Tris(pyrazolyl)borate Ti(IV) Complexes Containing Phenoxy Ligands

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Organometallics 2009, 28, 1942–1949

Tris(pyrazolyl)borate Ti(IV) Complexes Containing Phenoxy Ligands: Effective Catalyst Precursors for Ethylene Polymerization That Proceeds via Cationic Ti(IV) Species Koji Itagaki, Kenichi Kakinuki, Shohei Katao, Tossapol Khamnaen,† Michiya Fujiki, Kotohiro Nomura,* and Shinya Hasumi Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), 8916-5 Takayama, Ikoma, Nara 630-0101, Japan ReceiVed December 27, 2008

A series of phenoxy-substituted tris(pyrazolyl)borate titanium complexes, Tp′TiCl2(OAr) and Tp*TiMe2(OAr) [Tp ) HB(pyrazolyl)3, Tp* ) HB(3,5-Me2-pyrazolyl)3; Ar ) Ph, 2,6-Me2C6H3, 2,6i Pr2C6H3], were prepared, and their structures were determined by X-ray crystallography. These complexes exhibited from moderate to remarkable catalytic activities for ethylene polymerization in the presence of MAO; TpTiCl2(OPh) exhibited the highest catalytic activity for ethylene polymerization. The cationic Ti(IV)-methyl complex, [Tp*TiMe(O-2,6-Me2C6H3)]+[MeB(C6F5)3]- · (THF)2, polymerizes ethylene to give polyethylene with a uniform molecular weight distribution, clearly indicating that the cationic Ti(IV) species plays an essential role as the active species. Introduction Designing efficient catalysts for well-controlled olefin polymerization is one of the attractive targets in organometallic chemistry, catalysis, as well as in polymer chemistry,1-3 and half-titanocenes containing anionic donor ligands (Y) of type Cp′TiX2(Y) (Cp′ ) cyclopentadienyl group, X ) halogen, alkyl, Y ) aryloxo, ketimide, phosphinimide, etc.) are promising candidates,2d,3 especially in terms of syntheses of new polymers by ethylene copolymerizations demonstrated by using the aryloxo/ketimide analogues.3,4 It is known that group 4 metal tris(pyrazolyl)borate complexes, Tp′MCl3 [Tp′ ) tris(pyrazolyl)borate; M ) Ti, Zr, Hf], can be activated by methylalumoxane (MAO) to produce highly active olefin polymerization catalysts,5-8 and the cationic species, generated from Tp*Zr(CH2Ph)3 [Tp* ) HB(3,5-Me2-pyrazolyl)3] or TpMs*Hf(CH2Ph)3 [TpMs* ) HB(3-mesitylpyrazolyl)2(5-mesitylpyra* Corresponding author. Tel.: +81-743-72-6041. Fax: +81-743-72-6049. E-mail: [email protected]. † Present address: Thai Polyethylene Co., Ltd., 10 I-1 Maptaphud Industrial Estate, Muang District, Rayong Province, 21150 Thailand. (1) (a) Gladysz, J. A., Ed. Frontiers in Metal-Catalyzed Polymerization (special issue). Chem. ReV. 2000, 100. For example: (b) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100, 1169. (c) Alt, H. G.; Ko¨ppl, A. Chem. ReV. 2000, 100, 1205. (d) Chen, E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391. (2) Recent reviews (accounts), see: (a) Gibson, V. C.; Spitzmesser, S. K. Chem. ReV. 2003, 103, 283. (b) Coates, G. W.; Hustad, P. D.; Reinartz, S. Angew. Chem., Int. Ed. 2002, 41, 2236. (c) Bolton, P. D.; Mountford, P. AdV. Synth. Catal. 2005, 347, 355. (d) Stephan, D. W. Organometallics 2005, 24, 2548. (e) Domski, G. J.; Rose, J. M.; Coates, G. W.; Bolig, A. D.; Brookhart, M. Prog. Polym. Sci. 2007, 32, 30. (3) Nomura, K.; Liu, J.; Padmanabhan, S.; Kitiyanan, B. J. Mol. Catal. A 2007, 267, 1, and references cited therein. (4) Examples in ethylene copolymerizations, see: (a) Nomura, K.; Okumura, H.; Komatsu, T.; Naga, N. Macromolecules 2002, 35, 5388. (b) Wang, W.; Fujiki, M.; Nomura, N. J. Am. Chem. Soc. 2005, 127, 4582. (c) Zhang, H.; Nomura, K. J. Am. Chem. Soc. 2005, 127, 9364. (d) Nomura, K.; Wang, W.; Fujiki, M.; Liu, J. Chem. Commun. 2006, 2659. (e) Itagaki, K.; Fujiki, M.; Nomura, K. Macromolecules 2007, 40, 6489. (f) Nomura, K.; Liu, J.; Fujiki, M.; Takemoto, A. J. Am. Chem. Soc. 2007, 129, 14170. (g) Liu, J.; Nomura, K. Macromolecules 2008, 41, 1070. (h) Nomura, K.; Kakinuki Fujiki, M.; Itagaki, K. Macromolecules 2008, 41, 8974.

zolyl)-] and [Ph3C][B(C6F5)4], polymerize ethylene.9 Moreover, the effect of steric bulk in Tp′ toward the ethylene polymerization behavior using Tp′TiCl3-MAO catalysts was known.5a Although examples for ethylene polymerization using certain mono aryloxo-substituted titanium complexes were known,5d,7 studies including the structural analysis and effect of ligand toward the activity in olefin polymerization have not been reported.10 Moreover, examples for isolation of the cationic tris(pyrazolyl)borate alkyl complexes especially of titanium have not so far been reported. In this article, we thus wish to present the synthesis and structural analysis of a series of Tp′TiX2(OAr) [Tp′ ) HB(pyrazolyl)3 or Tp*; OAr ) aryloxo], and their use as catalysts in ethylene polymerization including isolation of

(5) (a) Murtuza, S.; Casagrande, O. L., Jr.; Jordan, R. F. Organometallics 2002, 21, 1882. (b) Michiue, K.; Jordan, R. F. Macromolecules 2003, 36, 9707. (c) Michiue, K.; Jordan, R. F. Organometallics 2004, 23, 460. (d) Michiue, K.; Jordan, R. F. J. Mol. Catal. A 2008, 282, 107. (6) (a) Gil, M. P., Jr. Appl. Catal., A 2007, 332, 110. (b) Gil, M. P.; dos Santos, J. H. Z.; Casagrande, O. L., Jr. Mol. Catal. A 2004, 209, 163. (c) Furlan, L. G.; Gil, M. P.; Casagrande, O. L., Jr. Macromol. Rapid Commun. 2000, 21, 1054. (d) Gil, M. P.; Casagrande, O. L., Jr. J. Organomet. Chem. 2004, 689, 286. (e) Gil, M. P.; dos Santos, J. H. Z.; Casagrande, O. L., Jr. Macromol. Chem. Phys. 2001, 202, 319. (7) Nakazawa, H.; Ikai, S.; Imaoka, K.; Kai, Y.; Yano, T. J. Mol. Catal. A 1998, 132, 33. (8) (a) Karam, A.; Jimeno, M.; Lezama, J.; Catari, E.; Figueroa, A.; de Gascue, B. R. J. Mol. Catal. A 2001, 176, 65. (b) Karam, A.; Casas, E.; Catari, E.; Pekerar, S.; Albornoz, A.; Mendez, B. J. Mol. Catal. A 2005, 238, 233. (c) Karam, A.; Pastran, J.; Casas, E.; Mendez, B. Polym. Bull. 2005, 55, 11. (d) Casas, E.; Karam, A.; Diaz-Barrios, A.; Albano, C.; Sanchez, Y.; Mendez, B. Macromol. Symp. 2007, 257, 131. (9) (a) Lee, H.; Jordan, R. F. J. Am. Chem. Soc. 2005, 127, 9384. (b) Lee, H.; Nienkemper, K.; Jordan, R. F. Organometallics 2008, 27, 5075. (c) Nienkemper, K.; Lee, H.; Jordan, R. F.; Ariafard, A.; Dang, L.; Lin, Z. Organometallics 2008, 27, 5867. (10) In ref 7, Tp*TiCl2(O-4-XC6H4) (X ) H, Me, CN) were used as catalyst precursors for ethylene polymerization in the presence of MAO or MMAO. However, no descriptions for syntheses and identification were seen. In ref 5d, the synthesis of TpMs*TiCl2(O-2,4,6-tBu3C6H2) identified on the basis of NMR spectra and elemental analysis and its use as the catalyst for ethylene polymerization and copolymerization with 1-hexene in the presence of MAO were reported.

10.1021/om801220b CCC: $40.75  2009 American Chemical Society Publication on Web 02/27/2009

Tris(pyrazolyl)borate Ti(IV) Complexes Scheme 1

stable cationic alkyl complex that polymerizes ethylene to afford polyethylene with a uniform molecular weight distribution.11

Results and Discussion 1. Synthesis and Structural Analysis of Tris(pyrazolyl)borate Ti(IV) Dichloride Complexes Containing Phenoxy Ligands, Tp′TiCl2(OAr), and Their Use in Catalysis for Ethylene Polymerization. A series of Tp′TiCl2(OAr) [Tp′ ) Tp (1), Tp* (2); Ar ) Ph (a), 2,6-Me2C6H3 (b), 2,6-iPr2C6H3 (c)] could be prepared by treating Tp′TiCl3 with LiOAr in Et2O or in toluene, and their procedures are somewhat analogous to those for Cp′TiCl2(OAr).12 The resultant complexes (1a-c, 2a-c) (Scheme 1) were identified on the basis of 1H, 13C NMR spectra, and elemental analyses, and all of their structures were determined by X-ray crystallography.13 The structures (for 1a-c, 2a-c) are shown in Figure 1, and the selected bond distances and angles are summarized in Table 1.13 These complexes fold a rather distorted octahedral geometry around titanium, and the two Cl atoms are placed in cis-form [Cl(1)-Ti-Cl(2) bond angles: 97.20(2)-98.02(3)° for 1, 95.90(2)-97.82(3)° for 2], and the phenoxy ligand is positioned trans to one of the pyrazolyl moieties [O-Ti-N bond angles: 169.71(5)-170.18(7)° for 1a-c, 172.35(5)-179.14(9)° for 2a-c]. The Ti-Cl bond distances in 2a-c [2.3057(5)-2.3216(10) Å] are rather longer than those in 1a-c [2.2867(5)-2.3034(9) Å], probably due to a steric bulk of the methyl group in Tp*; the Ti-O bond distances in 2a-c [1.773(2)-1.7820(15) Å] are also rather longer than those in 1a-c [1.764(2)-1.7687(15) Å]. TheobservedTi-O-C(phenyl)bondangles[170.86(11)-175.70(10)° for 1a-c, 2b,c] are rather larger than those in a series of Cp′TiCl2(OAr) [155.5(2)-163.1(2)°],3 except Cp*TiCl2(O-2,6i Pr2C6H3) [173.0(3)°].12 These angles are thus influenced by substituents in both the aryloxo and the tris(pyrazolyl)borate ligands.13 Ethylene polymerization using 1a-c, 2a-c was conducted in toluene at 25 °C in the presence of dried MAO [prepared by removing toluene and AlMe3 from ordinary MAO (PMAO-S, Tosoh Finechem Co.), according to the procedure described below]. The results (under optimized Al/Ti molar ratios) are summarized in Table 2.14 TpTiCl2(OPh) (1a) showed notable catalyticactivitiesunderoptimizedAl/Timolarratios[48 700-55 100 kg PE/mol Ti · h, runs 7, 8, 10], and the activity was influenced (11) Some of these results were presented at the 23rd International Conference on Organometallic Chemistry (ICOMC 2008), July 2008, Rennes, France. (12) For example: Nomura, K.; Naga, N.; Miki, M.; Yanagi, K.; Imai, A. Organometallics 1998, 17, 2152. (13) Crystallographic analysis results (structure reports, CIF files) are shown in the Supporting Information. (14) As described in the text, the catalytic activities and the Mw/Mn values were highly affected by the Al/Ti molar ratios (amount of MAO in the mixture), and the optimized Al/Ti molar ratio was also sensitive to the polymerization temperature. The selected GPC traces are shown in the Supporting Information.

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by the Al/Ti molar ratios (runs 1-9, 11, 12).14 The activity of 73 200 kg PE/mol Ti · h was achieved under low Ti concentration conditions (run 12), but the activity decreased at higher temperature (40, 55 °C, runs 13-15). The activities by the 2,6Me2C6H3 and the 2,6-iPr2C6H3 analogues (1-2b,c) were lower than those by the Ph analogues (1-2a). It thus seems that an increase in steric bulk of the phenoxy substituent led to a decrease in the activity. Although the molecular weight distributions (Mw/Mn) in the resultant polymers were broad in most cases,14 the Mw values in the resultant polymer prepared by the Tp analogues (1a-c) were higher than those prepared by the Tp* analogues (2a-c). The Mw/Mn values were highly dependent upon the Al/Ti molar ratios employed,14 suggesting that several catalytically active species were generated in the mixture probably due to the subsequent decomposition (in the presence of excessive MAO). In contrast, the resultant polymers prepared by 1a under optimized Al/Ti molar ratios possessed unimodal molecular weight distributions (runs 7, 10), suggesting that the polymerization proceeded with uniform catalytically active species under these conditions. Note that the activities by 1a under the optimized Al/Ti molar ratios (affording polymers with unimodal molecular weight distributions, runs 7, 10) were higher than that by Cp*TiCl2(O-2,6-iPr2C6H3) reported previously (runs 33, 34)3,13 even under much lower Al/Ti molar ratios [ex. 200 (run 7) vs 30 000 (run 34)]. 2. Synthesis and Structural Analysis of Tp*TiMe2(OAr): Isolation of the Cationic Ti(IV)-Methyl Complex, [Tp*TiMe(O-2,6-Me2C6H3)]+[MeB(C6F5)3]- · (THF)2. The Tp*-dimethyl analogues, Tp*TiMe2(OAr) (3b,c), could be prepared in high yields (>80%) by treating 2b,c with MeLi in Et2O (Scheme 2), and the complexes were identified on the basis of 1H, 13C NMR spectra and elemental analyses; their structures were determined by X-ray crystallography.13 The structures are shown in Figure 2, and the selected bond distances and angles are summarized in Table 3.13 These complexes also fold a rather distorted octahedral geometry around Ti, and two methyl groups are placed in cisform [C(1)-Ti-C(2) bond angles: 99.03(12)°, 98.90(10)° for 3b,c, respectively], and the phenoxy ligand is positioned trans to one of the pyrazolyl moieties [175.67(8)°, 176.73(7)° for 3b,c, respectively] with large Ti-O-C(phenyl) bond angles [O-Ti-N bond angles: 174.75(17)°, 176.86(13)° for 3b,c, respectively].13 Attempts for isolations of the dimethyl analogues from 1a, 2a (by treatments with MeLi, MeMgBr, Me2Zn in Et2O) were unsuccessful at this moment. As shown in Table 4, complex 3b also showed moderate catalytic activity (close to that by 2b) for ethylene polymerization in the presence of MAO, affording polyethylene with a relatively narrow molecular weight distribution (run 35).14 Note that the reaction of 3b with B(C6F5)3 in THF afforded the cationic complex, [Tp*TiMe(O-2,6-Me2C6H3)]+[MeB(C6F5)3]- · (THF)2 (4), quantitatively (Scheme 2), and the complex was identified on the basis of 1H, 13C NMR spectra, and elemental analysis.15 The isolated 4 is thermally stable, and the complex did not decompose at room temperature in ordinary experimental procedures. The reaction with [Ph3C][B(C6F5)4] in THF also gave a pure product confirmed by the 1H NMR spectrum.16 Importantly, 4 showed the moderate catalytic activity (very close to that by 3b) without MAO (in the presence of a small (15) For examples for the synthesis of AlMe3 and ZnMe2 adducts of cationic (imido)titanium methyl species, see: (a) Bolton, P. D.; Clot, E.; Cowley, A. R.; Mountford, P. Chem. Commun. 2005, 3313. (b) Bolton, P. D.; Clot, E.; Cowley, A. R.; Mountford, P. J. Am. Chem. Soc. 2006, 128, 15005.

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Figure 1. ORTEP drawings for 1a (top, left), 1b (top, middle), 1c (top, right), and 2a (bottom, left), 2b (bottom, middle), 2c (bottom, right). Thermal ellipsoids are drawn at the 50% probability level, and H atoms are omitted for clarity. Details in the analyses are shown in the Supporting Information.13 Table 1. Selected Bond Distances and Angles for Tp′TiCl2(OAr) [Tp′ ) Tp (1), Tp* (2); Ar ) Ph (a), 2,6-Me2C6H3 (b), 2,6-iPr2C6H3 (c)]a 1a Ti(1)-Cl(1) Ti(1)-Cl(2) Ti(1)-O(1) Ti(1)-N(2) Ti(1)-N(4) Ti(1)-N(6) O(1)-C(10) Cl(1)-Ti(1)-Cl(2) Cl(1)-Ti(1)-O(1) Cl(1)-Ti(1)-N(2) Cl(1)-Ti(1)-N(4) Cl(1)-Ti(1)-N(6) Cl(2)-Ti(1)-O(1) Cl(2)-Ti(1)-N(2) Cl(2)-Ti(1)-N(4) Cl(2)-Ti(1)-N(6) O(1)-Ti(1)-N(2) O(1)-Ti(1)-N(4) O(1)-Ti(1)-N(6) N(2)-Ti(1)-N(4) N(2)-Ti(1)-N(6) N(4)-Ti(1)-N(6) Ti(1)-O(1)-C(10) a

2.2895(5) 2.2958(6) 1.7667(12) 2.1882(14) 2.1481(16) 2.1734(15) 1.355(2) 97.20(2) 97.83(4) 89.59(4) 90.62(4) 167.96(4) 96.94(5) 89.16(4) 167.38(4) 88.94(4) 169.71(5) 91.76(6) 91.67(5) 80.98(5) 80.12(5) 81.66(6) 170.86(11)

1b 2.2932(10) 2.3034(9) 1.764(2) 2.184(2) 2.153(2) 2.157(2) 1.376(3) 98.02(3) 97.84(7) 86.80(7) 90.22(6) 165.72(6) 98.27(7) 89.93(7) 167.43(7) 87.94(7) 169.89(9) 89.94(9) 94.09(9) 81.02(9) 80.22(9) 81.96(8) 174.59(18)

1c Selected Bond 2.2867(5) 2.2918(6) 1.7687(15) 2.1890(18) 2.1550(19) 2.1690(16) 1.375(2) Selected Bond 97.98(2) 97.53(4) 87.19(4) 89.18(4) 165.72(4) 99.00(5) 88.82(5) 166.62(4) 89.11(5) 170.18(7) 91.20(7) 93.56(6) 80.22(7) 80.55(6) 81.59(6) 173.52(11)

2a Distances (Å) Ti(1)-Cl(1) Ti(1)-Cl(2) Ti(1)-O(1) Ti(1)-N(2) Ti(1)-N(4) Ti(1)-N(6) O(1)-C(16) Angles (deg) Cl(1)-Ti(1)-Cl(2) Cl(1)-Ti(1)-O(1) Cl(1)-Ti(1)-N(2) Cl(1)-Ti(1)-N(4) Cl(1)-Ti(1)-N(6) Cl(2)-Ti(1)-O(1) Cl(2)-Ti(1)-N(2) Cl(2)-Ti(1)-N(4) Cl(2)-Ti(1)-N(6) O(1)-Ti(1)-N(2) O(1)-Ti(1)-N(4) O(1)-Ti(1)-N(6) N(2)-Ti(1)-N(4) N(2)-Ti(1)-N(6) N(4)-Ti(1)-N(6) Ti(1)-O(1)-C(16)

2.3216(10) 2.3164(9) 1.773(2) 2.214(2) 2.136(2) 2.155(2) 1.358(3) 97.82(3) 93.89(7) 86.96(7) 88.87(7) 167.10(6) 93.66(7) 86.38(7) 168.16(8) 91.36(7) 179.14(9) 95.62(10) 94.55(9) 84.23(9) 84.59(9) 80.61(9) 159.2(2)

2b 2.3070(4) 2.3097(4) 1.7752(8) 2.2132(10) 2.1672(12) 2.1697(11) 1.3585(16) 96.709(13) 95.34(3) 90.03(3) 90.73(3) 171.87(3) 96.96(3) 86.84(3) 166.34(2) 88.45(3) 173.01(4) 93.73(4) 90.25(4) 81.70(4) 83.96(4) 83.00(4) 175.70(10)

2c 2.3057(5) 2.3089(5) 1.7820(15) 2.2240(19) 2.1747(13) 2.1461(16) 1.370(2) 95.90(2) 96.89(5) 87.66(4) 89.73(4) 168.43(4) 97.39(4) 88.22(3) 169.42(5) 89.56(3) 172.35(5) 90.80(6) 92.50(6) 83.06(5) 82.31(6) 83.38(5) 171.45(10)

Detailed analysis results are shown in the Supporting Information.13

amount of AliBu3 scavenger), affording polyethylene with a uniform molecular weight distribution (run 37).17,18 The Mw value was close to that prepared by 3b-MAO catalyst (as well as by 2b-MAO catalyst). The result thus clearly indicates that

the cationic complex polymerizes ethylene as the catalytically active species. We have prepared and identified Tp′TiCl2(OAr) (1a-c, 2a-c) that exhibited moderate/remarkable catalytic activities for eth-

Tris(pyrazolyl)borate Ti(IV) Complexes


Table 2. Ethylene Polymerization by Tp′TiCl2(O-2,6-R2C6H3) [Tp′ ) Tp (1), Tp* (2); R ) H (a), Me (b), iPr (c)]-MAO Catalyst Systemsa run e

1 2 3 4 5 6f 7f 8f 9f 10f 11 12 13 14 15 16 17 18 19 20 21f 22 23 24 25 26 27 28 29 30 31 32 33 34

complex 1a (2.0) 1a (2.0) 1a (2.0) 1a (2.0) 1a (2.0) 1a (0.1) 1a (0.1) 1a (0.1) 1a (0.1) 1a (0.05) 1a (0.01) 1a (0.01) 1a (0.05) 1a (0.05) 1a (0.05) 1b (2.0) 1b (2.0) 1b (2.0) 1b (2.0) 1b (2.0) 1c (2.0) 2a (2.0) 2a (2.0) 2a (2.0) 2a (2.0) 2a (2.0) 2b (2.0) 2b (2.0) 2b (2.0) 2b (2.0) 2b (2.0) 2c (2.0) Cp-Arh (0.1) Cp-Arh (0.1)

MAO/mmol (Al/Ti)b 0.20 (100) 0.50 (250) 1.00 (500) 2.00 (1000) 3.00 (1500) 0.010 (100) 0.020 (200) 0.030 (300) 0.040 (400) 0.020 (400) 0.010 (1000) 0.020 (2000) 0.010 (200) 0.020 (400) 0.010 (200) 0.20 (100) 0.50 (250) 1.00 (500) 2.00 (1000) 3.00 (1500) 0.20 (100) 0.20 (100) 0.50 (250) 1.00 (500) 2.00 (1000) 3.00 (1500) 0.20 (100) 0.50 (250) 1.00 (500) 2.00 (1000) 3.00 (1500) 0.50 (250) 1.00 (10000) 3.00 (30000)

temp/°C

yield/mg

activityc

Mwd × 10-5

Mw/Mnd

25 25 25 25 25 25 25 25 25 25 25 25 40 40 55 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25

>507 164 175 127 60 138 459 442 96 203 119 122 144 32 53 92 95 61 48 49 55 147 215 136 42 17 97 138 118 20 20 34 145 205

>5070 492 525 381 180 16 600 55 100 53 000 11 500 48 700 71 400 73 200 17 280 3840 6360 280 280 180 140 150 330 441 645 408 130 51 240 414 354 60 60 100 7250 12 300

15.6

8.4

18.2 22.9 18.2 13.3 22.1

7.3 2.9 5.9 6.2 2.9

13.2 22.7 10.8 15.1 9.63 6.25 5.60

4.2 3.3 3.6 4.1 20 8.8 27

8.25 4.27 3.30 2.94 3.77

168 118 57 36 48

4.98 3.83 3.85 4.34

69 40 26 19

7.98 23.2 29.3

189 3.0 2.9

e

a Conditions: toluene 30 mL, ethylene 4 atm, 10 min, MAO (prepared by removing toluene and AlMe3 from the commercially available MAO). Molar ratio of Al/Ti. c Activity in kg polymer/mol Ti · h. d GPC data in o-dichlorobenzene versus polyethylene standards. e Polymerization had to be terminated after 3 min due to difficulty stirring the mixture. f Polymerization time 5 min. g Insoluble for GPC measurement. h Cp-Ar: Cp*TiCl2(O-2,6-iPr2C6H3). b

Scheme 2

ylene polymerization in the presence of MAO; 1a showed exceptionally high catalytic activity especially in the presence of a small amount of MAO (Al/Ti molar ratio ) 200), affording polymers with uniform molecular weight distributions. Both the dimethyl complex (3b) and the cationic methyl complex (4) showed moderate catalytic activities (close to 2b), affording polymers with uniform molecular weight distributions. The (16) 1H NMR spectra for reactions of 3b with B(C6F5)3, [Ph3C][B(C6F5)4] in THF, including their peak assignments, are shown in the Supporting Information. (17) Addition of AliBu3 was necessary to remove THF as well as impurities in the solvent under the reaction conditions, and an increase in the Al/Ti molar ratios led to a decrease in the activity and broadening of the molecular weight distributions due to decomposition by reacting with Al. (18) Synthesis of [Ti(N-2-tBuC6H4){C(3,5-Me2-pyrazolyl)3}Cl(THF)]+ and ethylene polymerization in the presence of MAO, AliBu3: Bigmore, H. R.; Dubberley, S. R.; Kranenburg, M.; Lawrence, S. C.; Sealey, A. J.; Selby, J. D.; Zuideveld, M. A.; Cowley, A. R.; Mountford, P. Chem. Commun. 2006, 436.

information concerning effects of substituents in both the phenoxide and the Tp′ toward the activity are unique contrasts to those by Tp′TiCl3-MAO catalysts5,7,9 and should be useful for designing more efficient catalyst. Moreover, stable isolation of the cationic Ti(IV) complex (4) that plays a key role as the catalytically active species for the polymerization should also be promising for better understanding as well as for the catalyst design.9 We thus highly believe that these facts strongly suggest that further modifications of both Tp′ and anionic donor ligand in Tp′MX2(Y) should be promising for more efficient catalysts for well-controlled olefin polymerization.

Experimental Section General Experimental Procedures. All experiments were carried out under a nitrogen atmosphere in a Vacuum Atmospheres drybox or using standard Schlenk techniques. All chemicals used were of reagent grades and were purified by standard purification procedures. Anhydrous grade toluene and n-hexane (Kanto Chemi-

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Figure 2. ORTEP drawings for 3b (left) and 3c (right). Thermal ellipsoids are drawn at the 50% probability level, and H atoms are omitted for clarity. Details in the analyses are shown in the Supporting Information.13 Table 3. Selected Bond Distances and Angles for Tp*TiMe2(OAr) [Ar ) 2,6-Me2C6H3 (3b), 2,6-iPr2C6H3 (3c)]a 3b Ti(1)-O(1) Ti(1)-N(2) Ti(1)-N(4) Ti(1)-N(6) O(1)-C(16)

O(1)-Ti(1)-N(2) O(1)-Ti(1)-N(4) O(1)-Ti(1)-N(6) N(2)-Ti(1)-N(4) N(2)-Ti(1)-N(6) N(4)-Ti(1)-N(6) Ti(1)-O(1)-C(16)

a

3c

Selected Bond Distances (Å) 1.7775(18) 2.254(2) 2.251(2) 2.238(2) 1.371(3) Ti(1)-C(24) 2.126(3) Ti(1)-C(25) 2.130(3)

1.7938(15) 2.2628(18) 2.2528(17) 2.2503(18) 1.364(2) Ti(1)-C(28) 2.124(2) Ti(1)-C(29) 2.130(2)

Selected Bond Angles (deg) 175.67(8) 95.45(8) 96.44(8) 80.79(8) 80.90(8) 80.58(8) 174.75(17) O(1)-Ti(1)-C(24) 95.47(11) O(1)-Ti(1)-C(25) 97.46(10) N(2)-Ti(1)-C(24) 86.73(10) N(2)-Ti(1)-C(25) 85.85(10) N(4)-Ti(1)-C(24) 90.46(10) N(4)-Ti(1)-C(25) 163.15(10) N(6)-Ti(1)-C(24) 165.72(10) N(6)-Ti(1)-C(25) 87.23(10) C(24)-Ti(1)-C(25) 99.03(12)

176.73(7) 97.74(6) 95.69(6) 80.06(6) 81.61(6) 81.15(6) 176.86(13). O(1)-Ti(1)-C(28) 96.57(8) O(1)-Ti(1)-C(29) 96.56(8) N(2)-Ti(1)-C(28) 85.78(8) N(2)-Ti(1)-C(29) 85.29(8) N(4)-Ti(1)-C(28) 87.68(8) N(4)-Ti(1)-C(29) 163.47(8) N(6)-Ti(1)-C(28) 164.41(8) N(6)-Ti(1)-C(29) 89.22(8) C(28)-Ti(1)-C(29) 98.90(10)

Detailed analysis results are shown in the Supporting Information.13 Table 4. Ethylene Polymerization by Tp*TiMe2(O-2,6-Me2C6H3) (3b)-MAO Catalyst System or by [Tp*TiMe(O-2,6-Me2C6H3)]+[MeB(C6F5)3]- · (THF)2 (4)a run

complex

MAO/mmol (Al/Ti)b

temp/°C

yield/mg

activityc

Mwd × 10-5

Mw/Mnd

28 35 36 37 38

2b (2.0) 3b (2.0) 4 (2.0) 4 (2.0) 4 (2.0)

0.50 (250) 0.50 (250) none AliBu3 0.050 (25)e AliBu3 0.20 (100)e

25 25 25 25 25

138 98 trace 90 43

414 290 trace 270 129

3.83 1.97

40 1.3

3.95 4.25

2.0 3.8

a Conditions: toluene 30 mL, ethylene 4 atm, 25 °C, 10 min, MAO (prepared by removing toluene and AlMe3 from the commercially available MAO). b Molar ratio of Al/Ti. c Activity in kg polymer/mol Ti · h. d GPC data in o-dichlorobenzene versus polystyrene standards. e AliBu3 was used as a scavenger (in place of MAO).

cal Co., Inc.) were stored in the drybox in the presence of molecular sieves (mixture of 3A 1/16 and 4A 1/8, and 13X 1/16) after passing through an alumina short column under nitrogen. Anhydrous

dichloromethane and diethyl ether (Kanto Chemical Co., Inc.) were stored in the drybox in the presence of molecular sieves (mixture of 3A 1/16 and 4A 1/8, and 13X 1/16). TpTiCl3 and Tp*TiCl3 were

Tris(pyrazolyl)borate Ti(IV) Complexes


Table 5. Crystal and Data Collection Parameters for Tp′TiCl2(O-2,6-R2C6H3) [Tp′ ) Tp (1), Tp* (2); R ) H (a), Me (b), iPr (c)]a complex formula; formula weight habits crystal size (mm) crystal system space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z value Dcalcd (g/cm3) F000 temp (K) µ (Mo KR) (cm-1) no. of reflections measured

no. of observations no. of variables residuals: R1; Rw GOF max (minimum) peak in final diff. map (e-/Å3) a

Tp, H (1a)

Tp, Me (1b)

Tp, iPr (1c)

Tp*, H (2a)

Tp*, Me (2b)

Tp*, iPr (2c)

C15H15BCl2N6OTi; 424.94 red, block 0.40 × 0.38 × 0.30 monoclinic P21/c (No. 14) 9.4610(4) 16.7774(7) 12.0042(5)

C17H19BCl2N6OTi; 452.99 red, block 0.15 × 0.10 × 0.06 monoclinic P21/n (No. 14) 9.9436(6) 20.7533(10) 10.0498(5)

C63H70B2Cl4N12O2Ti2; 1286.56 red, block 0.20 × 0.12 × 0.08 monoclinic P21/n (No. 14) 9.7007(4) 20.3442(7) 17.2797(8)

C23H31BCl2N6OTi; 537.15 red, block 0.42 × 0.35 × 0.30 monoclinic P21/c (No. 14) 14.7492(4) 9.9928(3) 19.0194(5)

C27H39BCl2N6OTi; 593.26 red, block 0.40 × 0.30 × 0.20 monoclinic Cc (No. 9) 17.8222(7) 9.5655(3) 19.4654(9)

102.2595(14)

97.2040(17)

106.3583(15)

106.0602(8)

115.8357(14)

1862.00(13) 4 1.516 864.00 193 7.634 total: 17 801 unique: 4235 (Rint ) 0.023) 3664 250 0.0300; 0.1121 1.005 0.50 (-0.30)


C21H27BCl2N6OTi; 509.10 red, block 0.37 × 0.32 × 0.10 triclinic P1j (No. 2) 9.7436(4) 9.8171(4) 14.1166(5) 71.4051(11) 74.4772(11) 76.4601(12) 1216.66(8) 2 1.390 528.00 193 5.967 total: 12 037 unique: 5548 (Rint ) 0.016) 4964 316 0.0341; 0.0877 1.004 0.42 (-0.34)




Detailed analysis results are shown in the Supporting Information.13 Table 6. Crystal and Data Collection Parameters for Tp*TiMe2(O-2,6-Me2C6H3) (3b) and Tp*TiMe2(O-2,6-iPr2C6H3) (3c)a complex formula; formula weight habits crystal size (mm) crystal system space group a (Å) b (Å) c (Å) β (deg) V (Å3) Z value Dcalcd (g/cm3) F000 temp (K) µ (Mo KR) (cm-1) no. of reflections measured no. of observations no. of variables residuals: R1; Rw GOF max (minimum) peak in final diff. map (e-/Å3)

a

Tp*TiMe2(O-2,6-Me2C6H3) (3b) C25H37BN6OTi; 496.32 red, block 0.20 × 0.15 × 0.10 orthorhombic Pbca (No. 61) 16.4059(4) 15.9210(4) 20.6856(6) 5403.0(2) 8 1.220 2112.00 193 3.447 total: 42 685 Unique: 4921 (Rint ) 0.054) 3072 344 0.0396; 0.0994 1.013 0.23 (-0.28)

Tp*TiMe2(O-2,6-iPr2C6H3) (3c) C29H45BN6OTi; 552.42 red, block 0.15 × 0.15 × 0.14 monoclinic P21/n (No. 14) 10.1593(3) 16.0503(6) 19.4198(7) 99.4513(11) 3123.60(18) 4 1.175 1184.00 193 3.047 total: 25 590 Unique: 5682 (Rint ) 0.043) 4062 424 0.0374; 0.0984 1.007 0.23 (-0.29)

Detailed analysis results are shown in the Supporting Information.13

prepared according to the published procedures.19 B(C6F5)3 (Aldrich), [Ph3C][B(C6F5)4] (Asahi Glass Co., Ltd.), and AliBu3 (Kanto Chemical Co., Inc.) were stored in the drybox and were used as received. Ethylene of polymerization grade (Sumitomo Seika Chemicals, Ltd.) was used as received without further purification. Toluene and AlMe3 in the commercially available methylaluminoxane [PMAO-S, 9.5 wt % (Al) toluene solution, Tosoh Finechem Co.] were removed under reduced pressure (at ca. 50 °C for removing toluene, AlMe3, and then heated at >100 °C for 1 h for completion) in the drybox to give white solids. All 1H and 13C NMR spectra were recorded on a JEOL JNMLA400 spectrometer (399.78 MHz for 1H and 100.53 MHz for 13C). All spectra were obtained in the solvent indicated at room temperature unless otherwise noted. Chemical shifts are given in ppm and are referenced to SiMe4 (δ 0.00, 1H, 13C). Elemental (19) Kouba, J. K.; Wreford, S. S. Inorg. Chem. 1976, 9, 2313.

analyses were performed by using a PE2400II Series (Perkin-Elmer Co.), and some analytical runs were performed twice to confirm the reproducibility in the independent analysis/synthesis runs. In particular, these confirmations were required because the resultant microcrystals in the dichloride complexes (1a-b and 2a) contained organic solvents in most cases even after the microcrystals were placed in vacuo, in highly reproducible ratios. Certain C values were somewhat lower than those calculated, whereas their N and H values were as expected; this is due to incomplete combustion (to form titanium carbide). Molecular weights and molecular weight distributions for the poly(ethylene) were measured by gel permeation chromatography (GPC, Tosoh HLC-8121GPC/HT) using a RI-8022 detector (for high temperature, Tosoh Co.) with polystyrene gel column (TSK gel GMHHR-H HT × 2, 30 cm × 7.8 mmφ ID, ranging from

Tris(pyrazolyl)borate Ti(IV) Complexes Containing Phenoxy Ligands

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