The first bis-Rh(I) metal complex of N-confused porphyrin

Article abstract of DOI:10.1039/b104004a

An inner- and outer-N coordinated bis-Rh(I) metal complex was obtained from the reaction of N-confused porphyrin and [Rh(CO)₂C1]₂ and the structure was confirmed by a single crystal X-ray analysis.

Full text of DOI:10.1039/b104004a

The first bis-Rh( ) metal complex of N-confused porphyrin†
I
Alagar Srinivasan,a Hiroyuki Furuta*ab and Atsuhiro Osuka*a
a Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
E-mail: hfuruta@kuchem.kyoto-u.ac.jp; osuka@kuchem.kyoto-u.ac.jp
b PRESTO, Japan Science and Technology Corporation (JST), Japan
Received (in Cambridge, UK) 4th May 2001, Accepted 20th July 2001
First published as an Advance Article on the web 15th August 2001
An inner- and outer-N coordinated bis-Rh( ) metal complex
I
was obtained from the reaction of N-confused porphyrin and
[Rh(CO)2Cl]2 in CH2Cl2 and the structure was confirmed by
a single crystal X-ray analysis.
N-Confused porphyrin (NCP) is a porphyrin isomer in which
one of the pyrrole rings is confused or inverted.1,2 Because of
the unique NCP structure, which has peripheral nitrogen and
inner core carbon atoms, entirely different coordination chem-
istry from the parent porphyrin system has been expected and
revealed gradually.3–5 Recently, we reported a new type of
double-decker Pd NCP dimer complex that used both the inner-
and outer-N coordination sites with the help of a carbon–metal
bond from an ortho-position of a meso-aryl ring (A).6 At that
Scheme 1 Syntheses of bis-Rh(I) metal complexes.
the cavity. Relative to NCTPP (1), there is significant shielding
of the inner a-CH and the outer b-CH signals (Dd = 1.28 and
0.11 ppm) suggesting that the peripheral nitrogen also partici-
pates in the metal coordination. In contrast, the absence of NH
signals for complex 4 inferrs that all four nitrogens are involved
in the metal coordination.
point, it was really a question whether outer-N coordination was
general and whether the complex formed could be stabilized
without any assistance from the surroundings (B). Such
coordination, if manipulated easily, would be of particular
interest for potential use in metal catalysts.7 Herein, we report
the X-ray structure of a bis-Rh(
I
) NCP complex where the Rh( )
I
The absorption spectrum of 2 in CH2Cl2 displays a Soret-like
band at 488 nm and four Q-type bands in the region of 545–780
nm (Fig. 1). In general, the metal complexation is accompanied
by a red-shift of both the Soret and Q-type bands.9 The bis-
metallic complex of 2 also shows 50 nm and 44 nm red-shifts of
the Soret and the Q-type bands, respectively, as compared to 1.
This proves that the peripheral nitrogen coordination should not
perturb the p electron delocalization much, while the Rh
coordinated inside the cavity is expected to perturb the
metal atoms are coordinated to the inner- and the outer-nitrogen
atoms. For comparison, the X-ray structure of the bis-Rh( )
I
tetraphenylporphyrin (TPP) complex is also presented.8 To the
best of our knowledge, the structures are the first examples of
bis-Rh( ) complexes of meso-phenylporphyrin and NCP.
I
When N-confused tetraphenylporphyrin (NCTPP, 1) was
treated with 1 equiv. of [Rh(CO)2Cl]2 in the presence of 10
equiv. of sodium acetate in refluxing CH2Cl2 for 2 h, bis-Rh(
NCTPP complex 2 was obtained as a blue-greenish solid in 53%
yield. Using the same procedure with TPP (3), bis-Rh( ) TPP
I)
I
complex 4 was obtained as a purple solid in 36% yield (Scheme
1). FAB mass spectra of 2 and 4 showed molecular ion peaks at
m/z 967.5 and 930.6, respectively, indicating the presence of
two Rh metal ions connected with a chloride and four carbonyl
ligands in 2 and the absence of the chloride ligand in 4. 1H NMR
spectral peaks of complex 2 in CDCl3 appeared distinctly in the
region from 24 ppm to 9 ppm. The appearance of peaks
corresponding to inner b-CH, outer a-CH and an inner NH at
23.83, 8.89 and 1.06 ppm, respectively, proved that they do not
participate in the metal coordination and further confirms that
only two pyrrolic nitrogens are coordinated to the Rh metal in
† Electronic supplementary information (ESI) available: synthetic proce-
dures and X-ray structure information for 2 and 4. See http://www.rsc.org/
suppdata/cc/b1/b104004a/
Fig. 1 Electronic absorption spectra of 2 and 4 in CH2Cl2.
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Chem. Commun., 2001, 1666–1667
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b104004a

Fig. 2 X-Ray structures of (a) 2 and (b) 4. The meso-aryl rings are omitted for clarity in the side views (bottom). Selected bond lengths (Å) for 2: Cl1–Rh1,
2.349(3); Rh1–N1, 2.104(6); Rh2–N3, 2.099(6); Rh2–N4, 2.0877(6); and for 4: Rh1–N1, 2.067(6), Rh1–N2, 2.074(6).
delocalization pathway, and this is reflected in the larger optical
absorption band shifts. This trend is further confirmed by the
absorption spectrum of 4 where both the Rh are coordinated
inside the cavity leading to strong distortion of the molecule and
resulting in bands at 371, 460 and 704 nm (Fig. 1).
at the peripheral nitrogen. Studies on the synthesis of such
hetero bis-metal NCP complexes are currently underway.
Notes and references
1 H. Furuta, T. Asano and T. Ogawa, J. Am. Chem. Soc., 1994, 116,
767.
2 P. J. Chmielewski, L. Latos-Graz˙yn´ski, K. Rachlewicz and T. Glowiak,
Angew. Chem., Int. Ed. Engl., 1994, 33, 779.
3 L. Latos-Graz˙yn´ski, in The Porphyrin Handbook, ed. K. M. Kadish,
K. M. Smith and R. Guilard, Academic Press, San Diego, 1999, vol. 2,
ch. 14.
4 P. J. Chmielewski, L. Latos-Graz˙yn´ski and T. Glowiak, J. Am. Chem.
Soc., 1996, 118, 5690; P. J. Chmielewski, L. Latos-Graz˙yn´ski and I.
Schmidt, Inorg. Chem., 2000, 39, 5475; P. J. Chmielewski and L. Latos-
Graz˙yn´ski, Inorg. Chem., 2000, 39, 5639.
5 H. Furuta, T. Ogawa, Y. Uwatoko and K. Araki, Inorg. Chem., 1999, 38,
2676; T. Ogawa, H. Furuta, M. Takahashi, A. Morino and H. Uno,
J. Organomet. Chem., 2000, 611, 551; H. Furuta, H. Maeda and A.
Osuka, J. Am. Chem. Soc., 2000, 122, 803.
6 H. Furuta, N. Kubo, H. Maeda, T. Ishizuka, A. Osuka, H. Nanami and
T. Ogawa, Inorg. Chem., 2000, 39, 5424.
7 J. Tsuji, Palladium Reagents and Catalysts, Wiley, Chichester, 1995,
p. 87.
The explicit structural details of the bis-Rh( ) complexes 2
I
and 4 were derived from the single crystal X-ray diffraction
analyses (Fig. 2).10 As predicted from the above observations,
in the bis-metallic complex of 2, there are two Rh atoms
attached in the NCP skeleton. One imino (N3) and one amino
(N4) nitrogen of the macrocycle are coordinated to the Rh2 ion
and the other two coordination sites are occupied by the
carbonyl ligands. The other Rh1 ion is coordinated to the
periphery nitrogen (N1) and the remaining coordination sites
are occupied by a chloride and the two carbonyl ligands. Both
the Rh( ) ions are located above the NCP plane and the
I
geometry around the metal centers is close to square planar
(Cl1–Rh1–N1, 87.6(2)°; N3–Rh2–N4, 85.7(2)°). The angles
between the planes containing the Rh1 and the Rh2 with their
coordinated atoms and the mean NCP plane are 117.29° and
61.30°, respectively, and the distance between the two Rh metal
centers is 6.286 Å.
8 The crystal structure of bis-Rh(I)OEP was reported. A. Takenaka, Y.
Sasada, T. Omura, H. Ogoshi and Z. Yoshida, J. Chem. Soc., Chem.
Commun., 1973, 792.
9 M. Gouterman, in The Porphyrins, ed. D. Dolphin, Academic Press,
New York, 1978, vol. 3, pp. 1–165.
10 Bis-Rh(I)NCP (2): green prism, C48.5H31N4Rh2O4.5Cl2, Mw 1018.52,
On the other hand, the metalloporphyrin of 4 is centrosym-
metric and the two Rh( ) metal ions are bonded to two
I
dipyrromethene units, one above and one below the macro-
cyclic plane. Like 2, the geometry around the metal centers is
close to square planar (N1–Rh1–N2, 84.9(2)°). The angle
between the plane containing the Rh(1) with its coordinated
atoms and the mean TPP plane is 131.59° and the distance
between the two metal centers is 3.166 Å, which is considerably
monoclinic, space group C2/c (#15), a = 18.0381(3), b = 31.4290(5),
c = 17.1686(3) Å, b = 111.3050(6)°, V = 9068.0(2) Å3, Z = 8, Dcalc.
= 1.492 g cm23, T = 23 °C. Final R = 0.039 (GOF = 0.49) for 7278
observed reflections with I > 3.00s(I), Rw = 0.072 for 10611 all unique
longer than the Rh(
I
)–Rh(
) single bond (2.617–2.705 Å).11
I
data. Bis-Rh(
monoclinic, space group C2/c (#15), a = 21.695(2), b = 11.1778(7), c
= 21.600(1) Å, b = 120.957(3)°, V = 4492.0(5) Å3, Z = 4, Dcalc.
I)TPP (4): brown prism, C49H30N4Rh2O4Cl2, Mw 1015.52,
These results are comparable with the bis-Rh(
I
) octaethylpor-
phyrin (OEP) complex.8
=
In conclusion, we have synthesized two new bis-Rh(
I) metal
1.501 g cm23, T = 23 °C. Final R = 0.046 (GOF = 1.91) for 3014
observed reflections with I > 3.00s(I), Rw = 0.0763 for 5415 all unique
data. CCDC reference numbers 164092 and 164093. See http://
www.rsc.org/suppdata/cc/b1/b104004a/ for crystallographic data in CIF
or other electronic format.
complexes and disclosed their solid state structures. Inner- and
outer-metallation is characteristic of NCP ligands, thus, for 2,
rich and diverse coordination chemistry similar to the parent
porphyrin (1) can be expected. The present study has also
exploited the interaction of only Rh(
I) metal ions, but other
11 O. S. Mills and E. F. Paulus, J. Organomet. Chem., 1967, 10, 331; O. S.
Mills and J. P. Nice, J. Organomet. Chem., 1967, 10, 337.
metal ions are likely to interact with the macrocycle, especially
Chem. Commun., 2001, 1666–1667
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