Organometallic chemistry of carbaporphyrinoids: Synthesis and characterization of nickel(II) and palladium(II) azuliporphyrins

Article abstract of DOI:10.1039/b200131b

Brief treatment of azuliporphyrins 5 with nickel(II) or palladium(II) acetate in refluxing DMF afforded excellent yields of the related chelates; these novel organometallic compounds retain cross-conjugated borderline aromatic structures as judged by UV-V

Full text of DOI:10.1039/b200131b

Organometallic chemistry of carbaporphyrinoids: synthesis and
characterization of nickel(II) and palladium(II) azuliporphyrins†
Shelley R. Graham, Gregory M. Ferrence and Timothy D. Lash*
Department of Chemistry, Illinois State University, Normal, Illinois 61790-4160, USA.
E-mail: tdlash@ilstu.edu; Fax: +1-(309) 438-5538; Tel: +1-(309) 438-8554
Received (in Corvallis, OR, USA) 27th December 2001, Accepted 12th March 2002
First published as an Advance Article on the web 25th March 2002
Brief treatment of azuliporphyrins 5 with nickel(II) or
palladium(II) acetate in refluxing DMF afforded excellent
yields of the related chelates; these novel organometallic
compounds retain cross-conjugated borderline aromatic
structures as judged by UV-Vis and NMR spectroscopy, and
X-ray crystallography.
N-confused porphyrins (NCPs; 1), a group of porphyrin isomers
that have an inverted pyrrole subunit, were first reported in
1994.1,2 NCPs were shown to form nickel(II) complexes1,3,4
with a direct carbon–metal bond by simply heating the system
with nickel(II) acetate, and organometallic derivatives of
copper(II), palladium(II), nickel(III) and silver(III) were subse-
quently noted.5 Soon after the initial discovery of N-confused
porphyrins, a series of carbaporphyrinoids with carbocyclic
rings in place of one of the usual pyrrole rings were reported,6–8
including oxybenziporphyrin (2),6 carbaporphyrins (e.g. 3),9
tropiporphyrin (4)10 and azuliporphyrins 5.11 However, while
these systems share the same inner core as 1, with three internal
nitrogen atoms and one carbon atom, initial attempts to generate
organometallic complexes from carbaporphyrins 3 were un-
successful.12 NCP’s have three internal hydrogens, but when
M(II) complexes are generated two protons are displaced while
the third is relocated to the external nitrogen atom.1,3 This is not
an option for carbaporphyrins 3 and this may well be a factor in
limiting the coordination chemistry of this system.13,14 On the
other hand, azuliporphyrin only has two hydrogen atoms within
the macrocyclic cavity and therefore holds greater promise in
the generation of novel organometallic derivatives. We now
report the first metallo-derivatives of the azuliporphyrins.
Azuliporphyrins 5a and 5b were treated with nickel(II
)
acetate in DMF at 80–90 °C for 10 min. Following chromatog-
raphy on silica eluting with chloroform and recrystallization
from chloroform–hexanes the nickel(II) complexes 6 were
isolated in 64–73% yield. The UV-Vis spectra for the metal
chelates were not particularly porphyrin-like, showing moder-
ate bands for 6a at 385, 454 and 546 nm while 6b gave slightly
red shifted absorptions at 392, 457 and 558 nm (Fig. 1A). The
proton NMR spectra for these diamagnetic complexes were also
consistent with cross-conjugated species that retain a degree of
aromatic character.‡ In the case of 6a, for instance, the meso-
protons resonated at 8.51 and 9.13 ppm, considerably upfield of
the values expected for fully aromatic porphyrinoids although
the data are consistent with some contributions from dipolar
canonical forms such as 7. The plane of symmetry present in
these chelates was confirmed by carbon-13 NMR spectroscopy,
and the identity of 6a and 6b were further demonstrated by high
resolution EI MS. In the case of the diphenyl derivative 6b, dark
green single crystal rods were grown by diffusion of hexanes
into a CH2Cl2 solution, and the molecular structure confirmed
by X-ray crystallographic analysis (Fig. 2).§ The nickel(II) atom
is essentially situated over the center of the macrocyclic cavity
and draws the macrocycle into a bowl (Fig. 2b) with the nickel
atom slightly above the C(21), N(22), N(23), N(24) plane. The
Fig. 1 A. UV-Vis spectra of nickel(II) chelates 6a and 6b in chloroform. The
trace due to 6a is indicated with arrows. B. UV-Vis spectra of palladium(II
chelates 8a and 8b in chloroform. In this case, the trace due to 8b is
† Part 20 of the series ‘Conjugated Macrocycles Related to the Porphyrins’.
Part 19: S. R. Graham, D. A. Colby and T. D. Lash, Angew. Chem., 2002,
in press.
)
indicated with arrows.
894
CHEM. COMMUN., 2002, 894–895
This journal is © The Royal Society of Chemistry 2002

metal is centered between the donor ligands with equivalent
trans-N–N, 1.934(3) and 1.928(3) Å bond lengths, and a
slightly distended cis-Ni(1)–N(23) bond length of 1.964(2) Å.
The latter may be explained by the trans-effect of the more
Lewis basic alkenyl, C(21), donor. The shorter Ni(1)–C(21)
bond length of 1.897(3) Å is consistent with the smaller
covalent bonding radius of carbon compared to nitrogen.
As the nickel(II) complexes 6 were formed under very mild
conditions, the corresponding palladium chelates 8 were
considered to be viable targets for synthesis. Indeed, reaction of
5a or 5b with palladium(II) acetate in DMF afforded 8a and 8b
in 72–93% yield. The UV-Vis spectra showed three moderate
bands in the Soret region (368, 412 and 447 nm for 8a and
slightly red shifted values for the diphenyl chelate 8b) together
with a broad band near 580 nm Fig. 1B). The system shows
slightly downfield shifted meso-resonances compared to the
nickel(II) chelates (Dd ≈ 0.15 ppm) suggesting that the
palladium chelates possess a larger diatropic ring current than
the corresponding nickel derivatives.‡ In porphyrins, the methyl
substituents commonly resonate near 3.6 ppm. In 6b, the methyl
unit appears at 3.09 ppm while the related palladium complex
8b gave a value of 3.18 ppm. Again, these values suggest that
the diatropic ring current for the palladium chelates 8 is
significantly greater than in the nickel(II) derivatives 6, although
neither series of azuliporphyrin chelates show shifts that are
comparable to fully aromatic porphyrinoid systems. The
structures of the palladium complexes were confirmed by
carbon-13 NMR spectroscopy and high resolution EI MS. At
this time, it has not proven possible to obtain X-ray crystallo-
graphic data for 8a or 8b. Reaction of azuliporphyrins 5 with
copper(II) acetate has been shown to afford stable derivatives
but these paramagnetic derivatives have not yet been fully
characterized.
The preliminary results demonstrate that the CNNN cavity of
azuliporphyrins is well suited for the synthesis of novel
organometallic derivatives and this system will provide a
valuable platform for coordination chemistry.
This work was supported by the National Science Foundation
under Grant Nos. CHE-9732054 and CHE-0134472, and the
Donors of the Petroleum Research Fund, administered by the
American Chemical Society. The authors thank Dr R. McDo-
nald and the University of Alberta X-ray Crystallography
Laboratory for the collection of low-temperature, CCD X-ray
data.
Notes and references
‡ Selected spectroscopic data: 6b: mp > 300 °C; UV-Vis (CHCl3): lmax
(log10e) 392 (4.72), 457 (4.52), 558 (4.32), 641 nm (4.10); 1H NMR (d5-
pyridine): d 1.51 (6H, t, J = 7.6 Hz), 3.09 (6H, s), 3.33 (4H, q, J = 7.6 Hz),
7.45–7.61 (9H, m), 7.76 (4H, d), 9.10 (2H, s), 9.23 (2H, d), 9.63 (2H, s); 13
C
NMR (d5-pyridine): d 10.9, 16.6, 19.4, 99.5, 108.0, 127.9, 128.9, 129.6,
131.7, 132.1, 135.8, 136.5, 138.3, 138.9, 142.1, 143.3, 146.1, 147.4, 151.3,
153.9, 155.5; HRMS: calcd for C44H35N3Ni: m/z 663.2184. Found:
663.2182. Anal. Calcd. for C44H35N3Ni: C, 79.53; H, 5.31; N, 6.32. Found:
C, 79.09; H, 5.17; N, 6.41%. 8b: mp > 300 °C; UV-Vis (CHCl3): lmax
1
(log10e) 380 (4.82), 415 (4.78), 450 (4.69), 580 (4.15), 638 nm (3.92); H
NMR (d5-pyridine): d 1.58 (6H, t), 3.18 (6H, s), 3.42 (4H, q), 7.45–7.58
(9H, m), 7.66 (2H, t), 8.03 (2H, d), 9.25 (2H, s), 9.80 (2H, s); 13C NMR (d5-
pyridine): d 10.9, 16.6, 19.5, 100.2, 110.2, 126.4, 127.9, 129.0, 132.2, 132.6,
137.2, 137.5, 139.3, 141.3, 142.8, 143.7, 143.8, 146.0, 148.8, 149.2, 155.5;
HRMS: calcd for C44H35N3Pd: m/z 711.1866. Found: 711.1882. Anal.
Calcd. for C44H35N3Pd: C, 73.89; H, 4.93; N, 5.87. Found: C, 73.28; H,
4.70; N, 5.72%.
§ Crystal data for 6b: C44H35N3Ni, M = 664.5, monoclinic space group
P21/n (no. 14), Dc = 1.378 g cm23, Z = 4, a = 31.028(2), b = 8.8409(6),
c = 11.7434(8) Å, b = 96.166(2)°, V = 3202.8(4) Å3, T = 193 K, m =
(Mo-Ka) = 0.644 mm21, 14860 reflections measured, 6534 unique, final
2
R1 = 0.052, wR2(F2) = 0.116 for 433 parameters and 4718 data with Fo
>
2s(Fo2). CCDC 179074. See http://www.rsc.org/suppdata/cc/b2/
b200131b/ for crystallographic files in .cif or other electronic format.
1 P. J. Chmielewski, L. Latos-Grazynski, K. Rachlewicz and T. Glowiak,
Angew. Chem., Int. Ed. Engl., 1994, 33, 779.
2 H. Furuta, T. Asano and T. Ogawa, J. Am. Chem. Soc., 1994, 116,
767.
3 L. L. Latos-Grazynski, in The Porphyrin Handbook, Vol. 2, ed. K. M.
Kadish, K. M. Smith and R. Guilard, Academic Press, San Diego, 2000,
pp. 361–416.
4 P. J. Chmielewski and L. Latos-Grazynski, J. Chem. Soc., Perkin Trans.
2, 1995, 503; P. J. Chmielewski, L. Latos-Grazynski and T. Glowiak, J.
Am. Chem. Soc., 1996, 118, 5690; T. D. Lash, D. T. Richter and C. M.
Shiner, J. Org. Chem., 1999, 64, 7973.
5 (a) P. J. Chmielewski and L. Latos-Grazynski, Inorg. Chem., 1997, 36,
840; (b) H. Furuta, T. Ogawa, Y. Uwatoko and K. Araki, Inorg. Chem.,
1999, 38, 2676; (c) P. J. Chmielewski, L. Latos-Grazynski and I.
Schmidt, Inorg. Chem., 2000, 39, 3475; (d) H. Furuta, N. Kubo, H.
Maeda, T. Ishizuka, A. Osuka, H. Nanami and T. Ogawa, Inorg. Chem.,
2000, 39, 5424.
6 T. D. Lash, Angew. Chem., Int. Ed. Engl., 1995, 34, 2533; T. D. Lash,
S. T. Chaney and . Richter, J. Org. Chem., 1998, 63, 9076; D. T. Richter
and T. D. Lash, Tetrahedron, 2001, 57, 3659.
7 T. D. Lash, Synlett, 2000, 279.
8 T. D. Lash, in The Porphyrin Handbook, Vol. 2, ed. K. M. Kadish, K.
M. Smith and R. Guilard, Academic Press, San Diego, 2000, pp
125–199.
9 T. D. Lash and M. J. Hayes, Angew. Chem., Int. Ed. Engl., 1997, 36,
840.
10 T. D. Lash and S. T. Chaney, Tetrahedron Lett., 1996, 37, 8825.
11 T. D. Lash and S. T. Chaney, Angew. Chem., Int. Ed. Engl., 1997, 36,
839.
12 M. J. Hayes, J. D. Spence and T. D. Lash, Chem. Commun., 1998,
2409.
Fig. 2 (a) Arial view ORTEP drawing (50% probability level) of 6b, with
hydrogen atoms arbitrarily drawn small. Selected bond lengths (Å) and
angles (°): Ni(1)–C(21) 1.897(3), Ni(1)–N(22) 1.934(3), Ni(1)–N(23)
1.964(2), Ni(1)–N(24) 1.928(3), C(1)–C(21) 1.417(5), C(4)–C(21)
1.426(5); C(1)–C(21)–C(4) 105.3(3), C(1)–C(21)–Ni(1) 127.5(2), C(4)–
C(21)–Ni(1) 127.2(2), C(21)–Ni(1)–N(23) 177.2(1), C(21)–Ni(1)–N(24)
89.8(2), N(22)–Ni(1)–N(24) 176.2(2), N(22)–Ni(1)–C(21) 90.4(2). (b)
Edge view ORTEP drawing of 6b.
13 However the first examples of organometallic derivatives of benzi- and
oxybenziporphyrins have recently been reported: (a) M. Stepian, L.
Latos-Grazynski, T. D. Lash and L. Szterenberg, Inorg. Chem., 2001,
40, 6892; (b) M. Stepien and L. Latos-Grazynski, Chem. Eur. J., 2001,
7, 5113.
14 Recently, carbaporphyrins 3 have been shown to react with silver(I)
acetate to afford the related silver(III) chelates: M. A. Muckey, L. F.
Szczepura, G. M. Ferrence and T. D. Lash, unpublished work.
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