Reactivity of a Zwitterionic Stable Silylene toward Halosilanes and

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Organometallics 2009, 28, 1927–1933

1927

Reactivity of a Zwitterionic Stable Silylene toward Halosilanes and Haloalkanes Yun Xiong, Shenglai Yao, and Matthias Driess* Technische UniVersita¨t Berlin, Institute of Chemistry: Metalorganic and Inorganic Materials, Sekr. C2, Strasse des 17. Juni 135, 10623 Berlin, Germany ReceiVed December 5, 2008

The insertion of the thermally stable ylide-like silylene LSi: (1) {L ) CH[(CdCH2)CMe][N(Ar)]2], Ar ) 2,6-iPr2C6H3} into C-X and Si-X bonds of various small haloalkanes and halosilanes (MeI, PhCH2Br, CH2Cl2, CH2ClI, CH2Br2, CHCl3, MeCCl3, HSiCl3, and MeSiCl3) has been investigated. Surprisingly, the outcome of the reactions is in marked contrast to previous results employing related isolable silylenes. Exclusive formation of 1,1-insertion products LSi(R)X is observed, in a few cases along with a small amount of dihalosilane LSiX2 or monohalosilane LSi(H)X. It is proposed that the reaction occurs via polar 1,4-addition and subsequent rearrangement of the latter kinetic (initial) product to give the 1,1-insertion product. The new compounds have been characterized by 1H, 13C, and 29Si NMR spectroscopy and by single-crystal X-ray diffraction analyses. Introduction Silylenes, that is, divalent silicon compounds, represent indispensable building blocks in organosilicon chemistry.1,2 Because of their relatively high reactivity caused by electronic and coordinative unsaturation on silicon, they readily insert into a series of X-Y bonds, for instance, into Li-C,3 M-N (M ) Li, Na, K),4 C-H,5 O-H,6,7 and P-P bonds,8 respectively. In fact, silylenes pave the way to new classes of organosilicon compounds with unique reactivity features.9 Likewise, they can serve as potent Lewis bases, acting as donors for the formation * To whom correspondence should be addressed. Phone: +49(0)30-31422265. Fax: +49(0)30-314-29732. E-mail: [email protected]. Website: http://www.driess.tu-berlin.de. (1) Gaspar, P. P.; West, R. In The Chemistry of Organic Silicon Compounds, 2nd ed.; Rappoport, Z., Apeloig, Y., Eds.; Wiley: New York, 1999; Part 3, p 2463. (2) (a) Haaf, M.; Schmedake, T. A.; West, R. Acc. Chem. Res. 2000, 33, 704. (b) Gehrhus, B.; Lappert, M. F. J. Organomet. Chem. 2004, 607. (c) Hill, N. J.; West, R. J. Organomet. Chem. 2004, 689, 4165. (d) Gehrhus, B.; Hitchcock, P. B.; Pongtavornpinyo, R.; Zhang, L. Dalton Trans. 2006, 15, 1847. (3) Cai, X.; Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F.; Slootweg, J. C. J. Organomet. Chem. 2002, 651, 150. (4) (a) Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F.; Slootweg, J. C. Chem. Commun. 2000, 1427. (b) Antolini, F.; Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F.; Slootweg, J. C. Dalton Trans. 2004, 3288. (5) Yao, S.; van Wu¨llen, C.; Sun, X.-Y.; Driess, M. Angew. Chem., Int. Ed. 2008, 47, 3250. (6) (a) Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F.; Heinicke, J.; Boese, R.; Bla¨ser, D. J. Organomet. Chem. 1996, 521, 211. (b) Haaf, M.; Schmiedl, A.; Schmedake, T. A.; Powell, D. R.; Millevolte, A. J.; Denk, M.; West, R. J. Am. Chem. Soc. 1998, 120, 12714. (7) Yao, S.; Brym, M.; van Wu¨llen, C.; Driess, M. Angew. Chem., Int. Ed. 2007, 46, 4159. (8) Xiong, Y.; Yao, S.; Brym, M.; Driess, M. Angew. Chem., Int. Ed. 2007, 46, 4511. (9) (a) Gehrhus, B.; Hitchcock, P. B.; Parruci, M. Dalton Trans. 2005, 2720. (b) Ishida, S.; Iwamoto, T. M.; Kabuto, C.; Kira, M. Nature 2003, 421, 725. (c) Schmedake, T. A.; Haaf, M.; Apeloig, Y.; Mu¨ller, T.; Bukalov, S.; West, R. J. Am. Chem. Soc. 1999, 121, 9479. (d) Denk, M. K.; Hatano, K.; Lough, A. J. Eur. J. Inorg. Chem. 1998, 1067. (e) Scha¨fer, A.; Saak, W.; Weidenbruch, M.; Marsmann, H.; Henkel, G. Chem. Ber./Recl. 1997, 130, 1733. (f) Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F. Angew. Chem., Int. Ed. Engl. 1997, 36, 2514. (g) Drost, C.; Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F. Chem. Commun. 1997, 1845.

of transition metal-silylene complexes.10 Since Denk and West et al. reported the first isolable silylene A in 1994,11 other types of stable silylenes have been prepared by taking advantage of the concept of π-donor stabilization of low-valent silicon through nitrogen donor atoms and/or steric congestion by encumbering organic groups, including B,12 C,13 D,14 and 1,15 respectively (Scheme 1). One striking feature of isolable silylenes A-D is that they react with haloalkanes (RX) to form unexpected products involving radical species as reactive intermediates.16 Thus, the insertion of stable silylenes into a C-X bond of haloalkanes RX represents an alternative route to particular halosilanes, which are difficult to prepare by the direct process employing elemental silicon and haloalkanes.17 Previous investigation also showed that the insertion products are strongly dependent on the nature of the haloalkanes molecule. In most cases, employing haloalkanes yielded upon radical-induced Si-Si bond formation disilanes of the type LSi(X)-Si(R)L, while using dihaloalkanes afforded the corresponding twice 1,1-insertion compounds (LSiX)2CR′2 as predominant products (Scheme 2). Moreover, sterically congested haloalkanes RX (R ) tBu, Ph) lead to the formation of respective 1,1-insertion products LSi(R)X, and (10) (a) GasparP. P.; West, R. In The Chemistry of Organosilicon Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley: New York, 1998. (b) Gehrhus, B.; Lappert, M. F. J. Organomet. Chem. 2001, 617, 209. (11) Denk, M.; Lennon, R.; Hayashi, R.; West, R.; Haaland, A.; Belyakov, H.; Verne, P.; Wagner, M.; Metzler, N. J. Am. Chem. Soc. 1994, 116, 2691. (12) Gehrhus, B.; Lappert, M. F.; Heinicke, J.; Boose, R.; Blaser, D. J. Chem. Soc., Chem. Commun. 1995, 1931. (13) Kira, M.; Ishida, S.; Iwamoto, T.; Kabuto, C. J. Am. Chem. Soc. 1999, 121, 9722. (14) Haaf, M.; Schmedake, T. A.; Paradiese, B. J.; West, R. Can. J. Chem. 2000, 78, 1526. (15) Driess, M.; Yao, S.; Brym, M.; van Wu¨llen, C.; Lenz, D. J. Am. Chem. Soc. 2006, 128, 9628. (16) (a) Moser, D. F.; Naka, A.; Guzei, L. A.; Mu¨ller, T.; West, R. J. Am. Chem. Soc. 2005, 127, 14730. (b) Delawar, M.; Gehrhus, B.; Hitchcock, P. B. Dalton Trans. 2005, 2945. (c) Gehrhus, B.; Hitchcock, P. B.; Jansen, H. J. Organomet. Chem. 2006, 691, 811. (d) Ishida, S.; Iwamoto, T.; Kabuto, C.; Kira, M. Chem. Lett. 2001, 1102. (17) Pachaly, B.; Weis, J. In Organosilicon Chemistry. III; Auner, N., Weis, J., Eds.; Wiley-VCH: Weinheim, 1998; p 478.

10.1021/om801157u CCC: $40.75  2009 American Chemical Society Publication on Web 02/27/2009

1928 Organometallics, Vol. 28, No. 6, 2009

Xiong et al. Scheme 1. Several Isolable Silylenes

Scheme 2. Reaction of Silylenes with Haloalkanesa

a

LSi ) A-D; R ) tBu, Ph; R′ ) H, Me; R′′ ) CHCl2, CH2Cl; X ) Cl, Br, I.

Scheme 3. Distinct Reactivity of Silylene 1

Table 1. Reactions of LSi: (1) with Halosilanes and Haloalkanes halosilanes haloalkanes MeI PhBr PhCH2Br CH2Cl2 CH2ClI CH2Br2 Me2CCl2 CHCl3 MeCCl3 HSiCl3 MeSiCl3 Ph2SiCl2 PhSiCl3

main product (yielda) LSi(Me)I no reaction LSi(CH2Ph)B LSi(CH2Cl)Cl LSi(CH2Cl)I LSi(CH2Br)Br no reaction LSi(CHCl2)Cl LSi(CMeCl2)Cl LSi(SiHCl2)Cl LSi(SiMeCl2)Cl no reaction no reaction

minor product (yielda)

2 (98%) 3 4 5 6

(98%) (98%) (98%) (58%)

8 (65%) 10 (65%) 11 (80%) 13 (80%)

LSiBr2

7 (42%)

LSiCl2 LSiCl2 LSi(H)Cl LSi(H)Cl

9 (35%) 9 (35%) 12 (20%) 12 (20%)

a Estimated according to 1H NMR spectra. For isolated yield, see the Experimental Section.

Results and Discussion perhalogenated hydrocarbons yield dihalosilanes LSiX2, which can be rationalized in terms of a free-radical mechanism.16a Because of the ylide-like character of the stable silylene 1, its reactivity is markedly different from that of other silylenes (Scheme 3). Accordingly, DFT calculations suggest that the mesomeric ylide form 1b plays a key role for understanding the reactivity. While formation of 1,1-insertion products is favored by the divalent Si atom akin to the behavior of other silylenes,16 the 1,4-dipolar nature of 1 facilitates a remarkably distinct reactivity toward both electrophiles and nucleophiles in comparison to the behavior of stable silylenes A-D. This is exemplarily shown by the reaction of 1 with B(C6F5)3 and H+, to form the corresponding silyliumylidene species I and II, respectively,18 water addition to give the siloxy silylene III,7 and formation of the 1,4-adduct IV through addition of Me3SiOTf (OTf ) OSO2CF3) onto 1 (Scheme 3).15 The different behavior of 1 prompted us to examine its reactivity toward C-X and Si-X bonds in haloalkanes and halosilanes, respectively. As expected, compound 1 shows a peculiar reactivity in comparison to that observed for the related N-heterocyclic silylenes A, B, and D. Herein, we report the synthesis, spectroscopic, and structural characterization of a new series of silylene insertion products. (18) Driess, M.; Yao, S.; Brym, M.; van Wu¨llen, C. Angew. Chem., Int. Ed. 2006, 45, 6730.

Synthesis. A series of different haloalkanes and halosilanes are allowed to react with silylene 1, affording the products 2-13, which are summarized in Table 1. In contrast to the related N-heterocyclic silylenes A, B, and D, compound 1 forms exclusively 1,1-insertion products and in some cases also dihaloor hydrohalosilanes, respectively. Thus, reaction of 1 with the simple halomethane MeI is completed within 2 h and furnishes solely the 1,1-insertion product LSi(Me)I 2. However, 1 does not react with PhBr even after several weeks at room temperature. This is in opposition to the behavior of silylene A, which furnishes the corresponding 1,1-insertion product and the Si-Si coupling product (disilane) in 67% and 33% yield, respectively.16a In addition, silylene 1 inserts readily into the aliphatic C-Br bond of PhCH2Br, yielding the corresponding 1,1-insertion product LSi(CH2Ph)Br 3. In contrast, silylene A reacts with PhCH2Cl affording solely the corresponding disilane.16a Similar differences can be observed when silylene 1 is allowed to react with dihaloalkanes such as CR2X2 (R ) H, Me; X ) Cl, Br, I). The reaction with CH2Cl2 is completed after several weeks at room temperature, affording the 1,1insertion product LSi(CH2Cl)Cl 4 in almost quantitative yield. As expected, the analogous reaction with CH2ClI proceeds much faster and reaches completion in 8 h, leading exclusively to the iodo(chloromethyl)silane LSi(CH2Cl)I 5, irrespective of the relative molar ratio of the starting materials. This is again in marked contrast to the reactivity of A, B, and C, which lead to the formation of disilanes or twice carbon-halogen insertion

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Organometallics, Vol. 28, No. 6, 2009 1929

Scheme 4. Proposed Reaction Mechanism for 1,1-Insertion via Formation of 1,4-Adducta

a

R ) Me, CH2Cl, CH2Cl, CH2Br, CHCl2, MeCCl2, HSiCl2, MeSiCl2; X ) Cl, Br, I; Ar ) 2,6-iPrC6H3.

Table 2. δ 29Si{1H} NMR Spectroscopic Data of 2-13 in C6D6 (ppm) compound LSi(Me)I (2) LSi(CH2Ph)Br (3) LSi(CH2Cl)Cl (4) LSi(CH2Cl)I (5) LSi(CH2Br)Br (6) LSiBr2 (7) LSi(CHCl2)Cl (8) LSiCl2 (9) LSi(CMeCl2)Cl (10) LSi(SiHCl2)Cl (11) LSi(H)Cl (12) LSi(SiMeCl2)Cl (13)

-35.0 -26.3 -30.6 -38.3 -32.4 -52.7 -39.4 -40.0 -41.7 -35.8(s, SiN2), -8.1 -36.0 -37.1 (s, SiN2), -14.2

(s, SiHCl2) (s, SiMeCl2)

products.16 While the reaction of B with CH2Br2 leads to a complicated mixture of polysilanes,16b the analogous reaction of 1 with CH2Br2 affords the 1,1-insertion product LSi(CH2Br)Br 6 along with the dibromosilane LSiBr2 7 in 58% and 42% yields, respectively. Moreover, silylene 1 is resistant toward Me2CCl2, whereas silylene B reacts with Me2CCl2 to give the corresponding Si-Si coupling product (disilane).16b Even treatment of 1 with perhalogenated hydrocarbons affords the respective 1,1-insertion products. This is shown by the reaction with CHCl3 and MeCCl3 to give the chloro(dichloroalkyl)silanes LSi(CHCl2)Cl 8 and LSi(CMeCl2)Cl 10, respectively, along with a small amount of dihalosilane LSiCl2 9. It is noteworthy that the reaction of 1 with CHCl3 is completed within a few minutes, leading to a dark violet solution. We believe that the color results from impurities, because the products 8 and 9 are colorless. The reaction of 1 with MeCCl3 can be completed in 1 day, indicated by the disappearing of the yellow color of the reaction mixture. Likewise, reaction of 1 with the trichlorosilanes HSiCl3 and MeSiCl3 leads to the corresponding 1,1-insertion compound LSi(SiHCl2)Cl 11 and LSi(SiMeCl2)Cl 13, respectively, as the main product. In both cases, the minor product LSi(H)Cl 12 can be identified by NMR spectroscopy and mass spectrometry, similar to the reactivity of B toward HSiCl3 and MeSiCl3, respectively.16c Sterically more congested chlorosilanes like Ph2SiCl2 and PhSiCl3 are resistant toward 1. Proposed Mechanism. How could one rationalize the preferred formation of 1,1-insertion products and the peculiar absence of a radical reactivity channel? Although the reaction mechanism is still unknown and reaction intermediates could not be detected, we propose that the reaction occurs via 1,4addition (kinetic product) and subsequent rearrangement to give the 1,1-addition thermodynamic product (Scheme 4). This is in accordance with our previous DFT calculations, which suggested that addition of R-X electrophiles to 1 leads to the 1,4-addition product because of the zwitterionic character of 1.15 The latter represents the kinetic product, which rearranges to the corresponding 1,1-insertion isomer as thermodynamic product. The

Figure 1. The molecular structure of 3. Thermal ellipsoids are drawn at 50% probability level. Hydrogen atoms (except for those at C1 and C30) are omitted for clarity. For selected distances and angles, see Table 3.

driving force for the rearrangement of the 1,4-adduct is the high Lewis basicity of the Si(II) lone pair electrons. However, a direct insertion pathway cannot be excluded at this stage, and further investigations are needed. Apparently, silylene 1 does not react with bulky haloalkanes and halosilanes such as Me2CCl2, Ph2SiCl2, and PhSiCl3, presumably for steric reasons. For the same reason, the formation of a twice C-X insertion product using CH2X2 substrates is disfavored. Whether the insertion product of 1 into a C-X (X ) Cl, Br) or Si-Cl bond shows a tendency for dihalogen (X2) or hydrogenhalide (HCl) transfer and formation of LSiX2 and LSi(H)X, respectively, depends on the nature of the starting material. Apparently, perhalogenated haloalkanes have a strong tendency to serve as halogen transfer reagents. Similarly, perhalogenated organosilanes are capable of releasing HX.19 A similar situation has been observed for related Ge-X compounds.20 Spectroscopic Characterization. The composition and constitution of compounds 2-13 are proven by 1H, 13C, and 29Si NMR spectroscopy, EI-MS, and/or correct combustion (H, C, N) analyses. In particular, the 1H and 13C NMR spectra prove the presence of a CH[(CdCH2)(CMe)(N-aryl)2] backbone. In contrast to 1, the Si atoms in the products show characteristically highfield resonances in the 29Si NMR spectra (Table 2), while the insertion products of the related stable silylenes A-C display relatively lowfield resonances ranging from -8.9 to 37.1 ppm.16 X-ray Structure Analysis. The molecular structures of compounds 3, 4, 5, 9, 10, and 11 deduced from 1H, 13C, and (19) Oka, K.; Nakao, R. J. Organomet. Chem. 1990, 390, 7. (20) Driess, M.; Yao, S.; Brym, M.; van Wu¨llen, C. Angew. Chem., Int. Ed. 2006, 45, 4349.

1930 Organometallics, Vol. 28, No. 6, 2009

Xiong et al.

in the CMeCl2 group are disordered, discussion of structural parameter is precluded. Similar to the situation observed in 5, the Cl1 and Cl2 (Cl3) atoms in 11 have a gauche conformation, with a Cl1-Si1-Si2-Cl2 torsion angle of -53.4° and Cl1-Si1-Si2-Cl3 angle of 64.2°, respectively. The Si1-Cl1 distance of 2.082(1) Å is significantly larger than the Si2-Cl2 (2.048(1) Å) and Si2-Cl3 (2.025(1) Å) values. The Si-Si distance of 2.344(1) Å in 11 is in the expected range for related disilanes.16a,b

Conclusions

Figure 2. The molecular structure of 4. Thermal ellipsoids are drawn at 50% probability level. Hydrogen atoms (except for those at C30 and C1) are omitted for clarity. For selected distances and angles, see Table 3. 29

Si NMR spectroscopy were confirmed by single-crystal X-ray diffraction analyses as shown in Figures 1-6. The structure of compound 7 has already been described in a previous publication,15 and the X-ray diffraction data for 13 are not suitable for discussion. Selected interatomic distances and angles are given in Table 3, and data collection parameters and refinement statistics are listed in Table 4. While compounds 3 and 5 crystallize in the triclinic space group P1j, compounds 4, 9, and 11 crystallize in the monoclinic space groups P21/m, P21/c, and P21/n, respectively, and compound 10 in the orthorhombic space group P212121. The compounds consist of differently puckered six-membered C3N2Si rings with folding angles ranging from 21.9° to 33.1° (Table 3). The endo- and exocyclic C-C distances of the ligand backbone represent alternating C-C single and double bonds, suggesting marginally perturbation of the buta-1,3-diene π system by the nitrogen atoms, similar to the situation in LSiBr2 as reported earlier.15 Expectedly, the Si atoms are tetrahedral coordinated. The Br-Si-C30 angle of 108.8(1)° in 3 is larger than the corresponding values in the other structures due to the steric congestion of the benzyl group. Accordingly, the Si1-Br1 distance of 2.249(1) Å in 3 is slightly longer than the Si-Br bond in LSiBr2 (7) (average 2.20(1) Å),15 but significantly shorter than those observed in a related monosilane and disilane [2.296(1)-2.326(1) Å].16a The molecular structures of 4, featuring two chlorine atoms in a gauche-conformation with a torsion angle Cl1-Si1-C30-Cl2 of 40.8°, differ significantly from its iodine analogue 5, in which the chlorine and the iodine atom are nearly in the antiposition with a torsion angle I1-Si1-C30-Cl1 of 163.8°. This can be rationalized in terms of the larger steric demand of the iodine atom. Additionally, the six-membered C3N2Si ring in compound 5 is strongly puckered with the Si1 and N2 atoms profoundly bending out of the plane defined by the N1, C2, C3, and C4 atoms. The Si1-Cl1 distance of 2.067(1) Å in 4 is in the normal range of related monochlorosilanes. The Cl-Si-Cl angle of 103.9(1)° in 9 is very similar to that in the bromine analogue 7. The Si-Cl bond lengths of 2.031(1) and 2.051(1) Å are comparable to the analogous values observed in 4, 10, and 11. The folding angle of the C3N2Si ring in 10 (33.1°) is the largest in the series due to the steric demand of the CMeCl2 group. Because the methyl group and the two chlorine atoms

We have reported on the distinctly different reactivities of the stable ylide-like silylene LSi: 1 toward haloalkanes and halosilanes. In contrast to the behavior of other isolable silylenes, compound 1 leads solely to 1,1-insertion products. The exclusive formation of 1,1-insertion products is in accordance with previously reported results from DFT calculations, which predict that the initial step is a dipolar 1,4-addition and subsequent rearrangement of the latter kinetic product to the 1,1-adduct. Reductive dehalogenation of the 1,1-insertion products 4-6 may lead to SidC compounds with a ylide-like SidC bond. Respective investigations are in progress.

Experimental Section General Considerations. All experiments and manipulations were carried out under dry oxygen-free nitrogen using standard Schlenk techniques or in an MBraun inert atmosphere drybox containing an atmosphere of purified nitrogen. Solvents were dried by standard methods and freshly distilled prior to use. The starting material silylene 1 was prepared according to the literature procedure.15 The NMR spectra were recorded with Bruker spectrometers ARX200, AV400 and with residual solvent signals as internal reference (1H and 13C{H}) or with an external reference (SiMe4 for 29Si, BF3 · Et2O for 19F). Abbreviations: s ) singlet; d ) doublet; t ) triplet; sept ) septet; m ) multiplet; br ) broad. Reaction of 1 with MeI. MeI (0.05 mL, d ) 2.28 g/mL, 0.80 mmol) was added to a solution of the silylene 1 (0.36 g, 0.80 mmol) in n-hexane (8 mL) at room temperature. After 2 h, the reaction was completed. Colorless crystals of 2 (0.44 g, 0.75 mmol, 93%) were achieved by cooling the reaction mixture to -20 °C. Mp 152 °C (decomp.). 1H NMR (200.13 MHz, C6D6, 298 K): δ 0.33 (s, 3H, Si-CH3), 1.12-1.53 (8 × d, 3JHH ) 7 Hz, 24H, CHMe2), 1.45 (s, 3H, NCMe), 3.26 (sept, 3JHH ) 7 Hz, 1H, CHMe2), 3.34 (s, 1H, NCCH2), 3.65 (sept, 3JHH ) 7 Hz, 1H, CHMe2), 3.77 (sept, 3JHH ) 7 Hz, 1H, CHMe2), 3.98 (s, 1H, NCCH2), 4.08 (sept, 3JHH ) 7 Hz, 1H, CHMe2), 5.56 (s, 1H, γ-CH), 7.02-7.22 (m, br, 6H, 2, 6-iPr2C6H3). 13C{1H} NMR (100.61 MHz, C6D6, 298 K): δ -24.3 (Si-CH3), 21.2-29.1 (CHMe2), 89.2 (NCCH2), 109.8 (γ-C), 124.3-149.8 (NCMe, NCCH2, 2,6-iPr2C6H3). 29Si{1H} NMR (79.49 MHz, C6D6, 298 K): δ -35 (s). EI-MS m/z (%): 586.2 (6.19, [M]+), 571.2 (100, [M - Me]+), 543.2 (60.8, [M - iPr]+). Anal. Calcd for C30H43N2SiI: C, 61.42; H, 7.39; N, 4.77. Found: C, 61.33; H, 7.30; N, 4.79. Reaction of 1 with PhCH2Br. To a solution of the silylene 1 (1.60 g, 3.60 mmol) in diethyl ether (20 mL) was added benzyl bromide (0.44 mL, d ) 1.43 g/mL, 3.60 mmol) at room temperature. The reaction was completed after 2 h. By cooling at -20 °C, the product 3 crystallized as colorless crystals in the solution. Yield: 1.68 g (2.73 mmol), 75.8%. Mp 194 °C (decomp.). 1H NMR (200.13 MHz, C6D6, 298 K): δ 0.81-1.39 (8 × d, JHH ) 7 Hz, 24H, CHMe2), 1.46 (s, 3H, NCMe), 2.29 (s, 2H, CH2Ph), 3.41 (s, 1H, NCCH2), 3.64 (sept, 3JHH ) 7 Hz, 1H, CHMe2), 3.72 (sept, 3 JHH ) 7 Hz, 1H, CHMe2), 3.82 (sept, 3JHH ) 7 Hz, 2H, CHMe2), 4.01 (s, NCCH2, 1H), 5.44 (s, 1H, γ-CH), 6.07-6.09 (m, 2H, Ph), 6.76 (m, 3H, Ph), 7.00-7.28 (m, br, 6H, 2,6-iPr2C6H3). 13C{1H}

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Organometallics, Vol. 28, No. 6, 2009 1931

Table 3. Selected Bond Distances (Å) and Angles (deg) Si1-X1 Si1-E(X2, C30, Si2) Si1-N1 Si1-N2 C1-C2 C2-C3 C3-C4 C4-C5 N1-C2 N2-C4 N1-Si1-N2 X1-Si1-E(X2,C30,Si2) N1-Si1-X1 N2-Si1-E(X2,C30, Si2) Si2-Cl2 Si2-Cl3 folding anglea a

3

4

5

9

10

11

2.249(1) 1.855(2) 1.722(2) 1.722(2) 1.389(3) 1.418(3) 1.377(3) 1.442(3) 1.422(3) 1.428(3) 105.7(1) 108.8(1) 110.0(1) 115.8(1)

2.067(1) 1.896(3) 1.714(3) 1.707(3) 1.368(5) 1.444(5) 1.355(5) 1.464(5) 1.421(4) 1.425(4) 106.1(1) 105.6(1) 110.9(1) 112.6(1)

2.446(1) 1.853(4) 1.721(2) 1.711(2) 1.339(4) 1.458(4) 1.347(4) 1.494(4) 1.422(3) 1.422(4) 106.6(1) 98.7(1) 112.9(1) 117.3(1)

2.051(1) 2.031(1) 1.699(3) 1.705(3) 1.345(5) 1.459(5) 1.347(5) 1.488(5) 1.446(4) 1.438(4) 107.9(1) 103.9(1) 111.6(1) 111.5(1)

2.066(2) 1.906(4) 1.722(3) 1.714(3) 1.376(5) 1.446(5) 1.368(5) 1.460(5) 1.415(5) 1.409(5) 105.1(2) 102.0(1) 112.0(1) 114.8(2)

2.082(1) 2.344(1) 1.702(1) 1.713(2) 1.353(3) 1.432(3) 1.357(3) 1.467(3) 1.417(2) 1.416(2) 105.6(1) 102.2(1) 111.7(1) 114.9(1) 2.048(1) 2.025(1) 23.7

31.0

24.3

26.7

21.9

33.1

The planes defined by the N1, Si1, N2 atoms (plane 1) and the N1, C2, C3, C4, N2 atoms (plane 2). Table 4. Crystal and Refinement Data for 3, 4, 5, 9, 10, and 11

empirical formula M crystal system space group a/Å b/Å c/Å R/deg β/deg γ/deg V/Å3 Z dcalc/Mg m-3 µ (Mo KR) mm-1 reflections collected independent reflections R(int) reflections with I > 2σ(I) data/parameters final R indices [I > 2σ(I)] R1 R indices (all data) wR2

3

4

5

9

10

11

C36H47BrN2Si 615.76 triclinic P1j 8.7511(5) 12.1062(6) 16.5833(9) 109.092(4) 97.563(4) 94.229(4) 1633.0(2) 2 1.252 1.322 14 894 5747 0.0401 3870 370 0.0346 0.0744

C30H42Cl2N2Si 529.65 monoclinic P21/m 15.220(4) 11.608(4) 16.663(5) 90 91.04 90 2943.4(15) 4 1.195 0.282 14 028 5114 0.0593 3449 325 0.0669 0.1691

C30H42ClIN2Si 621.10 triclinic P1j 10.8539(4) 12.5672(4) 13.3929(5) 66.973(3) 74.202(3) 65.382(4) 1515.36(9) 2 1.361 1.205 12 647 5310 0.0241 4261 322 0.0305 0.0817

C29H40Cl2N2Si 515.62 monoclinic P21/c 17.0459(6) 13.1535(4) 13.6811(5) 90 109.111(1) 90 2898.4(2) 4 1.182 0.285 16 470 5065 0.1306 3859 316 0.0744 0.1481

C31H43Cl3N2Si 578.11 orthorhombic P212121 9.8353(5) 14.9032(7) 21.2164(8) 90 90 90 3109.8(2) 4 1.235 0.356 17 375 5466 0.0974 2523 354 0.0478 0.0528

C29H41Cl3N2Si2 580.19 monoclinic P21/n 12.430(1) 20.754(2) 12.430(1) 90 106.04 90 3081.5(4) 4 1.251 0.396 23 008 5388 0.0455 4943 338 0.0399 0.0967

NMR (100.61 MHz, C6D6, 298 K): δ 21.0-28.8 (CHMe2, NCMe, CH2Ph), 88.0 (NCCH2), 106.6 (γ-C), 124-150 (NCMe, NCCH2, 2,6-iPr2C6H3). 29Si NMR (79.49 MHz, C6D6, 298 K): δ -26.3 (s). EI-MS m/z (%): 616 (17.5, [M]+), 601.7 (100, [M - Me]+), 573 (79.8, [M - iPr]+). Anal. Calcd for C36H47N2SiBr: C, 70.22; H, 7.69; N, 4.55. Found: C, 70.12; H, 7.59; N, 4.45. Reaction of 1 with CH2Cl2. The silylene 1 (2.50 g, 5.62 mmol) was added to 20 mL of methylene chloride at room temperature. The reaction mixture was allowed to stay at room temperature for 1 week. The 1H NMR spectrum shows that only compound 4 is formed. After the reaction was completed, the solution was concentrated to about 5 mL and cooled at -20 °C. The product 4 crystallized in the form of colorless crystals. Yield: 1.40 g (2.64 mmol), 47%. Mp 157 °C (decomp.). 1H NMR (200.13 MHz, C6D6, 298 K): δ 1.16-1.44 (8 × d, 3JHH ) 7 Hz, 24H, CHMe2), 1.45 (s, 3H, NCMe), 2.68 (s, 2H, CH2Cl), 3.40 (s, 1H, NCCH2), 3.51 (sept, 3 JHH ) 6.8 Hz, 1H, CHMe2), 3.68 (sept, 3JHH ) 6.8 Hz, 2H, CHMe2), 3.75 (sept, 3JHH ) 6.8 Hz, 1H, CHMe2), 3.98 (s, 1H, NCCH2), 5.36 (s, 1H, γ-CH), 6.99-7.23 (m, br, 6H, 2,6-iPr2C6H3). 13 C{1H} NMR (100.61 MHz, C6D6, 298 K): δ 21.3-28.8 (CHMe2, NCMe, CH2Cl), 89.2 (NCCH2), 107.3 (γ-C), 124.0-149.0 (NCMe, NCCH2, 2,6-iPr2C6H3). 29Si NMR (79.49 MHz, C6D6, 298 K): δ -30.6 (s). EI-MS m/z (%): 528 (12.4, [M]+), 513 (100, [M - Me]+), 485 (27, [M - iPr]+). Anal Calcd for C30H42N2SiCl2: C, 68.03; H, 7.99; N, 5.29. Found: C, 67.97; H, 7.70; N, 5.16. Reaction of 1 with CH2ClI. Chloroiodomethane (0.21 mL, d ) 2.43 g/mL, 2.90 mmol) was added to a solution of silylene 1

(1.29 g, 2.90 mmol) in hexane (20 mL) at room temperature. The reaction mixture was allowed to stay at room temperature for 24 h. The 1H NMR spectrum showed that only compound 5 was formed. After the reaction was completed, the solution was concentrated to about 5 mL and cooled at -20 °C. The product 5 crystallized as colorless crystals. Yield: 1.21 g (1.90 mmol), 67%. Mp 161 °C (decomp.). 1H NMR (200.13 MHz, C6D6, 298 K): δ 1.20-1.44 (8 × d, 3JHH ) 7 Hz, 24H, CHMe2), 1.50 (s, 3H, NCMe), 3.06 (s, 2H, CH2Cl), 3.43 (s, 1H, NCCH2), 3.63 (sept, 3JHH ) 6.8 Hz, 2H, CHMe2), 3.75 (sept, 3JHH ) 6.8 Hz, 2H, CHMe2), 4.01 (s, 1H, NCCH2), 5.39 (s, 1H, γ-CH), 7.01-7.24 (m, br, 6H, 2,6-iPr2C6H3). 13 C{1H} NMR (100.61 MHz, C6D6, 298 K): δ 22.1-35.6 (CHMe2, NCMe, CH2Cl), 90.4 (NCCH2), 108.6 (γ-C), 124.0-149.0 (NCMe, NCCH2, 2,6-iPr2C6H3). 29Si NMR (79.49 MHz, C6D6, 298 K): δ -38.3 (s). EI-MS m/z (%): 620 (12.74, [M]+), 605 (100, [M Me]+), 577 (94.5, [M - iPr]+). Anal. Calcd for C30H42N2SiClI: C, 58.01; H, 6.82; N, 4.51. Found: C, 57.95; H, 6.70; N, 4.36. Reaction of 1 with CH2Br2. CH2Br2 (0.025 mL, d ) 2.497 g/mL, 0.36 mmol) was added to the silylene 1 (0.16 g, 0.36 mmol) at room temperature. After 2 days, the yellow color of the solution remained unchanged. However, the 1H NMR spectra showed that two compounds 6 and 7 were formed in 58% and 42% yield, respectively. Although they could not be separated, their composition could be unequivocally deduced by means of 1H, 13C, and 29Si NMR spectroscopy. Compound 7 was identified by 1H NMR spectroscopy in accordance with literature data.15 Identification of 6, 1H NMR (200.13 MHz, C6D6, 298 K): δ 1.17-1.45 (8 × d,

1932 Organometallics, Vol. 28, No. 6, 2009

Xiong et al.

Figure 3. The molecular structure of 5. Thermal ellipsoids are drawn at 50% probability level. Hydrogen atoms (except for those at C30 and C1) are omitted for clarity. For selected distances and angles, see Table 3.

Figure 5. The molecular structure of 10. Thermal ellipsoids are drawn at 50% probability level. Hydrogen atoms (except for those at C1) are omitted for clarity. For selected distances and angles, see Table 3.

Figure 4. The molecular structure of 9. Thermal ellipsoids are drawn at 50% probability level. Hydrogen atoms (except for those at C1) are omitted for clarity. For selected distances and angles, see Table 3.

Figure 6. The molecular structure of 11. Thermal ellipsoids are drawn at 50% probability level. Hydrogen atoms (except for those at C1 and Si2) are omitted for clarity. For selected distances and angles, see Table 3.

JHH ) 7 Hz, 24H, CHMe2), 1.46 (s, 3H, NCMe), 2.51 (s, CH2Br), 3.42 (s, 1H, NCCH2), 3.46-3.77 (m, 3JHH ) 7 Hz, 4H, CHMe2), 3.98 (s, 1H, NCCH2), 5.39 (s, 1H, γ-CH), 6.93-7.18 (m, br, 6H, 2,6-iPr2C6H3). 13C{1H} NMR (100.61 MHz, C6D6, 298 K): δ 21.6-29.1 (CHMe2, CHMe2, CH2Br), 90.7 (NCCH2), 108.3 (γC), 124.4-149.3 (NCMe, NCCH2, 2,6-iPr2C6H3). 29Si NMR (79.49 MHz, C6D6, 298 K): δ -32.4 (s). EI-MS m/z (%): 618.6 (9.7, [M]+), 603.6 (23, [M - Me]+). Reaction of 1 with CHCl3. At room temperature to the yellow silylene 1 (0.75 g, 1.68 mmol) was added excess CHCl3 (5 mL, 1.48 g/mL, 62.0 mmol). The color of the solution immediately changed to violet, and the reaction was completed in a few minutes. The 1H NMR spectrum shows that two compounds 8 and 9 in a molar ratio of 2:1 were formed. The mixture of 8 and 9 is inseparable by fractional crystallization due to their similarly high solubility in organic solvents. However, compound 9 as the potential silylene 1 precursor has been synthesized according to a pathway similar to that for 7 (see below) and characterized through X-ray analysis. The comparison and extraction of the known NMR signals of 9 enable the assignment of the rest of the signals for compound 8. For compound 8, 1H NMR (200.13 MHz, C6D6, 298 K): δ 1.13-1.40 (8 × d, 3JHH ) 7 Hz, 24H, CHMe2), 1.42 (s, 3H, NCMe), 3.43 (s, 1H, NCCH2), 3.48-3.70 (m, 3JHH ) 7 Hz, 4H, CHMe2), 3.99 (s, 1H, NCCH2), 5.34 (s, 1H, γ-CH), 5.41 (s, 1H, CHCl2),

7.00-7.21 (m, br, 6H, 2,6-iPr2C6H3). 13C{1H} NMR (100.61 MHz, C6D6, 298 K): δ 15.5 (CHCl2), 21.4-28.7 (CHMe2, NCMe), 88.0 (NCCH2), 104.5 (γ-C), 124.5-149.5 (NCMe, NCCH2, 2,6i Pr2C6H3). 29Si NMR (79.49 MHz, C6D6, 298 K): δ -39.4 (s). EIMS m/z (%): 564.2 (4.0, [M]+), 549.1 (23.0, [M - Me]+), 521 (17.0, [M - iPr]+). For compound 9, 1H NMR (200.13 MHz, C6D6, 298 K): δ 1.07-1.44 (8 × d, 3JHH ) 7 Hz, 24H, CHMe2), 1.45 (s, 3H, NCMe), 3.43 (s, 1H, NCCH2), 3.42-3.70 (m, 3JHH ) 7 Hz, 4H, CHMe2), 3.96 (s, 1H, NCCH2), 5.34 (s, 1H, γ-CH), 6.93-7.18 (m, br, 6H, 2,6-iPr2C6H3). 13C{1H} NMR (100.61 MHz, C6D6, 298 K): δ 21.4-28.9 (NCMe, CHMe2, CHMe2, CHCl2), 90.0 (NCCH2), 107.5 (γ-C), 124.7-149.0 (NCMe, NCCH2, 2,6-iPr2C6H3). 29Si NMR (79.49 MHz, C6D6, 298 K): δ -40.0 (s). EI-MS m/z (%): 514.6 (4.5, [M]+), 499.3 (100.0, [M - Me]+), 471.2 (42.0, [M i Pr]+). The synthesis of authentic sample 9: To a cooled (-40 °C) solution of LiL′ {L′ ) CH[CMeN(aryl)2], aryl ) 2,6-iPr2C6H3} (2.42 g, 5.70 mmol) and N,N,N′,N′-tetramethylethylenediamine (0.66 g, 5.70 mmol) in diethyl ether (40 mL) was dropwise added SiCl4 (0.97 g, 5.70 mmol) with stirring. The reaction mixture was slowly warmed to room temperature and stirred overnight. Volatiles were removed in vacuo, and the residue was extracted with n-hexane (90 mL). Filtration and subsequent concentration afforded, after 12 h of cooling at -20 °C, colorless crystals of 9 (2.20 g, 4.28 mmol, 75%). Mp 157 °C (decomp.). The NMR spectra (1H, 13C,

3

ReactiVity of a Zwitterionic Stable Silylene 29 Si) are the same as those given above. Anal. Calcd for C29H40N2SiCl2: C, 67.55; H, 7.82; N, 5.43. Found: C, 67.36; H, 7.81; N, 5.34. Reaction of 1 with MeCCl3. MeCCl3 (0.61 mL, 6.10 mmol) was added to a solution of the silylene 1 (2.71 g, 6.10 mmol) in hexane (20 mL) at room temperature. The yellow color of the solution turned slowly pale yellow. After 4 h, a clear solution could be obtained via centrifugation. The 1H NMR spectrum shows that two compounds 10 and 9 were formed in the molar ratio of 2:1. The main product 10 crystallized at first from the solution at 0 °C. Yield: 0.60 g (1.04mmol), 17%. For compound 10: Mp 158 °C (decomp.). 1H NMR (200.13 MHz, C6D6, 298 K): δ 1.11-1.42 (8 × d, 3JHH ) 7 Hz, 24H, CHMe2), 1.50 (s, 3H, Me), 1.55 (s, 3H, Me), 3.52 (s, 1H, NCCH2), 3.60-4.03 (m, 3JHH ) 7 Hz, 4H, CHMe2), 4.10 (s, 1H, NCCH2), 5.38 (s, 1H, γ-CH), 7.00-7.24 (m, br, 6 H, 2,6-iPr2C6H3). 13C{1H} NMR (100.61 MHz, C6D6, 298 K): δ 22.1 (NCMe), 23.9-27.0 (CHMe2), 28.5-29.8 (CHMe2), 36.2 (CMeCl2), 91.8 (NCCH2), 107.0 (γ-C), 124.3-149.3 (NCMe, NCCH2, 2,6-iPr2C6H3). 29Si NMR (79.49 MHz, C6D6, 298 K): δ -41.7 (s). EI-MS m/z (%): 578.2 (17.8, [M]+), 563.1 (26.6, [M Me]+). Anal. Calcd for C31H43N2SiCl3: C, 64.40; H, 7.50; N, 4.85. Found: C, 64.41; H, 7.57; N, 4.84. Reaction of 1 with HSiCl3. To a yellow solution of the silylene 1 (2.16 g, 4.86 mmol) in diethyl ether (25 mL) was added at -50 °C freshly distilled trichlorosilane HSiCl3 (0.50 mL, 4.86 mmol). After 2 h, the reaction mixture was allowed to warm slowly to room temperature and stirred for another 3 h. The yellowish solution was concentrated and cooled by -20 °C. The main product 11 (80% according to 1H NMR spectrum) crystallized from the solution at first. Yield: 1.19 g (2.05 mmol), 42.2%. Mp 140 °C (decomp.). 1H NMR (200.13 MHz, C6D6, 298 K): δ 1.08-1.42 (8 × d, 3JHH ) 7 Hz, 24H, CHMe2), 1.39 (s, 3H, NCMe), 3.40 (s, 1H, NCCH2), 3.60 (m, 3JHH ) 7 Hz, 4H, CHMe2), 3.94 (s, 1H, NCCH2), 5.21 (s, 1H, γ-CH), 5.34 (s, 1H, SiHCl2), 6.93-7.18 (m, br, 6H, 2,6-iPr2C6H3). 13 C{1H} NMR (100.61 MHz, C6D6, 298 K): δ 21.1 (NCMe), 23.3-26.4 (CHMe2), 28.3-30.0 (CHMe2), 88.8 (NCCH2), 105.4 (γ-C), 124.2-150.1 (NCMe, NCCH2, 2,6-iPr2C6H3). 29Si NMR (79.49 MHz, C6D6, 298 K): δ -8.06 (s, SiHCl2), -35.87 (s, SiN2). EI-MS m/z (%): 580.2 (0.55, [M]+), 565.1 (1.24, [M - Me]+, 537.2 (2.12, [M - iPr]+). Anal. Calcd for C29H41N2Si2Cl3: C, 60.04; H, 7.12; N, 4.83. Found: C, 60.18; H, 6.98; N, 4.72. The byproduct 12 (20% according to NMR spectrum) was detected through NMR spectra and mass spectrometry and identified with an authentic sample prepared by the reaction of 1 (0.15 g, 0.34 mmol) with HNEt3Cl (0.34 g, 0.36 mmol) in C6D6 (0.60 mL) at room temperature, which give the same 1H, 13C, and 29Si NMR spectra and EI-MS data as compound 12. 1H NMR (200.13 MHz, C6D6, 298 K): δ 1.13-1.50 (8 × d, 3JHH ) 7 Hz, 24H, CHMe2), 1.51 (s, 3H, NCMe), 3.43 (s, 1H, NCCH2), 3.42-3.70 (m, 3JHH ) 7 Hz, 4H, CHMe2), 3.98 (s, 1H, NCCH2), 5.31 (s, 1H, γ-CH), 5.61 (s, 1H, LSiH), 6.99-7.24 (m, br, 6H, 2,6-iPr2C6H3). 13C{1H} NMR

Organometallics, Vol. 28, No. 6, 2009 1933 (100.61 MHz, C6D6, 298 K): δ 15.5 (NCMe), 21.4-28.7 (CHMe2), 88.0 (NCCH2), 104.5 (γ-C), 124.5-149.5 (NCMe, NCCH2, 2,6i Pr2C6H3). 29Si NMR (79.49 MHz, C6D6, 298 K): δ -36.0 (s). EIMS m/z (%): 481.3 (3.65, [M]+), 466.3 (33.9, [M - Me]+), 403.3 (98.2, [M - iPr - Cl]+). Reaction of 1 with MeSiCl3. To a solution of the silylene 1 (1.84 g, 4.14 mmol) in diethyl ether (20 mL) was added at -40 °C trichloromethylsilane MeSiCl3 (0.50 mL, d ) 1.27 g/mL, 4.14 mmol). After 5 min, the reaction mixture was allowed to warm to room temperature. After 10 days, the reaction was completed. The reaction mixture was concentrated to 5 mL and cooled to -20 °C. The main product 13 (80% according to the 1H NMR spectrum) crystallized as colorless crystals from toluene. Yield: 0.98 g (1.65 mmol), 40%. Mp 201 °C (decomp.). 1H NMR (200.13 MHz, C6D6, 298 K): δ 0.03 (s, 3H, SiMeCl2), 1.12-1.44 (8 × d, 3JHH ) 7 Hz, 24H, CHMe2), 1.49 (s, 3H, NCMe), 3.48 (s, 1H, NCCH2), 3.70 (m, 3JHH ) 7 Hz, 4H, CHMe2), 4.05 (s, 1H, NCCH2), 5.32 (s, 1H, γ-CH), 7.03-7.19 (m, br, 6H, 2,6-iPr2C6H3). 13C{1H} NMR (100.61 MHz, C6D6, 298 K): δ 7.93 (MeSiCl2), 21.5-30.2 (CHMe2, NCMe), 89.3 (NCCH2), 105.7 (γ-C), 124.2-150.2 (NCMe, NCCH2, 2,6i Pr2C6H3). 29Si NMR (79.49 MHz, C6D6, 298 K): δ -14.23 (s, SiMeCl2), -37.13 (s, SiN2). EI-MS m/z (%): 594.4 (7.23, [M]+), 579.2 (43.32, [M - Me]+), 551.2 (40.88, [M - iPr]+). Anal. Calcd for C30H43N2Si2Cl3: C, 60.64; H, 7.29; N, 4.71. Found: C, 60.50; H, 6.72; N, 4.53. The byproduct 12 (20% according to NMR spectrum) was detected through NMR spectra and mass spectrometry. Single-Crystal X-ray Structure Determination. Crystals were each mounted on a glass capillary in perfluorinated oil and measured in a cold N2 flow. The data were collected on an Oxford Diffraction Xcalibur S Sapphire at 150 K (Mo KR radiation, λ ) 0.71073 Å). The structures were solved by direct methods and were refined on F2 with the SHELX-9721 software package. The positions of the H atoms were calculated and considered isotropically according to a riding model. All disordered groups were refined with distance restraints and restraints for the anisotropic displacement parameters. The CH2Cl group and I atom in 5 are disordered over two orientations in a population ratio of 0.95:0.05. The C31 and Cl3 atoms in 10 also are disordered over two orientations in a population ratio of 0.90:0.10.

Acknowledgment. This work was supported by the Deutsche Forschungsgemeinschaft. Supporting Information Available: Details of the crystal structure determination for 3, 4, 5, 9, 10, and 11. This material is available free of charge via the Internet at http://pubs.acs.org. OM801157U (21) Sheldrick, G. M. SHELX-97 Program for Crystal Structure Determination; Universita¨t Go¨ttingen: Germany, 1997.