electrophiles to produce a wide variety of heterocyclic
compounds, including borazoles, silylazoles, benzazepines,
indoles, and pyrroles.7
suitable for X-ray diffraction analysis was obtained repro-
ducibly in varying yields from 20 to 50%. Quite surprisingly,
each of the dianions 1-3 was obtained in a different and
wholly unique aggregation state despite the fact that the only
differences among the separate reactions are the alkyl groups
attached to the silicon.
Corriu et al. first noted the relatively mild conditions, i.e.,
0 °C, diethyl ether, n-BuLi, required to form the dianion of
N-trimethylsilyl (TMS) allylamine. Hence, we set out to
generate the dianion of N-TMS allylamine and to crystallize
it in an attempt to determine the aggregation state, the
coordination number, and the geometry of the anionic centers
in these species. In so doing we have discovered three novel
and unique aggregates derived from the dianions of N-
trimethylsilyl, N-triisopropylsilyl, and N-tert-butyldimeth-
ylsilyl allylamines (1-3).
The tert-butyl dimethyl silyl (TBDMS) substituted dianion
1 crystallizes as the hexamer depicted in Figure 1.8 Note
The mono-N-silyl amines depicted in Scheme 1 were
prepared in one step from allylamine and the trialkylsilyl
chlorides. Reaction of these amines dissolved in diethyl ether
under identical conditions with slightly more than 2 equiv
of n-butyllithium yielded the dianions 1-3. Formation of
the dianions was established by quenching the reaction
mixtures with D2O followed by analysis of the product for
deuterium incorporation. In all cases, GC-MS analysis
revealed >90% deuterium incorporation at the terminal
vinylic position. Solutions of the dianions were allowed to
stand for an extended period ranging from overnight to
several days at -20 °C, and crystalline material directly
(7) (a) Wrackmeyer, B.; Ordung, I.; Schwarze, B. Z. Naturforsch. B 1997,
52(3), 427-430. (b) Corriu, R. J. P.; Geng, B.; Moreau, J. J. E. J. Org.
Chem. 1993, 58(6), 1443-1448. (c) Smith, A. B., III; Visnick, M.
Tetrahedron Lett. 1985, 26, 3757-2760. (d) Schulze, J.; Boese, R.; Schmid,
G. Chem. Ber. 1981, 114, 1297-1305. (e) Schulze, J.; Schmid, G. J.
Organomet. Chem. 1980, 193, 83-91. (f) Ha¨nnssgen, D.; Odenhausen, E.
Chem. Ber. 1979, 112, 2389-2393.
Figure 1. The hexameric aggregate of the lithium dianion 1 derived
from tert-butyldimethylsilylallylamine showing only the aggregate
core.
(8) X-ray data were collected in 0.3° steps on a four-circle diffractometer
in the φ-scan mode equipped with a Bruker SMART CCD 1K detector
(Mo K_ radiation, λ ) 0.71073 Å). All structures were solved by direct
methods and refined with full matrix least squares on all reflections based
on F2 using the SHELXTL programs commerically available from Bruker
Analytical Instruments. Crystallographic data follows. (a) Hexameric
aggregate derived from the TBDMS-allylamine anion 1: crystallographic
asymmetric unit [C9H19Li2NSi]3; Mr ) 549.67; clear, colorless crystal of
dimension 0.3 × 0.4 × 0.45 mm mounted on a quartz fiber under a stream
of dry N2 gas at -40 °C; monoclinic space group P21/n; a ) 14.20 (0.10),
b ) 12.65 (0.9), and c ) 20.61 (0.13) Å, â ) 100.32 (3)°; V ) 3644 (4)
× 106 pm3; Z ) 4; Fcalcd ) 1.002 g cm-3; µ ) 0.148 mm-1 (no correction
applied); 16011 reflections collected, 5155 independent (Rint ) 0.0866); θ
range 1.61-23.37°, 97.3% completeness; 355 parameters; R1 ) 0.0756,
wR2 ) 0.169 [I > 2σ(I)] for 5155 data; max/min. +0.339 and -0.279 e
Å-3; H atoms located in density maps and refined in fixed idealized
positions. (b) Tetrameric aggregate derived from TIPS allylamine anion
2‚pentane solvate: crystallographic asymmetric unit [C12H25Li2NSi]4‚C5H12;
Mr ) 973.35; clear, colorless crystal of dimension 0.2 × 0.2 × 0.15 mm
mounted on a quartz fiber under a stream of dry N2 gas at -40 °C; triclinic
space group P-1; a ) 13.46 (0.20), b ) 15.64 (0.3), and c ) 17.89 (0.2) Å,
R ) 111.95 (10)°, â ) 100.32 (3)°, γ ) 90.76(10)°; V ) 3454.2 (9) × 106
pm3; Z ) 2; Fcalcd ) 0.936 g cm-3; µ ) 0.117 mm-1 (no correction applied);
13380 reflections collected, 9316 independent (Rint ) 0.0380); θ range 1.24-
23.30°, 93.6% completeness; 601 parameters; R1 ) 0.0901, wR2 ) 0.2632
[I > 2σ(I)] for 9316 data; max/min. +1.479 and -0.397 e Å-3; H atoms
located in density maps and refined in fixed idealized positions. (c) Mixed
aggregate derived from TMS allylamine anion 3 was extremely unstable
so that several differnt crystals were utilized: crystallographic asymmetric
unit [C6H13Li2NSi]3‚C6H14LiNSi‚C4H13Li‚C4H10O; Mr ) 726.70; clear,
colorless crystals of dimension 0.2 × 0.2 × 0.15 mm mounted on a quartz
fibers under a stream of dry N2 gas at -40 °C; triclinic space group P-1;
a ) 13.46 (3.0), b ) 13.73 (2.0), and c ) 16.30 (10.0) Å, R ) 92.64 (10)°,
â ) 110.93 (3)°, γ ) 105.86 (10)°; V ) 2673.1(9) × 106 pm3; Z ) 2; Fcalcd
) 0.903 g cm-3; µ ) 0.136 mm-1 (no correction applied); 11331 reflections
collected, 7095 independent (Rint ) 0.3703); θ range 1.72-23.26°, 92.6%
completeness; 469 parameters; R1 ) 0.1383, wR2 ) 0.3417 [I >2σ(I)] for
7095 data; max/min. +1.389 and -0.619 e Å-3; H atoms located in density
maps and refined in fixed idealized positions.
that the hydrogen atoms are not shown in this or any other
crystal structure plots for clarity. The key infrastructure in
this aggregate is a central hexagonal prismatic core made
up of six lithiums and the terminal vinylic carbon atom of
six allylamines. This hexagonal prismatic core in this
aggregate was found in structures of cyclohexyllithium,9
susbtututed cyclopropyllithium,10 and lithium imines.11 This
aggregate is by far the most intricate of this type reported to
date.
If the TBDMS group is replaced with triisopropyl (TIPS),
the dianion 2 crystallizes as the tetrameric aggregate depicted
(9) Zerger, R.; Rhine, W.; Stucky, G. J. Am. Chem. Soc. 1974, 96, 6048-
6055.
(10) Maercker, A.; Bsata, M.; Buchmeier, W.; Engelen, B. Chem. Ber.
1984, 117, 1884, 2547.
(11) (a) Shearer, H. M. M.; Wade, K.; Whitehead, G. J. Chem. Soc.,
Chem. Commun. 1979, 943. (b) Clegg, W.; Snaith, R.; Shearer, H. M. M.;
Wade, K.; Whitehead, G. J. Chem. Soc., Dalton Trans. 1983, 1309.
(12) (a) Chitsaz, S.; Neumuller, B.; Dehnicke, K. Z. Anorg. Allg. Chem.
1999, 625, 9. (b) Barr, D.; Clegg, W.; Mulvey, R. E.; Snaith, R. Chem.
Commun. 1989, 57. (c) Knizek, J.; Krossing, I.; Noth, H.; Schwenk, H.;
Seifert, T. Chem. Ber. 1997, 130, 1053. (d) Kunert, M.; Dinjus, E.; Nauck,
M.; Sieler, J. Chem. Ber. 1997, 130, 1461. (e) Barnett, N. D.; Mulvey, R.
E.; Clegg, W.; O’Neil, A. P. Polyhedron 1992, 112, 809.
(13) Other aggregates that incorporate n-butyllithium are as follows: (a)
Davies, R. P.; Raithby, P. R.; Snaith, R. Angew. Chem., Int. Ed. Engl. 1997,
36(11), 1215-1217. (b) Sun, C.; Williard, P. G. J. Am. Chem. Soc. 1997,
119(48), 11693-11694.
(14) Stucky, G.; Rundle, R. E. J. Am. Chem. Soc. 1964, 86, 4821.
2754
Org. Lett., Vol. 2, No. 18, 2000