Synthesis, characterization, and electrochemical studies of β,β′-fused metallocenoporphyrins

Article abstract of DOI:10.1021/ic062303l

β,β′-Fused monoruthenocenylporphyrins, Cp*Ru(III)[1, 2-[M(II)-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)-porphyrinato] -3-methyl-cyclopentadienide] (M = Ni (20), Cu (21), Zn (22)), and bisferrocenoporphyrins, Fe(II) bis[1,2-[M(II)-5,10,15,20- tetraphenylporphyrinato]-3-methyl-cyclopentadienide] (M = Ni (24), Cu (25), Zn (26)), were synthesized and characterized. A novel synthetic approach to β,β′-fused porphyrins through Pd(0)-catalyzed [3 + 2] cycloaddition was implemented in this work. UV-vis spectra of these compounds show largely broadened and red-shifted bands (relative to their precursors) indicating potential electronic communication between the attached organometallic moiety and the porphyrin core. The electrochemistry of these molecules suggests significant electronic interactions between the metallocene and metalloporphyrin in molecules 20 and 24. The crystal structure of the bisferrocenoporphyrin 26, Fe(II) bis[1,2-[Zn(II)-5,10,15,20- tetraphenylporphyrinato]-3-methyl-cyclopentadienide], was determined: {Cp ₂Fe[ZnTPP(THF)]₂}{Cp₂Fe[ZnTPP(THF)ZnTPP(MeOH)]} ·3MeOH-6THF, M = 3804.35, monoclinic, space group P2₁/c, a = 33.327(5) A, b = 19.145(3) A, c = 29.603(5) A, β = 106.309(2)°, V = 18128(5) A³, Z = 4. In this molecule, one porphyrin ring is rotated by about 72° with respect to the other in the 5-fold axis of the Cp ring.

Full text of DOI:10.1021/ic062303l

Inorg. Chem. 2007, 46, 2898−2913
Synthesis, Characterization, and Electrochemical Studies of
Metallocenoporphyrins
â,â′-Fused
Hong J. H. Wang,† Laurent Jaquinod,† Marilyn M. Olmstead,† M. Grac
¸
a H. Vicente,†,‡ Karl M. Kadish,§
Zhongping Ou,§ and Kevin M. Smith*,†,‡
Department of Chemistry, UniVersity of California, DaVis, California 95616,
Department of Chemistry, Louisiana State UniVersity, Baton Rouge, Louisiana 70803, and
Department of Chemistry, UniVersity of Houston, Houston, Texas 77204-5003
Received December 3, 2006
â
,
â′-Fused monoruthenocenylporphyrins, Cp*Ru(III)[1,2-[M(II)-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)-porphyrinato]-
3-methyl-cyclopentadienide] (M Ni (20), Cu (21), Zn (22)), and bisferrocenoporphyrins, Fe(II) bis[1,2-[M(II)-
5,10,15,20-tetraphenylporphyrinato]-3-methyl-cyclopentadienide] (M Ni (24), Cu (25), Zn (26)), were synthesized
and characterized. A novel synthetic approach to â′-fused porphyrins through Pd(0)-catalyzed [3 2] cycloaddition
was implemented in this work. UV vis spectra of these compounds show largely broadened and red-shifted bands
)
)
â,
+
−
(relative to their precursors) indicating potential electronic communication between the attached organometallic
moiety and the porphyrin core. The electrochemistry of these molecules suggests significant electronic inter-
actions between the metallocene and metalloporphyrin in molecules 20 and 24. The crystal structure of the
bisferrocenoporphyrin 26, Fe(II) bis[1,2-[Zn(II)-5,10,15,20-tetraphenylporphyrinato]-3-methyl-cyclopentadienide], was
determined:
space group P21/c, a
4. In this molecule, one porphyrin ring is rotated by about 72o with respect to the other in the 5-fold axis of the
Cp ring.
{
Cp2Fe[ZnTPP(THF)]2}{Cp2Fe[ZnTPP(THF)ZnTPP(MeOH)]}‚3MeOH
‚
6THF, M
)
3804.35, monoclinic,
)
)
33.327(5) Å, b 19.145(3) Å, c 29.603(5) Å, â ) 106.309(2)
)
)
°
, V
18128(5) Å3, Z
)
Introduction
transfers.11-13 Most of these applications hinge more or less
on the effective interaction between the two fragments within
one molecule. It is suggested that the communication between
the two moieties depends on the type of spacer, relative
spatial orientation, and distance between them. Numerous
porphyrin systems appended with redox groups, such as
ferrocene, have been prepared,13-19 but effective communica-
Molecular systems containing both porphyrin and metal-
locene fragments have been attracting significant attention
over the past two decades as they show great potential
in solar energy conversion,1-6 small molecule activation,7
molecular devices,8-10 and porphyrin-assisted electron
* To whom correspondence should be addressed. E-mail: kmsmith@
lsu.edu.
(9) Thornton, N. B.; Wojtowicz, H.; Netzel, T.; Zixon, D. W. J. Phys.
Chem. B 1998, 102, 2101.
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Gordon, K. C.; Jameson, G. B.; Officer, D. L.; Zhao, Z. Chem.
Commun. 1999, 637.
(11) Kondo, T.; Kanai, T.; Iso-o, K; Uosaki, K. Z. Phys. Chem. 1999, 212,
S. 23.
† University of California, Davis.
‡ Louisiana State University.
§ University of Houston.
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Y.; Ito, O.; Zhu, D. Tetrahedron 2006, 4285.
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2898 Inorganic Chemistry, Vol. 46, No. 7, 2007
10.1021/ic062303l CCC: $37.00
© 2007 American Chemical Society
Published on Web 02/27/2007

â,â′-Fused Metallocenoporphyrins
tion between them has been rarely observed. Recently,
Burrell and co-workers20 have reported the synthesis and
studies of a series of functionalized porphyrins in which a
porphyrin and an aryl group are connected with a conjugated
link. Their investigation indicated that in certain cases
communication between the functionality on the aryl group
and the porphyrin core was apparent. Encouraged by the
positive results, they prepared ferrocene-functionalized por-
phyrins21 connecting in a similar fashion; unfortunately, their
compounds failed to give evidence of strong interaction
between the moieties. In a publication by Boyd and co-
workers,10 strong electronic metal-metal coupling between
two remote ferrocenyl centers spaced by a porphyrin core
was observed and supported by DFT calculations. Even
though the precise factors leading to the strong coupling
remained obscure, they suggested that the crowded substit-
uents at porphyrin â-positions inhibit the rotation of the bulky
meso-ferrocenyl moieties in such a way that extensive mixing
of the molecular orbitals of the two systems results.
In most of the reported porphyrin-ferrocene systems,
porphyrin and ferrocene are connected through various
spacers at the porphyrin â- or meso-positions of the mac-
rocycle. Direct connection through C-C single bond has only
been reported for the meso-positions.10,22-25 One can easily
see that molecular orbitals of the two fragments in these
molecules are not likely to overlap because of unfavorable
alignment of the moieties within the molecule, arising partly
from the bulkiness of the ferrocenyl group. We believe that
to observe useful properties it is essential to design metal-
locene-appended porphyrin molecules with effective mixing
of π-orbitals of the two systems. We decided to synthesize
a series of metallocene-porphyrin conjugates, including
monometallocenylporphyrins and bisporphyrinyl-metal-
locenes, in which the porphyrin and the metallocene frag-
ments are directly fused to the porphyrin chromophore
through â-positions. We assume that by “fusing” them in
this way, the π-systems of each are “forced” to overlap and
will thus enhance the interactions between them. One can
envision that novel photo- and electrochemical properties will
result from the fused molecules.
synthesis and crystal structure of a fused monoruthenoce-
nylporphyrin (Cp*Ru(III)[1,2-[Ni(II)-5,10,15,20-tetrakis(3,5-
di-tert-butylphenyl)-porphyrinato]-3-methyl-cyclopentadien-
ide) (Cp* ) pentamethylcyclopentadienide) and a bisporphyrin
([Ni(II)-2,3-(â-methyl)propeno-5,10,15,20-tetrakis(3,5-di-
tert-butylphenyl)-porphyrin]2) as a byproduct. In the present
paper, the synthesis of a series of monoruthenocenylpor-
phyrins and bisporphyrinylferrocenes is detailed, the novel
Pd(0)-catalyzed [3 + 2] cycloaddition reaction with activated
porphyrins is investigated, and a new crystal structure of a
bisporphyrinylferrocene (26) is reported. Electrochemical
studies of these compounds indicate significant electronic
communications within some of the molecules.
Experimental Section
Melting points (mp) were measured on a Thomas/Bristoline
1
microscopic hot stage apparatus and were uncorrected. H NMR
spectra were obtained in deuterochloroform solution at 300 or 400
MHz using a Mercury 300 or Inova 400 spectrometer; chemical
shifts are expressed in ppm relative to chloroform (7.26 ppm).
Elemental analyses were performed at Midwest Microlabs., Inc.,
Indianapolis, IN. Electronic absorption spectra were measured using
a Hitachi U-2000 spectrophotometer. Mass spectra (MALDI-TOF)
were obtained at the Facility for Advanced Instrumentation,
University of California, Davis.
Cyclic voltammetry was carried out using an EG&G Princeton
Applied Research (PAR) 173 or 273 potentiostat/galvanostat. A
homemade three-electrode cell was used for cyclic voltammetry
and consisted of a platinum button or glassy carbon working
electrode, a platinum counter electrode, and a homemade saturated
calomel reference electrode (SCE). The SCE was separated from
the bulk of the solution by a fritted glass bridge of low porosity
that contained the solvent/supporting electrolyte mixture. Thin-layer
UV-vis spectroelectrochemical experiments were performed with
a home-built thin-layer cell which had a light-transparent platinum-
net working electrode. Potentials were applied and monitored with
an EG&G PAR model 173 potentiostat. Time-resolved UV-vis
spectra were recorded with a Hewlett-Packard model 8453 diode
array spectrophotometer.
All solvents and inorganic reagents were obtained from Fisher
Scientific. All other chemicals were purchased from either Aldrich
or Acros and were used without further purifications. Dichlo-
romethane was distilled over CaCl2; tetrahydrofuran was distilled
over Na; N2O4 gas was prepared by reacting concentrated HNO3
with zinc metal. Benzonitrile (PhCN) was obtained from Fluka or
Aldrich Chemical Co. and was distilled over P2O5 under vacuum
prior to use. Tetra-n-butylammonium perchlorate (TBAP) was
purchased from Sigma Chemical or Fluka Chemika, recrystallized
from ethyl alcohol, and dried under vacuum at 40 °C for at least
one week prior to use.
To attain the fused system, we explored a novel Pd(0)-
catalyzed [3 + 2] cycloaddition reaction in the porphy-
rin series. This cycloaddition reaction effects tandem car-
bon-carbon bond formation on an electron-deficient double
bond to generate a five-membered carbocycle in one step.
In a previous communication26 we briefly reported the
(18) Patoux, C.; Coudret, C.; Launay, J.-P.; Joachim, C.; Gourdon, A. Inorg.
Chem. 1997, 36, 5037.
(19) Shoji, O.; Okade, S.; Satake, A.; Kobuke, Y. J. Am. Chem. Soc. 2005,
127, 2201.
(20) Bonfantini, E. E.; Burrell, A. K.; Officer, D. L.; Reid, D. C. W.;
McDonald, M. R.; Cocks, P. A.; Gordon, K. C. Inorg. Chem. 1997,
36, 6270.
(21) Burrell, A. K.; Campbell, W. M; Officer, D. L.; Scott, S. M.; Gordon,
K. C.; MacDonald, M. R. J. Chem. Soc., Dalton Trans. 1999, 3349.
(22) Rhee, S. W.; Park, B. B.; Do, Y.; Kim, J. Polyhedron 2000, 19, 1961.
(23) Wollmann, R. G.; Hendrickson, D. N. Inorg. Chem. 1977, 16, 3079.
(24) Loim, N. M.; Abramova, N. V.; Sokolov, V. I. MendeleeV Commun.
1996, 46.
X-ray diffraction measurements were carried out on a Bruker
SMART 1000 with the use of Mo KR radiation (λ ) 0.71073 Å).
Solution and refinement software used were SAINT for data
reduction, SHELXS-97 for solution, and SHELXL97 for refinement.
Due to the small crystal size and weak diffraction, the number of
observed data was only 13 times the number of parameters when
the Zn and Fe atoms were assigned anisotropic thermal parameters.
Therefore, the remainder of the atoms were kept as isotropic.
(25) Narayanan, S. J.; Venkataraman, S.; Dey, S. J.; Sridevi, B.; Anand,
V. R. G.; Chandrashekar, T. K. Synlett 2000, 1834.
(26) Wang, H. J. H.; Jaquinod, L.; Nurco, D. J.; Vicente, M. G. H.; Smith,
K. M. Chem. Commun. 2001, 2646.
Inorganic Chemistry, Vol. 46, No. 7, 2007 2899

Wang et al.
(26) {Cp2Fe[ZnTPP(THF)]2}{Cp2Fe[ZnTPP(THF) ZnTPP-
(MeOH)]}‚3MeOH‚6THF.
fraction was collected. This fraction was then subjected to size
exclusion chromatography (Sephadex LH-20), eluting with THF.
Two fractions were collected. Fraction 1: red crystals, 23, 27 mg,
15% yield; UV-vis (CH2Cl2), λmax 424 nm (ꢀ, 105 000), 545 (ꢀ,
C232H211Fe23N16O13Zn4, 1, M ) 3804.35, monoclinic, a )
33.327(5) Å, b ) 19.145(3) Å, c ) 29.603(5) Å, â ) 106.309(2)°,
1
3
V )18128(5) Å3, space group P21/c, Z ) 4, T ) 91(2) K, Dcalcd
)
15 900); H NMR, δ, 8.95 ppm (br, 1H), 8.84 (d, J (H,H) ) 5.1
Hz, 1H), 8.75 (d, 3J (H,H) ) 4.5 Hz, 2H), 8.74 (d, 3J (H,H) ) 4.8
Hz, 2H), 8.67 (d, 3J (H,H) ) 5.1 Hz, 2H), 8.66 (d, 3J (H,H) ) 4.5
1.394 Mg m-3, µ(Mo KR) ) 0.749 mm-1, 170 844 reflections
measured, 26 022 unique (Rint ) 0.161) used in all calculations.
The final wR2 was 0.2470 (all data) and R1(14 016 I > 2σ(I)) )
0.0906, 1079 parameters. Residual electron density was 1.503 and
3
Hz, 2H), 8.57 (d, J (H,H) ) 4.8 Hz, 2H), 8.24 (br, 4H), 7.75 (t,
4
4J (H,H) ) 1.8 Hz, 2H), 7.72 (t, J (H,H) ) 1.8 Hz, 2H), 7.70 (t,
-1.143 e Å-3
.
4J (H,H) ) 1.8 Hz, 2H), 7.69 (br, 2H), 7.50 (br, 4H), 7.26 (br,
4H), 6.58 (br, 4H), 6.43 (br, 4H), 5.09 (s, 2H)), 3.53 (s, 2H), 3.49
(s, 6H), 1.5-1.4 (m, 144H); calcd for C160H190N8Ni2, 2342.7146;
found MS (MALDI-TOF) m/z 2338.6. Anal. Calcd for C160H190N8-
Ni2: C, 82.03; H, 8.17; N, 4.78. Found: C, 82.87; H, 8.88; N,
4.03. Fraction 2: recrystallized from CH2Cl2/MeOH as a green
powder, 20, 60 mg, 25% yield; mp >350 °C (dec); UV-vis (THF),
Synthesis
Nickel(II) 2,3-(â-Methylenepropano)-5,10,15,20-tetrakis(3,5-
di-tert-butylphenyl)porphyrin (4). Strict air-free conditions and
Schlenck techniques were used in the palladium(0)-catalyzed [3 +
2] coupling reactions. A mixture of 30 mg (0.13 mmol) of
Pd(OAc)2 and 200 µL (0.77 mmol) triisopropyl phosphite in 15
mL of THF was stirred at room temperature for 30 min. Measures
of 1.17 g (1 mmol) of 2-nitroporphyrin 1 and 257 µL (1.3 mmol)
of 2-[(trimethylsilyl)methyl]-2-propen-1-yl acetate were added. The
reaction mixture was heated at 90 °C for 2 days and then at 100
°C for 2 days. The solvent was removed in vacuo, and the resi-
due was purified by chromatography on silica gel (elution with
CH2Cl2/cyclohexane ratio of 1:3), affording porphyrin 4 as red
crystals (1 g, 85% yield): mp >300 °C; UV-vis (CH2Cl2), 404
λ
max 412 nm (ꢀ, 103 000), 450 (77 000), 534 (18 100), 576 (16 100),
1
3
640 (18 500); H NMR (CDCl3), δ, 8.57 ppm (d, J (H,H) ) 4.8
Hz, 2H), 8.46 (s, 2H), 8.46 (d, J (H,H) ) 4.8 Hz, 2H), 7.80 (br,
8H), 7.66 (t, J (H,H) ) 1.8 Hz, 2H), 7.63 (t, J (H,H) ) 1.8 Hz,
2H), 3.88 (s, 2H), 1.74 (s, 3H), 1.43 (m, 72H), 0.89 (s, 15H); calcd
for C90H110N4NiRu, 1407.6558; found MS (MALDI-TOF) m/z
1408.0. Anal. Calcd for C90H110N4NiRu: C, 76.79; H, 7.88; N, 3.98.
Found: C, 77.05; H, 8.10; N, 3.82.
3
4
4
[Nickel(II) 2,3-(â-Methylpropeno)-5,10,15,20-tetrakis(3,5-di-
tert-butylphenyl)porphyrin]2 (23). Compound 13 (79 mg (0.067
mmol)) was dissolved in 5 mL of THF; 84 µL of LDA (2 M in
THF, 0.17 mmol) was added at -78 °C under argon. The resulting
mixture was stirred at 0 °C for 30 min and allowed to warm to
room temperature for 30 min. The reaction mixture was then
transferred to a solution of 11 mg (0.067 mmol) of FeCl3 in
5 mL of THF under strict air-free conditions. The resulting mix-
ture was heated to reflux for 2 days. It was cooled and then fil-
tered through Celite to remove inorganic salts. The filtrate was
evaporated to dryness under vacuum. The residue was then
dissolved in 30 mL of CH2Cl2 and washed with 5% HCl and then
water. The product was isolated on silica gel plates eluting with
cyclohexane/CH2Cl2 (v/v, 6:1) as red crystals (12 mg, 15% yield)
and was found to be spectroscopically identical with the material
described above.
1
nm (ꢀ, 133 000), 532 (35 100), 568 (14 700); H NMR (CDCl3),
3
3
δ, 8.86 ppm (d, J (H,H) ) 5.1 Hz, 2H), 8.81 (d, J (H,H) ) 5.1
4
Hz, 2H), 8.77 (s, 2H), 7.86 (d, J (H,H) ) 1.5 Hz, 4H), 7.7 (m,
8H), 4.95 (s, 2H), 3.41 (s, 4H), 1.46 (s, 36H), 1.44 (s, 36H); calcd
for C80H96N4Ni, 1172.3652; found MS (MALDI-TOF) m/z 1172.8.
Anal. Calcd for C80H96N4Ni‚2H2O: C, 79.55; H, 8.34; N, 4.63.
Found: C; 79.15; H, 8.16; N, 4.75.
Nickel(II) 2,3-(â-Methylpropeno)-5,10,15,20-tetrakis(3,5-di-
tert-butylphenyl)porphyrin (13). A mixture of 1.4 g (1.2 mmol)
of 4 and 0.04 g (0.21 mmol) of p-TsOH in 30 mL of chloroform
was heated at reflux for 24 h. It was cooled and then filtered to
remove excess p-TsOH. The filtrate was washed with aqueous
saturated Na2CO3 and then water. The solvent was then removed
and the resulting residue was applied to a short silica gel plug and
eluted with CH2Cl2/cyclohexane (v/v, 1:1). The first fraction was
collected. The desired porphyrin 13 was recrystallized from
CH2Cl2/MeOH to give red crystals (1.3 g, 93% yield): mp 285-
286 °C; UV-vis (CH2Cl2), 416 nm (ꢀ, 239 500), 540 (15 900),
Nickel(II) 2,3-(â-Methylenepropano)-5,10,15,20-tetraphen-
ylporphyrin (8). The title compound was prepared from Ni(II)
2-nitro-5,10,15,20-tetraphenylporphyrin (6) (0.85 g, 1.2 mmol) and
2-[(trimethylsilyl)methyl]-2-propen-1-yl acetate (0.36 mL, 1.8
mmol) using the procedure described for porphyrin 4. It was
obtained as red crystals in 83% yield: mp >300 °C; UV-vis
(CH2Cl2), λmax 414 nm (ꢀ, 195 000), 527 (20 000), 612 (1300); 1H
1
3
581 (ꢀ, 980); H NMR (CDCl3), δ, 8.84 ppm (d, J (H,H) ) 5.4
Hz, 1H), 8.82 (d, 3J (H,H) ) 5.2 Hz, 1H), 8.77 (overlapping d, 3J
4
(H,H) ) 4.8 Hz, 2H), 8.73 (m, 2H), 7.84 (d, J (H,H) ) 1.6 Hz,
2H), 7.83 (d, 4J (H,H) ) 2.0 Hz, 2H), 7.71 (m, 3H), 7.66 (m, 3H),
5.46 (s, 1H), 3.00 (s, 2H), 2.03 (s, 3H), 1.42 (m, 72H); calcd for
C80H96N4Ni, 1172.3652; found MS (MALDI-TOF) m/z 1172.2.
Anal. Calcd for C80H96N4Ni‚CH3OH‚2H2O: C, 78.38; H, 8.45; N,
4.52. Found: C, 78.71; H, 9.00; N, 4.75.
3
NMR (CDCl3), δ, 8.77 ppm (d, J (H,H) ) 5.1 Hz, 2H), 8.73 (d,
3
3J (H,H) ) 4.8 Hz, 2H), 8.73 (s, 2H), 8.00 (m, 4H), 7.86 (d, J
(H,H) ) 7.8 Hz, 4H), 7.68 (m, 12H), 5.00 (s, 2H), 3.48 (s, 4H);
calcd for C48H32N4Ni, 723.5076; found MS (MALDI-TOF) m/z
722.8. Anal. Calcd for C48H32N4Ni‚3H2O: C, 74.14; H, 4.92; N,
7.21. Found: C, 74.15; H, 4.84; N, 7.05.
Cp*ruthenium(III) [1,2-[Nickel(II)-5,10,15,20-tetrakis(3,5-di-
tert-butylphenyl)porphyrinato]-3-methyl-cyclopentadienide] (20)
and [Nickel(II) 2,3-(â-Methyl)propeno-5,10,15,20-tetrakis(3,5-
di-tert-butylphenyl)porphyrin]2 (23). Compound 13 (200 mg, 0.17
mmol) was dissolved in 15 mL of THF, and 350 µL of LDA (2 M
in THF, 0.70 mmol) was added. The mixture was stirred at 0 °C
under argon for 1 h. Cp*RuCl2 (65 mg, 0.21 mmol) was added,
and the resulting mixture was stirred at room temperature under
strict air-free conditions for 2 days. The reaction mixture was then
filtered through Celite to remove inorganic salts. The filtrate was
evaporated to dryness. The residue was applied to a silica gel
column, eluting with CH2Cl2/cyclohexane (v/v, 1:5). The second
Nickel(II) 2,3-(â-Methylpropeno)-5,10,15,20-tetraphenylpor-
phyrin (11). The title compound was prepared from porphyrin 8
(0.66 g, 0.92 mmol) and p-TsOH (0.03 g, 0.16 mmol) using the
procedure described for porphyrin 13 in 85% yield as red crystals:
mp >300 °C; UV-vis (CH2Cl2), λmax 416 nm (ꢀ, 426 000), 534
1
(34 000); H NMR (CDCl3), δ, 8.74 ppm (m, 6H);7.89 (m, 8H),
7.66 (m, 12H), 5.57 (s, 1H), 3.09 (s, 2H), 2.10 (s, 3H); calcd for
C48H32N4Ni, 723.5076; found MS (MALDI-TOF) m/z 723.1. Anal.
Calcd for C48H32N4Ni‚2H2O: C, 75.83; H, 4.78; N, 7.37. Found:
C, 75.50; H, 4.86; N, 7.15.
2900 Inorganic Chemistry, Vol. 46, No. 7, 2007

â,â′-Fused Metallocenoporphyrins
Iron(II) Bis[1,2-[Ni(II)-5,10,15,20-tetraphenylporphyrinato]-
3-methyl-cyclopentadienide] (24). Compound 11 (0.21 g, 0.29
mmol) was dissolved in 25 mL of THF, and 0.36 mL of LDA (2
M in THF, 0.72 mmol) was added at 0 °C. The resulting mixture
was stirred at 0 °C for 30 min and allowed to warm to room
temperature for 30 min. FeCl2 (6 mg, 0.44 mmol) was added under
strict air-free conditions. The mixture was then heated at reflux
for 2 days under argon. It was then cooled and filtered through
Celite to remove inorganic salts. The filtrate was evaporated to
dryness using a rotary evaporator. The residue was dissolved in
100 mL of CH2Cl2 and washed with 5% HCl and then water. The
solvent was again removed. The residue was purified on a size-
exclusion column (Sephadex LH-20), eluting with THF, to give
the title compound as a dark brown powder (65 mg, 30% yield):
mp >300 °C; UV-vis (THF), λmax 416 nm (ꢀ, 170 000), 530 (br);
no well-defined Q bands were observed; 1H NMR (CDCl3), δ, 8.40
ppm (s, 4H), 8.01 (d, 3J (H,H) ) 4.8 Hz, 4H), 7.83 (d, 3J (H,H) )
6.9 Hz, 8H), 7.70 (m, 16H), 7.44 (d, 3J (H,H) ) 4.8 Hz, 4H), 7.30
(br, 8H), 6.80 (br, 8H), 3.01 (s, 4H), 1.82 (s, 6H); calcd for
C96H62N8FeNi2, 1500.8464; found MS (MALDI-TOF) m/z 1499.9.
Zinc(II) 2,3-(â-Methylene)-propano-5,10,15,20-tetraphenylpor-
phyrin (18). The title compound was prepared from Zn(II) 2-nitro-
5,10,15,20-tetraphenylporphyrin (0.2 g, 0.28 mmol) and 2-[(tri-
methylsilyl)methyl]-2-propen-1-yl acetate (0.072 mL, 0.36 mmol)
using the procedure described for porphyrin 4 except a longer
reaction time was employed (8 days). It was obtained in 2% yield
as red crystals: mp >300 ïC; UV-vis (CH2Cl2), λmax, 412 nm (ꢀ,
20 mL of TFA. This mixture was stirred at room temperature for
15 min. Saturated aqueous Na2CO3 was carefully added to neutralize
the acids. After being stirred at room temperature for 10 min, this
mixture was extracted with CH2Cl2. The organic layer was separated
and washed with aqueous NaHCO3 and then water. The solvent
was removed using a rotary evaporator. The product (a mixture of
16 and 15) was crystallized from CH2Cl2/MeOH to give 0.4 g (90%
yield). This material (80 mg) was then treated with 10 mg of
p-TsOH in chloroform under reflux temperature for 1 day; pure 16
was obtained as red crystals after chromatography (Al2O3, eluted
with CH2Cl2) and recrystallization (CH2Cl2/MeOH) (70 mg, 88%
yield): mp >300 °C (dec); UV-vis, λmax 424 nm (ꢀ, 182 000),
1
520 (14 500), 553 (7900), 593 (5900), 647 (4900); H NMR, δ,
8.87 ppm (overlapping d, 2H), 8.77 (overlapping d, 2H), 8.74 (d,
3J (H,H) ) 5.1 Hz, 1H), 8.70 (d, 3J (H,H) ) 5.1 Hz, 1H), 8.22 (m,
3
4
4H), 8.15 (dd, J (H,H) ) 8.4 Hz, J (H,H) ) 1.8 Hz, 2H), 8.08
3
4
(dd, J (H,H) ) 8.4 Hz, J (H,H) ) 2.1 Hz, 2H), 7.75 (m, 12H),
5.78 (s, 1H), 3.30 (s, 2H), 2.22 (s, 3H), -2.89 (br, 2H); calcd for
C48H34N4, 666.8234; found MS (MALDI-TOF) m/z 670.2. Anal.
Calcd for C48H34N4‚3H2O: C, 79.96; H, 5.59; N, 7.77. Found: C,
79.55; H, 5.83; N, 7.27.
Zinc(II) 2, 3-(â-Methylpropeno)-5,10,15,20-tetraphenylpor-
phyrin (17). Compound 16 (0.32 g, 0.48 mmol) was dissolved in
60 mL of CH2Cl2, and 1.3 g (5.9 mmol) of Zn(OAc)2 in 20 mL of
MeOH was added. This mixture was stirred at room temperature
for 1 day and then filtered through Celite to remove excess Zn-
(OAc)2. The solvent was removed. The residue was applied to a
short alumina plug, eluting with CH2Cl2. The first fraction was
collected. The solvent was again removed. The product was
recrystallized from CH2Cl2/MeOH to give the title compound as
purple crystals (0.26 g, 74% yield): mp >300 °C (dec); UV-vis
(CH2Cl2), λmax, 418 nm (ꢀ, 249 000), 515 (4100), 551 (12 400),
1
185 000), 525 (9600); H NMR, δ, 3.6 ppm (s, 4H), 5.1 (s, 2H),
7.75 (m, 10H), 8.06 (overlapping d and s, 4J (H,H) ) 8.1 Hz, 4H),
4
4
8.22 (m, 6H), 8.82 (d, J (H,H) ) 4.8 Hz, 2H); 8.94 (d, J (H,H)
) 4.5 Hz, 2H), 8.93 (d, 4J (H,H) ) 4.8 Hz, 2H); calcd for C48H32N4-
Zn, 730.1876; found MS (MALDI-TOF) m/z 729.4. Anal. Calcd
for C48H32N4Zn‚CH3OH: C, 77.16; H, 4.76; N, 7.35. Found: C,
77.67; H, 5.08; N, 7.30.
1
606 (11 600), 697 (3900); H NMR, δ, 8.94 ppm (overlapping d,
4H), 8.89 (d, 3J (H,H) ) 5.0 Hz, 1H), 8.84 (d, 3J (H,H) ) 5.0 Hz,
3
4
1H), 8.22 (m, 4H), 8.15 (dd, J (H,H) ) 8.0 Hz, J (H,H) ) 1.5
Copper(II) 2,3-(â-Methylenepropano)-5,10,15,20-tetraphen-
ylporphyrin (9). The title compound was prepared from Cu(II)
2-nitro-5,10,15,20-tetraphenylporphyrin (1.0 g, 1.39 mmol) and
2-[(trimethylsilyl)methyl]-2-propen-1-yl acetate (0.355 mL, 1.8
mmol) using the procedure described for porphyrin 4 in 80% yield
as red crystals: mp >300 °C (dec); UV-vis (CH2Cl2), λmax, 410
nm (ꢀ, 385 000), 535 (22 000), 571 (1900); calcd for C48H32N4Cu,
728.3536; found MS (MALDI-TOF) m/z 727.9. Anal. Calcd for
C48H32N4Cu‚0.5CH3OH: C, 78.22; H, 4.61; N, 7.52. Found: C,
79.22; H, 5.72; N, 7.05.
Copper(II) 2,3-(â-Methylpropeno)-5,10,15,20-tetraphenylpor-
phyrin (12). The title compound was prepared from porphyrin 9
(0.45 g, 0.62 mmol) and p-TsOH (0.03 g, 0.16 mmol) using the
procedure described for porphyrin 11 in 90% yield as red crystals:
mp >350 °C (dec); UV-vis (CH2Cl2), λmax, 411 nm (ꢀ, 323 000),
540 (22 900); calcd for C48H32N4Cu, 728.3536; found MS (MALDI-
TOF) m/z 727.6. Anal. Calcd for C48H32N4Cu‚H2O‚0.5CH3OH: C,
78.19; H, 4.61; N, 7.52. Found: C, 78.70; H, 5.68; N, 7.01.
Iron(II) Bis[1,2-[copper(II)-5,10,15,20-tetraphenylporphyri-
nato]-3-methyl-cyclopentadienide] (25). The title compound was
prepared from compound 12 (0.27 g, 0.37 mmol), LDA (2 M in
THF, 0.93 mmol), and FeCl2 (0.094 g, 0.74 mmol) using the
procedure described for 27 in 8% yield as a brown powder: mp
>300 °C; UV-vis (CH2Cl2), λmax, 410 nm (ꢀ, 132 000), no well-
defined Q bands; calcd for C96H62N8FeNi2,1510.5384; found MS
(MALDI-TOF) m/z 1508.9.
3
4
Hz, 2H), 8.09 (dd, J (H,H) ) 7.8 Hz, J (H,H) ) 1.5 Hz, 2H),
7.74 (m, 12H), 5.70 (s, 1H), 3.2 (s, 2H), 2.2 (s, 3H); calcd for
C48H32N4Zn, 730.1876; found MS (MALDI-TOF) m/z 729.1. Anal.
Calcd for C48H32N4Zn: C, 78.96; H, 4.42; N, 7.67. Found: C, 78.89;
H, 4.78; N, 7.71.
Iron(II) Bis[1,2-[zinc(II)-5,10,15,20-tetraphenylporphyrinato]-
3-methyl-cyclopentadienide] (26). The title compound was pre-
pared from compound 17 (190 mg, 0.26 mmol), LDA (2 M in THF,
0.65 mmol), and FeCl2 (66 mg, 0.52 mmol) using the procedure
described for compound 24 in 35% yield as purple crystals: mp
>300 °C; UV-vis (CHCl3), λmax, 412 nm (ꢀ, 200 000), 520
(15 900), 553 (8600), 629 (7200); 1H NMR (CDCl3), δ, 8.62 ppm
(s, 4H), 8.29 (d, 3J (H,H) ) 4.5 Hz, 4H), 8.21(br, 6H), 7.92 (d, 3J
(H,H) ) 7.5 Hz, 4H), 7.76 (br, 8H), 7.63 (rb, 6H), 7.26 (m, 16H),
7.09 (d, 3J (H,H) ) 7.2 Hz, 6H), 6.10 (br, 4H), 5.41 (br, 4H), 3.28
(s, 4H), 2.02 (s, 6H); calcd for C96H62N8FeZn2, 1514.2064; found
MS (MALDI-TOF) m/z 1512.2.
Copper(II) 2-Nitro-5,10,15,20-tetrakis(3,5-di-tert-butyl)phen-
ylporphyrin (5). The title compound was prepared from Cu(II)
5,10,15,20-tetrakis(3,5-di-tert-butyl)phenylporphyrin (35) (1.2 g,
1.07 mmol) and freshly made N2O4 gas, in 89% yield, as purple
crystals: mp >300 °C (dec); UV-vis (CH2Cl2), λma, 425 nm (ꢀ,
130 000), 549 (9000), 590 (5700); calcd for C76H91CuN5O,
1170.1132; found MS (MALDI-TOF) m/z 1169.6. Anal. Calcd for
C76H91CuN5O‚2H2O: C, 75.93; H, 7.82; N, 5.83. Found: C, 75.74;
H, 7.77; N, 5.89.
2,3-(â-Methylenepropano)-5,10,15,20-tetraphenylporphyrin
(15) and 2,3-(â-Methylpropeno)-5,10,15,20-tetraphenylporphy-
rin (16). Compound 9 (0.5 g) was mixed with 1 mL of H2SO4 and
Copper(II) 2,3-(â-Methylenepropano)-5,10,15,20-tetrakis(di-
tert-butyl-phenyl)porphyrin (10). The title compound was pre-
Inorganic Chemistry, Vol. 46, No. 7, 2007 2901

Wang et al.
pared from compound 5 (1.1 g, 0.94 mmol) and 2-[(trimethylsilyl)-
methyl]-2-propen-1-yl acetate (0.24 mL, 1.22 mmol) using the
procedure described for porphyrin 4 in 87% (1.0 g) yield as red
crystals: mp >300 °C (dec); UV-vis (CH2Cl2), λmax 416 nm (ꢀ,
242 000), 549 (14 100), 570 (1400); calcd for C80H96CuN4,
1177.2112; found MS (MALDI-TOF) m/z 1175.9. Anal. Calcd for
C80H96Cu N4O‚C4H8O: C, 81.04; H, 8.42; N, 4.50. Found: C,
81.34; H, 9.28; N, 4.39.
Copper(II) 2,3-(â-Methylpropeno)-5,10,15,20-tetrakis(di-tert-
butyl-phenyl)porphyrin (14). The title compound was prepared
from porphyrin 10 (0.15 g, 0.12 mmol) and p-TsOH (0.01 g, 0.05
mmol) using the procedure described for porphyrin 13 in 80% (0.12
g) yield as red crystals: mp >350 °C; UV-vis (CH2Cl2), λmax 418
nm (ꢀ, 275 000), 544 (18 600); calcd for C80H96Cu N4, 1177.2112;
found MS (MALDI-TOF) m/z 1176.2. Anal. Calcd for C80H96-
CuN4O‚0.5CH3OH: C, 81.03; H, 8.28; N, 4.69. Found: C, 81.07;
H, 9.19; N, 4.56.
The desired compound was recrystallized from CH2Cl2/MeOH (0.1
g, 73% yield): mp >300 °C; UV-vis (CH2Cl2), λmax, 420 nm (ꢀ,
1
130 000), 559 (3500) 608 (9100), 697 (3800); H NMR, δ, 8.97
ppm (mixture of two d, 5H), 8.87 (d, 3J (H,H) ) 4.8 Hz 1H), 8.08
(t, 4J (H,H) ) 1.6 Hz, 4H), 8.01 (d, 4J (H,H) ) 2.0 Hz, 2H), 7.92
4
(d, J (H,H) ) 2.0 Hz, 2H), 7.81 (m, 2H), 7.75 (m, 2H), 5.62 (s,
1H), 3.17 (s, 2H), 2.12 (s, 3H); calcd for C80H96N4Zn, 1179.0452;
found MS (MALDI-TOF) m/z 1180.9. Anal. Calcd for C80H96N4-
Zn‚CH3OH: C, 80.26; H, 8.32; N, 4.62. Found: C, 80.45; H, 8.15;
N, 4.64.
Cp*ruthenium(II) [1,2-[Zinc(II)-5,10,15,20-tetrakis(3,5-di-
tert-butylphenyl)-porphyrinato]-3-methyl-cyclopentadienide] (22).
The title compound was prepared from 19 (70 mg, 0.059 mmol),
LDA (2 M in THF, 0.15 mmol), and Cp*Ru(III)Cl2 (0.038 g, 0.12
mmol) using the procedure described for 20 in 2% (2 mg) yield.
MS (MALDI-TOF) m/z 1414.9. Further characterization was not
possible due to instability.
Nickel(II) 2,3-(â-Methylenepropano)-7-nitro-5,10,15,20-tet-
rakis(di-tert-butyl-phenyl)porphyrin, Nickel(II) 2,3-(â-Methyl-
enepropano)-8-nitro-5,10,15,20-tetrakis(di-tert-butyl-phenyl)-
porphyrin, and Nickel(II) 2,3-(â-Methylenepropano)-17-nitro-
5,10,15,20-tetrakis(di-tert-butyl-phenyl)porphyrin. The mixture
of the title compounds was prepared from Ni(II) 5,10,15,20-tetrakis-
(3,5-di-tert-butyl)phenylporphyrin (4) (0.65 g, 0.55 mmol) and
freshly made N2O4 gas using the procedure described for compound
1 in 89% (0.6 g) yield. This mixture was not further separated and
was used directly in the following step.
Cp*ruthenium(II) [1,2-[Copper(II)-5,10,15,20-tetrakis(3,5-di-
tert-butylphenyl)porphyrinato]-3-methyl-cyclopentadienide] (21).
The title compound was prepared from porphyrin 14 (0.12 g, 0.10
mmol), LDA (2 M in THF, 0.25 mmol), and Cp*RuCl2 (0.062 g,
0.20 mmol) using the procedure described for porphyrin 20 in 14%
(20 mg) yield as a brownish-green powder: mp >300 °C; UV-
vis (CH2Cl2), λmax, 423 nm (ꢀ, 106 000), 548 (5600); calcd for
C90H110CuN4Ru, 1412.5018; found MS (MALDI-TOF) m/z 1412.0.
Anal. Calcd for C90H110Cu N4Ru‚2H2O: C, 74.65; H, 7.93; N, 3.87.
Found: C, 74.53; H, 8.56; N, 4.29.
Nickel(II) 2,3;17,18-Bis(â-methylenepropano)-5,10,15,20-tet-
rakis(di-tert-butyl-phenyl)porphyrin (27) and Nickel(II) 2,3;7,8-
Bis(â-methylenepropano)-5,10,15,20-tetrakis(di-tert-butyl-phenyl)-
porphyrin (28).
2,3-(â-Methylenepropano)-5,10,15,20-tetrakis(3,5-di-tert-bu-
tyl)phenylporphyrin (36) and 2,3-â-(Methylpropeno)-5,10,15,-
20-tetrakis(3,5-di-tert-butyl)porphyrin (37). Compound 10 (0.65
g, 0.55 mmol) was treated with 27.5 mL of 10% (v/v) H2SO4 in
TFA for 10 min at room temperature. To this mixture was added
25 mL of water and 50 mL of CH2Cl2. The organic layer was
separated and washed with saturated aqueous Na2CO3 and then
water. The solvent was removed using a rotary evaporator. The
residue was passed through a short alumina plug, eluting with
CH2Cl2. The mixture of 36 and 37 was crystallized from CH2Cl2/
MeOH as purple crystals: calcd for C80H98N4, 1115.681; found
MS (MALDI-TOF) m/z 1114.3. Anal. Calcd for C80H98N4‚
CH3OH: C, 84.87; H, 8.97; N, 4.89. Found: C, 84.84; H, 8.71; N,
5.03.
The title compounds were prepared from the preceding mixture
(0.5 g, 0.4 mmol) and 2-[(trimethylsilyl)methyl]-2-propen-1-yl
acetate (0.20 mL, 1.02 mmol) using the procedure described for
porphyrin 4 as a mixture of 27 and 28 that was separated on silica
gel plates, eluting with cyclohexane/CH2Cl2 (v/v, 15:1). Yields: 27,
50 mg; 28, 50 mg. Compound 27: mp >300 °C; UV-vis, λmax
416 nm (ꢀ, 219 000), 528 (12 500); 1H NMR, δ, 8.87 ppm (s, 4H),
7.8 (m, 12H), 4.93 (s, 4H), 3.39 (s, 8H), 1.4 (s, 72H); calcd for
C84H100N4Ni, 1224.4408; found MS (MALDI-TOF) m/z 1223.3.
Anal. Calcd for C84H100N4Ni‚0.5H2O: C, 81.80; H, 8.25; N, 4.54.
ï
Found: C, 81.97; H, 8.37; N, 4.71. Compound 28: mp >300 C;
2,3-(â-Methylpropeno)-5,10,15,20-tetrakis(3,5-di-tert-butyl)-
porphyrin (37). The title compound was prepared from a mixture
of 36 and 37 (0.4 g, 0.36 mmol) and p-TsOH (0.01 g, 0.05 mmol)
using the procedure described for porphyrin 16 in 88% (0.35 g)
yield as red crystals: mp >300 °C; UV-vis (CH2Cl2), λmax 427
nm (ꢀ, 218 000), 523 (10 400), 551 (3100), 594 ( 600), 648 (2500);
1H NMR, δ, 8.94 ppm (br, 2H), 8.83 (br, 2H), 8.82 (d, 3J (H,H) )
UV-vis, λmax 413 nm (ꢀ, 203 000), 527 (20 000); calcd for
C84H100N4Ni, 1224.4408; found MS (MALDI-TOF) m/z 1223.2.
Nickel(II) 2,3;17,18-Bis(â-methylpropeno)-5,10,15,20-tetrakis-
(3,5-di-tert-butyl)porphyrin (29)/(30). The title compounds were
prepared as a mixture from porphyrin 27 (0.1 g, 0.08 mmol) and
p-TsOH (0.01 g, 0.05 mmol) using the procedure described for
porphyrin 13 in 80% yield as a mixture of two isomeric compounds.
This mixture was not further separated and was used directly in
the bisruthenocenoporphyrin-forming reaction. Calcd for C84H100N4-
Ni: 1224.4408; found MS (MALDI-TOF) m/z 1224.1.
Nickel(II) 2,3-(â-Oxopropano)-5,10,15,20-tetraphenylporphy-
rin (33). Compound 8 (0.3 g, 0.41 mmol) was dissolved in 60 mL
of THF and 20 mL of dioxane. NaIO4 (0.66 g) in 6 mL of water
was added. Argon was bubbled through the solution for 5 min.
OsO4 (30 mg) was then added. The resulting mixture was stirred
at room temperature under argon for 4 h. It was then filtered through
Celite to remove inorganic salts. The filtrate was evaporated to
dryness, and the residue thus obtained was redissolved in 100 mL
of CH2Cl2 and washed with water. The solvent was then removed
under reduced pressure. The residue was subjected to a silica gel
column, eluted with CH2Cl2. Two fractions were collected. The
3
5.4 Hz, 1H), 8.75 (d, J (H,H) ) 5.4 Hz, 1H), 8.09 (mixture of
4
4
4
two d, J (H,H) ) 2.0 Hz, J (H H) ) 2.0 Hz, 4H), 8.03 (d, J
4
(H,H) ) 1.8 Hz, 2H), 7.94 (d, J (H,H) ) 1.8 Hz, 2H), 7.83 (m,
2H), 7.77 (m, 2H), 5.73 (s, 1H), 3.24 (s, 2H), 2.17 (s, 3H), 1.54
(br, 72H), -2.85 (br, 2H); calcd for C80H98N4, 1115.681; found
MS (MALDI-TOF) m/z 1114.3. Anal. Calcd for C80H98N4: C,
86.13; H, 8.85; N, 5.02. Found: C, 85.84; H, 8.96; N, 5.11.
Zinc(II) 2,3-(â-Methylpropeno)-5,10,15,20-tetrakis(3,5-di-tert-
butyl)porphyrin (19). Compound 37 (0.13 g, 0.12 mmol) was
dissolved in 15 mL of CHCl3, and 0.27 g (1.2 mmol) of Zn(OAc)2
in 5 mL of MeOH was added. Argon was bubbled through this
mixture for 5 min. It was then stirred at room temperature under
argon, overnight. The solvent was removed using a rotary evapora-
tor. The residue was applied to a short alumina plug, eluting with
cyclohexane/CH2Cl2 (v/v, 2:1). The first red fraction was collected.
2902 Inorganic Chemistry, Vol. 46, No. 7, 2007

â,â′-Fused Metallocenoporphyrins
Scheme 1
first fraction was unreacted starting material (10 mg); the second
fraction was the desired porphyrin 33 (0.15 g, 50% yield): mp
1
>300 °C; UV-vis, λmax 414 nm (ꢀ, 317 000), 527 (18 100); H
3
NMR, δ, 8.77 ppm (d, J (H,H) ) 5.2 Hz 2H), 8.73 (s, 2H), 8.73
(d, 3J (H,H) ) 5.2 Hz, 2H), 7.97 (dd, 3J (H,H) ) 7.8 Hz, 4J (H,H)
3
4
) 1.8 Hz, 4H), 7.83 (dd, J (H,H) ) 5.2 Hz, J (H,H) ) 1.6 Hz,
4H), 7.65 (m, 12H), 3.33 (s, 4H); calcd for C47H30N4NiO, 725.4802;
found MS (MALDI-TOF) m/z 725.9. Anal. Calcd for C47H30N4-
NiO‚H2O: C, 75.93; H, 4.34; N, 7.54. Found: C, 76.35; H, 4.43;
N, 7.52.
whole porphyrin macrocycle? This stimulated us to inves-
tigate how the two moieties would fuse together and how
reactive the whole system might be.
Nickel(II) 2,3-(â-Hydroxypropano)-5,10,15,20-tetraphenylpor-
phyrin (34). TiCl3(DME)1.5 (50 mg, 0.17 mmol) (DME )
dimethoxyethane) and 46 mg of Zn-Cu couple were mixed in 15
mL of THF. Argon was bubbled through this mixture for 5 min. It
was then heated under reflux for 2.5 h. The reaction mixture was
cooled, and 50 mg (0.069 mmol) of 33 in 5 mL of THF containing
one drop of pyridine was added. Argon was again bubbled through
this mixture for 5 min. The mixture was then heated under reflux
overnight before being cooled and then filtered through Celite to
remove inorganic salts. The filtrate was evaporated to dryness. The
residue was dissolved in CH2Cl2 and washed with 5% HCl and
then water. After re-evaporation of the solvent, the residue was
subjected to a short silica gel plug, eluting with cyclohexane/
CH2Cl2 (v/v, 2:1). The second fraction was collected. Compound
34 was recrystallized from CH2Cl2/MeOH as red crystals (20 mg,
40% yield): mp >300 °C; UV-vis, λmax 414 nm (ꢀ, 496 000),
Pd(0)-Catalyzed [3 + 2] Cycloaddition Reaction on
2-Nitroporphyrins. To introduce a fused five-membered ring
into the porphyrin periphery as the precursor of Cp-, we
investigated a [3 + 2] cycloaddition reaction catalyzed by
Pd(0) (Scheme 1). This cycloaddition produces a five-
membered ring bearing an exo-double bond function, sim-
plifying the subsequent transformation to afford a methyl-
cyclopentadienide ion.
This type of cycloaddition reaction has been described
before for isolated activated double bonds.33-36 An electron-
deficient double bond and an in situ generated 1,3-dipole
are required for the reaction to occur. Strongly electron-
withdrawing groups, such as ester, nitrile, nitro, ketone, and
sulfone, are deemed necessary to activate the double bonds.
To apply this chemistry to a porphyrin, we chose 2-nitro-
5,10,15,20-tetraarylporphyrins because these porphyrins are
readily prepared by scalable, chromatography-free procedures
and possess a unique set of reactivities that facilitate
peripheral functionalization.37-39 2-Nitro-5,10,15,20-tetra-
phenylporphyrin has been shown to undergo nucleophilic
attack at the â,â′ double bond bearing the nitro group, leading
to a range of â-substituted porphyrins. The strong ability of
the nitro group to activate a meso-tetraarylporphyrin toward
[3 + 2] cycloaddition and its propensity to act as leaving
group were also demonstrated in the related syntheses of
pyrroloporphyrins.39
Ni(II) 2-nitro-5,10,15,20-tetrakis-(3,5-di-tert-butyl)phen-
ylporphyrin (1) (Scheme 2) was prepared by nitration of
Ni(II) porphyrin 2 with N2O439 in CH2Cl2. Metalation of free
base porphyrin 3 is necessary to avoid insertion of Pd into
the porphyrin core in the subsequent step. The Pd(0) catalyst
was prepared40 in situ by treatment of Pd(OAc)2 with
triisopropylphosphite at room temperature for 30 min under
strictly air-free conditions. To this freshly made Pd(0) catalyst
was added nitroporphyrin 1 and 2-[(trimethylsilyl)methyl]-
2-propen-1-yl acetate, with exclusion of air. This mixture
was placed in a preheated (90 °C) oil bath for 2 days.
1
3
527 (45 000); H NMR, δ, 8.78 ppm (d, J (H,H) ) 5.2 Hz, 2H),
3
3
8.74 (s, 2H), 8.73 (d, J (H,H) ) 5.2 Hz, 2H), 8.00 (dd, J (H,H)
) 8.0 Hz, J (H,H) ) 1.2 Hz, 4H), 7.86 (br, 4H), 7.7 (m, 12H),
4
2
3
4.89 (m, 1H), 3.2 (dd, J (H,H) ) 16.4 Hz, J (H,H) ) 6.4 Hz,
2
3
2H), 2.6 (dd, J (H,H) ) 16.4 Hz, J (H,H) ) 3.0 Hz, 2H); calcd
for C47H32N4NiO, 727.496; found MS (MALDI-TOF) m/z 727.09.
Anal. Calcd for C47H32N4NiO‚H2O: C, 75.65; H, 4.60; N, 7.51.
Found: C, 75.60; H, 4.28; N, 7.54.
Results and Discussions
Synthesis. Porphyrin macrocycles possess 22 π-electrons,
but only 18 of them are involved in any specific delocal-
ization pathway. Upon peripheral annelation, one or even
two 6 π-electron cyclopentadienide anions can be added to
form 26 or 30 π-electron systems that still maintain the
aromatic stability of the porphyrin chromophore. Examples
of metallocenes prepared from cyclopentadienide ions con-
taining condensed aromatic rings have been described.27-30
Those studies suggest that annelation or “fusion” does not
necessarily cause the electrons to become less available to
the cyclopentadienide ion. However, the fact that porphyrins
can act as a π-ligand to transition metals either through one
pyrrolic31 ring or through the porphyrin core32 leads to
reactivity uncertainties; for example, once prepared, would
the anion from the fused cyclopentadiene ring be localized
to the five-membered ring or diffusely delocalized over the
(33) Holzapfel, C. W.; van der Merwe, T. L. Tetrahedron Lett. 1996, 37,
2303.
(34) Shimizu, I.; Ohashi, Y.; Tsuji, J. Tetrahedron Lett. 1984, 25,
5183.
(35) Ejiri, S.; Yamago, S.; Nakamura, E. J. Am. Chem. Soc. 1992, 114,
8707.
(36) Trost, B. M.; Matelich, M. C. J. Am. Chem. Soc. 1991, 113, 9007.
(37) Shea, K. M.; Jaquinod, L.; Khoury, R. G.; Smith, K. M. Chem.
Commun. 1998, 759.
(38) Krattinger, B.; Nurco, D. J.; Smith, K. M. Chem. Commun. 1998, 757.
(39) Jaquinod, L.; Gros, C.; Olmstead, M. M.; Antolovich, M.; Smith, K.
M. Chem. Commun. 1996, 1475.
(27) Yoshizawa, K.; Yahara, K.; Taniguchi, A.; Yamabe, T.; Kinoshita,
T.; Takeuchi, K. J. Org. Chem. 1999, 64, 2821.
(28) Sudhakar, A.; Katz, T. J.; Yang, B.-W. J. Am. Chem. Soc. 1986, 108,
2790.
(29) Sudhakar, A.; Katz, T. J. J. Am. Chem. Soc. 1986, 108, 179.
(30) Gassman, P. G.; Winter, C. H. J. Am. Chem. Soc. 1988, 110, 6130.
(31) Dailey, K. K.; Yap, G. P. A.; Rheingold, A. L.; Rauchfuss, T. B.
Angew. Chem., Int. Ed. Engl. 1996, 35, 1833.
(32) Janczak, J.; Kubiak, R.; Svoboda, I.; Jezierski, A.; Fuess, H. Inorg.
Chim. Acta 2000, 304, 150.
(40) Anderson, H. L. Chem. Commun. 1999, 2323.
Inorganic Chemistry, Vol. 46, No. 7, 2007 2903

Wang et al.
Scheme 2
Reaction progress was monitored using TLC and indicated
formation of a single new green compound. H NMR and
giving ∼80% yields. However, the [3 + 2] cycloaddition
reaction with Zn(II) 2-nitro-5,10,15,20-tetraphenylporphyrin
(prepared by nitration of free base TPP with ZnNO2 followed
by insertion of Zn(II)) required higher temperature and longer
reaction time and afforded a very low yield of the desired
porphyrin 18 (no more than 5% yield). This suggests that
Zn(II) porphyrins are less activated toward this [3 + 2]
cycloaddition, possibly because of the greater electron back-
donating ability of Zn(II) (d10) relative to Ni(II) (d8) and
Cu(II) (d9).
Fused Cyclopentadienylporphyrins: The Precursor to
Metallocenoporphyrin. Migration of the exo double bond
was catalyzed by p-toluenesulfuric acid (Scheme 2).41
Porphyrins 8, 9, 4, and 10 were refluxed in CHCl3 in the
presence of p-TsOH for 1 day, and porphyrins 11, 12, 13,
and 14 were obtained in 80-95% yield, along with recovery
of a small amount of starting material (less than 10%).
Migration of the double bond in 8, 9, 4, and 10 was
confirmed by the splitting of the porphyrin â-protons, shifting
1
MS (MALDI-TOF) spectra of the isolated product revealed
that it was a complex mixture. Fortunately, it was noticed
later that the green spot on TLC later turned red. It seemed
that the green spot, which was believed to be an isomeric
mixture of nitrochlorin A, was not stable. The loss of the
nitro group occurred upon exposure to silica gel. This mixture
was then mixed with silica gel in THF at 90 °C for 2 days,
and pure porphyrin 4 was obtained. The appearance of two
new sets of chemical shifts at 4.9 (s, 2H) and 3.4 ppm (s,
1
4H) in the H NMR spectrum confirmed the successful
synthesis of propanoporphyrin 4. Porphyrin 4 could also be
obtained directly from the [3 + 2] cycloaddition reaction in
one-pot synthesis via prolonged heating at a higher temper-
ature (100 °C). This reaction was clean and high yielding
(up to 88%).
Similar reactions carried out with Cu(II) 2-nitro-5,10,15,-
20-tetrakis-di-tert-butylphenylporphyrin (5), Ni(II) 2-nitro-
5,10,15,20-tetraphenylporphyrin (6), and Cu(II) 2-nitro-
5,10,15,20-tetraphenylporphyrin (7) were also successful,
(41) Trost, B. M.; Chan, D. M. T. J. Am. Chem. Soc. 1981, 103, 5972.
2904 Inorganic Chemistry, Vol. 46, No. 7, 2007

â,â′-Fused Metallocenoporphyrins
Scheme 3
of the two peaks at 3-5 ppm, and appearance of a new peak
at ∼2.0 ppm (s, 3H) in their H NMR spectra.
chromatography and are stable in air, Zn(II) porphyrin 22
decomposed on silica gel. Pure 22 could not therefore be
obtained. A porphyrin dimer 23 was isolated along with the
ruthenoceno-NiII-porphyrin 20. We speculate that this
oxidative (Cp*RuIIICl2 serving as the oxidant) is similar to
the dimerization of substituted cyclopentadienide derivatives
using FeCl3 as the oxidant.44 Reactions carried out with
deprotonated porphyrin 13 in the presence of FeCl3 (replacing
Cp*RuIIICl2) led to the same dimer 23 (Scheme 5).
1
Fused Zn(II) Cyclopentadienylporphyrins. As men-
tioned above, Zn(II) 2-nitroporphyrins gave very poor yields
of cycloaddition products. To prepare the Zn(II) analogues
of 8 and 4, the corresponding Cu(II) porphyrins were first
demetalated, followed by reinsertion of Zn(II) (Scheme 3).
Thus, Cu(II) porphyrin 9 was treated with 5% H2SO4 in TFA
for 10 min at room temperature, and free base porphyrin
was obtained quantitatively. The product turned out to be a
mixture of the desired porphyrin 15 and its regioisomer 16
(major). Double-bond migration occurred in tandem with
demetalation under the strongly acidic conditions. The free
base character of the porphyrins was confirmed with the
A similar dimerization was not observed with Cu(II) and
Zn(II) porphyrins 14 and 19.
Porphyrins 11, 12, and 17 were deprotonated at 0 °C with
LDA followed by addition of FeCl2 at reflux to give the
bisporphyrinatoferrocenes 24, 25, and 26. Mass spectrometry
(MALDI-TOF) confirmed their identity (m/z 1499.9, 1508.9,
and 1512.2, respectively). In their 1H NMR spectra, protons
of the fused cyclopentadienyl ring were observed as a singlet
at 3.01 ppm for 24 and at 3.28 ppm for 26. Compounds 24
and 25 are only slightly soluble, whereas 26 is soluble in
most organic solvents. This may be explained by noting the
different π-stacking features of these compounds arising from
the different coordination chemistry of their central metal
ions. All three compounds displayed greater stability in the
air compared with their respective Ru analogues.
Attempted Demetalation of Metallocenoporphyrins.
The optical properties of porphyrin molecules can be tuned,
apart from the peripheral substituents, by changing the metal
center, its oxidation state, and axial ligands. Metallocenopor-
phyrins 24, 25, 26, 20, and 21 were subjected to demetalat-
ion under acidic conditions. Metalloceno-Ni(II)-porphyrins
24 and 20 underwent complete decomposition, whereas
demetalation of 25, 26, and 21 led to degradation of the
metallocene part of the molecules.
1
appearance of a broad peak at -2.91 ppm (NH) in the H
NMR spectra. These two isomers were not further separated.
The mixture of 15 and 16 was then treated with p-TsOH to
ensure complete conversion of 15 into its regioisomer 16,
followed by insertion of Zn(II) to give 17. Porphyrin 19 was
obtained in a similar way.
Fused Metallocenylporphyrins. Porphyrins 13, 14, and
19 were deprotonated with lithium diisopropylamide
(LDA)31,42,43 at 0 °C (Scheme 4). The participation of elec-
trons from the porphyrin in the aromatic delocalization
pathway of the fused cyclopentadienide ring induced a
color change from red (porphyrin-like compound) to green
(chlorin-like compound). The above mixture reacted with
Cp*RuIIICl2 under argon at room temperature, leading to the
desired ruthenocenoporphyrins 20, 21, and 22 in 25%, 14%,
and 2% yields, respectively. Formation of 20, 21, and 22
was confirmed by MALDI-TOF mass spectrometry. The
structure of 20 was confirmed by X-ray single-crystal
diffraction.26 In contrast to 20 and 21, both of which survive
Bisruthenocenoporphyrin. Porphyrin 4 was nitrated with
N2O4 in CH2Cl2 (Scheme 6), and a mixture of three
(42) Lichtenberger, D. L.; Elkadi, Y.; Gruhn, N. E. Organometallics 1997,
16, 5209.
(43) Beck, C. U.; Field, L. D.; Hambley, T. W.; Humphrey, P. A.; Masters,
A. F.; Turner, P. J. Organomet. Chem. 1998, 565, 283.
(44) Sitzmann, H.; Bollmann, C.; Dehmlow, E. V. Tetrahedron Lett. 1994,
35, 5619.
Inorganic Chemistry, Vol. 46, No. 7, 2007 2905

Wang et al.
Scheme 4
Scheme 5
mononitration products was obtained, as expected. A [3 +
2] cycloaddition reaction carried out with this mixture gave
two regioisomers 27 and 28. Compounds 27 and 28 were
separated on silica gel plates, eluting with cyclohexane/
CH2Cl2 (v/v, 10:1). Weak-acid-catalyzed double-bond migra-
tion converted 27 into two regioisomers 29 and 30 (Scheme
7). These two regioisomers, which were not further separated,
were treated with LDA and (C5H5)RuIIICl2 at room temper-
ature. Two compounds, 31 and 32, were expected from this
reaction. Mass spectra of the reaction mixture implied the
formation of bisruthenocenoporphyrin (MALDI-TOF, m/z
1693). However, though the desired bisruthenocenoporphyrin
compound was formed, it was not stable enough to survive
the workup conditions.
mation, Figure S1). Monoruthenocenoporphyrin 20 showed
unusual absorptions; its Soret band has a broad shoulder
spanning a range of 380-500 nm. All other metallocenopo-
rphyrins displayed broad Soret bands and largely flattened
Q bands. No significant bathochromic shift relative to their
precursor porphyrins was observed for these metallocenopor-
phyrins. It should be noted that the extinction coefficients
(ꢀ) decrease significantly (by more than 50%) for each
metallocenoporphyrin. These data suggest that intramolecular
charge transfer might occur in these molecules.
X-ray Crystal Structure of Bisporphyrinatoferrocene
26. Figure 1 shows different views of the crystal structure
of 26. There are two different molecules (Figure 1) in each
asymmetric unit. In both molecules the central Zn(II) ions
are five-coordinated with the fifth ligands bound at the axial
position outside of the ferrocene sandwich. In one molecule,
UV-vis Spectra. Compounds 21-22 and 24-26 possess
interesting electronic absorption spectra (Supporting Infor-
2906 Inorganic Chemistry, Vol. 46, No. 7, 2007

â,â′-Fused Metallocenoporphyrins
Scheme 6
Scheme 7
both the central zinc ions have THF as the fifth ligand with
metal-to-plane (defined by the C20N4 porphyrin skeleton)
displacements of 0.058 and 0.300 Å toward THF, respec-
tively; in the other molecule, one central Zn(II) coordinates
with MeOH, whereas the other one is coordinated with THF.
The displacements of Zn out of the porphyrin plane are 0.065
Å toward MeOH and 0.137 Å toward THF. These two
porphyrin macrocycles in each molecule are not strictly
parallel. The dihedral angles between them are 10.2° and
3.3°, respectively. In each molecule, one porphyrin ring is
rotated with respect to the other by about 72° in the 5-fold
axis of the Cp ring. The ferrocene part of this molecule
adopts an essentially eclipsed conformation by deviation of
6°. The two Cp rings in each molecule are off-parallel by
10.4° and 8.1° (with rough interplanar distances of 3.38 and
3.31 Å), respectively. The molecular arrangement in one
asymmetric unit is displayed in the Supporting Information
(Figure S2).
Electrochemistry
Monomeric Ni(II) Porphyrins 2, 13, and 20. Ni(II)
porphyrins with numerous structures have been electro-
chemically characterized in our laboratories.45-50 The reduc-
tions invariably involve the stepwise addition of one or two
electrons to the porphyrin macrocycle, giving π-anion
radicals and dianions. The oxidations often occur via a
stepwise abstraction of two electrons from the conjugated
macrocycle, giving a π-cation radical and dication, but in
Inorganic Chemistry, Vol. 46, No. 7, 2007 2907

Wang et al.
Figure 1. X-ray crystal structure of bisporphyrinatoferrocene 26. (a) One molecule in the unit cell with THF and MeOH as the fifth axial ligands; (b) the
other molecule in the unit cell with THF as both of the axial ligands.
many cases these processes are overlapped in potential
leading to an overall two-electron conversion from a Ni(II)
porphyrin to the Ni(II) porphyrin dication.46 In either case
the formation of a Ni(III) dication may be generated at more
positive potentials although this reaction is not always
observed.
Both the specific solvent-supporting electrolyte system and
nature of axial ligation to the Ni(II) porphyrin play key roles
in the prevailing oxidative behavior of the complexes, and
specific changes in solvent and/or axial coordination can in
some cases “direct” the initial electron abstraction to involve
the metal center, here leading to an initial Ni(II)/Ni(III)
reaction, followed at more positive potentials by the two ring-
centered oxidations.45
Ni(II) porphyrin 13 with a fused cyclopentadienyl ring
shows two well-resolved one-electron oxidations located at
E1/2 ) 0.99 and 1.19 V in PhCN containing 0.1 M TBAP.
This contrasts with what is observed for tert-butyl Ni(II)
porphyrin 2 where two overlapping one-electron oxidations
are observed at the same E1/2 value of 1.13 V (Figure 2).
Compound 13 also undergoes two one-electron reductions,
located at E1/2 ) -1.36 and -1.95 V in PhCN (see Figure
Figure 2. Cyclic voltammograms of Ni(II) porphyrins 2, 13, and 20 in
2 and Supporting Information, Table S1). The first reduction
and first oxidation of 13 are shifted negatively in potential
by 50 and 140 mV, respectively, as compared to E1/2 values
PhCN containing 0.1 M TBAP. Scan rate ) 0.10 V/s.
for oxidation and reduction of the structurally related tert-
butyl Ni(II) porphyrin 2 under the same solution conditions.
The direction of the potential shift upon going from 2 to 13
can be accounted for by the electron-donating nature of the
fused cyclpentadiene group on 13, and this electron-donating
effect influences to a greater extent the oxidation than the
reduction, as indicated by the ∆E1/2 values between the two
related compounds.
Differences are also obtained in the HOMO-LUMO gap
of 2 and 13 under the same solution conditions. This value
is 2.35 V for 13 and 2.44 V for 2. Both HOMO-LUMO
gaps fall within the range reported for most Ni(II) porphyrins
where the oxidations and reductions all occur at the
conjugated macrocycle.45,46
(45) Kadish, K. M.; Van Caemelbecke, E.; Royal, G. In The Porphyrin
Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic
Press: Boston, 2000; Vol. 8, Chapter 55, pp 1-260.
(46) Kadish, K. M.; Lin, M.; Van Caemelbecke, E.; De Stefano, G.;
Medforth, C. J.; Nurco, D. J.; Nelson, N. Y.; Krattinger, B.; Muzzi,
C. M.; Jaquinod, L.; Xu, Y.; Shyr, D. C.; Smith, K. M.; Shelnutt, J.
A. Inorg. Chem. 2002, 41, 6673.
(47) Kadish, K. M.; Van Caemelbecke, E.; Boulas, P.; D’Souza, F.; Vogel,
E.; Kisters, M.; Medforth, C. J.; Smith, K. M. Inorg. Chem. 1993, 32,
4177.
(48) Kadish, K. M.; Franzen, M. M.; Han, B. C.; Araullo-McAdams, C.;
Sazou, D. J. Am. Chem. Soc. 1991, 113, 512.
(49) Kadish, K. M.; Sazou, D.; Liu, Y. M.; Saoiabi, A.; Ferhat, M.; Guilard,
R. Inorg. Chem. 1988, 27, 1198.
(50) Kadish, K. M.; Guo, N.; Van Camelbecke, E.; Paolesse, R.; Monti,
D.; Tagliatesta, P. J. Porphyrins Phthalocyanines 1998, 2, 439.
2908 Inorganic Chemistry, Vol. 46, No. 7, 2007

â,â′-Fused Metallocenoporphyrins
Figure 3. Thin-layer UV-vis spectral changes obtained during the electron transfer reactions of Ni 13 and Ni 2 in PhCN, 0.1 M TBAP. The direction of
spectral changes is illustrated by the arrows.
Compound 20 differs from 2 and 13 in that it contains a
fused electroactive ruthenocene unit which not only increases
the number of observed oxidations but also leads to shifts
in potentials for oxidation of both the porphyrin and the
ruthenocene parts of the molecule as compared with the two
electroactive units themselves when they are not fused to
each other, i.e., ruthenocene and tert-butylphenylporphyrin
2. In contrast with the oxidations, the presence of the linked
ruthenocene group on 20 has little or no effect on the
reduction potentials as seen in Figure 2 where 20 undergoes
an initial one-electron addition at -1.32 V as compared to
E1/2 ) -1.31 V for 2 and -1.36 V for 13. The expected
second reduction of 20 was not observed but should be close
to the negative potential limit of the PhCN solvent.
The UV-vis spectral changes obtained during oxidation
or reduction of nickel porphyrins have often been used to
determine the site of electron transfer.45 When the intensity
of the porphyrin Soret band significantly decreases after a
reduction or oxidation, the electron-transfer site is generally
porphyrin-ring-centered, leading to formation of a π-anion
or π-cation radical.45 However, when the Soret band is only
slightly shifted in wavelength and undergoes little or no
change in absorptivity upon reduction or oxidation, the
electron-transfer reactions can then often be assigned as
metal-centered, leading either to the formation of singly
charged Ni(I) or Ni(III) porphyrins or, alternately, to redox
reactions involving another electroactive site on the molecule
in addition to the conjugated porphyrin macrocycle.
During the first oxidation of Ni 13 at 1.10 V, the bands at
424 and 538 nm both decrease in intensity while a new broad
band grows in at 353 nm. A further decrease in intensity of
the 424 nm Soret band intensity is seen during the second
oxidation at -1.40 V. The spectral changes are identical with
those observed upon oxidation of Ni 2 (Figure 3) and
indicate, in both compounds, the stepwise formation of a
π-cation radical and dication upon the first and second one-
electron oxidations.
The most significant difference between 2, 13, and 20 is
in the oxidation behavior of the compounds. Three well-
defined one-electron oxidations are observed for 20, the first
and third of which are reversible in PhCN, 0.1 M TBAP
(Figure 2). Ruthenocene is reported to undergo an irrevers-
ible two-electron oxidation between 0.60 and 0.78 V in
CH3CN,51-53 and two oxidations at similar potentials are also
seen in the case of 20. The fused ruthenocene group is
therefore proposed as the initial site of electron abstraction
in 20, where the two one-electron oxidations associated with
this ruthenocene-centered reaction are located at E1/2 ) 0.58
and Epa ) 0.93 V vs SCE in PhCN for a scan rate of 0.1
V/s. The fact that the initial ruthenocene-centered one-
electron oxidation is reversible in the case of 20 and not in
the case of ruthenocene itself indicates that the porphyrin
macrocycle acts as a stabilizing ligand for the single oxidized
(ruthenocene)+ and also prevents dimerization which occurs
in the absence of the porphyrin.54
The first reduction of compound 13 at a controlled
potential of -1.50 V also leads to a significant loss of Soret
band intensity as seen in Figure 4. After completion of
electrolysis, the initial Soret band at 424 nm has shifted to
410 nm, the initial visible band at 538 nm has disappeared,
and two new broad visible bands are seen at 490 and 585
nm. The UV-vis spectral changes of 13 during this reduction
are similar to what is seen during reduction of compound 2
(Figure 4b) and indicate electron addition to the macrocycle
in both cases, i.e., formation of a Ni(II) π-anion radical after
addition of one-electron to the initial compound.
(51) Denisovich, L. I.; Zakurin, N. V.; Bezrukova, A. A.; Gubin, S. P. J.
Organomet. Chem. 1974, 81, 207.
(52) Kuwana, T.; Bublitz, D. E.; Hoh, G. J. Am. Chem. Soc. 1960, 82,
5811.
(53) Gubin, S. P.; Smirnova, S. A.; Denisovich, L. I.; Lubovich, A. A. J.
Organomet. Chem. 1971, 30, 243.
(54) Trupia, S.; Nafady, A.; Geiger, W. Inorg. Chem. 2003, 42, 5480.
The spectral changes of compound 20 obtained after
electrooxidation differ from those of 2 and 13. The neutral
compound 20 has a split Soret band at 418 and 456 nm
(Figure 5a) whereas the neutral compounds 13 and 2 have
Inorganic Chemistry, Vol. 46, No. 7, 2007 2909

Wang et al.
Figure 4. Thin-layer UV-vis spectral changes of Ni 13 and Ni 2 obtained
upon reduction in PhCN, 0.1 M TBAP.
an unsplit Soret band located at 424 and 421 nm, respectively
(Figures 3 and 4). After the first oxidation of 20 at 0.80 V,
the absorption at 418 shifts to 426 nm whereas after further
oxidation at 1.02 V the Soret band maximum shifts to 429
nm as seen in parts a-c of Figure 5. In neither case is there
a significant loss of Soret band intensity, and the shift in
position of the Soret band can be accounted for by an
increased positive charge on the porphyrin after each
oxidation. Both results strongly suggest that the first two
oxidations of 20 are ruthenocene-centered. This is also the
conclusion which results from the fact that the first two
oxidations of 20 are similar to potentials for the oxidation
of ruthenecene itself in the absence of the porphyrin.51-53
The third oxidation of compound 20 (Figure 2) must
therefore be a porphyrin ring-centered electron transfer, and
this is the conclusion that results from analyzing the spectral
changes in Figure 5d during oxidation of the compound at
1.38 V in PhCN.
Figure 5. UV-vis spectra of neutral and electrooxidized Ni 20 in PhCN,
0.1 M TBAP.
indicates that the two porphyrin rings act as electron-
donating substituents, thus producing an easier oxidation of
the linked ferrocene group on 24. The second quasi-reversible
oxidation of Ni 24 at 1.22 V is an overall four-electron
process. One electron is initially abstracted from the linked
Fc unit, and four electrons are then abstracted at the same
or very similar potentials from the two porphyrin π-ring
systems, thus giving as final product two Ni(II) porphyrin
dications linked by a singly oxidized ferrocene group. This
process is well-precedented in similar dimeric systems.55 The
overall porphyrin-centered oxidation of 24 is 100 mV greater
than the porphyrin-centered oxidation of (TPP)Ni. This is
consistent with the electron-withdrawing effect of the fer-
rocene group in 24, thus leading to a harder porphyrin-
centered oxidation and an easier Fc-centered oxidation in
the molecule.
Linked Ni(II) 24 and Cu(II) 25 Dyads. Compound 24
contains two identical Ni(II) tetraphenylporphyrins connected
by a fused ferrocene group. Two reversible oxidations are
observed for this compound. The first is located at E1/2
)
0.39 V vs SCE and assigned to the Fc/Fc+ reaction of the
linking group. The second oxidation occurs at E1/2 ) 1.22
V and is, on the basis of its similarly to the (TPP)Ni oxidation
(Figure 6a), assigned as a π-ring-centered reaction of the
porphyrin.
Each porphyrin macrocycle of 24 undergoes a reversible
one-electron reduction, but the potentials are not overlapped
in this case. One porphyrin unit is reduced at E1/2 ) -1.24
V and the other at E1/2 ) -1.35 V (see Figure 6a). This
Compared to the first oxidation potential of ferrocene itself
under the same solution conditions (E1/2 ) 0.49 V), the
oxidation of the ferrocene unit in compound 24 is neg-
atively shifted by 100 mV to E1/2 ) 0.39 V. This result
(55) Kadish, K. M.; Guo, N.; Van Caemelbecke, E.; Paolesse, R.; Monti,
D.; Tagliatesta, P. J. Porphyrins Phthalocyanines 1998, 2, 439.
2910 Inorganic Chemistry, Vol. 46, No. 7, 2007

â,â′-Fused Metallocenoporphyrins
Figure 7. Thin-layer UV-vis spectral changes of Cu 25 obtained upon
oxidations in PhCN, 0.1 M TBAP.
Figure 6. Cyclic voltammograms for oxidation and reduction of Ni 24,
Cu 25, and corresponding (TPP)M and Fc units in PhCN, 0.1 M TBAP, at
a scan rate of 0.10 V/s.
difference in E1/2 indicates a strong interaction between the
π-ring systems of the two equivalent porphyrin macrocycles.
Similar electrochemical behavior is seen for the copper
dyad 25 (Figure 6b). The initial reversible one-electron
oxidation at E1/2 ) 0.40 V is ferrocene-centered, whereas
the following four-electron oxidation at E1/2 ) 1.17 V is
porphyrin-centered. Two reductions are observed at E1/2
)
-1.38 and -1.87 V, and these are proposed to involve two
electrons in each process, thus leading to first a bisporphyrin
π-anion radical and then, at more negative potentials, to a
bisporphyrin dianion. The fact that each porphyrin macro-
cycle of 25 is reduced at the same potential is consistent
with only a weak interaction between the two equivalent
π-ring systems that are connected to each other via the
ferrocene group.
Time-resolved UV-vis spectra upon controlled potential
oxidation and reduction of Cu 25 were recorded in PhCN,
0.1 M TBAP, and are consistent with the cyclic voltammetric
data. These spectral changes are shown in Figures 7 and 8.
The initial broad Soret band of Cu 25 at 417 nm decreases
only slightly in intensity upon the first oxidation at 0.70 V
(Figure 7a) as would be expected for an oxidation at the
ferrocene part of the molecule.
Figure 8. Thin-layer UV-vis spectral changes of Cu 25 obtained upon
reduction in PhCN, 0.1 M TBAP.
Two different sets of spectral changes are observed upon
the second oxidation at 1.40 V, each of which displays
isosbestic behavior. The first occurs from 0 to 110 s and
leads to a “normal” copper tetraphenylporphyrin spectrum
with a strong Soret band at 424 nm and a well-defined visible
band at 544 nm (Figure 7b). The second set of spectral
changes occurs from 110 to 445 s and results in much
decreased intensity of the Soret band (Figure 7c). The latter
reaction is clearly porphyrin ring-centered under the given
experimental conditions. The “sharpening” of the Soret band
upon going from Cu 25 to Cu 25+ is also consistent with an
oxidation at the linking Fc group and a concomitant decrease
in interaction between the two porphyrin π-ring systems.
Inorganic Chemistry, Vol. 46, No. 7, 2007 2911

Wang et al.
Scheme 8
Derivatives of â,â′-Fused Propanoporphyrins. As il-
phyrin periphery. A series of â,â′-fused monoruthenoceno-
metalloporphyrins and bismetalloporphyrinatoferrocenes with
different central metals were prepared. Whereas all three
bismetalloporphyrinatoferrocenes (24, 25, and 26) and
monoruthenoceno-metalloporphyrins (20 and 21) are stable
for a certain amount of time in the air, monoruthenoceno-
Zn(II)-porphyrin 22 decomposed readily, possibly due to the
electron-rich nature of both the central metal (Zn(II)) and
the porphyrin ring. Efforts to synthesize metallocene free
base porphyrin compounds failed. The formation of bismet-
alloceno-Ni(II)-porphyrins (31, 32) was detected by MS
(MALDI-TOF). A porphyrin dimer (23) was identified along
with monoruthenoceno-Ni(II)-porphyrin 20. All three bis-
metalloporphyrinatoferrocenes (24, 25, and 26) exhibited
similar UV-vis spectra with broad Soret bands and no well-
defined Q bands. The electrochemistry of 20 was compared
with its precursor compounds 2 and 13 and showed
significant difference. The fact that the initial ruthenocene-
centered one-electron oxidation is reversible in the case of
20 and not in the case of Rc itself indicates that the porphyrin
macrocycle acts as a stabilizing ligand for the single oxidized
Rc+ and also prevents dimerization, which occurs in the
absence of the porphyrin. Whereas porphyrinatoferrocene 25
only displayed weak interaction between the two equivalent
porphyrin π-ring systems, strong interaction was detected
for porphyrinatoferrocene 24, another example of the im-
portant role the central metallic ion can play in electronic
lustrated in Scheme 8, porphyrin 8 was oxidized to keto-
porphyrin 33 using OsO4 (catalytic amount)/NaIO4. This
reaction proceeded smoothly. Porphyrin 33 was then sub-
jected to the McMurry reaction in DME56-59 in the hope that
a dimeric McMurry product with an extended π-system
would be obtained. However, only starting material was
recovered. This might result from the low solubility of
porphyrin 33 in DME. McMurry reactions carried out in THF
also failed to give the desired McMurry product; they instead
led to the hydroxy-porphyrin 34 in reasonable yield. Addition
of a base to the reaction mixture generated the same product.
However, it should be mentioned that, by examination of
the structure of 33, the enol form of this keto-porphyrin is
relatively stable due to the conjugation of the enol double
bond into the porphyrin macrocycle. This may account
partially for the failure of the McMurry reaction and explain
the fact that porphyrin 34 was reproducibly obtained in these
reactions.
Conclusions
In this work, a Pd(0)-catalyzed [3 + 2] cycloaddition
reaction was successfully applied to 2-nitro-meso-tetraarylpor-
phyrins to fuse a five-membered carbocycle onto the por-
(56) Ishida, A.; Mukaiyama, T. Chem. Lett. 1976, 1127.
(57) Jaquinod, L.; Nurco, D. J.; Medforth, C. J.; Pandey, R. K.; Forsyth,
T. P.; Olmstead, M. M.; Smith, K. M. Angew. Chem., Int. Ed. Engl.
1996, 35, 1013.
(58) McMurry, J. E. Chem. ReV. 1989, 89, 1513.
(59) Ephritikhine, M. Chem. Commun. 1998, 2549.
2912 Inorganic Chemistry, Vol. 46, No. 7, 2007

â,â′-Fused Metallocenoporphyrins
properties of porphyrin molecules. A crystal structure of bis-
Zn(II)-meso-tetraphenylporphyrinatoferrocene (26) was ob-
tained. The porphyrin macrocycles in the two molecules
within the crystal are essentially planar due to the coordina-
tion to the organometallic moieties. In these molecules, one
porphyrin ring is rotated with respect to the other by about
72° in the 5-fold axis of the Cp ring.
Welch Foundation (KMK Grant E-680); we also thank Mr.
Guido Stephano for his help in preliminary experiments.
Supporting Information Available: UV-vis spectra of com-
pounds 20, 21, and 24-26; X-ray crystal structure of compound
26 showing one asymmetric unit; table of electrochemical half-
wave potentials; CIF for compound 26. This material is available
free of charge via the Internet at http://pubs.acs.org.
We acknowledge the support of the National Science
Foundation (KMS Grant CHE-0296012) and the Robert A.
IC062303L
Inorganic Chemistry, Vol. 46, No. 7, 2007 2913