Substitution Effects in Highly Syndioselective Styrene Polymerization Catalysts Based on Single-Component Allyl ansa-Lanthanidocenes: An Experimental and Theoretical Study

Abstract

International audienceA series of allyl ansa-lanthanidocenes, [{Me2C(C5H4)-(Flu)}Nd(1,3-C3H3(SiMe3)(2))(2)]K (Flu = 9-fluorenyl; 1-Nd-K(allyl)) and {R2C(C5H4)(R'R'Flu)}Ln(1,3-C3H3(SiMe3)(2))(THF)(x) (R = Me, R' = 2,7-tBu(2), Ln = Y (2-Y), Sc (2-Sc), x = 0; Ln = La (2-La), Pr (2-Pr), Nd (2-Nd), Sm (2-Sm), x = 1; R = Me, R' = oct = octamethyloctahydrodibenzo, Ln = Nd, x = 1 (3-Nd); R = Ph, R' = H, Ln = Nd, x = 1 (4-Nd); R = Me, R' = 3,6-tBu(2), Ln = Nd, x = 1 (5-Nd)), were prepared in good yields and characterized by NMR spectroscopy (for diamagnetic complexes 2-Sc, 2-Y, and 2-La) and by single-crystal X-ray diffraction (1-Nd-K(allyl), 2-La, 2-Pr, 2-Nd, 2-Sm, and 4-Nd). Those complexes, especially 1-Nd-K(allyl), 2-Nd, 4-Nd, 2-La, and 2-Sm, act as single-component catalyst precursors for polymerization of styrene (in bulk or in aliphatic hydrocarbon solutions, (nBu)(2)Mg as scavenger, T-polym = 60-140 C), affording highly syndiotactic polystyrene (sPS) ([r](5) = 63-88%; T-m up to 260 C). High productivities (up to 4560 kg(sPS) mol(Ln)(-1) h(-1)) were achieved at 120-140 C, at low catalyst loadings ([St]/[Nd] = 20000-76000 equiv), with 2-Nd and 2-Pr. On the other hand, precursors having bulky substituents on the fluorenyl moieties in 3,6-positions (3-Nd, 5-Nd) or based on small ionic radius metals (2-Y, 2-Sc) were poorly or not active under standard polymerization conditions. These results have been rationalized by DFT computations, which included the solvent, carried out on the putative 1-Nd, and the isolated 2-Nd and 5-Nd complexes. Three consecutive styrene insertions were studied, and it was revealed that (i) the formation of sPS is thermodynamically controlled by two effects-minimization of repulsions between fluorenyl/styrene phenyl ring and (in the initiation phase) fluorenyl/SiMe3 substituents of the allyl ligand-and (ii) the presence of bulky substituents on the fluorenyl moiety does not influence the activation barrier of monomer insertion, but it may destabilize thermodynamically the insertion product

Stereoselective Copolymerization of Styrene with Terpenes Catalyzed by an Ansa-Lanthanidocene Catalyst: Access to New Syndiotactic Polystyrene-Based Materials

“…On the other hand, all poly(S-co-Fa) samples were white powders. The catalyst productivity decreased with an increase of the cases of styrene/β-myrcene and styrene/farnesene copolymerization, respectively, entries 4-10 and entries [13][14][15][16][17]; this is consistent with the fact that 1 is poorly active towards β-myrcene and farnesene homopolymerization (entries 1-2 and 11-12). On the other hand, as the [terpene] 0 /[St] 0 feed ratio was raised, the terpene content in the resulting copolymers increased as expected; thus, a wide range of compositions was obtained (My content = 5.6-30.8 mol % and Fa content = 1.5-9.8 mol %).…”

“…Homopolymerization of β-myrcene with {Me 2 C(C 5 H 4 )(2,7-tBu 2 Flu)}Nd(1,3-C 3 H 3 (SiMe 3 ) 2 )(THF) (1) in the presence of 10 equiv of (nBu) 2 Mg as scavenger was first assessed (Table 1, entries 1 and 2) [16]; this showed, however, very low productivity (0.74 kg·mol −1 ·h −1 at 60 • C; 5.0 kg·mol −1 ·h −1 at 120 • C). Signals in the 1 H NMR spectrum of the recovered poly(My) recorded in 1,1,2,2-tetrachloroethane-d 2 were assigned using the previously reported NMR data for poly(β-myrcene) samples [4,18].…”

“…Very recently, we reported new neutral allyl {Cp/Flu}-type neodymium and samarium complexes of the type {R 2 C(C 5 H 4 )(R'R'Flu)}Ln(1,3-C 3 H 3 (SiMe 3 ) 2 )(THF) x (Flu = 9-fluorenyl) that act as single-component catalysts for homo-and copolymerization of styrene with ethylene, featuring high syndioselectivity, good productivities and good control over the incorporated ethylene content [16]. Previous work conducted by our group also demonstrated syndioselective styrene/isoprene (/ethylene) co(ter)polymerizations using the neutral {(Me 2 C(Cp)(Flu)}Nd(C 3 H 5 )(THF) complex [17].…”

Preparation of High-Purity Ammonium Tetrakis(pentafluorophenyl)borate for the Activation of Olefin Polymerization Catalysts

“…The GPC data were obtained in 1,2,4-trichlorobenzene at 160 • C, using a PL-GPC 220 system equipped with an RI detector (HLC-8321 GPC/HT RI detector (Tosoh)) and two columns (PLgel mixed-B 7.5 × 300 mm from Varian (Polymer Lab)). We obtained 1-ZrMe 2 , 2-ZrMe 2 , and 5-TiMe 2 from Precious Catalysts Inc, and 3-HfMe 2 [52], 4-HfMe 2 [53], 6-TiMe 2 [41], and 7-TiMe 2 [54] were prepared according to a previously reported method. 4H), 1.12 (quintet, J = 7.8 Hz, 4H), 0.94 (t, J = 7.2 Hz, 6H), 0.87 (quintet, J = 7.2 Hz, 4H), 0.80 (m, 4H) ppm.…”

Synthesis, Characterization, and Syndio‐Specific Styrene Polymerization of Pyrrolyl‐Substituted Cyclopentadienyl Scandium Complexes

“…The first neutral rare‐earth metal complexes [FluCMe 2 Cp]Ln(C 3 H 5 )(THF), and the first cationic rare‐earth metal catalyst system (C 5 Me 4 SiMe 3 )Ln(CH 2 SiMe 3 ) 2 (THF)/[Ph 3 C][B(C 6 F 5 ) 4 ], for syndio‐specific polymerization of styrene were discovered independently by Carpentier and Hou till 2005. Later on, intensive attention is still ongoing to establish rare‐earth metal catalysts for syndio‐specific styrene polymerization, and it showed that cationic scandium species [LSc‐ R ] + (L = monoanionic ancillary ligands, R = alkyl, benzyl, or allyl groups) usually demonstrated high efficiency , …”