Formation of cyclic organosilicon compounds via organopolysilyl anions starting from methoxymethyldisilanes. A mechanistic study

In the presence of a catalytic amount of sodium methoxide, sym-dimethoxytetramethyldisilane was converted into α,ω-dimethoxypermethylpolysilanes, MeO(SiMe₂)_nOMe where n ? 3, at room temperature. On the other hand, similar treatment of the disilane in THF solution gave cyclic polysilanes, (Me₂Si)_n where n = 5–7. Decomposition of the disilane in the presence of diphenylacetylene afforded a trisilacyclopentene derivative under similar conditions. This compound was obtained also by the reaction between α,ω-dimethoxypermethylpolysilanes and diphenylacetylene in the presence of sodium methoxide. These cyclic products most likely were formed via permethyl polysilyl anion intermediates derived from α,ω-dimethoxypermethylpolysilanes. Also, the formation of α,ω-dimethoxypermethylpolysilanes could be elucidated in terms of the mechanism involving the base-assisted, concerted nucleophilic substitution or stepwise substitution by silyl anions, rather than the successive dimethylsilylene (Me₂Si:) insertion reaction.     

Synthesis of new layered-type and new mixed-layered-type bismuth compounds

Four new compounds, PbBi₂TiTaO₈F, PbBi₂TiNbO₈F, Bi₅Ti₂WO₁₄F, and Bi₇Ti₅O₂₀F, were prepared and identified by X-ray diffraction analysis. Two of them are new members of a family called layered bismuth compounds. The other two are new members of a family called mixed-layered bismuth compounds. Thermal properties of the new compounds were studied. Moreover, the possibility of the existence of other new members belonging to the family called mixed-layered bismuth compounds is discussed.     

Pyrimidines-19: Ring transformation of 5-nitrouracil into nitroresorcinols

The first intermolecular right transformation of a uracil derivative into the benzene system is reported. Treatment of 1,3-dimethyl-5-nitrouracil (1) with acetone in NaOMe/MeOH afforded 6-acetonyl-5,6-dihydro-1,3-dimethyl-5-nitrouracil (6) which was converted into 4-nitroresorcinol (5) upon treatment with NaOEt/EtOH at reflux. Reaction of1 with butanone gave two major products, 3-(5,6-dihydro-1,3-dimethyl-5-nitrouracil-6-yl)butanone (7) and the 1-(uracil-6-yl)butanone isomer (8). Prolonged treatment of7 with NaOEt/EtOH afforded 4-methyl-6-nitro-resorcinol (9) whereas8 was converted into 2-methyl-4-nitro-resorcinol (10). Treatment of1 with diethyl acetonedicar?ylate in NaOEt/EtOH afforded diethyl-2-(5,6-dihydro-1,3-dimethyl-5-nitrouracil-6-yl)-acetonedicar?ylate (2). Prolonged treatment of2 with NaOEt/EtOH at reflux afforded (5,6-dihydro-1,3-dimethyl-6-nitrouracil-6-yl)-acetate (3). Apparently,2 underwent a retroClaisen reaction to give3. Reaction of1 with ethyl acetoacetate in NaOEt/EtOH gave adduct isomers4 which underwent transformation reaction to give eventually 6-nitroresorcinol (5).     

Novel Azaferrocenyliminonickel Catalysts for Olefin Polymerization

Summary: The azaferrocenyliminonickel dibromide complexes 1 bearing a pentaphenylcyclopentadienyl group and a wide range of N‐aryl groups were synthesized and examined as catalysts for ethylene polymerization. Both the ortho‐ (R¹) and para‐substituents (R²) of the N‐aryl groups in 1 were found to strongly influence both the polymerization activity and the properties of the obtained polyethylenes. The effect of changing the polymerization conditions, such as temperature, ethylene pressure, and cocatalyst, was also examined.

Azaferrocenyliminonickel(II ) complexes.     

N‐Heterocyclic Carbenes as Efficient Organocatalysts for CO2 Fixation Reactions

Getting a fix : N‐heterocyclic carbenes (NHCs) and NHC–CO₂ adducts serve as potent organocatalysts for carbonate synthesis by the addition of a CO₂ unit to propargylic alcohols or epoxides under mild and solvent‐free reaction conditions (see scheme). The enhanced Lewis basicity of imidazol‐2‐ylidenes bearing electron‐donating alkyl groups on the nitrogen atoms leads to utilizing CO₂ as a nucleophilic fragment in the chemical fixation processes.

     

Oxygenation of alkyl sulfides with ferrous perchlorate/ascorbic acid/oxygen system

In the oxidation of alkyl sulfides bearing acidic α-hydrogens eiher with phenobarbital induced rabbit liver microsomal cytochrome P-450, or with the Udenfriend's model system (ferous perchlorate/ascorbic acid/oxygen system), both S-dealkylation and S-monoxygenation took place concurrently. Meanwhile, in the oxidation of simple alkyl sulfides, steeoselective S-monooxygenation was found of occur predominantly.     

Reactions of 1,2-dimethoxytetramethyldisilane with styrenes: Formation of a new type of silacyclopentanes having phenyl substituents on ring carbons

The reaction of 1,2-dimethoxytetramethyldisilane with styrene and α-methylstyrene in the presence of NaOMe catalyst in tetrahydrofuran (THF) gave the new silacyclopentanes 1,1-dimethyl-2,4-diphenyl-1-silacyclopentane (IIIa) and 1,1,2,4-tetramethyl-2,4-diphenyl-1-silacyclopentane (IIIb), respectively. These silacyclopentanes were found to exist as cis-trans mixtures. The use of sodium metal in place of NaOMe afforded similar results. Reactions of a polysilane mixture, MeO-(SiMe₂)_nOMe (n ≧ 3), with the styrenes also gave similar results. In some cases, polysilacycloalkanes such as 1,2,3-trisilacyclopentanes (IV) and 1,2,3,4-tetrasilacyclohexanes (V) were obtained as by-products. A mechanism for the formation of the silacyclopentanes and polysilacycloalkanes is presented. It was found that electron impact decomposition of silacyclopentanes IIIa and IIIb, trisilacycloalkane IV and tetrasilacycloalkane V gave molecular ions corresponding to the silacyclopropane, cyclotrisilane and cyclotetrasilane systems.     

Liquid-liquid extraction and spectrophotometric determination of palladium with 2-mercaptobenz-amide

2-Mercaptobenzamide (MBA) was investigated as a reagent for the extraction of palladium. The palladium complex of MBA was extracted into tributyl phosphate (TBP). The pK_a of the ligand was 5.45 with the stability constant of the palladium complex β₂=10^7.1. The composition of the complex in TBP was Pd:MBA:TBP=1:2:2. Addition of sodium chloride accelerated the rate of extraction. Various interfering ions could be masked with EDTA; Ag(I), Au(III), Os(VIII), Se(IV), Te(IV) etc. interfered. The molar absorptivity was 1.59×10⁴ l mol^?1 cm^?1; 1–35 μg Pd could be determined at pH 6.0.