Insights into the Formation Process of Yttrium–Aluminum Bimetallic

We elucidated the step-reaction mechanism between the yttrium dialkyl complex ... model complexes (Chart 1C and Chart 2D–F)(12a,c,d,i) were synthesi...
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Article Cite This: Organometallics XXXX, XXX, XXX−XXX

Insights into the Formation Process of Yttrium−Aluminum Bimetallic Alkyl Complexes Supported by a Bulky Phosphazene Ligand Weifeng Rong,†,‡ Meiyan Wang,§ Shihui Li,† Jianhua Cheng,† Dongtao Liu,*,† and Dongmei Cui*,† †

State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People’s Republic of China ‡ Shandong Institute of non-metallic materials, Jinan 250031, People’s Republic of China § Institute of Theoretical Chemistry, Jilin University, Changchun 130012, People’s Republic of China S Supporting Information *

ABSTRACT: The reaction of the yttrium dialkyl precursor [N[Ph2PNC6H3(iPr)2]2Y(CH2SiMe3)2] (1) with more than 3 equiv of trimethylaluminum or triethylaluminum afforded the dinuclear heterometallic complexes N[Ph2PNC6H3(iPr)2]2Y{(μ-R)2AlR2}R (R = Me (2), Et (3)). When trimethylaluminum loading was reduced to 2 equiv, the same reaction gave the product N[Ph2PNC6H3(iPr)2]2Y{(μ-Me)2(μ-CH2SiMe3)AlMe}Me (4), with quite a different bonding mode. All of these complexes were characterized by NMR spectra, X-ray crystallography, and elemental analysis. We elucidated the step-reaction mechanism between the yttrium dialkyl complex based on bulky phosphazene ligand and trialkylaluminum, which might shed new light on the formation process of active species in organoaluminum-dependent Ziegler−Natta catalytic systems.

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INTRODUCTION Organoaluminum compounds (AlR3) have become the most widely used cocatalysts in the polymerization of olefins, since the epoch-making discovery of the Ziegler−Natta catalytic system (TiCl4/AlEt3 or TiCl3/AlEt3) for the polymerizations of ethylene or propylene in the 1950s.1,2 With the innovation of the single-site metallocene precursors (1970s), methylaluminoxane (MAO), a hydrolysis product of AlMe3, was the best activator to replace the organoaluminum compounds. In the meantime, the excellent performances of the catalytic combination of organometallic precursors with organoborates and AlR3 drew researchers’ attention back to AlR3, which turned out to be the essential component of the catalytic system again to scavenge impurities of the polymerization system and, more importantly, to affect the activity and selectivity. Major achievements have revealed that AlR3 is involved in every stage of the polymerization, including olefin coordination (initiation)3 and insertion (propagation),4,5 as well as β-hydrogen elimination4,5 and β-alkyl elimination (termination).6 Therefore, AlR3 has occupied an irreplaceable position in the development of olefin polymerization, and investigations of the interaction of AlR3 with the catalytic precursors to find the truly active species to govern the activity and selectivity of the resultant catalytic systems have never stopped.2 The successful synthesis of the Tebbe reagent [Cp2Ti{(μ-CH2)(μ-Cl)Al(CH3)2}], although it was only used in the methylenation of carbonyl compounds,7a aroused scientists’ research interest because it gave some hints to the real active species of Ziegler−Natta catalysts for olefin polymerizations.7b,c In this regard, Pearce and Lappert did much pioneering work on the alkyl-bridged aluminum and the © XXXX American Chemical Society

d-/f-block metal complexes bearing a cyclopentadienyl ancillary ligand (Chart 1A),8 which rendered the lanthanide alkyl Chart 1. Typical Examples of Methylaluminate Rare-EarthMetal Complexes

complexes to be excellent models for clarifying the active sites.9 Evans and Anwander investigated the homo-10 and heteroleptic11 tetramethylaluminate rare-earth-metal complexes (Chart 1B,C) and the innovative chemistry of their methylidene and methine species,12 which significantly fueled the development of Ln−Al heterobimetallic complexes in olefin polymerization catalysis9f,11f,13 as well as in specially designed organic reactions.14 It is notable that most of the related model complexes (Chart 1C and Chart 2D−F)12a,c,d,i were synthesized by treatment of a permethylated lanthanide−aluminum precursor (Chart 1B)2,15 with ligand precursors. Moreover, these complexes tended to assemble to polylanthanide− polyaluminum [LnnAln]12a,13h,22a or monolanthanide−polyaluminum [LnAln]10c,11,12f,13,14b along with a few monolanthaReceived: December 28, 2017

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precursor and the cocatalysts as well as the design of catalytic combinations.

Chart 2. Selected Structural Models Originating from Ln(AlMe4)3 as Precursors

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RESULTS AND DISCUSSION Reaction of [N(Ph2PNC6H4iPr2)2]Y(CH2SiMe3)2 with an Excess of AlMe3. Considering that excess amounts of organoaluminum were always employed during the polymerization of conjugated dienes, we initially treated the yttrium dialkyl complex [N(Ph2PNC6H4iPr2)2]Y(CH2SiMe3)2 (1) with excess amounts of AlMe3 (3−10 equiv) in toluene at ambient temperature to give complex 2 as a white solid in a good yield (Scheme 1). The NMR spectral data of 2 in benzene-d6 were intriguing and inconsistent with what we expected for the usual bis(tetramethylaluminate) species LLn(AlMe4)2 (L = monoanionic ligand).10−15 For example, the 1H NMR spectrum in C6D6 (Figure S3) of 2 shows two sets of peaks for isopropyl groups with a 3JHH coupling constant of 6.8 Hz. The presence of more than one peak for a Y−Al fragment is indicative of an asymmetric structure. A doublet at δ 0.07 ppm with an integration of 9 is observed with the low coupling constant JYH = 0.8 Hz, indicating a 4JYH coupling, not a 2JYH coupling (around 2.4 Hz),13d which should be assigned to the three same methyl groups. Moreover, two different signals with an approximate integral ratio of 3:3 indicate clearly that there are two kinds of Y−CH3, which further excludes the formation of the bis(tetramethylaluminate) species LLn(AlMe4)2. Thus, a Y(η1-μ-CH3)Al(CH3)3-bonded linkage could be confirmed in C6D6 solution. However, an X-ray diffraction study shows a different structure. In the solid state, complex 2 adopts a distortedpentagonal-pyramidal coordination geometry (Figure 1). The terminal CH3 group (C49) is in the apical position, and N1, N2, and N3 from the ligand and the bridging methyl groups (C50 and C51) of the Al(CH3)4 occupy the equatorial plane. The Al(CH3)4 moiety shows a planar η2 coordination to Y3+ ion (Figure 4A), instead of η1-methyl coordination. This suggested a very fast exchange of bridging and terminal methyl groups in Al(CH3)4, where η1 coordination is preferred in solution and η2 coordination is preferred in the solid state. The difference proves the high coordinational flexibility of the tetramethylaluminate ligand and its ability to adapt perfectly to the given stereoelectronic requirements of the rare-earth-metal center. The molecular structure of complex 2 is very similar to that of the documented aluminate yttrium complex with a bulky hydrotris(pyrazolyl)borate ligand ((TptBu,Me)Y{η1-μ-(CH3)Al(CH3)3}(CH3)) (Chart 2E),12c,d bearing the similar monoaluminate core [Ln1Al1] (Figure 4D). However, the pincer-type ligand coordinates to the Y3+ ion in a κ3 fashion with Y−N bond lengths ranging from 2.422(3) to 2.468(3) Å and the

nide−monoaluminum complexes.9a,f,11i,16 However, in the polymerization procedure, the active species is generated by a direct reaction between the catalytic precursors bearing the ancillary ligands and organoaluminum. Therefore, the isolation of lanthanide−aluminum binuclear complexes is rather challenging but obviously important. Organolanthanide bis(alkyl) complexes bearing a monoanionic ancillary ligand with the activation of trialkylaluminum have proved to be extremely successful in olefin17 and conjugated diene polymerizations.18 Of these, rare-earth-metal bis(alkyl) complexes supported by phosphazene ligands have been documented not only in the polymerization of dienes19 but also in the synthesis of hydride20 and terminal imido complexes, owing to the versatile steric hindrance around the metal centers.21 We reported previously that the monoanionic phosphazene ligand stabilized the rare-earth-metal complexes [N(Ph2PNPh)2]Ln(CH2SiMe3)2,19 upon activation of AlR3 and organoborate, and showed a high activity toward the trans-1,4polymerization of isoprene. However, the analogous complex [N(Ph2PNAr)2]Ln(CH2SiMe3)2 (Ar = 2,6-diisopropylphenyl) was totally inert under the same conditions, which might be ascribed to the more crowded environment around the active metal center hindering the coordination of the monomer. This sterically bulky active metal center, on the other hand, might form a stable adduct with mono-AlR3, the structural model that mimics the real active species and is ubiquitous in the monoanionic ligand attached rare-earth-metal catalyst systems;11f,13 this adduct, however, has not been obtained to date. Herein we present the reaction of the yttrium complex 1, [N(Ph2PNC6H4iPr2)2]Y(CH2SiMe3)2, with AlR3 to afford monoanionic phosphazene-ligated Y−Al bimetallic complexes. The structures vary with the loading and type of AlR3. Hence, a fundamental understanding of the precursor−cocatalyst interaction and structure−reactivity relationship was established. This work sheds some new light on the mechanism of coordination polymerization and the choice of catalytic Scheme 1. Synthesis of Complex 2

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Figure 1. X-ray structure of 2 with 35% probability thermal ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): Y1−C49 2.374(5), Y1−C50 2.612(5), Y1−C51 2.697(5), Y1−N3 2.422(3), Y1−N2 2.424(3), Y1−N1 2.468(3), Al1− C53 1.975(5), Al1−C52 1.982(6), Al1−C51 2.028(5), Al1−C50 2.034(6); C49−Y1−N3 104.26(13), C49−Y1−N2 106.64(14), N3− Y1−N2 116.36(11), C49−Y1−N1 97.72(14), N3−Y1−N1 60.88(11), N2−Y1−N1 60.87(11).

Figure 2. X-ray structure of 3 with 35% probability thermal ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): Y1−C1 2.395(4), Y1−N2 2.420(4), Y1−N3 2.494(4), Y1−N1 2.475(4), Y1−C9 2.615(5), Y1−C3 2.702(6), Al1−C7 1.980(12), Al1−C3 2.031(5), Al1−C9 2.049(6), Al1−C5 2.098(12); C1−Y1−N2 108.65(15), C1−Y1−N3 103.09(17), N2− Y1−N3 114.34(13), C1−Y1−N1 95.09(16), N2−Y1−N1 61.03(14), N3−Y1−N1 60.20(13).

distance between yttrium atom and terminal carbon being 2.374(5) Å, close to the reported values.12c The bridging Y−C bonds are relatively longer (2.612(5) and 2.697(5) Å, respectively). The formation of such a constitution of mono(tetramethylaluminate) and a yttrium terminal methyl moiety instead of bis(tetramethylaluminate) clearly demonstrates that the sterically saturated environment imposed on the central yttrium by the bulky phosphazene ligand tends to produce metal complexes with low coordination numbers.12d,22b Reaction of [N(Ph2PNC6H4iPr2)2]Y(CH2SiMe3)2 with an Excess of AlEt3. Triethylaluminum is also a widely used cocatalyst in Ziegler−Natta catalyst systems.23 To date, only a few ethylaluminate rare-earth complexes have been authenticated by X-ray diffraction: for example, divalent ethylaluminate rare-earth-metal complexes,16,24 homoleptic Ln(III) complexes,25 and heteroleptic Ln(III) metallocene complexes.9a,f,13b,26 Following the procedure described for the preparation of 2, treatment of 1 with excess amounts of AlEt3 afforded complex 3 as colorless crystals (Scheme 2). The 1H NMR spectrum showed that 3 might feature the same η1 coordination in Y−Al fragment as that for 2 in solution (Figure S5). X-ray single-crystal diffraction showed that 3 and 2 are almost isostructural, crystallizing in the monoclinic space group P21/n for complex 3 in comparison to P21/c for complex 2 (Figure 2). Complex 3 contains η2-Y-(μ-Et)2-Al coordination (Figure 4F) and one terminal ethyl group, instead of the η1ethyl coordination depicted above. The change from methyl to

ethyl groups seems to slightly elongate all tof he bonds (Ln−C and Ln−N), as AlEt3 is more bulky than AlMe3, consistent with Anwander’s observation.25 Investigation of the Reaction Process between Complex 1 and Trimethylaluminum. The successful isolation of complexes 2 and 3 stimulated us to carefully explore the detailed reaction process. When 1 equiv of AlMe3 was added to a toluene solution of complex 1, a precipitate was generated instantly, which was a mixture of intractable components with poor solubility, inhibiting further characterization. Nevertheless, we eventually obtained the pure product 4 after another 1 equiv of AlMe3 was added (Scheme 3). Complex 4 was characterized by elemental analysis and the NMR spectrum. In the 1H NMR spectrum (Figure S7), similar to that of 2, two sets of peaks for isopropyl groups were observed at δ 3.71 and 3.91 ppm for −CH− groups, obviously different from those in the dialkyl precursor 1. The methylene and trimethylsilane protons showed two singlets at δ −0.67 and 0.20 ppm with an integral ratio of 2:9, which showed 4 to be a partially methylated compound. A slightly broad signal was assigned to the Y−CH3 group at δ 0.70 ppm. Colorless single crystals of 4 were obtained by recrystallization from a toluene/ hexane mixture at −30 °C. Complex 4 is a rather uncommon seven-coordinate monomer where the yttrium center displays a heavily distorted pentagonal bipyramidal coordination geometry, where C1 and C3 occupy the two apical positons while the

Scheme 2. Synthesis of Complex 3

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minate complex [La{(μ 2 -Me) 2 AlMe 2 } 2 {(μ 2 -Me) 3 AlMe}] (2.772(3), 2.980(3), 2.892(3) Å, average 2.881(3) Å).13d Taking the variances of metal radii into consideration, 4 features a true η3 coordination. To our knowledge this is the first well-defined mononuclear tetramethylaluminate complex [LnAl] with a hetero-η3-coordination mode in rare-earth chemistry. As expected, 2 was generated again by addition of more AlMe3 to 4. Accordingly, a reaction pathway has been deduced. The coordination of two AlMe3 groups to 1 generates 4, with release of one molecule of AlMe2(CH2SiMe3). Upon activation of another AlMe3, 4 releases a fragment of AlMe2(CH2SiMe3) to form 2, which can isomerize to complex 2′ by methyl exchange.

three N atoms, Y1, C2, and C4 form the equatorial plane (Figure 3). It is worthwhile to note that 4 features a η3-

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CONCLUSIONS In summary, we have demonstrated that the sterically crowded, monoanionic phosphazene ligand provides a unique environment for the isolation of yttrium−aluminum complexes N[Ph2PNC6H3(iPr)2]2Y{(μ-R)2AlR2}R (R = Me, Et) through the reaction of the corresponding dialkyl precursor [N(Ph2PNC6H4iPr2)2]Y(CH2SiMe3)2 with an excess of AlMe3 or AlEt3. By reduction of the loading of AlMe3, the first welldefined aluminate complex N[Ph 2 PNC 6 H 3 ( i Pr) 2 ] 2 Y{(μMe)2(μ-CH2SiMe3)AlMe}Me with a hetero-η3-coordination mode was isolated. Accordingly, a reaction pathway has been deduced to provide us with a full understanding of the detailed mechanism. Thus, the chemistry reported herein provides new insight into the active species of Ziegler−Natta catalysts and may cause some consideration of the foundation of new catalyst models.

Figure 3. X-ray structure of 4 with 35% probability thermal ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): C1−Y1 2.462(4), C2−Al1 2.032(5), C2−Y1 2.796(5), C3−Al1 2.041(5), C3−Y1 2.767(5), C4−Al1 2.018(5), C4−Y1 2.832(5), C5−Al1 1.963(5); Si1−C2−Al1 113.9(2), Si1−C2− Y1 173.4(2), Al1−C2−Y1 72.50(14), Al1−C3−Y1 73.05(14), Al1− C4−Y1 71.82(14), N3−Y1−N2 121.27(10), N3−Y1−N1 60.86(10), N2−Y1−N1 60.92(10), N3−Y1−C1 107.26(12), N2−Y1−C1 94.60(12), N1−Y1−C1 105.44(11).

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EXPERIMENTAL SECTION

General Methods and Materials. All reactions were carried out under a dry and oxygen-free argon atmosphere by using Schlenk techniques or under a nitrogen atmosphere in an MBraun glovebox. All solvents were purified with an MBraun SPS system. Organometallic samples for NMR spectroscopic measurements were prepared in the glovebox by use of NMR tubes sealed with paraffin film. 1H and 13 C{1H} NMR spectra were recorded on a Bruker AV400 or AV600 (FT, 400 MHz for 1H, 100 MHz for 13C; 600 MHz for 1H, 150 MHz for 13C) spectrometer. Elemental analyses were performed at the National Analytical Research Centre of the Changchun Institute of Applied Chemistry (CIAC). AlMe3 and AlEt3 were purchased as pure products from Aldrich. The yttrium dialkyl complex 1 was prepared according to literature procedures.19 X-ray Crystallographic Studies. Crystals for X-ray analysis were obtained as described in the preparations. The crystals were manipulated in a glovebox. Data collections were performed at −88.5 °C on a Bruker SMART APEX diffractometer with a CCD area detector, using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). The determination of crystal class and unit cell parameters was carried out with the SMART program package. The raw frame data were processed using SAINT and SADABS to yield the reflection data file. The structures were solved by using the SHELXTL program.

Figure 4. Structurally characterized Ln−Al coordination modes ([LnAl]; A,22a B,22a C,13d,22a D,12c,d E,16a F,16b G,9f,16c H).

coordinated aluminate group (Figure 4H), which has three similar Y−C bond lengths (2.796(5), 2.767(5), 2.832(5) Å, average 2.798(5) Å) and a short Y···Al separation of 2.920(14) Å. These η3-coordinated Y−C bonds are significantly longer than the normal terminal Y−C1 bond (2.462(4) Å) of complex 4 and the η2-coordinated Y−C (μ2-CH3) bonds (average 2.655(5) Å) of complex 2 but are very close to those in the pentanuclear neodymium cluster [Cp* 5 -η 3 -Nd 5 {(μ 2 Me)3AlMe}(μ4-Cl)(μ3-Cl)2(μ2-Cl)6] (2.878(18), 2.875(16), 2.779(16) Å, average 2.844(16) Å)22a and the tetramethylaluD

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Organometallics Refinement was performed on F2 anisotropically for all non-hydrogen atoms by the full-matrix least-squares method. All non-hydrogen atoms were found from Fourier syntheses of electron density and were refined anisotropically and isotropically for hydrogens. All of the hydrogen atoms were placed in calculated positions and were refined in the riding model. More details on the crystallographic measurements can be found in Table S1. CCDC 1046172 (4), 1046173 (2), and 1046174 (3) contain supplementary crystallographic data for this paper. Synthesis of Complex 2. Under a nitrogen atmosphere, to a toluene (10 mL) solution of [N(PPh2NPh(iPr)2)2]Y(CH2SiMe3)2 (0.3 g, 0.3 mmol) was slowly added 3 equiv of AlMe3 (0.064 g, 0.9 mmol, in 2 mL of toluene). The solution was stirred for 24 h at ambient temperature. The yellow solution was concentrated to 2 mL under reduced pressure, and several drops of diethyl ether were added after filtration. Colorless crystals of 2 could be obtained after standing at ambient temperature for several days (0.172 g, 62%). 1H NMR (400 MHz, C6D6, 7.16 ppm, 25 °C): δ −0.39, −0.27 (s s, 3H, YCH3Al), 0.06 (d, 4JYH = 0.8 Hz, 9H, Y(CH3)Al(CH3)3), 0.40 (d, 3JHH = 6.8 Hz, 6H, CH(CH3)2), 0.62 (d, 3JHH = 6.8 Hz, 6H, CH(CH3)2), 0.70 (d, 2 JYH = 2.4 Hz, 3H, YCH3), 1.35 (d, 3JHH = 6.8 Hz, 6H, CH(CH3)2), 1.42 (d, 3JHH = 6.8 Hz, 6H, CH(CH3)2), 3.70 (hept, 3JHH = 6.8 Hz, 2H, CH(CH3)2), 3.90 (hept, 3JHH = 6.8 Hz, 2H, CH(CH3)2), 6.54 (m, 4H, Ar-H), 6.71 (m, 2H, Ar-H), 6.90 (m, 4H, Ar-H), 6.97 (m, 2H, ArH), 7.07 (m, 4H, Ar-H), 7.12 (s, 6H, Ar-H), 7.51 ppm (m, 4H, Ar-H). 13 C{1H} NMR (100 MHz, C6D6, 128.06 ppm, 25 °C) δ −0.30, 3.02 (s s, Y(CH3)Al(CH3)3), 21.43 (s, Y(CH3)Al(CH3)3), 23.41 (s, C6H3CH(CH3)2), 23.59 (s, C6H3CH(CH3)2), 27.00 (s, C6H3CH(CH3)2), 27.18 (s, C6H3CH(CH3)2), 28.83 (s, C6H3CH(CH3)2), 29.11(s, C6H3CH(CH3)2), 30.26 (d, JYC = 55 Hz, YCH3), 124.32 (s, aromatic CH), 124.82 (s, aromatic CH), 125.28 (s, aromatic CH), 125.70 (s, aromatic CH), 129.33 (s, aromatic CH), 131.37 (s, aromatic C), 131.89 (s, aromatic C), 132.23 (m, aromatic C), 132.44 (d, aromatic ipso-C), 132.68 (m, aromatic C), 133.28 (m, aromatic C), 133.41 (d, aromatic ipso-C), 134.43 (s, aromatic C), 137.90 (s, aromatic C), 140.91 (s, aromatic C), 145.15 (s, aromatic C), 146.58 ppm (s, aromatic C). Anal. Calcd for C53H69N3P2AlY: C, 68.75; H, 7.51; N, 4.54. Found: C, 69.07; H, 7.26; N, 4.36. Synthesis of Complex 3. By a procedure similar to that described for the preparation of 2, treatment of [N(PPh2NPh(iPr)2)2]Y(CH2SiMe3)2 (0.3 g, 0.3 mmol) with 3 equiv of AlEt3 (0.103 g, 0.90 mmol) gave 3 as a white solid. Colorless crystals could be obtained from a mixture of toluene and hexane after standing at ambient temperature for 2 days (0.164 g, 55%). 1H NMR (400 MHz, C6D6, 7.16 ppm, 25 °C): δ 0.20−0.27 (m, 2H, Y(μ-CH2CH3)Al(CH2CH3)3), 0.32 (m, 6H, Y(μ-CH2CH3)Al(CH2CH3)3), 0.41 (d, 3 JHH = 6.8 Hz, 6H, CH(CH3)2), 0.47 (quar, 3JHH = 8.0 Hz, 2H, YCH2CH3), 0.74 (d, 3JHH = 6.8 Hz, 6H, CH(CH3)2), 1.31−1.48 (m, 24H, Y(μ-CH2CH3)Al(CH2CH3)3 + CH(CH3)2), 1.99 (t, 3JHH = 8.0 Hz, 3H, YCH2CH3), 3.62 (hept, 3JHH = 6.6 Hz, 2H, CH(CH3)2), 3.70 (hept, 3JHH = 6.6 Hz, 2H, CH(CH3)2), 6.44 (m, 4H, Ar-H), 6.61 (m, 2H, Ar-H), 6.94−7.26 (m, 16H, Ar-H), 7.63 ppm (m, 4H, Ar-H). 13 C{1H} NMR (100 MHz, C6D6, 128.06 ppm, 25 °C): δ 12.52 (s, Y(μ-CH2CH3)Al(CH2CH3)3), 16.55 (s, Y(μ-CH2CH3)Al), 24.18 (s, C6H3CH(CH3)2)), 25.51(s, C6H3CH(CH3)2), 26.37 (s, C6H3CH(CH3)2), 29.07 (s, Y(μ-CH2CH3)Al(CH2CH3)3(CH2CH3)), 29.19 (s, Y(μ-CH2CH3)Al(CH2CH3)3(CH2CH3)), 45.12 (d, JYC = 58 Hz, YCH2CH3), 124.71 (s, aromatic CH), 124.92 (s, aromatic CH), 125.70 (s, aromatic CH), 131.16 (s, aromatic CH), 131.97 (s, aromatic C), 132.11 (s, aromatic C), 132.27 (s, aromatic C), 132.54 (s, aromatic C), 133.18 (m, aromatic ipso-C), 134.30 (s, aromatic ipso-C), 141.70 (s, aromatic C), 144.26 (s, aromatic C), 146.03 ppm (s, aromatic C). Anal. Calcd for C58H79N3P2AlY: C, 69.93; H, 7.99; N, 4.22. Found: C, 69.67; H, 8.12; N, 4.31. Synthesis of Complex 4. Under a nitrogen atmosphere, to a toluene (10 mL) solution of [N(PPh2NPh(iPr)2)2]Y(CH2SiMe3)2 (0.3 g, 0.3 mmol) was slowly added 2 equiv of AlMe3 (0.043 g, 0.6 mmol, in 2 mL of toluene). The solution was stirred for 12 h at ambient temperature. The yellow solution was concentrated to 2 mL under

reduced pressure, and several drops of hexane were added after filtration. Colorless crystals of 4 could be obtained after standing at −30 °C for 2 days (0.18 g, 60%). 1H NMR: δ −0.67 (s, 2H, YCH2), 0.20 (s, 9H, SiMe3), 0.21 (s, 6H, Al((μ-CH3)2Y), 0.25 (s, 3H, AlCH3), 0.40 (d, 3JHH = 6.6 Hz, 6H, CH(CH3)2), 0.62 (d, 3JHH = 6.6 Hz, 6H, CH(CH3)2), 0.70 (s, 3H, YCH3), 1.39 (d, 3JHH = 6.6 Hz, 6H, CH(CH3)2), 1.44 (d, 3JHH = 6.6 Hz, 6H, CH(CH3)2), 3.70 (hept, 3JHH = 6.6 Hz, 2H, CH(CH3)2), 3.91 (hept, 3JHH = 6.6 Hz, 2H, CH(CH3)2), 6.54 (m, 4H, Ar-H), 6.72 (m, 2H, Ar-H), 6.90 (m, 4H, Ar-H), 6.96 (m, 2H, Ar-H), 7.07 (m, 10H, Ar-H), 7.50 ppm (m, 4H, Ar-H). 13C{1H} NMR (100 MHz, C6D6, 128.06 ppm, 25 °C): δ 2.71 (s, CH2Si(CH3)3), 3.03 (s, CH2SiMe3), 3.46 (s, AlCH3), 23.42 (s, C6H3CH(CH3)2), 23.58 (s, C6H3CH(CH3)2), 27.00 (s, Y(μ-CH3)2Al), 27.14 (s, C6H3CH(CH3)2), 27.25 (s, C6H3CH(CH3)2), 28.83 (s, C6H3CH(CH3)2), 29.09 (s, C6H3CH(CH3)2), 30.30 (d, JYC = 54 Hz, YCH3), 124.34 (s, aromatic CH), 124.87 (s, aromatic CH), 125.32 (s, aromatic CH), 131.24 (s, aromatic C), 131.41 (s, aromatic C), 131.70 (s, aromatic C), 131.91 (m, aromatic C), 132.21 (m, aromatic C), 132.41 (d, aromatic ipso-C), 132.68 (m, aromatic C), 133.22 (s, aromatic C), 133.44 (d, aromatic ipso-C), 134.37 (s, aromatic C), 140.90 (s, aromatic C), 145.12 (s, aromatic C), 146.58 ppm (s, aromatic C). Anal. Calcd for C56H77N3P2SiAlY: C, 67.38; H, 7.78; N, 4.21. Found: C, 67.02; H, 7.95; N, 4.59.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00911. 1 H and 13C{1H} NMR spectra of complexes 1−4 and crystallographic data for complexes 2−4 (PDF) Accession Codes

CCDC 1046172−1046174 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

*D.L.: e-mail, [email protected]. *D.C.: e-mail, [email protected]; fax, (+86) 431 85262774; tel, +86 431 85262773. ORCID

Dongmei Cui: 0000-0001-8372-5987 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was partially supported by the NSFC (Project Nos. 21634007, and 21674108), the MST “973” project (No. 2015CB654702), and the department of science and technology of Jilin province (Project No. 20160520001JH). The authors are grateful to the Computing Center of Jilin Province for essential support.

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REFERENCES

(1) (a) Ziegler, K.; Holzkamp, E.; Breil, H.; Martin, H. Das Mülheimer Normaldruck-Polyäthylen-Verfahren. Angew. Chem. 1955, 67, 541−547. (b) Natta, G. Une nouvelle classe de polymeres d’αolefines ayant une régularité de structure exceptionnelle. J. Polym. Sci. 1955, 16, 143−154.

E

DOI: 10.1021/acs.organomet.7b00911 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics (2) Fischbach, A.; Anwander, R. Rare-EarthMetals and Aluminum Getting Close in Ziegler-type Organometallics. Adv. Polym. Sci. 2006, 204, 155−281. (3) (a) Casey, C. P.; Hallenbeck, S. L.; Wright, J. M.; Landis, C. R. Formation and Spectroscopic Characterization of Chelated d0 Yttrium(III)-Alkyl-Alkene Complexes. J. Am. Chem. Soc. 1997, 119, 9680−9690. (b) Abrams, M. B.; Yoder, J. C.; Loeber, C.; Day, M. W.; Bercaw, J. E. Fluxional η3-Allyl Derivatives of ansa-Scandocenes and an ansa-Yttrocene. Measurements of the Barriers for the η3 to η1 Process as an Indicator of Olefin Binding Energy to d0 Metallocenes. Organometallics 1999, 18, 1389−1401. (4) Watson, L. Ziegler-Natta Polymerization: The Lanthanide Model. J. Am. Chem. Soc. 1982, 104, 337−339. (5) (a) Burger, B. J.; Thompson, M. E.; Cotter, W. D.; Bercaw, J. E. Ethylene Insertion and β-Hydrogen Elimination for Permethylscandocene Alkyl Complexes. A Study of the Chain Propagation and Termination Steps in Ziegler-Natta Polymerization of Ethylene. J. Am. Chem. Soc. 1990, 112, 1566−1577. (b) Piers, W. E.; Bercaw, J. E. α ″Agostic″ Assistance in Ziegler-Natta Polymerization of Olefins. Deuterium Isotopic Perturbation of Stereochemistry Indicating Coordination of an α C-H Bond in Chain Propagation. J. Am. Chem. Soc. 1990, 112, 9406−9407. (6) Watson, P. L.; Roe, D. C. β-Alkyl Transfer in a Lanthanide Model for Chain Termination. J. Am. Chem. Soc. 1982, 104, 6471−6473. (7) (a) Hartley, R. C.; McKiernan, G. J. Titanium reagents for the alkylidenation of carboxylic acid and carbonic acid derivatives. J. Chem. Soc. Perkin Trans. 1 2002, 2763−2793. (b) Tebbe, F. N.; Parshall, G. W.; Ovenall, D. W. Titanium-Catalyzed Olefin Metathesis. J. Am. Chem. Soc. 1979, 101, 5074−5075. (c) Tebbe, F. N.; Parshall, G. W.; Reddy, G. S. Olefin Homologation with Titanium Methylene Compounds. J. Am. Chem. Soc. 1978, 100, 3611−3613. (8) (a) Lappert, M. F.; Pearce, R. Stable Silylmethyl and Neopentyl Complexes of Scandium(III) and Yttrium(III). J. Chem. Soc., Chem. Commun. 1973, 126−126. (b) Ballard, D. G. H.; Pearce, R. Doubly Methyl Bridged Titanium-Aluminium and Yttrium-Aluminium Compounds. J. Chem. Soc., Chem. Commun. 1975, 621a−621a. (c) Holton, J.; Lappert, M. F.; Ballard, D. G. H.; Pearce, R. Dimeric μ-Dimethyl Lanthanide Complexes, a New Class of Electron-deficient Compound, and the Crystal and Molecular Structure of [Yb(η -C5H5)2Me]2. J. Chem. Soc. J. Chem. Soc., Chem. Commun. 1976, 480−481. (d) Holton, J.; Lappert, M. F.; Scollary, G. R.; Ballard, D. G. H.; Pearce, R.; Atwood, J. L.; Hunter, W. E. μ-Dialkyl Inner Transition Metal(III) Tetra-alkylaluminates; the Crystal and Molecular Structure of Di-μmethyl -(dimethylaluminium)biscyclopentadienylyttrium and − ytterbium. J. Chem. Soc., Chem. Commun. 1976, 425−426. (e) Atwood, J. L.; Hunter, W. E.; Rogers, R. D.; Holton, J.; McMeeking, J.; Pearce, R.; Lappert, M. F. Neutral and Anionic Silylmethyl Complexes of the Group 3a and Lanthanoid Metals; the X-Ray Crystal and Molecular Structure of [Li(thf)4][Yb{CH(SiMe3)2)3Cl]. J. Chem. Soc., Chem. Commun. 1978, 140−142. (f) Holton, J.; Lappert, M. F.; Ballard, D. G. H.; Pearce, R.; Atwood, J. L.; Hunter, W. E. Alkyl-bridged Complexes of the d- and f-Block Elements. J. Chem. Soc., Dalton Trans. 1979, 54− 61. (9) (a) Klimpel, M. G.; Eppinger, J.; Sirsch, P.; Scherer, W.; Anwander, R. The Lanthanide Ziegler-Natta Model: AluminumMediated Chain Transfer. Organometallics 2002, 21, 4021−4023. (b) Fischbach, A.; Perdih, F.; Sirsch, P.; Scherer, W.; Anwander, R. Rare-Earth Ziegler-Natta Catalysts: Carboxylate-Alkyl Interchange. Organometallics 2002, 21, 4569−4571. (c) Dietrich, H.; Zapilko, C.; Herdtweck, E.; Anwander, R. Ln(AlMe4)3 as New Synthetic Precursors in Organolanthanide Chemistry: Efficient Access to HalfSandwich Hydrocarbyl Complexes. Organometallics 2005, 24, 5767− 5771. (d) Evans, W.; Champagne, T.; Ziller, J. Samarium versus aluminium Lewis acidity in a mixed alkyl carboxylate complex related to alkylaluminium activation in diene polymerization catalysis. Chem. Commun. 2005, 5925−5927. (e) Evans, W.; Champagne, T.; Ziller, J. An Ethyl Aluminum Oxide (EAO) Complex with μ-η1:η2-Ethyl Coordination Derived from a Samarocene Carboxylate and Triethylaluminum. Organometallics 2005, 24, 4882−4885. (f) Evans,

W.; Champagne, T.; Giarikos, D.; Ziller, J. Lanthanide Metallocene Reactivity with Dialkyl Aluminum Chlorides: Modeling Reactions Used to Generate Isoprene Polymerization Catalysts. Organometallics 2005, 24, 570−579. (g) Gao, W.; Cui, D. Highly cis-1,4 Selective Polymerization of Dienes with Homogeneous Ziegler-Natta Catalysts Based on NCN-Pincer Rare Earth Metal Dichloride Precursors. J. Am. Chem. Soc. 2008, 130, 4984−4991. (10) (a) Evans, W. J.; Anwander, R.; Ziller, J. W. Inclusion of Al2Me6 in the Crystalline Lattice of the Organometallic Complexes LnAl3Me12. Organometallics 1995, 14, 1107−1109. (b) Klooster, W. T.; Lu, R. S.; Anwander, R.; Evans, W. J.; Koetzle, T. F.; Bau, R. Neutron Diffraction Study of [Nd(AlMe4)3]•0.5 Al2Me6 at 100 K: The First Detailed Look at a Bridging Methyl Group with a Trigonal-Bipyramidal Carbon Atom. Angew. Chem., Int. Ed. 1998, 37, 1268−1270. (c) Dietrich, H. M.; Raudaschl-Sieber, G.; Anwander, R. Trimethylyttrium and Trimethyllutetium. Angew. Chem., Int. Ed. 2005, 44, 5303−5306. (d) Occhipinti, G.; Meermann; Dietrich, H. M.; Litlabø; Auras, F.; Törnroos, K. W.; Maichle-Mössmer, C.; Jensen, V. R.; Anwander, R. Synthesis and Stability of Homoleptic Metal(III) Tetramethylaluminates. J. Am. Chem. Soc. 2011, 133, 6323−6337. (e) Dettenrieder, N.; Dietrich, H. M.; Schädle, C.; Maichle-Mössmer, C.; Törnroos, K. W.; Anwander, R. Organoaluminum Boryl Complexes. Angew. Chem., Int. Ed. 2012, 51, 4461−4465. (11) (a) Evans, W. J.; Ansari, M. A.; Ziller, J. W.; Khan, S. I. Utility of Arylamido Ligands in Yttrium and Lanthanide Chemistry. Inorg. Chem. 1996, 35, 5435−5444. (b) Anwander, R.; Klimpel, M. G.; Dietrich, H. M.; Shorokhov, D. J.; Scherer, W. High tetraalkylaluminate fluxionality in half-sandwich complexes of the trivalent rare-earth metals. Chem. Commun. 2003, 1008−1009. (c) Schrems, M. G.; Dietrich, H. M.; Törnroos, K. W.; Anwander, R. [LnIIAlIII 2(alkyl)8]x: donor addition instead of donor-induced cleavage. Chem. Commun. 2005, 5922−5924. (d) Fischbach, A.; Herdtweck, E.; Anwander, R. Synthesis and derivatization of halflanthanidocene aryl(alk)oxide complexes. Inorg. Chim. Acta 2006, 359, 4855−4864. (e) Zimmermann, M.; Törnroos, K. W.; Anwander, R. Implementation of Ln(AlMe4)3 as Precursors in Postlanthanidocene Chemistry. Organometallics 2006, 25, 3593−3598. (f) Hamidi, S.; Jende, L. N.; Dietrich, H. M.; Maichle-Mössmer, C.; Törnroos, K. W.; Deacon, G. B.; Junk, P. C.; Anwander, R. C−H Bond Activation and Isoprene Polymerization by Rare-Earth-Metal Tetramethylaluminate Complexes Bearing Formamidinato N-Ancillary Ligands. Organometallics 2013, 32, 1209−1223. (g) Kaneko, H.; Dietrich, H. M.; Schädle, C.; Maichle-Mössmer, C.; Tsurugi, H.; Törnroos, K. W.; Mashima, K.; Anwander, R. Synthesis of Rare-EarthMetal Iminopyrrolyl Complexes from Alkyl Precursors: Ln→Al NAncillary Ligand Transfer. Organometallics 2013, 32, 1199−1208. (h) Dettenrieder, N.; Hollfelder, C. O.; Jende, L. N.; MaichleMö ssmer, C.; Anwander, R. Half-Sandwich Rare-Earth-Metal Alkylaluminate Complexes Bearing Peripheral Boryl Ligands. Organometallics 2014, 33, 1528−1531. (i) Zimmermann, M.; Törnroos, K. W.; Anwander, R. Alkyl Migration and an Unusual Tetramethylaluminate Coordination Mode: Unexpected Reactivity of Organolanthanide Imino-Amido-Pyridine Complexes. Angew. Chem., Int. Ed. 2007, 46, 3126−3130. (j) Bojer, D.; Neumann, B.; Stammler, H.-G.; Mitzel, N. W. Subtle Size Effects in C−H Activation Reactions of Lanthanum and Praseodymium Tetramethylaluminates by Neutral Trinitrogen Bases. Eur. J. Inorg. Chem. 2011, 3791−3796. (k) Jende, L. N.; Maichle-Mössmer, C.; Anwander, R. Rare-Earth-Metal Alkylaluminates Supported by N-Donor-Functionalized Cyclopentadienyl Ligands: C-H Bond Activation and Performance in Isoprene Polymerization. Chem. - Eur. J. 2013, 19, 16321−16333. (12) (a) Dietrich, M.; Grove, H.; Törnroos, K. W.; Anwander, R. Multiple C-H Bond Activation in Group 3 Chemistry: Synthesis and Structural Characterization of an Yttrium-Aluminum-Methine Cluster. J. Am. Chem. Soc. 2006, 128, 1458−1459. (b) Dietrich, H. M.; Törnroos, K. W.; Anwander, R. Ionic Carbenes”: Synthesis, Structural Characterization, and Reactivity of Rare-Earth Metal Methylidene Complexes. J. Am. Chem. Soc. 2006, 128, 9298−9299. (c) Litlabø, R.; Zimmermann, M.; Saliu, K.; Takats, J.; Törnroos, K. W.; Anwander, R. A Rare-Earth Metal Variant of the Tebbe Reagent. Angew. Chem., Int. F

DOI: 10.1021/acs.organomet.7b00911 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Ed. 2008, 47, 9560−9564. (d) Zimmermann, M.; Takats, J.; Kiel, G.; Törnroos, K. W.; Anwander, R. Ln(III) methyl and methylidene complexes stabilized by a bulky hydrotris(pyrazolyl)borate ligand. Chem. Commun. 2008, 612−614. (e) Gerber, L. C. H.; Roux, E. L.; Tö rnroos, K. W.; Anwander, R. Elusive Trimethyllanthanum: Snapshots of Extensive Methyl Group Degradation in La-Al Heterobimetallic Complexes. Chem. - Eur. J. 2008, 14, 9555−9564. (f) Venugopal, A.; Kamps, I.; Bojer, D.; Berger, R. J. F.; Mix, A.; Willner, A.; Neumann, B.; Stammler, H.-G.; Mitzel, N. W. Neutral ligand induced methane elimination from rare-earth metal tetramethylaluminates up to the six-coordinate carbide state. Dalton Trans. 2009, 5755−5765. (g) Korobkov, I.; Gambarotta, S. Unusual Reactivity of a Tm-Pyrrolide/Aluminate Complex with a Metallocene-Type Structural Motif. Organometallics 2009, 28, 5560−5567. (h) Zimmermann, M.; Rauschmaier, D.; Eichele, K.; Törnroos, K. W.; Anwander, R. Amido-stabilized rare-earth metal mixed methyl methylidene complexes. Chem. Commun. 2010, 46, 5346−5348. (i) Bojer, D.; Venugopal, A.; Mix, A.; Neumann, B.; Stammler, H.G.; Mitzel, N. W. C-H Activation versus Yttrium-Methyl Cation Formation from [Y(AlMe4)3] Induced by Cyclic Polynitrogen Bases: Solvent and Substituent-Size Effects. Chem. - Eur. J. 2011, 17, 6248− 6255. (j) Hong, J.; Zhang, L.; Yu, X.; Li, M.; Zhang, Z.; Zheng, P.; Nishiura, M.; Hou, Z.; Zhou, X. Syntheses, Structures, and Reactivities of Homometallic Rare-Earth-Metal Multimethyl Methylidene and Oxo Complexes. Chem. - Eur. J. 2011, 17, 2130−2137. (k) Bojer, D.; Neumann, B.; Stammler, H.-G.; Mitzel, N. W. Substituent Size Effects in Lewis Base Induced Reductions in Organolanthanide Chemistry. Chem. - Eur. J. 2011, 17, 6239−6247. (l) Zhang, W.; Wang, Z.; Nishiura, M.; Xi, Z.; Hou, Z. Ln4(CH2)4 Cubane-Type Rare-Earth Methylidene Complexes Consisting of “(C5Me4SiMe3)LnCH2” Units. J. Am. Chem. Soc. 2011, 133, 5712−5715. (m) Kratsch, J.; Roesky, P. W. Rare-Earth-Metal Methylidene Complexes. Angew. Chem., Int. Ed. 2014, 53, 376−383. (13) (a) Fischbach, A.; Meermann, C.; Eickerling, G.; Scherer, W.; Anwander, R. Discrete Lanthanide Aryl(alk)oxide Trimethylaluminum Adducts as Isoprene Polymerization Catalysts. Macromolecules 2006, 39, 6811−6816. (b) Fischbach, A.; Perdih, F.; Herdtweck, E.; Anwander, R. Structure-Reactivity Relationships in Rare-Earth Metal Carboxylate-Based Binary Ziegler-Type Catalysts. Organometallics 2006, 25, 1626−1642. (c) Meermann, C.; Törnroos, K. W.; Nerdal, W.; Anwander, R. Rare-Earth Metal Mixed Chloro/Methyl Compounds: Heterogeneous-Homogeneous Borderline Catalysts in 1,3Diene Polymerization. Angew. Chem., Int. Ed. 2007, 46, 6508−6513. (d) Zimmermann, M.; Frøystein, N. Å.; Fischbach, A.; Sirsch, P.; Dietrich, H. M.; Törnroos, K. W.; Herdtweck, E.; Anwander, R. Homoleptic Rare-Earth Metal(III) Tetramethylaluminates: Structural Chemistry, Reactivity, and Performance in Isoprene Polymerization. Chem. - Eur. J. 2007, 13, 8784−8800. (e) Zimmermann, M.; Törnroos, K. W.; Anwander, R. Cationic Rare-Earth-Metal Half-Sandwich Complexes for the Living trans-1,4-Isoprene Polymerization. Angew. Chem., Int. Ed. 2008, 47, 775−778. (f) Zimmermann, M.; Törnroos, K. W.; Sitzmann, H.; Anwander, R. Half-Sandwich Bis(tetramethylaluminate) Complexes of the Rare-Earth Metals: Synthesis, Structural Chemistry, and Performance in Isoprene Polymerization. Chem. - Eur. J. 2008, 14, 7266−7277. (g) Robert, D.; Spaniol, T. P.; Okuda, J. Neutral and Monocationic Half-Sandwich Methyl Rare-Earth Metal Complexes: Synthesis, Structure, and 1,3-Butadiene Polymerization Catalysis. Eur. J. Inorg. Chem. 2008, 2008, 2801−2809. (h) Litlabø, R.; Lee, H. S.; Niemeyer, M.; Törnroos, K. W.; Anwander, R. Rare-earth metal bis(tetramethylaluminate) complexes supported by a sterically crowded triazenido ligand. Dalton Trans. 2010, 39, 6815−6825. (i) Chen, F.; Fan, S.; Wang, Y.; Chen, J.; Luo, Y. Unusual Si-H Bond Activation and Formation of Cationic Scandium Amide Complexes from a Mono(amidinate)-Ligated Scandium Bis(silylamide) Complex and Their Performance in Isoprene Polymerization. Organometallics 2012, 31, 3730−3735. (j) Zhang, L.; Nishiura, M.; Yuki, M.; Luo, Y.; Hou, Z. Isoprene Polymerization with Yttrium Amidinate Catalysts: Switching the Regio- and Stereoselectivity by Addition of AlMe3. Angew. Chem., Int. Ed. 2008, 47, 2642−2645.

(k) Sun, S.; Ouyang, H.; Luo, Y.; Zhang, Y.; Shen, Q.; Yao, Y. Synthesis of β-diketiminate-ligated bimetallic and monometallic lanthanide amide complexes and their reactivity with isoprene and AlMe3. Dalton Trans. 2013, 42, 16355−16364. (l) Litlabø, R.; Enders, M.; Tö rnroos, K. W.; Anwander, R. Bis(tetramethylaluminate) Complexes of Yttrium and Lanthanum Supported by a QuinolylSubstituted Cyclopentadienyl Ligand: Synthesis and Performance in Isoprene Polymerization. Organometallics 2010, 29, 2588−2595. (14) (a) Scott, J.; Basuli, F.; Fout, A. R.; Huffman, J. C.; Mindiola, D. J. Evidence for the Existence of a Terminal Imidoscandium Compound: Intermolecular C-H Activation and Complexation Reactions with the Transient Sc = NAr Species. Angew. Chem., Int. Ed. 2008, 47, 8502−8505. (b) Scott, J.; Fan, H.; Wicker, B. F.; Fout, A. R.; Baik, M.-H.; Mindiola, D. J. Lewis Acid Stabilized Methylidene and Oxoscandium Complexes. J. Am. Chem. Soc. 2008, 130, 14438−14439. (c) Huang, W.; Carver, C. T.; Diaconescu, P. L. Transmetalation Reactions of a Scandium Complex Supported by a Ferrocene Diamide Ligand. Inorg. Chem. 2011, 50, 978−984. (d) Hong, J.; Zhang, L.; Wang, K.; Zhang, Y.; Weng, L.; Zhou, X. Methylidene Rare-EarthMetal Complex Mediated Transformations of CN, NN and N-H Bonds: New Routes to Imido Rare-Earth-Metal Clusters. Chem. - Eur. J. 2013, 19, 7865−7873. (e) Li, T.; Nishiura, M.; Cheng, J.; Zhang, W.; Li, Y.; Hou, Z. Hydrogenolysis and Protonation of Polymetallic Lutetium Methylidene and Methyl Complexes. Organometallics 2013, 32, 4142−4148. (15) Zimmermann, M.; Anwander, R. Homoleptic Rare-Earth Metal Complexes Containing Ln-C σ-Bonds. Chem. Rev. 2010, 110, 6194− 6259. (16) (a) Zimmermann, M.; Estler, F.; Herdtweck, E.; Törnroos, K. W.; Anwander, R. Distinct C-H Bond Activation Pathways in Diamido-Pyridine-Supported Rare-Earth Metal Hydrocarbyl Complexes. Organometallics 2007, 26, 6029−6041. (b) Litlabø, R.; Saliu, K.; Ferguson, M. J.; McDonald, R.; Takats, J.; Anwander, R. Monomeric Tetraalkylaluminates of Divalent Ytterbium Stabilized by a Bulky Tris(pyrazolyl)borate Ligand. Organometallics 2009, 28, 6750−6754. (c) Yamamoto, H.; Yasuda, H.; Yokota, K.; Nakamura, A.; Kai, Y.; Kasai, N. Synthesis and X-Ray Structure Analysis of Novel EthylBridged Ytterbium-Triethylaluminum Complex: (η-C5Me5)2Yb·Al(C2H5)3(THF). Chem. Lett. 1988, 17, 1963−1966. (17) (a) Liu, D.; Yao, C.; Wang, R.; Wang, M.; Wang, Z.; Wu, C.; Lin, F.; Li, S.; Wan, X.; Cui, D. Highly Isoselective Coordination Polymerization of ortho-Methoxystyrene with β-Diketiminato RareEarth-Metal Precursors. Angew. Chem., Int. Ed. 2015, 54, 5205−5209. (b) Liu, D.; Wang, M.; Wang, Z.; Wu, C.; Pan, Y.; Cui, D. Stereoselective Copolymerization of Unprotected Polar and Nonpolar Styrenes by an Yttrium Precursor: Control of Polar-Group Distribution and Mechanism. Angew. Chem., Int. Ed. 2017, 56, 2714−2719. (c) Lin, F.; Liu, Z.; Wang, T.; Cui, D. Highly 2,3Selective Polymerization of Phenylallene and Its Derivatives with RareEarth Metal Catalysts: From Amorphous to Crystalline Products. Angew. Chem., Int. Ed. 2017, 56, 14653−14657. (d) Pan, Y.; Rong, W.; Jian, Z.; Cui, D. Ligands Dominate Highly Syndioselective Polymerization of Styrene by Using Constrained-geometry-configuration Rareearth Metal Precursors. Macromolecules 2012, 45, 1248−1253. (e) Lin, F.; Wang, X.; Pan, Y.; Wang, M.; Liu, B.; Luo, Y.; Cui, D. Nature of the Entire Range of Rare Earth Metal-Based Cationic Catalysts for Highly Active and Syndioselective Styrene Polymerization. ACS Catal. 2016, 6, 176−185. (f) Wang, Z.; Liu, D.; Cui, D. Statistically Syndioselective Coordination (Co)polymerization of 4-Methylthiostyrene. Macromolecules 2016, 49, 781−787. (g) Liu, D.; Wang, R.; Wang, M.; Wu, C.; Wang, Z.; Yao, C.; Wan, X.; Cui, D. Syndioselective coordination polymerization of unmasked polar methoxystyrenes using a pyridenylmethylene fluorenyl yttrium precursor. Chem. Commun. 2015, 51, 4685−4688. (h) Liu, D.; Luo, Y.; Gao, W.; Cui, D. Stereoselective Polymerization of Styrene with Cationic Scandium Precursors Bearing Quinolyl Aniline Ligands. Organometallics 2010, 29, 1916−1923. (i) Wang, Z.; Wang, M.; Liu, J.; Liu, D.; Cui, D. Rapid Syndiospecific (Co)Polymerization of Fluorostyrene with High Monomer Conversion. Chem. - Eur. J. 2017, 23, 18151−18155. (j) Huang, J.; Liu, Z.; G

DOI: 10.1021/acs.organomet.7b00911 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Cui, D.; Liu, X. Precisely Controlled Polymerization of Styrene and Conjugated Dienes by Group 3 Single-Site Catalysts. ChemCatChem 2018, 10, 42−61. (18) (a) Liu, B.; Li, S.; Wang, M.; Cui, D. Coordination Polymerization of Renewable 3-Methylenecyclopentene with RareEarth-Metal Precursors. Angew. Chem., Int. Ed. 2017, 56, 4560−4564. (b) Wu, C.; Liu, B.; Lin, F.; Wang, M.; Cui, D. cis-1,4 Selective Copolymerization of Ethylene and Butadiene: A Compromise between Two Mechanisms. Angew. Chem., Int. Ed. 2017, 56, 6975−6979. (c) Liu, B.; Cui, D.; Tang, T. Stereo- and Temporally Controlled Coordination Polymerization Triggered by Alternating Addition of a Lewis Acid and Base. Angew. Chem., Int. Ed. 2016, 55, 11975−11978. (d) Lin, F.; Wang, M.; Pan, Y.; Tang, T.; Cui, D.; Liu, B. Sequence and Regularity Controlled Coordination Copolymerization of Butadiene and Styrene: Strategy and Mechanism. Macromolecules 2017, 50, 849− 856. (e) Yao, C.; Lin, F.; Wang, M.; Liu, D.; Liu, B.; Liu, N.; Wang, Z.; Long, S.; Wu, C.; Cui, D. Highly Syndioselective 3,4-Trans Polymerization of (E)-1-(4-Methylphenyl)- 1,3-butadiene by Fluorenyl N-Heterocyclic Carbene Ligated Lutetium Bis(alkyl) Precursor. Macromolecules 2015, 48, 1999−2005. (f) Liu, B.; Cui, D. Regioselective Chain Shuttling Polymerization of Isoprene: An Approach To Access New Materials from Single Monomer. Macromolecules 2016, 49, 6226−6231. (g) Wang, Z.; Liu, D.; Cui, D. Highly Selective Polymerization of 1,3-Conjugated Dienes by Rare Earth Organometallic Complexes. Acta Polym. Sin. 2015, 9, 989−1009. (19) Rong, W.; Liu, D.; Zuo, H.; Pan, Y.; Jian, Z.; Li, S.; Cui, D. RareEarth-Metal Complexes Bearing Phosphazene Ancillary Ligands: Structures and Catalysis toward Highly Trans-1,4-Selective (Co)Polymerizations of Conjugated Dienes. Organometallics 2013, 32, 1166−1175. (20) Rong, W.; He, D.; Wang, M.; Mou, Z.; Cheng, J.; Yao, C.; Li, S.; Trifonov, A. A.; Lyubov, D. M.; Cui, D. Neutral binuclear rare-earth metal complexes with four μ2-bridging hydrides. Chem. Commun. 2015, 51, 5063−5065. (21) Rong, W.; Cheng, J.; Mou, Z.; Xie, H.; Cui, D. Facile Preparation of a Scandium Terminal Imido Complex Supported by a Phosphazene Ligand. Organometallics 2013, 32, 5523−5529. (22) (a) Dietrich, H. M.; Schuster, O.; Törnroos, K. W.; Anwander, R. Heterobimetallic Half-Lanthanidocene Clusters: Novel Mixed Tetramethylaluminato/Chloro Coordination. Angew. Chem., Int. Ed. 2006, 45, 4858−4863. (b) Marques, N.; Sella, A.; Takats, J. Chemistry of the Lanthanides Using Pyrazolylborate Ligands. Chem. Rev. 2002, 102, 2137−2159. (23) Ziegler Catalysts; Fink, G., Mühlhaupt, R., Brintzinger, H. H., Eds.; Springer-Verlag: Berlin, Germany, 1995. (24) (a) Klimpel, M. G.; Anwander, R.; Tafipolsky, M.; Scherer, W. Peralkylated Ytterbium(II) Aluminate Complexes YbAl2R8. New Insights into the Nature of Aluminate Coordination. Organometallics 2001, 20, 3983−3992. (b) Sommerfeldt, H.-M.; Meermann, C.; Schrems, M. G.; Törnroos, K. W.; Frøstein, N. Å.; Miller, R. J.; Scheidt, E.-W.; Scherer, W.; Anwander, R. Characterization and reactivity of peralkylated LnIIAlIII heterobimetallic complexes. Dalton Trans. 2008, 1899−1907. (25) Dietrich, H. M.; Törnroos, K. W.; Anwander, R. LaAl3Et12: A Homoleptic Ethyllanthanum Complex. Angew. Chem., Int. Ed. 2011, 50, 12089−12093. (26) Evans, W. J.; Chamberlain, L. R.; Ziller, J. W. Synthesis and Xray Crystal Structure of a Heterobimetallic Ethyl-Bridged Organoaluminum Complex. J. Am. Chem. Soc. 1987, 109, 7209−7211.

H

DOI: 10.1021/acs.organomet.7b00911 Organometallics XXXX, XXX, XXX−XXX