6 Spectroscopic data for 2: 1H NMR (200.13 MHz, C6D6, 298 K): d
1.40 (s, 3 H, NCMe), 2.11 (s, 6 H, 2,6-Me2C6H3), 2.31 (s, 6 H, 2,6-
Me2C6H3), 4.25 (d, 1 H, 4JHH = 2.7 Hz, a-CH), 4.47 (s, 1 H, NH), 4.76
(d, 1H,4JHH = 2.7 Hz, g-CH), 6.91–7.02 (m, br, 6 H, 2,6-Me2C6H3).
1
13C{ H} NMR (100.61 MHz, C6D6, 298 K): d 18.2–22.6 (Me), 78.12(a-
1
C), 100.4 (g-C), 125.6–155.2 (NCMe, NCCH2, 2,6-Me2C6H3). 29Si{ H}
NMR (79.49 MHz, C6D6, 298 K): d -31.4 (s). EI-MS: m/z (%): 492.3(5,
[M]+), 476.9 (6, [M - Me]+, 371.8 (7, [M - NHR]+, R = 2,6-Me2C6H3),
306.2 (35, [M - SiBr2]+), 291.1 (30.0, [M - SiBr2 - Me]+), 187.1(100,
[HSiBr2]+). Elemental analysis (%) calcd for C21H24N2SiBr2: C, 51.23;
H, 4.91; N, 5.69. Found: C, 50.82; H, 4.70; N, 5.44. Spectroscopic
data for 3: 1H NMR (200.13 MHz, C6D6, 298 K): d 1.36 (s, 3 H,
NCMe), 2.21 (s, 6 H, 2,6-Me2C6H3), 2.28 (s, 6 H, 2,6-Me2C6H3), 5.22
4
(d, 1 H,4JHH = 3.0Hz, a-CH), 5.96 (d, 1H, JHH = 3.0Hz, g-CH),
1
6.81–6.90 (m, br, 6 H, 2,6-Me2C6H3). 13C{ H} NMR (100.61 MHz,
C6D6, 298 K): d 19.3–22.7 (Me), 92.7 (a-C), 101.1 (g-C), 128.6–
153.7 (NCMe, NCCH2, 2,6-Me2C6H3). 29Si{ H} NMR (79.49 MHz,
1
Scheme 3 Proposed mechanism for the formation of 2 via the reactive
intermediates I, II, and III.
C6D6, 298 K): d -31.2 (s, SiBr2), -66.1 (s, SiBr3). EI-MS: m/z (%):
759.6(55, [M]+), 744.6 (21, [M - Me]+, 679.7 (35, [M-Br]+), 491.9 (14,
[M-SiBr3]+), 477.0(13, [M-SiBr3-Me]+), 371.7(13, [M-SiBr3-NHR]+,
R = 2,6-Me2C6H3). Elemental analysis (%) calcd for C21H23N2Si2Br5: C,
33.23; H, 3.05; N, 3.69. Found: C, 33.05; H, 3.21; N, 3.70. Spectroscopic
data for 4: 1H NMR (200.13 MHz, C6D6, 298 K):d 1.89 (s, 12 H, 2,6-
Me2C6H3), 2.61 (s, 6 H, NCMe), 4.10 (s, 1 H, g-CH), 6.72–6.98 (m,
br, 6 H, 2,6-Me2C6H3), 11.45 (s, 2H, NH); EI-MS: m/z (%): 307.1 (9,
[M - Br]+), 187.1 (100, [M - NC6H3Me2]+. Spectroscopic data for 5: 1H
NMR (200.13 MHz, C6D6, 298 K): d 1.32 (s, 3 H, NCMe), 2.39 (s, 6
H, 2,6-Me2C6H3), 2.49 (s, 6 H, 2,6-Me2C6H3), 3.56 (s, 1 H, NCCH2),
3.97 (s, 1 H, NCCH2), 5.36 (s, 1 H, g-CH), 6.87–7.14 (m, br, 6 H, 2,6-
centre in III is favoured by the a-Si effect10 leading to the formation
of 2. In other words, the formation of 2 involves a double C–H
bond activation induced by silicon. Apparently, 3 results from
silylation of 2 with SiBr4 under HBr elimination.
In summary, silylation of LALi 1 with SiBr4 in the presence or
absence of TMEDA as auxiliary base leads to remarkably different
products: While the N-heterocyclic dibromosilane 5 is formed in
the presence of TMEDA, the same conversion without TMEDA
affords the distinct product 2 and its SiBr3-derivative 3 along with
the HBr adduct of LAH. Both 2 and 3 are promising precursors for
novel isolable N-heterocyclic silylenes. Respective investigations
are in progress.
1
Me2C6H3). 13C{ H} NMR (100.61 MHz, C6D6, 298 K):d 20.1, 20.2,
21.2 (NCMe, 2,6-Me2C6H3), 87.5 (NCCH2), 105.9 (g-C), 129.2–144.7
1
(NCMe, NCCH2, 2,6-Me2C6H3). 29Si{ H} NMR (79.49 MHz, C6D6,
298 K):d -55.1 (s). EI-MS: m/z (%): 492.8 (7, [M]+), 491.8 (20, [M - H]+,
476.9 (100, [M - Me]+). Elemental analysis (%) calcd for C21H24N2SiBr2:
C, 51.23; H, 4.91; N, 5.69. Found: C, 51.08; H, 4.96; N, 5.99.
7 Crystal data for 2:† C21H24Br2N2Si, M = 492.33, monoclinic, space
˚
group P21/a, a = 14.9450(4), b = 8.2720(2), c = 17.7852(4) A, b =
◦
104.903(3) . V = 2124.73(9) A , Z = 4, rcalc = 1.539 Mg m-3, m(Mo
3
Acknowledgements
˚
Ka) = 3.879 mm-1, 13787 collected reflections, 3731 crystallographi-
cally independent reflections [Rint = 0.0370], 2656 reflections with I >
2s(l), qmax = 25.00◦, R(Fo) = 0.0305 (I > 2s(l)), wR(Fo2) = 0.0708
(all data), 240 refined parameters. Crystal data for 3: C21H23Br5N2Si2,
Financial support from the Deutsche Forschungsgemeinschaft is
gratefully acknowledged.
M = 759.14, orthorhombic, space group P212121, a = 11.1177(5),
3
˚
˚
b = 13.9333(7), c = 16.9301(4) A. V = 2622.6(2) A , Z = 4, rcalc
=
Notes and References
1.923 Mg m-3, m(Mo Ka) = 7.766 mm-1, 13453 collected reflections,
4586 crystallographically independent reflections [Rint = 0.0687], 3015
reflections with I > 2s(l), qmax = 25.00◦, R(Fo) = 0.0410 (I > 2s(l)),
wR(Fo2) = 0.0690 (all data), 276 refined parameters, Flack parameter:
005(14). Crystal data for 5: C21H24Br2N2Si, M = 492.33, orthorhombic,
1 For review, see: L. Bourget-Merle, M. F. Lappert and J. R. Severn,
Chem. Rev., 2002, 102, 3031.
2 Examples for stabilization of unusual oxidation states, see and the cited
references therein (a) S. Nagendran and H. W. Roesky, Organometallics,
2008, 27, 457; (b) S. P. Green, C. Jones and A. Stasch, Science, 2007,
318, 1754.
˚
space group Pna21, a = 18.7680(4), b = 7.8976(2), c = 14.2285(5) A.
3
V = 2108.98(10) A , Z = 4, rcalc = 1.551 Mg m-3, m(Mo Ka) =
˚
3 See, for example: (a) F. Basuli, U. J. Kilgore, D. Brown, J. C. Huffman
and D. J. Mindiola, Organometallics, 2004, 23, 6166; (b) H. Hamaki, N.
Takeda and N. Tokitoh, Organometallics, 2006, 25, 2457; (c) G. Bai, P.
Wei and D. W. Stephan, Organometallics, 2006, 25, 2649; (d) F. Basuli,
J. C. Huffman and D. J. Mindiola, Inorg. Chim. Acta, 2007, 360, 246;
(e) Z. Lu, M. Findlater and A. H. Cowley, Chem. Commun., 2007,
2873; (f) W. Wang, S. Yao, C. van Wu¨llen and M. Driess, J. Am. Chem.
Soc., 2008, 130, 9640.
4 See, for example: (a) Y. Ding, H. W. Roesky, M. Noltemeyer and H.-G.
Schmidt, Organometallics, 2001, 20, 4806; (b) B. Qian, S. W. Baek and
M. R. Smith, III, Polyhedron, 1999, 18, 2405; (c) S. Harder, Angew.
Chem., Int. Ed., 2003, 42, 3430; (d) L. A. Lesikar and A. F. Richards,
J. Organomet. Chem., 2006, 691, 4250; (e) Z. Lu, G. Reeske, J. A. Moore
and A. H. Cowley, Chem. Commun., 2006, 5060; (f) M. Driess, S. Yao,
M. Brym and C. van Wu¨llen, Angew. Chem., Int. Ed., 2006, 45, 4349.
5 (a) M. Driess, S. Yao, M. Brym, C. van Wu¨llen and D. Lentz, J. Am.
Chem. Soc., 2006, 128, 9628; (b) M. Driess, S. Yao, M. Brym and C. van
Wu¨llen, Angew. Chem., Int. Ed., 2006, 45, 6730; (c) S. Yao, M. Brym,
C. van Wu¨llen and M. Driess, Angew. Chem., Int. Ed., 2007, 46, 4659;
(d) Y. Xiong, S. Yao, M. Brym and M. Driess, Angew. Chem., Int. Ed.,
2007, 46, 4511; (e) S. Yao, C. van Wu¨llen, X.-Y. Sun and M. Driess,
Angew. Chem., Int. Ed., 2008, 47, 3250.
3.908 mm-1, 11209 collected reflections, 3592 crystallographically
independent reflections [Rint = 0.0431], 2875 reflections with I > 2s(l),
qmax = 25.00◦, R(Fo) = 0.0294 (I > 2s(l)), wR(Fo2) = 0.0521 (all data),
240 refined parameters, Flack parameter: 008(8). Crystals of 2, 3, and
5 were each mounted on a glass capillary in perfluorinated oil and
measured in a cold N2 flow. The data of compounds 2, 3 and 5 were
collected on an Oxford Diffraction Xcalibur S Sapphire at 150 K (Mo-
˚
Ka radiation, l = 0.71073 A). CCDC 705079–705081.
8 B. Ra¨ke, F. Zu¨lch, Y. Ding, J. Prust, H. W. Roesky, M. Noltemeyer and
H.-G. Schmidt, Z. Anorg. Allg. Chem., 2001, 627, 836.
9 (a) P. J. Ragogna, N. Burford, M. D’eon and R. McDonald, Chem.
Commun., 2003, 1052; (b) N. Burford, M. D’eon, P. J. Ragogna, R.
McDonald and M. J. Ferguson, Inorg. Chem., 2004, 43, 734; (c) P. B.
Hitchcock, M. F. Lappert and J. E. Nycz, Chem. Commun., 2003, 1142;
(d) D. Vidovic, Z. Lu, G. Reeske, J. A. Moore and A. H. Cowley, Chem.
Commun., 2006, 3501.
10 a-Si effect: a-Silyl-substituted hydrocarbons contain activated C–
H bonds (C-–H+) through negative hyperconjugation. See: A. R.
Bassindale and P. G. Taylor, Activating and directive effects of silicon,
in The Chemistry of Organic Silicon Compounds, ed. S. Patai and
Z. Rappoport, Wiley, New York, 1989, part 2, chapter 14, pp. 893–
963, and cited references therein.
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