N-confused double-decker porphyrins

Article abstract of DOI:10.1021/ic0010048

An inner-coordinated Pd complex and inner- and outer-N coordinated, double-decker Pd complexes of N-confused tetratolylporphyrin have been synthesized, and their structures were elucidated by X-ray single-crystal analyses.

Full text of DOI:10.1021/ic0010048

5424
Inorg. Chem. 2000, 39, 5424-5425
N-Confused Double-Decker Porphyrins
Hiroyuki Furuta,*,†,‡ Naoko Kubo,† Hiromitsu Maeda,† Tomoya Ishizuka,† Atsuhiro Osuka,*,† Hideki Nanami,§ and
Takuji Ogawa§
Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan, Precursory Research for Embryonic
Science and Technology, Japan Science and Technology Corporation, Kawaguchi, 332-0012, Japan, and Department of Chemistry, Faculty
of Science, Ehime University, Matsuyama 790-8577, Japan
ReceiVed September 1, 2000
Porphyrin assembly by metal coordination is one of the facile
strategies to develop potent optical and electronic materials.1,2
For such studies, coordinating ligands like pyridine and imidazole
have been widely used for bridging. However, there are few, if
any, reports on the formation of a metal-coordination-assisted
porphyrin dimer or oligomer directly linked at the pyrrolic
peripheral, where the strong interaction of the mutual π-electrons
could be anticipated.2,3 “N-Confused porphyrin” (NCP, Chart 1)
is a porphyrin isomer in which one of the pyrrolic rings is
inverted.4 Similarly to the normal porphyrins, NCP can coordinate
a metal in the porphyrin core by using the inner carbon and
nitrogens (type 1).4b,5,6 Owing to the outward pointing nitrogen,
outer-N coordination is also conceivable (type 2). If the metals
bind in both ways, bimetallic species would be formed (type 3).
Especially, in the outer-N coordination cases, the metal-bridged
dimer and polymer could be derived if the doubly N-confused
porphyrins6b are used. In this communication, two types of
palladium-NCP complexes, inner-coordinated Pd(II)-NCP (1)
and inner- and outer-N-coordinated, double-decker Pd complexes,7
(Pd(II)-NCP)2 (2a,b), are reported. To the best our knowledge,
the latter Pd dimers are the first examples of the outer-N
coordination in the NCP family.
Chart 1
solvent systems, CHCl3 and toluene. First, the reaction was
performed in CHCl3 under reflux. After stirring for 0.5 h, a
yellow-greenish Pd complex (1) was formed in 50% yield
(Scheme 1). No other identifiable products were obtained. The
optical absorption spectrum showed a broadened Soret band at
446 nm and five absorption peaks in the Q-band region from 532
to 766 nm in CHCl3 (Supporting Figure 1a, Supporting Informa-
tion). These spectral features are in marked contrast to that of a
normal Pd(II)-TTP complex, where the Soret band is observed
at 416 nm and the Q-band appears with two peaks at 523 and
1
554 nm. The H NMR spectrum of 1 in CDCl3 showed a signal
at 9.95 ppm ascribable to the outer NH resonance, while the
absence of inner NH and CH signals indicated metal coordination
of type 1.
Complexation of Pd with NCP was studied using N-confused
tetratolylporphyrin (NCTTP) and Pd(OAc)2 in the two different
Direct evidence of the structure of 1 was obtained from X-ray
single-crystal analysis (Figure 1a).8 Pd metal was located in the
middle of the porphyrin plane in a square-planar fashion. The
average distances of Pd-N and Pd-C are 2.09 and 2.00 Å, which
are comparable to those of Pd-N in the nearly square-planar
Pd(II)-TPP (2.009 Å)9 and Pd(II)-C σ-bond (2.00-2.05 Å).10
Next, the solvent was changed from CHCl3 to toluene, and
the solution was refluxed for 1 h. Two red-colored products (2a
and 2b) along with NCTTP-Pd (1) were isolated in yields of
27%, 36%, and 19%, respectively (Scheme 1). The FABMS
spectra of both 2a and 2b showed the parent peaks at 1550 au in
line with the corresponding dimeric species, (Pd-NCTTP)2. The
Soret and Q-bands of both complexes are red-shifted and
broadened compared to those of the monomeric Pd complex 1
(Supporting Figure 1b, Supporting Information), which suggested
the significant distortion of the porphyrin rings in 2a and 2b. In
CDCl3, a set of inner protons (CH, NH) was observed at (-4.40,
0.09) ppm in 2a, while two sets of signals were seen in 2b at
(-3.83, 0.04) and (-3.28, 0.51) ppm, presumably reflecting the
symmetrical and unsymmetrical structures of 2a and 2b, respec-
tively.
† Kyoto University.
‡ PRESTO, JST.
§ Ehime University.
(1) (a) Transition Metals in Supramolecular Chemistry; Sauvage, J.-P. Ed.;
Wiley: Chichester, 1999; p 415. (b) Fujita, M. Chem. Soc. ReV. 1998,
27, 417-425. (c) Leininger, S.; Olenyuk, B.; Stang, P. J. Chem. ReV.
2000, 100, 853-908.
(2) (a) Drain, C. M.; Lehn, J.-M. J. Chem. Soc., Chem. Commun. 1994,
2313-2315. (b) Kobuke, Y.; Miyaji, H. J. Am. Chem. Soc. 1994, 116,
4111-4112. (c) Chi, X.; Guerin, A. J.; Haycock, R. A.; Hunter, C. A.;
Sarson, L. D. J. Chem. Soc., Chem. Commun. 1995, 2567-2569. (d)
Stribrany, R. T.; Vasudevan, J.; Knapp, S.; Potenza, J. A.; Emge, T.;
Schugar, H. J. J. Am. Chem. Soc. 1996, 118, 3980-3981. (e) Funatsu,
K.; Imamura, T.; Ichimura, A.; Sasaki, Y. Inorg. Chem. 1998, 37, 4986-
4995. (f) Drain, C. M.; Nifiatis, F.; Vasenko, A.; Batteas, J. D. Angew.
Chem., Int. Ed. 1998, 37, 2344-2347. (g) Fan, J.; Whiteford, J. A.;
Olenyuk, B.; Levin, M. D.; Stang, P. J.; Fleischer, E. B. J. Am. Chem.
Soc. 1999, 121, 2741-2752. (h) Vannelli, T. A.; Karpishin, T. B. Inorg.
Chem. 1999, 38, 2246-2247. (i) Diskin-Posner, Y.; Dahal, S.; Goldberg,
I. Angew. Chem., Int. Ed. 2000, 39, 1288-1292.
(3) The crystal structure of meso-η1-palladioporphyrin is reported. Arnold,
D. P.; Sakata, Y.; Sugiura, K.; Worthington, E. I. Chem. Commun. 1998,
2331-2332.
(4) (a) Furuta, H.; Asano, T.; Ogawa, T. J. Am. Chem. Soc. 1994, 116, 767-
768. (b) Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Rachlewicz, K.;
Głowiak, T. Angew. Chem., Int. Ed. Engl. 1994, 33, 779-781. (c) Latos-
Graz˘yn´ski, L. In The Porphyrin Handbook; Kadish, K. M., Smith, K.
M., Guilard, R., Eds; Academic Press: San Diego, 1999; Vol. 2, Chapter
14.
(5) (a) Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Głowiak, T. J. Am. Chem.
Soc. 1996, 118, 5690-5971. (b) Chmielewski, P. J.; Latos-Graz˘yn´ski,
L. Inorg. Chem. 1997, 36, 840-845.
(6) (a) Furuta, H.; Ogawa, T.; Uwatoko, Y.; Araki, K. Inorg. Chem. 1999,
38, 2676-2682. (b) Furuta, H.; Maeda, H.; Osuka, A. J. Am. Chem.
Soc. 2000, 122, 803-807. (c) Ogawa T.; Furuta, H.; Morino, A.;
Takahashi, M.; Uno, H. J. Organomet. Chem., in press.
(7) Buchler, J. W.; Cian, A. D.; Fischer, J.; Kihn-Botulinski, M.; Paulus,
H.; Weiss, R. J. Am. Chem. Soc. 1986, 108, 3652-3659.
(8) Crystallographic data for 1: C48H36N4Pd, T ) 296 K, MW ) 775.24,
violet, monoclinic, P21/n, a ) 9.753(2) Å, b ) 9.228(2) Å, c ) 21.184(2)
Å, â ) 98.61(1)°, V ) 1885.1(5) Å3, Dc ) 1.366 g/cm3, Z ) 2, R )
0.047, Rw ) 0.046, GOF ) 1.400. There is a center of symmetry at the
center of the macrocycle; hence the inner C and N atoms are disordered
and not distinguishable in the X-ray structure.
(9) Fleischer, E. B.; Miller, C. K.; Webb, L. E. J. Am. Chem. Soc. 1964, 86,
2342-2347.
(10) Maitlis, P. M.; Espinet, P.; Russell, M. J. H. In ComprehensiVe
Organometallic Chemistry Vol. 6; Wilkinson, G., Stone, F. G. S., Abel,
E. W. Eds.; Pergamon: Oxford, 1982; p 236.
10.1021/ic0010048 CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/03/2000

Communications
Inorganic Chemistry, Vol. 39, No. 24, 2000 5425
Scheme 1
the weak coordinating nature of the dipyrryl group to arouse the
recombination of one of the Pd-N bonds in 2a. Both 2a and 2b
were stable under neutral conditions but decomposed instantly
to the monomeric NCP in the presence of a small amount of TFA
in CH2Cl2.
It is well-known that Pd(II) undergoes the facile palladation
of aromatic compounds which have a substituent containing
nitrogen at a position suitable for chelating.13,14 Mechanistically,
thus, the coordination of Pd(II) at outer-N and succeeding o-C
palladation to the meso-tolyl group, yielding an outer-N Pd
complex, might compete with the inner-N coordination. The latter
would transform to the stable inner Pd complex, 1. On the other
hand, the resulting outer-N coordinating monomers would react
with each other to give 2a and 2b, respectively. The transforma-
tion from 1 to 2a or 2b was not observed in the refluxing toluene.
We believe that the square-planar Pd site formed initially could
determine the geometry of the second Pd significantly, where the
selective formation of 2a and 2b is induced. Here, the sacrifice
of either the planarity of the porphyrin plane or the square-planar
geometry of Pd is necessary to form 2a or 2b. Thus, N-confused
double-decker porphyrins obtained seem to stand on the subtle
balance between the planarity and the distortion.15 The difference
of the reaction mode in the two solvents could be ascribed to the
activation energy for the o-C palladation which requires a high
temperature as in refluxing toluene.16
Figure 1. Molecular structures of (a) Pd(II)-NCTTP (1) and (b) (Pd-
(II)-NCTTP)2 (2b). For clarity, uncoordinated tolyl groups are omitted
in part b. Selected bond lengths (Å) for 2b: Pd(1)-N(1), 2.00(2); Pd-
(1)-N(6), 2.12(2); Pd(1)-N(7), 2.08(2); Pd(1)-C(22), 2.00(2); Pd(2)-
N(3), 2.29(2); Pd(2)-N(4), 2.03(1); Pd(2)-N(5), 2.05(2); Pd(2)-C(70),
1.99(2). Selected angles (deg) for 2b: N(1)-Pd(1)-C(22), 87.6(7);
C(22)-Pd(1)-N(7), 95.3(7); N(6)-Pd(1)-N(7), 86.2(6); N(1)-Pd(1)-
N(6), 91.1(6); N(3)-Pd(2)-N(4), 81.8(6); N(3)-Pd(2)-N(5), 107.3(6);
N(4)-Pd(2)-C(70), 91.6(7); N(5)-Pd(2)-C(70), 86.1(7).
The explicit structure of 2b was elucidated by single-crystal
X-ray analysis.11 Each Pd atom was tetracoordinated with the
outer-N of the confused pyrrole, o-C of meso-tolyl, and two
pyrrolic inner-N’s of the other NCTTP, affording a slipped dimer
of double-decker type (Figure 1b). Two Pd sites are nonequivalent,
namely, the typical dihedral angles of Pd containing planes (φs)
are 1.72° for φPd-N6-N7φPd-N7-C22 with Pd(1) and -24.86° for
φPd-C70-N5φPd-N5-N3 with Pd(2) (Supporting Figure 2, Supporting
Information). Thus, the geometry of Pd(1) is close to square-
planar but Pd(2) is significantly distorted to tetrahedral. The Pd-C
bond distances (Å) of both sites are almost the same: Pd(1)-
C(22), 2.00; Pd(2)-C(70), 1.99(2). However, those of Pd-N
differ largely: Pd(1)-N(1), 2.00(2); Pd(1)-N(6), 2.12(2);
Pd(1)-N(7), 2.08 (2); Pd(2)-N(3), 2.29(2); Pd(2)-N(4),
2.03(1); Pd(2)-N(5), 2.05(2).
The obtained structure of 2b can well explain the unsym-
metrical 1H NMR spectrum and, in turn, suggests the symmetrical
structure of the other complex 2a. At present, for the lack of the
crystal structure of 2a, the other isomeric structures which differ
with respect to the coordinating nitrogens cannot be ruled out.12
However, the observed transformation from 2a to 2b in triethyl-
amine/CHCl3 (v/v ) 1/1) at reflux can be simply interpreted by
In conclusion, we have prepared a new type of double-decker
porphyrin using NCTTP and Pd(OAc)2. The Pd coordination mode
was unique in that inner- and outer-N as well as o-C were
included. If the dimer 2a (or 2b) dissociates to monomers by
adding the second metal for the chelation in the core, the
coordination site of the Pd(II) would become available. Such
bimetallic NCP monomers (type 3) are attractive for use as
catalysts. Attempts to combine both inner and outer coordination
in the NCP monomer are currently underway.
Supporting Information Available: Listings of synthetic procedures,
spectral data, and absorption spectra for 1, 2a, and 2b; dihedral angles
of Pd-containing planes of 2b; isomeric structures of 2a; X-ray crystal-
lographic files. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC0010048
(13) Tsuji, J. Palladium Reagents and Catalysts; Wiley: Chichester, 1995; p
87.
(14) When the doubly N-confused porphyrin (N2CP) was subjected to the
similar Pd complexation reaction, inner C-arylated Pd(II)-N2CP complex
was obtained. Furuta, H.; Maeda, H.; Osuka, A.; Yasutake, M.;
Shinmyozu, T.; Ishikawa, Y. Chem. Commun. 2000, 1143-1144.
(15) The flexible sandwiched structure of the tetracoordinated Pd complex is
reported in the linear tetrapyrroles. Lord, P.; Olmstead, M. M.; Balch,
A. L. Angew. Chem., Int. Ed. 1999, 38, 2761-2763.
(11) Crystal data for 2b: C96H72N8Pd2, T ) 296 K, MW ) 1550.48, red,
triclinic, P1h, a ) 16.929(1) Å, b ) 22.7847(9) Å, c ) 14.5877(5) Å, R
) 95.559(3)°, â ) 103.133(5)°, γ ) 70.950(6)°, V ) 5178.1(6) Å3, Dc
) 0.994 g/cm3, Z ) 2, R ) 0.104, Rw ) 0.152, GOF ) 2.640.
(16) Formation of Pd dimers (2a and 2b) was also observed in other solvents
such as cyclohexane, CCl4, C6H6, and C6F6 over 60 °C.
(12) The possible isomeric structures are shown in the Supporting Information.