Abstract
Dendrimers containing terminal olefins or ruthenium-benzylidene terminal groups undergo olefin metathesis reactions (RCM and ROMP types), and essentially results from our group are reviewed here. Dendrimers have been loaded at their periphery with ruthenium-chelating bis-phosphines, which leads to the formation of dendrimer-cored stars by ring-opening-metathesis polymerization (ROMP). CpFe+-induced perallylation of polymethylaromatics (Cp = η5-C5H5) followed by ring-closing metathesis (RCM) and/or cross metathesis (CM) leads to poly-ring, cage, oligomeric and polymeric architectures. In the presence of acrylic acid or metha-crylate, stereospecific CM inhibits oligomerization, and dendritic olefins yield polyacid dendrimers. Finally, cros-metahesis reactions with dendronic acrylate allow dendritic construction and growth.
Highlights
The understanding of the mechanism of olefin metathesis by Yves Chauvin [1, 2] has generated considerable efforts in the design of efficient catalysts [3, 4] and ended up in many applications [5,6,7,8,9]
The alkene and alkyne metathesis reactions mostly deal with low-molecular weight unsaturated substrates with the synthesis of pharmaceutically important products [5, 6] and polymers [5, 7]
The analogous ruthenium benzylidene dendrimers were very recently synthesized with two tertiobutyl groups on each phosphorus, and they were slightly more reactive ring-openingmetathesis polymerization (ROMP) catalysts for the polymerization of norbornene than those involving the cyclohexyl substituents [22]
Summary
Résumé — Les réactions de métathèse des oléfines dans les dendrimères — Les réactions de métathèse avec les dendrimères récemment étudiées dans notre groupe de recherche sont brièvement résumées dans cette micro revue. Celles-ci incluent les réactions qui impliquent des catalyseurs de métathèse métallodendritique comportant des terminaisons bis-phosphines coordonnées au catalyseur de métathèse centré sur le ruthénium (polymérisation) et les réactions de peralkylation des polyméthylarènes induites par complexation temporaire de ces arènes avec le greffon CpFe+ (Cp = η5-C5H5) couplée avec la métathèse (RCM et croisée), catalysée par les catalyseurs de Grubbs de première et seconde génération. La revue mentionne également la polymérisation des alcynes terminaux par métathèse polymérisante dont la vitesse est considérablement accrue par couplage avec un catalyseur de transfert d’électron en chaîne. Abstract — The Olefin Metathesis Reactions in Dendrimers — Olefin metathesis reactions catalyzed by Ru benzylidene catalysts involving polymers and dendrimers have been investigated in our research group and are briefly reviewed. CpFe+-induced perallylation of polymethylaromatics (Cp = η5-C5H5) followed by ring-closing metathesis (RCM) and/or cross metathesis (CM) leads to poly-ring, cage, oligomeric and polymeric architectures. Tungsten-catalyzed polymerization of alkynes coupled with electron-transfer-chain catalysis leads to much faster and cleaner polymerization than with an 18-electron tungsten catalyst alone
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