they represent stoichiometric-variant stablemates of the zin-
cates (where x = 1 and M = Li) developed by Kondo et al.,
which are proving to be excellent reagents for selective proton
abstraction in for example the synthesis of substituted bromo-
pyridines and of asymmetrical benzynes.17 Thus looking to the
future, it would be interesting to compare the performance of
our amide-rich compounds with these amide-poor ones and,
with the option of changing the M, amide and organide
components, it may be possible to tune reagents for specific
applications.
We thank the EPSRC for financial support through grant
award no. GR/M78113.
Notes and references
Fig. 1 Asymmetric unit of the structure of 1 with atom labels and 50%
probability displacement ellipsoids. Hydrogen atoms have been omitted for
clarity. Key dimensions not in text (Å and °): N–Si; 1.703(4)–1.724(4);
N(1)–K(1)–N(2) 72.82(9), N(1)–Zn(1)–N(2) 114.06(13), N(1)–Zn(1)–
C(19) 115.59(15), N(2)–Zn(1)–C(19) 130.30(15), Zn(1)–C(19)–C(13)
117.0(3).
† 2 and 3 were prepared in a similar manner to 1 by replacing toluene by m-
xylene and mesitylene respectively. Yields of first batches, 39%, 55% and
42% for 1, 2 and 3 respectively. All form as colourless crystals and give
satisfactory (C, H, N) analyses. H NMR data ([2H8]-THF, 25 °C, 400.13
1
MHz) 1: d = 6.92 (d, 2H, o-Ar), 6.79 (t, 2H, m-Ar), 6.42 (t, 1H, p-Ar), 1.68
(s, 2H, CH2), 20.05 (s, 36H, SiMe3); 2: 6.79 (s, 1H, oA-Ar), 6.72-6.66
(overlapping m, 2H, o- and m-Ar), 6.27 (d, 1H, p-Ar), 2.12 (s, 3H, Me), 1.64
(s, 2H, CH2), 20.05 (s, 36H, SiMe3); 3: 6.57 (s, 2H, o-Ar), 6.11 (s, 1H, p-
Ar), 2.08 (s, 6H, Me), 1.60 (s, 2H, CH2), 20.05 (s, 36H, SiMe3). 13C NMR
data ([2H8]-THF, 25 °C, 100.61 MHz) 1: d = 155.0 (ipso-C), 127.5 (m-C),
127.1 (o-C), 118.2 (p-C), 30.0 (CH2), 6.8 (SiMe3); 2: 154.7 (ipso-C(CH2)),
136.0 (ipso-C(CH3)), 128.1 (oA-C), 127.4(o-C), 124.3 (m-C), 119.2 (p-C),
29.7 (CH2), 22.0 (CH3), 6.8 (SiMe3); 3 154.4 (ipso-C(CH2)), 135.6 (ipso-
C(CH3)), 125.3 (o-C), 120.3 (p-C), 29.5 (CH2), 21.9 (CH3), 6.8 (SiMe3).
Assignments confirmed by 1H/13C HMQC experiments.
‡ Crystal data for 1: C19H43KN2Si4Zn, M = 516.4, monoclinic, space group
P21/n, a = 9.2390(18), b = 20.764(4), c = 15.064(3) Å, b = 91.90(3)°, U
= 2888.3(10) Å3, Z = 4, T = 160 K; R(F; F2 > 2s) = 0.057, Rw(F2, all
data) = 0.177 for 4975 unique data and 257 refined parameters. CCDC
graphic files in CIF or other electronic format.
Fig. 2 A three-unit section of the extended chain structure of 1 highlighting
the glide plane.
1 C. H. Heathcock, in Comprehensive Organic Synthesis, eds B. M. Trost
and I. Fleming, Pergamon, New York, 1991, 2, ch. 1. 6; J. L. Rutherford
and D. B. Collum, J. Am. Chem. Soc., 2001, 123, 199.
2 J. Eames, Eur. J. Org. Chem., 2002, 393.
3 K. W. Henderson and W. J. Kerr, Chem. Eur. J., 2001, 7, 3420; J.-C.
Plaquevent, T. Perrard and D. Cahard, Chem. Eur. J., 2002, 8, 3301.
4 However, mixed-metal bases based on alkyl/alkoxide ligand systems,
‘superbases’, are well known: see, for example, L. Lochmann, Eur. J.
Inorg. Chem., 2000, 115.
[2.014(4) Å], which is comparable to the Zn–N bond lengths
[Zn–N(1), 2.010(3); Zn–N(2), 1.985(3) Å] and, most sig-
nificantly, is decidedly shorter than the Mg–C(benzyl) terminal
bond lengths (mean, 2.243 Å) in [{Li·TMEDA}+{Mg(CH-
2Ph)4Li·TMEDA}2].14 Electron-rich from the negative charge,
the p-face of the benzyl group coordinates to the K+ cation in
the next (KNZnN) ring, to extend the structure supramolecu-
larly through a chain with a glide plane. However, the spread of
bond lengths involved [K–C(13), 3.019(4); –C(14), 3.120(4);
–C(15), 3.328(5); –C(16), 3.429(5); –C(17), 3.347(5); –C(18),
3.126(4); –C(centroid), 2.919Å] is of the same magnitude as
that in the aforementioned magnesate [{[K(tolue-
ne)2]+[Mg(HMDS)3]2}n] (range of K–C bond lengths,
3.124–3.345 Å; range of K–C centroid lengths, 2.884–2.937 Å),
where the arene is neutral. Though long known experimentally
and much studied theoretically, alkali metal-p (arene) inter-
actions have recently taken on a new significance with the
suggestion that intramolecular cationic interactions with (elec-
tron-rich) aromatic centres can influence protein structures.15
The K+ coordination sphere in 1 is completed by two m-N atoms
from HMDS [lengths, 2.782(3) and 2.863(3) Å] and two short
intramolecular K…C(H3)SiMe2 (agostic) contacts [to C(1),
3.082, to C(10), 3.089 Å]. Regarding the latter contacts as
significant, the K-HMDS interactions could be interpreted as a
four-membered (KNSiC) ‘chelate’ ring, but the marked distor-
tion from linearity of the NSiC angles involved (both < 90°) in
such intramolecular contacts is usually characteristic of ex-
tremely weak dipole–dipole contacts.16
5 R. E. Mulvey, Chem. Commun., 2001, 1049.
6 W. Clegg, K. W. Henderson, A. R. Kennedy, R. E. Mulvey, C. T.
O’Hara, R. B. Rowlings and D. M. Tooke, Angew. Chem., Int. Ed.,
2001, 40, 3902.
7 D. R. Armstrong, A. R. Kennedy, R. E. Mulvey and R. B. Rowlings,
Angew. Chem., Int. Ed., 1999, 38, 131.
8 A. R. Kennedy, R. E. Mulvey and R. B. Rowlings, Angew. Chem., Int.
Ed., 1998, 37, 3180.
9 G. C. Forbes, A. R. Kennedy, R. E. Mulvey, R. B. Rowlings, W. Clegg,
S. T. Liddle and C. C. Wilson, Chem. Commun., 2000, 1759.
10 Y. Kondo, M. Shilai, M. Uchiyama and T. Sakamoto, J. Am. Chem. Soc.,
1999, 121, 3539.
11 A. P. Purdy and C. F. George, Organometallics, 1992, 11, 1955.
12 G. C. Forbes, A. R. Kennedy, R. E. Mulvey, B. A. Roberts and R. B.
Rowlings, Organometallics, 2002, 21, 5115.
13 P. C. Andrews, A. R. Kennedy, R. E. Mulvey, C. L. Raston, B. A.
Roberts and R. B. Rowlings, Angew. Chem., Int. Ed., 2000, 39, 1960.
14 B. Schubert and E. Weiss, Chem. Ber., 1984, 117, 366.
15 S. K. Burley and G. A. Petsko, FEBS Lett., 1986, 203, 139; G. K. Fukin,
S. V. Lindeman and J. K. Kochi, J. Am. Chem. Soc., 2002, 124, 8329.
16 K. W. Klinkhammer, Chem. Eur. J., 1997, 3, 1418.
17 T. Imahori, M. Uchiyama, T. Sakamoto and Y. Kondo, Chem.
Commun., 2001, 2450; M. Uchiyama, T. Miyoshi, Y. Kajihara, T.
Sakamoto, Y. Otani, T. Ohwada and Y. Kondo, J. Am. Chem. Soc.,
2002, 124, 8514.
The new compounds 1–3 can be classified by the general
formula [(M)(Zn)(amide)x(organide)32x], where x = 2. As such
CHEM. COMMUN., 2003, 406–407
407