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Preparation and crystal structures of silyl-substituted potassium cyclooctatetraenides
Journal of Organometallic Chemistry xxx (2017) 1e7
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Preparation and crystal structures of silyl-substituted potassium cyclooctatetraenides Volker Lorenz a, Phil Liebing b, Janek Rausch a, Steffen Blaurock a, Cristian G. Hrib a, Liane Hilfert a, Frank T. Edelmann a, * a b
€t Magdeburg, 39106 Magdeburg, Germany Chemisches Institut der Otto-von-Guericke-Universita ETH Zürich, Laboratorium für Anorganische Chemie, Vladimir-Prelog-Weg 1-5/10, 8093 Zürich, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 July 2017 Received in revised form 27 August 2017 Accepted 28 August 2017 Available online xxx
Cyclooctatetraenyl complexes of potassium are readily available by the reaction of silyl-substituted cyclooctatrienes C8H8-1,4-(SiR3)2 (SiR3 ¼ SiMe3, SiMet2Bu, SiPh3) with potassium hydride or potassium metal. While C8H8-1,4-(SiMe3)2 gave a mixture of K2{C8H6-1,3-(SiMe3)2} (1a) and K2{C8H7-SiMe3} (1b), the substitution pattern on the COT ring remained unchanged in the case of C8H8-1,4-(SiMet2Bu)2 and C8H8-1,4-(SiPh3)2. [{K2{C8H6-1,4-(SiMet2Bu)2}(PhMe)}∞] (2) crystallizes in the absence of DME, featuring a m4-bridging COT ring, while in [K2(C8H6-1,4-(SiPh3)2)(DME)4] (3) the substituted COT ligand adopts a highly symmetric m-h8:h8-coordination, resulting in an “inverse sandwich” architecture. Compound 3 could be oxidized by treatment with iodine to give the corresponding neutral cyclooctatetraene derivative C8H6-1,4-(SiPh3)2 (4). © 2017 Elsevier B.V. All rights reserved.
Dedicated to Professor William J. Evans on the occasion of his 70th birthday. Keywords: Potassium Cyclooctatetraenyl ligands Sandwich complexes Crystal structure
1. Introduction The planar, 10p-aromatic cyclooctatetraenide dianion, C8H2 8 (commonly abbreviated as COT), plays an indispensable role in the organometallic chemistry of f-elements since the discovery of iconic uranocene by Streitwieser and Müller-Westerhoff in 1968 [1]. Since then, numerous sandwich and half-sandwich COT complexes of lanthanides [2] and actinides [3] have been studied. Central precursor in most of their preparations is the di-potassium salt K2C8H8 or K2COT. K2C8H8 was first mentioned in the literature by Katz in 1960 [4]. Crystalline K2C8H8$THF was first made by Fritz and Keller in 1961 by direct reaction of 1,3,5,7-cyclooctatetraene with 2 equiv. of potassium metal in THF [5]. K2C8H8$THF forms yellow crystals which upon drying easily disintegrate to give a white powder of the unsolvated K2C8H8. A remarkable property of K2COT is its explosive decomposition in contact with air [5a]. The synthetic route to this important reagent was later improved by using inexpensive 1,5-cyclooctadiene as starting material [6]. Structurally characterized solvates of K2C8H8 include
* Corresponding author. E-mail address: [email protected] (F.T. Edelmann).
K2C8H8(diglyme) (diglyme ¼ (MeOCH2CH2)2O) [7] and K2C8H8(THF)3 [8]. More recently, bulky silyl-substituted COT ligands have entered the focus of attention. This remarkable recent development was possible mainly through the pioneering work of Cloke et al., who introduced silylated COT ligands of the type {C8H61,4-(SiR3)2}2e (e.g. R ¼ Me, iPr) in organolanthanide and -actinide chemistry [9,10]. It has been demonstrated that the {C8H6-1,4(SiMe3)2}2e ligand (¼ COT00 ) imparts improved solubility and crystallinity over the parent C8H2 8 and enables e.g. the synthesis of anionic sandwich complexes [Ln{C8H6-1,4-(SiMe3)2}2]e for the entire lanthanide series [11]. Moreover, the use of silyl-substituted COT ligands led to the discovery of unusual molecular architectures (e.g. triple- and tetradeckers) [12], novel Ln(COT)-based organometallic sandwich molecular wires (OSMWs) [13] and singlemolecule magnets (SMMs) [14] as well as unprecedented reactions of uranium COT complexes (e.g. carbon monoxide oligomerization) [15]. A new dimension in steric bulk was added to this chemistry by the introduction of the “superbulky” ligand COTbig (¼ 1,4-bis(triphenylsilyl)-cyclooctatetraenyl dianion) by us and the Evans group in 2011 [16]. The use of COTbig in organolanthanide and -actinide chemistry has led to interesting structural effects such as the formation of the significantly bent anionic CeIII sandwich
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V. Lorenz et al. / Journal of Organometallic Chemistry xxx (2017) 1e7
complex [Ce{C8H6-1,4-(SiPh3)2}2]e, the novel neutral cerocene [Ce {C8H6-1,3-(SiPh3)2}2] formed by SiPh3 group migration, as well as the first example of a bent uranocene, [U{C8H6-1,4-(SiPh3)2}2], which exhibits no additional ligands [16]. Key starting material in COT00 chemistry is the lithium derivative Li2{C8H6-1,4-(SiMe3)2}, which was first prepared by Cloke and coworkers [9]. Since then, Li2{C8H6-1,4-(SiMe3)2} has been utilized as precursor for numerous early transition metal, lanthanide and actinide COT00 complexes [9,12,14]. Structural studies have been carried out on the DME adduct [Li(DME)]2{C8H6-1,4-(SiMe3)2} and the dimeric THF adduct [Li(THF)2]2[Li2{C8H6-1,4-(SiMe3)2}2] [17]. The molecular structure of [Li(DME)]2{C8H6-1,4-(SiMe3)2} consists of a {C8H6-1,4-(SiMe3)2}2e dianion with the two lithium atoms coordinated to the ring in an h3-allyl-like fashion [17a]. In [Li(THF)2]2[Li2{C8H6-1,4-(SiMe3)2}2] two Liþ ions are sandwiched between two COT rings, while two Li(THF)þ 2 units are bonded to the outsides of the sandwich [17b]. The same authors reported the polymeric crystal structure of [Na2{C8H6-1,4-(SiMe3)2}(m-THF)2]n, which was prepared by treatment of [Li(THF)2]2[Li2{C8H6-1,4(SiMe3)2}2] with NaCl [17b]. The formation of K2{C8H6-1,4(SiMe3)2} was briefly mentioned in an early report [17a]. Alkali metal derivatives of COTbig have not yet been isolated nor structurally characterized. We report here the first thorough preparative and structural investigation of a series of bis(silylated) potassium cyclooctatetraenides. 2. Results and discussion
reaction conditions (r.t. or reflux temperature, stoichiometric amount or excess KH). Due to very similar solubility properties, the two species could not be separated. Single-crystals of 1a and 1b could only be distinguished by their cell parameters as determined by X-ray diffraction because both species outwardly appeared as colorless, plate-like crystals. The actual target product, K2{C8H6-1,4(SiMe3)2} has never been found in the reaction mixture. In this context it is worth mentioning that in the reaction of the tetrasilylated cyclooctatriene C8H6-1,3,6,6-(SiMe3)4 with KH, one equiv. of Me3SiH is selectively released and the trisilylated potassium derivative K2{C8H5-1,3,6-(SiMe3)3} (1c) has been isolated as the only product [18]. Similar treatment of C8H8-1,4-(SiR3)2 (R ¼ SitBuMe2, SiPh3) with potassium metal or potassium hydride in DME led to formation of the metal derivatives K2{C8H6-1,4-(SiR3)2}. The isolation of DME-solvated K2{C8H6-1,4-(SitBuMe2)2} (2) has been reported earlier [19]. A DME-free form of 2 has now been obtained by recrystallization of the crude product from toluene in 70% yield. In the case of the SiPh3-substituted ligand, the DME solvate [K2(C8H61,4-(SiPh3)2)(DME)4] (3) was the only product obtained in 76% isolated yield. In both cases the silyl substitution pattern of the COT ligand remained unchanged upon metalation with KH or potassium metal, respectively. Like the parent K2COT, the new potassium COT complexes are highly oxidation sensitive, as it was illustrated at the example of compound 3. Addition of iodine to a THF solution led to formation of the hitherto unknown cyclooctatetraene derivative C8H6-1,4(SiPh3)2 (4) which was obtained in the form of colorless, air-stable, high-melting crystals in 72% isolated yield (Scheme 2).
2.1. Preparation of the compounds 2.2. Crystal structures 1,4-Disilylated cycloocta-2,5,7-trienes C8H8-1,4-(SiR3)2 are readily deprotonated in the 1,4-positions upon treatment with n BuLi to yield the corresponding aromatic {C8H6-1,4-(SiR3)2}2e anions (SiR3 ¼ SiMe3, SitBuMe2, SiPh3) [9,10,17]. We now found that similar reactions with potassium hydride or potassium metal can take a different course. For example, reaction of C8H8-1,4-(SiMe3)2 with KH surprisingly afforded a mixture of K2{C8H6-1,3(SiMe3)2}(DME)2 (1a) and the monosilylated species K2{C8H7(SiMe3)}(DME)2 (1b; Scheme 1). The product ratio, determined by NMR spectroscopy, was always around 1:1, independent of the
Relevant interatomic distances in 1a, 1b and 2e4 are represented in Table 1, while experimental details on the structure analyses are summarized in Table 2. Both SiMe3-substituted complexes 1a and 1b crystallize in the orthorhombic space group Pnma, featuring very similar molecular structures. The COT rings each adopt a highly symmetric m-h8:h8-bridging coordination mode (Figs. 1 and 2). The so-formed “inverse sandwich”-like [17b,20] K2(COT) moieties are interconnected by two m-kO,O’:kO,O0 -coordinated DME ligands, leading to a one-dimensional polymeric
Scheme 1. Preparation of the potassium complexes 1ae3.
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V. Lorenz et al. / Journal of Organometallic Chemistry xxx (2017) 1e7
Scheme 2. Oxidation of the potassium complex 3 with iodine.
structure (Fig. 3). Consequently, each potassium atom is coordinated by four O atoms and one h8-COT ligand in a “piano stool” arrangement [21]. The molecular structure of 1a and 1b resembles that of the earlier described K2{C8H6-1,4-(SitBuMe2)2}(DME)2 [19]. The formation of chain polymers by bridging DME ligands is also typical for various other sodium and potassium compounds, e.g. arylamides [22]. The K-C distances are in the same range as in other COT complexes of potassium [18,19] and almost equal in both complexes. The K-COT coordination is therefore not considerably affected by the silyl substitution pattern. The same applies to the K-O separations, which are in the typical broad range of 2.75e3.10 Å. The molecular structure of the earlier reported tris(trimethylsilyl)substituted complex [{K2(C8H6-1,3,6-(SiMe3)3)(DME)2}∞] [18] is virtually identical with that of 1a and 1b. With [{K2{C8H6-1,4-(SiMet2Bu)2}(PhMe)}∞] (2), we succeeded in performing a crystal structure analysis of a potassium COT complex free of a strongly coordinating solvent (Fig. 4). Compound 2 crystallizes from toluene in the space group C2/m, featuring a onedimensional polymeric structure similar as in 1a and 1b. Both potassium atoms are attached to the mirror-symmetric {C8H6-1,4(SiMet2Bu)2}2e ligand in a typical h8-mode. Similar as in the previously described DME solvate K2{C8H6-1,4-(SitBuMe2)2}(DME)2 [19] the COT-derived ligand retained the original 1,4-substitution pattern and no isomerization to the 1,3-analogue has taken place. Due to the absence of DME, coordinative saturation of the potassium atoms is achieved by an additional h2-coordination of a symmetry-related COT ring, and therefore the full coordination mode of the {C8H6-1,4-(SitBuMe2)2}2e ligand is m4-h8:h8:h2:h2. Moreover, one of the two K atoms (K2) interacts with a toluene molecule, where a close K ∙∙∙ C(para) contact of 3.174(4) Å has been observed. Toluene coordination to the other potassium atom K1 is probably prevented by the two bulky tert-butyl groups in spatial proximity to this metal atom. As a result, the K2-(h8-COT) bond of the toluene-coordinated potassium is elongated to 2.3498(5) Å, while the K1-(h8-COT) separation is with 2.3042(5) Å very similar as in 1a and 1b. The additional K-(h2-COT) contacts are weaker than
3
the corresponding K-(h8-COT) bonds, with K-C separations of 3.149(2) Å (K1) and 3.249(1) Å (K2). [K2(C8H6-1,4-(SiPh3)2)(DME)4] (3) has been isolated as monoclinic crystals, space group P21/c, where one formula unit is present in the asymmetric unit (Fig. 5). Just as in 1a and 1b, the substituted COT ligand adopts a highly symmetric m-h8:h8-coordination, resulting in an “inverse sandwich” architecture [17b,20]. Both K atoms are again coordinated by each two DME ligands to form a “piano-stool” arrangement, but due to the high steric demand of the SiPh3 substituents the formation of chain polymers like in 1a and 1b is prevented. Thus, one K atom (K2) is coordinated by two chelating DME ligands, while the other K atom (K1) is attached to only one chelating and one monodentate DME ligand. The distances between the potassium atoms and the COT ring centroid are 2.4077(6) Å and 2.4305(6) Å, and therefore significantly larger than in 1a, 1b and 2. This finding can likely be traced back to the steric bulk of the (C8H6-1,4-(SiPh3)2)2e ligand. In contrast, the K-O bonds are with 2.777(2)e2.959(2) Å similar as in 1a and 1b. The C-C separations within the COT ring and the C-Si bond lengths are virtually equal in all four potassium complexes, implying that the bonding situation within the aromatic system is less influenced by the potassium coordination and silyl substitution pattern (Table 1). Crystal structure analysis of the oxidized C8H61,4-(SiPh3)2 ligand (4; triclinic, P1) revealed the presence of alternating short (av. C-C: 1.338(2) Å) and long C-C separations (av. C-C: 1.479(2) Å) within the COT ring, which fits to the model of four distinct double-bonds (Fig. 6). While the COT ring in the metal complexes 1ae3 are strictly planar, the COT ring in 4 is markedly twisted due to the loss of aromaticity. With 1.882(1) and 1.883(1) Å, the C-Si bonds in 4 are significantly elongated compared to the corresponding {COT-1,4-(SiPh3)2}2e ligand in 3.
3. Conclusions 1,4-Disilylated cyclooctatrienes react with potassium or potassium hydride to give K2COT-derived compounds which show a surprising structural variety. While C8H8-1,4-(SiMe3)2 gave a mixture of K2{C8H6-1,3-(SiMe3)2} (1a) and K2{C8H7-SiMe3} (1b), the substitution pattern of the COT ring remained unchanged in the case of C8H8-1,4-(SiMet2Bu)2 and C8H8-1,4-(SiPh3)2. [{K2{C8H6-1,4(SiMet2Bu)2}(PhMe)}∞] (2) crystallizes in the absence of DME, featuring a m4-bridging COT ring. In 1a and 1b as well as in [K2(C8H6-1,4-(SiPh3)2)(DME)4] (3) the substituted COT ligand adopts a highly symmetric m-h8:h8-coordination, resulting in an “inverse sandwich” architecture. Compounds 2 and 3 can be expected to serve as useful starting materials in future studies. Compound 3 could be oxidized by treatment with iodine to give the hitherto unknown neutral cyclooctatetraene derivative C8H6-1,4(SiPh3)2. (4).
Table 1 Selected bond lengths (Å) for compounds 1ae4.
1a 1b 2 3 4 a b c d
K-C
av. K-C
K-COTa
K-O
C-C
av. C-C
Si-C(COT)
2.927(3)e3.002(3) 2.902(2)e3.036(3) 2.870(1)e3.033(2)b 2.998(2)e3.134(2) e
2.969(3) 2.968(2) 2.970(2) 3.043(2) e
2.3200(8) 2.3097(7), 2.3378(5) 2.3042(5), 2.3498(5) 2.4077(6), 2.4305(6) e
2.746(2)e3.085(2) 2.809(2)e3.020(2) e 2.777(2)e2.959(2) e
1.403(6)e1.432(5) 1.402(3)e1.420(2) 1.402(2)e1.426(2) 1.400(3)e1.424(3) 1.333(2)e1.343(2), 1.465(2)e1.488(2)
1.418(6) 1.411(3) 1.415(2) 1.413(3) 1.338(2)c, 1.479(2)d
1.852(4), 1.858(4) 1.857(3) 1.861(2) 1.849(2), 1.850(2) 1.882(1), 1.883(1)
COT ring centroid. h8-coordination. Double-bonds. Single-bonds.
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Table 2 Crystal data and details on structure refinement of compounds 1ae4. Compound
1a
1b
2
3
4
CCDC deposition number Molecular formula sum Formula weight/g mol1 Crystal system Space group
1423497 C22H44K2O4Si2 506.95 orthorhombic Pnma
1535894 C19H36K2O4Si 434.77 orthorhombic Pnma
1535895 C27H44K2Si2 (þsolv.) 503.00 (þsolv.) monoclinic C2/m
1482608 C60H76K2O8Si2 1059.59 monoclinic P21/c
1482609 C44H36Si2 620.91 triclinic
Cell metric a/Å b/Å c/Å a/ b/ g/ Cell volume/Å3 Molecules per cell z Electrons per cell F000 Calcd. density r/g cm3 m/mm1 (radiation) Crystal size/mm T/K q range/ Absorption correction Reflections collected Reflections unique Reflections with I > 2s Completeness of dataset Rint Parameters R1 (all data, I > 2s(I)) wR2 (all data, I > 2s(I)) GooF (F2)
9.382(2) 16.569(3) 18.589(4) 90 90 90 2890(1) 4 1096 1.165 0.433 (Mo-Ka) 0.60 0.15 0.06 133(2) 2.19 … 25.00 none 12146 2628 2140 99.4% 0.0880 159 0.0806, 0.0596 0.1137, 0.1074 1.215
16.5510(8) 14.2280(7) 10.1702(4) 90 90 90 2395.0(2) 4 936 1.206 0.464 (Mo-Ka) 0.55 0.32 0.22 153(2) 2.35 … 25.00 numerical 7382 2185 1864 99.3% 0.0879 131 0.0550, 0.0460 0.1103, 0.1059 1.069
14.4758(6) 18.4651(6) 11.8728(5) 90 91.099(3) 90 3173.0(2) 4 1088 1.053 0.385 (Mo-Ka) 0.37 0.17 0.11 153(2) 2.21 … 26.00 none 11245 3221 2723 99.8% 0.0285 154 0.0439, 0.0339 0.0786, 0.0750 1.029
13.579(3) 21.753(4) 19.889(4) 90 101.21(3) 90 5763(2) 4 2264 1.221 0.258 (Mo-Ka) 0.60 0.60 0.38 153(2) 1.92 … 25.00 none 29176 10096 6907 99.5% 0.0675 658 0.0766, 0.0435 0.0903, 0.0829 0.0909
9.6095(1) 14.1142(2) 14.8031(2) 116.289(1) 95.982(1) 105.283(1) 1678.81(4) 2 656 1.228 1.182 (Cu-Ka) 0.18 0.14 0.09 100(2) 3.44 … 76.29 multi-scan 116551 6995 6406 99.6% 0.0505 415 0.0369, 0.0338 0.0949, 0.0920 1.068
Fig. 1. Molecular structure of [{K2(C8H6-1,3-(SiMe3)2)(DME)2}∞] (1a) in the crystal. Ellipsoids drawn at the 30% probability level, H atoms omitted for clarity. The COT ring (atoms C1eC8, Si1, Si2, C9, C11) is located on a mirror plane perpendicularly to the crystallographic b-axis. Symmetry codes: ' x, 0.5ey, z; '' 1ex, ey, 1ez; ''' 1ex, 0.5 þ y, 1ez.
4. Experimental 4.1. General procedures All reactions were performed under argon atmosphere using standard Schlenk techniques or in an M. Braun N2-filled glovebox with O2 levels maintained at or below 1 ppm. Glassware was dried at 120 C overnight. All solvents were dried by distillation from sodium/benzophenone under argon atmosphere prior to use. C8H81,4-(SiMe3)2 [9a], C8H8-1,4-(SitBuMe2)2 [23], and C8H8-1,4-(SiPh3)2 [16] were prepared following previously published procedures. All other reagents were commercially available and used as received.
P1
Fig. 2. Molecular structure of [{K2(C8H7(SiMe3))(DME)2}∞] (1b) in the crystal. Ellipsoids drawn at the 30% probability level, H atoms omitted for clarity. The atoms K1, K2, C1, C5, Si1 and C6 are located on a mirror plane perpendicularly to the crystallographic b-axis. Symmetry codes: ' x, 0.5ey, z; '' 0.5 þ x, y, 0.5ez; ''' 0.5 þ x, 0.5ey, 0.5ez.
NMR spectra were recorded in THF-D8 solution at 23(2) C on a Bruker DPX 400 spectrometer (1H: 400.1 MHz; 13C: 100.6 MHz; 29 Si: 79.5 MHz). COSY, HSQC and HMBC experiments were carried out for the unambiguous assignment of the 1H and 13C NMR signals. IR spectra were recorded between 4000 cm1 and 450 cm1, using a Bruker Vertex 70 V spectrometer equipped with a diamond ATR unit and a “Golden Gate” unit. Electron impact mass spectra were measured on a MAT 95 spectrometer with an ionization energy of 70 eV, and elemental analyses (C, H) were performed using a VARIO EL cube apparatus.
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Fig. 3. Representation of the polymeric chain structure of compound 1a, extending along the crystallographic b-axis.
Fig. 6. Molecular structure of C8H6-1,4-(SiPh3)2 (4) in the crystal. Ellipsoids drawn at the 30% probability level, phenyl H atoms omitted for clarity.
Fig. 4. Molecular structure of [{K2{C8H6-1,4-(SiMet2Bu)2}(PhMe)}∞] (2) in the crystal. Ellipsoids drawn at the 50% probability level, H atoms omitted for clarity. Symmetry codes: ' x, ey, z.
using the multi-scan method [25]. The structures were solved with SHELXS-97 using heavy atom (1a, 1b, 2, 3) or direct methods (4) [26] and refined by full matrix least-squares methods on F2 with SHELXL-2016/4 [27]. In the case of 2, highly disordered solvent was considered using the SQUEEZE routine of PLATON [28].
4.3. Synthesis of [{K2(C8H6-1,3-(SiMe3)2)(DME)2}∞] (1a) and [{K2(C8H7(SiMe3))(DME)2}∞] (1b)
Fig. 5. Molecular structure of [K2(C8H6-1,4-(SiPh3)2)(DME)4] (3) in the crystal. Ellipsoids drawn at the 30% probability level, H atoms omitted for clarity.
4.2. Single-crystal X-ray diffraction studies Single crystal X-ray intensity data of the potassium complexes 1a, 1b, 2 and 3 were collected on a STOE IPDS 2T diffractometer, using graphite-monochromated Mo-Ka radiation. For 1b, a numerical absorption correction was applied [24]. A single crystal of 4 was measured on a Xcalibur Atlas Nova System with mirrorfocussed Cu-Ka radiation, and absorption correction was applied
To a solution of C8H8-1,4-(SiMe3)2 (5.0 g, 20 mmol) in DME (100 ml), potassium hydride (1.93 g, 48 mmol) was added at r.t. The resulting suspension was stirred for 24 h at r.t., during which a color change from yellow to dark green took place. The solution was subsequently filtered, the filtrate reduced to approx. 15 ml in vacuo and then layered with n-pentane (60 ml). Colorless, plate-like crystals were obtained within a few days at 5 C, which were filtered off and carefully dried in vacuo. Yield: 6.78 g. Colorless, highly air-sensitive crystalline solid, soluble in THF and DME and poorly soluble in alkanes, Dec. 101 C. Compounds 1a and 1b were obtained simultaneously and could not be separated due to very similar solubility properties. Elemental analysis: calcd. for C22H44K2O4Si2, M ¼ 506.95 g/mol (1a): C 52.12%, H 8.75%; calcd. for C19H36K2O4Si, M ¼ 434.77 g/mol (1b): C 52.49%, H 8.35%; found: C 52.21%, H 8.56%. IR: n 3091s, 2961s, 2931s, 1959 m, 1634s, 1508w, 1504w, 1447 m, 1385 m, 1306w, 1293w, 1247 m, 1181 m, 1155 m, 1061 m, 985 m, 881 m, 839 m, 752 m, 704 m, 555w, 505w cm1. 1H NMR: d 0.23 (s, 18H; Si(CH3)3 1a), 0.26 (s, 9H; Si(CH3)3 1b), 3.21 (s, 12 þ 12H; CH3 DME), 3.34 (s, 8þ8H; CH2 DME), 5.68e6.08 (7 m, 5þ7H; CH COT), 6.18 (s, 1H; 2-CH COT 1a) ppm. The molar ratio 1a:1b corresponding to the signal intensities was approx. 1:1. X-Ray diffraction studies of several selected single-crystals, which always appeared as colorless plates, revealed the cell parameters of either 1a or 1b. 13C{1H}-NMR: d 2.6 (s; Si(CH3)3 1a), 2.7 (s; Si(CH3)3 1b),
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58.8 (s; CH3 DME), 72.4 (s; CH2 DME), 89.1e98.4 (10 s; CH and CSi COT) ppm. 29Si{1H}-NMR: d 3.6 (s; 1a), 2.7 (s; 1b) ppm. MS (EI): m/z 407 (27%, [K(C8H6(SiMe3)2)(DME)2 e4Me]þ), 375 (65%, [K(C8H6(SiMe3)2)(DME)]þ), 353 (24%, [K2(C8H6(SiMe3)2)(DME) e4Me]þ), 323 (27%, [K2(C8H6(SiMe3)2)(DME)e4Me]þ), 295 (7%, [K2(C8H6(SiMe3))(DME)e3Me]þ), 281 (26%, [K2(C8H6(SiMe3)) (DME)e4Me]þ), 265 (35%, [K2(C8H6)(DME)]þ), 249 (45%, [C8H6(SiMe3)2]þ), 235 (22%, [C8H6(SiMe3)2eMe]þ), 223 (61%, [C8H6(SiMe3)2e2Me]þ), 207 (100%, [C8H6(SiMe3)2e3Me]þ). 4.4. Synthesis of [{K2(C8H6-1,4-(SitBuMe2)2)(PhMe)}∞] (2) C8H8-1,4-(SitBuMe2)2 (11.4 g, 34 mmol) was treated with potassium hydride (3.0 g, 75 mmol) in DME (75 ml) as described for 1a/1b. The filtered green-brown solution was taken to dryness in vacuo, and the residue re-dissolved in toluene (50 ml). Reduction of the solvent volume to approx. 10 ml afforded colorless crystals within a few days, which were filtered off and dried in vacuo. Yield: 11.9 g (70%). Colorless, air-sensitive crystals, soluble in THF, DME and toluene and poorly soluble in alkanes, Dec. 98 C. Elemental analysis: calcd. for C27H44K2Si2, M ¼ 503.00 g/mol: C 63.64%, H 9.04%; found: C 63.03%, H 9.13%. IR: n 2938w, 2938s, 2852s, 1460 m, 1394w, 1355w, 1304w, 1244s, 1194w, 1054s, 973 m, 923s, 811s, 728s, 660s, 574s, 513 m, 460 s cm1. 1H NMR: d 0.33 (s, 12H; Si(CH3)2), 0.93 (s, 18H; C(CH3)3), 2.30 (s, 3H; PhCH3), 5.98 (m, 2H; 6,7-CH COT), 6.13 (m, 2H; 5,8-CH COT), 6.23 (s, 2H; 2,3-CH COT), 7.10 (2 m, 3H; o-CH þ p-CH PhMe), 7.18 (m, 2H; m-CH PhMe) ppm. 13C{1H}-NMR: d 2.2 (s; Si(CH3)2), 21.3 (s; PhCH3), 27.4 (s; C(CH3)3), 29.1 (s; C(CH3)3), 86.4 (s; CSi COT), 93.4 (s; 6,7-CH COT), 99.1 (s; 2,3-CH COT), 99.3 (s; 5,8-CH COT), 126.1 (s; p-CH PhMe), 128.9 (s; m-CH PhMe), 129.7 (s; o-CH PhMe), 138.4 (s; i-C PhMe) ppm. 29Si{1H}NMR: d 2.2 (s) ppm. MS (EI): m/z 332 (88%, [C8H6(SitBuMe2)2]þ), 275 (100%, [(C8H6(SitBuMe2)]þ), 219 (36%, [C8H6(SitBuMe2)2]þ e2tBu), 161 (84%, [(C8H7(SitBuMe2)]þ etBu), 115 (87%, [SitBuMe2]þ).
4.6. Synthesis of C8H6-1,4-(SiPh3)2) (4) A solution of 3 (0.20 g, 0.18 mmol) in THF (30 ml) was treated with iodine (0.05 g, 0.20 mmol), followed by stirring at r.t. for 5 h. The solvent was subsequently removed in vacuo and the residue extracted with diethyl ether (50 ml). Anaerobic conditions are no longer necessary from this point. The filtered extract was allowed to evaporate slowly to yield a colorless crystalline product. Yield: 0.08 g (72%). Colorless, air-stable crystals, soluble in nonpolar organic solvents and insoluble in water, M.p. 218 C. Elemental analysis: calcd. for C44H36Si2, M ¼ 620.9 g/mol): C 85.11%, H 5.84%; found: C 84.93%, H 5.89%. IR: n 3068w, 3000w, 1775w, 1659vw, 1587 m, 1567w, 1484 m, 1426s, 1383w, 1322w, 1307 m, 1261 m, 1221w, 1186 m, 1156w, 1107s, 1065w, 1029 m, 998 m, 971w, 921w, 869 m, 854 m, 759 m,742s, 696s, 681s, 652s, 619s, 556s, 530s, 521s, 513s, 471s, 450 s cm1. 1H NMR: d 5.86 (m, 2H; 6,7-CH COT), 6.11 (m, 2H; 5,8-CH COT), 6.25 (s, 2H; 2,3-CH COT), 7.33 (m, 12H; m-CH Ph), 7.36 (m, 6H; p-CH Ph), 7.59 (m, 12H; o-CH Ph) ppm. 13C{1H}-NMR: d 128.5 (s; m-CH Ph), 130.3 (s; p-CH Ph), 131.1 (s; 6,7-CH COT), 134.5 (s; CSi Ph), 136.4 (s; 5,8-CH COT), 137.1 (s; o-CH Ph), 144.1 (s; CSi COT), 147.4 (s; 2,3-CH COT) ppm. 29Si{1H}-NMR: d 17.7 (s) ppm. MS (EI): m/z 620 (25%, [M]þ), 259 (100%, [SiPh3]þ). Supplementary materials CCDC 1423497, 1535894, 1535895, 1482608 and 1482609 contains the supplementary crystallographic data for the title compounds. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif. Acknowledgments Financial support of this work by the Otto-von-Guericke-Uni€t Magdeburg is gratefully acknowledged. versita
4.5. Synthesis of [K2(C8H6-1,4-(SiPh3)2)(DME)4] (3)
References
C8H8-1,4-(SiPh3)2 (1.0 g, 1.6 mmol) was dissolved in DME (100 ml), and potassium chips (0.5 g, 25.6 mmol) were added. The reaction mixture was stirred at r.t. for 48 h with a glass-coated stirring bar, at which the solution turned from colorless to brownish. The excess potassium was subsequently filtered off and the solution reduced to 60 ml in vacuo. A colorless, crystalline precipitate was formed upon standing at 35 C for two weeks, which was filtered off and dried in vacuo. Yield: 1.3 g (76%). Colorless, air-sensitive, block-like crystals, soluble in THF and DME and poorly soluble in alkanes, Dec. 144 C. Elemental analysis: calcd. for C60H76K2O8Si2, M ¼ 1059.58 g/mol: C 68.01%, H 7.23%; found: 67.72%, H 7.01%. IR: n 3065 m, 3047 m, 2996 m, 2924 m, 2893 m, 2855 m, 2821 m,1960w, 1888w, 1825w, 1774w, 1660w, 1586s, 1566 m, 1545w, 1483s, 1455 m, 1426s, 1385 m, 1332w, 1322 m, 1305 m, 1259 m, 1219w, 1186s, 1156w, 1105s, 1055 m, 1029s, 996s, 968 m, 922s, 868 m, 854 m, 741s, 697s, 681s, 652s, 621 m, 577s, 560 s cm1. 1H NMR: d 3.27 (s, 24H; OCH3 DME), 3.44 (s, 16H; OCH2 DME), 6.11 (m, 2H; 6,7-CH COT), 6.43 (m, 2H; 5,8-CH COT), 6.49 (s, 2H; 2,3-CH COT), 7.20 (m, 12H; o-CH Ph), 7.53 (m, 6H; p-CH Ph), 7.71 (m, 12H; m-CH Ph) ppm. 13C{1H}-NMR: d 58.9 (s; OCH3 DME), 72.6 (s; OCH2 DME), 82.2 (s; CSi COT), 94.6 (s; 6,7-CH COT), 101.9 (s; 2,3-CH COT), 102.9 (s; 5,8-CH COT), 127.9 (s; o-CH Ph), 128.2 (s; p-CH Ph), 137.5 (s; m-CH Ph), 142.9 (s; CSi Ph) ppm. 29Si {1H}-NMR: d 6.3 (s) ppm. MS (EI): m/z 878 (3%, [M 2 DME]þ), 801 (10%, [M eSiPh3]þ), 792 (18%), 741 (13%), 714 (12%, [M eSiPh3 eDME]þ), 698 (10%, [M 4 DME]þ), 678 (10%), 655 (16%), 646 (30%), 620 (100%, [C8H6(SiPh3)2]þ).
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Preparation and crystal structures of silyl-substituted potassium cyclooctatetraenides Volker Lorenz a, Phil Liebing b, Janek Rausch a, Steffen Blaurock a, Cristian G. Hrib a, Liane Hilfert a, Frank T. Edelmann a, * a b
€t Magdeburg, 39106 Magdeburg, Germany Chemisches Institut der Otto-von-Guericke-Universita ETH Zürich, Laboratorium für Anorganische Chemie, Vladimir-Prelog-Weg 1-5/10, 8093 Zürich, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 July 2017 Received in revised form 27 August 2017 Accepted 28 August 2017 Available online xxx
Cyclooctatetraenyl complexes of potassium are readily available by the reaction of silyl-substituted cyclooctatrienes C8H8-1,4-(SiR3)2 (SiR3 ¼ SiMe3, SiMet2Bu, SiPh3) with potassium hydride or potassium metal. While C8H8-1,4-(SiMe3)2 gave a mixture of K2{C8H6-1,3-(SiMe3)2} (1a) and K2{C8H7-SiMe3} (1b), the substitution pattern on the COT ring remained unchanged in the case of C8H8-1,4-(SiMet2Bu)2 and C8H8-1,4-(SiPh3)2. [{K2{C8H6-1,4-(SiMet2Bu)2}(PhMe)}∞] (2) crystallizes in the absence of DME, featuring a m4-bridging COT ring, while in [K2(C8H6-1,4-(SiPh3)2)(DME)4] (3) the substituted COT ligand adopts a highly symmetric m-h8:h8-coordination, resulting in an “inverse sandwich” architecture. Compound 3 could be oxidized by treatment with iodine to give the corresponding neutral cyclooctatetraene derivative C8H6-1,4-(SiPh3)2 (4). © 2017 Elsevier B.V. All rights reserved.
Dedicated to Professor William J. Evans on the occasion of his 70th birthday. Keywords: Potassium Cyclooctatetraenyl ligands Sandwich complexes Crystal structure
1. Introduction The planar, 10p-aromatic cyclooctatetraenide dianion, C8H2 8 (commonly abbreviated as COT), plays an indispensable role in the organometallic chemistry of f-elements since the discovery of iconic uranocene by Streitwieser and Müller-Westerhoff in 1968 [1]. Since then, numerous sandwich and half-sandwich COT complexes of lanthanides [2] and actinides [3] have been studied. Central precursor in most of their preparations is the di-potassium salt K2C8H8 or K2COT. K2C8H8 was first mentioned in the literature by Katz in 1960 [4]. Crystalline K2C8H8$THF was first made by Fritz and Keller in 1961 by direct reaction of 1,3,5,7-cyclooctatetraene with 2 equiv. of potassium metal in THF [5]. K2C8H8$THF forms yellow crystals which upon drying easily disintegrate to give a white powder of the unsolvated K2C8H8. A remarkable property of K2COT is its explosive decomposition in contact with air [5a]. The synthetic route to this important reagent was later improved by using inexpensive 1,5-cyclooctadiene as starting material [6]. Structurally characterized solvates of K2C8H8 include
* Corresponding author. E-mail address: [email protected] (F.T. Edelmann).
K2C8H8(diglyme) (diglyme ¼ (MeOCH2CH2)2O) [7] and K2C8H8(THF)3 [8]. More recently, bulky silyl-substituted COT ligands have entered the focus of attention. This remarkable recent development was possible mainly through the pioneering work of Cloke et al., who introduced silylated COT ligands of the type {C8H61,4-(SiR3)2}2e (e.g. R ¼ Me, iPr) in organolanthanide and -actinide chemistry [9,10]. It has been demonstrated that the {C8H6-1,4(SiMe3)2}2e ligand (¼ COT00 ) imparts improved solubility and crystallinity over the parent C8H2 8 and enables e.g. the synthesis of anionic sandwich complexes [Ln{C8H6-1,4-(SiMe3)2}2]e for the entire lanthanide series [11]. Moreover, the use of silyl-substituted COT ligands led to the discovery of unusual molecular architectures (e.g. triple- and tetradeckers) [12], novel Ln(COT)-based organometallic sandwich molecular wires (OSMWs) [13] and singlemolecule magnets (SMMs) [14] as well as unprecedented reactions of uranium COT complexes (e.g. carbon monoxide oligomerization) [15]. A new dimension in steric bulk was added to this chemistry by the introduction of the “superbulky” ligand COTbig (¼ 1,4-bis(triphenylsilyl)-cyclooctatetraenyl dianion) by us and the Evans group in 2011 [16]. The use of COTbig in organolanthanide and -actinide chemistry has led to interesting structural effects such as the formation of the significantly bent anionic CeIII sandwich
http://dx.doi.org/10.1016/j.jorganchem.2017.08.018 0022-328X/© 2017 Elsevier B.V. All rights reserved.
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V. Lorenz et al. / Journal of Organometallic Chemistry xxx (2017) 1e7
complex [Ce{C8H6-1,4-(SiPh3)2}2]e, the novel neutral cerocene [Ce {C8H6-1,3-(SiPh3)2}2] formed by SiPh3 group migration, as well as the first example of a bent uranocene, [U{C8H6-1,4-(SiPh3)2}2], which exhibits no additional ligands [16]. Key starting material in COT00 chemistry is the lithium derivative Li2{C8H6-1,4-(SiMe3)2}, which was first prepared by Cloke and coworkers [9]. Since then, Li2{C8H6-1,4-(SiMe3)2} has been utilized as precursor for numerous early transition metal, lanthanide and actinide COT00 complexes [9,12,14]. Structural studies have been carried out on the DME adduct [Li(DME)]2{C8H6-1,4-(SiMe3)2} and the dimeric THF adduct [Li(THF)2]2[Li2{C8H6-1,4-(SiMe3)2}2] [17]. The molecular structure of [Li(DME)]2{C8H6-1,4-(SiMe3)2} consists of a {C8H6-1,4-(SiMe3)2}2e dianion with the two lithium atoms coordinated to the ring in an h3-allyl-like fashion [17a]. In [Li(THF)2]2[Li2{C8H6-1,4-(SiMe3)2}2] two Liþ ions are sandwiched between two COT rings, while two Li(THF)þ 2 units are bonded to the outsides of the sandwich [17b]. The same authors reported the polymeric crystal structure of [Na2{C8H6-1,4-(SiMe3)2}(m-THF)2]n, which was prepared by treatment of [Li(THF)2]2[Li2{C8H6-1,4(SiMe3)2}2] with NaCl [17b]. The formation of K2{C8H6-1,4(SiMe3)2} was briefly mentioned in an early report [17a]. Alkali metal derivatives of COTbig have not yet been isolated nor structurally characterized. We report here the first thorough preparative and structural investigation of a series of bis(silylated) potassium cyclooctatetraenides. 2. Results and discussion
reaction conditions (r.t. or reflux temperature, stoichiometric amount or excess KH). Due to very similar solubility properties, the two species could not be separated. Single-crystals of 1a and 1b could only be distinguished by their cell parameters as determined by X-ray diffraction because both species outwardly appeared as colorless, plate-like crystals. The actual target product, K2{C8H6-1,4(SiMe3)2} has never been found in the reaction mixture. In this context it is worth mentioning that in the reaction of the tetrasilylated cyclooctatriene C8H6-1,3,6,6-(SiMe3)4 with KH, one equiv. of Me3SiH is selectively released and the trisilylated potassium derivative K2{C8H5-1,3,6-(SiMe3)3} (1c) has been isolated as the only product [18]. Similar treatment of C8H8-1,4-(SiR3)2 (R ¼ SitBuMe2, SiPh3) with potassium metal or potassium hydride in DME led to formation of the metal derivatives K2{C8H6-1,4-(SiR3)2}. The isolation of DME-solvated K2{C8H6-1,4-(SitBuMe2)2} (2) has been reported earlier [19]. A DME-free form of 2 has now been obtained by recrystallization of the crude product from toluene in 70% yield. In the case of the SiPh3-substituted ligand, the DME solvate [K2(C8H61,4-(SiPh3)2)(DME)4] (3) was the only product obtained in 76% isolated yield. In both cases the silyl substitution pattern of the COT ligand remained unchanged upon metalation with KH or potassium metal, respectively. Like the parent K2COT, the new potassium COT complexes are highly oxidation sensitive, as it was illustrated at the example of compound 3. Addition of iodine to a THF solution led to formation of the hitherto unknown cyclooctatetraene derivative C8H6-1,4(SiPh3)2 (4) which was obtained in the form of colorless, air-stable, high-melting crystals in 72% isolated yield (Scheme 2).
2.1. Preparation of the compounds 2.2. Crystal structures 1,4-Disilylated cycloocta-2,5,7-trienes C8H8-1,4-(SiR3)2 are readily deprotonated in the 1,4-positions upon treatment with n BuLi to yield the corresponding aromatic {C8H6-1,4-(SiR3)2}2e anions (SiR3 ¼ SiMe3, SitBuMe2, SiPh3) [9,10,17]. We now found that similar reactions with potassium hydride or potassium metal can take a different course. For example, reaction of C8H8-1,4-(SiMe3)2 with KH surprisingly afforded a mixture of K2{C8H6-1,3(SiMe3)2}(DME)2 (1a) and the monosilylated species K2{C8H7(SiMe3)}(DME)2 (1b; Scheme 1). The product ratio, determined by NMR spectroscopy, was always around 1:1, independent of the
Relevant interatomic distances in 1a, 1b and 2e4 are represented in Table 1, while experimental details on the structure analyses are summarized in Table 2. Both SiMe3-substituted complexes 1a and 1b crystallize in the orthorhombic space group Pnma, featuring very similar molecular structures. The COT rings each adopt a highly symmetric m-h8:h8-bridging coordination mode (Figs. 1 and 2). The so-formed “inverse sandwich”-like [17b,20] K2(COT) moieties are interconnected by two m-kO,O’:kO,O0 -coordinated DME ligands, leading to a one-dimensional polymeric
Scheme 1. Preparation of the potassium complexes 1ae3.
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V. Lorenz et al. / Journal of Organometallic Chemistry xxx (2017) 1e7
Scheme 2. Oxidation of the potassium complex 3 with iodine.
structure (Fig. 3). Consequently, each potassium atom is coordinated by four O atoms and one h8-COT ligand in a “piano stool” arrangement [21]. The molecular structure of 1a and 1b resembles that of the earlier described K2{C8H6-1,4-(SitBuMe2)2}(DME)2 [19]. The formation of chain polymers by bridging DME ligands is also typical for various other sodium and potassium compounds, e.g. arylamides [22]. The K-C distances are in the same range as in other COT complexes of potassium [18,19] and almost equal in both complexes. The K-COT coordination is therefore not considerably affected by the silyl substitution pattern. The same applies to the K-O separations, which are in the typical broad range of 2.75e3.10 Å. The molecular structure of the earlier reported tris(trimethylsilyl)substituted complex [{K2(C8H6-1,3,6-(SiMe3)3)(DME)2}∞] [18] is virtually identical with that of 1a and 1b. With [{K2{C8H6-1,4-(SiMet2Bu)2}(PhMe)}∞] (2), we succeeded in performing a crystal structure analysis of a potassium COT complex free of a strongly coordinating solvent (Fig. 4). Compound 2 crystallizes from toluene in the space group C2/m, featuring a onedimensional polymeric structure similar as in 1a and 1b. Both potassium atoms are attached to the mirror-symmetric {C8H6-1,4(SiMet2Bu)2}2e ligand in a typical h8-mode. Similar as in the previously described DME solvate K2{C8H6-1,4-(SitBuMe2)2}(DME)2 [19] the COT-derived ligand retained the original 1,4-substitution pattern and no isomerization to the 1,3-analogue has taken place. Due to the absence of DME, coordinative saturation of the potassium atoms is achieved by an additional h2-coordination of a symmetry-related COT ring, and therefore the full coordination mode of the {C8H6-1,4-(SitBuMe2)2}2e ligand is m4-h8:h8:h2:h2. Moreover, one of the two K atoms (K2) interacts with a toluene molecule, where a close K ∙∙∙ C(para) contact of 3.174(4) Å has been observed. Toluene coordination to the other potassium atom K1 is probably prevented by the two bulky tert-butyl groups in spatial proximity to this metal atom. As a result, the K2-(h8-COT) bond of the toluene-coordinated potassium is elongated to 2.3498(5) Å, while the K1-(h8-COT) separation is with 2.3042(5) Å very similar as in 1a and 1b. The additional K-(h2-COT) contacts are weaker than
3
the corresponding K-(h8-COT) bonds, with K-C separations of 3.149(2) Å (K1) and 3.249(1) Å (K2). [K2(C8H6-1,4-(SiPh3)2)(DME)4] (3) has been isolated as monoclinic crystals, space group P21/c, where one formula unit is present in the asymmetric unit (Fig. 5). Just as in 1a and 1b, the substituted COT ligand adopts a highly symmetric m-h8:h8-coordination, resulting in an “inverse sandwich” architecture [17b,20]. Both K atoms are again coordinated by each two DME ligands to form a “piano-stool” arrangement, but due to the high steric demand of the SiPh3 substituents the formation of chain polymers like in 1a and 1b is prevented. Thus, one K atom (K2) is coordinated by two chelating DME ligands, while the other K atom (K1) is attached to only one chelating and one monodentate DME ligand. The distances between the potassium atoms and the COT ring centroid are 2.4077(6) Å and 2.4305(6) Å, and therefore significantly larger than in 1a, 1b and 2. This finding can likely be traced back to the steric bulk of the (C8H6-1,4-(SiPh3)2)2e ligand. In contrast, the K-O bonds are with 2.777(2)e2.959(2) Å similar as in 1a and 1b. The C-C separations within the COT ring and the C-Si bond lengths are virtually equal in all four potassium complexes, implying that the bonding situation within the aromatic system is less influenced by the potassium coordination and silyl substitution pattern (Table 1). Crystal structure analysis of the oxidized C8H61,4-(SiPh3)2 ligand (4; triclinic, P1) revealed the presence of alternating short (av. C-C: 1.338(2) Å) and long C-C separations (av. C-C: 1.479(2) Å) within the COT ring, which fits to the model of four distinct double-bonds (Fig. 6). While the COT ring in the metal complexes 1ae3 are strictly planar, the COT ring in 4 is markedly twisted due to the loss of aromaticity. With 1.882(1) and 1.883(1) Å, the C-Si bonds in 4 are significantly elongated compared to the corresponding {COT-1,4-(SiPh3)2}2e ligand in 3.
3. Conclusions 1,4-Disilylated cyclooctatrienes react with potassium or potassium hydride to give K2COT-derived compounds which show a surprising structural variety. While C8H8-1,4-(SiMe3)2 gave a mixture of K2{C8H6-1,3-(SiMe3)2} (1a) and K2{C8H7-SiMe3} (1b), the substitution pattern of the COT ring remained unchanged in the case of C8H8-1,4-(SiMet2Bu)2 and C8H8-1,4-(SiPh3)2. [{K2{C8H6-1,4(SiMet2Bu)2}(PhMe)}∞] (2) crystallizes in the absence of DME, featuring a m4-bridging COT ring. In 1a and 1b as well as in [K2(C8H6-1,4-(SiPh3)2)(DME)4] (3) the substituted COT ligand adopts a highly symmetric m-h8:h8-coordination, resulting in an “inverse sandwich” architecture. Compounds 2 and 3 can be expected to serve as useful starting materials in future studies. Compound 3 could be oxidized by treatment with iodine to give the hitherto unknown neutral cyclooctatetraene derivative C8H6-1,4(SiPh3)2. (4).
Table 1 Selected bond lengths (Å) for compounds 1ae4.
1a 1b 2 3 4 a b c d
K-C
av. K-C
K-COTa
K-O
C-C
av. C-C
Si-C(COT)
2.927(3)e3.002(3) 2.902(2)e3.036(3) 2.870(1)e3.033(2)b 2.998(2)e3.134(2) e
2.969(3) 2.968(2) 2.970(2) 3.043(2) e
2.3200(8) 2.3097(7), 2.3378(5) 2.3042(5), 2.3498(5) 2.4077(6), 2.4305(6) e
2.746(2)e3.085(2) 2.809(2)e3.020(2) e 2.777(2)e2.959(2) e
1.403(6)e1.432(5) 1.402(3)e1.420(2) 1.402(2)e1.426(2) 1.400(3)e1.424(3) 1.333(2)e1.343(2), 1.465(2)e1.488(2)
1.418(6) 1.411(3) 1.415(2) 1.413(3) 1.338(2)c, 1.479(2)d
1.852(4), 1.858(4) 1.857(3) 1.861(2) 1.849(2), 1.850(2) 1.882(1), 1.883(1)
COT ring centroid. h8-coordination. Double-bonds. Single-bonds.
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V. Lorenz et al. / Journal of Organometallic Chemistry xxx (2017) 1e7
Table 2 Crystal data and details on structure refinement of compounds 1ae4. Compound
1a
1b
2
3
4
CCDC deposition number Molecular formula sum Formula weight/g mol1 Crystal system Space group
1423497 C22H44K2O4Si2 506.95 orthorhombic Pnma
1535894 C19H36K2O4Si 434.77 orthorhombic Pnma
1535895 C27H44K2Si2 (þsolv.) 503.00 (þsolv.) monoclinic C2/m
1482608 C60H76K2O8Si2 1059.59 monoclinic P21/c
1482609 C44H36Si2 620.91 triclinic
Cell metric a/Å b/Å c/Å a/ b/ g/ Cell volume/Å3 Molecules per cell z Electrons per cell F000 Calcd. density r/g cm3 m/mm1 (radiation) Crystal size/mm T/K q range/ Absorption correction Reflections collected Reflections unique Reflections with I > 2s Completeness of dataset Rint Parameters R1 (all data, I > 2s(I)) wR2 (all data, I > 2s(I)) GooF (F2)
9.382(2) 16.569(3) 18.589(4) 90 90 90 2890(1) 4 1096 1.165 0.433 (Mo-Ka) 0.60 0.15 0.06 133(2) 2.19 … 25.00 none 12146 2628 2140 99.4% 0.0880 159 0.0806, 0.0596 0.1137, 0.1074 1.215
16.5510(8) 14.2280(7) 10.1702(4) 90 90 90 2395.0(2) 4 936 1.206 0.464 (Mo-Ka) 0.55 0.32 0.22 153(2) 2.35 … 25.00 numerical 7382 2185 1864 99.3% 0.0879 131 0.0550, 0.0460 0.1103, 0.1059 1.069
14.4758(6) 18.4651(6) 11.8728(5) 90 91.099(3) 90 3173.0(2) 4 1088 1.053 0.385 (Mo-Ka) 0.37 0.17 0.11 153(2) 2.21 … 26.00 none 11245 3221 2723 99.8% 0.0285 154 0.0439, 0.0339 0.0786, 0.0750 1.029
13.579(3) 21.753(4) 19.889(4) 90 101.21(3) 90 5763(2) 4 2264 1.221 0.258 (Mo-Ka) 0.60 0.60 0.38 153(2) 1.92 … 25.00 none 29176 10096 6907 99.5% 0.0675 658 0.0766, 0.0435 0.0903, 0.0829 0.0909
9.6095(1) 14.1142(2) 14.8031(2) 116.289(1) 95.982(1) 105.283(1) 1678.81(4) 2 656 1.228 1.182 (Cu-Ka) 0.18 0.14 0.09 100(2) 3.44 … 76.29 multi-scan 116551 6995 6406 99.6% 0.0505 415 0.0369, 0.0338 0.0949, 0.0920 1.068
Fig. 1. Molecular structure of [{K2(C8H6-1,3-(SiMe3)2)(DME)2}∞] (1a) in the crystal. Ellipsoids drawn at the 30% probability level, H atoms omitted for clarity. The COT ring (atoms C1eC8, Si1, Si2, C9, C11) is located on a mirror plane perpendicularly to the crystallographic b-axis. Symmetry codes: ' x, 0.5ey, z; '' 1ex, ey, 1ez; ''' 1ex, 0.5 þ y, 1ez.
4. Experimental 4.1. General procedures All reactions were performed under argon atmosphere using standard Schlenk techniques or in an M. Braun N2-filled glovebox with O2 levels maintained at or below 1 ppm. Glassware was dried at 120 C overnight. All solvents were dried by distillation from sodium/benzophenone under argon atmosphere prior to use. C8H81,4-(SiMe3)2 [9a], C8H8-1,4-(SitBuMe2)2 [23], and C8H8-1,4-(SiPh3)2 [16] were prepared following previously published procedures. All other reagents were commercially available and used as received.
P1
Fig. 2. Molecular structure of [{K2(C8H7(SiMe3))(DME)2}∞] (1b) in the crystal. Ellipsoids drawn at the 30% probability level, H atoms omitted for clarity. The atoms K1, K2, C1, C5, Si1 and C6 are located on a mirror plane perpendicularly to the crystallographic b-axis. Symmetry codes: ' x, 0.5ey, z; '' 0.5 þ x, y, 0.5ez; ''' 0.5 þ x, 0.5ey, 0.5ez.
NMR spectra were recorded in THF-D8 solution at 23(2) C on a Bruker DPX 400 spectrometer (1H: 400.1 MHz; 13C: 100.6 MHz; 29 Si: 79.5 MHz). COSY, HSQC and HMBC experiments were carried out for the unambiguous assignment of the 1H and 13C NMR signals. IR spectra were recorded between 4000 cm1 and 450 cm1, using a Bruker Vertex 70 V spectrometer equipped with a diamond ATR unit and a “Golden Gate” unit. Electron impact mass spectra were measured on a MAT 95 spectrometer with an ionization energy of 70 eV, and elemental analyses (C, H) were performed using a VARIO EL cube apparatus.
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Fig. 3. Representation of the polymeric chain structure of compound 1a, extending along the crystallographic b-axis.
Fig. 6. Molecular structure of C8H6-1,4-(SiPh3)2 (4) in the crystal. Ellipsoids drawn at the 30% probability level, phenyl H atoms omitted for clarity.
Fig. 4. Molecular structure of [{K2{C8H6-1,4-(SiMet2Bu)2}(PhMe)}∞] (2) in the crystal. Ellipsoids drawn at the 50% probability level, H atoms omitted for clarity. Symmetry codes: ' x, ey, z.
using the multi-scan method [25]. The structures were solved with SHELXS-97 using heavy atom (1a, 1b, 2, 3) or direct methods (4) [26] and refined by full matrix least-squares methods on F2 with SHELXL-2016/4 [27]. In the case of 2, highly disordered solvent was considered using the SQUEEZE routine of PLATON [28].
4.3. Synthesis of [{K2(C8H6-1,3-(SiMe3)2)(DME)2}∞] (1a) and [{K2(C8H7(SiMe3))(DME)2}∞] (1b)
Fig. 5. Molecular structure of [K2(C8H6-1,4-(SiPh3)2)(DME)4] (3) in the crystal. Ellipsoids drawn at the 30% probability level, H atoms omitted for clarity.
4.2. Single-crystal X-ray diffraction studies Single crystal X-ray intensity data of the potassium complexes 1a, 1b, 2 and 3 were collected on a STOE IPDS 2T diffractometer, using graphite-monochromated Mo-Ka radiation. For 1b, a numerical absorption correction was applied [24]. A single crystal of 4 was measured on a Xcalibur Atlas Nova System with mirrorfocussed Cu-Ka radiation, and absorption correction was applied
To a solution of C8H8-1,4-(SiMe3)2 (5.0 g, 20 mmol) in DME (100 ml), potassium hydride (1.93 g, 48 mmol) was added at r.t. The resulting suspension was stirred for 24 h at r.t., during which a color change from yellow to dark green took place. The solution was subsequently filtered, the filtrate reduced to approx. 15 ml in vacuo and then layered with n-pentane (60 ml). Colorless, plate-like crystals were obtained within a few days at 5 C, which were filtered off and carefully dried in vacuo. Yield: 6.78 g. Colorless, highly air-sensitive crystalline solid, soluble in THF and DME and poorly soluble in alkanes, Dec. 101 C. Compounds 1a and 1b were obtained simultaneously and could not be separated due to very similar solubility properties. Elemental analysis: calcd. for C22H44K2O4Si2, M ¼ 506.95 g/mol (1a): C 52.12%, H 8.75%; calcd. for C19H36K2O4Si, M ¼ 434.77 g/mol (1b): C 52.49%, H 8.35%; found: C 52.21%, H 8.56%. IR: n 3091s, 2961s, 2931s, 1959 m, 1634s, 1508w, 1504w, 1447 m, 1385 m, 1306w, 1293w, 1247 m, 1181 m, 1155 m, 1061 m, 985 m, 881 m, 839 m, 752 m, 704 m, 555w, 505w cm1. 1H NMR: d 0.23 (s, 18H; Si(CH3)3 1a), 0.26 (s, 9H; Si(CH3)3 1b), 3.21 (s, 12 þ 12H; CH3 DME), 3.34 (s, 8þ8H; CH2 DME), 5.68e6.08 (7 m, 5þ7H; CH COT), 6.18 (s, 1H; 2-CH COT 1a) ppm. The molar ratio 1a:1b corresponding to the signal intensities was approx. 1:1. X-Ray diffraction studies of several selected single-crystals, which always appeared as colorless plates, revealed the cell parameters of either 1a or 1b. 13C{1H}-NMR: d 2.6 (s; Si(CH3)3 1a), 2.7 (s; Si(CH3)3 1b),
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V. Lorenz et al. / Journal of Organometallic Chemistry xxx (2017) 1e7
58.8 (s; CH3 DME), 72.4 (s; CH2 DME), 89.1e98.4 (10 s; CH and CSi COT) ppm. 29Si{1H}-NMR: d 3.6 (s; 1a), 2.7 (s; 1b) ppm. MS (EI): m/z 407 (27%, [K(C8H6(SiMe3)2)(DME)2 e4Me]þ), 375 (65%, [K(C8H6(SiMe3)2)(DME)]þ), 353 (24%, [K2(C8H6(SiMe3)2)(DME) e4Me]þ), 323 (27%, [K2(C8H6(SiMe3)2)(DME)e4Me]þ), 295 (7%, [K2(C8H6(SiMe3))(DME)e3Me]þ), 281 (26%, [K2(C8H6(SiMe3)) (DME)e4Me]þ), 265 (35%, [K2(C8H6)(DME)]þ), 249 (45%, [C8H6(SiMe3)2]þ), 235 (22%, [C8H6(SiMe3)2eMe]þ), 223 (61%, [C8H6(SiMe3)2e2Me]þ), 207 (100%, [C8H6(SiMe3)2e3Me]þ). 4.4. Synthesis of [{K2(C8H6-1,4-(SitBuMe2)2)(PhMe)}∞] (2) C8H8-1,4-(SitBuMe2)2 (11.4 g, 34 mmol) was treated with potassium hydride (3.0 g, 75 mmol) in DME (75 ml) as described for 1a/1b. The filtered green-brown solution was taken to dryness in vacuo, and the residue re-dissolved in toluene (50 ml). Reduction of the solvent volume to approx. 10 ml afforded colorless crystals within a few days, which were filtered off and dried in vacuo. Yield: 11.9 g (70%). Colorless, air-sensitive crystals, soluble in THF, DME and toluene and poorly soluble in alkanes, Dec. 98 C. Elemental analysis: calcd. for C27H44K2Si2, M ¼ 503.00 g/mol: C 63.64%, H 9.04%; found: C 63.03%, H 9.13%. IR: n 2938w, 2938s, 2852s, 1460 m, 1394w, 1355w, 1304w, 1244s, 1194w, 1054s, 973 m, 923s, 811s, 728s, 660s, 574s, 513 m, 460 s cm1. 1H NMR: d 0.33 (s, 12H; Si(CH3)2), 0.93 (s, 18H; C(CH3)3), 2.30 (s, 3H; PhCH3), 5.98 (m, 2H; 6,7-CH COT), 6.13 (m, 2H; 5,8-CH COT), 6.23 (s, 2H; 2,3-CH COT), 7.10 (2 m, 3H; o-CH þ p-CH PhMe), 7.18 (m, 2H; m-CH PhMe) ppm. 13C{1H}-NMR: d 2.2 (s; Si(CH3)2), 21.3 (s; PhCH3), 27.4 (s; C(CH3)3), 29.1 (s; C(CH3)3), 86.4 (s; CSi COT), 93.4 (s; 6,7-CH COT), 99.1 (s; 2,3-CH COT), 99.3 (s; 5,8-CH COT), 126.1 (s; p-CH PhMe), 128.9 (s; m-CH PhMe), 129.7 (s; o-CH PhMe), 138.4 (s; i-C PhMe) ppm. 29Si{1H}NMR: d 2.2 (s) ppm. MS (EI): m/z 332 (88%, [C8H6(SitBuMe2)2]þ), 275 (100%, [(C8H6(SitBuMe2)]þ), 219 (36%, [C8H6(SitBuMe2)2]þ e2tBu), 161 (84%, [(C8H7(SitBuMe2)]þ etBu), 115 (87%, [SitBuMe2]þ).
4.6. Synthesis of C8H6-1,4-(SiPh3)2) (4) A solution of 3 (0.20 g, 0.18 mmol) in THF (30 ml) was treated with iodine (0.05 g, 0.20 mmol), followed by stirring at r.t. for 5 h. The solvent was subsequently removed in vacuo and the residue extracted with diethyl ether (50 ml). Anaerobic conditions are no longer necessary from this point. The filtered extract was allowed to evaporate slowly to yield a colorless crystalline product. Yield: 0.08 g (72%). Colorless, air-stable crystals, soluble in nonpolar organic solvents and insoluble in water, M.p. 218 C. Elemental analysis: calcd. for C44H36Si2, M ¼ 620.9 g/mol): C 85.11%, H 5.84%; found: C 84.93%, H 5.89%. IR: n 3068w, 3000w, 1775w, 1659vw, 1587 m, 1567w, 1484 m, 1426s, 1383w, 1322w, 1307 m, 1261 m, 1221w, 1186 m, 1156w, 1107s, 1065w, 1029 m, 998 m, 971w, 921w, 869 m, 854 m, 759 m,742s, 696s, 681s, 652s, 619s, 556s, 530s, 521s, 513s, 471s, 450 s cm1. 1H NMR: d 5.86 (m, 2H; 6,7-CH COT), 6.11 (m, 2H; 5,8-CH COT), 6.25 (s, 2H; 2,3-CH COT), 7.33 (m, 12H; m-CH Ph), 7.36 (m, 6H; p-CH Ph), 7.59 (m, 12H; o-CH Ph) ppm. 13C{1H}-NMR: d 128.5 (s; m-CH Ph), 130.3 (s; p-CH Ph), 131.1 (s; 6,7-CH COT), 134.5 (s; CSi Ph), 136.4 (s; 5,8-CH COT), 137.1 (s; o-CH Ph), 144.1 (s; CSi COT), 147.4 (s; 2,3-CH COT) ppm. 29Si{1H}-NMR: d 17.7 (s) ppm. MS (EI): m/z 620 (25%, [M]þ), 259 (100%, [SiPh3]þ). Supplementary materials CCDC 1423497, 1535894, 1535895, 1482608 and 1482609 contains the supplementary crystallographic data for the title compounds. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif. Acknowledgments Financial support of this work by the Otto-von-Guericke-Uni€t Magdeburg is gratefully acknowledged. versita
4.5. Synthesis of [K2(C8H6-1,4-(SiPh3)2)(DME)4] (3)
References
C8H8-1,4-(SiPh3)2 (1.0 g, 1.6 mmol) was dissolved in DME (100 ml), and potassium chips (0.5 g, 25.6 mmol) were added. The reaction mixture was stirred at r.t. for 48 h with a glass-coated stirring bar, at which the solution turned from colorless to brownish. The excess potassium was subsequently filtered off and the solution reduced to 60 ml in vacuo. A colorless, crystalline precipitate was formed upon standing at 35 C for two weeks, which was filtered off and dried in vacuo. Yield: 1.3 g (76%). Colorless, air-sensitive, block-like crystals, soluble in THF and DME and poorly soluble in alkanes, Dec. 144 C. Elemental analysis: calcd. for C60H76K2O8Si2, M ¼ 1059.58 g/mol: C 68.01%, H 7.23%; found: 67.72%, H 7.01%. IR: n 3065 m, 3047 m, 2996 m, 2924 m, 2893 m, 2855 m, 2821 m,1960w, 1888w, 1825w, 1774w, 1660w, 1586s, 1566 m, 1545w, 1483s, 1455 m, 1426s, 1385 m, 1332w, 1322 m, 1305 m, 1259 m, 1219w, 1186s, 1156w, 1105s, 1055 m, 1029s, 996s, 968 m, 922s, 868 m, 854 m, 741s, 697s, 681s, 652s, 621 m, 577s, 560 s cm1. 1H NMR: d 3.27 (s, 24H; OCH3 DME), 3.44 (s, 16H; OCH2 DME), 6.11 (m, 2H; 6,7-CH COT), 6.43 (m, 2H; 5,8-CH COT), 6.49 (s, 2H; 2,3-CH COT), 7.20 (m, 12H; o-CH Ph), 7.53 (m, 6H; p-CH Ph), 7.71 (m, 12H; m-CH Ph) ppm. 13C{1H}-NMR: d 58.9 (s; OCH3 DME), 72.6 (s; OCH2 DME), 82.2 (s; CSi COT), 94.6 (s; 6,7-CH COT), 101.9 (s; 2,3-CH COT), 102.9 (s; 5,8-CH COT), 127.9 (s; o-CH Ph), 128.2 (s; p-CH Ph), 137.5 (s; m-CH Ph), 142.9 (s; CSi Ph) ppm. 29Si {1H}-NMR: d 6.3 (s) ppm. MS (EI): m/z 878 (3%, [M 2 DME]þ), 801 (10%, [M eSiPh3]þ), 792 (18%), 741 (13%), 714 (12%, [M eSiPh3 eDME]þ), 698 (10%, [M 4 DME]þ), 678 (10%), 655 (16%), 646 (30%), 620 (100%, [C8H6(SiPh3)2]þ).
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