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Zirconium and Hafnium Complexes with Cycloheptane- or Cyclononane-Fused [OSSO]-Type Bis(phenolato) Ligands: Synthesis, Structure, and Highly Active 1‑Hexene Polymerization and Ring-Size Effects of Fused Cycloalkanes on the Activity Akihiko Ishii,*,† Keita Ikuma,† Norio Nakata,† Kazuaki Nakamura,† Hiroshi Kuribayashi,‡ and Kazuo Takaoki*,‡ †

Department of Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan ‡ Petrochemical Research Laboratory, Sumitomo Chemical Co., Ltd., 2-1 Kitasode, Sodegaura, Chiba 299-0295, Japan S Supporting Information *

ABSTRACT: Zirconium and hafnium complexes bearing cycloheptane- or cyclononane-fused [OSSO]-type bis(phenolato) ligands ([C7] and [C9], respectively) were prepared and subjected to the polymerization of 1-hexene as the precatalyst. The polymerizations produced poly(1-hexene)s with high activities and high isospecificity, where complexes bearing [C9] were more reactive than those bearing [C7]. Their activities were compared with those of the corresponding complexes bearing cyclohexane- and cyclooctanefused ligands ([C6] and [C8], respectively), which we reported previously, to show the order of activity [C8] > [C9] > [C7] > [C6]. The ring-size effect on the activity was investigated with the help of DFT calculations on active and dormant cationic zirconium species, π complexes of the active species with propene, and transition states for propene insertion into the Zr−C(iBu) bond. The order of activity speculated from the activation energy, that is the energy difference between the π complex and the corresponding transition state, was [C8] > [C7] > [C9] ≈ [C6]. However, calculations on active and dormant cationic zirconium complexes including [B(C6F5)4]− as the counteranion revealed that the active species are more stable than the dormant species by 9.1 kcal mol−1 for [C8] followed by 7.4 kcal mol−1 for [C9] and 3.1 kcal mol−1 for [C7] and, in contrast, that the active species with [C6] is less stable by 1.0 kcal mol−1 than the corresponding dormant species. Thus, the abundances of active species bearing [C6] and [C7] are reduced, which leads to the reversal of the order of [C7] and [C9] on the basis of activation energy to reproduce the order observed experimentally.

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INTRODUCTION

Chart 1. Octahedral Titanium and Zirconium Complexes 1− 4 Having [ONNO]- or [OSSO]-Type Bis(phenolato) Tetradentate Ligands

Group 4 metal catalysts for olefin polymerization have been attracting considerable attention from industry and academia since the advent of Ziegler−Natta catalysts1 and then metallocene (Kaminsky) catalysts.2 The metallocene and halfmetallocene catalysts are homogeneous and single-site catalysts, which enable stereoregular polymerization of α-olefins depending on the structure of ancillary metallocene ligands.3,4 In recent decades, so-called postmetallocene catalysts have also drawn much attention,3,5 concerning which, Kol reported dibenzyl zirconium precatalyst 1 bearing a tetradentate ligand, an [ONNO]-type bis(phenolato) ligand, in 2000 (Chart 1).6 The C2-symmetric octahedral precatalyst 1 with an activator performed isospecific and living polymerization of 1-hexene6 and homo- and copolymerization of propene,7 albeit with low activities (18 g mmol−1 h−1 of 1/B(C6F5)3 for 1-hexene6). Okuda8 and Kol9a independently developed Ti and Zr complexes 2 and 3, respectively, bearing [OSSO]-type © XXXX American Chemical Society

bis(phenolato) ligands with different chelate ring sizes for a central metal. These [OSSO]-type ligands feature the presence of soft sulfur atoms, in contrast with hard nitrogen donors in Received: August 1, 2017

A

DOI: 10.1021/acs.organomet.7b00586 Organometallics XXXX, XXX, XXX−XXX

Organometallics

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the [ONNO]-type ligand of 1;10 complexes 2 and 3 upon activation provide isotactic polystyrene8 and atactic poly(1hexene),9 respectively, with relatively high activities (1543 g mmol−1 h−1 for 2/methylaluminoxane (MAO) and 80 g mmol−1 h−1 for 3/B(C6F5)3). In 2009, we reported the synthesis of Zr complex 4 bearing an [OSSO]-type bis(phenolato) ligand and its application to 1hexene polymerization.11 The [OSSO]-type ligand in 4 features the fusion of a cyclooctane ring with Kol’s [OSSO]-type ligand in 3,9 and, upon activation with (Ph3C)[B(C6F5)4], 4 performed both high activity (2500 g mmol−1 h−1) and high isospecificity ([mmmm] > 95%) for the polymerization of 1hexene, which had not been achieved with similar catalytic systems so far reported. We have also reported applications of our [OSSO]-type ligand to the syntheses of group 412 and 513 metal and aluminum14 complexes, including their catalytic abilities. While it is clear that the cyclooctane ring in our [OSSO]type ligand plays a crucial role in both high activity and high isospecificity, the success raised a straightforward question: is the cyclooctane ring the best ring size or not? Thus, we started a study to explore the best ring size of fused cycloalkanes from the viewpoints of activity and isospecificity. Once some differences are observed depending on the ring size, elucidation of the ring-size effect would lead to a solution for a more root question: what is the role of the fused cycloalkane? Although analogous titanium and zirconium complexes 515 and 616 having cyclohexane-fused [ONNO]-type and [OSSO]-type ligands (Chart 2), respectively, have been reported to perform

Article

RESULTS AND DISCUSSION Synthesis of Zirconium and Hafnium Complexes and Structure Elucidations. trans-Cycloheptane-1,2-dithiol (7)18 was treated with 2 molar equiv of 3,5-di-tert-butyl-2hydroxybenzyl bromide (8)19 in the presence of triethylamine in THF at room temperature to give bis(phenol) [C7]H2 (9) in 63% yield (Scheme 1). In a similar manner, [C9]H2 (10) Scheme 1. Synthesis of trans-Cyclononane-1,2-dithiol (11) and Bis(phenol)s 9 ([C7]H2) and 10 ([C9]H2)

was prepared using trans-cyclononane-1,2-dithiol (11), prepared by reduction of trans-1,2-bis(thiocyanato)cyclononane,20 in 68% yield. X-ray crystallographic analyses confirmed their structures in the crystalline state (see Figures S1 and S2 in the Supporting Information). In [C7]H2 (9), the cycloheptane ring takes a twisted-chair conformation with two benzylthio substituents taking a gauche conformation (dihedral angle S− C−C−S = 89.7(1)°) similarly to those in [C8]H2 (S−C−C−S = 75.3(3)°)11 and in contrast with those in [C6]H2 taking axial positions (S−C−C−S = 167.1(2)°).17 In the case of [C9]H2 (10), the cyclononane ring takes a twist-boat-chair conformation and the two benzylthio arms take a conformation with a small S−C−C−S dihedral angle of 30.0(1)°. Dichloro zirconium and hafnium complexes [C7]ZrCl2 (12) and [C7]HfCl2 (13) were synthesized by the reaction of dilithium salt [C7]Li2, prepared by treatment of [C7]H2 (9) with BuLi in Et2O, with ZrCl4 or HfCl4, respectively, in high yields. Dichloro complexes 12 and 13 were converted to the corresponding dibenzyl complexes [C7]Zr(Bn)2 (14) and [C7]Hf(Bn)2 (15) in high yields by treatment with 2 molar equiv of PhCH2MgCl in Et2O (Scheme 2).8b,16b In a similar manner, [C9]ZrCl2 (16), [C9]HfCl2 (17), [C9]Zr(Bn)2 (18), and [C9]Hf(Bn)2 (19) were prepared. The structures of [C7]MX2 were elucidated by 1H and 13C NMR spectroscopic methods, which indicated that they have C2 symmetry in solution on the NMR time scale. Diastereotopic geminal benzyl protons in the [C7] ligand were observed as doublets with coupling constants of 14−15 Hz (12, δ 3.17 and 4.34 (Jgem = 14 Hz); 13, δ 3.20 and 4.37 (Jgem = 15 Hz); 14, δ 3.18 and 3.53 (Jgem = 15 Hz); 15, δ 3.16 and 3.44 (Jgem = 14 Hz)). In cases of dibenzyl complexes [C7]Zr(Bn)2 (14) and [C7]Hf(Bn)2 (15), the geminal benzyl protons in Bn ligands were observed as two doublets with coupling constants of 10 and 12 Hz, respectively. Similar patterns were observed for the [C9]MX2 series (16−19), indicating their C2-symmetric structures in solution on the NMR time scale. Single crystals suitable for X-ray crystallography were obtained for [C7]ZrCl2 (12), [C7]HfCl2 (13), [C7]Zr(Bn)2 (14), and [C9]ZrCl2 (16),

Chart 2. Octahedral Titanium, Zirconium, and Hafnium Complexes 5, 6, and [Cn]MX2 Having Cycloalkane-Fused [ONNO]- or [OSSO]-Type Bis(phenolato) Tetradentate Ligands

stereospecific homopolymerization and copolymerization of olefins, the ring-size effect in these ligands has never been reported so far. We reported previously on the polymerization of 1-hexene with a zirconium complex bearing a cyclohexanefused [OSSO]-type ligand, which resulted in less activity and slightly less isoselectivity in comparison with the cyclooctanefused complex 4.17 In this paper, we report the syntheses of zirconium and hafnium complexes having cycloheptane- and cyclononanefused [OSSO]-type ligands and their catalytic activities in 1hexene polymerization and compare their activities with those of the corresponding complexes having cyclohexane- and cyclooctane-fused ligands; as explicit differences in activity were observed there, the cause is elucidated on the basis of DFT calculations. Hereafter, we abbreviate those zirconium and hafnium complexes as [Cn]MX2 (n = 6−9; M = Zr, Hf; X = Cl, PhCH2 (Bn)), where [Cn] indicates n-membered cycloalkanefused [OSSO]-type bis(phenolato) ligands (Chart 2). B


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Organometallics Scheme 2. Synthesis of [C7]MX2 and [C9]MX2 (M = Zr, Hf; X = Cl, Bn)a

a

Conditions: (a) BuLi (2 equiv), Et2O, room temperature; (b) MCl4 (M = Zr, Hf), Et2O, −78 °C; (c) PhCH2MgCl (2 equiv), Et2O, −78 °C to room temperature.

and their structures were unambiguously determined. Figures 1 and 2 depict ORTEPs of [C7]Zr(Bn)2 (14) and [C9]ZrCl2

Figure 2. ORTEP of [C9]ZrCl2 (16) (50% thermal ellipsoids). One of two independent molecules is shown, and hydrogen atoms and two solvated toluene molecules are omitted for clarity. Selected bond lengths (Å) and bond angles (deg): Zr1−O1 1.968(2), Zr1−O2 1.981(2), Zr1−S1 2.734(1), Zr1−S2 2.710(1), Zr1−Cl1 2.405(1), Zr1−Cl2 2.408(1), S1−C1 1.830(4), S1−C10 1.839(3), S2−C2 1.841(4), S2−C25 1.833(4), C1−C2 1.530(5), O1−Zr1−O2 159.3(1), S1−Zr1−S2 73.89(3), Cl1−Zr1−Cl2 109.11(4), S1−C1− C2−S2 61.8(3).

coordination of the Bn ligand as was observed for previously reported dibenzyl zirconium complexes.11,16b,21 1-Hexene Polymerization. Experiments for the polymerization of 1-hexene (eq 1) were carried out as follows: a

Figure 1. ORTEP of [C7]Zr(Bn)2 (14) (50% thermal ellipsoids). Hydrogen atoms and a solvate toluene molecule are omitted for clarity. Selected bond lengths (Å), bond angles (deg), and atomic distances (Å): Zr1−S1 2.803(1), Zr1−S2 2.789(1), Zr1−O1 1.999(1), Zr1−O2 1.993(1), Zr1−C38 2.308(2), Zr1−C45 2.325(2), S1−C1 1.824(2), S1−C8 1.838(2), S2−C2 1.833(2), S2−C23 1.822(2), C1− C2 1.530(3), O1−Zr1−O2 157.90(5), S1−Zr1−S2 72.49(1), C38− Zr1−C45 114.53(7), Zr1−C38−C39 92.4(1), Zr1−C45−C46 118.7(1), S1−C1−C2−S2 73.0(1), Zr1···C39 2.787(2), Zr1···C46 3.304(2).

precatalyst [Cn]MX2 was treated with an activator, and then 3.0 g of 1-hexene was added to the mixture. As the activator, an equimolar amount of B(C6F5)3 or (Ph3C)[B(C6F5)4] was employed for [C7]Zr(Bn)2 and 250 molar equiv of dried methylaluminoxane (dMAO) for [Cn]MCl2 (n = 7, 9; M = Zr, Hf). The results are collected in Tables 1 and 2 together with previously reported data of [C6]Zr(Bn)2 and [C8]MX2 (M = Zr, Hf; X = Bn, Cl) for comparison. The polymerization of 1-hexene with the catalytic system [C7]Zr(Bn)2/B(C6F5)3 for 10 min produced 1.2 g of poly(1hexene) with an activity of 370 g mmol−1 h−1 and high isospecificity ([mmmm] > 95%) (Table 1, entry 2). The activity is comparable to that of [C6]Zr(Bn)2/B(C6F5)3 (entry 117) and less than that of [C8]Zr(Bn)2/B(C6F5)3 (entry 311), while the weight-averaged molecular weight (Mw) of 86000 is larger than those of [C6]Zr(Bn)2/B(C6F5)3 and [C8]Zr(Bn)2/ B(C6F5)3. In the case of (Ph3C)[B(C6F5)4] as the activator, the order of activity is [C6]Zr(Bn)2 < [C7]Zr(Bn)2 < [C8]Zr(Bn)2 (Table 1, entries 4−6). The catalytic system of [C7]Zr(Bn)2/ (Ph3C)[B(C6F5)4] (entry 5, 520 g mmol−1 h−1) is 1.5 times

(16) (see Figures S3 and S4 in the Supporting Information for 12 and 13); they took a distorted-octahedral geometry around the central metals with cis-α (Λ*,S*,S*) configuration; two sulfur atoms as well as two Cl or Bn ligands were located cis to the central metal, and two oxygen atoms were coordinated trans to the central metal. In dibenzyl zirconium complex 14, the angle Zr1−C38−C39 in a Bn ligand was much narrower (92.4(1)°), giving a short atomic distance of 2.787(2) Å between Zr1 and C39, in comparison to the other (Zr−C45− C46 118.7(1)°; Zr1···C46 3.304(2) Å), suggesting a η2 C


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Organometallics

Table 1. Polymerization of 1-Hexene with Dibenzyl Zirconium or Hafnium Complexes [Cn]M(Bn)2 (n = 6−8, M = Zr, Hf) upon Activation with B(C6F5)3 or Ph3C[B(C6F5)4]a entry

[Cn]

M

activator

time (min)

yield (g)

activityb

Mw (g mol−1)

PDIc

[mmmm]d (%)

ref

e

[C6] [C7] [C8] [C6] [C7] [C8] [C7] [C8]

Zr Zr Zr Zr Zr Zr Hf Hf

B(C6F5)3 B(C6F5)3 B(C6F5)3 Ph3C+ j Ph3C+ j Ph3C+ j B(C6F5)3 B(C6F5)3

15 10 5 15 10 5 30 10

1.8 1.2 2.8 1.8 1.8 2.9 1.7 2.0

370 370 >850i 370 520 >870i 170 610

40500 86000 43000 44000 88000 41000 n.d.k 191000

1.9 1.9 1.9 1.9 1.9 2.1 n.d.k 1.8

93 >95 >95 93 >95 >95 >95 >95

17

1 2e 3f 4e 5g 6f 7g 8h

11 17 11 12c

Conditions unless specified otherwise: 0.020 mmol of [Cn]Zr(Bn)2 and an activator, and 3.0 g (35.6 mmol) of 1-hexene at 25 °C. bIn units of g (mmol of precat.)−1 h−1. cMw/Mn determined by GPC (polystyrene standards). dDetermined by 13C{1H} NMR spectroscopy. eIn toluene (1 mL) and hexane (5 mL). fIn benzene (5 mL) and hexane (1 mL). gIn toluene (5 mL) at 33 °C, hIn benzene (1 mL). iThe polymerization had been completed before quenching. jPh3C+ = (Ph3C)[B(C6F5)4]. kn.d. = not determined. a

Table 2. Polymerization of 1-Hexene with Dichloro Complexes [Cn]MCl2 (M = Zr or Hf) upon Activation with dMAOa entry

[Cn]

M

temp (°C)

time (min)

yield (g)

activityb

Mw (g mol−1)

PDIc

[mmmm]d (%)

1 2 3f 4 5 6 7 8

[C7] [C7] [C8] [C9] [C7] [C7] [C8] [C9]

Zr Zr Zr Zr Hf Hf Hf Hf

0 25 25 25 0 25 25 25

10 5 3 5 240 30 10 30

1.17 0.71 1.81 0.86 1.69 0.76 0.35 1.0

3500 4300 18100 5200 210 760 1050 1000

192000 n.d.e 40000 52000 413000 225000 58600 37000

1.8 n.d.e 1.9 1.9 1.8 2.4 1.6 2.2

>95 >95 95 >95 >95 >95 >95 >95

ref

12f

12d

a

Conditions unless specified otherwise: 0.0020 mmol of [Cn]MCl2 and 0.50 mmol of activator in toluene (5 mL), and 3.0 g (35.6 mmol) of 1hexene at 25 °C for 5 min. bIb units of g (mmol of precat.)−1 h−1. cMw/Mn determined by GPC (polystyrene standards). dDetermined by 13C{1H} NMR spectroscopy. en.d. = not determined. fIn toluene (1 mL).

Scheme 3. (a) Cossee−Arlman Mechanism and (b) Modified Green−Rooney Mechanism22

more active than that of [C7]Zr(Bn)2/B(C6F5)3 (entry 2), and the Mw values of produced poly(1-hexene)s are comparable (88000 and 86000, respectively). Their PDI values (1.9) (entries 2 and 5) indicate that they worked under the single-site catalysis similarly to the cases of [C6]Zr(Bn)2 and [C8]Zr(Bn)2.11,17 The activity of [C7]Hf(Bn)2/B(C6F5)3 (Table 1, entry 7) was substantially small (170 g mmol−1 h−1) in comparison with that of [C8]Hf(Bn)2/B(C6F5)3 (610 g mmol−1 h−1, entry 812c). In these cases, high isotacticity ([mmmm] > 95%) of poly(1hexene)s was observed. When [C7]ZrCl2 (Table 2, entries 1 (0 °C) and 2 (25 °C)) was used with dMAO, the activity increased to 3500 and 4300 g mmol−1 h−1, respectively, the latter of which is 8−12 times larger than those when [C7]Zr(Bn)2 was used as the precatalyst with B(C6F5)3 or (Ph3C)[B(C6F5)4]. [C9]ZrCl2/dMAO showed a higher activity of 5200 g mmol−1 h−1 (entry 4) than [C7]ZrCl2/dMAO. These two catalytic systems gave isotactic poly(1-hexene)s with relatively large Mw values, but their activities were much lower than that of [C8]ZrCl2/dMAO (18100, entry 3).12f

In the case of dichloro hafnium complexes, the activities of [C7]HfCl2/dMAO and [C9]HfCl2/dMAO decreased to 760 g mmol−1 h−1 (Table 2, entry 6) and 1000 g mmol−1 h−1 (entry 8), respectively, in comparison with those of the corresponding dichloro zirconium complexes. Interestingly, Mw of the poly(1hexene) obtained in entry 6 is very large (225000) in comparison with the case of [C8]HfCl2/dMAO (58600, entry 7),12d and in contrast, Mw in entry 8 was conspicuously small (37000). Whereas the PDI of [C7]HfCl2/dMAO is somewhat large (2.4) (entry 6), the polymerization carried out at 0 °C provided poly(1-hexene) with a smaller PDI (1.8), larger Mw (413000), and lower activity (210 g mmol−1 h−1) (entry 5), suggesting that β-hydrogen elimination is suppressed by conducting polymerization at 0 °C. Taking the activity data collected in Tables 1 and 2 into consideration, we can conclude that the order of activity depending on ligands [Cn] is qualitatively [C8] > [C9] > [C7] > [C6], which is almost independent of the central metals (Zr or Hf), other ligands (Bn or Cl), and activators (B(C6F5)3, (Ph3C)[B(C6F5)4], or dMAO). D


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Organometallics

Scheme 4. Active Cationic Species [[Cn]Zr(iBu)]+, π-Complex with Propene [[Cn]Zr(iBu)(C3H6)]+, and Transition State [[Cn]Zr(iBu)(C3H6)]+⧧

Computational Study. Cossee−Arlman and modified Green−Rooney mechanisms have been widely accepted for the coordination polymerization of olefins;22 in the Cossee− Arlman mechanism an olefin coordinates on a cationic metal center and then inserts into the metal−carbon(polymer) bond, and the modified Green−Rooney mechanism includes α- and γ-agostic interactions in the catalytic cycle (Scheme 3). The agostic interactions are three-center−two-electron interactions between an electron-deficient metal center and a neighboring C−H bond and play an important role not only for the stereocontrol of olefin insertion but also for the stabilization of intermediates and transition states.22−25 In this theoretical elucidation, we focus our consideration on activation energies of the stage of olefin insertion (Scheme 4). In the model compounds, isobutyl, propene, and [B(C6F5)4]− were employed as polymer chain, α-olefin, and counteranion, respectively. We considered (1) stabilization energies of cationic zirconium complexes [[Cn]Zr(iBu)]+ by coordination of propene to give π complexes [[Cn]Zr(iBu)(C3H6)]+, (2) energies for 1,2-insertion of propene to lead to the corresponding transition states [[Cn]Zr(iBu)(C3H6)]+⧧, and (3) an equilibrium between active and dormant cationic species, to interpret the ring-size effect of [Cn] ligands on the order of activity observed experimentally. In the cases of (1) and (2), the structure optimizations were performed without effects of solvent or counteranion [B(C6F5)4]−,23 as Coussens and Linnolahti reported notable similarity of energy diagrams for the insertion of ethene to [Cp2ZrMe]+ with or without [B(C6F5)4]− as the counteranion after the formation of the ethene π complexes.26 In this computational study, stabilization by α- and β-agostic interactions was considered for three zirconium complexes in Scheme 4,27 and γ-agostic interaction and interconversion among them were not taken into consideration.28,29 β-Agostic Interactions in Optimized Structures of Cationic Zirconium Complexes and the π Complexes with Propene. The insertion of propene into the Zr−isobutyl bond starts from its π coordination on the cationic Zr center. To obtain stabilization energies due to the π coordination, structure optimizations were performed for counteranion-free cationic species and the corresponding π complexes with propene. Figure 3 depicts the optimized structures of [[C7]Zr(iBu)]+ and [[C7]Zr(iBu)(C3H6)]+ as the representatives (see also Figure S5 in the Supporting Information for others). In the four cationic species [[Cn]Zr(iBu)]+ (n = 6−9), their geometries around the zirconium atom are very similar to one another (see Table S1 in the Supporting Information). The βC−H bond in the iBu group is located on the pseudoplane

Figure 3. Optimized structures of (a) counteranion-free cation [[C7]Zr(iBu)]+ and (b) π complex [[C7]Zr(iBu)(C3H6)]+. Hydrogen atoms except for the β-H of iBu are omitted for clarity.

consisting of Zr, α-C of iBu, and two sulfur atoms, and the Zr−α-C−β-C bond angle is characteristically narrow (89.21− 89.44°), suggesting the presence of a β-agostic interaction between the cationic zirconium center and the β-C−H bond.22 Natural bond orbital (NBO) analysis30,31 or quantum theory of atoms in molecules (QTAIM) analysis24,31c,32 have been employed for the analysis of chemical bonding motifs involving agostic interactions. We chose NBO calculations to compute second-order perturbation energies (E(2)) from the β-C−H σ bond as the donor to vacant lone pair orbitals (LP*) of the zirconium atom as the acceptors in addition to Wiberg bond indices (WBI) for Zr···H and Zr···C. The results are summarized in Table 3 together with the geometries for the part of β-agostic interaction. Wiberg bond indices for Zr···H and Zr···C are in the narrow ranges of 0.1163−0.1186 and 0.1338−0.1388, respectively. Interestingly, in the second-order perturbation theory analysis, an exceptionally large stabilization energy (E(2)) was obtained for [[C8]Zr(iBu)]+ for the interaction of the β-C−H σ bond with vacant Zr 4d orbitals (171.44 kcal mol−1), implying that [[C8]Zr(iBu)]+ undergoes a large stabilization by the β-agostic interaction in comparison with others. In π complexes [[Cn]Zr(iBu)(C3H6)]+, the C1 of propene sits on the pseudoplane formed by Zr, S1, S2, and α-C. The dihedral angle α-C−Zr−C1−C2 was about 54° (Figure 4; see also Table S2 in the Supporting Information for relevant geometrical parameters). The distances between Zr and C1 and C2 of propene decrease in the order [C9] > [C6] > [C7] > E


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Organometallics

Table 3. Second-Order Perturbation Energies (E(2)) and Wiberg Bond Indices (WBI) Computed by NBO Calculationsa and Relevant Geometries for Counteranion-Free Cations [[Cn]Zr(iBu)]+ b NBO calculation WBI [Cn] [C6] [C7]

[C8]

[C9]

E(2)c (kcal mol−1) LP*(1) LP*(7) LP*(1) LP*(2) LP*(7) LP*(1) LP*(2) LP*(7) LP*(1) LP*(7)

17.39 40.35 14.10 36.66 16.98 11.77 171.44 17.43 13.73 24.38

geometry

Zr···H

Zr···β-C

Zr···β-H (Å)

Zr···β-C (Å)

β-C−H (Å)

Zr−α-C−β-C (deg)

0.1186

0.1388

2.233

2.694

1.157

89.31

0.1163

0.1375

2.242

2.698

1.156

89.44

0.1169

0.1385

2.237

2.694

1.156

89.26

0.1176

0.1338

2.235

2.693

1.157

89.21

a

At the B3LYP/6-31+G(d,p) (C, H, O, S) and LanL2DZ (Zr) level for structures optimized at the B3LYP/LanL2DZ level. bAt the B3LYP/ LanL2DZ level. cLP*(1), 4dx2−y2; LP*(2), 4dxy + 4dxz + 4dyz + 4dx2−y2 + 4dz2 ; LP*(7), 5py.

slightly larger than that with [C8]; the Zr···β-H distance is shortest in [C9] (2.277 Å) and longest in [C8] (2.359 Å) ([C8] > [C6] > [C7] > [C9]). A similar tendency is obtained in Zr···β-C distances ([C8] (2.784 Å) > [C6] = [C7] ≈ [C9] (2.741 Å)), but the difference is smaller. π complexes with [C6], [C7], and [C9] have almost the same β-C−H bond lengths (1.142−1.143 Å), which are slightly stretched in comparison with that with [C8] (1.135 Å). Results of NBO calculations on π complexes [[Cn]Zr(iBu)(C3H6)]+ are summarized in Table 4. [[C8]Zr(iBu)(C3H6)]+ has the smallest WBI values for Zr···β-H (0.0942) and Zr···β-C (0.1230), and [[C9]Zr(iBu)(C3H6)]+ has the largest values (0.1104 and 0.1312, respectively) of the four, suggesting that the contribution of the β-agostic interaction increases in the order [C8] < [C6] ≈ [C7] < [C9]. Concerning the part of πcoordinated propene, the second-order perturbation theory analysis shows that E(2) between the propene π bond and Zr LP*(1) is remarkably large in [[C8]Zr(iBu)(C3H6)]+ (47.56 kcal mol−1) in comparison with others (13.19−27.56 kcal mol−1). Thus, it seems that the π coordination of propene is relatively large for [[C8]Zr(iBu)(C3H6)]+ in the four π complexes, which is in contrast to the smallest β-agostic interaction mentioned above. Thus, the stabilization in the π complexes seems to be due to the interplay of the β-agostic interaction and the π coordination.

Figure 4. Relevant part of β-agostic interaction and π-coordination of propene in π complexes [[Cn]Zr(iBu)(C3H6)]+.

[C8] and [C6] > [C8] > [C7] > [C9], respectively. β-Agostic interactions remain in the π complexes, as suggested by short Zr···β-C−H distances and narrow Zr−α-C−β-C bond angles. Their geometrical parameters imply that the β-agostic interactions in π complexes with [C6], [C7], and [C9] are

Table 4. NBO Calculations: Second-Order Perturbation Theory Analysis (E(2)/kcal mol−1) and Wiberg Bond Indices (WBI) for π Complexes [[Cn]Zr(iBu)(C3H6)]+ a β-agostic interaction

π coordination WBI

[Cn] [C6] [C7] [C8] [C9]

E(2)b (kcal mol−1) LP*(2) LP*(8) LP*(2) LP*(8) LP*(2) LP*(8) LP*(2) LP*(8)

18.71 21.21 18.26 28.88 16.63 15.81 18.40 18.43

WBI

β-H

β-C

0.1083

0.1310

0.1089

0.1302

0.0942

0.1230

0.1104

0.1312

E(2)b (kcal mol−1) LP*(1) LP*(6) LP*(1) LP*(6) LP*(1) LP*(6) LP*(1) LP*(6)

27.56 21.67 16.76 13.19 47.56 18.80 16.16 14.73

C1

C2

0.1860

0.0888

0.1822

0.0897

0.1910

0.0867

0.1797

0.0910

a At the B3LYP/6-31+G(d,p) (C, H, O, S) and LanL2DZ (Zr) level for structures optimized at the B3LYP/LanL2DZ level. bLP*(1), 4dyz; LP*(2), 4dx2−y2; LP*(6), 5pz; LP*(8), 5py.

F


Article

Organometallics

4.5−4.6 kcal mol−1 than the sum of [[Cn]Zr(iBu)]+ and propene (Table 5). Thus, the activation energies (ΔE⧧), the energy differences between [[Cn]Zr(iBu)(C3H6)]+ and [[Cn]Zr(iBu)(C3H6)]+⧧, increase depending on ligands [Cn] in the order [C8] (7.1 kcal mol−1) < [C7] (8.6 kcal mol−1) < [C9] (9.9 kcal mol−1) ≈ [C6] (10.0 kcal mol−1). This order is consistent qualitatively with the order experimentally observed for the catalytic systems with [C8], [C7], and [C6]. However, the calculations do not reproduce the effect of [C9] on the activity being much higher than those of [C7] and [C6] and less than that of [C8]. Thus, we next considered the possibility of the presence of dormant species for cations [[Cn]Zr(iBu)]+. Dormant Species in Equilibrium with Active Species. In the case of cationic Zr complexes bearing [ONNO]-type bis(phenoxy-amine) ligands, it was proposed that cis-(N,N)-cis(O,O) isomers are inactive to olefins and are more stable than the corresponding cis-(N,N)-trans-(O,O) isomers.33 We obtained similar structures having an energy minimum as the dormant [[Cn]Zr(iBu)]+. As shown in Figure 6 (see Figure S7

Stabilization Energies of Cationic Zirconium Complexes by Coordination of Propene. The calculated stabilization energies by π coordination of propene on the cationic Zr center are given in Table 5. The stabilization energy Table 5. Energy Differences (ΔE) and Activation Energies (ΔE⧧) for π Complexes [[Cn]Zr(iBu)(C3H6)]+ and Transition States [[Cn]Zr(iBu)(C3H6)]+⧧ Relative to ([[Cn]Zr(iBu)]+ + propene)a ΔE (kcal mol−1) i

a

[Cn]

[[Cn]Zr( Bu)] + propene

[C6] [C7] [C8] [C9]

0 0 0 0

+

[[Cn]Zr(iBu) (C3H6)]+

[[Cn]Zr(iBu) (C3H6)]+‡

ΔE‡ (kcal mol−1)

−5.5 −4.0 −2.5 −5.4

4.5 4.6 4.6 4.5

10.0 8.6 7.1 9.9

At the B3LYP/LanL2DZ level.

is largest for [[C6]Zr(iBu)(C3H6)]+ (−5.5 kcal mol−1) and then decreases in the order [[C9]Zr(iBu)(C3H6)]+ (−5.4), [[C7]Zr(iBu)(C3H6)]+ (−4.0), and [[C8]Zr(iBu)(C3H6)]+ (−2.5). It seems that the reason for the smallest stabilization energy for [[C8]Zr(iBu)(C3H6)]+ is the large loss of E(2) by a β-agostic interaction in the free cation (171.44 kcal mol−1, Table 3), which is not sufficiently compensated by the π coordination of propene. Activation Energies of the 1,2-Insertion of Propene. An optimized structure of the transition state for [[C7]Zr+(iBu)(C3H6)]‡ is depicted in Figure 5 (see Figure S6 in the

Figure 6. Optimized structure of dormant [[C7]Zr(iBu)]+.

in the Supporting Information), these dormant species have distorted-square-pyramidal geometries possessing two cis sulfur atoms and two cis oxygen atoms at the basal positions, the central Zr atom located above the basal plane, and an isobutyl group at the apical position; there is no significant agostic interaction between any C−H bonds and the central Zr center and, more importantly, approach of propene from any directions is effectively hindered. A similar cis-(O,O)-cis-(S,S) configuration of an [OSSO]-type ligand was observed for the neutral, six-coordinated dichloro titanium complex [TiCl2(OC6H2-tBu2-4,6)2{S(CH2)3S}] in low-temperature NMR and in the crystalline state.8b,c,34,35 In addition, cis-(N,N)-cis(O,O) configurations of [ONNO]-type ligands in Ti,36 Zr,37 Hf,37 and V38 complexes have been reported. The DFT calculations showed that counteranion-free dormant [[Cn]Zr(iBu)]+ were more stable than the corresponding active trans-(O,O)-cis-(S,S) [[Cn]Zr(iBu)]+ mentioned above by 5.4−5.5 kcal mol−1 for all cases (Table 6). However, the calculations including [B(C6F5)4]− as the counteranion showed that active [[Cn]Zr(iBu)]+[B(C6F5)4]− of n = 7−9 were more stable than the corresponding dormant species by 3.1−9.1 kcal mol−1 and, in definite contrast, active [[C6]Zr(iBu)]+[B(C6F5)4]− is less stable than dormant species by 1.0 kcal mol−1 (Table 6).39 Table 6 also shows the relevant atomic distances between the Zr atom and the anionic center B atom (Zr···B) and between

Figure 5. Optimized structure of [[C7]Zr(iBu)(C3H6)]+‡. Hydrogen atoms except α-hydrogens of iBu are omitted for clarity.

Supporting Information for the others). The four transition states [[Cn]Zr(iBu)(C3H6)]+⧧ have very similar geometries; the four-membered rings including Zr are planar and are stabilized by the α-agostic interaction due to an α-C−H bond of the iBu group (see Table S3 in the Supporting Information). NBO calculations support the α-agostic interactions to similar extents (see Table S4 in the Supporting Information). [[Cn]Zr(iBu)(C3H6)]+⧧ (n = 6−9) are higher in energy by G


Article

Organometallics

ratios of active [[C6]Zr(iBu)]+[B(C6F5)4]− and [[C7]Zr(iBu)]+[B(C6F5)4]− to the corresponding dormant species are greatly reduced, in particular for the former, in comparison with those of [[C8]Zr(iBu)]+[B(C6F5)4]− and [[C9]Zr(iBu)]+[B(C6F5)4]−. This seems to be an important reason for the partial reversal of the order of ligands ([C8] > [C7] > [C9] ≈ [C6]) on the basis of activation energies to lead to the order in harmony with experimentally observed order, [C8] > [C9] > [C7] > [C6]. Figure 8 summarizes the relative energy diagrams for active and dormant species with a counteranion [[Cn]Zr(iBu)]+[B(C6F5)4]−, counteranion-free active species [[Cn]Zr(iBu)]+, π complexes [[Cn]Zr(iBu)(C3H6)]+, and transition states [[Cn]Zr(iBu)(C3H6)]+⧧.40

Table 6. Energy Difference (ΔE) and Zr···B and Zr···F Distances for Dormant and Active [[Cn]Zr(iBu)]+[B(C6F5)4]− a atomic distance ΔE (kcal/mol)

a

b

dormant species

active species

[Cn]

without [B(C6F5)4]−

with [B(C6F5)4]−

Zr···B

Zr···F

Zr···B

Zr···F

[C6] [C7] [C8] [C9]

−5.5 −5.4 −5.4 −5.4

−1.0 3.1 9.1 7.4

9.146 9.873 11.712 11.027

5.482 5.168 5.799 5.796

7.956 7.973 7.974 7.983

2.466 2.473 2.479 2.479

At the B3LYP/LanL2DZ level. bΔE = E(dormant) − E(active).

■

CONCLUSION The polymerization of 1-hexene with the Zr(IV) and Hf(IV) complexes having cycloheptane- or cyclononane-fused [OSSO]-type bis(phenolate) ligands ([C7] and [C9], respectively) as precatalysts produced highly isotactic poly(1hexene)s. They showed high activities, as did their analogous complexes having cyclohexane- or cyclooctane-fused [OSSO]type ligands ([C6] and [C8], respectively). The order of the activities was dependent on the ring size of fused cycloalkanes ([C8] > [C9] > [C7] > [C6]). The ring-size effect was elucidated with DFT calculations. Conclusively, in addition to activation energies in the stage of α-olefin insertion, the equilibrium between active trans-(O,O)-cis-(S,S) and dormant cis-(O,O)-cis-(S,S) cationic species [[Cn]Zr(iBu)]+ should be taken into consideration. Interestingly, whereas the dormant species were more stable than the active species in the absence of counteranion for all cases, the calculations employing [B(C6F5)4]− as the counteranion exhibited that the relative stabilities were influenced greatly due to the steric hindrance of fused cycloalkanes that destabilizes the dormant species by separating the counteranion from the cationic center. The present study clarifies that not only the neighborhood but also “the back side” of active sites can play a crucial role in activity and suggests that the design of ligands and counteranions along the line can contribute to the development of new catalysts for the coordination polymerization of α-olefin.

the Zr atom and the nearest F atom in the counteranion (Zr··· F) (see also Table S25 in the Supporting Information). Figure 7 shows optimized structures of active and dormant [[C6]Zr-

■

Figure 7. Optimized structures of active (a) [[C6]Zr(iBu)]+[B(C6F5)4]− and (b) [[C8]Zr(iBu)]+[B(C6F5)4]− and dormant (c) [[C6]Zr(iBu)]+[B(C6F5)4]− and (d) [[C8]Zr(iBu)]+[B(C6F5)4]−. Hydrogen atoms are omitted for clarity.

EXPERIMENTAL SECTION

General Considerations. All manipulations of air- and/or moisture-sensitive compounds were performed either using standard Schlenk-line techniques or in a UN-650F glovebox under an inert atmosphere of argon. Anhydrous hexane, toluene, Et2O, and THF were further dried by passage through columns of activated alumina and supported copper catalyst supplied by Hansen & Co., Ltd. 1Hexene and deuterated benzene (benzene-d6, C6D6) were dried and degassed over a potassium mirror by the freeze−thaw cycle prior to use. Other chemicals and gases were used as received. Column chromatography was performed using neutral Silica Gel 60 N (Kanto Chemical Co., Ltd.). Melting points were determined on a Mel-Temp capillary tube apparatus and are uncorrected. 1H (500 or 400 MHz) and 13C (125.8 or 100.7 MHz) spectra were obtained with Bruker Avance500, Bruker DRX400, or Bruker Avance400 spectrometers, respectively. Elemental analyses were performed at Molecular Analysis and Life Science Center of Saitama University. The molecular weights and molecular weight distributions of poly(1-hexene)s were determined against polystyrene standard by gel permeation chromatography with THF as the solvent on a HLC-8229 GPC apparatus (Tosoh Corporation) of the laboratory of Dr. Zhaomin Hou (RIKEN Advanced Science Institute) at room temperature, a HLC8220 GPC apparatus (Tosoh Corporation) using a TSK-GEL SUPERHZM-HZM-H column at 40 °C, or a SCL-10AVP/LC-

(iBu)]+[B(C6F5)4]− and [[C8]Zr(iBu)]+[B(C6F5)4]− (see also Figure S8 and Table S6 in the Supporting Information). In the dormant species, atomic distances Zr···B and Zr···F are in the ranges 9.146−11.712 and 5.168−5.799 Å, respectively, corresponding to outer-sphere ion pairs.26 There are substantial differences in the atomic distances depending on [Cn] ligands, showing that [C8] is most effective to push away [B(C6F5)4]− from the cationic Zr center, followed by [C9], [C7], and [C6]. It is apparent that dormant [[Cn]Zr(iBu)]+[B(C6F5)4]− becomes unstable as the counteranion is apart from the cationic center. On the other hand, in active [[Cn]Zr(iBu)]+[B(C6F5)4]−, the differences in Zr···B (7.956−7.983) and Zr···F (2.466−2.479 Å) are very small, corresponding to an innersphere ion pair;26 NBO calculations showed large WBI values for Zr···F (0.2197−0.2205) and E(2) for the interaction between a lone pair of electrons on F and vacant Zr orbitals (46.39−46.92 kcal mol−1) as well as β-agostic interactions (see Table S7 in the Supporting Information). Thus, equilibrium H


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Organometallics

Figure 8. Relative energy diagrams for all species considered. by GPC); 1H NMR (500 MHz, CDCl3) δ 1.41−1.50 (m, 2H), 1.50− 1.59 (m, 2H), 1.59−1.69 (m, 4H), 1.74−1.83 (m, 2H), 2.16−2.23 (m, 2H), 2.28−2.35 (m, 2H), 3.57−3.58 (m, 2H); 13C NMR (125.8 MHz, CDCl3) δ 22.40 (CH2), 22.43 (CH2), 23.6 (CH2), 31.0 (CH2), 52.3 (CH), 110.4 (C). Anal. Calcd for C11H16N2S2: C, 54.96; H, 6.71; N, 11.65. Found: C, 55.01; H, 6.66; N, 11.65. trans-Cyclononane-1,2-dithiol (11). A solution of trans-1,2bis(thiocyanato)cyclononane (586 mg, 2.44 mmol) in hexane (20 mL) and toluene (20 mL) was added to DIBAH (1.02 M hexane solution, 9.6 mL, 9.8 mmol) at −78 °C, and the mixture was stirred for 2 h at this temperature. Then, a suspension of LiAlH4 (215 mg, 5.67 mmol) in ether (30 mL) was added at −78 °C, and the mixture was warmed to 0 °C and stirred for 10 h. The reaction was quenched by addition of water and 1 M hydrochloric acid, and the mixture was extracted with diethyl ether. The organic layer was washed with water, dried over anhydrous sodium sulfate, and evaporated to dryness under reduced pressure. The residue was subjected to column chromatography (silica gel, dichloromethane/hexane 2/1) to give trans-cyclononane-1,2dithiol (11; 460 mg, 99%) as a colorless oil: 1H NMR (500 MHz, CDCl3) δ 1.38−1.66 (m, 10H), 1.87−2.01 (m, 4H), 2.09−2.14 (m, 2H), 3.06−3.12 (m, 2H). Anal. Calcd for C9H18S2: C, 56.78; H, 9.53. Found: C, 57.01; H, 9.46. trans-1,2-Bis(2-hydroxy-3,5-di-tert-butylbenzylsulfanyl)cyclononane ([C9]H2, 10). A mixture of trans-cyclononane-1,2dithiol (11; 514 mg, 2.70 mmol) and 3,5-di-tert-butyl-2-hydroxybenzyl bromide (8; 1.75 g, 5.83 mmol) was dissolved in THF (35 mL) under argon. To the solution cooled at 0 °C was added triethylamine (0.8 mL, 0.58 mg, 5.7 mmol), and the mixture was stirred for 1 h at 0 °C and overnight at room temperature. The precipitates that formed were removed by filtration, and the filtrate was concentrated under reduced pressure. The oily yellow residue was dissolved in ether, and aqueous ammonium chloride was added. The organic layer was washed with water, dried over anhydrous sodium sulfate, and evaporated to dryness under reduced pressure. The residue was subjected to column chromatography (silica gel, hexane/dichloromethane 1/1) to give [C9]H2 10 (1.15 g, 68%) as colorless crystals: mp 148−149 °C (hexane); 1H NMR (500 MHz, CDCl3) δ 0.72−0.84 (m, 4H), 1.03− 1.10 (m, 2H), 1.12−1.30 (m, 4H), 1.26 (s, 18H), 1.41 (s, 18H), 1.47− 1.60 (m, 4H), 2.75−2.80 (m, 2H), 3.78 (d, 2JHH = 14 Hz, 2H, SCH2),

10ATVP/DGU-14A/CTO-10ACVP/RID-10A apparatus (Shimadzu Corporation) using a GPC KF-804L (Shodex Corporation) column at room temperature. trans-1,2-Bis(2-hydroxy-3,5-di-tert-butylbenzylsulfanyl)cycloheptane ([C7]H2, 9). A mixture of trans-cycloheptane-1,2dithiol (7; 1.64 g, 10.1 mmol) and 3,5-di-tert-butyl-2-hydroxybenzyl bromide (8; 6.04 g, 20.2 mmol) was dissolved in THF (110 mL) under argon. To the solution cooled at 0 °C was added triethylamine (2.8 mL, 2.03 g, 20.2 mmol), and the mixture was stirred for 1 h at 0 °C and 12 h at room temperature. The precipitates formed were removed by filtration, and the filtrate was concentrated under reduced pressure. The oily yellow residue was dissolved in ether, and aqueous ammonium chloride was added. The organic layer was washed with water, dried over anhydrous sodium sulfate, and evaporated to dryness under reduced pressure. The residue was purified by column chromatography (silica gel, hexane/dichloromethane 1/1) to give [C7]H2 (9; 3.79 g, 63%) as colorless crystals: mp 109−110 °C (hexane); 1H NMR (500 MHz, CDCl3) δ 1.25−1.48 (m, 4H), 1.27 (s, 18H), 1.42 (s, 18H), 1.56−1.65 (m, 2H), 1.68−1.74 (m, 2H), 1.88− 1.93 (m, 2H), 2.66−2.71 (m, 2H), 3.72 (d, 2JHH = 13 Hz, 2H, SCH2), 3.78 (d, 2JHH = 13 Hz, 2H, SCH2), 6.80 (s, 2H), 6.89 (d, 4JHH = 2 Hz, 2H), 7.25 (d, 4JHH = 2 Hz, 2H); 13C NMR (100.7 MHz, CDCl3) δ 24.9 (CH2), 28.7 (CH2), 29.7 (CH3), 31.6 (CH3), 31.9 (CH2), 34.2 (C), 34.6 (CH2), 35.0 (C), 50.3 (CH), 121.4 (C), 123.7 (CH), 125.1 (CH), 137.3 (C), 142.1 (C), 152.1 (C). Anal. Calcd for C37H58O2S2: C, 74.19; H, 9.76. Found: C, 74.08; H, 9.84. trans-1,2-Bis(thiocyanato)cyclononane. A solution of bromine (2.49 g, 15.6 mmol) in acetic acid (15 mL) was added dropwise over 10 min to a suspension of lead thiocyanate (5.96 g, 18.4 mmol) in acetic acid (30 mL) at room temperature, and the mixture was stirred for 2 h at room temperature. Cyclononene (1.82 g, 14.6 mmol) was added to the mixture, and the mixture was stirred overnight at room temperature. After dilution with three parts of water and filtration through a pad of Celite, the filtrate was extracted with dichloromethane. The organic layer was washed with water, dried over anhydrous sodium sulfate, and evaporated to dryness under reduced pressure. The residue was subjected to column chromatography (silica gel, dichloromethane/hexane 2/1) to give trans-1,2-bis(thiocyanato)cyclononane (1.65 g, 47%) as a colorless solid: mp 63−64 °C (purified I


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Organometallics 3.91 (d, 2JHH = 14 Hz, 2H, SCH2), 6.90 (d, 4JHH = 2.5 Hz, 2H), 7.02 (s, 2H), 7.25 (d, 4JHH = 2.5 Hz, 2H); 13C NMR (125.8 MHz, CDCl3) δ 21.9 (CH2), 22.0 (CH2), 25.8 (CH2), 29.8 (CH3), 31.6 (CH3), 32.6 (CH2), 34.2 (C), 35.1 (C), 35.4 (CH2), 43.8 (CH), 121.7 (C), 124.0 (CH), 125.5 (CH), 137.6 (C), 142.1 (C), 152.3 (C). Anal. Calcd for C39H62O2S2: C, 74.70; H, 9.97. Found: C, 74.58; H, 10.04. Synthesis of [C7]ZrCl2 (12). To a solution of [C7]H2 (9; 587 mg, 0.980 mmol) in Et2O (20 mL) at 0 °C was added BuLi (1.59 M in hexane, 1.3 mL, 2.07 mmol). The solution was stirred for 1 h at room temperature. The resulting solution of [C7]Li2 was added to a suspension of ZrCl4 (251 mg, 1.08 mmol) in Et2O (30 mL) at −78 °C. The mixture was stirred for 15 h at room temperature, and the solvent was removed under reduced pressure. Toluene was added to the residue. The insoluble inorganic materials were removed by filtration. The solvent of the filtrate was removed in vacuo, and the residual solid was washed with hexane (2 mL) and dried in vacuo to give [C7]ZrCl2 (12; 620 mg, 83%) as colorless crystals: mp 190−191 °C dec; 1H NMR (500 MHz, C6D6) δ 0.63−0.73 (m, 2H), 0.93−1.10 (m, 6H), 1.19−1.30 (m, 2H), 1.27 (s, 9H), 1.83 (s, 9H), 2.37 (s, 2H), 3.17 (d, 2 JHH = 14 Hz, 2H, SCH2), 4.34 (d, 2JHH = 14 Hz, 2H, SCH2), 6.55 (s, 2H), 7.53 (s, 2H); 13C NMR (100.7 MHz, C6D6) δ 25.7, 29.6, 30.5, 31.1, 31.8, 34.5, 35.6, 36.0, 49.7, 120.9, 124.9, 125.9, 138.6, 142.7, 157.3. Anal. Calcd for C37H56O2S2: C, 58.54; H, 7.44. Found: C, 58.09; H, 7.26. Synthesis of [C7]HfCl2 (13). To a solution of [C7]H2 (9; 1.00 g, 1.67 mmol) in Et2O (20 mL) at 0 °C was added BuLi (1.59 M in hexane, 2.2 mL, 3.5 mmol). The solution was stirred for 1 h at room temperature. The resulting solution of [C7]Li2 was added to a suspension of HfCl4 (567 mg, 1.74 mmol) in Et2O (30 mL) at −78 °C. The mixture was stirred for 16 h at room temperature, and the solvent was removed under reduced pressure. Toluene was added to the residue. The insoluble inorganic materials were removed by filtration. The solvent of the filtrate was removed in vacuo, and the residual solid was washed with hexane (2 mL) and dried in vacuo to give [C7]HfCl2 (13; 1.09 g, 77%) as colorless crystals: mp 180−181 °C dec; 1H NMR (500 MHz, C6D6) δ 0.62−0.71 (m, 2H), 0.92−1.11 (m, 4H), 1.20−1.32 (m, 4H), 1.28 (s, 18H), 1.83 (s, 18H), 2.38−2.45 (m, 2H), 3.20 (d, 2JHH = 15 Hz, 2H, SCH2), 4.37 (d, 2JHH = 15 Hz, 2H, SCH2), 6.56 (d, 4JHH = 2 Hz, 2H), 7.58 (d, 4JHH = 2 Hz, 2H); 13C NMR (125.8 MHz, C6D6) δ 25.7, 29.6, 30.5, 31.2, 31.9, 34.4, 35.6, 36.0, 49.5, 120.5, 125.0, 125.6, 139.2, 142.3, 157.3. Synthesis of [C7]Zr(Bn)2 (14). To a solution of [C7]ZrCl2 (12; 205 mg, 0.270 mmol) in Et2O (15 mL) at −78 °C was added PhCH2MgCl (1.0 M in Et2O, 0.60 mL, 0.60 mmol). The yellow solution was then warmed to room temperature gradually, and the solvent was removed under reduced pressure. Toluene was added to the residue. The insoluble inorganic materials were removed by filtration. The solvent of the filtrate was removed in vacuo, and the residual solid was washed with hexane (2 mL) and dried in vacuo to give [C7]Zr(CH2Ph)2 (14; 198 mg, 84%) as yellow crystals: mp 160− 162 °C dec; 1H NMR (500 MHz, C6D6) δ 0.73−0.82 (m, 2H), 0.93− 1.00 (m, 2H), 1.08−1.20 (m, 4H), 1.20−1.35 (m, 2H), 1.26 (s, 18H), 1.83 (s, 18H), 2.25 (d, 2JHH = 10 Hz, 2H, CH2Ph), 2.28 (br s, 2H), 2.84 (d, 2JHH = 10 Hz, 2H, CH2Ph), 3.18 (d, 2JHH = 14.5 Hz, 2H, SCH2), 3.53 (d, 2JHH = 14 Hz, 2H, SCH2), 6.62 (d, 4JHH = 2 Hz, 2H), 6.89 (t, 3JHH = 7.3 Hz, 2H), 7.09 (t, 3JHH = 7.5 Hz, 4H), 7.27 (d, 3JHH = 7.5 Hz, 4H), 7.54 (d, 4JHH = 2.5 Hz, 2H); 13C NMR (100.7 MHz, C6D6) δ 25.8 (CH2), 29.8 (CH2), 30.6 (CH3), 31.0 (CH2), 31.8 (CH3), 34.3 (C), 34.7 (CH2), 35.7 (C), 49.1 (CH), 65.0 (CH2), 122.2 (C), 123.1 (CH), 124.4 (CH), 126.1 (CH), 128.7 (CH), 129.6 (CH), 137.9 (C), 141.1 (C), 146.0 (C), 158.0 (C). Synthesis of [C7]Hf(Bn)2 (15). To a solution of [C7]HfCl2 (13; 590 mg, 0.708 mmol) in Et2O (30 mL) at −78 °C was added PhCH2MgCl (1.0 M in Et2O, 1.5 mL, 1.5 mmol). The yellow solution was then warmed to room temperature gradually, and the solvent was removed under reduced pressure. Toluene was added to the residue. The insoluble inorganic materials were removed by filtration. The solvent of the filtrate was removed in vacuo, and the residual solid was washed with hexane (2 mL) and dried in vacuo to give [C7]Hf(Bn)2 (15; 498 mg, 81%) as yellow crystals: 1H NMR (400 MHz, C6D6) δ

0.67−0.78 (n, 2H), 0.89−0.98 (m, 2H), 1.03−1.14 (m, 4H), 1.14− 1.23 (m, 2H), 1.25 (s, 18H), 1.84 (s, 18H), 2.20−2.22 (m, 2H), 2.64 (d, 2JHH = 12 Hz, 2H, CH2Ph), 2.89 (d, 2JHH = 12 Hz, 2H, CH2Ph), 3.16 (d, 2JHH = 14 Hz, 2H, SCH2), 3.44 (d, 2JHH = 14 Hz, 2H, SCH2), 6.62 (d, 4JHH = 2 Hz, 2H), 6.78 (t, 3JHH = 7 Hz, 2H), 7.10 (t, 3JHH = 8 Hz, 4H), 7.30 (d, 3JHH = 7 Hz, 4H), 7.58 (d, 4JHH = 2 Hz, 2H); 13C NMR (100.7 MHz, C6D6) δ 25.9 (CH2), 29.7 (CH2), 30.6 (CH3), 31.4 (CH2), 31.8 (CH3), 34.2 (C), 34.3 (CH2), 35.7 (C), 49.4 (CH), 77.8 (CH2), 121.5 (CH), 121.9 (C), 124.6 (CH), 125.9 (CH), 127.5 (CH), 128.6 (CH), 138.5 (C), 141.4 (C), 148.5 (C), 157.9 (C). Synthesis of [C9]ZrCl2 (16). A solution of [C9]H2 (10; 654 mg, 1.04 mmol) in Et2O (20 mL) at 0 °C was added BuLi (1.59 M in hexane, 1.4 mL, 2.23 mmol). The solution was stirred for 1 h at room temperature. The resulting solution of [C9]Li2 was added to a suspension of ZrCl4 (273 mg, 1.17 mmol) in Et2O (30 mL) at −78 °C. The mixture was stirred for 21 h at room temperature, and the solvent was removed under reduced pressure. Toluene was added to the residue. The insoluble inorganic materials were removed by filtration. The solvent of the filtrate was removed in vacuo, and the residual solid was washed with hexane (2 mL) and dried in vacuo to give [C9]ZrCl2 (16; 403 mg, 49%) as colorless crystals: 1H NMR (400 MHz, C6D6) δ 0.82−1.34 (m, 14H), 1.28 (s, 18H), 1.83 (s, 18H), 2.58 (br s, 2H), 3.20 (d, 2JHH = 15 Hz, 2H, SCH2), 4.36 (d, 2JHH = 14 Hz, 2H, SCH2), 6.59 (d, 4JHH = 2 Hz, 2H), 7.54 (d, 4JHH = 2 Hz, 2H); 13C NMR (100.6 MHz, C6D6) δ 24.4 (CH2), 24.6 (CH2), 25.9 (CH2), 29.3 (CH2), 30.5 (CH3), 31.8 (CH3), 34.4 (C), 35.7 (CH2), 36.3 (C), 49.5 (CH), 120.9 (C), 125.1 (CH), 125.9 (CH), 139.1 (C), 142.4 (C), 157.5 (C). Synthesis of [C9]HfCl2 (17). To a solution of [C9]H2 (9; 247 mg, 0.395 mmol) in Et2O (10 mL) at 0 °C was added BuLi (1.59 M in hexane, 0.52 mL, 0.83 mmol). The solution was stirred for 1 h at room temperature. The resulting solution of [C9]Li2 was added to a suspension of HfCl4 (137 mg, 0.421 mmol) in Et2O (10 mL) at −78 °C. The mixture was stirred for 16 h at room temperature, and the solvent was removed under reduced pressure. Toluene was added to the residue. The insoluble inorganic materials were removed by filtration. The solvent of the filtrate was removed in vacuo, and the residual solid was washed with hexane (2 mL) and dried in vacuo to give [C9]HfCl2 (17; 166 mg, 48%) as colorless crystals: 1H NMR (400 MHz, C6D6) δ 0.80−1.34 (m, 14H), 1.28 (s, 18H), 1.83 (s, 18H), 2.60 (s, 2H), 3.22 (d, 2JHH = 14 Hz, 2H, SCH2), 4.36 (d, 2JHH = 14 Hz, 2H, SCH2), 6.60 (br s, 2H), 7.58 (d, 4JHH = 2 Hz, 2H); 13C NMR (100.6 MHz, C6D6) δ 24.4, 24.6, 26.0, 29.5, 30.5, 31.8, 34.4, 35.6, 36.2, 49.5, 120.5, 125.2, 125.8, 139.5, 142.0, 157.4. Synthesis of [C9]Zr(Bn)2 (18). To a solution of [C9]ZrCl2 (16; 368 mg, 0.468 mmol) in Et2O (30 mL) at −78 °C was added PhCH2MgCl (1.0 M in Et2O, 1.0 mL, 1.0 mmol). The yellow solution was then warmed to room temperature gradually, and the solvent was removed under reduced pressure. Toluene was added to the residue. The insoluble inorganic materials were removed by filtration. The solvent of the filtrate was removed in vacuo, and the residual solid was washed with hexane (2 mL) and dried in vacuo to give [C9]Zr(Bn)2 (18; 296 mg, 70%) as yellow crystals: 1H NMR (400 MHz, C6D6) δ 0.90−1.52 (m, 14H), 1.27 (s, 18H), 1.81 (s, 18H), 2.14 (d, 2JHH = 10 Hz, 2H, CH2Ph), 2.48 (s, 2H), 2.76 (d, 2JHH = 10 Hz, 2H, CH2Ph), 3.19 (d, 2JHH = 14 Hz, 2H, SCH2), 3.54 (d, 2JHH = 15 Hz, 2H, SCH2), 6.64 (d, 4JHH = 2 Hz, 2H), 6.91 (t, 3JHH = 7 Hz, 2H), 7.10 (t, 3JHH = 8 Hz, 4H), 7.24 (d, 3JHH = 7 Hz, 4H), 7.53 (d, 4JHH = 2 Hz, 2H); 13C NMR (100.6 MHz, C6D6) δ 24.6 (CH2), 25.8 (CH2), 29.4 (CH2), 30.7 (CH3), 31.8 (CH3), 34.3 (C), 35.2 (CH2), 35.7 (C), 48.9 (CH), 63.3 (CH2), 122.1 (C), 123.2 (CH), 124.5 (CH), 126.2 (CH), 128.9 (CH), 129.7 (CH), 138.2 (C), 140.9 (C), 145.8 (C), 158.2 (C). Synthesis of [C9]Hf(Bn)2 (19). To a solution of [C9]HfCl2 (17; 340 mg, 0.389 mmol) in Et2O (30 mL) at −78 °C was added PhCH2MgCl (1.0 M in Et2O, 0.80 mL, 0.80 mmol). The yellow solution was then warmed to room temperature gradually, and the solvent was removed under reduced pressure. Toluene was added to the residue. The insoluble inorganic materials were removed by filtration. The solvent of the filtrate was removed in vacuo, and the residual solid was washed with hexane (2 mL) and dried in vacuo to J


Article

Organometallics give [C9]Hf(Bn)2 (19; 165 mg, 43%) as yellow crystals: 1H NMR (400 MHz, C6D6) δ 0.85−1.44 (m, 14H), 1.26 (s, 18H), 1.83 (s, 18H), 2.39 (br s, 2H), 2.60 (d, 2JHH = 12 Hz, 2H, CH2Ph), 2.90 (d, 2 JHH = 12 Hz, 2H, CH2Ph), 3.15 (d, 2JHH = 15 Hz, 2H, SCH2), 3.43 (d, 2 JHH = 14 Hz, 2H, SCH2), 6.65 (d, 4JHH = 2 Hz, 2H), 6.79 (t, 3JHH = 7 Hz, 2H), 7.11 (t, 3JHH = 8 Hz, 4H), 7.30 (d, 3JHH = 8 Hz, 4H), 7.58 (d, 4 JHH = 2 Hz, 2H); 13C NMR (100.6 MHz, C6D6) δ 24.56 (CH2), 24.61 (CH2), 25.9 (CH2), 29.6 (CH2), 30.6 (CH3), 31.8 (CH3), 34.3 (C), 34.6 (CH2), 35.7 (C), 49.3 (CH), 76.7 (CH2), 122.5 (C), 121.9 (CH), 124.7 (CH), 126.0 (CH), 127.6 (CH), 128.6 (CH), 138.7 (C), 141.0 (C), 148.4 (C), 158.0 (C). Preparation of dMAO. A toluene solution of PMAO-S (Al content 6.1 wt %, 100 mL, Tosoh Finechem Corporation) was introduced to a flask under a nitrogen atmosphere, and volatile materials were removed in vacuo. The residual white solid was dissolved in dry toluene (100 mL), and then volatile materials were removed in vacuo. This operation was repeated two more times to give dMAO (14.1 g). Polymerization of 1-Hexene Catalyzed by [Cn]MX2 with an Activator (n = 7, 9, M = Zr, Hf, X = Cl, Bn). Table 1, entries 2, 5, and 7. In the glovebox, B(C6F5)3 (10.2 mg, 0.020 mmol) or (Ph3C)[B(C6F5)4] (18.4 mg, 0.020 mmol) was added to a solution of [C7]Zr(Bn)2 (14) in toluene (20 mM, 1.0 mL, 0.020 mmol) or [C7]Hf(Bn)2 (15) in toluene (20 mM, 1.0 mL, 0.020 mmol) at room temperature. After it was stirred for 5 min at 25 or 0 °C, the mixture was kept at that temperature, and 1-hexene (3.0 g, 35.6 mmol) was added. After the mixture was stirred for the time given in Table 1, the reaction was quenched by addition of methanol. The mixture was dissolved in dichloromethane. The organic layer was washed with water and dried over anhydrous sodium sulfate, and volatile materials were removed in vacuo at 110 °C overnight to leave poly(1-hexene). Table 2, entries 1, 2, 4−6, and 8. In the glovebox, a solution of [C7]ZrCl2 (12), [C9]ZrCl2 (16), [C7]HfCl2 (13), or [C9]HfCl2 (17) in toluene (2 mM, 1.0 mL, 0.0020 mmol) was added to a solution of dMAO (29.4 mg, 0.0020 mmol) in toluene (5 mL) at room temperature. After it was stirred for 5 min at 25 or 0 °C, the mixture was kept at that temperature, and 1-hexene (3.0 g, 35.6 mmol) was added. After the mixture was stirred for the time given in Table 2, the reaction was quenched by addition of methanol. The mixture was dissolved in dichloromethane. The organic layer was washed with water and dried over anhydrous sodium sulfate, and volatile materials were removed in vacuo at 110 °C overnight to leave poly(1-hexene). 13 C{1H} NMR data of poly(1-hexene)s were obtained in CDCl3 at 25 °C, and the pentads ([mmmm]) were estimated from the integral ratio for C3 carbons observed in the range of δ 33−35.41 X-ray Crystallography. Single crystals were obtained by recrystallization from hexane for [C7]H2 (9) and [C9]H2 (10), from dichloromethane for [C7]ZrCl2 (12), and from toluene for [C7]Zr(Bn)2 (14), [C7]HfCl2 (13), and [C9]ZrCl2 (16). The intensity data were collected at 90 K on a Bruker AXS SMART diffractometer employing graphite-monochromated Mo Kα radiation (λ = 0.71073 Å), and the structures were solved by direct methods and refined by full-matrix least-squares procedures on F2 for all reflections (SHELX-97).42 Crystallographic data have been deposited with the Cambridge Crystallographic Data Centre: deposition numbers CCDC1541468, 1541469, 1541470, 1541471, 1541472, and 1541473 for [C7]H2 (9), [C9]H2 (10), [C7]ZrCl2 (12), [C7]HfCl2 (13), [C7]Zr(Bn)2 (14), and [C9]ZrCl2 (16), respectively. Copies of the data can be obtained free of charge via http://www.ccdc.cam.ac.uk/ conts/retrieving.html (or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge, CB2 1EZ, UK; Fax: + 44 1223 336033; e-mail: [email protected]). Crystal data for [C7]H2 (9): colorless crystal, crystal size 0.34× 0.31 × 0.14 mm, C37H58O2S2, MW = 598.95, monoclinic, space group P21/ n, Z = 4, a = 9.5017(4) Å, b = 10.9338(5) Å, c = 34.4610(16) Å, β = 92.1320(10)°, V = 3577.7(3) Å3, Dcalcd = 1.112 g cm−3, R1 (I > 2σ(I)) = 0.0509, wR2 (all data) = 0.1199 for 6675 reflections, 384 parameters, GOF = 1.041. Crystal data for [C9]H2 (10): colorless crystal, crystal size 0.78 × 0.53 × 0.52 mm, C39H62O2S2, MW = 627.01, monoclinic, space group

P21/c, Z = 4, a = 15.0131(8) Å, b = 19.2587(10) Å, c = 13.8863(8) Å, β = 110.3570(10)°, V = 3764.2(4) Å3, Dcalcd = 1.106 g cm−3, R1 (I > 2σ(I)) = 0.0363, wR2 (all data) = 0.0948 for 6993 reflections, 636 parameters, GOF = 1.024. Crystal data for [C7]ZrCl2 (12): colorless crystal, crystal size 0.12 × 0.10 × 0.04 mm, C37H56Cl2O2S2Zr·CH2Cl2, MW = 843.98, triclinic, space group P1̅, Z = 2, a = 10.1458(8) Å, b = 10.1837(8) Å, c = 20.6967(16) Å, α = 93.9990(10)°, β = 103.4510(10)°, γ = 94.1220(10)°, V = 2066.1(3) Å3, Dcalcd = 1.357 g cm−3, R1 (I > 2σ(I)) = 0.0304, wR2 (all data) = 0.0824 for 7533 reflections, 436 parameters, GOF = 1.007. Crystal data for [C7]HfCl2 (13): colorless crystal, crystal size 0.15 × 0.08 × 0.04 mm, C37H56Cl2HfO2S2, MW = 846.33, triclinic, space group P1̅, Z = 2, a = 10.202(4) Å, b = 10.304(4) Å, c = 19.344(7) Å, α = 99.469(4)°, β = 103.111(4)°, γ = 93.969(5)°, V = 1941.5(12) Å3, Dcalcd = 1.448 g cm−3, R1 (I > 2σ(I)) = 0.0727, wR2 (all data) = 0.2020 for 6559 reflections, 410 parameters, GOF = 1.009. Crystal data for [C7]Zr(Bn)2 (14): yellow crystal, crystal size 0.20 × 0.08 × 0.06 mm, C51H70O2S2Zr·C7H8, MW = 962.54, monoclinic, space group P21/c, Z = 4, a = 23.811(9) Å, b = 10.384(4) Å, c = 21.385(8) Å, β = 96.619(4)°, V = 5252(3) Å3, Dcalcd. = 1.217 g cm−3, R1 (I > 2σ(I)) = 0.0334, wR2 (all data) = 0.0854 for 10292 reflections, 606 parameters, GOF = 1.021. Crystal data for [C9]ZrCl2 (16): colorless crystal, crystal size 0.17 × 0.14 × 0.08 mm, C39H60Cl2O2S2Zr·2(C7H8), MW = 971.38, orthorhombic, space group Pca21, Z = 8, a = 31.705(4) Å, b = 12.4842(15) Å, c = 26.248(3) Å, V = 10389(2) Å3, Dcalcd = 1.242 g cm−3, R1 (I > 2σ(I)) = 0.0384, wR2 (all data) = 0.0728 for 18992 reflections, 1081 parameters, 1 restraint, GOF = 0.929. Computational Study. Structure optimizations were performed at the B3LYP/LanL2DZ level with the Gaussian 09 program.43 No symmetrical limitation was included in any optimization. We also confirmed that each transition state structure has only one imaginary frequency.

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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.7b00586. Figures S1−S8, Tables S1−S7, NMR charts of new compounds, and NMR and GPC charts of poly(1hexene)s (PDF) Cartesian coordinates of calculated molecules (XYZ) Accession Codes

CCDC 1541468−1541473 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail for A.I.: [email protected]. *E-mail for K.T.: [email protected]. ORCID

Akihiko Ishii: 0000-0003-4638-1294 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Dr. Masayoshi Nishiura and Dr. Zhaomin Hou (Organometallic Chemistry Laboratory, RIKEN Advanced K


Article

Organometallics

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Science Institute) for measurement of molecular weight and distributions of some of poly(1-hexene)s.

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