Correlation of Solvolytic Reactivities. A New YBnBr Scale for Benzylic Bromides

Solvolysis of 2-bromo-2-(4′-fluoromethyl)phenyladamantane (4), and 2-bromo-2-(4′-trifluoromethyl)phenylpropane (5) were carried out in a number of solvents, and their rate constants measured. Significant deviation from linear logk-Y_Br plots was observed, and the order of reactivities, e.g., k(100M) > k(90E) > k(80A), was in the reverse order of Swain's solvent parameter B. Different extent of solvation to the localized and the delocalized cationic transition state was then likely to play an important role. Similar result was also found in the solvolysis of 1-bromo-2,2,2-trifluoro-1-(4′-methylphenyl)-1-phenylethane (6). A new Y scale, Y_BnBr, for the correlation of solvolytic reactivities of benzylic bromides based on k(4) was established. Intervention of solvent assistance in the solvolysis of 5 is discussed.     

Synthesis of a bis(phenoxyketimine) palladium(II) complex and its activity in the Suzuki-Miyaura reaction

The synthesis of a new charge-neutral, air- and moisture-stable fluorinated bis(phenoxyketimine) Pd(II) complex is presented. Its activity as a precatalyst in the Suzuki-Miyaura cross-coupling reaction of activated and unactivated bromides has been explored.     

The synthesis of oligoether-substituted benzimidazolium bromides and their use as ligand precursors for the Pd-catalyzed Heck coupling in water

The oligoether-substituted (CH₃(OCH₂CH₂)_n-; n = 1, 2 or 3) benzimidazolium bromides (3-7) and oligoether-linked (-CH₂(CH₂OCH₂)_nCH₂-, n = 1, 2 or 3) bisbenzimidazolium dibromides (8-13) were prepared by quarternization of N-substituted benzimidazoles (1 and 2) with the bulky benzyl bromides (ArCH₂Br: Ar = C₆H₂(CH₃)₃-2,4,6 and C₆(CH₃)₅). trans-Bis(carbene) palladium(II) complexes 14 and 15 derived from 4 and 6 were synthesized by using Ag complexes as carbene-transfer agents in dichloromethane at ambient temperature. In addition, the reactions of 4 and 6 with Pd(OAc)₂ and NaBr gave the Pd(II) dimers 16 and 17 which can readily be cleaved by triphenylphosphine to afford the benzannulated monocarbene (NHC) monophosphine Pd(II) complexes [PdBr₂(NHC)(PPh₃)] (18 and 19). All compounds have been fully characterized by using elemental analysis, ¹H, ¹³C and ³¹P NMR spectroscopies. X-ray diffraction studies on single crystals of 19a and 19b confirm the cis square planar geometry. In situ formed complexes from Pd(OAc)₂ and benzimidazolium salts (3-13) and preformed Pd(II) complexes 14, 15, 18 and 19 were tested as catalyst for the Heck coupling reaction in water. The influence of the oligoether and benzyl substituents on N atoms and CH₃-substituents on the 5,6-positions of benzimidazole frame were investigated under the same conditions in the Heck coupling reaction. In situ formed catalysts showed better conversions than the isolated Pd(II) complexes. The length of the oligoether spacer significantly increases the activity. The salts with two benzimidazole moieties connected by an oligoether as the spacer 8-13 showed similar catalytic activities in the Heck coupling reaction with the mono salts 3-7 bearing corresponding oligoethers on the N atom.     

溴代烯烃在金属催化偶联反应中的应用

溴代烯烃是一类重要的有机合成中间体,通过金属催化的偶联反应可以有效地形成碳-碳及碳-杂键.本文综述了溴代烯烃在金属催化偶联反应中应用的最新进展.     

Surfactant ion electrode measurements of sodium alkylsulfate and alkyltrimethylammonium bromide micellar solutions

EMF measurements in water at 25°C have been made using surfactant ion and counterion electrodes on two homologous series of long chain surfactants, the sodium alkylsulfates (R=n-C₈H₁₇ to n-C₁₄H₂₉) and the alkyltrimethylammonium bromides (R=C₁₀H₂₁ to C₁₆H₃₃). The data show evidence of association below the critical micelle concentration (CMC) but not of micelle ordering due to coulombic repulsion above this concentration.     

Direct synthesis of 3-arylpropionic acids by tetraphosphine/palladium catalysed Heck reactions of aryl halides with acrolein ethylene acetal

Through the use of [PdCl(C₃H₅)]₂/Cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)cyclopentane as a catalyst, a range of aryl bromides undergoes Heck reaction with acrolein ethylene acetal. With this acetal, the selective formation of 3-arylpropionic acids/esters was observed. The functional group tolerance on the aryl halide is remarkable; substituents such as fluoro, methyl, methoxy, acetyl, formyl, benzoyl, nitro or nitrile are tolerated. Furthermore, this catalyst can be used at low loading, even for reactions of sterically hindered aryl bromides.     

A new pathway for the preparation of diaryl acetylenes

A simple method for the preparation of diaryl acetylenes in yields up to 61% from aryl bromides and 1-bromo-2-chloroethane using the palladium catalyst (dppb)Pd(OAc)₂ under PTC conditions (solid KOH/18-crown-6) has been developed.     

Thermochemistry of adducts of some bivalent transition metal bromides with pyridine

The compounds [MBr₂(py)₂] (where M is Mn(II), Co(II), Ni(II), Cu(II) or Zn(II); py = pyridine) were synthesized and characterized by melting points, elemental analysis, thermal analysis and electronic and IR spectroscopy. The enthalpies of dissolution of the adducts, metal(II) bromides and pyridine in 25% (v/v) 1.2 M aqueous HCl in methanol were measured and by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reactions (Δ_rH^θ), the standard enthalpies of formation (Δ_fH^θ), the standard enthalpies of decomposition (Δ_DH^θ), the lattice standard enthalpies (Δ_MH^θ) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Δ_rH^θ(g)). The mean bond dissociation enthalpies of the M(II)-nitrogen bonds have been estimated as well as the enthalpies of the adducts formation in the gaseous phase.     

Samarium(II) Diiodide Induced Polarity Inversion of π-Allyl Palladium Complexes: The Formation of Allylic Selenides

As a versatile one-electron transfer reducing and coupling agent, samarium diiodide has been extensively used in organic synthesis in last decade. It has been reported that electrophilic p-allyl palladium complexes could undergo polarity inversion to nucleophilic species with the aid of SmI2, and could trap some electrophiles1. It is well known that allylic selenides are rather important intermediates in organic synthesis. They have been recognized as useful synthons of allylic anion stabi…     

Viscosities and densities of tetraalkylammonium bromides in dimethylformamide-water mixtures at 25 and 35°C

Viscosity and desity data for KCl, KBr, Me₄NBr, Et₄NBr, Pr₄NBr, and Bu₄NBr from 0.005 to 3M in aqueous dimethylformamide solutions at 25°C and 35°C are presented. The data for dilute solutions were analyzed by means of the Jones-Dole equation and the ionic B coefficients evaluated. The data for concentrated solutions were analyzed by the Breslau and Miller equation and the effective flow volume, V₃ of the electrolytes obtained as a function of concentration. The limiting effective flow volume, V _e ^o was obtained from the Vand equation in the form used by Eagland and Pilling and it is shown that B=2.5 V _e ^o . With increasing DMF concentration V _e ^o increases for Me₄NBr but decreases for Pr₄NBr and Bu₄NBr. The same effect was observed by increasing temperature. This behavior is explained in terms of the structuring effect of the constituent ions and the effect of DMF on the overall structure of the binary solvent.