Synthesis and Structures of Titanium and Zirconium Trisiloxides

Dec 3, 2008 - Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409, and Institut für Chemie der Universität Rostock...
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Organometallics 2009, 28, 382–385

Synthesis and Structures of Titanium and Zirconium Trisiloxides Clemens Krempner,*,† Ulrike Ja¨ger-Fiedler,‡ Martin Ko¨ckerling,‡ and Helmut Reinke‡ Department of Chemistry and Biochemistry, Texas Tech UniVersity, Lubbock, Texas 79409, and Institut fu¨r Chemie der UniVersita¨t Rostock, A.-Einstein-Strausse 3a, D-18059 Rostock, Germany ReceiVed September 24, 2008 Summary: The synthesis and structures of zirconium and titanium trisiloxides containing the tridentate ligand [MeSi(RMeSiO)3]3(rac-l,l-3)-3H (R ) Si(SiMe3)2Me) are reported. Reactions of racl,l-3 with M(OEt)4, where M ) Ti or Zr, gaVe tridentate complexes of formula [MeSi(RMeSiO)3]MOEt (l,l-4, M ) Ti; l,l-5, M ) Zr). In striking contrast, treatment of rac-l,l-3 with Zr(NEt)4 afforded the spirocyclic complex {[MeSi(RMeSiO)3]2Zr}H2 (l,l-7). These compounds feature bicyclooctane structures, which are hitherto unknown in the chemistry of metal siloxides.

Scheme 1. Synthesis of 3

Introduction There has been considerable interest in recent years in the chemistry and structures of titanium and zirconium siloxides, as these well-defined compounds have found application in catalysis and as soluble precursors for silicate materials.1 Synthetic and structural studies with respect to bidentate and tridentate siloxide complexes of titanium and zirconium have been reported by the groups of Feher,2 Duchateau3 and Edelmann,4 employing incompletely condensed polyhedral oligosilsesquioxanes (POSS) as supporting ligands. Tridentate complexes, featuring a classical bicyclooctane structure, Si(SiO)3M, however, are hitherto unknown, although their nitrogen analogues, Si(SiN)3M and C(SiN)3M, have been investigated in great detail by Gade and co-workers.5 We report here the synthesis and structures of the first titanium and zirconium trisiloxides derived from the trisilanol rac-l,lMeSi{[Me(Me3Si)2Si]MeSiOH}3 (rac-l,l-3).

Results and Discussion Recently, we reported the synthesis and isolation of the trisilanols rac-l,l-3 and rac-l,u-3, obtained as mixtures (ratio rac-l,l-3/rac-l,u-3 ≈ 1/3.5) by hydrolysis of the chlorosilane rac-l,u-2 in basic medium.6 We now have found that hydrolysis of rac-l,l-2 in 1 M * To whom correspondence should be addressed. E-mail: [email protected]. † Texas Tech University. ‡ Institut fu¨r Chemie der Universita¨t Rostock. (1) Reviews: (a) Murugavel, R.; Voigt, A.; Walawalkar, M. G.; Roesky, H. W. Chem. ReV. 1996, 96, 2205. (b) King, L.; Sullivan, A. C. Coord. Chem. ReV. 1999, 189, 19. (c) Murugavel, R.; Bhattacharjee, M.; Roesky, H. W. Appl. Organomet. Chem. 1999, 13, 227–243. (d) Lorenz, V.; Fischer, A.; Gieβmann, S.; Gilje, J. W.; Gun’ko, Y.; Jacob, K.; Edelmann, F. T. Coord. Chem. ReV. 2000, 321, 206–207. (e) Abbenhuis, H. C. L. Chem.Eur. J. 2000, 6, 25–32. (f) Marciniec, B.; Maciejewski, H. Coord. Chem. ReV. 2001, 223, 301. (g) Fujdala, K. L.; Brutchey, R. L.; Tilley, T. D. Topics Organomet. Chem. 2005, 16, 69. (2) (a) Feher, F. J. J. Am. Chem. Soc. 1986, 108, 3850. (b) Feher, F. J.; Walzer, F. J.; Blanski, R. L. J. Am. Chem. Soc. 1991, 113, 3618. (c) Feher, F. J.; Blanski, R. L. J. Am. Chem. Soc. 1992, 114, 5886. (d) Feher, F. J.; Tajima, T. L. J. Am. Chem. Soc. 1992, 116, 2145.

sulfuric acid furnished rac-l,l-3 as the major product in yields of ca. 60%. Starting from MeSi(SiMeCl2)3, (1) and without purifying the chlorosilane rac-l,l-2, the trisilanol could be isolated in total yields of more than 50% based on 1 (Scheme 1). This allowed us to use rac-l,l-3 as a precursor in the formation of transition metal trisiloxides that contain the tridentate ligand [MeSi(RMeSiO)3]3(rac-l,l-3)-3H. Suitable starting materials in the preparation of titanium and zirconium siloxides are the amides or alkoxides of these metals in Broensted acid-base reactions with appropriate silanols. In fact, the stoichiometric reaction of rac-l,l-3 with Ti(OEt)4 in hexanes at room temperature furnished [MeSi(RMeSiO)3]TiOEt (l,l-4) as a yellow microcrystalline material in 74% yield. The analogous reaction with Zr(OEt)4 at elevated temperatures in heptanes gave the corresponding zirconium trisiloxide [MeSi(RMeSiO)3]ZrOEt (l,l-5) as a colorless powder in 64% yields (Scheme 2). Both products could be identified by means of elemental analyses and multinuclear NMR spectroscopy. As in the free ligand l,l-3, the 1 H, 13C, and 29Si NMR spectra (THF-d8) of the C3-symmetric products indicate that all three (RMeSiO)3 groups are equivalent in solution with two sets of diastereotopic Me3Si resonances and two singlets corresponding to the MeSiO and MeSi groups. Interestingly, when a saturated hexane solution of the titanium compound 4 was exposed to air for several days, a yellow microcrystalline material was formed, which was identified by multinuclear NMR spectroscopy and X-ray crystallography as the (3) (a) Duchateau, R. Chem. ReV. 2002, 102, 3525, and references cited therein. (b) Duchateau, R.; Dijkstra, T. W.; van Santen, R. A.; Yap, G. P. A. Chem.-Eur. J. 2004, 10, 3979. (4) (a) Lorenz, V.; Edelmann, F. T. AdV. Organomet. Chem. 2005, 53, 101, and references cited therein. (b) Lorenz, V.; Giessmann, S.; Gun’ko, Y. K.; Fischer, A. K.; Gilje, J. W.; Edelmann, F. T. Angew. Chem., Int. Ed. 2004, 43, 4603. (5) Gade, L. H. Acc. Chem. Res. 2002, 35, 575, and references cited therein. (6) Krempner, C.; Ja¨ger-Fiedler, U.; Ko¨ckerling, M.; Ludwig, R.; Wulf, A. Angew. Chem., Int. Ed. 2006, 45, 6755–6759.

10.1021/om800930s CCC: $40.75  2009 American Chemical Society Publication on Web 12/03/2008

Notes

Organometallics, Vol. 28, No. 1, 2009 383

Figure 1. Molecular structure of 6 in the crystal. The thermal ellipsoids correspond to 30% probability. Hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and angles [deg]: Ti1-O4 1.795(6), Ti1-O1 1.796(5), Ti1-O3 1.802(4), Ti1-O2 1.817(5), Si3-O1 1.683(6), Si5-O4 1.681(5), Si10-O2 1.680(6), Si4-Si10 2.400(3), Si4-Si5 2.401(5), Si3-Si4 2.396(5), O4-Ti1-O1 117.6(3), O4-Ti1-O3 103.1(2), O1-Ti1-O3 105.2(3), O4-Ti1-O2 115.0(2), O1-Ti1-O2 107.9(2), O3-Ti1-O2 107.0(3), Ti1-O3-Ti1 124.6(4). Scheme 2. Synthesis of the Metal Trisiloxides 4-7

dinuclear titanium complex 6 (Scheme 2). In the 1H, 13C, and 29Si NMR spectra of 6, six signals for the SiMe3 (1:1:1:1:1:1 ratio) and four signals for the SiMe groups (1:1:1:1 ratio) were observed, whereas the free ligand rac-l,l-3 and the complexes 4 and 5 exhibit only two signals for the diastereotopic SiMe3 groups (1:1 ratio) and two signals for the SiMe groups (1:3 ratio). Moreover, in the 29 Si NMR spectrum of 6, the silicon atoms of the SiO moieties display three distinct signals appearing at 33.3, 27.9 and 26.0 ppm, respectively, indicating different chemical environments. By X-ray crystallography, the structure was determined unambiguously to be dinuclear, with the two tetracoordinated titanium atoms bridged by an oxygen atom (Figure 1). Each of the two siloxide ligands binds to the titanium atoms in a mono- and bidentate fashion as well. The inner Si-Si bonds [Si4-Si10 2.400(3), Si4-Si5 2.401(5), Si3-Si4 2.396(5) Å] are significantly elongated as compared to that of the free ligand rac-l,l-3 (2.383(3)Å) and zirconium complex 7 (average value 2.36 Å), indicating consider-

able strain in the molecule. The Si-O and Ti-O distances are in the expected range for related tetravalent titanium siloxides.7 A similar structural motif has been observed in a dinuclear complex derived from the reaction of cyclo-Ph4(SiO)4(OH)4 with Ti(OSiMe3)4.8 In this case, however, a water molecule bridges both titanium atoms. In addition, the structural interpretation has been confirmed by the independent synthesis of 6 from a wet sample of l,l-39 and Ti(OEt)4 in n-heptane under a nitrogen atmosphere. The NMR spectroscopic data of the raw product are identical to those found for 6 derived from solutions of 4 being exposed to air. Besides 4, small amounts of 6 could be detected in the 1H NMR spectra, and with increased reaction time under reflux conditions the relative concentrations of both compounds continue to change; 6 becomes the major product, whereas the concentration of 4 decreases. From these results it is likely that the formation of dinuclear 6 arises from hydrolysis of the Ti-OEt bond sequence of 4. This process may generate a reactive Ti-OH species, which then rapidly condenses or inserts into another molecule of 4 to form the oxo bridged titanium complex 6 after ligand scrambling. Attempted reactions of rac-l,l-3 with Ti(NEt2)4 under various conditions resulted in mixtures of products that could not be identified. Also stoichiometric reactions of rac-l,l-3 with Zr(NEt2)4 did not give the expected product [MeSi(RMeSiO)3]ZrNEt2; instead the formation of the spirocyclic zirconium trisiloxide l,l-7 was observed as the main product (Scheme 2). Best yields (51%) were obtained when 2 equiv of rac-l,l-3 and 1 equiv of Zr(NEt2)4 in n-heptane were employed. Complex 7, whose structure was determined by X-ray crystallography, contains formally a Zr4+ ion, with two ligands coordinating (Figure 2). Because we could not find counter cations in the difference map, we propose compound 7 to be of formula {[MeSi(RMeSiO)3]2Zr}H2 (R ) Si(SiMe3)2Me) in which two protons are weakly bonded to the oxygen atoms. However, four of the six coordinating OH-groups are deprotonated. Therefore, the coordination around the zirconium is not regular, but distorted octahedral, with four short Zr-O bonds (average length 2.008 Å, range 1.925-2.098 Å) and two longer ones (2.334 and 2.356 Å). The O atoms with the longer Zr-O bonds are carrying the protons. As expected, the average of the four Zr-O bond distances is slightly elongated as compared to tetracoordinated zirconium silsesquioxane complexes [(c-C6H11)7Si7O12]ZrCp* (1.96(3)Å),2a and [(c-C5H9)7Si7O11(OSiMePh2)]ZrCp2 (1.994(2), 1.995(2)Å),10a the pentacoordinated species {[(c-C5H9)7Si7O12]ZrCH2Ph}2 (1.958(5)Å)10b and [Me(Me3Si)3SiSiO]2Zr · NHEt2 (2.020(2), 1.960(2)Å).11 However, they compare well with compounds that have hexacoordinated zirconium, e.g. [(c-C5H9)7Si7O11(7) For comparison, see also: (a) Hoffmann, D.; Krempner, C.; Reinke, H. J. Organomet. Chem. 2002, 662, 1. (b) Krempner, C.; Koeckerling, M.; Reinke, H.; Weichert, K. Inorg. Chem. 2006, 45, 3203. (c) Krempner, C.; Reinke, H.; Weichert, K. Polyhedron 2007, 26, 3637. (d) Krempner, C.; Reinke, H.; Weichert, K. In Organosilicon Chemistry, Vol. VI; Auner, N., Weis, J., Eds.; VCH: Weinheim, 2005; p 344. (8) Hirotsu, M.; Taruno, S.; Yoshimura, T.; Ueno, K.; Unno, M.; Matsumoto, H. Chem. Lett. 2005, 34, 1542. (9) In the course of our studies we noticed that the yield and purity of titanium complex 4 is strongly influenced by the water content of the ligand precursor l,l-3. The latter, obtained as a finely divided powder from hydrolysis of l,l-2, contains significant amounts of water if not thoroughly dried under vacuum. (10) (a) Skowronska-Ptasinska, M. D.; Duchateau, R.; van Santen, R. A.; Yap, G. P. A. Organometallics 2001, 20, 3519. (b) Duchateau, R.; Abbenhuis, H. C. L.; van Santen, R. A.; Meetsma, A.; Thiele, S; K, H.; van, Tol; Maurits, F. H Organometallics 1998, 17, 5663. (11) Krempner, C.; Reinke, H.; Spannenberg, A.; Weichert, K. Polyhedron 2004, 23, 2475.

384 Organometallics, Vol. 28, No. 1, 2009

Notes

one considers that the acidity of silanols17 is progressively decreased as the substituents on the central SiOH moiety become more electropositive, consistent with the order (R3SiO)3SiOH > (Aryl)3SiOH > R3SiOH > (R3Si)3SiOH.18 In summary, tridentate titanium and zirconium trisiloxides derived from trisilanol rac-l,l-3 were synthesized and structurally characterized. The titanium and zirconium derivatives 4, 5, and 7 represent the first examples of a metal siloxides featuring a bicycloctane structure, Si(SiO)3M (M ) Ti, Zr).

Experimental Section

Figure 2. Molecular structure of 7 in the crystal. The thermal ellipsoids correspond to 30% probability. Hydrogen atoms are omitted for clarity. Only one of the two refined parts of the two disordered groups (and one Zr atom) is shown. Selected bond lengths [Å] and angles [deg]: Zr1-O1 2.075(2), Zr1-O2 2.334(2), Zr1-O3 1.932(2), O1-Si3 1.662(2), O2-Si5 1.676(2), O3-Si8 1.670(2), Si3-Si4 2.362(1), Si4-Si5 2.357(1), Si4-Si8 2.361(1), O1-Zr1-O1′ 163.52(3), O1-Zr1-O2 83.74(8), O2-Zr1-O2′ 168.18(5), O1-Zr1-O3 95.5(1), O2-Zr1-O3 88.0(1), O3-Zr1-O3′ 168.63(6), Zr1-O2′ 1.925(2), Zr1-O1′ 2.098(2), Zr1-O3′ 2.356(2) (symmetry operation for the primed atoms: 1-x, 2-y, -z).

(OSiMe3)]2Zr · 2THF (2.000(5)Å)10b and the zirconate complex [{O(SiPh2O)2}3Zr]Li2 · 3Pyr (ca. 2.015-2.132Å).12 The presence of OH groups in complex 7 is supported by IR spectroscopic measurements (nujol), which exhibit a sharp signal at 3605 cm-1 indicative for a nonassociated Si-OH group. However, as in the free ligand rac-l,l-3, the MeRSiO moieties are equivalent in the 1H, 13C and 29Si NMR spectra, indicating a symmetric coordination environment of the central zirconium. Two sets of SiMe3 groups (1:1 ratio), three SiMe groups (3:3:1 ratio), but none of the OH protons could be detected in the 1H NMR (C6D6), which implies fluxional behavior of the OH protons. It is somewhat surprising that diethylamine, which is released during the course of the reaction, does not abstract the OH protons to form the expected dianionic complex with H2NEt2+ as the countercation. We note that Ph2(OH)Si-O-Si(OH)Ph2 with pyridine readily forms its adduct [Ph2(OH)SiOSi(O)Ph2][PyrH]13 and reacts with Zr(NEt2)4 to give the hexa-coordinated zirconate [{O(SiPh2O)2}3Zr][H2NEt2]2.14 The fact that rac-l,l-3 can coordinate to the metal without being fully deprotonated15,16 is most likely due to its less pronounced acidity compared to siloxy substituted silanols such as Ph2(OH)Si-O-Si(OH)Ph2. This is plausible if (12) Motevalli, M.; Shah, D.; Sullivan, A. C. J. Chem. Soc., Dalton Trans. 1993, 2849. (13) Gunko, Y. K.; Kessler, V. G.; Reilly, R. Inorg. Chem. Commun. 2004, 7, 341. (14) Hossain, M. A.; Hursthouse, M. B. Inorg. Chim. Acta 1980, 44, L259. (15) Similar observation were made for {[(E)-{Me(Me3Si) 3SiSiO}2]2Al}H: Krempner, C.; Weichert, K.; Reinke, H. Organometallics 2007, 26, 1386. (16) Dimeric [Cl2Zr(CpSiMe2OH)]2 is the only other known zirconium complex with two SiOH groups coordinated to the zirconium atoms: Ciruelos, S.; Cuence, T.; Gomez-Sal, R.; Manzanera, A.; Royo, P. Polyhedron 1998, 17, 1055.

General Remarks. The manipulation of air-sensitive compounds involved standard Schlenk line and dry box techniques. All solvents were distilled under argon from alkali metals prior to use. THF-d8 and benzene-d6 were dried over activated molecular sieves and stored in the glovebox. The compounds MeSi(SiMe3)319 and MeSi(SiMeCl2)320 were prepared as previously described. Ti(OEt)4 was purchased from Alfa Aesar and Zr(OEt)4 from Aldrich. The 1H, 13C, and 29Si NMR spectra were obtained using Bruker AC 250 and ARX 300 spectrometers at 300 K if not otherwise stated. Microanalyses were carried out with a C/H/N/S-Analyzer Thermoquest Flash EA 1112 by addition of Pb3O4 for silicon containing compounds. MS: Intectra AMD 402. Synthesis of rac-l,l-3. In a Schlenk flask with magnetic stirrer were placed rapidly ButOK (12.93 g, 0.115 mmol) and MeSi(SiMe3)3 (30.32 g, 0.115 mol). After the flask was evacuated and refilled with argon three times, THF (300 mL) was added. The resulting yellow solution was stirred overnight to quantitatively form potassium silanide KSi(SiMe3)2Me. After the solvent had been replaced by n-pentane, the solution was transferred into a dropping funnel and slowly added to a vigorously stirred solution of MeSi(SiMeCl2)3 (1) (14.83 g, 0.0385 mol) in n-pentane (100 mL) at -78 °C. Stirring was continued for 30 min at -78 °C and the mixture was allowed to warm up to room temperature within 2 h. The reaction mixture was filtered, and the solution was concentrated and dried under high vacuum at 150 °C to afford raw l,l-2 as a highly viscous oil, which upon standing slowly solidified. The raw material was dissolved in ether (150 mL) and 1 M H2SO4 (200 mL) was added. The mixture was vigorously stirred at room temperature for one day after which a white powder precipitated. The white powder was filtered, washed several times with water, acetone, and pentane, and carefully dried under high vacuum for 24 h at ca. 50 °C to afford 15.86 g (52%) of the title compound. The NMR spectroscopic data are identical to those previously reported.6 Caution! Compound 3 can contain significant amounts of water. Therefore, drying the sample under vacuum for 24 h at ca. 50 °C prior to use or storing dry samples in the Glove box is strongly recommended. l,l-4: A suspension of Ti(OEt)4 (91 mg, 0.40 mmol), rac-l,l-3 (300 mg, 0.38 mmol) and n-heptane (4 mL) was stirred for ca. 10 min at room temperature until the suspension became a clear solution. This solution was left overnight and subsequently stored in a freezer at -20 °C to give yellow crystals (250 mg, 74%) of the title compound. Mp 260-270 °C (dec.). 1H NMR (THF-d8, 300 MHz): δ 4.52 (br, OCH2CH3, 2 H), 1.29 (br, OCH2CH3, 3 H), 0.85 (s, OSiCH3, 9 H), 0.38 (s, SiCH3, 3 H), 0.32 (s, SiCH3, 9 H), 0.23, 0.18 (2s, Si(CH3)3, 2 × 27 H). 13C NMR (THF-d8, 125.8 MHz): δ 70.6 (OCH2CH3), 18.7 (OCH2CH3), 9.0 (OSiCH3), 1.3, 1.0 (Si(CH3)3), -8.0, -9.7 (SiCH3). 29 Si NMR (THF-d8, 99.3 MHz): δ 27.8 (OSiCH3), -8.9, -9.6 (17) Silanols are thought to be more acidic than their carbon counterparts, the alcohols; see also: West, R.; Baney, R. H. J. Am. Chem. Soc. 1959, 81, 6145. (18) Chandrasekhar, V; Boomishankar, R; Nagendran, S. Chem. ReV. 2004, 104, 5847. (19) Marsmann, H. C.; Raml, W.; Hengge, E. Zeitschrift Naturf. B 1980, 35B, 1541. (20) Herzog, U.; Richter, R.; Brendler, E.; Roewer, G. J. Organomet. Chem. 1996, 507, 221.

Notes (Si(CH3)3), -71.1, -78.4 (SiCH3). Anal. calcd for C27H80O4Si13Ti (881.900): C, 36.77; H 9.14. Found: C, 36.51; H 9.07. l,l-5: A suspension of Zr(OEt)4 (113 mg, 0.42 mmol), rac-l,l-3 (300 mg, 0.38 mmol), and n-heptane (10 mL) was stirred at room temperature overnight and at 100 °C for ca. 20 h. The resulting solution was cooled to room temperature and filtered. Colorless crystals of l,l-5 (225 mg, 64%) were obtained after cooling the solution in a freezer at ca. -20 °C. Mp 267 °C. 1H NMR (THF-d8, 300 MHz): δ 4.25 (br, OCH2CH3, 2 H), 1.30 (br, OCH2CH3, 3 H), 0.81 (s, OSiCH3, 9 H), 0.31 (s, SiCH3, 3 H), 0.29 (s, SiCH3, 9 H), 0.22, 0.17 (2s, Si(CH3)3, 2 × 27 H). 13C NMR (THF-d8, 125.8 MHz): δ 65.5 (OCH2CH3), 20.3 (OCH2CH3), 10.4 (OSiCH3), 1.4, 1.1 (Si(CH3)3), -8.1, -9.5 (SiCH3). 29 Si NMR (THF-d8, 99.3 MHz): δ 16.4 (OSiCH3), -9.0, -9.9 (Si(CH3)3), -70.7, 79.8 (SiCH3). Anal. calcd for C27H80O4Si13Zr (925.257): C, 35.05; H 8.71. Found: C, 34.81; H 8.64. l,l-6: A stirred mixture of Ti(OEt)4 (86 mg, 0.38 mmol), wet racl,l-39 (300 mg, 0.38 mmol), and n-heptane (3 mL) was stirred at room temperature for 3 h at 100 °C and then cooled to room temperature. Yellow crystals of 6 (100 mg, 31%) were obtained after cooling the solution in a freezer at ca. 5 °C. Mp >230 °C. 1H NMR (C6D6, 500 MHz): δ 1.25, 1.17, 0.90 (3s, OSiCH3, 3 × 3 H), 0.68, 0.50, 0.49, 0.44 (4s, SiCH3, 4 × 3 H), 0.42 (s, Si(CH3)3, 2 × 9 H), 0.39, 0.32, 0.28, 0.24, (4s, Si(CH3)3, 4 × 9 H). 13C NMR (C6D6, 125.8 MHz): δ 11.1, 9.7, 8.0 (OSiCH3), 1.3, 1.3, 1.3, 1.2, 1.2 (Si(CH3)3), -7.9, -10.0, -10.2, -10.5 (SiCH3). 29Si NMR (C6D6, 99.4 MHz): δ 33.3, 27.9, 26.0 (OSiCH3), -9.7, -9.9, -10.3, -12.3, -12.6, -13.8 (Si(CH3)3), -75.5, -76.3, -76.4, -76.5, (SiCH3). Anal. calcd for C50H150O7Si26Ti2 (1689.71): C, 35.54; H 8.95. Found: C, 35.70; H 9.10. - MS (70 eV): m/z (%): 1689 (60) [M+], 1500 (100) [M+ - Si(SiMe3)2Me]. l,l-7: A stirred mixture of Zr(NEt2)4 (72 mg, 0.19 mmol), rac-l,l-3 (300 mg, 0.38 mmol), and n-heptane (3 mL) was heated to 100 °C for ca. 15 min until the suspension became a clear solution. Colorless crystals of l,l-7 (160 mg, 51%) were obtained after cooling slowly the hot solution to room temperature. Mp >230 °C. 1H NMR (C6D6, 500 MHz): δ 1.07 (s, OSiCH3, 9 H), 0.50 (s, SiCH3, 3 H), 0.45 (s, SiCH3, 9 H), 0.42, 0.28 (2s, Si(CH3)3, 2 × 27 H). 13C NMR (C6D6, 125.8 MHz): δ 9.9 (OSiCH3), 1.8, 1.0 (Si(CH3)3), -9.7, -10.1 (SiCH3). 29Si NMR (C6d6, 99.4 MHz): δ -11.0, -12.2 (Si(CH3)3), -12.0 (OSiCH3), -77.0, -80.8 (SiCH3). IR (nujol): νSiOH ) 3605 cm-1. Anal. calcd for C50H152O6Si26Zr (1671.19): C, 35.93; H 9.17. Found: C, 35.72; H 9.29. MS (70 eV): m/z (%): 1656 (13) [M+ - CH3], 1483 (57) [M+ - Si(SiMe3)2Me], 1467 (100) [M+ - Si(SiMe3)2Me - Me]. Crystal Structure Determination of 6 (CCDC 663365) and 7 (CCDC 663366). The relevant crystal data, data collection and refinement parameters are collected in Table 1. X-ray data were collected for 7 at low temperature (173(2) K) on a Bruker-Nonius Apex X8 diffractometer, equipped with a CCD detector and for 6 on a Siemens P4 diffractometer. Data were collected using graphitemonochromated Mo KR radiation (λ ) 0.71073 Å). Absorption correction for 7 was applied by using the SADABS routine. Both

Organometallics, Vol. 28, No. 1, 2009 385 Table 1. Crystal Data, Data Collection, and Structure Refinement Parameters for 6 and 7 empirical formula fw, g/mol crystal size, mm3 T, K cryst. sys. space group, Z a, Å b, Å c, Å β,° V, Å3 Dcalcd, g · cm-1 µ, mm-1 no. of measured reflns. no. of uniqe refln. transm. factors, min, max no. parameters R1(F)a wR2(F2)b weighting, A, Bc GOFd

6

7

C50H150O7Si26Ti2 1689.84 0.38 × 0.34 × 0.32 293(2) monoclinic C2/c, 4 30.47(2) 25.00(1) 16.228(9) 117.60(5) 10955(10) 1.025 0.463 5015 (up to 46°(2θ)) 4276 (Rint ) 0.0388) 384 0.0653 0.1761 0.0930, 0.0 1.013

C50H152O6Si26Zr 1671.20 0.43 × 0.19 × 0.18 173(2) monoclinic P21/c, 2 14.6636(7) 26.479(2) 14.9466(7) 115.082(2) 5256.2(5) 1.056 0.434 50770 (up to 52°(2θ)) 10327 (Rint ) 0.0421) 0.8666, 0.9260 387 0.0683 0.1977 0.0945, 4.53 1.096

a R1 ) ∑||Fo| - |Fc|| /∑|Fc|; b wR2 ) [∑{w(F2o - Fc2)2}/∑{w(F2o)2}]; w ) 1/[(σ2(Fo2) + (A · P)2 + B · P]; P ) (Fo2 + 2Fc2)/3; d GOF ) (Σ[w(Fo2 - Fc2)2]/(n - p))1/2, where n and p are the number of data and parameters. c

structures were solved by direct methods (SHELXS-97),21 completed by subsequent difference Fourier techniques, and refined by full matrix least-squares refinements on F2 (SHELXL-97)21 with initial isotropic thermal parameters. Anisotropic thermal parameters were used in the last cycles of refinement for all non-hydrogen atoms except those in disordered TMS groups. In 7 one TMS group is disordered and refined on two positions (as Si1A and Si1B), with an occupation of 63% for Me3Si1A and 37% for Me3Si1B as well as the Zr atom which is located slightly off the inversion center of Wyckoff site 1b. It is refined with 50% occupation. The carbon atoms involved in this disordered TMS group are refined isotropically. The same procedure was applied to one of the methyl groups on Si7, which is refined as C11A (60% occupation) and C11B (40%). Hydrogen atoms were included in calculated positions in both structures and were refined with positional and thermal parameters riding on the attached atoms. Supporting Information Available: Crystallographic data for 6 (CCDC 663365) and 7 (CCDC 663366) including CIF files. This material is available free of charge via the Internet at http://pubs.acs.org. OM800930S (21) Sheldrick, G. M. SHELXSL-97 and SHELXL-97, Programs for Crystal Structure Solution and Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1997.