Regio- and Stereospecific Cyclopolymerization of α,ω-Diynes by Cationic Molybdenum Imido Alkylidene N-Heterocyclic Carbene Complexes
| Autor: | Roman Schowner, Patrick Probst, Mathis J. Benedikter, Michael R. Buchmeiser, Iris Elser |
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| Rok vydání: | 2019 |
| Předmět: |
Polymers and Plastics
Polymers 02 engineering and technology 010402 general chemistry 01 natural sciences Medicinal chemistry Stereocenter Polymerization Diynes chemistry.chemical_compound Coordination Complexes Heterocyclic Compounds Cations Materials Chemistry Reactivity (chemistry) Molybdenum Organic Chemistry Cationic polymerization Imidazoles Regioselectivity Stereoisomerism 021001 nanoscience & nanotechnology 0104 chemical sciences Monomer chemistry Intramolecular force Stereoselectivity 0210 nano-technology Carbene Methane |
| Zdroj: | Macromolecular rapid communications. 41(1) |
| ISSN: | 1521-3927 |
| Popis: | Both solvent-free and acetonitrile-containing cationic molybdenum imido alkylidene N-heterocyclic carbene (NHC) complexes of the general formula [Mo(NR')(CHCMe2 R)(NHC)(X)+ A- ] (R' = 2,6-Cl2 -C6 H3 , tBu, 2-CF3 -C6 H4 , 2-tBu-C6 H4 , 2,6-iPr2 -C6 H3 , 2,6-Me2 -C6 H3 ; R = Me, Ph; NHC = 1,3-dimesitylimidazol-2-ylidene (IMes), 1,3-di-iPr-imidazol-2-ylidene (IPr), 1,3,5-triphenyl-1,3,4-triazol-2-ylidene); X = CF3 SO3 , C6 F5 O, OCH(CF3 )2 , OC(CF3 )3 , pyrrolide, C6 F5 COO, 2,6-(CF3 )2 -C6 H3 COO; A- = B(ArF )4- , Al(OC(CF3 )3 )4- ), have been investigated for their propensity to cyclopolymerize 4,4-disubstituted 1,6-heptadiynes. All metal complexes contain a stereogenic (chiral) metal center, which accounts for the high reactivity and high regioselectivity of insertion (>99%) that are observed for all metal complexes, leading to highly conjugated, α-insertion-derived polyenes that are based on a highly regular polymer backbone and that show absorption maxima close to 600 nm. With the chiral monomer 4-(ethoxycarbonyl)-4-(1S,2R,5S)-(-)-menthoxycarbonyl-1,6-heptadiyne, high syndiospecifity (>99% syndiotactic) is observed. A mechanism explaining the high regio- and stereoselectivity is presented. Thus, α-addition of the monomers proceeds chain-end-controlled trans to the NHC and is preferred over β-addition through intramolecular Mo-O chelation. Insertion of the monomers entails double inversion at the stereogenic metal center in the course of one complete monomer insertion. |
| Databáze: | OpenAIRE |
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