Alkoxide Bonds Research Articles

Ring-Opening Polymerization of Lactones and Lactides with Sn(IV) and Al(III) Initiators

A theoretical study is presented of the ring-opening polymerization (ROP) mechanism of 1,5-dioxepan-2-one (DXO) and glycolide with Sn(II) and Al(III) alkoxide initiators (SnMe3MeO, SnMe2(MeO)2, and AlMe2MeO). The B3LYP density functional method has been used to perform the quantum chemical calculations. A coordination−insertion mechanism is presented with two principal reaction steps. First, the alkoxide of the initiator performs a nucleophilic attack on the carbonyl carbon, and the carbonyl bond is broken. An intermediate is formed at this point, where the former carbonyl oxygen of the monomer is coordinated to tin via an alkoxide bond, while the carbonyl carbon assumes a sp3 bonding geometry. The second step involves the acyl−oxygen cleavage of the monomer. For all three initiators it was found that the transition state involving the breaking of the carbonyl double bond (TS1) represented the highest point on the potential energy surface for DXO. For glycolide, however, the transition state of the acyl−oxygen cleavage (TS2) was the least stable structure. The reaction barriers were calculated to 17.1 kcal/mol for DXO/SnMe3MeO, 18.7 kcal/mol for glycolide/SnMe3MeO, 14.3 kcal/mol for DXO/SnMe2(MeO)2, 14.5 kcal/mol for glycolide/SnMe2(MeO)2, 13.6 kcal/mol for DXO/AlMe2MeO, and 9.3 kcal/mol for glycolide/AlMe2MeO. Both electronic and steric properties of the monomer affect the reaction barriers. It was found that the more electrophilic initiators polymerized cyclic esters faster.

On the mechanism of polymerization of cyclic esters induced by tin(II) octoate

Mechanism of initiation and propagation in polymerization of ϵ-caprolactone and L,L-dilactide induced with tin(II) octoate (Sn(Oct)2) and Sn(Oct)2/n-butyl alcohol system is presented. Tin(II) alkoxide bond formation is required in reaction of Sn(Oct)2 with hydroxyl group containing compound to form a true initiator. Then tin(II) alkoxide end group is an active centre in the further propagation.

Kinetics and mechanism of cyclic esters polymerization initiated with tin(II) octoate, 1. Polymerization of -caprolactone

Kinetics of polymerization of ε-caprolactone (CL) initiated with tin(II) octoate (Sn(Oct)2) in THF as a solvent at 80°C was studied. The results strongly indicate that polymerization initiated with Sn(Oct)2 proceeds on the tin(II)-alkoxide bond and are not compatible with a mechanism in which propagation was proposed to proceed by a nucleophilic attack of the …OH ended macromolecules on the monomer-Sn(Oct)2 complex.

Carbonyl sulfide insertion into Group 2 metal–isopropoxide bonds; synthesis and crystal structures of [Mg(OCSOPri)2(PriOH)4]· 2PriOH and [{Sr(OCSOPri)2(PriOH)2}n

The insertion reactions of COS into the metal–alkoxide bonds of some alkaline-earth metals have been investigated. The resulting compounds have been studied spectroscopically (IR, 1H and 13C NMR), and by analytical techniques (TGA). The crystal structures of the strontium complex [{Sr(OCSOPri)2(PriOH)2}n] and the magnesium complex [Mg(OCSOPri)2(PriOH)4]·2PriOH have shown that whereas the former has a three dimensional structure the latter is monomeric.

Model reaction of epoxy-containing siloxane

3-glycidyloxypropyltrimethoxysilane (GPTS), which contains hydrolizable silicon alkoxide bonds and a ring-openable epoxy group, was used as the model substance for studying the reaction conditions in producing transparent and non-shrinking sol-gel epoxy-SiO2 composites. When GPTS reacts with the mixture of H2O and n-butyric acid (nBA, used as a model curing agent) using triethylamine (TEA), pyridine or triphenylphosphine (TPP) as a catalyst at 50°C, the GPTS undergoes both hydrolysis and ring-opening reaction simultaneously and independently. The ring-opening reaction shows an induction period in the initial stage of the reaction when TEA was used as catalyst, while no induction period was observed when pyridine and TPP were used as catalyst. The rate of ring-opening reaction of epoxide group catalyzed by TPP and pyridine is faster that that catalyzed by TEA, but is still slower than the hydrolysis of SiOMe bonds. When 2-hydroxyalkylmercaptan was used as the curing agent (TEA as catalyst), the ring-opening reaction of GPTS was so reactive that the epoxide group not only reacted with mercaptan, but also reacted with H2O, and hence it is of no use to the synthesis of transparent and non-shrinking sol-gel epoxy-SiO2 composites. From the detailed study of the influence of the structure of siloxanes on the reactivity of hydrolysis, it is suggested that RSi(OR′)3 is the better type of precursor for the synthesis of transparent and non-shrinking sol-gel epoxy-SiO2 composites. The structures of R and R′ are also discussed in this paper.

Synthesis and molecular structure of Ba 5(μ 5-OH)[μ 3-OCH(CF 3) 2] 4[μ 2-OCH(CF 3) 2] 4 [OCH(CF 3) 2](THF) 4(H 2O)·THF: a source of barium fluoride

The reaction between metallic barium and fluoroisopropanol or alcoholysis of [Ba(OPr i) 2] produces a pentanuclear fluoroalkoxide. Its X-ray structure determination showed its formulation to correspond to Ba 5(μ 5-OH)[μ 3-OCH(CF 3) 2] 4[μ 2-OCH(CF 3) 2] 4 [OCH(CF 3) 2](THF) 4(H 2O)·THF. The metallic core is based on a square pyramid encapsulating an hydroxo ligand. In addition to the bariumalkoxide bonds [2.53(3)–2.86(3) Å] neutral O-donors, four THF [2.82(2)–2.86(3) Å] and one H 2O [2.79(3) Å] and secondary bariumfluorine interactions [2.99(2)–3.31(2) Å] ensure high coordination numbers, from 9 to 11 for the metal centers. Hydrogen bonding between the apical fluoroisopropoxide, the water molecule and one THF molecule, non-bonded to a metal center, accounts for the stability of the hydrate and illustrates the Lewis acidity of fluoroalkoxides. Thermal decomposition leads to BaF 2.

Sulfur dioxide insertion reactions into metal–alkoxide bonds: synthesis and crystal structure of catena-bis(methylsulfito)bis(methanol)calcium; a one-dimensional polymer based on eight-coordinate calcium ions

Download options Please wait... Article information DOI https://doi.org/10.1039/C39940002695 Article type Paper Download Citation J. Chem. Soc., Chem. Commun., 1994, 2695-2696 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Sulfur dioxide insertion reactions into metal–alkoxide bonds: synthesis and crystal structure of catena-bis(methylsulfito)bis(methanol)calcium; a one-dimensional polymer based on eight-coordinate calcium ions V. Arunasalam, I. Baxter, M. B. Hursthouse, K. M. A. Malik, D. M. P. Mingos and J. C. Plakatouras, J. Chem. Soc., Chem. Commun., 1994, 2695 DOI: 10.1039/C39940002695 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author V-Cumaran Arunasalam Ian Baxter Michael B. Hursthouse K. M. Abdul Malik D. Michael P. Mingos John C. Plakatouras

Carbonyl insertion and reductive elimination chemistry of tungsten(II) alkoxides and aryloxides

Carbonyl insertion into the W–O bond in a series of novel WII alkoxides and aryloxides, containing a tridentate monoanionic [C,N,N′] ligand, results in the generation of alkoxycarbonyl- and aryloxycarbonyl-groups, which readily reductively eliminate to form new C–C bonds; in contrast, carbon dioxide insertion into the W–OMe alkoxide bond generates an η1;-carbonate ligand, which retains coordination to the metal centre.

(η 5-C 5Me 5) 2(Me)TiOC(Me)CH 2: titanum enolate or titanum alkoxide?

While proton and carbon NMR spectroscopy suggest that (Cp*) 2(Me)TiOC(Me)CH 2 ( 1, Cp* η 5-C 5Me 5 is a typical titanum enolate, this material does not exhibit typical enolate reactivity. Specifically, 1 does not react with either methyl iodide or with benzaldehyde. However, some reagents that are typically used in electrophilic attack of metalalkyl or metalalkoxide bonds do react with 1. In some cases the electrophile displaces the enolate moeity, while in other cases selectivity for substitution of the titanium-bound methyl group is displayed. Thus the reactivity of 1 is more typical of that expected from a titanum alkoxide or an alkyl titanium rather than a titanium enolate. The possible use of the (Cp*) 2(Me)Ti moiety as a protecting group for ketones is discussed.

ChemInform Abstract: Organometallic Thermochemistry. Metal Hydrocarbyl, Hydride, Halide, Carbonyl, Amide, and Alkoxide Bond Enthalpy Relationships and Their Implications in Pentamethylcyclopentadienyl and Cyclopentadienyl Complexes of Zirconium and Hafnium

ChemInformVolume 20, Issue 10 Article ChemInform Abstract: Organometallic Thermochemistry. Metal Hydrocarbyl, Hydride, Halide, Carbonyl, Amide, and Alkoxide Bond Enthalpy Relationships and Their Implications in Pentamethylcyclopentadienyl and Cyclopentadienyl Complexes of Zirconium and Hafnium L. E. SCHOCK, L. E. SCHOCK Dep. Chem., Northwest. Univ., Evanston, IL 60208, USASearch for more papers by this authorT. J. MARKS, T. J. MARKS Dep. Chem., Northwest. Univ., Evanston, IL 60208, USASearch for more papers by this author L. E. SCHOCK, L. E. SCHOCK Dep. Chem., Northwest. Univ., Evanston, IL 60208, USASearch for more papers by this authorT. J. MARKS, T. J. MARKS Dep. Chem., Northwest. Univ., Evanston, IL 60208, USASearch for more papers by this author First published: March 7, 1989 https://doi.org/10.1002/chin.198910066Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume20, Issue10March 7, 1989 RelatedInformation

Organometallic thermochemistry. Metal hydrocarbyl, hydride, halide, carbonyl, amide, and alkoxide bond enthalpy relationships and their implications in pentamethylcyclopentadienyl and cyclopentadienyl complexes of zirconium and hafnium

Organometallic thermochemistry. Metal hydrocarbyl, hydride, halide, carbonyl, amide, and alkoxide bond enthalpy relationships and their implications in pentamethylcyclopentadienyl and cyclopentadienyl complexes of zirconium and hafnium

ChemInform Abstract: Insertion of Carbon Dioxide into Metal Alkoxide Bonds. Synthesis and Structure of Tungsten Tetracarbonyl Carbonate.

AbstractThe recently prepared aryl oxide tungsten complexes (I) react with CO2 yielding the aryl carbonate pentacarbonyl species (II) which on hydrolysis accompanied by loss of a CO ligand leads to the title compound (III) (no yield given).

Insertion of carbon dioxide into metal alkoxide bonds. Synthesis and structure of tungsten tetracarbonyl carbonate

Insertion of carbon dioxide into metal alkoxide bonds. Synthesis and structure of tungsten tetracarbonyl carbonate

The Influence of Stereochemical Structure on the Kinetics and Mechanism of Ester-Ester Exchange Reactions by Mass Spectrometry. II

Abstract Exter-ester exchange reactions in polyesters, formulated from adipic acid and various linear and branched glycols, were studied by mass spectrometry employing the Dimer Analysis Method (DAM). Activation energies (E) and frequency factors (A) were obtained for the reaction systems at temperatures of 572–585 K. The kinetic behavior of these reactions was influenced by the stereochemical structures of carbonyl oxygens along the polymer chain backbone. Syndiotactic/syndiotactic systems reacted slower than syndiotactic/heterotactic and heterotactic/heterotactic systems, respectively. Correlation of frequency factors (A) and stereochemical structures showed an alternating trend in kinetic behavior. An “associative reaction mechanism” was postulated since it satisfied the energetic and geometric requirements necessary for the simultaneous making and breaking of alkoxide bonds, and also gives a good fit to the kinetic expression derived for an opposing bimolecular reaction.

Proteolytic enzymes: models for electrophilic assistance by NH in acylation

The effect of increasing dioxan content of the medium has been employed to examine the possibility of intramolecular electrophilic assistance by NH in alkaline hydrolysis of the methyl esters of 2-acetamidobenzoic (I), pyrrole-2-carboxylic (VII), and benzimidazole-4(7)-carboxylic (V) acids. Significant enhancement of rate constant is observed over isomers where no participation is possible. Enhancements increased steeply with increasing dioxan concentration in agreement with a ‘built-in’ solvation by the NH of the incipient alkoxide ion (derived from the carbonyl oxygen) of the transition-state. Heterocyclic types [(VII) and (V)] exhibited maxima in their rate enhancements as the dioxan content increased. Since the NH to alkoxide bond distance in the heterocyclic types is larger than normally found for direct hydrogen-bonding the maximum is argued to arise from a water bridge acting as a relay between electrophile NH and incipient alkoxide ion of the transition-state.