A strategy for the assembly of multiple porphyrin arrays based on the coordination chemistry of Ru-centered porphyrin pentamers

Article abstract of DOI:10.1021/jo001564o

An approach which employs pentameric porphyrin arrays as building blocks toward larger porphyrin arrays is described. Two flexible, and one relatively rigid, Ru-centered porphyrin pentamers (1-3) were synthesized and fully characterized. Their potential as building blocks toward larger porphyrin arrays has been studied via their coordination chemistry using bidentate and tetradentate ligands. DABCO (diazabicyclo[2.2.2]octane) can bind two monomeric porphyrins but was found to be too small to allow the complete formation of a 10-porphyrin array. On the other hand, titration of a larger bridging dipyridyl porphyrin ligand 17 (0.5 equiv) with 1 or 2 and tetrapyridyl ligand 18 (0.25 equiv) with 3 results in the formation of the 11-porphyrin and 21-porphyrin arrays, respectively, with the 21-porphyrin array containing porphyrins in three different metalation states. Changes in the chemical shift of the inner NH protons as well as the ortho- and meso-protons of the pyridyl groups of the porphyrin ligand clearly indicate the formation of large multiple porphyrin complexes. These studies demonstrate that by use of carefully designed building blocks and suitable bridging ligands, porphyrin arrays can be constructed with a dramatic increase in size in relatively few steps. Exploiting the fact that the strength of binding of pyridyl ligands is Ru > Zn > Ni, intra- vs intermolecular competition has been used to investigate aspects of the folding of the array. The photophysical properties of 3 are also described.

Full text of DOI:10.1021/jo001564o

4476
J . Org. Chem. 2001, 66, 4476-4486
A Str a tegy for th e Assem bly of Mu ltip le P or p h yr in Ar r a ys Ba sed
on th e Coor d in a tion Ch em istr y of Ru -Cen ter ed P or p h yr in
P en ta m er s
Chi Ching Mak,† Nick Bampos,*,† Scott L. Darling,† Marco Montalti,‡ Luca Prodi,‡ and
J eremy K. M. Sanders†
University Chemical Laboratory, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK,
and Dipartimento di Chimica G. Ciamician, Universita` degli Studi di Bologna, I-40126 Bologna, Italy
nb10013@cam.ac.uk
Received November 3, 2000
An approach which employs pentameric porphyrin arrays as building blocks toward larger porphyrin
arrays is described. Two flexible, and one relatively rigid, Ru-centered porphyrin pentamers (1-3)
were synthesized and fully characterized. Their potential as building blocks toward larger porphyrin
arrays has been studied via their coordination chemistry using bidentate and tetradentate ligands.
DABCO (diazabicyclo[2.2.2]octane) can bind two monomeric porphyrins but was found to be too
small to allow the complete formation of a 10-porphyrin array. On the other hand, titration of a
larger bridging dipyridyl porphyrin ligand 17 (0.5 equiv) with 1 or 2 and tetrapyridyl ligand 18
(0.25 equiv) with 3 results in the formation of the 11-porphyrin and 21-porphyrin arrays,
respectively, with the 21-porphyrin array containing porphyrins in three different metalation states.
Changes in the chemical shift of the inner NH protons as well as the ortho- and meso-protons of
the pyridyl groups of the porphyrin ligand clearly indicate the formation of large multiple porphyrin
complexes. These studies demonstrate that by use of carefully designed building blocks and suitable
bridging ligands, porphyrin arrays can be constructed with a dramatic increase in size in relatively
few steps. Exploiting the fact that the strength of binding of pyridyl ligands is Ru > Zn > Ni,
intra- vs intermolecular competition has been used to investigate aspects of the folding of the array.
The photophysical properties of 3 are also described.
In tr od u ction
of covalent porphyrin oligomers.4 The challenging syn-
thesis of covalently linked porphyrin systems may impose
a practical limit to the formation of large porphyrin
arrays. The strategy for construction of large assemblies
based solely on a covalent approach would prove too
difficult with nontrivial purification and the overall yields
modest. Furthermore, covalent assemblies lack structural
control as a result of the restrictions inherent in the bond
lengths and bond angles of the connecting units. To create
larger arrays, the self-assembly approach making use of
molecular recognition becomes an attractive alternative
to the traditional covalent strategy. Self-assembly pro-
vides efficient access to ordered arrays by spontaneous
build-up based on noncovalent interactions and directed
through molecular recognition events. Because of their
excellent photochemical and biomimetic properties,
Zn(II) or Mg(II) ions have often been used as the central
metals. However, these ions under the conditions and
solvents employed in this study are relatively labile with
Ks for pyridine < 104 M-1, such that the resulting self-
assembled arrays are an equilibrium mixture which
favors the monomers in solution at the low concentrations
employed in photophysical experiments. Ru(II)-porphy-
Natural light-harvesting complexes are remarkably
efficient despite involving the use of hundreds of chro-
mophores to transfer and funnel energy over long dis-
tances to the reaction center.1 The ability to mimic
natural photosynthetic processes could provide insight
into solar energy conversion and storage. Owing to the
size and complexity of naturally occurring light-harvest-
ing systems, considerable efforts have recently been
directed toward the design and characterization of syn-
thetic analogues that might elucidate or mimic key
mechanisms of photon capture and energy migration
processes.2 Arrays of five or more porphyrin units have
been constructed either through self-assembly of porphy-
rins bearing molecular recognition units3 or the synthesis
† University of Cambridge.
‡ Universita` degli Studi di Bologna.
(1) (a) Deisenhofer, J .; Epp, O.; Miki, K.; Huber, R.; Michel, H.
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Rees, D. C. Nature 1989, 339, 111. (c) Mauzerall, D. C.; Greenbaum,
N. L. Biochim. Biophys. Acta 1989, 974, 119. (d) Hunter, C. N.; van
Grondelle, R.; Olsen, J . D. Trends Biochem. Sci. 1989, 14, 72. (e)
Barber, J .; Andersson, B. Nature 1994, 370, 31. (f) McDermott, G.;
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10.1021/jo001564o CCC: $20.00 © 2001 American Chemical Society
Published on Web 06/01/2001

Assembly of Multiple Porphyrin Arrays
J . Org. Chem., Vol. 66, No. 13, 2001 4477
rins, however, exhibit much stronger binding even at low
concentrations; this can be harnessed in the construction
of supramolecular architectures.
covalently linked 9-porphyrin array,4a two types of por-
phyrins with different side-chain polarity were used in
order to control chromatographic mobility and ensure
that the 9-porphyrin array was easily isolated from the
starting materials. A second generation strategy em-
ployed Mitsunobu condensation as the key reaction and
gave a 9-porphyrin array which was designed to possess
greater flexibility.7 All the porphyrin units within this
9-porphyrin array have hexyl side chains in the â-posi-
tions, while the starting porphyrin components have
either polar hydroxyl or carboxyl groups. As a result, the
9-porphyrin array derived from these polar components
was very nonpolar and could be separated very easily
from both starting materials and any side products due
to incomplete reaction.
In the present study, we began by synthesizing two
flexible porphyrin pentamers (1 and 2, Chart 1) and one
comparatively more rigid porphyrin pentamer 3 on the
basis of our second strategy. Pentamers 1 and 2 are more
flexible because there are in total four three-carbon
saturated alkyl chains around the core Ru-porphyrin
while there are four carbon-carbon triple bonds in the
case of 3. Synthetic disconnections for the component
monomers are illustrated in Scheme 1. The unsym-
metrical porphyrins 4 and 5 were prepared by mixed
condensation of 4-tert-butyl- and 4-hydroxymethyl-9 ben-
zaldehydes with dipyrromethane 10 followed by meta-
lation.8 In a similar fashion, 6 was prepared in 21%
overall yield from aldehyde 11 as the unsymmetrical
analogue, followed by alkaline hydrolysis of the tetraester
porphyrin 12. Mitsunobu condensation9 of Ni-4 or Zn-5
porphyrin with porphyrin tetraacid 6 (0.25 equiv) in THF
afforded core free-base porphyrin pentamers 7 and 8 in
58 and 73% yield, respectively. Because of the forma-
tion of four ester linkages in both pentamers 7 and 8,
the 1H NMR spectra exhibited a sharp singlet in the
region δ 5.2-5.5 ppm corresponding to eight benzylic
protons resulting from the four consecutive condensation
reactions. Additional structural characterization was
provided by the correct integral intensities of the
meso-proton signals for the peripheral and core por-
phyrin units (4:1) and the molecular ion peaks in the
MALDI spectra at m/z 5185 (M + H)+ and 5212 (M +
H)+ for 7 and 8, respectively, indicating complete reaction
of 6 with four peripheral Ni-4 or Zn-5 porphyrins,
respectively.
In light of all this, self-assembly based on metal ligand
interactions becomes quite attractive, as we are afforded
the freedom to change metals, ligands, and coordination
geometries. In the work reported here, ruthenium was
identified as a suitable metal in the construction of the
large assemblies, as the interaction between pyridyl
ligands and ruthenium is much stronger than that with
zinc or magnesium.5
Although noncovalent assemblies are easily prepared,
they often afford imprecise structural control, while the
covalent strategy provides porphyrin arrays with some
structural diversity. To harness the advantages from both
strategies, we set out to apply a combination of covalent
and coordination chemistry to generate large porphyrin
arrays. In effect, we need to initially prepare several
porphyrin pentamers by conventional covalent chemistry
with one Ru-porphyrin in the center. Since Ru(II)-
porphyrins are stable to substitution and exhibit strong
binding affinities with nitrogen-based ligands, we believe
these pentamers can be used as the semilarge building
blocks which can in turn self-assemble around some core
or bridging ligands, generating porphyrin arrays with a
dramatic increase in size. In this report we present a
complete characterization of a number of covalently
linked pentamers and describe the interactions of three
different covalently linked pentamers with two bidentate
and one tetradentate ligand. To achieve this, we exploit
the fact that the strength of coordination of pyridyl
groups to metals used in this study follow the series Ru
. Zn . Ni, and show how inter- vs intramolecular
competition can be controlled through flexibility of as-
pects of the molecular structure. Some preliminary
results have been presented elsewhere.6
Resu lts a n d Discu ssion
Cova len t Ch em istr y tow a r d P en ta m er ic P or p h y-
r in Ar r a ys. In our initial strategy for preparation of a
(4) (a) Mak, C. C.; Bampos, N.; Sanders, J . K. M. Angew. Chem.,
Int. Ed. 1998, 37, 3020. (b) Davila, J .; Harriman, A.; Milgrom, L. R.
Chem. Phys. Lett. 1987, 136, 427. (c) Dubowchik, G. M.; Hamilton, A.
D. J . Chem. Soc., Chem. Commun. 1987, 293. (d) Wennerstro¨m, O.;
Ericsson, H.; Raston.; I.; Svensson, S.; Pimlott, W. Tetrahedron Lett.
1989, 30, 1129. (e) Nagata, T.; Osuka, A.; Maruyama, K. J . Am. Chem.
Soc. 1990, 112, 3054. (f) Osuka, A.; Liu, B.; Maruyama, K. Chem. Lett.
1993, 949. (g) Prathapan, S.; J ohnson, T. E.; Lindsey, J . S. J . Am.
Chem. Soc. 1993, 115, 7519. (h) Seth, J .; Palaniappan, V.; J ohnson, T.
E.; Prathapan, S.; Lindsey, J . S.; Bocian, D. F. J . Am. Chem. Soc. 1994,
116, 10578. (i) Wagner, R. W.; J ohnson, T. E.; Lindsey, J . S. J . Am.
Chem. Soc. 1996, 118, 11166. (j) Anderson, H. L.; Martin, S. J .; Bradley,
D. D. C. Angew. Chem., Int. Ed. Engl. 1994, 33, 655. (k) Anderson, S.;
Anderson, H. L.; Sanders, J . K. M. J . Chem. Soc., Perkin Trans. 1 1995,
2247. (l) Osuka, A.; Tanabe, N.; Nakajima, S.; Maruyama, K. J . Chem.
Soc., Perkin Trans. 2 1996, 199. (m) Officer, D. L.; Burrell, A. K.; Reid,
D. C. W. J . Chem. Soc., Chem. Commun. 1996, 1657. (n) Mongin, O.;
Papamicae¨l, C.; Hoyler, N.; Gossauer, A. J . Org. Chem. 1998, 63, 5568.
(o) Vicente, M. G. H.; Cancilla, M. T.; Lebrilla, C. B.; Smith, K. M. J .
Chem. Soc., Chem. Commun. 1998, 2355. (p) Biemans, H. A. M.;
Rowan, A. E.; Verhoeven, A.; Vanoppen, P.; Latterini, L.; Foekema,
J .; Schenning, A. P. H. J .; Meijer, E. W.; de Schryver, F. C.; Nolte, R.
J . M. J . Am. Chem. Soc. 1998, 120, 11054. (q) Nakano, A.; Osuka, A.;
Yamazaki, I.; Yamazaki, T.; Nishimura, Y. Angew. Chem., Int. Ed.
1998, 37, 3023. (r) Li, J .; Diers, J . R.; Seth, J .; Yang, S. I.; Bocian, D.
F.; Holten, D.; Lindsey, J . S. J . Org. Chem. 1999, 64, 9090. (s) Li, J .;
Lindsey, J . S. J . Org. Chem. 1999, 64, 9101. (s) Aratani, N.; Osuka,
A.; Kim, Y. H.; J eong, D. H.; Kim, D Angew. Chem., Int. Ed. 2000, 39,
1458.
Metalation of 7 and 8 with Ru3(CO)12 in refluxing
toluene10 provided Ru-centered pentamers 1 and 2 as
deep red solids in 66 and 61% yield, respectively. The
absence of reactive functional groups on the periphery
of precursors 7 and 8 eliminated Ru-mediated side
reactions during metalation. Successful metalation places
the Ru-coordinated CO ligand axially on one face of the
porphyrin, such that the ortho-aromatic protons of the
phenyl groups on the core porphyrin which are equivalent
(doublet) for 7 and 8 before metalation, become inequiva-
(7) (a) Mak, C. C.; Pomeranc, D.; Montalti, M.; Prodi, L.; Sanders,
J . K. M. J . Chem. Soc., Chem. Commun. 1999, 1083. (b) Zeng, F.;
Zimmerman, S. C. J . Am. Chem. Soc. 1996, 118, 5326.
(8) (a) Vidal-Ferran, A.; Bampos, N.; Sanders, J . K. M. Inorg. Chem.
1997, 36, 6117. (b) Clyde-Watson, Z.; Vidal-Ferran, A.; Twyman, L.
J .; Walter, C. J .; McCallien, D. W. J .; Fanni, S.; Bampos, N.; Wylie, R.
S.; Sanders, J . K. M. New. J . Chem. 1998, 22, 493. (c) Twyman, L. J .;
Sanders, J . K. M. Tetrahedron Lett. 1999, 40, 6681.
(9) (a) Mitsunobu, O. Synthesis 1981, 1. (b) Hughes, D. L. Org. React.
1992, 42, 335.
(10) Barley, M.; Becker, J . Y.; Domazetis, G.; Dolphin, D.; J ames,
B. R. Can. J . Chem. 1983, 61, 2389.
(5) Webb, S. J .; Sanders, J . K. M. Inorg. Chem. 2000, 39, 5912.
(6) Mak, C. C.; Bampos, N.; Sanders, J . K. M. J . Chem. Soc., Chem.
Commun. 1999, 1085.

4478 J . Org. Chem., Vol. 66, No. 13, 2001
Mak et al.
Ch a r t 1
lent and give rise to two sets of signals for 1 and 2 in the
δ 7.2-7.5 ppm region after metalation. Further evidence
of successful metalation is offered by the disappearance
Ru-porphyrin 16 contains the hydroxyl groups. Mit-
sunobu condensation of 13 and 16 (0.5 equiv) afforded 3
in 21% yield. While the pyrrolic methyl signals from the
core porphyrin were clearly separated from those of the
peripheral porphyrins and the ortho-aromatic protons of
the phenyl groups on the core porphyrin were inequiva-
lent in 1 and 2, only broad resonances corresponding to
1
of the inner NH proton signals in the H NMR spectra
and the appearance of a new molecular ion peak in the
MALDI mass spectra (with loss of CO)11 at m/z 5283 and
5314 for 1 and 2, respectively.
1
these signals were observed in the H NMR spectrum of
For the synthesis of the rigid pentamer 3, the func-
tional groups on the core and peripheral units were
reversed. The peripheral bis-porphyrin unit 13, which
was prepared from 3,5-diiodobenzoic acid 1412 and 154a
(Scheme 2), now bears the carboxylic group while the core
3. A MALDI-TOF spectrum afforded the ion peak at m/z
5432 [(M - 2H - CO)+], and the appearance of a proton
signal at δ 5.90 ppm corresponded to the formation of
two ester linkages.
(12) 14 was prepared by reductive deamination of 4-amino-3,5-
diiodobenzoic acid: Doyle, M. P.; Dellaria, J . F., J r.; Siegfried, B.;
Bishop, S. W. J . Org. Chem. 1977, 42, 3494.
(11) (a) Frauenkron, M.; Berkessel, A.; Gross, J . H. Eur. Mass.
Spectrom. 1997, 3, 427.

Assembly of Multiple Porphyrin Arrays
J . Org. Chem., Vol. 66, No. 13, 2001 4479
Sch em e 1
Sch em e 2
is almost isoenergetic with a charge-separated state
obtained by an electron transfer process from the Ru-
porphyrin to a peripheral component. It seems unlikely
that such an electron transfer process can occur in a non-
polar solvent or even in a rigid matrix at 77 K, where
the charge-separated state is strongly destabilized.14,15
As previously found for similar assemblies,15 the most
likely explanation for this phenomenon is the heavy-atom
effect caused by the presence of the ruthenium centers
enhancing intersystem crossing in the Zn-porphyrin
units. However, the thermodynamically feasible energy
transfer process to the lowest energy triplet excited state
centered on the Ru-porphyrin, T1(Ru), which lies below
the S1(Zn) state, cannot be ruled out (Figure 1). In turn,
T1(Ru) is also completely quenched, both in deaerated
solution at room temperature and at 77 K in rigid matrix.
Since electron transfer from T1(Ru), which has a lower
energy content than S1(Zn), is even more disfavored, this
quenching process can only be explained by an energy
transfer process occurring between the two different
The electronic absorption spectrum of 3 in dichlo-
romethane is essentially a superposition of the spectra
of the constituent core and peripheral components (15
with added pyridine acts as the reference compound).
Photophysical studies indicate that the typical fluores-
cence intensity of the Zn-porphyrin component is reduced
at room temperature to about 60%, in good agreement
with the observed decrease of the exited state lifetime
from 1.6 to 1.0 ns. From these data, a quenching rate
constant of 4 × 108 s-1 can be calculated; an even faster
rate constant, 1 × 109 s-1, was found in a rigid matrix at
77 K, where the lifetime is quenched from 2.0 to 0.5 ns.
According to the redox potentials and the energy of the
lowest energy singlet excited state centered on the Zn-
porphyrin,13,14 S1(Zn), in polar solvents this latter state
(14) Gaines, G. L., III; O’Neil, M. P.; Svec, W. A.; Niemczyk, M. P.;
Wasielewski, M. R. J . Am. Chem. Soc. 1990, 113, 719.
(13) Kalyanasundaram, K. Photochemistry of Polypyridine and
Porphyrin Complexes; Academic Press: London, 1991.
(15) Prodi, A.; Indelli, M. T.; Kleverlaan, C. J .; Scandola, F.; Alessio,
E.; Gianferrara, T.; Marzilli, L. G. Chem. Eur. J . 1999, 5, 2668.

4480 J . Org. Chem., Vol. 66, No. 13, 2001
Mak et al.
NMR spectra when up to 1.5 equiv of DABCO was added
to 7. On the other hand, significant changes were
observed during the titration with 8 (Figure 3). Most
notably, a new upfield signal at around δ -5.0 ppm was
observed when less than 2 equiv of DABCO was added
(Figures 3b and 3c). This upfield signal, which is diag-
nostic of the ligand sandwiched between two Zn-por-
phyrins,4a,19 disappeared after addition of more than 2
equiv of DABCO (Figure 3d) as there are only two
intramolecular binding sites within 8sexcess DABCO
will be in fast exchange.
Titration of DABCO into a mM solution of 1 gave
spectra which clearly indicated formation of both mono-
ligated and bis-ligated porphyrin complexes when up to
1
0.5 equiv of DABCO was added (Figure 4). The H NMR
and NOESY spectra suggested that these two species
were in slow exchange on the chemical shift time scale
but fast on the T1 time scale, giving a sharp signal at
-5.68 ppm (bis-ligated complex) and two triplet reso-
nances at 0.62 and -3.65 ppm (mono-ligated complex).
Methylene protons of DABCO which are closer to the Ru
center in the mononuclear complex will experience a
stronger ring current effect and display an upfield triplet
resonance (-3.65 ppm). This equilibrium may be at-
tributed to the small size of DABCO, such that the steric
interaction between the peripheral porphyrins of the two
pentamers does not favor the formation of a 10-porphyrin
array.
When less than 0.5 equiv of DABCO was added to 2
(Figure 5), the signals observed previously in the case of
1 were absent. Instead, two new triplets were recorded
at -5.20 and -5.58 ppm as a result of the intramolecular
coordination of DABCO between one peripheral Zn-
porphyrin and the core Ru-porphyrin (Figure 5a). As the
Ru-porphyrin has a stronger binding affinity than that
of Zn component, the methylene protons of the ligand
closer to the Ru center (-5.58 ppm) exhibited a sharper
upfield triplet signal. Intramolecular coordination is
favored over the intermolecular construction of the 10-
porphyrin array by the flexible linkers between the core
and the 4 peripheral porphyrins. In the presence of 2
equiv of DABCO, an additional signal, which is assigned
to the ligand sandwiched intramolecularly between two
Zn-porphyrins (observed previously in 8), appears (Figure
5d).
F igu r e 1. Energy diagram for the transitions of 3.
kinds of component, this time from T1(Ru), centered on
the core unit, to T1(Zn), localized on the periphery. The
T1(Zn) is in turn luminescent at 77 K, giving the typical
phosphorescence band with λmax ) 720 nm and lifetime
of 60 ms (at 77 K).
Coor d in a tion Ch em istr y of th e P en ta m er ic P or -
p h yr in Ar r a ys. Ru-porphyrin monomers have been used
as building blocks for small porphyrin arrays,16 but there
is little literature precedent for using larger porphyrin
building blocks to self-assemble around a multidentate
ligand to achieve large porphyrin arrays. Our first aim
was to study the coordination properties of our three Ru-
centered pentamers (1, 2, and 3), initially with bidentate
ligands (DABCO or bipyridyl porphyrin 17)17 and then a
tetradentate ligand such as tetrapyridyl porphyrin 18
(Chart 2). The progress of the coordination assembly as
well as the final structure of the coordinated arrays was
monitored as NMR titration experiments, typically on
3-8 mM solutions.
(a ) Titr a tion w ith DABCO. The coordination proper-
ties of the central Ru-porphyrin of 1 and 2 are modulated
by the Ni/Zn chemistry of the peripheral porphyrins in
addition to the spatial constraints imparted on the
complexes by the “sweep” of the flexible peripheral
1
Ni/Zn-porphyrins. The H NMR shifts of DABCO-bound
Ru and/or Zn are diagnostic of the coordinating environ-
ment by virtue of the porphyrin ring currents (Fig-
ure 2). In-plane Ru draws a coordinated nitrogen atom
closer to the shielding region of the porphyrin plane
than does a pyramidal Zn analogue, and the greater
deshielding is reflected in a high-field shift of the meso
resonance. Titration experiments on the respective core
free-base pentamers 7 and 8 (differing only in the metal
at the peripheral sites) were performed as control experi-
ments. Since Ni-porphyrins exhibit a low affinity for
nitrogenous ligands (for piperidine, K ≈ 200 M-1 in
toluene at 22 °C),18 no change was observed in the 1H
DABCO cannot form an analogous intramolecular
complex between the Ru- and Zn-porphyrins in 3, due to
the rigid linkers. Instead, a sharp signal at -5.72 ppm
attributed to the formation of the 10-porphyrin array was
observed when less than 0.5 equiv of ligand was added
(Figures 6a and 6b). Increasing the amount of DABCO
to 1 or 2 equiv (Figures 6c and 6d) results in broad
resonances in the range -4.5 to -5.7 ppm. This phe-
nomenon may be due to an equilibrium mixture of
complexes, in which DABCO is intermolecularly bound
between two Ru-porphyrins, two Zn-porphyrins, or one
Ru- and one Zn-porphyrin (Figure 7). The evidence
therefore suggests that DABCO is too small a bridging
ligand for the clean formation of 10-porphyrin arrays on
the basis of the Ru-centered pentamers prepared in this
(16) For Ru-porphyrin monomers used as building blocks in
porphyrin arrays, see: (a) Anderson, H. L.; Hunter, C. A.; Sanders,
J . K. M. J . Chem. Soc., Chem. Commun. 1989, 226. (b) Alessio, E.;
Macchi, M.; Heath, S.; Marzilli, L. G. J . Chem. Soc., Chem. Commun.
1996, 1411. (c) Funatsu, K.; Kimura, A.; Imamura, T.; Ichimura, A.;
Sasaki, Y. Inorg. Chem. 1997, 36, 1625. (d) Funatsu, K.; Imamura,
T.; Ichimura, A.; Sasaki, Y. Inorg. Chem. 1998, 37, 1798. (e) Funatsu,
K.; Imamura, T.; Ichimura, A.; Sasaki, Y. Inorg. Chem. 1998, 37,
4986.
(18) (a) LaMar, G. N.; Walker, F. A. In The Porphyrins; Dolphin,
D., Ed.; Academic Press: New York, 1979; Vol. IV, pp 129-130. (b)
Walker, F. A.; Hui, E.; Walker, J . M. J . Am. Chem. Soc. 1975, 97,
2390.
(17) Kim, H.-J .; Bampos, N.; Sanders, J . K. M. J . Am. Chem. Soc.
1999, 121, 8120.
(19) Hunter, C. A.; Meah, M. N.; Sanders, J . K. M. J . Am. Chem.
Soc. 1990, 112, 5773.

Assembly of Multiple Porphyrin Arrays
J . Org. Chem., Vol. 66, No. 13, 2001 4481
Ch a r t 2
F igu r e 2. Chemical shifts (δ ppm) of the Ru- and/or Zn-bound
DABCO ligand in the 1H NMR spectrum. For comparison, free
DABCO appears at 2.7 ppm.
F igu r e 4. High-field region of the 1H NMR spectrum of 1 (500
MHz, CDCl3, 300 K), showing the appearance of the bound
ligand resonances upon addition of 0.5 equiv of DABCO. This
region of the spectrum was free of resonances in the absence
of added ligand.
chemical shifts for ortho- and meta-protons of the pyridyl
groups of the porphyrin ligand (significant shift to lower
δ values) were diagnostic of the coordination to the axial
position of the central Ru metal of the porphyrin pen-
tamers. In addition, the changes in chemical shift of the
inner NH and meso-H on complexation clearly reflect the
effect of the porphyrin ring current.
Compared to the corresponding chemical shifts of the
free ligand, significant upfield shifts were observed for
all the proton resonances mentioned previously (Figure
8a-c). Furthermore, the integral intensity ratios of the
signals of the porphyrin pentamers and of NH or meso-H
of the bridging ligand 17 confirmed the integrity of the
porphyrin arrays. Titration of Ru-porphyrin monomer 19
with 17 (0.5 equiv) gave slightly upfield shifted signals
for all of the inner NH, meso-H, and 2,6-pyridyl protons
of 17 (Figure 8d).
(c) Titr a tion w ith Tetr a p yr id yl P or p h yr in 18. The
coordination of 18 to four Ru-porphyrin monomers has
been reported.16d However, owing to the large size of our
pentamers, the possibility of tetrapyridyl porphyrin 18
coordinating less than four pentamers cannot be ex-
cluded even when 4 equiv of a pentamer has been added.
As the ring current effect around 18 is cumulatively
dependent on the number of bound Ru-porphyrins,16d
titration of 18 with less than 4 equiv of Ru-porphyrin
monomer 19 should produce a statistical mixture of
complexes. Each complex will give rise to different inner
NH-proton signals, the chemical shift of which will be
sensitive to the number of Ru-porphyrin around ligand
18.20
F igu r e 3. High-field region of the 1H NMR spectrum of 8 (500
MHz, CDCl3, 300 K), showing the appearance of the bound
ligand resonance as a function of the number of equiv of
DABCO added: (a) 0, (b) 1.0, (c) 2.0, (d) 2.5. The structure
above represents only half of the 8‚DABCO complex.
study, although the titration of DABCO with 3 may
provide the 10-porphyrin array over a narrow stoichio-
metric regime.
(b) Titr a tion w ith Dip yr id yl P or p h yr in 17. The
large size of ligand 17 would be expected to prevent
intramolecular coordination between either two Zn-
porphyrins or between one Ru- and one Zn-porphyrin in
the manner discussed above and should also relieve steric
interactions between two bound pentamers. Indeed,
titration of 1 or 2 with less than 0.5 equiv of dipyridyl
porphyrin 17 clearly indicated the intermolecular as-
sembly of the flexible pentamers around the dipyridyl
ligand, forming an 11-porphyrin array in both cases. The
(20) Kariya, N.; Imamura, T.; Sasaki, Y. Inorg. Chem. 1997, 36, 833.

4482 J . Org. Chem., Vol. 66, No. 13, 2001
Mak et al.
F igu r e 6. High-field region of the 1H NMR spectrum of 3 (500
MHz, CDCl3, 300 K), showing the appearance of the bound
ligand resonances as a function of the number of equiv of
DABCO added: (a) 0.25, (b) 0.5, (c) 1.0, (d) 2.0. This region of
the spectrum was free of resonances in the absence of added
ligand.
F igu r e 5. High-field region of the 1H NMR spectrum of 2 (500
MHz, CDCl3, 300 K), showing the appearance of the bound
ligand resonances as a function of the number of equiv of
DABCO added: (a) 0.25, (b) 0.5, (c) 1.0, (d) 2.0, (e) 3.0. This
region of the spectrum was free of resonances in the absence
of added ligand. The structure above shows a DABCO molecule
coordinating to the central Ru-porphyrin of 2 and one of the
peripheral Zn-porphyrins; only half the molecule is repre-
sented.
Four types of NH proton signals corresponding to the
binding of one to four Ru-porphyrins were observed when
2 equiv of Ru-porphyrin monomer 20 was added to
tetrapyridyl porphyrin 18 (Figure 9). The value of the
chemical shift for the NH signals appears incrementally
upfield (by δ 0.5 ppm) with each additional bound Ru-
porphyrin. With these results in hand, we were able to
perform titration experiments of various pentamers with
18 (Figure 10) and follow the progress of the reaction by
registering the upfield shift of the NH proton signals.
Addition of 4 equiv of flexible pentamer 1 to 18 (Figure
10b) led to coordination of a maximum of 3 equiv of 1,
resulting in a 16-porphyrin array. The shape of the
resulting complex, with the four flexible terminal Ni
porphyrins of the constituent pentamer 1 sweeping a
large volume in space, may account for this result.
Addition of Ru-porphyrin monomer 20 to this mixture
caused scrambling (Figure 10c) as the smaller porphyrin
displaced the pentamers in the complex, giving a non-
statistical mixture of complexes including both three- and
four-coordinated species. On the other hand, titration
with 4 equiv of the rigid pentamer 3 indicated coordina-
tion of 4 equiv of 3, yielding a 21-porphyrin array (Figure
10d). The rigid structure of the pentamer 3 offers efficient
“spatial” coordination around the core ligand 18, com-
pared to the flexible pentamer 1, thus favoring the
saturated 21-porphyrin complex. A reduced upfield shift
F igu r e 7. Possible equilibria for DABCO sandwiched inter-
molecularly between two molecules of rigid pentamer 3 involv-
ing the core Ru and peripheral Zn porphyrins.
was detected for the NH-proton signals of both the three-
and four-coordinated complexes describe above, possibly

Assembly of Multiple Porphyrin Arrays
J . Org. Chem., Vol. 66, No. 13, 2001 4483
1
F igu r e 8. Selected regions of the H NMR spectrum (500 MHz, CDCl3, 300 K) showing (left to right) the meso, 3,5-pyridyl, and
inner NH proton resonances of 17: (a) free ligand, (b) with 2 equiv of pentamer 1, (c) with 2 equiv of pentamer 2, (d) with 2 equiv
of monomer 19.
1
F igu r e 10. High-field region of the H NMR spectrum of 18
(500 MHz, CDCl3, 300 K) showing the inner NH protons
resonances: (a) with 4 equiv of monomer 20, (b) with 4 equiv
of pentamer 1, (c) with 4 equiv of pentamer 1 and trace amount
of monomer 13, (d) with 4 equiv of pentamer 3.
flexibility of the molecules prepared and the binding
affinity of pyridyl ligands to three metals in the order
F igu r e 9. High-field region of the 1H NMR spectrum of 18
(500 MHz, CDCl3, 300 K) showing the inner NH protons
resonances (a) free ligand, (b) with 2 equiv of Ru monomer
20, (c) with 4 equiv of Ru monomer 20. The structure above
represents four Ru-porphyrins bound to 18.
Ru > Zn > Ni. The steric effect due to the porphyrin
arrays surrounding the core or bridging ligands is the
crucial factor controlling the formation of the large
porphyrin complexes. By careful design of building blocks
and choosing suitable bridging ligands, porphyrin arrays
can be fabricated with the size increasing dramatically
with very few steps. Photolytic removal and substitution
of the CO by additional ligands expands the scope of this
approach even further.21 While the present choice of
metals and the inclusion of amines is not ideal for
photochemical studies, we aim to exploit and extend the
methodology described here to design large arrays with
more suitable metals and functional groups.
attributed to the smaller cumulative shielding effect of
the pentamers due to some steric interactions around the
tetrapyridyl porphyrin 18, compared to case described
for the monomer 20.
Con clu sion s
This paper reports the synthesis and characterization
of new Ru-centered pentameric porphyrin arrays. J udi-
cious use of functional groups at the porphyrin periphery
help separate the desired material from the starting
material and possible side products. The NMR titration
experiments demonstrate the potential for these porphy-
rin arrays as large building blocks, self-assembling
around bi- and tetraddentate ligands to provide even
larger porphyrin arrays, by exploiting the inherent
Exp er im en ta l Section
1H NMR spectra (250, 400, or 500 MHz) were recorded on
Bruker AC-250, AM-400, or DRX-500 spectrometers, respec-
tively. 13C NMR spectra were obtained on an AM-400 operating
at 100.6 MHz or a Bruker AC-250 operating at 62.9 MHz. All
(21) Darling, S. L.; Mak, C. C.; Bampos, N.; Feeder, N.; Teat, S. J .;
Sanders, J . K. M. New J . Chem. 1999, 23, 359.

4484 J . Org. Chem., Vol. 66, No. 13, 2001
Mak et al.
NMR measurements were carried out at room temperature
in deuteriochloroform unless otherwise specified. Routine UV/
visible spectra were obtained on a Uvikon 810 spectrometer
in 10 mm oven-dried cuvettes. Distilled solvents were used
throughout and when used dry were freshly obtained from
solvent stills. Triethylamine and dichloromethane (CH2Cl2)
were distilled from CaH2 under argon while toluene and
tetrahydrofuran (THF) were distilled from CaH2 or sodium,
also under argon. Free-base porphyrins were converted into
zinc/nickel complexes in near quantitative yield by treatment
with zinc/nickel acetate dihydrate in CH2Cl2 or refluxing
chloroform, respectively. MALDI-TOF mass spectra were
recorded on a Kratos Analytical Ltd, Kompact MALDI IV mass
spectrometer. A nitrogen laser (337 nm, 85 kW peak laser
power, 3 ns pulse width) was used to desorb the sample ions,
and the instrument was operated in linear time-of-flight mode
with an accelerating potential of 20 kV. Results from 50 laser
shots were signal averaged to give one spectrum. An aliquot
(1 µL) of a saturated solution of the matrix (sinapinic acid)
was deposited on the sample plate surface. Before the matrix
completely dried, a small volume (1 µL) of analytes (dissolved
in dichloromethane/chloroform at 1 mg/mL) was layered on
the top of the matrix and allowed to air-dry.
Absorption spectra were recorded with a Perkin-Elmer λ 16
spectrophotometer. Uncorrected emission spectra, corrected
excitation spectra, and phosphorescence lifetimes were ob-
tained with a Perkin-Elmer LS50 spectrofluorimeter. The
fluorescence lifetimes (uncertainty, (5%) were obtained with
an Edinburgh single-photon counting apparatus (D2 filled flash
lamp). Emission spectra in a CH2Cl2 rigid matrix at 77 K were
recorded using quartz tubes immersed in a quartz Dewar filled
with liquid nitrogen. To allow comparison of emission intensi-
ties, corrections for instrumental response, inner filter effects,
and phototube sensitivity were performed.22
191.8; MS (FAB, m/z) 367 [(M + H)+]. Anal. Calcd for
C
19H26O7: C, 62.28; H, 7.15. Found: C, 61.94; H, 7.20.
5,15-Bis(3,5-(eth oxyca r bon yleth ylp r op yloxy)p h en yl)-
2,8,12,18-tetr a (n -h exyl)-3,7,13,17-tetr a m eth ylp or p h yr in
(12). 12 was obtained as a red powder in 49% overall yield
from 10 and 11 according to a previously published procedure:8
1H NMR (250 MHz, CDCl3) δ -2.43 (s, 2 H, NH), 0.92 (t, J )
7.1 Hz, 12 H, (CH2)5CH3), 1.25 (t, J ) 7.1 Hz, 12 H,
COOCH2CH3), 1.32-1.57 (2 × m, 16 H, (CH2)3(CH2)2CH3), 1.77
(apparent quintet, J ) 7.1 Hz, 8 Hz, (CH2)2CH2(CH2)2CH3),
2.18-2.25 (2 × m, 16 H, CH2CH2(CH2)3CH3 and OCH2CH2-
CH2), 2.58 (t, J ) 7.2 Hz, 8 H, CH2COOEt), 2.68 (s, 12 H,
pyrrolic CH3), 3.98-4.04 (m, 8H, CH2(CH2)4CH3), 4.10-4.19
(2 × m, 16 H, COOCH2CH3 and OCH2), 6.91 (t, J ) 2.2 Hz, 2
H, ArH), 7.26 (d, J ) 2.2 Hz, 4 H, ArH), 10.25 (s, 2 H, meso-
H); 13C NMR (62.9 MHz, CDCl3) δ 14.1, 14.4, 22.8, 24.8, 26.8,
30.0, 30.9, 32.0, 33.3, 60.4, 67.3, 96.9, 102.0, 112.9, 117.6, 136.1,
141.4, 143.3, 143.9, 144.8, 159.4, 173.2; MS (FAB, m/z) 1377
[(M + 2H)+]; UV/vis (CH2Cl2) λmax (log ꢀ) ) 408 (5.32), 506
(4.26), 538 (3.82), 576 (3.90), 622 (3.46). Anal. Calcd for
C
84H118N4O12: C, 73.33; H, 8.14; N, 4.07. Found: C, 73.23; H,
8.51; N, 4.09.
5,15-Bis(3,5-(4-eth er -bu ta n oic a cid )p h en yl)-2,8,12,18-
tetr a (n -h exyl)-3,7,13,17-tetr a m eth ylp or p h yr in (6). A solu-
tion containing 12 (200 mg, 0.145 mmol) and Na2CO3 (200 mg,
1.89 mmol) in a mixture of water/THF/ethanol (100 mL, 1/1/
2) was refluxed at 100 °C for 1 d. After removel most of the
solvents, EtOAc (200 mL) was added and the solution was
washed with water until the organic layer changed from green
to red color. The organic layer was then separated, washed
with brine, and dried (MgSO4) and the solvent removed. The
resulting solid was recrystallized from methanol to give 6 as
a dark violet crystalline solid (142 mg, 78%): 1H NMR (250
MHz, DMSO-d6) δ -2.62 (s, 2 H, NH), 0.86 (t, J ) 7.2 Hz, 12
H, (CH2)5CH3), 1.25-1.55 (2 × m, 16 H, (CH2)3(CH2)2CH3), 1.70
(apparent quintet, J ) 7.2, 8 H, (CH2)2CH2(CH2)2CH3), 1.90-
2.20 (2 × m, 16 H, CH2CH2(CH2)3CH3 and OCH2CH2CH2), 2.41
(t, J ) 7.3 Hz, 8 H, CH2COOH), 2.62 (s, 12 H, CH3), 3.80-
4.20 (m, 8 H, CH2(CH2)4CH3), 4.15 (t, J ) 6.4 Hz, 8 H, OCH2),
7.00 (t, J ) 2.1 Hz, 2 H, ArH), 7.21 (d, J ) 2.1 Hz, 4 H, ArH),
10.18 (s, 2 H, meso-H), 12.12 (s, 4 H, COOH); 13C NMR
(62.9 MHz, DMSO-d6) δ 14.3, 22.6, 24.8, 26.4, 29.9, 30.6, 31.8,
33.4, 67.6, 96.8, 102.4, 112.8, 118.2, 136.5, 141.0, 143.3, 143.7,
144.7, 159.6, 174.5; UV/vis (THF) λmax (log ꢀ) ) 408 (5.44),
504 (4.77), 580 (4.69), 538 (4.64), 610 (4.55). Anal. Calcd for
Dipyrrole 108c and porphyrins 154a and 1717 were prepared
according to previously published procedures. Tetrapyridyl
porphyrin 18 was used as purchased from Aldrich. 19 and 20
are the metalated analogues6 of 12 and its tetraacid7 prepared
according to the method described for 1 and 2 below.
4-Hyd r oxym eth ylben za ld eh yd e (9).23 A solution of tere-
phthalaldehyde (15.0 g, 112 mmol) in THF (100 mL) was cooled
to 0 °C. Sodium borohydride (1.50 g, 39.5 mmol) was added in
one portion at the same temperature and the mixture stirred
at room temperature for 1 h. Solvent was removed and the
residue taken up in EtOAc (200 mL). The solution was then
washed with water (2 × 100 mL) and brine and dried
(anhydrous MgSO4). Upon removal of the solvent, the residue
was chromatographed on SiO2, eluting with hexane/ethyl
acetate (gradient 2:1 to 1:1) to give 9 as a white solid (9.5 g,
62%): 1H NMR (250 MHz, CDCl3) δ 4.80 (s, 2 H, CH2OH), 7.53
(d, J ) 8.0 Hz, 2 H, ArH), 7.87 (d, J ) 8.0 Hz, 2 H, ArH), 10.0
(s, 1 H, CHO); 13C NMR (62.9 MHz, CDCl3) δ 64.4, 126.9, 130.0,
135.5, 148.1, 192.3.
3,5-B is (e t h o x y c a r b o n y le t h y lp r o p y lo x y )b e n za ld e -
h yd e (11). A solution of 3,5-dihydroxybenzaldehyde (1.0 g, 7.2
mmol) and K2CO3 (4.2 g, 30.4 mmol) in DMF (50 mL) was
heated to 80 °C under argon for 1 h. 4-Bromoethylbutanoate
(3.5 g 18.0 mmol) was added and the reaction mixture stirred
for 1 d at 80 °C. EtOAc (100 mL) was added and the reaction
mixture washed with water (3 × 100 mL), after which the
organic layer was separated, washed with brine (100 mL), and
dried (MgSO4) and the solvent removed. The resulting crude
product was purified by SiO2 chromatography eluting with
hexane/ethyl acetate (gradient 4:1 to 3:1) to give 11 as a white
solid (2.5 g, 94%): 1H NMR (250 MHz, CDCl3) δ 1.26 (t, J )
7.1 Hz, 6 H, COOCH2CH3), 2.11 (tt, J ) 6.1 and 7.2 Hz, 4 H,
OCH2CH2CH2), 2.50 (t, J ) 7.2 Hz, 4 H, OCH2CH2CH2), 4.03
(t, J ) 6.1 Hz, 4 H, OCH2CH2CH2), 4.15 (q, J ) 7.1 Hz, 4 H,
COOCH2CH3), 6.67 (t, J ) 2.3 Hz, 1 H, ArH), 6.97 (d, J ) 2.3
Hz, 2 H, ArH), 9.87 (s, 1 H, CHO); 13C NMR (62.9 MHz, CDCl3)
δ 14.2, 24.5, 30.7, 60.5, 67.2, 107.8, 108.0, 138.4, 160.5, 173.0,
C
76H102N4O12: C, 72.23; H, 8.13; N, 4.43. Found: C, 71.99; H,
7.98; N, 4.06.
3,5-Diiod oben zoic Acid (14).24 4-Amino-3,5-diiodobenzoic
acid (1.0 g, 2.6 mmol) suspended in DMF (10 mL) was added
dropwise to a rapidly stirred solution of tert-butylnitrite and
anhydrous DMF (5 mL) heated at 50 °C in a 100 mL three-
necked round-bottomed flask equipped with a reflux condenser.
Gas evolution was registered throughout the addition. After
addition was complete, the reaction mixture was stirred for a
further 15 min and then cooled to room temperature. The
resulting burnt orange solution was diluted with ether (30 mL)
and then poured into dilute HCl (50 mL, 3 N). After separation,
the etheral solution was washed with additional dilute HCl
(50 mL) and water and dried over anhydrous Na2SO4. Removal
of ether and recrystallization from MeOH afforded 14 as a pale
brown solid (0.6 g, 62%): 1H NMR (250 MHz, CDCl3) δ 8.29
(t, J ) 1.6 Hz, 1 H, ArH), 8.39 (d, J ) 1.6 Hz, 2 H, ArH); 13C
NMR (62.9 MHz, CDCl3) δ 94.5, 138.3, 150.1, 167.4, 208.5; MS
(FAB, m/z) 374 (M+). Anal. Calcd for C7H4I2O2: C, 22.49; H,
1.08. Found: C, 22.66; H, 1.06.
Bis(Zn -p or p h yr in ) Ben zoic Acid 13. A solution contain-
ing 15 (500 mg, 0.24 mmol) 14 (85 mg, 0.11 mmol), Pd2(dba)3
(22 mg, 0.022 mmol), and AsPh3 (37 mg, 0.12 mmol) in THF/
Et3N (20 mL, 1:1) in a Schlenk tube was degassed by two
freeze-pump-thaw cycles. The mixture was then stirred at
room temperature under argon for 14 h and the solvent
(22) Credi, A.; Prodi, L. Spectrochim. Acta, Part A 1998, 54, 159.
(23) Gennari, C.; Ceccarelli, S.; Piarulli, U.; Aboutayab, K.; Donghi,
M.; Paterson, I. Tetrahedron 1998, 54, 14999.
(24) (a) Wheeler, H. L.; Liddle, L. M. Am. Chem. J . 1909, 42, 441.
(b) Lulinski, P.; Skulski, L. Bull. Chem. Soc. J pn. 1997, 70, 1665.

Assembly of Multiple Porphyrin Arrays
J . Org. Chem., Vol. 66, No. 13, 2001 4485
removed, after which the residue was extracted into EtOAc
(50 mL), washed with water (2 × 50 mL) and brine, and dried.
After removel of the solvent, the crude product was purified
by SiO2 chromatography eluting with hexane/ethyl acetate
(gradient 1:9 to MeOH/ethyl acetate, 1:20) to give 13 as a
purple solid (380 mg, 75%): 1H NMR (250 MHz, CDCl3) δ 0.93
(t, J ) 7.0 Hz, 24 H, (CH2)5CH3), 1.20-1.90 (3 × m, 48 H,
(CH2)2(CH2)3CH3), 1.53 (s, 36 H, t-Bu), 2.10-2.30 (m, 16 H,
CH2CH2(CH2)3CH3), 2.46 (s, 12 H, pyrrolic CH3), 2.58 (s, 12
H, pyrrolic CH3), 3.99 (br t, 16 H, CH2(CH2)4CH3), 7.83 (br t,
2 H, ArH), 7.96 (br d, 4 H, ArH), 8.03 (d, J ) 7.9 Hz, 4 H,
ArH), 8.18 (d, J ) 7.9 Hz, 4 H, ArH), 8.25-8.45 (2 × m, 3 H,
ArH), 10.21 (s, 4 H, meso-H); MS (MALDI, m/z) 2229 [(M +
H)+]; UV/vis (CH2Cl2) λmax (log ꢀ) 412 (6.22), 538 (4.93), 574
(4.65). HRMS calcd for C147H186N8O2NaZn2 2246.3174, found
2246.3111.
F lexible P en ta m er 7. A solution of DIAD (160 mg, 0.79
mmol) in 5 mL of THF was added slowly to a solution
containing 4 (230 mg, 0.23 mmol), 6 (55 mg, 0.044 mmol), and
PPh3 (320 mg, 1.22 mmol) in THF (30 mL) at room tempera-
ture. After stirring the mixture at room temperature for 3 h,
the solvent was removed and the residue was purified by SiO2
chromatography eluting with hexane/ethyl acetate (gradient
10:1 to 5:1) to give 7 as a deep red solid (130 mg, 58%): 1H
NMR (250 MHz, CDCl3) δ -2.41 (br s, 2 H, NH), 0.70-1.10
(m, 60 H, (CH2)5CH3), 1.20-2.50 (4 × m, 168 H, CH2(CH2)4-
CH3 and CH2CH2COO), 1.55 (s, 36 H, t-Bu), 2.21 (s, 24 H,
pyrrolic CH3), 2.25 (s, 24 H, pyrrolic CH3), 2.75 (s, 12 H, core
pyrrolic CH3), 2.81 (t, J ) 7.3 Hz, 8 H, CH2CH2COO), 3.45-
3.75 (m, 32 H, CH2(CH2)4CH3), 3.89 (br t, 8 H, core CH2(CH2)4-
CH3), 4.30 (t, J ) 6.2 Hz, 8 H, ArOCH2CH2), 5.44 (s, 8 H,
COOCH2Ar), 7.05 (br t, 2 H, core ArH), 7.36 (br d, 4 H, core
ArH), 7.60 (d, J ) 8.2 Hz, 8 H, ArH), 7.64 (d, J ) 8.2 Hz, 8 H,
ArH), 7.76 (d, J ) 7.8 Hz, 8 H, ArH), 7.84 (d, J ) 7.8 Hz, 8 H,
ArH), 9.40 (s, 8 H, meso-H), 10.14 (s, 2 H, meso-H);13C NMR
(100.6 MHz, CDCl3 with 5% pyridine-d5) δ 14.1, 14.5, 15.1,
15.4, 22.7, 25.0, 26.3, 26.8, 27.0, 29.3, 29.7, 29.8, 30.0, 31.1,
31.7, 31.9, 32.0, 32.8, 33.3, 34.9, 66.3, 67.3, 96.3, 97.0, 102.1,
112.9, 115.7, 116.7, 117.5, 124.2, 126.9, 128.4, 128.6, 132.6,
133.2, 136.0, 136.1, 138.2, 138.6, 139.2, 139.3, 139.4, 140.2,
140.7, 141.4, 143.4, 143.8, 143.9, 144.1, 144.8, 151.5, 159.5,
173.1; MS (MALDI, m/z) 5185 [(M + H)+]; UV/vis (CH2Cl2) λmax
(log ꢀ) 408 (5.99), 528 (4.76), 564 (4.86). Anal. Calcd for
Nick e l-5-(4-ter t-b u t ylp h e n yl)-10-(4-h yd r oxym e t h yl-
p h en yl)-2,8,12,18-t et r a h exyl-3,7,13,17-t et r a m et h ylp or -
p h yr in (4). 4 was prepared (0.5-1.0 g scale) as a red powder
in 26% overall yield from 10 by mixed aldehyde condensation
and metalation according to a previously reported procedure:8
1H NMR (400 MHz, CDCl3) δ 1.00 (t, J ) 7.2 Hz, 12 H,
(CH2)5CH3), 1.37-1.57 (2 × m, 16 H, (CH2)3(CH2)2CH3), 1.62
(s, 9 H, t-Bu), 1.71 (apparent quintet, J ) 7.3 Hz, 8 H,
(CH2)2CH2(CH2)2CH3), 2.10 (apparent quintet, J ) 7.3 Hz, 8
H, CH2CH2(CH2)3CH3), 2.30 (s, 6 H, pyrrolic CH3), 2.32 (s, 6
H, pyrrolic CH3), 3.73 (t, J ) 7.6 Hz, 8 H, CH2(CH2)4CH3), 5.01
(s, 2 H, CH2OH), 7.65 (d, J ) 7.9 Hz, 2 H, ArH), 7.70 (d, J )
8.2 Hz, 2 H, ArH), 7.82 (d, J ) 8.1 Hz, 2 H, ArH), 7.89 (d, J )
7.9 Hz, 2 H, ArH), 9.52 (s, 2 H, meso-H); 13C NMR (100.6 MHz,
CDCl3) δ 10.3, 11.3, 11.6, 19.4, 23.1, 23.2, 26.8, 26.9, 28.9, 29.0,
29.1, 30.1, 32.3, 64.6, 97.5, 118.3, 119.1, 127.1, 128.8, 136.0,
136.6, 141.9, 142.5, 143.0, 143.1, 143.2, 144.2, 144.6, 144.7,
144.8, 147.9, 148.0, 156.0; MS (MALDI, m/z) 998 (M+); UV/vis
(CH2Cl2) λmax (log ꢀ) 408 (5.20), 528 (4.12), 564 (3.99). HRMS
calcd for C65H86N4ONaNi 1019.6047, found 1019.6041.
Zin c -5-(4-t er t -b u t y lp h e n y l)-10-(4-h y d r o x y m e t h y l-
p h en yl)-2,8,12,18-t et r a h exyl-3,7,13,17-t et r a m et h ylp or -
p h yr in (5). Zn porphyrin 5 was prepared (0.5-1.0 g scale) in
32% overall yield from 10 by mixed aldehyde condensation and
metalation according to a previously reported procedure:8 1H
NMR (250 MHz, CDCl3) δ 0.92 (t, J ) 7.1 Hz, 12 H,
(CH2)5CH3), 1.20-1.58 (2 × m, 16 H, (CH2)3(CH2)2CH3), 1.64
(s, 9 H, t-Bu), 1.75 (apparent quintet, J ) 7.4 Hz, 8 H,
(CH2)2CH2(CH2)2CH3), 2.18 (apparent quintet, J ) 7.4 Hz, 8
H, CH2CH2(CH2)3CH3), 2.45 (s, 6 H, pyrrolic CH3), 2.46 (s, 6
H, pyrrolic CH3), 3.95 (t, J ) 7.3 Hz, 8 H, CH2(CH2)4CH3), 5.06
(d, J ) 4.0 Hz, 2 H, CH2OH), 7.72 (d, J ) 7.3 Hz, 2 H, ArH),
7.75 (d, J ) 8.2 Hz, 2 H, ArH), 7.97 (d, J ) 7.8 Hz, 2 H, ArH),
8.07 (d, J ) 8.2 Hz, 2 H, ArH), 10.16 (s, 2 H, meso-H); 13C
NMR (62.9 MHz, CDCl3) δ 14.1, 15.1, 15.4, 22.7, 26.8, 30.0,
31.8, 32.0, 33.3, 35.0, 65.5, 97.5, 118.8, 119.6, 124.2, 125.9,
132.7, 133.4, 137.9, 138.4, 140.6, 140.8, 143.2, 143.3, 143.4,
146.3, 146.4, 147.6, 148.0, 151.5; MS (MALDI, m/z) 1004 (M+);
UV/vis (CH2Cl2) λmax (log ꢀ) 410 (5.26), 538 (3.91), 574 (3.65).
HRMS calcd for C65H86N4ONaZn 1025.5985, found 1025.6010.
(Ca r b on yl)-r u t h e n iu m -b is(5,10-(4-h yd r oxym e t h yl-
p h en yl)-2,8,12,18-t et r a h exyl-3,7,13,17-t et r a m et h ylp or -
p h yr in (16). 16 was prepared, according to the metalation
procedure described for 1 and 2 below, in 59% yield from the
free-base porphyrin isolated as a side product in the prepara-
tion of 5: 1H NMR (400 MHz, CDCl3 with 5% pyridine-d5) δ
0.79 (t, J ) 7.3 Hz, 12 H, (CH2)5CH3), 1.20-1.45 (2 x m, 16 H,
(CH2)3(CH2)2CH3), 1.60 (apparent quintet, J ) 7.4 Hz, 8 H,
(CH2)2CH2(CH2)2CH3), 1.95-2.10 (m, 8 H, CH2CH2(CH2)3CH3),
2.28 (s, 12 H, pyrrolic CH3), 3.73 (t, J ) 7.5 Hz, 8 H, CH2(CH2)4-
CH3), 5.03 (s, 4 H, CH2OH), 7.64 (d, J ) 7.1 Hz, 2 H, ArH),
7.66 (d, J ) 7.1 Hz, 2 H, ArH), 7.88 (d, J ) 7.8 Hz, 2 H, ArH),
7.92 (d, J ) 7.8 Hz, 2 H, ArH), 9.74 (s, 2 H, meso-H); 13C NMR
(100.6 MHz, CDCl3 with 5% pyridine-d5) δ 14.1, 15.4, 22.7,
26.7, 30.0, 31.9, 33.0, 64.9, 98.7, 119.2, 125.4, 125.7, 132.7,
133.3, 137.2, 140.9, 141.2, 143.0; MS (MALDI, m/z) 1015 [(M
+ H - CO)+]; UV/vis (CH2Cl2) λmax (log ꢀ) 402 (5.31), 524 (4.23),
554 (4.12). HRMS calcd for C63H80N4O3Ru 1042.4232, found
1043.5393.
C
336H438N20O12Ni4: C, 77.85; H, 8.52; N, 5.40. Found: C, 77.71;
H, 8.56; N, 5.39.
F lexible P en ta m er 8. A solution of DIAD (100 mg, 0.50
mmol) in THF (5 mL) was added slowly to a solution contain-
ing 5 (120 mg, 0.12 mmol), 6 (30 mg, 0.024 mmol), and PPh3
(200 mg, 0.76 mmol) in THF (15 mL) at room temperature.
After stirring the mixture at room temperature for 3 h, the
solvent was removed and the residue was purified by SiO2
chromatography eluting with hexane/ethyl acetate (gradient
10:1 to 5:1) to give 8 as a purple solid (90 mg, 73%): 1H NMR
(400 MHz, CDCl3) δ -2.49 (br s, 2 H, NH), 0.70-0.95 (m, 60
H, (CH2)5CH3), 1.20-1.48 (2 × m, 80 H, (CH2)3(CH2)2CH3), 1.60
(s, 36 H, t-Bu), 1.60-1.72 (m, 40 H, (CH2)2CH2(CH2)2CH3),
2.00-2.20 (2 × m, 48 H, CH2CH2(CH2)3CH3 and CH2CH2COO),
2.28 (s, 24 H, pyrrolic CH3), 2.36 (s, 24 H, pyrrolic CH3), 2.60
(t, J ) 7.4 Hz, 8 H, CH2CH2COO), 2.71 (s, 12 H, core pyrrolic
CH3), 3.70 (t, J ) 7.7 Hz, 16 H, CH2(CH2)4CH3), 3.78 (t, J )
7.7 Hz, 16 H, CH2(CH2)4CH3), 3.80-3.90 (m, 8 H, core
CH2(CH2)4CH3), 4.21 (t, J ) 6.1 Hz, 8 H, ArOCH2CH2), 5.21
(s, 8 H, COOCH2Ar), 7.05 (t, J ) 2.1 Hz, 2 H, core ArH), 7.30
(d, J ) 2.1 Hz, 4 H, core ArH), 7.55 (d, J ) 7.9 Hz, 8 H, ArH),
7.69 (d, J ) 8.3 Hz, 8 H, ArH), 7.89 (d, J ) 8.3 Hz, 8 H, ArH),
7.93 (d, J ) 7.9 Hz, 8 H, ArH), 9.90 (s, 8 H, meso-H), 10.08 (s,
2 H, meso-H); 13C NMR (100.6 MHz, CDCl3) δ 14.1, 14.5, 15.0,
15.3, 22.8, 24.8, 26.6, 26.7, 29.8, 30.0, 30.1, 31.0, 31.9, 32.0,
33.3, 35.0, 66.4, 67.3, 96.9, 97.3, 102.0, 113.0, 117.5, 118.3,
119.5, 124.2, 126.9, 128.4, 128.6, 132.8, 133.4, 135.0, 136.1,
137.6, 138.2, 140.6, 141.4, 143.3, 143.4, 144.2, 144.8, 146.1,
146.2, 147.4, 147.9, 151.4, 159.5, 173.1; MS (MALDI, m/z) 5212
[(M + H)+]; UV/vis (CH2Cl2) λmax (log ꢀ) 410 (6.20), 540 (4.90),
574 (4.59). Anal. Calcd for C336H438N20O12Zn4‚2H2O: C, 76.92;
H, 8.49; N, 5.34. Found: C, 76.71; H, 8.12; N, 4.82.
F lexible P en ta m er 1. Tris-ruthenium dodecacarbonyl10 (80
mg, 0.13 mmol) was added to a solution of 7 (125 mg, 0.024
mmol) in toluene (30 mL). The mixture was freeze-pump-
thaw degassed once and stirred at reflux for 18 h. The mixture
was allowed to cool; the solvent was then removed and the
residue purified by SiO2 chromatography eluting with hexane/
ethyl acetate (gradient 10:1 to 5:1) to give 1 as a deep red solid
(85 mg, 66%): 1H NMR (250 MHz, CDCl3) δ 0.70-1.10 (m, 60
H, (CH2)5CH3), 1.20-1.70 (3 × m, 120 H, CH2CH2(CH2)3CH3),
1.56 (s, 36 H, t-Bu), 1.70-1.90 (m, 8 H, CH2CH2COO), 1.90-
2.40 (m, 40 H, CH2CH2(CH2)3CH3), 2.22 (s, 24 H, pyrrolic CH3),
2.24 (s, 24 H, pyrrolic CH3), 2.69 (s, 12 H, core pyrrolic CH3),
2.78 (t, J ) 7.5 Hz, 8 H, CH2CH2COO), 3.64 (br t, J ) 7.2 Hz,
32 H, CH2(CH2)4CH3), 3.91 (br t, 8 H, CH2(CH2)4CH3), 4.20-
4.40 (m, 8 H, ArOCH2CH2), 5.42 (br s, 8 H, COOCH2Ar), 7.03
(br t, 2 H, core ArH), 7.29-7.34 (m, 2 H, core ArH), 7.34-7.40

4486 J . Org. Chem., Vol. 66, No. 13, 2001
Mak et al.
(m, 2 H, core ArH), 7.59 (d, J ) 7.8 Hz, 8 H, ArH), 7.63 (d, J
) 8.2 Hz, 8 H, ArH), 7.75 (d, J ) 7.8 Hz, 8 H, ArH), 7.84 (d,
J ) 8.2 Hz, 8 H, ArH), 9.43 (s, 8 H, meso-H), 10.03 (s, 2 H,
meso-H);13C NMR (250 MHz, CDCl3) δ 14.2, 15.2, 15.5, 22.8,
25.0, 26.4, 27.0, 29.9, 30.3, 31.1, 31.8, 31.9, 32.0, 32.8, 33.3,
34.9, 66.3, 67.4, 96.4, 99.4, 102.3, 112.9, 113.6, 115.7, 116.7,
119.7, 124.2, 126.9, 132.6, 133.2, 136.0, 136.1, 137.6, 138.2,
138.7, 139.3, 139.4, 139.5, 140.3, 140.7, 141.4, 141.5, 143.5,
143.5, 143.9, 144.0, 145.0, 151.5, 159.3, 159.5, 173.2; MS
(MALDI, m/z) 5283 [(M - CO)+]; UV/vis (CH2Cl2) λmax (log ꢀ)
406 (5.98), 526 (4.83), 562 (4.87). Anal. Calcd for C337H436N20O13-
Ni4Ru‚2H2O: C, 75.70; H, 8.29; N, 5.24. Found: C, 75.50; H,
8.06; N, 4.96.
140.6, 141.4, 141.5, 143.0, 143.3, 143.4, 145.0, 146.1, 146.2,
147.4, 147.9, 151.4, 159.5, 173.1; MS (MALDI, m/z) 5309 [(M
- CO)+]; UV/vis (CH2Cl2) λmax (log ꢀ) 410 (6.27), 540 (5.08),
574 (4.78). Anal. Calcd for C337H436N20O13Zn4Ru‚3H2O: C,
75.07; H, 8.26; N, 5.20. Found: C, 74.78; H, 8.06; N, 5.09.
Rigid P en ta m er 3. A solution of DIAD (85 mg, 0.42 mmol)
in THF (5 mL) was added slowly to a solution containing 13
(190 mg, 0.085 mmol), 16 (36 mg, 0.035 mmol), and PPh3 (200
mg, 0.76 mmol) in THF (25 mL) at 0 °C. After stirring of the
mixture at room temperature for 15 h, solvent was removed
and the residue was purified by SiO2 chromatography eluting
with hexane/ethyl acetate (10:1) to give 3 as a red solid (40
mg, 21%): 1H NMR (400 MHz, CDCl3) δ 0.80-1.00 (m, 60 H,
(CH2)5CH3), 1.30-1.60 (2 × m, 80 H, (CH2)3(CH2)2CH3), 1.51
(s, 72 H, t-Bu), 1.65-1.85 (m, 40 H, (CH2)2CH2(CH2)2CH3),
2.10-2.30 (m, 40 H, CH2CH2(CH2)3CH3), 2.44 (s, 24 H, Zn-
pyrrolic CH3), 2.58 (s, 24 H, Zn-pyrrolic CH3), 2.40-2.60 (br
resonances, 12 H, Ru-pyrrolic CH3), 3.80-4.06 (m, 16 H,
CH2(CH2)4CH3), 5.91 (s, 4 H, ArCH2O), 7.81 (t, J ) 1.8 Hz, 4
H, ArH), 7.93 (d, J ) 1.7 Hz, 8 H, ArH), 7.90-8.30 (br
resonances, 8 H, ArH), 8.06 (d, J ) 8.1 Hz, 8 H, ArH), 8.19 (d,
J ) 8.1 Hz, 8 H, ArH), 8.33 (t, J ) 1.7 Hz, 2 H, ArH), 8.63 (d,
J ) 1.7 Hz, 4 H, ArH), 10.01 (s, 2 H, meso-H), 10.21 (s, 8 H,
meso-H); MS (MALDI, m/z) 5432 [(M - 2H - CO)+]; UV/vis
(CH2Cl2) λmax (log ꢀ) 412 (6.11), 540 (4.87), 574 (4.58). Anal.
Calcd for C357H448N20O5Zn4Ru‚2H2O: C, 77.99; H, 8.29; N, 5.09.
Found: C, 77.72; H, 8.23; N, 4.49.
F lexible P en ta m er 2. Tris-ruthenium dodecacarbonyl10 (20
mg, 0.031 mmol) was added to a solution of 8 (40 mg, 0.008
mmol) in toluene (15 mL). The mixture was freeze-pump-
thaw degassed once and stirred at 100 °C for 39 h. The mixture
was allowed to cool; the solvent was removed and the residue
then purified by SiO2 chromatography eluting with hexane/
ethyl acetate (gradient 10:1 to 5:1) to give 2 as a red solid (25
mg, 61%): 1H NMR (250 MHz, CDCl3) δ 0.70-1.00 (m, 60 H,
(CH2)5CH3), 1.20-1.60 (m, 80 H, (CH2)3(CH2)2CH3), 1.60-2.40
(3 × m, 88 H, CH2(CH2)2(CH2)2CH3 and CH2CH2COO), 1.61
(s, 36 H, t-Bu), 2.29 (s, 24 H, pyrrolic CH3), 2.35 (s, 24 H,
pyrrolic CH3), 2.58 (br t, 8 H, CH2CH2COO), 2.68 (s, 12 H,
core pyrrolic CH3), 3.60-4.00 (m, 40 H, CH2(CH2)4CH3), 4.10-
4.30 (m, 8 H, ArOCH2CH2), 5.18 (s, 8 H, COOCH2Ar), 7.04 (br
t, 2 H, core ArH), 7.20-7.40 (2 × m, 4 H, core ArH), 7.55 (d,
J ) 7.9 Hz, 8 H, ArH), 7.70 (d, J ) 8.2 Hz, 8 H, ArH), 7.89 (d,
J ) 7.9 Hz, 8 H, ArH), 7.95 (d, J ) 8.2 Hz, 8 H, ArH), 9.90 (br
s, 8 H, meso-H), 10.00 (s, 2 H, meso-H); 13 C NMR (100.6 MHz,
CDCl3) δ 14.1, 15.0, 15.2, 22.8, 24.8, 26.6, 29.9, 30.1, 30.2, 30.9,
31.8, 32.0, 33.3, 34.9, 66.3, 67.3, 97.3, 99.3, 112.9, 118.3, 119.5,
119.6, 124.2, 126.9, 132.7, 133.3, 135.8, 137.5, 137.6, 138.2,
Ack n ow led gm en t. We wish to thank The Croucher
Foundation, the EPSRC, the University of Cambridge,
and the Italian MURST for financial support.
J O001564O