The marriage of peripherally metallated and directly linked porphyrins: Bromidobis(phosphine)platinum(II) as a cation-stabilizing substituent on directly linked and fused triply linked diporphyrins

Article abstract of DOI:10.1002/asia.201300633

A meso-bromidoplatiniobis(triphenylphosphine) η¹- organometallic porphyrin monomer was prepared by the oxidative addition of meso-bromoZnDPP (DPP=dianion of 5,15-diphenylporphyrin) to a platinum(0) species. The meso-meso directly linked dimeric porphyrin (5) was prepared from this monomer by silver(I)-promoted oxidative coupling and planarized to give a triply linked dizinc(II) porphyrin dimer (8). Acidic demetallation of 8 afforded the bis(free base) 9. Dimer 5 was demetallated then remetallated with nickel(II) to give the dinickel(II) analogue 10, the X-ray crystal structure of which showed a twisted molecule with ruffled, orthogonal NiDPP rings, terminated by square-planar trans-[Pt(PPh₃)₂Br] units. New compounds were fully characterized spectroscopically, and the fused diporphyrin exhibited a broad, low-energy, near-IR electronic absorption band near 1100 nm. Electrochemical measurements of this series indicate that the organometallic fragment is a strong electron donor towards the porphyrin ring. The triply linked organometallic diporphyrin has a substantially lowered first one-electron oxidation potential (-0.35 V versus the ferrocene/ferrocenium couple (Fc/Fc⁺)) and a narrow HOMO-LUMO gap of 0.96 V. Solutions prepared for NMR spectroscopy slowly decompose with degradation of the signals, which is attributed to partial oxidation to the cation radical. This paramagnetic species can be reduced in situ by hydrazine to restore the NMR spectrum to its former appearance. The combined influence of the two [Pt(PPh₃) ₂Br] electron-donating substituents is sufficient to make dimer 5 too aerobically unstable to allow further elaboration. Closing the gap: meso-meso-Directly linked and meso-meso,β-β,β-β-triply linked diporphyrins terminated by trans-[Pt(PPh₃)₂Br] units are described (see picture). The organometallic substituents raise the HOMO levels such that the dimers are very easily oxidized, and the fused Zn ₂ dimer has a voltammetric HOMO-LUMO gap of only 0.96 eV. Copyright

Full text of DOI:10.1002/asia.201300633

FULL PAPER
DOI: 10.1002/asia.201300633
The Marriage of Peripherally Metallated and Directly Linked Porphyrins:
Bromidobis(phosphine)platinum(II) as a Cation-Stabilizing Substituent on
Directly Linked and Fused Triply Linked Diporphyrins
Regan D. Hartnell,[a] Tomoki Yoneda,[b] Hirotaka Mori,[b] Atsuhiro Osuka,*[b] and
Dennis P. Arnold*[a]
Abstract: A meso-bromidoplatiniobis(-
triphenylphosphine) h1-organometallic
porphyrin monomer was prepared by
the oxidative addition of meso-bro-
moZnDPP (DPP=dianion of 5,15-di-
phenylporphyrin) to a platinum(0) spe-
cies. The meso–meso directly linked di-
meric porphyrin (5) was prepared from
this monomer by silver(I)-promoted
oxidative coupling and planarized to
give a triply linked dizinc(II) porphyrin
dimer (8). Acidic demetallation of 8 af-
forded the bis(free base) 9. Dimer 5
was demetallated then remetallated
with nickel(II) to give the dinickel(II)
analogue 10, the X-ray crystal structure
of which showed a twisted molecule
with ruffled, orthogonal NiDPP rings,
terminated by square-planar trans-[Pt-
(PPh3)2Br] units. New compounds were
tron oxidation potential (À0.35 V
versus the ferrocene/ferrocenium
couple (Fc/Fc+)) and
narrow
AHCTUNGTRENNUNG
fully characterized spectroscopically,
and the fused diporphyrin exhibited
a broad, low-energy, near-IR electronic
absorption band near 1100 nm. Electro-
chemical measurements of this series
indicate that the organometallic frag-
ment is a strong electron donor to-
wards the porphyrin ring. The triply
linked organometallic diporphyrin has
a substantially lowered first one-elec-
a
HOMO–LUMO gap of 0.96 V. Solu-
tions prepared for NMR spectroscopy
slowly decompose with degradation of
the signals, which is attributed to par-
tial oxidation to the cation radical. This
paramagnetic species can be reduced in
situ by hydrazine to restore the NMR
spectrum to its former appearance. The
combined influence of the two [Pt-
AHCTUNTGREN(GNNU PPh3)2Br] electron-donating substitu-
ents is sufficient to make dimer 5 too
aerobically unstable to allow further
elaboration.
Keywords: electrochemistry
ganometallic compounds
·
or-
·
NMR
spectroscopy · platinum · porphyri-
noids
Introduction
a metal–carbon bond between the metal bound in the cen-
tral cavity of the porphyrin macrocycle with either an alkyl
or aryl moiety of either s- or p-bonding character.[1] Por-
phyrinoid macrocycles with modified cavities, such as invert-
ed or “N-confused” porphyrins and azuli- and carbaporphyr-
ins,[2] as well as various expanded porphyrinoids,[3] have
markedly extended the realm of traditional organometallic
porphyrin chemistry. There are also several examples of por-
phyrinoid compounds covalently bound to organometallic
fragments, such as metallocenes, or with one of the porphy-
rin pyrrolic rings or bonds participating in a hn-pyrrolyl-p-
metal arrangement.[4]
There has been considerable interest in the synthesis and
properties of various types of organometallic porphyrins.
These organometallic porphyrins have been investigated as
model compounds for cytochrome P450 and coenzyme B12
and to provide potential insight into several events of bio-
logical importance. Organometallic porphyrins have also
been used for the activation of small molecules. Traditional-
ly the “organometallic” nature of the molecule arises from
[a] Dr. R. D. Hartnell, Prof. D. P. Arnold
School of Chemistry, Physics and Mechanical Engineering
Queensland University of Technology
G.P.O. Box 2434, Brisbane 4001 (Australia)
Fax : (+61)7-3138-2482
Apart from the examples of organometallic porphyrins
discussed above, there is another group of h1-organometallic
porphyrins that have been investigated recently in which the
metal fragment is directly bonded to the periphery of the
macrocycle. Recent reviews on these types of organometallic
porphyrins have been published.[5] Arnold and co-workers
first reported peripherally platinated and palladated por-
phyrins in 1998,[6] and later papers included several X-ray
crystal structures of derivatives with different centrally coor-
dinated metal ions,[7] as well as the only report of such com-
plexes containing non-racemic chiral diphosphines.[8] More-
E-mail: d.arnold@qut.edu.au
[b] T. Yoneda, H. Mori, Prof. A. Osuka
Department of Chemistry, Graduate School of Science
Kyoto University, Sakyo-ku, Kyoto, 606-8502 (Japan)
Fax : (+81)75-753-3970
E-mail: osuka@kuchem.kyoto-u.ac.jp
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201300633.
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over, platinum(II) examples with chelating N-ligands and
supramolecular multiporphyrin arrays[9] were also prepared.
Osuka and co-workers more recently took advantage of
their discoveries in selective b-arylation of porphyrins, to
prepare and investigate palladium and platinum pincer com-
plexes, in which the neutral supporting ligands were two b-
2-pyridyl moieties.[10] Other examples include the b-palladio
cyclometallated complexes reported by Matano et al.,[11] and
then immediately react with the desired haloporphyrin.[9]
The newly formed zero-valent platinum species ([Pt(PPh3)3]
or [Pt(PPh3)2A(dba)]; dba=dibenzylideneacetone) undergoes
ACHTUNGTRENNUNG
G
CHTUNGTRENNUNG
an oxidative addition reaction with the haloporphyrin to
form the organometallic meso-platinioporphyrin. The halo-
porphyrin is usually consumed within one hour, depending
on the steric and electronic properties of the monophos-
phine (PPh3 or PEt3), the haloporphyrin (whether Br or I),
and the metal coordinated within the central cavity of the
porphyrin macrocycle. The initial product that forms after
oxidative insertion is the cis isomer, which isomerizes during
heating for approximately five hours to give the more stable
trans isomer.[7] These organoplatinum porphyrins are nor-
mally very air- and moisture-stable in solution for several
weeks and indefinitely in the solid state, and may be puri-
fied by column chromatography on silica gel with no degra-
dation, as long as solvents used in the chromatographic pu-
rification are de-acidified. Although free-base porphyrins
may be used for the oxidative addition step, platinum coor-
dination to the central cavity of the porphyrin does not
occur. Other metal ions may then be coordinated within the
central cavity of the porphyrin under typical metallation
conditions, with no degradation of the organometallic frag-
ment.[7b]
N-confused porphyrin palladium(II) and platinumACTHNUTRGENUG(N II/IV) di-
nuclear complexes in which the exomacrocyclic metal ion is
coordinated by the external nitrogen atom and an ortho-
metallated meso-aryl ring.[12]
This type of transition-metal chemistry gives rise to com-
pounds, such as 1, which are key intermediates involved in
À
À
palladium-catalyzed C C or C X coupling reactions of
meso-haloporphyrins with various substrates (Scheme 1).[13]
Scheme 1. h1-meso-Palladioporphyrins as intermediates in coupling reac-
tions.
Herein, [PtACHTNUGTRENUNG(dba)2] was treated with triphenylphosphine
and 2 in degassed toluene at 908 for 6 h, resulting in excel-
lent yields (>90%) of 3. Then zinc(II) complex 4 was
formed by heating free-base organometallic porphyrin 3 in
chloroform at reflux with a saturated solution of zinc(II)
acetate in methanol (Scheme 2). This metal insertion reac-
The initial step in these couplings is the oxidative addition
of the meso-carbon–halogen bond to a zero-valent palladi-
um species, usually a bis(phosphine) moiety. Indeed, our ini-
tial isolation of a meso-palladioporphyrin resulted from
a failed catalytic reaction.[6] To expand our research in this
field, we are investigating new porphyrinic systems in which
to incorporate these organometallic fragments. Thus, we
might be able to exploit both the electronic effects and
supramolecular coordination possibilities of a robust organ-
ometallic fragment, and the remarkable optical and elec-
tronic properties of multi-porphyrin systems. As an initial
foray into this area, we have prepared several new porphy-
rin dimers of the meso–meso directly linked class terminated
uniquely by organoplatinum(II) fragments, and investigated
their chemical, optical, and redox properties. By further oxi-
dative coupling, triply linked (fused) diporphyrins were also
prepared, and their chemistry revealed the profound elec-
tronic effects of the platinum(II) substituent.
Scheme 2. Synthesis of ZnDPP[Pt
phenylporphyrin.
ACHTUNGTRNE(NUNG PPh3)2Br] 4. DPP=dianion of 5,15-di-
Results and Discussion
Synthesis and NMR Spectroscopic Characterization
tion was easily followed by TLC and UV-visible spectrosco-
py and was completed within one hour. Excess metal salt
was removed by simply washing the product with water or
by filtering the reaction mixture through a short plug of
silica gel. Recrystallization of the residue and collection of
the product gave an almost quantitative yield of zinc(II) 4.
The silver(I)-promoted dimerization of 4 was initially inves-
Organometallic h1-meso-platinio- and palladioporphyrins
are readily prepared by the oxidative addition of a zero-
valent metal precursor to a haloporphyrin.[6–9] The easiest
way to prepare those compounds that utilize monophos-
phine supporting ligands (e.g., PPh3 or PEt3) is by generat-
ing the desired zero-valent precursor in situ, so that it may
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There are several significant changes to the 1H NMR
1
spectrum upon dimerization of 4. First, the H NMR spec-
trum of 5 displayed one set of porphyrin resonances, which
indicated that the two halves of the dimer were equivalent.
The absence of any porphyrin meso-proton resonances and
the relative simplicity of the spectrum indicated that dimeri-
zation occurred exclusively at the meso positions and that
no b-coupling reactions complicated the preparation of 5.
As expected, the b-hydrogen atoms nearest the direct meso–
meso linkage underwent the biggest changes compared with
monomeric 4. In the spectrum of 5, the signals of the b-hy-
drogen atoms nearest the meso–meso link were shifted up-
field by Dd=0.72 and 0.92 ppm relative to those of 4; this
reflected the shielding effect of the second (orthogonal) por-
phyrin ring. The resonances of the distal b-hydrogen atoms
were only slightly shifted after dimerization. These trends
are now familiar in the literature.[15] The resonances for the
phenyl hydrogen atoms of the phosphine ligands were shift-
ed downfield by approximately 0.2 ppm in 5 relative to
those of 4. The 31P NMR spectrum of 5 displays a singlet
resonance at d=23.3 ppm for the four equivalent triphenyl-
phosphine groups, which is flanked by 195Pt satellites, with
Scheme 3. Synthesis of meso–meso-linked diplatinated diporphyrin 5.
tigated by using the procedure of Osuka and co-workers
(Scheme 3).[14–16] This utilizes half an equivalent of the one-
electron oxidant ([AgPF6]) to maximize the populations of
neutral and radical cationic porphyrin species because dime-
rization occurs by nucleophilic attack on the porphyrin radi-
cal cation by a neutral porphyrin. In the case of 4, these re-
action conditions were too mild and the reaction did not go
to completion, even after prolonged reaction times. The low
reactivity of the porphyrin radical cation is presumably due
to the electron-donating effects of the organometallic frag-
ment. However, when a fivefold excess of the oxidant was
used, dimerization proceeded smoothly and the starting ma-
terial was consumed within one hour.
À
a Pt P coupling constant of 2990 Hz; a typical value for
trans phosphine groups in PtII organometallics.[7]
Having obtained the directly linked species in high yield
and purity, we attempted the oxidative double-ring closure/
planarization of 5 by using the methodology of Osuka and
Tsuda (Scheme 4).[17] Substrate 5 was heated at reflux with
The 1H NMR spectrum of the crude product indicated
a mixture of several products. The absence of porphyrin
meso-proton signals showed that dimerization did indeed go
to completion and the other compounds were various meso–
meso-linked porphyrin dimers, as well as the desired dimer
5. The presence of an NH resonance at dꢀÀ3 ppm showed
that one of the contaminants was the free-base analogue 6.
Separation of 5 and 6 was difficult by TLC, but the chroma-
tograms did show the presence of a very polar spot, which
was postulated to be the Br/PF6 singly or doubly metathe-
sized products, such as 7, owing to bromide abstraction by
excess silver(I). Instead of separating the desired dimer
from various byproducts, a better method was to reverse the
metathesis to re-form the desired dimer. This was readily
achieved by heating the crude mixture with excess LiBr.
Then all free-base species were re-metallated by the addi-
tion of excess zinc acetate as a saturated solution in metha-
Scheme 4. Synthesis of dizinc triply linked diporphyrin 8 and free-base 9.
DDQ=2,3-dichloro-5,6-dicyano-1,4-benzoquinone.
DDQ and scandiumACTHNUTRGNEUNG(III) triflate in toluene for one hour.
During this period, the reaction mixture changed from an
olive–green color to bright blue–green, which indicated that
a major change had occurred. After isolation and chroma-
tography, the desired meso–meso,b–b,b–b-triply linked
1
nol to the same reaction mixture at reflux. H NMR spec-
troscopy analysis showed that indeed our ideas were correct
because within one hour only the desired dizinc meso–meso
linked dibromido dimer 5 was present. The reaction mixture
was filtered through a short plug of silica gel to remove
excess salts. After recrystallization, compound 5 was collect-
ed as dark olive–green crystals in 92% yield.
1
dimer 8 was obtained in 68% yield. The H NMR spectrum
of 8 was relatively simple owing to the high symmetry of the
molecule, but it was very clear that the desired planarization
occurred. The distal b protons of 8 appeared as a pair of
3
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broad doublets (J=4.4 Hz) at d=8.72 and 7.26 ppm. These
resonances have been shifted significantly upfield by Dd=
1.22 and 1.24 ppm, respectively, relative to 5, which demon-
strates the large effects of planarization and the reduced ar-
omatic ring current in the dimer.[16] The b protons next to
the inter-ring bonds were represented by a broad singlet at
d=7.19 ppm. The resonances that arose from the phosphine
phenyl groups were shifted slightly compared with 5, espe-
cially the m,p-H resonances, which moved downfield by
0.3 ppm. Complete assignment of all proton resonances was
facilitated by DQF-COSY and proton NOESY experiments.
The 31P NMR spectrum of 8 has a singlet at d=22.7 ppm
NMR sample of 8 did not cause any improvement to the de-
graded spectrum. Contemplation of these facts led us to be-
lieve that the porphyrin dimer was partially oxidized to the
radical cation, producing a paramagnetic species and leading
to the broadening of the NMR signals. Confirmation was
provided by addition of hydrazine to the NMR sample to
try to reduce the cation radical back to the neutral species.
The signals of 8 were immediately restored, and the spec-
trum was then identical to that of the freshly prepared
sample (Figure 1, bottom). Removal of hydrazine under
high vacuum and preparation of a new sample for NMR
spectroscopy revealed that the sample initially in the neutral
state was slowly oxidized to the cation radical. Addition of
hydrazine to this sample fully reduced the cation radical and
restored normal NMR sensitivity.
À
with a P Pt coupling constant of 3016 Hz.
If the NMR sample was left as a solution overnight, the
signal of the porphyrin dimer 8 degraded and no resonances
from the b-H or phenyl groups could be detected. The only
visible resonances were those of the phosphine groups,
which were very broad (Figure 1, top). Isolation and recrys-
Similar deterioration of the NMR signal was seen in
31P NMR spectroscopy, which too was fully restored after
the addition of hydrazine. To rule out aggregation phenom-
ena as the cause of the problematic NMR spectroscopy, the
À
central metal ions were removed (without cleaving the C Pt
bonds) from a small sample of 8 by treatment with 2m HCl
in methanol to produce free-base 9. Addition of acid to 8
immediately gave a bright purple solution. Neutralization of
this solution with excess triethylamine caused an immediate
change, and the solution reverted to an intense green/blue
color. The NMR spectrum of free-base 9 was similar to that
of metallated 8; this indicated that only demetallation of the
macrocycle occurred, without cleavage of the platinum frag-
ments. The signal arising from the free-base protons could
not be definitively identified, and was possibly obscured by
the broad H2O signal near d=1.5 ppm; this is where this
NH signal is found for similar compounds.[16] Similarly to
the NMR behavior of 8, the spectrum of 9 also dramatically
improved after the addition of hydrazine. This suggests that
a small population of both 8 and 9 prefers to exist as the
radical cation in solution and is easily reduced to the neutral
species by treatment with hydrazine. The ESI mass spectrum
of 8 (Figure 2) displayed a strong cluster at m/z 2643.26,
which corresponded very well with the predicted isotope
pattern (calculated for [M+H]+: m/z 2643.27) for the as-
signed structure of 8.
X-ray Crystal Structure Determination
Unfortunately the sensitivity of dimers 8 and 9 to light and
air precluded us from obtaining single crystals suitable for
X-ray analysis. Because nickel(II) porphyrins are more diffi-
cult to oxidize than the zinc(II) complexes, the directly
linked dizinc dimer 5 was demetallated to 6 then remetallat-
ed with nickel(II) bis(acetylacetonate) to yield dimer 10
(Scheme 5). Single crystals of this analogue were grown
from a solution in dichloromethane/pentane, and the molec-
ular structure is shown in Figure 3. This is the first crystal
structure of a meso–meso-directly linked nickel(II) dipor-
phyrin, although other similar compounds, namely, copper-
Figure 1. Downfield region of the 1H NMR spectrum of 8 recorded in
CDCl3 before (top) and after (bottom) the addition of 80% hydrazine
(20 mL).
tallization of the sample, followed by preparation of a new
solution for NMR spectroscopy, restored the spectrum to
that previously seen. Similar behavior is known for zinc por-
phyrins that suffer from aggregation problems, although
such spectra are usually improved by the addition of pyri-
dine to act as an axial ligand and reduce intermolecular ag-
gregation artifacts. The addition of [D5]pyridine to the
AHCTUNGTRENNUNG
(II)[18] and free-base diporphyrins,[19] zinc(II) triporphyr-
ins,[20] and more complex arrays[21] have been reported.
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Figure 3. The X-ray crystal structure of 10: a) the coordination geometry
about the PtII centers, the orthogonality of the porphyrin rings, the ruf-
fling of the NiII porphyrin units, and the disposition of two phenyl groups
of the triphenylphosphine ligands above and below the planes of the por-
Figure 2. Experimental (top) and calculated isotopic distribution pattern
(bottom) of [M+H]+ for 8.
phyrin rings; and b) the orientations of the {PtACHTNURTGNE(UNG PPh3)2Br} substituents.
Hydrogen atoms and solvent molecules omitted for clarity.
square planar, with a very minor tetrahedral distortion. In
our previous reports on the crystal structures of meso-metal-
loporphyrins with phenylphosphine ligands, we noted that
one of the three rings of each phosphine lay over the macro-
cycle,[7] and this is emphasized in Figure 3a.
So far, we have been unable to characterize the triply
linked systems crystallographically, but the NMR and other
spectroscopic data confirm the integrity of the terminal [Pt-
AHCTUNTGREN(NGNU PPh3)2Br] units, and the fusion of the porphyrins.
Electronic Absorption Spectra
The electronic absorption spectra of dimeric 5 and 8 are
compared in Figure 4. Complex 4 displays a normal elec-
tronic spectrum for a zinc porphyrin: a sharp Soret band at
l=430 nm and weak Q bands at l=555 and 599 nm. Typical
Scheme 5. Synthesis of dinickel meso–meso-linked diplatinated dipor-
phyrin 10. acac=acetylacetone.
The two macrocycles in the molecule of 10 are strongly
ruffled, which is often found for meso-tetrasubstituted nick-
el(II) porphyrins,[22] including other dimers with 5,15- or
5,10-diaryl substituents.[13g,23] Typically for a directly linked
diporphyrin, the macrocycles are almost orthogonal. These
two demands result in a curved, twisted overall geometry;
the two views shown in Figure 3a and b make this clear.
The single bond between the porphyrins is 1.492(15) ꢁ long,
which is the same as those recorded previously for structures
of analogous di- and triporphyrins. The coordination planes
of the platinum(II) units are also near-orthogonal to their
attached macrocycles, but the two meso-C-Pt-Br vectors are
À
not parallel. The Pt C bond lengths are equal, within exper-
imental error, at 2.026(14) and 1.987(14) ꢁ. The coordina-
tion geometries at the platinum(II) centers are almost
Figure 4. The electronic absorption spectra of meso–meso linked
(dashed) and triply linked 8 (solid).
5
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Atsuhiro Osuka, Dennis P. Arnold et al.
changes are seen after dimerization through a meso–meso
linkage. The most dramatic of these is the splitting of the
Soret band in 5, with peaks at l=437 and 470 nm of similar
intensity. Understandably there is a reduction in the extinc-
tion coefficient of these two peaks, compared with mono-
meric 4. The characteristic appearance of the Soret bands
indicates that the planes of the two porphyrins are essential-
ly perpendicular to each other, that is, a D2 twisted confor-
mation.[14–16] Thus, there is a strong excited-state interpor-
phyrin interaction, but no conjugation in the ground state.
The Q bands of 5 are also redshifted by 20 nm. After oxida-
tive double ring-closure, the absorbance spectrum of 8 is
strongly perturbed and indicative of a totally conjugated bis-
porphyrin system.[16,17] There is now a large splitting of the
bands (labeled I and II), formerly attributable to the Soret
bands in 4 and 5, and the lowest energy band (III) extends
well into the near-IR region beyond l=1100 nm. In addi-
tion, the {PtL2Br} substituents induce a further redshift be-
cause the lowest-energy band for the Ni2 analogue with aryl
groups in the terminal 15,15’-positions has a maximum at
l=933 nm.[16] Bands I and II have been assigned to Soret-
like transitions along the two axes of the molecule (short
and long, respectively). The high intensity of band III, com-
pared with simple monomeric porphyrins, arises from the
loss of degeneracy in the unoccupied levels, and the redshift
to the strong splitting of the monomer occupied and unoccu-
pied frontier orbitals, which narrows the HOMO–LUMO
gap of the dimer. The lowering of the energy of this transi-
tion by the organometallic substituents is a result of their
electron-donating tendency, apparently raising the energy of
the HOMO further. This is consistent with the voltammetry
results described below.
The absorption spectra of zinc(II) 8 and free-base 9 did
not show any substantial changes after the addition of hy-
drazine. This presumably indicates that there is only a small
population of the radical cation in solution and it is not de-
tectable by either UV-visible or near-IR spectroscopy. In the
case of 8, there was a slight redshift of all peaks after the ad-
dition of hydrazine, which may be interpreted as a manifesta-
tion of the axial coordination of hydrazine to the zinc(II)
centers.
The emission properties of this series have not been inves-
tigated because monomeric free-base and zinc(II) porphyr-
ins peripherally metallated with [PtACHTNUTRGNE(UNG PPh3)2Br] have fluores-
cence quantum yields about 1000-fold less than their unsub-
stituted analogues.[24] We expect similar measurements for
the present series would also be unrewarding, although un-
derstanding the effects of these heavy-metal substituents on
the emission properties of porphyrins is a future target.
ing 0.5m Bu4NPF6 as the supporting electrolyte, with a stan-
dard three-electrode cell under an atmosphere of nitrogen.
Electrochemical measurements of ZnDPP were carried out
on a saturated solution, owing to poor solubility of ZnDPP
in the electrolyte-rich solvent, which gave rise to relatively
high background current. Interestingly for platinum com-
plexes 4, 5, and 8, the presence of the electrolyte in the sol-
vent seemed to improve the solubility of the substrates, so
the measurements were performed on solutions with a por-
phyrin concentration of about 10À3 m. Accurate measure-
ments of the second reductive waves could not be made on
4 and 5, and the reductions of ZnDPP were irreversible and
poorly characterized. The derived data are shown in Table 1.
Table 1. Cyclic voltammetry data for reference monomer ZnDPP, mono-
mer platinum complex 4, and dimers 5 and 8 in Bu4NPF6/CH2Cl2 versus
the ferrocene/ferrocenium couple (Fc/Fc+) at 0.00 V.
E0
[V]
E0
[V]
E0
[V]
E0
[V]
DE(ox)
DEACHTUNGTRENNUNG(gap)
red2
red1
ox1
ox2
[mV][a]
[V][b]
ZnDPP
–
–
–
–
+0.30
+0.20
+0.15
-0.35
+0.75
+0.55
+0.26
+0.07
–
–
110
420
–
4
5
8
À1.73
À1.94
À1.31
1.93
2.09
0.96
À1.6
[a] The voltammetric gap between the first and second one-electron (per
porphyrin unit) oxidations. [b] The electrochemical HOMO–LUMO gap
(DEACHTGNUTRENNUNG
The platinum-containing species showed reproducible and
reversible first and second oxidation waves in all cases. The
first oxidation potentials of ZnDPP and 4, +0.30 and
+0.20 V (vs. Fc/Fc+), respectively, clearly demonstrate the
cation-stabilizing effect of the platinum(II) fragment. The
cathodic shift of 100 mV supports the premise that the
meso-bonded {PtACTHUNTRGNE(UNG PPh3)2Br} fragment is an electron donor.
However, this cathodic shift is somewhat smaller than that
reported for similar free-base and nickel(II) meso-platinio-
porphyrins, which exhibited a larger cathodic shift of ap-
proximately 300 mV.[7b] A second reversible oxidation of 4
was seen at +0.55 V (DEox =350 mV). The first reduction
potential of 4 is at À1.73 V, which translates to an electro-
chemical HOMO–LUMO gap of 1.93 V. Singly linked dimer
5 displayed two closely spaced one-electron redox waves,
typical for other meso–meso linked dimers,[16] owing to the
removal of one electron from each of the orthogonal por-
phyrin macrocycles. The first and second oxidation poten-
tials for 5 are +0.15 and +0.26 V (DE=ca. 110 mV), re-
spectively, which compare well with that of the meso–meso
analogue that lacks the organometallic fragments, which dis-
plays splitting of the first two oxidation potentials of
130 mV.[16] Unfortunately, direct comparisons of actual half-
wave potentials are not possible owing to different solvents
and electrolyte concentrations used for the electrochemical
measurements of our compounds and those in the literature,
but the trends are consistent. Arnold and co-workers dis-
cussed the frequent over-interpretation of such “mixed-va-
lence” splittings in diporphyrins as being directly indicative
of the degree of inter-porphyrin conjugation.[25] Because
Electrochemical Investigations
Initially we wished to investigate the effect of the organo-
metallic fragment on the redox properties of the porphyrin
ring. Cyclic voltammetry measurements were carried out on
ZnDPP (as a reference compound) and platinum complexes
4, 5, and 8. Experiments were carried out in CH2Cl2 contain-
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Atsuhiro Osuka, Dennis P. Arnold et al.
values of about 100 mV are also seen in indisputably strong-
ly conjugated dimers, such as bis(porphyrinyl)butadiynes,
such conclusions are invalid when comparing different link-
age types and planar conjugated dimers with orthogonal
dimers that are not conjugated.
IR band near l=1100 nm, and is similar to that reported by
Andersonꢂs group for their quinoidal triply linked porphyrin
dimer, which had a HOMO–LUMO gap of 1.00 V.[27] The
fused dizinc diporphyrin studied by Diederich and co-work-
ers showed a HOMO–LUMO gap of 1.10 V in CH2Cl2,[26]
whereas tetraprotonated b–b-directly linked N-confused
porphyrin dimers exhibited electrochemical HOMO–
LUMO gaps of ꢁ1.11 V.[28]
Comparison of the first oxidation potentials between 4
and 5, +0.20 and +0.15 V respectively, confirms that there
is only slight elevation of the HOMO after dimerization.
The first reduction potential of 5 occurs at À1.94 V, with
a voltammetric HOMO–LUMO gap of 2.09 V, which is ac-
tually larger than that of 4, demonstrating again the lack of
electronic interaction between the rings in the ground state.
Planarization of 5 through oxidative double ring closure re-
sults in several interesting electrochemical changes. The full
cyclic voltammogram of 8, including first and second reduc-
tion and oxidation potentials, was measured and was suffi-
ciently well defined to reveal some interesting electrochemi-
cal properties of this compound (Figure 5).
Conclusion
Monomeric zinc(II) meso-h1-organoplatinum porphyrins
were readily dimerized by silver(I) oxidative coupling to
give the meso–meso singly linked dimer 5 in high yields. Ox-
idative double ring closure was also facile and provided easy
access to triply linked porphyrin dimers with organometallic
termini. Electrochemical measurements of the former dimer
demonstrated that the organometallic fragment was a good
electron donor. This trend was maintained after fusion and
planarization to generate a very easily oxidizable triply
linked bis-zinc(II) dimer 8, with a narrow electrochemical
HOMO–LUMO gap of about 0.96 V, and its lowest-energy
electronic absorption band near l=1100 nm. Although the
triply linked dimers proved to be too sensitive for the
growth of high-quality single crystals, the crystal structure of
the singly linked bis-nickel(II) analogue 10 confirmed the
attachment of terminal trans-[PtACHTUNTRGNEUNG(PPh3)2Br] fragments. Incor-
poration of these organometallic porphyrins into supra-
molecular arrangements and their attachment to surfaces
and electrodes may be rewarding in the future.
Figure 5. Cyclic voltammogram (100 mVsÀ1) for dimer 8 in Bu4NPF6/
CH2Cl2, versus Fc/Fc+ at 0.00 V.
The first of these is the dramatic lowering of the first oxi-
dation potential for 8 (E0ox1 =À0.35 V) by approximately
500 mV when compared with 4 and 5. The second reversible
oxidation occurs at +0.07 V, with DEox =420 mV. This is
very similar to that found for the Ni2 dimer reported by
Osuka and co-workers (410 mV CHCl3).[16] Diederich and
co-workers reported voltammetric data for a series of direct-
ly linked and triply linked dizinc diporphyrins with 15,15’-
aryl substituents that were subsequently conjugated to ful-
lerenes.[26] In their case, however, the “mixed-valence” oxi-
dative splitting was only 290 mV, which was very similar to
that for the dizinc diporphyrin reported by Osuka and co-
workers (250 mV in CHCl3).[16] The significance of the con-
siderably smaller gap for zinc(II) is presently unclear, and
spectroelectrochemical studies are required to determine
this.
The first and second reduction potentials (À1.31 and
À1.57 V, respectively, DEred =260 mV) were also reversible,
although the waves were near the solvent limit under our
conditions. From these half-wave potentials, planarization to
form 8 results in substantial raising of the HOMO and low-
ering of the LUMO, to give a HOMO–LUMO gap of only
0.96 V, which is less than half of that for dimer 5. This
HOMO–LUMO gap is compatible with the redshifted near-
Experimental Section
General Procedures
Syntheses that involved zero-valent metal precursors were carried out in
an atmosphere of high-purity argon by using conventional Schlenk tech-
niques. Porphyrin starting materials, 5,15-diphenylporphyrin[29] and [Pt-
AHCTUNGTRENNUNG
(dba)2],[30] were prepared by methods reported in the literature. All other
reagents and ligands were used as received from Sigma–Aldrich. Toluene
was AR grade, stored over sodium wire, and degassed by purging with
argon at about 908C. All other solvents were AR grade, and dichlorome-
thane and chloroform were stored over anhydrous sodium carbonate.
Analytical TLC was performed by using Merck silica gel 60 F254 plates
and column chromatography was performed by using Merck silica gel
(230–400 mesh; Brisbane) and Wakogel C-300 or C-400 (Kyoto). NMR
spectra were recorded in Brisbane on Bruker Avance 400 MHz or Varian
Unity 300 MHz instruments in CDCl3, with CHCl3 as the internal refer-
1
ence at d=7.26 ppm for H spectra, and external 85% H3PO4 as the ref-
erence for proton-decoupled 31P spectra. 1H NMR spectra were recorded
in Kyoto on a JEOL ECA-600 spectrometer (operating at 600.17 MHz
for 1H and 242.95 MHz for 31P). UV/Vis spectra were recorded on
a Cary 3 spectrometer (Brisbane) and a Shimadzu UV-3600PC spectrom-
eter (Kyoto) in dichloromethane. Near-IR measurements were carried
out on a Nicolet Nexus FTIR instrument equipped with a quartz halogen
lamp, quartz beam splitter, and an InGaAs detector operating at room
temperature.
X-ray data for compound 10 were collected at À1808C with a Rigaku
RAXIS-RAPID diffractometer by using graphite monochromated CuKa
radiation (l=1.54187 ꢁ). The structures were solved by direct methods
7
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Atsuhiro Osuka, Dennis P. Arnold et al.
(SHELXS-97).[31] ESI mass spectra were recorded on a Bruker BioApex
47e FTMS instrument fitted with an Analytica electrospray source. The
samples were dissolved in dichloromethane and diluted with either 1:1 di-
chloromethane/methanol or methanol and solutions were introduced into
the source by direct infusion (syringe pump) at 60 mLhÀ1, with a capillary
voltage of 80 V. The instrument was calibrated by using internal NaI clus-
ters. Positive ion FAB mass spectra were recorded on a Kratos Concept
instrument at the Central Science Laboratory, University of Tasmania.
Samples were dissolved in dichloromethane and dispersed in a 4-nitro-
benzyl alcohol matrix. In the data below, masses given are for the stron-
gest observed peak in the molecular ion cluster. In all compounds, this
m/z value agreed with the predicted molecular mass, although in most
cases it represented a mixture of [M] and [M+1] peaks. The accurate-
mass ESI-TOF mass spectrum of 10 was recorded on a Bruker microTOF
model in positive mode in acetonitrile. Elemental analyses were carried
out by the Microanalytical Service, The University of Queensland. For
electrochemical measurements, a standard three-electrode configuration
was used, with a Pt button working electrode and a Pt wire counter elec-
trode. The reference electrode comprised a silver wire coated with silver
chloride separated from the working solution by two fritted jackets. The
internal chamber containing the wire was filled with 0.05m Bu4NCl/0.45m
Bu4NPF6, and the external chamber contacting the working solution was
filled with 0.5m Bu4PF6, all solutions were prepared in CH2Cl2. The work-
ing solution was pre-purged and subsequently protected with ultra-high
purity N2. The voltammetry measurements were carried out in CH2Cl2
(freshly distilled from CaH2 under argon) containing 0.5m Bu4NPF6,
using an EG&G Princeton Applied Research Model 272A Potentiostat
linked to a PC interface and controlled by PowerSuite software. Elec-
trode potentials are reported by using ferrocene as an internal standard
(E0 =0.00 V).
reaction vessel was protected from light and the mixture was stirred for
1 h. LiBr (100 mg, 1.15 mmol) was added to the reaction mixture and the
solution was heated at reflux for 30 min.
A solution of ZnACHTUNGTRENNUNG(OAc)2
(100 mg, 0.55 mmol) in methanol was added and the solution further
heated at reflux for 1 h. The reaction mixture was cooled to room tem-
perature and the solvent removed under reduced pressure. The dark
green residue was purified by column chromatography (66% CHCl3/
hexane) and the major band collected. The solution was evaporated to
dryness and the residue recrystallized from CHCl3/pentane to give dimer
5 (91 mg, 92%). 1H NMR: d=6.40–6.60 (m, 36H; PPh3), 7.30–7.40 (m,
12H; PPh3), 7.55–7.65 (m, 12H; m,p-H on 10,20-phenyl), 8.05–8.15 (m,
8H; o-H on 10,20-phenyl), 7.98, 8.47, 8.50, 9.30 ppm (each d, 3J=4.7 Hz,
1
4H; b-H); 31P NMR: d=23.5 ppm (s, J
(P,Pt)=2990 Hz); UV/Vis: lmax
G
103)=437 (210), 470 (221), 571 (42.0), 610 nm (17.0 molÀ1 m3 cmÀ1); ele-
mental analysis calcd (%) for C136H96Br2N8P4Pt2Zn2: C 61.71, H 3.66, N
4.23; found: C 61.68, H 3.52, N 4.16.
meso–meso,b–b,b–b-Bis{trans-bromido[10,20-
diphenylporphyrinatozinc(II)-5-yl]bis(triphenylphosphine)platinum(II)} 8
Directly meso–meso-linked dimer 5 (50 mg, 0.019 mmol) was dissolved in
dry toluene (25 mL) under an argon atmosphere. ScACTHNUGTRENUNG(OTf)3 (47 mg,
0.095 mmol) and DDQ (22 mg, 0.095 mmol) were added and the mixture
was heated at reflux for 1 h. The mixture was cooled to room tempera-
ture and the solvent removed under reduced pressure. The residue was
dissolved in minimum ethyl acetate and loaded onto a short silica-gel
column and eluted with ethyl acetate. The blue/green fraction was col-
lected, the solvent removed, and the residue recrystallized from CHCl3/
cyclohexane. Product 5 was collected as a very dark blue/green solid
(34 mg, 68%). 1H NMR: d=6.80–6.90 (m, 36H; PPh3), 7.19 (s, 4H;
2,2’,8,8’-b-H), 7.26 (d, 3J=4.4 Hz, 4H; 12,12’,18,18’-b-H), 7.30–7.50 (m,
24H; PPh3) 7.50–7.60 (m, 12H; m,p-H on 10,20-phenyl), 7.70–7.80 (m,
8H; o-H on 10,20-phenyl), 8.72 ppm (d, 3J=4.4 Hz, 4H; 13,13’,17,17’-b-
trans-Bromido[10,20-diphenylporphyrinato-5-
yl]bis(triphenylphosphine)platinum(II) 3
H); 31P NMR: d=22.7 ppm (s, 1J (e/103)=
ACHTNUTRGENN(UG P,Pt)=3016 Hz); UV/Vis: lmaxACHTUNGTRENNUNG
Toluene (200 mL) was added to a Schlenk flask and degassed by bubbling
426 (59.7), 489 (40.5), 608 (88.5), 670 sh (25.2), 936 sh (11.9), 1066 nm
(33.4 molÀ1 m3 cmÀ1); ESI MS: m/z calcd for C136H93Br2N8P4Pt2Zn2(+1):
2643.27; found: 2643.26; elemental analysis calcd (%) for
C136H92Br2N8P4Pt2Zn2·2CH2Cl2: C 58.93, H 3.44, N 3.98; found: C 58.79,
H 3.28, N 3.91.
argon through the solution at 908C. Bromoporphyrin
2 (200 mg,
0.37 mmol) was added and stirred for 5 min. [Pt(dba)2] (290 mg,
AHCTUNGTRENNUNG
0.44 mmol) and triphenylphosphine (346 mg, 1.32 mmol) were added and
the solution was stirred at 908C. TLC analysis of the reaction mixture
(50% CHCl3/49% hexane/1% Et3N) clearly showed disappearance of
the starting material after about 30 min and that the initially formed cis
isomer was slowly being converted into the trans isomer. After about 6 h,
isomerization was considered complete and the reaction mixture was
cooled to room temperature and the solvent removed under reduced
pressure. The residue (now air stable) was purified on a silica gel column
eluting with 50% CHCl3/49% hexane/1% Et3N and the major purple
fraction was collected and the solvent removed in vacuo. The residue was
recrystallized from CHCl3/pentane to give 3 as dark purple crystals
(431 mg, 94%). The 1H and 31P NMR spectroscopic data for this com-
pound agreed with those of an authentic sample prepared previously
meso–meso,b–b,b–b-Bis{trans-bromido[10,20-diphenylporphyrinato-5-
yl]bis(triphenylphosphine)platinum(II)} 9
HCl (500 mL of a 2m solution in methanol) was added to a stirred solu-
tion of metallated 8 (3 mg, 0.0014 mmol) in CHCl3. The solution immedi-
ately turned purple and was neutralized with Et3N (1 mL), after which it
changed back to a deep blue/green color. The CHCl3 layer was washed
twice with water and dried over anhydrous MgSO4. The solvent was re-
moved under reduced pressure and dried thoroughly under high vacuum
at 508C for 2 h. Free-base 9 was formed quantitatively and was pure ac-
cording to 1H and 31P NMR spectroscopy. 1H NMR: d=6.80–6.90 (m,
36H; PPh3), 7.0 (s, 4H; 2,2’,8,8’-b-H), 7.19 (d, 3J=4.0 Hz, 4H;
12,12’,18,18’-b-H), 7.40–7.50 (m, 24H; PPh3) 7.50–7.60 (m, 12H; m,p-H
on 10,20-phenyl), 7.60–7.70 (m, 8H; o-H on 10,20-phenyl), 8.74 ppm (d,
with [PtACHTUNGTRENNUNG
(PPh3)3].[7]
trans-Bromo[10,20-diphenylporphyrinatozinc(II)-5-
yl]bis(triphenylphosphine)platinum(II) 4
3J=4.0 Hz, 4H; 13,13’,17,17’-b-H); 31P NMR: d=23.3 ppm (s, 1J
ACHTUNGTRENNUNG(P,Pt)=
Free-base 3 (200 mg, 0.16 mmol) was dissolved in CHCl3 (100 mL) and
2996 Hz); UV/Vis: lmax (rel. int.) 422 (4.9), 488 (3.5), 604 (6.0), 934 sh
Zn
G
(1.0), 1055 nm (2.1).
methanol. The solution was heated at reflux for 1 h and cooled to room
temperature. This solution was concentrated to approximately 50 mL and
applied to a short silica-gel chromatography column. The column was
eluted with CHCl3 and the major purple/green band collected. The sol-
vent was removed under reduced pressure and the residue recrystallized
from CHCl3/pentane to give 4 as metallic purple crystals (208 mg, 97%).
The 1H and 31P NMR spectroscopic data for this compound agreed with
those of an authentic sample.[7b]
meso–meso-Bis{trans-bromido[10,20-diphenylporphyrinatonickel(II)-5-
yl]bis(triphenylphosphine)platinum(II)} 10
Directly meso–meso-linked dimer 5 (10 mg, 3.8 mmol) was dissolved in
CHCl3 (5 mL) and aqueous HCl (100 mL of a 3m solution) was added to
the reaction solution and stirred for 2.5 h at room temperature. The reac-
tion mixture was washed with aqueous Na2CO3 and the products were
extracted with CH2Cl2. The organic extract was dried over anhydrous
Na2SO4, and the solvent was evaporated under reduced pressure. The res-
idue was dissolved in toluene (5 mL) and nickel acetylacetonate (29 mg,
30 equiv) was added and the solution was heated at reflux for 3 h. The re-
action mixture was cooled to room temperature and the solvent removed
under reduced pressure. The residue was purified by column chromatog-
meso,meso-Bis{trans-bromido[10,20-diphenylporphyrinatozinc(II)-5-
yl]bis(triphenylphosphine)platinum(II)} 5
ACHTUNGTRENNUNG[AgPF6] (95 mg, 0.375 mmol) was added as a solution in acetonitrile to
a solution of monomer 4 (100 mg, 0.075 mmol) in CHCl3 (50 mL). The
8
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Atsuhiro Osuka, Dennis P. Arnold et al.
raphy (50% CH2Cl2/hexane) and the major band collected. The solution
was evaporated to dryness and the residue recrystallized from CH2Cl2/
hexane to give complex 10 (7.0 mg, 70%). 1H NMR: d=6.6–6.8 (m,
36H; PPh3), 7.32 (m, 24H; PPh3), 7.45–7.55 (m, 12H; m,p-H on 10,20-
phenyl), 7.84 (m, 8H; o-H on 10,20-phenyl), 7.93, 8.17, 8.27, 9.44 ppm
D. L. Officer, P. D. W. Boyd, Z. Zhao, P. A. Cocks, K. C. Gordon,
Chem. Commun. 1999, 637–638; d) O. Shoji, S. Okada, A. Satake,
Y. Kobuke, J. Am. Chem. Soc. 2005, 127, 2201–2210; e) H. J. H.
Wang, L. Jaquinod, D. J. Nurco, M. G. H. Vicente, K. M. Smith,
Chem. Commun. 2001, 2646–2647; f) K. K. Dailey, T. B. Rauchfuss,
Polyhedron 1997, 16, 3129–3138; g) K. K. Dailey, G. P. A. Yap, A. L.
Rheingold, T. B. Rauchfuss, Angew. Chem. 1996, 108, 1985–1987;
Angew. Chem. Int. Ed. Engl. 1996, 35, 1833–1835; h) S. Yamaguchi,
H. Shinokubo, A. Osuka, J. Am. Chem. Soc. 2010, 132, 9992–9993.
[5] a) S. Richeter, C. Jeandon, J.-P. Gisselbrecht, R. Ruppert in Hand-
book of Porphyrin Science, Vol. 3 (Eds.: K. M. Kadish, K. M. Smith,
R. Guilard), World Scientific Publishing, Singapore, 2010, pp. 429–
483; b) F. Atefi, D. P. Arnold, J. Porphyrins Phthalocyanines 2008,
12, 801–831; c) B. M. J. M. Suijkerbuijk, R. J. M. Klein Gebbink,
Angew. Chem. 2008, 120, 7506–7532; Angew. Chem. Int. Ed. 2008,
47, 7396–7421.
(each d, 3J=4.7 Hz, 4H; b-H); 31P NMR: d=22.78 ppm (s, 1J
ACTHNUTRGNEU(GN P,Pt)=
2927 Hz); UV/Vis: lmaxACTHNUTRGNEUNG
(e/103)=436 (153), 464 (241), 552 nm
(51.4 molÀ1 m3 cmÀ1); ESI-HRMS: m/z calcd for C136H96N8P4Br2Ni2Pt2
[M]+: 2633.3058; found 2633.3045.
Crystal Data for 10
¯
C136H96Br2N8Ni2P4Pt2·2.5
N
(no. 2); a=13.8776(3), b=19.9966(4), c=24.1466(4) ꢁ; a=101.1999(10),
b=93.5439(10), g=107.1007(11)8; V=6231.8(2) ꢁ3; Z=2; 1calcd
1.500 gcmÀ3
T=93 K; R1 =0.1306 [I>2s(I)]; W =0.3897 (all data);
GOF=1.025. Crystals were grown from CH2Cl2/n-pentane.
=
;
R
[6] D. P. Arnold, Y. Sakata, K.-i. Sugiura, E. I. Worthington, Chem.
Commun. 1998, 2331–2332.
CCDC 936169 contains the supplementary crystallographic data for the
complex 10. These data can be obtained free of charge from the Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif.
[7] a) D. P. Arnold, P. C. Healy, M. J. Hodgson, M. L. Williams, J. Orga-
nomet. Chem. 2000, 607, 41–50; b) M. J. Hodgson, P. C. Healy, M. L.
Williams, D. P. Arnold, J. Chem. Soc. Dalton Trans. 2002, 4497–
4504; c) R. D. Hartnell, A. J. Edwards, D. P. Arnold, J. Porphyrins
Phthalocyanines 2002, 6, 695–707.
[8] M. J. Hodgson, V. V. Borovkov, Y. Inoue, D. P. Arnold, J. Organo-
met. Chem. 2006, 691, 2162–2170.
Acknowledgements
[9] a) R. D. Hartnell, D. P. Arnold, Eur. J. Inorg. Chem. 2004, 1262–
1269; b) R. D. Hartnell, D. P. Arnold, Organometallics 2004, 23,
391–399.
R.D.H. thanks the Faculty of Science, Queensland University of Technol-
ogy, for a Post-Graduate Scholarship, and Dr. Llew Rintoul for the near-
IR measurements. T.Y. and H.M. thank the JSPS for Fellowships for
Young Scientists.
[10] a) S. Anabuki, H. Shinokubo, N. Aratani, A. Osuka, Angew. Chem.
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[2] For a selection of recent references to N-confused (inverted), carba-
porphyrins, and azuliporphyrins with organometallic bonds, see:
´
a) M. Pawlicki, L. Latos-Graz˙ynski in Handbook of Porphyrin Sci-
ence, Vol. 2 (Eds.: K. M. Kadish, K. M. Smith, R. Guilard), World
Scientific Publishing, Singapore, 2010, pp. 103–192; b) N. Grzegor-
´
zek, L. Latos-Graz˙ynski, L. Szterenberg, Org. Biomol. Chem. 2012,
[11] a) Y. Matano, K. Matsumoto, H. Hayashi, Y. Nakao, T. Kumpulai-
nen, V. Chukharev, N. V. Tkachenko, H. Lemmetyinen, S. Shimizu,
N. Kobayashi, D. Sakamaki, A. Ito, K. Tanaka, H. Imahori, J. Am.
Chem. Soc. 2012, 134, 1825–1839; b) Y. Matano, K. Matsumoto, Y.
Nakao, H. Uno, S. Sakaki, H. Imahori, J. Am. Chem. Soc. 2008, 130,
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ÝÝ These are not the final page numbers!

FULL PAPER
Closing the gap: meso–meso-Directly
linked and meso–meso,b–b,b–b-triply
linked diporphyrins terminated by
Porphyrinoids
Regan D. Hartnell, Tomoki Yoneda,
Hirotaka Mori, Atsuhiro Osuka,*
trans-[PtACHTUNGTRENNUNG(PPh3)2Br] units are described
(see picture). The organometallic sub-
stituents raise the HOMO levels such
that the dimers are very easily oxi-
dized, and the fused Zn2 dimer has
a voltammetric HOMO–LUMO gap of
only 0.96 eV.
Dennis P. Arnold*
&&&& — &&&&
The Marriage of Peripherally Metal-
lated and Directly Linked Porphyrins:
Bromidobis(phosphine)platinum(II) as
a Cation-Stabilizing Substituent on
Directly Linked and Fused Triply
Linked Diporphyrins
11
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Chem. Asian J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
These are not the final page numbers! ÞÞ