Search results for "metathesis"

Comparison of living polymerization systems

1994

Recent developments in the field of living polymerization are surveyed. Comparison of the available mechanistic and kinetic information is made for living anionic, cationic, free radical, group transfer, ring-opening metathesis, Ziegler-Natta and immortal polymerizations. This evaluation indicates that the majority of living polymerizations involve quasiliving equilibrium between active (propagating) and dormant (nonpropagating) polymer chains. On the basis of the kinetics of a general model for quasiliving and ideal living polymerizations it is concluded that ideal living polymerization is a special subclass of quasiliving polymerizations. Classification of living polymerization systems is…

Poly(phosphonate)-mediated Horner–Wadsworth–Emmons reactions

2015

A novel, general protocol for a polymer-mediated Horner–Wadsworth–Emmons (HWE) reaction is reported. The polyvalent polymeric reagent was prepared via acyclic diene metathesis (ADMET) polymerization. Homo- and copolymers of reactive poly(phosphonate)s with molecular weights up to 40 000 g·mol−1 and molecular weight dispersities Đ < 2 were successfully synthesized. Subsequent application of these polymers in the HWE reaction to prepare a library of aromatic α,β-unsaturated ketones (chalcons) has proven to be an efficient synthetic pathway to minimize purification efforts, as the polymeric side-product can be removed by simple precipitation. In this paper we also demonstrate for the first tim…

Synthesis and characterization of poly(phenylacetylenes) featuring activated ester side groups

2010

Four monomers based on 4-ethynylbenzoic acid have been synthesized, one of those featuring an activated ester. With the metathesis catalytic system WCI 6 /Ph 4 Sn, these acetylenic monomers could successfully be polymerized yielding conjugated polymers with molecular weights of around 10,000 to 15,000 g/mol and molecular weight distributions M w / M n < 2.1. Also the copolymerization of phenylacetylene or methyl 4-ethynylbenzoate with pentafluorophenyl 4-ethynyl-benzoate as reactive unit was conducted. Polymer analogous reactions of the reactive polymers and copolymers with amines have been investigated and it was found that poly(pentafluorophenyl 4-ethynylbenzoate) featured a significant r…

Thiol-functionalized ROMP polymers via Sacrificial Synthesis

2009

The synthesis of well-defined and highly functionalized thiol-functionalized polymers has been accomplished via the ring-opening metathesis polymerization (ROMP). A sacrificial synthesis-based approach was chosen for this interesting functional group since it has proven to give precise control over molecular weight and selective placement of end-groups on a different functionality before. Thiol-functionalized ROMP-polymers were successfully synthesized employing thioacetal monomers, which can be cleaved by hydrogenation leaving the desired thiol group behind. The placement of this highly reactive functional group at one chain end of a poly(norborneneimide) is demonstrated by analytical meth…

Postsynthetic Approach for the Rational Design of Chiral Ferroelectric Metal–Organic Frameworks

2017

International audience; Ferroelectrics (FEs) are materials of paramount importance with a wide diversity of applications. Herein, we propose a postsynthetic methodology for the smart implementation of ferroelectricity in chiral metal−organic frameworks (MOFs): following a single-crystal to single-crystal cation metathesis, the Ca2+ counterions of a preformed chiral MOF of formula Ca6II{CuII24[(S,S)-hismox]12(OH2)3}·212H2O (1), where hismox is a chiral ligand derived from the natural amino acid l-histidine, are replaced by CH3NH3+. The resulting compound, (CH3NH3)12{CuII24[(S,S)-hismox]12(OH2)3}·178H2O (2), retains the polar space group of 1 and is ferroelectric below 260 K. These results op…

Asymmetric synthesis of fluorinated cyclic beta-amino acid derivatives through cross metathesis.

2006

The asymmetric synthesis of several fluorinated cis-2-aminocycloalkane carboxylic acids (cis-2-ACACs) with a cross metathesis (CM) reaction as the key step has been carried out, constituting the first time a metathesis protocol has been undertaken with fluorinated imidoyl chlorides. Subsequent chemoselective hydrogenation of the olefin moiety, Dieckmann condensation, and stereoselective reduction of the iminic double bond afforded the corresponding beta-amino esters with several ring sizes. The asymmetric version of the process was achieved by using (-)-8-phenylmenthol as a chiral auxiliary.

Metallocene sulfide chemistry of niobium and tantalum: new insights into the formation of niobium-polysulfido complexes and synthesis, structure, and…

1992

The previously described reaction of Cp'2NbH3 (Cp' = t-BuC5H4) with S8 was investigated with regard to the kinetic stabilization of as yet elusive intermediates during the formation of the polysulfide complex Cp'4Nb2S9 (1). Therefore, the permethylated complex Cp*2NbS3H (2; Cp* = C5Me5) and the Ta complex Cp'2TaS2H (3) were synthesized in a related reaction and structurally investigated. Despite the problematic localization of the hydride atom during X-ray crystallographic studies, the molecules can be described in a proper manner: Characteristic of 2 and 3 are M(eta(2)-S2) cores to which either an SH (2) or a H (3) ligand is attached. Complex 3 is the first known tantalocene sulfide. It re…

Heterotelechelic Ring-Opening Metathesis Polymers

2009

By combining sacrificial synthesis with the vinyl lactone termination technique, heterotelechelic polymers were synthesized. The nonterminating nature of sacrificial synthesis was utilized to introduce a hydroxyl group at the start of the polymer chain. Lactone termination was used to functionalize the chain ends with aldehydes or carboxylic acids. The synthesis of well-defined heterotelechelic polymers was thus accomplished employing the Grubbs’ first generation catalyst as the initiator. The living nature of this polymerization allowed for precise control over the molecular weight and guaranteed full functionalization of both polymer chain ends. The presence of the functional groups is sh…

Sacrificial Synthesis of Hydroxy-Telechelic Metathesis Polymers via Multiblock-Copolymers

2009

The synthesis of well-defined telechelic ring-opening metathesis polymers has been achieved by Sacrificial Synthesis. With the formation of cleavable triblock-copolymers, precise control over the molecular weight and the degree of functionalization was achieved. Introducing cleavable monomers that can be addressed separately, sequential deprotection was accomplished which opened the path to more sophisticated polymeric materials bearing different substituents at their respective chain ends. Sacrificial penta- and heptablock-copolymers are also presented which allow the synthesis of well-defined telechelic polymers in good yields and significantly improved initiator efficiency.

1976

Polyoctenylenes and polydodecenylenes prepared by the methathesis reaction exhibit a bimodal molecular weight distribution. The low molecular weight fraction consists of cyclic oligomers, the high molecular weight fraction is assumed to contain linear polymers. The distribution of cyclic oligomers together with the polymer material indicates a ring-chain equilibrium. The slope of the plot log Kx (molar cyclization equilibrium constant) vs. log x (degree of polymerization) is close to −2,5 as predicted by the Jacobson and Stockmayer theory for unstrained macrocycles. Polyoctenylene und Polydodecenylene, dargestellt mit Hilfe der Metathese-Reaktion, weisen eine bimodale Molekulargewichtsverte…