+
voltammograms of 3 and 4 were run under identical
conditions. The significantly larger current response observed
for the latter suggests that it undergoes multielectron oxida-
tion. Controlled potential coulometry at E ) 0.87 V suggests
that removal of more than one electron from 4 occurs at this
potential. Nevertheless, a broad five-line ESR signal assigned
analogue 22 did not show an observable D splitting in its
3
matrix ESR spectrum probably because its D value is
2+
2+
smaller (and hence unresolved) than that for 3 due to 2 ’s
extended conformation of p-phenyelenediamine groups.
Over the limited temperature range of 113-83 K, the
intensity of the half-field signal of triplet 3 obeys the
Curie-Weiss law. However, measurement of the solution
2
+
+
.
as a(2N) ) 5.5 G of 4 is observed when 4 is treated with
5
+
-
+
2+
1
mol equiv of thianthrenium perchlorate (TH ClO
4
) in
3
magnetic susceptibility of 3 and 3 in CDCl at 298 K by
7
CH Cl . The higher order polycation states of 4 are less stable
2
2
NMR shift analysis gives µeff values of 1.74 ( 0.01 and
2.18 ( 0.04, respectively. Theoretical values for doublet and
triplet molecules are 1.73 and 2.83. Thus, it appears that 32
is a mixture of singlet and triplet states at room temperature.
If so, then (µeff) /(2.83) gives the mole fraction of triplet
as 60% in this case. Degenerate singlet and triplet states
yield a 75% triplet solution because of the 3:1 triplet:singlet
than those of 3 and will need to be further evaluated at low
+
temperature to gain definitive ESR data.
+
-
Oxidation of 3 by 1 or 2 mol equiv of TH ClO
4
yields
2
2
+
2+
stable solutions of 3 and 3 at 298 K. No fine structure is
2
+
+
-
3
observed in the ESR spectrum of 3 ‚ClO
4 2 2
in CH Cl over
a large concentration and temperature range, so we have been
2+
statistical bias. Therefore, we conclude that 3 is a thermally
populated triplet dication with a singlet ground state in CDCl
3
unable to evaluate its spin distribution. The dication diradical
2
+
-
3
4 2
‚(ClO ) shows a triplet ESR signal (Figure 4) with a D
-
1
solution at 298 K with ∆ES,T ≈ 0.4 kcal mol .
Despite the conformational rigidity imposed by the mac-
rocyclic skeleton and the dual N,N′-2,7-naphthyl coupling
2+
of the p-phenylenediamine radical cations in 3 , a low-spin
ground state prevails in this diradical. Of course, the acyclic
2+
analogue 2 did not show a strong triplet preference, having
3
essentially degenerate singlet and triplet states. Furthermore,
2
+
it is certain that the 3 conformation, while fairly rigid, is
also not perfectly planar and so both spin dilution at nitrogen
(over the p-phenylenediamine unit) coupled with a degree
of deconjugative twisting at the 2,7-naphthalene connections
may combine to diminish the preference for spin alignment
2
+
in the 3 diradical and ultimately result in a singlet ground
state. Further work on cyclic arylamines is underway to better
address the issues of spin coupling between amine-based
radical cations within rigid macrocyclic frameworks.
Figure 4. ESR spectrum of 32+ in PrCN at 100 K.
Acknowledgment. We thank the NSF-MRSEC (DMR-
9
809423) for financial aid and R. D. and L. Rogers for
assistance with X-ray crystallography. We also thank J. F.
Hartwig for a preprint of ref 4.
value of 0.0027 cm- and no well-resolved E value. This D
1
6
2+
value is close to that observed by Bushby et al. for 6 ,
which has a similar average spin-spin distance. Acyclic
Supporting Information Available: X-ray structure
tables, description of synthetic procedures, and compound
spectral data. This material is available free of charge via
the Internet at http://pubs.acs.org.
OL991040E
(5) Caution! Thianthrenium perchlorate is a shock-sensitive explosive
solid that should be handled only on a small scale and with due care. For
preparation and properties see: Murata, Y.; Shine, H. J. J. Org. Chem.
1
969, 34, 3368.
6) Bushby, R. J.; McGill, D. R.; Ng, K. M.; Taylor, N. J. Chem. Soc.,
Perkin Trans. 2 1997, 1405.
7) (a) Evans, D. F. J. Chem. Soc. 1959, 2003. (b) Live, D. H.; Chan, S.
I. Anal. Chem. 1970, 42, 791.
(
(
Org. Lett., Vol. 1, No. 13, 1999
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