Alkali Metal Alkoxides Research Articles

ChemInform Abstract: Asymmetric Alkylation Catalyzed by Chiral Alkali Metal Alkoxides of TADDOL. Synthesis of α‐Methyl Amino Acids.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Asymmetric alkylation catalyzed by chiral alkali metal alkoxides of TADDOL. Synthesis of α-methyl amino acids

It is shown that sodium alkoxides formed from (4R,5R)-2,2-dimethyl-1,3-dioxolane-4,5-bis(diphenylmethanol) ((R,R)-TADDOL) and some of its derivatives can be used as chiral catalysts for enantioselective alkylation of Schiff's bases derived from alanine with reactive alkyl halides. Acid hydrolysis of the reaction products affords (R)-α-methylphenyl-alanine, (R)-α-allylalanine, and (R)-α-methylnaphthylalanine in 61–93% yields and withee 69–94%. When (S,S)-TADDOL is used, the (S)-amino acid is formed. A mechanism explaning the observed features of the reaction is proposed.

Alkali Metal Alkoxide Clusters: Convenient Catalysts for the Synthesis of Methylphosphonates.

Alkali metal alkoxides are good catalysts (1-8 mol %) for promoting the interchange reaction between carbonyl and phosphorus esters. This reactivity leads to convenient methodologies for the synthesis of symmetric and unsymmetric alkyl-substituted methylphosphonates from dimethyl methylphosphonate (DMMP). Reactions rates are high with initial turnover frequencies (N(t)) in excess of 1 x 10(6) h(-)(1) observed and with KO(t)Bu > NaO(t)Bu > LiO(t)Bu. The reactions were sensitive to steric effects in the product methylphosphonates with reaction rates paralleling the size of the transferring alkoxide (n-alkyl > isoalkyl >> tert-alkyl). For the test reaction DMMP + isopropyl acetate, substitution kinetics were consistent with a scenario wherein each methoxide is replaced sequentially, and the substitution rate for the second displacement is substantially slower than the first. Kinetic studies on the first substitution process were indicative of a concentration dependent rate law; a scenario most easily accounted for by a coupled transesterification wherein alkoxide reversibly and independently adds to phosphonate and ester.

ARC Study of Thermal Stability of Alkali Metal Alkoxides

Alkali metal alkoxides can be formed by the direct reaction of alkali metals with the corresponding alcohol. Under certain conditions, however, these reactions become dangerous. One of the reasons for the instability build-up in the reaction mixture is related to the electrochemical behaviour of the heterogeneous medium. Another reason is the instability introduced by the simultaneous presence of oxygen and alkali metal atoms in the reagents. Accelerating rate calorimetry is an excellent way to determine safe working conditions for the handling of such compounds. The hazards that are encountered are discussed by means of some examples.

Regioselective ring‐opening anionic polymerization of β‐lactones

AbstractNew aspects of anionic polymerization of 4‐membered lactones are presented, attention being paid to regioselectivity of ß‐lactones ring‐opening reactions. It has been demonstrated that supramolecular complexes of alkali metal alkoxides used as initiators enable control of lactones polymerization, and due to anion activation yield polymers with specific molecular architecture. Synthesis of the analogue of natural polymer poly(3‐hydroxybutyrate) via anionic polymerization of ß‐butyrolactone is discussed.

“New” Catalysts for the Ester-Interchange Reaction: The Role of Alkali-Metal Alkoxide Clusters in Achieving Unprecedented Reaction Rates

The catalytic effect of alkali-metal tert-butoxide clusters on the rate of ester interchange for several pairs of esters has been determined in nonpolar and weakly polar solvents. Reactivities increase in the order (Li+ < Na+ < K+ < Rb+ < Cs+) with the fastest rates reaching 107 catalytic turnovers per hour (TO/h). Ester interchange rates were sensitive to the size of both the transferring OR groups and the ester substituent. Phenyl esters did not exchange with aliphatic esters due to nonstatistical breakdown patterns in the tetrahedral intermediate. A first-order equilibration analysis on the interchange between tert-butyl acetate (tBuAc) and methyl benzoate (MeBz) (5 mol % NaOtBu) indicated enhanced reaction rates as the reaction proceeded. Isolation and quenching (DCl/D2O) of precipitated catalyst points to a mechanism whereby sequential methoxy incorporation into the catalyst cluster increases activity, but eventually precipitates out of solution as a 3:1 OMe:OtBu cluster. The rate law was determined to be kobs[MeBz]1[tBuAc]0[NaOtBu]x, where x = 1.2(1), 1.4(1), and 0.85(1) in hexane, ether, and THF, respectively, under conditions where tetrameric catalyst aggregates are expected. Reaction rates were generally observed to be higher in nonpolar solvents (hexane > toluene, ether > THF). Eyring analysis over a 40 °C range yielded ΔH‡ = 10.0(1) kcal mol-1 and ΔS‡ = −32(3) eu. A Hammett (σ) plot generated with para-substituted methyl benzoates gave ρ = +2.35 (R = 0.996). These results are interpreted in terms of a catalytic cycle composed of two coupled transesterification reactions with a turnover-limiting addition of a tert-butoxy-containing cluster (tetramer) to methyl benzoate. Catalyst relative reactivities (Cs+ > Rb+ > K+ > Na+ > Li+) are interpreted in terms of competitive electrostatic interactions between the alkali-metal and ground-state and transition-state anions. This analysis predicts the observed linear dependence between log(kobs) and 1/rionic.

ChemInform Abstract: The First Case of Asymmetric Michael Reaction Catalyzed by Chiral Alkali Metal Alkoxides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The first example of asymmetric Michael reaction catalyzed by chiral alkali metal alkoxides

Some chiral sodium alkoxides can be used as catalysts in the asymmetric Michael reaction as exemplified by the 1,4-addition of an achiral NiII complex of the Schiff base derived from glycine andN-(2-pyridylcarbonyl)-o-aminobenzophenone (1) to methyl methacrylate (2) or methyl acrylate (14). The products of the reaction of1 with2,viz., the corresponding diastereomeric complexes of 4-methylglutamic acid, are formed in dissimilar amounts (de 26–85%); theee value for the major diastereomer (2S,4R)-3a is 28%. After recrystallization, the enantiomeric purity of complex3a increases toee>85%. Acidcatalyzed hydrolysis of the enantiomerically enriched complex3a affords (2S,4R)-4-methylglutamic acid (ee>85%). The complex of glutamic acid15 resulting from the reaction of1 with14 is formed with anee of 45%. After recrystallization, the enantiomeric purities of complex15 and glutamic acid increase toee>90%.

Alkoxide and Aryloxide Derivatives of a (Triamidoamine)uranium Complex.

The (triamidoamine)uranium chloride complex [{U(NN(3))(&mgr;-Cl)}(2)] [NN(3) = N(CH(2)CH(2)NSiMe(3))(3)] reacts with alkali metal alkoxides and aryloxides to give a range of complexes [U(NN(3))(OR)] (R = Bu(t), t-C(4)F(9), Ph, 2,6-Bu(t)(2)-4-MeC(6)H(2)). Crystallographic investigations (including the molecular structure of the perfluoro-tert-butoxido derivative [U(NN(3))(O-t-C(4)F(9))]), molecular weight determinations, and NMR spectroscopic data are consistent with these molecules being monomeric with a 3-fold symmetric arrangement of the triamidoamine fragment. The three turquoise ate complexes [U(NN(3))(OR)(OR')Li(THF)(n)()] (R, R' = Bu(t) or Ph), are prepared by reaction of the corresponding uranium alkoxides with lithium phenoxide or tert-butoxide. The complex with R = Ph, R' = Bu(t), n = 1 is shown by X-ray crystallography to have a capped trigonal bipyramidal structure. A lithium atom is incorporated into the ligand sphere by coordination to an amido nitrogen and a tert-butoxido oxygen. The mixed alkoxide ate complex [U(NN(3))(OBu(t))(OPh)Li(THF)] gives only [U(NN(3))(OBu(t))] on heating in vacuo. The one-electron oxidation of these ate complexes to the three neutral pentavalent compounds [U(NN(3))(OR)(OR')] (R, R' = Bu(t) or Ph) has been characterized by cyclic voltammetric studies and performed on the chemical scale by reaction with [FeCp(2)][PF(6)].

The Remarkable Catalytic Activity of Alkali-Metal Alkoxide Clusters in the Ester Interchange Reaction

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTThe Remarkable Catalytic Activity of Alkali-Metal Alkoxide Clusters in the Ester Interchange ReactionMatthew G. Stanton and Michel R. GagnéView Author Information Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599 Cite this: J. Am. Chem. Soc. 1997, 119, 21, 5075–5076Publication Date (Web):May 28, 1997Publication History Received21 February 1997Published online28 May 1997Published inissue 1 May 1997https://doi.org/10.1021/ja970556vCopyright © 1997 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1565Altmetric-Citations34LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (120 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Catalysts,Cluster chemistry,Equilibrium,Organic compounds,Solvents Get e-Alerts

Synthesis and characterization of poly(ε‐caprolactone)‐poly(ethylene glycol) block copolymer

Poly(e-caprolactone)-poly(ethylene glycol ) -poly(e-caprolactone) triblock copolymers (PECL) covering a wide range of poly (ethylene glycol) (PEG) lengths were synthesized with alkali metal alkoxide derivatives of poly(ethylene glycol). The effects of various factors, such as amount of the initiator, reaction time and temperature, polarity of solvent, length of PEG segment, and counterion on the polymerization were investigated. The copolymers were characterized by 1 H-NMR, IR, GPC, and DSC. It was found that THF system is superior to toluene system. The conversion of the monomer increased with increase of the initiator concentration. High molecular weight of the copolymer and high conversion of the monomer was obtained at below 30°C within 5 min. The polymerization process was studied by GPC and the coexistence of propagation and transesterification reaction was found, which leaded to relatively broad molecular weight distribution of the copolymers.

ChemInform Abstract: (Alk‐1‐ynyl)oxiranes in the Reaction of (Alk‐1‐ynyl)chlorocarbenes with Alkali Metal Alkoxides.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A New Heterogeneous Williamson Synthesis of Ethers Using t-Alkyl Substrates.

In general, the reactions of t-alkyl halides with alkali metal alkoxides and phenoxides in polar solvents give olefins (E) almost alone. However, we found a new method for the preparation of t-alkyl ethers (SN) in the reactions of t-alkyl substrates with metal alkoxides and aryl oxides in nonpolar solvents. Alkali metal phenoxides (PhO- M+; M+=Li+, Na+ and K+) reacted with t-butyl bromide and iodide in hexane at 60 °C for few hours to give t-butyl phenyl ether in 41-59% yields. A similar SN reaction of alkaline earth metal phenoxides also gave the ether in 54-60% yields. More hindered 1-adamantyl methanesulfonate, which is resistant to elimination compared with t-butyl halide, reacted with metal alkoxides in octane at 100-110 °C to give corresponding 1-adamantyl alkyl ethers in good yields. The comparable reaction of 1-adamantyl iodide was much slower than the case of 1-adamantyl methanesulfonate. Aprotic polar solvents (DMF, DMSO) were unfavorable for the SN reaction. On the other hand, alkali metal alkoxides reacted with t-butyl halide in heptane to give 2-methylpropene (E) exclusively, but strontium and barium alkoxides gave 15-50% of alkyl t-butyl ether (SN) at 80-95 °C. The selectivity of SN/E was governed by solvent, metal cation (Li+, Na+, K+, Mg2+, Ca2+, Sr2+, and Ba2+), nucleophile, and substrate. The nonpolar solvents were much more effective than polar solvents for the SN reaction. The addition of crown ether to the system decreased markedly the SN/E ratio. The addition effect of radical scavenger, galvinoxyl was not recognized.

Stereochemical Control in the Anionic Polymerization of β-Butyrolactone Initiated with Alkali-Metal Alkoxides

The anionic polymerization of (R)-β-butyrolactone initiated with either 18-crown-6 complexes of a potassium alkoxide or a simple carboxylate (reference initiator) proceeded with inversion of configuration. As a result (R)-β-butyrolactone formed an isotactic poly((S)-β-hydroxybutyrate) with these initiators at room temperature. Polymerization of (R,S)-β-butyrolactone under the same conditions gave an atactic polymer, but at lower temperatures the predominantly syndiotactic form of poly((R,S)-β-hydroxybutyrate) was produced from the racemic monomer.

Metalation, a Novel Route for the Functionalization of Reactive Elastomers. 1. Superbases in the Metalation of Poly(isobutylene-co-p-methylstyrene)

A variety of strong bases and hydrocarbon-soluble superbases (SB) have been used for the selective metalation of poly(isobutylene-co-p-methylstyrene) at the benzylic p-methyl position. The reaction was monitored by quenching the metalated polymer with chlorotrimethylsilane and measuring the resulting functionalization by 1H NMR spectrometry. A study of different SB's prepared from butyllithium and a heavier alkali metal alkoxide showed the importance of the alkali metal used in the alkoxide. Both the degree of metalation and the selectivity increase with the size of the metal cation (Li+ < Na+ < K+ < Cs+). Best results for the quantitative metalation of all of the benzylic p-methyl groups of the copolymer were obtained using a 2-fold molar excess of the SB derived from s-BuLi and cesium l-(−)-menthoxide in the ratio of 1:3. Ring metalation is estimated to less than 2%, and the polymer backbone is unreactive. Time-dependent metalation reactions carried out between −78 and +65 °C reveal that, regardless of ...

Anionic Polymerization of Pivalolactone Initiated by Alkali Metal Alkoxides

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAnionic Polymerization of Pivalolactone Initiated by Alkali Metal AlkoxidesZbigniew Jedlinski, Piotr Kurcok, Marek Kowalczuk, Andrzej Matuszowicz, Philippe Dubois, Robert Jerome, and Hans R. KricheldorfCite this: Macromolecules 1995, 28, 21, 7276–7280Publication Date (Print):October 1, 1995Publication History Published online1 May 2002Published inissue 1 October 1995https://doi.org/10.1021/ma00125a035RIGHTS & PERMISSIONSArticle Views290Altmetric-Citations18LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (603 KB) Get e-Alerts Get e-Alerts

Structure and Bonding in Organometallic Anions of Heavy Group 14 and 15 Elements

AbstractAlkali metal organometallic complexes (containing C–metal bonds) and the frequently structrually related alkali metal amides and alkoxides have been investigated extensively both in the solid state and in solution in the past two decades. However, until recently, the related complexes containing the heavier metallic and semi‐metallic p block elements and the alkali and alkaline earth metals had rarely been studied in their own right. Recent solid‐state structural studies have illustrated the immense structural diversity and bonding modes to be found within these species. One of the principal focuses of recent studies has been complexes containing organometallic anions of p block metals (e.g., triorganostannates, containing R3Sn−) in which metal–metal bonds occur between the heavy p block metal and the alkali or alkaline earth metal and the investigation of the nature of this bonding. The development of new synthetic routes has also allowed the preparation of a variety of anionic ligands with p block metal centers which promise new opportunities in coordination chemistry. In addition, the synthesis of a family of homologous anionic π complexes has given a fresh direction in the chemistry of p block metal metallocene complexes.

Substituent effect in anionic polymerization of β‐lactones initiated by alkali metal alkoxides

AbstractThe influence of methyl substituent on the mechanism of the ring‐opening polymerization of β‐lactones initiated by alkali metal alkoxides is discussed. Attention has been paid to the effect of the substituent position in the monomer molecule on the ring‐opening mechanism, the 3,3‐dimethyl‐2‐oxetanone (pivalolactone), 4‐methyl‐2‐oxetanone (β‐butyrolactone) and 2‐oxetanone (β‐propiolactone) being chosen as model monomers. Moreover, it was found unexpectedly that in the case of pivalolactone polymerization, besides open‐chain polymers, cyclic oligomers are produced.

The Synthesis of Biodegradable Polymers

Abstract Biodegradable polyesters such as poly(lactic acid) were synthesised by ring opening polymerization of anhydrosulfites. Considerable success has been achieved with the use of anionic initiators. High molecular weight polymer, Mn ∼37 700 has been synthesised using tert-butyl lithium as the initiator, which has turned out to be the most successful amongst the alkali metal alkoxides, alkyls and amides. Polymers produced were characterized with respect to structure (1H and 13C NMR spectroscopy) and molecular weight (Gel Permeation Chromatography).

Novel anionic polymerization of β‐lactones mediated by alkali metal supramolecular complexes

AbstractThe anionic polymerization of β‐lactones mediated by supramolecular complexes of alkali metal alkoxides and naphthalenides is demonstrated. The novel chemistry of the initiation and the propagation steps of polymerization is discussed.