Mellitic triimides: C3-symmetric, three-electron acceptors for supramolecular chemistry

Full text of DOI:10.1021/ja016043c

J. Am. Chem. Soc. 2001, 123, 6453-6454
6453
Scheme 1. Thermal Decomposition of Ammonium Mellate4
Mellitic Triimides: C3-Symmetric, Three-Electron
Acceptors for Supramolecular Chemistry
Kathryn A. McMenimen and Darren G. Hamilton*
Department of Chemistry, Mount Holyoke College
South Hadley, Massachusetts 01075
ReceiVed April 18, 2001
ReVised Manuscript ReceiVed May 22, 2001
Supramolecular systems containing electroactive components,
i.e. units that are readily oxidized or reduced, have tended to favor
1
a limited range of building blocks. This observation highlights
the fact that these popular units may be confidently incorporated
in a supramolecular design, and synthetic scheme, since their
properties are well-known and synthetic utility well documented.
A number of more exotic electron donors and acceptors have been
prepared but, principally due to their synthetic inaccessibility,
Chart 1. Isolated Products from Mitsunobu Alkylation of the
Residue Obtained from Decomposition of Ammonium Mellate
2
these units tend not to appear in complex assemblies. We report
here a general route to systems containing a surprisingly simple
C -symmetric core via elaboration of mellitic triimide 1 by simple
3
substitution processes. These system possess the capacity to accept
up to three electrons, each at a distinct and well separated
potentialsan unusual ability, especially for a simple organic
system.3
Mellitic acid was converted to ammonium mellate by dissolu-
tion in hot aqueous ammonia solution: the crystalline hydrate is
obtained on cooling. This salt was then dehydrated in a lyophilizer,
spread on a watch glass, and baked in a standard drying oven at
The literature relating to 1 is scant, dated, and inextricably
linked to that of euchroic acid, 2: only three reports have been
made in the past 160 years. Chaigneau describes, in passing,
the formation of material designated as mellitic triimide 1 from
6 2 4 6
the thermal decomposition of ammonium mellate (C (CO NH ) ),
but this assignment was made solely on the basis of elemental
data. We examined this work with the aim of isolating useful
amounts of mellitic triimide 1.
150 °C for 4 days (Scheme 1).
4
In our first experiments the gruesomely insoluble postbaking
residues were alkylated directly with n-pentanol under Mitsunobu
conditions (Ph P/DIAD/THF). From these reactions the predomi-
3
nant isolable product was dialkyl euchroate 4 (≈20%), though
with careful chromatographic separation target triimide 3a (<10%)
5
could also be isolated. These materials are accompanied by a
*
Address correspondence to this author. E-mail: hamilton@mtholyoke.edu.
significant number of side products, among which diimide 5 and
hexa-ester 6 have been identified. Chaigneau reported that above
(
1) In this context ubiquitous electron acceptors are bipyridinium salts and
aromatic diimides, see: (a) Wiederrecht, G. P.; Niemczyk, M. P.; Svec, W.
A.; Wasielewski, M. R. J. Am. Chem. Soc. 1996, 118, 81-88. (b) Lokey, R.
S.; Kwok, Y.; Guelev, V.; Pursell, C. J.; Hurley, L. H.; Iverson, B. L. J. Am.
Chem. Soc. 1997, 119, 7202-7210. (c) Hamilton, D. G.; Montalti, M.; Prodi,
L.; Fontani, M.; Zanello, P.; Sanders, J. K. M. Chem. Eur. J. 2000, 6, 608-
165 °C decomposition of ammonium mellate is complicated by
a variety of side reactions. It seems clear that these reactions also
occur to an appreciable extent at 150 °C, i.e. the situation is more
complex than that shown in Scheme 1, and that one of these
reactions is decarboxylation of ammonium euchroate to pyro-
6
17. (d) Buchwalter, S. L.; Iyengar, R.; Viehbeck, A.; O’Toole, T. R. J. Am.
Chem. Soc. 1991, 113, 376-377. (e) Amabilino, D. B.; Ashton, P. R.; Balzani,
V.; Boyd, S. E.; Credi, A.; Lee, J. Y.; Menzer, S.; Stoddart, J. F.; Venturi,
M.; Williams, D. J. J. Am. Chem. Soc. 1998, 120, 4295-4307. (f) Miller, L.
L.; Mann, K. R. Acc. Chem. Res. 1996, 29, 417-423.
6
mellitic diimide (the precursor to 5). Additionally, it would appear
that thermal decomposition of ammonium mellate is a rather
delicate process: the isolation of both 5, from oVer-reaction in
the baking process, and 6, presumably derived from unchanged
ammonium mellate, suggests that a bake temperature of 150 °C
represents an unavoidable compromise between inertness and
decarboxylation. The array of products obtained from the alkyl-
ation reaction prompted attempts to purify the post baking residue
prior to further use. We eventually found that Soxhlet extraction
3
(2) For examples of C -symmetric electron donors that conform to this
general description see: (a) Gonzalez, A.; Segura, J. L.; Martin, N. Tetrahedron
Lett. 2000, 41, 3083-3086. (b) Fouormigu e´ , M.; Johannese, I.; Boubekeur,
K.; Nelson, C.; Batail, P. J. Am. Chem. Soc. 1993, 115, 3752-3759. The
electron donating units in these systems are not electronically coupled, they
3
are simply arrayed with C symmetry.
(
3) Benzophenone and perylene diimides share this distinction though both
possess, from a supramolecular perspective, rather unwieldy structures, see:
Viehbeck, A.; Goldberg, M. J.; Kovac, C. A. J. Electrochem. Soc. 1990, 137,
1
460-1466.
(4) Chaigneau, M. C. R. Hebd. Seances Acad. Sci. 1955, 240, 2324-2326.
(5) 3a: mp 141.5-143 °C; 13C (63 MHz, CDCl
(0), 39.54 (2), 29.10 (2), 28.05 (2), 22.42 (2) 14.11 (3) ppm; H (270 MHz,
3
) δ 162.62 (0), 133.52
1
This work describes the isolation and structural characterization of euchroic
acid 2, a molecule first reported and named by W o¨ hler over 100 years
previously (W o¨ hler, F. Ann. Der Ch. Und Ph. 1841, 37, 268. Schwarz, H.
Ann. Der Ch. Und Ph. 1848, 66, 52). To the best of our knowledge these are,
to date, the only published reports relating to the chemistry of euchroic acid
or mellitic triimide.
CDCl ) δ 3.80 (t, J ) 7 Hz, 6H), 1.72 (quintet, J ) 7 Hz, 6H), 1.34 (multiplet,
3
+
12 H), 0.88 (t, J ) 7 Hz, 9H) ppm; ESI-MS (positive ion) 496.3 ([M + H] ,
+
5%), 518.3 ([M + Na] , 100%).
(6) The complex nature of the product mixtures is only apparent once
soluble and relatively nonpolar derivatives are generated.
1
0.1021/ja016043c CCC: $20.00 © 2001 American Chemical Society
Published on Web 06/07/2001

6454 J. Am. Chem. Soc., Vol. 123, No. 26, 2001
Communications to the Editor
Figure 1. X-ray structure of triimide 3b (disorder in two of the three
butyl side chains has been omitted for purposes of clarity).
Figure 2. Possible forms, with their reduction potentials, for the radical
anion, dianion, and radical trianion obtained on reduction of triimide 3a
2 3
Scheme 2. Cs CO Mediated Alkylation of Mellitic Triimide
1
3
(drawn to preserve a quinoidal substructure for the latter two species).
3
reductions, yielding first radical anions, then dianions. A simple
arrow pushing sketch indicated that it was theoretically possible
to introduce three electrons into the triimide framework presented
here. Theory is borne out by experiment: triimide 3a undergoes
three sequential, well separated, one electron reductions (Figure
12
2
). Thus, the triimide has four accessible electronic states:
neutral, radical anion, dianion, and radical trianion.
We anticipate that the electron accepting ability of these
systems, coupled with their symmetry and synthetic accessibility,
will lead to numerous applications. Macrobicyclic cryptands from
with water (to remove carboxylate based materials) followed by
suspension in, and filtration from, warm DMF gave refined
7
“
mellitic triimide” 1. Alkylation of this material with n-pentanol
under Mitsunobu conditions gave 30-35% yields of 3a after
separation and recrystallization. Comparable yields of 3b could
be obtained by alkylation with 1-bromobutane in the presence of
cesium carbonate (Scheme 2), expanding the synthetic options
available from the core 1.8
3
-fold linking of two triimides represent an attractive initial target
which we are exploring: in the solid state, replacing a C
symmetric diimide with a C -symmetric triimide could prompt
2
-
3
the formation of networks. Trisubstitution also potentially sur-
rounds the core with a high level of insulation from its environ-
ment. A unit functionalized with three dendrimeric wedges would
provide an isolated electron sink,14 and substitution with per-
fluorinated alkyl chains could yield suitable derivatives for
electronic device manufacture.15
2
Crystals of triimide 3b (from DMF/H O) proved suitable for
9
X-ray analysis (Figure 1). The structure reveals the triimide
framework to be essentially planar, thereby confirming a recent
prediction, based on analysis of the related trianhydride, that no
substantial nonbonded contacts exist between the carbonyl func-
tions.10 The structure otherwise holds no surprises, other than
the observation that despite the N-butyl substituents the triimide
11
Acknowledgment. We thank Mount Holyoke College (MHC) for
financial support, Amy L. Clark (MHC) for initial studies of ammonium
mellate, Dr. S. Scheuneman (MHC) for electrochemical expertise, the
X-ray Structural Characterization Laboratory at UMass, Amherst (NSF
grant CHE-9974648), and Drs. A. Chandrasekaran (UMass) and D. E.
Lynch (University of Coventry, UK) for data collection, structure solution,
and refinement of 3b. The contribution of Dr. and Mrs. S. Samuels
3
packs in perfect C symmetry.
The well documented electrochemical profiles of benzene and
naphthalene diimides prompted the use of cyclic voltammetry to
probe the electron accepting potential of the triimide framework.
Aromatic diimides typically undergo two sequential one electron
(Wilbraham, MA) in translating ref 4 is also gratefully acknowledged.
(7) The efficiency of conversion of mellitic acid to mellitic triimide is low,
a not unexpected result given the plethora of materials formed in the baking
step. We are currently exploring alternative routes to 1 and its derivatives,
and other methods for refining the postbaking residue.
Supporting Information Available: Procedures for the conversion
of mellitic acid to mellitic triimide 1, isolation and characterization of
3a, 3b, 4, 5, and 6, CV trace for 3a, and crystal data for 3b (PDF). This
material is available free of charge via the Internet at http://pubs.acs.org.
(8) The yields for both reactions are rather lower than we would wish.
Under the same conditions pyromellitic diimide affords around 60% yields
of N-substituted derivatives, indicating that even our “refined” residue probably
contains less than half mellitic triimide 1.
JA016043C
(
9) Crystal data for 3b: C24
H
27
N
3
O
6
, M
r
) 453.49, T ) 293(2) K, λ )
n
0
.71073 Å, trigonal, a )27.6903(4) Å, and c ) 10.8284(2) Å, V ) 7190.4(2)
(12) Recorded as a 2 mM solution in anhydrous THF (0.1 M Bu
4
NPF
6
3
3h
3
Å , space group R , colorless crystal (0.75 × 0.40 × 0.35 mm ), Z ) 12,
supporting electrolyte) versus an Ag/AgCl reference electrode at a sweep rate
of 200 mV s . Under these conditions the reductions are electrochemically
-3
-1
F
calcd ) 1.257 g cm . The crystal contains 1.333 molecules per asymmetric
unit and has two disordered alkyl chains that were treated using split-site
refinements. The final R value was 4.9% (S ) 1.060).
10) The trianhydride deviates substantially from planarity in the solid state,
quasi-reversible, though chemically fully reversible.
1
(13) For comparison, typical first and second reduction potentials for
benzene diimides (e.g. 5) are -0.9 and -1.5 V, for naphthalene diimides
-0.7 and -1.1 V (all (0.1 V depending on N-substitution, ref 1c).
(14) Liwporncharoenvong, T.; Luck, R. L. J. Am. Chem. Soc. 2001, 123,
3615-3616 and references therein.
(15) Katz, H. E.; Johnson, J.; Lovinger, A. J.; Li, W. J. Am. Chem. Soc.
2000, 122, 7787-7792. The first reduction potential of the systems reported
here, close to those of C60 and naphthalene diimides, suggests they may be
useful molecular electronic components, see: W u¨ rthner, F. Angew. Chem.,
Int. Ed. 2001, 40, 1037-1039.
(
adopting a chiral propeller form induced by anhydride oxygen lone pair-
carbonyl LUMO interactions, see: Ermer, O.; Neud o¨ rfl, J. HelV. Chim. Acta
2
000, 83, 300-309.
(11) No bond localization effect within the aromatic ring resulting from
the presence of the fused 5-membered imide rings is found for 3b. The
emergence of such a property, the Mills-Nixon effect, remains a goal in
aromatic structural chemistry, see: Frank, N. L.; Baldridge, K. K.; Siegel, J.
S. J. Am. Chem. Soc. 1995, 117, 2102-2103.