Extending conjugation in porphyrin dimer carbocations

Article abstract of DOI:10.1039/c003715j

The addition of alkynyl porphyrins to carbonyl compounds was used to prepare a series of porphyrin dimer tertiary alcohols. Treatment of these alcohols with acid gave conjugated carbocations with three to nine carbon atoms bridging between the porphyrins. All these carbocations show strong absorption in the near-IR region between 1000-1800 nm. The absorption spectra exhibit a length-dependence similar to that of polymethine cyanines, with a bathochromic shift of approximately 200 nm (900 cm^-1) per alkyne. The longest of these chromophores has an absorption maximum at 1623 nm (in CHCl₃ with 2% trifluoroacetic acid). The symmetry of the π-system has a strong effect on the position, intensity and width of the absorption bands. The stability of the cations in solution decreases with increasing bridge length. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/c003715j

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PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Extending conjugation in porphyrin dimer carbocations†
Karl J. Thorley and Harry L. Anderson*
Received 4th March 2010, Accepted 21st May 2010
First published as an Advance Article on the web 4th June 2010
DOI: 10.1039/c003715j
The addition of alkynyl porphyrins to carbonyl compounds was used to prepare a series of porphyrin
dimer tertiary alcohols. Treatment of these alcohols with acid gave conjugated carbocations with three
to nine carbon atoms bridging between the porphyrins. All these carbocations show strong absorption
in the near-IR region between 1000–1800 nm. The absorption spectra exhibit a length-dependence
similar to that of polymethine cyanines, with a bathochromic shift of approximately 200 nm (900 cm-1)
per alkyne. The longest of these chromophores has an absorption maximum at 1623 nm (in CHCl3 with
2% trifluoroacetic acid). The symmetry of the p-system has a strong effect on the position, intensity and
width of the absorption bands. The stability of the cations in solution decreases with increasing bridge
length.
Introduction
Nonlinear optical dyes operating in the near-IR spectral region
(1000–2000 nm wavelength) have important potential applications
for telecommunications.1 These include all-optical signal process-
ing devices such as optical switches,2,3 optical correlators4,5 and
optical limiters.6,7 Absorption of near-IR light is important for
photodetectors used in applications such as thermal imaging and
night vision. Dyes absorbing in the near-IR are needed for light
harvesting applications.8,9
Near-IR
dyes
include
cyanines,
squaraines
and
phthalocyanines.10,11 Dyes absorbing beyond 1000 nm are
rare and include cationic porphyrinoids,12 quinoidal structures13,14
extended aromatic systems,15–17 cyanines18 and donor–acceptor
systems.19 The fused porphyrin tapes reported by Osuka exhibit
the longest wavelength absorption bands of any organic dyes,
which extend into the vibrational region of the infrared.20
We have previously reported the synthesis and properties of
cationic porphyrin dimers, such as 1+, which we loosely referred to
as “porpho-cyanines”.21 The conjugated bridge differs from that
of traditional cyanines as it features ethynyl groups to increase
electronic communication by avoiding steric repulsion.22 Despite
the large bond length alternation, these compounds show linear
and nonlinear optical properties which are similar to those of
cyanine dyes, but at longer wavelengths. The near-IR band of
1+ has an absorption maximum at 1243 nm, with an exctinction
coefficient of 1.7 ¥ 105 M-1 cm-1 (Fig. 1). The position of this
absorption maximum is sensitive to changes in substituents on the
central phenyl group; para-nitro or methoxy substituents result in
shifts of around 100 nm.
Fig. 1 Structure of cationic porphyrin dimer 1+ and the UV/Vis/NIR
spectrum measured in CHCl3/2% TFA at 298 K. Ar = 3,5-di-t-butyl
phenyl.
we report an investigation of the relationship between the length
of the bridge in extended analogues of porphyrin dimer cations
such as 1+ and their optical properties. At the outset of this
work, it was not clear whether extending the acetylenic link in
cation 1+ would result in a fully conjugated system. Increasing
the distance of the carbocation centre from the porphyrins might
be expected to reduce the electronic coupling resulting in a blue-
shifted absorption. However, we found that the extended systems
have strongly red-shifted absorption spectra.
Results and discussion
Cyanines show a strong correlation between optical properties
and molecular length, L,1,23 with the polarisability a scaling as
L3 and the second hyperpolarisability g scaling with L7. Here
Synthesis
The previously reported porpho-cyanine 1+ was prepared by ad-
dition of trifluoroacetic acid to porphyrin dimer alcohol 5, which
was synthesised by deprotonation of acetylenic porphyrin 2 and
subsequent trapping with an aromatic ester (Scheme 1). Using a
similar methodology, longer systems were synthesised. Butadiyne
porphyrin monomer 3 was prepared by Glaser–Hay coupling of
the acetylene porphyrin with an excess of trihexylsilylacetylene.24,25
Department of Chemistry, Chemistry Research Laboratory, University
of Oxford, 12 Mansfield Road, Oxford, UK OX1 3TA. E-mail: harry.
anderson@chem.ox.ac.uk; Fax: +44 1865 285002; Tel: +44 1865 275704
† Electronic supplementary information (ESI) available: 1H NMR spectra
of novel porphyrin compounds and 13C NMR of selected porphyrin dimer
alcohols. See DOI: 10.1039/c003715j
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Scheme 2 Reagents and conditions; i) 2, Pd2(dba)3, PPh3, CuI, NEt3,
PhMe, 40 ◦C, 48%; ii) Bu4NF, CH2Cl2, 20 ◦C, quant. iii) PhCO2Me,
LiN(SiMe3)2, THF, 20 ◦C, 14%.
Scheme 1 Reagents and conditions: i) Bu4NF, CH2Cl2, 20 ◦C, quant. ii)
HCCSiHex3, CuCl, TMEDA, air, CH2Cl2, THF, 20 ◦C (3: 91%; 4: 95%);
iii) PhCO2Me, LiN(SiMe3)2, THF, 20 ◦C (5: 53%; 6: 31%; 7: N/A); iv)
CF3CO2H, CHCl3.
of the successive alkyne groups was explored as an approach to
increase the stability of the porphyrin dimer, both as the alcohol
and eventually as the carbocation. The porphyrin monomer 10
was formed by a selective Sonogashira coupling reaction of 4-
bromo-iodobenzene, before reaction to give dimer 11 under the
conditions used for dimers 5–7.
Reaction of 3 with methyl benzoate gave the extended nine-carbon
dimer 6 (Scheme 1). Addition of trifluoroacetic acid to a solution
of 6 in CHCl3 resulted in formation of cation 8+.
Similarly, Glaser–Hay coupling between butadiyne monomer
3 and an excess of trihexylsilylacetylene gave the hexatriyne
porphyrin 4. Subsequent deprotection and reaction with methyl
benzoate, gave the thirteen-carbon dimer 7. This dimer proved to
be fairly unstable during chromatography and could not be fully
purified.
In addition to forming longer systems using the original
methodology, it was possible to form dimers in a stepwise manner.
This gave access to unsymmetrical porphyrin dimers. Formyl
porphyrin 12 was prepared by Vilsmeier formylation.26 Reaction
of acetylene porphyrin 2 with the formyl porphyrin under basic
conditions gave the three-carbon bridged dimer 13. Similarly, a
porphyrin dimer with five bridging carbons was formed by reaction
of butadiyne porphyrin 3 with formyl porphyrin 12 (Scheme 3).
Another extended porphyrin dimer (11, Scheme 2) was synthe-
sised with para-phenylene spacers in the bridge. The separation
Scheme 3 Reagents and conditions: i) 2 (after silyl deprotection), LiN(SiMe3)2, THF, 20 ◦C, 30%; ii) CF3CO2H, CHCl3; iii) 3 (after silyl deprotection),
LiN(SiMe3)2, THF, 20 ◦C, 63%.
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Finally for the synthesis of a seven-carbon dimer 18, the
intermediate ketone 17 was required. This was achieved by reacting
the acetylene porphyrin with N-methyl-N-methoxy benzamide.27
Reaction of the resulting ketone with the butadiyne porphyrin
monomer 3 gave the seven-carbon dimer (Scheme 4).
and 19+ showed absorption bands in the near-IR, while addition
of trifluoroacetic acid to extended dimers 7 (which contained
some monomer impurities) and 11 did not result in any near-IR
absorption. A reduction in intensity of the Soret band at 400 nm
was observed, suggesting that the desired carbocations may be
formed, but, if they are formed, they decompose before their near-
IR absorption spectra can be observed.
The absorption spectra of the porphyrin carbocations are shown
in Fig. 2. The increase in lmax with bridge length is immediately
obvious. There is an approximate 200 nm shift with each alkyne
added. However, the unsymmetrical cationic dimers 14+ and 19+
show weaker and broader absorption bands than the symmetrical
systems. Furthermore, the absorption maximum for the seven-
carbon dimer 19+ does not lie directly between those for the five-
and nine-carbon dimers.
Fig. 2 Absorption spectra of cations 14+ (C3, black dash), 1+ (C5, black
solid), 19+ (C7, grey dash) and 8+ (C9, grey solid) measured in CHCl3/2%
TFA at 298 K. Spectra are normalised to the Soret maxima of the parent
alcohols.
It is interesting to compare the absorption spectra of the two
C5 bridge compounds 16+ and 1+ (Fig. 3). The lower symmetry of
16+ results in a substantially broader absorption band (FWHM =
2324 cm-1, vs. 920 cm-1 for 1+). The higher symmetry of 1+ also
shifts the absorption to longer wavelength (1248 nm vs. 1087 nm
for 16+), although the central Ph group in 1+ also contributes to
this shift. The absorption spectrum of 16+ is more similar to that
of the C3 bridged cation 14+ in position, but is again broader. This
similarity can be accounted for by comparison of the structures of
the two cations; the positive charge is formed adjacent to one of
the porphyrins in both cases, with the second porphyrin located
further away via an alkynyl bridge.
Scheme 4 Reagents and conditions: i) Bu4NF, CH2Cl2, 20 ◦C, quant.
ii) PhC(O)N(OMe)Me, LiN(SiMe3)2, THF, 20 ◦C, 83%; iii) 3 (after silyl
deprotection), LiN(SiMe3)2, THF, 20 ◦C, 30%; iv) CF3CO2H, CHCl3.
Absorption spectra
Addition of trifluoroacetic acid to the tertiary alcohols re-
sulted in the formation of the corresponding cations (Table 1).
UV/Vis/NIR spectroscopy was used as the primary technique for
investigating the cations. Cationic porphyrin dimers 8+, 14+, 16+
Table 1 NIR absorption properties of cations generated in situ from alcohols by addition of 2% TFA (by volume). Extinction coefficients are calculated
assuming quantitative cation formation.28
Cation
Bridge (x : y)
R
l
max/nm
e/mM-1cm-1
FWHM/cm-1
14+
16+
1+
0 : 1
0 : 2
1 : 1
1 : 2
2 : 2
H
H
Ph
Ph
Ph
1042
1087
1248
1378
1623
0.12
0.095
0.17
0.094
0.16
2175
2324
920
1634
1134
19+
8+
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Fig. 3 Absorption spectrum of cations 14+ (C3, black dash), 16+
(unsymmetrical C5, black solid) and 1+ (symmetrical C5, grey solid)
measured in CHCl3/2% TFA at 298 K.
The trend in absorption maximum can be summarised by
plotting lmax against the bridge length, N (number of carbons
in the bridge). Theoretically, for true cyanine structures, as the
polymethine chain becomes infinitely long, the wavelength of
absorption tends to an infinite value. This trend is more obvious
when plotting the frequency against the reciprocal bridge length,
where the HOMO–LUMO gap tends toward zero as N-1 tends to
zero.1 Fig. 4 shows the data for the five porphyrin carbocations. A
clear length dependence can be seen, with the shortest compounds
having the highest energy absorption maxima. The lines join
points of equal symmetry (x = y, y + 1 or y + 2). The gradients
of these lines show that the most symmetrical dimers exhibit a
stronger length dependence and lower energy transitions than
the unsymmetrical dimers. The synthesis of additional porphyrin
cations of differing length and symmetry is needed to fully explore
this effect, although changing substituents and steric environments
makes it difficult to directly compare different series.
Fig. 5 MALDI-TOF spectra of porphyrin dimer alcohols ROH = 13, 5,
18 and 6 (a) to d) respectively). The red lines show the calculated isotopic
patterns for the alcohol [ROH]∑+ and cation formed by protonation and
dehydration R+ in each case. Dithranol was used as the matrix.
increases from 13 to 6, the alcohol peak becomes more intense than
the carbocation peak. Direct oxidation of the porphyrin p-system
is more favourable in the longer systems, whereas protonation and
dehydration is more favourable in the shorter systems.
Cation stability
Upon increasing the bridge length, there is a decrease in the
stability of the carbocation, with the thirteen-carbon dimer 7
showing no detectable near-IR band upon addition of acid. To
investigate this further, the absorption spectra of the cationic
dimersweremonitoredovertime. Thefive-carbondimer1+ showed
slow decomposition over a period of days to give an absorption
spectrum consistent with a non-conjugated porphyrin, although
not identical to the alcohol precursor.
Fig. 4 Plot of nmax against N-1 where N is the number of carbon atoms in
the alkyne bridge. The lines join compounds of similar symmetry i.e. x =
y (black), x = y + 1 (red) and x = y + 2 (green). nmax is the frequency of
the peak of the absorption band, measured in CHCl3/2% TFA.
Mass spectrometry
The mass spectra of the tertiary alcohols provide some insight
into the stability of the carbocations (Fig. 5). In each case, two
peaks were observed with a difference of 17 Da between the two
peaks. The higher molecular weight peak was due to the alcohol
[ROH]∑+, while the lower molecular weight peak corresponded
to the carbocation R+ formed by protonation and loss of water.
There are two competing ionisation processes. As the bridge length
In contrast, the absorption spectrum of the C9 dimer 8+ changed
rapidly, with a half life of 570 s at an acid concentration of 1% TFA
(Fig. 6). At low acid concentrations, the band at 1623 nm was seen
to decrease, while a new band appeared at 1250 nm (Fig. 7a). Other
alkynyl bridged carbocations have previously been shown to react
with water to give pyrylium ions.29 The relative rates of reaction
of 1+ and 8+ are consistent with this decomposition pathway, as
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were also determined. Plotting -k0 against the acid concentration
gave the same optimum acid concentration (Fig. 7d, crosses).
Conclusions
A series of carbocation porphyrin dimers, based on the previously
reported structure 1+, were synthesised which varied by the length
of the conjugated bridge between the porphyrin end groups.
Delocalised carbocations with bridge lengths of three to nine
carbon atoms were found to be stable enough for UV/Vis/NIR
absorption measurements under ambient conditions. The absorp-
tion spectra of the series of stable carbocations show a shift of
approximately 200 nm per alkyne, which is similar to the length
dependence in cyanine dyes, despite large bond length alternation.
The symmetry of the p-system is important to the position,
intensity and width of the absorption bands.
Fig. 6 Absorption at lmax plotted against time for cation 1+ measured in
CHCl3/1% TFA (solid line) and cation 8+ measured in CHCl3/1% TFA
(dashed line) and in CHCl3/10% TFA (dotted line).
the more sterically hindered bridge of the C5 dimer is the more
stable. Formation of a pyrylium is also consistent with the observed
changes in the NIR spectra, but the final products could not be
identified due to the broadness of their NMR spectra.
At higher acid concentrations the additional near-IR band at
1250 nm is not observed, and the cation is more stable (Fig. 7b). At
acid concentrations above 15% by volume the stability decreased.
The stability of cation 8+ at different acid concentrations was
compared by plotting the absorption at lmax over time (Fig. 7c). By
plotting the absorption after an arbitrary time of 500 s against the
acid concentration (Fig. 7d, bars), the optimum stability was found
to be between 10 and 15% TFA by volume (1.3 M and 2.0 M).
By fitting the data to exponential decay curves, the initial rates k0
Unfortunately, while increasing the bridge length gave large
shifts in absorption, a reduction in stability was also observed.
Attempts at synthesising a carbocation with thirteen carbon atoms
in the bridge were unsuccessful; C9 appears to represent the limit
of stability. This could be due to the decrease in steric bulk around
the bridge, or due to the onset of a “cyanine limit” effect from
a reduction in electronic coupling.30 The stability of the five and
nine-carbon bridged carbocations was found to be dependant on
the acid concentration.
The longest near-IR band was observed for the C9 dimer
8+, with lmax of 1623 nm and an extinction coefficient of
160 000 M-1cm-1. This is among the longest wavelength electronic
absorption bands observed for an organic p-system. The near-IR
Fig. 7 NIR absorption spectra of cation 8+ measured at regular intervals in a) CHCl3/2% TFA and b) CHCl3/10% TFA. c) Absorption at lmax plotted
over time at different acid concentrations. d) Absorption after 500 s, A500, against acid concentration (bars) and initial rate of reaction, k0, against acid
concentration (crosses). Initial rates were determined by fitting the data to an exponential decay.
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bands are more intense and narrower than charge-transfer type
transitions in this region.31,32
7.99 (2H, dd, J = 7.8, 1.5 Hz), 7.86 (4H, d, J = 1.7 Hz), 7.74 (2H,
t, J = 1.7 Hz), 7.64–7.70 (3H, m), 1.49 (36H, s), 1.44–1.46 (9H,
m), 1.36–1.38 (12H, m), 0.84–0.95 (12H, m), 0.77–0.81 (6H, m);
13C NMR (125 MHz, CDCl3) d 149.1, 145.9, 143.7, 142.4, 140.1,
139.4, 133.7, 133.5, 132.4, 132.4, 131.2, 128.9, 127.8, 126.9, 121.4,
121.3, 120.9, 96.3, 91.9, 89.7, 81.7, 35.0, 33.2, 31.7, 31.6, 23.9,
22.7, 14.2, 13.3; m/z (MALDI-TOF, +ve) 1149.97 (C76H94N4NiSi
requires 1149.66).
Experimental Section
Reactions were carried out under nitrogen or argon atmospheres,
unless otherwise stated. Copper(I) chloride was freshly prepared
from copper(II) chloride.33 Trihexylsilylacetylene,34 trimethylsi-
lylethynyl bromobenzene 935 and formyl porphyrin 1226 were
synthesised by published procedures. Ethynyl porphyrin 2 was
prepared as in previous work.21 Dry toluene and THF were
obtained by passing through a column of activated alumina.
Triethylamine was freshly distilled from CaH2. All other reagents
were used as supplied.
[5,15-bis(3,5-di-tert-butylphenyl)-10-phenyl-20-hexatriynyl
porphinato] nickel(II) 4
Butadiyne porphyrin 3 was deprotected by the general method.
The deprotected porphyrin (0.020 g, 0.023 mmol) and trihexylsi-
lylacetylene (0.18 mL, 0.46 mmol) were dissolved in CH2Cl2 (10
mL) and THF (5 mL) and stirred vigorously in a 500 mL flask
fitted with a CaCl2 drying tube under air. After 20 min, cop-
per(I) chloride (0.068 g, 0.69 mmol) and N,N,N¢,N¢-tetramethyl
ethylenediamine (0.079 mL, 0.53 mmol) were added, and the
reaction stirred for 4 h. The mixture was passed through a
Column chromatography was carried out on silica gel 60 under
a positive pressure of nitrogen. Where mixtures of solvents were
used, ratios are reported by volume.
NMR spectra were recorded at 300 K using a Brucker DPX400
(400 MHz) spectrometer. Spectra recorded on the Brucker
AVANCE AVC500 (500 MHz) spectrometer were recorded by
Dr B. Odell. Chemical shifts are quoted as parts per million
(ppm) relative to tetramethylsilane (0.00 ppm). Coupling constants
(J) are quoted in Hertz (Hz). UV-Vis spectra were recorded
in solution on a Perkin-Elmer lambda 20 UV-Vis spectrometer.
UV-Vis-NIR absorption spectra were recorded in solution using
a JASCO V-570 spectrometer. Mass spectra were measured
by matrix assisted laser desorption ionisation—Time of Flight
(MALDI-TOF) using a Micromass LCT premier spectrometer.
Dithranol (1,8-dihydroxy-9,10-dihydroanthracen-9-one) was used
as the matrix. Only molecular ions and major peaks are given.
◦
silica plug, before further chromatography (40–60 C petroleum
ether/CH2Cl2, 10 : 1) to give the hexatriyne porphyrin 4 as a purple
solid (0.026 g, 95%). m.p. > 250 ◦C; lmax (CHCl3)/nm (log e) 441
(5.40), 552 (4.14), 590 (4.36); 1H NMR (400 MHz, CDCl3) d 9.43
(2H, d, J = 4.8 Hz), 8.84 (2H, d, J = 4.8 Hz), 8.70 (2H, d, J =
4.8 Hz), 8.67 (2H, d, J = 4.8 Hz), 7.98 (2H, d, J = 6.0 Hz), 7.85
(4H, d, J = 1.7 Hz), 7.75 (2H, t, J = 1.7 Hz), 7.64–7.70 (3H, m),
1.49 (36H, s), 1.28–1.47 (21H, m), 0.91–0.95 (9H, m), 0.84–0.89
(3H, m), 0.69–0.73 (6H, m); 13C NMR (125 MHz, CDCl3) d 149.1,
146.2, 143.9, 142.5, 142.4, 140.6, 130.3, 133.9, 133.5, 132.5, 132.4,
130.1, 128.8, 127.9, 126.9, 121.7, 121.4, 121.4, 95.3, 89.7, 89.3,
81.6, 77.9, 69.8, 68.0, 62.1, 35.0, 33.1, 31.7, 31.5, 23.8, 22.6, 14.2,
13.1; m/z (MALDI-TOF, +ve) 1173.37 (C78H94N4NiSi requires
1173.67).
Silyl deprotections—general method
Alkynyl porphyrins were stored and characterised as the silyl
protected compounds. Before reaction, the silyl group was re-
moved. The silyl protected porphyrin (0.055 mmol) was dissolved
in CH2Cl2 (6 mL). Tetrabutylammonium fluoride (1.0 M in THF,
0.06 mL, 0.06 mmol) was added and the reaction stirred for 15 min.
The crude reaction mixture was poured onto a silica plug and
eluted with CH2Cl2. Removal of solvents gave the free acetylene in
quantitative yield, which was characterised only by TLC analysis
before the silica plug.
[5,15-bis(3,5-di-tert-butylphenyl)-10-phenyl-20-[ethynyl-p-
(trimethylsilylethynyl)phenyl] porphinato] nickel(II) 10
Sonogashira coupling was carried out following a reported
procedure.36 Acetylene porphyrin 2 was deprotected by the general
method. The deprotected porphyrin (0.035 g, 0.041 mmol),
trimethylsilylethynyl bromobenzene 9 (0.104 g, 0.410 mmol),
tris(dibenzylideneacetone)-dipalladium(0) (1.9 mg, 2.1 mmol),
triphenylphosphine (1.1 mg, 4.1 mmol) and copper(I) iodide
(0.4 mg, 2.1 mmol) were dissolved in dry toluene (1 mL) and
triethylamine (1 mL) and the solution was freeze-thaw degassed.
The reaction was stirred at 40 ◦C for 2 h. The crude mixture
was passed through a short silica plug (CH2Cl2) before further
purification by column chromatography (40–60 ◦C petroleum
ether/CH2Cl2; 5 : 1) to give a red/purple solid (0.020 g, 48%).
1H NMR (400 MHz, CDCl3) d 9.58 (2H, d, J = 4.8 Hz), 8.87
(2H, d, J = 4.8 Hz), 8.72 (2H, d, J = 4.8 Hz), 8.68 (2H, d, J =
4.8 Hz), 7.99 (2H, dd, J = 7.9, 1.5 Hz), 7.87–7.89 (6H, m), 7.74
(2H, t, J = 1.9 Hz), 7.64–7.68 (4H, m), 7.62 (2H, d, J = 8.5 Hz),
1.50 (36H, s), 0.32 (9H, s); 13C NMR (125 MHz, CDCl3) d 149.1,
144.6, 143.4, 142.6, 142.5, 139.5, 133.5, 133.3, 132.4, 132.2, 132.2,
131.3, 131.1, 128.9, 127.8, 126.8, 123.9, 123.0, 121.3, 121.2, 120.3,
104.8, 98.3, 96.5, 96.5, 92.4, 34.9, 31.6, -0.1; m/z (MALDI-TOF,
+ve) 1015.29 (C67H68N4NiSi requires 1014.46).
[5,15-bis(3,5-di-tert-butylphenyl)-10-phenyl-20-butadiynyl
porphinato] nickel(II) 3
Glaser–Hay coupling was achieved by a literature procedure.24,25
Acetylene porphyrin 2 was deprotected by the general method.
The deprotected porphyrin (0.10 g, 0.12 mmol) and trihexylsily-
lacetylene (0.93 mL, 2.4 mmol) were dissolved in CH2Cl2 (50 mL)
and THF (25 mL) and stirred vigorously in a 1 L flask fitted with
a CaCl2 drying tube under air. After 20 min, copper(I) chloride
(0.36 g, 3.6 mmol) and N,N,N¢,N¢-tetramethyl ethylenediamine
(0.42 mL, 2.8 mmol) were added, and the reaction stirred for
4 h. The mixture was passed through a silica plug, before further
chromatography (40–60 ◦C petroleum ether/CH2Cl2, 10 : 1) to give
the butadiyne porphyrin 3 as a purple solid (0.025 g, 91%). m.p. >
250 ◦C; lmax (CHCl3)/nm (log e) 435 (5.38), 548 (4.17), 584 (4.16);
1H NMR (400 MHz, CDCl3) d 9.49 (2H, d, J = 4.9 Hz), 8.85 (2H,
d, J = 4.9 Hz), 8.70 (2H, d, J = 4.9 Hz), 8.67 (2H, d, J = 4.9 Hz),
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[5,15-bis(3,5-di-tert-butylphenyl)-10-phenyl-20-(ethynylphenone)
porphinato] nickel(II) 17
room temperature for 1 h. The reaction was quenched with aque-
ous ammonium chloride (5 mL), extracted with CH2Cl2 (10 mL)
and washed with H2O (3 ¥ 10 mL◦). The product was purified
by column chromatography (40–60 C petroleum ether/CH2Cl2;
2 : 1) to give a purple solid (0.008 g, 63%). m.p. > 300 ◦C; lmax
(CHCl3)/nm (log e) 423 (5.00), 437 (5.05), 542 (4.06), 583 (3.96);
1H NMR (400 MHz, CDCl3) d 9.81 (2H, d, J = 4.9 Hz), 9.37 (2H,
d, J = 4.9 Hz), 8.97 (2H, d, J = 4.9 Hz), 8.75–8.77 (4H, m), 8.72
(2H, d, J = 4.9 Hz), 8.66 (2H, d, J = 4.9 Hz), 8.65 (2H, d, J =
4.9 Hz), 8.00 (2H, dd, J = 7.1, 2.0 Hz), 7.96 (2H, dd, J = 7.5, 1.9
Hz), 7.92 (1H, d, J = 3.7 Hz), 7.87 (4H, d, J = 1.7 Hz), 7.81 (4H,
d, J = 1.7 Hz), 7.71–7.73 (4H, overlapping t), 7.64–7.68 (6H, m),
3.56 (1H, d, J = 3.7 Hz), 1.45–1.48 (72H, overlapping s); 13C NMR
(125 MHz, CDCl3) d 149.1, 149.0, 145.6, 143.6, 143.0, 142.4, 142.4,
142.2, 142.1, 141.1, 139.5, 139.4, 133.9, 133.6, 133.5, 133.5, 132.5,
132.4, 132.3, 129.8, 128.8, 126.9, 126.8, 121.4, 121.2, 120.9, 120.4,
82.2, 80.3, 67.9, 34.9, 34.9, 31.6, 31.6; m/z (MALDI-TOF, +ve)
1716.07, 1698.98 (C113H112N8Ni2O requires 1714.77, –OH requires
1697.77).
Acetylene porphyrin 2 was deprotected by the general method.
The deprotected porphyrin (0.020 g, 0.024 mmol) was dissolved in
THF (1 mL) and the solution freeze-thaw degassed. N-Methoxy-
N-methylbenzamide (0.014 mL, 0.095 mmol) was added, followed
by a solution of lithium bis(trimethylsilyl)amide (1.0 M in THF,
0.095 mL, 0.095 mmol) and the mixture stirred for 1 h at room
temperature. The reaction was quenched by addition of aqueous
ammonium chloride (5 mL). The product was extracted with
CH2Cl2 (10 mL), washed with H2O (3 ¥ 10 mL) and purifed by
chromatography on silica (40–60 ◦C petroleum ether/CH2Cl2 4 : 1)
to give the product as a purple-green solid (0.019 g, 83%). m.p. >
300 ◦C; 1H NMR (400 MHz, CDCl3) d 9.63 (2H, d, J = 4.9 Hz),
8.93 (2H, d, J = 4.9 Hz), 8.73 (2H, d, J = 4.9 Hz), 8.69 (2H, d, J =
4.9 Hz), 8.58 (2H, d, J = 8.0 Hz), 8.00 (2H, d, J = 7.3 Hz), 7.87
(4H, d, J = 1.9 Hz), 7.66–7.76 (8H, m), 1.50 (36H, s); 13C NMR
(125 MHz, CDCl3) d 178.0, 149.2, 145.9, 144.2, 142.7, 142.4, 140.5,
139.3, 137.8, 134.3, 134.0, 133.5, 132.8, 132.5, 129.6, 128.9, 128.9,
128.0, 126.9, 122.2, 122.1, 121.5, 95.4, 95.1, 93.6, 35.0, 31.7; m/z
(MALDI-TOF, +ve) 946.51 (C63H60N4NiO requires 946.41).
[5,15-bis(3,5-di-tert-butylphenyl)-10-phenyl-20-butadiynyl
porphinato] [5,15-bis(3,5-di-tert-butylphenyl)-10-phenyl-20-
ethynyl porphinato]benzenemethanolato nickel(II) 18
[5,15-bis(3,5-di-tert-butylphenyl)-10-phenyl-20-ethynyl
porphinato] [5,15-bis(3,5-di-tert-butylphenyl)-10-phenyl
porphinato] methanolato nickel(II) 13
Butadiyne porphyrin 3 was deprotected by the general method.
The deprotected porphyrin (0.010 g, 0.011 mmol) and ethynyl
ketone porphyrin 17 (0.007 g, 0.007 mmol) were dissolved in dry
THF (1 mL). Lithium bis(trimethylsilyl)amide solution (1.0 M in
THF, 0.044 mL, 0.044 mmol) was added and the reaction was
stirred at room temperature for 1 h. The reaction was quenched
with aqueous ammonium chloride (5 mL), extracted with CH2Cl2
(10 mL) and washed with H2O (3 ¥ 10 mL). The product
was purified by column chromatography (40–60 ◦C petroleum
ether/CH2Cl2; 2 : 1) to give a purple solid (0.004 g, 30%). m.p. >
300 ◦C; lmax (CHCl3)/nm (log e) 434 (5.07), 545 (3.97), 584 (3.90);
1H NMR (400 MHz, CDCl3) d 9.58 (2H, d, J = 4.9 Hz), 9.53 (2H,
d, J = 4.9 Hz), 8.88 (2H, d, J = 4.9 Hz), 8.85 (2H, d, J = 4.9
Hz), 8.72 (2H, d, J = 4.9 Hz), 8.66–8.72 (6H, m), 8.36 (2H, d, J =
7.6 Hz), 7.97–8.01 (4H, m), 7.84–7.86 (8H, m), 7.63–7.73 (14H,
m), 7.54 (1H, m), 3.60 (1H, s), 1.47 (36H, s), 1.45 (36H, s); m/z
(MALDI-TOF, +ve) 1816.11, 1799.05 (C121H116N8Ni2O requires
1814.80, –OH requires 1797.80).
Acetylene porphyrin 2 was deprotected by the general method.
The deprotected porphyrin (0.050 g, 0.059 mmol) and formyl
porphyrin 12 (0.010 g, 0.012 mmol) were dissolved in dry THF
(1 mL). Lithium bis(trimethylsilyl)amide solution (1.0 M in THF,
0.059 mL, 0.059 mmol) was added and the reaction was stirred at
room temperature for 1 h. The reaction was quenched with aque-
ous ammonium chloride (5 mL), extracted with CH2Cl2 (10 mL)
and washed with H2O (3 ¥ 10 mL◦). The product was purified
by column chromatography (40–60 C petroleum ether/CH2Cl2;
2 : 1) to give a purple solid (0.006 g, 30%). m.p. > 300 ◦C; lmax
1
(CHCl3)/nm (log e) 421 (5.22), 538 (4.31), 601 (4.15); H NMR
(400 MHz, CDCl3) d 10.17 (2H, d, J = 4.9 Hz), 9.52 (2H, d, J =
4.9 Hz), 9.07 (2H, d, J = 4.9 Hz), 8.81 (2H, d, J = 4.9 Hz), 8.76–
8.79 (4H, m), 8.70–8.74 (4H, m), 8.39 (1H, d, J = 3.8 Hz), 8.06
(2H, d, J = 7.1 Hz), 8.02 (2H, d, J = 7.5 Hz), 7.92 (4H, d, J =
1.6 Hz), 7.85 (4H, d, J = 1.6 Hz), 7.75–7.78 (4H, m), 7.68–7.72
(6H, m), 3.81 (1H, d, J = 3.8 Hz), 1.49–1.51 (72H, overlapping
s); 13C NMR (125 MHz, CDCl3) d 149.0, 149.0, 144.8, 143.4,
142.9, 142.5, 142.3, 142.1, 140.8, 140.6, 139.5, 133.9, 133.5, 133.5,
133.3, 132.5, 132.4, 132.3, 132.1, 129.9, 128.9, 128.7, 127.7, 126.9,
126.8, 121.1, 121.0, 120.4, 90.3, 65.6, 34.9, 34.9, 31.6, 31.6; m/z
(MALDI-TOF, +ve) 1691.76, 1674.73 (C111H112N8Ni2O requires
1690.77, –OH requires 1673.77).
bis[5,15-bis(3,5-di-tert-butylphenyl)-10-phenyl-20-butadiynyl
porphinato]benzenemethanolato nickel(II) 6
Butadiyne porphyrin 3 was deprotected by the general method.
The deprotected porphyrin (0.045 g, 0.052 mmol) was dissolved
in dry THF (2 mL). Methyl benzoate (3.3 mL, 0.026 mmol) and
lithium bis(trimethylsilyl)amide solution (1.0 M in THF, 0.208 mL,
0.208 mmol) was added and the reaction was stirred at room
temperature for 1 h. The reaction was quenched with aqueous
ammonium chloride (5 mL), extracted with CH2Cl2 (10 mL) and
washed with H2O (3 ¥ 10 mL). The product was purified by column
chromatography (40–60 ◦C petroleum ether/CH2Cl2; 2 : 1) to give
a purple solid (0.030 g, 31%). m.p. > 300 ◦C; lmax (CHCl3)/nm (log
e) 435 (5.65), 549 (4.52), 585 (4.57); 1H NMR (400 MHz, CDCl3)
d 9.53 (4H, d, J = 4.8 Hz), 8.87 (4H, d, J = 4.8 Hz), 8.71 (4H, d,
J = 4.8 Hz), 8.67 (4H, d, J = 4.8 Hz), 8.12 (2H, d, J = 8.1 Hz),
[5,15-bis(3,5-di-tert-butylphenyl)-10-phenyl-20-butadiynyl
porphinato] [5,15-bis(3,5-di-tert-butylphenyl)-10-phenyl
porphinato] methanolato nickel(II) 15
Butadiyne porphyrin 3 was deprotected by the general method.
The deprotected porphyrin (0.010 g, 0.011 mmol) and formyl
porphyrin 12 (0.0062 g, 0.0073 mmol) were dissolved in dry THF
(1 mL). Lithium bis(trimethylsilyl)amide solution (1.0 M in THF,
0.044 mL, 0.044 mmol) was added and the reaction was stirred at
3478 | Org. Biomol. Chem., 2010, 8, 3472–3479
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The Royal Society of Chemistry 2010
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7.99 (4H, dd, J = 7.3, 1.5 Hz), 7.85 (8H, d, J = 1.5 Hz), 7.74 (4H,
t, J = 1.5 Hz), 7.64–7.70 (6H, m), 7.61 (2H, dd, J = 7.3 Hz, 8.1
Hz), 7.52 (1H, t, J = 7.3 Hz), 3.38 (1H, s), 1.48 (72H, s); 13C NMR
(125 MHz, CDCl3) d 149.1, 145.8, 143.8, 142.5, 142.4, 140.6, 139.4,
133.9, 133.5, 132.5, 132.4, 131.1, 129.4, 128.9, 128.9, 127.9, 126.9,
126.2, 121.7, 121.3, 121.2, 95.5, 82.5, 82.3, 79.9, 71.9, 66.6, 35.0,
31.7; m/z (MALDI-TOF, +ve) 1840.05, 1823.06 (C123H116N8Ni2O
requires 1838.80, –OH requires 1821.80).
2 A. Bahtiar, K. Koynov, Y. Mardiyati, H.-H. Horhold and C. Bubeck,
J. Mater. Chem., 2009, 19, 7490–7497.
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(trimethylsilylethynyl)phenyl]porphinato] benzenemethanolato
nickel(II) 11
9 C.-L. Mai, W.-K. Huang, H.-P. Lu, C.-W. Lee, C.-L. Chiu, Y.-R. Liang,
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Porphyrin 10 was deprotected by the general method. The
deprotected porphyrin (7.0 mg, 7.4 mmol) was dissolved in dry
THF (1 mL). Methyl benzoate (0.5 mL, 3.7 mmol) and lithium
bis(trimethylsilyl)amide solution (1.0 M in THF, 0.030 mL,
0.030 mmol) was added and the reaction was stirred at room
temperature for 1 h. The reaction was quenched with aqueous
ammonium chloride (5 mL), extracted with CH2Cl2 (10 mL) and
washed with H2O (3 ¥ 10 mL). The product was purified by column
chromatography (40–60 ◦C petroleum ether◦/CH2Cl2; 2 : 1) to give
a purple solid (0.002 g, 14%). m.p. > 300 C; lmax (CHCl3)/nm
(log e) 440 (5.61), 548 (4.46), 587 (4.51); 1H NMR (400 Hz, CDCl3)
d 9.59 (4H, d, J = 4.9 Hz), 8.88 (4H, d, J = 4.9 Hz), 8.72 (4H, d,
J = 4.9 Hz), 8.68 (4H, d, J = 4.9 Hz), 8.04 (2H, d, J = 7.5 Hz),
8.00 (4H, dd, J = 7.7, 1.5 Hz), 7.93 (4H, d, J = 8.2 Hz), 7.88 (8H,
d, J = 1.8 Hz), 7.65–7.75 (16H, m), 7.52–7.56 (2H, m), 7.45–7.48
(2H, m), 3.18 (1H, s), 1.50 (72H, s); m/z (MALDI-TOF, +ve)
1991.52, 1974.59 (C135H124N8Ni2O requires 1990.56, –OH requires
1973.56).
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28 The extinction coefficients in Table 1 were estimated by assuming that
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Procedure for stability experiments
The stability of the cationic species in solution was investigated by
UV/Vis spectroscopy. Trifluoroacetic acid (Acros) and chloroform
(Fisher, stabilised with 100 ppm amylene) were used as supplied.
A stock solution of the precursor was prepared in CHCl3.
10 mL of this solution was added to a cuvette containing 3 mL
of CHCl3. 10 mL of trifluoroacetic acid was added and the
absorption at 1611 nm was measured every 10 s in time course
measurement mode. This procedure was repeated while varying
the concentration of the acid. The initial absorbance was around
0.5, but to directly compare different conditions, each data set was
normalised.
Acknowledgements
We thank the DARPA-MORPH Program and EPSRC for fi-
nancial support, and the EPSRC Mass Spectrometry Centre
(Swansea) for mass spectra.
33 R. N. Keller and H. D. Wycoff, Inorg. Synth., 1946, 2, 1.
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This journal is
The Royal Society of Chemistry 2010
Org. Biomol. Chem., 2010, 8, 3472–3479 | 3479
©