Ligands Dominate Highly Syndioselective Polymerization of Styrene

Siqian Liu , Gaixia Du , Jianyun He , Yingyun Long , Shaowen Zhang , and Xiaofang Li. Macromolecules .... Rui Tan , Fang Guo , Yang Li. Polymer Chemis...
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Ligands Dominate Highly Syndioselective Polymerization of Styrene by Using Constrained-geometry-configuration Rare-earth Metal Precursors Yupeng Pan,†,‡ Weifeng Rong,†,‡ Zhongbao Jian,†,‡ and Dongmei Cui*,† †

State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China ‡ Graduate School of the Chinese Academy of Sciences, Beijing 100039, China S Supporting Information *

ABSTRACT: A series of novel constrained-geometry-configuration (CGC) rare-earth metal complexes (RCH2−Py)Ln(CH2SiMe3)2(THF)n (Py = pyridyl; Ln = Y, n = 1, R = C5Me4 (Cp′) (1); Ln = Y, n = 1, R = C9H6 (Ind) (2); Ln = Y, n = 1, R = C13H8 (Flu) (3a); Ln = Lu, n = 1, R = C13H8 (Flu) (3b); Ln = Sc, n = 0, R = C13H8 (Flu) (3c)) have been synthesized by treating rare-earth metal trisalkyls with PyCH2−Cp′, PyCH2− Ind, and PyCH2−Flu compounds, respectively, and fully characterized by NMR and X-ray diffraction analyses. Complexes 1, 2, and 3a−b are monomeric THF solvates while the scandium complex 3c is solvent-free, in which all the CGC ligands adopt a η5/κ1 bonding mode via coordination of five carbon atoms from the cyclopentadienyl fragment and the pyridyl nitrogen atom with the central metals. Upon activation with AliBu3 and [Ph3C][B(C6F5)4], these complexes showed different performances toward styrene polymerization. The Cp′CH2−Py and IndCH2−Py ligated yttrium complexes 1 and 2 showed very low activity to afford syndiotactic enriched polystyrene. Strikingly, the bulky FluCH2−Py supported complexes 3a−c displayed outstanding activities up to 1.56 × 107 g/(molLn·h) and perfect syndioselectivity (rrrr > 99%), giving high molecular weight sPS; in particular, thus excellent performance was independent of the central metal type for the first time. In addition, the relationship of the ligand structure with the catalytic performances toward specific selective polymerization of styrene was reasonably revealed by comparison with the other Flu-based rare-earth metal catalysts reported previously by us. This might open a new pathway for designing catalysts for specifically selective polymerizations.

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INTRODUCTION Syndiotactic polystyrene (sPS), discovered first by Ishihara at Idemitsu in 1986 by using unlinked half-sandwich titanium catalysts,1 is a promising engineering plastic due to its high melting point (Tm = 270 °C), rapid crystallization ability, high tensile modulus, low dielectric constant, and excellent resistance to heat and chemicals.2 Since this breakthrough, a large number of titanium analogues generally formulated as [LTiX3], where L is an alkyl or alkoxyl- and amino-substituted cyclopentadienyl (Cp), indenyl (Ind), or fluorenyl (Flu) moiety, while X is halogen or alkoxyl group, have been extensively investigated, which exhibited obvious improvements in both catalytic activity and syndioselectivity for styrene polymerization.3 In contrast, rare-earth metal catalysts have been noted for their inertness or low specific selectivity toward styrene polymerization.4 In 2004, great successes were achieved by using two type of catalytic systems based on the unlinked half-sandwich cationic scandium alkyl species5 and neutral lanthanidocene bearing Flu−CMe2−Cp ligand,6 both displayed good activity to provide perfect sPS. Later on some derivatives supported by the substituted Cp′, hetero(B, N, P)−Cp′, oxygen-linked Cp′ and Ind′ ligands have also been reported © 2012 American Chemical Society

as efficient catalysts for the syndioselective styrene polymerization.7 Note that the common feature of these precursors is that their central metals are scandium having close electronics with titanium (only one case is based on the larger neodymium). Other rare-earth metal complexes, especially those attached to the cheapest yttrium, exhibited non or low activities. Recently, we developed a linked half-Sandwich rare-earth metal diallyl complexes (Py−C5Me4)Ln(η3-C3H5)2,8 among which the lutetium complex for the first time showed a similar activity and perfect syndioselectivity (99%) for the polymerization of styrene to its scandium analogue, unfortunately, the performance of the congenous yttrium complex was still far less promising. Moreover, the attempts to improve the catalytic activity and to obtain high molecular weight sPS by introducing bulky indenyl or fluorenyl ligands were failed. Herein, we reported a series of rare-earth metal complexes bearing the pyridyl-methylene functionalized Cp′/Ind/Flu ligands, among Received: November 23, 2011 Revised: January 10, 2012 Published: January 31, 2012 1248

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Figure 1. X-ray structures of complexes 1, 2, 3a, 3b with 35% probability of thermal ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): 1, Y1−CCp′(av) 2.388(3), Y1−C1 2.614(6), Y1−C2 2.660(6), Y1−C3 2.724(6), Y1−C4 2.715(6), Y1−C5 2.664 (6), Y1−C17 2.434(6), Y1−C16 2.431(6), Y1−N1 2.548(5), Cp′cent−Y1−N1 90.87(3), Cp′cent−Y1−C16 120.56(3), Cp′cent−Y1−C17 118.36(3); 2, Y1−CInd (av) 2.410(3), Y1−C4 2.666(4), Y1−C5 2.687(4), Y1−C6 2.734(4), Y1−C7 2.710(4), Y1−C8 2.689(4), Y1−C25 2.416(4), Y1−C16 2.423(4), Y1−N1 2.512(3), Indcent−Y1−N1 91.94(3), Indcent−Y1−C16 126.43(3), Indcent−Y1−C25 117.65(3); 3a, Y1−CFlu(av) 2.465(3), Y1−C4 2.845(5), Y1−C5 2.712(4), Y1−C7 2.606(4), Y1−C8 2.845(5), Y1−C9 2.852(5), Y1−C24 2.404(5), Y1−C25 2.372(6), Y1−N1 2.513(4), Flucent−Y1−N1 92.01(3), Flucent−Y1−C24 119.53(3), Flucent−Y1−C25 121.22(3); 3b, Lu1−CFlu(av) 2.502(3), Lu1−C6 2.904(4), Lu1−C7 2.717(4), Lu1−C13 2.585(4), Lu1−C30 2.944(4), Lu1−C31 2.755(4), Lu1−C17 2.355(4), Lu1−C19 2.340(4), Lu1−N1 2.462(3), Flucent−Lu1− N1 92.16(3), Flucent−Lu1−C17 116.26(3), Flucent−Lu1−C19 136.75(3).

targeted bis(alkyl) complexes L1Y(CH2SiMe3)2(THF) (1), L2Y(CH2SiMe3)2(THF) (2), L3Ln(CH2SiMe3)2(THF)n (n = 1, Ln = Y (3a); n = 1, Lu (3b); n = 0, Sc (3c)) in high yields. 1 H and 13C NMR spectroscopic analysis of these complexes showed the disappearance of the Cp−H proton of the ligands, and the formation of M−σ−C bond between the rare-earth metal ion and the methylene carbons (δ 30.38−45.27 ppm in the 13C NMR).11 The methylene protons of Y−CH2SiMe3 in 1 give a singlet resonance at −0.90 ppm, suggesting that they are equivalent. In contrast, the broad resonances around −1.09, −1.35, and −1.46 ppm assigned to the methylene protons arising from Y−CH2SiMe3 in 2 and 3a and Lu−CH2SiMe3 in 3b, respectively, suggested these metal alkyl moieties are fluxional in the solution state. The 1H NMR spectrum of complex 3c gives an AB spin (JH−H = 11.2 Hz) around −0.88 ppm, indicating that the scandium methylene protons Sc− CH2SiMe3 are diastereotopic. The molecular structures of complexes 1, 2, 3a,b were further confirmed by X-ray diffraction analyses, as shown in Figure 1. All the metal centers

which those bearing bulky Flu moiety upon activation with AliBu3 and [Ph3C][B(C6F5)4], showed unprecedented high activities (1.56 × 107 g/(molLn·h)) and excellent syndioselectivity (rrrr > 99%) to afford high molecular weight sPS irrespective with the central metal type (such as Sc, Y, or Lu) for the first time. The successful characterization of the molecular structures of these complexes allowed us to probe into the relationship between the structures of the ligands and catalytic performances of the attached central metals.

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RESULTS AND DISCUSSION Synthesis and Characterization of Complexes 1, 2, and 3a−c. The pyridyl-methylene functionalized Cp′, Ind, and Flu compounds HL1−3 (HL1 = Cp′CH2−Py; HL2 = IndCH2− Py; HL3 = FluCH2−Py) were synthesized by treatment of chloromethylpyridine hydrochloride PyCH2Cl·HCl with Cp′, Ind, and Flu lithium salts, respectively. Deprotonation of HL1−3 by the corresponding rare-earth metal tris(alkyl)s, Ln(CH2SiMe3)3(THF)2, with releasing SiMe4 afforded the 1249

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yttrium complex 3a reached to 1.56 × 107 g·PS/(molY·h), which ranked top of the most active catalysts, as far as we are aware (Table 1, runs 18−20). Meanwhile the molecular weight of the resultant PS increased correspondingly from Mn = 5.4 × 104 g/mol to 49.5 × 104 g/mol close to the theoretic value (Table 1, runs 3−7), indicative of well controlled polymerization. Pleasing to us, the obtained PS was pure syndiotacticity (rrrr >99%) evidenced by the 13C NMR spectrum14 as well as the high melting points around 270 °C in the DSC traces. In particular, we found that the central metal type had no influence on the catalytic performances, because all the Y, Lu, and Sc complexes 3a−c behaved in similar activity and syndioselectivity (Table 1, runs 3−17), which was in contrast to the previous results that the central metal ion is a crucial factor for governing the catalytic activity.5 This ligand dominated catalytic performance was investigated further. We employed the similar bulky pyridyl-functionalized Flu ligated Y, Sc and Lu complexes (Chart 1, B), however, all showed very low activity with moderate syndioselectivity (Table 1, run 22). The difference is that the five-membered ring of the pyridylfunctionalized Flu ligand coordinates to the central metal ions in an asymmetric η3-allyl coordination mode rather than the η5coordination mode of the Py−CH2−Flu ligands in complexes 3, which was analogous to the previous results that the coordination mode (η5 or η1) can show dramatic influence on the polymerization activity.10 This η3-allyl coordination mode may block the electron delocalization over the phenyl rings that are electron-withdrawing, and thus the ligand is more electron donating as compared with that in complexes 3,15 which arouse lowering of the Lewis acidity of the metal center; meanwhile the η3-coordination mode was less steric shielding to the metal center compared with the η5-bonding mode, resulting in low selectivity . To confirm this, we also employed our previously reported ethylene-bridged carbene modified Flu rare-earth metal complexes, (Flu−CH 2 CH 2−NHC)Ln(CH 2 SiMe 3 ) 2 (Chart 1A), as the precursor where the Flu moiety coordinates to the metal center in η5-coordination mode providing enough steric shieding to the metal center by providing a living fashion with an unprecedented 3,4-selectivity (99%) toward isoprene polymerization,9 which, unfortunately, were absolutely inert to the styrene polymerization. This could be ascribed to the highly electron-donating nature of the N-heterocyclic carbene (NHC) side arm of Flu−CH2CH2−NHC ligand that the Lewis acidity of the central metal ion was lowered. Moreover, the bite angle of Flucent−Y−C in A is much larger than those in complex 3a, suggesting that coordination environment of the metal center is not opened enough for the insertion of the bulky monomer such as styrene (vide supra). These results were in consistent with those found for complexes 1−3 in this work that the catalytic activity trend followed FluCH2−Py > IndCH2−Py > Cp′CH2−Py, demonstrating that a ligand of more bulky but leaving opening coordination sphere and electron less donating facilitated the attached central metals providing higher activity and syndioselectivity,16 indicative of the crucial role of the ligand compared with that of central metal. The similar result is reported by Hou et al. that larger Cp′ ligated scandium complexes provides higher activity.7i

are bonded to one ligand unit, two alkyl groups and a THF molecule, generating a tetrahedral geometry with the center of Cp ring as the apex. Noteworthy is that all the Cp-based auxiliaries coordinate to the central metal ions in the η5/κ1 mode via the Cp carbons and the dangling pyridyl nitrogen atom, forming the typical constrain-geometry-configuration mode. The two alkyl species are located in cis-positions with one endo and the other exo with respect to the pyridyl ring. The bite angles of Cp′cent−Y(1)−N(1) (90.87(3)°) in 1, Indcent−Y(1)−N(1) (91.94 (3)°) in 2, Flucent−Y(1)−N(1) (92.01(3)°) in 3a, and Flucent−Lu(1)−N(1) (92.16°) in 3b are larger than that of Flucent−Y(1)−N(1) (82.97(3)°) in (Flu− Py)Y(CH2SiMe3)2(THF),12 but smaller than that of Flucent− Y−C (102(3)°) in (Flu−CH2CH2−NHC)Y(CH2SiMe3)2.9 Correspondingly, the averaging bond distances between the carbon atoms of the cyclopentadienyl moieties and the central metal ions CCp′−Y(1) 2.388(3) Å in 1, CInd−Y(1) 2.410(3) Å in 2, CFlu−Y(1) 2.465(3) Å in 3a, and CFlu−Lu(1) 2.502(3) Å in 3b are longer than CFlu−Lu(1) 2.357 Å in (Flu−CH2CH2− NHC)Lu(CH2SiMe3)2,9 if the difference of ionic radius of Y, Lu, and Sc central metals is ignored.13 These crystallographic data indicate that all these complexes have a relatively opening environment around the cental metals, which allows the insertion of bulky styrene monomer. Scheme 1. Synthesis of CGC Complexes 1, 2, and 3a−c

Syndioselective Polymerization of Styrene. All these complexes under the activation of aluminum alkyls and organoborates construct ternary systems, exhibited various catalytic activities and syndioselectivities for styrene polymerization under room temperature as shown in Table 1. Both the Cp′CH2−Py ligated complex 1 and the IndCH2−Py ligated complex 2 showed low activity to transfer 1000 equiv of styrene to polystyrene with low conversions (57% vs 67%) within 4 h (Table 1, runs 1, 2). The generated polystyrenes had moderate syndiotacticity of rrrr = 60% and 84%, respectively.14 Surprisingly to us, when the catalytic precursors were switched to complexes 3 bearing bulky FluCH2−Py ligand, under the same conditions, the polymerization achieved completeness in less than 1 min. Moreover, the polymerization could be performed fluently under a broad range of St-to-Y molar ratios up to 5000 within 2 min. Thus, the highest activity of the

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CONCLUSIONS In summary, a series of new rare-earth metal complexes bearing pyridyl methyl functionalized Cp′ and its indenyl and fluorenyl derivatives (η5-Cp′-CH2Py)Y(CH2SiMe3)2(THF), (η5-IndCH 2 Py) Y(CH 2 SiMe 3 ) 2 (THF) and (η 5 -Flu-CH 2 Py)Ln1250

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Table 1. Syndiospecific Polymerization of Styrene with Rare-Earth Metal Precursors 1−3 under Various Conditionsa run

cat

[St]/[Ln]

t (min)

convn (%)

sPSb (%)

activityc

Mnd × 10−4

Mw/Mnd

Tm (°C)e

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18f 19g 20h 21i 22j

1 2 3a 3a 3a 3a 3a 3b 3b 3b 3b 3b 3c 3c 3c 3c 3c Sc Nd Lu A B

1000 1000 500 1000 2000 3000 5000 500 1000 2000 3000 5000 500 1000 2000 3000 5000 2500 600 1000 500 500

240 240 1 1 2 2 2 1 1 2 2 2 1 1 2 2 2 1 5 1 360

57 67 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 87 84 >99 5

60 84 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 >99 -

15 17 3120 6240 6240 9360 15 600 3120 6240 6240 9360 15 600 3120 6240 6240 9360 15 600 13 618 1710 6240 0.4

3.0 3.6 5.4 10.4 22.9 33.2 49.5 5.7 10.2 22.5 33.6 48.7 5.8 10.2 22.4 33.4 48.5 37.9 5.4 22.3 -

1.44 1.56 2.15 2.15 2.16 2.34 2.58 1.73 1.76 1.87 2.32 2.35 1.73 1.79 1.89 2.34 2.38 1.37 1.73 1.88 -

228 234 269 270 270 270 270 270 270 270 270 270 270 270 270 270 270 273 264 270 -

a Polymerization conditions: Ln (10 μmol), [Ln]/AliBu3/[Ph3C][B(C6F5)4] = 1/10/1 (mol/mol/mol), toluene/monomer =5/1 (v/v), Tp = 20 °C, unless otherwise noted. bMeasured by 1H NMR and 13C NMR spectroscopy in tetrachloroethane-d2 at 125 °C. cGiven in kg of polymer/(molLn·h). d Determined by GPC in 1,2,4-trichlorobenzene at 150 °C against polystyrene standard. eDetermined by DSC. f(C5Me4SiMe3)Sc(CH2SiMe3)2(THF), ref 5. g(Cp−CMe2−Flu)Nd(η3-C3H5)(THF), ref 6. h(C5Me4−C5H4N)Lu(η3-C3H5)2, ref 8. i(Flu−CH2CH2−NHC)Ln(CH2SiMe3)2, ref 9. j(Flu−Py)Ln (CH2SiMe3)2 (THF), ref 12.

nature of the η5-Flu-CH2Py ligand that increased the Lewis acidity of the central metal ion while its steric bulkiness endowed the metal center specific selectivity. This was proved by the less steric and electron donating η5-Cp′-CH2Py and η5Ind-CH2Py supported rare-earth metal counterparts that provided poor performances, and the electron donating ethylene-carbene functionalized fluorenyl rare-earth metal complexes were completely inert. The low activity of the electron less donating pyridyl fluorenyl rare-earth metal complexes were ascribed to η3-allyl coordination mode of the Cp fragment that inhibited the electrons delocalizing over the phenyl rings in the ligand increasing its electron donating power. This constructed relationship between catalyst structures and performances is expected to open a new route for designing more efficient and specifically selective catalysts.

Chart 1

(CH2SiMe3)2(THF)n (Ln = Sc, n = 0; Y, Lu, n = 1) have been synthesized and well characterized. These complexes together with pyridyl fluorenyl rare-earth metal complexes (η3-FluCH2Py)Ln(CH2SiMe3)2(THF) (Ln = Sc, Y, Lu) and Nheterocyclic carbene rare-earth metal complexes (NHC− CH2CH2−Flu)Ln(CH2SiMe3)2 (Ln = Sc, Y, Lu) have been evaluated as precursors, upon activation with organoborates and aluminum alkyls, for the polymerization of styrene. Among these systems, the precursors bearing η5-Flu-CH2Py ligand exhibited distinguished catalytic activities up to 1.56 × 107 g/ (molLn·h) to provide pure sydiotactic sPS (rrrr > 99%), while those stabilized by the analogous η5-Cp′-CH2Py and η5-IndCH2Py and the deriative η3-Flu-CH2Py exhibited poor performances both in activity and syndioselectivity. Complexes (NHC−CH2CH2−Flu)Ln(CH2SiMe3)2 were absolutely inert. This indicated that ligand played a crucial role on governing the catalytic performances of the attached metal centers while the type of the central metal ions showed almost no influence, in contrast to the previously reported results. Thus, for the first time, a yttrium based complex exhibited a competitive distinguished activity to its scandium analogue. The high activity was significantly attributed to the electron less donating

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EXPERIMENTAL SECTION

General Methods and Materials. All reactions were carried out under a dry and oxygen-free argon atmosphere by using Schlenk techniques or under a nitrogen atmosphere in an MBraun glovebox. All solvents were purified from an MBraun SPS system. Samples of organo rare-earth metal complexes for NMR spectroscopic measurements were prepared in the glovebox by use of NMR tubes sealed by paraffin film. 1H and 13C NMR spectra were recorded on a Bruker AV400 or 600 (FT, 400 or 600 MHz for 1H; 100 or 150 MHz for 13C) spectrometer. 1H, 13C NMR spectra of polymer samples were recorded on a Bruker AV400 (FT, 400 MHz for 1H; 100 MHz for 13 C) spectrometer in tetrachloroethane-d2. The molecular weight and molecular weight distribution of the polymers were measured by means of gel permeation chromatography (GPC) on a PL-GPC 220 type high-temperature chromatography equipped with three PL-gel 10 μm Mixed-B LS type columns at 150 °C. Tm of polystyrene samples was measured through differential scanning calorimetry (DSC) analyses, which were carried out on a Q 100 DSC from TA 1251

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Synthesis of complex (FluCH2−Py)Y(CH2SiMe3)2(THF) (3a). Under a nitrogen atmosphere, to a mixture solution of hexane with THF (10 mL) of Y(CH2SiMe3)3(THF)2 (0.451 g, 1.0 mmol), 1 equiv of HL3 (0.257 g, 1.0 mmol) was added slowly at 30 °C. The mixture was stirred for 2 h to afford a clear dark yellow solution. Evaporation of the solvent left 3a as light yellow crystalline solids (0.284 g, 48.1%). Recrystallization from hexane gave single crystals suitable for X-ray analysis. 1H NMR (400 MHz, C6D6, 25 °C): δ −1.35 (br s, 4H, Y− CH2SiMe3), 0.06 (s, 18H, CH2SiMe3), 1.31 (br s, 4H, THF), 3.43 (br s, 4H, THF), 4.45 (s, 2H, C5H4NCH2), 6.62 (t, 3JH−H = 6.0 Hz, 1H, C5H4N), 6.85 (d, 1H, 3JH−H = 8.0 Hz, C5H4N), 7.05 (m, 3H, C13H9), 7.29 (t, 3JH−H = 8.4 Hz, 2H, C13H9), 7.41 (d, 3JH−H = 8.4 Hz, 2H, C13H9), 7.93 (d, 3JH−H = 8.4 Hz, 2H, C13H9), 8.82 ppm (d, 3JH−H = 4.8 Hz, 1H, ipso-C5H4N). 13C NMR (100 MHz, C6D6, 25 °C): δ 4.82 (s, 6C, CH2SiMe3), 25.72 (br s, 2C, THF), 33.53 (s, 2C, C5H4NCH2), 35.36 (d, 2C, JY−C = 41.0 Hz, Y-CH2SiMe3), 71.13 (br s, 2C, THF), 118.38 (s, 2C, C13H9), 119.68 (s, 2C, C13H9), 121.86 (s, 2C, C13H9), 122.31 (s, 2C, C13H9), 124.38 (s, 2C, C13H9),125.49 (s, 1C, C13H9), 128.27 (s, 2C, C13H9), 128.51 (s, 1C, C5H4N), 128.75 (s, 1C, C5H4N), 132.23 (s, 1C, C5H4N), 138.82 (s, 1C, C5H4N), 150.63 (s, 1C, ipsoC5H4N) ppm. Anal. Calcd for C31H44ONSi2Y (%): C, 62.92; H, 7.49; N, 2.37. Found: C, 62.72; H, 7.47; N, 2.20. Synthesis of complex (FluCH2−Py)Lu(CH2SiMe3)2(THF) (3b). Under a nitrogen atmosphere, to a mixture solution of hexane with THF (10 mL) of Lu(CH2SiMe3)3(THF)2 (0.562 g, 1.0 mmol), 1 equiv of HL3 (0.257 g, 1.0 mmol) was added slowly at 30 °C. The mixture was stirred for 1 h to afford a clear dark yellow solution. Evaporation of the solvent left 3b as light yellow crystalline solids (0.316 g, 46.7%). Recrystallization from hexane gave single crystals suitable for X-ray analysis. 1H NMR (400 MHz, C6D6, 25 °C): δ −1.46 (br s, 4H, Lu−CH2SiMe3), 0.06 (s, 18H, CH2SiMe3), 1.30 (br s, 4H, THF), 3.41 (br s, 4H, THF), 4.42 (s, 2H, C5H4NCH2), 6.6 (t, 3 JH−H = 7.2 Hz, 1H, C5H4N), 6.8 (d, 3JH−H = 7.6 Hz, 1H, C5H4N), 6.94 (t, 3JH−H = 7.6 Hz, 1H, C5H4N), 7.10 (m, 3H, C13H9), 7.29 (t, 2H, C13H9),7.38 (d, 3JH−H = 8.4 Hz, 2H, C13H9), 7.98 (d, 3JH−H = 7.6 Hz, 2H, C13H9), 8.74 (d, 3JH−H = 5.2 Hz, 1H, ipso-C5H4N) ppm. 13C NMR (100 MHz, C6D6, 25 °C): δ 4.85 (s, 6C, CH2SiMe3), 25.75 (br s, 2C, THF), 33.41 (s, 2C, C5H4NCH2), 40.36 (s, 2C, Lu-CH2SiMe3), 71.38 (br s, 2C, THF), 118.33 (s, 2C, C13H9), 119.50 (s, 2C, C13H9), 121.15 (s, 2C, C13H9), 121.98 (s, 2C, C13H9), 122.37 (s, 1C, C13H9), 124.59 (s, 1C, C13H9), 125.64 (s, 2C, C13H9), 128.26 (s, 1C, C13H9), 128.50 (s, 1C, C5H4N),128.74 (s, 1C, C5H4N), 132.98 (s, 1C, C5H4N), 138.94 (s, 1C, C5H4N), 150.08 (s, 1C, ipso-C5H4N) ppm. Anal. Calcd for C31H44 ONSi2Lu (%): C, 62.92; H, 7.49; N, 2.37. Found: C, 62.85; H, 7.46; N, 2.35. Synthesis of complex (FluCH2−Py)Sc(CH2SiMe3)2 (3c). Under a nitrogen atmosphere, to a mixture solution of hexane with THF (10 mL) of Sc(CH2SiMe3)3(THF)2 (0.450 g, 1.0 mmol), 1 equiv of HL3 (0.257 g, 1.0 mmol) was added slowly at 30 °C. The mixture was stirred for 1 h to afford a clear dark yellow solution. Evaporation of the solvent left 3c as light yellow crystalline solids (0.222 g, 46.7%). Recrystallization from hexane gave single crystals suitable for X-ray analysis. 1H NMR (400 MHz, C6D6, 25 °C): δ −0.88 (AB, 2JH−H = 11.2 Hz, 4H, Sc−CH2SiMe3), 0.05 (s, 18H, CH2SiMe3), 4.14 (s, 2H, C5H4NCH2), 6.32 (t, 3JH−H = 6.4 Hz, 1H, C5H4N), 6.61 (d, 3JH−H = 12.0 Hz, 1H, C5H4N), 6.79 (t, 3JH−H = 8.60 Hz, 1H, C5H4N), 7.10 (m, 3H, C13H9), 7.21 (m, 2H, C13H9), 7.26 (m, 4H, C13H9), 8.29 (d, 3JH−H = 8.0 Hz, 2H, C13H9), 8.34 (d, 3JH−H = 5.2 Hz, 1H, ipso-C5H4N) ppm. 13 C NMR (100 MHz, C6D6, 25 °C): δ 4.15 (s, 6C, CH2SiMe3), 32.18 (s, 2C, C5H4NCH2), 45.27 (s, 2C, Sc-CH2SiMe3), 94.29 (s, 2C, C13H9), 119.15 (s, 2C, C13H9), 119.90 (s, 2C, C13H9), 120.65 (s, 2C, C13H9), 122.48 (s, 1C, C13H9),124.94 (s, 1C, C13H9), 125.024 (s, 2C, C13H9), 126.63 (s, 1C, C13H9), 132.18 (s, 1C, C5H4N), 140.12 (d, 2C, C5H4N),148.50 (s, 1C, C5H4N), 169.70 (s, 1C, ipso-C5H4N) ppm. Anal. Calcd for C27H36NSi2Sc (%): C, 68.17; H, 7.63; N, 2.94. Found: C, 68.15; H, 7.53; N, 2.48. Typical Procedure for Styrene Polymerization. A typical polymerization procedure is as follows (Table 1, run 3): In a glovebox, styrene (1.04 g, 10 mmol) was added into a 25 mL flask. Then, 10 equiv AliBu3 (0.20 mL, 0.5 mol/L), a toluene solution (3.0 mL) of 3a

Instruments under nitrogen atmosphere. Elemental analyses were performed at National Analytical Research Centre of Changchun Institute of Applied Chemistry (CIAC). Styrene was dried over CaH2 under stirring for 48 h and distilled under reduced pressure before use. n BuLi (2.5 M in hexane) was purchased from Aldrich. The pyridene methylene tetramethylcyclopentadienyl ligand HL1 (C5Me4HCH2− Py) was synthesized by treatment of chloromethylpyridine hydrochloride Py-CH2Cl·HCl with C5Me4Li. The corresponding Ind and Flu compunds HL2,3 (HL2 = IndCH2−Py; HL3 = FluCH2−Py) were synthesized following the same procedure. Ln(CH2SiMe3)3(THF)2 were prepared according to the literature.17 [Ph3C][B(C6F5)4] was prepared following the literature procedures.18 X-ray Crystallographic Studies. Crystals for X-ray analysis were obtained as described in the preparations. The crystals were manipulated in a glovebox. Data collections were performed at −88.5 °C on a Bruker SMART APEX diffractometer with a CCD area detector, using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). The determination of crystal class and unit cell parameters was carried out by the SMART program package. The raw frame data were processed using SAINT and SADABS to yield the reflection data file. The structures were solved by using the SHELXTL program. Refinement was performed on F2 anisotropically for all non-hydrogen atoms by the full-matrix least-squares method. The hydrogen atoms were placed at the calculated positions and were included in the structure calculation without further refinement of the parameters. Synthesis of Complex (Cp′CH2−Py)Y(CH2SiMe3)2(THF) (1). Under a nitrogen atmosphere, to a hexane solution (10 mL) of Y(CH2SiMe3)3(THF)2 (0.451 g, 1.0 mmol), 1 equiv of HL1 (0.213 g, 1.0 mmol) was added slowly at −30 °C. The mixture was stirred for 4 h to afford a clear red solution. Removal of dark red oily residue yielded a deep-red solution. Evaporation of the solvent left 1 as dark red crystalline solids. Recrystallization from hexane and toluene gave single crystals suitable for X-ray analysis (0.31 g, 40.0%). 1H NMR (600 MHz, C6D6, 25 °C): δ −0.90 (br s, 4H, Y−CH2SiMe3), 0.25 (s, 18H, CH2SiMe3), 1.38 (br, 4H, THF), 2.01(s, 6H, C5H5Me4), 2.04(s, 6H, C5H5Me4), 3.75 (br, 4H, THF), 3.84 (s, 2H, C5H4NCH2), 6.58 (d, 3JH−H = 6.0 Hz, 1H, C5H4N), 6.62 (d, 3JH−H = 7.8 Hz, 1H, C5H4N), 6.84 (t, 3JH−H = 7.2 Hz, 1H, C5H4N), 8.78 ppm (d, 3JH−H = 4.8 Hz, 1H, ipso-C5H4N). 13C NMR (150 MHz, C6D6, 25 °C): δ 5.38 (s, 6C, CH2SiMe3), 11.82(s, 2C, C5Me4), 12.21(s, 2C, C5Me4),2 5.67 (br s, 2C, THF), 30.38 (d, JY−C = 25.5, 2C, Y-CH2SiMe3), 33.84 (br s, 2C,THF), 71.22(s, 2C, THF), 116.98(s, 1C, C5H5Me4), 117.17(s, 2C, C5H5Me4),117.74 (s, 2C, C5H5Me4), 121.51 (s, 1C, C5H4N), 123.94 (s, 1C, C5H4N), 138.35 (s, 1C, C5H4N), 150.09 (s, 1C, C5H4N), 168.90 ppm (s, 1C, ipso-C5H4N). Anal. Calcd for C27H48NOSi2Y (%): C, 41.71, H, 6.22, N, 1.80. Found: C,41.61, H, 6.17, N,1 0.75. Synthesis of Complex (IndCH2−Py)Y(CH2SiMe3)2(THF) (2). Under a nitrogen atmosphere, to a hexane solution (10 mL) of Y(CH2SiMe3)3(THF)2 (0.451 g, 1.0 mmol), 1 equiv of HL2 (0.207 g, 1.0 mmol) was added slowly at −30 °C. The mixture was stirred for 12 h to afford a clear red solution. Removal of dark red oily residue yielded a deep-red solution. Evaporation of the solvent left 2 as dark red crystalline solids. Recrystallization from hexane and toluene gave single crystals suitable for X-ray analysis (0.254 g, 40.1%). 1H NMR (600 MHz, C6D6, 25 °C): δ −1.09 (br s, 4H, Y−CH2SiMe3), 0.12 (s, 18H, CH2SiMe3), 1.36 (br, 4H, THF), 3.73 (br, 4H, THF), 4.15, 4.28 (AB system, JH−H = 18.6 Hz, 2H, C5H4NCH2), 6.15 (d, 3JH−H = 3.6 Hz, 1H, C9H7),6.56 (m, 1H, C9H7), 6.69 (d, 3JH−H = 7.8 Hz, 1H, C9H7), 6.89−6.91 (m, 1H, C9H7), 6.97 (d, 3JH−H = 3.0 Hz, 1H, C9H7), 7.01−7.07 (m, 3H, C9H7), 7.29 (d, 3JH−H = 7.8 Hz, 1H, C5H4N), 7.43 (d, 3JH−H = 7.8 Hz, 1H, C5H4N), 8.78 ppm (d, 3JH−H = 4.8 Hz, 1H, ipso-C5H4N). 13C NMR (150 MHz, C6D6, 25 °C): δ 4.58 (s, 6C, CH2SiMe3), 25.25 (br s, 2C, THF), 35.01 (br s, 2C, Y-CH2SiMe3), 70.70 (br s, 2C,THF), 96.49(s, 2C, C5H4N) 119.83 (s, 1C, C9H7), 120.61 (s, 1C, C9H7), 121.46 (s, 1C, C9H7), 121.95 (s, 1C, C9H7), 123.51(s, 1C, C9H7), 126.68 (s, 1C, C9H7), 126.95 (s, 1C, C9H7), 128.32 (s, 1C, C9H7), 128.54 (s, 1C, C5H4N), 129.31 (s, 1C, C5H4N), 137.87 (s, 1C, C5H4N), 149.95 (s, 1C, C5H4N), 167.86 ppm (s, 1C, ipso-C5H4N). Anal. Calcd for C27H35NOSi2Y (%): C, 60.65, H, 6.59, N, 2.62. Found: C, 60.61, H, 6.57, N, 2.46. 1252

dx.doi.org/10.1021/ma202558g | Macromolecules 2012, 45, 1248−1253

Macromolecules

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(5.9 mg, 10 μmol), and 1 equiv [Ph3C][B(C6F5)4] (9.7 mg, 10 μmol) was added to the flask. After the reaction was stirred for 1 min, methanol was injected to terminate the polymerization. The viscous mixture was poured into a large quantity of methanol. The obtained white polymer was filtered and then dried under vacuum at 40 °C to a constant weight.

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ASSOCIATED CONTENT

S Supporting Information *

NMR spectra and DSC charts of representative polymer products.This material is available free of charge via the Internet at http://pubs.acs.org. CCDC-850069 (1), 844680 (2a), 844681 (3a), and 844682(3b) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Fax: (+86) 431 85262774. Telephone: +86 431 85262773. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was partly supported by The National Natural Science Foundation of China for Project Nos. 20934006, 51073148, and 51021003. The Ministry of Science and Technology of China for Projects Nos. 2009AA03Z501 and 2011DF50650.

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dx.doi.org/10.1021/ma202558g | Macromolecules 2012, 45, 1248−1253