Unexpected Reactions between Ziegler–Natta Catalyst Components

Article pubs.acs.org/IC

Unexpected Reactions between Ziegler−Natta Catalyst Components and Structural Characterization of Resulting Intermediates Piotr Sobota,* Józef Utko, Tadeusz Lis, Łukasz John, Rafał Petrus, and Anna Drąg-Jarząbek Faculty of Chemistry, University of Wrocław, 14 F. Joliot-Curie, 50-383 Wrocław, Poland S Supporting Information *

ABSTRACT: In this work, we investigated precursors and procatalysts with well-defined crystal structures and morphologies in Ziegler−Natta systems to improve our understanding of the nature of the active metal sites. Molecular cluster precursors such as [Mg4Ti3(μ6-O)(μ3-OH)3(μ-OEt)9(OEt)3(EtOH)3Cl3], [Mg4Ti3(μ6-O)(μ3-OH)(μ3-OEt)2(μ-OEt)9(OEt)3(EtOH)3Cl3], and [Mg6Ti4(μ6-O)2(μ3-OH)4(μ-OEt)14(OEt)4(EtOH)2Cl2] were prepared via simple elimination of the cyclopentadienyl ring from Cp2TiCl2 as CpH in the presence of magnesium metal and ethanol. Titanocene dichloride acts as both a source of titanium and a magnesium-chlorinating agent. The resulting novel complexes were characterized using single-crystal X-ray diffraction. In these compounds, Ti(OEt)4 molecules are grafted onto Mg4 and Mg6 ethoxide cubane-like surfaces; this strongly affects the procatalyst morphology, which is transferred to the polymer. Mg4(OR)8 units act as carriers for the AlR3 co-catalyst, resulting in return of alkyl functions to the Ti center.

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INTRODUCTION The beneficial effects of electropositive metal components, such as MgX2 and TiX4 (where X = Cl, OR) and AlR3, on Ziegler− Natta (Z−N) catalyst polymerization activity is widely recognized,1−14 but still poorly understood.15−27 Thousands of patents have been published that describe a wide range of combinations of pure or mixed main-group alkyls with transition-element compounds and different internal and external Lewis base donors (EDs); each have claimed to have advantages. Comprehensive contributions to this topic have been made by Hlatky,28 Gibson and Spitzmesser,29 and Chen and Marks.30 Although there are many chemical combinations that provide active systems, research has been concentrated on certain preferred components. Many TiX4 /MgX2/AlR3/ED/SiO2 (X = Cl, OR) combinations provide active systems that can produce olefin polymers in high yields and, in the case of catalysts for propylene polymerization, with high selectivity for stereoregular polymers as well. There are still many gaps to fill in our knowledge of Z−N systems; for example, little work has been done on direct investigation of the active sites in heterogeneous Z−N catalysts, and the information available in the literature mainly comes from detailed analysis of the microstructure of the resulting polypropylene,31 rather than that of the catalyst itself. One current challenge is the preparation of compounds by reacting Mg(OEt)2 with TiX4 in suitable crystalline forms, to give crystalline procatalysts that have excellent productivity and selectivity, and a spherical surface that is very close to the optimum morphology and is transferred to the polymer. Catalysts based on magnesium species such as MgCl2 and Mg(OR)2 have similar activities. However, the morphology of © 2016 American Chemical Society

the alkoxy catalyst is much better, in terms of particle shape, and results in a more appropriate polymer morphology (spherilene technique).32 The reaction of magnesium with simple alcohols such as methanol or ethanol is complex. Solidstate magnesium methoxide consists of crystalline molecules composed of four types of residue, i.e., (i) neutral [Mg4(μ3-OMe)4 (OMe) 4 (MeOH) 8 ] cubane, (ii) [Mg4 (μ 3 -OMe) 4 (OMe) 2 (MeOH)10]2+ cubane cations, (iii) [(MeO)2H]− anions, and (iv) eight crystallographically independent noncoordinated solvating methanol molecules.33 Another equivalent method involves the use of magnesium metal and MgCl2 in a 3:1 molar ratio in the presence of methanol. In this approach, the solution concentrations and conditions must be carefully controlled to obtain crystalline [Mg4(μ3-OMe)4(OMe)2(MeOH)10]Cl2. If the concentrations of the compounds in the solution are too high or too low, the magnesium compounds tend to aggregate, which is undesirable.34 The crystal structure of Mg(OEt)2 is still unknown. However, the formation of Mg(OEt)2 in solution proceeds via nucleation to give spherical particles with a well-ordered densely packed crystalline core bearing residual ligands; these act as an interface to the surrounding solution, and they provide stability and protect against aggregation.35,36 The spherical morphology arises from minimization of the surface energy through maximum interactions with the solvent; it can be converted to a polyhedral form, with a lower surface area. Received: February 26, 2016 Published: April 12, 2016 4636

DOI: 10.1021/acs.inorgchem.6b00489 Inorg. Chem. 2016, 55, 4636−4642

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Inorganic Chemistry Scheme 1. Synthesis of Compounds 1−3

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RESULTS AND DISCUSSION In this study, we focused on the precursors and procatalysts in Z−N systems with well-defined crystal structures, to obtain a better understanding of the nature of the active metal sites.37 Our developed approach is new in this area of inorganic and polymer chemistry. We used Cp2TiCl2 as the staring material. Cp can act as a leaving group; therefore, Cp2TiCl2 is an attractive and inexpensive reagent, which can be used as a titanium source and for chlorination of magnesium species. First, we reacted Cp2TiCl2 and magnesium turnings (molar ratio 1:2), in a mixture of ethanol and tetrahydrofuran (THF) (1:3), as shown in Scheme 1. The reaction was conducted at room temperature under a gaseous nitrogen (N2) atmosphere. The solution slowly changed color from red to blue and then to light yellow. This synthetic method involves complete elimination of the cyclopentadienyl ring from Cp2TiCl2 as CpH, in the presence of Mg(OEt)2 in ethanol as a source of protons.38−44 Workup gave colorless hexagonal crystals of the well-known ionic45 compound [Mg(EtOH)6]Cl2 (1) and a postlike monomeric complex [MgCl2(EtOH)2(THF)2] (2). X-ray diffraction (XRD) analysis showed that 2 consists of a six-coordinated distorted octahedron surrounded by two Cl− anions and four O atoms derived from two ethanol and two THF molecules in trans positions to each other (Figure 1; see the process description in

studies have been performed, but this compound has not previously been isolated. After a few days, 1 and 2 were separated by hand from the filtrate. We noticed that a small amount of the cluster [Mg4Ti3(μ6-O)(μ3-OH)3(μ-OEt)9(OEt)3(EtOH)3Cl3] (3) formed next to 1 and 2. In this system, crystals of 2 and 3 attach to the walls of hexagonal 1, because coalescence occurs along the similar geometric lattice planes (see Figures 2a and 2b).

Figure 2. (a, b) Planar, colorless, hexagonal crystal of 1 and colorless postlike 2; (c) postlike crystals of 3 covered with small colorless crystals of 3 (the yellowish color comes from the mother liquor).

The presence of OH groups in compound 3 suggests that its formation is caused by hand manipulation, during which moisture could penetrate the Schlenk flask or is affected by traces of water in ethanol. When the same reaction was carried out in air, the first few crystals of cluster 3 crystallized in analytically pure form, and then grafted onto the surfaces of freshly crystallized 1 and 2 (see Figure 2c). Compound 3 is a discrete heptanuclear Mg−Ti cluster, containing a Mg4Ti3O19Cl3 central core structure with an interstitial μ6-O atom, and three μ3-O and nine μ-O bridges. Formally, 3 can be considered as a hexametalate {Mg3Ti3(μ6-O)(μ3-OH)3(μ-OEt)9(OEt)3Cl3}2− moiety with a {Mg(EtOH)3}2+ subunit connected via three μ3-OH groups to Mg atoms in a triangular arrangement on the surface of the cluster (Figure 3 (left); also see the ESI and CIF file). This type of structural motif is uncommon and so far has only observed in polyoxometalate clusters.47−50 When the filtrate was evaporated to dryness in a vacuum and the residue was redissolved in hexane, we obtained a small amount of the co-crystallite [Mg4Ti3(μ6-O)(μ3-OH)3(μ-OEt)9

Figure 1. Molecular structure of 2; hydrogen atoms are omitted for the sake of clarity.

the Supporting Information (ESI) and the CIF file that has also been supplied as Supporting Information). The isolation of 2 in a pure crystalline form is surprising, because since the first study by Kashiwa46 of magnesium dichloride as a support for TiCl4 catalysts in 1968, extensive 4637

DOI: 10.1021/acs.inorgchem.6b00489 Inorg. Chem. 2016, 55, 4636−4642

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Inorganic Chemistry

Figure 3. (Left) Molecular structure of 3; hydrogen atoms are omitted for the sake of clarity. (Right) Polyhedral representation of central Mg4Ti3O19Cl3 core structure.

Scheme 2. Synthesis of Compounds 4 and 5

different unit-cell parameters (see Table S1 in the ESI). The molecular structure of 4 consists of a centrosymmetric Mg−Ti cluster containing a Mg2Ti2O16 double-opened, face-shared dicubane core with two missing vertices. Octahedrally coordinated metal atoms surrounded by O6 donor sets are held together by four μ-alkoxide and two μ3-alkoxide ligands. The vertices of the common face of the defective dicubane unit are occupied by the Mg1 and Mg1i ions, and the external vertices are Ti1 and Ti1i ions. The interactions between magnesium and titanium alkoxides were intensively studied by Turova, who reported the formation of magnesium ethoxotitanates of variable composition, i.e., MgnTi4−n(OEt)16−2n·2nEtOH (n = 0−2.0) in the reaction of Ti(OEt)4 with magnesium metal in ethanol solution.51 However, no unusual distortion of metal atoms was observed in 4 that was synthesized using our developed method. When the same reaction was performed in an open flask, a new molecular cluster, [Mg6Ti4(μ6-O)2(μ3-OH)4(μ-OEt)14(OEt)4(EtOH)2Cl2] (5), was formed (see Figure 5 and Scheme 2). Compound 5 consists of a decametalate Mg6Ti4O26Cl2 core, in which the metal ions are held together by 20 O-donor atoms

(OEt)3(EtOH)3Cl3]·[Mg4Ti3(μ6-O)(μ3-OH)(μ3-OEt)2(μ-OEt)9 (OEt)3(EtOH)3Cl3] (3·3a); the species ratio was 1:1. Co-crystallite 3·3a consists of two chemically independent 3 and 3a molecules, which are statistically distributed in the crystal. This gives rise to disorder around the Mg atoms of the μ3-bridging ligands occupied partly by −OH and −OEt groups (see Figure S1 in the ESI and also the 3·3a data in the CIF file). These findings confirm that Mg4Ti3 cluster formation is affected by traces of moisture present in ethanol, which causes substitution of the μ3-OEt groups around the Mg atoms in 3a by μ3-OH groups to give 3. It should be noted that, as mentioned above, the reactant concentrations should be carefully controlled. If the concentration of the components in the solution is too low or too high, only ionic compound 1 is obtained. When Cp2TiCl2 was reacted with magnesium turnings in a mixture of toluene and ethanol (Scheme 2), tetrameric [Mg2Ti2(μ3-OEt)2(μ-OEt)4(OEt)6(EtOH)4] (4) was formed. This compound, which was synthesized under N2, has an open dicubanelike structure (see Figure 4, as well as the ESI and the CIF file). Compound 4 consists of a mixture of two crystalline forms. Both forms crystallize in the triclinic space group P1̅, with two 4638

DOI: 10.1021/acs.inorgchem.6b00489 Inorg. Chem. 2016, 55, 4636−4642

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Inorganic Chemistry

Figure 4. (Left) Molecular structure of 4. Second disordered counterpart of alkoxy group and H atoms are omitted for the sake of clarity [symmetry code: (i) −x + 1, −y + 1, −z + 1]. (Right) Polyhedral representation of central Mg2Ti2O16 core structure.

Figure 5. (Left) Molecular structure of 5·2EtOH. Second disordered counterpart of alkoxy group, solvent molecules, and hydrogen atoms are omitted for the sake of clarity [symmetry code: (i) −x + 1, − y + 1, −z + 1]. (Right) Polyhedral representation of central Mg6Ti4O26Cl2 core structure.

from 14 μ-OEt, 4 μ3-OH, and 2 μ6-O groups. The metal atoms adopt octahedral coordination environments with O6 donor sets for Ti, and O6 or O5Cl donor sets for the Mg center. The polyhedral representation of the central core in Figure 5 (right) shows that it was formed exclusively by edge-sharing interactions. The cluster 5 was formed via the coordination of 4 Ti(OEt)4 molecules with a magnesium dicubane [Mg6(O)2(OH)4(OEt)2(EtOH)2Cl2] unit, involving 2 axial edges defined by Mg1−O1−Mg3 and Mg1i−O1i−Mg3i atoms. This shows the capping of Ti atoms on the Mg4 alkoxy cubane surface by μ6-O oxo atoms and μ-OEt bridging ethoxide groups. This is noteworthy because the procatalyst crystalline surface morphology is transferred to the polymer. Such a phenomenon was observed for industrial catalyst prepared from magnesium ethoxide.34 The results of our previous research and identification of various compounds fit well with the above results; for example, we found that the reaction of magnesium alkoxide [Mg4(thffo)8] (where thffo = 2-tetrahydrofurfuroxide) with [Ti(dipp)4] (dippOH = 2,6diisopropylphenol) led to [Mg4(thffo)6{OTi(dipp)3}2] (6).52,53

Furthermore, the tetramer [Mg4(thffo)8] can be trapped by Ph3SiOH to form [Mg4(thffo)6(OSiPh3)2] (7) (see Scheme 3).54 This shows that magnesium alkoxides can easily be trapped by  SiOH silica surface groups during heterogeneous catalyst preparation. It is also worth noting that an ethylene polymerization test performed on a [Mg4(dipp)6Cl2]/TiCl4/AlR3 catalyst gave ∼170 kg of polyethylene (g of Ti)−1 h−1.55 In the reaction of [Mg4(thffo)8] with AlMe3, the catalyst components unexpectedly yielded the methylalumoxane cluster [Al3Mg(μ3-O)(thffo)3(Me)6] (8).53 In this compound, three AlMe2+ moieties are held together by μ3-oxo atoms to form a trinuclear [Al3(μ3-O)(Me)6]+ macro unit, which is trapped by Mg(thffo)3− anions. This is important, because it shows that an alumoxane activator can be formed in the Z−N TiX4/Mg(OR)2/AlR3 (X= Cl, OR) catalytic system. This is significant in understanding how active catalytic centers arise. Further studies showed that no crystalline compounds can be isolated from the reaction of methylalumoxane cluster 8 with TiCl4. However, as 4639

DOI: 10.1021/acs.inorgchem.6b00489 Inorg. Chem. 2016, 55, 4636−4642

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Inorganic Chemistry Scheme 3. Synthesis of Compounds 6 and 7

Scheme 4. Synthesis of Compound 9

atom to form an [Al3(μ3-O)(Me)5]2+ unit (Scheme 4). The 1 H NMR spectrum of the rubberlike byproduct shows the chemical shifts characteristic of a THF polymer formed by ring-opening polymerization after coordination to a metal site. The signals typical of a cyclopentadienyl ring in a metallocene compound were also observed, but the titanium species was not isolated with satisfactory purity. The solid-state structure of 9 offers insights into the possible binding environments of methylalumoxane on a MgX2 (X = Cl, OR) surface and provides a molecular model that helps in understanding the reaction intermediates. It was established that, in the first step, Cp2TiCl2 reacts with 8, terminating the cluster structure, and provides alkyl functions on the Ti atom. This leads to the formation of a highly active titanocene intermediate, which immediately catalyzes the polymerization of THF. The [Al3(μ3-O) (Me)5]2+ unit in cluster 9 has one methyl group less than the corresponding moiety, [Al3(μ3-O)(Me)6]+, in 8, which is capped by a [Mg3Cl4(thffo)4(THF)]2− macro unit; this provides strong evidence for the methylation of Ti atoms.

shown in Scheme 4, the resulting cluster 8 and Cp2TiCl2 combined at room temperature in toluene/THF solution. After 1 h, the solution became cloudy and a precipitate of [MgCl2(THF)2] settled. No gas evolution was observed. Workup gave neutral air-sensitive crystalline [Al3Mg3(μ3-O) (thffo)4(Me)5Cl4(THF)] (9) in 10% isolated yield and a colorless rubberlike side product.56 The X-ray crystal structure of 9 is shown in Figure 6. Two AlMe2+ and one AlMe2+ moieties are held together by a μ3-oxo

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CONCLUSIONS In conclusion, our attempts to prepare new Z−N procatalysts and to understand the chemistry of their formation, led to the observation of unexpected reactions, which could be used to synthesize well-defined heterogeneous olefin polymerization catalysts. The crystal structures of intermediate clusters 3−5 showed that Ti(OEt)4 molecules are coordinated with Mg4 and Mg6 ethoxide cubane surfaces, retaining the memory of the previous step; this affects the procatalyst morphology, which is transferred to the polymer. The discovery that Mg4(OR)8 is a support material for the co-catalyst AlR3, and that it forms welldefined species 8 and 9, shows possible methylalumoxane environments on the MgCl2/Mg(OR)2 surface for the first time. This could have a direct impact on their use, and resultant financial benefits.

Figure 6. Molecular structure of 9; hydrogen atoms are omitted for the sake of clarity [symmetry code: (i) x, −y + 0.5, z]. 4640

DOI: 10.1021/acs.inorgchem.6b00489 Inorg. Chem. 2016, 55, 4636−4642

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Inorganic Chemistry

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1648 (s), 1621 (s), 1461 (m), 1377 (m), 1274 (w), 1177 (w), 1093 (w), 1024 (w), 956 (w), 924 (w), 880 (w), 806 (w), 722 (w). [Mg4Ti3(μ6-O)(μ3-OH)3(μ-OEt)9(OEt)3(EtOH)3Cl3] (3). Anal. Calcd for C30H81Cl3O19Mg4Ti3: C, 32.96; H, 7.47; Cl, 9.73; Mg, 8.89; Ti, 13.14. Found: C, 32.46; H, 7.52; Cl, 9.75; Mg, 8.87; Ti, 13.17. 1 H NMR (500 MHz, CD2Cl2, ppm): δ [4.50, 4.32, 4.17−3.71 (m, CH2, OH, 33H)], 1.38−1.26 (m, CH3, 45H). 13C NMR (125 MHz, CD2Cl2, ppm): δ [73.1, 73.0, 69.6, 69.4, 69.2, 68.2, 67.8, 59.2, 58.8 (CH2, 15C)], [19.9, 19.7, 19.4, 19.3, 19.0, 18.8, 18.7, 18.6 (CH3, 15C)]. IR (cm−1, Nujol mull): 3114 (s), 2929 (vs), 2858 (vs), 2714 (w), 1922 (w), 1641 (w), 1406 (s), 1379 (s), 1356 (w), 1261 (m), 1148 (s), 1128 (s), 1091 (s), 1076 (s), 1049 (s), 930 (m), 895 (m), 803 (m), 722 (w), 671 (w), 644 (w), 614 (w), 577 (w), 534 (w), 502 (w), 455 (w). Synthesis of Pure [Mg4Ti3(μ6-O)(μ3-OH)3(μ-OEt)9(OEt)3(EtOH)3Cl3] (3). Compound 3 was obtained according to the procedure described above for the mixture of 1−3, but with exposure of the resulting solution to atmospheric air. The reaction system was aerated by opening a Schlenk flask for 0.5−1 h. The solution volume was reduced under vacuum to 5−6 mL and left to crystallize at room temperature. Crystals of 3 grew over a period of 1−4 days as light-yellow, transparent, block-shaped crystals. The analytical analyses results for 3 are the same as those given above. Synthesis of [Mg2Ti2(μ3-OEt)2(μ-OEt)4(OEt)6(HOEt)4] (4). All manipulations were performed under dry N2. A Schlenk flask was charged with Cp2TiCl2 (0.99 g; 3.98 mmol), Mg (0.217 g; 8.93 mmol), ethanol (25 mL), and toluene (15 mL). The mixture was stirred vigorously at 65 °C for 18 h. When all the metal had been consumed, the light-brown solution was filtered and the filtrate volume was reduced by half. Hexane (20 mL) was slowly added, forming a colorless layer over the solution. Block crystals of 4 formed at room temperature over 3−7 days. The crystals were washed with a mixture of ethanol and hexane (1:5; 3 × 5 mL). The filtrate was concentrated to 10 mL and left at 10 °C. Crystals of 4 grew over a period of 2 days. Anal. Calcd for C32H84O16Mg2Ti2: C, 44.21; H, 9.74; Mg, 5.59; Ti, 11.01. Found: C, 44.26; H, 9.76; Mg, 5.62; Ti, 11.03. 1H NMR (500 MHz, CD2Cl2, ppm): δ [4.27, 3.74 (m, CH2, 32H)], 2.30 (s, OH, 4H), 1.22 (m, CH3, 48H). 13C NMR (125 MHz, CD2Cl2, ppm): δ [68.9, 58.5 (CH2, 16C)], [19.9, 19.6 (CH3, 16C)]. IR (cm−1, Nujol mull): 3315 (vw), 2958 (vs), 2855 (vs), 2710 (m), 2599 (w), 1944 (vw), 1647 (vw), 1462 (vs), 1375 (vs), 1351 (m), 1324 (w), 1283 (w), 1146 (vs), 1104 (vs), 1059 (vs), 928 (m), 892 (s), 802 (w), 720 (m), 561 (s). Synthesis of [Mg6Ti4(μ6-O)2(μ3-OH)4(μ-OEt)14(OEt)4(HOEt)2Cl2] (5). A Schlenk flask was charged with Cp2TiCl2 (0.80 g; 3.21 mmol), Mg (0.157 g; 6.46 mmol), ethanol (20 mL), and toluene (10 mL). The mixture was vigorously stirred under reflux for 1 h. The resulting lightbrown solution was cooled to room temperature, concentrated to 10−15 mL, and then hexane (10 mL) was added. Crystals of 4 formed during standing for several days at room temperature. After separation of the crystals, the reaction vessel was opened for 1 h to expose the solution to atmospheric air. The solution volume was then reduced to 5−10 mL and the solution was left to crystallize at room temperature. The formation of block-shaped crystals of 5 was observed after 6 weeks. Anal. Calcd for C40H106Cl2O26Mg6Ti4: C, 34.04; H, 7.57; Cl, 5.02; Mg, 10.33; Ti, 13.57. Found: C, 34.12; H, 7.59; Cl, 5.12; Mg, 10.23; Ti, 13.68. 1H NMR (500 MHz, CD2Cl2, ppm): δ 4.58−3.62 (m, CH2, OH, 44H), [1.4−1.30, 1.27 (m, CH3, 60H)]. 13C NMR (125 MHz, CD2Cl2, ppm): δ [73.3, 73.2, 73.0, 71.9, 69.5, 69.4, 68.6, 68.3, 68.1, 68.0, 67.9, 67.8, 59.2, 59.1, 58.9 (CH2, 20C)], [19.9, 19.8, 19.7, 19.4, 19.3, 19.2, 19.0, 18.9, 18.7, 18.6 (CH3, 20C)]. IR (cm−1, Nujol mull): 3309 (vs), 2940 (vs), 2869 (vs), 2711 (w), 1924 (w), 1645 (w), 1461 (m), 1378 (m), 1279 (w), 1260 (w), 1134 (s), 1098 (s), 1052 (s), 928 (w), 898 (w), 879 (w), 805 (w), 728 (w), 571 (w). Synthesis of [Al3Mg3(μ3-O) (thffo)4(Me)5Cl4(THF)] (9). Cp2TiCl2 (0.68 g; 2.75 mmol) was added to a solution of 854 (1.40 g; 2.75 mmol) in toluene (50 mL) and THF (20 mL). The resulting suspension was stirred at room temperature for ∼12 h. A white precipitate of [MgCl2(THF)2] formed. After filtration, the solution volume was reduced under vacuum to 40 mL and n-hexane (10 mL) was added. Colorless crystals of 9 were obtained after 2 weeks. Yield: 0.21 g. Anal.

EXPERIMENTAL SECTION

General Procedures and Methods. Selected reactions were performed in a N2 atmosphere, using standard Schlenk and vacuumline techniques. The commercially available solvents were purified by conventional methods as follows: toluene and hexane were distilled from sodium, and THF was distilled from Na/benzophenone. Other reagents were purchased from Aldrich and used without further purification. Microanalyses were performed using a Model 2400 CHNS Vario EL III (Elementar) elemental analyzer. The metal ion concentrations were determined using inductively coupled plasma−atomic emission spectroscopy (ICP-AES) (ARL 3410 sequential spectrometer, Fisons Instruments). Fourier-transform infrared (FT-IR) spectra were recorded as Nujol mulls, using a Bruker 66/s FT-IR spectrometer. NMR spectroscopy was performed using a Bruker Model AVANCE 500 MHz spectrometer. XRD data were collected at 100 K for 2, 4, and 5, 120 K for 3, 80 K for 3·3a, and 280 K for 4a, using an Xcalibur Ruby or KUMA KM4 CCD diffractometer (ω scan technique).57 The experimental details and crystal data are given in Table S1 in the ESI). The structures were solved by direct methods and refined by the fullmatrix least-squares method on F2, using the SHELXTL package.58 Non-hydrogen atoms were refined with anisotropic thermal parameters. All hydrogen atoms were positioned geometrically and added to the structure factor calculations, but were not refined. The molecular graphics were created using Diamond software, version 3.1e.59 Crystallographic data for the structural analyses reported in this paper have been deposited with the Cambridge Crystallographic Data Centre (CCDC), Nos. CCDC 1450279−CCDC 1450284. Copies of the information may be obtained free of charge from the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (Fax: + 44-1223336033; E-mail: [email protected]; homepage: http://www. ccdc.cam.ac.uk). Synthesis of [Mg(EtOH)6]Cl2 (1), [MgCl2(EtOH)2(THF)2] (2), and [Mg4Ti3(μ6-O)(μ3-OH)3(μ-OEt)9(OEt)3(EtOH)3Cl3] (3). All manipulations were performed under dry N2. A Schlenk flask was charged with Cp2TiCl2 (1.365 g; 5.48 mmol), Mg (0.266 g; 10.94 mmol), ethanol (40 mL), and THF (20 mL). The mixture was stirred vigorously at room temperature until all the metal was consumed (usually 24 h). The magnesium underwent an exothermic reaction and the resulting dark-red solution slowly changed color to bottle green, then navy blue, and finally light yellow. The resulting cloudy solution was filtered and a small amount of an orange−brown solid was collected. The filtrate was concentrated under vacuum to 20 mL; hexane (15 mL) was added and formed a layer over the solution. After 1−2 days at room temperature, planar, colorless, hexagonal crystals of 1 and colorless posts of 2 were obtained. The crystals were separated by filtration and the filtrate volume was reduced under vacuum to ca. 10 mL. The filtrate was allowed to stand for 3 days at room temperature, and colorless block-shaped crystals of 3 were obtained. The crystals were separated by hand for spectroscopic analysis. [Mg(EtOH)6]Cl2 (1). Anal. Calcd for C12H36Cl2O6Mg: C, 38.78; H, 9.76; Cl, 19.08; Mg, 6.54. Found: C, 38.80; H, 9.79; Cl, 19.09; Mg, 6.57. 1H NMR (500 MHz, CD2Cl2, ppm): δ 4.47 (s, OH, 6H), 3.80 (q, J = 7.0 Hz, CH2, 12H), 1.27 (t, J = 7.0 Hz, CH3, 18H). 13C NMR (125 MHz, CD2Cl2, ppm): δ 59.2 (CH2, 6C), 18.0 (CH3, 6C). IR (cm−1, Nujol mull): 3187 (vs), 2950 (vs), 2865 (vs), 2729 (w), 2686 (w), 2542 (w), 1649 (w), 1632 (w), 1452 (s), 1426 (s), 1377 (m), 1366 (w), 1359 (w), 1312 (w), 1276 (m), 1126 (w), 1089 (s), 1045 (s), 880 (s), 800 (w), 670 (m), 474 (w). [MgCl2(EtOH)2(THF)2] (2). Anal. Calcd for C12H28Cl2O4Mg: C, 43.47; H, 8.51; Cl, 21.39; Mg, 7.33. Found: C, 43.49; H, 8.53; Cl, 21.41; Mg, 7.23. 1H NMR (500 MHz, CD2Cl2, ppm): δ 4.14 (s, OH, 2H), 3.82 (q, J = 7.0 Hz, CH2EtOH, 4H), 3.74 (m, CH2THF, 8H), 1.83 (m, CH2THF, 8H), 1.27 (t, J = 7.0 Hz, CH3, 6H). 13C NMR (125 MHz, CD2Cl2, ppm): 68.4 (CH2THF, 4C), 59.2 (CH2EtOH, 2C), 25.9 (CH2THF, 4C), 18.0 (CH3, 2C). IR (cm−1, Nujol mull): 3483 (s), 2939 (vs), 2865 (vs), 2727 (w), 2690 (w), 2537 (w), 2506 (w), 2404 (w), 2260 (w), 2203 (w), 2072 (w), 1923 (m), 1805 (w), 1754 (w), 4641

DOI: 10.1021/acs.inorgchem.6b00489 Inorg. Chem. 2016, 55, 4636−4642

Article

Inorganic Chemistry Calc. for C29H59O10Cl4Al3Mg3: C, 40.3; H, 6.9; Cl, 16.4; Al, 9.4; Mg, 8.5. Found: C, 39.9; H, 7.1; Cl, 16.6; Al, 9.1; Mg, 8.7%. 1H NMR (C6D6, ppm): 3.83−3.84 (m, CH, 4H), 3.70−3.72 (m, THF, 4H), 3.60−3.63 (m, CH2, 8H), 3.55−3.58 (m, CH2, 8H), 1.51−1.54 (m, THF, 4H), 1.36−1.41 (m, CH2, 16H), −0.26 to −0.17 (m, CH3, 15H). 27Al NMR (C6D6, ppm): δ1 158 and δ2 181. 1H NMR spectrum of rubberlike product: 1H NMR (C6D6, ppm): 6.00 (m, C5H5); 3.86, 3.74, 2.83, 2.78, 2.21, 1.64 [s, (C4H8O)n polymer]. IR (cm−1, Nujol mull): 1299 (m), 1190 (s), 1071 (vs), 1040 (vs), 1012 (vs), 994 (s), 960 (s), 939 (m), 857 (m), 823 (m), 587 (m), 493 (m), 426 (m), 390 (m), 359 (m), 319 (m), 279 (m).

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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.inorgchem.6b00489. Additional crystallographic data for 2−5 (PDF) XRD data for 2−5 (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge the National Science Centre, Poland (Grant No. 2014/13/B/ST5/01512) for financial support. REFERENCES

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DOI: 10.1021/acs.inorgchem.6b00489 Inorg. Chem. 2016, 55, 4636−4642