This work was made possible by generous support from the
Swiss National Science Foundation (grant #116868), the
Herman Legerlotz Stiftung, and the University of Zurich.
¨
Notes and references
z Under these reaction conditions weakly bound metal ions like Sn(II)
and Hg(II) were also removed from GPcs, and Zn(II) was quantita-
tively removed from porphyrins.
1
2
3
4
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Scheme 2 Synthesis of guanidino phthalocyanines (GPcs). Counter
ions for 3–5 are trifluoroacetate.
5 H. Zollinger, Color Chemistry: Synthesis, Properties, and Applica-
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Scheme 3 Demetallation of tetrasubstituted metallophthalocyanines
18
and isolated yields (‘‘n.d.’’ ¼ no product detected).
9
M. Wyler, US Pat., 2 197 458, 1940.
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0 (a) J. W. Steed, D. R. Turner and K. J. Wallace, Core Concepts in
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¨ ¨
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1
1 W. J. Youngblood, J. Org. Chem., 2006, 71, 3345.
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Scheme 4 Demetallation of C symmetric zinc phthalocyanines and
(
b) D. Wohrle, G. Schnurpfeil and G. Knothe, Dyes Pigm., 1992,
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4
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¨
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,6,8,10
1
1
starting materials (Scheme 1).
The main problem with
¨
this approach has been the lack of reported conditions for
the subsequent removal of such ions to generate metal-free
and I. Degirmencioglu, Chem. Commun., 2001, 285;
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8
,10a,11
phthalocyanines.
During our synthesis of guanidinium-
containing phthalocyanines we discovered a new demetalla-
tion reaction that, to the best of our knowledge, provided
the first examples of Zn(II) removal without destroying the
phthalocyanine itself. This demetallation reaction appears to
be general as it works for electron rich, electron poor,
alkyl-, ether-, and even unsubstituted zinc phthalocyanines.
Zn(II)-templated cyclotetramerization, followed by Zn(II)
removal, therefore provides a new high-yielding route to
diverse, metal-free phthalocyanines. These products are, in
turn, important starting materials for making Pcs and
GPcs with variable metal centers. Given the industrial and
academic importance of these compounds, it is expected
that this new demetallation reaction will find numerous
applications.
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1
8 Where ‘‘guanidine’’ ¼ diisopropylguanidinium, and ‘‘amide’’ ¼
NHC(O)CH CH CO H.
2
2
2
1
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(
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This journal is ꢁc The Royal Society of Chemistry 2009
Chem. Commun., 2009, 1970–1971 | 1971