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Alternating Ring‐Opening Metathesis Copolymerization by Grubbs‐Type Initiators with Unsymmetrical N‐Heterocyclic Carbenes
Author(s) -
Lichtenheldt Martin,
Wang Dongren,
Vehlow Kati,
Reinhardt Ingrid,
Kühnel Christa,
Decker Ulrich,
Blechert Siegfried,
Buchmeiser Michael R.
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200900384
Subject(s) - copolymer , cyclopentene , polymer chemistry , chemistry , romp , pyridine , metathesis , polymerization , olefin fiber , ethylene , medicinal chemistry , polymer , organic chemistry , catalysis
A series of Ru IV –alkylidenes based on unsymmetrical imidazolin‐2‐ylidenes, that is, [RuCl 2 {1‐(2,4,6‐trimethylphenyl)‐3‐R‐4,5‐dihydro‐(3 H )‐imidazol‐1‐ylidene}(CHPh)(pyridin)] (R=CH 2 Ph ( 5 ), Ph ( 6 ), ethyl ( 7 ), methyl ( 8 )), have been synthesized. These and the parent initiators [RuCl 2 (PCy 3 ){1‐(2,4,6‐trimethylphenyl)‐3‐R‐4,5‐dihydro‐(3 H )‐imidazol‐1‐ylidene}(CHC 6 H 5 )] (R=CH 2 C 6 H 5 ( 1 ), C 6 H 5 ( 2 ), ethyl ( 3 )) were used for the alternating copolymerization of norborn‐2‐ene (NBE) with cis ‐cyclooctene (COE) and cyclopentene (CPE), respectively. Alternating copolymers, that is, poly(NBE‐ alt ‐COE) n and poly(NBE‐ alt ‐CPE) n containing up to 97 and 91 % alternating diads, respectively, were obtained. The copolymerization parameters of the alternating copolymerization of NBE with CPE under the action of initiators 1 – 3 and 5 – 8 were determined by using both a zero‐ and first‐order Markov model. Finally, kinetic investigations using initiators 1 – 3 , 6 , and 7 were carried out. These revealed that in contrast to the 2nd‐generation Grubbs‐type initiators 1 – 3 the corresponding pyridine derivatives 6 and 7 represent fast and quantitative initiating systems. Hydrogenation of poly(NBE‐ alt ‐COE) n yielded a fully saturated, hydrocarbon‐based polymer. Its backbone can formally be derived by 1‐olefin polymerization of CPE (1,3‐insertion) followed by five ethylene units and thus serves as an excellent model compound for 1‐olefin polymerization‐derived copolymers.