Rapid defunctionalization of carbonyl group to methylene with polymethylhydrosiloxane-B(C(6)F(5))(3)

The polymethylhydrosiloxane-B(C(6)F(5))(3) combination is found to be a versatile carbonyl defunctionalization system under mild and rapid conditions. For the first time, B(C(6)F(5))(3) has been used as a nonconventional Lewis acid catalyst to activate PMHS. Aromatic and aliphatic carbonyl compounds were effectively reduced to give the corresponding alkanes in high yields.     

Facile synthesis of 9-(arenethenyl)purines via Heck reaction of 9-vinylpurines and aryl halides

The first example of a Heck reaction with 9-vinylpurines and aryl halides is described. It gives exclusively E-9-(arenethenyl)purines in high yields. Subsequent hydrogenation furnishes 9-(arenethyl)purines quantitatively.     

Ruthenium(II) complexes with 2-(benzylimino-methyl)-4-R-phenol containing the trans(PPh3),cis(CO,Cl)-{Ru(PPh3)2(CO)Cl} unit

Reactions of [Ru(PPh₃)₃Cl₂] with 2-(benzylimino-methyl)-4-R-phenol (H^RL, R = H, Cl, Br and OMe) in boiling methanol in presence of triethylamine afford ruthenium(II) complexes of general formula [Ru(^RL)(PPh₃)₂(CO)Cl] in 57-64% yield. Microanalysis, spectroscopic (infrared, electronic and NMR) and cyclic voltammetric measurements have been used for the characterization of the complexes. Crystal structures of two representative complexes have been determined by X-ray crystallography. The carbonyl, the chloride, the N,O-donor ^RL⁻ and the two mutually trans PPh₃ molecules assemble a distorted octahedral CClNOP₂ coordination sphere around the metal centre in each complex. The complexes display the Ru(II) → Ru(III) oxidation in the potential range 0.62-1.16 V (vs. Ag/AgCl).     

High-temperature reactions in systems of interest for spectrochemical analysis

Summary Reactions taking place in the systems graphite—boron carbide—a third component in the controlled temperature range of 1000–2000° C have been investigated by the spectrochemical and X-ray diffraction methods. It has been found that boron evaporates at 1200° C when NaF or LiF were added, at 1600° C when ZnF₂ was added and at 1900° C when CaF₂ was added as a third component.In the boron carbide-graphite-magnesium oxide system, magnesium borate, Mg₃(BO₃)₂, was found to be formed at high temperatures. A new phase, aluminium borate, 9 Al₂O₃·2 B₂O₃, was also found with addition of aluminium trioxide as the third component. Vanadium pentoxide added forms vanadium boride, VB₂. In the graphite—boron carbide—silicon dioxide system several phases are found but not identified. With calcium fluoride as the third component no changes occured up to 1900° C, while at 2000° C there is a hardly visible formation of calcium hexaboride. In the case of sodium fluoride new phases are sometimes found, but not identified.

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Hochtemperaturreaktionen in spektralanalytisch wichtigen Systemen1. Reaktionen in den Systemen von Graphit und Borcarbid mit einer dritten Komponente

Zusammenfassung Die Reaktionen wurden im Bereich von 1000–2000° C durch Spektralanalyse und Röntgendiffraktometrie untersucht. Dabei wurde gefunden, daß Bor bei 1200° C verdampft, wenn NaF oder LiF zugesetzt werden, bei 1600° C bei Zugabe von ZnF₂ und bei 1900° C bei Zusatz von CaF₂. Im System Borcarbid-Graphit-MgO wurde bei hohen Temperaturen Mg₃(B0₃)₂ gebildet. Bei Gemischen mit Al₂O₃ wurde 9 Al₂O₃·2 B₂O₃ gefunden. Bei Zusatz von V₂O₅ wurde VB₂ gebildet. Mehrere Phasen, die aber nicht identifiziert wurden, konnten im System Graphit—Borcarbid—SiO₂ gefunden werden. Mit CaF₂ wurden bis 1900° C keine Veränderungen beobachtet, während bei 2000° C CaB₆ in geringen Mengen auftritt. Im Falle von NaF treten gelegentlich neue Phasen auf, die jedoch nicht identifiziert wurden.

     

The trimethylsilyl xylyl (TIX) ether: a useful protecting group for alcohols

A new protecting group for alcohols, the p-trimethylsilyl xylyl (TIX) group has been developed. The TIX group is used to protect various alcohols under acidic as well as basic conditions. The protected ethers thus formed had noteworthy chemoselectivity upon deprotection in the presence of other benzyl ethers and commonly used protecting groups. The stability of the TIX group towards various reagents has also been examined.     

Study of Thermal Decomposition Kinetics of Low-temperature Reaction of Ammonium Perchlorate by Isothermal TG

The kinetics of the thermal decomposition of ammonium perchlorate at temperatures between 215 and 260°C is studied, in this work, by measuring the sample mass loss as a function of time applying the isothermal thermogravimetric method. From the maximum decomposition rate – temperature dependence two different decomposition stages, corresponding to two different structural phases of ammonium perchlorate, are identified. For the first region (215–235°C), corresponding to the orthorhombic phase, the mean value of the activation energy of 146.3 kJ mol^–1, and the pre-exponential factor of 3.43⋅10¹⁴ min^–1 are obtained, whereas for the second region (240–260°C), corresponding to the cubic phase, the mean value of the activation energy of153.3 kJ mol^–1, and the pre-exponential factor of 4.11⋅10¹⁴ min^–1 are obtained. This revised version was published online in August 2006 with corrections to the Cover Date.     

Tris(pentafluorophenyl)borane catalyzed Ferrier azaglycosylation with sulfonamides and carbamates

The reaction of tri-O-acetyl-d-glucal with different nitrogen nucleophiles was effectively promoted by a catalytic amount of tris(pentafluorophenyl)borane for the first time in acetonitrile at room temperature to produce a variety of azapseudoglycals via Ferrier rearrangement in good yields and preferential anomeric selectivity.     

Novel Tin Complexes Containing an Oximato Ligand: Synthesis,Characterization, and Computational Investigation

Organotin complexes 1 – 6 of the general formula [SnR₂L] and [(SnR₃)₂L] (L=phenanthrenequinone dioximato – a bidentate ligand, R=Me, Bu, and Ph) were synthesized by the reaction of the sodium salt of the ligand H₂L (prepared in situ with MeONa) and SnR₂Cl₂/SnR₃Cl in 1 : 1 and 1 : 2 molar ratios. The physical and spectral properties of the newly synthesized complexes 1 – 6 are described. DFT and HF Calculations were performed to confirm the proposed structures.     

Network Polymer Properties Engineered Through Polymer Backbone Dispersity and Structure

Dispersity (Ð or M_w/M_n) is an important parameter in material design and as such can significantly impact the properties of polymers. Here, polymer networks with independent control over the molecular weight and dispersity of the linear chains that form the material are developed. Using a RAFT polymerization approach, a library of polymers with dispersity ranging from 1.2—1.9 for backbone chain-length (DP) 100, and 1.4—3.1 for backbone chain-length 200 were developed and transformed to networks through post-polymerization crosslinking to form disulfide linkers. The tensile, swelling, and adhesive properties were explored, finding that both at DP 100 and DP 200 the swelling ratio, tensile strength, and extensibility were superior at intermediate dispersity (1.3—1.5 for DP 100 and 1.6—2.1 for DP 200) compared to materials with either substantially higher or lower dispersity. Furthermore, adhesive properties for materials with chains of intermediate dispersity at DP 200 revealed enhanced performance compared to the very low or high dispersity chains.     

A smooth access to benzotriazoles via azide-benzyne cycloaddition

A facile synthesis of 1-alkyl benzotriazoles is achieved through fluoride triggered azide-benzyne cycloaddition. Various alkyl azides were treated with 2-(trimethylsilyl) phenyl triflate in the presence of CsF in acetonitrile to afford the corresponding substituted benzotriazoles in good yield.