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6. T. J. R. Weakley, H. T. Evans, Jr., J. S. Showell, G. F. Toume, and
Ñ. M. Toume, J. Chem. Soc. Chem. Commun., 139 (1973).
7. R. G. Finke, M. Droege, J. R. Hutchinson, and O. Gansow, J. Am.
Chem. Soc. 103, 1587 (1981).
8. S. H. Wasfi, A. L. Rheingold, G. F. Kokoszka, and A. S. Goldstein,
Inorg. Chem. 26, 2934 (1987).
9. Ñ. M. Tourne, G. F. Toume, and F. Zonnevijlle, J. Chem. Soc., Dalton
Trans., 143 (1991).
10. R. G. Finke, M. W. Droege, and P. J. Domaille, Inorg. Chem. 26, 3886
7. DIPYRRYL AND PORPHYRINIC PRECURSORS TO SUPRAMOLECULAR
CONJUGATED (PORPHINATO)METAL ARRAYS: SYNTHESES OF DIPYRRYLMETHANE AND
Submitted by VICTOR S.-Y. LIN, PETER M. IOVINE.
STEPHEN G. DiMAGNO, and MICHAEL J. THERIEN*
Checked by STEVE MALINAK and DIMITRI COUCOUVANIS
Metal-mediated cross-coupling reactions involving mej'o-haloporphyrins
enable the fabrication of porphyrin arrays that exhibit exceptional
electronic interactions between their constituent porphyrinic building
blocks.1-3 Because mew-halopor-phyrins derive from direct halogenation of
the porphyrinic aromatic macrocycle, porphyrins bearing unsubstituted me
so positions are important synthetic precursors to these supramolecular,
Department of Chemistry, University of Pennsylvania, Philadelphia, PA
56 Syntheses of Selected Supramolecules
Archetypal examples of these strongly coupled (porphinato)metal
assemblies are highlighted by a meso-to-meso ethynyl or butadiynyl
linkage topology between the porphyrin units of the array and feature a
linear arrangement of chromophores, typified by structures I and II (Pig.
Similar design elements can be incorporated into more elaborate
supramole-cular structures (III and IV, Fig. I),4 which serve as models
in which to probe ground- and ex cited-state electronic interactions
along multiple conjugation
R R R
Figure 1. Highly conjugated ethyne-bridged (porphinato) zinc(II) arrays
7. Dipyrryl and Porphyrinic Precursors
Figure 1 (Continued)
pathways as well as important oligochromophoric precursors to higher-
While the 5-phenylporphyrin and 5,10-diphenylporphyrin components of
conjugated porphyrin arrays III and IV can be prepared by a number of
58 Syntheses of Selected Supramolecules
Scheme 1. Clezy's synthetic route to dipyrrylmethane.6
routes exploiting McDonald-type 2 + 2 acid-catalyzed condensations of
dipyrry 1 precursors to such asymmetrically me^-substituted parent
porphyrin complexes offer numerous advantages with respect to syntheses
that rely on the direct reaction of organic aldehydes with monopyrroles,
the most important of which is significantly simplified chromatographic
purification of products. As such, dipyrrylmethane along with its à-
substituted and a,a'-disubstituted derivatives, are key building blocks
for these highly conjugated multiporphyrin structures.
Although a variety of synthetic methods for /3-unsubstituted-mejo-
substituted, Q- subs ti tuted-meso-substituted, and ^-substituted-mejo-
unsubstituted dipyrryl-methanes have been reported in the past,5 the
preparation of the parent compound dipyrrylmethane has generally been
accomplished using a three-step synthesis developed by Clezy (Scheme l).6
Drawbacks to this method include the toxicity of thiophosgene as well as
the difficult isolation of the thioketone and its tendency to polymerize;
such difficulties make large-scale preparations of dipyrrylmethane
problematic. Recently, Bruce published an improved procedure for
dipyrrylmethane synthesis involving a one-step reaction of excess pyrrole
and paraformaldehyde in a mixture of methanol and acetic acid.7 The poor
solubility of paraformaldehyde in most organic solvents coupled with the
required chromatographic purification of the product, however, likewise
precluded large-scale preparations of this compound.
We report herein a significantly improved and simplified preparation
of dipyrrylmethane, which is based on Lindsey's route to mejo-substituted
dipyrryl porphyrin precursors,8 as well as the syntheses of (5,15-
diphenylporphinato)-zinc(II), a key building block of conjugated
porphyrin arrays I-IV (Fig. 1).
Standard Schlenk techniques were employed to manipulate air-sensitive
solutions. All manipulations involving air-sensitive materials were
carried out under nitrogen previously passed through an 02 scrubbing
tower (Schweizerhall R3-11 catalyst) and a drying tower (Linde 3-A
molecular sieves). All solvents utilized in this work were obtained from
Fisher Scientific (HPLC Grade). Methylene chloride was distilled from
calcium hydride under N2. Chromatographic purification (Silica Gel 60,