Neutral Hexacoordinate Silicon(iv) Complexes with ... - ACS Publications

Organometallics 2009, 28, 2311–2317

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Neutral Hexacoordinate Silicon(IV) Complexes with an SiSO3NC Skeleton and a Neutral Pentacoordinate Silicon(IV) Complex Containing a Trianionic Tetradentate O,N,O,O Ligand Stefan Metz, Christian Burschka, and Reinhold Tacke* UniVersita¨t Wu¨rzburg, Institut fu¨r Anorganische Chemie, Am Hubland, D-97074 Wu¨rzburg, Germany ReceiVed December 22, 2008

The neutral hexacoordinate silicon(IV) complexes 8-10 (SiSO3NC skeleton) were synthesized by replacement of the chloro ligand of the pentacoordinate chlorosilicon(IV) complex 5 by monoanionic bidentate O,O ligands of the acetylacetonato type. For that purpose, compound 5 was treated with compounds of the formula type R1C(O)-CHdC(OSiMe3)R2 (R1 ) R2 ) Me; R1 ) R2 ) Ph; R1 ) Me, R2 ) Ph). In contrast, treatment of 5 with PhC(O)-CHdC(OSiMe3)CF3 afforded the neutral pentacoordinate silicon(IV) complex 11 · CH3CN (SiO3NC skeleton). The identities of 8-10 and 11 · CH3CN were established by elemental analyses and solid-state and solution NMR experiments; additionally, the solvates 8 · CH3CN, 9 · CH3CN, 10 · CH3CN, and 11 · 2CH3CN were studied by single-crystal X-ray diffraction. Introduction Higher-coordinate silicon(IV) complexes have been studied extensively over the last three decades.1,2 Most of these compounds have been synthesized from silane precursors (i.e., compounds with tetracoordinate silicon atoms), whereas it is rare to find higher-coordinate silicon compounds themselves used as starting materials. Compounds 1,3 2,4 3,5 and 45 are selected examples for hexacoordinate silicon(IV) complexes that have been obtained from higher-coordinate silicon precursors. * To whom correspondence should be addressed. Phone: +49-931-8885250. Fax: +49-931-888-4609. E-mail: [email protected]. (1) Selected reviews dealing with higher-coordinate silicon compounds: (a) Chuit, C.; Corriu, R. J. P.; Reye, C.; Young, J. C. Chem. ReV. 1993, 93, 1371–1448. (b) Verkade, J. G. Coord. Chem. ReV. 1994, 137, 233–295. (c) Lukevics, E.; Pudova, O. A. Chem. Heterocycl. Compd. (Engl. Transl.) 1996, 32, 1381–1418. (d) Holmes, R. R. Chem. ReV. 1996, 96, 927–950. (e) Kost, D.; Kalikhman, I. In The Chemistry of Organic Silicon Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley: Chichester, U.K., 1998; Vol. 2, Part 2, pp 1339-1445. (f) Pestunovich, V.; Kirpichenko, S.; Voronkov, M. In The Chemistry of Organic Silicon Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley: Chichester, U.K., 1998; Vol. 2, Part 2, pp 14471537. (g) Chuit, C.; Corriu, R. J. P.; Reye, C. In Chemistry of HyperValent Compounds; Akiba, K.-y., Ed.; Wiley-VCH: New York, 1999; pp 81146. (h) Tacke, R.; Pu¨lm, M.; Wagner, B. AdV. Organomet. Chem. 1999, 44, 221–273. (i) Brook, M. A. Silicon in Organic, Organometallic, and Polymer Chemistry; Wiley: New York, 2000; pp 97-114. (j) Tacke, R.; Seiler, O. In Silicon Chemistry: From the Atom to Extended Systems; Jutzi, P., Schubert, U., Eds.; Wiley-VCH: Weinheim, Germany, 2003; pp 324337. (k) Kost, D.; Kalikhman, I. AdV. Organomet. Chem. 2004, 50, 1–106. (2) Selected recent publications dealing with higher-coordinate silicon compounds: (a) Spiniello, M.; White, J. M. Organometallics 2008, 27, 994– 999. (b) Negrebetsky, V. V.; Taylor, P. G.; Kramarova, E. P.; Shipov, A. G.; Pogozhikh, S. A.; Ovchinnikov, Y. E.; Korlyukov, A. A.; Bowden, A.; Bassindale, A. R.; Baukov, Y. I. J. Organomet. Chem. 2008, 693, 1309– 1320. (c) Gonza´lez-Garcı´a, G.; Gutie´rrez, J. A.; Cota, S.; Metz, S.; Bertermann, R.; Burschka, C.; Tacke, R. Z. Anorg. Allg. Chem. 2008, 634, 1281–1286. (d) Lippe, K.; Gerlach, D.; Kroke, E.; Wagler, J. Inorg. Chem. Commun. 2008, 11, 492–496. (e) Haga, R.; Burschka, C.; Tacke, R. Organometallics 2008, 27, 4395–4400. (f) Fester, G. W.; Wagler, J.; Brendler, E.; Bo¨hme, U.; Roewer, G.; Kroke, E. Chem. Eur. J. 2008, 14, 3164–3176. (g) Theis, B.; Burschka, C.; Tacke, R. Chem. Eur. J. 2008, 14, 4618–4630. (h) Setaka, W.; Nirengi, T.; Kabuto, C.; Kira, M. J. Am. Chem. Soc. 2008, 130, 15762–15763. (i) Yamamura, M.; Kano, N.; Kawashima, T.; Matsumoto, T.; Harada, J.; Ogawa, K. J. Org. Chem. 2008, 73, 8244– 8249. (j) Kertsnus-Banchik, E.; Kalikhman, I.; Gostevskii, B.; Deutsch, Z.; Botoshansky, M.; Kost, D. Organometallics 2008, 27, 5285–5294.

The pentacoordinate silicon(IV) complexes 66 and 77 are further examples; they can be synthesized from the corresponding chlorosilicon(IV) complex 56 via chloro/iodo and chloro/nitrato exchange by treatment of 5 with Me3SiI and Me3SiONO2, respectively. Inspired by these results, we have attempted to use an analogous strategy to prepare novel neutral hexacoordinate silicon(IV) complexes with an SiSO3NC skeleton by replacing the chloro ligand of 5 (SiClSONC skeleton) with monoanionic bidentate O,O ligands of the acetylacetonato type. This was a challenging approach as so far only three hexacoordinate silicon(IV) complexes with Si-S bonds have been described in the literature (compounds with two identical dianionic S,N,O ligands and SiS2O2N2 skeletons each).8 Furthermore, this approach should allow the synthesis of novel hexacoordinate silicon(IV) complexes with different types of mono-, bi-, and tridentate ligands with varied ligand atoms. Utilizing this strategy, we have succeeded in synthesizing compounds 8-10 by treatment of 5 with compounds of the formula type R1C(O)-CHdC(OSiMe3)R2 (R1 ) R2 ) Me; R1 ) R2 ) Ph; R1 ) Me, R2 ) Ph). In contrast, treatment of 5 with the related reagent PhC(O)-CHdC(OSiMe3)CF3 afforded the pentacoordinate silicon(IV) complex 11. We report here on the syntheses of compounds 8-10 and 11 · CH3CN and their characterization by solid-state (13C, 15N, 29Si) and solution NMR spectroscopy (1H, 13C, 19F (11 only), 29Si). In addition, the solvates 8 · CH3CN, 9 · CH3CN, 10 · CH3CN, and 11 · 2CH3CN were structurally characterized by single-crystal X-ray diffraction. (3) Kalikhman, I.; Gostevskii, B.; Kingston, V.; Krivonos, S.; Stalke, D.; Walfort, B.; Kotte, T.; Kocher, N.; Kost, D. Organometallics 2004, 23, 4828–4835. (4) Schley, M.; Wagler, J.; Roewer, G. Z. Anorg. Allg. Chem. 2005, 631, 2914–2918. (5) Seiler, O.; Burschka, C.; Fenske, T.; Troegel, D.; Tacke, R. Inorg. Chem. 2007, 46, 5419–5424. (6) Metz, S.; Burschka, C.; Platte, D.; Tacke, R. Angew. Chem. 2007, 119, 7136–7139; Angew. Chem., Int. Ed. 2007, 46, 7006-7009. (7) Metz, S.; Burschka, C.; Tacke, R. Organometallics 2008, 27, 6032– 6034. (8) Metz, S.; Burschka, C.; Tacke, R. Eur. J. Inorg. Chem. 2008, 4433– 4439.

10.1021/om801208t CCC: $40.75  2009 American Chemical Society Publication on Web 03/11/2009

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Metz et al. Scheme 2

Results and Discussion Syntheses. Compounds 8-10 were synthesized by treatment of 5 with the respective acetylacetone derivatives of the formula type R1C(O)-CHdC(OSiMe3)R2 (12, R1 ) R2 ) Me; 13, R1 ) R2 ) Ph; 14, R1 ) Me, R2 ) Ph; Scheme 1). All syntheses were carried out in acetonitrile at 20 °C, and all products were isolated as solids (yields: 8, 57%; 9, 89%; 10, 87%). Treatment of 5 with PhC(O)-CHdC(OSiMe3)CF3 (15) in acetonitrile did not yield the expected hexacoordinate silicon(IV) complex 11′. Instead, the pentacoordinate silicon(IV) complex 11 was obtained (isolated as the solvate 11 · CH3CN; 79% yield; Scheme 2). A possible explanation for the formation of 11 (SiO3NC skeleton) is as follows: in the first step, the expected product 11′ is formed, followed by cleavage of the Si-S bond and intramolecular formation of a new S-C bond, thereby generating a tetradentate trianionic O,N,O,O ligand. The coordination of this ligand to the silicon atom leads to a tetracyclic ring system consisting of two 6-membered rings, one 7-membered ring, and one 9-membered ring. The silicon atom and the CF3-bound carbon atom represent the two bridgehead atoms of this system. The assumption that 11′ is formed as an intermediate is supported by the color change of the reaction mixture: a solution of 5 in acetonitrile is yellow, and upon Scheme 1

addition of the pale yellow reagent 15 an orange-colored mixture is formed. This mixture turns pale yellow after a short time, and upon storage at -20 °C for a few days colorless crystals of 11 · 2CH3CN are obtained. As compounds 8-10 are also colored (8, yellow; 9, red; 10, orange), the transient orange color of the reaction mixture could be assigned to the intermediate 11′. However, all attempts to identify 11′ unequivocally by NMR studies (1H, 13C, 19F, and 29Si) of freshly prepared mixtures of 5 and 15 in CD3CN failed. The different behavior of 8-10 (stable compounds) and 11′ (transformation into 11) might be explained by the high electrophilicity of the CF3-bound carbon atom of 11′. However, further studies are necessary to evaluate the reaction mechanism for the formation of 11.9 In this context it should be mentioned that analogous thermally induced rearrangements of compounds 8-10 to the respective pentacoordinate species (heating of solutions of 8-10 in C2D2Cl4 to 80 °C for 6 h (8 and 10) or 30 h (9)) were not observed. Crystal Structure Analyses. The crystal data and the experimental parameters used for the crystal structure analyses of 8 · CH3CN, 9 · CH3CN, 10 · CH3CN, and 11 · 2CH3CN are given in Table 1. The molecular structures of 8-11 are shown in Figures 1-4; selected bond distances and angles are given in the respective figure legends. The Si-coordination polyhedra of 8-10 are distorted octahedra. The maximum deviation from the ideal 180° and 90° angles are 8.00(8)° and 7.50(8)°, respectively. The tridentate S,N,O ligand shows a mer coordination, with S-Si-O1 angles in the range 172.59(4)-174.06(6)°). These angles differ significantly from the S-Si-O angles of the pentacoordinate silicon compounds 5-7 (S-Si-O, 124.37(8)-129.24(5)°), where the sulfur and oxygen ligand atoms of the tridentate S,N,O ligand occupy equatorial sites of a trigonal-bipyramidal Sicoordination polyhedron, whereas the nitrogen ligand atom is found in an axial position. The Si-S bond lengths of 8-10 range from 2.2744(7) to 2.3142(4) Å and are similar to those of the structurally related neutral hexacoordinate silicon(IV) complexes 16 and 17 (SiS2O2N2 skeletons; 2.2666(5)-2.2988(9) Å).8 The Si-N (Si-C) distances of 8-10 are in the range 1.9058(8)-1.9297(12) Å (1.928(2)-1.9415(14) Å). The Si-O1 bond lengths (1.7733(15)-1.7900(11) Å) are somewhat shorter than the Si-O2 and Si-O3 distances of the bidentate O,O ligands. The Si-O2 bond lengths are in the range 1.8437(8)(9) All attempts to isolate the free tetradentate ligand by treatment of 11 with ethanol failed. (10) (a) Seiler, O.; Bertermann, R.; Buggisch, N.; Burschka, C.; Penka, M.; Tebbe, D.; Tacke, R. Z. Anorg. Allg. Chem. 2003, 629, 1403–1411. (b) Tacke, R.; Bertermann, R.; Penka, M.; Seiler, O. Z. Anorg. Allg. Chem. 2003, 629, 2415–2420.

Neutral Hexacoordinate Silicon(IV) Complexes

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Table 1. Crystal Data and Experimental Parameters for the Crystal Structure Analyses of 8 · CH3CN, 9 · CH3CN, 10 · CH3CN, and 11 · 2CH3CN empirical formula formula mass, g mol-1 collection T, K λ(Mo KR), Å crystal system space group (No.) a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z D(calc), g cm-3 µ, mm-1 F(000) crystal dimensions, mm 2θ range, deg index ranges no. of collected reflns no. of independent reflns Rint no. of reflns used no. of parameters restraints Sa weight parameters a/bb R1c [I > 2σ(I)] wR2d (all data) max/min residual electron density, e Å-3 c

8 · CH3CN

9 · CH3CN

10 · CH3CN

11 · 2CH3CN

C24H26N2O3SSi 450.62 98(2) 0.71073 triclinic P1j (2) 7.5308(7) 11.6477(12) 14.5508(16) 106.609(4) 101.440(4) 102.127(4) 1149.4(2) 2 1.302 0.221 476 0.18 × 0.04 × 0.04 3.04-55.12 -9 e h e 9, -15 e k e 14, -18 e l e 18 19955 5222 0.0625 5222 285 0 1.018 0.0776/0.3264 0.0492 0.1388 +0.724/-0.481



C31H28F3N3O3SSi 607.71 193(2) 0.71073 monoclinic C2/c (15) 26.673(4) 11.1479(17) 22.257(3) 90 112.343(15) 90 6121.2(15) 8 1.319 0.200 2528 0.5 × 0.5 × 0.4 5.18-56.04 -35 e h e 35, -14 e k e 14, -29 e l e 29 39014 7293 0.0349 7293 412 84 1.043 0.0682/2.3814 0.0428 0.1193 +0.369/-0.307

a S ) {Σ[w(Fo2 - Fc2)2]/(n - p)}0.5; n ) no. of reflections; p ) no. of parameters. b w-1 ) σ2(Fo2) + (aP)2 + bP, with P ) [max(Fo2,0) + 2Fc2]/3. R1 ) Σ|Fo| - |Fc|/Σ|Fo|. d wR2 ) {Σ[w(Fo2 - Fc2)2]/Σ[w(Fo2)2]}0.5.

Figure 1. Molecular structure of 8 in the crystal of 8 · CH3CN (probability level of displacement ellipsoids 50%). Selected bond lengths (Å) and angles (deg): Si-S 2.2965(8), Si-O1 1.7733(15), Si-O2 1.8505(16), Si-O3 1.7988(15), Si-N1 1.9107(17), Si-C1 1.928(2), O1-C8 1.316(2), C8-C9 1.364(3), C9-C10 1.409(3), C10-N1 1.328(3), O3-C18 1.299(3), C18-C19 1.374(3), C19-C20 1.390(3), O2-C20 1.282(2); S-Si-O1 174.06(6), S-Si-O2 89.36(5), S-Si-O3 91.02(5), S-Si-N1 85.32(5), S-Si-C1 94.03(6), O1-Si-O2 84.96(7), O1-Si-O3 90.73(7), O1-Si-N1 92.22(7), O1-Si-C1 91.66(8), O2-Si-O3 89.91(7), O2-Si-N1 82.95(7), O2-Si-C1 176.61(8), O3-Si-N1 172.00(8), O3-Si-C1 89.84(8), N1-Si-C1 97.50(8).

Figure 2. Molecular structure of 9 in the crystal of 9 · CH3CN (probability level of displacement ellipsoids 50%). Selected bond lengths (Å) and angles (deg): Si-S 2.2744(7), Si-O1 1.7900(11), Si-O2 1.8492(10), Si-O3 1.8006(11), Si-N1 1.9297(12), Si-C1 1.9415(14), O1-C3 1.3150(17), C3-C4 1.363(2), C4-C5 1.431(2), C5-N1 1.3236(16), O3-C24 1.3016(15), C24-C25 1.3861(18), C25-C26 1.4088(17), O2-C26 1.2851(15); S-Si-O1 173.81(4), S-Si-O2 89.92(4), S-Si-O3 90.65(4), S-Si-N1 86.68(4), S-Si-C1 93.09(5), O1-Si-O2 83.90(5), O1-Si-O3 89.55(5), O1-Si-N1 92.41(5), O1-Si-C1 93.10(6), O2-Si-O3 89.37(5), O2-Si-N1 84.14(5), O2-Si-C1 176.95(6), O3-Si-N1 172.98(5), O3-Si-C1 90.09(5), N1-Si-C1 96.53(6).

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Metz et al. Table 2. Bond Lengths (Å) of the Ligand Backbones of 8 · CH3CN, 9 · CH3CN, and 10 · CH3CN bidentate ligand

tridentate ligand

Figure 3. Molecular structure of 10 in the crystal of 10 · CH3CN (probability level of displacement ellipsoids 50%).12 Selected bond lengths (Å) and angles (deg): Si-S 2.3142(4), Si-O1 1.7795(8), Si-O2 1.8437(8), Si-O3 1.8049(7), Si-N1 1.9058(8), Si-C1 1.9313(10), O1-C16 1.3148(12), C16-C15 1.3742(14), C15-C14 1.4213(14), N1-C14 1.3254(12), O2-C21 1.2851(12), O3-C19 1.2933(13), C19-C20 1.3826(17), C20-C21 1.3957(15); S-Si-O1 172.58(3), S-Si-O2 87.47(3), S-Si-O3 92.66(3), S-Si-N1 85.44(3), S-Si-C1 93.82(3), O1-Si-O2 85.69(3), O1-Si-O3 90.23(4), O1-Si-N1 90.98(4), O1-Si-C1 93.03(4), O2-Si-O3 90.42(4), O2-Si-N1 83.71(4), O2-Si-C1 178.71(4), O3-Si-N1 173.90(4), O3-Si-C1 89.54(4), N1-Si-C1 96.37(4).

Figure 4. Molecular structure of 11 in the crystal of 11 · 2CH3CN (probability level of displacement ellipsoids 50%). Selected bond lengths (Å) and angles (deg): Si-O1 1.8150(11), Si-O2 1.7388(10), Si-O3 1.6855(12), Si-N1 1.8247(14), Si-C1 1.8815(16), S-C17 1.7677(18), S-C19 1.9004(16), O1-C8 1.303(2), C8-C9 1.374(3), C9-C10 1.401(2), C10-N1 1.349(2), O2-C19 1.3845(17), O3-C21 1.3693(17), C19-C20 1.486(2), C20-C21 1.338(2); O1-Si-O2 179.54(6), O1-Si-O3 84.90(5), O1-Si-N1 89.30(6), O1-Si-C1 89.45(6), O2-Si-O3 94.69(5), O2-Si-N1 91.07(5), O2-Si-C1 90.60(6), O3-Si-N1 114.75(6), O3-Si-C1 124.41(7), N1-Si-C1 120.43(7), C17-S-C19 99.23(7).

1.8505(16) Å and are about 0.05 Å longer than the respective Si-O3 bond distances (1.7988(15)-1.8049(7) Å). These differences between the two Si-O bond lengths of the bidentate O,O ligands are larger than those determined for the related compounds 3 and 18-205,10 and similar to those of 21.11 This might indicate that the electrons in the O,O ligand backbones of 8-10 are not ideally delocalized, implying an increase of

bond

8 · CH3CN

9 · CH3CN

10 · CH3CN

O2-C O3-C ∆(O-C) (O2-)C-C C-C(-O3) ∆(C-C) O1-C N-C (O1-)C-C C-C(-N) ∆(C-C)

1.282(2) 1.299(3) 0.017 1.390(3) 1.374(3) 0.016 1.316(2) 1.328(3) 1.364(3) 1.409(3) 0.045

1.2851(15) 1.3016(15) 0.017 1.4088(17) 1.3861(18) 0.023 1.3150(17) 1.3236(16) 1.363(2) 1.431(2) 0.068

1.2851(12) 1.2933(12) 0.008 1.3957(15) 1.3826(17) 0.013 1.3144(18) 1.3249(18) 1.374(2) 1.421(2) 0.047

the carbonyl character of the C-O2 bond. Further evidence for this can be seen in the differences between the respective C-O and C-C bond distances of the (O)C-C-C(O) ligand backbones (Table 2). Nevertheless, these bond distances indicate a high degree of electron delocalization. In contrast, the (O)C-C-C(N) backbones of the tridentate ligands of 8-10 are best described as imino-enolato-type ligands, with differences between the respective C-C bond distances in the range 0.045-0.068 Å, which are significantly larger than the analogous differences observed for the bidentate ligands (0.013-0.023 Å).

The Si-coordination polyhedron of 11 is best described as a slightly distorted trigonal bipyramid, with maximum deviations from the ideal 180° and 90° angles of 0.46(6)° and 5.10(5)°, respectively. The equatorial bond angles O3-Si-N1, O3-Si-C1, and N1-Si-C1 are in the range 114.75(6)-124.41(7)°; the sum of these angles is 360°. The Si-N1 bond length was found to be 1.8247(14) Å. As expected, the equatorial Si-O3 bond distance (1.6855(12) Å) is shorter than the axial Si-O1 and Si-O2 bond lengths. Interestingly, the Si-O1 bond (1.8150(11) Å) is significantly longer than the Si-O2 bond (1.7388(10) Å), probably due to the different degree of electron delocalization in the respective ligand backbones. The O2-C19 and O3-C21 bond distances of 11 are greater than the analogous O-C bond lengths of 8-10 and can be described as single bonds; both the C19-C20 (1.486(2) Å) and C20-C21 bond distances (1.338(2) Å) differ significantly. Compared with 8-10, the degree of electron delocalization in the (O)C-C-C(N) skeleton appears (11) Xu, C.; Baum, T. H.; Rheingold, A. L. Inorg. Chem. 2004, 43, 1568–1573. (12) The phenyl group of the bidentate ligand of 10 · CH3CN is slightly disordered; however, starting from disordered carbon atoms of the phenyl moiety and refinement of the structural parameters did not give a significantly better R1 value.

Neutral Hexacoordinate Silicon(IV) Complexes

to be higher in the case of 11, because the C8-C9 (1.374(3) Å) and C9-C10 bond lengths (1.401(2) Å) are very similar. This increases the carbonyl character of the O1-C8 bond and thus results in an elongation of the Si-O1 bond of 11. NMR Studies. The isotropic 29Si chemical shifts obtained in the solid-state NMR studies of 8-10 clearly indicate the presence of hexacoordinate silicon atoms (8, δ -160.6; 9, δ -159.1; 10, δ -157.9). These chemical shifts correlate well with those found for structurally related silicon(IV) complexes with an SiS2O2N2 skeleton (16, δ -156.9; 17, δ -172.6).8 The 29 Si chemical shifts obtained in the solution NMR studies (solvent, CD2Cl2: 8, δ -158.9; 9, δ -158.3; 10, δ -158.7) are very similar to those obtained in the solid state, indicating that 8-10 also exist in solution. 29Si NMR studies of 11 · CH3CN (solid state, δ -124.6; solution (solvent, CD2Cl2), δ -124.6) also indicate that the molecular structures in the solid state and in solution are similar; no evidence to suggest the existence of a hexacoordinate silicon species can be seen. The isotropic 15N chemical shifts of 8-10 in the solid state (8, δ -171.8; 9, δ -171.8; 10, δ -166.2) are very similar, differing significantly from that of 11 · CH3CN (δ -204.6). This can be explained by different binding situations of the nitrogen atoms. The solution 1 H NMR spectra of 9 and 11 (solvent, CD2Cl2) showed well resolved resonance signals at 296 K. In contrast, the 1H NMR spectrum of 8 showed one broad resonance signal for the two methyl groups of the bidentate O,O ligand (solvent, CD2Cl2; 296 K; δ 1.9-2.1 (br. s, 6 H)). High-temperature measurements led to one sharp singlet at 353 K (solvent, C2D2Cl4; δ 2.00 (s, 6 H)), whereas low-temperature experiments gave two different resonance signals for the two methyl groups (solvent, CD2Cl2; 253 K; δ 1.8 (br. s, 3 H) and 2.10 (s, 3 H)). A further decrease of the temperature led to a broadening of all resonance signals, indicating the existence of more than one isomer. At 193 K, two signal sets were detected, but most signals were still broad and poorly resolved. In the case of 10, the 1H NMR spectrum at 296 K showed broad resonance signals, and similar results were obtained in the 13C and 29Si NMR measurements. The 1H NMR spectra at higher temperatures (solvent, C2D2Cl4; 363 K) showed a better resolved single signal set for 10. Lowtemperature 1H NMR experiments (solvent, CD2Cl2; 263 K) produced two different sets of resonance signals, indicating the existence of two isomers (ratio, ca. 2:1). This assumption is supported by the 29Si NMR spectrum of 10, which also showed two resonance signals at 263 K (δ -159.3 and -159.1). Again, upon further cooling, broadening of the resonance signals was observed, indicating the existence of more than two isomers. Unfortunately, the low stability of 8 and 10 in solution at higher temperatures did not allow the measurement of 29Si NMR spectra. All variable-temperature effects in the NMR spectra of 8 and 10 were reversible and can be interpreted in terms of dynamic isomerization processes. Although the nature of the isomers could not be determined, one can speculate that mer or fac coordination of the tridentate S,N,O ligand to the silicon atom is possible. The high flexibility of this ligand is reflected by the different coordination modes observed for 5-7 and 8-10 (in this context, see also ref 8). In the case of 10, different coordination modes of the unsymmetric bidentate O,O ligand can also lead to different isomers, which might explain why the low-temperature NMR experiments with 10 indicate the existence of more isomers than in the case of 8 that contains a symmetric bidentate O,O ligand.

Conclusions Replacement of the chloro ligand of the neutral pentacoordinate chlorosilicon(IV) complex 5 by other monoanionic

Organometallics, Vol. 28, No. 7, 2009 2315

monodentate ligands via elimination of chlorotrimethylsilane is an efficient method for the synthesis of further neutral pentacoordinate silicon(IV) complexes with different types of monodentate ligands, such as compounds 6 and 7. With the preparation of 8-10, we have now demonstrated that the same approach is also useful for the synthesis of neutral hexacoordinate silicon(IV) complexes. Compounds 8-10 are the first examples of this type that contain an SiSO3NC skeleton. Future studies have yet to evaluate whether this approach can be used for the synthesis of further hexacoordinate silicon compounds with other combinations of ligand atoms in the silicon coordination sphere. The synthesis of the neutral pentacoordinate silicon(IV) complex 11 shows that the Si-S bond of 5 can also serve as a reactive site. The transformation of 5 into 11 (probably via the intermediate 11′) is a remarkable example for the formation of a new ligand system in the silicon coordination sphere. From a formal point of view, a dianionic tridentate S,N,O ligand and a monoanionic bidentate O,O ligand are fused to give a novel trianionic tetradentate O,N,O,O ligand.

Experimental Section General Procedures. All syntheses were carried out under dry nitrogen. The organic solvents used were dried and purified according to standard procedures and stored under nitrogen. Melting points were determined with a Bu¨chi Melting Point B-540 apparatus using samples in sealed glass capillaries. The 1H, 13C, 19F, and 29Si solution NMR spectra were recorded at 23 °C (unless otherwise stated) on a Bruker DRX-300 (1H, 300.1 MHz; 13C, 75.5 MHz; 19 F, 282.4 MHz; 29Si, 59.6 MHz) or a Bruker Avance 500 NMR spectrometer (1H, 500.1 MHz; 13C, 125.8 MHz; 29Si, 99.4 MHz) using CD2Cl2 or C2D2Cl4 as the solvent. Chemical shifts (ppm) were determined relative to internal CHDCl2 (1H, δ 5.32), internal C2HDCl4 (1H, δ 5.91), internal CD2Cl2 (13C, δ 53.8), external CFCl3 (19F, δ 0), or external TMS (29Si, δ 0). The solid-state 13C, 15N, and 29Si VACP/MAS NMR spectra were recorded at 22 °C on a Bruker DSX-400 NMR spectrometer with bottom layer rotors of ZrO2 (diameter, 7 mm) containing ca. 300 mg of sample (13C, 100.6 MHz; 15N, 40.6 MHz; 29Si, 79.5 MHz; external standard, TMS (13C, 29 Si; δ 0) or glycine (15N, δ -342.0); spinning rate, 5.5-7 kHz; contact time, 2 ms (13C), 3 ms (15N), or 5 ms (29Si); 90° 1H transmitter pulse length, 3.2-3.6 µs; repetition time, 4-5 s. Preparation of Compound 5. This compound was synthesized according to ref 6. Preparation of Compound 8. Compound 12 (311 mg, 1.80 mmol) was added at 20 °C in a single portion to a stirred suspension of 5 (500 mg, 1.45 mmol) in acetonitrile (25 mL). The resulting mixture was stirred at 20 °C for 2 min, the undissolved residue was filtered off and discarded, and the filtrate was kept undisturbed at 20 °C for 2 days. The resulting yellow solid was isolated by filtration, washed with diethyl ether (10 mL), and dried in vacuo (0.01 mbar, 40 °C, 6 h). Yield: 337 mg (823 µmol, 57%); mp >115 °C (dec). 1H NMR (CD2Cl2, 300.1 MHz): δ 1.91 (s, 3 H, CCH3), 2.0 (br. s, 6 H, CCH3), 2.34 (s, 3 H, CCH3), 5.43 (s, 1 H, CCHC), 5.82 (s, 1 H, CCHC), 6.78-6.88, 6.95-6.98, 7.00-7.11, and 7.60-7.64 (m, 9 H, SC6H4N, SiPh). 13C NMR (CD2Cl2, 75.5 MHz): δ 24.1 (CCH3), 24.5 (CCH3), 25.8 (2 C, CCH3), 102.2 (CCHC), 104.2 (CCHC), 121.8, 123.5, 125.7 (2 C), 125.9, 126.4, 129.5, 135.2 (2 C), 140.6, 141.0, and 154.4 (SC6H4N, SiPh), 170.8 (CN or CO), 177.8 (CN or CO), CO resonance signals of the bidentate O,O ligand not detected. 29Si NMR (CD2Cl2, 59.6 MHz): δ -158.9. 13 C VACP/MAS NMR: δ 22.8 (CCH3), 23.6 (CCH3), 25.3 (CCH3), 27.7 (CCH3), 102.3 (CCHC), 105.6 (CCHC), 123.7, 124.1, 125.4, 126.2, 127.4 (2 C), 129.1, 134.8, 135.8, 139.9, 141.2, and 155.6 (SC6H4N, SiPh), 171.1 (CN or CO), 178.6 (CN or CO), 189.9 (CO), 192.2 (CO). 15N VACP/MAS NMR: δ -171.8. 29Si VACP/MAS

2316 Organometallics, Vol. 28, No. 7, 2009 NMR: δ -160.6. Anal. Calcd for C22H23NO3SSi (409.58): C, 64.52; H, 5.66; N, 3.42; S, 7.83. Found: C, 63.23; H, 5.30; N, 3.54; S, 7.73. Preparation of Compound 9. Compound 13 (536 mg, 1.81 mmol) was added at 20 °C in a single portion to a stirred suspension of 5 (500 mg, 1.45 mmol) in acetonitrile (15 mL). The resulting mixture was stirred at 20 °C for 5 min, the undissolved residue was filtered off and discarded, and the filtrate was kept undisturbed at 20 °C for 24 h. The resulting red solid was isolated by filtration, washed with diethyl ether (5 mL), and dried in vacuo (0.01 mbar, 40 °C, 4 h). Yield: 685 mg (1.28 mmol, 89%); mp >155 °C (dec). 1 H NMR (CD2Cl2, 500.1 MHz): δ 1.90 (s, 3 H, CCH3), 2.43 (s, 3 H, CCH3), 5.43 (s, 1 H, CCHC), 7.19 (s, 1 H, CCHC), 6.92-7.00, 7.11-7.20, 7.33-7.35, 7.49-7.54, 7.59-7.63, 7.86-7.88, and 8.07-8.10 (m, 19 H, SC6H4N, SiPh, CPh). 13C NMR (CD2Cl2, 125.8 MHz): δ 24.1 (CCH3), 24.7 (CCH3), 95.0 (CCHC), 104.6 (CCHC), 122.0, 123.4, 125.89, 125.95, 126.6, 127.5, 128.6, 128.7, 128.9, 129.06, 129.15, 130.1, 133.6, 133.7, 135.5, 141.2, 141.7, and 154.6 (SC6H4N, SiPh, CPh), 170.8 (CN or CO), 178.7 (CN or CO), 183.3 (CO), 183.8 (CO). 29Si NMR (CD2Cl2, 99.4 MHz): δ -158.3. 13C VACP/MAS NMR: δ 23.9 (CCH3), 25.0 (CCH3), 94.6 (CCHC), 105.4 (CCHC), 121.1, 125.8, 127.2, 130.1, 131.7, 134.1, 135.2, 136.6, 142.0, 144.9, and 157.2 (SC6H4N, SiPh, CPh), 170.1 (CN or CO), 179.3 (CN or CO), 181.3 (CO), 182.2 (CO). 15N VACP/MAS NMR: δ -171.8. 29Si VACP/MAS NMR: δ -159.1. Anal. Calcd for C32H27NO3SSi (533.72): C, 72.01; H, 5.10; N, 2.62; S, 6.01. Found: C, 71.98; H, 5.11; N, 2.74; S, 6.08. Preparation of Compound 10. Compound 14 (423 mg, 1.80 mmol) was added at 20 °C in a single portion to a stirred suspension of 5 (500 mg, 1.45 mmol) in acetonitrile (40 mL). The resulting mixture was stirred at 20 °C for 1 min, the undissolved residue was filtered off and discarded, and the filtrate was kept undisturbed at 20 °C for 2 days. The resulting orange-colored solid was isolated by filtration, washed with n-pentane (10 mL), and dried in vacuo (0.01 mbar, 40 °C, 6 h). Yield: 591 mg (1.25 mmol, 87%); mp >115 °C (dec).1H NMR (CD2Cl2, 500.1 MHz, 263 K; the resonance signals of the major isomer are marked with an asterisk): δ 1.88* (s, 2 H, CCH3), 1.91 (s, 1 H, CCH3), 2.0 (br. s, 1 H, CCH3), 2.27* (s, 2 H, CCH3), 2.37 (s, 1 H, CCH3), 2.40* (s, 2 H, CCH3), 5.41* (s, 0.66 H, CCHC), 5.46 (s, 0.34 H, CCHC), 6.50* (s, 0.66 H, CCHC), 6.55 (s, 0.34 H, CCHC), 6.84-7.15, 7.26-7.52, 7.55-7.60, 7.70-7.78, and 7.94-7.97 (m, 14 H, SC6H4N, SiPh, CPh). 13C NMR (CD2Cl2, 125.8 MHz, 263 K; assignment of the resonance signals to the two isomers was not possible): δ 24.0 (CCH3), 24.1 (CCH3), 24.5 (2 C, CCH3), 26.48 (CCH3), 26.51 (CCH3), 98.2 (CCHC), 98.4 (CCHC), 104.1 (CCHC), 104.3 (CCHC), 121.81, 121.84, 123.3, 125.6, 125.68, 125.74, 126.3, 126.4, 128.25, 128.31, 128.7, 128.9, 129.3, 129.7, 133.4, 133.5, 135.0, 135.2, 140.4, 140.8, 141.0, 154.3, and 154.4 (SC6H4N, SiPh, CPh), 170.71 (CN or CO), 170.75 (CN or CO), 177.8 (CN or CO), 178.1 (CN or CO), 181.6 (CO), 182.4 (CO), 192.3 (CO), 193.0 (CO). 29Si NMR (CD2Cl2, 99.4 MHz, 263 K; the resonance signal of the major isomer is marked with an asterisk): δ -159.3*, -159.1. 29Si NMR (CD2Cl2, 99.4 MHz, 296 K): δ -158.7. 13C VACP/MAS NMR: δ 20.3 (CCH3), 23.6 (CCH3), 25.4 (CCH3), 98.2 (CCHC), 105.2 (CCHC), 123.3, 124.0, 126.0, 127.0, 127.6, 128.4, 129.2, 130.2, 132.6, 133.6, 135.2, 136.3, 141.1, and 154.8 (SC6H4N, SiPh, CPh), 172.4 (CN or CO), 175.5 (CN or CO), 180.8 (CO), 193.6 (CO). 15N VACP/ MAS NMR: δ -166.2. 29Si VACP/MAS NMR: δ -157.9. Anal. Calcd for C27H25NO3SSi (471.65): C, 68.76; H, 5.34; N, 2.97; S, 6.80. Found: C, 68.33; H, 5.31; N, 3.15; S, 6.73. Preparation of Compound 11 · CH3CN. Compound 15 (625 mg, 2.17 mmol) was added at 20 °C in a single portion to a stirred suspension of 5 (600 mg, 1.73 mmol) in acetonitrile (10 mL). The resulting mixture was stirred at 20 °C for 45 min, the undissolved residue was filtered off and discarded, and the filtrate was kept undisturbed at -20 °C for 4 days. The resulting colorless solid

Metz et al. was isolated by filtration, washed with n-pentane (10 mL), and dried in vacuo (0.01 mbar, 20 °C, 1 h). Yield: 776 mg (1.37 mmol, 79%); mp >55 °C (dec). 1H NMR (CD2Cl2, 300.1 MHz): δ 1.76 (s, 3 H, CCH3), 1.96 (s, 3 H, CH3CN), 2.37 (s, 3 H, CCH3), 5.80 (s, 1 H, CCHC), 5.84 (s, 1 H, CCHC), 6.99-7.02, 7.23-7.40, 7.61-7.68, and 7.73-7.76 (m, 14 H, SC6H4N, SiPh, CPh). 13C NMR (CD2Cl2, 75.5 MHz): δ 2.0 (CH3CN), 25.1 (CCH3), 25.2 (CCH3), 85.6 (q, 2 J(C,F) ) 31.7 Hz, CCF3), 97.1 (q, 3J(C,F) ) 1.5 Hz, CCHC), 102.4 (CCHC), 125.1 (2 C), 126.6, 127.4 (2 C), 128.6 (2 C), 128.9, 129.3, 129.5, 130.0, 130.9, 136.4, 137.0 (2 C), 137.2, 139.3, and 148.3 (SC6H4N, SiPh, CPh), 156.4 (CN or CO), 176.9 (CN or CO), 187.4 (CO), CF3 not detected. 19F NMR (CD2Cl2, 282.4 MHz): δ -81.9. 29Si NMR (CD2Cl2, 59.6 MHz): δ -124.6. 13C VACP/MAS NMR: δ -0.3 (CH3CN), 25.3 (2 C, CCH3), 86.1 (CCF3), 97.8 (CCHC), 101.2 (CCHC), 124.6, 126.5, 127.3, 128.8, 129.9, 131.8, 136.6, 137.5, and 148.2 (SC6H4N, SiPh, CPh), 157.5 (CN or CO), 176.1 (CN or CO), 188.8 (CO). 15N VACP/MAS NMR: δ -204.6, CH3CN not detected. 29Si VACP/MAS NMR: δ -124.6. Anal. Calcd for C29H25F3N2O3SSi (566.68): C, 61.47; H, 4.45; N, 4.94; S, 5.66. Found: C, 61.40; H, 4.60; N, 4.90; S 5.72. Preparation of 4-(Trimethylsilyloxy)pent-3-en-2-one (12). This compound was synthesized according to ref 13. Preparation of 1,3-Diphenyl-3-(trimethylsilyloxy)prop-2-en1-one (13). This compound was synthesized according to ref 14. Preparation of 4-Phenyl-4-(trimethylsilyloxy)but-3-en-2-one (14). This compound was synthesized according to ref 14. Preparation of 4,4,4-Trifluoro-1-phenyl-3-(trimethylsilyloxy)but-2-en-1-one (15).15 N,O-Bis(trimethylsilyl)acetamide (7.76 g, 38.1 mmol) was added at 20 °C within 3 min to a stirred solution of 4,4,4-trifluoro-1-phenylbutan-1,3-dione (7.50 g, 34.7 mmol) in acetonitrile (30 mL), and the reaction mixture was stirred at 20 °C for 3 h. The solvent was removed in vacuo and the residue purified by bulb-to-bulb distillation (60-80 °C, 0.02 mbar) to give a yellowish liquid. Yield: 7.16 g (24.8 mmol, 72%). 1H NMR (CD2Cl2, 500.1 MHz):16 δ 0.28 (s, 9 H, SiCH3), 6.71 (s, 1 H, CCHC), 7.49-7.52 (m, 2 H, H-3/H-5, Ph), 7.59-7.62 (m, 1 H, H-4, Ph), 7.92-7.94 (m, 2 H, H-2/H-6, Ph). 13NMR (CD2Cl2, 125.8 MHz):16 δ 0.3 (SiCH3), 106.9 (m, CCHC), 120.3 (q, 1J(C,F) ) 277 Hz, CF3), 128.6 (C-2/C-6, Ph), 129.1 (C-3/C-5, Ph), 133.7 (C4, Ph), 138.2 (C-1, Ph), 148.9 (q, 2J(C,F) ) 34 Hz, F3CC), 189.0 (CO). 19F NMR (CD2Cl2, 282.4 MHz):16 δ -74.6. 29Si NMR (CD2Cl2, 99.4 MHz):16 δ 28.7. Anal. Calcd for C13H15F3O2Si (288.34): C, 54.15; H, 5.24. Found: C, 54.02; H, 5.34. Crystal Structure Analyses. Suitable single crystals of 8 · CH3CN, 9 · CH3CN, 10 · CH3CN, and 11 · 2CH3CN were isolated directly from the respective reaction mixtures. The crystals were mounted in inert oil (perfluoropolyalkyl ether, ABCR) on a glass fiber and then transferred to the cold nitrogen gas stream of the diffractometer (Bruker Nonius KAPPA APEX II (8 · CH3CN and 10 · CH3CN; Goebel mirror, Mo KR radiation, λ ) 0.71073 Å) and Stoe IPDS (9 · CH3CN and 11 · 2CH3CN; graphite-monochromated Mo KR radiation, λ ) 0.71073 Å)). The structures were solved by direct methods.17 The non-hydrogen atoms were refined anisotropically.18 A riding model was employed in the refinement of the (13) Jullien, J.; Pechine, J. M.; Perez, F.; Piade, J. J. Tetrahedron 1982, 38, 1413–1416. (14) Purrington, S. T.; Bumgardner, C. L.; Lazaridis, N. V.; Singh, P. J. Org. Chem. 1987, 52, 4307–4310. (15) A general procedure for the synthesis of 15 has been reported, but 15 has not been isolated and characterized: Bumgardner, C. L.; Sloop, J. C. J. Fluorine Chem. 1992, 56, 141–146. (16) The NMR spectra of 15 show more than one set of resonance signals indicating the existence of isomers. The NMR data given are those of the major isomer. (17) (a) Sheldrick, G. M. SHELXS-97; University of Go¨ttingen: Go¨ttingen, Germany, 1997. (b) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467–473. (18) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen: Go¨ttingen, Germany, 1997.

Neutral Hexacoordinate Silicon(IV) Complexes CH hydrogen atoms. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with The Cambridge Crystallographic Data Centre as supplementary publication nos. CCDC-721252 (8 · CH3CN), CCDC-721253 (9 · CH3CN), CCDC-721254 (10 · CH3CN), and CCDC-721255 (11 · 2CH3CN). Copies of the data can be obtained free of charge

Organometallics, Vol. 28, No. 7, 2009 2317 on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax, (+44)-1223/336033; e-mail, [email protected]). Supporting Information Available: Crystallographic data. This material is available free of charge via the Internet at http://pubs.acs.org. OM801208T

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