Zinc complex of N-confused calix[4]phyrin

Article abstract of DOI:10.1016/S1387-7003(02)00797-9

A zinc(II) complex of N-confused calix[4]phyrin (isoporphyrin) (2-Zn) has been synthesized and the structure was revealed by ¹H NMR and X-ray analyses. The atomic distance between zinc metal and the inner-core carbon was about 0.2 ? longer compared with that of zinc(II) N-confused porphyrin complexes, suggesting the weaker side-on η¹-coordination with the inner-core-carbon in 2-Zn.

Full text of DOI:10.1016/S1387-7003(02)00797-9

Inorganic Chemistry Communications 6 (2003) 398–401
www.elsevier.com/locate/inoche
Zinc complex of N-confused calix[4]phyrin
a,b,c,
a
a
Hiroyuki Furuta
*, Tomoya Ishizuka , Atsuhiro Osuka
a
Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
b
Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, Fukuoka 812-8581, Japan
c
PRESTO, Japan Science and Technology Corporation, Japan
Received 14 September 2002; accepted 28 October 2002
Abstract
A zinc(II) complex of N-confused calix[4]phyrin (isoporphyrin) (2-Zn) has been synthesized and the structure was revealed by 1H
ꢀ
NMR and X-ray analyses. The atomic distance between zinc metal and the inner-core carbon was about 0.2 A longer compared with
that of zinc(II) N-confused porphyrin complexes, suggesting the weaker side-on g1-coordination with the inner-core-carbon in 2-Zn.
Ó 2002 Elsevier Science B.V. All rights reserved.
Keywords: N-confused porphyrin; Isoporphyrin; Zinc complex; Organometallics; Side-on g1-coordination
1. Introduction
distance is longer than usual covalent bond and the in-
ner carbon bears a hydrogen in an sp2-fashion. Apart
from NCP, we have found N-confused calix[4]phyrin
(isoporphyrin) (NCiP, 2), a non-conjugated type of N-
confused porphyrinoids, could also form analogous or-
ganometallic complexes with Ni(II) and Cu(II) (2-Ni
and 2-Cu) [12]. Owing to the similarity of the preorga-
nized N3C-core, NCiP could be used as a model ligand
to examine the effect of p-conjugation for the interaction
between the central metal and inner-core-carbon.
Herein, we report the first X-ray structure of Zn(II)
NCiP complex (2-Zn) and discuss the environment of
side-on g1-coordination in comparison with that of NCP
Zn(II) complexes, 1-Zn.
In the past decade, N-confused porphyrin (NCP, 1), a
porphyrin isomer in which one of the pyrrolic rings is
linked with meso-carbons through a; b0-positions, has
widely attracted attention as a potential ligand for a
variety of organometals [1–9]. Up to the date, several
metals such as nickel(II) [2], copper(II) [5], silver(III) [6],
palladium(II) [7], and manganese(III) [8], have been
examined and the square-planar connection to the inner-
carbon of confused pyrrole ring and three pyrrolic ni-
trogens was established. Recently, we have found the
other type of metal coordination in the X-ray structures
of monomeric and dimeric zinc(II) NCP complexes. In
the complexes, the center Zn(II) metal can be considered
to be connected with the inner-carbon of confused pyr-
role in a side-on g1-coordination (or agostic interaction)
[10] besides pyrrolic nitrogens, as judged by the short
atomic distance between the carbon and Zn(II) metal
[11]. Such g1-coordination, if existed, seems to be im-
portant in the prior stage of metal-carbon bond for-
mation for NCP. The side-on g1-coordination, however,
is not so obvious compared with the metal-carbon
bonds of other NCP organometals because the bond
2. Results and discussion
An isopropanol coordinated Zn(II)-NCP complex
(1b-Zn) and the title complex (2-Zn) were synthesized
from NCP and NCiP with excess ZnðOAcÞ2 Á 2H2O in
CH2Cl2, followed by treatment with isopropanol and
aqueous NaCl, respectively, at room temperature
(Scheme 1). The optical absorption spectrum of 1b-Zn in
10% isopropanol–CH2Cl2 showed Soret-like transition
at 465 nm and four broad Q-like bands in the region
from 580 to 800 nm. On the other hand, 2-Zn in CH2Cl2
showed the split Soret-like band at 398 and 424 nm and
* Corresponding author. Tel.: +81-92-642-3548; fax: +81-92-651-
5606.
E-mail address: hfuruta@cstf.kyushu-u.ac.jp (H. Furuta).
1387-7003/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved.
doi:10.1016/S1387-7003(02)00797-9

H. Furuta et al. / Inorganic Chemistry Communications 6 (2003) 398–401
399
The explicit structures of 1b-Zn and 2-Zn were de-
rived from the single crystal X-ray analyses. In 1b-Zn,
the central Zn atom was pentacoordinated with three
pyrrolic nitrogens, inner-carbon of the confused pyrrole,
and an axial isopropanol oxygen. The confused pyrrole
ring bent at 28.9° to the mean plane consisting of core 24
ꢀ
atoms. The Zn(II) atom was located 0.45 A above the
plane and connected to the inner-CH carbon in a side-
1
ꢀ
on g -coordination with the distance of 2.40 A (Fig. 2).
On the other hand, the central Zn atom was coordinated
with three pyrrolic nitrogens, inner-carbon, and an axial
chloride in 2-Zn. The porphyrinoid core was distorted
due to the repulsion between Zn atom and the CH hy-
drogen in the core. In particular, the confused pyrrole
was largely tilted to the core plane with a dihedral angle
of 46.81°. The mean deviation of the least square plane
ꢀ
ꢀ
was 0.315 A and the Zn atom was 0.56 A above the
plane. In the crystals, 2-Zn, like 2-Cu and 2-Ni, existed
as dimer with hydrogen bondings between outer amide
group, where the atom distance between N(1) and O0(1)
Scheme 1.
ꢀ
of the neighboring amide was 2.85 A (Fig. 3).
For 2-Zn, the bond lengths of Zn(1)–N(2), Zn(1)–
ꢀ
N(3), and Zn(1)–N(4), 2.158(8), 1.992(9), 2.076(8) A,
respectively, were comparable to that of Zn(II)-tetra-
ꢀ
phenylporphyrin (TPP) (2.042(7) A) [13] and Zn(II)
ꢀ
NCP complexes (1a,b-Zn) (1.99–2.09 A). However, the
a relatively weak band around 800 nm (Fig. 1). Com-
pared with the free base form of 2, the broad band in the
long wavelength region in 2-Zn was about 200 nm red-
shifted.
1
The H NMR spectrum of 1b-Zn in 10% isopropa-
nol–CDCl3 showed the characteristic inner-CH signal of
confused pyrrole ring at )3.68 ppm, as observed with 1a-
Zn in CDCl3. On the other hand, reflecting the non-
conjugated property of 2, the inner-CH signal of 2-Zn
was observed at 9.14 ppm. The remaining outer amide-
NH and three sets of the pyrrolic b-hydrogens were
resonated at 7.49 ppm and around 6.0–6.8 ppm, re-
spectively. Interestingly, gem-dimethyl group that was a
singlet peak in 2 became diastereotopic in 2-Zn and was
observed as two distinct signals at 1.88 and 2.00 ppm.
ꢀ
atom distance between Zn(1) and C(2), 2.67(1) A, was
ꢀ
longer than that of 1a,b-Zn (2.40–2.49 A) (Table 1). For
1a-Zn complex, side-on g1-coordination was proposed
between Zn atom and the inner carbon of confused
pyrrole ring [11]. The longer atomic distance observed
Fig. 1. Optical absorption spectra of 1b-Zn, 2, and 2-Zn. (1b-Zn: in
10% iPrOH–CH2Cl2, 2, and 2-Zn: in CH2Cl2, absorbance: in arbitrary
scale)
Fig. 2. Molecular structure of 1b-Zn: (a) top view and (b) side view.
Thermal ellipsoids are drawn at the 50% probability level. meso-Phenyl
groups were omitted for clarity in (b).

400
H. Furuta et al. / Inorganic Chemistry Communications 6 (2003) 398–401
Chart 1.
Fig. 3. Molecular structure of 2-Zn: (a) top view and (b) side view.
Thermal ellipsoids are drawn at the 50% probability level. meso-Tolyl
groups were omitted for clarity in (b).
in the core, but the side-on g1-coordination of Zn(II)
metal to the inner carbon of NCiP was smaller than that
of NCP as judged by the longer atomic distance between
Zn and the carbon atoms (see Chart 1).
Table 1
The selective bond lengths (A) of 1b-Zn and 2-Zn in the crystal
structures
ꢀ
3. Experimental section
1b-Zn
2-Zn
Zn(1)–Cl(1)
Zn(1)–O(1)
Zn(1)–N(2)
Zn(1)–N(3)
Zn(1)–N(4)
Zn(1)Á Á ÁC(2)
–
2.240(3)
–
1b-Zn: Compound 1b-Zn was synthesized by recrys-
tallization of Zn(II) NCP dimer from CH2Cl2-isopro-
panol. When the crystal of 1b-Zn was dissolved in
CH2Cl2, the axial isopropanol molecule was removed
and the compound changed into self-coordinated Zn(II)
NCP dimer [11].
2.047(7)
2.081(8)
1.990(8)
2.085(8)
2.404(9)
2.158(8)
1.992(9)
2.076(8)
2.67(1)
for 2-Zn suggests the carbon–metal interaction is weaker
than that of 1a,b-Zn. The difference of the coordination
distance between 1a,b-Zn and 2-Zn is not simply as-
cribable to the p-conjugation circuit at this moment
because of the structural differences, such as outer amide
moiety or axial ligand species coordinating to the Zn
metal. The finding proved in this manuscript that NCiP
can complex Zn(II) metal as NCP does, however, is
important for the further study of side-on g1-coordina-
tion of N-confused porphyrinoids in general. The large
flexibility of the confused pyrrole ring due to the meso
sp3-carbon in NCiP may allow the systematic study on
the relationship between the electron density of center
Zn metal and the atomic distances between Zn and in-
ner-carbon. The synthesis of NCP Zn(II) complex
bearing amide moiety would also be important to dis-
cuss the side-on g1-coordination further.
2-Zn: To a CH2Cl2 (30 ml) solution of NCiP[12]
(14.42 mg, 0.023 mmol), ZnðOAcÞ2 Á 2H2O powder
(11.06 mg, 0.050 mmol) was added, and the mixture was
stirred at room temperature for 3 h. After washing with
1% NaCl(aq), dried over anhydrous Na2SO4, the solvent
was removed under reduced pressure. The residue was
recrystallized from CH2Cl2–hexane to give green crys-
tals of 2-Zn (12.2 mg, 0.017 mmol) in 74% yield. M.p.
270–280°C (dec); 1H NMR (CDCl3): d 1.88 (s, 3H), 2.00
(s, 3H), 2.38 (s, 3H), 2.41 (s, 3H), 6.05 (d, J ¼ 4:5 Hz,
1H), 6.22 (d, J ¼ 4:5 Hz, 1H), 6.27 (d, J ¼ 4:5 Hz, 1H),
6.66 (m, 2H), 6.77 (d, J ¼ 5:0 Hz, 1H), 7.23 (m, 12H),
7.49 (s, 1H), 9.14 (d, J ¼ 1:0 Hz, 1H). UV–Vis
(CH2Cl2): kmax [nm] ¼ 796.0, 424.0, 398.0. FAB-MS: m/
z ¼ 722.48 (calcd. for C43H35N4OZnCl [Mþ] 722.1791).
Anal. Calcd. for C43H35N4OZnCl: C, 71.27; H, 4.87; N,
7.73. Found: C, 70.47; H, 4.87; N, 7.49.
In conclusion, a zinc complex of N-confused ca-
lix[4]phyrin (isoporphyrin) (NCiP, 2) has been synthe-
sized and characterized by 1H NMR and X-ray
analyses. Similar to NCP, the Zn(II) metal was coordi-
nated with three pyrrolic nitrogens and an axial ligand
Diffraction data for 1b-Zn and 2-Zn complex were
collected on a Rigaku R-axis imaging plate system dif-
ꢀ
fractometer (123 K, Mo-Ka radiation (k ¼ 0:7107 A)).
The structures were solved by direct methods and re-
fined by F with observed reflections I > 3rðIÞ. Hydrogen

H. Furuta et al. / Inorganic Chemistry Communications 6 (2003) 398–401
401
atoms were calculated in ideal positions. The programs
used were structure determination by SIR97 and refined
by teXsan for Windows.
References
[1] H. Furuta, T. Asano, T. Ogawa, J. Am. Chem. Soc. 116 (1994)
767.
_ ꢁ
[2] P.J. Chmielewski, L. Latos-Grazynski, K. Rachlewicz, T. Głow-
iak, Angew. Chem., Int. Ed. Engl. 33 (1994) 779.
Supplementarymaterial
_ ꢁ
[3] L. Latos-Grazynski, in: Core Modified Heteroanalogues of
Porphyrins and Metalloporphyrins, The Porphyrin Handbook,
vol. 2, Academic Press, New York, 2000, p. 361.
[4] H. Furuta, H. Maeda, A. Osuka, Chem. Commun. (2002) 1795.
Table of crystal and refinement data, bond lengths
and angles, atomic coordinates and thermal parameters
for 1b-Zn and 2-Zn are available from the author on
request as well as CCDC (No. 191989 and 189819).
1. Crystal data for 1b-Zn: C47H36N4OZn Á 3:5
C3H8O; FW ¼ 948:54, monoclinic, space group P21=n
_ ꢁ
[5] P.J. Chmielewski, L. Latos-Grazynski, I. Schmidt, Inorg. Chem.
39 (2000) 5475.
[6] H. Furuta, T. Ogawa, Y. Uwatoko, K. Araki, Inorg. Chem. 38
(1999) 2676.
[7] H. Furuta, N. Kubo, H. Maeda, T. Ishizuka, A. Osuka, H.
Nanami, T. Ogawa, Inorg. Chem. 39 (2000) 5424.
[8] D.S. Bohle, W.-C. Chen, C.-H. Hung, Inorg. Chem. 41 (2002)
3334.
ꢀ
ꢀ
(No. 14), Z ¼ 4; a ¼ 14:8688ð3Þ A, b ¼ 21:1462ð3Þ A,
ꢀ
ꢀ3
c ¼ 15:9935ð3Þ A, b ¼ 94:4348ð3Þ°; V ¼ 5013:6 ð2ÞA ;
qcalcd ¼ 1:257 g cmꢀ3; R ¼ 0:069; wR ¼ 0:132, GOF ¼
1.495.
[9] W.-C. Chen, C.-H. Hung, Inorg. Chem. 40 (2001) 5070.
[10] This type of metal–carbon interaction (side-on g1-coordination)
_ ꢁ
was initially proposed by Latos-Grazynski and co-workers to the
Ni(II) complex of dimethylated NCP (P.J. Chmielewski, Latos-
2. Crystal data for 2-Zn: C43H35N4OZnClÁ
C6H14; FW ¼ 789:62, orthorhombic, space group Pbca
_ ꢁ
Grazynski, T. Głowiak, J. Am. Chem. Soc. 118 (1996) 5690). To
date, the similar carbon–metal interactions were reported in the
ꢀ
ꢀ
(No. 61), Z ¼ 8; a ¼ 18:8350ð3Þ A, b ¼ 15:3040ð3Þ A,
ꢀ
ꢀ3
c ¼ 26:2150ð5Þ A, V ¼ 7556:5ð2ÞA ; qcalcd ¼ 1:388 g
cmꢀ3; R ¼ 0:094; wR ¼ 0:123, GOF ¼ 2.526. The rela-
tively high R value was ascribable to the disordered
structure of a meso-phenyl ring in the crystal.
zinc(II), iron(II) and manganese(II) NCP complexes ([5,8,9,11]).
_ ꢁ
Very recently, Latos-Grazynski et al. has reported the interesting
‘‘side-on g2-coordination’’ between central cadmium(II) and the
ꢁ
two inner-carbons of p-benziporphyrin (M. Stepien, Latos-
z
_ ꢁ
Grazynski, J. Am. Chem. Soc. 124 (2002) 3838).
[11] H. Furuta, T. Ishizuka, A. Osuka, J. Am. Chem. Soc. 124 (2002)
5622.
Acknowledgements
[12] H. Furuta, T. Ishizuka, A. Osuka, Y. Uwatoko, Y. Ishikawa,
Angew. Chem. Int. Ed. 40 (2001) 2323.
T.I. thanks JSPS for a Research Fellowship for
Young Scientists.
[13] E.B. Fleisher, C.K. Miller, L.E. Webb, J. Am. Chem. Soc. 86
(1964) 2342.