Ring Opening Metathesis Polymerization of Norbornene and Derivatives by the Triply Bonded Ditungsten Complex Na[W2(µ-Cl)3Cl4(THF)2]·(THF)3

Polymers

Georgios Floros²  Nikolaos Saragas²  Patrina Paraskevopoulou²  Nikolaos Psaroudakis²  Spyros Koinis²  Marinos Pitsikalis¹  Nikos Hadjichristidis¹ 

[1] Department of Industrial Chemistry, Faculty of Chemistry, University of Athens, Panepistimioupoli Zographou, Athens 15771, Greece;Department of Inorganic Chemistry, Faculty of Chemistry, University of Athens, Panepistimioupoli Zographou, Athens 15771, Greece;

关键词: catalysis;    metal–metal bonds;    norbornenes;    ROMP;    tungsten;   

DOI  :  10.3390/polym4041657

来源: mdpi

【 摘 要 】

In this study, the reactions of the bimetallic compound Na[W₂(µ-Cl)₃Cl₄(THF)₂]·(THF)₃ (1, (W ³ W)⁶⁺, a'²e'⁴) with norbornene (NBE) and some of its derivatives (5-X-2-NBE; X = COOH (NBE–COOH), OH (NBE–OH), CN (NBE–CN), COOMe (NBE–COOMe), CH=CH₂ (VNBE); norbornadiene (NBD)) are described. Complex 1 contains a tungsten–tungsten triple bond, bearing three halide bridges and two labile THF ligands, in a cisoidal relationship along the metal–metal axis. The complex was found to be a highly efficient room temperature homogeneous and heterogeneous unicomponent initiator for the catalytic ring opening metathesis polymerization (ROMP) of most substrates. NBE provides polynorbornene (PNBE) of high molecular weight (M_w) in high yields, soluble in organic solvents. The reaction proceeds with high cis-stereoselectivity (80%–86% cis), independently of the reaction conditions. Strongly coordinating pendant groups (–COOH, –OH, –CN) deactivate 1, whereas substrates bearing softer ones (–COOMe, –CH=CH₂) are quantitatively polymerized. NBD gives quantitatively insoluble PNBD. The polymers have been characterized by ¹H, ¹³C NMR and Size Exclusion Chromatography (SEC). Monitoring the reactions in situ by ¹H NMR (1/NBD or NBE) provides direct evidence of the metathetical nature of the polymerization with the observation of the active tungsten alkylidene propagating polymeric chains. Mechanistic aspects of the reactions are discussed.

【 授权许可】

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