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Cryptophane Radical Cations as Components of Three-Dimensional Charge-Transfer Salts.

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Cryptophane Radical Cations as Components
of Three-Dimensional Charge-Transfer Salts **
By Anne Renault, Daniel Talham, Josette Canceill,
Patrick Batail, Andrt Collet, and Janine Lujzerowicz*
Most organic donors known to date are flat molecules
such as tetrathiafulvalene (TTF), which, when associated
with suitable electron acceptors, tend to form charge-transfer (CT) salts of low dimensionality.['] The use of increasingly larger inorganic anions,"] or of electron-rich molecules
that cannot achieve a flat conformation (e.g., para-cyclophanes)[31has been recently considered as a way to increase
the dimensionality of these materials. We report here a series
of three-dimensional charge-transfer complexes in which a
large, essentially spherical (10 A in diameter) cryptophanc
molecule is employed as the donor. A cryptophane[41such as
1 15] is made of two electron-rich cyclotriveratrylene units 2
held together rigidly by three short chains. We anticipated
that oxidation of 1 would afford radical cation species which
might be stabilized by delocalization over the entire molecule.
Fig. 1. Cyclic voltammogram of I 161: 0.1 M nBu,NPF, as electrolyte;
Ag/AgNO, reference electrode in acetonitrile; scan rate 100 mVs-'.
at a platinum wire anode by constant-current electrolysis
(20.5 pA cm-') of a CH,Cl,/CHCl, (4: 1) mixture containM) and the tetrabutylammonium salts (lo-' M)
ing 1
of various Xo ions (BF? , CIO?, PF," , and ReOy) as supporting electrolytes. Their unit-cell parameters are similar
(Table l), which indicates that their structures are related.
Table 1. Single-crystal lattice parameters for charge-transfer complexes of I"
with inorganic anions [a].
a [A1
b [A1
[a] Rhombohedra1 lattice with hexagonal cell parameters, z
y = 120" for all complexes.
Indeed, we found that cryptophane-E 1 in acetonitrile solution showed two reversible oxidations (Fig. l ) at 0.69 V
(1/1@)and 0.85 V (1@/l2@)
versus Ag/Ag@.[61We also observed another oxidation (12@/13@),
approaching chemical
reversibility, at 1.11 V. The behavior of 1 contrasts markedly
with that of cyclotriveratrylene itself, which, under the same
conditions, shows two nonreversible waves at 0.87 and
1.03 V; irreversibility in the latter case might be due to a
conformational change (crown to saddle) occurring on oxidation and leading to reactive species, as in the case of the
cyclotriveratrylene cation itself;14] such a conformational
change cannot take place in cryptophane 1.
Well-faceted, blue-green hexagonal single crystals of a series of charge-transfer salts [(l'@)(Xe)(CHCl,)] were grown
Prof. Dr. J. Lajzerowicz, Dr. A. Renault
Laboratoire de Spectrometrie Physique
Universite Joseph Fourier-Grenoble I
B.P. 87, F-38402 Saint-Martin-d'Heres Cedex (France)
Dr. J. Canceill
Chimie des Interactions Moltculaires, E.R. C.N.R.S. 285
College de France
F-75231 Paris Cedex 05 (France)
Dr. D. Talham, Dr. P. Batail
Labordtoire de Physique des Solides, L.P. C.N.R.S. 02
Unwersitt Paris-Sud
Bit. 510, F-91405 Orsay Cedex (France)
Prof. Dr. A. Collet
U.M.R. C.N.R.S.-E.N.S.L. 117
Stereochimie et Interactions Moleculaires
Ecole Normale Superieure de Lyon
F-69364 Lyon Cedex 07 (France)
We are grateful to Dr. P. Rey (D.R.E.C.E.N.G.) for carrying out the spin
susceptibility measurements.
Anget+ Chem In1 Ed Engl 28 (1989) N r 9
v [A3]
=p =
The stoichiometry of the salts has been determined by the
crystal structure analysis['] of [(l'@)(PF~)(CHCl,)](Fig. 2).
Indeed, this salt is a fully charge-transferred 1 :1 complex,
since the asymmetric unit consists of one oxidized cage 1"
and one PF," ion and also contains a chloroform molecule
Fig. 2. Projection of the structure of[(l'e)(PFf)(CHCI,)] onto a plane perpeiidicular to the threefold axis; A and A centers of 1 at z = 0 and z = 1/3,
respectively: 0 center of PF," at z = 1/6.
VCH Verlagqesellschaft mbH, 0-6940 Weinhelm, 1989
0570 0833/89/0909-1249 S 02 50j0
accommodated within the cryptophane cavity, as in the
[l . CHCl,] complex.r81The packing is a face-centered cubic
array of the large spherical cations, with the anions (roughly
thirteen times smaller) located in all the octahedral sites
(at the edge centers and body centers of the cubic unit
ESR spectra of single crystals of [(l'@)(PF~)(CHCI,)]at
room temperature displayed a single line with g = 2.0030
and with a line width of ca. 1.8 - 2 gauss. This further demonstrates the existence of quasi-free, delocalized 7~ electrons.
Also, the paramagnetic signal was still present when the crystals were dissolved in dichloromethane, from which we conclude that la@
is a stable species.
For some single crystals of [( l'@)(PF~)(CHCI,)]the temperature dependence of the spin susceptibility was measured
directly using a squid susceptometer in the range of 4 to
300 K and found to follow a Curie-Weiss law with a weak
antiferromagnetic coupling. The corrected magnetic moment is 1.7 p*, corresponding to one essentially noninteracting spin (S = 1/2) per molecule of 1. The observed insulating
character of the complex is thus a consequence of the purely
ionic nature of the salt and indicates the lack of stabilization
of any intermolecular mixed valence state in the solid, presumably because of the very poor overlap between the radical cations.
In conclusion, we would like to focus on the following
ideas: (1) The above results suggest that 1 and presumably
other cryptophanes easily form a radical cation on oxidation
and hence represent a new family of organic donors. (2)
These large, spherical molecules drive the crystal structure
toward three-dimensional close-packed arrays, in contrast to
flat donor molecules which often stack in unidimensional
columns. (3) The cryptophane cavity can accommodate relatively large guest species14' (here, a chloroform molecule);
this feature may aid in the design of new materials. (4) Finally, we wish to point out that the second oxidation wave of 1
(not investigated thus far), which is also chemically reversible, generates a dication with a potential triplet ground
state (D,symmetry).["]
Received: April 14, 1989 [Z 3293 IE]
German version: Angew. Chem. 101 (1989) 1251
[I] J. B. Torrance in D. Jerome and L. G. Caron (Eds.): Low-Dimensional
Conductors and Superconductors, NATO AS1 ser. B: Physics, Vol. i5S,
Plenum Press, New York 1987, p. 113.
121 P. Batail, L. Ouahab, Mol. Cryst. Liq. Cryst. 125 (1985) 205; P. Batail, L.
Ouahab, J. B. Torrance, M. L. Pylman, S. S. P. Parkin, Solid State Commun. 55 (1985) 597.
[3] A. Renault, C. Cohen Addad, J. Lajzerowicz, E. Canadell, 0. Eisenstein,
Mol. Cryst. Liq. Cryst. 164 (1988) 179.
[4] A. Collet, Tetrahedron 43 (1987) 5725, and references cited therein.
151 For a short synthesis of 1 (cryptophane-E) see: J. Canceill, A. Collet, J.
Chem. Soc. Chem. Commun. 1988. 582.
[6] All electrochemical criteria for reversibility are satisfied for scan speeds
below 200 mi's-'; for details see: A. J. Bard, L . P. Faulner: Electrochemical Methods, Wiley, New York 1980, p. 224.
[7] Details on these X-ray crystal structure determinations will be discussed in
a forthcoming article.
[8] J. Canceill, M. Cesario, A. Collet, J. Guilhem, L. Lacombe, B. Lozach, C.
Pascard, Angew. Chem. 101 (1989) 1249; Angew. Chem. Int. Ed. Engl. 28
(1989) 1246.
[9] Note that, since this is an fcc array of cations, it is formally an anti-NaC1
type of structure. For another example of a giant charge-transfer rock salt,
see: A. Pemcaud, P. Batail, S. Tomic, D. Jerome, C. Coulon, A. Perrin, to
be published.
[lo] T. J. LePage, R. Breslow, J. Am. Chem. Soc. 109 (1987) 6412-6421; J.
Thomaides, P. Maslak, R. Breslow, ibid. 110 (1988) 3970-3979; J. S .
Miller, A. J. Epstein, W. M. Reiff, Arc. Chem. Res. 21 (1988) 114- 120; J. B.
Torrance, P. S. Bagus, I. Johannsen, A. I. Nazzal, S. S. P. Parkin, P.
Appl. Phys., 43 (1988), 2962-2965.
Batail, .
Verlagsgesellschaft mbH, 0-6940 Weinheim, 1989
A Distillable C- and N-Silylated Nitrile Imine""
By Florence Castan, Antoine Baceiredo, and Guy Bertrand*
Since the famous Huisgen reviews['] in 1963, 1-3 dipolar
cycloadditions have been the subject of a tremendous number of papers. In this area, much work has been dedicated to
the study of nitrile imines.''' However, it was only in 1988
that the first compound of this type, (2), was i~olated!~]
It was of interest to know if the method used for synthesizing 2 was generally applicable to the preparation of other
stable nitrile imines with common substituents, which could
be of use for the facile synthesis of a variety of heterocycles.
Here we wish to report the synthesis and reactivity of a
distillable C- and N-silylated nitrile imine.
Bulky substituents are necessary in order to kinetically stabilize highly reactive species. We therefore chose to study the
action of the lithium salt of triisopropylsilyldiazomethane on
the triisopropysilyl chloride. The reaction occurred between
- 90" and - 100 "C, in dry THF, in the presence of a crown
ether, affording the desired nitrile imine 4.141
1) BuLi
2) iPr,SiCI
Interestingly, compound 4 is stable enough to be purified
by distillation at 90-100 "C (0.15 torr) without noticeable
decomposition (80% yield) as a pale yellow oil (A,,, =
272 nm). The strong and broad absorption in the IR spectrum at 2120cm-' was slightly shifted compared to that
observed for N-silylated nitrile imines in a matrixf5]but its
position excluded the diazirine and isodiazirine isomers as
possible products. The non-equivalence of the silicon atoms,
demonstrated in the 29SiNMR spectrum, excluded the four
other isomers, namely the diazo compounds carbodiimide,
cyanamide and isocyanamide. The I3C NMR signal for the
quarternary carbon is shifted downfield compared to that in
the starting diazo compound 3. This was also observed for
compound 2 (Table 1).
Table 1. 13C,29Si,and IR spectroscopic data for the compounds 1-4 and 8.
The "C and 29Si NMR spectra were recorded at 75.469 and 59.628 MHz,
respectively, in CDCI, (1-3) and in C,D, (4,8); the IR spectra in pentane.
6 (CN)
40 28
61 04
14 99
46 73
124 25
6 13
0 71, 6 40
3 60
2040 (br , s)
2120 (br , s)
2200 (br , s)
[*] Dr. G. Bertrand, F. Castan, Dr. A. Baceiredo
Laboratoire de Chimie de Coordination du CNRS,
associe a I'Universite Paul Sabatier
205, Route de Narbonne, F-31062 Toulouse Cedex (France)
This work was supported by the Pierre-Fabre-Medicaments Company. We
thank Dennis E g g for helpful discussions.
Angew. Chem. Inr. Ed. Engl. 28 (1989) Nr. 9
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salt, cryptophane, dimensions, components, transfer, three, radical, cation, charge
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