Structures and Ligand Exchange of N-Confused Porphyrin Dimer Complexes with Group 12 Metals

Article abstract of DOI:10.1021/ic035294e

N-confused 5,20-diphenylporphyrin (NCDPP, 1) formed 2:2 dimer complexes with group 12 metals both in the solid state and in solution. X-ray single-crystal analyses of the Zn(II) and Cd(II) complexes (7, 8) revealed that each metal ion is coordinated with three inner core nitrogens and a peripheral nitrogen of the other NCDPP in the pair. In the ¹H NMR spectra of 7, 8, and the Hg(II) complex (9), the outer α-H signals of the confused pyrrole ring appeared in the upfield region at 2.57, 3.44, and 3.60 ppm, respectively, due to the ring current effect by the coordinated porphyrins. In the case of the Cd(II) and Hg(II) complexes (8, 9), additional magnetic couplings with the metal nuclei of the partner rings were observed. The equilibrium constants (K) of the monomer exchange reaction at 25 °C were determined to be 2.5, 1.3, and 0.6 for the (Zn-Cd), (Cd-Hg), and (Zn-Hg) heterodimer complexes, respectively, from the ¹H NMR spectra of a solution containing two different dimers. Furthermore, a metal-transfer reaction from a Zn(II) NCP dimer complex to the free base porphyrin was demonstrated.

Full text of DOI:10.1021/ic035294e

Inorg. Chem. 2004, 43, 1618−1624
Structures and Ligand Exchange of N-Confused Porphyrin Dimer
Complexes with Group 12 Metals
Hiroyuki Furuta,*,†,‡ Tatsuki Morimoto,†,§ and Atsuhiro Osuka§
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu UniVersity,
Fukuoka 812-8581, Japan, and PRESTO, JST, and Department of Chemistry, Graduate School of
Science, Kyoto UniVersity, Kyoto 606-8502, Japan
Received November 9, 2003
N-confused 5,20-diphenylporphyrin (NCDPP, 1) formed 2:2 dimer complexes with group 12 metals both in the solid
state and in solution. X-ray single-crystal analyses of the Zn(II) and Cd(II) complexes (7, 8) revealed that each
metal ion is coordinated with three inner core nitrogens and a peripheral nitrogen of the other NCDPP in the pair.
In the 1H NMR spectra of 7, 8, and the Hg(II) complex (9), the outer R-H signals of the confused pyrrole ring
appeared in the upfield region at 2.57, 3.44, and 3.60 ppm, respectively, due to the ring current effect by the
coordinated porphyrins. In the case of the Cd(II) and Hg(II) complexes (8, 9), additional magnetic couplings with
the metal nuclei of the partner rings were observed. The equilibrium constants (K) of the monomer exchange
reaction at 25 °C were determined to be 2.5, 1.3, and 0.6 for the (Zn−Cd), (Cd−Hg), and (Zn−Hg) heterodimer
complexes, respectively, from the 1H NMR spectra of a solution containing two different dimers. Furthermore, a
metal-transfer reaction from a Zn(II) NCP dimer complex to the free base porphyrin was demonstrated.
Chart 1. Schematic Drawings of the Typical Coordination Modes of
Introduction
NCP: (a) Square Planar; (b) Side-On η1-Interaction; (c) Outer-N
Coordination
Metalloporphyrins bearing an additional binding center at
the periphery are attracting considerable attention as useful
building blocks for the multiporphyrin assemblies.1 Among
such porphyrins, N-confused porphyrin (NCP),2 an isomer
of porphyrin, is of particular interest because it possesses
two metal binding sites already in the framework, namely,
the inner N3C core and the peripheral N of the confused
pyrrole ring. Hitherto, NCP has been shown to coordinate
(II),3a,b Cu(III),3c Pd(II),3d Pt(II),3e Mn(III),3f Ag(III),3g
a
metals in the core forming neutral square-planar complexes
hexacoordinated complex with Sb(V),3h and side-on η1-
coordination type complexes with Zn(II),4a Mn(II),3f,4b and
Fe(II)4c (Chart 1b). On the other hand, outer-N coordinated
possessing a carbon-metal bond (Chart 1a) for Ni(II),2b Cu-
* To whom correspondence should be addressed. E-mail: hfuruta@
cstf.kyushu-u.ac.jp.
† Kyushu University.
(3) (a) Chmielewski, P. J.; Latos-Graz˘yn´ski, L.; Schmidt, I. Inorg. Chem.
2000, 39, 5475-5482. (b) Maeda, H.; Osuka, A.; Ishikawa, Y.;
Aritome, I.; Hisaeda, Y.; Furuta, H. Org. Lett. 2003, 5, 1293-1296.
(c) Maeda, H.; Ishikawa, Y.; Matsuda, T.; Osuka, A.; Furuta, H. J.
Am. Chem. Soc. 2003, 125, 11822-11823. (d) Furuta, H.; Kubo, N.;
Maeda, H.; Ishizuka, T.; Osuka, A.; Nanami, H.; Ogawa, T. Inorg.
Chem. 2000, 39, 5424-5425. (e) Furuta, H.; Youfu, K.; Maeda, H.;
Osuka, A. Angew. Chem., Int. Ed. 2003, 42, 2186-2188. (f) Bohle,
D. S.; Chen, W.-C.; Hung, C.-H. Inorg. Chem. 2002, 41, 3334-3336.
(g) Furuta, H. Ogawa, T.; Uwatoko, Y.; Araki, K. Inorg. Chem. 1999,
38, 2676-2682. (h) Ogawa, T.; Furuta, H. Takahashi, M.; Morino,
A.; Uno, H. J. Organomet. Chem. 2000, 611, 551-557.
(4) (a) Furuta, H.; Ishizuka, T.; Osuka, A. J. Am. Chem. Soc. 2002, 124,
5622-5623. (b) Harvey, J. D.; Ziegler, C. J. Chem. Commun. 2002,
1942-1943. (c) Chen, W.-C.; Hung, C.-H. Inorg. Chem. 2001, 40,
5070-5071. (d) Hung, C.-H.; Chen, W.-C.; Lee, G.-H.; Peng, S.-M.
Chem. Commun. 2002, 1516-1517.
‡ PRESTO, JST.
§ Kyoto University.
(1) (a) Wojaczyn´ski, J.; Latos-Graz˘yn´ski, L. Coord. Chem. ReV. 2000,
204, 113-171. (b) Richeter, S.; Jeandon, C.; Gisselbrecht, J.-P.;
Ruppert, R.; Callot, H. J. J. Am. Chem. Soc. 2002, 124, 6168-6179.
(c) Michelsen, U.; Hunter, C. A. Angew. Chem., Int. Ed. 2000, 39,
764-767. (d) Takahashi, Y.; Kobuke, Y. J. Am. Chem. Soc. 2003,
125, 2372-2373. (e) Imamura, T.; Funatsu, K.; Ye, S.; Morioka, Y.;
Uosaki, K.; Sasaki, Y. J. Am. Chem. Soc. 2000, 122, 9032-9033.
(2) (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, CA,
2000; Vol. 2, Chapter 14. (d) Furuta, H.; Maeda, H.; Osuka, A. Chem.
Commun. 2002, 1795-1804.
1618 Inorganic Chemistry, Vol. 43, No. 5, 2004
10.1021/ic035294e CCC: $27.50 © 2004 American Chemical Society
Published on Web 02/06/2004

Porphyrin Dimer Complexes with Group 12 Metals
Chart 2. Structures of N-Confused Porphyrins and Normal Porphyrins
Scheme 1. Syntheses of Dimer Metal Complexes (7-9) of
NCDPP (1)a
a Key: (i) M(OAc)2‚2H2O (M ) Zn, Cd) or Hg(OAc)2, CH2Cl2; (ii) 1%
Et4NOH(aq); (iii) crystallization from CH2Cl2/hexane.
complexes have been also synthesized with Rh(I)5 (Chart
1c), and the combination of both inner and outer coordination
was seen in the dimer complexes of Pd(II)3d, Zn(II),4a
Mn(II),4b and Fe(II).4d
complex was formed initially, which was transformed into
a dinuclear complex after treatment with an alkaline solution.4a
In the case of the Cd(II) complex, direct formation of 8 was
suggested from the absorption spectral change during the
reaction. Similarly, the Hg(II) complex (9) was obtained
without alkali treatment using 1 equiv of Hg(OAc)2 in
refluxed CH2Cl2. When 2 equiv of Hg(OAc)2 was used under
the same conditions as those of the Cd(II) complex, a
complicated mixture was produced. In the case of the Hg(II)
complex, the dimer was not isolated due to its inherent
instability, but the formation of structure of 9 was unambigu-
Previously, we showed the facile formation of a mutually
coordinating Zn(II) dimer complex of N-confused tetraphen-
ylporphyrin (NCTPP, 3) in solution.4a Thereafter, the crystal
structures of dimeric Mn(II)4b and Fe(II)4d NCP complexes
were reported by Ziegler’s and Hung’s groups, respectively.
However, a comparison of these structures with the Zn(II)
complex in solution was unfeasible owing to the paramag-
netism of the Mn(II) and Fe(II) species. Thus, the question
of the exact structure of the Zn(II) complex remained
unanswered. Herein, we report the first X-ray structures of
air-stable dimeric Zn(II) and Cd(II) NCP complexes (7, 8)
1
ously confirmed by the H NMR analysis.
The dimer structures of 7 and 8 were explicitly elucidated
by single-crystal X-ray analyses (Figure 1a,b and Table 1).
In accordance with the predicted structure of the Zn(II)
NCTPP complex,4a the two Zn(II) metals in 7 are coordinated
with the N3C core and the outer N of the other NCDPP in a
pair, respectively. The structures of the Zn(II) and Cd(II)
dimer complexes are nearly equivalent and, interestingly, are
similar to the Mn(II) and Fe(II) complexes (Figure 1c) except
for the relative orientation of the confused pyrrole rings, i.e.,
a molecular symmetry of C2 for 7 and 8 and Ci for the Mn(II)
and Fe(II) complexes. In other words, the dimers 7 and 8
are formed with two NCP rings of the same chirality while
the Mn(II) and Fe(II) complexes consist of both enantiomers
in a molecule. In the crystals, two confused pyrrole rings in
7 (and 8) are tilted by 47.5(3) and 49.9(3)° (41.3(5) and 42.9-
(5)°) from the corresponding N3 mean plane comprising the
three inner nitrogen atoms. The Zn atoms of 7 (and Cd of
8) are separated from each other by a distance of 5.217(2)
Å (5.230(2) Å) and located 0.61(1) and 0.64(1) Å (0.87(1)
and 0.85(1) Å) above the mean planes, respectively, with
an average N-Zn (and N-Cd) distance of 2.07(1) Å (2.24-
(1) Å). Furthermore, the distance between the inner carbon
and the nearest Zn (Cd) atom, 2.53(1) Å (2.57(1) Å), is short
enough for a side-on η1-coordination.
Structures of Dimer Complexes in Solution. The simi-
larity of the structure of the Cd(II) dimer complex to the
Zn(II) complex in solution was inferred from the analogous
profile of the absorption spectra (Figure 2). Namely, a broad
Soret-like band and strong Q-band at the longest wavelength
were observed at 447 and 738 nm and 459 and 741 nm for
7 and 8, respectively. In fact, the 1H NMR spectrum of 7 in
CDCl3 showed the inner and outer CH signals (H1, H2) at
-3.99 and 2.57 ppm, respectively (Figure 3 (top)), and the
corresponding signals of 8 and 9 were observed in almost
1
in addition to the H NMR spectra of 7, 8, and the Hg(II)
complex (9). For crystallographic reasons, the less crowded
NCP derivative, 5,20-diphenyl-NCP (NCDPP, 1),6 was
investigated in this work (Chart 2). The structures of the
dimer complexes with group 12 metals are similar to the
Fe(II) and Mn(II) complexes with the exception of the
relative orientation of the two confused pyrrole rings. The
thermodynamic parameters of the monomer ligand exchange
reactions between dimer complexes as well as the metal-
transfer reaction from the Zn(II) NCP complex to a normal
porphyrin are also reported.
Results and Discussion
Preparation of Zn(II), Cd(II), and Hg(II) Dimer
Complexes (7-9). The Zn(II), Cd(II), and Hg(II) NCDPP
dimer complexes (7-9) were prepared by using 1 and the
corresponding metal acetates in CH2Cl2 (Scheme 1). For
example, the Zn(II) complex (7) was obtained by stirring a
mixture of 1 and Zn(OAc)2‚2H2O at room temperature for
2 h. After washing with 1% aqueous Et4NOH, complex 7
was crystallized from a CH2Cl2/hexane solution (81% yield).
The Cd(II) complex (8) was synthesized from 1 and Cd-
(OAc)2‚2H2O in 83% yield by a similar method except for
a longer reaction time (2 days). Under the same reaction
conditions, NCTPP (3) yielded the corresponding Cd(II)
dimer complex in only a 60% yield, suggesting the higher
reactivity of the less crowded ligand 1. The formation process
of the Cd(II) complex was apparently different from that of
the Zn(II) dimer. In the case of Zn(II), a tetranuclear dimer
(5) Srinivasan, A.; Furuta, H.; Osuka, A. Chem. Commun. 2001, 1666-
1667.
(6) Furuta, H.; Morimoto, T.; Osuka, A. Org. Lett. 2003, 5, 1427-1430.
Inorganic Chemistry, Vol. 43, No. 5, 2004 1619

Furuta et al.
Figure 1. Dimer structures of (a) Zn(II) NCDPP (7), (b) Cd(II) NCDPP (8), and (c) Ziegler’s Mn(II) complex. The phenyl groups and solvent molecules
are omitted for clarity. Selected bond lengths (Å) for 7: Zn(1)-N(5), 2.062(9); Zn(1)-N(2), 2.145(6); Zn(1)-N(3), 2.012(7); Zn(1)-N(4), 2.103(8); Zn-
(2)-N(1), 2.060(8); Zn(2)-N(6), 2.134(8); Zn(2)-N(7), 1.992(7); Zn(2)-N(8), 2.098(6). Selected bond lengths (Å) for 8: Cd(1)-N(5), 2.23(2); Cd(1)-
N(2), 2.28(1); Cd(1)-N(3), 2.20(1); Cd(1)-N(4), 2.25(1); Cd(2)-N(1), 2.21(2); Cd(2)-N(6), 2.28(1); Cd(2)-N(7), 2.21(1); Cd(2)-N(8), 2.25(1). Note:
Mn(II) structure c was taken from ref 4b-reproduced by permission of The Royal Society of Chemistry.
Table 1. Crystal Data for Zn(II)- and Cd(II)-NCDPP Dimer
Complexes (7, 8)
7‚2CH2ClCH2Cl
8‚C6H14
empirical formula
fw
space group (No.)
cryst syst
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C68H48N8Zn2Cl4
1249.75
P1h (No. 2)
triclinic
C70H54N8Cd2
1232.07
P1h (No. 2)
triclinic
12.379(8)
15.64(1)
17.46(1)
63.24(6)
78.22(6)
67.43(6)
2784.9(3)
-150
13.9012(4)
14.5110(3)
16.5462(4)
67.493(4)
81.366(3)
63.664(5)
2762.7(2)
-150
T, °C
Z
D
2
2
calcd, g cm-3
1.502
1.469
cryst size, mm
θ, deg
0.40 × 0.40 × 0.18
0.20 × 0.20 × 0.10
27.5
27.4
no. of reflcns measd
no. of reflcns obsd
radiatn λ, Å
12 164
10 192
0.710 69 (Mo KR)
11.149
1.378
0.089
0.121
8592
4499
0.710 75 (Mo KR)
8.167
0.991
0.085
0.110
µ(Mo KR), cm-1
GOF (I > 3σ(I))
Ra (I > 3σ(I))
Figure 3. 1H NMR spectra (300 MHz, 25 °C, CDCl3) of Zn(II) (7, top),
Cd(II) (8, middle), and Hg(II) (9, bottom) complexes.
b
Rw
satellite doublet signals with J ) 4 and 36 Hz in 8 and 9,
respectively. In the upfield region, the doublet inner CH (H1)
signals at -4.15 and -3.27 ppm for 8 and 9, respectively,
were also associated with satellite doublet signals (J ) 12
and 30 Hz) assignable to the coupling between inner CH
and η1-coordinated metal (MC) of Cd(II) and Hg(II), respec-
tively.8,9 In complex 8, the shoulder signals with J ) 4 Hz
were associated with the same H1 signal, which was
interpreted as a coupling with the CdN metal in the partner
NCP ring. This long-range coupling is direct evidence for
dimer formation in solution.10 Correlations of the mutual
magnetic couplings are summarized in Figure 3.
2
a R ) Σ||Fo| - |Fc||/Σ|Fo|. b Rw ) [Σw(|Fo| - |Fc|)2/Σ|Fo| ]1/2
.
Figure 2. Absorption spectra of 7 (solid line) and 8 (broken line) in CH2-
Cl2.
(7) In the single crystal, the distances between the N3 mean plane and
the outer R-carbon of the opposite NCP for the Zn complex (7) are
3.005(9) and 3.082(9) Å, which are shorter than those of the Cd
complex (8), 3.20(2) and 3.12(2) Å.
(8) A similar Cd-H coupling (JCd-H ) 4.4 Hz) was reported in the
tetraphenyl-p-benziporphyrin: Ste¸pien´, M.; Latos-Graz˘yn´ski, L. J. Am.
Chem. Soc. 2002, 124, 3838-3839.
(9) Although MN is equivalent to MC, the two center metals are
distinguished here as a matter of convenience.
(10) The formation of complexes 7 and 8 in solution was also supported
from vapor pressure osmometry (VPO), which showed the dimer
molecular weight at 976 ( 78 (calcd 1052) and 1101 ( 88 (calcd
1146) g/mol, respectively.
the same region (Figure 3 (middle, bottom)). One significant
difference is the outer CH signals at 3.44 and 3.60 ppm for
8 and 9, respectively, which are shifted downfield by ca. 1
ppm compared with 7. This is attributable to the weaker ring
current effect due to the longer distance between the NCP
planes in the dimer.7 Furthermore, the magnetic coupling
between the nuclear spin of the outer N-coordinated metal
MN (M ) Cd, Hg) and the outer CH (H2) was observed as
1620 Inorganic Chemistry, Vol. 43, No. 5, 2004

Porphyrin Dimer Complexes with Group 12 Metals
Scheme 2. Ligand Exchange Equilibrium of a Mixed Solution of 7
and 8
ment of the two confused pyrrole rings in solution, consistent
with the solid state.13
Figure 4. 1H NMR signals of a mixed solution of 7 and 8 (1:1, 2 mM
each) in CDCl3 at 50 °C. A-D represent the outer CH signals of 8 and 7
and the inner CH signals of 7 and 8, respectively.
In the solution of 7 and 8, the monomer species were
1
detected neither by H NMR nor absorption spectroscopy.
The chemical shift differences (∆δ) between the signals
As the shape of the absorption spectra did not change even
at a low concentration around 10-5 M, the concentration of
the monomer species should be extremely low. Assuming
that the dimers 7 and 8 are in equilibrium as shown in the
Scheme 2, the equilibrium constant (K) was estimated to be
2.5 and 2.7 at 25 and 50 °C, respectively. Because the K
values are lower than 4, the value expected from only the
mixing entropy term,14 the stability of the heteronuclear dimer
should be smaller than homodimers. Supporting this, the
thermodynamic parameters (∆H and ∆S) were estimated at
0.68 kJ/mol and 10 J/(K mol), respectively, from the van’t
Hoff plots. The positive ∆H value indicates the relatively
unfavorable formation of the heteronuclear dimer complex,
which is probably attributable to the distortion of the dimer
structure due to the difference of outer N coordination of
both NCP rings. The ∆S value is nearly equal to the statistical
value (R ln 4 ) 11.5 J/(K mol), where R is gas constant).
From these values, it is clear that the dominant formation of
the heteronuclear dimer complex in the equilibrium is
attributable to the larger entropy term (T∆S > ∆H).
Similarly, the corresponding heteronuclear dimers were
also produced by mixing the complexes of Zn(II) (7) and
Hg(II) (9), as well as Cd(II) (8) and Hg(II) (9). In contrast
with the heterodimer derived from 7 and 8, the ligand
exchange process is relatively slow and requires more harsh
conditions in both the cases. Specifically, the equilibrium
constant after mixing for 0.5 h was estimated as K ) 0.3 at
25 °C, but the final equilibrium states had K ) 0.6 and 1.3
at 25 °C, respectively; these states were accomplished by
additional stirring at 50 °C for 1 h. These results indicate
that the heteronuclear complexes containing Hg(II) ion are
less stable compared to those of Zn(II) or Cd(II), probably
due to the imbalance of the ion sizes. On the other hand,
introduction of additional meso-phenyl groups did not affect
the equilibrium process so much as judged by the 1H NMR
1
at the both ends in the H NMR spectra are 12.7, 12.9, and
11.9 ppm for 7-9, respectively. The smaller ∆δ value
observed in 9 is probably due to the loose dimer structure
as the result of the larger ion radius of Hg(II). Support for
the η1-interaction between the sp2 inner carbon atoms and
the center metals in 8 and 9 was obtained from the 13C NMR
spectra.11 Specifically, the 13C signals of the inner carbons
of 8 and 9 were observed at 76.0 and 86.5 ppm, respectively;
these are closer to the value of the sp2 hybridized inner
carbon atom’s signal (99.0 ppm) in the free base 1 than that
of the inner sp3-hybridized carbon (34.1 ppm) of the inner-C
alkylated NCTPP Ni(II) complex.12
Ligand Exchange Equilibrium in Solution. As described
above, the dimer complexes use both the inner and outer
coordination sites simultaneously. The tetradentate macro-
cycle will clearly bind metals more strongly than the
monodentate outer coordination site. To evaluate the stability
of these dimers in solution, the solution equilibria in several
mixed dimer systems were examined.
At first, the complexes 7 and 8 were mixed and stirred
for 0.5 h at room temperature in CDCl3. The dimer
1
equilibrium was then analyzed directly from the H NMR
spectra. As shown in Figure 4, apart from the original signals
(A-D), the resulting solution exhibits new signals (H1-H4)
bearing Cd-H couplings of a heterodimer complex contain-
ing both Zn(II) and Cd(II) metals. The most upfield-shifted
signal at -4.32 ppm (H1) is assignable to the inner CH of
the NCP ring containing the Cd(II) ion as judged by the small
double doublet signals (J ) 12 and 1 Hz). The other shoulder
signals seen in 8 are not observed due to the lack of Cd(II)
ion in the paired NCP ring (compare the H1 signal with the
signal D). Instead, the signal at -3.75 ppm (H3), assignable
to the inner CH of the NCP ring having Zn(II), has a shoulder
due to the long-range coupling with the Cd(II) ion in the
partner NCP ring. Here, the strong NOE correlation between
two outer protons (H2 and H4) also supports the C2 arrange-
(13) In the present crystal structures, the distances between the two outer
CH carbons of the dimers are 3.26(1) and 3.18(2) Å for the Zn(II)
and Cd(II) complexes, respectively, while the two carbons of Ziegler’s
Mn dimer complex are separated by 4.99(1) Å. See the Supporting
Information.
(11) The 13C signal of Zn dimer 7 was not obtained due to the poor
solubility. However, the corresponding signal of the Zn(II) NCTPP
dimer complex (10) was observed at 78.3 ppm.4a
(14) Kaim, W.; Klein, A.; Glo¨ckle, M. Acc. Chem. Res. 2000, 33, 755-
(12) Schmidt, I.; Chmielewski, P. J. Chem. Commun. 2002, 92-93.
763.
Inorganic Chemistry, Vol. 43, No. 5, 2004 1621

Furuta et al.
Table 2. Equilibrium Constants (K) between Homo- and Heteronuclear
Dimer Complexes at 25 °C in CDCl3
8, the obtained spectra showed only four sets of inner CH
signals, which were assignable to the starting dimer com-
plexes (8 and 11) and a heterodimer consisting of the
monomer ligands derived from both the homodimer com-
plexes (Figure 5). In the second mechanism, the newly
formed dimer should consist of a set of monomer of (Cd-
2) and (Zn-1) moieties; on the other hand, in the third
mechanism, the combination should be that of (Zn-2) and
(Cd-1) parts. The detailed comparison of the chemical shifts
of the inner CH signals of H1 and H3 in Figure 5 with those
of (Zn-1)(Cd-1) and (Zn-2)(Cd-2) strongly indicates that
the newly formed dimer consists of (Zn-2) and (Cd-1)
moieties, which is fully consistent with the third mecha-
nism.15 This result implies that the inner coordinated metals
are tightly bound by each of the NCP inner core and not
exchangeable in the dimer complex. In solution, both outer
nitrogens dissociate metals of paired NCP rings more
readily16 and exchange the monomer parts in forming a new
dimer complex.
a
homonuclear complexes
K
hetero-nuclear (or ligand) complex
7 + 8
8 + 9
2.5
1.3
0.6
3.8
(Zn-1)(Cd-1)
(Cd-1)(Hg-1)
(Hg-1)(Zn-1)
(Zn-3)(Zn-1)
9 + 7
10 + 7
a 1: NCDPP. 3: NCTPP. 7: (Zn-1)2. 8: (Cd-1)2. 9: (Hg-1)2. 10:
(Zn-3)2.
Scheme 3. Three Possible Mechanisms for the Formation of a
Heteronuclear Dimer Complex
Metal-Transfer Reactions. Compared with a square-
planar complex of a normal porphyrin, the present nonplanar
NCP complexes are expected to coordinate and release metal
ions readily because of the weak side-on η1-coordination of
the sp2 carbon in the core. This would be an advantage when
using NCP for a metalation catalyst or metal carrier. To
examine this possibility, we treated the Zn(II) NCP complex
with a free base porphyrin as a metal acceptor.
analyses of a mixture solution of Zn(II) NCDPP (7) and
Zn(II) NCTPP (10), where the exchange reaction was as fast
as that of 7 and 8 and had an equilibrium constant K ) 3.8
at 25 °C. This is almost same as the statistical value 4, which
suggests that ∆H of this heterodimer formation is nearly
equal to zero; namely, the homo- and heterodimer have the
same stability. The K values obtained are summarized in
Table 2.
The above results indicate that the formation of hetero-
nuclear NCP dimer is general for these complexes with group
12 metals. Mechanistically, three possible schemes can be
considered in the dimer formation process according to the
sites of coordinated metal bound. The first one is a free metal
exchange reaction in which two metals are rapidly exchang-
ing in the dimer complex and behave as if metal ions are
unbound (Scheme 3a). The second one is a free monomer
ligand exchange at the core, in which a metal is bound tightly
at the outer N site (Scheme 3b), and the third one is the
ligand exchange at the core where the metal is bound in the
core (Scheme 3c). To clarify the mechanism, a cross
experiment was performed by using a mixture of Zn(II) 5,-
20-di-p-tolyl-NCP dimer (11) and Cd(II) NCDPP complex
(8). If the reaction proceeds in the first mechanism, 16 kinds
of inner CH signals from 10 dimer complexes should appear
in the upfield region. However, just like the system of 7 and
In the control experiment, a toluene solution of the Zn(II)
complex of TPP (5,10,15,20-tetraphenylporphyrin, 5) and
free base TTP (5,10,15,20-tetra-p-tolylporphyrin, 6) was
refluxed for 5 days but the composition of the solution did
not change at all. On the other hand, when Zn(II) dimer
complexes of NCTPP (3) and free base TTP (6) were stirred
under the same conditions, the Zn(II) complex of 6 and the
free base NCTPP (3) as well as the starting two species were
1
detected by H NMR (Figure 6a). The production of the
Zn(II) complex of 6 was confirmed by the â-proton signals
at 8.96 ppm. This is clear evidence that the center Zn(II)
ion of NCP was released and transferred to the free base
porphyrin.
Similarly, the metal-transfer reaction of Zn(II) NCTPP
complex (10) to free base NCTTP (N-confused 5,10,15,20-
tetra(p-tolyl)porphyrin, 4) was examined under the same
1
conditions. In the H NMR spectrum, the inner CH signals
of NCTPP and NCTTP as well as the inner CH signals of
the Zn(II) complexes of NCTPP and NCTTP were observed
in the region from -3.5 to -5.0 ppm. The other signals were
assigned to the heteronuclear dimer complex (Figure 6b).
Scheme 4. Metal-Transfer Reaction of Zn(II) NCTPP Dimer (10) and Free Base Porphyrins (a) TTP (6) and (b) NCTTP (4)
1622 Inorganic Chemistry, Vol. 43, No. 5, 2004

Porphyrin Dimer Complexes with Group 12 Metals
Figure 5. 1H NMR (300 MHz, 25 °C, CDCl3) signals of a mixture of 8 and 10 (1:1, 2 mM each). A and B represent the outer CH signals of 8 and 10,
and C and D the inner CH signals of 10 and 8, respectively.
Figure 6. 1H NMR spectra after metal-transfer reactions of Zn(II) NCTPP dimer (10) and free base porphyrins (a) TTP (6) and (b) NCTTP (4).
This result indicates that the center Zn(II) ion in the dimer
complex was transferred to the other NCP free base,
producing the corresponding dimer complex and successively
exchanging their monomer parts with one another at toluene
refluxing temperature.
solid state and in solution. Reflecting the weaker binding
ability of the outer nitrogen, the dimer complexes of different
metals can readily exchange their monomer parts with one
another, forming heteronuclear dimer complexes. The equi-
librium constants of the exchange reaction and the stability
of the dimer complexes depend largely on the coordinated
metal ions. Furthermore, the center metal ions can be
removed and transferred to the other porphyrin cores.
Conclusion
N-confused porphyrin forms dimer complexes with group
12 metals in which the metal ions are coordinated by the
three inner nitrogens as well as one carbon in the core and
the outer nitrogen of the paired NCP, respectively, in the
Conceptually, the dynamic exchange of the monomer
partner by the reversible coordination of the present system
can be considered as a type of “porphyrin metathesis”. By
the recombination of the dimer species, the information of
one molecule can be transferred to the other. As a lot of
information could be implanted on this type of dimer
complex by using various ligands, enriched nuclear spin,
different metals, and so on, we think the present system is
promising for a variety of applications in the area of
supramolecular informatics chemistry.17
(15) The inner CH signals of (Zn-1) in (Zn-1)(Cd-1) and (Zn-2) in
(Zn-2)(Cd-2) were observed at -3.79 and -3.66 ppm at 25 °C,
respectively. On the other hand, the inner CH signals of (Cd-1) in
(Zn-1)(Cd-1) and (Cd-2) in (Zn-2)(Cd-2) were observed at -4.38
and -4.25 ppm at 25 °C, respectively. Assuming that the chemical
shift difference is mainly due to the change of meso-aryl groups, the
signal at -3.66 ppm in Figure 5 is assignable to the inner CH proton
of (Zn-2) and the signal at -4.36 ppm to that of (Cd-1). See the
Supporting Information.
(16) In fact, analyses of the dimer complexes by FABMS or MALDI-TOF-
MS showed the signal corresponding to the monomer part with the
center metal.
(17) Glaser, S. J. Angew Chem., Int. Ed. 2001, 40, 147-149.
Inorganic Chemistry, Vol. 43, No. 5, 2004 1623

Furuta et al.
1% Et4NOH aqueous solution and water twice. The solvent was
removed in vacuo, and the obtained solid was recrystallized from
CH2Cl2/hexane to afford a green solid (81% yield). 1H NMR (300
MHz, 25 °C, CDCl3, ppm): δ 8.70 (s, 2H, meso-H), 8.60 (d, J )
4.2 Hz, 2H, â-H), 8.43 (d, J ) 4.8 Hz, 2H, â-H), 8.40 (d, J ) 4.5
Hz, 2H, â-H), 8.35 (d, J ) 4.5 Hz, 2H, â-H), 8.23 (d, J ) 4.2 Hz,
2H, â-H), 8.22 (s, 2H, meso-H), 8.08 (d, J ) 4.8 Hz, 2H, â-H),
7.72-7.43 (m, 16H, Ph), 6.68 (br, 4H, Ph), 2.57 (d, J ) 1.2 Hz,
2H, outer R-H), -3.99 (d, J ) 1.2 Hz, 2H, inner CH). UV/vis
(CH2Cl2; λmax, nm (10-4ꢀ)): 311 (8.62), 394 (10.3), 447 (18.0),
584 (1.58), 687 (2.51), 738 (5.86). VPO: 976 ( 78 g/mol (calcd
1052 g/mol).
Experimental Section
Materials. Free base 5,20-NCDPP (1) and N-confused 5,20-di-
p-tolyl-NCP (2) for the dimer complex 11 were synthesized with
the corresponding 2,4-bis(arylhydroxymethyl)pyrrole and meso-
unsubstituted tripyrrane by a [3 + 1] acid-catalyzed condensation
reaction, followed by oxidation.6 Free base NCTPP (3) and NCTTP
(4) were prepared as described before.18 Commercially available
reagents and solvents were used without further purification.
Instrumentation. 1H NMR and 13C NMR spectra were recorded
on a JEOL JNM-AL270 FT NMR system operating at 300 MHz
1
1
for H NMR and 75.5 MHz for 13C NMR. The residual H NMR
and 13C NMR resonances of the deuterated solvents were used as
the internal reference. UV/visible spectra were recorded on a
Shimadzu UV-3150 spectrometer. Vapor pressure osmometry
(VPO) data were obtained on a Gonotec Osmomat 070.
Cd(II) Dimer Complex of 2-Aza-5,20-diphenyl-21-carbapor-
phyrin (8). NCDPP (1) was treated with 2 equiv of Cd(OAc)2‚
2H2O in CH2Cl2 for 2 days. After a workup identical with that
described above or without base treatment, the residue was
recrystallized from CH2Cl2/hexane twice to afford a green product
(83% yield). 1H NMR (300 MHz, 25 °C, CDCl3, ppm): δ 8.77 (s,
2H, meso-H), 8.63 (d, J ) 4.5 Hz, 2H, â-H), 8.60 (s, 2H, meso-
H), 8.54 (d, J ) 4.5 Hz, 2H, â-H), 8.45 (d, J ) 4.5 Hz, 2H, â-H),
8.41 (d, J ) 3.6 Hz, 2H, â-H), 8.40 (d, J ) 3.6 Hz, 2H, â-H), 8.07
(d, J ) 4.5 Hz, 2H, â-H), 7.74-7.23 (m, 16H, Ph), 6.56 (br, 4H,
Ph), 3.44 (d, J ) 1.2 Hz, 2H, outer R-H), -4.17 (d, J ) 1.2 Hz,
2H, inner CH). UV/vis (CH2Cl2; λmax, nm (10-4ꢀ)): 313 (9.31),
459 (18.3), 687 (3.69), 741 (5.86). VPO: 1101 ( 88 g/mol (calcd
1146 g/mol).
X-ray Crystallography. The crystal data for 7 and 8 are listed
in detail in Table 1. Single crystals of 7 and 8 were obtained by
vapor diffusion of hexane into a CH2ClCH2Cl solution of 7 and a
CH2Cl2 solution of 8, respectively. All measurements were made
on a Rigaku Raxis Rapid imaging plate area detector with graphite-
monochromated Mo KR radiation. The structures were solved by
direct methods19 for 7 and heavy-atom Patterson methods20 for 8
and expanded using Fourier techniques.21 Some non-hydrogen atoms
were refined anisotropically, while the rest were refined isotropi-
cally. Hydrogen atoms were refined using the standard riding
model.22
Hg(II) Dimer Complex of 2-Aza-5,20-diphenyl-21-carbapor-
phyrin (9). NCDPP (1) was treated with 1 equiv of Hg(OAc)2 in
refluxing CH2Cl2 for 1.5 days. After a workup identical with that
described in 8, the residue was recrystallized from CH2Cl2/hexane
several time to afford the brown product, which was contaminated
at least by 1. 1H NMR (300 MHz, 25 °C, CDCl3, ppm): δ 8.58 (d,
J ) 4.5 Hz, 2H, â-H), 8.56 (s, 2H, meso-H), 8.48 (d, J ) 4.5 Hz,
2H, â-H), 8.42 (s, 2H, meso-H), 8.27-8.24 (m, 6H, â-H), 7.97 (d,
J ) 4.5 Hz, 2H, â-H), 7.72-7.21 (m, 12H, Ph), 6.84-6.35 (br,
8H, Ph), 3.60 (d, J ) 1.2 Hz, 2H, outer R-H), -3.27 (d, J ) 1.2
Hz, 2H, inner CH).
Determination of the Equilibrium Constant K. K values were
evaluated as [heterodimer]2/{[homodimer 1][homodimer 2]} for the
mixture system of homodimer 1 and homodimer 2. If one takes
into account the dimension of the constant, it can be substituted by
Ihetero2/(Ihomo1 homo2
), where I is the integral value for a paticular
I
signal. In this study, we employed the signals of the inner CH proton
of the confused pyrrole ring because they appear far apart enough
1
to be distinguished from each other in the H NMR spectra.
Zn(II) Dimer Complex of 2-Aza-5,20-diphenyl-21-carbapor-
phyrin (7). NCDPP (1) was treated with 2 equiv of Zn(OAc)2‚
2H2O in CH2Cl2. After 2 h, the reaction mixture was washed with
In both 8 and 9, all the signals except those of the phenyl groups
are coupled with Cd(II) and Hg(II). To avoid the complication, the
data of heteroatom couplings are not shown here (see Supporting
Information Figures S2 and S3).
(18) Geier, G. R., III; Haynes, D. M.; Lindsey, J. S. Org. Lett. 1999, 1,
1455-1458.
(19) SIR97: Altomare, A.; Burla, M.; Camalli, M.; Cascarano, G.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115-119.
(20) PATTY: Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman,
W. P.; Garcia-Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla,
C. The DIRDIF program system; Technical Report of the Crystal-
lography Laboratory, University of Nijmegen: Nijmegen, The Neth-
erlands, 1992.
(21) DIRDIF99: Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman,
W. P.; de Gelder, R.; Israel, R.; Smits, J. M. M. The DIRDIF-99
program system; Technical Report of the Crystallography Laboratory,
University of Nijmegen: Nijmegen, The Netherlands, 1999.
(22) CRYSTALS: Watkin, D. J.; Prout, C. K.; Carruthers, J. R.; Betteridge,
P. W. CRYSTALS. Issue 10; Chemical Crystallography Laboratory:
Oxford, England, 2000.
Supporting Information Available: Crystallographic data
(CIF) and ORTEP drawings for 7 and 8, 1H NMR spectra of 7-9,
1
a van’t Hoff plot for the exchange reaction of 7 and 8, H NMR
spectra of mixture solutions of 7/8, 8/9, 9/7, and 10/7, an NOE
difference 1H NMR spectrum of mixture solutions of 7 and 8, and
1
an H NMR spectrum of mixture solutions of 8-11 with spectra
of (Zn-1)(Cd-1) and (Zn-2)(Cd-2). This material is available
free of charge via the Internet at http://pubs.acs.org.
IC035294E
1624 Inorganic Chemistry, Vol. 43, No. 5, 2004