Molecular addition compounds. 16. New, highly reactive borane adducts with N,N-dialkyl-tert-alkylamines for hydroboration

Several N,N-diethyl-tert-alkylamines, such as N,N-diethyl-2-methyl-2-butylamine (1, t-PentNEt2), N,N-diethyl-2,3-dimethyl-2-butylamine (2, t-HexNEt2), N,N-diethyl-2,3,3-trimethyl-2-butylamine (3, t-HeptNEt2), and N,N-diethyl-1,1,3,3-tetramethylbutylamine (4, t-OctNEt2) with varying steric bulk around nitrogen (by changing the tert-alkyl group) have been prepared and examined as borane carriers. The complexing ability of these N,N-diethyl-tert-alkylamines with borane decreases in the order: t-BuNEt2 > t-PentNEt2 > t-HeptNEt2 > t-HexNEt2 > or = t-OctNEt2. From these preliminary studies, the more promising tert-octyldialkylamines were selected for detailed studies. The optimum steric bulk around the nitrogen atom was established by comparing various tert-octyldialkylamines containing variable steric requirements for both the alkyl groups. The complexing ability of these amines with borane decreases in the order shown: t-OctNMe2 (5) > t-OctNEtMe (6) > t-OctN-(CH2CH2)2O (7) > t-OctNEt2 (4) > t-OctNBuiMe (8) > t-OctNPr(n)2 (9). The reactivity of the corresponding borane adducts toward 1-octene increases in the reverse order. Among the various tert-octyldialkylamine-boranes prepared and examined, only t-OctNEt2 (4) forms a highly reactive liquid borane adduct, which hydroborates 1-octene in tetrahydrofuran rapidly at room temperature. Accordingly, detailed hydroboration studies with this new, highly reactive amine-borane adduct, t-OctEt2N:BH3 (10) and representative mono-, di-, tri-, and tetra-substituted olefins were carried out at room temperature (22 +/- 3 degrees C) in selected solvents, tetrahydrofuran, dioxane, tert-butyl methyl ether, n-pentane and dichloromethane. Simple unhindered olefins were hydroborated to the trialkylborane stage, whereas hindered olefins were partially hydroborated to the mono or dialkylborane stage. The hydroborations can be carried out conveniently in a variety of solvents. The amine-borane adduct showed enhanced reactivity in dioxane but low reactivity in dichloromethane. The alkylboranes obtained after hydroboration were oxidized with hydrogen peroxide/sodium hydroxide and the product alcohols were obtained in quantitative yields, as established by GC analysis. The carrier amine was recovered by simple acid-base manipulations in good yield and can be readily recycled back to the borane adduct.     

Effect of mixed glass formers on the crystallization kinetics in AgI–Ag<Subscript>2</Subscript>O–V<Subscript>2</Subscript>O<Subscript>5</Subscript>–MoO<Subscript>3</Subscript> glassy superionic system

The crystallization and glass transition kinetics using differential scanning calorimetry (DSC) in 50AgI–33.33Ag₂O–16.67[(V₂O₅)_1−x –(MoO₃) _x ] superionic glassy system is discussed. Thermal stability of glass, studied using various criteria, does not vary significantly with glass former variation. However, the activation energies for structural relaxation (E _s) at glass transition temperature and crystallization (E _c) obtained using Moynihan and Kissinger, Matusita-Sakka formulations found to exhibit interesting trends with MoO₃ substitution in the glass matrix. It is noticed that the electrical conductivity (σ)–temperature (T) cycles obtained at a typical heating rate of 1 °C/min do exhibit significant thermal events. The conductivity after first heating cycle at room temperature is found to be increasing with MoO₃ content and maximum for x = 0.3 (~10⁻³ Ω⁻¹ cm⁻¹ at 30 °C) which is comparable to that of the host 50AgI–33.33Ag₂O–16.67V₂O₅ glassy system. The parameters obtained from σ–T plots and DSC scans do complement each other in a particular range of composition.     

CONTROLLING THE 3D NANOSCALE ORGANIZATION OF BULK HETEROJUNCTION POLYMER SOLAR CELLS

In this study,the three dimensional nanoscale organization in the photoactive layers of poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM) is revealed by transmission electron tomography.After annealing treatment,either at elevated temperature or during slow solvent evaporation,nanoscale interpenetrating networks are formed with high crystalline order and favorable concentration gradients of both components through the thickness of the photoactive layer.Such a tailored morphology acco...     

Exploiting phosphonate chemistry in metal-mediated dearomatization: stereoselective construction of functionalized spirolactams from arene ruthenium complexes

Arene ruthenium complexes possessing beta-amido phosphonate side chains participate in intramolecular spirocyclization reactions to deliver stable cyclohexadienyl ruthenium adducts. Spirocyclization is accomplished via a tandem two-step sequence that involves stereoselective nucleophilic aromatic addition to the ipso position of the coordinated arene, followed by intermolecular Horner-Wadsworth-Emmons olefination. The resulting eta5-cyclohexadienyl complexes can then be diastereoselectively converted to metal-free azaspiro[4.5]decane derivatives upon oxidative demetalation in the presence of suitable nucleophiles. An asymmetric spirocyclization was demonstrated through application of this procedure to a beta-amido phosphonate prepared from (S)-(-)-alpha-methyl benzylamine. The expected spirolactam product was obtained as a single enantiomer.     

The Design of 3D-Printed Polylactic Acid–Bioglass Composite Scaffold: A Potential Implant Material for Bone Tissue Engineering

Bio-based and patient-specific three-dimensional (3D) scaffolds can present next generation strategies for bone tissue engineering (BTE) to treat critical bone size defects. In the present study, a composite filament of poly lactic acid (PLA) and 45S5 bioglass (BG) were used to 3D print scaffolds intended for bone tissue regeneration. The thermally induced phase separation (TIPS) technique was used to produce composite spheres that were extruded into a continuous filament to 3D print a variety of composite scaffolds. These scaffolds were analyzed for their macro- and microstructures, mechanical properties, in vitro cytotoxicity and in vivo biocompatibility. The results show that the BG particles were homogeneously distributed within the PLA matrix and contributed to an 80% increase in the mechanical strength of the scaffolds. The in vitro cytotoxicity analysis of PLA-BG scaffolds using L929 mouse fibroblast cells confirmed their biocompatibility. During the in vivo studies, the population of the cells showed an elevated level of macrophages and active fibroblasts that are involved in collagen extracellular matrix synthesis. This study demonstrates successful processing of PLA-BG 3D-printed composite scaffolds and their potential as an implant material with a tunable pore structure and mechanical properties for regenerative bone tissue engineering.     

Thermal,magnetic and spectral studies of metal-quinone complexes. Part II. Media effect on Coligation of Aqua Ligands

Syntheses of phthiocol complexes with Cu(II) in inert media resulted in anhydrous monomer Cu-4: [Cu(NQ)₂] and dimer Cu-5: [Cu(NQ)(NSQ)]₂, however synthesis in air generates polymeric hydrated Cu-6: [Cu(NQ)₂(H₂O)₂]_n. Media and colligation give rise to charge transfers in coordination compounds and lead to different redox ligations of 3-methyl-2-hydroxy-1,4-naphthoquinone. These redox forms are determined from quantitization of activation energies (E _a) of different pyrolytic steps in TG using the rising temperature expression of Coats and Redfern. 'Tyrosinase'-type mechanism is discussed for the redox-type ligation. Characteristic six-line EPR signals of dimeric Cu-5 lead to zero field splitting parameters D=0.01608 cm^-1and E=0.01576 cm^-1. Cu-6 shows molecular association through hydrogen bonding. Variable temperature magnetic measurement data of Cu-6 from 6 to 300 K is fitted to the polymeric expression of Bonner and Fisher model. The best fit was obtained with antiferrromagnetic exchange coupling constantJ=-2 cm^-1, g=2.2 having R=4.2·10^-4. This revised version was published online in July 2006 with corrections to the Cover Date.