Electrochemical, Spectroelectrochemical, and Structural Studies of Mono- and Diphosphorylated Zinc Porphyrins and Their Self-Assemblies

Article abstract of DOI:10.1021/acs.inorgchem.9b00268

Three series of porphyrins containing a Zn(II) central metal ion and zero, one, or two phosphoryl groups at the meso-positions of the macrocycle were characterized as to their electrochemical, spectroscopic, and structural properties in nonaqueous media.

Full text of DOI:10.1021/acs.inorgchem.9b00268

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Electrochemical, Spectroelectrochemical, and Structural Studies of
Mono- and Diphosphorylated Zinc Porphyrins and Their Self-
Assemblies
Yuanyuan Fang,† Xiaoqin Jiang,† Karl M. Kadish,*,† Sergey E. Nefedov,‡ Gayane A. Kirakosyan,‡,§
Yulia Y. Enakieva,§,∥ Yulia G. Gorbunova,‡,§ Aslan Y. Tsivadze,‡,§ Christine Stern,∥
Alla Bessmertnykh-Lemeune,*,∥ and Roger Guilard∥
†Department of Chemistry, University of Houston, Houston, Texas 77204-5003, United States
‡Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninsky Pr. 31, Moscow, 119991, Russia
§Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Pr. 31, build. 4, Moscow,
119071, Russia
∥
́
́
́
́
Institut de Chimie Moleculaire de l’Universite de Bourgogne, Universite Bourgogne Franche-Comte, UMR CNRS 6302, 9 Avenue
Alain Savary, BP 47870, Dijon 21078 CEDEX, France
S
* Supporting Information
ABSTRACT: Three series of porphyrins containing a Zn(II)
central metal ion and zero, one, or two phosphoryl groups at
the meso-positions of the macrocycle were characterized as to
their electrochemical, spectroscopic, and structural properties
in nonaqueous media. The investigated compounds are
represented as 5,15-bis(4′-R-phenyl)porphyrinatozinc, 10-
(diethoxyphosphoryl)-5,15-bis(4′-R-phenyl)porphyrinatozinc,
and 5,15-bis(diethoxyphosphoryl)-10,20-bis(4′-R-phenyl)por-
phyrinatozinc, where R = OMe, Me, H, or CN. Linear-free
energy relationships are observed between the measured redox
potentials at room temperature and the electronic nature of the substituents at the 5 and 15 meso-phenyl groups of the
macrocycle. The mono- and bis-phosphoryl derivatives with two p-cyanophenyl substituents provide electrochemical evidence
for aggregation at low temperature, a greater degree of aggregation being observed in the case of 5,15-bis(diethoxyphosphoryl)-
10,20-bis(4′-cyanophenyl)porphyrinatozinc(II). This compound was characterized in further detail by variable-temperature 1H
and 31P{1H} NMR spectroscopy in solution combined with single crystal X-ray analysis in the solid state. The data obtained
from these measurements indicate that this porphyrin has a dimeric structure in CDCl3 at 223−323 K but forms a 2D polymeric
network when it is crystallized from a CHCl3/MeOH mixture.
molecules to a target task is to vary the substitution pattern
of aryl groups at the meso-positions of the porphyrin
macrocycle. The synthesis of porphyrins bearing functional
groups directly attached to the macrocycle has also been
widely investigated, and powerful synthetic strategies based on
transition-metal-catalyzed carbon−carbon and carbon−hetero-
atom (N, O, S, Se, B) bond forming reactions have been
developed.15−24 However, the low air and photostability of
many porphyrins bearing electron-donating functional groups
at the macrocycle periphery is a serious drawback for their
practical application. In this context, electron-deficient with-
drawing phosphorus(V)-substituted porphyrins are of partic-
ular interest, since these compounds have been shown to be
highly stable.
INTRODUCTION
■
Porphyrins and related tetrapyrrolic macrocycles are widely
used by living systems for the optimal organization of
important processes such as oxygen transport, catalytic
reactions, light-harvesting, photoinduced charge separation,
and electron transport.1−4 Synthetic porphyrins have unparal-
leled significance for understanding these naturally occurring
processes5−8 and are regarded as a way of dealing more
efficiently with major societal challenges.9−14 The physico-
chemical features of these pigments have continued to attract
attention from scientists in the fields of physics, biology,
medicine, material science, and burgeoning new areas such as
molecular recognition and nanotechnology.
It has been well documented in the literature that the
physicochemical properties of porphyrins can be dramatically
tuned by introducing substituents with different electronic and
steric effects at the periphery of the macrocycle.14 One key
strategy to adapt the structural properties of porphyrin
Received: January 29, 2019
© XXXX American Chemical Society
A
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The first examples of meso-phosphorylporphyrins prepared
from meso-haloporphyrins under palladium- and copper-
catalyzed conditions were reported independently by the
groups of Arnold and Matano.25−27 Later, palladium catalysts
were employed to facilitate the reaction of readily accessible
meso- and β-bromoporphyrins with dialkyl phosphites, giving a
concise and versatile method for preparing porphyrinylphos-
phonic acid derivatives in reasonably good yield.28−30 In
particular, many new A2B-, A2BC-, and trans-A2B2-type
porphyrins (B = diethoxyphosphoryl) were prepared taking
advantage of the relatively simple separation of the target
molecules from crude mixtures of the polar porphyrin
derivatives.31
Chart 1. Structure of the Investigated Porphyrins
These photo- and air-stable porphyrin pigments with
phosphoryl groups show promise for high-value-added
applications in the areas of energy production, optoelectronics,
fine chemicals synthesis, and health care.26,27,32−43 For
instance, porphyrinylphosphonic acids and their monoalkyl
esters have led to the preparation of water-soluble porphyrins
which have been extensively investigated for use in
biomedicine (e.g., molecular imaging, photodynamic therapy,
and oxygen detection).34,44 Several investigations of hybrid
organic−inorganic materials have demonstrated that transition
metal complexes containing phosphonate anchoring groups
can be easily heterogenized by grafting onto metal oxides or
through the incorporation in coordination polymer net-
works.45−52 These are attractive synthetic routes to prepare
detectors, sensitizers, and catalysts based on porphyrin
derivatives.
In addition, phosphorylporphyrins are important molecular
building blocks for the elaboration of supramolecular
porphyrin assemblies which mimic natural photosynthesis
processes.27,29,38,53,54 Indeed, the phosphoryl group is an
oxygen donor which can axially ligate the central metal ion of
another porphyrin molecule or bind to external metal ions,
giving coordination-assembled porphyrin systems. These
molecular algorithms can then be used in crystal engineering
or in solution chemistry to prepare elaborate coordination
frameworks.28,55
An understanding of the electrochemical properties of
phosphorylated porphyrins should provide a solid basis for
the design and optimization of these compounds’ properties
when employed in electron-transfer processes, catalytic
reactions, and crystal engineering as molecules, supramolecular
architectures, or hybrid functional materials. The addition of
one or more phosphoryl groups to a porphyrin macrocycle can
significantly modify chemical and physical properties of the
compound, with the type and magnitude of the effect being
dependent in large part on the position of the substituents. In
this regard, three series of phosphorylated porphyrins have to
date been examined as to their electrochemical properties.
These are (i) meso-4′-(diethoxyphosphoryl)phenyl substituted
derivatives,53 (ii) β-pyrrole substituted porphyrins,54 and (iii)
meso-phosphorylporphyrins.53,56
In the current paper, we describe electrochemical and
spectroscopic properties for three series of Zn(II) porphyrins
containing phosphoryl groups on the meso-positions of the
macrocycle. Structures of the investigated porphyrins are
shown in Chart 1 and are represented as 5,15-bis(4′-R-
phenyl)porphyrinatozinc (1a−d), 10-(diethoxyphosphoryl)-
5,15-bis(4′-R-phenyl)porphyrinatozinc (2a−d), and 5,15-bis-
(diethoxyphosphoryl)-10,20-bis(4′-R-phenyl)porphyrinatozinc
(3a−d).
The phosphoryl groups on the porphyrins of Chart 1 are
electron-withdrawing, and these derivatives have been earlier
demonstrated to undergo more facile reductions at the
porphyrin macrocycle than the related tetraphenylporphyrins
with the same central metal ions.53 More importantly, a
coordination self-assembly was previously observed for
structurally related β- and meso-phosphorylated Zn(II)
porphyrins,27,54 and these self-assemblies were sometimes
electrochemically detected at low temperature by a splitting of
the first oxidation process,27,54 suggesting the presence of
equivalent and interacting redox centers in the molecule.
Another example for the electrochemical detection of
phosphorylporphyrin self-aggregation is given by the methox-
yphenyl-containing compound 3a in Chart 1 where the
current−voltage curves for reduction by cyclic voltammetry
in CH2Cl2 suggested the presence of monomers at room
temperature but aggregates when the measurements on a 10−3
M solution were carried out at −75 °C.53 UV−visible data for
the same compound in CDCl3 indicated the presence of a
concentration dependent equilibrium, where monomers were
present at 10−6 M and aggregates at 10−4 M.53 No explanation
was given in the paper for this apparently contradictory data
for millimolar solutions of the porphyrin at room temperature,
but the fact that the monomeric species were easier to
electrochemically reduce than the aggregate by 150 mV in
CH2Cl2 would favor conversion of any higher porphyrin
aggregates in solution to the more easily reducible monomer at
the electrode surface under the application of an applied
potential.
This is further investigated in the current study for the
mono- and bis-phosphoryl series of compounds in Chart 1
where we wished to also examine how the electrochemically
detected self-aggregation on reduction would be effected by
increasing the number of electron-withdrawing meso-P(O)-
(OEt)2 groups on the porphyrin from one to two while also
increasing the electron-withdrawing properties of the para-
substituent on the two meso-phenyl rings of the compounds,
from OMe on one extreme to CN on the other.
As it will be shown, a well-defined splitting of the first
reduction potential is observed at low temperature for the CN-
phenyl containing porphyrins 2d and 3d, again indicating a
coordination self-assembly of these complexes under the
electrochemical solution conditions. The largest degree of
self-assembly under the electrochemical conditions was
observed for compound 3d, and this porphyrin was then
1
further investigated by variable-temperature H and 31P{1H}
NMR spectroscopies in solution and single crystal X-ray
diffraction in the solid state. When crystals of the 2D
coordination polymer (3d)n were dissolved in chloroform, an
B
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accessory (Pike) was used in order to obtain IR spectra of solid
samples.
interesting structural modification was observed, leading to the
formation of dimer (3d)2. This is the first example of a
phosphorylporphyrin exhibiting a dimeric structure in chloro-
form at room temperature and also displaying different
supramolecular organization in crystals and in solution.
All of the spectrometers except for the Nexus (Nicolet)
spectrophotometer and the Bruker Avance III 600 MHz and Avance
II 300 MHz spectrometers (Shared Facility Centers at the Institute of
Physical Chemistry and Electrochemistry RAS and Institute of
General and Inorganic Chemistry RAS, respectively) were available
EXPERIMENTAL SECTION
̂
́
at the “Pole Chimie Moleculaire”, the technological platform for
chemical analysis and molecular synthesis (http://www.wpcm.fr)
which relies on the Institute of the Molecular Chemistry of University
of Burgundy and WelienceTM, a Burgundy University private
subsidiary.
■
General Considerations. Unless otherwise noted, all chemicals
were obtained commercially from Acros or Aldrich and used without
further purification. Tetra-n-butylammonium perchlorate (TBAP) was
purchased from Sigma-Aldrich Co. Caution! Perchlorate salts are
potentially explosive and should be handled with care.
Cyclic voltammetry was carried out at 298 K using an EG&G
Princeton Applied Research (PAR) 173 potentiostat/galvanostat. A
homemade three-electrode cell was used for cyclic voltammetric
measurements and consisted of a glassy carbon working electrode, a
platinum counter electrode, and a homemade saturated calomel
reference electrode (SCE). The SCE was separated from the bulk of
the solution by a fritted glass bridge of low porosity, which contained
the solvent/supporting electrolyte mixture.
Thin-layer UV−vis spectroelectrochemical experiments were
performed using a home-built thin-layer cell, which has a transparent
platinum net working electrode. Potentials were applied and
monitored with an EG&G PAR Model 173 potentiostat. High purity
N2 from Trigas was used to deoxygenate the solution and kept over
the solution during each electrochemical and spectroelectrochemical
experiment.
Crystals suitable for single crystals X-ray analysis were grown by a
slow diffusion of heptane in an open glass tube of 3d in a CHCl3/
MeOH solvent mixture (97:3 v/v, c = 10−3 M). Details on the
SCXRD experiment and refinement are given in the Supporting
Information. Crystallographic data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif (CCDC 1890813).
[5,15-Bis(4′-methoxyphenyl)porphyrinato(2-)]zinc (1a),57 [5,15-
bis(4′-methylphenyl)porphyrinato(2-)]zinc (1b),58 5,15-bis(4′-
phenyl)porphyrinato(2-)]zinc (1c),58 [5,15-bis(4′-cyanophenyl)por-
phyrinato(2-)]zinc (1d),42 [10-(diethoxyphosphoryl)-5,15-bis(4′-
methoxyphenyl)porphyrinato(2-)]zinc (2a),58 [10-(diethoxyphos-
phoryl)-5,15-bis(4′-tolyl)porphyrinato(2-)]zinc (2b),58 [10-(dieth-
oxyphosphoryl)-5,15-diphenylporphyrinato(2-)]zinc (2c),58 [10-
(diethoxyphosphoryl)-5,15-bis(4′-cyanophenyl)porphyrinato(2-
)]zinc (2d),58 [5,15-bis(diethoxyphosphoryl)-10,20-bis(4′-tolyl)por-
phyrinato(2-)]zinc (3b),53 [5,15-bis(diethoxyphosphoryl)-10,20-bis-
(phenyl)porphyrinato(2-)]zinc (3c),28,53 [10-bromo-5,15-bis(4′-
methoxyphenyl)porphyrinato(2-)]zinc (4a),58 [10-bromo-5,15-bis-
(4′-tolyl)porphyrinato(2-)]zinc (4b),58 [10-bromo-5,15-bis(phenyl)-
porphyrinato(2-)]zinc (4c),28,53 [10-bromo-5,15-bis(4′-cyano-
phenyl)porphyrinato(2-)]zinc (4d),58 [5,10-dibromo-10,20-bis(4′-
tolyl)porphyrinato(2-)]zinc (5b),53 and 5,10-dibromo-10,20-bis-
(phenyl)porphyrinato(2-)]zinc (5c)53 were prepared according to
published procedures.
Reactions were performed in air unless otherwise noted. Column
chromatography purification was carried out on silica gel (Silica 60,
63−200 μm, Aldrich). Analytical thin-layer chromatography (TLC)
was carried out using Merck silica gel 60 F-254 plates (precoated
sheets, 0.2 mm thick, with fluorescence indicator F254). All solvents
were dried by standard procedures (dichloromethane: distillation
from CaH2; absolute EtOH: distillation over Mg; benzonitrile:
distillation over P2O5; toluene: distillation over sodium).
Powder XRD experiment was carried out on a Bruker D8 Advance
Diffractometer with a goniometer radius of 217.5 mm, Gobel Mirror
̈
parallel-beam optics, 2° Sollers slits, and 0.2 mm receiving slit. PXRD
patterns from 3° to 45° 2θ were recorded at room temperature using
Cu Kα radiation (1.5418 Å) under the following measurement
conditions: tube voltage of 40 kV, a tube current of 40 mA, step scan
mode with a step size of 0.02° 2θ, and a counting time of 2.5 s/step.
The sample of porphyrin 3d was analyzed without being crushed. The
crystal X-ray diffraction analysis was performed at the Shared Facility
Center of the Kurnakov Institute of General and Inorganic Chemistry
of RAS.
Synthesis of Porphyrins 5a and 5d. General Procedure for
Bromination of [5,15-Diarylporphyrinato(2-)]zinc. [5,15-
Diarylporphyrinato(2-)]zinc (1 equiv) and pyridine (10 equiv) were
dissolved in chloroform (4 mM), and the resulting mixture was stirred
for 15 min at room temperature. After cooling the reaction mixture to
the relevant temperature, NBS (2.2 equiv) was added in one portion.
The reaction mixture was stirred for 20 min, then quenched with
acetone (3 mL) and concentrated under reduced pressure. The
resulting crude solid was purified on a short silica gel column using a
CHCl3/methanol mixture as an eluent to afford the dibromides 5a
and 5d. Spectral data of compounds 5a,d are presented in the SI
(Figures S9−S14).
1H and 31P{1H} NMR spectra were acquired on Bruker Avance III
600 MHz, 500 MHz and Avance II 300 MHz and Nanobay 300 MHz
spectrometers and referenced to the solvent residual protons (CDCl3,
7.24 ppm) and concentrated H3PO4, respectively.
Diffusion ordered NMR 1H DOSY measurements were carried out
on a Bruker Avance III 600 MHz spectrometer equipped with a
standard 10 A gradient amplifier and a BBO probe head with a PFG
Z-axis coil having a gradient strength of 5.57 G/cm A. Spectra were
recorded at 323 K, using the standard Bruker Topspin 3.2 dstegp3s
pulse sequence employing double stimulated echo and longitudinal
eddy delay with 3 spoil gradients. Smoothed chirp pulses with 2 ms
duration were used. The strength of gradient pulses was varied linearly
from 5% to 95% of the maximum current (10 A) in 16 steps. For each
increment, 8 transients (+ four dummy scans) were acquired into
128k data points using a spectral width of 15 000 Hz. All increments
were corrected for phase and baseline distortions before mono-
exponential fitting into 256k points in the diffusion dimension using
the T1/T2 analysis module of Topspin 3.2.
[5,15-Dibromo-10,20-bis(4′-methoxyphenyl)porphyrinato(2−)]-
zinc (5a).59 The dibromide was prepared from [5,15-bis(4′-
methoxyphenyl)porphyrinato(2-)]zinc (1a) (74 mg, 0.13 mmol).
The reaction was performed at −40 °C. The solid residue was
chromatographed using a CHCl3/CH3OH (97:3, v/v) mixture as an
eluent to give porphyrin 5a as a purple crystalline powder in 58% yield
(55 mg). 1H NMR (300 MHz, CDCl3/CD3OD, 2:1 v/v, 25 °C): δ =
9.40 (d, JH,H = 4.7 Hz, 4H, Hβ), 8.64 (d, JH,H = 4.7 Hz, 4H, Hβ),
7.82 (d, 3JH,H = 8.5 Hz, 4H, o-Ph), 7.05 (d, 3JH,H = 8.5 Hz, 4H, m-Ph)
ppm. MS (MALDI-TOF): m/z calcd. for C34H22Br2N4O2Zn [M]+
739.9; found 739.7. UV−vis (CHCl3): λmax [log (ε/M−1 cm−1)] =
430 (5.55), 566 (4.33), 608 (4.17) nm.
UV−visible spectra of the compounds were obtained on a Varian
Cary 50 spectrophotometer by using a rectangular quartz cell
(Hellma, 100-QS, 45 × 12.5 × 12.5 mm, path length: 10 mm,
chamber volume: 3.5 mL).
MALDI-TOF mass spectra were obtained on a Bruker Ultraflex II
LRF 2000 mass spectrometer in positive ion mode with a dithranol
matrix. Accurate mass measurements (HRMS) were made on a
THERMO LTQ Orbitrap XL equipped with an electrospray
ionization (ESI) source in positive mode unless otherwise stated.
Solutions in CHCl3/methanol (1:1) were used for the analysis.
IR spectra were registered on Nicolet Nexus and Bruker Vector 22
FT-IR spectrophotometers. A universal micro-ATR sampling
3
3
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[5,15-Dibromo-10,20-bis(4′-cyanophenyl)porphyrinato(2−)]zinc
(5d).58 The dibromide was prepared from 5,15-bis(4′-cyanophenyl)-
porphyrinato(2-)]zinc (1d) (20 mg, 0.035 mmol). The reaction was
performed at −20 °C. The crude product was purified by column
chromatography using a CHCl3/MeOH (99:1, v/v) mixture as an
eluent to give porphyrin 5d as a purple crystalline powder in 98%
yield (25 mg). 1H NMR (300 MHz, CDCl3, 25 °C): δ = 9.72 (d, 3JH,H
CH2O), 3.91 (s, 6H, OCH3), 1.17 (t, 3JH,H = 7.1 Hz, 12H, CH3) ppm.
13C NMR (150 MHz, CDCl3/CD3OD (2:1), 25 °C): δ 159.35 (2C,
CArOCH3), 151.90 (d, JC,P = 2.6 Hz, 4C, α-C), 151.08 (4C, α-C),
2
135.33 (4C, m-CHAr), 135.17 (2C, CAr), 133.03 (4C, β-CH), 132.71
(4C, β-CH), 122.37 (2C, meso-C), 111.96 (4C, o-CHAr), 101.99 (d,
2
2JC,P = 183 Hz, 2C, meso-C), 62.84 (d, JC,P = 4.7 Hz, 4C, OCH2),
3
55.44 (2C, OCH3), 16.14 ppm (d, JC,P = 6.6 Hz, 4C, OCH2CH3).
3
= 4.7 Hz, 4H, Hβ), 8.77 (d, JH,H = 4.7 Hz, 4H, Hβ), 8.27 and 8.07
31P{1H} NMR (300 MHz, CDCl3/CD3OD, 2:1 v/v, 25 °C): δ 27.8
(AB system, JAB = 8.1 Hz, 8 H, m-Ph and o-Ph, respectively) ppm. MS
(MALDI-TOF): m/z calcd. for C34H16Br2N6Zn [M + H]+ 730.9;
found 732.2. UV−vis (CHCl3): λmax [log (ε/M−1 cm−1)] = 431
(5.47), 565 (4.17), 606 (3.82) nm.
ppm. HRMS (ESI): m/z calcd. for C42H42N4NaO8P2Zn [M + Na]+
879.16616; found 879.16723. IR (neat): ν 2962 (w), 2928 (w), 2830
(w), 1606 (m), 1526 (m), 1510 (m), 1474 (m), 1463 (m), 1439 (m),
1407 (m), 1389 (m), 1325 (m), 1292 (m), 1245 (s, PO), 1222
(m), 1200 (m, PO), 1172 (m), 1087 (m), 1033 (m), 1013 (m, P−
O), 982 (s, P−O), 951 (s), 886 (s), 842 (s), 796 (s), 745 (s), 715
(m), 668 (m), 639 (m), 579 (s), 564 (s), 553 (s) cm−1. UV−vis
(CHCl3): λmax [log (ε/M−1 cm−1)] = 427 (5.45), 565 (3.92), 603
(4.35) nm.
[5,15-Bis(diethoxyphosphoryl)-10,20-bis(4′-methoxyphenyl)por-
phyrinato(2−)]zinc (3a). A two-neck round-bottom flask equipped
with a condenser, a magnetic stirrer bar, and a gas outlet was charged
with dibromoporphyrin 5a (46 mg, 0.062 mmol) and Pd(PPh3)4
(0.018 mg, 0.015 mmol). The reaction vessel was evacuated and
purged with nitrogen three times. Subsequently, a mixture of
anhydrous toluene and ethanol (1:1 v/v, 3 mL), diethyl H-
phosphonate (3.1 mmol, 0.396 mL), and NEt3 (0.928 mmol, 0.130
mL) were added by syringes. The reaction mixture was stirred at
reflux for 1 day when monitored by MALDI-TOF and 1H NMR. After
complete conversion of dibromide 5a and [5-bromo-15-diethox-
yphosphoryl-10,20-bis(4′-methoxyphenyl)porphyrinato(2−)]zinc,
the reaction mixture was cooled to room temperature and
concentrated under reduced pressure. The solid residue was taken
up in chloroform and subjected to column chromatography on silica
gel using a CHCl3/CH3OH mixture (98:2, v/v) as an eluent. Three
fractions containing porphyrins were obtained. These solids were
characterized as 5,15-bis(4′-methoxyphenyl)porphyrin,60 compound
2a58 (31% yield), and a mixture of porphyrin 3a with
triphenylphosphine oxide in a 1:1 molar ratio (37.5 mg). A further
purification of porphyrin 3a by column chromatography on silica gel
using different eluents was unsuccessful. Therefore, to obtain a pure
solid, the product was transformed into the corresponding free base
porphyrin, purified, and reacted with a zinc salt according to the
following procedures.
Porphyrin 3a was also prepared using the Pd(OAc)2/PPh3 (1/3
molar ratio) catalytic system. However, under these conditions, the
product isolation was also tedious and the product yield was low. For
example, the reaction carried out in the presence of 10 mol %
Pd(OAc)2/PPh3 afforded 3a in 10% yield. Attempts to simplify
product isolation by using 10 mol % of the Pd(OAc)2/dppf catalytic
system gave only partial success because the product yield decreased
to 10% owing to an acceleration of the side hydrodebromination
reaction.
Synthesis of [5,15-Bis(diethoxyphosphoryl)-10,20-bis(4′-
cyanophenyl)porphyrinato(2−)]zinc (3d). A two-neck round-
bottom flask equipped with a reflux condenser, a magnetic stirrer bar,
and a gas outlet was charged with bromoporphyrin 5d (45.6 mg,
0.062 mmol), Pd(OAc)2 (1.4 mg, 0.0062 mmol), and dppf (7 mg,
0.0125 mmol). The reaction vessel was evacuated and purged with
nitrogen three times. Subsequently, 3 mL of an anhydrous toluene/
ethanol mixture (1:1, v/v), diethyl H-phosphonate (3.1 mmol, 0.396
mL), and NEt3 (0.928 mmol, 0.130 mL) were added by syringes. The
reaction mixture was stirred at reflux for 3 days. The course of the
reaction was monitored by MALDI-TOF and 1H NMR spectroscopy.
After complete conversion of dibromide 5d and [5-bromo-15-
diethoxyphosphoryl-10,20-bis(4′-cyanophenyl)porphyrinato(2−)]-
zinc, the reaction mixture was allowed to cool to room temperature
and concentrated under reduced pressure. The solid residue was
dissolved in chloroform and subjected to column chromatography on
silica gel using a CHCl3/CH3OH mixture (98:2, v/v) as eluent to
Trifluoroacetic acid (0.25 mL) was added to the crude solution
(37.5 mg) in CHCl3 (37 mL), and the resulting mixture was stirred at
room temperature for 3 h. After washing with aqueous NaHCO3 (2 ×
15 mL) and water (1 × 15 mL), the reaction mixture was dried over
MgSO4 and concentrated under reduced pressure. The solid residue
was taken up in CH2Cl2 and chromatographed on silica gel using a
CH2Cl2/CH3OH mixture (99.5:0.5, v/v) as an eluent to afford 5,15-
bis(diethoxyphosphoryl)-10,20-bis(4′-methoxyphenyl)porphyrin (23
mg, 88%). Then, 5,15-bis(diethoxyphosphoryl)-10,20-bis(4′-meth-
oxyphenyl)porphyrin (23 mg, 0.029 mmol) and zinc acetate dihydrate
(31.8 mg, 0.145 mmol) in a CHCl3 (9 mL)/CH3OH (0.5 mL)
mixture was stirred at room temperature for 2 h. Then, the reaction
mixture was washed with water (3 × 10 mL) to remove an excess of
Zn(OAc)2·2H2O. The organic layer was dried over MgSO4 and
concentrated under reduced pressure. The resulting crude solid was
purified by column chromatography on silica gel using a CHCl3/
CH3OH mixture (98:2, v/v) as an eluent to afford 3a (23.8 mg, 96%).
The yield of porphyrin 3a calculated on the dibromide 5a is 45%.
5,15-Bis(diethoxyphosphoryl)-10,20-bis(4′-methoxyphenyl)-
porphyrin. 1H NMR (300 MHz, CDCl3/CD3OD, 2:1 v/v, 25 °C): δ
1
afford 3d in 71% yield (37.4 mg). H NMR (300 MHz, CDCl3/
3
CD3OD, 2:1 v/v, 25 °C): δ 10.10 (d, JH,H = 4.9 Hz, 4H, Hβ), 8.57
(d, 3JH,H = 4.9 Hz, 4H, Hβ), 8.11 and 7.90 (AB system, JAB = 8.0 Hz, 8
H, m-Ph and o-Ph, respectively), 4.37−4.25 (m, 4H, CH2O), 4.13−
3
4.00 (m, 4H, CH2O), 1.17 (t, JH,H = 7.1 Hz, 12H, CH3) ppm. 13C
NMR (150 MHz, CDCl3/CD3OD (2:1), 25 °C): δ 152.29 (d, 4JC,P
=
2.3 Hz, 4C, α-C), 149.83 (4C, α-C), 147.85 (2C, CAr), 134.77 (4C,
m-CHAr), 134.02 (4C, β-CH), 132.07 (4C, β-CH), 130.34 (4C, o-
CHAr), 120.20 (2C, meso-C), 118.93 (2C, CArCN), 111.57 (2C, CN),
103.42 (d, 2JC,P = 184.5 Hz, 2C, meso-C), 63.05 (d, 2JC,P = 5.3 Hz, 4C,
3
OCH2), 16.18 (d, JC,P = 6.6 Hz, 4C, OCH2CH3). 31P{1H} NMR
(300 MHz, CDCl3/CD3OD, 2:1 v/v, 25 °C): δ 26.79 ppm. HRMS
(ESI): m/z calcd. for C42H36N6NaO6P2Zn [M + Na]+ 869.1355;
found 869.13201. IR (neat): ν 2978 (w), 2925 (w), 2896 (w), 2228
(s, CN), 1604 (m), 1530 (m), 1475 (m), 1410 (m), 1393 (m),
1324 (w), 1221 (s), 1199 (s, PO), 1161 (w), 1094 (m), 1083 (m),
1040 (s), 1014 (s, P−O), 981 (s, P−O), 959 (s), 939 (s), 890 (s),
868 (m), 855 (s), 804 (w), 798 (s), 745 (s), 725 (m), 712 (s), 670
(m), 667 (m), 661 (m), 647 (m), 585 (s), 564 (s), 558 (s), 551 (s)
cm−1. UV−vis (CHCl3): λmax [log (ε/M−1 cm−1)] = 426 (5.45), 563
(4.07), 602 (4.32) nm.
3
3
9.98 (d, JH,H = 5.0 Hz, 4H, Hβ), 8.70 (d, JH,H = 5.1 Hz, 4H, Hβ),
7.87 (d, 3JH,H = 8.6 Hz, 4H, o-Ph), 7.12 (d, 3JH,H = 8.6 Hz, 4H, m-Ph),
4.35−4.24 (m, 4H, CH2O), 4.10−3.97 (m, 4H, CH2O), 3.92 (s, 6H,
OCH3), 1.15 (t, 3JH,H = 7.1 Hz, 12H, CH3) ppm. 31P{1H} NMR (300
MHz, CDCl3/CD3OD, 2:1 v/v, 25 °C): δ 25.8 ppm. MS (MALDI-
TOF): m/z calcd. for C42H45N4O8P2 [M + H]+ 795.3; found 795.1.
UV−vis (CHCl3): λmax [log (ε/M−1 cm−1)] = 420 (5.34), 522 (4.16),
561 (4.26), 598 (3.96), 653 (4.24) nm.
[5,15-Bis(diethoxyphosphoryl)-10,20-bis(4′-methoxyphenyl)por-
1
Porphyrin 3d was also prepared in the presence of a 10 mol % of
Pd(OAc)2/PPh3 (1/3 molar ratio) catalytic system. The product was
obtained in low (15%) yield according to NMR characterization of
the solid residue obtained after evaporation of the reaction mixture.
phyrinato(2−)]zinc (3a). H NMR (300 MHz, CDCl3/CD3OD, 2:1
v/v, 25 °C): δ 10.02 (d, 3JH,H = 4.9 Hz, 4H, Hβ), 8.69 (d, 3JH,H = 4.9
Hz, 4H, Hβ), 7.85 (d, 3JH,H = 8.5 Hz, 4H, o-Ph), 7.09 (d, 3JH,H = 8.6
Hz, 4H, m-Ph), 4.37−4.23 (m, 4H, CH2O), 4.11−3.98 (m, 4H,
D
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solvents (PhCN, CH2Cl2, and Py) containing 0.1 M TBAP.
Examples of the voltammograms obtained for compounds 2a−
2d in PhCN are illustrated in Figure 1, and the measured half-
RESULTS AND DISCUSSION
■
Synthesis. The trans-A2-type porphyrins 1a−d were
prepared according to the previously reported procedures
(see Experimental Section). The phosphorylporphyrins 2a−d
were synthesized by Pd-catalyzed cross-coupling of the
bromoporphyrins 4a−d with diethyl H-phosphonate (Scheme
1) as earlier reported.58
Scheme 1. Synthesis of Diethoxyphosphorylporphyrins 2a−
d and 3a−d
All compounds were obtained in good yield (60−85%)
using triethylamine as a base in the presence of the Pd(OAc)2/
PPh3 catalytic precursor.
Figure 1. Cyclic voltammograms of investigated monophosphorylated
porphyrins 2a−d in PhCN containing 0.1 M TBAP.
The diphosphonates 3a−d were first prepared from the
meso-dibromoporphyrins 5a−d and diethyl H-phosphonate
according to a similar procedure as for monophosphorylated
derivatives (Scheme 1). This synthetic approach to the
diphosphonates 3b53 and 3c28 was previously reported. Unlike
similarly as what was observed in the synthesis of the
phosphonates 2a−d, the product yield of 3a−d was strongly
dependent on the nature of the meso-aryl substituents when the
Pd(OAc)2/PPh3 catalytic system was employed for phospho-
nylation of the dibromides 5a−d. A good yield for 3c (51%)
was obtained only from the dibromide 5c, whereas the yield
decreased to 34% for the porphyrin 3b and fell to 10−15% for
the diphosphonate porphyrins 3a and 3d where the hydro-
debromination reaction was predominant under these
experimental conditions. Thus, an optimization of the reaction
procedure was performed. It was determined that the nature of
catalyst is a key parameter to increase the efficiency of this Pd-
catalyzed reaction. Diphosphonate 3a was prepared in 45%
yield using Pd(PPh3)4, whereas 3d was isolated in good yield
(71%) only when this catalyst was replaced by Pd(OAc)2/
dppf.
It should be noted that the yield of both products 3a and 3d
as determined by NMR was as high as 75−80%, but
chromatographic purification of the porphyrin 3a from
triphenylphosphine oxide was tedious. This compound was
obtained in pure form only after its transformation into the
corresponding free base porphyrin, which was purified by
column chromatography and then reacted with zinc acetate
dihydrate to give the target product. This reaction sequence
involving three column chromatography purifications led to
the pure product, but in lower isolated yield.
wave potentials for the first reversible reduction and two
reversible oxidations in this solvent are summarized in Table 1.
Table 1. Half-Wave and Peak Potentials (V vs SCE) of
Investigated Porphyrins in PhCN Containing 0.1 M TBAP
oxidation
second
reduction
c
R
Cpd
first
first
H-L
OMe
1a
2a
3a
1b
2b
3b
1c
2c
1.10
1.16
1.16
1.11
1.20
1.18
1.12
1.21
1.32
1.17
1.27
1.27
0.78
0.94
1.00
0.79
0.96
1.01
0.81
0.98
1.06
0.89
1.06
1.13
−1.43
−1.22
−1.01
−1.42
−1.21
−1.00
−1.40
−1.24
−0.97
−1.32
−1.11
2.21
2.16
2.01
2.21
2.17
2.01
2.21
2.12
2.03
2.21
2.17
2.05
Me
H
a
b
a
3c
CN
1d
2d
3d
−0.92
b
a
Irreversible peak potential at a scan rate = 0.1 V/s. Data taken from
c
ref 53. The HOMO−LUMO gap (V).
Not included in the table are potentials for the second or third
reductions, the first of which involves a coupled chemical
reaction to give a phlorin anion radical and the second a
reversible one-electron reduction of this homogeneously
generated product.56
Similar chemical reactions of the doubly reduced porphyrin
are seen for the diphosphorylated derivatives 3a−3d as shown
in Figure 2 for compound 3d. As seen in this figure, adding one
Electrochemistry. Each zinc porphyrin in the three series
was characterized by cyclic voltammetry in three nonaqueous
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Figure 2. Cyclic voltammograms of 1d, 2d, and 3d in PhCN
containing 0.1 M TBAP. Scan rate = 0.1 V/s.
Figure 3. Correlation between number of P(O)(OEt)2 groups on the
porphyrin and the first reduction or oxidation of compounds 1c, 2c,
and 3c in PhCN, 0.1 M TBAP.
phosphoryl group to a meso-position of the nonphosphorylated
porphyrin 1d to give 2d shifts of E1/2 for the first reduction by
210 mV (from −1.32 to −1.11 V) and a further 190 mV shift
toward positive potentials is seen when a second meso-
phosphoryl group is added to the porphyrin to give compound
3d which is reduced at −0.92 V in the first one-electron
addition.
slopes of the E1/2 vs number of P(O)(OEt)2 groups which are
0.21 and 0.12 V for the oxidation and reduction, respectively.
Because the two slopes are not equal, the electrochemically
measured HOMO−LUMO gap decreases with increase in the
number of phosphoryl groups on the porphyrin, going from
2.21 V for compound 1c to 2.03 V for compound 3c.
Substituent Effects of the Two meso-Phenyl Groups.
It has long been known that the addition of electron-donating
or electron-withdrawing groups to the periphery of a porphyrin
macrocycle will modify both the physical properties and the
chemical reactivity of the compounds.61 The effect of
substituents on redox potentials for a given set of closely
related compounds can generally be quantitated by the linear
free energy relationship E1/2 = Σσρ, where E1/2 is the half-wave
potential for each redox process of the compound, σ is the
Hammett substituent constant, and ρ, measured in volts,
represents the sensitivity of the given redox reaction to the
change of substituents.
Figure S17 illustrates how redox potentials of the four
investigated monophosphorylated porphyrins vary as a
function of the phenyl ring substituents in PhCN. As shown
in the figure, a linear relationship is observed for the first
reduction as well as for the first and second oxidations. These
three processes each involve reversible one-electron transfers in
PhCN, and the 52−63 mV slopes of the E1/2 vs σ plots are
within the range observed for numerous porphyrins having
meso-phenyl groups with electron-donating or electron-with-
drawing substituents.61
Axial Ligand Binding by Porphyrins 2d and 3d. The
self-assembly of porphyrins having a phosphoryl group has
previously been demonstrated, both in the solid state and in
solution.27,31,38,62,63 This assembly results when the phosphoryl
group from one porphyrin molecule axially binds to the metal
center of another molecule, leading to the formation of
laterally shifted cofacial dimers29 or 1D26 or 2D28 polymer
networks.
The axial ligand binding reaction involving the Zn(II) metal
center in the associated dimers can be simulated by a titration
of the phosphoryl porphyrins with Ph3PO, and this was done
in the current study for compounds 1d, 2d and 3d, with the
The second reduction of compounds 2d and 3d to form the
porphyrin dianions is located at Ep = −1.59 and −1.33 V,
respectively (see Figure 2), while the third reductions of these
two porphyrins are assigned to reduction of the in situ
generated phlorin anion radicals, reactions which occur at
virtually the same half-wave potentials of −1.69 and −1.68 V.
Similar reduction potentials are also seen in PhCN for the
third reduction of compounds 2b (E1/2 = −1.89 V, Figure 1)
and 3b (E1/2 = −1.90 V). It should also be noted that the
measured shifts in the two reversible oxidation potentials are
both larger upon going from compound 1d to 2d in PhCN
(170 mV for the first oxidation and 100 mV for the second)
than the shifts in E1/2 upon going from compounds 2d to 3d
(70 mV for the first oxidation and 0 mV for the second).
As shown in a previous publication,56 the rate of phlorin
formation decreases when changing the electrochemical
solvent from CH2Cl2 or PhCN to a more coordinating and
basic solvent such as pyridine, and this effect of solvent is also
observed for the currently investigated porphyrins as shown in
Table S1 and Figures S15 and S16 which compare voltammo-
grams for the reductions of 1d−3d and 2a−2d in pyridine
containing 0.1 M TBAP. The potentials for the first and second
one-electron additions to the phosphorylated porphyrins 2d
and 3d in pyridine are both shifted positively from 1d due to
the electron-withdrawing effect of the phosphoryl groups.
More importantly, there is much less phlorin anion
formation following generation of the porphyrin dianion in
the second reduction as judged by the anodic peak current on
the return voltammetric scan (Figure S15).
The potentials for the first reduction and first oxidation of
related porphyrins with the same set of meso-phenyl
substituents are linearly related to the number of meso-
P(O)(OEt)2 groups on the compound as shown graphically in
Figure 3 for compounds 1c, 2c, and 3c. The first reduction is
more affected by the number of meso-phosphorylated groups
on the porphyrin than the first oxidation, this being seen by the
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process being spectroscopically monitored in a CHCl3/MeOH
(9:1) mixture.
A binding of Ph3PO to the Zn(II) center of the porphyrin
readily occurs, and this leads to the spectral changes illustrated
in Figure 4 where the Soret band is shifted by 10 nm and the
meso-P(O)(OEt)2 substituents also follows from the ease of
dimerization for the di- and monophosphorylated porphyrins
as described in other sections of this paper.
Attempts to Electrochemically Detect Dimerization.
A dimerization was not electrochemically observed for any of
the porphyrins at room temperature as well at low temperature
except for compounds 2d and 3d in CH2Cl2. For example, in
the case of 3d at room temperature, the first reduction is
reversible and located at E1/2 = −0.92 V (Figure 5a), but as the
temperature is lowered, first to −25 °C and then −50 °C, the
first reduction splits into two reversible processes located at
E
1/2 = −0.88 and −1.03 V. Although the first reduction is split
into two processes at low temperature, the second reduction
remains irreversible and is located at almost the same peak
potential of about −1.33 V at all temperatures, thus indicating
that the chemical reaction following the second reduction is
fast, even at low temperature.
It has to be noted that the decrease of temperature induced
only a small change in oxidation potentials for the porphyrin
3d where well-defined and well-separated one-electron
processes were seen (figure not shown). This contrasts with
previously described covalently linked cofacial porphyrin
dimers which could exhibit a splitting of both the reduction
and oxidation potentials.64 Moreover, in the case of an earlier-
reported laterally shifted cofacial dimer formed through
coordinative bonding of a meso- or β-pyrrolic dialkoxyphos-
phoryl group to the Zn(II) center of another molecule, only a
splitting of the first oxidation potential was observed.27,54
Thus, the behavior of the currently examined self-assembled
dimer (3d)2 is unusual and might result from the presence of
two strong electron-withdrawing diethoxyphosphoryl substitu-
ents on the porphyrin macrocycle. Indeed, these substituents
should favor a stabilization of the dimeric anion radical but
induce a dissociation of the corresponding cation radical dimer
formed in the oxidation. Similar electrochemical behavior was
previously reported for compound 3b by our lab,53 but a
splitting of the first reduction wave for this compound was
Figure 4. UV−vis spectral change of (a) 1d, (b) 2d, and (c) 3d in
CHCl3/MeOH (9:1) upon addition of Ph3PO (inset shows the Hill
plots).
Q-band by 9−13 nm after the binding of one Ph3PO group.
Calculated equilibrium constants (log K) for the binding of
one Ph3PO molecule were 2.4, 2.8, and 3.4 for 1d, 2d and 3d,
respectively. This trend in log K with increase in the number of
Figure 5. Cyclic voltammograms of 3d in CH2Cl2 at different temperatures before (a) and after (b) addition of 1000 equiv of triphenylphosphine
oxide (Ph3PO).
G
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Scheme 2. Conversion between Monomeric and Aggregated Redox Active Forms of Porphyrin 3d in CH2Cl2 Solution
1
Figure 6. H VT-NMR spectra of 3d in CDCl3 at 223−323 K. Stars correspond to the signals of impurities.
much less pronounced as compared to the porphyrin 3d which
contains four electron-withdrawing meso-substituents, two of
P(O)(OEt)2 and two of PhCN.
potential scan). Moreover, if the rate of conversion between
the two forms of the porphyrin were sufficiently fast at room
temperature, only the monomer redox processes would be
electrochemically detected, thus giving the “false impression”
that only monomers existed in solution, despite strong spectral
and structural evidence to the contrary (see following sections
of the paper).
Cyclic voltammograms of 3d obtained in CH2Cl2 containing
1000 equiv of Ph3PO are also shown in Figure 5b and
demonstrate that the first reduction involves a reversible one-
electron transfer at all temperatures from RT to −50 °C. This
is because the porphyrin Zn(II) center is coordinated to the
added Ph3PO axial ligand which prevents self-association.
In summary, two redox active forms of compound 3d are
proposed to exist in the CH2Cl2 solution under the
electrochemical conditions (Scheme 2). One is a dimer or
higher aggregate ((3d)n is shown as an example in Scheme 2),
which is reduced at −1.03 V at temperatures between −25 and
A similar temperature dependent equilibrium between two
forms of the redox active species is also seen for the
monophosphoryl porphyrin 2d as shown in Figure S18, but
lower temperatures are needed in order to observe split redox
processes during the electroreduction in CH2Cl2. For example,
no splitting of reduction potentials is observed at −35 °C for
porphyrin 2d, but a split process starts to be seen at −60 °C as
illustrated in Figure S18. Again, like in the case of compound
3d, only a single well-defined reduction is observed after
addition of 1000 equiv of Ph3PO to the solution where only
monoligated Ph3PO monomers are present and the reversible
reduction potential under these conditions (−1.31 V) is
virtually the same as the potential for reduction of the higher
aggregate at LT (−1.32 V). Also like in the case of 3d, the
difference in reduction potential between the monomer and
the aggregate amounts to 150 mV, thus leading again to
formation of the more easily reducible monomer at the
electrode surface during the negative potential scan.
−50 °C, and the other is a monomer which is reduced at E1/2
−0.88 V at LT and at −0.92 V at RT as seen in Scheme 2.
=
The potential for reduction of (3d)2 (or (3d)n) is the same
as for the reversible one-electron reduction of the monomer
when complexed with Ph3PO (E1/2 = −1.01 V). This result is
consistent with similar binding constants for complexation of
the Zn(II) center in one molecule of 3d with a P(O)(OEt)2
group from another porphyrin molecule or Ph3PO, when
added to a CH2Cl2 solution of the compound.
The fact that monomeric 3d is electrochemically easier to
reduce than the higher aggregate by 150 mV in CH2Cl2 would
thus favor a shift of equilibrium shown in Scheme 2 to its more
easily reducible monomeric form at the electrode surface under
the application of an applied potential (during the negative
1H and 31P{1H} NMR Studies of Self-Assembly in
Solution. To gain a deeper insight into the structure and
stability of the self-assembled species formed in solution of the
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1
phosphorylporphyrin 3d, this complex was investigated by H
map (Figure S21). The signals of the 3,7- and 2,8-β-protons
were upshifted to δH 7.15 and 8.13 ppm, respectively (for the
numbering, see Chart 2) due to the shielding effect of the
porphyrin ring current on the β-pyrrolic protons in the vicinity
of the coordination site.
and 31P{1H} NMR spectroscopy.
1
A well-resolved H NMR spectrum of porphyrin 3d was
obtained in a CDCl3/CD3OD (5:1, v/v) mixture at 323 K
(Figure S19a). Four signals were observed in the aromatic
region as expected for [5,15-bis(diethoxyphosphoryl)-10,20-
bis(4′-R-phenyl)porphyrinatozinc exhibiting C2v symmetry,
and this indicated the presence of a monomer species 3d in
the studied solution. In contrast, when 3d was dissolved in
CDCl3 (10−4−10−2 M) at 298−323 K, the 1H NMR spectrum
was broadened and the data could not be used for structural
analysis (Figure S19a). However, when CD3OD was gradually
added to this solution, all broadened signals of the β-pyrrolic
and methylene protons shifted downfield and narrowed
(Figure S19c,d). This is a typical spectral behavior for self-
assembled phosphorylporphyrins and results when replace-
ment of the coordinated phosphonate group by methanol
molecules in the coordination sphere of the Zn(II) ions occurs,
thus suppressing the coordination-driven self-assembly of the
porphyrin molecules.28
Chart 2. Numbering of Protons in Dimer (3d)2
Variable-temperature NMR (VT-NMR) studies (223−323
K) of 3d in CDCl3 provide important structural information
because the temperature variation significantly influences the
association process. The 1H and 31P{1H} VT-NMR spectra are
shown in Figures 6 and 7, respectively.
The other signals of the macrocycles observed at δH 8.73
and 10.29 ppm can be assigned to protons of the two pyrrole
rings adjacent to the noncoordinated (free) phosphonate
group (Pf) (12,18 and 13,17, respectively). The shielding of
the peripheral β-protons upon going from a dimer (3d)2 to the
reference monomer species in a CDCl3/CD3OD mixture
increases in the order 13,17 (ΔδH = 0 ppm) < 2,8 (ΔδH = 0.65
ppm) < 3,7 (ΔδH = 3.14 ppm). These values perfectly
correspond to resonances observed for similar cofacial dimers
formed by 5-di-n-butoxyphosphoryl-10,15,20-tris(3′,5′-di-tert-
butylphenyl)porphyrinatozinc (6) (Chart 3, Figure S24).27
Chart 3. Structure of Previously Reported Porphyrins
Displaying Self-Organization in Crystals and in Solutions
The protons 12 and 8 are somewhat deshielded (ΔδH = 0.08
ppm) relative to the corresponding signal for the reference
monomer 3d. This is in contrast to the change observed for the
dimer (6)2 in which these protons are shifted upfield (ΔδH =
−0.05 ppm) compared to the signal of the monomeric species
6. This inconsistency may reflect a difference in the orientation
of the aryl substituents with respect to the macrocyclic plane of
the dimer (3d)2 and the sterically hindered complex (6)2.
Figure 7. 31P{1H} VT-NMR spectra of 3d in CDCl3 at 223−323 K.
1
A decrease of the temperature to 223 K led to resolved H
and 31P{1H} NMR spectra which perfectly correspond to the
spectra expected for a laterally shifted cofacial dimer (3d)2
(Scheme 2). Indeed, the 31P{1H} NMR spectrum at 223 K
showed two phosphorus signals (ΔδP 5.26 ppm) (Figure 7).
The upfield signal (δP 18.19 ppm) was assigned to the
phosphonate group coordinated to the Zn(II) center (Pc)
which was subjected to the shielding effect of the porphyrin π
system. A set of proton signals characteristic for a
centrosymmetric porphyrin species with nonequivalent pro-
tons of meso-aryl substituents also appeared in the aromatic
1
The set of H NMR signals for the two diethoxyphosphoryl
groups are still broadened at 223 K, but their spectral patterns
are typical for a laterally shifted cofacial dimer. Diastereotopic
methylene protons of the free diethoxyphosphoryl group (Pf)
appear as two broad singlets at δH 4.68 and 4.39 ppm. The
methylene signals of the coordinated phosphorus substituent
(Pc) are overlapped with a broad signal of water molecules as
1
1
region of the H NMR spectrum (Figure 6).
indicated by H−1H COSY NMR experiments. The methyl
All proton signals were assigned on the basis of chemical
protons of the Pf and Pc diethoxyphosphoryl groups appear as
shifts, relative intensities, and cross-peaks in the 1H−1H COSY
two broad singlets at δH 1.46 and 0.47 ppm, respectively.
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Raising the temperature from 223 to 293 K leads to the
pairwise coalescence of the signals belonging to the inward-
and outward-oriented ortho and meta protons of the aryl
substituents, as well as of two pairs of β-pyrrolic protons. The
signals of the ethoxy groups of the two phosphorus
substituents Pc and Pf are also gradually shifted toward each
other and their coalescences are observed at 273−278 K. The
symmetry of the porphyrin species present in the solution at
323 K is similar to that of the monomer 3d. However, chemical
shifts of all protons and particularly those of the 3,7-β and
methylene groups are different from the corresponding signals
of the reference monomer 3d in CDCl3/MeOH-d4 (99:1)
(ΔδH = 1.23 and 0.97 ppm, respectively). This indicates that
the self-assembly of complex 3d still persists in the studied
solution and the observed spectral pattern reflects a rapid
exchange of porphyrin molecules in the self-assembled system
(3d)2 (Scheme 2).
When comparing the corresponding proton signals of 3d in
CDCl3 at 273−323 K with signals of the dimer (3d)2 at 223 K
and those of the monomer 3d in the CDCl3/MeOH-d4 (99:1)
mixture at 273−323 K (Figure S22), it can be concluded that
the molar fraction of the monomeric species is small in the
studied solution. Indeed, the expected chemical shifts for the
dimeric species exhibiting a rapid exchange of porphyrin
molecules (the midpoint between the two pairwise signals at
223 K; for example, 2,8- and 12,18-β-protons) are very close to
those observed in the spectra at 273−323 K, with the only
exception being the 3,7-β-proton shift. These protons appear at
δH = 9.09 ppm at 323 K, whereas the calculated value of their
chemical shift is δH = 8.65 ppm. It seems likely that the signals
of the 3,7-β-pyrrolic protons are much more temperature-
dependent than those of the other protons due to the presence
of the adjacent phosphonate group which exhibits weak
conjugative dπ−pπ interactions,65 magnetic anisotropy, and
Figure 8. Primary structural unit of 2D polymer (3d)n·(0.5 CHCl3)n
formed through the axial Zn···OP coordination (view along the a
axis). Hydrogen atoms and chloroform molecules are omitted for
clarity.
The porphyrin macrocycle is almost planar, and the
maximum deviation of carbon atoms from the ZnN4 plane is
0.228 Å, which is observed for the C8 and C8A atoms. The
twist angles of the aryl rings with respect to the ZnN4 plane
group results from an axial coordination of its oxygen atom to
the Zn(II) center of a neighboring molecule and hydrogen
bonding between this atom and the β-pyrrolic proton of the
same macrocycle. This spatial orientation of the diethox-
yphosphoryl group and the porphyrin macrocycle is typical for
metal complexes of porphyrins bearing a meso-diethoxyphos-
phoryl substituent directly attached to the macrocycle and was
earlier observed in nickel(II), copper(II), and palladium(II)
complexes having noncoordinated phosphorus substituents as
well as in self-assembled associates of zinc phosphorylpor-
phyrinates and 1D polymers where the diethoxyphosphoryl
groups are coordinated to external metal ions.55,62,63
The metal atom of 3d has a distorted octahedral geometry
and is axially bonded with two phosphorus substituents
(Figure 8). The Zn−O distance is equal to 2.4346(10) Å.
This coordination bonding leads to the formation of 2D
polymer in which the primary subunit can be described as a
rhombus relying on four neighboring zinc atoms and having a
side length of 8.360 Å and an inside angle of 84.3°. This
arrangement gives rise to a two-dimensional paddle-wheel-like
structure in which all metal atoms of the layer are located in
the same plane with a layer depth of 15.5 Å. These layers are
separated one from another by pendant aryl substituents with
the distance between the nearest zinc atoms belonging to
adjacent layers being 16.454 Å (Figure 9).
hydrogen bonding62 with these protons. The H VT-NMR
1
spectrum of the reference monomer 3d recorded in CDCl3/
CD3OD (5:1) is in accordance with this hypothesis (Figure
S22).
31P{1H} VT-NMR data obtained for a CDCl3 solution of
porphyrin 3d are in agreement with the formation of the
fluxional dimer (3d)2. Raising the temperature from 223 to
323 K results in a rapid positional exchange between Pc and Pf
so that the corresponding signals coalesce at 273 K, giving a
broad peak at δP 20.94 ppm.
The dimerization of porphyrin 3d in a CDCl3 solution even
at a high temperature of 323 K was also confirmed by diffusion
ordered spectroscopy (DOSY) data which are presented in
Table S2 and Figure S23. The observed difference between the
diffusion coefficients of 3d in CDCl3 and CDCl3/CD3OD
(10:1) is consistent with a 2-fold decrease in the molecular
weight of 3d upon going from the solution in CDCl3 to the
solution in CDCl3/MeOH-d4.
Crystal Structure of Porphyrin 3d. Single crystals of 3d
were grown by slow diffusion of a heptane solution of this
porphyrin in a CHCl3/methanol mixture (97:3, v/v). X-ray
analysis of the obtained crystals revealed that porphyrin 3d
displays a 2D polymer structure, being crystallized under these
conditions.
Distorted chloroform molecules fill a space between the aryl
groups of two adjacent porphyrin layers, forming numerous
short contacts with the macrocyclic scaffold and the aryl
substituents.
It should be noted that Zn(II), Cd(II), and Cu(II) 5,10-
bis(diethoxyphosphoryl)-10,20-diphenylporphyrins (3c, 7, and
8)28,62,63 as well as an Fe(II) 5,10,15,20-tetra(4′-pyridyl)-
porphyrin (9)66 (Chart 3) also exhibit 2D polymer structures
in the crystalline phase.
In the centrosymmetric molecule of 3d, the zinc atom is
bonded to four nitrogen donor atoms of the macrocycle
pyrrole moieties (Zn−N = 2.0375(8)−2.0456(10) Å) and is
located in the N4 plane (Figure 8 and Figure S25).
Despite the significant structural difference between
diethoxyphosphoryl and pyridyl groups, all of the 2D
coordination polymers are formed by paddle-wheel-like layers.
J
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Article
Figure 9. Spatial arrangement of layers in (3d)n·(0.5 CHCl3)n viewed along the b axis. Hydrogen atoms and chloroform molecules are omitted for
clarity.
The difference in orientation of the electron pair of the donor
groups with respect to the macrocycle axes in the pyridyl- and
diethoxyphosphoryl-substituted porphyrins induces only a
small distortion in spatial orientation of adjacent molecules
which leads to the formation of rhombus primary subunits with
an inside angle of 84.3−87.8° in the phosphorus(V)-
containing polymers (3c,d)n, (7)n, and (8)n. In contrast, the
arrangement of the porphyrin layers is strongly influenced by
both the nature of the coordinating group and aryl substituents
of the macrocycle. Dense structures were obtained for two
polymorphs of the 2D polymer (9)n and phosphorylporphyrins
(3c)n, (7)n, and (8)n, whereas introduction of a cyano
substituent at the meso-aryl group of the porphyrin leads to
formation of the chloroform solvated complex (3d·0.5
CHCl3)n.
The switching from a 2D polymer network observed in
crystals of the porphyrin 3d to a dimeric structure after
dissolving of this porphyrin in CDCl3 is remarkable. To our
knowledge, examples of self-assembled porphyrins exhibiting
different supramolecular structures are limited to two
complementary porphyrins bearing nitrogen donor sites.
Dynamic equilibrium between a self-assembled trimer and
tetramer of Co(III) 1-methyl-5-imidazolylporphyrin in differ-
ent solvents was described by Kobuke and co-workers.67
Another interesting example is Zn(II) 5-(4′-pyridyl)-10,15,20-
triphenylporphyrinate, which displays a 1D polymer structure
in crystals but seems to form discrete tetramers in
solution.68−70
leads to formation of a porphyrin π-anion radical, while the
second reduction generates an unstable porphyrin dianion
which undergoes a fast chemical reaction in PhCN or CH2Cl2
to form a phlorin anion radical. The electrochemically
measured HOMO−LUMO gap decreases with an increase in
the number of phosphoryl groups, and the redox potentials
also vary as a function of the phenyl ring substituents as
evidenced by plots of E1/2 vs the Hammett substituent
constants for groups on the two meso-phenyl units of the
compounds.
An equilibrium between a monomeric and aggregated redox
active forms of compounds 2d and 3d is shown to exist in
CH2Cl2 solutions under the electrochemical conditions. Such
an equilibrium was previously shown to be concentration
dependent for related porphyrins, and this equilibrium is also
dependent upon temperature as shown in the present study.
The rate of conversion of the aggregated porphyrins 2d and 3d
to their more easily reducible monomeric form appears to be
sufficiently high at room temperature to suggest only
monomers in solution, but this is not the case at LT where
the rate of dissociation is sufficiently slowed down so that both
forms of the redox active porphyrins can then be electro-
chemically detected during reduction.
To gain a deeper insight into the structure of the associates,
the structure of the self-assembled supramolecular system(s)
forming by zinc porphyrin 3d was also investigated by X-ray
diffraction structural analysis in the solid state and NMR
spectroscopy in CDCl3 solutions. Coordination of one
phosphonate group to the metal center of another porphyrin
molecule leads to formation of a laterally shifted cofacial dimer
(3d)2 when the compound 3d is dissolved in chloroform, a
solvent not so different from CH2Cl2 used for electro-
chemistry. In contrast to earlier-reported analogous self-
assembled dialkoxyphosphorylporphyrin dimers such as (6)2,
the dimer (3d)2 is stable at room temperature and exhibits a
fluxional behavior. A rapid exchange of porphyrin molecules in
the dimer (3d)2 is observed at room temperature on the NMR
time scale. In the crystalline phase, this compound displays a
CONCLUSION
■
The electrochemical and spectroscopic properties for a series
of zinc porphyrins 2a−d and 3a−d bearing the diethox-
yphosphoryl group at one or two meso-positions of the
porphyrin macrocycle were investigated. A systematic study of
these compounds with comparison to the same compounds
lacking these meso-substituents leads to a better understanding
of the meso-(diethoxyphosphoryl)porphyrin redox properties.
The first reduction of these compounds is ring-centered and
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Article
(3) Denisov, I. G.; Makris, T. M.; Sligar, S. G.; Schlichting, I.
Structure and chemistry of cytochrome P450. Chem. Rev. 2005, 105
(6), 2253−2278.
(4) Kruse, O.; Rupprecht, J.; Mussgnug, J. H.; Dismukes, G. C.;
Hankamer, B. Photosynthesis: A blueprint for solar energy capture
and biohydrogen production technologies. Photochem. Photobiol. Sci.
2005, 4 (12), 957−970.
(5) Balaban, T. S. Self-assembling porphyrins and chlorins as
synthetic mimics of the chlorosomal bacteriochlorophylls. In
Handbook of Porphyrin Science; Kadish, K. M., Smith, K. M.,
Guilard, R., Eds.; World Scientific: Singapore, 2010; Vol. 1, pp
221−306.
(6) Morisue, M.; Kobuke, Y. Supramolecular organization of
porphyrins and phthalocyanines by use of biomimetic coordination
methodology. In Handbook of Porphyrin Science; Kadish, K. M., Smith,
K. M., Guilard, R., Eds.; World Scientific: Singapore, 2014; Vol. 32,
pp 1−126.
2D polymer network formed through the coordination of
Zn(II) centers by two phosphoryl groups belonging to
adjacent porphyrin molecules. Accordingly, in the solid
phase, both phosphonate groups of each porphyrin molecule
are ligated with adjacent Zn(II) centers.
The reported data indicate that structural organization of the
phosphorylporphyrins strongly depends upon the environ-
mental conditions, and these compounds are of interest for
better understanding the role of structural parameters on self-
assembly of the natural tetrapyrrolic systems.
Finally, the coordination self-assembly of electron-deficient
porphyrins could be electrochemically observed by the
presence of a temperature dependent splitting of their first
reduction potential. Thus, electrochemical characterization
might in the future provide a roadmap for the rational design
of self-assembled phosphorylporphyrin systems, as described in
the present paper for the self-assembly of Zn(II) porphyrin 3d.
(7) Tamiaki, H.; Kunieda, M. Photochemistry of chlorophylls and
their synthetic analogs. In Handbook of Porphyrin Science; Kadish, K.
M., Smith, K. M., Guilard, R., Eds.; World Scientific: Singapore, 2011;
Vol. 11, pp 223−290.
ASSOCIATED CONTENT
* Supporting Information
■
S
(8) Bessmertnykh-Lemeune, A. G.; Stern, C.; Guilard, R.; Enakieva,
Y. Y.; Gorbunova, Y. G.; Tsivadze, A. Y.; Nefedov, S. E. Biomimetic
studies of porphyrin self-assembled systems. In Supramolecular
Systems: Chemistry, Types and Applications; Nova Science Publishers:
Hauppauge, NY, 2016; pp 213−278.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.9b00268.
Crystallographic information, Tables S1−S3, and
Figures S1−S28 (PDF)
(9) Barber, J. Photosynthetic energy conversion: natural and
artificial. Chem. Soc. Rev. 2009, 38 (1), 185−196.
(10) Meunier, B.; de Visser, S. P.; Shaik, S. Mechanism of oxidation
reactions catalyzed by cytochrome P450 enzymes. Chem. Rev. 2004,
104 (9), 3947−3980.
Accession Codes
CCDC 1890813 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(11) Che, C.-M.; Lo, V. K.-Y.; Zhou, C.-Y.; Huang, J.-S. Selective
functionalisation of saturated C-H bonds with metalloporphyrin
catalysts. Chem. Soc. Rev. 2011, 40 (4), 1950−1975.
(12) Liu, W.; Groves, J. T. Manganese catalyzed C−H halogenation.
Acc. Chem. Res. 2015, 48 (6), 1727−1735.
(13) Medforth, C. J.; Wang, Z.; Martin, K. E.; Song, Y.; Jacobsen, J.
L.; Shelnutt, J. A. Self-assembled porphyrin nanostructures. Chem.
Commun. 2009, No. 47, 7261−7277.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: kkadish@uh.edu. Phone: (+1) 713-743-2740
(K.M.K.).
■
(14) See, for example: The Porphyrin Handbook; Kadish, K. M.,
Smith, K. M., Guilard, R., Eds.; Academic Press: San Diego, CA, 2006;
Vols. 1−20 and the references therein.
*E-mail: Alla.Lemeune@u-bourgogne.fr. Phone: (+33) (0)3-
80-39-61-26 (A.B.-L.).
ORCID
Karl M. Kadish: 0000-0003-4586-6732
Yulia G. Gorbunova: 0000-0002-2333-4033
Alla Bessmertnykh-Lemeune: 0000-0001-6707-6868
Roger Guilard: 0000-0001-7328-3695
(15) Sharman, W. M.; Van Lier, J. E. Use of palladium catalysis in
the synthesis of novel porphyrins and phthalocyanines. J. Porphyrins
Phthalocyanines 2000, 04 (05), 441−453.
(16) Setsune, J.-i. Palladium chemistry in recent porphyrin research.
J. Porphyrins Phthalocyanines 2004, 08 (01), 93−102.
(17) Liu, C.; Chen, Q.-Y. General and efficient synthesis of meso-A
and β-perfluoroalkylated porphyrins via Pd-catalyzed cross-coupling
reaction. Synlett 2005, 2005 (8), 1306−1310.
Notes
(18) Takanami, T.; Hayashi, M.; Chijimatsu, H.; Inoue, W.; Suda, K.
Palladium-catalyzed cyanation of porphyrins utilizing cyanoethylzinc
bromide as an efficient cyanide ion source. Org. Lett. 2005, 7 (18),
3937−3940.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(19) Bringmann, G.; Rudenauer, S.; Gotz, D. C. G.; Gulder, T. A.
̈
̈
We gratefully acknowledge support from the Robert A. Welch
Foundation (K.M.K., Grant E-680) and the French-Russian
Associated Laboratory “LAMREM” supported by the CNRS
and Russian Academy of Sciences, Russian Foundation for
Basic Research (Grant no. 17-53-16028). The authors thank
Dr. K. Birin for helpful discussions on NMR experiences.
M.; Reichert, M. Axially chiral directly linked bisporphyrins: Synthesis
and stereostructure. Org. Lett. 2006, 8 (21), 4743−4746.
(20) Esdaile, L. J.; Senge, M. O.; Arnold, D. P. New palladium
catalysed reactions of bromoporphyrins: Synthesis and crystal
structures of nickel(II) complexes of primary 5-aminoporphyrin,
5,5′-bis(porphyrinyl) secondary amine, and 5-hydroxyporphyrin.
Chem. Commun. 2006, No. 40, 4192−4194.
REFERENCES
(21) Tremblay-Morin, J.-P.; Ali, H.; van Lier, J. E. Palladium
catalyzed coupling reactions of cationic porphyrins with organo-
boranes (Suzuki) and alkenes (Heck). Tetrahedron Lett. 2006, 47
(18), 3043−3046.
(22) Liu, C.; Shen, D.-M.; Chen, Q.-Y. Practical and efficient
synthesis of various meso-functionalized porphyrins via simple ligand-
■
(1) Wilson, M. T.; Reeder, B. J. Oxygen binding haem proteins. Exp.
Physiol. 2008, 93 (1), 128−132.
(2) Meunier, B. Metalloporphyrins as versatile catalysts for oxidation
reactions and oxidative DNA cleavage. Chem. Rev. 1992, 92 (6),
1411−1456.
L
DOI: 10.1021/acs.inorgchem.9b00268
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
free nickel-catalyzed C-O, C-N, and C-C cross-coupling reactions. J.
Org. Chem. 2007, 72 (8), 2732−2736.
(23) Beyler, M.; Beemelmanns, C.; Heitz, V.; Sauvage, J.-P. Various
synthetic routes to a gable-like bis(porphyrin) constructed on a 1,10-
phenanthroline chelate. Eur. J. Org. Chem. 2009, 2009 (17), 2801−
2805.
(38) Atefi, F.; Arnold, D. P. Porphyrins with metal, metalloid or
phosphorus atoms directly bonded to the carbon periphery. J.
Porphyrins Phthalocyanines 2008, 12 (7), 801−831.
(39) Borbas, K. E.; Kee, H. L.; Holten, D.; Lindsey, J. S. A compact
water-soluble porphyrin bearing an iodoacetamido bioconjugatable
site. Org. Biomol. Chem. 2008, 6 (1), 187−194.
(24) Filatov, M. A.; Guilard, R.; Harvey, P. D. Selective stepwise
Suzuki cross-coupling reaction for the modelling of photosynthetic
donor-acceptor systems. Org. Lett. 2010, 12 (1), 196−199.
(25) Atefi, F.; McMurtrie, J. C.; Arnold, D. P. Multiporphyrin
coordination arrays based on complexation of magnesium(II)
porphyrins with porphyrinylphosphine oxides. Dalton Trans. 2007,
No. 21, 2163−2170.
(26) Atefi, F.; McMurtrie, J. C.; Turner, P.; Duriska, M.; Arnold, D.
P. meso-Porphyrinylphosphine oxides: Mono- and bidentate ligands
for supramolecular chemistry and the crystal structures of monomeric
{[10,20-diphenylporphyrinatonickel(II)-5,15-diyl]-bis-[P(O)Ph2]
and polymeric self-coordinated {[10,20-diphenylporphyrinatozinc-
(II)-5,15-diyl]-bis-[P(O)Ph2]}. Inorg. Chem. 2006, 45 (16), 6479−
6489.
(27) Matano, Y.; Matsumoto, K.; Terasaka, Y.; Hotta, H.; Araki, Y.;
Ito, O.; Shiro, M.; Sasamori, T.; Tokitoh, N.; Imahori, H. Synthesis,
structures, and properties of meso-phosphorylporphyrins: Self-
organization through P-oxo-zinc coordination. Chem. - Eur. J. 2007,
13 (3), 891−901.
(28) Enakieva, Y. Y.; Bessmertnykh, A. G.; Gorbunova, Y. G.; Stern,
C.; Rousselin, Y.; Tsivadze, A. Y.; Guilard, R. Synthesis of meso-
polyphosphorylporphyrins and example of self-assembling. Org. Lett.
2009, 11 (17), 3842−3845.
(29) Vinogradova, E. V.; Enakieva, Y. Y.; Nefedov, S. E.; Birin, K. P.;
Tsivadze, A. Y.; Gorbunova, Y. G.; Bessmertnykh Lemeune, A. G.;
Stern, C.; Guilard, R. Synthesis and self-organization of zinc
(dialkoxyphosphoryl)porphyrins in the solid state and in solution.
Chem. - Eur. J. 2012, 18 (47), 15092−15104.
(30) Lemeune, A.; Mitrofanov, A. Y.; Rousselin, Y.; Stern, C.;
Guilard, R.; Enakieva, Y. Y.; Gorbunova, Y. G.; Nefedov, S. E.
Supramolecular architectures based on phosphonic acid diesters.
Phosphorus, Sulfur Silicon Relat. Elem. 2015, 190 (5−6), 831−836.
(31) Enakieva, Y. Y.; Volostnykh, M. V.; Nefedov, S. E.; Kirakosyan,
G. A.; Gorbunova, Y. G.; Tsivadze, A. Y.; Bessmertnykh-Lemeune, A.
G.; Stern, C.; Guilard, R. Gallium(III) and indium(III) complexes
with meso-monophosphorylated porphyrins: Synthesis and structure.
A first example of dimers formed by the self-assembly of meso-
porphyrinylphosphonic acid monoester. Inorg. Chem. 2017, 56 (5),
3055−3070.
(40) Stern, C.; Bessmertnykh-Lemeune, A.; Gorbunova, Y. G.;
Tsivadze, A. Y.; Guilard, R. Effect of the anchoring group in porphyrin
sensitizers: Phosphonate versus carboxylate linkages. Turk. J. Chem.
2014, 38, 980−993.
̈
(41) Urbani, M.; Gratzel, M.; Nazeeruddin, M. K.; Torres, T. Meso-
substituted porphyrins for dye-sensitized solar cells. Chem. Rev. 2014,
114 (24), 12330−12396.
(42) Liu, X.; Li, H.; Zhang, Y.; Xu, B.; A, S.; Xia, H.; Mu, Y.
Enhanced carbon dioxide uptake by metalloporphyrin-based micro-
porous covalent triazine framework. Polym. Chem. 2013, 4 (8), 2445−
2448.
(43) Griffith, M. J.; Sunahara, K.; Wagner, P.; Wagner, K.; Wallace,
G. G.; Officer, D. L.; Furube, A.; Katoh, R.; Mori, S.; Mozer, A. J.
Porphyrins for dye-sensitised solar cells: New insights into efficiency-
determining electron transfer steps. Chem. Commun. 2012, 48 (35),
4145−4162.
(44) Liu, T. W.; Huynh, E.; MacDonald, T. D.; Zheng, G.
Porphyrins for imaging, photodynamic therapy, and photothermal
therapy. In Cancer Theranostics; Academic Press: Oxford, U.K., 2014;
Chapter 14, pp 229−254.
(45) Deniaud, D.; Schollorn, B.; Mansuy, D.; Rouxel, J.; Battioni, P.;
Bujoli, B. Synthesis and catalytic properties of manganese porphyrins
incorporated into phosphonate networks. Chem. Mater. 1995, 7 (5),
995−1000.
(46) Deniaud, D.; Spyroulias, G. A.; Bartoli, J. F.; Battioni, P.;
Mansuy, D.; Pinel, C.; Odobel, F.; Bujoli, B. Shape selectivity for
alkane hydroxylation with a new class of phosphonate-based
heterogenised manganese porphyrins. New J. Chem. 1998, 22 (8),
901−905.
(47) Clearfield, A. Metal phosphonate chemistry. In Progress in
Inorganic Chemistry; Karlin, K. D., Ed.; John Wiley & Sons, Inc.:
Hoboken, NJ, 1998; pp 371−510.
́
(48) Queffelec, C.; Petit, M.; Janvier, P.; Knight, D. A.; Bujoli, B.
Surface modification using phosphonic acids and esters. Chem. Rev.
2012, 112, 3777−3807.
(49) Guerrero, G.; Alauzun, J. G.; Granier, M.; Laurencin, D.;
Mutin, P. H. Phosphonate coupling molecules for the control of
surface/interface properties and the synthesis of nanomaterials. Dalton
Trans. 2013, 42 (35), 12569−12585.
(50) Wang, X.-S.; Chrzanowski, M.; Yuan, D.; Sweeting, B. S.; Ma, S.
Covalent heme framework as a highly active heterogeneous
biomimetic oxidation catalyst. Chem. Mater. 2014, 26 (4), 1639−
1644.
(32) Loewe, R. S.; Ambroise, A.; Muthukumaran, K.; Padmaja, K.;
Lysenko, A. B.; Mathur, G.; Li, Q. L.; Bocian, D. F.; Misra, V.;
Lindsey, J. S. Porphyrins bearing mono or tripodal benzylphosphonic
acid tethers for attachment to oxide surfaces. J. Org. Chem. 2004, 69
(5), 1453−1460.
(33) Li, Q. L.; Surthi, S.; Mathur, G.; Gowda, S.; Zhao, Q.;
Sorenson, T. A.; Tenent, R. C.; Muthukumaran, K.; Lindsey, J. S.;
Misra, V. Multiple-bit storage properties of porphyrin monolayers on
SiO2. Appl. Phys. Lett. 2004, 85 (10), 1829−1831.
(34) Kubat, P.; Lang, K.; Anzenbacher, P. Modulation of porphyrin
binding to serum albumin by pH. Biochim. Biophys. Acta, Gen. Subj.
2004, 1670 (1), 40−48.
(35) Morisue, M.; Haruta, N.; Kalita, D.; Kobuke, Y. Efficient charge
injection from the S-2 photoexcited state of special-pair mimic
porphyrin assemblies anchored on a titanium-modified ITO anode.
Chem. - Eur. J. 2006, 12 (31), 8123−8135.
(36) Officer, D. L.; Lodato, F.; Jolley, K. W. Zinc-porphyrin
phosphonate coordination: Structural control through a zinc
phosphoryl-oxygen interaction. Inorg. Chem. 2007, 46 (12), 4781−
4783.
(51) Zhao, M.; Ou, S.; Wu, C.-D. Porous metal−organic frameworks
for heterogeneous biomimetic catalysis. Acc. Chem. Res. 2014, 47 (4),
1199−1207.
(52) Barona-Castano, C. J.; Carmona-Vargas, C. C.; Brocksom, J. T.;
̃
de Oliveira, T. K. Porphyrins as catalysts in scalable organic reactions.
Molecules 2016, 21 (3), 310.
(53) Kadish, K. M.; Chen, P.; Enakieva, Y. Y.; Nefedov, S. E.;
Gorbunova, Y. G.; Tsivadze, A. Y.; Bessmertnykh-Lemeune, A.; Stern,
C.; Guilard, R. Electrochemical and spectroscopic studies of
poly(diethoxyphosphoryl)porphyrins. J. Electroanal. Chem. 2011,
656 (1−2), 61−71.
(54) Fang, Y.; Kadish, K. M.; Chen, P.; Gorbunova, Y.; Enakieva, Y.;
Tsivadze, A.; Bessmertnykh-Lemeune, A.; Guilard, R. Electrochemical
and spectroelectrochemical studies of β-phosphorylated Zn porphyr-
ins. J. Porphyrins Phthalocyanines 2013, 17 (10), 1035−1045.
(55) Uvarova, M. A.; Sinelshchikova, A. A.; Golubnichaya, M. A.;
Nefedov, S. E.; Enakieva, Y. Y.; Gorbunova, Y. G.; Tsivadze, A. Y.;
Stern, C.; Bessmertnykh-Lemeune, A.; Guilard, R. Supramolecular
assembly of organophosphonate diesters using paddle-wheel com-
(37) Habdas, J.; Boduszek, B. Synthesis peptidyl phosphonates
containing 4-(4’-carboxyphenyl)-10,15,20-tritolylporphyrin. Heteroat.
Chem. 2008, 19 (1), 107−111.
M
DOI: 10.1021/acs.inorgchem.9b00268
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
plexes: First examples in porphyrin series. Cryst. Growth Des. 2014, 14,
5976−5984.
(56) Fang, Y.; Gorbunova, Y. G.; Chen, P.; Jiang, X.; Manowong,
M.; Sinelshchikova, A. A.; Enakieva, Y. Y.; Martynov, A. G.; Tsivadze,
A. Y.; Bessmertnykh-Lemeune, A.; Stern, C.; Guilard, R.; Kadish, K.
M. Electrochemical and spectroelectrochemical studies of diphos-
phorylated metalloporphyrins. Generation of a phlorin anion product.
Inorg. Chem. 2015, 54 (7), 3501−3512.
(57) Mitra, R.; Bauri, A. K.; Bhattacharya, S. Study of non-covalent
interaction between a designed monoporphyrin and fullerenes (C60
and C70) in absence and presence of silver nanoparticles. Spectrochim.
Acta, Part A 2012, 96, 485−492.
(58) Enakieva, Y. Y.; Michalak, J.; Abdulaeva, I. A.; Volostnykh, M.
V.; Stern, C.; Guilard, R.; Bessmertnykh-Lemeune, A. G.; Gorbunova,
Y. G.; Tsivadze, A. Y.; Kadish, K. M. General and scalable approach to
A2B- and A2BC-type porphyrin phosphonate diesters. Eur. J. Org.
Chem. 2016, 2016 (28), 4881−4892.
(59) Ogi, S.; Sugiyasu, K.; Manna, S.; Samitsu, S.; Takeuchi, M.
Living supramolecular polymerization realized through a biomimetic
approach. Nat. Chem. 2014, 6, 188−195.
(60) Manka, J. S.; Lawrence, D. S. High yield synthesis of 5,15-
diarylporphyrins. Tetrahedron Lett. 1989, 30 (50), 6989−6992.
(61) Kadish, K. M.; Van Caemelbecke, E.; Royal, G. Electro-
chemistry of metalloporphyrins in nonaqueous media. In The
Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.;
Academic Press: San Diego, CA, 2000; Vol. 8, pp 1−114.
(62) Sinelshchikova, A. A.; Nefedov, S. E.; Enakieva, Y. Y.;
Gorbunova, Y. G.; Tsivadze, A. Y.; Kadish, K. M.; Chen, P.;
Bessmertnykh-Lemeune, A.; Stern, C.; Guilard, R. Unusual formation
of a stable 2D copper porphyrin network. Inorg. Chem. 2013, 52 (2),
999−1008.
(63) Zubatyuk, R. I.; Sinelshchikova, A. A.; Enakieva, Y. Y.;
Gorbunova, Y. G.; Tsivadze, A. Y.; Nefedov, S. E.; Bessmertnykh-
Lemeune, A.; Guilard, R.; Shishkin, O. V. Insights into the crystal
packing of phosphorylporphyrins based on the topology of their
intermolecular interaction energies. CrystEngComm 2014, 16, 10428−
10438.
(64) Le Mest, Y.; L’Her, M.; Hendricks, N. H.; Kim, K.; Collman, J.
P. Electrochemical and spectroscopic properties of dimeric cofacial
porphyrins with nonelectroactive metal centers. Delocalization
processes in the porphyrin.pi.-cation-radical systems. Inorg. Chem.
1992, 31 (5), 835−847.
(65) Kemp, R. H.; Thomas, W. A.; Gordon, M.; Griffin, C. E. The
proton magnetic resonance spectra of some triheteroarylphosphine
oxides and heteroarylphosphonates. J. Chem. Soc. B 1969, 527−530.
(66) Pan, L.; Kelly, S.; Huang, X.; Li, J. Unique 2D metalloporphyrin
networks constructed from iron(ii) and meso-tetra(4-pyridyl)-
porphyrin. Chem. Commun. 2002, No. 20, 2334−2335.
(67) Tanaka, A.; Ryuno, A.; Okada, S.; Satake, A.; Kobuke, Y.
Dynamic equilibrium of self-assembled cyclic trimer and tetramer of
1-methyl-5-imidazolylcobalt(III)porphyrin. Isr. J. Chem. 2005, 45 (3),
281−291.
(68) Shachter, A. M.; Fleischer, E. B.; Haltiwanger, R. C.
Characterization of a 5-pyridyl-10,15,20-triphenylporphyrinatozinc-
(II) polymer. J. Chem. Soc., Chem. Commun. 1988, No. 14, 960−961.
(69) Fleischer, E. B.; Shachter, A. M. Coordination oligomers and a
coordination polymer of zinc tetraarylporphyrins. Inorg. Chem. 1991,
30 (19), 3763−3769.
(70) Ercolani, G.; Ioele, M.; Monti, D. Physical basis of self-
assembly. Part 2. A theoretical and experimental study of the self-
assembly of a zinc meso-pyridyl porphyrin. New J. Chem. 2001, 25 (6),
783−789.
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DOI: 10.1021/acs.inorgchem.9b00268
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