Published on Web 09/15/2004
Arylene Ethynylene Macrocycles Prepared by Precipitation-Driven Alkyne
Metathesis
Wei Zhang and Jeffrey S. Moore*
Roger Adams Laboratory, Departments of Chemistry and Materials Science & Engineering, UniVersity of Illinois at
Urbana-Champaign, Urbana, Illinois 61801
Received June 11, 2004; E-mail: jsmoore@uiuc.edu
Here we outline a convenient, multigram synthesis of arylene
ethynylene macrocycles near room temperature through reversible
alkyne metathesis. Driven by the precipitation of a diarylacetylene
byproduct, the desired macrocycles are obtained in one step from
monomers in high yields.
Shape-persistent arylene ethynylene macrocycles have attracted
attention in the fields of supramolecular chemistry and materials
science over the past decade due to their novel properties and
potential applications.1 Considerable efforts have been devoted to
the development of methodologies allowing selectively function-
alized structures to be obtained in high yields. The reversibility of
the alkyne metathesis reaction is envisioned as a potentially
powerful tool for preparing phenylene ethynylene macrocycles.2,3
The availability of highly active Mo(VI) alkylidyne catalysts
synthesized by a reductive recycle strategy4 prompted us to
reinvestigate this idea.
the metathesis of benzoylbiphenyl-substituted monomers 1e,f in
CCl4 provided the highest yields of macrocycles 2e,f. Multigram
synthesis of 2e was accomplished in one-step using the precipita-
tion-driven strategy under optimized conditions (5.68 g, 77%).5,6
To demonstrate the generality of the precipitation-driven strategy,
we next applied the approach to the synthesis of square-shaped
macrocycle 4 from monomer 3. The only product observed was
tetracycle 4 isolated in 84% yield (eq 2). The predominant formation
In our initial attempts, alkyne metatheses were performed under
open, driven conditions (1 mmHg) to facilitate complete removal
of the 2-butyne byproduct. We chose 1,2,4-trichlorobenzene as a
high-boiling solvent for these reactions. Phenylene ethynylene
macrocycles 2a-d were obtained in good yields on a small scale
(15-33 mg, 61-76%) from monomers 1a-d at a concentration
of 0.13 M (eq 1).5 However, several attempts to increase the scale
of macrocycles 2a-f and 4 presumably reflects the thermodynamic
stability of these products.7 The scope and mechanism of this
precipitation-driven macrocycle synthesis are being investigated and
will be reported in due course.
Acknowledgment. This work is supported by the National
Science Foundation (Grant No. 0345254) and the U.S. Department
of Energy, Division of Materials Sciences (Award No. DEFG02-
91ER45439), through the Frederick Seitz Materials Research
Laboratory at the University of Illinois at Urbana.
Supporting Information Available: Experimental procedures,
characterization data for 1-4. This material is available free of charge
References
(1) (a) Ho¨ger, S. Chem. Eur. J. 2004, 10, 1320-1329. (b) Zhao, D.; Moore,
J. S. Chem. Commun. 2003, 807-818. (c) Yamaguchi, Y.; Yoshida, Z.
Chem. Eur. J. 2003, 9, 5430-5440. (d) Bunz, U. H. F.; Rubin, Y.; Tobe,
Y. Chem. Soc. ReV. 1999, 28, 107-119.
(2) Rowan, S. J.; Cantrill, S. J.; Cousins, G. R. L.; Sanders, J. K. M.; Stoddart,
J. F. Angew. Chem., Int. Ed. 2002, 41, 898-952.
(3) Bunz previously reported the synthesis of macrocycles via alkyne
metathesis. Under their conditions, which required high temperature (150
°C), the desired products were only obtained in 0.5-6% yields. Ge, P.-
H.; Fu, W.; Herrmann, W. A.; Herdtweck, E.; Campana, C.; Adams, R.
D.; Bunz, U. H. F. Angew. Chem., Int. Ed. 2000, 39, 3607-3610.
(4) (a) Zhang, W.; Kraft, S.; Moore, J. S. Chem. Commun. 2003, 832-833.
(b) Zhang, W.; Kraft, S.; Moore, J. S. J. Am. Chem. Soc. 2004, 126, 329-
335.
(5) A small amount of pentameric macrocycle is present in the isolated
macrocyclic product. For the large-scale synthesis of 2e, the macrocyclic
product was a 9:1 hexacycle/pentacycle mixture. The pentacycle could
be separated from the hexacycle by column chromatography.
(6) Initial monomer concentration was 0.038 M in CCl4; 10 mol % catalyst.
(7) Preliminary studies have shown the reversibility of macrocycle formation
in the case of 2e and 2f. The macrocyclic products appear to be
thermodynamically favored over larger macrocycles and open-chain
oligomer and polymer, analogous to the molecular architectures prepared
via coordination reactions. See: Leininger, S.; Olenyuk, B.; Stang, P. J.
Chem. ReV. 2000, 100, 853-908.
of the procedure using the vacuum-driven strategy resulted in poor
macrocycle yields, low conversions, and considerable amounts of
oligomeric products. Failure may be due to the introduction of air
into the reaction vessel, leading to catalyst decomposition, or the
consumption of catalyst by polymerization of the 2-butyne byprod-
uct, which cannot be removed fast enough in gram-scale batches.4b
We imagined that a poorly soluble, less reactive byproduct would
allow the desired metathesis reaction to be performed in a closed
system. Precipitation rather than evaporation thus serves as the
driving force to shift the metathesis equilibrium. Numerous
arylethynyl-substituted monomers were tested in various solvents;
JA046531V
9
12796
J. AM. CHEM. SOC. 2004, 126, 12796
10.1021/ja046531v CCC: $27.50 © 2004 American Chemical Society