Synthesis and supramolecular properties of a novel octaphosphonate porphyrin

Article abstract of DOI:10.1002/ejoc.200900589

Two complementary routes were developed for preparing novel octaphosphonate porphyrins. The use of protected/deprotected phosphonate-substituted precursors in the rational synthesis gave an overall yield 16%. A more streamlined synthetic path gave 21 % overall yield, of the target molecule. Octaphosphonate porphyrin possesses promising properties in supramolecular aggregate formation with cyclam. Cofacial reversible self-assembly of a meso-substituted octaphosphonate porphyrin with cyclam yields micrometer-long nanowires with a height of about 1-1.5 nm. The resulting wires were characterized by UV/Vis absorption, emission and atomic force microscopy and transmission electron microscopy. ( Wiley-VCH Verlag GmbH & Co. KGaA.

Full text of DOI:10.1002/ejoc.200900589

FULL PAPER
DOI: 10.1002/ejoc.200900589
Synthesis and Supramolecular Properties of a Novel Octaphosphonate
Porphyrin
Sheshanath V. Bhosale,*[a] Mohan B. Kalyankar,[a,b] Steven J. Langford,[a]
Sidhanath V. Bhosale,*[b] and Ruth F. Oliver[a]
Dedicated to Professor Dr. M. S. Shingare
Keywords: Porphyrinods / Self-assembly / Supramolecular chemistry / Nitrogen heterocycles / Nanostructures / Electron
microscopy
Two complementary routes were developed for preparing
novel octaphosphonate porphyrins. The use of protected/de-
phonate porphyrin with cyclam yields micrometer-long
nanowires with a height of about 1–1.5 nm. The resulting
protected phosphonate-substituted precursors in the rational wires were characterized by UV/Vis absorption, emission
synthesis gave an overall yield 16%. A more streamlined
synthetic path gave 21% overall yield of the target molecule.
Octaphosphonate porphyrin possesses promising properties
in supramolecular aggregate formation with cyclam. Cofacial
reversible self-assembly of a meso-substituted octaphos-
and atomic force microscopy and transmission electron mi-
croscopy.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
important role in determining the final mode of aggrega-
tion.[7] The question lies in the identification and use of
such moieties for efficient self-assembly.
Introduction
The formation of self-assembled materials with well-
defined shapes and dimensions presents both a great chal-
lenge and opportunity with potential application in cataly-
sis, molecular electronics and materials science.[1] It is well
known that the porphyrin macrocycle provides a useful na-
nometer-sized rigid and planar building block for the con-
struction of well-defined assemblies.[2] Judicious choice of
outer periphery functionality can lead to geometric tectons
displaying 90° and 180° geometries,[3] or cofacial arrange-
ments that manifest themselves as nanowires, nanotubes,
helical ribbons or liquid crystalline aggregate topograph-
ies.[4,5] Pseudo-1D topologies are of particular interest as
molecular wires for energy, electron and charge transport.[6]
Recent reports suggest that the introduction of hydrogen-
bonding groups to the periphery of the porphyrin play an
Phosphate groups are essential to metabolism and bio-
synthesis, gene regulation, muscle contraction, cellular en-
ergy generation and antibiotic resistance.[8] Phosphate re-
ceptor binding in aqueous solution requires polytopic inter-
actions by hydrogen bonding, usually in the presence of
polyamines.[9] Furthermore, the interaction of phosphon-
ates with ZrIV salts has been shown to be a useful strategy
to form stable (irreversible) fibrous materials.[10] Although
many multiporphyrin systems have been reported in the lit-
erature,[1–7,10] there are only few examples in which the
phosphonate group of the porphyrin of fascinating molecu-
lar architectures is self-assembled on the surface[7d,10] or at-
tached to the surface[11] for studies of molecular-based in-
formation storage on oxide surfaces. New methodologies
to functionalize porphyrins with phosphonate substituents
other than normal aromatic groups are of particular inter-
est for the preparation of nanomaterials. Reported herein is
the novel synthesis of a meso-substituted porphyrin bearing
an octaphosphonate group and the preparation of discrete
supramolecular nanowires on the basis of its self-assembly
with cyclam from aqueous solutions on a gold surface,
without the need of metal ion additives. To the best of our
knowledge, this is the first report of the synthesis of octa-
phosphonate porphyrin and its self-assembly with cyclam.
[a] School of Chemistry, Monash University Clayton,
Clayton, Victoria 3800, Australia
Fax: +61-03-99054597
E-mail: sheshanath.bhosale@sci.monash.edu.au
bsheshanath@yahoo.co.in
[b] Department of Organic Chemistry, North Maharashtra Univer-
sity,
Jalgaon, MH 425001, India
E-mail: Sidhanath2003@yahoo.co.in
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.200900589.
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Supramolecular Properties of a Novel Octaphosphonate Porphyrin
Results and Discussion
Synthesis of the Porphyrin-Based Molecule Bearing
Peripheral Octaphosphonate Groups
The synthesis strategy employed to prepare targeted oc-
taphosphonate porphyrin 1 was focused toward careful
functional group protection to achieve a high overall yield
(Scheme 1). Synthesis of 1 began by performing a mono
deprotection of commercially available triethyl benzene-
1,3,5-tricarboxylate (3) to afford 3,5-bis(ethoxycarbonyl)-
benzoic acid (4) by treatment with KOH (0.9 equiv.), fol-
lowed by selective reduction of the free carboxylic acid by
using BH3·DMS to give 6 in 78% yield over two steps. The
benzylic alcohol of 5 was then TBDPS protected (99%
yield), allowing reduction of the two ethyl ester sites of 6
to proceed smoothly whilst retaining the TBDPS masked
alcohol. Diol 7 was brominated by using carbon tetrabro-
mide and triphenylphosphane to afford dibrominated prod-
uct 8 in 78% yield. Conversion of 8 into diphosphonate
ethyl ester 9 was achieved in high yield by heating in neat
triethyl phosphite. The TBDPS protecting group of 9 was
then removed with TBAF and oxidized to desired aldehyde
11 by using PCC in 59% yield after chromatographic sepa-
ration. Porphyrin synthesis was then performed by first tre-
ating the aldehyde with an equimolar amount of pyrrole
along with a catalytic amount of BF3·OEt2 to form the por-
phyrinogen in situ, followed by the addition of p-chloranil
to oxidize the newly formed tetraaza macrocycle to desired
octaethyl ester porphyrin 12 in 21% yield after column
chromatography. Deprotection of the octaethyl ester of por-
phyrin 12 was executed by simple hydrolysis with trimethyl-
silyl iodide at –40 °C in dry dichloromethane followed by
aqueous workup to give targeted porphyrin 1 in 95% yield.
A more streamlined synthetic path was later considered
to minimize handling time, as detailed in Scheme 2. Rather
than relying on careful protection for the synthesis of benz-
aldehyde 11, a more direct route was taken that required
chromatographic separation at the bromination step. This
method had been reported previously in the formation of
selective polyarene dendrimers bearing electron-donating
and electron-withdrawing moieties through Heck and
Horner–Wadsworth Emmons reactions by using the corre-
sponding phosphonate with aromatic aldehyde.[12] Com-
plete reduction of tricarboxylate 3 by using LiAlH4 was first
performed to give the tribenzyl alcohol in 97% yield after
aqueous workup. Bromination with the use of carbon tetra-
bromide and triphenylphosphane led to a mixture of
mono-, di- and tribrominated products, which could be sep-
arated by column chromatography to give desired dibromo
compound 14 in 51% yield.
Scheme 1. Synthesis of octaphosphonate porphyrin 1. Reagents
and conditions: (a) KOH, EtOH/THF, 12 h; (b) BH3·(CH3)2S, 0 to
60 °C, N2, overnight, THF; (c) TBDPSCl, DMAP, Py, 0 °C to
room temp., 24 h, DCM; (d) LAH, N2, 3 h, THF; (e) PBr3, diethyl
ether, 0 °C to room temp., 4 h; (f) triethyl phosphite, 120 °C, 12 h;
(g) TBAF, THF, room temp., overnight; (h) PCC (pyridinium chlo-
rochromate), DCM, room temp., 2 h, (i) BF3·OEt2, DCM, room
temp., Ar, 14 h, p-chloranil 2 h; (j) TMSI (trimethylsilyl iodide),
CHCl3, –40 °C to room temp., 1 h.
It should be noted that the monobrominated product re-
mains synthetically useful, as it may be further brominated
to the dibromo adduct later. The benzylic alcohol of 14 was
cleanly oxidized to aldehyde 15 by using freshly prepared
MnO2 in an 80% yield, and finally installation of the phos-
phonate ester functionality at the 3,5-positions was quanti-
Scheme 2. Alternative route for the synthesis of phosphonate alde-
tatively performed by using the same protocol as for 9 hyde 11.
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Shesh. V. Bhosale, Sid. V. Bhosale et al.
FULL PAPER
(Scheme 1). Treatment of 15 with triethyl phosphite at ure 1b, broken line). The Soret band shifted to 422 nm and
140 °C afforded diphosphonate ethyl ester 11 in high iso- the four Q bands shifted to 521, 561, 584 and 644 nm (Fig-
lated yield. Comparison of the overall yield of aldehyde 11 ure 1b, broken line). In the Soret band region, the redshift
clearly shows that the latter synthesis protocol is the pre- is a sign of J-type aggregate formation, whereas the blue-
ferred method, as it provides rapid access to 12 with mini- shift is a sign of H-aggregate formation.[13]
mal handling in a higher isolated yield (26 vs. 16% overall).
The evolution of the absorption spectrum of compound
1 with cyclam addition indicated the formation of a J-type
aggregate, with an angle between the molecule transition
dipole moment. The turbidity of the solution after the ad-
dition of cyclam also indicated the formation of an aggre-
gate. Furthermore, the fluorescence intensity dramatically
decreased, which supports the aggregation of porphyrin–
cyclam (Figure 1b, inset). UV/Vis spectroscopy (in water)
indicated a long wavelength shift by 4 nm and a decrease in
the intensity with loss of fluorescence, which can be attrib-
uted to the formation of larger aggregates than just π–π-
stacked dimers or oligomers. Therefore, atomic force micro-
scopy (AFM) and transmission electron microscopy (TEM)
were performed to further investigate the self-assembly of 1
in aqueous medium.
Supramolecular Self-Assembly of Octaphosphonate
Porphyrin with Cyclam
The absorption spectrum of octaphosphonate
1
(0.01 mmol) in water at pH 7.0 with protonated phos-
phonate groups (pKa = 7.8) has a strong Soret band at
440 nm and four weak Q bands at 599 and 655 nm (Fig-
ure 1a, broken line). The addition of 0.1  NaOH to this
solution (pH 9) brings about distinct changes in the absorp-
tion spectrum of compound 1, as the Soret band is shifted
to 418 nm and the Q bands are shifted to 518, 553, 583 and
636 nm (Figure 1a, solid line). At pH 3–7, the phosphonate
group and the internal NH are protonated, and upon ad-
dition of sodium hydroxide to the solution we observed de-
protonation of the internal NH. Upon addition of cyclam
(0.01 mmol at pH 9), the absorption band shifted to longer
wavelength with broadening of the peaks and loss of fine
structure accompanied by a decrease in intensity (Fig-
AFM and TEM of Supramolecular Self-Assembled
Phosphonate Porphyrin and Cyclam
Surface patterning experiments were performed by mix-
ing equimolar solutions (1ϫ10–4 ) of porphyrin 1 in 0.1 
aqueous NaOH and cyclam 2 in water and then applying
them, after ultrafiltration, to a freshly prepared gold sur-
face.[7d] An example of the obtained AFM images is shown
in Figure 2, which clearly displays wire-like aggregates. The
ratio of the diameter and height of the nanowires formed
by 1 and 2 was estimated to be approximately 1–1.5 nm
with typical lengths of 1–12 µ (for height profiles, see the
Supporting Information; Figure S1A, c and d). The col-
lected images show no evidence for the nanowires to align
further with one another once formed.
Figure 1. (a) UV/Vis absorption spectra of porphyrin 1 (1ϫ10–4 )
in H2O at pH 7.0 (broken line) and pH = 9.0 (solid line); (b) upon
addition of cyclam 2 with porphyrin 1 at pH 9.0 (broken line) with-
out cyclam (solid line). Inset shows emission of 1 with (broken line)
and without cyclam (broken line), respectively.
Figure 2. (a) AFM topography images of the self-assembled (phos-
phonato)porphyrin–cyclam structure deposited on a freshly pre-
pared gold surface; (b) section analysis showing 1–2 nm heights of
wires. All samples were measured at room temperature in air.
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Supramolecular Properties of a Novel Octaphosphonate Porphyrin
The orientation of the porphyrinic units to the Au(111) Proposed Model of Supramolecular Self-Assembly
surface is proposed to be planar; however, a canted dom-
We propose that this arrangement is driven by noncoval-
ino-like stacking arrangement is also plausible given that
ent interactions, where the cyclam macrocycle bridges the
the obtained images do not give full molecular resolution.
porphyrin units, as graphically depicted in Scheme 3. The
The growing process initiated by stepwise additions and
spacing of the NH sites along the propyl section of the cy-
phosphonate 1 and cyclam 2, which are stabilized by weak
clam approximately match the positions of the phosphonate
hydrogen bonds and van der Waals forces, arrange at the
groups, which presumably drive the linear growth of the
ends of the growing fibres co-facially. However, a deck-of-
cards arrangement is also plausible, wherein the porphyrins
wires (see inset in Scheme 3).
are more parallel to the surface. This may provide evidence
for the fact that hydrophilized surfaces provide more space
for π–π interactions (between porphyrin and surfaces). One
may expect to obtain a 3D self-assembly because of the
octaphosphonate group of the porphyrin with cyclam, but
cross links between the porphyrin and cyclam fibres do not
occur because of the rigidity of the building blocks; only
co-facial growth was observed (Supporting Information;
Figure S1A, c and d).[14] Nanowires formed between 1 and
2 were air stable and were found to be stable for several
months. The fact that neither porphyrin 1 nor cyclam 2 de-
posited individually on the gold surface, which would lead
to a regular surface pattern under the same preparative con-
ditions, infers that the interaction between 1 and 2 is crucial
to the formation of the nanowires (Supporting Information,
Figure S1a). At pH values below 9.0, no aggregation was
detected, because the phosphonic groups are fully proton-
ated, but the concomitant inner nitrogen protonation (in-
ducing two central positive charges) hinders aggregation
with cyclam (Supporting Information, Figure S1A, b).
Furthermore, TEM images of a sample of an equimolar
(1ϫ10–4 ) aqueous (pH 9) solution of 1 and 2 deposited
on a carbon grid stained by 1% phosphotungstate also pro-
vided direct visualization of self-assembled porphyrin–
cyclam entities that were several nanometers long (Fig-
ure 3). In this case, the aggregated structures are formed in
which strands are entangled with one another. Attempts to
obtain individual nanowires by dilution of the deposition
mixture or to detect termination of the wire sections and
thus determine the individual strand lengths failed. We have
observed stepwise growth of nanowires in TEM with dif-
ferent time interval (Supporting Information, Figure S2B).
Scheme 3. Systematic illustration of the hydrogen-bonded self-as-
sembly of octaphosphonate porphyrin 1 and cyclam 2 with a cofa-
cial arrangement. Inset shows interaction of phosphonate with cy-
clam through H-bonding after MM2 calculation.
Conclusions
In summary, two complementary routes were developed
to prepare octaphosphonate porphyrins. The use of pro-
tected/deprotected phosphonate-substituted precursors in
the rational synthesis of porphyrin 1 gives an overall yield
16%. A more streamlined synthetic path gives a 21% over-
all yield of the target molecule. Novel octaphosphonate
porphyrin possesses promising properties in supramolecular
aggregate formation with cyclam. This has led to the devel-
opment of a novel strategy for the formation of nanowires
based on the interaction of phosphonate porphyrins with
cyclam on gold surfaces and on carbon grids. This new ap-
proach opens up some appealing opportunities, especially
as it seems easily applicable to a large variety of porphyrinic
Figure 3. Transmission electron microscopy (TEM) images of sub-
micrometer long porphyrin–cyclam aggregated wires on a carbon
grid (negative stain: 2% phosphotungstate). The bar indicates the
scale.
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ized by the addition of H2O/glacial acetic acid (1:2). The reaction
mixture was dissolved in hot ethanol and precipitated into water
to retrieve a white powder. A final recrystallization from ethanol
yielded 5 as white crystals (3.6 g, 78%). M.p. 79 °C (ref.[16] 78 °C).
architectures on surfaces. The presented methodology is ex-
pected to provide a basis for the synthesis of other molecu-
lar nanostructures on surfaces, as the ionic components
may be easily varied. This facilitates the positioning of the
nanowires at electrode junctions and may offer a convenient
method to fabricate more complex arrangements. We are
also currently producing the porphyrin phosphonate fibres
from zinc and tin(IV) complexes to measure electric con-
ductivities of cation and anion π–radical stacks.[15]
3
1H NMR (300 MHz, CDCl3, 25 °C): δ = 1.24 (t, JH,H = 7.1 Hz, 6
H), 3.45 (s, 1 H, OH), 4.67 (s, 2 H), 4.33 (q, J = 7.1 Hz, 4 H), 8.15
(s, 2 H, Ar), 8.23 (s, 1 H, Ar) ppm. 13C NMR (75 MHz, CDCl3,
25 °C): δ = 14.1, 61.3, 66.2, 129.4, 130.5, 136.3, 141.9, 165.7 ppm.
IR (KBr): ν = 3417 (O–H stretching of primary alcohol), 3100 (C–
˜
H stretching of aromatic), 2984–2873 (C–H stretching of methyl-
ene), 1724 (C=O stretching of ester), 1445–1371 (C–H bending of
methylene and methyl group), 1242 (C–O stretching of ester), 1024
(C–O stretching of primary alcohol) cm–1. MS (EI): m/z = 253.2
[M + H]+. C13H16O5 (252.0): calcd. C 61.90, H 6.34; found C 62.03,
H 6.39.
Experimental Section
General: 1H and 13C NMR spectra were recorded with a Varian
Gemini (300 MHz for 1H NMR and 75 MHz for 13C NMR), a
Varian Mercury (400 MHz for 1H NMR and 100 MHz for 13C
NMR) or a Varian Unity Inova (500 MHz for 1H NMR and
125 MHz for 13C NMR) spectrometer. Chemical shifts are reported
in ppm downfield from tetramethylsilane (TMS; δ = 0 ppm) at
room temperature using CDCl3 as solvent and internal standard
unless otherwise indicated. Abbreviations used for splitting pat-
terns are s = singlet, d = doublet, dd = doublet of doublets, t =
triplet, q = quartet, m = multiplet and br. = broad, with coupling
constants (J) given in Hz. IR spectra were recorded with a Perkin–
Elmer 1600 FTIR (UATR) spectrometer; band intensities are indi-
cated as s (strong), m (medium) and w (weak). Electrospray ioniza-
tion (ESI) mass spectrometry was performed with a Q/TOF Ultima
GLOBAL mass spectrometer (Micromass, Manchester, UK)
equipped with a Z-spray source. Elemental analyses were carried
out using a Perkin–Elmer 2400 instrument. Unless stated other-
wise, column chromatography was carried out on silica gel 60
(Fluka, 40–63 µ). [α]2D0 values were recorded with a Jasco P-1030
Polarimeter, and melting points were recorded on a heating table
from Reichert (Austria). Analytical TLC was performed on silica
gel 60 (Fluka, 0.2 m). Other reagents were purchased from Acros
or Aldrich and were used without further purification. THF was
dried with sodium metal wire, and pyridine was dried with 4 Å
molecular sieves.
Diethyl 5-[(tert-Butyldiphenylsilyloxy)methyl]isophthalate (6):[17,18]
To a solution of 5 (5 g, 19.82 mmol), DMAP (0.126 g) and pyridine
(3.2 mL) in CH2Cl2 (40 mL) under an atmosphere of argon and
cooled to 0 °C was added dropwise TBDPSCl (8.15 g, 29.4 mmol,
1.5 equiv.), and the mixture was stirred for 24 h at room tempera-
ture. The reaction mixture was quenched with 1  HCl (20 mL).
The aqueous layer was washed with CH2Cl2 (200 mL). The com-
bined organic layer was then washed with water (2ϫ50 mL), dried
with Na2SO4 and filtered, and the solvent was removed under re-
duced pressure. Flash chromatography [SiO2, CHCl3/hexane (1:1)]
gave 6 as a colourless oil (9.7 g, quant.). 1H NMR (300 MHz,
3
CDCl3, 25 °C): δ = 0.98 (s, 9 H, SiMe3), 1.4 (t, JH,H = 7.0 Hz, 6
H), 4.45 (q, J = 7.0 Hz, 4 H), 4.80 (s, 2 H), 7.47–7.36 (m, 6H Ar),
7.70–7.67 (m, 4 H, Ar), 8.25 (s, 2 H, Ar), 8.55 (s, 1 H) ppm. 13C-
NMR: (75 MHz, CDCl3, 25 °C): δ = 26.8, 61.2, 64.7, 127.8, 129.2,
129.6, 129.8, 130.9, 131.2, 133.1, 134.8, 135.2, 135.5, 141.9,
165.9 ppm. MS (EI): m/z = found 491.8 [M + H]. C29H34O5Si
(490.2): calcd. C 70.99, H 6.98; found C 70.87; H 6.84.
{5-[(tert-Butyldiphenylsilyloxy)methyl]-1,3-phenylene}dimethanol (7):[19]
Isophthalate 6 (15.4 g, 3.16 mmol) in dry THF (50 mL) was added
dropwise to a slurry of lithium aluminium hydride (1.80 g) in dry
THF (150 mL) under an atmosphere of argon. The reaction mix-
ture was stirred at room temperature for 3 h and it turned green.
The reaction mixture was quenched, followed by hydrolysis, using
methanol (10 mL) and water (30 mL). The mixture was filtered,
and the white precipitate was washed several times with methanol
(3ϫ10 mL) followed by THF (2ϫ10 mL). The combined liquid
phases were evaporated under reduced pressure to give a yellow oil.
Recrystallization from hexane gave white crystals of 7 (11.05 g,
85%). M.p. 93 °C (ref.[19] 93 °C). 1H NMR (300 MHz, CDCl3,
25 °C): δ = 1.01 (s, 9 H, SiMe3), 3.34 (s, 2 H, CH2OH), 4.41 (s, 4
H), 5.01 (s, 2 H), 7.20 (s, 2 H), 7.22 (s, 1 H), 7.39 (m, 6 H), 7.69
(m, 4 H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 19.8, 26.9,
65.0, 65.4, 123.9, 124.1, 127.7, 129.7, 133.4, 135.6, 141.2 ppm. IR
3,5-Bis(ethoxycarbonyl)benzoic acid (4):[16] Triethyl benzene-1,3,5-
tricarboxylate (3; 28.2 g, 0.096 mol) was combined with absolute
EtOH (75 mL) and THF (50 mL) in a 250-mL, three-necked flask.
The mixture was heated to reflux, thus ensuring dissolution of the
entire solid. Powdered KOH (8.7%, 5.3 g, 84.0 mmol) was then
added portionwise over a 30 min period at room temperature. The
solution was then heated at reflux for 12 h. The reaction mixture
was concentrated in vacuo to afford a thick slurry, which was parti-
tioned between water and CH2Cl2. The aqueous phase was washed
with CH2Cl2, and concentrated HCl (8.5 mL) was added to precipi-
tate the product. The product was recrystallized from absolute
EtOH to afford 4 as white crystals (18.9 g, 76%). M.p 152–153 °C
(KBr): ν = 3239 (O–H stretching of alcohol), 3070 (C–H stretching
˜
1
(ref.[16] 153–154 °C). H NMR (300 MHz CDCl3, 25 °C): δ = 1.18
of phenyl ring), 2929, 2856 (C–H stretching of methylene group),
1471–1309 (C–H bending of methylene), 1105 (C–O stretching of
primary alcohol) cm–1. MS: (EI): m/z = 407 [M + H]+. C25H30O3Si
(406): calcd. C 73.85, H 7.44; found C 73.78, H 7.68.
(t, J = 7.1 Hz, 6 H), 4.21 (q, J = 7.1 Hz, 4 H), 8.50 (d, 1 H, Ar),
8.53 (d, 2 H, Ar), 11.02 (br. s, 1 H) ppm. 13C NMR (75 MHz,
CDCl3, 25 °C):
δ = 14.8, 61.9, 129.4, 135.7, 136.2, 165.7,
169.4 ppm. MS (FAB–, Xe): m/z = 266.4 [M]+.. C13H14O6 (266.4):
[3,5-Bis(bromomethyl)benzyloxy](tert-butyl)diphenylsilane (8):[19,20]
A solution of PBr3 (3.03 g, 11.2 mmol) in dry diethyl ether (50 mL)
was slowly added to a cooled (0 °C) solution of 7 (3.248 g, 8 mmol)
in dry diethyl ether (120 mL). Once all the PBr3 solution was added
the reaction mixture was warmed to room temperature and stirred
for a further 4 h. After this period of time, water (50 mL) was
added and the aqueous layer was extracted with diethyl ether
(200 mL). The organic layers were combined, dried with Na2SO4
calcd. C 58.64, H 5.30; found C 58.39, H 5.49.
Diethyl 5-(Hydroxymethyl)isophthalate (5):[16] Tricarboxylate 4 (5 g,
18.7 mmol) was dissolved in THF (30 mL) in a 250-mL, round-
bottomed flask, and the mixture was cooled to 0 °C in an ice bath.
BH3·(CH3)2S (2.0  in THF, 102 mL, 20.4 mmol) was added over
a period of 3 h. After completion of addition, the reaction mixture
was heated at 60 °C overnight. The reaction mixture was neutral-
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Supramolecular Properties of a Novel Octaphosphonate Porphyrin
and filtered. The solvent was evaporated under reduced pressure.
Purification of the crude mixture was performed by column
chromatography [SiO2, hexane/ethyl acetate (9:1)] to yield white
crystals of 8 (4.26 g, 78%). M.p. 90 °C. 1H NMR (300 MHz,
CDCl3, 25 °C): δ = 0.98 (s, 9 H, SiMe3), 4.54 (s, 4 H), 4.74 (s, 2
H), 7.27 (s, 2 H, Ar), 7.68 (m, 4 H); 7.28 (s, 1 H, Ar), 7.39 (m, 6
H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 19.3, 26.8, 31.6,
33.0, 33.9, 64.9, 126.7, 127.8, 128.1, 129.8, 135.6, 138.3 ppm. MS:
(EI): m/z = 533, 530. C25H28Br2OSi (532): calcd. C 56.40, H 5.30;
found C 56.37, H 5.16.
added and the mixture was stirred for another 2 h, after which time
the reaction mixture had turned a deep violet colour. After stand-
ing for 30 min, the solution was concentrated and silica gel (10 g)
was added. The slurry was dried to afford a dark powder that was
then poured onto the top of a chromatography column of silica.
The desired compound was eluted using a solvent mixture of chlo-
roform/acetonitrile/methanol (10:10:1). A second column was
needed to give the desired porphyrin 12 as a red/purple solid
(474 mg, 21%). C84H118 N4P2O24 (1814.6). 1H NMR (500 MHz,
3
CDCl3, 25 °C): δ = –2.8 (s, 2 H, 2-NH), 1.28 (t, JH,H = 7.1 Hz 48
2
H, CH3CH2), 3.58 [d, J = 22.0 Hz, 16 H, CH2P(O) (O Et)2], 4.2–
Tetraethyl {5-[(tert-butyldiphenylsilyloxy)methyl]-1,3-phenylene}bis-
(methylene)diphosphonate (9):[21] Triethyl phosphite (5 mL) and 8
(2.70 g, 5 mmol) were combined in a round-bottomed flask with
stirring under an atmosphere of argon at 120 °C for 12 h. The ex-
cess triethyl phosphite was then removed under reduced pressure.
The crude, oily product was purified with column chromatography
[SiO2, CHCl3/MeOH (95:5)]. Two columns were performed to
achieve pure compound 9 as a colourless oil (2.54 g, 77%). 1H
4.35 (m, 32 H, CH2CH3), 7.89 (s, 4 H, Ar), 8.50 (br. s, 8 H, Ar),
8.81 (s, 8 H Ar) ppm. 13C NMR (125 MHz, CDCl3, 25 °C): δ =
16.6, 33.4, 62.4, 121.9, 128.1, 134.9, 138.8, 145.9, 190.4, 196.1 ppm.
MS: (FAB–, Xe): m/z = 1816.3 [M + H]+.
5,10,15,20-Tetrakis [3,5-Bis(diphosphonoxylatophosphorylmethyl)-
phenyl]porphyrin (1):[25] To a solution of 12 (200 mg, 1ϫ10–4 ) in
chloroform (20 mL) cooled to –40 °C was added trimethylsilyl io-
dide (0.26 mL) with a syringe needle. The reaction mixture was
kept at –40 °C for 30 min, then warmed to room temperature and
stirred for another 1 h. Water (5 mL) and triethylamine (1.5 mL)
were added, and after stirring for 5 min the solvents were removed
under vacuum to give desired compound 1 as a purple solid
3
NMR (300 MHz, CDCl3, 25 °C): δ = 0.99 (s, 9 H), 1.25 (t, JH,H
= 7.1 Hz, 12 H), 3.12 (s, 2 H), 3.11 (s, 2 H), 4.21 (m, 8 H), 4.74 (s,
2 H), 7.10 (m, 2 H), 7.18 (br., 1 H), 7.39 (m, 6 H), 7.68 (m, 4 H)
ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 16.3, 26.8, 40.3, 68.9,
126.1, 129.3, 130.0, 130.7, 132.5, 134.2, 141.7 ppm. MS: (FAB–,
Xe): m/z = 646.6 [M + H]+.
1
(150 mg, 95%). H NMR (400 MHz, D2O, 25 °C): δ –2.8 (s, 2 H,
2-NH) 3.16 [m, 16 H, CH2P(O) (OH)2], 7.63 (s, 4 H), 7.97 (br. s, 8
H), 9.32 (br. s, 8 H) ppm. 13C NMR (125 MHz, D2O, 25 °C): δ =
34.2, 122.8, 128.6, 136.2, 139.8, 144.7, 190.1, 196.8 ppm. HRMS
(MALDI-TOF): calcd. for C51H55N4O24P9 1386.7586; found
1386.6793.
Tetraethyl [5-(Hydroxymethyl)-1,3-phenylene]bis(methylene)diphos-
phonate (10):[22] Tetrabutyl ammonium fluoride (14 mL, 13 mmol)
was added to solution of 9 (6 g, 9.28 mmol) in THF (80 mL), and
the reaction mixture was left to stir overnight. The reaction mixture
was quenched by the addition of glacial acetic acid (2 mL), and the
solvent was then removed in vacuo. The crude product was purified
by column chromatography (SiO2, 1% MeOH in CHCl3) to give
10 as a white solid (3.64 g, 96%). 1H NMR (400 MHz, CDCl3,
Self-Assembled Standard Porphyrin Solution for Atomic Force Mi-
croscopy (AFM): Porphyrin 9 (0.01 mmol) was dissolved in 0.1 
NaOH (10 mL). Cyclam (0.01 mmol) was dissolved in water
(10 mL) at pH 7.0. Both samples were mixed together in 1:1 ratio
and the resulting solution was stirred for 1 h, deposited in a freezer
at 5 °C and after 2 weeks the aggregated side products were re-
moved by simple ultrafiltration and applied as a AFM probe on
freshly prepare gold surface.
3
25 °C): δ = 1.25 (t, JH,H = 7.1 Hz 12 H), 3.17 (s, 2 H), 3.20 (s, 2
H), 4.00 (m, 8 H), 4.58 (s, 2 H), 7.09 (s, 2 H), 7.15 (s, 1 H) ppm.
13C NMR (125 MHz, CDCl3, 25 °C): δ = 16.9, 40.4, 62.3, 65. 5,
126.7, 130.5, 132.8, 141.3 ppm. IR (KBr): ν = 3417, 3121, 2981,
˜
2877, 1758, 1452, 1369 1248, 1029 cm–1. MS: (FAB–, Xe): m/z =
409.4 [M + H]+.
Atomic Force Microscopy: AFM images were recorded using a
MultiMode IIIa scanning probe microscopy with Entender Module
(Digital Instruments, Inc., Santa Barbara, CA) that was operated
in the dynamical modus. Olympus etched silicon cantilevers were
mostly used with a typical resonance frequency in the range 200–
400 MHz and spring constant of 42 N/m. All samples were mea-
sured at room temperature in air environments. The sample was
first adjusted with an optical light microscopy (Nano Scope, Op-
tical Viewing System). The microscope was than mounted on a
vibration isolation table (Halcyonics, MOD-1) and under a glass
bell for reduction of acoustical noise. The typical scanning speed
was 1 lines–1. Data analysis was performed after plane-fit, height
measurements based on the cross-sectional profiles.
Diethyl 5-Formylisophthalate (11):[23] To a suspended solution of
pyridinium chlorochromate (2.85 g, 13 mmol) in CH2Cl2 (20 mL)
was added a solution of 10 (3.6 g, 8.8 mmol) in CH2Cl2 (10 mL),
and the reaction mixture was stirred for 2 h. The reaction mixture
was diluted with diethyl ether (200 mL), and the solvent was de-
canted from the solid residues, which were washed again with ether
(200 mL). The organic layer was collected, dried with Na2SO4 and
evaporated under reduced pressure. Flash column chromatography
[SiO2, CHCl3/MeOH (10:0.5)] gave pure compound 11 as a colour-
less oil (2.10 g, 59%). 1H NMR (400 MHz, CDCl3, 25 °C): δ = 1.27
(t, 3JH,H = 7.4 Hz, 12 H, 4ϫCH3CH2), 3.21 (s, 4 H), 3.98–4.07 (m,
8 H, 4ϫCH3CH2), 7.53 (br. s, 1 H, Ar), 7.72 (m, 2 H, Ar), 9.91 (s,
1 H, CHO) ppm. 13C NMR (125 MHz, CDCl3, 25 °C): δ = 16.1,
Transmission Electron Microscopy (TEM): A droplet (5 mL) of the
freshly sonicated aqueous solution (above self-assembled standard
porphyrin–cyclam solution) was placed on hydrophilized carbon
films on copper wire grids (60 s plasma treatment at 8 W using a
BALTEC MED 020 device). Excess fluid was blotted off and air
dried on the grids. Microscopy was carried out by using a Philips
CM12 TEM operated at 100 kV accelerating voltage at a low elec-
tron dose (Ͻ100 eÅ–1).
36.9, 62.1, 127.4, 133.9, 136.4, 137.7, 191.3 ppm. IR (KBr): ν =
˜
2817 and 2733 (aldehyde C–H stretching), 2982–2872 (C–H stretch-
ing of methylene group), 1699 (C=O stretching of aldehyde), 1477–
1367 (C–H bending of methylene), 1249 (C–O stretching of alde-
hyde) cm–1. MS: (FAB–, Xe): m/z = 407.6 [M + H]+.
5,10,15,20-Tetrakis-[3,5-bis(diethoxyphosphorylmethyl)phenyl]por-
phyrin (12):[24] A mixture of CH2Cl2 (600 mL), 11 (2.03 g, 5 mmol)
and pyrrole (0.335 g, 5 mmol) was stirred under an atmosphere of
nitrogen at room temperature in the dark for 15 min. To this solu-
tion, BF3·OEt2 (0.265 mL) in CH2Cl2 (10 mL) was added, and the
reaction mixture was left to stir for 14 h. p-Chloranil (1.2 g) was
Supporting Information (see footnote on the first page of this arti-
1
cle): H NMR spectra of important compounds; AFM and TEM
images of self-assembled octaphosphonate porphyrin 1 with cyclam
2.
Eur. J. Org. Chem. 2009, 4128–4134
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4133

Shesh. V. Bhosale, Sid. V. Bhosale et al.
FULL PAPER
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Received: May 29, 2009
Published Online: July 14, 2009
4134
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 4128–4134