Hafnium Amidoquinoline Complexes: Highly Active Olefin

Aug 16, 2012 - Performance Plastics R&D, The Dow Chemical Company, Freeport, Texas 77541, United States. Jerzy Klosin. Corporate R&D, The Dow ...
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Hafnium Amidoquinoline Complexes: Highly Active Olefin Polymerization Catalysts with Ultrahigh Molecular Weight Capacity Philip P. Fontaine* Performance Plastics R&D, The Dow Chemical Company, Freeport, Texas 77541, United States

Jerzy Klosin Corporate R&D, The Dow Chemical Company, 1776 Building, Midland, Michigan 48674, United States

Nolan T. McDougal Corporate R&D, The Dow Chemical Company, Freeport, Texas 77541, United States S Supporting Information *

ABSTRACT: The preparation and characterization of a new class of polyolefin procatalysts is described. Hafnium tribenzyl procatalysts, supported by amidoquinoline ligands, were prepared in two steps from commercially available materials. Solid-state structures, determined by single-crystal X-ray analyses, revealed that all the hafnium complexes display approximate trigonal-bipyramidal geometry around the metal center. The complexes were evaluated in an ethylene/1-octene copolymerization study and were found to be highly active at elevated temperatures (120 °C). The best catalyst, derived from ((2,6-dimethylphenyl)(2,4-dimethylquinolin-8-yl)amino)tribenzylhafnium (6d), compares favorably to previously reported systems supported by bidentate nitrogen-based ligands. In particular, this catalyst exhibits very high molecular weight capacity and high catalytic activity, with a moderate 1-octene response. Alkyl substitution at the carbon ortho to the quinolino nitrogen was found to be an important factor for improving polymer compositional homogeneity, as evidenced by a narrowing of the polydispersity index and a single melting temperature in the resulting copolymer.

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INTRODUCTION The polyolefins industry continues to seek new catalysts1 that are capable of producing materials with fundamentally new microstructures and properties2 or that can improve the current polymerization processes.3 Ideally, these catalysts should comprise supporting ligand frameworks that are inexpensive, easily prepared, and modular in nature. Moreover, high activities and the ability to operate at elevated temperatures are often critical features when assessing commercial viability. As of yet, there are still relatively few supporting ligand frameworks that can satisfy all the above-mentioned requirements. In this regard, there has been an increasing focus on nonmetallocene systems,4 which can be attractive targets owing to their ease of preparation and high temperature stability. Additionally, such catalysts have been used to access novel and industrially relevant polyolefin structures such as olefin block copolymers (OBCs).2e Of particular interest are several recent reports describing group IV complexes comprising simple bidentate nitrogen-based ligands, which are useful procatalysts for polyolefin polymerizations.5 In addition to being highly active over wide temperature ranges, these systems © 2012 American Chemical Society

are capable of producing olefin copolymers with high molecular weight and readily engage in reversible chain transfer with diethylzinc, allowing for OBC production.2e,f One drawback of several of the previously reported systems is the relatively low stability of the procatalysts or ligand precursors. For example, previously reported imino-amido complexes undergo structural rearrangements at elevated temperature to produce species that are less catalytically competent (e.g., 1a → 1b and 2a → 2b, Scheme 1).5a,e The thermal instability was eliminated for analogous cyclic iminoenamido complexes (e.g., 3a), although the ligand itself is prone to acid-induced isomerization, resulting in a new ligand, which upon metalation gives rise to a less competent catalyst (3b) (Scheme 2).5f Such rearrangements are undesirable, as they can make it more difficult to prepare or store a given catalyst, and hence limit commercial viability. Our goal, then, was to develop a ligand scaffold that retains (or improves upon) the positive attributes of the above-mentioned catalytic systems, while suppressing some of these unwanted isomerization pathways. Received: June 15, 2012 Published: August 16, 2012 6244

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Scheme 1. Thermal Rearrangements of Imino-Amido Complexesa,5a,e

Figure 1. Molecular structure of 5d. Hydrogen atoms, except H1, are omitted for clarity. Thermal ellipsoids are shown at the 40% probability level. Selected bond lengths (Å) and angles (deg): C1− N1 = 1.3843(15), C6−N2 = 1.3701(14), C1−C6 = 1.4338(15), C1− N1−C10 119.62(9). a

Scheme 3. Synthesis and Metalation of Aminoquinoline Ligands

DIP = 2,6-diisopropyl; Bn = benzyl.

Scheme 2. Isomerization of Imino-Enamido Ligands5f

We postulated that aminoquinolines6,7 could provide such a scaffold, since the aforementioned rearrangements would be precluded by the aromatic framework. Additionally, the core structure of the previously reported complexes, a fivemembered metallacycle formed by coordination of the two nitrogen donors to the hafnium center, would be retained. This report details the synthesis of such aminoquinoline ligands, their respective hafnium tribenzyl complexes, and their utility in copolymerization reactions of ethylene and 1-octene.

dimethylaniline group (Figure 1). Bond angles and distances are similar to previously characterized aminoquinolines.6,8 The 1H NMR spectrum of 5a at ambient temperature shows a single broad resonance corresponding to the CH3 groups of the isopropyl moieties, indicative of a relatively slow chemical exchange process. This is likely due to hindered rotation of the aniline group as a result of steric interactions between the ortho isopropyl groups and the quinolino core. Fast (on the NMR time scale) rotations of the isopropyl groups and the anilino group itself along the C−N bond axis would result in the chemical equivalence of all four of the CH3 groups, which would appear as one doublet in the 1H NMR spectrum. In the case of 5c, containing only one ortho isopropyl group, a single sharp doublet was observed for the two CH3 groups, indicating fast rotation of the 2-isopropylphenyl fragment along the N− C(ipso) bond. Isopropyl groups are convenient indicators of a ligand’s rotational flexibility; the analogous information on rotational barriers cannot be gleaned from the ligands containing ortho methyl groups, 5b and 5d. Synthesis and Characterization of Hafnium Amidoquinoline Complexes. The metalations proceeded readily by stirring the aminoquinolines in a toluene solution with tetrabenzylhafnium (Scheme 3). These reactions are charac-

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RESULTS AND DISCUSSION Preparation of Aminoquinoline Ligands. An attractive feature of the targeted aminoquinoline ligands is their ease of preparation. Starting from commercially available 8-bromoquinolines (4a and 4b), the ligands can be synthesized in a single synthetic step (Scheme 3). Specifically, a Pd-catalyzed coupling reaction of 4a or 4b with the desired substituted aniline furnished the desired compounds (5a−d) in modest to good (38−73%) isolated yields. Purification was accomplished via flash chromatography; 5a, 5b, and 5d were isolated as yellow solids, while 5c was isolated as a viscous yellow oil. All solid ligands showed appreciable solubility in aliphatic hydrocarbons and could be recrystallized if desired. The solid-state structure of 5d shows a planar quinolino core with an orthogonal 2,66245

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Table 1. Crystallographic Data for Complexes 6a−d, 1a, and 3a 6a

6b

Hf−N1 Hf−N2 Hf−Bn1 Hf−Bn2 Hf−Bn3

2.3453(18) 2.1155(16) 2.2698(22) 2.2344(22) 2.2723(22)

2.3418(1) 2.1170(1) 2.2535(1) 2.2743(0) 2.2858(1)

N1−Hf−N2 N1−Hf−Bn1 N1−Hf−Bn2 N1−Hf−Bn3

72.02(6) 125.06(7) 111.55(8) 92.46(7)

71.61(5) 123.63(5) 112.58(6) 91.18(6)

6c

6d

Bond Lengths 2.340(2) 2.1176(20) 2.2688(25) 2.2559(18) 2.2903(21) Bond Angles 71.57(6) 125.88(8) 107.56(7) 89.83(7)

terized by an immediate color change to orange-red, indicative of the formation of the desired complexes. Generally, the reactions were quite clean, although recrystallization was performed for all products in order to obtain the complexes in high purity. The isolated hafnium tribenzyl complexes were orange to red in color, and all showed limited solubility in aliphatic hydrocarbons and excellent solubility in toluene and benzene. The structures of all the hafnium complexes (6a−d) were confirmed by single-crystal X-ray diffraction, and all show similar bond distances and angles. These metrical parameters also match closely with the previously reported imino-amido complexes5e,f (Table 1). Figure 2 shows the structures of 6a and 6d as representative examples for the substituted and unsubstituted quinolino cores, respectively (molecular structures of 6b and 6c are presented in the Supporting Information). For the nitrogen donors of the hafnium-bound amidoquinolines, the anionic Hf−N bond is notably shorter, by about 0.22 Å, than the neutral quinolino donor, while the Hf− C bonds to the benzyl groups are all comparable in length. For 6a−c, there is an apparent interaction between the hafnium center and an ipso carbon from one of the benzyl groups. Pi donation from the aromatic system to the metal center would be expected in this case, as the electron-deficient (formally a 10electron count) complexes would likely be stabilized in this manner. All the complexes adopt an approximate trigonalbipyramidal structure in the solid state, with the anilino donor and two of the benzyl ligands occupying the equatorial plane. The axial quinolino donor is canted slightly to accommodate the five-membered metallacycle. That is, the rigidity of the ligand backbone dictates a N−Hf−N angle of ∼72° within the five-membered ring, rather than the 90° expected for trigonalbipyramidal geometry. Likewise, the interactions of the hafnium center with the ipso carbons of the benzyl groups in 6a−c result in some deviations from the expected bond angles (Table 1). The dynamic nature of 6a−d was evidenced by NMR spectroscopy, which shows the chemical equivalence of the three benzyl groups, in contrast with their solid-state structures. More specifically, the 1H NMR spectra for both 6b and 6c at ambient temperature show sharp resonances at 2.20 and 2.27 ppm, respectively, corresponding to the three equivalent benzyl groups. For 6a and 6d, however, the analogous resonances are broad at ambient temperature, indicative of a higher barrier for the benzyl group exchange process. Fluxional behavior was further confirmed by heating the NMR solutions of 6a and 6d, resulting in the expected sharpening of the broad resonances. The aromatic region of variable-temperature 1H NMR spectra of 6d in toluene-d8 is presented in Figure 3, showing resonance coalescence at 30 °C and fast exchange at 100 °C. This

1a

3a

2.351(3) 2.102(3) 2.166(6) 2.209(6) 2.286(4)

2.313(2) 2.100(2) 2.243(2) 2.288(2) 2.266(2)

2.301(3) 2.074(3) 2.288(3) 2.259(3) 2.253(3)

72.47(10) 123.8(3) 120.1(3) 87.39(12)

72.57(10) 116.63(11) 123.33(12) 92.93(12)

72.03(6) 117.91(7) 118.56(7) 88.93(7)

Figure 2. Molecular structures of 6a (top) and 6d (bottom). Hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown at the 40% probability level.

dynamic exchange could be the result of a Berry pseudorotation or a turnstile motion, well-known dynamic processes for trigonal-bipyramidal organometallic complexes.9 The barrier of 6246

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incorporation, and higher polymer molecular weight. Note that 6a can be viewed as analogous to 1a and 3a since all these derivatives contain a 2,6-diisopropylanilino moiety, although for the amidoquinoline ligand decreasing the bulk of the ortho groups results in several desirable catalytic properties. Similarly, a comparison of 6a and 6c shows that the latter, with one unsubstituted ortho position, resulted in poorer efficiency, comonomer incorporation, and decreased polymer molecular weight. The copolymers produced by 6a and 6b comprised multiple crystallization temperatures, as determined by DSC. This bimodality is evidence for multiple active catalytic species, a relatively common phenomenon for high-temperature solutionphase copolymerization reactions. However, it is often desirable that the catalyst produce polymers with compositional homogeneity (i.e., single-site behavior). In general, single-site catalysts are more easily modeled and controlled in continuous production processes, and the resulting compositional homogeneity can lead to certain microstructural changes, such as narrowed polydispersity index (PDI). One hypothesis for the cause of the multisite behavior in the present case is that the carbon ortho to the quinolino nitrogen could be prone to attack during the course of the polymerization reaction. Additions of organometallic reagents to this position are well known, resulting in dearomatized 2-alkylated quinolines, and can be mediated by lithium, magnesium, or aluminum species.10 One possible culprit in the present example, then, is a reaction between the active catalyst and an aluminum component of MMAO-3A, which was used as an impurity scavenger in the copolymerization reactions. For example, the addition of trimethylaluminum, a component of MMAO-3A, to quinolines has been reported.10d,e Although additions of trialkylaluminums across carbon−nitrogen double bonds of nitrogen-containing heterocycles are notoriously sluggish, in our case the reactivity could be enhanced by the binding to a strongly Lewis acidic cationic hafnium center, and the elevated temperatures should enhance the kinetic feasibility of such a reaction. We reasoned that an alkyl substitution at this ortho position might protect against such an attack and decided to prepare a procatalyst containing the 2,4-dimethylquinoline framework (6d). Indeed, the copolymer produced by 6d showed a single crystallization temperature by DSC (Figure 4) and a narrow PDI, evidence that a single active catalytic species was dominant in this case. Gratifyingly, 6d also provided a substantial increase in polymer molecular weight, while retaining good catalytic efficiency and comonomer incorporation. From this set of data, it is apparent that the catalyst derived from 6d possessed the most desirable combination of catalytic

Figure 3. Fragment of the variable-temperature 1H NMR spectra of 6d in toluene-d8 at 30, 65, and 100 °C.

this process seems to trend with the steric bulk of the aniline group, as a higher barrier is observed for 6a than for 6b or 6c. The notion that the substitution pattern on the aniline can impact the energetics of the metal-bound alkyls suggests that this might be an important element in determining the nature of the resulting active polymerization catalyst. It is also worth noting that again the presence of isopropyl moieties on the aniline ring can provide additional information about the dynamics of metal complexes. In the case of both 6a and 6c, two chemically inequivalent CH3 groups are observed as doublets, indicating hindered rotation about the C−N bond. The same phenomenon may be occurring for complexes 6b and 6d, which contain a 2,6-dimethylaniline fragment, although this cannot be probed directly using NMR spectroscopy. Copolymerization Study. All new complexes 6a−d were evaluated as procatalysts for ethylene/1-octene copolymerizations within a one gallon batch reactor at 120 °C, with 425 psi of ethylene pressure and 250 g of 1-octene. For comparison, procatalysts 1a and 3a were also tested under the same reactor conditions. The copolymers obtained were characterized by density measurements, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and comonomer content via NMR spectroscopy. The complete results are presented in Table 2. Procatalysts 6a−c entail variations in the aniline moiety, with the quinolino core left unsubstituted. Indeed, the aniline substitution pattern was observed to have a substantial impact on the resulting polymerization behavior. The smaller methyl ortho groups of 6b, in comparison with the isopropyl groups of 6a, resulted in higher catalytic efficiency, improved comonomer

Table 2. Batch Reactor Ethylene/1-Octene Copolymerization Data at 120 °Ca procatalyst

octene incorp (wt %)

polymer (g)

activity (g poly/mmol cat)

MW (g/mol)

Mn (g/mol)

PDI

TC (°C)

1a 3a 6a 6b 6c 6d

9.8 18.3 13.4 16.5 6.9 14.9

18.3 23.5 19.2 30.9 10.6 28.3

24 339 31 352 25 599 41 165 14 094 37 715

390 690 604 130 280 300 403 610 159 800 632 200

124 180 145 290 100 500 116 760 54 580 212 500

3.27 4.16 2.79 3.46 2.93 2.97

108 87 95, 107 89, 115 122 93

a

Reactor size = 1 gal. Ethylene pressure = 425 psi (145 g of ethylene). The reactor was also charged with 250 g of 1-octene, 1350 g of Isopar E, and 20 mmol of H2 and heated to 120 °C. Then 0.75 μmol of each catalyst was injected along with 0.85 μmol of cocatalyst ([HNMe(C18H37)2][B(C6F5)4]) and 22.5 μmol of MMAO-3A. Run time was 10 min; all catalysts were inactive after 10 min run time under these conditions, as evidenced by ethylene uptake monitoring.8 6247

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result of which was the rapid and exothermic production of poly-1-octene.8

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SUMMARY An ongoing goal in our research is to develop new and improved polyolefin catalysts based on ligands that are easily accessible, thermally and chemically stable, modular in nature, and that lead to highly active catalysts at elevated temperatures. The amidoquinoline complexes described here, inspired by previously reported polyolefin catalysts comprising bidentate nitrogen ligands,5e,f meet the above requirements. The ligands were prepared in a single step, utilizing standard coupling methods, and the subsequent metalations proceeded cleanly to provide the desired procatalysts in high yields as hafnium tribenzyl complexes. Importantly, the aromaticity of these ligands provides a supporting framework that is resistant to the isomerization reactions inherent to the previously reported imino-amido systems. Each of the hafnium complexes adopted an approximate trigonal-bipyramidal geometry in the solid state, although in solution an exchange process was observed that rendered the three benzyl groups equivalent. The rate of this process, likely a Berry pseudorotation or a turnstile rotation, is influenced by the steric bulk of the ligand. For the complexes of the larger ligands, 6a and 6d, the barrier for this dynamic process is high enough at ambient temperatures that broad resonances corresponding to the benzyl groups are observed. The procatalyst 6d was reacted with B(C6F5)3, resulting in the clean formation of the ion-separated dibenzyl complex 7d, which we propose is the active species for the polymerization catalysis. The modularity of the aminoquinoline framework was demonstrated by the preparation of procatalysts with substitution variations in both the anilino and the quinolino portions of the ligand, which in turn resulted in the formation of catalysts with substantially different properties. Specifically, the alkyl groups in both ortho positions of the aniline group were found to be beneficial, with 2,6-dimethylaniline being the optimal choice in the set presented here. Subsequent modification of the quinolino core, the substitution of methyl groups in the C2 and C4 positions, served to further improve the catalytic properties. The resultant procatalyst, 6d, compares favorably to the previously reported catalysts, providing incremental improvements in activity and molecular weight capacity.

Figure 4. DSC overlay of copolymers produced by 6b and 6d.

attributes. To further investigate the nature of the active species, an NMR experiment was conducted in which B(C6F5)3, a commonly used activator, was added to a solution of 6d in C6D5Cl (Scheme 4). The 1H NMR spectrum showed relatively Scheme 4. Reaction of 6d with B(C6F5)3 to Form an Ion Pair

clean conversion to the cationic dialkyl species 7d, which is the result of benzyl group abstraction by the borane activator. The 1 H NMR spectrum indicates the formation of a Cs symmetric species with benzyl groups symmetrically positioned above and below the plane of symmetry. This is evidenced by the appearance of two doublets at 2.03 and 1.83 ppm (2JH−H = 10.3 Hz), which correspond to two diastereotopic methylene protons of the benzyl groups. Additionally, the abstracted benzyl group is chemically distinct; for example the B-CH2-Ph protons appear as a slightly broad singlet at 3.35 ppm. Similarly, the 19F NMR spectrum of 7d is also indicative of ion pair formation. The chemical shift difference between the meta and para fluorine resonances (Δδ(m,p-F)) of the major species is only 2.75 ppm, which indicates that the anion is not coordinated to the metal center.11 The noncoordinating nature of the borate anion was also observed for 2a, in which case the formation of a separated ion pair was ascribed to steric congestion at the metal center.5a For 7d though, a second minor species (∼3%) is observable with a larger Δδ(m,p-F) of 4.49 ppm, consistent with a borate anion coordinated to the hafnium center, although the exact nature of this complex could not be established with certainty. It should be noted that, upon standing at ambient temperature overnight, most of 7d decomposed into three different major species. The thermal stability is of course an important parameter of the active species; however, ultimately it is the corresponding thermal stability in the presence of ethylene, along with the polymerization kinetics, that dictates the catalyst activity. In order to confirm that 7d was in fact an active species, it was added (3 μmol) to neat 1-octene (11 mL) at room temperature, the

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EXPERIMENTAL SECTION

General Considerations. Materials were obtained from Aldrich and used directly, except where noted below. The bromoquinolines 4a and 4b were purchased from ArkPharm Inc. and Princeton BioMolecular Research, respectively; both were used directly. rac[1,1′-Binaphthalene]-2,2′-diol (rac-BINAP) was obtained from Fluka and used directly. Isopar E was obtained from Exxon Mobil. [HNMe(C18H37)2][B(C6F5)4] was obtained from Boulder Scientific. MMAO-3A was obtained from AkzoNobel. Air-sensitive manipulations were performed in a Vacuum Atmospheres inert atmosphere glovebox under a dry nitrogen atmosphere or by using standard Schlenk and vacuum line techniques. Toluene, hexane, and Isopar E were degassed and dried over alumina and molecular sieves prior to use as solvents for the air-sensitive procedures. NMR spectra were recorded on Bruker Avance-400 and Varian VNMRS-400 spectrometers. 1H NMR data are reported as follows: chemical shift (multiplicity (br = broad, s = singlet, d = doublet, t = triplet, q = quartet, sp = septet, and m = multiplet), integration, and assignment). Chemical shifts for 1H NMR data are reported in ppm 6248

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downfield from internal tetramethylsilane (TMS, δ scale) using residual protons in the deuterated solvent (C6D6, 7.15 ppm; toluened8, 2.09 ppm) as references. 13C NMR data were determined with 1H decoupling, and the chemical shifts are reported in ppm vs tetramethylsilane (C6D6, 128 ppm; toluene-d8, 20.4 ppm). Elemental analyses were performed at Midwest Microlab, LLC. High-resolution mass spectroscopy (HRMS) analyses were carried out using flow injection (0.5 mL of 50/50 v/v % of 0.1% formic acid in water/THF) on an Agilent 6520 quadrupole-time-of-flight MS system via a dualspray electrospray interface operating in the positive ion mode. Synthesis of Aminoquinolines. A general procedure is as follows. A round-bottomed flask equipped with a reflux condenser was charged with Pd2(dba)3 (0.090 mmol), rac-BINAP (0.207 mmol), and NaOt-Bu (4.05 mmol) in toluene (15 mL). To the resulting suspension were added the substituted aniline (2.88 mmol) and the desired bromoquinoline (2.88 mmol). The mixture was heated under reflux overnight and then pumped down to dryness under vacuum. The crude residue was purified by flash column chromatography eluting with 9:1 pentane/diethyl ether. N-(2,6-Diisopropylphenyl)quinolin-8-amine (5a): yellow solid in 38% yield. 1H NMR (C6D6): 8.56 (1H, d, 3JH−H = 3.5 Hz), 7.92 (1H, s, NH), 7.53 (1H, d, 3JH−H = 8.1 Hz), 7.23−7.04 (4H, m), 6.79 (1H, d, 3 JH−H = 8.1 Hz), 6.77 (1H, dd, 3JH−H = 8.1, 4.0 Hz), 6.35 (1H, d, 3JH−H = 7.5 Hz), 3.32 (2H, sp, 3JH−H = 6.8 Hz), 1.10 (12H, br). 13C{1H} NMR (C6D6): 148.3, 147.3, 145.5, 138.4, 136.1, 135.8, 129.3, 128.1, 124.3, 121.7, 114.9, 106.5, 28.8, 24.9, 23.3. ES-HRMS (m/e): calcd for C21H24N2 (M + H)+ 305.201, found 305.201. N-(2,6-Dimethylphenyl)quinolin-8-amine (5b): pale yellow solid in 73% yield. 1H NMR (C6D6): 8.60 (1H, dd, 3JH−H = 4.0 Hz, 4JH−H = 1.5 Hz), 7.83 (1H, s, NH), 7.59 (1H, dd, 3JH−H = 8.1 Hz, 4JH−H = 1.5 Hz), 7.11 (1H, t, 3JH−H = 7.9 Hz), 7.03 (3H, br), 6.92 (1H, d, 3JH−H = 8.1 Hz), 6.83 (1H, dd, 3JH−H = 8.3, 4.0 Hz), 6.35 (1H, dd, 3JH−H = 7.7 Hz, 4 JH−H = 0.7 Hz), 2.15 (6H, s). 13C{1H} NMR (C6D6): 147.2, 143.5, 138.7, 138.6, 137.0, 136.0, 129.3, 128.9, 128.1, 126.6, 121.5, 115.1, 106.2, 18.4. ES-HRMS (m/e): calcd for C17H16N2 (M + H)+ 249.131, found 249.139. N-(2-Isopropylphenyl)quinolin-8-amine (5c): viscous yellow oil in 57% yield. 1H NMR (C6D6): 8.57 (1H, dd, 3JH−H = 4.2 Hz, 4JH−H = 1.7 Hz), 8.37 (1H, s, NH), 7.59 (1H, dd, 3JH−H = 8.1 Hz, 4JH−H =1.3 Hz), 7.52 (1H, 3JH−H = 7.5 Hz), 7.25 (1H, dd, 3JH−H = 7.3 Hz, 4JH−H = 1.3 Hz), 7.17−7.05 (m, 4H), 6.94 (1H, dd, 3JH−H = 7.7 Hz, 4JH−H = 1.3 Hz), 6.83 (1H, dd, 3JH−H = 8.3, 4JH−H = 4.2 Hz), 3.35 (1H, sp, 3JH−H = 6.8 Hz), 1.14 (6H, d, 3JH−H = 6.8 Hz). 13C{1H} NMR (C6D6): 147.4, 142.99, 142.97, 139.2, 139.1, 136.1, 129.3, 127.9, 126.8, 126.7, 124.9, 124.2, 121.7, 115.8, 107.3, 28.4, 23.3. ES-HRMS (m/e): calcd for C18H19N2 (M + H)+ 263.154, found 263.154. N-(2,6-Dimethylphenyl)-2,4-dimethylquinolin-8-amine (5d): pale yellow solid in 46% yield. 1H NMR (C6D6): 7.95 (1H, s, NH), 7.16− 7.05 (5H, m), 6.97 (1H, s), 6.41 (1H, d, 3JH−H = 7.3 Hz, 4JH−H = 0.9 Hz), 2.55 (3H, s), 2.25 (3H, s), 2.21 (6H, s). 13C{1H} NMR (C6D6): 155.2, 144.2, 143.5, 139.1, 137.8, 137.1, 128.9, 127.4, 126.8, 126.5, 123.0, 111.1, 106.3, 25.1, 18.7, 18.5. ES-HRMS (m/e): calcd for C19H20N2 (M + H)+ 277.170, found 277.170. Synthesis of Hafnium Tribenzyl Complexes. Full multinuclear and multidimensional spectroscopic characterization by NMR was conducted, and the complete results, including actual NMR spectra, are presented in the Supporting Information. From these data, 1H NMR and 13C{1H} NMR assignments were made, where possible, as indicated below. The numbering convention used for these assignments is consistent with that used for the solid-state structures. ((2,6-Diisopropylphenyl)(quinolin-8-yl)amino)tribenzylhafnium (6a). A solution of 5a (0.285 g, 0.936 mmol) in toluene (5 mL) was cooled to −40 °C, then added to a vial containing HfBn4 (0.480 g, 0.883 mmol). The resulting solution turned deep red immediately and was allowed to warm to room temperature and stirred for 1 h. The volume of toluene was reduced to ca. 2 mL, and hexane (ca. 8 mL) was added, at which point the solution was cooled to −40 °C. After 1 day, the resulting deep red crystals were collected and dried under vacuum, affording the desired product in high purity (0.515 g, 80%). 1H NMR (C6D6): 7.72 (1H, dd, 3JH−H = 5.0 Hz, 4JH−H = 1.5 Hz, H9), 7.42 (1H,

dd, 3JH−H = 8.2 Hz, 4JH−H = 1.5 Hz, H7), 7.30 (3H, m, H12, H13, and H14), 7.06 (6H, br t, 3JH−H = 7.5 Hz, H19, H21), 6.94 (1H, t, 3JH−H = 8.2 Hz, H3), 6.81 (3H, br t, 3JH−H = 7.5 Hz, H20), 6.70 (6H, br d, 3 JH−H = 7.5 Hz, H18, H21), 6.59 (1H, dd, 3JH−H = 8.2 Hz, 4JH−H = 1.0 Hz, H4), 6.46 (1H, dd, 3JH−H = 5.0, 8.2 Hz, H8), 6.07 (1H, dd, 3JH−H = 8.2 Hz, 4JH−H = 1.0 Hz, H2), 3.32 (2H, sp, 3JH−H = 6.8 Hz, C11− CH(Me)2 and C15−CH(Me)2), 2.33 (6H, br s, H16), 1.30 (6H, d, 3 JH−H = 6.8 Hz, CH(CH3)2), 0.98 (6H, d, 3JH−H = 6.8 Hz, CH(CH3)2). 13 C{1H} NMR (C6D6): 154.6, 148.8 (C9), 145.5, 145.0, 144.0, 140.6 (C7), 139.5, 129.6, 129.2 (C3), 128.9, 128.0 (C18, C22), 127.2 (C13), 125.1 (C12, C14), 122.4 (C20), 120.5 (C8), 114.8 (C4), 112.7 (C2), 86.7 (C16), 28.9 (C11-CH(Me)2 and C15-CH(Me)2), 26.1 (CH(CH3)2), 24.4 (CH(CH3)2). Anal. Calcd for C42H44N2Hf: C 66.79, H 5.87, N 3.71. Found: C 66.53, H 5.92, N 3.73. ((2,6-Dimethylphenyl)(quinolin-8-yl)amino)tribenzylhafnium (6b). A solution of 5b (0.206 g, 0.830 mmol) in toluene (5 mL) was

cooled to −40 °C, then added to a vial containing HfBn4 (0.425 g, 0.783 mmol). The resulting solution turned red immediately and was allowed to warm to room temperature and stirred for 1 h. The volume of toluene was reduced to ca. 2 mL, and hexane (ca. 8 mL) was added, at which point the solution was cooled to −40 °C. After 1 day, the resulting red crystals were collected and dried under vacuum, affording the desired product in high purity (0.390 g, 71%). 1H NMR (C6D6): 7.73 (1H, dd, 3JH−H = 5.0, 4JH−H = 1.5 Hz, H9), 7.45 (1H, dd, 3JH−H = 8.2, 4JH−H = 1.4 Hz, H7), 7.16 (2H, d, 3JH−H = 7.3 Hz, H12 and H14), 7.07 (1H, dd, 3JH−H = 7.3, 7.3 Hz, H13), 7.04 (6H, br t, 3JH−H = 7.4 Hz, H19 and H21), 6.96 (1H, t, 3JH−H = 7.9 Hz, H3), 6.81 (3H, t, 3 JH−H = 7.4 Hz, H20), 6.66 (6H, d, 3JH−H = 7.4 Hz, H18, H22), 6.62 (1H, dd, 3JH−H = 7.9 Hz, 4JH−H = 1.0 Hz, H4), 6.49 (1H, dd, 3JH−H = 5.0, 8.2 Hz, H8), 6.06 (1H, dd, 3JH−H = 7.9 Hz, 4JH−H = 1.0 Hz, H2), 2.20 (6H, s, H16), 2.09 (6H, s, C11−CH3 and C15−CH3). 13C{1H} NMR (C6D6): 152.7, 148.7 (C9), 147.1, 144.5 (C7), 140.5, 139.8, 135.3, 130.3 (C3), 129.5 (C12 and C14), 129.3, 129.0 (C19 and C21), 128.2 (C18 and C22), 126.2 (C13), 122.6 (C20), 120.5 (C8), 114.6 (C4), 110.1 (C2), 85.3 (C16), 18.4 (C11-CH3 and C15-CH3). Anal. Calcd for C38H36N2Hf: C 65.28, H 5.19, N 4.01. Found: C 65.09, H 5.31, N 4.07. ((2-Isopropylphenyl)(quinolin-8-yl)amino)tribenzylhafnium (6c). A solution of 5c (0.203 g, 0.774 mmol) in toluene (5 mL) was cooled to −40 °C, then added to a vial containing HfBn4 (0.396 g, 0.730 mmol). The resulting solution turned orange immediately and was allowed to warm to room temperature and stirred for 1 h. The volume of toluene was reduced to ca. 2 mL, and hexane (ca. 8 mL) was added, at which point the solution was cooled to −40 °C. After 1 day, the resulting orange crystals were collected and dried under vacuum, affording the desired product in high purity (0.383 g, 74%). 1H NMR (C6D6): 7.72 (1H, dd, 3JH−H = 5.0 Hz, 4JH−H = 1.5 Hz, H9), 7.43 (1H, 6249

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dd, 3JH−H = 8.2 Hz, 4JH−H = 1.5 Hz, H7), 7.40 (1H, m, H12), 7.22 (2H, m, H13, H14), 7.03 (6H, dd, 3JH−H = 7.4, 7.8 Hz, H19 and H21), 6.95 (1H, t, J = 8.0 Hz, H3), 6.87 (1H, m, H15), 6.78 (3H, t, J = 7.4 Hz, H20), 6.68 (6H, d, J = 7.8 Hz, H18 and H22), 6.60 (1H, dd, 3JH−H = 8.0, 4JH−H = 1.0 Hz, H4), 6.50 (1H, dd, 3JH−H = 5.0, 8.2 Hz, H8), 6.07 (1H, dd, 3JH−H = 8.0 Hz, 3JH−H = 1.0 Hz, H2), 3.31 (1H, sp, 3JH−H = 6.8 Hz, C11−CH(Me)2), 2.29 (3H, d, 2JH−H = 12.1 Hz, H16), 2.25 (3H, d, 2JH−H = 12.1 Hz, H16), 1.28 (3H, d, 3JH−H = 6.8 Hz, CH(CH3)2), 1.04 (3H, d, 3JH−H = 6.8 Hz, CH(CH3)2). 13C{1H} NMR (C6D6): 154.8, 148.5 (C9), 146.11, 146.08, 144.3, 140.2 (C7), 139.9, 129.8 (C3), 129.3 (C15), 129.0 (C19 and C21), 128.1 (C18 and C22), 127.7 (C12), 127.5 (C14), 127.0 (C13), 125.6, 122.5 (C20), 120.6 (C8), 114.4 (C4), 111.7 (C2), 84.7 (C16), 28.0 (C11CH(Me)2), 25.3 (CH(CH3)2), 24.1 (CH(CH3)2). Anal. Calcd for C39H38N2Hf: C 65.68, H 5.37, N 3.93. Found: C 65.76, H 5.59, N 3.72. ((2,6-Dimethylphenyl)(2,4-dimethylquinolin-8-yl)amino)tribenzylhafnium (6d). A solution of 5d (0.155 g, 0.561 mmol) in

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JH−H = 7.4 Hz, H18, H22), 6.09 (1H, dd, 3JH−H = 7.3 Hz, 3JH−H = 1.3 Hz, H2), 3.35 (2H, br, B(CH2Ph)), 2.36 (3H, s, C7-CH3), 2.03 (2H, d, 3JH−H = 10.3 Hz. H16a), 1.93 (C11-CH3 and C15-CH3), 1.83 (2H, d, 3JH−H = 10.3 Hz, H16b), 1.54 (3H, s, C9-CH3). 19F NMR (C6D5Cl): (major species, free anion) −130.5 (2F, d, 3JF−F = 23 Hz, ortho-C6F5), −164.1 (1F, t, 3JF−F = 21 Hz, para-C6F5), −166.9 (2F, dd, 3 JF−F = 21, 23 Hz, meta-C6F5); (minor species, coordinated anion) −130.8 (2F, d, 3JF−F = 21 Hz, ortho-C6F5), −159.4 (1F, t, 3JF−F = 21 Hz, para-C6F5), −163.9 (2F, t, 3JF−F = 21 Hz, meta-C6F5). Structure Determinations of 5d, 6a, 6b, 6c, and 6d. X-ray intensity data were collected on a Bruker SMART diffractometer using Mo Kα radiation (λ = 0.71073 Å) and an APEXII CCD area detector. Raw data frames were read by the program SAINT12 and integrated using 3D profiling algorithms. The resulting data were reduced to produce hkl reflections and their intensities and estimated standard deviations. The data were corrected for Lorentz and polarization effects, and numerical absorption corrections were applied based on indexed and measured faces. The structure was solved and refined in SHELXTL6.1, using full-matrix least-squares refinement. The non-H atoms were refined with anisotropic thermal parameters, and all of the H atoms were calculated in idealized positions and refined riding on their parent atoms. The refinement was carried out using F2 rather than F values. R1 is calculated to provide a reference to the conventional R value, but its function is not minimized. Batch Reactor Ethylene/Octene Copolymerizations. A one gallon (3.79 L) stirred autoclave reactor is charged with ca. 1.35 kg of Isopar E mixed alkanes solvent and 1-octene (250 g). The reactor is heated to the desired temperature and charged with hydrogen (20 mmol) followed by approximately 125 g of ethylene to bring the total pressure to ca. 425 psig (2.95 MPa). The ethylene feed was passed through an additional purification column. The catalyst composition is prepared in a drybox under inert atmosphere by mixing the catalyst and cocatalyst (mixture of 1.2 equiv of [HNMe(C18H37)2][B(C6F5)4] and 50 equiv of triisobutylaluminum-modified alumoxane (MMAO3A)) with additional solvent to give a total volume of about 17 mL. The activated catalyst mixture is injected into the reactor over ca. 4 min by a pump system. The reactor pressure and temperature are kept constant by feeding ethylene during the polymerization and cooling the reactor as needed. After 10 min, the ethylene feed is shut off and the solution transferred into a nitrogen-purged resin kettle. An additive solution containing a phosphorus stabilizer (Irgafos 168 from Ciba Geigy Corp.) and phenolic antioxidant (Irganox 1010 from Ciba Geigy Corp.) is added to give a total additive content of approximately 0.1% in the polymer. The polymer is thoroughly dried in a vacuum oven. The reactor is thoroughly rinsed with hot Isopar E between polymerizations. Polymer Characterization. Melting and crystallization temperatures of polymers were measured by differential scanning calorimetry (DSC 2910, TA Instruments, Inc.). Samples were first heated from room temperature to 180 °C at 10 °C/min. After being held at this temperature for 2−4 min, the samples were cooled to −40 °C at 10 °C/min, held for 2−4 min, and then heated to 160 °C. Weight average molecular weights (Mw) and polydispersity values (PDI) were determined by analysis on a Viscotek HT-350 gel permeation chromatograph (GPC) equipped with a low-angle/right-angle lightscattering detector, a four-capillary inline viscometer, and a refractive index detector. The GPC utilized three Polymer Laboratories PLgel 10

toluene (5 mL) was cooled to −40 °C, then added to a vial containing HfBn4 (0.287 g, 0.529 mmol). The resulting solution turned orange immediately and was allowed to warm to room temperature and stirred for 1 h. The volume of toluene was reduced to ca. 2 mL, and hexane (ca. 8 mL) was added, at which point the solution was cooled to −40 °C. After 1 day, the resulting orange crystals were collected and dried under vacuum, affording the desired product in high purity (0.325 g, 85%). 1H NMR (toluene-d8): 7.14 (2H, d, 3JH−H = 7.6 Hz, H12 and H14), 7.06 (1H, dd, 3JH−H = 7.6 Hz, 7.6 Hz, H13), 7.00 (1H, t, 3JH−H = 8.0 Hz, H3), 6.87 (6H, br, H19 and H21), 6.80 (1H, dd, 3 JH−H = 8.0 Hz, 4JH−H = 1.0 Hz, H4), 6.66 (3H, br, H20), 6.55 (6H, br, H18 and H22), 6.27 (1H, s, H8), 6.12 (1H, dd, 3JH−H = 8.0 Hz, 4JH−H = 1.0 Hz, H2), 2.46 (6H, br, H16), 2.14 (6H, s, C11-CH3 and C15CH3), 2.06 (3H, s, C7-CH3), 2.03 (3H, s, C9-CH3). 13C{1H} NMR (toluene-d8): 163.1, 156.4, 154.8, 151.7, 151.3 (br), 143.6, 142.1, 140.0, 134.3 (C12 and C14), 133.5 (C3), 132.9 (br, C19 and C21), 132.3 (C18 and C22), 130.8 (C13), 128.9 (C8), 126.7 (br, C20), 116.1 (C4), 115.4 (C2), 93.9 (br, C16), 29.9 (C9-CH3), 23.30 (C11-CH3 and C15-CH3), 23.28 (C7-CH3). Anal. Calcd for C40H40N2Hf: C 66.06, H 5.54, N 3.85. Found: C 66.35, H 5.43, N 3.70. [((2,6-Dimethylphenyl)(2,4-dimethylquinolin-8-yl)amino)dibenzylhafnium] [tris(pentafluorophenyl)benzylborate] (7d). Complex 6d (25 mg, 0.03 mmol) was dissolved in 0.6 mL of C6D5Cl. This solution was added to a vial containing 16.9 mg (0.03 mmol) of B(C6F5)3. NMR spectra were taken 10 min after mixing. 1H NMR (C6D5Cl): 7.16 (4H, m, H3, H13, ortho-C6H5CH2B), 7.10 (3H, m, H4, H12, H14), 6.95 (2H, t, 3JH−H = 7.6 Hz, meta-C6H5CH2B), 6.85 (6H, tm 3JH−H = 7.8 Hz, H19, H21), 6.80 (1H, tt, 3JH−H = 7.3 Hz, 4 JH−H = 1.3 Hz, para-C6H5CH2B), 6.78 (1H, t, 4JH−H = 0.9 Hz, H8), 6.63 (2H, tt, 3JH−H = 7.6 Hz, 4JH−H = 1.1 Hz, H20), 6.18 (4H, dm, 6250

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μm MIXED-B columns (300 × 7.5 mm) at a flow rate of 1.0 mL/min in 1,2,4-trichlorobenzene at either 145 or 160 °C. Octene incorporation was determined by 13C NMR.13 The samples were prepared by adding approximately 2.7 g of a 50/50 mixture of tetrachloroethane-d2/ortho-dichlorobenzene containing 0.025 M Cr3+ to 0.25 g of the respective copolymer sample in a Norell 1001-7 10 mm NMR tube. The samples were dissolved and homogenized by heating the tube and its contents to 150 °C using a heating block and heat gun. Each sample was visually inspected to ensure homogeneity. The data were collected using a Bruker AVANCE 400 MHz spectrometer equipped with a Bruker Dual DUL high-temperature CryoProbe. The data were acquired using 320 transients per data file, a 6 s pulse repetition delay, 90 degree flip angles, and inverse gated decoupling with a sample temperature of 120 °C. All measurements were made on nonspinning samples in locked mode. Samples were allowed to thermally equilibrate for 7 min prior to data acquisition. The 13C NMR chemical shifts were internally referenced to the EEE triad at 30.0 ppm.

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26, 3896−3899. (b) Mashima, K.; Ohnishi, R.; Yamagata, T.; Tsurugi, H. Chem. Lett. 2007, 36, 1420−1421. (c) Tsurugi, H.; Ohnishi, R.; Kaneko, H.; Panda, T. K.; Mashima, K. Organometallics 2009, 28, 680−687. (d) Kaneko, H.; Tsurugi, H.; Panda, T. K.; Mashima, K. Organometallics 2010, 29, 3463−3466. (e) Froese, R. D.; Jazdzewski, B. A.; Klosin, J.; Kuhlman, R. L.; Theriault, C. N.; Welsh, D. M.; Abboud, K. A. Organometallics 2011, 30, 251−262. (f) Figueroa, R.; Froese, R. D.; He., Y.; Klosin, J.; Theriault, C. N.; Abboud, K. A. Organometallics 2011, 30, 1695−1709. (6) For selected examples of metal complexes of aminoquinolines, see: (a) Lee, J. C.; Muller, B.; Pregosin, P.; Yap, G. P. A.; Rheingold, A. L.; Crabtree, R. H. Inorg. Chem. 1995, 34, 6295−6301. (b) Peters., J. C.; Harkins, S. B.; Brown, S. D.; Day, M. W. Inorg. Chem. 2001, 40, 5083−5091. (c) Pi, C.; Zhang, Z.; Pang, Z.; Zhang, J.; Luo, J.; Chen, Z.; Weng, L.; Zhou, X. Organometallics 2007, 26, 1934−1946. (d) Betley, T. A.; Qian, B. A.; Peters, J. C. Inorg. Chem. 2008, 47, 11570−11782. (e) Deraeve, C.; Maraval, A.; Vendier, L.; Faugeroux, V.; Pitie, M.; Meunier, B. Eur. J. Inorg. Chem. 2008, 36, 5622−5631. (f) Betley, T. A.; Qian, B. A.; Peters, J. C. Inorg. Chem. 2008, 47, 11570−11582. (g) Malassa, A.; Koch, C.; Stein-Schaller, B.; Gorls, H.; Friedrich, M.; Westerhausen, M. Inorg. Chim. Acta 2008, 361, 1405− 1414. (h) O’Neill, M. K.; Trappey, F. A.; Battle, P.; Boswell, C. L.; Blauch, D. N. Dalton Trans. 2009, 3391−3394. (i) Liu, D.; Cui, D. Dalton Trans. 2011, 40, 7755−7761. (j) Liu, D.; Luo, Y.; Gao, W.; Cui, D. Organometallics 2010, 29, 1916−1923. (7) For examples of polymerization catalysts utilizing quinoline-based ligands, see: (a) Nagy, S.; Krishnamurti, R.; Tyrell, J. A.; Cribbs, L. V.; Cocoman, M. (Occidental Chemical Corporation, USA), Appl.WO9633202, 1996. (b) Fontaine, P. P.; Kuhlman, R. L. (Dow Global Technologies), Appl. WO2011102990, 2011. (c) Nagy, S.; Winslow, L. N.; Mihan, S.; Chevalier, R.; Lukesova L.; Nifant’ev, I. E.; Ivchenko, P. V.; (Equistar Chemicals), Appl. WO2011011040, 2011. (d) Nagy, S.; Winslow, L. N.; Mihan, S.; Chevalier, R.; Lukesova L.; Nifant’ev, I. E.; Ivchenko, P. V.; Lynch, M. W. (EquistarChemicals), Appl. WO2011011041, 2011. (e) Lamberti, M.; Bortoluzzi, M.; Paolucci, G.; Pellecchia, C. J. Mol. Catal. A: Chem. 2011, 351, 112−119. (f) Nagy, S.; Winslow, L. N.; Mihan, S.; Lukesova, L.; Nifant’ev, I. E.; Ivchenko, P. V.; Bagrov, V. V. (Basell Polyolefine GmbH, Germany), Appl. US20120016092, 2012. (g) Song, S.; Xiao, T.; Wang, L.; Redshaw, C.; Wang, F.; Sun, W.-H. J. Organomet. Chem. 2012, 699, 18−25. (8) Full experimental details are provided in the Supporting Information. (9) Ugi, I.; Marquardinh, D.; Klusacek, H.; Gillespie, P.; Ramirez, F. Acc. Chem. Res. 1971, 4, 288−296. (10) For selected examples of organometallic additions to quinolines, see: (a) Gilman, H.; Eisch, J.; Soddy, T. S. J. Am. Chem. Soc. 1959, 81, 4000−4003. (b) Goldstein, S. W.; Dambek, P. J. Synthesis 1989, 3, 221−222. (c) Rezgui, F.; Mangeney, P.; Alexakis, A. Tetrahedron Lett. 1999, 40, 6241−6244. (d) Wang, Z.-X.; Li, Y.-X. Organometallics 2003, 22, 4900−4904. (e) Amiot, F.; Cointeaux, L.; Silve, E. J.; Alexakis, A. Tetrahedron 2004, 60, 8221−8231. (11) Horton, A. D.; de With, J.; van der Linden, A. J.; van de Weg, H. Organometallics 1996, 15, 2672−2674. (12) Sheldrick, G. M. SHELXTL6.1. Crystallographic Software Package; Bruker AXS, Inc.: Madison, Wisconsin, USA, 2008. (13) Qiu, X.; Redwine, D.; Gobbi, G.; Nuamthanom, A.; Rinaldi, P. L. Macromolecules 2007, 40, 6879−6884.

ASSOCIATED CONTENT

S Supporting Information *

This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENTS The authors are grateful to Donald Lowry for carrying out the batch reactor experiments and Manjiri Paradkar for 13C NMR determination of octene incorporation.

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REFERENCES

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dx.doi.org/10.1021/om3005417 | Organometallics 2012, 31, 6244−6251