Exploring the Reactivity of Na[W2(μ-Cl)3Cl4(THF)2]∙(THF)3 towards the Polymerization of Selected Cycloolefins

Abstract

Abstract:The bimetallic compound Na 3 Cl 4 (THF) 2 ]¨(THF) 3 (1, {W 3 W} 6+ , a 12 e 14 ) is a highly efficient room-temperature initiator for ring opening metathesis polymerization (ROMP) of norbornene (NBE) and some of its derivatives. In most cases, addition of phenylacetylene (PA) as co-initiator improves the catalytic activity and retains the high cis-stereoselectivity. On the other hand, 1 can polymerize cyclopentadiene (CPD), not via a metathetic, but rather, via a cationic mechanism. Here, we present a comparison of the reactivity of the two catalytic systems (1 and 1/PA) between themselves and with other systems reported in the literature, the characterization of the polymers formed and mechanistic aspects of the corresponding reactions.

Metathesis Polymerization Reactions Induced by the Bimetallic Complex (Ph4P)2[W2(μ-Br)3Br6]

“…The 1 H NMR spectrum of PVNBE ( Figure S9) could not provide information about the configuration of the polymer, because signals of olefinic protons of the polymeric chain overlap with the vinylic ones, but indicated that the ring-strained C=C bond was cleaved, while the vinylic one was left intact and available for functionalization [23]. The same reactivity was observed with 2 [19] and 2/PA [20] and is rather unusual. The pendant vinyl group is usually involved in metathesis reactions, leading to cross-linked products; therefore, that monomer is used for the synthesis of self-healing polymers [24].…”

“…In addition, it showed similar reactivity with 2/PA towards the ROMP of DCPD [20], which seems to be the least reactive of the monomers studied, as long reaction times were required with either system.…”

“…Regarding the ROMP of NBD, catalytic system 1/AgBF 4 was almost equally reactive to 2, which also provided quantitative yields within short reaction times [19,20]. In addition, it showed similar reactivity with 2/PA towards the ROMP of DCPD [20], which seems to be the least reactive of the monomers studied, as long reaction times were required with either system.…”

“…The fraction of cis double bonds (σ c = 0.62) was estimated by integration of the signals at δ H 2.79 (HC 1,4 cis-PNBE) and 2.43 ppm (HC 1,4 trans-PNBE). By comparison to 2 [19] or 2/PA [20], the present catalytic system was less stereoselective, but provided quantitatively very high molecular weight polymers.…”

“…That complex acts as a unicomponent initiator in most cases. Addition of small amounts of phenylacetylene (PA) generates a more reactive system, which is also more tolerant to coordinating side groups [20].…”