Bis(m-terphenyl)silanes - Organometallics (ACS Publications)

Note pubs.acs.org/Organometallics

Bis(m‑terphenyl)silanes Artem Schröder, Enno Lork, and Jens Beckmann* Institut für Anorganische Chemie, Universität Bremen, Leobener Straße, 28359 Bremen, Germany S Supporting Information *

ABSTRACT: The synthesis and full characterization of the first bis(mterphenyl)silanes, namely, (2,6-Mes2C6H3)2SiF2, (2,6-Mes2C6H3)2SiHF, and (2,6-Mes2C6H3)2SiH2, is reported.

B

ulky m-terphenyl substituents have been instrumental for the kinetic stabilization of numerous reactive main-group and transition-metal species.1 Only a small number of these species contain two of these m-terphenyl substituents, which is arguably due to their rather difficult preparation. Examples include species of the elements Mn,2,3 Fe,2,4,5 Co,2,6,7 Zn,8−10 Cd, 8,9 Hg, 8,9,11 Al, 12,13 Ga, 14−17 In, 18 Tl, 19 Ge, 20−30 Sn,21,22,24,26,29 Pb,20,22 and Bi,31 the majority of which are low-coordinate and/or contain heavier elements possessing larger atomic radii. While mono(m-terphenyl)silanes are abundantly known,32−58 to the best of our knowledge there is no reported case of bis(m-terphenyl)silanes. We now describe synthetic protocols that provide access to the first three members of this compound class. All three compounds can be prepared starting from 2,6Mes2C6H3SiHCl2, which is accessible by the reaction of 2,6Mes2C6H3Li with HSiCl3.32 Fluorination of (2,6-Mes2C6H3)SiHCl2 with ZnF2·4H2O and anhydrous ZnF2 provided two different products, namely, the previously known compound (2,6-Mes2C6H3)SiF3 (1)33 and the new compound (2,6Mes2C6H3)SiHF2 (2) in 62 and 92% yield, respectively (Scheme 1). Compound 2 is a colorless crystalline solid, the 29 Si NMR spectrum (CDCl3) of which shows a doublet of triplets centered at δ = −30.9 ppm [1J(29Si−1H) = 290 Hz; 1 29 J( Si−19F) = 302 Hz]. The reactions of 1 and 2 with 2,6Mes2C6H3Li produced the bis(m-terphenyl)silanes (2,6Mes2C6H3)2SiF2 (3) and (2,6-Mes2C6H3)2SiHF (4) in 43 and 49% yield, respectively (Scheme 1). No evidence for (2,6Mes2C6H3)2SiHCl was found when (2,6-Mes2C6H3)SiHCl2 was reacted with 2,6-Mes2C6H3Li in a similar way. These results are consistent with the observation that F atoms are superior leaving groups compared with Cl atoms in reactions of tert-BuLi with chloro- and fluorosilanes.59 Compounds 3 and 4 are colorless crystals, the 29Si NMR spectra (CDCl3) of which exhibit a triplet and a doublet of doublets, respectively, centered © 2014 American Chemical Society

Scheme 1. Synthesis of Bis(m-terphenyl)silanes 3−5

at δ = −32.9 ppm [1J(29Si−19F) = 304 Hz] and δ = −9.1 ppm [1J(29Si−1H) = 238 Hz; 1J(29Si−19F) = 291 Hz]. Reduction of 4 using potassium graphite and subsequent hydrolysis afforded (2,6-Mes2C6H3)2SiH2 (5) in 35% yield as colorless crystals (Scheme 1). The 29Si NMR spectrum (CDCl3) of 5 shows a triplet centered at δ = −53.7 ppm [1J(29Si−1H) = 224 Hz]. It is noteworthy that attempts to prepare 5 from 3 or 4 using LiAlH4 in diethyl ether failed, leaving the starting material unchanged. Received: September 2, 2014 Published: October 2, 2014 6263

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Organometallics

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1H), 7.14 (d, 3J(1H,1H) = 7.6 Hz, 2H), 6.96 (s, 4H), 4.15 (t, J(1H,19F) = 71 Hz, 1J(1H,29Si) = 290 Hz, 1H), 2.35 (s, 6H), 2.02 (s, 12H). 13C{1H} NMR (CDCl3): δ = 147.8, 138.8, 137.5, 136.5, 131.0, 128.5, 128.3, 127.9, 21.2, 20.8. 19F NMR (CDCl3): δ = −139.52 (d, 2 1 19 J( H, F) = 71 Hz, 1J(19F,29Si) = 302 Hz). 29Si NMR (CDCl3): δ = −30.9 (dt, 1J(19F,29Si) = 302 Hz), 1J(1H,29Si) = 290 Hz). IR (KBr): ṽ(Si−H) = 2172 cm−1. Anal. Calcd for C24H26F2Si (380.55): C, 75.75; H, 6.89. Found: C, 75.71; H, 6.81. Synthesis of 3. To a solution of 1 (1.87 g, 5.00 mmol) in Et2O (80 mL) cooled to −78 °C was slowly added a solution of 2,6-Mes2C6H3Li (2.24 g, 7.00 mmol) in Et2O (100 mL) with a dropping funnel. The solution was stirred for another 16 h and slowly warmed to room temperature. The volatile materials were removed under reduced pressure, and the solid residue was extracted with CH2Cl2 (3 × 50 mL). Filtration over a short silica gel column and concentration under vacuum afforded 3 as colorless crystals (1.49 g, 2.15 mmol, 43%, mp >230 °C). 1H NMR (CDCl3): δ = 7.50 (t, 3J(1H,1H) = 7.6 Hz, 2H), 7.15 (d, 3J(1H,1H) = 7.6 Hz, 4H), 6.99 (s, 8H), 2.37 (s, 18H), 2.12 (s, 18H). 13C{1H} NMR (CDCl3): δ = 149.7, 140.4, 137.0, 136.5, 131.0, 130.3, 128.1, 21.7, 21.3. 19F NMR (CDCl3): δ = −114.45 (s, 1 19 29 J( F, Si) = 304 Hz). 29Si NMR (CDCl3): δ = −32.9 (t, 1J(19F,29Si) = 304 Hz). Anal. Calcd for C48H50F2Si (693.01): C, 83.19; H, 7.27. Found: C, 83.06; H, 7.11. Synthesis of 4. To a solution of 2 (1.78 g, 5.00 mmol) in Et2O (80 mL) cooled to −78 °C was slowly added a solution of 2,6-Mes2C6H3Li (2.24 g, 7.00 mmol) in Et2O (100 mL) with a dropping funnel. The solution was stirred for 16 h and slowly warmed to room temperature. The volatile materials were removed under reduced pressure, and the solid residue was extracted with CH2Cl2 (3 × 50 mL). Filtration over a silica gel column and concentration under vacuum gave 4 as colorless crystals (1.65 g, 2.45 mmol, 49%, mp >230 °C). 1H NMR (CDCl3): δ = 7.27 (t, 3J(1H,1H) = 7.6 Hz, 2H), 6.77 (s, 8H), 6.71 (d, 3J(1H,1H) = 7.6 Hz, 4H), 4.90 (d, 2J(1H,19F) = 44 Hz, 1J(1H,29Si) = 238 Hz, 1H), 2.35 (s, 12H), 1.63 (s, 12H), 1.60 (s, 12H). 13C{1H} NMR (CDCl3): δ = 149.3, 140.4, 136.9, 136.3, 133.1, 133.0, 130.4 (d, 2J(13C,19F) = 15 Hz), 129.9, 128.2, 128.0, 21.6, 21.6, 21.5, 21.3. 19F NMR (CDCl3): δ = −157.49 (d, 2J(1H,19F) = 44 Hz, 1J(19F,29Si) = 291 Hz). 29Si NMR (CDCl3): δ = −9.1 (dd, 1J(19F,29Si) = 291 Hz, 1J(1H,29Si) = 238 Hz). IR (KBr): ṽ(Si−H) = 2248 cm−1. Anal. Calcd for C48H51FSi (675.01): C, 85.41; H, 7.62. Found: C, 85.36; H, 7.51. Synthesis of 5. THF (500 μL) was condensed into a solid mixture of 4 (100 mg, 0.15 mmol) and KC8 (56 mg, 0.42 mmol) at −50 °C. The suspension was slowly warmed up to room temperature over 16 h before it was quenched with water (50 μL). The graphite was removed by filtration over glass wool and the volatile materials were condensed off under reduced pressure. The solid residue was redissolved in CH2Cl2 (1 mL) and hexane (500 μL). Slow evaporation of the solvent yielded colorless crystals of 5 (35 mg, 0.05 mmol, 35%, mp >230 °C). 1 H NMR (CDCl3): δ = 7.47 (t, 3J(1H,1H) = 7.6 Hz, 2H), 7.19 (d, 3 1 1 J( H, H) = 7.6 Hz, 2H), 6.96 (d, 3J(1H,1H) = 7.6 Hz, 2H), 5.02 (s, 1 1 29 J( H, Si) = 224 Hz, 2H), 2.07 (s, 12H), 1.46 (s, 24H). 13C{1H} NMR (CDCl3): δ = 148.7, 141.6, 139.5, 136.9, 136.3, 130.7, 128.9, 128.5, 128.0, 21.5, 21.2. 29Si NMR (CDCl3): δ = −53.7 (t, 1J(1H,29Si) = 224 Hz). IR (KBr): ṽ(Si−H) = 2158 cm−1. Anal. Calcd for C48H52Si (657.02): C, 87.75; H, 7.98. Found: C, 87.49; H, 7.82. Crystallography. Intensity data were collected on a STOE IPDS 2T area detector (3) or a Siemens P4 diffractometer (4 and 5) fitted with a Siemens LTII at 173 K using graphite-monochromatized Mo Kα radiation (λ = 0.7107 Å). All structures were solved by direct methods and refined on the basis of F2 by use of the SHELX program package as implemented in WinGX.62 All non-hydrogen atoms were refined using anisotropic displacement parameters. Hydrogen atoms attached to carbon atoms were included in geometrically calculated positions using a riding model. Hydrogen atoms attached to silicon atoms were located in the last refinement cycle and refined isotropically. In 4, the H1 and F1 atoms were disordered over sites (occupancies 1:1). Figures were created using DIAMOND.63 Crystallographic data (excluding structure factors) for the structural analyses have been deposited with the Cambridge Crystallographic

Compounds 3−5 crystallize in the orthorhombic space group Fdd2 and are therefore isomorphous with (2,6Mes2C6H3)2GeH2 and (2,6-Mes2C6H3)2GeHF.23,27 The molecular structure of 3 is shown in Figure 1, and selected bond

2

Figure 1. Molecular structure of 3 showing 30% probability ellipsoids and the numbering scheme. Selected bond parameters of 3 [Å, deg]: Si1−F1 1.583(1), Si1−C10 1.895(2), F1−Si1−F1a 103.6(1), F1− Si1−C10 107.69(8), F1−Si1−C10a 102.82(7), C10−Si1−C10a 129.7(1). Selected bond parameters of 4 [Å, deg]: Si1−F1 1.510(3), Si1−C10 1.893(2), F1−Si1−C10 110.2(1), F1−Si1−C10a 106.2(1), C10−Si1−C10a 129.4(2). Selected bond parameters of 5 [Å, deg]: Si1−C10 1.911(2), C10−Si1−C10a 128.4(1).

parameters of 3−5 are collected in the caption of the figure. The spatial arrangement of the Si atoms is strongly distorted tetrahedral. The distortion is reflected in the large C−Si−C angles of 3 [129.7(1)°], 4 [129.4(2)°], and 5 [128.4(1)°], which compare well with the C−Ge−C angles of (2,6Mes2C6H3)2GeHF [132.0(1)°] and (2,6-Mes2C6H3)2GeH2 [127.9(1)°].23,27 By contrast, moderately bulky diarylsilanes, such as Mes2SiH2, show significantly smaller C−Si−C angles [114.2(2)°].60 The steric crowding is further evidenced by the alignment of the central aromatic ring (C10−C15), which substantially bends away from the Si1−C10 vector. We are actively pursuing utility studies of 3−5 for the preparation of novel kinetically stabilized Si species.

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EXPERIMENTAL SECTION

All manipulations were carried out under anaerobic and anhydrous conditions in an atmosphere of argon using standard Schlenk and glovebox techniques. The compounds ZnF2 (ABCR) and ZnF2·4H2O (Sigma-Aldrich) were used as purchased. The aryllithium reagent 2,6Mes2C6H3Li was prepared according to a literature procedure.61 Solvents were dried through activated columns using an MBRAUN MB-SPS-800 solvent drying system and degassed prior to use. 1H, 13C, and 29Si NMR spectra were recorded in CDCl3 solutions using a Bruker AVANCE NB 360 NMR spectrometer. 29Si NMR chemical shifts are reported relative to tetramethylsilane (TMS). IR data were recorded using a PerkinElmer Spectrum 1000 FT-IR spectrometer on samples prepared as KBr pellets. Synthesis of 2. To a suspension of anhydrous ZnF2 (1.03 mg, 10.0 mmol) in THF (10 mL) cooled to 0 °C was added a solution of (2,6Mes2C6H3)SiHCl2 (2.07 g, 5.00 mmol) in THF (60 mL) with a dropping funnel. The solution was slowly warmed to room temperature and stirred for 3 days. The volatile materials were removed under reduced pressure, and the solid residue was extracted with a mixture of hexane (50 mL) and toluene (25 mL). After removal of the solvent, the crude product was washed with ethanol (30 mL) and dried in vacuum to give 2 as colorless crystals (1.64 g, 4.60 mmol, 92%, mp 187 °C). 1H NMR (CDCl3): δ = 7.66 (t, 3J(1H,1H) = 7.6 Hz, 6264

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Data Centre (CCDC nos. 1018718−1018720). Copies of this 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]; Web: http://www.ccdc.cam. ac.uk).

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ASSOCIATED CONTENT

S Supporting Information *

Crystal and refinement data for 3−5, figures showing the molecular structures of 4 and 5, and CIF files containing the crystallographic data for 3−5. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

* E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The Deutsche Forschungsgemeinschaft (DFG) is gratefully acknowledged for financial support. REFERENCES

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