- Email: [email protected]
Tris(trimethylsilyl)stannyl alkali derivatives: Syntheses and NMR spectroscopic properties
Inorganica Chimica Acta 358 (2005) 3174–3182 www.elsevier.com/locate/ica
Tris(trimethylsilyl)stannyl alkali derivatives: Syntheses and NMR spectroscopic properties Roland Fischer *, Judith Baumgartner, Christoph Marschner, Frank Uhlig Institut fu¨r Anorganische Chemie, Technische Universita¨t Graz, Stremayrgasse 16, A-8010 Graz, Austria Received 4 February 2005; received in revised form 4 February 2005; accepted 4 April 2005 Available online 2 June 2005
Abstract Starting from tetrakis(trimethylsilyl)stannane, the tris(trimethylsilyl)stannyl alkali derivatives (Me3Si)3SnM, (M = Li, Na, K, Rb, Cs) were prepared in excellent yields. Reaction with MgBr2 Æ Et2O afforded bis[tris(trimethylsilyl)stannyl]magnesium. Reaction products were investigated by means of multinuclear NMR spectroscopy. At low temperatures, coupling of 7Li and 119Sn between [(Me3Si)3Sn] and [Li Æ 3THF]+ (337 Hz) or [Li Æ 12Cr4]+ (275 Hz), was observed. NMR chemical shifts and coupling constants of the stannyl anions exhibit a strong dependency on the nature of the cation, solvent system, concentration and temperature. In addition, the molecular structure of tris(trimethylsilyl)stannyl sodium Æ 15Cr5 was determined by X-ray crystallography. The ˚ in length. [Na Æ 15Cr5]+ and [(Me3Si)3Sn] units are joined by a direct Sn–Na contact, 3.0775(18) A 2005 Elsevier B.V. All rights reserved. Keywords: X-ray crystal structures; NMR spectroscopy; Alkali stannides; Preparation
1. Introduction Despite the great synthetic potential of metalated tris(trimethylsilyl) heavier Group 14 element compounds (Me3Si)3EM (E = Si, Ge, Sn) in main group and transition metal chemistry only the chemistry of the silicon congener is well developed [1]. Much less attention was drawn to the heavier germanium and tin analogues. Structural and NMR spectroscopic investigations of tris(trimethylsilyl)germyl alkali and alkaline earth compounds [2] and their application in synthetic main group transition metal chemistry were reported recently [3]. Tris(trimethylsilyl)stannyllithium was applied in the synthesis of various main group and transition metal compounds [4]. The synthetic potential of the [(Me3Si)3Sn] moiety lies in the large steric demand which goes along with excellent kinetic stabilization. In *
Corresponding author. Tel.: +0043 316 873 8703; fax: +0043 316 873 8701. E-mail address: fi[email protected] (R. Fischer). 0020-1693/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2005.04.006
addition, the ease of preparation, the high solubility of products in organic solvents and the combination of four different NMR active nuclei which can act as spectroscopic probes even for subtle effects in electronic properties are further advantages. Among the Group 14 elements mentioned above, only tin has two sensitive NMR active nuclei and it displays the largest range of NMR spectroscopic shifts and coupling constants. As a consequence, even small differences in the electronic environment of the tin nucleus result in well detectable NMR spectroscopic changes. Heavier alkali metal tris(trimethylsilyl)stannyl derivatives or alkaline earth derivatives displaying different reactivity from the lithium derivative were to the best of our knowledge not reported previously. Yet it is highly desirable to have a greater choice of such alkali and alkaline earth metal derivatives as nucleophilicity and redox potential may be adjusted. Cleavage of silicon–tin bonds in tetrakis(trimethylsilyl)stannane with methyllithium was previously investigated by Preuss et al. [5] and Becker et al. [6].
R. Fischer et al. / Inorganica Chimica Acta 358 (2005) 3174–3182
Tris(trimethylsilyl)stannyl lithium Æ 3THF has also directly been obtained from the reaction of tin(IV) chloride and trimethylchlorosilane with lithium [7]. All reactions were carried out in THF, DME or TMEDA as solvents. Less polar solvents, e.g., diethylether or benzene were found unsuitable for this reaction.
2. Results and discussion 2.1. Syntheses 2.1.1. Preparation of tris(trimethylsilyl)stannyl lithium In contrast to previous syntheses of tris(trimethylsilyl)stannyl lithium 2, which were carried out in ethereal solvents, we examined the reactivity of methyl lithium with tetrakis(trimethylsilyl)stannane in aromatic solvents in the presence of 12-crown-4 (12Cr4). When a diethylether solution of methyl lithium/lithium chloride is added to a solution of tetrakis(trimethylsilyl)stannane 1 and two equivalents 12-crown-4 (12Cr4) in benzene, the reaction proceeds smoothly at room temperature to give access to a benzene solution of the crown ether adduct of 2 with exact stoichiometry. The second equivalent of crown ether is presumably necessary in order to chelate lithium halide introduced with methyl lithium. DME solutions of 2 used in the NMR spectroscopic investigations were prepared following literature procedures. Addition of a stoichiometric amount of 12-crown-4 provided the DME solution of 2 Æ 12Cr4. SiMe3
SiMe3 Me3Si
Sn
SiMe3
MeLi/12Cr4 benzene
Me3Si
Sn
Li.12Cr4 + Me4Si
SiMe3
SiMe3
1
2
(1)
THF and DME adducts 2 Æ 3THF and 2 Æ 2DME were prepared by metallation of 1 with MeLi in the respective solvent followed by removal of all volatiles in vacuo, repeated addition and removal of benzene and filtration of insoluble lithium chloride after dissolving the residue in benzene. 2.1.2. Preparation of tris(trimethylsilyl)stannyl sodium, -potassium and -rubidium Alkali tert-butoxides tBuOM (M = Na, K, Rb, Cs) have found widespread application in metalation reactions of (R3Si)4E (E = Si [8,9] Ge [2,3]) and (Me3Si)3P [10] species. In contrast to lithium alkyls solutions t BuOM species are solids which are easy to store and handle. Thus, exact stoichiometry is easy to control, which is a major advantage over lithium alkyls. The stoichiometry of lithium alkyls solutions has to be controlled by titra-
3175
tion and in addition the solutions often contain lithium halides which may cause problems in further reactions. The cleavage of Me3Si–E bonds (E = Si, Ge, P) with t BuOM was readily expanded to the respective tin derivatives. Metalation of tetrakis(trimethylsilyl)stannane 1 with tBuOM (M = Na, K, Rb) was found to proceed very rapidly in both, ethereal solvents like DME or THF and aromatic solvents, where the latter require the use of at least one equivalent of crown ether. Generally speaking, silicon tin derivatives are easier to metallate compared to their silicon analogues. The reaction of tetrakis(trimethylsilyl)silane with sodium tert-butoxide in THF requires elevated temperatures of about 50 C and elongated reaction times, typically around 24 h. The reaction of sodium tert-butoxide with the tin homologue in THF, however, completes within 10 min, even at room temperature. SiMe3
SiMe3 Me3Si
Sn
SiMe3
MOtBu/crown benzene
Me3Si
Sn
M.crown + Me3SiOtBu
SiMe3
SiMe3
1
3 M=Na, crown=15Cr5 4 M=K, crown=18Cr6 5 M=Rb, crown=18Cr6
(2)
Rubidium derivative 5 was found to be most reactive among compounds 3–5. Apparently its basicity is sufficient to slowly abstract a proton from concomitantly formed tBuOSiMe3 or tBuORb if applied in excess. In contrast to its lighter congeners, (Me3Si)3SnH is unstable and decomposes. As a result, formation of elemental tin together with 1 and (Me3Si)3SnSn(SiMe3)2Rb is observed.1 Similar problems were reported earlier in this context for the reaction of (Me3Si)4Si [9]. However, this obstacle is readily overcome by employing stoichiometric amounts of tBuORb and removal of Me3SiOtBu in vacuo. Tris(trimethylsilyl)stannyl rubidium was found to be stable in both ethereal and aromatic solvents over elongated periods. 2.1.3. Preparation of tris(trimethylsilyl)stannyl cesium Fluoride mediated cleavage reactions of stannasilanes were pioneered by the work of Mori and coworkers [11]. We found that cesium fluoride is also a convenient reagent for the cleavage of silicon–tin bonds in tetrakis(trimethylsilyl)stannane. The reaction has to be carried out in polar solvents, i.e., THF or DME. Alternatively, the metalation may be carried out in aromatic solvents in the presence of 18-crown-6 (18Cr6) or [2.2.2]crypt. Trimethylfluorosilane was identified as the second reaction product by means of NMR spectroscopy.
1 Experimental details and spectroscopic data for (Me3Si)3SnSn(SiMe3)2M will be reported elsewhere.
R. Fischer et al. / Inorganica Chimica Acta 358 (2005) 3174–3182
Cs.18Cr6 + Me3SiF
1
6
(3)
12.95, 13.03, 12.88, 12.73, 13.15, 12.83, 12.87, 12.86, 12.79, 12.80, 12.73, 894.7 890.3 896.8 890.0 876.4 902.0 900.3 902.6 901.8 903.6 902.0 DME solutions 2 (Me3Si)3SnLi 3 (Me3Si)3SnNa 4 (Me3Si)3SnK 5 (Me3Si)3SnRb 6 (Me3Si)3SnCs 2 Æ 12Cr4 (Me3Si)3SnLi Æ 12Cr4 3 Æ 15Cr5 (Me3Si)3SnNa Æ 15Cr5 4 Æ 18Cr6 (Me3Si)3SnK Æ 18Cr6 5 Æ 18Cr6 (Me3Si)3SnRb Æ 18Cr6 6 Æ 18Cr6 (Me3Si)3SnCs Æ 18Cr6 6 Æ [2.2.2]crypt (Me3Si)3SnCs[2.2.2]crypt
(4)
7
Table 1 119 Sn, 29Si and
13
[7]
13, 134/128 13.38, 107/102 12.7 13.40, 138/132 12.95, 204/195 12.93, 220/210 12.70, 271/259 12.60, 297/283 12.56, 345/328 12.63, 348/330 12.28, 123/117 878 872.2 873.7 873.4 882.1 881.6 892.2 890.3 899.4 901.2 830.2
C chemical shifts and coupling constants of compounds 1–7
119
9.74, 351/335
2.2. NMR spectroscopy Compounds 2–7 were studied by 1H, 13C, 29Si and Sn NMR spectroscopy. Selected 29Si, 119Sn and 13C NMR spectroscopic data are given in Table 1. It was interesting to study the influence of solvent system and nature of the cation on chemical shifts and coupling constants. 29Si and 119Sn coupling constants and to a smaller extent also chemical shifts showed a variation with concentration. Concentration effects were eliminated by using exactly 0.4 molar solutions of 2–7. Compared to starting material tetrakis(trimethylsilyl)stannane 1, 119Sn and 29Si NMR shifts are generally observed at higher field as a consequence of a higher shielding due to the negative charge of stannides. This is in contrast to 13C and 1H resonances of compounds 2–7 which are observed at lower field compared to 1. For compounds 2–7, 3 J 1 H–119=117 Sn coupling constants values ranging from 6 to 15 Hz and for 2 J 13 C–119=117 Sn from 21 to 28 Hz are observed. Thus, compared to tetrakis(trimethylsilyl)stannane 1 (3 J 1 H–119=117 Sn ¼ 21.8=20.9 Hz and 2 J 13 C–119=117 Sn ¼ 40=38 Hz, respectively) substantially smaller 2J and 3J coupling constants are observed for metalated species 2–7. The most pronounced effect in benzene solutions of crown ether adducts of compounds 2–6 is a 29Si–119Sn coupling constant which is increasing with decreasing electronegativity of the alkali metal. The smallest values
287/274 262/249 295/282 300/287 311/298 328/311 331/316 343/329 347/332 358/343 355/339
d 29Si (ppm) J 29 Si–117=119 Sn (Hz) d 119Sn (ppm)
SiMe3 + 2 KBr
SiMe3
4.32, 40/38
Mg Sn
SiMe3
664.4
Sn
1 (Me3Si)4Sn Benzene solutions 2 Æ 3THF (Me3Si)3SnLi Æ 3THF 2 Æ 3THF (Me3Si)3SnLi Æ 3THF 2 Æ 2TMEDA (Me3Si)3SnLi Æ 2TMEDA 2 Æ 2DME (Me3Si)3SnLi Æ 2DME 2 Æ 12Cr4 (Me3Si)3SnLi Æ 12Cr4 3 Æ 15Cr5 (Me3Si)3SnNa Æ 15Cr5 4 Æ 18Cr6 (Me3Si)3SnK Æ 18Cr6 5 Æ 18Cr6 (Me3Si)3SnRb Æ 18Cr6 6 Æ 18Cr6 (Me3Si)3SnCs Æ 18Cr6 6 Æ [2.2.2]crypt (Me3Si)3SnCs Æ [2.2.2]crypt 7 (Me3Si)3SnMgSn(SiMe3)3
Me3Si
References
4
THF
d 13C (ppm) J 13 C–117=119 Sn (Hz)
K + 1MgBr2 Et 2O
SiMe3
2
Sn
SiMe3
d 29Si (ppm) J 29 Si–117=119 Sn (Hz)
2 Me3Si
SiMe3 .
1
SiMe3
1
2.1.4. Preparation of bis(tris(trimethylsilyl)stannyl) magnesium Metathesis reaction of (Me3Si)3EM (E = Si, Ge; M = Li, K) with less electropositive element halides M 0 X2 (M = Mg, Ca, Sr, Ba, Zn; X = Cl, Br, I) proved to be a convenient method for the preparation of – depending on stoichiometry applied – (Me3Si)3EMX and (Me3Si)3EM 0 E(SiMe3)3 [12]. Therefore, it was not surprising that the reaction of two equivalents of tris(trimethylsilyl)stannyl potassium 4 with magnesium bromide in THF cleanly yielded bis[(trimethylsilyl)stannyl]magnesium 7.
[6]
SiMe3
2
SiMe3
23 22 24 24 22 22 22 28
Sn
22 22 21 22 22 23 21 22 21 21 21
Me3Si
23 24
DME
8.12, 7.74, 8.2 7.81, 8.39, 8.35, 8.58, 8.79, 8.97, 9.05, 6.55,
SiMe3
d 119Sn (ppm)
Sn
CsF/18Cr6
8.37, 8.23, 8.36, 8.39, 8.45, 8.55, 8.63, 8.66, 8.70, 8.75, 8.81,
SiMe3
SiMe3 Me3Si
d 13C (ppm) J 13 C–117=119 Sn (Hz)
3176
R. Fischer et al. / Inorganica Chimica Acta 358 (2005) 3174–3182
for 1 J 29 Si–119=117 Sn are observed for the lithium derivatives 2 Æ 3THF (107/102 Hz), 2 Æ 2DME (138/132 Hz) and 2 Æ 12Cr4 (204/195 Hz), being only 30–58% of the value observed for 6 Æ 18cr6. The increase in coupling constants with atomic number is accompanied by successively upfield shifted 119Sn resonances, which are in good accordance with the Pauling electronegativities of the alkali metals. 13C and 29Si shifts on contrary successively move to lower field with increasing atomic number of the alkali metal. A similar, but much less pronounced trend concerning 29Si–119Sn coupling is observed with DME solutions of compounds 2–6. 119Sn chemical shifts, however, show a parabolic dependency on the nature of the cation with the highest upfield shift for potassium. Moreover, when one equivalent of crown ether is added to the DME solutions, differences in 119 Sn, 29Si, 13C and 1H chemical shifts and coupling almost completely level out. 119Sn resonances are found slightly above 900 ppm (900.3 to 903.6) and differ by some 3 ppm and 1 J 29 Si–119=117 Sn coupling constants lie between 328/311 and 358/343 Hz. 13C resonances are found between 8.55 and 8.75 ppm, 29Si shifts lie between 12.79 and 12.87 ppm. Similar shifts and coupling constants are also found for benzene solutions of 6 Æ 18Cr6 and 6 Æ [2.2.2]crypt. [(Me3Si)3Sn]2Mg Æ 2THF 7 exhibits compared to compounds 2–6 downfield shifted 119Sn and 29Si resonances and a rather small 1 J 29 Si–119=117 Sn coupling constant (123/117 Hz) in benzene. 3 J 1 H–119=117 Sn ð9 HzÞ and 2 J 13 C–119=117 Sn ð28 HzÞ values are significantly larger than in compounds 2–6. These findings suggested a strong inter-
Fig. 1. Temperature dependent 7Li and
3177
action between the [(Me3Si)3Sn] unit and the ether adducts of the lighter alkali cations and magnesium in benzene solution, presumably strong enough to, e.g., NMR spectroscopically observe coupling between 7Li and 119Sn nuclei. Variable temperature NMR spectroscopy reveals coupling to exist for 2 Æ 3THF and 2 Æ 12Cr4 at temperatures below 213 and 233 K, respectively. 2 Æ 3THF has previously been investigated but no coupling was observed [7]. Fig. 1 displays 7Li and 119Sn low temperature spectra for 2 Æ 3THF with a well resolved quartet with a 1 J 7 Li–119=117 Sn of 337 Hz line separation. Apparently, different modes of lithium–tin interaction give rise to more than only one set of signals. A second resonance which also shows coupling to lithium with a coupling constant of 368 Hz is present in the spectra. In the case of 2 Æ 12Cr4, the situation is even more complicated, although a well resolved quartet with 275 Hz linesplitting is clearly seen. The larger 7Li–119Sn coupling constants of 2 Æ 3THF are accompanied by smaller values for 1 J 29 Si–119=117 Sn compared to 2 Æ 12Cr4. This coupling behaviour may be understood in terms of orbital hybridization. Si–Sn bonds in 2 Æ 3THF presumably have a higher p-character compared to 2 Æ 12Cr4. On the other hand, this goes along with a higher s-orbital contribution in Sn–Li bonding of 2 Æ 3THF, giving rise to a larger 1 J 7 Li–119=117 Sn coupling constant of 2 Æ 3THF compared to 2 Æ 12Cr4 [13,14]. Previously 119Sn–7Li coupling constants were reported for Bu3SnLi in diethylether [15] (402.5 Hz, 154 K), Ph3SnLi Æ PMDETA in toluene [16,17] (412 Hz, 183 K) and (tBu2MeSi)3SnLi [18] (572 Hz, 295 K).
119
Sn NMR spectra for 2 Æ 3THF.
3178
R. Fischer et al. / Inorganica Chimica Acta 358 (2005) 3174–3182 Table 2 Crystallographic data for compound 3 Æ 15cr5 3 Æ 15cr5
Fig. 2. The molecular structure and numbering of 3 Æ 15cr5 with 30% probability thermal ellipsoids; all hydrogen atoms have been omitted for clarity. Only one molecule of two in the unit cell is drawn. Selected ˚ ] and bond angles [] with estimated standard bond lengths [A deviations: Na(1)–Sn(1) 3.0755(18), Si(1)–Sn(1) 2.563(6), Si(2)–Sn(1) 2.593(5), Si(3)–Sn(1) 2.588(9), Si(1)–Sn(1)–Si(2) 97.56(17), Si(1)–Sn(1)– Si(3) 100.3(2), Si(2)–Sn(1)–Si(3) 99.7(2), Na(1)–Sn(1)–Si(1) 115.63(15), Na(1)–Sn(1)–Si(2) 128.7(2), Na(1)–Sn(1)–Si(3) 109.72(17).
However, no coupling between 7Li and 119Sn is observed for 2 Æ 2DME down to 193 K, yet strong linebroadening is detected.
Empirical formula Mw Temperature (K) Size (mm) Crystal system Space group Unit cell dimensions ˚) a (A ˚) b (A ˚) c (A a () b () c () ˚ 3) V (A Z qcalc (g cm3) Absorption coefficient (mm1) F (0 0 0) h range Number of reflections collected/unique Rint Completeness to h (%) Absorption correlation Number of data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2r(I)] R indices (all data) ˚ 3] Largest difference in peak/hole [e/A
C19H47NaO5Si3Sn 581.52 100(2) 0.44 · 0.32 · 0.20 monoclinic P2(1) 10.244(2) 15.376(3) 10.872(2) 90 117.18(3) 90 1523.4(5) 2 1.268 0.993 608 2.11–26.33 12 091/5952 [0.0391] 26.33 [99.8] SADABS 5952/109/391 1.087 R1 = 0.0402, wR2 = 0.1010 R1 = 0.0465, wR2 = 0.1062 1.209 and 0.921
2.3. X-ray crystallography 3 Æ 15Cr5 was subjected to X-ray crystal structure analysis. It crystallizes in the monoclinic space group P2(1) and contains two independent molecules per asymmetric unit. The [(Me3Si)3Sn] entity is found disordered with the [(Me3Si)3Sn] units twisted along the Sn–Na axis by about 30 (see Fig. 2). X-ray crystallographic results clearly show a direct ˚ in length. Si–Sn bond Sn–Na contact of 3.0775(18) A ˚. distances are found between 2.563(5) and 2.623(6) A The sum of angles spanned by the trimethylsilyl groups and the central tin atoms are 297.56 and 297.23 for the two subunits. Thus, the [(Me3Si)3Sn] parts in 3 Æ 15Cr5 and (Me3Si)3SnLi Æ 3THF [19] and {[(Me3Si)3Sn](lLi)(l-Li Æ THF)} [19] are structurally almost identical.
All structures share a high degree of pyramidalization with a sum of Si–Sn–Si bond angles close to 300, which is substantially less than 329.13 for a regular tetrahedron. This is probably due to a high degree of p-character in Si–Sn bonding orbitals which agrees well with the small 29Si–119/117Sn NMR coupling constants observed for 2, 3 and 7. However, structures of tris(trimethylsilyl)stannyl alkali derivatives strongly differ from other trisilylstannide units as in [(tBu2MeSi)3Sn]Li Æ 2THF, [(tBu2MeSi)3Sn]K Æ [2.2.2]crypt, [(tBu2MeSi)3SnLi]2 and [(tBu2MeSi)3Sn]Li Æ benzene [18]. Sum of angles spanned by the bulkier tBu2MeSi units and the central tin atom and Si–Sn bond lengths are generally found larger. A summary is given in Table 3.
Table 3 Structural data for tris(triorganosilyl)stannyl alkali derivatives ˚) Bond length Si–M (A
˚) Bond length Si–Sn (A
Cone angle R Si–Sn–Si ()
References
3 Æ 15Cr5 (Me3Si)3SiLi Æ 3THF {[(Me3Si)3Sn] (l-Li)(l-Li Æ THF)} [(tBu2MeSi)3Sn]Li Æ 2THF [(tBu2MeSi)3Sn]K Æ [2.2.2]crypt [(tBu2MeSi)3SnLi]2 [(tBu2MeSi)3Sn]Li Æ benzene
2.563(5)–2.623(6) 2.5633(9)–2.5815(8) 2.570(3)–2.583(3) 2.6479(7)–2.6672(7) 2.6442(7)–2.6509(9) 2.6757(11)–2.7041(10) 2.6520(6)–2.6688(6)
297.23/297.56 296.24 303.41/303.81 338.62 334.8 342.13 338.105
[7] [17] [16] [16] [16] [16]
3.0775(18) 2.865(5) 2.764(15)–2.926(18) 2.831(6) 7.9 2.985(7)/3.141(7) 2.771(4)
R. Fischer et al. / Inorganica Chimica Acta 358 (2005) 3174–3182
3. Experimental All reactions were carried out in a glove box under an atmosphere of dry nitrogen. Solvents were dried using a column solvent purification system [20]. Potassium tertbutoxide was purchased exclusively from MERCK. All other chemicals were used as received from several different chemical suppliers. 1 H (300 MHz), 13C (75.4 MHz), and 29Si (59.3 MHz) NMR spectra were recorded on a Varian MercuryPlus 300 spectrometer. Samples for 29Si spectra were either dissolved in deuterated solvents or in cases of reaction samples and DME solutions measured with a D2O capillary in order to provide a lock frequency signal. NMR shifts were referenced to solvent residual peaks. To eliminate the temperature dependence of chemical shifts, spectra were recorded at 25 C and samples were allowed to equilibrate thermally for 10 min. To compensate for the low isotopic abundance of 29Si the INEPT pulse sequence was used for the amplification of the signal [21]. The completeness of reactions was usually controlled by NMR spectroscopy. For Xray structure analysis crystals were mounted onto the tip of a glass fiber, and data collection was performed with a BRUKER-AXS SMART APEX CCD diffractometer using graphite monochromated Mo Ka radia˚ ). The data were reduced to F 2 and tion (0.71073 A o corrected for absorption effects with SAINT [22] and SADABS [23], respectively. The structure was solved using direct methods and refined by full-matrix least-squares method (SHELXL97) [24]. All non-hydrogen atoms were refined with anisotropic displacement parameters. All hydrogen atoms were located in calculated positions to correspond to standard bond lengths and angles. Crystallographic data can be found in Table 2. More detailed information to all structures can be found in the Supporting Information. Elemental analyses were attempted with a Heraeus VARIO ELEMENTAR EL analyzer. No satisfactory elemental analyses of the alkali metal stannides could be obtained. This is in accordance with our own previous observations and also those of other authors which report about similar problems with alkali silyl and germyl compounds [3,9]. Tetrakis(trimethylsilyl)stannane has been prepared following a previously published procedure [6]. 3.1. General procedure 1: preparation of 2 Æ 3THF, 2 Æ 2DME and 2 Æ 12Cr4 To a solution of 100 mg (0.243 mmol) (Me3Si)4Sn 1 in ca. 3 ml THF, DME or benzene and 80 ll (86 mg, 0.490 mmol 12Cr4) 0.15 ml of a 1.6 M solution of MeLi Æ LiBr in diethylether was added with stirring. The reaction mixture immediately turned yellow. Reaction completed within 1 h (THF and DME as solvent) to
3179
12 h (benzene/12Cr4). After quantitative conversion, solvent and all volatiles were removed in vacuo (0.01 mbar, room temperature). The residue was dissolved in 2 ml of the respective solvent which was afterwards evaporated to ensure complete removal of diethylether and other volatiles. To the yellow residue 0.600 ml of C6D6 or DME were added to give samples for NMR spectroscopy from which LiBr was removed by centrifugation prior to use. 3.2. Tris(trimethylsilyl)stannyllithium Æ 3THF, benzene solution NMR data (d in ppm): 1H (C6D6): 3.52 (m, 12H, CH2O), 1.46 (m, 12H, CH2CH2O), 0.55 (s, 27H, (H3C)3 Si, 3 J 1 H–117=119 Sn : 9.9 Hz); 13C (C6D6): 68.51 (CH2O), 25.23 (CH2CH2O), 7.74 ((H3C)3Si, 2 J 13 C–117=119 Sn : 29 24 Hz; 1 J 13 C–29 Si : 36 Hz); Si (C6D6): 13.38 119 (1 J 29 Si–117=119 Sn : 107=102 Hz); Sn (C6D6): 872.2. 3.3. Tris(trimethylsilyl)stannyllithium Æ 2DME, benzene solution NMR data (d in ppm): 1H (C6D6): 3.07 (s, 12H, CH2O), 3.04 (s, 18H, CH3O), 0.49 (s, 27H, (H3C)3Si), 3 J 1 H–117=119 Sn : 9.1 Hz; 13C (C6D6): 70.51 (CH2O), 78.70 2 (CH3O), 7.81 ((H3C)3Si), J 13 C–117=119 Sn : 23 Hz; 1 J 13 C–29 Si : 35 Hz; 29Si (C6D6): 13.40 (1 J 29 Si–117=119 Sn : 138=132 Hz); 119Sn (C6D6): 873.4. 3.4. Tris(trimethylsilyl)stannyllithium Æ 12Cr4, benzene solution NMR data (d in ppm): 1H (C6D6): 3.46 (s, 16H, CH2O), 0.60 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 7.5 Hz); 13C (C6D6): 2 66.85 (CH2O), 8.39 ((H3C)3Si, J 13 C–117=119 Sn : 29 1 22 Hz; J 13 C–29 Si : 34 Hz); Si (C6D6): 12.95 (1 J 29 Si–117=119 Sn : 204=195 Hz); 119Sn (C6D6): 882.1. 3.5. Tris(trimethylsilyl)stannyllithium, DME solution NMR data (d in ppm): 1H (D2O-cap.): 3.87 (s, CH2O), 3.69 (s, CH3O), 0.54 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.8 Hz); 13C (D2O-cap.): 72.21 (CH2O), 2 58.70 (CH3O), 8.37 ((H3C)3Si, J 13 C–117=119 Sn : 29 1 22 Hz; J 13 C–29 Si : 33 Hz); Si (D2O-cap.): 12.95 (1 J 29 Si–117=119 Sn : 287=274 Hz); 119Sn (D2O-cap.): 894.7. 3.6. Tris(trimethylsilyl)stannyllithium Æ 12Cr4, DME solution NMR data (d in ppm): 1H (D2O-cap.): 4.05 (s, 16H, CH2O, 12Cr4), 3.82 (s, CH2O), 3.66 (s, CH3O), 0.51 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.4 Hz); 13C (D2Ocap.): 72.28 (CH2O), 69.77 (CH2O, 12Cr4), 58.56 2 (CH3O), 8.55 ((H3C)3Si, J 13 C–117=119 Sn : 23 Hz;
3180
R. Fischer et al. / Inorganica Chimica Acta 358 (2005) 3174–3182
J 13 C–29 Si : 35 Hz); 29Si (D2O-cap.): 12.83 (1 J 29 Si–117=119 Sn : 328=311 Hz); 119Sn (D2O-cap.): 902.0.
1
3.7. General procedure 2: preparation of 3, 4 and 5 To a solution of 100 mg (0.243 mmol) (Me3Si)4Sn 1 in ca. 3 ml benzene, one equivalent of the respective crown ether (15Cr5 for the preparation of 3 and 18Cr6 for 4 and 5) were added. Upon addition of one equivalent tBuOM and mixing the reaction mixture rapidly turned yellow. The reactions completed within 30 min. Alternatively, one equivalent of tBuOM was added to a solution of 100 mg (0.243 mmol) (Me3Si)4Sn 1 in 3 ml DME to instantly give bright yellow solution. Afterwards solvent and all volatiles were removed in vacuo. The NMR samples were prepared by dissolving the residue in 0.600 ml C6D6. Addition of one equivalent crown ether to the DME solutions provided the solutions of (Me3Si)3SnM Æ crown in DME. 3.8. Tris(trimethylsilyl)stannylsodium Æ 15Cr5, benzene solution Starting materials: 100 mg (0.243 mmol) 1, 24 mg (0.243 mmol) NaOtBu, 48 ll (54 mg, 0.243 mmol) 15Cr5; NMR data (d in ppm): 1H (C6D6): 3.17 (s, 20 H, CH2O), 0.60 (s, 27 H, (H3C)3Si, 3 J 1 H–117=119 Sn : 8.3 Hz); 13 C (C6D6): 68.70 (CH2O), 8.35 ((H3C)3Si, 2 J 13 C–117=119 Sn : 29 24 Hz; 1 J 13 C–29 Si : 34 Hz); Si (C6D6): 12.93 119 (1 J 29 Si–117=119 Sn : 220=210 Hz); Sn (C6D6): 881.6. Crystals suitable for X-ray crystallography of 3 Æ 15cr5 were grown from a solution in toluene at 35 C. 3.9. Tris(trimethylsilyl)stannylpotassium Æ 18Cr6, benzene solution Starting materials: 100 mg (0.243 mmol) 1, 27 mg (0.243 mmol) KOtBu, 64 mg (0.243 mmol) 18Cr6; NMR data (d in ppm): 1H (C6D6): 3.11 (s, 24H, CH2O), 0.59 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 7.3 Hz); 13 C (C6D6): 69.68 (CH2O), 8.58 ((H3C)3Si, 2 J 13 C–117=119 Sn : 24 Hz; 1 J 13 C–29 Si : 34 Hz); 29Si (C6D6): 12.70 (1 J 29 Si–117=119 Sn : 271=259 Hz); 119Sn (C6D6): 892.2. 3.10. Tris(trimethylsilyl)stannylrubidium Æ 18Cr6, benzene solution Starting materials: 100 mg (0.243 mmol) 1, 39 mg (0.243 mmol) RbOtBu, 64 mg (0.243 mmol) 18Cr6; NMR data (d in ppm): 1H (C6D6): 3.20 (s, 24H, CH2O), 0.64 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.5 Hz); 13 C (C6D6): 69.66 (CH2O), 8.79 ((H3C)3Si, 2 J 13 C–117=119 Sn : 22 Hz; 1 J 13 C–29 Si : 33 Hz); 29Si (C6D6): 12.60 (1 J 29 Si–117=119 Sn : 297=283 Hz); 119Sn (C6D6): 890.3.
3.11. Tris(trimethylsilyl)stannylsodium, DME solution Starting materials: 100 mg (0.243 mmol) 1, 24 mg (0.243 mmol) NaOtBu; NMR data (d in ppm): 1H (D2Ocap.): 3.85 (s, CH2O), 3.69 (s, CH3O), 0.54 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 7.1 Hz); 13C (D2O-cap.): 72.21 (CH2O), 58.70 (CH3O), 8.23 ((H3C)3Si, 2 J 13 C–117=119 Sn : 21 Hz; 1 J 13 C–29 Si : 34 Hz); 29Si (D2O-cap.): 13.03 (1 J 29 Si–117=119 Sn : 262=249 Hz); 119Sn (D2O-cap.): 890.3. 3.12. Tris(trimethylsilyl)stannylpotassium, DME solution Starting materials: 100 mg (0.243 mmol) 1, 27 mg (0.243 mmol) KOtBu; NMR data (d in ppm): 1H (D2Ocap.): 3.85 (s, CH2O), 3.67 (s, CH3O), 0.54 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 7.0 Hz); 13C (D2O-cap.): 72.21 (CH2O), 58.60 (CH3O), 8.36 ((H3C)3Si, 2 J 13 C–117=119 Sn : 21 Hz; 1 J 13 C–29 Si : 33 Hz); 29Si (D2O-cap.): 12.88 (1 J 29 Si–117=119 Sn : 295=282 Hz); 119Sn (D2O-cap.): 896.8. 3.13. Tris(trimethylsilyl)stannylrubidium, DME solution Starting materials: 100 mg (0.243 mmol) 1, 39 mg (0.243 mmol) RbOtBu; NMR data (d in ppm): 1H (D2Ocap.): 3.85 (s, CH2O), 3.69 (s, CH3O), 0.54 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.6 Hz); 13C (D2O-cap.): 72.21 (CH2O), 58.70 (CH3O), 8.39 ((H3C)3Si, 2 J 13 C–117=119 Sn : 22 Hz; 1 J 13 C–29 Si : 34 Hz); 29Si (D2O-cap.): 12.73 (1 J 29 Si–117=119 Sn : 300=287 Hz); 119Sn (D2O-cap.): 890.0. 3.14. Tris(trimethylsilyl)stannylsodium Æ 15Cr5, DME solution Starting materials: 100 mg (0.243 mmol) 1, 24 mg (0.243 mmol) NaOtBu, 48 ll (54 mg, 0.243 mmol) 15Cr5; NMR data (d in ppm): 1H (D2O-cap.): 4.00 (s, 20H, CH2O, 15Cr5), 3.81 (s, CH2O), 3.64 (s, CH3O), 0.49 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.3 Hz); 13C (D2O-cap.): 72.25 (CH2O), 70.27 (CH2O, 15Cr5), 58.63 2 (CH3O), 8.63 ((H3C)3Si, J 13 C–117=119 Sn : 21 Hz; 29 1 J 13 C–29 Si : 33 Hz); Si (D2O-cap.): 12.87 (1 J 29 Si–117=119 Sn : 331=316 Hz); 119Sn (D2O-cap.): 900.3. 3.15. Tris(trimethylsilyl)stannylpotassium Æ 18Cr6, DME solution Starting materials: 100 mg (0.243 mmol) 1, 27 mg (0.243 mmol) KOtBu, 64 mg (0.243 mmol) 18Cr6; NMR data (d in ppm): 1H (D2O-cap.): 4.03 (s, 16H, CH2O, 18Cr6), 3.83 (s, CH2O), 3.66 (s, CH3O), 0.50 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.1 Hz); 13C (D2Ocap.): 72.23 (CH2O), 70.55 (CH2O, 18Cr6), 58.50 (CH3O), 8.66 ((H3C)3Si, 2 J 13 C–117=119 Sn : 22 Hz; 1 J 13 C–29 Si : 33 Hz); 29Si (D2O-cap.): 12.86 (1 J 29 Si–117=119 Sn : 343=329 Hz); 119Sn (D2O-cap.): 902.6.
R. Fischer et al. / Inorganica Chimica Acta 358 (2005) 3174–3182
3.16. Tris(trimethylsilyl)stannylrubidium Æ 18Cr6, DME solution Starting materials: 100 mg (0.243 mmol) 1, 39 mg (0.243 mmol) RbOtBu, 64 mg (0.243 mmol) 18Cr6; NMR data (d in ppm): 1H (D2O-cap.): 4.00 (s, 24H, CH2O, 18Cr6), 3.82 (s, CH2O), 3.66 (s, CH3O), 0.50 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.0 Hz); 13C (D2Ocap.): 72.30 (CH2O), 70.61 (CH2O, 18Cr6), 58.60 2 (CH3O), 8.70 ((H3C)3Si, J 13 C–117=119 Sn : 21 Hz; 29 1 J 13 C–29 Si : 33 Hz); Si (D2O-cap.): 12.79 (1 J 29 Si–117=119 Sn : 347=332 Hz); 119Sn (D2O-cap.): 901.8. 3.17. General procedure 3: preparation of 6 A suspension of 100 mg (Me3Si)4Sn 1 in 2 ml DME with 11 mg CsF (0.729 mmol, threefold excess) was stirred at room temperature for 48 h. Solutions of 6 Æ 18Cr6 and 6 Æ [2.2.2]crypt in benzene were prepared by performing the reactions in benzene in the presence of one equivalent crown ether and cryptand, respectively. After removal of excess CsF and all volatiles, NMR samples were prepared by dissolving the residue in C6D6 or DME, respectively. 3.18. Tris(trimethylsilyl)stannylcesium Æ 18Cr6, benzene solution Starting materials: 100 mg (0.243 mmol) 1, 111 mg (0.729 mmol) CsF, 64 mg (0.243 mmol) 18Cr6; NMR data (d in ppm): 1H (C6D6): 3.18 (s, 24H, CH2O), 0.63 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.0 Hz); 13C (C6D6): 69.23 (CH2O), 8.97 ((H3C)3Si, 2 J 13 C–117=119 Sn : 22 Hz; 1 J 13 C–29 Si : 33 Hz); 29Si (C6D6): 12.56 (1 J 29 Si–117=119 Sn : 345=328 Hz); 119Sn (C6D6): 899.4. 3.19. Tris(trimethylsilyl)stannylcesium Æ [2.2.2]crypt, benzene solution Starting materials: 100 mg (0.243 mmol) 1, 111 mg (0.729 mmol) CsF, 92 mg (0.243 mmol) [2.2.2]crypt; NMR data (d in ppm): 1H (C6D6): 3.11 (s, 12H, CH2O), 3.00 (t, 5.1 Hz, 12H, CH2O), 2.04 (t, 5.1 Hz, 12H, CH2O), 0.50 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.0 Hz); 13C (C6D6): 70.48 (CH2O), 68.34 (CH2O), 55.10 (CH2N), 9.05 ((H3C)3Si, 2 J 13 C–117=119 Sn : 22 Hz; 1 J 13 C–29 Si : 34 Hz); 29Si (C6D6): 12.63 (1 J 29 Si–117=119 Sn : 348=330 Hz); 119Sn (C6D6): 901.2. 3.20. Tris(trimethylsilyl)stannylcesium, DME solution Starting materials: 100 mg (0.243 mmol) 1, 111 mg (0.729 mmol) CsF; NMR data (d in ppm): 1H (D2Ocap.): 3.84 (s, CH2O), 3.67 (s, CH3O), 0.53 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.5 Hz); 13C (D2O-cap.): 72.21 (CH2O), 58.70 (CH3O), 8.45 ((H3C)3Si,
3181
J 13 C–117=119 Sn : 22 Hz; 1 J 13 C–29 Si : 34 Hz); 29Si (D2Ocap.): 13.15 (1 J 29 Si–117=119 Sn : 311=298 Hz); 119Sn (D2Ocap.): 876.4.
2
3.21. Tris(trimethylsilyl)stannylcesium Æ 18Cr6, DME solution Starting materials: 100 mg (0.243 mmol) 1, 111 mg (0.729 mmol) CsF, 64 mg (0.243 mmol) 18Cr6; NMR data (d in ppm): 1H (D2O-cap.): 4.00 (s, 24H, CH2O, 18Cr6), 3.82 (s, CH2O), 3.66 (s, CH3O), 0.50 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 5.9 Hz); 13C (D2O-cap.): 72.30 (CH2O), 70.35 (CH2O, 12Cr4), 58.58 (CH3O), 8.75 ((H3C)3Si, 2 J 13 C–117=119 Sn : 21 Hz; 1 J 13 C–29 Si : 33 Hz); 29Si (D2O-cap.): 12.80 (1 J 29 Si–117=119 Sn : 358=343 Hz); 119Sn (D2O-cap.): 903.6. 3.22. Tris(trimethylsilyl)stannylcesium Æ [2.2.2]crypt, DME solution Starting materials: 100 mg (0.243 mmol) 1, 111 mg (0.729 mmol) CsF, 92 mg (0.243 mmol) [2.2.2]crypt; NMR data (d in ppm): 1H (D2O-cap.): 3.99 (s, 12H, OCH2CH2O, [2.2.2]crypt), 3.90 (t, 5.1 Hz, 12H, NCH2CH2O, [2.2.2]crypt), 3.81 (CH2O), 3.66 (CH3O), 2.95 (t, 5.1 Hz, 12H, NCH2CH2O, [2.2.2]crypt), 0.51 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 5.9 Hz); 13C (D2Ocap.): 72.33 (CH2O), 71.33 (OCH2CH2O, [2.2.2]crypt), 69.95 (OCH2CH2N, [2.2.2]crypt), 58.60 (CH3O), 56.77 (OCH2CH2N, [2.2.2]crypt), 8.82 ((H3C)3Si, 2 J 13 C–117=119 Sn : 21 Hz; 1 J 13 C–29 Si : 32 Hz); 29Si (D2Ocap.): 12.73 (1 J 29 Si–117=119 Sn : 355=339 Hz); 119Sn (D2Ocap.): 903.6. 3.23. Bis(tris(trimethylsilyl)stannyl)magnesium Æ 2THF To a solution of 125 mg (0.5 mmol) MgBr2 Æ Et2O in 5 ml THF a solution of 1.0 mmol (Me3Si)3SnK (prepared from the reaction of 411 mg 1 and 112 mg KOtBu in THF) in 5 ml THF was added dropwise. Upon addition, the yellow colour of the anion solution vanished and white precipitate was formed. After complete addition, the reaction mixture was stirred for 30 min after which all volatiles are removed in vacuo. The residue was extracted three times with 2 ml portions of n-pentane. Upon concentration to incipient crystallization and cooling to 35 C 342 mg (81% yield) colourless needles of 7 Æ 2THF were obtained. NMR data (d in ppm): 1H (C6D6): 3.59 (m, 8H, CH2O), 1.20 (m, 8H, CH2CH2O), 0.42 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 14.6 Hz); 13C (C6D6): 69.52 (CH2O), 24.80 (CH2CH2O), 6.55 ((H3C)3Si, 2 J 13 C–117=119 Sn : 28 Hz; 1 J 13 C–29 Si : 42 Hz); 29Si (C6D6): 12.28 (1 J 29 Si–117=119 Sn : 123=117 Hz); 119Sn (C6D6): 830.2.
3182
R. Fischer et al. / Inorganica Chimica Acta 358 (2005) 3174–3182
4. Supplementary material Data for 3 Æ 15Cr5 has been deposited at the Cambridge Crystallographic Deposition Centre: CCDC 262663. The data can be retrieved via www.ccdc.cam. ac.uk/conts/retrieving.html or can be ordered at the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB21Ez, fax: +44 1223 336 033.
Acknowledgements The authors acknowledge funds from the Fonds zur Fo¨rderung der Wissenschaftlichen Forschung (FWF, Austria) (START project Y-120), the Graz University of Technology (Austria), the Deutsche Forschungsgemeinschaft (DFG, Germany) and the Fonds der chemischen Industrie (Germany). WACKER GmbH, Burghausen, Germany is gratefully acknowledged for donation of chlorosilanes. References [1] (a) P.D. Lickiss, C.M. Smith, Coord. Chem. Rev. 145 (1995) 75; (b) K. Tamao, A. Kawachi, Adv. Organomet. Chem. 38 (1995) 1; (c) J. Belzner, U. Dehnert, in: Z. Rappoport, Y. Apeloig (Eds.), The Chemistry of Organic Silicon Compounds, vol. 2, Wiley, New York, 1998, pp. 779–825; (d) A. Sekiguchi, V.Y. Lee, M. Nanjo, Coord. Chem. Rev. 210 (2000) 11; (e) R. Fischer, D. Frank, W. Gaderbauer, C. Kayser, C. Mechtler, J. Baumgartner, C. Marschner, in: P. Jutzi, U. Schubert (Eds.), Silicon chemistry, Verlag Chemie, Weinheim, 2003, pp. 118–129. [2] W. Teng, K. Ruhlandt-Senge, Organometallics 23 (2004) 952. [3] J. Fischer, J. Baumgartner, C. Marschner, Organometallics 24 (2005) 1263. [4] P. Riviere, A. Castel, M. Riviere-Baudet, in: Z. Rappoport (Ed.), The Chemistry of Organic Germanium, Tin and Lead Compounds, vol. 2, Wiley, New York, 2002, pp. 653–748. [5] F. Preuss, T. Wieland, J. Perner, G. Heckmann, Z. Naturforsch. 47B (1992) 1355. [6] G. Becker, M. Gekeler, H.-M. Hartmann, O. Mundt, M. Westerhausen, in: Synthetic Methods in Organometallic and Inorganic Chemistry (Series Editor: W. A. Herrmann), vol. 2 (Volume Editors: N. Auner, U. Klingebiel), Thieme, Stuttgart, 1996, pp. 186–192.
[7] C.J. Cardin, D.J. Cardin, W. Clegg, S.J. Coles, S.P. Constantine, J.R. Rowe, S.J. Teat, J. Organomet. Chem. 573 (1999) 96. [8] (a) C. Marschner, Eur. J. Inorg. Chem. (1998) 221–226; (b) C. Kayser, R. Fischer, J. Baumgartner, C. Marschner, Organometallics 21 (2002) 1023; (c) R. Fischer, D. Frank, W. Gaderbauer, C. Kayser, C. Mechtler, J. Baumgartner, C. Marschner, Organometallics 22 (2003) 3723. [9] D.M. Jenkins, W. Teng, U. Englich, D. Stone, K. RuhlandtSenge, Organometallics 20 (2001) 4600. [10] U. Englich, K. Hassler, K. Ruhlandt-Senge, F. Uhlig, Inorg. Chem. 37 (1998) 3532. [11] H. Sato, N. Isono, K. Okamura, T. Date, M. Mori, Tetrahedron Lett. 35 (1994) 2035. [12] (a) J.D. Farwell, M.F. Lappert, C. Marschner, C. Strissel, T.D. Tilley, J. Organomet. Chem. 603 (2000) 185–188; (b) W. Teng, K. Ruhlandt-Senge, Organometallics 23 (2004) 2694; (c) J. Arnold, T.D. Tilley, A.L. Rheingold, S.J. Geib, Inorg. Chem. 26 (1987) 2106; (d) H.F. Klein, J. Montag, U. Zucha, Inorg. Chim. Acta 177 (1990) 43; (e) M. Nanjo, T. Oda, K. Mochida, Chem. Lett. (2002) 108; (f) M. Nanjo, T. Oda, K. Mochida, J. Organomet. Chem. 672 (2003) 100. [13] M.A. Paver, C.A. Russell, D.S. Wright, Angew. Chem. 107 (1995) 1679. [14] M.A. Paver, C.A. Russell, D.S. Wright, Angew. Chem., Int. Ed. Engl. 34 (1995) 1545. [15] H.J. Reich, J.P. Borst, R.R. Dykstra, Organometallics 13 (1994) 1. [16] D. Reed, D. Stalke, D.S. Wright, Angew. Chem 103 (1991) 1539. [17] D. Reed, D. Stalke, D.S. Wright, Angew. Chem., Int Ed. Engl. 30 (1991) 1459. [18] T. Fukawa, M. Nakamoto, V.Y. Lee, A. Sekiguchi, Organometallics 23 (2004) 2376. [19] M. Nanjo, E. Nanjo, K. Mochida, Eur. J. Inorg. Chem. (2004) 2961. [20] A.B. Pangborn, M.A. Giardello, R.H. Grubbs, R.K. Rosen, F.J. Timmers, Organometallics 15 (1996) 1518. [21] (a) G.A. Morris, R.J. Freeman, J. Am. Chem. Soc. 101 (1979) 760; (b) B.J. Helmer, R. West, Organometallics 1 (1982) 877. [22] SAINTPLUS: Software Reference Manual, Version 6.45, BrukerAXS, Madison, WI, 1997–2003. [23] R.H. Blessing, Acta Crystallogr. Sect., A 51 (1995) 33, SADABS: Bruker/Siemens Area Detector Absorption and Other Corrections Version 2.10 Bruker AXS 1998–2003. [24] G.M. Sheldrick, SHELX97 Programs for Crystal Structure Analysis (Release 97-2), Universita¨t Go¨ttingen, Go¨ttingen, Germany, 1998.
Tris(trimethylsilyl)stannyl alkali derivatives: Syntheses and NMR spectroscopic properties Roland Fischer *, Judith Baumgartner, Christoph Marschner, Frank Uhlig Institut fu¨r Anorganische Chemie, Technische Universita¨t Graz, Stremayrgasse 16, A-8010 Graz, Austria Received 4 February 2005; received in revised form 4 February 2005; accepted 4 April 2005 Available online 2 June 2005
Abstract Starting from tetrakis(trimethylsilyl)stannane, the tris(trimethylsilyl)stannyl alkali derivatives (Me3Si)3SnM, (M = Li, Na, K, Rb, Cs) were prepared in excellent yields. Reaction with MgBr2 Æ Et2O afforded bis[tris(trimethylsilyl)stannyl]magnesium. Reaction products were investigated by means of multinuclear NMR spectroscopy. At low temperatures, coupling of 7Li and 119Sn between [(Me3Si)3Sn] and [Li Æ 3THF]+ (337 Hz) or [Li Æ 12Cr4]+ (275 Hz), was observed. NMR chemical shifts and coupling constants of the stannyl anions exhibit a strong dependency on the nature of the cation, solvent system, concentration and temperature. In addition, the molecular structure of tris(trimethylsilyl)stannyl sodium Æ 15Cr5 was determined by X-ray crystallography. The ˚ in length. [Na Æ 15Cr5]+ and [(Me3Si)3Sn] units are joined by a direct Sn–Na contact, 3.0775(18) A 2005 Elsevier B.V. All rights reserved. Keywords: X-ray crystal structures; NMR spectroscopy; Alkali stannides; Preparation
1. Introduction Despite the great synthetic potential of metalated tris(trimethylsilyl) heavier Group 14 element compounds (Me3Si)3EM (E = Si, Ge, Sn) in main group and transition metal chemistry only the chemistry of the silicon congener is well developed [1]. Much less attention was drawn to the heavier germanium and tin analogues. Structural and NMR spectroscopic investigations of tris(trimethylsilyl)germyl alkali and alkaline earth compounds [2] and their application in synthetic main group transition metal chemistry were reported recently [3]. Tris(trimethylsilyl)stannyllithium was applied in the synthesis of various main group and transition metal compounds [4]. The synthetic potential of the [(Me3Si)3Sn] moiety lies in the large steric demand which goes along with excellent kinetic stabilization. In *
Corresponding author. Tel.: +0043 316 873 8703; fax: +0043 316 873 8701. E-mail address: fi[email protected] (R. Fischer). 0020-1693/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2005.04.006
addition, the ease of preparation, the high solubility of products in organic solvents and the combination of four different NMR active nuclei which can act as spectroscopic probes even for subtle effects in electronic properties are further advantages. Among the Group 14 elements mentioned above, only tin has two sensitive NMR active nuclei and it displays the largest range of NMR spectroscopic shifts and coupling constants. As a consequence, even small differences in the electronic environment of the tin nucleus result in well detectable NMR spectroscopic changes. Heavier alkali metal tris(trimethylsilyl)stannyl derivatives or alkaline earth derivatives displaying different reactivity from the lithium derivative were to the best of our knowledge not reported previously. Yet it is highly desirable to have a greater choice of such alkali and alkaline earth metal derivatives as nucleophilicity and redox potential may be adjusted. Cleavage of silicon–tin bonds in tetrakis(trimethylsilyl)stannane with methyllithium was previously investigated by Preuss et al. [5] and Becker et al. [6].
R. Fischer et al. / Inorganica Chimica Acta 358 (2005) 3174–3182
Tris(trimethylsilyl)stannyl lithium Æ 3THF has also directly been obtained from the reaction of tin(IV) chloride and trimethylchlorosilane with lithium [7]. All reactions were carried out in THF, DME or TMEDA as solvents. Less polar solvents, e.g., diethylether or benzene were found unsuitable for this reaction.
2. Results and discussion 2.1. Syntheses 2.1.1. Preparation of tris(trimethylsilyl)stannyl lithium In contrast to previous syntheses of tris(trimethylsilyl)stannyl lithium 2, which were carried out in ethereal solvents, we examined the reactivity of methyl lithium with tetrakis(trimethylsilyl)stannane in aromatic solvents in the presence of 12-crown-4 (12Cr4). When a diethylether solution of methyl lithium/lithium chloride is added to a solution of tetrakis(trimethylsilyl)stannane 1 and two equivalents 12-crown-4 (12Cr4) in benzene, the reaction proceeds smoothly at room temperature to give access to a benzene solution of the crown ether adduct of 2 with exact stoichiometry. The second equivalent of crown ether is presumably necessary in order to chelate lithium halide introduced with methyl lithium. DME solutions of 2 used in the NMR spectroscopic investigations were prepared following literature procedures. Addition of a stoichiometric amount of 12-crown-4 provided the DME solution of 2 Æ 12Cr4. SiMe3
SiMe3 Me3Si
Sn
SiMe3
MeLi/12Cr4 benzene
Me3Si
Sn
Li.12Cr4 + Me4Si
SiMe3
SiMe3
1
2
(1)
THF and DME adducts 2 Æ 3THF and 2 Æ 2DME were prepared by metallation of 1 with MeLi in the respective solvent followed by removal of all volatiles in vacuo, repeated addition and removal of benzene and filtration of insoluble lithium chloride after dissolving the residue in benzene. 2.1.2. Preparation of tris(trimethylsilyl)stannyl sodium, -potassium and -rubidium Alkali tert-butoxides tBuOM (M = Na, K, Rb, Cs) have found widespread application in metalation reactions of (R3Si)4E (E = Si [8,9] Ge [2,3]) and (Me3Si)3P [10] species. In contrast to lithium alkyls solutions t BuOM species are solids which are easy to store and handle. Thus, exact stoichiometry is easy to control, which is a major advantage over lithium alkyls. The stoichiometry of lithium alkyls solutions has to be controlled by titra-
3175
tion and in addition the solutions often contain lithium halides which may cause problems in further reactions. The cleavage of Me3Si–E bonds (E = Si, Ge, P) with t BuOM was readily expanded to the respective tin derivatives. Metalation of tetrakis(trimethylsilyl)stannane 1 with tBuOM (M = Na, K, Rb) was found to proceed very rapidly in both, ethereal solvents like DME or THF and aromatic solvents, where the latter require the use of at least one equivalent of crown ether. Generally speaking, silicon tin derivatives are easier to metallate compared to their silicon analogues. The reaction of tetrakis(trimethylsilyl)silane with sodium tert-butoxide in THF requires elevated temperatures of about 50 C and elongated reaction times, typically around 24 h. The reaction of sodium tert-butoxide with the tin homologue in THF, however, completes within 10 min, even at room temperature. SiMe3
SiMe3 Me3Si
Sn
SiMe3
MOtBu/crown benzene
Me3Si
Sn
M.crown + Me3SiOtBu
SiMe3
SiMe3
1
3 M=Na, crown=15Cr5 4 M=K, crown=18Cr6 5 M=Rb, crown=18Cr6
(2)
Rubidium derivative 5 was found to be most reactive among compounds 3–5. Apparently its basicity is sufficient to slowly abstract a proton from concomitantly formed tBuOSiMe3 or tBuORb if applied in excess. In contrast to its lighter congeners, (Me3Si)3SnH is unstable and decomposes. As a result, formation of elemental tin together with 1 and (Me3Si)3SnSn(SiMe3)2Rb is observed.1 Similar problems were reported earlier in this context for the reaction of (Me3Si)4Si [9]. However, this obstacle is readily overcome by employing stoichiometric amounts of tBuORb and removal of Me3SiOtBu in vacuo. Tris(trimethylsilyl)stannyl rubidium was found to be stable in both ethereal and aromatic solvents over elongated periods. 2.1.3. Preparation of tris(trimethylsilyl)stannyl cesium Fluoride mediated cleavage reactions of stannasilanes were pioneered by the work of Mori and coworkers [11]. We found that cesium fluoride is also a convenient reagent for the cleavage of silicon–tin bonds in tetrakis(trimethylsilyl)stannane. The reaction has to be carried out in polar solvents, i.e., THF or DME. Alternatively, the metalation may be carried out in aromatic solvents in the presence of 18-crown-6 (18Cr6) or [2.2.2]crypt. Trimethylfluorosilane was identified as the second reaction product by means of NMR spectroscopy.
1 Experimental details and spectroscopic data for (Me3Si)3SnSn(SiMe3)2M will be reported elsewhere.
R. Fischer et al. / Inorganica Chimica Acta 358 (2005) 3174–3182
Cs.18Cr6 + Me3SiF
1
6
(3)
12.95, 13.03, 12.88, 12.73, 13.15, 12.83, 12.87, 12.86, 12.79, 12.80, 12.73, 894.7 890.3 896.8 890.0 876.4 902.0 900.3 902.6 901.8 903.6 902.0 DME solutions 2 (Me3Si)3SnLi 3 (Me3Si)3SnNa 4 (Me3Si)3SnK 5 (Me3Si)3SnRb 6 (Me3Si)3SnCs 2 Æ 12Cr4 (Me3Si)3SnLi Æ 12Cr4 3 Æ 15Cr5 (Me3Si)3SnNa Æ 15Cr5 4 Æ 18Cr6 (Me3Si)3SnK Æ 18Cr6 5 Æ 18Cr6 (Me3Si)3SnRb Æ 18Cr6 6 Æ 18Cr6 (Me3Si)3SnCs Æ 18Cr6 6 Æ [2.2.2]crypt (Me3Si)3SnCs[2.2.2]crypt
(4)
7
Table 1 119 Sn, 29Si and
13
[7]
13, 134/128 13.38, 107/102 12.7 13.40, 138/132 12.95, 204/195 12.93, 220/210 12.70, 271/259 12.60, 297/283 12.56, 345/328 12.63, 348/330 12.28, 123/117 878 872.2 873.7 873.4 882.1 881.6 892.2 890.3 899.4 901.2 830.2
C chemical shifts and coupling constants of compounds 1–7
119
9.74, 351/335
2.2. NMR spectroscopy Compounds 2–7 were studied by 1H, 13C, 29Si and Sn NMR spectroscopy. Selected 29Si, 119Sn and 13C NMR spectroscopic data are given in Table 1. It was interesting to study the influence of solvent system and nature of the cation on chemical shifts and coupling constants. 29Si and 119Sn coupling constants and to a smaller extent also chemical shifts showed a variation with concentration. Concentration effects were eliminated by using exactly 0.4 molar solutions of 2–7. Compared to starting material tetrakis(trimethylsilyl)stannane 1, 119Sn and 29Si NMR shifts are generally observed at higher field as a consequence of a higher shielding due to the negative charge of stannides. This is in contrast to 13C and 1H resonances of compounds 2–7 which are observed at lower field compared to 1. For compounds 2–7, 3 J 1 H–119=117 Sn coupling constants values ranging from 6 to 15 Hz and for 2 J 13 C–119=117 Sn from 21 to 28 Hz are observed. Thus, compared to tetrakis(trimethylsilyl)stannane 1 (3 J 1 H–119=117 Sn ¼ 21.8=20.9 Hz and 2 J 13 C–119=117 Sn ¼ 40=38 Hz, respectively) substantially smaller 2J and 3J coupling constants are observed for metalated species 2–7. The most pronounced effect in benzene solutions of crown ether adducts of compounds 2–6 is a 29Si–119Sn coupling constant which is increasing with decreasing electronegativity of the alkali metal. The smallest values
287/274 262/249 295/282 300/287 311/298 328/311 331/316 343/329 347/332 358/343 355/339
d 29Si (ppm) J 29 Si–117=119 Sn (Hz) d 119Sn (ppm)
SiMe3 + 2 KBr
SiMe3
4.32, 40/38
Mg Sn
SiMe3
664.4
Sn
1 (Me3Si)4Sn Benzene solutions 2 Æ 3THF (Me3Si)3SnLi Æ 3THF 2 Æ 3THF (Me3Si)3SnLi Æ 3THF 2 Æ 2TMEDA (Me3Si)3SnLi Æ 2TMEDA 2 Æ 2DME (Me3Si)3SnLi Æ 2DME 2 Æ 12Cr4 (Me3Si)3SnLi Æ 12Cr4 3 Æ 15Cr5 (Me3Si)3SnNa Æ 15Cr5 4 Æ 18Cr6 (Me3Si)3SnK Æ 18Cr6 5 Æ 18Cr6 (Me3Si)3SnRb Æ 18Cr6 6 Æ 18Cr6 (Me3Si)3SnCs Æ 18Cr6 6 Æ [2.2.2]crypt (Me3Si)3SnCs Æ [2.2.2]crypt 7 (Me3Si)3SnMgSn(SiMe3)3
Me3Si
References
4
THF
d 13C (ppm) J 13 C–117=119 Sn (Hz)
K + 1MgBr2 Et 2O
SiMe3
2
Sn
SiMe3
d 29Si (ppm) J 29 Si–117=119 Sn (Hz)
2 Me3Si
SiMe3 .
1
SiMe3
1
2.1.4. Preparation of bis(tris(trimethylsilyl)stannyl) magnesium Metathesis reaction of (Me3Si)3EM (E = Si, Ge; M = Li, K) with less electropositive element halides M 0 X2 (M = Mg, Ca, Sr, Ba, Zn; X = Cl, Br, I) proved to be a convenient method for the preparation of – depending on stoichiometry applied – (Me3Si)3EMX and (Me3Si)3EM 0 E(SiMe3)3 [12]. Therefore, it was not surprising that the reaction of two equivalents of tris(trimethylsilyl)stannyl potassium 4 with magnesium bromide in THF cleanly yielded bis[(trimethylsilyl)stannyl]magnesium 7.
[6]
SiMe3
2
SiMe3
23 22 24 24 22 22 22 28
Sn
22 22 21 22 22 23 21 22 21 21 21
Me3Si
23 24
DME
8.12, 7.74, 8.2 7.81, 8.39, 8.35, 8.58, 8.79, 8.97, 9.05, 6.55,
SiMe3
d 119Sn (ppm)
Sn
CsF/18Cr6
8.37, 8.23, 8.36, 8.39, 8.45, 8.55, 8.63, 8.66, 8.70, 8.75, 8.81,
SiMe3
SiMe3 Me3Si
d 13C (ppm) J 13 C–117=119 Sn (Hz)
3176
R. Fischer et al. / Inorganica Chimica Acta 358 (2005) 3174–3182
for 1 J 29 Si–119=117 Sn are observed for the lithium derivatives 2 Æ 3THF (107/102 Hz), 2 Æ 2DME (138/132 Hz) and 2 Æ 12Cr4 (204/195 Hz), being only 30–58% of the value observed for 6 Æ 18cr6. The increase in coupling constants with atomic number is accompanied by successively upfield shifted 119Sn resonances, which are in good accordance with the Pauling electronegativities of the alkali metals. 13C and 29Si shifts on contrary successively move to lower field with increasing atomic number of the alkali metal. A similar, but much less pronounced trend concerning 29Si–119Sn coupling is observed with DME solutions of compounds 2–6. 119Sn chemical shifts, however, show a parabolic dependency on the nature of the cation with the highest upfield shift for potassium. Moreover, when one equivalent of crown ether is added to the DME solutions, differences in 119 Sn, 29Si, 13C and 1H chemical shifts and coupling almost completely level out. 119Sn resonances are found slightly above 900 ppm (900.3 to 903.6) and differ by some 3 ppm and 1 J 29 Si–119=117 Sn coupling constants lie between 328/311 and 358/343 Hz. 13C resonances are found between 8.55 and 8.75 ppm, 29Si shifts lie between 12.79 and 12.87 ppm. Similar shifts and coupling constants are also found for benzene solutions of 6 Æ 18Cr6 and 6 Æ [2.2.2]crypt. [(Me3Si)3Sn]2Mg Æ 2THF 7 exhibits compared to compounds 2–6 downfield shifted 119Sn and 29Si resonances and a rather small 1 J 29 Si–119=117 Sn coupling constant (123/117 Hz) in benzene. 3 J 1 H–119=117 Sn ð9 HzÞ and 2 J 13 C–119=117 Sn ð28 HzÞ values are significantly larger than in compounds 2–6. These findings suggested a strong inter-
Fig. 1. Temperature dependent 7Li and
3177
action between the [(Me3Si)3Sn] unit and the ether adducts of the lighter alkali cations and magnesium in benzene solution, presumably strong enough to, e.g., NMR spectroscopically observe coupling between 7Li and 119Sn nuclei. Variable temperature NMR spectroscopy reveals coupling to exist for 2 Æ 3THF and 2 Æ 12Cr4 at temperatures below 213 and 233 K, respectively. 2 Æ 3THF has previously been investigated but no coupling was observed [7]. Fig. 1 displays 7Li and 119Sn low temperature spectra for 2 Æ 3THF with a well resolved quartet with a 1 J 7 Li–119=117 Sn of 337 Hz line separation. Apparently, different modes of lithium–tin interaction give rise to more than only one set of signals. A second resonance which also shows coupling to lithium with a coupling constant of 368 Hz is present in the spectra. In the case of 2 Æ 12Cr4, the situation is even more complicated, although a well resolved quartet with 275 Hz linesplitting is clearly seen. The larger 7Li–119Sn coupling constants of 2 Æ 3THF are accompanied by smaller values for 1 J 29 Si–119=117 Sn compared to 2 Æ 12Cr4. This coupling behaviour may be understood in terms of orbital hybridization. Si–Sn bonds in 2 Æ 3THF presumably have a higher p-character compared to 2 Æ 12Cr4. On the other hand, this goes along with a higher s-orbital contribution in Sn–Li bonding of 2 Æ 3THF, giving rise to a larger 1 J 7 Li–119=117 Sn coupling constant of 2 Æ 3THF compared to 2 Æ 12Cr4 [13,14]. Previously 119Sn–7Li coupling constants were reported for Bu3SnLi in diethylether [15] (402.5 Hz, 154 K), Ph3SnLi Æ PMDETA in toluene [16,17] (412 Hz, 183 K) and (tBu2MeSi)3SnLi [18] (572 Hz, 295 K).
119
Sn NMR spectra for 2 Æ 3THF.
3178
R. Fischer et al. / Inorganica Chimica Acta 358 (2005) 3174–3182 Table 2 Crystallographic data for compound 3 Æ 15cr5 3 Æ 15cr5
Fig. 2. The molecular structure and numbering of 3 Æ 15cr5 with 30% probability thermal ellipsoids; all hydrogen atoms have been omitted for clarity. Only one molecule of two in the unit cell is drawn. Selected ˚ ] and bond angles [] with estimated standard bond lengths [A deviations: Na(1)–Sn(1) 3.0755(18), Si(1)–Sn(1) 2.563(6), Si(2)–Sn(1) 2.593(5), Si(3)–Sn(1) 2.588(9), Si(1)–Sn(1)–Si(2) 97.56(17), Si(1)–Sn(1)– Si(3) 100.3(2), Si(2)–Sn(1)–Si(3) 99.7(2), Na(1)–Sn(1)–Si(1) 115.63(15), Na(1)–Sn(1)–Si(2) 128.7(2), Na(1)–Sn(1)–Si(3) 109.72(17).
However, no coupling between 7Li and 119Sn is observed for 2 Æ 2DME down to 193 K, yet strong linebroadening is detected.
Empirical formula Mw Temperature (K) Size (mm) Crystal system Space group Unit cell dimensions ˚) a (A ˚) b (A ˚) c (A a () b () c () ˚ 3) V (A Z qcalc (g cm3) Absorption coefficient (mm1) F (0 0 0) h range Number of reflections collected/unique Rint Completeness to h (%) Absorption correlation Number of data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2r(I)] R indices (all data) ˚ 3] Largest difference in peak/hole [e/A
C19H47NaO5Si3Sn 581.52 100(2) 0.44 · 0.32 · 0.20 monoclinic P2(1) 10.244(2) 15.376(3) 10.872(2) 90 117.18(3) 90 1523.4(5) 2 1.268 0.993 608 2.11–26.33 12 091/5952 [0.0391] 26.33 [99.8] SADABS 5952/109/391 1.087 R1 = 0.0402, wR2 = 0.1010 R1 = 0.0465, wR2 = 0.1062 1.209 and 0.921
2.3. X-ray crystallography 3 Æ 15Cr5 was subjected to X-ray crystal structure analysis. It crystallizes in the monoclinic space group P2(1) and contains two independent molecules per asymmetric unit. The [(Me3Si)3Sn] entity is found disordered with the [(Me3Si)3Sn] units twisted along the Sn–Na axis by about 30 (see Fig. 2). X-ray crystallographic results clearly show a direct ˚ in length. Si–Sn bond Sn–Na contact of 3.0775(18) A ˚. distances are found between 2.563(5) and 2.623(6) A The sum of angles spanned by the trimethylsilyl groups and the central tin atoms are 297.56 and 297.23 for the two subunits. Thus, the [(Me3Si)3Sn] parts in 3 Æ 15Cr5 and (Me3Si)3SnLi Æ 3THF [19] and {[(Me3Si)3Sn](lLi)(l-Li Æ THF)} [19] are structurally almost identical.
All structures share a high degree of pyramidalization with a sum of Si–Sn–Si bond angles close to 300, which is substantially less than 329.13 for a regular tetrahedron. This is probably due to a high degree of p-character in Si–Sn bonding orbitals which agrees well with the small 29Si–119/117Sn NMR coupling constants observed for 2, 3 and 7. However, structures of tris(trimethylsilyl)stannyl alkali derivatives strongly differ from other trisilylstannide units as in [(tBu2MeSi)3Sn]Li Æ 2THF, [(tBu2MeSi)3Sn]K Æ [2.2.2]crypt, [(tBu2MeSi)3SnLi]2 and [(tBu2MeSi)3Sn]Li Æ benzene [18]. Sum of angles spanned by the bulkier tBu2MeSi units and the central tin atom and Si–Sn bond lengths are generally found larger. A summary is given in Table 3.
Table 3 Structural data for tris(triorganosilyl)stannyl alkali derivatives ˚) Bond length Si–M (A
˚) Bond length Si–Sn (A
Cone angle R Si–Sn–Si ()
References
3 Æ 15Cr5 (Me3Si)3SiLi Æ 3THF {[(Me3Si)3Sn] (l-Li)(l-Li Æ THF)} [(tBu2MeSi)3Sn]Li Æ 2THF [(tBu2MeSi)3Sn]K Æ [2.2.2]crypt [(tBu2MeSi)3SnLi]2 [(tBu2MeSi)3Sn]Li Æ benzene
2.563(5)–2.623(6) 2.5633(9)–2.5815(8) 2.570(3)–2.583(3) 2.6479(7)–2.6672(7) 2.6442(7)–2.6509(9) 2.6757(11)–2.7041(10) 2.6520(6)–2.6688(6)
297.23/297.56 296.24 303.41/303.81 338.62 334.8 342.13 338.105
[7] [17] [16] [16] [16] [16]
3.0775(18) 2.865(5) 2.764(15)–2.926(18) 2.831(6) 7.9 2.985(7)/3.141(7) 2.771(4)
R. Fischer et al. / Inorganica Chimica Acta 358 (2005) 3174–3182
3. Experimental All reactions were carried out in a glove box under an atmosphere of dry nitrogen. Solvents were dried using a column solvent purification system [20]. Potassium tertbutoxide was purchased exclusively from MERCK. All other chemicals were used as received from several different chemical suppliers. 1 H (300 MHz), 13C (75.4 MHz), and 29Si (59.3 MHz) NMR spectra were recorded on a Varian MercuryPlus 300 spectrometer. Samples for 29Si spectra were either dissolved in deuterated solvents or in cases of reaction samples and DME solutions measured with a D2O capillary in order to provide a lock frequency signal. NMR shifts were referenced to solvent residual peaks. To eliminate the temperature dependence of chemical shifts, spectra were recorded at 25 C and samples were allowed to equilibrate thermally for 10 min. To compensate for the low isotopic abundance of 29Si the INEPT pulse sequence was used for the amplification of the signal [21]. The completeness of reactions was usually controlled by NMR spectroscopy. For Xray structure analysis crystals were mounted onto the tip of a glass fiber, and data collection was performed with a BRUKER-AXS SMART APEX CCD diffractometer using graphite monochromated Mo Ka radia˚ ). The data were reduced to F 2 and tion (0.71073 A o corrected for absorption effects with SAINT [22] and SADABS [23], respectively. The structure was solved using direct methods and refined by full-matrix least-squares method (SHELXL97) [24]. All non-hydrogen atoms were refined with anisotropic displacement parameters. All hydrogen atoms were located in calculated positions to correspond to standard bond lengths and angles. Crystallographic data can be found in Table 2. More detailed information to all structures can be found in the Supporting Information. Elemental analyses were attempted with a Heraeus VARIO ELEMENTAR EL analyzer. No satisfactory elemental analyses of the alkali metal stannides could be obtained. This is in accordance with our own previous observations and also those of other authors which report about similar problems with alkali silyl and germyl compounds [3,9]. Tetrakis(trimethylsilyl)stannane has been prepared following a previously published procedure [6]. 3.1. General procedure 1: preparation of 2 Æ 3THF, 2 Æ 2DME and 2 Æ 12Cr4 To a solution of 100 mg (0.243 mmol) (Me3Si)4Sn 1 in ca. 3 ml THF, DME or benzene and 80 ll (86 mg, 0.490 mmol 12Cr4) 0.15 ml of a 1.6 M solution of MeLi Æ LiBr in diethylether was added with stirring. The reaction mixture immediately turned yellow. Reaction completed within 1 h (THF and DME as solvent) to
3179
12 h (benzene/12Cr4). After quantitative conversion, solvent and all volatiles were removed in vacuo (0.01 mbar, room temperature). The residue was dissolved in 2 ml of the respective solvent which was afterwards evaporated to ensure complete removal of diethylether and other volatiles. To the yellow residue 0.600 ml of C6D6 or DME were added to give samples for NMR spectroscopy from which LiBr was removed by centrifugation prior to use. 3.2. Tris(trimethylsilyl)stannyllithium Æ 3THF, benzene solution NMR data (d in ppm): 1H (C6D6): 3.52 (m, 12H, CH2O), 1.46 (m, 12H, CH2CH2O), 0.55 (s, 27H, (H3C)3 Si, 3 J 1 H–117=119 Sn : 9.9 Hz); 13C (C6D6): 68.51 (CH2O), 25.23 (CH2CH2O), 7.74 ((H3C)3Si, 2 J 13 C–117=119 Sn : 29 24 Hz; 1 J 13 C–29 Si : 36 Hz); Si (C6D6): 13.38 119 (1 J 29 Si–117=119 Sn : 107=102 Hz); Sn (C6D6): 872.2. 3.3. Tris(trimethylsilyl)stannyllithium Æ 2DME, benzene solution NMR data (d in ppm): 1H (C6D6): 3.07 (s, 12H, CH2O), 3.04 (s, 18H, CH3O), 0.49 (s, 27H, (H3C)3Si), 3 J 1 H–117=119 Sn : 9.1 Hz; 13C (C6D6): 70.51 (CH2O), 78.70 2 (CH3O), 7.81 ((H3C)3Si), J 13 C–117=119 Sn : 23 Hz; 1 J 13 C–29 Si : 35 Hz; 29Si (C6D6): 13.40 (1 J 29 Si–117=119 Sn : 138=132 Hz); 119Sn (C6D6): 873.4. 3.4. Tris(trimethylsilyl)stannyllithium Æ 12Cr4, benzene solution NMR data (d in ppm): 1H (C6D6): 3.46 (s, 16H, CH2O), 0.60 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 7.5 Hz); 13C (C6D6): 2 66.85 (CH2O), 8.39 ((H3C)3Si, J 13 C–117=119 Sn : 29 1 22 Hz; J 13 C–29 Si : 34 Hz); Si (C6D6): 12.95 (1 J 29 Si–117=119 Sn : 204=195 Hz); 119Sn (C6D6): 882.1. 3.5. Tris(trimethylsilyl)stannyllithium, DME solution NMR data (d in ppm): 1H (D2O-cap.): 3.87 (s, CH2O), 3.69 (s, CH3O), 0.54 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.8 Hz); 13C (D2O-cap.): 72.21 (CH2O), 2 58.70 (CH3O), 8.37 ((H3C)3Si, J 13 C–117=119 Sn : 29 1 22 Hz; J 13 C–29 Si : 33 Hz); Si (D2O-cap.): 12.95 (1 J 29 Si–117=119 Sn : 287=274 Hz); 119Sn (D2O-cap.): 894.7. 3.6. Tris(trimethylsilyl)stannyllithium Æ 12Cr4, DME solution NMR data (d in ppm): 1H (D2O-cap.): 4.05 (s, 16H, CH2O, 12Cr4), 3.82 (s, CH2O), 3.66 (s, CH3O), 0.51 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.4 Hz); 13C (D2Ocap.): 72.28 (CH2O), 69.77 (CH2O, 12Cr4), 58.56 2 (CH3O), 8.55 ((H3C)3Si, J 13 C–117=119 Sn : 23 Hz;
3180
R. Fischer et al. / Inorganica Chimica Acta 358 (2005) 3174–3182
J 13 C–29 Si : 35 Hz); 29Si (D2O-cap.): 12.83 (1 J 29 Si–117=119 Sn : 328=311 Hz); 119Sn (D2O-cap.): 902.0.
1
3.7. General procedure 2: preparation of 3, 4 and 5 To a solution of 100 mg (0.243 mmol) (Me3Si)4Sn 1 in ca. 3 ml benzene, one equivalent of the respective crown ether (15Cr5 for the preparation of 3 and 18Cr6 for 4 and 5) were added. Upon addition of one equivalent tBuOM and mixing the reaction mixture rapidly turned yellow. The reactions completed within 30 min. Alternatively, one equivalent of tBuOM was added to a solution of 100 mg (0.243 mmol) (Me3Si)4Sn 1 in 3 ml DME to instantly give bright yellow solution. Afterwards solvent and all volatiles were removed in vacuo. The NMR samples were prepared by dissolving the residue in 0.600 ml C6D6. Addition of one equivalent crown ether to the DME solutions provided the solutions of (Me3Si)3SnM Æ crown in DME. 3.8. Tris(trimethylsilyl)stannylsodium Æ 15Cr5, benzene solution Starting materials: 100 mg (0.243 mmol) 1, 24 mg (0.243 mmol) NaOtBu, 48 ll (54 mg, 0.243 mmol) 15Cr5; NMR data (d in ppm): 1H (C6D6): 3.17 (s, 20 H, CH2O), 0.60 (s, 27 H, (H3C)3Si, 3 J 1 H–117=119 Sn : 8.3 Hz); 13 C (C6D6): 68.70 (CH2O), 8.35 ((H3C)3Si, 2 J 13 C–117=119 Sn : 29 24 Hz; 1 J 13 C–29 Si : 34 Hz); Si (C6D6): 12.93 119 (1 J 29 Si–117=119 Sn : 220=210 Hz); Sn (C6D6): 881.6. Crystals suitable for X-ray crystallography of 3 Æ 15cr5 were grown from a solution in toluene at 35 C. 3.9. Tris(trimethylsilyl)stannylpotassium Æ 18Cr6, benzene solution Starting materials: 100 mg (0.243 mmol) 1, 27 mg (0.243 mmol) KOtBu, 64 mg (0.243 mmol) 18Cr6; NMR data (d in ppm): 1H (C6D6): 3.11 (s, 24H, CH2O), 0.59 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 7.3 Hz); 13 C (C6D6): 69.68 (CH2O), 8.58 ((H3C)3Si, 2 J 13 C–117=119 Sn : 24 Hz; 1 J 13 C–29 Si : 34 Hz); 29Si (C6D6): 12.70 (1 J 29 Si–117=119 Sn : 271=259 Hz); 119Sn (C6D6): 892.2. 3.10. Tris(trimethylsilyl)stannylrubidium Æ 18Cr6, benzene solution Starting materials: 100 mg (0.243 mmol) 1, 39 mg (0.243 mmol) RbOtBu, 64 mg (0.243 mmol) 18Cr6; NMR data (d in ppm): 1H (C6D6): 3.20 (s, 24H, CH2O), 0.64 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.5 Hz); 13 C (C6D6): 69.66 (CH2O), 8.79 ((H3C)3Si, 2 J 13 C–117=119 Sn : 22 Hz; 1 J 13 C–29 Si : 33 Hz); 29Si (C6D6): 12.60 (1 J 29 Si–117=119 Sn : 297=283 Hz); 119Sn (C6D6): 890.3.
3.11. Tris(trimethylsilyl)stannylsodium, DME solution Starting materials: 100 mg (0.243 mmol) 1, 24 mg (0.243 mmol) NaOtBu; NMR data (d in ppm): 1H (D2Ocap.): 3.85 (s, CH2O), 3.69 (s, CH3O), 0.54 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 7.1 Hz); 13C (D2O-cap.): 72.21 (CH2O), 58.70 (CH3O), 8.23 ((H3C)3Si, 2 J 13 C–117=119 Sn : 21 Hz; 1 J 13 C–29 Si : 34 Hz); 29Si (D2O-cap.): 13.03 (1 J 29 Si–117=119 Sn : 262=249 Hz); 119Sn (D2O-cap.): 890.3. 3.12. Tris(trimethylsilyl)stannylpotassium, DME solution Starting materials: 100 mg (0.243 mmol) 1, 27 mg (0.243 mmol) KOtBu; NMR data (d in ppm): 1H (D2Ocap.): 3.85 (s, CH2O), 3.67 (s, CH3O), 0.54 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 7.0 Hz); 13C (D2O-cap.): 72.21 (CH2O), 58.60 (CH3O), 8.36 ((H3C)3Si, 2 J 13 C–117=119 Sn : 21 Hz; 1 J 13 C–29 Si : 33 Hz); 29Si (D2O-cap.): 12.88 (1 J 29 Si–117=119 Sn : 295=282 Hz); 119Sn (D2O-cap.): 896.8. 3.13. Tris(trimethylsilyl)stannylrubidium, DME solution Starting materials: 100 mg (0.243 mmol) 1, 39 mg (0.243 mmol) RbOtBu; NMR data (d in ppm): 1H (D2Ocap.): 3.85 (s, CH2O), 3.69 (s, CH3O), 0.54 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.6 Hz); 13C (D2O-cap.): 72.21 (CH2O), 58.70 (CH3O), 8.39 ((H3C)3Si, 2 J 13 C–117=119 Sn : 22 Hz; 1 J 13 C–29 Si : 34 Hz); 29Si (D2O-cap.): 12.73 (1 J 29 Si–117=119 Sn : 300=287 Hz); 119Sn (D2O-cap.): 890.0. 3.14. Tris(trimethylsilyl)stannylsodium Æ 15Cr5, DME solution Starting materials: 100 mg (0.243 mmol) 1, 24 mg (0.243 mmol) NaOtBu, 48 ll (54 mg, 0.243 mmol) 15Cr5; NMR data (d in ppm): 1H (D2O-cap.): 4.00 (s, 20H, CH2O, 15Cr5), 3.81 (s, CH2O), 3.64 (s, CH3O), 0.49 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.3 Hz); 13C (D2O-cap.): 72.25 (CH2O), 70.27 (CH2O, 15Cr5), 58.63 2 (CH3O), 8.63 ((H3C)3Si, J 13 C–117=119 Sn : 21 Hz; 29 1 J 13 C–29 Si : 33 Hz); Si (D2O-cap.): 12.87 (1 J 29 Si–117=119 Sn : 331=316 Hz); 119Sn (D2O-cap.): 900.3. 3.15. Tris(trimethylsilyl)stannylpotassium Æ 18Cr6, DME solution Starting materials: 100 mg (0.243 mmol) 1, 27 mg (0.243 mmol) KOtBu, 64 mg (0.243 mmol) 18Cr6; NMR data (d in ppm): 1H (D2O-cap.): 4.03 (s, 16H, CH2O, 18Cr6), 3.83 (s, CH2O), 3.66 (s, CH3O), 0.50 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.1 Hz); 13C (D2Ocap.): 72.23 (CH2O), 70.55 (CH2O, 18Cr6), 58.50 (CH3O), 8.66 ((H3C)3Si, 2 J 13 C–117=119 Sn : 22 Hz; 1 J 13 C–29 Si : 33 Hz); 29Si (D2O-cap.): 12.86 (1 J 29 Si–117=119 Sn : 343=329 Hz); 119Sn (D2O-cap.): 902.6.
R. Fischer et al. / Inorganica Chimica Acta 358 (2005) 3174–3182
3.16. Tris(trimethylsilyl)stannylrubidium Æ 18Cr6, DME solution Starting materials: 100 mg (0.243 mmol) 1, 39 mg (0.243 mmol) RbOtBu, 64 mg (0.243 mmol) 18Cr6; NMR data (d in ppm): 1H (D2O-cap.): 4.00 (s, 24H, CH2O, 18Cr6), 3.82 (s, CH2O), 3.66 (s, CH3O), 0.50 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.0 Hz); 13C (D2Ocap.): 72.30 (CH2O), 70.61 (CH2O, 18Cr6), 58.60 2 (CH3O), 8.70 ((H3C)3Si, J 13 C–117=119 Sn : 21 Hz; 29 1 J 13 C–29 Si : 33 Hz); Si (D2O-cap.): 12.79 (1 J 29 Si–117=119 Sn : 347=332 Hz); 119Sn (D2O-cap.): 901.8. 3.17. General procedure 3: preparation of 6 A suspension of 100 mg (Me3Si)4Sn 1 in 2 ml DME with 11 mg CsF (0.729 mmol, threefold excess) was stirred at room temperature for 48 h. Solutions of 6 Æ 18Cr6 and 6 Æ [2.2.2]crypt in benzene were prepared by performing the reactions in benzene in the presence of one equivalent crown ether and cryptand, respectively. After removal of excess CsF and all volatiles, NMR samples were prepared by dissolving the residue in C6D6 or DME, respectively. 3.18. Tris(trimethylsilyl)stannylcesium Æ 18Cr6, benzene solution Starting materials: 100 mg (0.243 mmol) 1, 111 mg (0.729 mmol) CsF, 64 mg (0.243 mmol) 18Cr6; NMR data (d in ppm): 1H (C6D6): 3.18 (s, 24H, CH2O), 0.63 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.0 Hz); 13C (C6D6): 69.23 (CH2O), 8.97 ((H3C)3Si, 2 J 13 C–117=119 Sn : 22 Hz; 1 J 13 C–29 Si : 33 Hz); 29Si (C6D6): 12.56 (1 J 29 Si–117=119 Sn : 345=328 Hz); 119Sn (C6D6): 899.4. 3.19. Tris(trimethylsilyl)stannylcesium Æ [2.2.2]crypt, benzene solution Starting materials: 100 mg (0.243 mmol) 1, 111 mg (0.729 mmol) CsF, 92 mg (0.243 mmol) [2.2.2]crypt; NMR data (d in ppm): 1H (C6D6): 3.11 (s, 12H, CH2O), 3.00 (t, 5.1 Hz, 12H, CH2O), 2.04 (t, 5.1 Hz, 12H, CH2O), 0.50 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.0 Hz); 13C (C6D6): 70.48 (CH2O), 68.34 (CH2O), 55.10 (CH2N), 9.05 ((H3C)3Si, 2 J 13 C–117=119 Sn : 22 Hz; 1 J 13 C–29 Si : 34 Hz); 29Si (C6D6): 12.63 (1 J 29 Si–117=119 Sn : 348=330 Hz); 119Sn (C6D6): 901.2. 3.20. Tris(trimethylsilyl)stannylcesium, DME solution Starting materials: 100 mg (0.243 mmol) 1, 111 mg (0.729 mmol) CsF; NMR data (d in ppm): 1H (D2Ocap.): 3.84 (s, CH2O), 3.67 (s, CH3O), 0.53 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 6.5 Hz); 13C (D2O-cap.): 72.21 (CH2O), 58.70 (CH3O), 8.45 ((H3C)3Si,
3181
J 13 C–117=119 Sn : 22 Hz; 1 J 13 C–29 Si : 34 Hz); 29Si (D2Ocap.): 13.15 (1 J 29 Si–117=119 Sn : 311=298 Hz); 119Sn (D2Ocap.): 876.4.
2
3.21. Tris(trimethylsilyl)stannylcesium Æ 18Cr6, DME solution Starting materials: 100 mg (0.243 mmol) 1, 111 mg (0.729 mmol) CsF, 64 mg (0.243 mmol) 18Cr6; NMR data (d in ppm): 1H (D2O-cap.): 4.00 (s, 24H, CH2O, 18Cr6), 3.82 (s, CH2O), 3.66 (s, CH3O), 0.50 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 5.9 Hz); 13C (D2O-cap.): 72.30 (CH2O), 70.35 (CH2O, 12Cr4), 58.58 (CH3O), 8.75 ((H3C)3Si, 2 J 13 C–117=119 Sn : 21 Hz; 1 J 13 C–29 Si : 33 Hz); 29Si (D2O-cap.): 12.80 (1 J 29 Si–117=119 Sn : 358=343 Hz); 119Sn (D2O-cap.): 903.6. 3.22. Tris(trimethylsilyl)stannylcesium Æ [2.2.2]crypt, DME solution Starting materials: 100 mg (0.243 mmol) 1, 111 mg (0.729 mmol) CsF, 92 mg (0.243 mmol) [2.2.2]crypt; NMR data (d in ppm): 1H (D2O-cap.): 3.99 (s, 12H, OCH2CH2O, [2.2.2]crypt), 3.90 (t, 5.1 Hz, 12H, NCH2CH2O, [2.2.2]crypt), 3.81 (CH2O), 3.66 (CH3O), 2.95 (t, 5.1 Hz, 12H, NCH2CH2O, [2.2.2]crypt), 0.51 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 5.9 Hz); 13C (D2Ocap.): 72.33 (CH2O), 71.33 (OCH2CH2O, [2.2.2]crypt), 69.95 (OCH2CH2N, [2.2.2]crypt), 58.60 (CH3O), 56.77 (OCH2CH2N, [2.2.2]crypt), 8.82 ((H3C)3Si, 2 J 13 C–117=119 Sn : 21 Hz; 1 J 13 C–29 Si : 32 Hz); 29Si (D2Ocap.): 12.73 (1 J 29 Si–117=119 Sn : 355=339 Hz); 119Sn (D2Ocap.): 903.6. 3.23. Bis(tris(trimethylsilyl)stannyl)magnesium Æ 2THF To a solution of 125 mg (0.5 mmol) MgBr2 Æ Et2O in 5 ml THF a solution of 1.0 mmol (Me3Si)3SnK (prepared from the reaction of 411 mg 1 and 112 mg KOtBu in THF) in 5 ml THF was added dropwise. Upon addition, the yellow colour of the anion solution vanished and white precipitate was formed. After complete addition, the reaction mixture was stirred for 30 min after which all volatiles are removed in vacuo. The residue was extracted three times with 2 ml portions of n-pentane. Upon concentration to incipient crystallization and cooling to 35 C 342 mg (81% yield) colourless needles of 7 Æ 2THF were obtained. NMR data (d in ppm): 1H (C6D6): 3.59 (m, 8H, CH2O), 1.20 (m, 8H, CH2CH2O), 0.42 (s, 27H, (H3C)3Si, 3 J 1 H–117=119 Sn : 14.6 Hz); 13C (C6D6): 69.52 (CH2O), 24.80 (CH2CH2O), 6.55 ((H3C)3Si, 2 J 13 C–117=119 Sn : 28 Hz; 1 J 13 C–29 Si : 42 Hz); 29Si (C6D6): 12.28 (1 J 29 Si–117=119 Sn : 123=117 Hz); 119Sn (C6D6): 830.2.
3182
R. Fischer et al. / Inorganica Chimica Acta 358 (2005) 3174–3182
4. Supplementary material Data for 3 Æ 15Cr5 has been deposited at the Cambridge Crystallographic Deposition Centre: CCDC 262663. The data can be retrieved via www.ccdc.cam. ac.uk/conts/retrieving.html or can be ordered at the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB21Ez, fax: +44 1223 336 033.
Acknowledgements The authors acknowledge funds from the Fonds zur Fo¨rderung der Wissenschaftlichen Forschung (FWF, Austria) (START project Y-120), the Graz University of Technology (Austria), the Deutsche Forschungsgemeinschaft (DFG, Germany) and the Fonds der chemischen Industrie (Germany). WACKER GmbH, Burghausen, Germany is gratefully acknowledged for donation of chlorosilanes. References [1] (a) P.D. Lickiss, C.M. Smith, Coord. Chem. Rev. 145 (1995) 75; (b) K. Tamao, A. Kawachi, Adv. Organomet. Chem. 38 (1995) 1; (c) J. Belzner, U. Dehnert, in: Z. Rappoport, Y. Apeloig (Eds.), The Chemistry of Organic Silicon Compounds, vol. 2, Wiley, New York, 1998, pp. 779–825; (d) A. Sekiguchi, V.Y. Lee, M. Nanjo, Coord. Chem. Rev. 210 (2000) 11; (e) R. Fischer, D. Frank, W. Gaderbauer, C. Kayser, C. Mechtler, J. Baumgartner, C. Marschner, in: P. Jutzi, U. Schubert (Eds.), Silicon chemistry, Verlag Chemie, Weinheim, 2003, pp. 118–129. [2] W. Teng, K. Ruhlandt-Senge, Organometallics 23 (2004) 952. [3] J. Fischer, J. Baumgartner, C. Marschner, Organometallics 24 (2005) 1263. [4] P. Riviere, A. Castel, M. Riviere-Baudet, in: Z. Rappoport (Ed.), The Chemistry of Organic Germanium, Tin and Lead Compounds, vol. 2, Wiley, New York, 2002, pp. 653–748. [5] F. Preuss, T. Wieland, J. Perner, G. Heckmann, Z. Naturforsch. 47B (1992) 1355. [6] G. Becker, M. Gekeler, H.-M. Hartmann, O. Mundt, M. Westerhausen, in: Synthetic Methods in Organometallic and Inorganic Chemistry (Series Editor: W. A. Herrmann), vol. 2 (Volume Editors: N. Auner, U. Klingebiel), Thieme, Stuttgart, 1996, pp. 186–192.
[7] C.J. Cardin, D.J. Cardin, W. Clegg, S.J. Coles, S.P. Constantine, J.R. Rowe, S.J. Teat, J. Organomet. Chem. 573 (1999) 96. [8] (a) C. Marschner, Eur. J. Inorg. Chem. (1998) 221–226; (b) C. Kayser, R. Fischer, J. Baumgartner, C. Marschner, Organometallics 21 (2002) 1023; (c) R. Fischer, D. Frank, W. Gaderbauer, C. Kayser, C. Mechtler, J. Baumgartner, C. Marschner, Organometallics 22 (2003) 3723. [9] D.M. Jenkins, W. Teng, U. Englich, D. Stone, K. RuhlandtSenge, Organometallics 20 (2001) 4600. [10] U. Englich, K. Hassler, K. Ruhlandt-Senge, F. Uhlig, Inorg. Chem. 37 (1998) 3532. [11] H. Sato, N. Isono, K. Okamura, T. Date, M. Mori, Tetrahedron Lett. 35 (1994) 2035. [12] (a) J.D. Farwell, M.F. Lappert, C. Marschner, C. Strissel, T.D. Tilley, J. Organomet. Chem. 603 (2000) 185–188; (b) W. Teng, K. Ruhlandt-Senge, Organometallics 23 (2004) 2694; (c) J. Arnold, T.D. Tilley, A.L. Rheingold, S.J. Geib, Inorg. Chem. 26 (1987) 2106; (d) H.F. Klein, J. Montag, U. Zucha, Inorg. Chim. Acta 177 (1990) 43; (e) M. Nanjo, T. Oda, K. Mochida, Chem. Lett. (2002) 108; (f) M. Nanjo, T. Oda, K. Mochida, J. Organomet. Chem. 672 (2003) 100. [13] M.A. Paver, C.A. Russell, D.S. Wright, Angew. Chem. 107 (1995) 1679. [14] M.A. Paver, C.A. Russell, D.S. Wright, Angew. Chem., Int. Ed. Engl. 34 (1995) 1545. [15] H.J. Reich, J.P. Borst, R.R. Dykstra, Organometallics 13 (1994) 1. [16] D. Reed, D. Stalke, D.S. Wright, Angew. Chem 103 (1991) 1539. [17] D. Reed, D. Stalke, D.S. Wright, Angew. Chem., Int Ed. Engl. 30 (1991) 1459. [18] T. Fukawa, M. Nakamoto, V.Y. Lee, A. Sekiguchi, Organometallics 23 (2004) 2376. [19] M. Nanjo, E. Nanjo, K. Mochida, Eur. J. Inorg. Chem. (2004) 2961. [20] A.B. Pangborn, M.A. Giardello, R.H. Grubbs, R.K. Rosen, F.J. Timmers, Organometallics 15 (1996) 1518. [21] (a) G.A. Morris, R.J. Freeman, J. Am. Chem. Soc. 101 (1979) 760; (b) B.J. Helmer, R. West, Organometallics 1 (1982) 877. [22] SAINTPLUS: Software Reference Manual, Version 6.45, BrukerAXS, Madison, WI, 1997–2003. [23] R.H. Blessing, Acta Crystallogr. Sect., A 51 (1995) 33, SADABS: Bruker/Siemens Area Detector Absorption and Other Corrections Version 2.10 Bruker AXS 1998–2003. [24] G.M. Sheldrick, SHELX97 Programs for Crystal Structure Analysis (Release 97-2), Universita¨t Go¨ttingen, Go¨ttingen, Germany, 1998.