Synthesis and Structural Analysis of Zr–Al Heterobimetallic

Mar 15, 2016 - Timothy P. Brewster , Tan H. Nguyen , Zhongjing Li , William T. Eckenhoff , Nathan D. Schley , and Nathan J. DeYonker. Inorganic Chemis...
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Synthesis and Structural Analysis of Zr−Al Heterobimetallic Complexes, [ZrX{(O-2,4‑tBu2C6H2‑6-CH2)3(μ2‑O-2,4‑tBu2‑C6H2‑6CH2)}N][R2Al(μ2‑OiPr)] [X = Cl, Et, iBu; R = Me, Et, iBu]. Unique Reactivity of the iBu Complex Udomchai Tewasekson, Ken Tsutsumi, and Kotohiro Nomura* Department of Chemistry, Faculty of Science and Engineering, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji, Tokyo 192-0397, Japan S Supporting Information *

ABSTRACT: A series of heterobimetallic Zr−Al complexes, [ZrCl{(O-2,4- t Bu 2 C 6 H 2 -6-CH 2 ) 3 (μ 2 -O-2,4- t Bu 2 -C 6 H 2 -6CH2)}N][R2Al(μ2-OiPr)] [R = Me (3), Et (4)] and [ZrR{(O2,4-tBu2C6H2-6-CH2)3(μ2-O-2,4-tBu2-C6H2-6-CH2)}N][R2Al(μ2-OiPr)] [R = Et (5), iBu (6)], have been prepared by reactions of Zr(OiPr)[(O-2,4-tBu2C6H2-6-CH2)3N] (1) with 1.0 equiv of Al alkyls (Me2AlCl, Et2AlCl, AlEt3, and AliBu3), and their structures (3, 5, 6) were determined by X-ray crystallography. The isobutyl complex (6) is stable in C6D6 and toluene-d6 at 45 °C; the thermolysis of 6 at >60 °C gradually afforded 1 with liberation of AliBu3. These complexes exhibited remarkable catalytic activities for ethylene polymerization at 80−120 °C in the presence of MAO; only complex 6 exhibited the high activity even at 45−60 °C.

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INTRODUCTION Since the discovery of Ziegler−Natta catalysts, design and synthesis of efficient molecular catalysts for precise olefin coordination/insertion polymerization has been an attractive research subject.1−5 Studies on the synthesis of the related organometallic complexes and their reaction chemistry are thus considered to be important not only for basic understanding of reaction mechanism but also for better catalyst design. In the polymerization process, transition-metal complexes are generally activated by organometallic reagents (called cocatalysts) to generate cationic alkyl species (as proposed active species);3f,6,7 Al reagents, such as Al alkyls and methylaluminoxane (MAO), play an important key role as cocatalysts.6−8 These Al complexes are known to be involved in the catalysis as heterobimetallic complexes or counteranions.6,9,10 Therefore, synthesis and reaction chemistry of heterobimetallic complexes consisting of transition metal and Al attract considerable attention in terms of basic understanding of both reaction mechanism and organometallic chemistry. We recently reported the synthesis and some reactions of heterobimetallic Ti−Al complexes containing tris(aryloxo)amine ligands11 (so-called titanatranes)12−17 of the type [TiX{(μ2-O-2,4-R2C6H2-6-CH2)(O-2,4-R2C6H2-6-CH2)2N}][Me2Al(μ2-OR′)] [R = Me, tBu; X = Me, Et; R′ = iPr, tBu, 2,6F2C6H3, C6F5, CH(CF3)2, C(CF3)3, etc., Chart 1], which were generated by reaction of [TiX′(O-2,4-R 2 C 6 H 2 -6CH2)3N}]11−13 (X′ = alkoxo, aryloxo, etc.) with Al alkyls (AlMe3 , AlEt3 ). These isolated Ti−Al heterobimetallic © XXXX American Chemical Society

complexes, exhibited from moderate to high catalytic activities for ethylene polymerization in the presence of MAO at 100− 120 °C.11 It also turned out that the activity by TiX′[(O-2,4R2C6H2-6-CH2)3N] was affected by the terminal donor ligand (X′) and the substituent on the atrane ligand (R);11,13 good relationships between the effect of teminal ligand (X′) toward the activity upon addition of AlMe3 (small amount) and the formation of the heterobimetallic Ti−Al complexes were observed.11b,c Moreover, certain Ti−Al heterobimetallic complexes showed the activity even in the absence of MAO.11a,14a It was thus demonstrated that the bimetallic species play a role in this catalysis, and the cationic species generated by cleavage of the Ti−O bonds would be thus assumed as the active species. In contrast to the reported examples in titanatranes,11−13,16 as far as we know, reports for ethylene (propylene) polymerization using the Zr analogues still have been limited; a report that the Zr benzyl and hydride complexes with a tris(amido) ligand incorporated ethylene at 70−90 °C was known.18 We recently reported synthesis and structural analysis of the heterobimetallic Zr− and Hf−Al complexes, [MMe{(O2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2C6H2-6-CH2)N}][Me2Al(μ2-OiPr)] [M = Zr (2), Hf],19 prepared by reaction of M(OiPr)[(O-2,4-tBu2C6H2-6-CH2)3N]20 [M = Zr (1), Hf] with AlMe3, and their use as the catalyst precursors for ethylene polymerization. The Zr−Al analogue (2) showed the high catalytic activities, affording polymers with unimodal molecular Received: December 28, 2015

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DOI: 10.1021/acs.organomet.5b01027 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Chart 1. Examples for Isolated Heterobimetallic Ti−Al Complexes11

Scheme 1. Synthesis of Various Zr−Al Heterobimetallic Complexes (2−6) Prepared by Reaction of Zirconatranes (1) with Al Alkyls

various Al alkyls (Scheme 1). Reaction of 1 with Me2AlCl (1.0 equiv) afforded [ZrCl{(O-2,4- t Bu 2 C 6 H 2 -6-CH 2 ) 2 (μ 2 -O2,4-tBu2-C6H2-6-CH2)N}][Me2Al(μ2-OiPr)] (3) in moderate yield (65%), whereas the similar reactions of Ti(OiPr)[(O-2,4R′2C6H2-6-CH2)3N] (R′ = Me, tBu) with Me2AlCl afforded monomeric chloride, TiCl[(O-2,4-R′2C6H2-6-CH2)3N].11b Similarly, reaction of 1 with Et2AlCl (1.0 equiv) in toluene afforded [ZrCl{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H26-CH2)N}][Et2Al(μ2-OiPr)] (4, 68% yield). These complexes (3, 4) were identified by NMR spectra and elemental analysis, and the structure of 3 was determined by X-ray crystallography (described below, Figure 1).21 In 1H NMR spectra (in CDCl3 at 25 °C), resonances ascribed to methyl (in 3) or methylene (in 4) protons bound to Al were observed at rather high magnetic fields [δ −0.80 and −0.33 ppm (Al-CH3 in 3), δ −0.06 and 0.41 ppm (Al-CH2 in 4), respectively]. Although protons corresponding to two methyl groups in the OiPr ligand in 1 are equivalent (δ 1.32 ppm),20 two signals assigned to the methyl protons were observed in 3 and 4 [δ 1.38 and 1.59 ppm (3), δ 1.39 and 1.62 ppm (4), respectively]. 13C NMR spectra also showed a different set of the methyl signals [δ 24.9 and 26.2 ppm (3), δ 24.9 and 26.0 ppm (4), respectively]. These

weight distributions, whereas the Hf−Al analogues afforded polymers with bimodal (multimodal) molecular weight distributions (suggesting formation of several catalytically active species in the reaction mixture);19 the activity by 2 at 80 °C was higher than that by the Ti−Al analogues.11a In this paper, we thus present syntheses of several heterobimetallic Zr−Al complexes by reaction of Zr(OiPr)[(O-2,4-tBu2 C6H 2-6CH2)3N] (1)20 with Al alkyls, and their use as catalyst precursors in ethylene polymerization, including isolation of the isobutyl complex [ZriBu{(O-2,4-tBu2C6H2-6-CH2)3(μ2-O2,4-tBu2-C6H2-6-CH2)}N][iBu2Al(μ2-OiPr)] (6) that exhibits unique reactivity in solution.

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RESULTS AND DISCUSSION Synthesis and Structural Analysis of Zr−Al Heterobimetallic Complexes Containing Tris(aryloxo)amine ligands, [ZrX{(O-2,4- t Bu 2 C 6 H 2 -6-CH 2 ) 2 (μ 2 -O-2,4- t Bu 2 C6H2-6-CH2)N}][R2Al(μ2-OiPr)] [X = Cl, R = Me (3), Et (4); X = R = Et (5), iBu (6)]. On the basis of our reported result for the synthesis of [ZrMe{(O-2,4-tBu2C6H2-6-CH2) 2(μ2-O2,4-tBu2-C6H2-6-CH2)N}][Me2Al(μ2-OiPr)] (2),19 we explored reactions of Zr(OiPr)[(O-2,4-tBu2C6H2-6-CH2)3N] (1)20 with B

DOI: 10.1021/acs.organomet.5b01027 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

Figure 1. ORTEP drawings for [ZrCl{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H2-6-CH2)N}][Me2Al(μ2-OiPr)] (3, left), [ZrEt{(O2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H2-6-CH2)N}][Et2Al(μ2-OiPr)] (5, right). Thermal ellipsoids are drawn at the 50% probability level, and H atoms are omitted for clarity.21

Figure 2. ORTEP drawings for [ZriBu{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H2-6-CH2)N}][R2Al(μ2-OiPr)] (6). Thermal ellipsoids are drawn at the 50% probability level, and H atoms are omitted for clarity.21

bridging structures between Al and Zr, which are similar to those in 3 and 4 (as also confirmed by their crystal structures shown in Figures 1 and 2). Moreover, new signals assigned to protons in methylene attached to Zr were observed around 1.00 ppm [δ 0.94 ppm (5), 1.04 ppm (6), respectively]; these chemical shifts are close to those corresponding to protons in the ZrCH3 signal in 2 (δ 0.99 ppm in benzene-d6 at 25 °C).19 It should be noted that complex 6 showed high thermal stability in C6D6 and toluene-d8 solutions. Although 6 possesses an isobutyl group on zirconium, the complex is stable in solution at 25 °C for a while, and no further reactions (βhydrogen elimination or decomposition, etc.) occurred at 45 °C (in C6D6 and in toluene-d8 for 30 min, Figures S1-1 and S1-

analysis results clearly suggest that the isopropoxy ligand bridges between Zr and Al for 3 and 4, as shown in Scheme 1 as well as Figure 1. Note that reaction of 1 with AlEt3 or AliBu3 (1.0 equiv) in toluene afforded [ZrEt{(O-2,4- t Bu 2 C 6 H 2 -6-CH 2 ) 2 (μ 2 -O2,4-tBu2-C6H2-6-CH2)N}][Et2Al(μ2-OiPr)] (5) or [ZriBu{(O2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H2-6-CH2)}N][iBu2Al(μ2-OiPr)] (6), respectively. These complexes (5, 6) were identified by NMR spectra and elemental analysis, and their structures were determined by X-ray crystallography (described below; Figures 1 and 2). In 1H NMR spectra, a different set of resonances ascribed to protons in the Al alkyls and OiPr group was observed, suggesting that 5 and 6 reveal the oxygenC

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Organometallics

Table 1. Selected Bond Distances (Å) and Angles (deg) for [ZrCl{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H2-6CH2)N}][Me2Al(μ2-OiPr)] (3) and [ZrR{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H2-6-CH2)N}][R2Al(μ2-OiPr)] [R = Me (2),19 Et (5), iBu (6)]a 2b Zr(1)−O(1) Zr(1)−O(2) Zr(1)−O(3) Zr(1)−O(4) Zr(1)−N(1) Zr(1)−C(1) Al(1)−O(1) Al(1)−O(2) O(1)−Zr(1)−O(2) O(1)−Zr(1)−O(3) O(1)−Zr(1)−O(4) O(1)−Zr(1)−N(1) O(2)−Zr(1)−O(3) O(2)−Zr(1)−O(4) O(2)−Zr(1)−N(1) O(3)−Zr(1)−O(4) O(3)−Zr(1)−N(1) O(1)−Zr(1)−C(1) O(2)−Zr(1)−C(1) O(3)−Zr(1)−C(1) N(1)−Zr(1)−C(1) Zr(1)−O(1)−Al(1) Zr(1)−O(2)−Al(1) O(1)−Al(1)−O(2) C(2)−Al(1)−C(3) a

2.179(2) 2.179(2) 1.967(2) 1.961(2) 2.483(3) 2.234(4) 1.836(3) 1.859(2) 67.86(8) 88.48(9) 159.87(9) 87.75(9) 149.06(9) 95.48(9) 81.53(8) 102.47(9) 77.76(9) 97.66(12) 100.39(12) 102.37(12) 174.58(12) 104.79(11) 103.07(10) 82.94(11) 116.89(18)

3

5

selected bond distances (Å) 2.182(3) 2.199(3) 2.199(3) 2.229(2) 1.960(3) 1.973(2) 1.955(3) 1.970(2) 2.423(3) 2.469(3) 2.4291(13) Zr(1)−Cl(1) 2.272(4) 1.838(3) 1.831(3) 1.867(3) 1.868(2) selected bond angles (deg) 68.08(9) 67.98(8) 88.75(10) 88.63(8) 160.42(10) 159.02(9) 88.18(9) 86.27(8) 150.19(10) 149.01(8) 95.24((9)) 95.13(8) 82.39(9) 80.99(8) 103.01(10) 101.89(9) 78.22(10) 77.32(9) 96.62(7) O(1)−Zr(1)−Cl(1) 96.68(10) 100.74(7) O(2)−Zr(1)−Cl(1) 97.44(10) 100.35(8) O(3)−Zr(1)−Cl(1) 105.53(11) 174.98(7) N(1)−Zr(1)−Cl(1) 175.90(10) 104.68(11) 104.68(10) 103.03(11) 102.29(10) 82.92(11) 84.02(10) 117.91(17) C(1)−Al(1)−C(2) 116.44(16) C(3)−Al(1)−C(5)

6 2.199(3) 2.223(3) 1.972(3) 1.979(3) 2.471(3) 2.283(4) 1.837(3) 1.883(3) 67.69(9) 88.78(10) 159.66(9) 87.49(9) 149.35(8) 95.20(10) 81.60(10) 102.79(11) 77.86(10) 94.26(11) 96.52(13) 104.89(13) 176.75(12) 105.27(11) 102.77(12) 82.91(12) 121.69(17) C(5)−Al(1)−C(9)

Details are shown in the Supporting Information. bCited from ref 19.

2).22 Moreover, a gradual conversion from 6 to the monomeric complex (1) with liberation of AliBu3 was observed, when the solutions were heated at 60 °C in C6D6 and at 60−100 °C in toluene-d8.22 It should also be noted that an attempted insertion reaction of 6 with styrene (1.1 equiv) in C6D6 at 60 °C afforded 1, accompanied by liberation of AliBu3 in a certain degree (Figures S1−S3).22 On the basis of crystallographic analysis (Figure 2), no significant interactions between βhydrogen on the isobutyl group and zirconium were observed, probably due to a steric bulk in the tBu group on the atrane ligand.22 The isobutyl group in 6 thus showed unique thermal stability without β-hydrogen elimination nor subsequent insertion even in the presence of styrene. Structural Analysis for [ZrCl{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H2-6-CH2)N}][Me2Al(μ2-OiPr)] (3) and [ZrR{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H2-6-CH2)N}][R2Al(μ2-OiPr)] [R = Et (5), iBu (6)]. Figure 1 shows ORTEP drawings for the Zr−Al heterobimetallic complexes, [ZrCl{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H2-6-CH2)N}][Me2Al(μ2-OiPr)] (3) and [ZrEt{(O-2,4-tBu2C6H2-6CH2)2(μ2-O-2,4-tBu2-C6H2-6-CH2)N}][Et2Al(μ2-OiPr)] (5), and Figure 2 shows ORTEP drawings for the isobutyl analogue, [Zr i Bu{(O-2,4- t Bu 2 C 6 H 2 -6-CH 2 ) 2 (μ 2 -O-2,4- t Bu 2 -C 6 H 2 -6CH2)}N][iBu2Al(μ2-OiPr)] (6). The selected bond distances and angles are summarized in Table 1.21 The analysis results for the methyl analogue (2) are also placed for comparison. These complexes fold a distorted octahedral geometry around zirconium consisting of a Cl−Zr−N or C−Zr−N axis [bond angles for N(1)−Zr(1)−Cl(1): 174.98(7)° for 3; N(1)−

Zr(1)−C(1): 174.58(12)° for 2; 175.90(10)° for 5; 176.75(12)° for 6] and a distorted plane of one alkoxo ligand and three aryloxo chelate ligands [total bond angles of the O(1)−Zr(1)−O(2), O(2)−Zr(1)−O(4), O(3)−Zr(1)−O(4), and O(1)−Zr(1)−O(3) for 3, 5, 6 were 355.08, 353.63, 354.46°, respectively], as observed in 2 (354.29°).19 The coordination sphere of zirconium consists of one carbon (or Cl in 3), four oxygen atoms including three oxygen atoms from the atrane ligand, and the zirconium atom in 3, 5, 6 are ligated via a transannular interaction stemming from the bridgehead amino nitrogen. The average O−Zr−N bond angles are 81.99° (3), 80.79° (5), 81.45° (6), respectively, suggesting a displacement of the zirconium atom toward the axial oxygen, similar to the observation made in the case of the other Ti−Al heterobimetallic complexes.11a As observed in 2 (81.34°), these values (80.79−81.99°) are somewhat smaller than those in [TiMe{(O-2,4-R′2C6H2-6-CH2)2(μ2-O-2,4-R2-C6H2-6-CH2)N}][Me2Al(μ2-OiPr)] [83.85° (R′ = Me), 83.80° (R′ = t Bu)],11a probably due to influences of smaller O(3)−Zr−N, O(4)−Zr−N bond angles (77.32−79.15° in 3, 5, 6) compared to those in Ti (79.99−83.09°).11a It should be noted that Al atoms in these complexes (2, 3, 5, 6) are ligated through oxygen atoms in the terminal alkoxo ligand and the atrane ligand, and Zr−O (in μ2-O) bond distances [2.179(2)−2.229(2) Å, corresponding to Zr−O(1) and Zr−O(2) distances] are thus longer than the other Zr−O distances in the aryloxo ligands [1.955(3)−1.979(3) Å, corresponding to Zr−O(3) and Zr−O(4) distances]. These distances are also longer than those in Al−O bond distances D

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Organometallics

Table 2. Ethylene Polymerization by [ZrCl{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H2-6-CH2)}N][R2Al(μ2-OiPr)] [R = Me (3), Et (4)], [ZriBu{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H2-6-CH2)}N][iBu2Al(μ2-OiPr)] (6) − MAO Catalyst Systemsa run d

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

catalyst

MAO/mmol

2 2 2 2 3 3 3 3 3 3 3 4 4 4 4 4 4 6 6 6 6 6 6 6 6 6 1f 1f 1f 1f

3.0 3.0 2.0 3.0 3.0 3.0 2.0 3.0 4.0 2.0 3.0 3.0 3.0 2.0 3.0 4.0 3.0 3.0 3.0 3.0 2.0 3.0 4.0 2.0 3.0 3.0 3.0 3.0 3.0

Al cocatalystb

temp./°C

yield/mg

activityc

3.0 70.6 40.2 32.6 22.5 28.5 34.3 98.0 88.9 65.2 92.2 36.1 52.6 57.3 113.7 123.7 126.2 17.6 62.6 52.5 none 50.3 44.7 30.8 62.2 110.5 111.6 102.5 117.9 94.3

180 4240 2410 1960 1350 1710 2060 5880 5330 3910 5530 2170 3160 3440 6820 7420 7570 1060 3760 3150

Me2AlCl Et2AlCl AliBu

50 80 100 120 60 80 100 100 100 120 120 60 80 100 100 100 120 45 60 80 100 100 100 100 120 120 100 100 100 100

3020 2680 1850 3730 6630 6700 6150 7070 5660

Conditions: catalyst 0.10 μmol, n-octane 30.0 mL, 10 min. bAl 1.0 μmol (Al/Zr = 10). cActivity in kg-PE/mol-Zr·h. dCited from ref 19. eCatalyst 6 10.0 μmol, 20 min. fZr(OiPr)[(O-2,4-tBu2C6H2-6-CH2)3N] (1). a

[1.831(3)−1.883(3) Å, corresponding to Al−O(1) and Al− O(2) distances]. Moreover, the bond angles of O(1)−Zr(1)− O(2) [67.69(9)−68.08(9)°] are smaller than those for O(3)− Zr(1)−O(4) [101.89(9)−103.01(10)°], as observed in 2 [67.86(8)°, 102.47(9)°, respectively]. The results thus clearly indicate that these complexes possess Zr−alkyl (or Zr−Cl) bonds by replacement of the OiPr group. These complexes also fold a distorted tetrahedral geometry around Al, although the O(1)−Al(1)−O(2) bond angles were rather small [82.91(12)− 84.02(10)°]. As described above, Al−O bond distances [1.831(3)−1.883(3) Å] are shorter than the Zr−O (in μ2-O) bond distances [2.179(2)−2.229(2) Å]. Note that the bond angles in O(1)−Zr(1)−C(1) and O(2)− Zr(1)−C(1) in [ZrR{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2C6H2-6-CH2)N}][R2Al(μ2-OiPr)] [R = Me (2), Et (5), iBu (6)] decreased in the order: 2 [97.66(12)°, 100.39(12)°, respectively] > 5 [96.68(10)°, 97.44(10)°, respectively] > 6 [94.26(11)°, 96.52(13)°, respectively]. In contrast, the bond angle in N(1)−Zr−C(1) increased in the order: 2 [174.58(12)°] > 5 [175.90(10)°] > 6 [176.75(12)°]. The Zr−O(1) bond distances in 5, 6 [2.199(3) Å] are longer than that in 2 [2.179(2) Å], and the Zr−O(4) distance increased in the order: 2 [1.961(2) Å] < 5 [1.970(2) Å] < 6 [1.979(3) Å]. Moreover, the Zr−C(1) bond length also increased in the order: 2 [2.234(4) Å] < 5 [2.272(4) Å] < 6 [2.283(4) Å]. A similar observation was seen in the Al−O(2) bond distance: 2

[1.859(2) Å] < 5 [1.868(2) Å] < 6 [1.883(3) Å]. These observations would be probably explained as due to an influence of the alkyl substituent on Zr. Ethylene Polymerization by [ZrCl{(O-2,4-tBu2C6H2-6CH2)2(μ2-O-2,4-tBu2-C6H2-6-CH2)}N][R2Al(μ2-OiPr)] [R = Me (3), R = Et (4)], [ZriBu{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O2,4-tBu2-C6H2-6-CH2)}N][iBu2Al(μ2-OiPr)] (6). Ethylene polymerizations using [ZrCl{(O-2,4-tBu2C6H2-6-CH2) 2(μ2-O2,4-tBu2-C6H2-6-CH2)}N][R2Al(μ2-OiPr)] [R = Me (3), Et (4)] and [ZriBu{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2C6H2-6-CH2)}N][iBu2Al(μ2-OiPr)] (6) were conducted in noctane in the presence of MAO, and the results are summarized in Table 2. The results by the methyl analogue (2)19 are also placed for comparison. As reported previously by 2, the observed catalytic activities (on the basis of polymer yields) by 3, 4, 6 were affected by the amount of MAO (Zr/Al molar ratio). The activities were also affected by the polymerization temperature. It turned out that the chloride analogues (3, 4) showed higher catalytic activities than the methyl analogue (2) at 100−120 °C (runs 3, 4, 7−11, 14−17), whereas the activity by 2 at 80 °C was higher than those by 3, 4 [run 2 (2) vs runs 6 (3), 13 (4)]. The activities by 4 at 100−120 °C were higher than those by 2, 3 under the same conditions (with optimized Al/Zr molar ratio), although the exact reason is not clear at this moment. E

DOI: 10.1021/acs.organomet.5b01027 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

AlMe3 from commercially available methylaluminoxane [TMAO, 9.5 wt % (Al) toluene solution, Tosoh Finechem Co.] were removed under reduced pressure (at ca. 50 °C for removing toluene and AlMe3 and then heated at >100 °C for 1 h for completion) in the drybox to give white solids. Zr(OiPr)[(O-2,4-tBu2C6H2-6-CH2)3N] (1)20 was prepared according to published procedures. Molecular weights and molecular weight distributions for polyethylene were measured by gel permeation chromatography (Tosoh HLC-8121GPC/HT) with a polystyrene gel column (TSK gel GMHHR-H HT × 2, 30 cm × 7.8 mmφ, ranging from 99.9%, Sumitomo Seika Co. Ltd.) was used as received. Toluene and F

DOI: 10.1021/acs.organomet.5b01027 Organometallics XXXX, XXX, XXX−XXX

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Organometallics 1H, 2JHH = 13.7 Hz, NCH2), 6.48 (brd, 1H, 4JHH = 1.6 Hz, Ar-H), 6.73 (brd, 1H, 4JHH = 1.6 Hz, Ar-H), 6.89 (brd, 1H, 4JHH = 1.6 Hz, Ar-H), 7.02 (brd, 1H, 4JHH = 1.6 Hz, Ar-H), 7.19 (brd, 1H, 4JHH = 1.6 Hz, ArH), 7.26 (brd, 1H, 4JHH = 1.6 Hz, Ar-H). 13C NMR (CDCl3): δ 2.7 (AlCH2), 4.4 (AlCH2), 9.1 (AlCH2CH3), 9.2 (AlCH2CH3), 24.9 (OCH(CH3)2), 26.0 (OCH(CH3)2), 29.7 (C(CH3)3), 30.2 (C(CH3)3), 31.3 (C(CH3)3), 31.7 (C(CH3)3), 31.7 (C(CH3)3), 32.1 (C(CH3)3), 33.8 (C(CH3)3), 34.1 (C(CH3)3), 34.4 (C(CH3)3), 34.5 (C(CH3)3), 35.0 (C(CH3)3), 35.5 (C(CH3)3), 62.1 (NCH2), 63.6 (NCH2), 65.1 (NCH2), 71.0 (OCH(CH3)2), 121.8, 123.4, 124.1, 124.2, 124.4, 125.1, 125.6, 126.7, 126.9, 136.2, 137.2, 138.3, 141.4, 142.8, 144.4, 150.6, 154.7, 155.8 (aromatic carbon resonances). Anal. Calcd for C52H83AlClNO4Zr·hexane: C, 67.89; H, 9.53; N, 1.37. Found: C, 67.58; H, 9.33; N, 1.30. Synthesis of [ZrEt{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2C6H2-6-CH2)}N][Et2Al(μ2-OiPr)] (5). Complex 5 was prepared according to a similar procedure as that for 3, except that AlEt3 (0.166 g, 1.04 M n-hexane solution) was used in place of Me2AlCl. The colorless solution was then filtered through a Celite pad, and the filtrate was removed under vacuum to obtain white solids. The complex was isolated as colorless microcrystals from n-hexane solution. Yield: 0.092 g (40%). 1H NMR (CDCl3): δ −0.18 (m, 1H, AlCH2), −0.049 (m, 1H, AlCH2), 0.32 (m, 1H, AlCH2), 0.44 (m, 1H, AlCH2), 0.78 (t, 3H, 3JHH = 8.1 Hz, AlCH2CH3), 0.94 (q, 3JHH = 7.9 Hz, 2H, ZrCH2CH3), 0.99 (s, 9H, C(CH3)3), 1.18−1.21 (m, 21H, C(CH3)3 x 2, AlCH2CH3), 1.31 (s, 9H, C(CH3)3), 1.41 (d, 3H, 3JHH = 6.3 Hz, OCH(CH3)), 1.45 (s, 18H, C(CH3)3 x 2), 1.54 (t, 3H, 3JHH = 7.9 Hz, ZrCH2CH3), 1.59 (d, 3H, 3JHH = 6.0 Hz, OCH(CH3)), 2.94 (d, 1H, 2 JHH = 14.5 Hz, NCH2), 3.11 (d, 1H, 2JHH = 12.9 Hz, NCH2), 3.25 (d, 1H, 2JHH = 13.4 Hz, NCH2), 3.84 (d, 1H, 2JHH = 14.5 Hz, NCH2), 4.23 (d, 1H, 2JHH = 12.9 Hz, NCH2), 4.49 (d, 1H, 2JHH = 13.4 Hz, NCH2), 4.65 (m, 1H, OCH(CH3)2, 6.43 (brs, 1H, Ar-H), 6.68 (brs, 1H, Ar-H), 6.86 (brs, 1H, Ar-H), 6.97 (brs, 1H, Ar-H), 7.15 (brs, 1H, Ar-H), 7.24 (brs, 1H, Ar-H). 13C NMR (CDCl3): δ 2.8 (AlCH2), 4.9 (AlCH2), 9.2 (AlCH2CH3), 9.4 (AlCH2CH3), 13.6 (ZrCH2CH3), 25.8 (OCH(CH3)2), 26.1 (OCH(CH3)2), 29.8 (C(CH3)3), 30.2 (C(CH3)3), 31.3 (C(CH3)3), 31.7 (C(CH3)3), 31.7 (C(CH3)3), 32.2 (C(CH3)3), 33.8 (C(CH3)3), 34.1 (C(CH3)3), 34.3 (C(CH3)3), 34.6 (C(CH3)3), 35.1 (C(CH3)3), 35.7 (C(CH3)3), 48.1 (ZrCH2), 61.3 (NCH2), 62.9 (NCH2), 64.4 (NCH2), 70.4 (OCH(CH3)2), 122.2, 122.9, 123.8, 125.0, 125.1, 126.0, 126.2, 126.4, 127.1, 136.0, 136.8, 138.0, 140.5, 141.9, 144.0, 150.8, 155.4, 156.6 (aromatic carbon resonances). Synthesis of [ZriBu{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2C6H2-6-CH2)}N][iBu2Al(μ2-OiPr)] (6). Complex 6 was prepared according to a similar procedure as that for 3, except that AliBu3 (0.189 g, 1.04 M n-hexane solution) was used in place of Me2AlCl. The colorless solution was then filtered through a Celite pad, and the filtrate was removed under vacuum to obtain white solids. The complex was isolated as colorless microcrystals from n-hexane solution. Yield: 0.119 g (48%). 1H NMR (CDCl3): δ −0.05 (dd, 1H, 2JHH = 14.3 Hz, 3JHH = 7.5 Hz, AlCH2CH), 0.08 (dd, 1H, 2JHH = 14.3 Hz, 3 JHH = 5.7 Hz, AlCH2CH), 0.39 (dd, 1H, 2JHH = 14.7 Hz, 3JHH = 6.9 Hz, AlCH2CH), 0.40 (d, 3H, 3JHH = 6.6 Hz, AlCH2CH(CH3)), 0.60 (dd, 2JHH = 14.7 Hz, 3JHH = 6.2 Hz, 1H, AlCH2CH), 0.77 (d, 3H, 3JHH = 6.6 Hz, AlCH2CH(CH3)), 0.97 (d, 3H, 3JHH = 6.6 Hz, ZrCH2CH(CH3)), 0.97 (d, 3H, 3JHH = 6.3 Hz, ZrCH2CH(CH3)), 0.99 (s, 9H, C(CH3)3), 1.00 (d, 3H, 3JHH = 6.3 Hz, AlCH2CH(CH3)), 1.04 (d, 3H, 3JHH = 6.6 Hz, AlCH2CH(CH3)), 1.04 (m, 2H, ZrCH2CH), 1.18 (s, 9H, C(CH3)3), 1.18 (s, 9H, C(CH3)3), 1.31 (s, 9H, C(CH3)3), 1.39 (d, 3H, 3JHH = 6.3 Hz, OCH(CH3), 1.45 (s, 9H, C(CH3)3), 1.46 (s, 9H, C(CH3)3), 1.50−1.55 (m, 1H, ZrCH2CH), 1.54 (d, 3H, 3JHH = 6.3 Hz, OCH(CH3), 1.98 (m, 1H, AlCH2CH), 2.52 (m, 1H, AlCH2CH), 2.90 (d, 1H, 2JHH = 14.4 Hz, NCH2), 3.10 (d, 1H, 2JHH = 13.3 Hz, NCH2), 3.27 (d, 1H, 2JHH = 13.6 Hz, NCH2), 3.87 (d, 1H, 2JHH = 14.4 Hz, NCH2), 4.34 (d, 1H, 2JHH = 13.3 Hz, NCH2), 4.60 (d, 1H, 2JHH = 13.6 Hz, NCH2), 4.62 (m, 1H, OCH(CH3)2), 6.38 (brd, 1H, 4JHH = 2.6 Hz, Ar-H), 6.69 (brd, 1H, 4 JHH = 2.2 Hz, Ar-H), 6.87 (brd, 1H, 4JHH = 2.4 Hz, Ar-H), 6.97 (brd, 1H, 4JHH = 2.4 Hz, Ar-H), 7.14 (brd, 1H, 4JHH = 2.2 Hz, Ar-H), 7.24 (brd, 1H, 4JHH = 2.6 Hz, Ar-H). 13C NMR (CDCl3): 25.1, 25.6, 25.8

(OCH(CH 3 ) 2 , AlCH 2 CH(CH 3 ) 2 , ZrCH 2 CH(CH 3 ) 2 ), 26.0 (AlCH2CH(CH3)2), 26.2 (AlCH2CH(CH3)2), 26.5, 27.3, 28.4, 28.4, 28.8, 28.9, 29.0, 29.4 (OCH(CH3)2, AlCH2CH(CH3)2, ZrCH2CH(CH3)2), 30.0 (C(CH3)3), 30.5 (C(CH3)3), 31.3 (C(CH3)3), 31.7 (C(CH3)3), 31.7 (C(CH3)3), 32.3 (C(CH3)3), 33.7 (C(CH3)3), 34.0 (C(CH3)3), 34.3 (C(CH3)3), 34.6 (C(CH3)3), 35.1 (C(CH3)3), 35.6 (C(CH3)3), 61.7 (NCH2), 63.1 (NCH2), 64.6 (NCH2), 70.3 (OCH(CH3)2), 71.5 (ZrCH2), 122.4, 123.1, 123.8, 125.0, 125.2, 126.1, 126.4, 126.5, 127.1, 136.0, 136.8, 137.9, 140.5, 142.0, 144.1, 151.0, 155.6, 156.4 (aromatic carbon resonances). Anal. Calcd for C60H100AlClNO4Zr: C, 70.81; H, 9.90; N, 1.38. Found: C, 70.91; H, 9.90; N, 1.38. Ethylene Polymerization. Ethylene polymerizations were conducted in n-octane by using a 100 mL scale autoclave. The typical procedure (run 8, Table 2) was performed as follows. n-Octane (29.0 mL) and d-MAO (3.0 mmol) prepared by removing toluene and AlMe3 from the commercially available MAO (TMAO, Tosoh Finechem Co.) were charged into an autoclave in the drybox, and the apparatus was placed into an oil bath preheated at 100 °C under an ethylene atmosphere (1 atm). After the addition of n-octane solution (1.0 mL) containing [ZrCl{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2C6H2-6-CH2)N}][Me2Al(μ2-OiPr)] (3) via a syringe, the reaction apparatus was pressurized to 7 atm (total 8 atm), and the mixture was stirred magnetically for 10 min. After the above procedure, ethylene was purged, and the mixture was then poured into MeOH (150 mL) containing HCl (10 mL). The resultant polymer was collected on a filter paper by filtration and was adequately washed with MeOH and then dried in vacuo. Ethylene polymerizations by Zr(OiPr)[(O2,4-tBu2C6H2-6-CH2)3N] (1) in the presence of Al alkyls were conducted similarly except that the prescribed amount of Al alkyls (AliBu3 1.4 M in n-hexane, Me2AlCl 1.08 M in n-hexane, Et2AlCl 1.05 in n-hexane) was added into an n-octane solution containing 1 at −30 °C in the drybox. The solution (in a Schlenk tube) was then immediately added partly (as a 1.0 mL n-octane solution) into the autoclave via a syringe.11c Crystallographic Analysis. The measurement was made on a Rigaku XtaLAB mini diffractometer with graphite-monochromated Mo Kα radiation. All structures were solved by direct methods25 and expanded using Fourier techniques, and the non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included but not refined. All calculations were performed using the CrystalStructure26 crystallographic software package except for refinement, which was performed using SHELXL-97.27 Selected crystal collection parameters are shown in Table S1 (in the Supporting Information), and the detailed structure reports including their CIF files are shown in the Supporting Information.21

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.5b01027. Additional data (NMR spectra) for thermolysis of [ZriBu{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H26-CH2)N}][iBu2Al(μ2-OiPr)] (6) in C6D6 and in toluene-d8 and reaction of styrene in C6D6 monitored by NMR spectra, ORTEP drawing of 6 with full hydrogen, and structure reports (including table for crystal data and collection parameters) for [ZrX{(O2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H2-6-CH2)N}][R2Al(μ2-OiPr)] [X = Cl, R = Me (3); X,R = Et (5) X,R = iBu (6)] (PDF) Crystallographic data for 3, 5, and 6 (CIF) G

DOI: 10.1021/acs.organomet.5b01027 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

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(6) Recent review article: (a) Bochmann, M. The Chemistry of Catalyst Activation: The case of Group 4 Polymerization Catalyst. Organometallics 2010, 29, 4711 and related references cited therein. (b) Kaminsky, W. Discovery of Methylaluminoxane as Cocatalyst for Olefin Polymerization. Macromolecules 2012, 45, 3289. (7) For example (review):3f (a) Macchioni, A. Chem. Rev. 2005, 105, 2039. (b) Li, H.; Marks, T. J. Nuclearity and cooperative effects in binuclear catalysts and cocatalysts. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 15295. (c) Dagorne, S.; Fliedel, C. In Modern Organoaluminium Reagents; Woodward, S., Dagorne, S., Eds.; Topics in Organometallic Chemistry 41; Springer-Verlag: Berlin, 2013; p 125. (8) (a) Boor, J., Jr. Ziegler-Natta Catalysts and Polymerizations; AcademicPress: New York, 1979. (b) Chien, J. C. W., Ed. Coordination Polymerization; Academic Press: New York, 1975. (c) Andresen, A.; Cordes, H. G.; Herwig, H.; Kaminsky, W.; Merck, A.; Mottweiler, R.; Pein, J.; Sinn, H.; Vollmer, H. J. Angew. Chem., Int. Ed. Engl. 1976, 15, 630. (d) Sinn, H.; Kaminsky, W.; Vollmer, H.-J.; Woldt, R. Angew. Chem., Int. Ed. Engl. 1980, 19, 390. (e) Sinn, H.; Kaminsky, W. Adv. Organomet. Chem. 1980, 18, 99. (9) For example (heterodinuclear AlMe3 adducts), see: (a) Bochmann, M.; Lancaster, J. J. Angew. Chem., Int. Ed. Engl. 1994, 33, 1634. (b) Petros, R. A.; Norton, J. R. Organometallics 2004, 23, 5105. (c) Schröder, L.; Brintzinger, H. H.; Babushkin, D. E.; Fischer, D.; Mülhaupt, R. Organometallics 2005, 24, 867. (d) Bryliakov, K. P.; Babushkin, D. E.; Talsi, E. P.; Voskoboynikov, A. Z.; Gritzo, H.; Schröder, L.; Damrau, H. R. H.; Wieser, U.; Schaper, F.; Brintzinger, H. H. Organometallics 2005, 24, 894. (e) Bolton, P. D.; Clot, E.; Cowley, A. R.; Mountford, P. Chem. Commun. 2005, 3313. (f) Bolton, P. D.; Clot, E.; Cowley, A. R.; Mountford, P. J. Am. Chem. Soc. 2006, 128, 15005. (g) Bryliakov, K. P.; Talsi, E. P.; Voskoboynikov, A. Z.; Lancaster, S. J.; Bochmann, M. Organometallics 2008, 27, 6333. (10) For examples: (a) Janas, Z.; Jerzykiewicz, L. B.; Sobota, P.; Szczegot, K.; Wiceniewska, D. Organometallics 2005, 24, 3987. (b) Fandos, R.; Gallego, B.; Otero, A.; Rodriguez, A.; Ruiz, M. J.; Terreros, P.; Pastor, C. Organometallics 2007, 26, 2896. (c) Gurubasavaraj, P. M.; Mandal, S. K.; Roesky, H. W.; Oswald, R. B.; Pal, A.; Noltemeyer, M. Inorg. Chem. 2007, 46, 1056. (d) Gurubasavaraj, P. M.; Roesky, H. W.; Nekoueishahraki, B.; Pal, A.; Herbst-Irmer, R. Inorg. Chem. 2008, 47, 5324. (11) (a) Gurubasavaraj, P. M.; Nomura, K. Organometallics 2010, 29, 3500. (b) Takii, Y.; Gurubasavaraj, P. M.; Katao, S.; Nomura, K. Organometallics 2012, 31, 8237. (c) Nomura, K.; Tewasekson, U.; Takii, Y. Organometallics 2015, 34, 3272. (12) Examples for synthesis of titanium(IV) complexes containing amine triphenolate ligands; see: (a) Kol, M.; Shamis, M.; Goldberg, I.; Goldschmidt, Z.; Alfi, S.; Hayut-Salant, E. Inorg. Chem. Commun. 2001, 4, 177. (b) Kim, Y.; Verkade, J. G. Organometallics 2002, 21, 2395. (c) Kim, Y.; Jnaneshwara, G. K.; Verkade, J. G. Inorg. Chem. 2003, 42, 1437. (d) Ugrinova, V.; Ellis, G. A.; Brown, S. N. Chem. Commun. 2004, 468. (e) Fortner, K. C.; Bigi, J. P.; Brown, S. N. Inorg. Chem. 2005, 44, 2803. (f) Nielson, A. J.; Shen, C.; Waters, J. M. Polyhedron 2006, 25, 2039. (g) Licini, G.; Mba, M.; Zonta, C. Dalton Trans. 2009, 5265. Perspective for synthesis and use of amine triphenolate complexes: (h) Lionetti, D.; Medvecz, A. J.; Ugrinova, V.; QuirozGuzman, M.; Noll, B. C.; Brown, S. N. Inorg. Chem. 2010, 49, 4687. (13) Use of titanatranes, [TiX(O-2,4-R2C6H2-6-CH2)3N}], as catalyst precursors for ethylene polymerization in the presence of Al cocatalyst: Wang, W.; Fujiki, M.; Nomura, K. Macromol. Rapid Commun. 2004, 25, 504. (14) Synthesis of titanatranes containing chelate bis(aryloxo)(alkoxo)amine ligands and their use as the catalyst precursors for ethylene polymerization; see: (a) Padmanabhan, S.; Katao, S.; Nomura, K. Organometallics 2007, 26, 1616. (b) Padmanabhan, S.; Wang, W.; Katao, S.; Nomura, K. Macromol. Symp. 2007, 260, 133. (c) Gurubasavaraj, P. M.; Nomura, K. Inorg. Chem. 2009, 48, 9491. (15) Some early stage examples of atrane ligand based complexes: (a) Voronkov, M. G.; Dyakov, V. M.; Kirpichenko, S. V. J. Organomet. Chem. 1982, 233, l. (b) Schrock, R. R. Acc. Chem. Res. 1997, 30, 9−16. (c) Gade, L. H. Chem. Commun. 2000, 173.

AUTHOR INFORMATION

Corresponding Author

*Tel.: +81-42-677-2547. Fax: +81-42-677-2547. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The present research is partly supported by a Grant-in-Aid for Scientific Research (B) from the Japan Society for the Promotion of Science (JSPS, No. 15H03812). U.T. expresses his thanks to the Tokyo Metropolitan Government (Asian Human Resources Fund) for the predoctoral fellowship, and the project was partly supported by the advanced research program (Tokyo Metropolitan Government). The authors also express their thanks to Tosoh Finechem Co. for donating MAO (TMAO). The authors express their heartfelt thanks to Profs. A. Inagaki and S. Komiya (Tokyo Metropolitan University) for fruitful discussion.

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REFERENCES

(1) Selected reviews/accounts in the 1990s; see: (a) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 428. (b) McKnight, A. L.; Waymouth, R. M. Chem. Rev. 1998, 98, 2587. (c) Suhm, J.; Heinemann, J.; Wörner, C.; Müller, P.; Stricker, F.; Kressler, J.; Okuda, J.; Mülhaupt, R. Macromol. Symp. 1998, 129, 1. (d) Kaminsky, W.; Arndt, M. Adv. Polym. Sci. 1997, 127, 144. (e) Bochmann, M. J. Chem. Soc., Dalton Trans. 1996, 255. (f) Marks, T. J. Acc. Chem. Res. 1992, 25, 57. (g) Jordan, R. F. Adv. Organomet. Chem. 1991, 32, 325. (h) Kaminsky, W., Ed. Metalorganic Catalysts for Synthesis and Polymerization: Recent Results by Ziegler-Natta and Metallocene Investigations; Springer-Verlag: Berlin, 1999. (2) Selected special issues: (a) Frontiers in Metal-Catalyzed Polymerization. Gladysz, J. A. Chem. Rev. 2000, 100 (4), 1167. (b) Metallocene Complexes as Catalysts for Olefin Polymerization. Alt, H. G. Coord. Chem. Rev. 2006, 250 (1−2), 1. (c) Metal-Catalysed Polymerisation. Dalton Trans. 2009, 41, 8769. DOI: 10.1039/ b920329j. (d) Advances in Metal-Catalysed Polymerisation and Related Transformations. Mountford, P. Dalton Trans. 2013, 42, 8977. (3) Selected reviews, accounts, and books; see: (a) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283. (b) Mason, A. F.; Coates, G. W. In Macromolecular Engineering; Matyjaszewski, K., Gnanou, Y., Leibler, L., Eds.; Wiley-VCH: Weinheim, Germany, 2007; Vol. 1, p 217. (c) Metal Catalysts in Olefin Polymerization; Guan, Z., Ed.; Topics in Organometallic Chemistry 26; Springer-Verlag: Berlin, 2009. (d) Nomura, K.; Zhang, S. Chem. Rev. 2011, 111, 2342. (e) Makio, H.; Terao, H.; Iwashita, A.; Fujita, T. Chem. Rev. 2011, 111, 2363. (f) Delferro, M.; Marks, T. J. Chem. Rev. 2011, 111, 2450. (g) Redshaw, C.; Tang, Y. Chem. Soc. Rev. 2012, 41, 4484. (h) Organometallic Reactions and Polymerization; Osakada, K., Ed.; The Lecture Notes in Chemistry 85; Springer-Verlag: Berlin, 2014. (i) Metal−metal cooperative effects in olefin polymerization.3f. McInnis, J. P.; Delferro, M.; Marks, T. J. Acc. Chem. Res. 2014, 47, 2545. (4) Review articles, accounts for half-metallocenes; see: (a) Nomura, K.; Liu, J.; Padmanabhan, S.; Kitiyanan, B. J. Mol. Catal. A: Chem. 2007, 267, 1. (b) Nomura, K. Dalton Trans. 2009, 8811. (c) Nomura, K.; Liu, J. Dalton Trans. 2011, 40, 7666. (5) Selected review articles for living polymerization; see: (a) Coates, G. W.; Hustad, P. D.; Reinartz, S. Angew. Chem., Int. Ed. 2002, 41, 2236. (b) Domski, G. J.; Rose, J. M.; Coates, G. W.; Bolig, A. D.; Brookhart, M. Prog. Polym. Sci. 2007, 32, 30. (c) Kempe, R. Chem. Eur. J. 2007, 13, 2764. (d) Sita, L. R. Angew. Chem., Int. Ed. 2009, 48, 2464. (e) Miyake, G. M.; Chen, E.-Y. X. Polym. Chem. 2011, 2, 2462. (f) Valente, A.; Mortreux, A.; Visseaux, M.; Zinck, P. Coordinative Chain Transfer Polymerization. Chem. Rev. 2013, 113, 3836. H

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Organometallics (16) Reports concerning ethylene/1-hexene polymerization using titanium complexes containing tris(alkoxo)amine ligands: Sudhakar, P.; Amburose, C. V.; Sundararajan, G.; Nethaji, M. Organometallics 2004, 23, 4462. (b) Sudhakar, P.; Sundararajan, G. Macromol. Rapid Commun. 2005, 26, 1854. (17) Selected reports concerning syndiospecific styrene polymerization using titanatranes containing cyclopentadienyl ligands: (a) Kim, Y.; Hong, E.; Lee, M. H.; Kim, J.; Han, Y.; Do, Y. Organometallics 1999, 18, 36. (b) Kim, Y.; Han, Y.; Hwang, J.-W.; Kim, M. W.; Do, Y. Organometallics 2002, 21, 1127. (18) The catalytic activity at 90 °C was low (30 g-PE/mol-Zr·h): Jia, L.; Ding, E.; Rheingold, A. L.; Rhatigan, B. Organometallics 2000, 19, 963. (19) Takii, Y.; Inagaki, A.; Nomura, K. Dalton Trans. 2013, 42, 11632. (20) Davidson, M. G.; Doherty, C. L.; Johnson, A. L.; Mahon, M. F. Chem. Commun. 2003, 1832. (21) Structure reports including CIF files for [ZrCl{(O2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H2-6-CH2)N}][Me2Al(μ2OiPr)] (3), [ZrEt{(O-2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H2-6CH2)N}][Et2Al(μ2-OiPr)] (5), [ZriBu{(O-2,4-tBu2C6H2-6-CH2)2(μ2O-2,4-tBu2-C6H2-6-CH2)}N][iBu2Al(μ2-OiPr)] (6) are shown in the Supporting Information. (22) Additional data (NMR spectra) for thermolysis of [ZriBu{(O2,4-tBu2C6H2-6-CH2)2(μ2-O-2,4-tBu2-C6H2-6-CH2)N}][iBu2Al(μ2OiPr)] (6) in C6D6 and in toluene-d8 and reaction of styrene in C6D6 monitored by NMR spectra, and ORTEP drawing of 6 with all hydrogen atoms are shown in the Supporting Information. (23) The catalytic activity by Zr(OiPr)[(O-2,4-tBu2C6H2-6-CH2)3N] (1) at 100 °C under the same conditions (complex 0.10 μmol, MAO 3.0 mmol, 100 °C) was 6700 kg-PE/mol-Zr·h, and the activity decreased upon addition of 10 equiv of AliBu3 (5660 kg-PE/mol-Zr·h). On the basis of independent thermolysis experiment in toluene-d8 and C6D6 (shown in the Supporting Information),22 it seems likely that an increase in the activity at 120 °C would be due to formation of the other catalytically active species formed from 1 by liberation of AliBu3 from the bimetallic complex (6). (24) We highly appreciate Dr. Kazuo Takaoki (Sumitomo Chemical Co., Ltd.) for careful GPC analysis for the resultant polymers prepared by 1 − MAO catalyst (upon addition of Al alkyls), and by 3 −, 4 −, 6 − MAO catalysts. (25) SIR92: Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla, M.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435. (26) CrystalStructure 4.0: Crystal Structure Analysis Package; Rigaku and Rigaku Americas: Tokyo, Japan, 2000−2010; pp 196−8666. (27) SHELX97: Program for Crystal Structure Refinement; University of Göttingen: Göttingen, Germany, 1997. Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112.

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DOI: 10.1021/acs.organomet.5b01027 Organometallics XXXX, XXX, XXX−XXX