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

Abstract

Abstract:The reactivity of the bimetallic complex (Ph 4 P) 2 [W 2 (µ-Br) 3 Br 6 ] ({W 2.5 W} 7+ , a 12 e 3 ) towards ring opening metathesis polymerization (ROMP) of norbornene (NBE) and some of its derivatives, as well as the mechanistically related metathesis polymerization of phenylacetylene (PA), is presented. Our results show that addition of a silver salt (AgBF 4 ) is necessary for the activation of the ditungsten complex. Polymerization of PA proceeds smoothly in tetrahydrofuran (THF) producing polyphenylacetylene (PPA) in high yields. On the other hand, the ROMP of NBE and its derivatives is more efficient in CH 2 Cl 2 , providing high yields of polymers. 13 C Cross Polarization Magic Angle Spinning (CPMAS) spectra of insoluble polynorbornadiene (PNBD) and polydicyclopentadiene (PDCPD) revealed the operation of two mechanisms (metathetic and radical) for cross-linking, with the metathesis pathway prevailing.

Copolymerization of Norbornene and Norbornadiene Using a cis-Selective Bimetallic W-Based Catalytic System

“…The ratio of olefinic/aliphatic carbons depends on the mechanism of cross-linking and is equal to 4/3 (metathesis) and 2/5 (olefin coupling). Therefore, the olefin coupling contribution can be calculated via Equation (3), which takes the ratio of the integrated areas of the corresponding 13 C CPMAS peaks as input [16]. Thus, C olefinic refers to the total sp 2 carbons, C aliphatic to the total sp 3 carbons and x is the fraction of polymer double bonds that participate in cross-linking via olefin coupling.…”

“…The use of bimetallic complexes with metal-metal bonds is less common [13,14], although they provide more precise control over stereoselectivity, since both metal centers can be involved in the reaction. We have previously reported that ditungsten clusters Na[W 2 ( μ -Cl) 3 Cl 4 (THF) 2 ]·(THF) 3 ({W 2 }, {W 3 W} 6+ , a′ 2 e′ 4 ) and (Ph 4 P) 2 [W 2 ( μ -Br) 3 Br 6 ] ({W 2.5 W} 7+ , a′ 2 e′ 3 ) are highly efficient and stereoselective room temperature homogeneous and/or heterogeneous initiators for the metathesis polymerization of alkynes [15,16] and the ROMP of norbornene derivatives [16,17,18,19].…”

“…Tuning the conformation of polymers has been a long-standing problem [20,21]. W-based catalytic systems usually favor formation of polymers with higher cis content [16,17,18,22,23,24,25,26], while Ru-based catalytic systems show the opposite trend [27,28,29,30], with notable exceptions though [31,32]. Interestingly, {W 2 }-based catalytic systems provide high- cis polymers [17,18,19].…”

Catalytic polymerization of olefins and cycloolefins with transition metal complexes

“…Therefore, the olefin coupling contribution can be calculated via equation (1) that takes the ratio of the integrated areas of the corresponding 13 C CPMAS peaks as input. 54 Thus, C olefinic refers to the total sp 2 carbons, C aliphatic to sp 3 carbons and x is the fraction of polymer double bonds that participate in crosslinking via olefin coupling. Integration of PNBD spectra provided an olefinic/aliphatic carbons ratio equal to 1.36 (Figure 19), showing that no crosslinking via olefin coupling takes place (x ≈ 0).…”

“…IV) towards the ROMP of NBE and derivatives has been also investigated 54. Despite the fact that bromide ligands are more labile than the chloride ones, addition of AgBF 4 is necessary in order to activate the ditungsten complex.…”