triflate ion (2.92 Å) is also observed normal to the (approx-
imate) C2N2 plane.
N
Future work in this area will address the behaviour of other
metal ions in the presence of L1, as well as structural
modifications to the macrocycle (O, S analogues) which should
further expand its scope as a novel ligand.
Ag
This research was supported by a grant from the European
Commission (to J. H.), and we would like to thank Martin
Schro¨der for helpful discussions.
N
Notes and References
* E-mail pczmm@vax.ccc.nottingham.ac.uk
†
Single
crystal
structure
determinations:
[CuL1]BF4·H2O:
C
24H33BCuF4N3]·H2O, Mr = 531.90, colourless irregular plate 0.39 3 0.39
¯
3 0.10 mm, triclinic, space group P1 (no. 2), a = 9.937(12), b = 10.094(6),
13.656(15) Å, a 83.23(7), b 81.19(12), g 61.24(6)°,
U = 1185.0(17) Å3, Z = 2, Dc = 1.491 g cm23, m(Mo-Ka) = 0.976 mm21
T = 150 K. Stoe Stadi-4 four-circle diffractometer, Mo-Ka radiation
(l 0.71073 Å) 2qmax 50°. Numerical absorption corrections
c
=
=
=
=
,
N
=
=
(T = 0.756–0.908). The structure was solved by automatic direct methods
(G. M. Sheldrick, SHELXS-96. Acta Crystallogr., Sect. A, 1990, 46, 467)
and refined by full-matrix least squares on F2 (G. M. Sheldrick, SHELXL-
96. University of Go¨ttingen, Germany, 1996) with all non-H atoms assigned
anisotropic displacement parameters. Methylene H atoms were placed
geometrically, others being located from DF syntheses; thereafter those of
H2O were refined freely with others constrained to ride on their parent
atoms. Final R1 [Fo > 4s(Fo)] = 0.0551, wR2 (all data) = 0.1264 for 4150
unique reflections and 328 refined parameters.
Fig. 3 Crystal structure of [AgL1]OTf. Displacement ellipsoids are
represented at the 20% probability level and the H-atoms and counter-ion
are omitted for clarity. Only the major component of disorder affecting the
free nitrogen [N3] is shown.
between which the metal is located. An interesting feature of
this structure is the relationship of Cu to the benzene rings. This
[AgL1]OTf: C25H33AgF3N3O3S, Mr = 620.5, colourless plate 0.53 3
0.48 3 0.11 mm, monoclinic, space group P21/c (no. 14), a = 13.152(5),
b = 10.655(5), c = 19.306(4) Å, b = 106.50(2)°, U = 2594.0(9) Å3, Z = 4,
Dc = 1.589 g cm23, m(Mo-Ka) = 0.911 mm21, T = 220 K. Data were
1
may involve either the metal acting as an electron acceptor in h
bonds to C,5 or three-centre, two-electron s complexation to the
aromatic C–H bonds.6 The Cu···C distances are 2.38 and 2.40 Å,
and the 0.57 Å displacement of the metal away from C(9)–C(18)
axis puts the contacts to the midpoint of the C–H bonds at 2.37
and 2.39 Å. The downfield shift in the NMR of the protons
involved argues in favour of this type of interaction and against
agostic bonding to the H, which would normally result in an
upfield shift.7 It is noted that interactions between copper(i) and
aryl rings are somewhat of a novelty in any case, with only five
other structurally characterised examples appearing in the
literature.8 All of these show exclusively h interactions to
collected as for [CuL1]BF4 H2O and absorption corrections
.
(T = 0.582–0.775) based on azimuthal scans were applied. The structure
was solved and refined as for [CuL1]BF4 H2O. Static disorder was modelled
.
in the region of the non-coordinating N, with major (0.76) and minor (0.24)
components and with restraints applied to C–C and C–N distances. The H
atom on the minor component was omitted, that on the major was restrained
during refinement and all others were riding on their parent atoms. Final R1
[Fo > 4s(Fo)] = 0.0414, wR2 (all data) = 0.1071 for 4561 unique
reflections and 328 refined parameters. CCDC 182/710.
2
carbon, most with the Cu located over a p bond in an h
1 L. F. Lindoy, The Chemistry of Macrocyclic Ligand Complexes,
Cambridge University Press, Cambridge, 1989; A. J. Blake and
M. Schro¨der, Adv. Inorg. Chem., 1990, 35, 1.
2 M. Mascal, J.-L. Kerdelhue´, A. S. Batsanov and M. J. Begley, J. Chem.
Soc., Perkin Trans. 1, 1996, 1141.
3 Modelling of L1 was carried out using MACROMODEL, version 4.0,
with the MM3 force field: F. Mohamadi, N. G. J. Richards, W. C. Guida,
R. Liskamp, M. Lipton, C. Caufield, G. Chang, T. Hendrickson and
W. C. Still, J. Comput. Chem., 1990, 11, 440. An X-ray crystal structure
of L1 which confirms structural predictions has been obtained and will be
presented when the work is published in full.
fashion.9
We then examined the dynamics of ligand exchange in
1
[CuL1]. The H NMR spectrum (CDCl2CDCl2) shows tem-
perature dependent fluxional behaviour, with collapse of the
two aromatic signals to a single, broad peak occurring around
95 °C. Migration of the copper nominally involves breaking
away from one of the nitrogens and both carbons [or C–H(s) ?
Cu bonds] of a C2N2 ligand set before regaining the same from
another set, although progression from site to site would take
place under the continuous influence of the p system.
4 Adaptation of the classic method of: A. J. Hubert, J. Chem. Soc. C, 1967,
6, who described an all-hydrocarbon analog of L1.
Reaction of the macrobicycle with AgOTf in THF gave the
corresponding complex [AgL1]OTf. Unlike [CuL1]BF4, the
proton NMR (CD2Cl2) of this material showed a single
resonance in the aromatic region at room temperature, and only
on cooling below 250 °C did the signal split analogously to the
copper(i) system into two sharp peaks (1:2), separated in this
case by 0.27 ppm. This indicated a much greater degree of
mobility for the silver ion than for CuI. The X-ray crystal
structure of [AgL1]OTf† (Fig. 3) was comparable to that of
[CuL1]BF4, the major difference being that only one of the two
CCNCC chains needed to distort from the ideal all-trans
conformation to accommodate the larger silver ion (Ag–N 2.32
Å). The outward displacement of the silver from the C9–C18
axis (0.40 Å) is slightly less than that for copper(i), but the same
1
5 For a description of h coordination of benzene to silver(i) see: K. Shelly,
D. C. Finster, Y. J. Lee, W. R. Scheidt and C. A. Reed, J. Am. Chem. Soc.,
1985, 107, 5955.
6 R. H. Crabtree, Angew. Chem., Int. Ed. Engl., 1993, 32, 789.
7 M. Brookhart, M. L. H. Green and L.-L. Wong, Prog. Inorg. Chem.,
1988, 36, 1.
8 Cambridge Structural Database: F. H. Allen and O. Kennard, Chemical
Design Automation News, 1993, 8, 31.
9 R. W. Turner and E. L. Amma, J. Am. Chem. Soc., 1966, 88, 1877;
G. B. Ansell, M. A. Modrick and J. S. Bradley, Acta Crystallogr., Sect.
C, 1984, 40, 365; H. Schmidbaur, W. Bublak, B. Huber, G. Reber and
G. Mu¨ller, Angew. Chem., Int. Ed. Engl., 1986, 25, 1089; C. J. Brown,
P. J. McCarthy, I. D. Salter, K. P. Armstrong, M. McPartlin and
H. R. Powell, J. Organomet. Chem., 1990, 394, 711; D. Ohlmann,
H. Pritzkow, H. Gru¨tzmacher, M. Anthamatten and R. Glasser, J. Chem.
Soc., Chem. Commun., 1995, 1011.
1
general NMR and structural arguments apply and either h
complexation or two electron donation from the C–H bonds can
be invoked. A longer range contact to one of the oxygens of the
Received in Cambridge, UK, 13th October 1997; 7/07354B
356
Chem. Commun., 1998