Synthesis and characterization of a cyclic bis-silver(I) assembly of four 2-aza-21-carbaporphyrinatosilver(III) subunits

Article abstract of DOI:10.1002/anie.200502208

(Figure Presented) Four-gone confusion! An assembly of four N-confused porphyrinatosilver(III) subunits (see structure; N blue, Ag olive-colored, C silver/red) placed on the perimeter of a cyclic structure that comprises two silver(I) ions is effectively formed from a bis(N-confused porphyrin) free base and a silver(I) salt.

Full text of DOI:10.1002/anie.200502208

Angewandte
Chemie
phyrin 1[5] is particularly attractive owing to its unique
structure, which allows multimodal coordination of the
confused pyrrole to metal ions,[6] and its reactivity. The
exposed position of the external nitrogen atom (N2) makes
this fragment of molecule susceptible to interactions with
metal ions.[7]
Metalloporphyrinoids
DOI: 10.1002/anie.200502208
Synthesis and Characterization of a Cyclic
Bis-silver(i) Assembly of Four 2-Aza-21-
carbaporphyrinatosilver(iii) Subunits**
Piotr J. Chmielewski*
Porphyrins and metalloporphyrins constitute a class of build-
ing blocks for the construction of multicomponent 2D and 3D
molecular arrays that are being considered as possible
biomimetic models, catalysts, or materials for the transport
of charge, molecules, and ions. Covalent[1] as well as coordi-
nation linkages[2] have been exploited in the design of a
variety of discrete porphyrin assemblies. Recently, special
attention has been given to systems built up of directly linked
porphyrins with strongly interacting aromatic subunits,[3]
which represent some of the most promising candidates for
potential applications.
Recently, we reported the synthesis of the dimeric N-
confused porphyrin 2 (Ar= phenyl, p-tolyl (p-Tol)),[8] which is
a unique isomer that preserves the basic skeleton of a directly
b–b-linked bis(porphyrin).[9] The cyclic assemblies 3, whose
synthesis and characterization are presented herein, exem-
plify a new type of carbaporphyrinoid array that consists of
both covalent and coordinating links between the subunits.
Owing to the steric factors imposed by meso-aryl substituents,
the bipyrrolic fragment adopts a cisoid conformation in 2 but
deviates strongly from planarity. Such an arrangement
determines the coordination mode of this fragment, which,
unlike the planar bipyrrole system present in corroles,[10] is
preorganized to coordinate two metal ions rather than to form
a chelate ring.
Porphyrin analogues[4] exhibit many distinct features that
can be exploited in the construction of novel molecular and
supramolecular systems. Among them, the N-confused por-
[*] Prof. P. J. Chmielewski
Department of Chemistry
University of Wrocław
F. Joliot-Curie Street 14, 50 383 Wrocław (Poland)
Fax: (+48)713-282-348
E-mail: pjc@wchuwr.chem.uni.wroc.pl
Reaction of bis(carbaporphyrinoid) 2 with AgX (X =
À
À
BF4 or CF3SO3 ) was carried out at room temperature in
THF for 30 minutes. After evaporation of the solvent, the
residue was dissolved in CH2Cl2, and washed with water to
remove the excess of silver(i) ions and the acid liberated upon
insertion of the metal. The composition and molecular
structure of 3 was established on the basis of ESI-MS, NMR
[**] This work was supported by the Polish Ministry of Scientific
Research and Information Technology (Grant 3 T09A 16228).
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
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spectroscopy, and single-crystal X-ray analyses. Owing to the
structure of the bipyrrolic moiety. The relatively short
distance between the bridging silver atoms Ag3–Ag3*
(3.107(2) Š) suggests that an “argentophilic” interaction[12]
stabilizes the assembly. Such interactions have been shown to
influence the outcome of several supramolecular assemblies,
and their importance has been crystallographically investi-
gated.[13] The distances within the macrocyclic core (Ag1-C21:
1.974(9); Ag1-N22: 2.030(9); Ag1-N23: 2.052(7); Ag1-N24:
2.027(8) Š) are slightly shorter than those observed in
monomeric neutral silver(iii) complexes of 1,[11] an O-con-
fused porphyrin derivative,[14] or the so-called “true” carba-
porphyrin.[15] The distances between the external nitrogen
atoms and the bridging silver ions (Ag3-N2: 2.175(8); Ag3-
N26: 2.169(8)) are typical for the monovalent silver complex-
es.[13g]
As a consequence of the crystal-packing forces, the
molecule displays only twofold symmetry in the solid state.
In contrast, the effective symmetry of the molecule in solution
is fourfold, as inferred from the 1H NMR spectra
which reveal only one set of signals (Figure 2a,b).
The spectra support the stereoselectivity of the
formation of the assembly, as diastereomers are
expected to exhibit different 1H NMR spectra.
Owing to the nonplanar character of the system
and freezing of rotation of the meso-aryl substituents,
each proton of the subunit in 3 is represented by a
unique signal and can be assigned on the basis of
2D NMR experiments (see Supporting Information).
Analysis of the chemical shifts and interprotonic
through-space interactions observed in NOESY or
ROESYexperiments allowed a model to be built that
has the same molecular topology as the solid-state
structure of 3a but which displays fourfold symmetry.
A neutral diamagnetic bis-silver(iii) complex 4
can be obtained by treating a solution of 3 in
chloroform with either an aqueous solution of
sodium halogenide or with a solution of tetraalky-
lammonium bromide in chloroform to remove bridg-
ing silver(i) ions.[16] Protonation of 3 with one
equivalent of trifluoroacetic acid or the addition of
pyridine (500-fold excess) breaks the assembly rever-
sibly. The process can be fully reversed upon addition
of water or by evaporation of the solvents. Thus,
reconstruction of 3 is possible as long as silver(i) ions
are present in the solution.
dicationic character of the complex, the dominant peak in the
mass spectrum corresponds to the dication (m/z = 1657,
100%) with a characteristic half-unit isotopic pattern. The
fragmentation peak at m/z = 1549.5 (47%) reflects liberation
of the dimeric fragment 4.
À
The solid-state structure of 3a-(OTf)2 (OTf = CF3SO3 )
presents an assembly of four 2-aza-21-carbapor-
phyrinatosilver(iii) subunits,[11] which are organized on the
perimeter of a ten-membered ring that contains two silver(i)
ions (Figure 1). The assembly of the axially chiral[8] dimeric
subunits 4 on the bis-silver(i) template may lead to the
formation of diastereomers. However, only S,S and R,R enan-
tiomers are observed in the crystal structure (see Supporting
Information). Although both monovalent silver centers are
two-coordinate, the N-Ag-N fragments are far from linear,
being bent outwards with an angle of 147.0(3)8. This is likely
due to the geometric constraints imposed on the ring by the
A slow exchange reaction can be observed upon
mixing of the solutions of 3a and 3b to result, after
20 h at room temperature, in an equilibrium of
starting complexes and a mixed-ligand species 3c
that can be identified by ESI-MS (observed: m/z =
1
1602.4; calcd: m/z = 1601.7) and H NMR spectros-
copy (Figure 2d). Formation of 3c, which exhibits
twofold symmetry, indicates the lability of the system
but also provides additional support for the preser-
vation of the tetrameric structure in solution.
The charge on the external nitrogen atom of the
Figure 1. Molecular structure of the assembly 3a. Top: ORTEP view with thermal ellipsoids
scaled at the 30% probability level (hydrogen atoms, triflate anions, and solvent molecules
are omitted); bottom: wire-frame representation of the structure with all aryl substituents
omitted for clarity.
confused pyrroles strongly influences redox proper-
ties of the metal ion that is coordinated in the
macrocyclic core.[7f,17] Thus, it can be expected that
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Experimental Section
3a-(BF4)2:
3,3’-Bis(5,10,15,20-tetrakis(p-tolyl)-2-aza-21-carbapor-
phyrin) (2a; 20 mg, 0.015 mmol) was dissolved in THF (20 mL) and
stirred with silver tetrafluoroborate (10 mg, 0.115 mmol) for 0.5 h.
The solvent was then removed by evaporation, and the solid residue
was dissolved in dichloromethane (10 mL). The solution was shaken
with three portions of water (10 mL each). After separation of the
organic phase, the solution was filtered and then the solvent was
removed. The solid residue was dissolved in dichloromethane, and the
solution was left to crystallize slowly after the addition of hexane to
yield the olive-colored product 3a-(BF4)2 (26 mg, 94%). A similar
procedure using AgOTf instead of AgBF4 or 2b instead of 2a yielded
3a-(OTf)2 or 3b-(BF4)2, respectively. Spectral data recorded in the
solution state were independent of the counteranion present in the
complex. See Supporting Information for NMR spectroscopic data
for 3a and 3b.
3a-(BF4)2: UV/Vis (CH2Cl2): lmax (loge) = 258 (5.23), 313 (5.00),
378 (5.08), 451 (sh), 472 (5.51), 533 (4.80), 596 (4.67), 636 (sh), 686 nm
(4.52); ESI-MS: m/z calcd for C192H136N16Ag6: 1657.7 ([M]2+); found:
1657.4; elemental analysis: calcd (%) for C192H136N16Ag6B2F8·2-
(CH2Cl2): C 63.70, H 3.86, N 6.13; found: C 63.40, H 3.56, N 6.12.
3b-(BF4)2: UV/Vis (CH2Cl2): lmax (loge) = 256 (5.19), 323 (sh),
378 (5.08), 452 (sh), 471 (5.47), 531 (4.75), 594 (4.67), 641 (sh), 691 nm
(4.48); ESI-MS: m/z calcd for C176H104N16Ag6: 1545.7 ([M]2+); found:
1545.2; elemental analysis: calcd (%) for C176H104N16Ag6B2F8·2-
(CH2Cl2): C 62.27, H 3.17, N 6.53; found: C 62.40, H 3.32, N 6.23.
Crystals of suitable quality for X-ray analysis were obtained by
slow diffusion of hexane into a solution of 3a-(OTf)2 in toluene.
Crystal data for 3a-(OTf)2: C231.5H172N16Ag6·2CF3SO3, MW = 4099.19,
T= 100 K, CuKa radiation, monoclinic, space group C2/c, a =
24.208(4), b = 34.279(4), c = 24.175(4) Š, b = 103.35(3), V=
Figure 2. Fragments of the 1H NMR spectra (CDCl3, 298 K) of the
assemblies a) 3a, b) 3b, c) 3a + 3b immediately after mixing, and
d) 3a + 3b 40 h after mixing (some of the new features, attributed to
&
the mixed-ligand species 3c, are indicated by ). Signal assignments
of the most upfield-shifted meso-aryl protons in 3a and 3b are pre-
sented in (a) and (b), with numbers indicating meso positions.
coordination of the AgI cation to the external nitrogen atom
destabilizes the trivalent silver center in each subunit to allow
the reduction of the metal. Such a reduction process has not
been observed to date for any of the carbaporphyrinoid
silver(iii) complexes. In cyclic voltammograms of 3a and 3b
(CH2Cl2 solutions; tetrabutylammonium perchlorate as the
supporting electrolyte; glassy carbon as a working electrode;
all data are referenced to ferrocene/ferrocenium internal
standard), a pair of two-electron couples (E1/2 = À1100 mV,
19519(5) Š3, Z = 4, 1calcd = 1.395 mgmÀ3
,
l = 1.54178 Š, m =
5.485 mmÀ1, F(000) = 8356, Oxford Diffraction Xcalibur PX with
KM4CCD Sapphire detector, 3.19 ꢀ q ꢀ 68.008, 15171 collected
reflections, 8504 independent reflections with I > 2s(I), 1104 param-
eters, R1(F) = 0.0827, wR2(F2) = 0.2102, S = 1.064, largest difference
peak and hole 1.861 and À1.06 eŠÀ3. All non-hydrogen atoms were
refined with anisotropic displacement parameters except for those of
the disordered solvents, triflate anion, and one meso-tolyl ring.
Hydrogen atoms were excluded from the geometry of molecules and
refined isotropically. The asymmetric unit contains half of the
molecule of 3a, consisting of two subunits linked by a silver ion,
one disordered triflate anion, a half molecule of hexane, and one and
DEac = 40 mV, E1/2 = À1230 mV, DEac = 46 mV for 3a; E1/2
=
À1055 mV, DEac = 40 mV, E1/2 = À1175 mV, DEac = 46 mV for
3b) is attributable to a stepwise reduction of silver(iii) centers
in the strongly interacting covalently linked subunits.[8,18]
Each reduction step takes place at the same potential in two
nondirectly connected, and thus non-interacting subunits,
which is accounted for by the two-electron character of the
processes. Two overlapping couples observed for 3a around
À1425 mVand those better-resolved for 3b (E1/2 = À1330 mV,
DEac = 36 mV, E1/2 = À1440 mV, DEac = 30 mV) reflect reduc-
tions of the ligand. For 4 only ligand reductions represented
by two couples at À1470 and À1600 mV are observed.
In conclusion, we have shown the very facile diastereo-
selective formation of a molecular assembly that consists of
four carbaporphyrinoids and which is effectively formed
despite steric overcrowding imposed by the substituents in the
vicinity of the donor sites. It seems that access to the bridging
silver–silver fragment is hindered which may stabilize the
cyclic structure. Experiments are underway to explore the
application of this novel coordination mode of the nonplanar
bipyrrolic moiety in the construction of larger redox-active
assemblies that consist of covalently linked N-confused
porphyrin derivatives.
a
half molecules of toluene displaced into six different sites.
CCDC 276104 contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
4: Complex 3a (10 mg, 3 mmol) was dissolved in CH2Cl2 (20 mL),
and the solution was stirred vigorously for 0.5 h with a 1m aqueous
solution of NaBr (10 mL) until the originally olive-colored solution
turned red-brown. The layers were then separated, and the organic
phase was washed with two 10-mL portions of water. After drying
over a small amount of anhydrous K2CO3 and filtration, the volume of
the solution was reduced to 10 mL, and hexane (5 mL) was added
which caused precipitation of 4 as a brown powder (6.1 mg, 65%).
1H NMR: see Supporting Information; UV/Vis (CH2Cl2): lmax
(loge) = 254 (5.20), 285 (sh), 323 (5.02), 384(sh), 412(sh), 450 (sh),
468 (5.50), 533 (4.88), 621 (sh), 661 nm (4.45); ESI-MS: m/z calcd for
C96H68N8Ag2: 1549.4 ([M+1]+); found: 1549.5; elemental analysis:
calcd (%) for C96H68N8Ag2·CH2Cl2·C6H14: C 71.90, H 4.89, N 6.51;
found: C 71.94, H 4.78, N 6.22.
Received: June 23, 2005
Published online: September 8, 2005
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Communications
2186; d) H. Furuta, T. Morimoto, A. Osuka, Inorg. Chem. 2004,
43, 1618; e) I. Schmidt, P. J. Chmielewski, Z. Ciunik, J. Org.
Chem. 2002, 67, 8917; f) P. J. Chmielewski, I. Schmidt, Inorg.
Chem. 2004, 43, 1885; g) C.-H. Hung, W.-C. Chen, G.-H. Lee, S.-
M. Peng, Chem. Commun. 2002, 1516; h) K. Rachlewicz, S.-L.
Keywords: nitrogen heterocycles · oligomers · porphyrinoids ·
silver · supramolecular chemistry
.
[1]a) M. G. H. Vicente, L. Jaquinod, K. M. Smith, Chem. Commun.
1999, 1771; b) A. K. Burrell, D. L. Officer, P. G. Plieger, D. C. W.
Reid, Chem. Rev. 2001, 101, 2751.
´
Wang, J.-L. Ko, C.-H. Hung, L. Latos-Graz˙ynski, J. Am. Chem.
Soc. 2004, 126, 4420; i) J. D. Harvey, C. J. Ziegler, Chem.
Commun. 2002, 1942.
´
´
[2]a) J. Wojaczyn ski, L. Latos-Graz˙ynski, Coord. Chem. Rev. 2000,
204, 113; b) S. Richeter, C. Jeandon, R. Ruppert, H. J. Callot,
Chem. Commun. 2001, 91; c) S. Richeter, C. Jeandon, C. Sauber,
J.-P. Gisselbrecht, R. Ruppert, H. J. Callot, J. Porphyrins
Phthalocyanines 2002, 6, 423; d) S. Richeter, C. Jeandon, J.-P.
Gisselbrecht, R. Ruppert, H. J. Callot, J. Am. Chem. Soc. 2002,
124, 6; e) S. Richeter, C. Jeandon, R. Ruppert, H. J. Callot,
Chem. Commun. 2002, 266.
[8]P. J. Chmielewski, Angew. Chem. 2004, 116, 5773; Angew. Chem.
Int. Ed. 2004, 43, 5655.
[9]a) Y. Deng, C. K. Chang, D. G. Nocera, Angew. Chem. 2000, 112,
1108; Angew. Chem. Int. Ed. 2000, 39, 1066; b) H. Hata, H.
Shinokubo, A. Osuka, J. Am. Chem. Soc. 2005, 127, 8264.
[10]a) L. Simkhovich, I. Luobeznova, I. Goldberg, Z. Gross, Chem.
Eur. J. 2003, 9, 201; b) C. Bruckner, Ch. A. Barta, R. P. Brinas,
J. A. Krause-Bauer, Inorg. Chem. 2003, 42, 1673.
[3]a) A. Osuka, H. Shimidzu, Angew. Chem. 1997, 109, 93; Angew.
Chem. Int. Ed. Engl. 1997, 36, 135; b) T. Ogawa, Y. Nishimoto, N.
Yoshida, N. Ono, A. Osuka, Chem. Commun. 1998, 337; c) T.
Ogawa, Y. Nishimoto, N. Yoshida, N. Ono, A. Osuka, Angew.
Chem. 1999, 111, 140; Angew. Chem. Int. Ed. 1999, 38, 176; d) N.
Yoshida, A. Osuka, Tetrahedron Lett. 2000, 41, 9287;e) A.
Tsuda, Y. Nakamura, A. Osuka, Chem. Commun. 2003, 1096;
f) Y. H. Kim, D. H. Jeong, D. Kim, S. C. Jeoung, H. S. Cho, S. K.
Kim, N. Aratani, A. Osuka, J. Am. Chem. Soc. 2001, 123, 76;
g) A. Tsuda, A. Nakano, H. Furuta, H. Yamochi, A. Osuka,
Angew. Chem. 2000, 112, 572; Angew. Chem. Int. Ed. 2000, 39,
558; h) A. Tsuda, A. Osuka, Adv. Mater. 2002, 14, 75; i) A.
Takagi, Y. Yanagawa, A. Tsuda, N. Aratani, T. Matsumoto, A.
Osuka, T. Kawai, Chem. Commun. 2003, 2986; j) N. Aratani, A.
Osuka, Y. H. Kim, D. H. Jeong, D. Kim, Angew. Chem. 2000,
112, 1517; Angew. Chem. Int. Ed. 2000, 39, 1458; k) H. Segawa,
Y. Senshu, J. Nakazaki, K. Susumu, J. Am. Chem. Soc. 2004, 126,
1354; l) H. Segawa, D. Machida, Y. Senshu, J. Nakazaki, K.
Hirakawa, F. Wu, Chem. Commun. 2002, 3032.
[11]H. Furuta, T. Ogawa, Y. Uwatoko, K. Araki, Inorg. Chem. 1999,
38, 2676.
[12]M. A. Rawashdeh-Omary, M. A. Omary, H. H. Patterson, J. Am.
Chem. Soc. 2000, 122, 10371.
[13]a) S. Sailaja, M. V. Rajasekharan, Inorg. Chem. 2003, 42, 5675;
b) V. J. Catalano, H. M. Kar, B. L. Bennett, Inorg. Chem. 2000,
39, 121; c) V. J. Catalano, S. J. Horner, Inorg. Chem. 2003, 42,
8430; d) V. J. Catalano, M. A. Malwitz, Inorg. Chem. 2003, 42,
5483; e) V. J. Catalano, M. A. Malwitz, A. O. Etogo, Inorg.
Chem. 2004, 43, 5714; f) O. Kristiansson, Inorg. Chem. 2001, 40,
5058; g) S. M. Cortez, R. G. Raptis, Coord. Chem. Rev. 1998, 169,
363; A. N. Khlobystov, A. J. Blake, N. R. Champness, D. A.
Lemenovskii, A. G. Majouga, N. V. Zyk, M. Schrꢀder, Coord.
Chem. Rev. 2001, 222, 155.
´
[14]M. Pawlicki, L. Latos-Graz˙ynski, Chem. Eur. J. 2003, 9, 4650.
[15]a) M. A. Muckey, L. F. Szczepura, G. M. Ferrence, T. D. Lash,
Inorg. Chem. 2002, 41, 4840; b) T. D. Lash, J. M. Rasmussen,
K. M. Bergman, D. A. Colby, Org. Lett. 2004, 6, 549.
[16]After isolation from the solution, 4 is sparingly soluble in organic
solvents, which may suggest its association leading to the
formation of a polymer. Solid 4 is readily converted back into
3a upon its treatment with a solution of a silver salt in THF or
methanol.
´
[4]L. Latos-Graz˙ynski in The Porphyrin Handbook, Vol. 2 (Eds.:
K. M. Kadish, K. M. Smith, R. Guilard), Academic Press, San
Diego, CA 2000, p. 361.
´
[5]a) P. J. Chmielewski, L. Latos-Graz˙ynski, K. Rachlewicz, T.
Głowiak, Angew. Chem. 1994, 106, 805; Angew. Chem. Int. Ed.
Engl. 1994, 33, 779; b) H. Furuta, T. Asano, T. Ogawa, J. Am.
Chem. Soc. 1994, 116, 767; c) G. R. Geier III, D. M. Haynes, J. S.
Lindsey, Org. Lett. 1999, 1, 1455.
[17]a) H. Maeda, Y. Ishikawa, H. Matsueda, A. Osuka, H. Furuta, J.
Am. Chem. Soc. 2003, 125, 11822; b) I. Schmidt, P. J. Chmie-
lewski, Inorg. Chem. 2003, 42, 5579.
[6]J. D. Harvey, C. J. Ziegler, Coord. Chem. Rev. 2003, 247, 1.
[7]a) A. Srinivasan, H. Furuta, A. Osuka, Chem. Commun. 2001,
1666; b) H. Furuta, T. Ishizuka, A. Osuka, J. Am. Chem. Soc.
2002, 124, 5622; c) H. Furuta, K. Youfu, H. Maeda, A. Osuka,
Angew. Chem. 2003, 115, 2236; Angew. Chem. Int. Ed. 2003, 42,
[18]Probably as a result of the labile character of the assembly, an
irreversible reduction of “free” silver(i) ion takes place to result
in the deposition of metallic silver on the surface of the
electrode. The appearance of an oxidation peak at 380 mV
follows cathodic scans below À950 mV.
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