Mitsuhiko Shionoya et al.
The component of the fibrous product was confirmed by
STEM measurement. The observed elemental profiles of
carbon, palladium, and chlorine strongly suggest that the re-
sulting fibers contain all these atoms along the fibers (Fig-
ure 3c). In other words, fibers are composed uniformly of
PdII complexes 3 with Cl atoms, that are possibly a mixture
about 6 ꢂ, so that there seems little steric hindrance in both
isomers when complexed. Similarly to the packing structure
of model complex 5, the flat complex 3 should allow p–p in-
ꢀ
teractions and C H···Cl hydrogen bonding, thus leading to
p-stacked structures as the microscopic observations sug-
gest.
of trans and cis forms of [Pd
below.
As the dinuclear cyclopalladated complex 3 was found dif-
ficult to crystallize, the model ligand 4, 2,9-diphenyl-1,10-
phenanthroline, was examined for PdII complexation under
the same conditions (Figure 4a). The ligand 4 was mixed
(Hꢀ21)Cl2] (3) as described
The aggregation behavior of the metallo-macrocycle of
1 varies with the kind of metal ions. For instance, dinuclear
ZnII complexes prepared from 1 and ZnCl2 do not form fi-
brous but instead form round-shaped aggregates in low
1
polar solvents, as was suggested by the broadened H NMR
resonances and by the AFM images (Figures S27 and S28,
see the Supporting Information). ZnII ions bound by the
inward phenanthroline of 1 prefer a tetrahedral geometry as
proven in our previous report,[4] unlike the square-planar
PdII ions. Such non-flat complexes would exhibit a different
aggregation behavior depending on the nature of metal ions
and ligands other than the macrocycle.
In conclusion, the macrocyclic skeletons of ligand 1 and
its PdII complex 3 allow their stacked arrangement to form
one-dimensional, organic and organometallic fibrous aggre-
gates. Formation of PdII-containing nanofibers was unambig-
uously confirmed by STEM and EDS measurements. Such
molecular aggregates formed by continuous stacking of mac-
rocycles would provide a tubular space for molecular trans-
portation and metal arrangement. In particular, the tubular
space of 3 arranging cyclopalladated moieties has great po-
tential to serve as a highly active nano-reactor for a variety
of Pd-catalyzed reactions as an organometallically function-
alized pore.
Figure 4. a) Scheme for PdII complexation of a model ligand 4. b) The
crystal structure of PdII complex 5. Hydrogen atoms are omitted for clari-
ty. The molecular structure is represented with 50% thermal ellipsoids
(C: gray, N: light blue, Cl: green, Pd: orange).[10] c) A molecular packing
ꢀ
structure. C H···Cl hydrogen bonds are represented as dashed lines.
with [PdCl2ACHTUNGTRENNUNG(CH3CN)2] in CDCl3/CD3CN at 608C, and the
Acknowledgements
1H NMR spectrum of the resulting PdII complex (5) indicat-
ed the formation of an N^N^C-type PdII complex (Fig-
ure S21, see the Supporting Information). This was also con-
firmed by ESI-TOF mass spectrometry (m/z: 478.04 as [Pd-
This study was supported by Grants-in-Aids from MEXT of Japan and
Global COE Program for Chemistry Innovation through Cooperation of
Science and Engineering. We are grateful to Prof. S. Ohkoshi for AFM
measurements. TEM, STEM, and EDS measurements were conducted in
the Research Hub for Advanced Nano Characterization, The University
of Tokyo, supported by the MEXT, Japan.
G
ACHTUNGTRENNUNG
(CH3CN)]+, Figure S22 in the Supporting Informa-
The molecular structure of 5 was determined by single-
crystal X-ray analysis (Figure 4b).[10] In the resulting struc-
ture, a PdII ion is bound by two phenanthroline nitrogen
atoms, one deprotonated C atom of the phenyl group at-
tached to phenanthroline, and one Cl ion to form a neutral
square-planar complex. In the molecular packing structure,
Keywords: cyclometallation · macrocycles · nanotubes ·
palladium · self-assembly
[2] For reviews: a) D. T. Bong, T. D. Clark, J. R. Granja, M. R. Ghadiri,
ꢀ
ꢀ
p–p interactions and weak C H···Cl hydrogen bonds (C Cl
distance 3.804 ꢂ) serve to form a stacked structure (Fig-
ure 4c).
The crystal structure of the N^N^C-type PdII model com-
plex 5 strongly suggests that the coordination structure of
the dinuclear PdII complex of macrocycle 1, [Pd
2ACHTNUGTRNE(UGN Hꢀ21)Cl2]
(3), is similar to that of complex 5, except that the dinuclear
PdII complex 3 exists as an isomeric mixture, trans-3 and cis-
3, as shown in Figure 1b; however, the ratio of the isomers
remains unclear because of severe broadening of the NMR
resonances under various conditions.[11] In both structures,
the distance between the two Cl atoms is estimated to be
[3] a) S. H. J. Idziak, N. C. Maliszewskyj, P. A. Heiney, J. P. McCau-
3
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