In this study, the reactions of the bimetallic compound Na[W
2(
µ-Cl)
3Cl
4(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=CH
2 (
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 (
Mw) 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=CH
2) 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.
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