional Electron Gas in a Strong Magnetic Field

We study the limiting behavior of a singularly perturbed Schr?dinger-Poisson system describing a 3-dimensional electron gas strongly confined in the vicinity of a plane (x, y) and subject to a strong uniform magnetic field in the plane of the gas. The coupled effects of the confinement and of the magnetic field induce fast oscillations in time that need to be averaged out. We obtain at the limit a system of 2-dimensional Schr?dinger equations in the plane (x, y), coupled through an effective selfconsistent electrical potential. In the direction perpendicular to the magnetic field, the electron mass is modified by the field, as the result of an averaging of the cyclotron motion. The main tools of the analysis are the adaptation of the second order long-time averaging theory of ODEs to our PDEs context, and the use of a Sobolev scale adapted to the confinement operator.     

Borohydride complexes of rare earths,and their applications in various organic transformations

Borohydride complexes of the rare earths have attracted increasing interest during the last decade. This review aims to cover recent results over this period with respect to the preparation, characterization, structure, and applications in organic chemistry of this family of compounds, including inorganic and organometallic complexes. Special emphasis is made on their use for polymerization catalysis.