Synthesis, characterization, structure, electrochemistry, and spectroscopy of porphyrins that have a conjugated connection to donor/acceptor groups

Article abstract of DOI:10.1021/ic9702330

The reaction of ((tetraphenylporphyrinyl)methyl)triphenylphosphonium chloride and benzaldehydes (CHO-C₆H₄R; R = H, NO₂, NMe₂, OMe, Me, CHO) yields the styryl porphyrin derivatives. These new styryl-substituted porphyrins have been studied using electrochemistry, electronic absorbance, and resonance Raman spectroelectrochemical techniques. The substituents on the styryl group have a modest perturbation on the electronic spectrum of the porphyrin core. The resonance Raman data suggest that a charge-transfer interaction is observed between the porphyrin core and the NO₂ group for the 4-NO₂ compound.

Full text of DOI:10.1021/ic9702330

6270
Inorg. Chem. 1997, 36, 6270-6278
Synthesis, Characterization, Structure, Electrochemistry, and Spectroscopy of Porphyrins
That Have a Conjugated Connection to Donor/Acceptor Groups
Edia E. Bonfantini, Anthony K. Burrell,* David L. Officer,* and David C. W. Reid
Department of Chemistry, Massey University, Private Bag 11222, Palmerston North, New Zealand
Michael R. McDonald, Paul A. Cocks, and Keith C. Gordon*
Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand
ReceiVed February 27, 1997X
The reaction of ((tetraphenylporphyrinyl)methyl)triphenylphosphonium chloride and benzaldehydes (CHO-C6H4-
R; R ) H, NO2, NMe2, OMe, Me, CHO) yields the styryl porphyrin derivatives. These new styryl-substituted
porphyrins have been studied using electrochemistry, electronic absorbance, and resonance Raman spectroelec-
trochemical techniques. The substituents on the styryl group have a modest perturbation on the electronic spectrum
of the porphyrin core. The resonance Raman data suggest that a charge-transfer interaction is observed between
the porphyrin core and the NO2 group for the 4-NO2 compound.
Introduction
The study of electron transfer to and from porphyrins has
been an area of active research for several years. This is largely
due to their relationship to the chlorins which play a decisive
role in photosynthetic systems.1 Many model systems have been
prepared in an effort to understand the natural photosynthetic
systems. As a result the number and variety of synthetic routes
toward functionalized porphyrins have expanded rapidly. How-
ever, the procedures required to generate functionalized por-
phyrins generally require either a large number of synthetic steps
or rely on the outcome of one or more reactions that produce
statistical mixtures. A simple change in the target porphyrin
often requires the construction of a completely new synthetic
strategy. We have endeavored to develop a synthetic strategy
that enables the use of a readily prepared porphyrin that is
capable of being simply converted to a wide variety of functional
groups. The key to such a system is the use of a single
porphyrin starting material in a common reaction with a diverse
selection of substrates, to provide a variety of functionalized
porphyrins. Toward this end we have been examining substi-
tuted porphyrins that are derived from 5,10,15,20-tetraphen-
ylporphyrin (TPP).2 The result of this investigation has been
the preparation of a TPP phosphonium salt derivative 1, shown
in Figure 1.3 This reagent has provided a general synthetic
procedure for the formation of olefin-substituted derivatives of
Figure 1. TPP phosphonium salt derivative.
TPP in essentially one step. In this work we report the synthesis
of several of these compounds. Of particular interest in these
compounds is the effectiveness of the vinyl linker in transferring
information to and from the porphyrin core.4 The level of
communication between the porphyrin core and the various aryl
groups may be compared by observing the effect of those
substituents on the electrochemistry, optical spectroscopy, and
Raman spectroscopy of the compounds.
Results
X Abstract published in AdVance ACS Abstracts, December 1, 1997.
(1) (a) Deisenhofer, J.; Epp, O.; Miki, K.; Huber, R.; Michel, H. J. Mol.
Biol. 1984, 180, 385. (b) Deisenhofer, J.; Epp, O.; Miki, K.; Huber,
R.; Michel, H. Nature 1985, 318, 618. (c) Chang, C.-H.; Schiffer,
M.; Tiede, D.; Smith, U.; Norris, J. J. Mol. Biol. 1985, 186, 201. (d)
Chang, C.-H.; Tiede, D.; Tang, J.; Smith, U.; Norris. J.; Schiffer, M.
FEBS Lett. 1986, 205, 82. (e) Allen, J. P.; Feher, G.; Yeates, T. O.;
Rees, D. C.; Deisenhofer, J.; Huber, R. Proc. Natl. Acad. Sci. U.S.A.
1986, 83, 8589. (f) Allen, J. P.; Feher, G.; Yeates, T. O.; Komiya, H.;
Rees, D. C. Proc. Natl. Acad. Sci. U.S.A. 1987, 84, 5730. (g) Allen,
J. P.; Feher, G.; Yeates, T. O.; Komiya, H.; Rees, D. C. Proc. Natl.
Acad. Sci. U.S.A. 1987, 84, 6162. (h) Pearlstein, R. H. New Compr.
Biochem. 1987, 15, 299. (i) Fleming, G. R.; Martin, J.-L.; Breton, J.
Nature 1988, 333, 190.
Synthesis. The phosphonium salt 1 is prepared from TPP
in five steps in an overall yield of 85%.3 The reaction of 1
with aryl aldehydes, shown in Scheme 1, can be carried out at
room temperature with no special precautions. Thus, the
treatment of a solution of 1 and 4-tolualdehyde with base results
in the rapid formation of a cis/trans mixture of the olefin 3. It
is not necessary to isolate or purify the cis/trans mixture because
treatment with iodine gives the trans isomer exclusively. Simple
chromatography then gives 3 in 61% yield. The exclusive
(2) TPP can be obtained commercially or prepared in large quantities by
a simple procedure: Barnett, G. H.; Hudson, M. F.; Smith, K. M.
Tetrahedron Lett. 1973, 30, 2887-2888.
(3) Bonfantini, E. E.; Officer, D. L. Tetrahedron Lett. 1993, 34, 8531-
8534.
(4) Related compounds have been examined in this respect: (a) Wied-
errecht, G. P.; Svec, W. A.; Niemczyk, M. P.; Wasielewski, M. R. J.
Phys. Chem. 1995, 99, 8918-8926. (b) Wiederrecht, G. P.; Svec, W.
A.; Niemczyk, M. P.; Wasielewski, M. R. J. Am. Chem. Soc. 1996,
118, 81-88.
S0020-1669(97)00233-4 CCC: $14.00 © 1997 American Chemical Society

Porphyrins Conjugated to Donor/Acceptor Groups
Inorganic Chemistry, Vol. 36, No. 27, 1997 6271
Scheme 1
presence of the trans olefin can be unequivocally determined
by 1H NMR spectroscopy. The vinyl protons resonances appear
as 16 Hz coupled doublets at 7.30 and 6.96 ppm, respectively.
The other notable feature of the 1H NMR spectrum is the signal
due to the lone â-pyrrolic proton5 that appears at 9 ppm as a
singlet. This singlet is a general feature that appears in 1H NMR
spectra of all of the substituted compounds. Using the same
procedure a variety of functionalized porphyrins can be obtained
in reasonable yield (Scheme 1). The reaction of 1 with
4-nitrobenzaldehyde proceeds rapidly to give an 81% yield of
4 after purification. Once again the trans geometry can be
assigned from the presence of two 16 Hz coupled doublets (7.11
and 7.28 ppm) in the 1H NMR spectrum. In general, all of the
reactions proceed with reasonable yields although some of the
benzaldehydes give lower yields than others; the reactions are
apparently influenced by subtle combinations of steric and
electronic factors. The lower yields obtained in the formation
of the compounds 5 and 10 do not pose a significant problem
as the reactions have been successfully scaled-up to give
reasonable amounts of product. Thus, the reaction of 614 mg
of 1 with isophthalaldehyde yields 343 mg (70%) of 7 after
purification. Further modification of these compounds is
possible Via the coordination of metals to the porphyrin core.
This is achieved for simple first-row transition metals using
standard techniques.6
Structure. The presence of the conjugated link between the
porphyrin core and the functionalized styrene provides the
opportunity for significant communication between these groups.
The possibility for there to be communication between the two
“ends” of the molecule is strengthened by the geometry observed
in the solid-state of 6‚Cu.7 A single-crystal X-ray diffraction
study, shown in Figure 2, of 6‚Cu was carried out, and the
porphyrin, olefin, aryl ring, and aldehyde are effectively co-
planar. Although the structure in solution may differ from that
observed in the solid-state, clearly there is no significant barrier
to a planar system. It is also reasonable to assume that all of
the 4-substituted derivatives have similar structures to 6‚Cu.
Simple modeling using CPK models indicates it is possible for
Figure 2. Molecular structure of 6‚Cu with the meso phenyl rings in
the lower view omitted for clarity.
Table 1. Electrochemical Data for Porphyrins in CH2Cl2
E°′/V a
oxidation
reduction
compd
2
3
4
5
1.03
1.04
1.06
1.05
1.01
0.67
1.04
1.09
1.20
-1.16
-1.41
-1.44
-1.41
-1.48
-1.44
-1.53
-1.61
-1.21
1.21
1.21
1.20
irrevb
irrev
1.17
1.21
-1.19
-1.16
-1.14
-1.17
-1.22
-1.27
-1.04
9
10
2‚Ni
4‚Ni
a Versus SCE. b Process is irreversible.
the 2- and the 3-substituted aryl groups to also be coplanar with
the porphyrin ring. This raises the question as to how good is
the communication between the two parts of the molecule. If
the porphyrin and peripheral unit are very strongly coupled, then
a large perturbation of the porphyrin properties may be expected.
However, the level of coupling may be rather small, resulting
in only subtle changes in the porphyrin properties.
Electrochemistry and Spectroscopy. The electrochemical
data for the porphyrins are presented in Table 1. Typically the
porphyrins show two oxidations and two reductions. It was
found that, under the experimental conditions used, the first
oxidation and reduction for all systems were reversible.
(5) This signal shows a single weak coupling to one of the olefinic protons
in a COSY spectrum.
(6) Falk, J. E. In Porphyrins and Metalloporphyrins; Smith, K. M., Ed.;
Elsevier: Amsterdam, 1975.
(7) Burrell, A. K.; Officer, D. L.; Reid, D. C. W. Angew. Chem., Int. Ed.
Engl. 1995, 34, 900.

6272 Inorganic Chemistry, Vol. 36, No. 27, 1997
Bonfantini et al.
Table 2. Electronic Spectral Data for Porphyrins and Their
Oxidized and Reduced Products in CH2Cl2 at Room Temperature
oxidation, a new band being observed at 604 nm. The changes
in the absorption spectrum on going from 4‚Ni to 4‚Ni+ also
show a bleach of the Q bands. 4‚Ni+ has a feature at 423 nm,
and weak absorbances at 538 and 579 nm. These spectral
changes are similar to those reported for the oxidation of TPP‚-
Ni11 and related complexes.12
λ/nm (ꢀ × 10-3/M-1 cm-1
)
compd
2
424 (290) 523 (21)
445 (127)
420 (140) 518 (sh)
562 (10)
599 (6.5) 655 (2.4)
667 (14)
604 (2.6) 656 (6.8)
2ox a
2-
554 (sh)
As the potential is stepped through the oxidation wave, the
behavior of the electronic spectra for the free-base systems is
interesting. For 2, oxidation results in a depletion of the B band
at 424 nm. A new feature grows in at 445 nm. The four Q
bands of 2 are bleached upon oxidation with a new feature
appearing at 667 nm with a shoulder at 608 nm. The electronic
spectral changes occurring upon oxidation of 3 and 5 and of 9
and 10 are similar to those reported for 2.
3
424 (218) 524 (19)
447 (82)
420 (60)
563 (9.1) 601 (5.7) 655 (6.3)
667 (8.3)
3ox
3-
4
429 (144) 525 (17)
568 (11)
553 (sh)
602 (7.7) 659 (4.5)
600 (2.4) 656 (3.2)
4ox
4-
421 (130) 518 (sh)
5
427 (257) 524 (19)
445 (79)
422 (91)
563 (9.1) 600 (6.1) 656 (2.2)
5ox
5-
669 (13)
656 (2.2)
The spectral changes observed for the oxidation of the free-
base ligands are unlike those of the nickel(II) complexes. It
has been reported that the electrochemical oxidation of H2TPP
readily leads to the formation of other products when attempting
to form the monocation.13 In a series of protonation studies of
H2TPP and related systems, spectral changes almost identical
to those observed in this work are reported.14 The observation
of a red-shifted B band and absorption at ca. 655 nm is the
9
422 (151) 524 (9.7) 564 (5.1) 600 (2.7) 657 (1.0)
9ox
9-
447 (193)
419 (102)
667 (22)
10
421 (166) 521 (16)
447 (108)
572 (7.4) 605 (7.3) 660 (2.0)
670 (12)
10ox
2‚Ni
425 (209) 540 (18)
577 (11)
604 (9.1)
2‚Ni+ 418 (43)
spectral signature for the dication species H4TPP2+
.
4‚Ni
431 (189) 541 (17)
583 (14)
579 (1.8)
4‚Ni+ 423 (240) 538 (11)
The monocation of H2TPP has been observed by photooxi-
dation in low-temperature glasses.15,16 The spectrum shows
vibronic structure in the Q band region. This is absent from
our oxidized spectra of free-base porphyrins.
a “ox” indicates oxidized species.
The oxidation potential for 10 is significantly lower than that
for the other compounds. This suggests that the NMe2 group
is strongly perturbing the porphyrin ring, stabilizing it toward
oxidation, or that the oxidation is centered off the porphyrin
and at the NMe2 functionality. The E°′ for C6H5NMe2 lies at
0.65 V vs SCE.8 Thus, the oxidation potential observed for 10
is close to the potential expected for direct oxidation at the
styryl-NMe2 moiety.
We believe that our spectroelectrochemical experiments are
probing the dication rather than monocation species for the free-
base systems. To determine this further, the electronic spectra
of 3 and 5 were measured in the presence of 2 mole equivalents
of trifluoroacetic acid. The spectra observed are identical to
those measured in the UV-OTTLE experiment.
The electronic spectral data for species formed by the
electrochemical reduction of the porphyrins and nickel com-
plexes are shown in Table 2. The reduction of 3 f 3- results
in a depletion of the B band. The reduced species absorbs at
420 nm and into the visible region. The intensity of this
absorption is much less than that of the neutral species B
transition. Porphyrins 2, 4, 5, and 9 behave in a very similar
fashion to 3 with the B bands bleaching and a new transition
appearing to the blue of the B band. The nickel complexes
show a depletion of the B band when reduced. For 4‚Ni the
radical anion band lies at 419 nm; the species absorbs out to
approximately 750 nm.
The electronic spectral data for the compounds and their
reduced and oxidized products are given in Table 2. The
spectrum of 2 is typical of a free-base porphyrin showing a
strong B band at about 420 nm and four weaker Q bands to the
red of the B transition. The presence of the styryl group in 2
shifts the B band to 424 nm. In H2TPP the B band lies at 416
nm.9 The substitution of a methoxy group at the para position
of the styryl group 9 has no effect on the wavelength of the B
band, lying at 422 nm. The para substitution of methyl group
3 also has little effect on the wavelength of the B band.
However, substitution of a nitro group at para 4 or meta 5
positions on the styryl group results in a red-shift of the B band
to 429 and 427 nm, respectively. Electron donating groups such
as NMe2 result in a blue-shift in the B band to 420 nm. Thus,
the substituents on the styryl group have a modest perturbation
on the electronic spectrum of the porphyrin core.
Resonance Raman spectra (RRS) of the free-base compounds
are presented in Figure 3. The resonance Raman signals are
very intense from these samples, and the solvent bands are too
weak to observe. Table 3 shows the frequencies for all
prominent bands in the spectra, which for most of the neutral
free-base species are similar. For all of the porphyrins, except
10, bands lie at 1620, 1550, 1450, 1370, and 1236 cm-1. These
common features may be assigned by comparison with the RRS
of H2TPP. Normal coordinate analyses of H2TPP have been
The interchelation of nickel into porphyrins 2 and 4 has little
effect on the wavelength of the B band. The metal increases
the microsymmetry of the ring to D4h. This is borne out by the
observation of only two Q bands over the four present for the
free-base systems, which have D2h symmetry.10
The electronic spectral data of the oxidized products of 2-5,
9, 10, 2‚Ni, and 4‚Ni are shown in Table 2. The B band is
bleached upon oxidation of 2‚Ni, the new feature growing in is
blue-shifted, to 418 nm, and much less intense than the original
B band. The two Q bands observed in 2‚Ni are bleached with
(11) Wolberg, A.; Manassen, J. J. Am. Chem. Soc. 1970, 92, 2982.
(12) Lin, C.-Y.; Hu, S.; Rush, T., III; Spiro, T. G. J. Am. Chem. Soc. 1996,
118, 9452.
(13) Carnieri, N.; Harriman, A. Inorg. Chim. Acta, 1982, 62, 103.
(14) Ojadi, C. A.; Linschitz, H.; Gouterman, M.; Walter, R. I.; Lindsey, J.
S.; Wagner, R. M.; Droupadi, P. R.; Wang, W. J. Phys. Chem. 1993,
97, 13192.
(8) Meyer, T. J. Prog. Inorg. Chem. 1983, 30, 389.
(9) Thomas, W.; Martell, A. E. J. Am. Chem. Soc. 1956, 78, 1338.
(10) Gouterman, M. In The Porphyrins; Dolphin, D., Ed.; Academic:
London, 1978; Vol. 3, Chapter 1.
(15) Gaysna, Z.; Browett, W. R.; Stillman, M. J. Inorg. Chim. Acta 1984,
92, 37.
(16) Gaysna, Z.; Browett, W. R.; Stillman, M. J. Inorg. Chem. 1985, 24,
2440.

Porphyrins Conjugated to Donor/Acceptor Groups
Inorganic Chemistry, Vol. 36, No. 27, 1997 6273
this is that the nitro group at the para position in 4 has a much
greater influence over the electronic structure of the porphyrin
ring than does the nitro at the meta position. In the case of 4,
photoexcitation into the B transition may involve an excited
state in which the excited electron is stabilized by the nitro group
at the para position. Thus the nitro stretch will alter the
molecular geometry of the porphyrin in a similar fashion to that
of the resonant photoexcitation. This would result in strong
enhancement of this mode in the RRS.19 In the case of 5 the
nitro at the meta position is less able to perturb the electronic
structure of the phenyl group,20 in terms of stabilizing the excited
electron charge, and thus shows weaker resonance enhancement.
The resonance Raman spectrum of the dimethylamino
compound 10 (Figure 3e) is also strikingly different from those
of the other porphyrins. The strongest feature is at 1393 cm-1
;
other bands lie at 1430 and 1519 cm-1. Only the 1519 cm-1
band is present in the spectra of the other porphyrins. This
strong enhancement of non-porphyrin modes may be due to the
following. The B transition is strongly perturbed such that the
modes enhanced are primarily styryl group vibrations or the
substitution of the NMe2 moiety on the styryl group perturbs
the vibrations of the porphyrin core shifting them to new
frequencies. The latter explanation may be discounted because
the infrared absorbance spectrum of 10 shows a porphyrin
signature. It is also possible that photodecomposition of the
porphyrin is occurring.
The features observed at 1393 and 1430 cm-1 do not
correspond well with porphyrin modes. The Raman spectrum
of dimethylaminobenzene (DMA) has bands at 1605, 1348,
1195, and 995 cm-1 which show moderate to strong intensity.
It is possible that these modes would be shifted upon bonding
of the DMA unit to the porphyrin.21
Figure 3. Resonance Raman spectrum of (a) 3, (b) 4, (c) 5, (d) 9, (e)
10, and (f) 2 in CH2Cl2 (ca. 1 mM), measured with 457.9 nm CW
excitation.
published.17 Using one of these analyses,17a the bands at 1607-
1596 cm-1 are assigned as belonging to the phenyl groups
attached at the meso carbons. The strong features at ∼1550
cm-1 belong to the Câ-Câ stretch of the porphyrin ring system.
This is labeled as ν2 for H2TPP. The 1450 cm-1 feature is
assigned as the porphyrin ring CR-Cm stretch (labeled as ν11
for H2TPP). The band in the region 1380-1360 cm-1 has two
possible assignments: It may be the porphyrin symmetric stretch
for CR-N, termed ν4 for H2TPP, or it may be the asymmetric
stretch of the ring system for CR-Câ, termed ν28.
The free-base porphyrin spectra show some bands that do
not correspond to those observed for H2TPP. Each has a feature
at ∼1620 cm-1. We assign this band to the phenyl ring system
attached through the double bond to the Câ of the porphyrin
ring. Consistent with this assignment, the RRS of 2-methyltet-
raphenylporphyrin, which has no styryl group, has no feature
in this region.
In the case of H2TPP the ν28 band is depolarized having B1g
symmetry in the D2h point group. The depolarization ratios for
the bands observed in the 1380-1360 cm-1 region for these
porphyrins show that the modes are polarized, hence the possible
The RRS of the nickel complexes, 4‚Ni (4-nitrophenyl-
substituted) and 2‚Ni (phenyl substituted) are shown in Figures
4 and 5, respectively. The spectra differ slightly from those of
the corresponding free-base porphyrins. The frequencies of the
observed bands (Table 4) may be compared to those of TPP‚Ni.
A normal coordinate analysis of the Raman spectrum of TPP‚Ni
has been performed by Li et al.22 Using this analysis the
following assignments are made for the strongest features in
the Raman spectrum of 2‚Ni: The band at 1600 cm-1 is assigned
as a phenyl stretch (φ4). The 1570 cm-1 band is assigned as
the Câ-Câ stretch (ν2). The 1377 cm-1 is assigned as the
pyrrole half-ring symmetric stretch (ν4). The 1239 cm-1 band
is assigned as the Cm-Ph stretch (ν1). These features lie at
1600, 1574, 1373, and 1273 cm-1, respectively, for TPP‚Ni.
One further band is present at 1624 cm-1. This is assigned as
a styryl group vibration because of its similarity in frequency
to that for the free-base systems.
ν28 assignment is discarded. The ν4 band has A1g symmetry in
H2TPP and is hence polarized. The strong feature at 1236 cm-1
in each of the spectra is assigned as the Cm-Ph stretch.
The RRS of the p-nitrophenyl derivative 4 and the p-
(dimethylamino)phenyl compound 10 are significantly different
from those of the other porphyrins reported here. First, the Cm-
Ph stretch band of 4 at 1238 cm-1 is of much lower intensity
than for the other spectra. Secondly a very strong feature is
observed at 1342 cm-1. This feature is much more intense than
the ν4 band discussed above and is significantly shifted from
the anticipated frequency of the ν4 band. Aromatic species with
nitro groups typically show a strong feature at 1340 cm-1
ascribed to the nitro group.18 We assign the feature at 1342
cm-1 as that of the nitro group for 4 on the basis of its frequency.
It is somewhat surprising that the meta-nitro-substituted isomer,
5, does not show this strong feature. Its spectrum more closely
resembles those of 2, 3, and 9. One possible explanation for
The spectrum of 4‚Ni shows the following strong bands which
are assigned as TPP‚Ni vibrations;23 1604 (φ4), 1577 (ν2), 1376
(17) (a) Stein, P.; Ulman, A.; Spiro, T. G. J. Phys. Chem. 1984, 88, 369.
(b) Bell, S. E. J.; Al-Obaidi, A. H. R.; Hegarty, M. J. N.; McGarvey,
J. J.; Hester, R. E. J. Phys. Chem. 1995, 99, 3959. (c) Li, X.-Y.;
Zgierski, M. Z. J. Phys. Chem. 1991, 95, 4268.
(18) Dollish, F. R.; Fateley, W. G.; Bentley, F. F. In Characteristic Raman
Frequencies of Organic Compounds; John Wiley & Sons: New York,
1974.
(19) Clark, R. J. H.; Dines, T. J. Angew. Chem., Int. Ed. Engl. 1986, 25,
131.
(20) Fukui, K.; Yonezawa, T.; Nagata, C.; Shingu, H. J. Chem. Phys. 1954,
22, 1433.
(21) Brouver, A. M.; Wilbrandt, R. J. Phys. Chem., 1996, 100, 9678.
(22) Li, X.-Y.; Czernuszewicz, R. S.; Kincaid, J. R.; Su, Y. O.; Spiro, T.
G. J. Phys. Chem. 1990, 94, 31.

6274 Inorganic Chemistry, Vol. 36, No. 27, 1997
Bonfantini et al.
assignmentb
Table 3. Frequencies (cm-1) for Raman Bands of Porphyrins in CH2Cl2
H2TPPa
2
3
4
5
9
10
labela
1624
1598
1551
1517
1505
1450
1380
1370
1621
1607
1551
1517
1503
1449
1380
1369
1624
1596
1554
1518
1505
1450
1379
1368
1342
1625
1600
1551
1516
1504
1451
1380
1363
1622
1605
1551
1519
1503
1449
1381
1368
1626 vw
styryl
phenyl
ν(Câ-Câ) pyr-H
1597
1550
φ4
ν2
1519 vw
1499
1438
1383
1357
ν12
ν11
ν28
ν4
ν(Câ-Câ) pyr
ν(CR-Cm)sym
ν(CR-Câ)asym
ν(pyr half-ring)sym
NO2
1430
1393
1327
1319
1292
1330
1329
1324
1305
1261
1236
1209
1329
1318
1287
1259
1236
1210
1330
1320
1302
1263
1236
1207
δ(N-H)in/out plane
1320
ν12
ν1
ν(pyr half-ring)sym pyr
ν(Cm-Ph)
1264
1238
1200
1234
1205 sh
1235
a Taken from ref 17a. b Assignments taken from refs 17a-c. “sh” denotes shoulder. “vw” denotes peak of very weak intensity.
Figure 4. Resonance Raman spectrum of 4‚Ni in CH2Cl2 (ca. 1 mM),
measured with 457.9 nm CW excitation. S denotes solvent band.
Figure 5. Resonance Raman spectrum of 2‚Ni (lower trace) and 2‚Ni+
(upper trace) in CH2Cl2 (ca. 1 mM), measured with 457.9 nm CW
excitation. S denotes solvent band.
(ν4), and 1238 (ν1) cm-1. A styryl vibration is observed at 1629
cm-1 and a nitro vibration at 1342 cm-1
.
Table 4. Frequencies (cm-1) for Raman Bands of Nickel
a
Porphyrins in CH2Cl2
Two features common to the Raman spectra of the oxidized
products of 2-5 and 9 are strong bands at ca. 1542 and ca.
2‚Ni
1624
1600 sh
1570
4‚Ni
1629
1604
2‚Ni
4‚Ni
1385 cm-1
.
1314 w
1306
1239
1200 w
1178 w
1133 w
1083 w
1010 w
1319
1238
1207 w
1199 w
1179 w
1109 w
Complete oxidation of the probed volume is confirmed for
each sample by the disappearance of neutral species’ bands.
For 3 these lie at 1551, 1449, and 1369 cm-1. For 4 bands at
1554 and 1342 cm-1 are bleached. For 5 the 1551 and 1363
cm-1 bands are lost upon oxidation, for 9 the 1551 and 1449
cm-1 bands disappear, and for 2 bands at 1551 and 1450 cm-1
are lost. For each system the spectrum observed for the oxidized
product has no residual neutral species signal.
1577
1546 sh
1495 w
1462 w
1376
1462 w
1377
1346 w
1342
1010 w
a “sh” denotes a shoulder. “w” denotes a peak of weak intensity.
The spectra observed in the Raman OTTLE experiment can
be reproduced by acidifying the free-base porphyrin with
trifluoroacetic acid. Identical bands are observed, confirming
that the oxidized free-base systems are dicationic in nature.
The RRS of the oxidized products of the nickel complex 2 is
shown in Figure 5. The Raman spectrum of 2‚Ni+ shows a
weaker 1570 cm-1 band than in the neutral species. Complete
conversion to the oxidized complex is confirmed by the absence
of the 1624 cm-1 band. The spectrum of the oxidized species
shows an intense band at 1363 cm-1 and a weaker peak at 1534
cm-1. Attempts to generate the Raman spectrum of 4‚Ni+ were
unsuccessful. The observed spectra were those of the neutral
species.
Discussion
The similar value of the first oxidation potential for 2-5 and
9 with that of H2TPP suggests that this oxidation is ring based.
For metal porphyrins a relationship between the first oxidation
(E
ox) and first reduction (Ered) exists as expounded by Kadish
et al.24 For δ ) 2.20 ( 0.15 V (where δ ) Eox - Ered) it is
found that the oxidation is ring, rather than metal, based. The
δ for 2‚Ni and 4‚Ni lie in this range.
(23) Assignments, as labeled in the preceding reference, are given in
parentheses.

Porphyrins Conjugated to Donor/Acceptor Groups
Inorganic Chemistry, Vol. 36, No. 27, 1997 6275
The optical absorption spectra of the porphyrins offer some
insight into the level of perturbation of the porphyrin chro-
mophore by the styryl groups. The electronic spectra of the
porphyrin chromophores arise through transitions from the
HOMOs of a1u and a2u symmetry to the eg LUMOs from the
four orbital model.25 The most important factor in determining
the wavelengths and oscillator strengths for the B and Q
transitions is the configuration interaction between the a1u and
a2u orbitals.25 The effects of substituents upon the energies of
the highest occupied orbitals may be predicted, but the relation-
ship between orbital energy and transition wavelength is not
straightforward. Because the four-orbital model has been
calculated for a D4h point group, it is applicable to the nickel
complexes in this study. Shelnutt’s26 analysis of the transition
center for metalloporphyrins.25 In a study of the Raman and
electronic spectroscopy of OEP‚Ni (OEP is octaethylporphyrin),
Kitigawa30 noted a correlation between the modes discussed
above and the EQ values. The metal center perturbs the energy
of the a2u orbital because of the high wavefunction amplitude
of a2u on the nitrogen atoms of the porphyrin. The a1u orbital
has negligible amplitude at the nitrogens. The presence of a
metal results in stabilization of the a2u orbital which causes the
MO to become more bonding, thereby increasing bond order
of the porphyrin ring. The increased bond order results in an
increase in vibrational frequency for the porphyrin modes.
This explanation appears appropriate for 2 and 2‚Ni. A
stabilization of the a2u MO would have little affect on the bond
order within the phenyl groups appended at the meso carbon or
the Cm-φ bond. Consistent with this there is little shift in the
φ4 or Cm-Ph vibrational frequencies. However, for the Câ-
Câ stretch (ν2) the a2u orbital is bonding therefore a more
substantial frequency increase would be predicted for this mode.
This is indeed observed. The ν4 band involves the extension
of the CR-N linkage concomitant with the compression of the
CR-Câ bond and motion of the N toward the metal center. For
the a2u orbital, the CR-Câ bond is weakly antibonding, the
CR-N more strongly antibonding, and the N-metal strongly
bonding. This last interaction appears to be the most important
as the ν4 band shifts up in frequency with nickel insertion. A
very similar correlation exists for 4 and 4‚Ni. The EQ values
are 16.4 × 103 and 17.1 × 103 cm-1, respectively. The shifts
with nickel insertion are +8, +23, +8, and 0 cm-1 for the φ4,
ν2, ν4, and ν1 modes, respectively.23
The highest occupied energy MOs in a porphyrin system are
those with a1u and a2u symmetry. The spectral features observed
upon oxidation will depend on which of these MOs is
depopulated. This can be determined from analysis of the
resonance Raman spectral changes upon oxidation of the species.
The resonance Raman spectra of the porphyrins and their radical
cations are well understood,31 and the shift patterns on going
from neutral to oxidized species provide evidence as to the
nature of the MO depopulated. In the spectra of 2‚Ni, the most
notable shifts occur from 1570 f 1534 cm-1 (ν2 Câ-Câ stretch)
and from 1377 f 1363 cm-1 (ν4). Similar shifts are observed
in the spectra of TPP‚Cu and TPP‚Cu+. The shift of the ν2
band is particularly useful because the a1u MO is antibonding
with respect to the Câ-Câ linkage whereas the a2u MO is
bonding over Câ-Câ. The observation of the frequency
downshift in the ν2 band indicates that the electron has been
taken from an MO of a2u symmetry.
energies of B and Q bands (EB and EQ, respectively) to the
2
square of the dipole strengths for these transitions (qB2 and qQ
,
respectively) reveals that the closer in energy the a1u and a2u
2
2
orbitals are the smaller qB /qQ and the smaller EB - EQ are.
The EB - EQ values are 6430, 6130, and 6050 cm-1 for TPP‚-
2
2
Ni, 2‚Ni, and 4‚Ni, respectively. The qB /qQ values are 0,26
0.028, and 0.053, respectively.27 The bandwidth of the B band
for 4‚Ni is considerably greater than that of 2‚Ni (2500 and
1700 cm-1, respectively). These values imply that the energies
of the a1u and a2u orbitals are further apart in these systems
than in TPP complexes.
The poor correlation between the oscillator strengths and
transition energies may be caused by the very small data set
used or the presence of the styryl group which may modify the
orbitals involved because of symmetry reduction. It may also
be due to the presence of the nitro group. This may result in
one or both of the transitions having charge-transfer character.
Spectra of amino-substituted porphyrins show a marked increase
in B transition bandwidth which has been attributed to increased
CT character in the transition.28
The most likely explanation for the poor correlation is the
small size of the data set. Furthermore, this illustrates the
difficulty in analyzing the optical spectra of these porphyrins.
The changes in the electronic spectra upon oxidation are
interesting. For the nickel complexes, the oxidation results in
a blue-shift of the B-band. This is typical of oxidized
metalloporphyrins in which the oxidation occurs at the porphyrin
ring.28 Unfortunately the blue-shift of the absorption and its
diminished intensity reduce the resonance effect at the available
excitation wavelength. Thus the RRS of the oxidized nickel
complexes are weaker than the neutral species. For 4‚Ni+ no
appreciable signal is observed.
Insertion of the nickel into the porphyrin ring has a number
of effects relative to the free-base porphyrins; the frequency of
some bands and the energy of the Q bands increase.29
The ν2 band in 2‚Ni lies at 1570 cm-1, 19 cm-1 higher than
the ν2 band for 2. The ν4 band lies at 1377 cm-1, 7 cm-1 higher
than 2. The Cm-Ph mode is 4 cm-1 higher, and the φ4 is 2
cm-1 higher. The values for EQ are 17.3 × 103 and 16.8 ×
103 cm-1 for 2‚Ni and 2, respectively.
Conclusions
The reactions of 1 with aryl aldehydes represents a simple
high yielding method for functionalizing porphyrins. The
reaction is tolerant of a range of functional groups on the
aldehyde. Thus compounds with both electron-withdrawing
(NO2) and electron-donating (NMe2) groups are readily pre-
pared. X-ray structural data indicate that the porphyrin core
and the styryl groups are coplanar.
The value of EQ is related to the electronegativity of the metal
The perturbation of the porphyrin core by the substituted
styryl substituents is rather more subtle than that observed for
other porphyrin systems, which are linked by bridging units.
For the substitutents used here only modest changes in electronic
spectra and electrochemistry are seen. Furthermore the Q bands
behave as they would in D2h (for free-base systems) and D4h
(metal complexes) symmetry environments. This is consistent
(24) Fuhrhop, J.-H.; Kadish, K. M.; Davis, D. G. J. Am. Chem. Soc. 1973,
95, 5140.
(25) Gouterman, M. J. Chem. Phys. 1959, 30 1139.
(26) (a) Shelnutt, J. A. J. Phys. Chem. 1984, 88, 4988. (b) Shelnutt, J. A.;
Ortiz, V. J. Phys. Chem. 1985, 89, 4733.
(27) The value of qB2/qQ was taken from ref 26. q2 ∼ f/E where f is the
2
oscillator strength. f ∼ ꢀmax∆ν, where ꢀmax is the maximum extinction
coefficient value and ∆ν is the bandwidth of the transition in cm-1
.
2
The error in qB2/qQ would be ( 10%.
(28) Fuhrhop, J.-H. Struct. Bond. 1974, 18, 1.
(30) Kitagawa, T. J. Phys. Chem. 1975, 79, 2629.
(31) Czernuszewicz, R. S.; Macor, K. A.; Li, X.-Y.; Kincaid, J. R.; Spiro,
T. G. J. Am. Chem. Soc. 1989, 111, 3860.
(29) EQ for the free-base is calculated as the average energy for the two
0-0 transitions.

6276 Inorganic Chemistry, Vol. 36, No. 27, 1997
Bonfantini et al.
(trans-2-(5,10,15,20-Tetraphenylporphyrin-2-yl)ethen-1-yl)ben-
zene (2). To a solution of phosphonium salt 1 (75 mg, 81 µmol) and
benzaldehyde (25 mg, 0.24 mmol) in CH2Cl2 (0.4 mL) was added a
45% aqueous NaOH solution (0.3 mL). After stirring for 1 h at room
temperature, water (30 mL) was added and the mixture extracted twice
with CH2Cl2 (30 mL, 20 mL). The combined organic phases were
washed with water (50 mL) and dried (MgSO4). The solvent was
removed, and the residue was purified by flash column chromatography
(silica, 1:1 CH2Cl2/hexane). The resulting material was recrystallized
from CH2Cl2/MeOH, to give 2 (51 mg, 88%) as a purple solid. 1H-
NMR (270 MHz, CDCl3): δ -2.61 (br s, 2H, NH), 6.99 (d, 1H, 3J )
15.9 Hz, Hethenyl), 7.26-7.37 (m, 6H, HAr and Hethenyl), 7.70-7.83 (m,
12H, Hm,pPh), 8.17-8.26 (m, 8H, HoPh), 8.71-8.83 (m, 6H, Hpyrrole),
9.00 (s, 1H, Hpyrrole). UV-vis (CH2Cl2): λmax (log ꢀ) 424 (5.46), 523
(4.32), 562 (4.00), 599 (3.81), 655 (3.38) nm. HRMS, m/z: calcd for
MH+ (C52H37N4), 717.3018; found, 717.3023.
with the substituents having a very small effect on the porphyrin
core. However, the substituents do have a subtle effect which
suggests the styryl group and porphyrin ring are coplanar. This
is evidenced by the enhancement of the styryl vibrations in the
resonance Raman spectra and by the nitro vibration in 4 and
4‚Ni. The increase in bandwidth for the B-band also suggests
a charge-transfer interaction from the electron-withdrawing nitro
moiety to the porphyrin.
It would appear that substituents on the Câ position linked
by a double bond are planar but do not strongly perturb the
porphyrin. This offers the interesting possibility of creating an
array of porphyrins which maintain the individual chromophoric
and redox properties of the monomer porphyrin while allowing
interactions between the porphyrin components of the array.
4-(trans-2-(5,10,15,20-Tetraphenylporphyrin-2-yl)ethen-1-yl))-
toluene (3). Phosphonium salt 1 (100 mg, 0.108 mmol) and tolual-
dehyde (14 µL, 14.2 mg, 0.119 mmol) were dissolved in CH2Cl2 (4
mL) and stirred at room temperature before adding DBU (100 µL, 0.669
mmol). After 5 min, the reaction mixture was flash column chromato-
Experimental Procedures
For electrochemical and spectroscopic measurements spectroscopic
grade CH2Cl2 was used. The supporting electrolyte used in the
electrochemical measurements was tetrabutylammonium perchlorate
(TBAP). This was purified by repeated recrystallizations from ethanol/
water.32
Physical Measurements. A Perkin-Elmer λ-19 spectrometer was
used for collection of electronic absorption spectra. Extinction coef-
ficients were obtained from a least squares analysis of a series of
solutions at different concentrations.
Cyclic voltammograms (CVs) were obtained from degassed solutions
of compound (ca. 1 mM) with 0.1 M concentration of TBAP present.
The electrochemical cell consisted of a 1.6 mm diameter platinum
working electrode embedded in a Kel-F cylinder with a platinum
auxiliary electrode and a saturated potassium chloride calomel reference
electrode. The potential of the cell was controlled by an EG&G PAR
273A potentiostat with model 270 software.
Raman scattering was generated using a Spectra-Physics model 166
argon ion laser with an excitation wavelength of 457.9 nm. Raman
spectra were collected in a backscattering geometry with a two lens
arrangement.33 The irradiated volume was imaged into a Spex 750M
spectrograph equipped with an 1800 groove/mm holographic grating.
A Princeton Instruments 1152-EUV CCD was used for photon
detection. A 150 µm entrance slit was used; with 457.9 nm excitation,
this provided a resolution of approximately 5 cm-1 for the Raman
spectra reported.
1
graphed (silica, 1:2 CH2Cl2/hexane) to give a cis/trans (∼1:3 by H
NMR) mixture of products. The material was dissolved in CH2Cl2
(10 mL), and I2 (8.5 mg, 33 µmol) was added before stirring at room
temperature for 16 h. The reaction was diluted with CH2Cl2 (20 mL)
and washed with 1 M aqueous Na2S2O3 (2 × 20 mL) and H2O (2 × 20
mL), dried (MgSO4), and the solvent was removed under reduced
pressure. Flash chromatography (silica, 1:1 CH2Cl2/hexane) followed
by recrystallization from CH2Cl2/CH3OH, yielded 3 (48 mg, 61%) as
a purple solid. 1H-NMR (270 MHz, CDCl3): δ -2.59 (br s, 2H, NH),
3
2.41 (s, 3H, HMe), 6.96 (d, 1H, J ) 16.0 Hz, Hethenyl), 7.17 (s, 4H,
HAr), 7.30 (d, 1H, 3J ) 16.0 Hz, Hethenyl), 7.72-7.85 (m, 12H, Hm,pPh),
8.19-8.29 (m, 8H, HoPh), 8.71-8.87 (m, 6H, Hpyrrole), 9.01 (s, 1H,
H
pyrrole). UV-vis (CH2Cl2) λmax (log ꢀ) 424 (5.37), 524 (4.32), 563
(4.09), 601 (3.88), 655 (3.41) nm. HRMS, m/z: calcd for MH+
(C53H39N4), 731.3175; found, 731.3189.
4-(trans-2-(5,10,15,20-Tetraphenylporphyrin-2-yl)ethen-1-yl)ni-
trobenzene (4). To a solution of phosphonium salt 1 (66 mg, 71 µmol)
and 4-nitrobenzaldehyde (18 mg, 0.12 mmol) in CH2Cl2 (0.5 mL) was
added aqueous 25% NaOH solution (0.5 mL). After being stirred for
30 min, the mixture was diluted with CH2Cl2 (3 mL) and stirred for an
additional 10 min. Water was added, and the mixture was extracted
with CH2Cl2 (40 mL, 30 mL). The combined organic phases were
washed with water (2 × 40 mL) and dried (MgSO4). The solvent was
removed in Vacuo, and the residue purified by flash column chroma-
tography (silica, 3:2 CH2Cl2/hexane). The major band gave a mixture
of cis/trans isomers (1:3 by 1H NMR). This mixture was stirred with
I2 (20 mg, 79 µmol) in CH2Cl2 (3 mL) for 24 h, diluted with CH2Cl2,
and washed with 15% aqueous Na2S2O3 (2 × 20 mL) and then water
(2 × 20 mL). After drying (MgSO4), solvent removal in Vacuo, and
recrystallization from CH2Cl2/MeOH, 4 (44 mg, 81%) was obtained.
1H-NMR (270 MHz, CDCl3): δ -2.60 (br s, 2H, NH), 7.11 (d, 1H, 3J
Raman spectra were calibrated using emission lines from the argon
ion excitation source or a neon lamp. The calibrations were checked
against a known solvent spectrum; peak frequency reproducibility was
found to be good to 1 cm-1 34
.
Spectroelectrochemical measurements (Raman and electronic absorp-
tion) were made using an optically transparent thin-layer electrochemical
(OTTLE) cell.35 For the electronic absorption measurements the cell
was set to a potential for 10 min and then the spectrum recorded. Spectra
were measured at a series of potentials spanning the reduction or
oxidation. For the Raman measurements the potential was set past
the E°′ for the oxidation or reduction of interest. Measurements were
made only at this potential.
1H nuclear magnetic resonance spectra were obtained at 270 MHz
using a JEOL GX270 spectrometer. 1H nuclear magnetic resonance
data are expressed in ppm downfield shift from tetramethylsilane as
an internal reference and are reported as position (δH), relative integral,
multiplicity (s ) singlet, d ) doublet, dd ) double of doublet, ddd )
double double doublet, t ) triplet, q ) quartet, and m ) multiplet),
coupling constant (J, Hz) and assignment. Flash chromatography used
Merck Kieselgel 60 (230-400 mesh) with the indicated solvents. Thin-
layer chromatography was performed using precoated silica gel plates
(Merck Kieselgel 60F254). The syntheses of 13 and 67 have been
reported previously.
3
) 16.0 Hz, Hethenyl), 7.28 (d, 1H, J ) 16.0 Hz, Hethenyl), 7.30 (d, 2H,
3J ) 8.6 Hz, HAr), 7.71-7.83 (m, 12H, Hm,pPh), 8.14-8.26 (m, 10H,
HoPh and HAr), 8.72-8.84 (m, 6H, Hpyrrole), 9.02 (s, 1H, Hpyrrole). UV-
vis (CH2Cl2): λmax (log ꢀ) 429 (5.16), 525 (4.23) 568 (4.04), 602 (3.89),
659 (3.65) nm. HRMS, m/z: calcd for MH+ (C52H36N5O2), 762.2869;
found, 762.2891.
3-(trans-2-(5,10,15,20-Tetraphenylporphyrin-2-yl)ethen-1-yl)ni-
trobenzene (5). Phosphonium salt 1 (202 mg, 0.218 mmol) and
3-nitrobenzaldehyde (34 mg, 0.22 mmol) were dissolved in CH2Cl2 (4
mL) and stirred at room temperature before addition of DBU (0.2 mL,
1.34 mmol). After 1 h, the reaction mixture was flash column
chromatographed (silica, 1:1 CH2Cl2/hexane) to give a cis/trans (3:5
1
by H NMR) mixture of products as a purple solid. The solid was
dissolved in CH2Cl2 (20 mL), and I2 (15 mg, 59 µmol) was added before
stirring at room temperature for 16 h. The reaction was diluted with
CH2Cl2 (20 mL), washed with 1 M aqueous Na2S2O3 (2 × 40 mL) and
H2O (2 × 20 mL), dried (MgSO4) and solvent removed under reduced
pressure. Flash chromatography as before followed by recrystallization
from CH2Cl2/CH3OH yielded 5 (73 mg, 44%) as a purple solid. 1H-
NMR (270 MHz, CDCl3): δ -2.58 (br s, 2H, NH), 7.07 (d, 1H, 3J )
(32) House, H. O.; Feng, E.; Peet, N. P. J. Org. Chem. 1971, 36, 2371.
(33) Strommen, D. P.; Nakamoto, K. Laboratory Raman Spectroscopy; John
Wiley & Sons Inc.: New York, 1984.
(34) Ferraro, J. R.; Nakamoto, K. Introductory Raman Spectroscopy;
Academic Press Inc.: San Diego, CA, 1994.
(35) McQuillan, A. J.; Babaei, A. J. Chem. Educ., in press.

Porphyrins Conjugated to Donor/Acceptor Groups
Inorganic Chemistry, Vol. 36, No. 27, 1997 6277
3
16.2 Hz, Hethenyl), 7.31 (d, 1H, J ) 16.2 Hz, Hethenyl), 7.43-7.58 (m,
Hz, Hethenyl), 7.74-7.89 (m, 12H, Hm,pPh), 8.22-8.34 (m, 8H, HoPh),
8.75-8.95 (m, 6H, Hpyrrole), 9.05 (s, 1H, Hpyrrole). UV-vis (CH2Cl2):
λmax (log ꢀ) 422 (5.18), 524 (3.99), 564 (3.71), 600 (3.43), 657 (3.00)
nm. HRMS, m/z: calcd for M+ (C53H38N4O), 746.3046; found,
746.3025.
2H, HAr), 7.74-7.96 (m, 12H, Hm,pPh), 8.05-8.12 (m, 2H, HAr), 8.20-
8.29 (m, 8H, HoPh), 8.77-8.86 (m, 6H, Hpyrrole), 9.04 (s, 1H, Hpyrrole).
UV-vis (CH2Cl2): λmax (log ꢀ) 427 (5.36), 524 (4.29), 563 (3.99), 600
(3.82), 656 (3.40) nm. HRMS, m/z: calcd for MH+ (C52H36N5O2),
762.2869; found, 762.2861.
3-(trans-2-(5,10,15,20-Tetraphenylporphyrin-2-yl)ethen-1-yl)-
benzaldehyde (7). To a solution of phosphonium salt 1 (614 mg, 0.663
mmol) and isophthalaldehyde (89 mg, 0.66 mmol) in CH2Cl2 (6 mL),
was added a 28% aqueous NaOH solution (8 mL). After 3 h of stirring
at room temperature, water (50 mL) was added and the mixture
extracted with CH2Cl2 (2 × 50 mL). The combined organic phases
were washed with water (2 × 50 mL) and dried (MgSO4) before the
solvent was removed under reduced pressure. The residue was purified
by flash column chromatography (silica, 2:1 CH2Cl2/hexane) to give a
4-(trans-2-(5,10,15,20-Tetraphenylporphyrin-2-yl)ethen-1-yl)-
N,N-dimethylaniline (10). To a solution of phosphonium salt 1 (90
mg, 97 µmol) and 4-(dimethylamino)benzaldehyde (23 mg, 154 µmol)
in CH2Cl2 (0.6 mL) was added an aqueous 40% NaOH solution (0.6
mL). The mixture was stirred for 105 min and then poured into water
(50 mL) and extracted with CH2Cl2 (50 mL, 30 mL). The combined
organic extracts were washed with water (2 × 50 mL) and dried
(MgSO4). The solvent was removed in Vacuo, and the residue was
purified by flash column chromatography (silica, 1:1 CH2Cl2/hexane).
The resulting material was recrystallized from CH2Cl2/MeOH, affording
10 (48 mg, 65%) as a purple solid. 1H-NMR (270 MHz, CDCl3): δ
1
cis/trans (∼1:2 by H NMR) mixture of products as a purple solid.
3
3
-2.56 (br s, 2H, NH), 6.70 (d, 2H, J ) 8.9 Hz, HAr), 6.77 (d, 1H, J
) 16.2 Hz, Hethenyl), 7.16 (d, 2H, 3J ) 8.9 Hz, HAr), 7.27 (d, 1H, 3J )
15.9 Hz, Hethenyl), 7.71-7.83 (m, 12H, Hm,pPh), 8.14-8.26 (m, 8H, HoPh),
8.72-8.84 (m, 6H, Hpyrrole), 9.02 (s, 1H, Hpyrrole). UV-vis (CH2Cl2):
λmax (log ꢀ) 421 (5.22), 521 (4.20), 572 (3.87), 605 (3.86), 660 (3.30)
nm. HRMS, m/z: calcd for MH+ (C54H42N5), 760.3440; found,
760.3419.
The solid was dissolved in CH2Cl2 (100 mL) and I2 (35 mg, 0.14 mmol)
added. After stirring at room temperature in the dark for 16 h, the
reaction mixture was washed with 1 M Na2S2O3 (2 × 50 mL), water
(50 mL), and saturated aqueous NaHCO3 (50 mL). The porphyrin
solution was dried (MgSO4), and solvent was removed under reduced
pressure. Flash chromatography as before and recrystallization from
CH2Cl2/MeOH yielded 7 (343 mg, 70%) as a purple solid. 1H-NMR
3
(270 MHz, CDCl3), δ -2.59 (br s, 2H, NH), 7.05 (d, 1H, J ) 16.0
Hz, Hethenyl), 7.30 (d, 1H, J ) 16.0 Hz, Hethenyl), 7.42-7.47 (m, 2H,
2‚Ni. Free-base porphyrin 2 (40 mg, 56 µmol) was refluxed in
CHCl3 (4 mL) and a slurry of Ni(OAc)2‚4H2O (117 mg, 0.47 mmol)
in CH3OH/H2O (1 mL/0.2 mL) added. Triethylamine (3 drops) was
added, and refluxing continued for 16 h. After cooling, the reaction
mixture was diluted with CH2Cl2 (20 mL) and washed with water (20
mL) and saturated aqueous NaHCO3 (20 mL). Drying (MgSO4) and
removal of solvent under reduced pressure gave a purple solid. Flash
column chromatography (silica, CH2Cl2/cyclohexane 1:2) followed by
recrystallization from CH2Cl2/CH3OH, gave 2‚Ni (26 mg, 60%) as a
red-purple solid as well as recovered starting material (12 mg, 30%).
3
HAr), 7.67-7.85 (m, 14H, Hm,pPh and HAr), 8.15-8.27 (m, 8H, HoPh),
8.71-8.84 (m, 6H, Hpyrrole), 9.01 (s, 1H, Hpyrrole), 10.05 (s, 1H, CHO).
UV-vis (CH2Cl2): λmax (log ꢀ) 426 (5.37), 524 (4.30), 563 (4.03), 599
(3.85), 656 (3.41) nm. HRMS, m/z: calcd for MH+ (C53H37N4O),
745.2967; found, 745.3028.
2-(trans-2-5,10,15,20-Tetraphenylporphyrin-2-yl))ethen-1-yl)-
benzaldehyde (8). To a solution of phosphonium salt 1 (416 mg, 0.449
mmol) and phthalaldehyde (61 mg, 0.455 mmol) in CH2Cl2 (6 mL)
was added a 40% aqueous NaOH solution (6 mL). After being stirred
for 10 min at room temperature, water (50 mL) was added and the
mixture was extracted with CH2Cl2 (100 mL). The extract was washed
with water (2 × 50 mL) and dried (MgSO4) before the solvent was
removed under reduced pressure. The residue was purified by flash
column chromatography (silica gel, 2:1 CH2Cl2/hexane) to give a cis/
3
1H-NMR (270 MHz, CDCl3): δ 6.87 (d, 1H, J ) 16.0 Hz, Hethenyl),
3
7.18-7.34 (m, 5H, HAr), 7.14 (d, 1H, J ) 16.0 Hz, Hethenyl), 7.65-
7.76 (m, 12H, Hm,pPh), 7.97-8.07 (m, 8H, HoPh), 8.69-8.73 (m, 6H,
H
pyrrole), 8.90 (s, 1H, Hpyrrole). UV-vis (CH2Cl2): λmax (log ꢀ) 425
(5.32), 540 (4.26), 577 (4.04) nm. HRMS, m/z: calcd for M+
(C52H34N458Ni), 772.2137; found, 772.2132.
1
4‚Ni. Nitrobenzene (4) (28 mg, 37 µmol) was refluxed in CHCl3
(30 mL) and a slurry of Ni(OAc)2‚4H2O (102 mg, 0.41 mmol) in CH3-
OH/H2O (1 mL/0.2 mL) added. The mixture was refluxed for 16 h,
cooled, washed with water (20 mL), and dried (MgSO4), and solvent
was removed under reduced pressure. Recrystallization from CH2Cl2/
CH3OH gave 4‚Ni (30 mg, quantitative) as a red-purple solid. 1H-
NMR (270 MHz, CDCl3): δ 6.92 (d, 1H, 3J ) 15.9 Hz, Hethenyl), 7.06
trans (∼1:3 by H-NMR) mixture of products as a purple solid. The
solid was dissolved in CH2Cl2 (100 mL) and I2 (30 mg, 0.12 mmol)
added. After stirring at room temperature in the dark for 16 h, the
reaction mixture was washed with 1 M Na2S2O3 (2 × 50 mL), water
(50 mL), and saturated aqueous NaHCO3 (50 mL). The porphyrin
solution was dried (MgSO4), and solvent was removed under reduced
pressure. Flash chromatography as before and recrystallization from
CH2Cl2/MeOH yielded 8 (263 mg, 79%) as a purple powder. 1H-NMR
3
3
(d, 1H, J ) 15.9 Hz, Hethenyl), 7.14 (d, 2H, J ) 8.5 Hz, HAr), 7.58-
7.73 (m, 12H, Hm,pPh), 7.90-8.03 (m, 8H, HoPh), 8.05 (d, 2H, 3J ) 8.6
Hz, HAr), 8.63-8.72 (m, 6H, Hpyrrole), 8.89 (s, 1H, Hpyrrole). UV-vis
(CH2Cl2): λmax (log ꢀ) 431 (5.28), 541 (4.23), 583 (4.15) nm. HRMS,
m/z: calcd for MH+ (C52H34N5O258Ni), 818.2066; found, 818.2096.
6‚Cu. Aldehyde 6 (31 mg, 42 µmol) was refluxed in CHCl3 (8
mL), and a slurry of Cu(OAc)2‚H2O (97 mg, 0.49 mmol) in CH3OH/
H2O (0.5 mL/0.1 mL) was added. Refluxing was continued for 90
min. The reaction mixture was diluted with CH2Cl2 (20 mL), washed
with water (20 mL), and dried (MgSO4), and solvent was removed
under reduced pressure. Flash column chromatography (silica, 2:1 CH2-
Cl2/hexane) followed by recrystallization from CH2Cl2/CH3OH gave
6‚Cu (29 mg, 86%) as a red-purple solid. UV-vis (CH2Cl2): λmax
(log ꢀ) 428 (5.35), 549 (4.36), 587 (4.13) nm. HRMS, m/z: calcd for
MH+ (C53H35N4O63Cu), 806.2107; found, 806.2091.
3
(270 MHz, CDCl3): δ -2.59 (br s, 2H, NH), 6.96 (d, 1H, J ) 15.9
Hz, Hethenyl), 7.19 (d, 1H, 3J ) 7.3 Hz, HAr), 7.34 (app t, 1H, 3J ) 7.3
Hz, HAr), 7.52 (app t of d, 1H, 3J ) 7.3 Hz, 4J ) 1.2 Hz, HAr), 7.65-
7.80 (m, 13H, Hm,pPh and HAr), 8.13-8.27 (m, 9H, HoPh and Hethenyl),
3
3
8.69 (d, 1H, J ) 4.9 Hz, Hpyrrole), 8.78 (d, 1H, J ) 4.9 Hz, Hpyrrole),
8.80-8.86 (m, 4 H, Hpyrrole), 9.06 (s, 1H, Hpyrrole), 10.37 (s, 1H, CHO).
UV-vis (CH2Cl2), λmax (log ꢀ) 427 (5.51), 523 (4.44), 564 (4.16), 600
(3.99), 657 (3.59) nm. HRMS, m/z: calcd for M+ (C53H36N4O),
744.2889; found, 744.2908.
4-(trans-2-(5,10,15,20-Tetraphenylporphyrin-2-yl)ethen-1-yl)ani-
sole (9). Phosphonium salt 1 (80 mg, 86 µmol) and anisaldehyde (15
mg, 0.110 mmol) were dissolved in CH2Cl2 (5 mL), and the solution
was stirred at room temperature before adding DBU (80 µL, 0.535
mmol). After 10 min, the reaction mixture was flash column chro-
matographed (silica, 1:1 CH2Cl2/hexane) to give a cis/trans mixture
(∼1:4 by 1H NMR) of products as a purple solid. The solid was
dissolved in CH2Cl2 (10 mL) and I2 (8.5 mg, 33 µmol) added before
stirring at room temperature for 16 h. The reaction was diluted with
CH2Cl2 (20 mL), washed with 1 M aqueous Na2S2O3 (2 × 20 mL) and
H2O (2 × 20 mL), and dried (MgSO4), and solvent was removed under
reduced pressure. Flash column chromatography as before, followed
by recrystallization from CH2Cl2/CH3OH, yielded 9 (40 mg, 62%) as
a purple solid. 1H-NMR (270 MHz, CDCl3): δ -2.55 (br s, 2H, NH),
3.89 (s, 3H, HOMe), 6.89 (d, 1H, 3J ) 16.0 Hz, Hethenyl), 6.92 (d, 2H, 3J
) 8.7 Hz, HAr), 7.25 (d, 2H, 3J ) 8.7 Hz, HAr), 7.32 (d, 1H, 3J ) 16.0
6‚Ni. Aldehyde 6 (33 mg, 44 µmol) was heated at reflux temperature
in CHCl3 (10 mL) and a slurry of Ni(OAc)2‚4H2O (97 mg, 0.39 mmol)
in CH3OH/H2O (1 mL) added. A little triethylamine was added, and
the reflux continued for 36 h. The reaction mixture was diluted with
CH2Cl2 (20 mL), washed with water (20 mL), and dried (MgSO4), and
solvent was removed under reduced pressure. Flash column chroma-
tography (silica, 1:1 CH2Cl2/hexane) followed by recrystallization from
CH2Cl2/CH3OH gave 6‚Ni as a red-purple solid (25 mg, 71%). 1H-
NMR (CDCl3, 270 MHz): δ 7.02 (d, 1H, 3J ) 15.9 Hz, Hethenyl), 7.15
3
3
(d, 1H, J ) 15.9 Hz, Hethenyl), 7.29 (d, 2H, J ) 8.2 Hz, HAr), 7.65-
3
7.78 (m, 12H, Hm,pPh), 7.80 (d, 2H, J ) 8.1 Hz, HAr), 7.97-8.07 (m,

6278 Inorganic Chemistry, Vol. 36, No. 27, 1997
Bonfantini et al.
3
8H, HoPh), 8.69-8.75 (m, 6H, Hpyrrole), 8.94 (s, 1H, Hpyrrole), 9.99 (s,
1H, CHO). UV-vis (CH2Cl2): λmax (log ꢀ) 430 (5.24), 541 (4.22),
579 (4.10). HRMS, m/z: calcd for MH+ (C53H35N4O58Ni), 801.2164;
found, 801.2164.
(app t, 1H, J ) 7.6 Hz, HAr), 7.58-7.74 (m, 12H, Hm,pPh), 7.79 (dd,
1H, 3J ) 7.6, 4J ) 1.2 Hz, HAr), 7.92-8.06 (m, 9H, HoPh and Hethenyl),
8.65-8.70 (m, 6H, Hpyrrole), 8.95 (s, 1H, Hpyrrole), 10.40 (s, 1H, CHO).
UV-vis (CH2Cl2): λmax (log ꢀ) 427 (5.36), 539 (4.33), 576 (4.12) nm.
HRMS, m/z: calcd for M+ (C53H34N4O58Ni), 800.2086; found, 800.2030.
6‚Pd. Aldehyde 6 (10 mg, 13 µmol) was refluxed in toluene (5
mL), and PdCl2(NCPh)2 (11 mg, 29 µmol) was added. After 30 min
of refluxing, TLC showed no further change, so the solvent was
removed under pressure and the resulting black material flash column
chromatographed (silica, 3:2 CH2Cl2/hexane). The first bright red
fraction was collected, the solvent was removed under reduced pressure,
and the solid was recrystallized from CH2Cl2/CH3OH to give 6‚Pd (10
mg, 91%) as a red-purple powder. 1H-NMR (270 MHz, CDCl3): δ
7.11 (d, 1H, 3J ) 15.9 Hz, Hethenyl), 7.22 (d, 1H, 3J ) 15.9 Hz, Hethenyl),
8‚Pd. Aldehyde 8 (13 mg, 17 µmol) was refluxed in CH2Cl2 (10
mL) and PdCl2(NCPh)2 (29 mg, 76 µmol) added. After 16 h of
refluxing, TLC showed no further change so the solvent was removed
under pressure and the resulting black material flash column chro-
matographed (silica, 1:1 CH2Cl2/hexane). The first bright red fraction
was collected, the solvent removed under reduced pressure, and the
solid was recrystallized from CH2Cl2/CH3OH to give 8‚Pd (10 mg,
69%) as a red-purple powder. 1H-NMR (270 MHz, CDCl3): δ 6.96
3
7.33 (d, 2H, J ) 8.2 Hz, HAr), 7.68-7.84 (m, 14H, Hm,pPh and HAr),
3
3
(d, 1H, J ) 15.9 Hz, Hethenyl), 7.22 (d, 1H, J ) 7.9 Hz, HAr), 7.40
8.10-8.21 (m, 8H, Hz, HoPh), 8.66-8.81 (m, 6H, Hpyrrole), 9.01 (m,
1H, Hpyrrole), 9.99 (s, 1H, CHO). UV-vis (CH2Cl2): λmax (log ꢀ) 426
(5.36), 533 (4.45), 569 (4.27) nm. HRMS, m/z: calcd for M+
(C53H34N4O106Pd), 848.1767; found, 848.1752.
3
3
(app t, 1H, J ) 7.9 Hz, HAr), 7.52 (app t, 1H, J ) 7.9 Hz, HAr),
3
7.65-7.82 (m, 12H, Hm,pPh), 7.84 (d, 1H, J ) 7.9 Hz, HAr), 8.09 (d,
1H, 3J ) 15.9 Hz, Hethenyl), 8.10-8.22 (m, 8H, HoPh), 8.66 (d, 1H, 3J )
4.9 Hz, Hpyrrole), 8.74 (d, 1H, 3J ) 4.9 Hz, Hpyrrole), 8.76-8.81 (m, 4H,
7‚Ni. Aldehyde 7 (51 mg, 68 µmol) and NiBr2 (36 mg, 0.16 mmol)
were heated to reflux in DMF (5 mL). Almost immediately TLC
indicated no starting material remained. The solvent was removed
under high vacuum and the resulting material flash column chromato-
graphed (silica, 1:1 CH2Cl2/hexane). Recrystallization from CH2Cl2/
MeOH gave 7‚Ni (43 mg, 79%) as a purple solid. 1H-NMR (270 MHz,
CDCl3): δ 6.96 (d, 1H, 3J ) 16.0 Hz, Hethenyl), 7.17 (d, 1H, 3J ) 16.0
Hz, Hethenyl), 7.44-7.49 (m, 2H, HAr), 7.64-7.80 (m, 14H, Hm,pPh and
HAr), 7.99-8.08 (m, 8H, HoPh), 8.69-8.79 (m, 6H, Hpyrrole), 8.94 (s,
1H, Hpyrrole), 10.06 (s, 1H, CHO). UV-vis (CH2Cl2): λmax (log ꢀ) 425
(5.33), 538 (4.26), 574 (4.03) nm. HRMS, m/z: calcd for M+
(C53H34N4O58Ni), 800.2086; found, 800.2129.
H
λ
pyrrole), 9.04 (s, 1H, Hpyrrole), 10.41 (s, 1H, CHO). UV-vis (CH2Cl2):
max 424, 531, 567 nm. HRMS, m/z: calcd for M+ (C53H34N4O106Pd),
848.1767; found, 848.1777.
Acknowledgment. We are grateful for support of this work
from The Public Good Science Fund (MAU602), the Massey
University Research Fund, the Massey University Postgraduate
Scholarship and Graduate Research Fund, the William Georgetti
Scholarship, and the Young Scientists’ Fund, Royal Society of
New Zealand (D.C.W.R.). Support from the New Zealand
Lottery Commission and the University of Otago Research
Committee is gratefully acknowledged and support in part from
The Public Good Science Fund (UOO-508). We also thank the
University of Otago Chemistry Department for the award of a
Ph.D. scholarship to P.A.C.
8‚Ni. Aldehyde 8 (31 mg, 42 µmol) was refluxed in CHCl3 (10
mL), and a slurry of Ni(OAc)2‚4H2O (149 mg, 0.60 mmol) in CH3-
OH/H2O (1.5 mL/ 0.2 mL) was added. After 5 days, TLC indicated
that no 8 remained, so the reaction mixture was diluted with CH2Cl2
(20 mL), washed with water (2 × 20 mL), and dried (MgSO4), and
solvent was removed under reduced pressure. Flash column chroma-
tography (silica 1:1 CH2Cl2/hexane) followed by recrystallization from
CH2Cl2/CH3OH gave 8‚Ni (30 mg, 89%) as a red-purple solid. 1H-
NMR (270 MHz, CDCl3): δ 6.86 (d, 1H, 3J ) 15.9 Hz, Hethenyl), 7.11
Supporting Information Available: Figures showing the electronic
spectral changes of 2-5, 9, 10, 2‚Ni, and 4‚Ni and RR spectra of 3 (9
pages). Ordering information is given on any current masthead page.
3
3
(d, 1H, J ) 7.6 Hz, HAr), 7.34 (app t, 1H, J ) 7.6 Hz, HAr), 7.45
IC9702330