Table 1 Selected geometric parameters for 3 and 4
Compound
av. Zr–Nendo/Å av. Zr–Nexo/Å
endo-N–Zr–NA/° MeN–Zr–NAMe/° Cipso–N–Zr/°
D(C6H4–C6H4)a/Å
C6H4/C6H4 displ.b/Å
3
4
2.094(2)
2.086(2)
2.031(2)
2.026(2)
119.32(8)
121.21(8)
105.29(10)
102.11(9)
122.9(2),
103.7(2)
115.31(12),
107.27(12)
3.43
3.48
0.75
0.15
a This refers to the distance between the two C6 planes. b This refers to the lateral displacement of the two C6 planes.
Notes and references
‡ Selected spectroscopic data: for 1: 1H NMR (300.1 MHz, 298 K,
C6D5CD3) d 7.04 (t, J 7.2 Hz, 1H), 6.58 (d, J 7.2 Hz, 2H), 6.25 (s, 1H), 2.84
(s, NMe2, 36H), 0.23 (s, SiMe3, 18H). 13C{1H} NMR (75.5 MHz, 298 K,
C6D5CD3) d 151.3, 132.0, 126.6, 122.9 (C6H4), 42.3 (NMe2), 1.8 (SiMe3).
For 2: 1H NMR (300.1 MHz, 298 K, C6D6) d 6.91 (s, 4H), 2.87 (s, NMe2,
36H), 0.24 (s, SiMe3, 18H). 13C{1H} NMR (75.5 MHz, 298 K, C6D6) d
142.8, 128.9 (C6H4), 41.9 (NMe2), 1.5 (SiMe3). For 3: 1H NMR (300.1
MHz, 298 K, C6D5CD3) d 6.68 (t, J 7.0 Hz, 1H), 6.28 (d, J 7.0 Hz, 2H), 6.08
(s, 1H), 3.05 (s, NMe2 12H), 0.14 (s, SiMe3, 18H). 13C{1H} NMR (75.5
MHz, 298 K, C6D5CD3) d 150.2, 130.9, 125.6, 121.8 (C6H4), 43.4 (NMe2),
2.3 (SiMe3). For 4: 1H NMR (300.1 MHz, 298 K, C6D6) d 6.50 (s, 4H), 3.10
(s, NMe2, 12H), 0.18 (s, SiMe3, 18H). 13C{1H} NMR (75.5 MHz, 298 K,
C6D6) d 144.0, 127.9 (C6H4), 43.2 (NMe2), 2.0 (SiMe3).
§ Crystal data: for 3, C32H68N8Si4Zr2, M = 859.7, T = 173(2) K, space
group C2/c (no. 15), a = 14.234(2), b = 17.771(4), c = 18.860(4) Å, b =
109.55(2)°, U = 4496(2) Å3, Z = 4, m(Mo-Ka) = 0.60 mm21, specimen
0.40 3 0.30 3 0.30 mm, 4123 reflections collected for 2 < q < 25°, 3963
independent (Rint = 0.0167), R1 = 0.031 for 3288 reflections with I >
2s(I), wR2 = 0.077 for all data. For 4, C32H68N8Si4Zr2, M = 859.7, T =
Fig. 2 The molecular structure of 4.
¯
173(2) K, space group P1 (no. 2), a = 9.005(4), b = 10.128(8), c =
are compared in Table 1. The aromatic rings are related by a
crystallographic twofold axis for 3 and an inversion centre for 4.
They are parallel in both structures, the planes being separated
by 3.43 (3) or 3.48 (4) Å but show a sideways displacement (3
> 4). The endocyclic N–Zr–NA bond angle is somewhat wider
in 4 than 3 but the converse is so for the Me2N–Zr–NAMe2 angle;
while for each, the average endocyclic Zr–N bond length is
significantly longer than the exocyclic, but both are unexcep-
tional; for example, the average Zr–N bond lengths are 2.08 Å
13.168(9) Å, a = 69.17(6), b = 80.33(4), g = 78.63(5)°, U = 1094(1) Å3,
Z = 1, m(Mo-Ka) = 0.62 mm21, specimen 0.3 3 0.33 0.3 mm, 6379
reflections collected for 2 < q < 25°, all independent, R1 = 0.031 for 5617
reflections with I > 2s(I), wR2 = 0.082 for all data. CCDC 182/1351. See
format.
¶ Polymerisation data: an aliquot (25 cm3) of a solution (3 or 4), or a
suspension (5) in toluene [6 3 1024 mol l21 catalyst, MAO (3 3 1021 mol)
in toluene (1 l)] was pressurised with C2H4 (2.4 bar) at 20 °C for 15 min,
whereafter the mixture was quenched by addition of methanolic HCl. The
polymer was filtered off, washed with successively 1 M aq. HCl, water and
MeOH and then dried at 80 °C. The activity corresponded to 0.11 (3) [or
0.15 (4) or 14.72 (5)] 3 103 g polymer bar21 h21 (mol cat)21. The polymer
had high average molecular weight ( ≈ 2 3 106 g mol21), determined by
viscosity determinations; solubility problems excluded the use of traditional
GPC experiments.
5
for [Zr({N(SiPri3)}2C6H4-1,2)2],5 and 2.06 Å for [Zr{h -
5
C5H4C(Me)2C9H6-h }(NMe2)2].7 The sum of the angles at each
nitrogen atom is close to 360°.
Each of the metallocyclophanes 3 and 4, in the presence of
MAO, was active as a catalyst for the polymerisation of
ethylene, and this activity was substantially enhanced if 4 was
pretreated with an excess (10 mol) of chlorotrimethylsilane to
yield 5; the polyethylenes had very high average molecular
1 F. G. N. Cloke, T. J. Geldbach, P. B. Hitchcock and J. B. Love,
J. Organomet. Chem., 1996, 506, 343.
2 J. D. Scollard and D. H. McConville, J. Am. Chem. Soc., 1996, 118,
10008.
3 G. J. P. Britovsek, V. C. Gibson and D. F. Wass, Angew. Chem., Int. Ed.
Engl., 1999, 38, 428.
weights.¶ Complex
5
is tentatively formulated as
RN(C6H4)N(R)Zr(Cl)2N(R)(C6H4)N(R)ZrCl2, an analogue of 4
(having only the terminal amido groups displaced by chloride
ligands).
Compounds 1–4 are the first binuclear, four-coordinate
zirconium(iv) amides and are also unusual in being heteroleptic.
The cyclophanes 3 and 4 are of further interest in being
macrocycles having both Lewis acid (Zr) and base [N(R) and
C6] sites and having parallel C6 rings separated by distances
close to that (3.35 Å) found in graphite. This ambiphilicity, as
well as the catalytic properties of these compounds, are under
further investigation as are comparisons of the use of these
meta- and para-N,NA-bis(trimethylsilyl)bis(amido)benzene
ligands in the context of complexes of other metals [for GeII and
SnII, see refs. 8 and 9].
4 H. Braunschweig, B. Gehrhus, P. B. Hitchcock and M. F. Lappert,
Z. Anorg. Allg. Chem., 1995, 621, 1922.
5 K. Aoyagi, P. K. Gantzel, K. Kalai and T. D. Tilley, Organometallics,
1996, 15, 923.
6 M. B. Inoue, E. F. Velazquez, F. Medrano, K. L. Ochoa, J. C. Galvez, M.
Inoue and Q. Fernando, Inorg. Chem., 1998, 37, 4070.
7 W. A. Herrmann, M. J. A. Morawietz and T. Priermei, J. Organomet.
Chem., 1996, 506, 351.
8 H. Braunschweig, C. Drost, P. B. Hitchcock, M. F. Lappert and L. J.-M.
Pierssens, Angew. Chem., Int. Ed. Engl., 1997, 36, 261.
9 H. Braunschweig, P. B. Hitchcock, M. F. Lappert and L. J.-M. Pierssens,
Angew. Chem., Int. Ed. Engl., 1994, 33, 1156.
We thank the EU for the award of a Marie Curie fellowship
to S. D. and to Dr M. Kristen and BASF (Ludwigshafen) for
other support.
Communication 9/03921J
1910
Chem. Commun., 1999, 1909–1910