Action des composes dicarbonyles-1,2 sur des composes du phosphore dicoordonne a liaison pn et sur leurs oligomeres.

Triazaphospholes react with 1,2-diketones to give spirocyclic phosphorus compounds by a 1.1 addition at phosphorus atom; with o-quinones one obtains spirobicyclic hexacoordinated phosphorus compounds. The reaction of 1,2-diketones with λ³-phosphazene oligomers appears different, to some extent, and can be used as a test for the existence of a monomer-oligomer equilibrium.     

Hexacoordination du phosphore par complexation intramoleculaire

An equilibrium occurs between penta- and hexacoordinated phosphorus when a basic function is located at the end of a branched ligand on pentacoordinate phosphorus. Generally the hexacoordinated form are thermodynamic stable species in solution at room temperature. Eight hexacoordinated compounds (9–11, 13, 14, 18–20, Tables 2 and 3) have been isolated. In few cases, in solution, the pentacoordinated form (15–17, 24) can be observed. The parameters from these equilibria are discussed.     

THE PREPARATION OF TRIALKYL PHOSPHITES DIRECTLY FROM THE ELEMENT

Abstract

The reaction between finely divided white phosphorus and several alkoxide ions in the presence of tetrachloromethane and excess of alcohol has been investigated under a variety of conditions. High yields of trialkylphosphite are obtained when two equivalents of alkoxide are used. With one equivalent of alkoxide, dialkylphosphonate is formed in comparable yield. Maximum yields of triester are obtained within 1–3 h at room temperature. Prolonged treatment results in the conversion of trialkylphosphite to phosphate by reaction with tetrachloromethane. Phenolate ions are unreactive under the same experimental conditions. The mechanism of the reaction is discussed.     

Modification Study of Aluminum sec-Butoxide by Acrylic Acid

A new way of modifying aluminum sec-butoxide (Al(OBu^s)₃) is proposed. This synthesis is carried out by reacting Al(OBu^s)₃ dissolved in tetrahydrofuran with an unsaturated acid, viz. acrylic acid.The structure evolution of Al(OBu^s)₃ with increasing acrylic acid amounts is investigated by infrared, ¹H NMR, ¹³ C NMR, and ²⁷Al NMR spectroscopies and viscosity measurements. Information obtained suggests that the exchange reaction occurring between butoxy groups and acrylate ligands is stopped for an acid/alkoxide molar ratio within the range 1.6–1.7. This value leads us to assume that the dominant trimeric species of precursor is preserved after modification. Moreover, ²⁷Al NMR analysis only reveals the presence of hexacoordinated Al sites in the structure of the modified Al(OBu^s)₃.Evidence of the acrylic acid reaction with sec-butanol released during the alkoxide modification is also proved by the infrared and ¹³ C NMR data. However the produced ester amount can be considered as negligible.     

硫代四配位磷化物与邻苯二酚反应

前文报^[1]道的硫代磷酰二氯在三乙胺存在下与邻苯二酚反应,不仅具有理论意义,而且是合成该类磷化物的新方法。本文将继续报道硫代磷酰一氯以及其它硫代四配位磷化物与邻苯二酚反应的结果,以期进一步揭示这类反应的本质及其影响因素。     

One-step stereoselective synthesis and NMR chiral shift properties of a novel hexacoordinated phosphorus cation

[reaction: see text] Tropolone, binol, and PCl(5) react in CH(2)Cl(2) at reflux to generate in one step a novel C(2)-symmetric hexacoordinated phosphorus cation of configuration controlled by the binol ligand. It behaves as an efficient NMR chiral shift agent for chiral anionic phosphate and borate anions.     

Activation Mechanisms of Trialkylaluminum in Alkali Metal Alkoxides or Tetraalkylammonium Salts / Propylene Oxide Controlled Anionic Polymerization

The anionic polymerization of propylene oxide (PO) initiated by alkali metal alkoxides is in non polar solvents a very slow and non controlled reaction process. Transfer reaction to monomer is predominant, allowing only the preparation of low molar masses PPO. The influence of the addition of trialkylaluminium to either an alkali metal alkoxide or a tetraalkylammonium salt used as initiator for PO polymerization in hydrocarbon media was investigated. A strong enhancement of the polymerization rate accompanied by a drastic decrease of the transfer reactions is observed, allowing the synthesis of PPO with well controlled molar masses. At constant monomer and alkali metal alkoxide concentrations, the polymerization rate increases with increasing trialkylaluminium concentration. Results indicate that the trialkylaluminium derivative is involved in the formation of two distinct complexes, one with the alkali metal alkoxide or the tetraalkylammonium salt and another one with the PO monomer which is strongly activated towards nucleophilic active species. Significant differences between the alkali metal and tetraalkylammonium based initiators are observed. In particular much less trialkylaluminum activator is needed with the ammonium salt to get the same rate of propagation and controlled polymerization.     

Stereochemical consequences of the use of chiral N-phosphoryl oxazolidinones in the attempted kinetic resolution of bromomagnesium alkoxides

A number of chiral N-phosphoryl oxazolidinones have been prepared and evaluated as asymmetric phosphoryl transfer agents with the magnesium alkoxide of 1-phenyl ethanol. The reaction proceeded with little stereoselection, which was shown to be a consequence of the reaction mechanism that occurs with inversion of configuration at phosphorus consistent with in-line attack opposite the leaving group.     

KINETIC STUDY OF ALKOXIDE PROMOTED DECOMPOSITION OF ORGANIC PHOSPHONIUM COMPOUNDS Evidence for Hexacovalent Intermediate

Abstract

This study reports rate data of the alkoxide promoted decomposition of triphenyl 3-hydroxypropyl phosphonium chloride, diphenyl di(3-hydroxypropyl)phosphonium chloride, and tetraphenyl phosphonium bromide. Comparison of kinetics, rate constants, and activation parameters of the alkoxide promoted decompositions points to different mechanism as compared to the hydroxyl promoted reaction. The alkoxide reaction is believed to proceed via a hexacovalent intermediate. Reasons for the hexacovalent route are discussed.     

The Effect of Very Bulky Groups on the Equilibrium of Penta- and Hexacoordinated Phosphoranes 1

The synthesis of dithio-diphenol 4 and sulfonyl-diphenol 5, both with very bulky groups, provided starting materials for reaction sequences that led to the formation of the very stable hexacoordinated phosphorane 2 and sensitive pentacoordinated phosphorane 3. Hexacoordination was established in 2 by an intramolecular donor interaction at the phosphorus center from an oxygen atom of the sulfonyl group present as part of the eight-membered ring. The solid state structures of 2 and 3 were established by X-ray analysis, as was that of phosphite 1 formed in the reaction sequence leading to 2. In solution, 2 has two forms existing in a dynamic equilibrium between a pentacoordinated and the more dominant hexacoordinated form as determined by ³¹P and ¹⁹F NMR spectroscopy. The high stability of 2 with respect to hydrolysis and alcoholysis reactions suggests that an associative process is responsible as the controlling reaction mechanism.     

Synthesis and Characterization of Alkoxy Spirophosphoranes Prepared from Hydrospirophosphoranes and Sodium Alcoholates

The Atherton–Todd‐type reaction of hydrospirophosphoranes (HSPs) and sodium alcoholates was investigated. Direct alkoxylation of HSPs was accomplished with sodium alcoholates in acetonitrile under nitrogen atmosphere. The stereochemistry mechanism of the alkoxidation of HSPs was proposed by the ³¹P NMR tracing experiment. The reaction proceeded via the chlorinated spirophosphorane intermediate with stereoretention of the configuration at phosphorus, followed by the rear and front attack of alkoxide anions to produce alkoxy spirophosphoranes. The reaction mechanism well explained the results of the reaction of HSPs with sodium alcoholates.     

Fragmentation of conjugate bases of esters derived from multifunctional alcohols including triacylglycerols

Enolate anions of esters from 1,2 and 1,3 diols undergo an internal nucleophilic substitution reaction that produces a β-ketoester and an alkoxide ion within the molecular species. These intermediate ions undergo two competitive fragmentation pathways. The first pathway corresponds to a second nucleophilic substitution of the ketoester by the alkoxide that yields a neutral cyclic ether and the β-ketoacid carboxylate. The latter then loses carbon dioxide and produces the enolate anion of the corresponding ketone. The second proposed pathway is stepwise: it starts with a proton transfer from the methylene group between the two carbonyls to the alkoxide anion that produces an alcohol and the enolate ion of the β-ketoester inside the molecular species. The latter undergoes cleavage of the ester bond induced by the negative charge to yield an ion-dipole complex composed of a neutral acylketene and an alkoxide ion. The direct dissociation of this ion-dipole complex competes with an internal proton exchange to yield a new complex that consists of an alcohol molecule and the anion of the acylketene, which can also dissociate. The fragmentation pathway that leads to the ketone enolate is sensitive to the relative positions (1,2 or 1,3) of the esters on the molecular backbone. This position-sensitive reaction is useful for the assignment of the primary and secondary positions in triacylglycerols, even in mixtures, as shown by some examples.     

Reaction of Elemental (White) Phosphorus with (Alkoxymethyl)dialkylamines

The reaction of elemental (white) phosphorus with (alkoxymethyl)dialkylamines in the presence of sodium alkoxide results in complete conversion of P₄ in proton-donor solvents only. ³¹P NMR spectroscopy allowed detection of the initial formation of PIII compounds whose subsequent transformations primarily provide phosphinate and phosphonate structures. Under the reaction conditions, trialkyl phosphites further react with (alkoxymethyl)dialkylamines to form dialkyl (dialkylamino)methylphosphonates.     

分子筛催化的戊烯骨架异构反应机理

在密度泛函理论中的B3LYP/6-31G(d,p)水平上研究了分子筛催化戊烯骨架异构的微观作用机制,分别对各个基元反应进行了内禀反应坐标(IRC)解析。结果表明:戊烯的骨架异构存在2种反应机理:烷氧基中间体机理和类甲基环丙烷中间体机理。而烷氧基中间体机理又包括2个反应途径,1个是甲基迁移,另1个是乙基迁移。因此,整个异构反应存在3个反应途径。甲基迁移机理和乙基迁移机理都含有3个基元步骤,其中速控步骤分别是甲基迁移和乙基迁移,对应的活化能分别为206.17和207.31 kJ·mol-1,二者几乎相等,表明2个反应途径从能量的角度来说是互相竞争的。类甲基环丙烷中间体机理分2步,碳链扭转和甲基的迁移,反应中间体具有高离子性和高能量的物种。反应速控步骤是碳链扭转反应,其活化能是147.93 kJ·mol-1,明显低于甲基迁移和乙基迁移2个反应途径的能垒,意味着类甲基环丙烷中间体的反应途径更容易发生。     

六配位磷质离子溶液的核磁共振研究

本文用含有两个不同双环五配位磷化物与甲氧基负离子反应, 通过加成和取代, 形成六配位磷负离子顺、反异构体. 反式体为动力学控制产物顺式体为热力学控制产物.     

A Hexacoordinated P-Bridged Calixarene Derivative -- Phosphorylation of p-tert -Butylthiacalix[4]arene

p-tert -Butylthiacalix[4]arene ( 1 ) reacts with phosphorus pentachloride under participation of the sulfur atoms to a hexacoordinated phosphorus derivative ( 2 ) of the thiacalixarene. Hydrolysis of 2 leads to the twofold 1,2-bridged thiacalixarene bis(chlorophosphate) 3 .     

The reaction of thiophosphoryl dichloride with catechol

Phenyl thiophosphonyl dichloride reacted with catechol n the presence of triethylamine to yield a pentacoordinated phosphorus compound 3. The reactions of a number of phosphorodi-chloridothioates with catechol gave a hexacoordinated phosphorus compound 8. The mechanism of these reactions are discussed.     

Skeletal isomerization of butene in ferrierite: assessing the energetic and structural differences between carbenium and alkoxide based pathways

In this study, the results from a systematic analysis of two different mechanisms for the skeletal isomerization of cis-butene to isobutene in ferrierite (FER) are presented. One involves a conventional mechanism that proceeds via stable alkoxide intermediates and the other is one which proceeds via carbenium ions only. A 27T QM cluster model has been used in this study, which is described using the M06-2X DFT functional. It is found that the alkoxide intermediates formed over the course of the conventional pathway are considerably lower in energy than the carbenium ion formed over the course of the alternate pathway. However, the rate determining step in the latter pathway is predicted to be almost 10 kcal/mol lower in energy. The higher barrier for the latter process is due to the inherent stability of the alkoxide intermediates formed within FER. These results appear to suggest that while these intermediates are formed over the course of the reaction, the skeletal isomerization of linear butenes to form isobutene in FER may occur via a carbenium based mechanism. This proposal is consistent with experimental results that show alkoxide intermediates are experimentally observed species.     

Reaction mechanism and the role of copper in the photooxidation of alcohol over Cu/Nb2O5

Loading of a small amount of copper on Nb(2)O(5) significantly enhances the activity of alcohol photooxidation without organic solvents. Alcohol is adsorbed on the Lewis acid site (Nb(V)) to form an alkoxide species. Photogenerated holes and electrons on Cu/Nb(2)O(5) are trapped by the adsorbed alkoxide and Cu(II) species to form the alkoxide carbon radical and Cu(I) species. The formed alkoxide carbon radical is converted to a carbonyl compound and then desorbed. Finally, the reduced Cu(I) sites are reoxidized by reaction with O(2). The alcohol photooxidation over Nb(2)O(5) takes place under not only UV irradiation but also under visible light irradiation up to 450 nm, although the band gap of Nb(2)O(5) is 390 nm (3.2 eV). DFT calculations reveal that 1) the surface donor level derived from the adsorbed alkoxide species is located in the forbidden band, 2) direct electron transition from the surface donor level to the conduction band takes place by absorbing a photon, 3) the excitation energy from surface donor level to the Nb 4d conduction band is lower than that from the O 2p valence band to Nb 4d. The kinetic study and FT/IR spectra suggest that Cu(I) acts as an effective desorption site for the products. Based on these results, we conclude that copper functions as an effective redox promoter and desorption site for the product.     

Anionic polymerization of acrylates. III. Polymerization of 2-ethylhexyl acrylate initiated by lithium-tert-butoxide

The polymerization of 2-ethylhexyl acrylate (EtHA) initiated with lithium-tert-butoxide (t-BuOLi) in tetrahydrofuran (THF) and in the temperature range between ?60 and 20°C was investigated. The reaction rate is distinctly temperature-dependent and at ?60°C is already very low, similarly to the polymerization of methacrylates. Molecular weights of the polymers thus formed, particularly at higher temperatures, are inversely proportional to conversion of the monomer due to the slow initiation reaction. This is documented by the low consumption of alkoxide even at long reaction times, which also depends on the reaction temperature. At higher temperatures the polymerization stops spontaneously, due to the greater extent of autotermination reactions. The weak initiating efficiency of the alkoxide decreases still more with decreasing concentration of the monomer during the polymerization, as confirmed by the concentration dependence of the reaction rate in toluene at ?20°C. The results suggest a negligible initiating effect of alkoxides in complex bases, particularly at lower polymerization temperatures. © 1992 John Wiley & Sons, Inc.