Synthesis and self-organization of zinc β-(dialkoxyphosphoryl) porphyrins in the solid state and in solution

Article abstract of DOI:10.1002/chem.201202596

The first synthesis and self-organization of zinc β- phosphorylporphyrins in the solid state and in solution are reported. β-Dialkoxyphosphoryl-5,10,15,20-tetraphenylporphyrins and their Zn ^II complexes have been synthesized in good yields by using Pd-and Cu-mediated carbon-phosphorous bond-forming reactions. The Cu-mediated reaction allowed to prepare the mono-β-(dialkoxyphosphoryl)porphyrins 1 Zn-3 Zn starting from the β-bromo-substituted zinc porphyrinate ZnTPPBr (TPP=tetraphenylporphyrin) and dialkyl phosphites HP(O)(OR)₂ (R=Et, iPr, nBu). The derivatives 1 Zn-3 Zn were obtained in good yields by using one to three equivalents of CuI. When the reaction was carried out in the presence of catalytic amounts of palladium complexes in toluene, the desired zinc derivative 1 Zn was obtained in up to 72 % yield. The use of a Pd-catalyzed C-P bond-forming reaction was further extended to the synthesis of β-poly(dialkoxyphosphoryl)porphyrins. An unprecedented one-pot sequence involving consecutive reduction and phosphorylation of H₂TPPBr ₄ led to the formation of a mixture of the 2,12-and 2,13-bis(dialkoxy)phosphorylporphyrins 5 H₂ and 6 H₂ in 81 % total yield. According to the X-ray diffraction studies, 1 Zn and 3 Zn are partially overlapped cofacial dimers formed through the coordination of two Zn centers by two phosphoryl groups belonging to the adjacent molecules. The equilibrium between the monomeric and the dimeric species exists in solutions of 1 Zn and 3 Zn in weakly polar solvents according to spectroscopic data (UV/Vis absorption and NMR spectroscopy). The ratio of each form is dependent on the concentration, temperature, and traces of water or methanol. These features demonstrated that zinc β-phosphorylporphyrins can be regarded as new model compounds for the weakly coupled chlorophyll pair in the photosynthesis process.

Full text of DOI:10.1002/chem.201202596

DOI: 10.1002/chem.201202596
Synthesis and Self-Organization of Zinc b-(Dialkoxyphosphoryl)porphyrins
in the Solid State and in Solution
Ekaterina V. Vinogradova,[a] Yulia Y. Enakieva,[a, b] Sergey E. Nefedov,[b]
Kirill P. Birin,[a, b] Aslan Y. Tsivadze,[a, b] Yulia G. Gorbunova,*[a, b]
Alla G. Bessmertnykh Lemeune,[c] Christine Stern,[c] and Roger Guilard*[c]
Abstract: The first synthesis and self-
organization of zinc b-phosphorylpor-
phyrins in the solid state and in solu-
tion are reported. b-Dialkoxyphosphor-
yl-5,10,15,20-tetraphenylporphyrins and
their ZnII complexes have been synthe-
sized in good yields by using Pd- and
was carried out in the presence of cata-
lytic amounts of palladium complexes
in toluene, the desired zinc derivative
1Zn was obtained in up to 72% yield.
to the X-ray diffraction studies, 1Zn
and 3Zn are partially overlapped cofa-
cial dimers formed through the coordi-
nation of two Zn centers by two phos-
phoryl groups belonging to the adja-
cent molecules. The equilibrium be-
tween the monomeric and the dimeric
species exists in solutions of 1Zn and
3Zn in weakly polar solvents according
to spectroscopic data (UV/Vis absorp-
tion and NMR spectroscopy). The ratio
of each form is dependent on the con-
centration, temperature, and traces of
water or methanol. These features
demonstrated that zinc b-phosphoryl-
porphyrins can be regarded as new
model compounds for the weakly cou-
pled chlorophyll pair in the photosyn-
thesis process.
À
The use of a Pd-catalyzed C P bond-
forming reaction was further extended
to the synthesis of b-poly(dialkoxy-
phosphoryl)porphyrins. An unprece-
dented one-pot sequence involving
consecutive reduction and phosphory-
lation of H2TPPBr4 led to the forma-
tion of a mixture of the 2,12- and 2,13-
Cu-mediated
carbon–phosphorous
bond-forming reactions. The Cu-medi-
ated reaction allowed to prepare the
mono-b-(dialkoxyphosphoryl)porphyr-
ins 1Zn–3Zn starting from the b-
bromo-substituted zinc porphyrinate
ZnTPPBr (TPP=tetraphenylporphyr-
bisACTHNUTRGENUG(N dialkoxy)phosphorylporphyrins 5H2
and 6H2 in 81% total yield. According
in)
and
dialkyl
phosphites
HP(O)(OR)2 (R=Et, iPr, nBu). The
derivatives 1Zn–3Zn were obtained in
good yields by using one to three
equivalents of CuI. When the reaction
Keywords: aggregation · phospho-
nates · porphyrins · self-organiza-
tion · transition metals
Introduction
Porphyrin synthesis has attracted a large number of re-
searchers in chemistry, physics, material science, engineer-
ing, biology, and medicine.[1] Indeed, structural, photophysi-
cal, magnetic, electrical, and catalytic properties of these tet-
rapyrrolic macrocycles are widely observed in natural and
artificial processes. Their optical properties, for example,
make them attractive for various photonic applications such
as photodynamic therapy (PDT) of tumors,[2–4] holographic
data storage,[5,6] optical power limiting,[7–11] and sensor-
ing.[12–15] Moreover, various porphyrin architectures assem-
bled through non-covalent bonds find further applications in
many fields, such as, for example, they are used to mimic
the photosynthetic mechanism, to design efficient light-har-
vesting systems, or to prepare porous materials for gas mole-
cules storage.[16–19] Thus, much effort has been devoted to
the synthesis of new classes of metalloporphyrins bearing
peripheral donor groups at the b-pyrrolic and/or the meso-
positions of the porphyrin core to elaborate coordination
networks and polynuclear species.[20] Recently, phosphorous-
substituted porphyrins have arisen as promising molecular
blocks for the design of coordination networks. Indeed, pol-
ynuclear systems and 1D coordination polymers have been
[a] E. V. Vinogradova, Dr. Y. Y. Enakieva, Dr. K. P. Birin,
Prof. A. Y. Tsivadze, Prof. Y. G. Gorbunova
Russian Academy of Sciences
Frumkin Institute of Physical Chemistry and Electrochemistry
Leninsky pr., 31, GSP-1, 119071, Moscow (Russia)
Fax : (+7)495 952-25-66
E-mail: yulia@igic.ras.ru
[b] Dr. Y. Y. Enakieva, Prof. S. E. Nefedov, Dr. K. P. Birin,
Prof. A. Y. Tsivadze, Prof. Y. G. Gorbunova
Russian Academy of Sciences
Kurnakov Institute of General and Inorganic Chemistry
Leninsky pr., 31, GSP-1, 119991, Moscow (Russia)
Fax : (+7)495 952-25-66
E-mail: yulia@igic.ras.ru
[c] Dr. A. G. Bessmertnykh Lemeune, Dr. C. Stern, Prof. R. Guilard
Institut de Chimie Molꢀculaire de l’Universitꢀ de Bourgogne
(ICMUB-UMR CNRS 6302)
9 Avenue Alain Savary-BP 47870
21078 Dijon Cedex (France)
E-mail: Roger.Guilard@u-bourgogne.fr
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201202596.
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Chem. Eur. J. 2012, 18, 15092 – 15104

FULL PAPER
synthesized from mono-substituted meso-phosphoryl metal-
loporphyrins (M=Zn, Mg, Ni, Pd).[21–25] Meso-5,15-di(die-
thoxyphosphoryl)porphyrinatozinc building blocks have also
been successfully used to prepare a 2D coordination net-
work.[26] Self-organization of this metalloporphyrin proceeds
more easily than the assembling of meso-5,15-di(4-diethoxy-
phosphorylaryl)porphyrinatozinc molecules, because direct
attachment of the electron-withdrawing diethoxyphosphoryl
substituent at the meso-position of the tetrapyrrolic macro-
cycle increases the affinity of the metal cation to the axial
ligand.[27] The b-substituted derivatives commonly used to
form porphyrin supramolecular systems in Nature demon-
strate the potential utility of b-diethoxyphosphoryl-substitut-
ed porphyrins as precursors of self-assembling systems. To
the best of our knowledge, the synthesis of these porphyrin
derivatives has not been described so far.
phorylporphyrins in the solid state and in solution is also
studied. The described results clearly demonstrate that b-
phosphoryl-substituted metalloporphyrins is prospective
building blocks to elaborate supramolecular ensembles and
coordination networks.
Results and Discussion
Synthesis of b-(dialkoxyphosphoryl)porphyrins: H2TPPBr
was chosen as the starting halide precursor, because this
compound is readily available by a standard bromination
procedure.[60,64] First, the reaction of H2TPPBr with diethyl
phosphite in the presence of the copper iodide/N,N’-dime-
thyldiaminoethane (L) catalytic system and cesium carbo-
nate as a base was studied (Scheme 1). This catalytic system
A few decades ago, porphyrins were mainly prepared
from pyrroles, which are readily obtained from acyclic pre-
cursors. Modification of a preformed porphyrin backbone
was used predominantly for natural (e.g., protoporphyrin,
hematoporphyrin), low-cost porphyrins, however this ap-
proach was limited to a basic substitution pattern. Recently,
transition-metal-catalyzed reactions have been used to de-
velop a new powerful synthetic strategy for the post-modifi-
cation of porphyrin macrocycles. Indeed, transition-metal-
mediated carbon–carbon and carbon–heteroatom (N, O, S,
Se, P, B) bond forming reactions allow an efficient synthesis
of a large number of porphyrin derivatives starting from
halogenated precursors.[28–38] The versatility of this method-
ology has been demonstrated in many applications, includ-
ing the synthesis of natural products, pharmaceuticals, and
other key biologically active compounds, new ligands, and
advanced materials. Generally, readily accessible meso-halo-
porphyrins were used as precursors. The reactivity of b-bro-
moporphyrins has been studied less, although Pd-catalyzed
carbon–carbon bond-forming reactions have been first de-
scribed over twenty-five years ago.[39–46]
The studies related to the b-functionalization of porphyr-
ins are often limited by the availability of the starting b-hal-
oporphyrins. Regioselective substitution reactions with
iodine and chlorine atoms have been described,[40,47–50] how-
ever b-bromoporphyrins still remain the most easily accessi-
ble b-halogenated derivatives.[51,52] A number of different
procedures have been described for the synthesis of b-octab-
romo-substituted porphyrins.[53–58] Regioselective bromina-
tion at selected b-positions represents a more challenging
task, however, recent improvements of synthetic procedures
for 2-mono-,[59,60] 2,3-di-,[59,61,62] 2,3,12,13-tetra-,[63] and
2,3,7,8,12,13-hexabromoporphyrins[61] made these derivatives
more accessible for further preparation of a large variety of
functionalized porphyrins. For example, 2-bromo-5,10,15,20-
tetraphenylporphyrin (H2TPPBr) was transformed into a va-
riety of b-functionalized porphyrins through Pd-catalyzed
carbon–heteroatom (N, O, S) bond-forming reactions.[60]
Herein, we extend the scope of transition-metal-mediated
carbon–phosphorous bond-forming reactions to b-bromo-
porphyrins. The self-organization of the new class of b-phos-
Scheme 1. Cu-mediated phosphorylation of ZnTPPBr.
developed by Buchwald et al.[65] has been previously success-
fully used to prepare meso-(dialkoxyphosphoryl)porphyrins
from the corresponding meso-iodo-substituted derivatives.[21]
H2TPPBr was initially transformed into the zinc porphyri-
nate ZnTPPBr by a standard metallation procedure to avoid
porphyrin metallation by copper iodide under the phosphor-
ylation reaction conditions.
When ZnTPPBr was treated with diethyl phosphite in the
presence of 20 mol% of CuI, 1.5 equivalents of diamine L
and an excess of Cs2CO3, only traces of the desirable prod-
uct 1Zn were detected by MALDI-TOF mass spectrometry
even after two days (Scheme 1), Table 1, entry 1). Product
1Zn was obtained in higher yield (35%) when a stoichio-
metric amount of copper iodide and seven equivalents of
the diamine L were used (Table 1, entry 2). The amount of
the base has only a negligible effect on the reaction outcome
(Table 1, entry 3), but an excess of diethyl phosphite leads
to a higher reaction yield (Table 1, entries 2–,4). However, it
has to be noted that the conversion of ZnTPPBr and the re-
action yield were still moderate when twelve equivalents of
the reagent was used (Table 1, entry 4). It is noteworthy that
the presence of the diamine L is a key factor for the reac-
tion course, because no product was detected by MALDI-
TOF mass spectrometry of the reaction mixture in the ab-
sence of the amine L (Table 1, entry 5). By using the same
conditions, di-n-butyl phosphite was more reactive and the
corresponding phosphonate 2Zn was obtained in 50% yield,
whereas diethyl phosphite afforded the product 1Zn in 35%
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R. Guilard et al.
Table 1. Copper-mediated phosphorylation of ZnTPPBr with dialkyl
phosphites.[a]
Table 2. Pd-mediated phosphorylation of H2TPPBr with diethyl phos-
AHCTUNGTRENNUNG
phite.[a]
[c]
HP(O)(OR)2 CuI Cs2CO3 Conv
L
Product Yield
[%][c]
Base
[Pd]/L ([equiv])
Conv
[%][b]
Yield [%]
G
N
[equiv] [%][b]
1H2
H2TPP
1
2
3
4
5
7
8
9
3 (Et)
6 (Et)
3 (Et)
12 (Et)
24 (Et)
3 (nBu)
24 (nBu)
24 (iPr)
0.2
1
1
1
1
1
3
3
3
1.5
7
7
7
–
7
7
35
16
7
5 (95) 1Zn
<5[d]
35
24
35 (65) 1Zn
25 (74) 1Zn
50 (49) 1Zn
1[d]
2
3
4
5
6
7
8
NEt3
NEt3
Pd
Pd
Pd
Pd
Pd
Pd
Pd
[Pd
[Pd
[Pd
N
10
100
100
100
100
0
50
90
79
70
5[e]
87
5[e]
11
44
N
A
84[e]
63[e]
70[e]
–
16[e]
37[e]
30[e]
–
0
1Zn
0[d]
7
7
50 (49) 2Zn
100 (0) 2Zn
100 (0) 3Zn
50
94
86
N
N
U
21
21
21
14
14
14
NEt3
NEt3
NEt3
NEt3
35
84
72
43
5
10 24 (tBu)
0
4Zn
0[d]
G
6
9
R
5[i]
[a] Reaction conditions: ZnTPPBr (0.02–0.04 mmol each), HP(O)(OR)2,
CuI, L, and Cs2CO3 were heated to reflux in toluene (3 mL) for two days
under N2. [b] Conversion was estimated by H NMR spectroscopic analy-
10[j]
A
20[i]
1
[a] Reaction conditions: H2TPPBr (0.03 mmol), HP(O)ACTHNGUTERNN(UG OEt)2 (12 equiv),
sis of the crude reaction mixture; yields of isolated starting material
ZnTPPBr are given in brackets. [c] Yields of isolated product. [d] Yield
estimated by 1H NMR spectroscopic analysis of the crude reaction mix-
ture.
[Pd]/L, and the base (15 equiv) were heated to reflux in toluene (3 mL)
for two days under N2. [b] Conversion estimated by 1H NMR spectro-
scopic analysis of the crude reaction mixture. [c] Yield of isolated prod-
uct. [d] Ethanol was used as a solvent. [e] 1H NMR spectroscopic yield
according to the crude reaction mixture analysis. [f] Cy=cyclohexyl.
[g] Dppf=1,1’-bis(diphenylphosphino)ferrocene. [h] BINAP=2,2’-bis(di-
phenylphosphino)-1,1’-bi-naphthyl. [i] Yield determined by 1H NMR
spectroscopy of the isolated mixture of H2TPPBr and H2TPP. [j] 25 equiv-
yield (Table 1, entries 2 and 7). Full conversion of the start-
ing material ZnTPPBr was observed when the amount of all
reagents was increased up to 24 equivalents of di-n-butyl
phosphite, 14 equivalents of Cs2CO3, three equivalents of
CuI, and 21 equivalents of the amine L (Table 1, entry 8).
Under these conditions the yield of the isolated target prod-
uct 2Zn was 94%. A high yield (86%) of the phosphonate
was also obtained when ZnTPPBr was reacted with di-iso-
propyl phosphite (Table 1, entry 9), however, sterically hin-
dered di-tert-butyl phosphite did not react under these con-
ditions (Table 1, entry 10).
alents of HP(O)ACTHNUTRGNE(UNG OEt)2 and 30 equivalents of NEt3 were also tested and
gave similar results.
metric amounts of the catalytic system (Table 2, entry 1).
This can be attributed to the low solubility of H2TPPBr in
ethanol. Further investigations proved toluene to be a good
reaction solvent. Full conversion of H2TPPBr was achieved
after two days in the presence of one equivalent of [Pd-
AHCTUNTGREN(NGUN OAc)2/3PPh3] when a large excess of diethyl phosphite
Next, we set out to develop conditions for the palladium-
catalyzed formation of b-diethoxyphosphoryl derivatives
(Scheme 2). It has previously been shown that the Pd-cata-
lyzed carbon–phosphorous bond-forming reaction is effi-
cient for the synthesis of meso-bis(diethoxyphosphoryl)por-
phyrins.[26,27]
(12 equiv) and NEt3 (15 equiv) was used (Table 2, entry 2).
The product 1H2 was isolated in 87% yield, H2TPP being
the only byproduct. A number of amines and ligands was
tested in order to avoid the hydrodebromination side reac-
tion leading to the formation of H2TPP, however none of
them were superior to the first examined system (Table 2,
entries 3–6). When H2TPPBr
was reacted with di-n-butyl
phosphite under the optimal
conditions (Table 2, entry 2),
full conversion of the starting
bromide was observed and the
target product 2H2 was isolated
in 92% yield.
Further, catalytic conditions
were studied to perform the
Scheme 2. Pd-mediated phosphorylation of H2TPPBr.
coupling of H2TPPBr with di-
ethyl phosphite. Decreasing the
The obtained results are summarized in Table 2. Interest-
ingly, the reactivity of H2TPPBr and ZnTPPBr in the pres-
ence of palladium catalysts was different compared to meso-
dibromoporphyrins. Ethanol was found to be the best sol-
vent for the reaction of meso-dibromoporphyrins with dieth-
amount of [Pd
sion of the starting bromide (Table 2, entry 7). It should be
noted that [Pd(PPh3)4] was more efficient (Table 2, entries 8
and 9) and the product was obtained in 72% yield by using
25 mol% of this catalyst. Further decrease in the catalyst
loading to 15 mol% led to an incomplete conversion of
H2TPPBr (Table 2, entry 10) and a significant increase of by-
product formation (H2TPP), even when the reaction was
carried out in the presence of 25 equivalents of diethyl phos-
ACHTUNGTRNE(NUNG OAc)2/3PPh3] led to an incomplete conver-
AHCTUNGTRENNUNG
yl phosphite in the presence of a [PdACTHNUTRGEN(UNG OAc)2/3PPh3] catalytic
system and NEt3. When H2TPPBr was reacted with diethyl
phosphite under the same conditions, the yield of the target
product 1H2 was very low even in the presence of stoichio-
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Zinc b-(Dialkoxyphosphoryl)porphyrins
FULL PAPER
phite (Table 2, entry 9). The potential metallation of
H2TPPBr by palladium complexes can be excluded accord-
ing to MALDI-TOF mass spectrometry data. The low cata-
lyst efficiency can be explained by the formation of catalyti-
cally inactive palladium complexes containing diethyl phos-
phite as a ligand,[66] however, the attempts to perform the
reaction in the presence of smaller amounts of diethyl phos-
phite (1.2 equiv) and NEt3 (1.5 equiv) were unsuccessful.
The low H2TPPBr conversion observed under these condi-
tions shows that the carbon–
easy approach to the unknown 2,12(13)-bis(diethoxyphos-
phoryl)porphyrins 5H2 and 6H2. These compounds cannot
À
be obtained by direct metal-mediated C P bond-forming re-
actions, because the corresponding b-dibromoporphyrins are
not available by selective dibromination of H2TPP. There-
fore, we set out to develop conditions for the selective syn-
thesis of the bis(phosphoryl) porphyrins 5H2 and 6H2 start-
ing from H2TPPBr4 (Scheme 3). Extending the reaction
time, raising the amounts of diethyl phosphite and NEt3, as
phosphorous bond formation is
slow when diethyl phosphite is
used in small excess.
It
was
expected
that
ZnTPPBr would be more reac-
tive compared to H2TPPBr as
has been observed in the reac-
tions of meso-dibromoporphyr-
ins.[26] In fact, their reactivity is
similar and full conversion of
the starting bromide was ob-
served only in the presence of a
stoichiometric amount of [Pd-
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
excess of diethyl phosphite
(12 equiv) and triethylamine
(15 equiv). Moreover, the prod-
uct purification by column
Scheme 3. Synthesis of 2,12(13)-bis(diethoxyphosphoryl)porphyrins 5H2, 6H2, 5Zn, and 6Zn.
chromatography was more difficult due to the coordination
of triphenylphosphine oxide formed during the reaction to
porphyrinatozinc 1Zn. In this case, an additional demetalla-
tion step was required to obtain the pure product 1H2.
well as by using two equivalents of palladium acetate, led to
complex mixtures of products, whereas the conversion did
not exceed 50%. Low conversions were also observed when
toluene was replaced by THF or ethanol. Although no phos-
phorylated products were observed in the reaction mixtures
by MALDI-TOF mass spectrometry, the use of ethanol as
the solvent did promote the reduction step of the sequence.
Thus, a mixture of toluene and ethanol was used to increase
the solubility of the porphyrin, to facilitate the reduction,
and to allow the consecutive phosphorylation of the result-
ing bromoporphyrins (Table 3).
Interestingly, the ratio of the solvents was a key parame-
ter influencing the conversion and the yields of the bis(phos-
phoryl)porphyrins 5H2 and 6H2 (Table 3, entries 1–4). The
best result was observed when ethanol and toluene were
used in a 2:3 ratio (Table 3, entry 3). By using these condi-
tions, the bis(phosphoryl)porphyrins 5H2 and 6H2 were ob-
tained in equal amounts with a total yield of 81%. Both in-
creasing and decreasing of ethanol content led to an incom-
plete reaction and lower yields of the target products
À
The developed conditions for the Pd-catalyzed C P bond-
forming reaction were further applied to the synthesis of b-
poly(dialkoxyphosphoryl)porphyrins. 2,3,12,13-Tetrabromo-
5,10,15,20-tetraphenylporphyrin (H2TPPBr4), was readily
prepared through controlled bromination of H2TPP with N-
bromosuccinimide.[62] When H2TPPBr4 was reacted with di-
ethyl phosphite by using the conditions optimized for
H2TPPBr (Table 2, entry 2), the starting material and a com-
plex mixture of products were observed according to
MALDI-TOF mass spectrometry. However, the products
formed in the course of the stepwise phosphorylation of
H2TPPBr4
(e.g.,
H2TPP(X)Br3,
H2TPP(X)2Br2,
H2TPP(X)3Br, where X=P(O)AHCTUGNTR(EUNNNG OEt)2) were not observed
indicating that the dibromopyrrole moiety did not directly
react with diethyl phosphite. It is possible to assume that the
phosphorylation reaction takes place only after the reduc-
tion of one of the neighboring bromine atoms leading to the
formation of a mono-b-diethoxyphosphoryl-substituted pyr-
role moiety. This distinguishes the developed transformation
from the previously described Pd-catalyzed b-functionaliza-
tion reactions, where both of the bromine atoms get substi-
tuted with the used nucleophile.[67]
(Table 3, entries 2 and 4). When the amount of [PdACHTUNGTRENNUNG(OAc)2/
3PPh3] was decreased twice, the conversion of H2TPPBr4
was still complete but the target products 5H2 and 6H2 were
obtained in a slightly lower yield (68%). The separation of
the regioisomers 5H2 and 6H2 by column chromatography
was quite delicate. However, the corresponding porphyrina-
tozinc complexes 5Zn and 6Zn, easily obtained by metalla-
tion of the mixture of 5H2 and 6H2 (Scheme 3), were sepa-
A controlled one-pot reaction involving consecutive re-
duction and phosphorylation of H2TPPBr4 would provide an
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15095

R. Guilard et al.
Table 3. Pd-mediated phosphorylation of H2TPPBr4 with diethyl phos-
phite.[a]
Ethanol/Toluene
Conv
[%][b]
Yield [%][c]
[d]
5H2, 6H2
1H2
H2TPP
1
2
3
5:95
25:75
40:60
50:50
40:60
<25[e]
70
100
60
n/i[f]
10
81
20
68
n/i
n/i
17
15
21
n/i
25
<2
20
6
[g]
4
5[h]
100
[a] Reaction conditions: H2TPPBr4 (0.01–0.04 mmol), HP(O)
ACHTUNGERTN(NUNG OEt)2
(12 equiv), [Pd(OAc)2/3PPh3] (1 equiv), and NEt3 (15 equiv) were heated
ACHTUNGTRENNUNG
to reflux in the solvent mixtures (3 mL) for two days under N2. [b] Con-
version was estimated by 1H NMR spectroscopy. [c] Yield of isolated
product. [d] The regioisomers of 5H2 and 6H2 were obtained in equal
amounts in all the reactions. [e] A complex mixture of products contain-
ing 5H2, 6H2, 1H2, mono- and dibromo-substituted derivatives of 1H2
and H2TPP according to MALDI-TOF mass spectrometry was obtained.
[f] n/i not isolated [g] A complex mixture of products containing 1H2
bromo-substituted derivatives according to MALDI-TOF mass spectrom-
Figure 1. Molecular structure of 1Zn (30% probability ellipsoids). Hy-
drogen atoms and phenyl groups are omitted for clarity.
etry was obtained. [h] 0.5 equivalents of [PdACHTUNTGRNEUNG(OAc)2/3PPh3] were used.
rated by column chromatography on silica gel by using
CH2Cl2/MeOH (99:1) as eluent.
To get some insight into the reaction course, H2TPPBr4
was reacted with diethyl phosphite in the presence of NEt3
without the Pd catalyst. Partial reduction of the gem-dibro-
moalkenes to the bromoalkenes is possible under these con-
ditions.[68,69] Recently, a one-pot reaction including consecu-
tive reduction and copper-mediated phosphorylation reac-
tions of gem-dibromoalkenes was described.[70] However, the
reaction did not proceed when H2TPPBr4 was heated to
reflux with diethyl phosphite and NEt3 in the ethanol/tol-
uene mixture (2:3) for two days. Thus, both ethanol and a
palladium catalyst are needed to achieve the H2TPPBr4 re-
duction. Moreover, H2TPPBr4 does not react with diethyl
phosphite directly, because tri- and tetra-diethoxyphosphor-
yl-substituted porphyrins were never observed in the reac-
tion mixtures by MALDI-TOF mass spectrometry. There-
fore, the Pd-catalyzed hydrodebromination reaction of
H2TPPBr4 probably leads to the formation of partially re-
Figure 2. Molecular structure of 3Zn (30% probability ellipsoids). Hy-
drogen atoms and phenyl groups are omitted for clarity.
À
duced products, which then participate in consecutive C P
bond-forming reactions giving 5H2 and 6H2 along with 1H2
and H2TPP.
partially overlapped. As a result each phosphoryl-substitut-
ed pyrrole fragment is located above the second porphyrin
core. Significant difference in the dimer geometry was ob-
served for compound 3Zn compared to 1Zn, which possess-
es the less-bulky ethoxy substituents at the phosphoryl
group. The distance between two porphyrin N4 planes is sig-
nificantly different and is equal to 3.90 and 4.51 ꢂ in 1Zn
and 3Zn, respectively. Moreover, displacement of the zinc
atom from the porphyrin N4 plane increases by 0.067 ꢂ. The
P-O-Zn angle varies from 147.9(5) to 160.2(2)8 and the
O(1)-P(1)-C angle changes from 116.3(5) to 106.0(2)8 for
1Zn and 3Zn, respectively. Relatively short contacts (3.4–
3.7 ꢂ) were observed between the carbon atoms of the iso-
propoxy substituents and the atoms of the closest pyrrole
ring of the adjacent porphyrin macrocycle in the dimer of
3Zn. These contacts give rise to a decrease in the angle be-
Crystal structures of the zinc b-phosphoryl porphyrins 1Zn
and 3Zn: Single crystals of complexes 1Zn and 3Zn were
grown by slow evaporation of methanol/benzene and metha-
nol/CHCl3/heptane mixtures, respectively, and their struc-
tures were elucidated by X-ray crystallography. According
to the X-ray diffraction data, both complexes are zinc b-
mono-phosphorylporphyrinate cofacial dimers formed by
À
two P O···Zn coordination bonds (Figures 1 and 2). The
zinc atom is located within the center of the porphyrin ring
À
À
(Zn N 2.047(8)–2.076(8) ꢂ in 1Zn, Zn N 2.061(4)–
2.083(5) ꢂ in 3Zn) and the fifth position in the tetragonal-
pyramidal environment of the Zn atom is occupied by one
oxygen atom of the phosphoryl substituent of the adjacent
À
tween the Zn(1A) N(1A) line and the Zn(1A)O(1A)P(1A)
plane from 22.58 in 1Zn to 16.18 in 3Zn. At the same time,
the Zn···P distance in 3Zn (3.520 ꢂ) increases compared to
À
porphyrin molecule (Zn O 2.086(7) ꢂ for 1Zn and
2.098(4) ꢂ for 3Zn). Two cofacial porphyrin molecules are
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Chem. Eur. J. 2012, 18, 15092 – 15104

Zinc b-(Dialkoxyphosphoryl)porphyrins
FULL PAPER
1Zn (3.413 ꢂ). Two benzene molecules are present in the
crystal structure of 1Zn, methanol and water molecules—in
3Zn. It is interesting to note that in both cases the solvent
molecules do not have any contacts with the porphyrin
dimers.
Matano and co-workers have reported similar dimers
formed by mono-substituted meso-dialkoxyphosphorylpor-
phyrin and 5-di-n-butoxyphosphoryl-10,15,20-tris(3,5-di-tert-
yphosphoryl group on the porphyrin core. The ZnII atom
adopts a distorted tetragonal-pyramidal coordination geom-
etry. Displacement of the five-coordinated zinc ion from the
mean porphyrin N4 plane in 1Zn (0.317 ꢂ) and in 3Zn
(0.384 ꢂ), is similar to that observed in meso-monoPZn
(0.331 ꢂ) but the average deviation of the nitrogen atoms
from the porphyrin plane varies from an almost flat arrange-
ment in 1Zn and meso-monoPZn (deviation from the N4
plane is 0.001 and 0.009 ꢂ, respectively) up to 0.028 ꢂ in
the sterically hindered 3Zn. In contrast, the Zn atoms are
located exactly in the center of the porphyrin ring in the 2D
coordination network formed by meso-diPZn. The Zn···O=P
butylphenyl)porphyrinatozinc(II)
(meso-monoPZn)
(Figure 3).[21] Moreover, it was previously shown by us that
distances are similar for the three dimers ACTHNUTRGNEUNG(2.086(7), 2.098(4),
and 2.102(3) ꢂ, respectively) and are significantly longer in
the 2D polymer (2.465(2) ꢂ). It should be noted, that the in-
terplanar distance between the two porphyrin N4 planes in
the dimer increases from 3.04 to 3.90 ꢂ when the position of
the diethoxyphosphoryl substituent is changed from meso to
b at the porphyrin core, and further increases up to 4.51 ꢂ
À
in the more sterically hindered compound 3Zn. The Zn Zn
Figure 3. Structures of meso-monoPZn and meso-diPZn.
distance changes in the same order (6.253, 7.187, and
7.336 ꢂ, respectively). Considering the value of these two
parameters, Matano and co-workers have proposed the
meso-monoPZn dimer as a new model for a weakly coupled
chlorophyll pair in the photosynthetic reaction center.[21]
Indeed, in the special pair P700 formed by two chlorophylls
in photosystem I (PSI) the metal separation is equal to
6.3 ꢂ and differs from the special pair formed by the bacter-
iochlorophylls in the purple bacterial reaction center
(PbRC),[71] where the MgII separation is larger (7.6 ꢂ).[72]
Thus, b-dialkoxyphosphorylporphyrins can be regarded as
model compounds for the weakly coupled chlorophyll pairs
in photosynthesis as well as meso-monoPZn. Moreover, the
functional group is located at the b-position in these com-
pounds as in the naturally occurring chlorophyll. The metal–
metal separation and interplanar porphyrin distance can be
tuned by changing the size and the position of the alkoxy
substituents of the phosphoryl group as it was shown above
for 1Zn, 3Zn, and meso-monoPZn.
self-assembling of 5,15-bis(diethoxyphosphoryl)-10,20-di-
phenyl-porphyrinatozinc(II) (meso-diPZn) (Figure 3) led to
a 2D coordination polymer formed by interconnection of
the porphyrinatozinc(II) units through the coordination of
the Zn centers by two phosphoryl groups belonging to two
adjacent molecules.[26] Selected structural parameters of four
phosphoryl porphyrin derivatives are summarized in
Table 4. A number of the parameters are similar for the b-
and the meso-substituted porphyrin dimers 1Zn, 2Zn, and
meso-monoPZn despite the different location of the dialkox-
Table 4. Selected bond lengths [ꢂ] and angles [8] of four (dialkoxyphos-
phoryl)porphyrinate zinc complexes.
1Zn[a]
3Zn[a]
meso-
meso-
monoPZn[b] diPZn[c]
À
Zn(1) O(1)
2.086(7)
1.460(7)
2.098(4) 2.102(3)
1.474(4) 1.478(3)
2.465(2)
1.473(3)
1.574(3)
1.583(3)
–
–
–
–
À
P(1) O(1)
[d]
1.494(11)[d] 1.561(4) 1.579(3)
À
P(1) O(2)
IR studies: Infrared spectroscopy was used to get insight
into the structures of 2Zn, 5Zn, and 6Zn in the solid state.
It was shown that the position of the P=O stretching vibra-
tion band, which is observed in the region of n˜ =1180–
1280 cmÀ1 of the IR spectrum reflects the formation of P=
O···Zn coordination bonds involving adjacent porphyrin
molecules. In the IR spectra of the self-assembling zinc por-
phyrinates, these vibration bands were observed at lower
frequencies (Dn˜ =7–30 cmÀ1) than those of the correspond-
ing free-base porphyrins.[26] Moreover, two distinct vibra-
tions at n˜ =1259 and 1233 cmÀ1 were detected in powder
samples of the 2D coordination polymer of meso-diPZn.
The vibration frequency of the first one was similar to the
P=O band of 5,15-bis(diethoxyphosphoryl)-10,20-diphenyl-
porphyrin (n˜ =1250 cmÀ1) and was assigned to the vibration
of an uncoordinated peripheral phosphoryl group. The
second band was attributed to the vibration of a coordinated
À
P(1) O(3)
1.561(8)
0.317
1.577(4) 1.580(4)
À
Zn plane N4
0.384
0.028
4.51
0.331
0.0086
3.04
À
Zn porphyrin N4 plane 0.0006
N4 N4 planes
Zn···Zn
À
3.90
7.187
3.413
7.336
3.520
6.253
3.296
Zn···P
–
Zn(1)-O(1)-P(1)
O(1)-P(1)-O(2)[d]
O(1)-P(1)-O(3)
O(2)-P(1)-O(3)[e]
O(1)-P(1)-C
Zn-N(C)/ZnPO
angle Ph/N4
147.9(5)
110.5(6)
115.3(4)
106.3(6)
116.3(5)
22.5
99.9
64.4
66.7
160.2(2) 133.4(2)
115.7(2) 108.1(2)
113.2(2) 111.9(2)
102.7(2) 105.97(19)
158.20(15)
112.99(15)
113.95(16)
100.58(15)
–
–
–
106.0(2)
16.1
–
–
96.9
119.7[e]
103.3
94.4
75.8
73.9
58.4
63.5
[a] Data from this work. [b] Data from reference [21]. [c] Data from ref-
erence [26]. [d] The [OEt] fragment (O(2), C(45), C(46)) in 1Zn is disor-
dered at practically the same sites. [e] 3,5-Di-tert-butylphenyl substitu-
ents.
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15097

R. Guilard et al.
phosphoryl group P=O···Zn, because only this band was ob-
served in the IR spectrum of a monocrystalline solid sample
of the 2D coordination polymer of meso-diPZn.
In accordance with this data and the X-ray diffraction
data on a single crystal, a strong P=O stretching vibration
band of 1Zn (n˜ =1228 cmÀ1) was observed at lower frequen-
cies than the corresponding band in the free-base porphyrin
1H2 (n˜ =1245 cmÀ1). Only one
nACTHUNGTERNNU(G P=O) band at n˜ =
1213 cmÀ1 corresponding to the vibration of a coordinated
phosphoryl group, was observed in the spectrum of 3Zn, re-
flecting a molecular self-assembling through P=O···Zn inter-
actions in the solid state. A similar frequency shift of the P=
O bands was observed for the solid state IR spectra of 2Zn
(n˜ =1220 cmÀ1) and 2H2 (n˜ =1250 cmÀ1). Thus, the intercon-
nection of the metalloporphyrin units through the coordina-
tion of Zn centers by the di-n-butoxyphosphoryl group also
exists in the solid state samples of 2Zn. Taking into account
the structural similarity of 1Zn, 2Zn, and 3Zn, formation of
cofacial dimers seems to be the most probable pathway for
the self-organization of 2Zn in the solid state. Vibrations of
coordinated phosphoryl groups observed in the spectra of
5Zn and 6Zn (n˜ =1232 and 1240 cmÀ1, respectively) are
very similar to those observed for the 2D coordination poly-
mer of meso-diPZn (n˜ =1232 cmÀ1).
Association in solution: Association of porphyrins 1Zn and
3Zn in solution was first investigated by UV/Vis spectrosco-
py in toluene and chloroform. As expected, the UV/Vis
spectra of the free-base porphyrins 1H2 and 2H2 are not
concentration dependent. Figure 4 shows the concentration
dependence of the absorption spectrum of the metallopor-
phyrin 1Zn in toluene. Increasing the concentration of 1Zn
leads to a bathochromic shift and broadening of all the por-
phyrin bands in the spectrum. The Soret band shifts only by
3 nm when the 1Zn concentration increases from 1.4ꢃ10À5
to 3.6ꢃ10À4 m. The Q-band shifts are observable at higher
concentrations due to the lower intensity of these bands.
Again, significant shifts (from l=557 up to 569 nm, Dl=
12 nm and from l=596 up to 612 nm, Dl=16 nm) were de-
tected when the compound concentration was increased
from 1.8ꢃ10À5 to 1.4ꢃ10À3 m indicating that molecular asso-
ciation takes place at this concentration range.
Figure 4. UV/Vis absorption spectra of 1Zn in toluene at different con-
centrations. The spectra are normalized for comparison.
Molecular association of 3Zn in toluene also induced
bathochromic shifts of the Q-bands and the broadening of
the Soret band (see the Supporting Information, Figure S3).
The nature of the alkyl substituents located on the phos-
phoryl group does not significantly influence the concentra-
tion limits of the association process. The law of Lambert is
observed at concentrations lower than 5ꢃ10À5 m in toluene
and 1ꢃ10À4 m in chloroform for 1Zn and 3Zn.
Consequently, UV/Vis absorption spectroscopy can be
used to estimate more precisely the concentration limits
where self-association of compound 1Zn takes place.
Indeed, an expected linear evolution of the intensity of the
Soret band (l=429 nm) occurs in the concentration range
of 1ꢃ10À7–5ꢃ10À5 m (see the Supporting Information, Fig-
ure S1). A significant deviation from the law of Lambert is
observed only for concentrations of 1Zn higher than 5ꢃ
10À5 m, whereas the bathochromic shift of all porphyrin
bands is observed. Increasing the concentration of 1Zn in
chloroform does not lead to the bathochromic shift of the
Soret band (l=430 nm). However, the deviation from the
law of Lambert is observed when the concentration of the
compound is higher than 1ꢃ10À4 m (see the Supporting In-
formation, Figure S2).
1H and 31P{1H} NMR spectroscopic studies: The 1H NMR
spectra of the free-base porphyrins 1H2 and 3H2 in CDCl3
reveal the expected resonances of all the protons (1H NMR
spectrum for 1H2 shown as an example, see the Supporting
1
Information, Figure S4). In contrast, the H NMR spectrum
of 1Zn in CDCl3 (10À2–10À4 m) at 303 K consists of a broad,
poorly resolved set of signals, which prevents the structure
determination (Figure 5). However, a well-resolved spec-
trum could be obtained after the addition of 30% v/v of
[D4]MeOH (Figure 5). In this spectrum all the expected
proton signals are observed, but some of the phenylic and
pyrrolic protons occasionally overlap. The downfield doublet
(d=9.5 ppm) was attributed to the proton of the P1 frag-
ment (see Figure 6 for the proton numbering). Resonances
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Zinc b-(Dialkoxyphosphoryl)porphyrins
FULL PAPER
Figure 6. Schematic representation and designation of the protons of pos-
sible associated species of 1Zn and 3Zn in solution.
Figure 5. Aromatic region of the 1H NMR spectra of 1Zn in CDCl3
(10À3 m) at 303 K before and after the addition of different amounts of
[D4]MeOH.
could be expected, that is, the formation of a dimer species
through a single phosphoryl group coordination (Figure 6B)
and a polymeric 1D-chain structure (Figure 6C).
of the P2 and P3 pyrrolic protons are observed as broadened
singlets at dꢀ8.8 ppm. In contrast, the protons of the P4
fragment appear as two doublets with significantly different
chemical shifts. The resonances of the P4(7) protons are shift-
ed upfield due to the ring current effects of the sterically
hindered phenyl substituent Ph1. It is important to note that
the most significant variation in the chemical shifts of the
pyrrolic protons and the line widths of the alkoxy groups
were observed after the addition of only trace amounts of
[D4]MeOH (1% v/v). The observed influence of methanol
on the spectrum of 1Zn allows to conclude that weak mo-
lecular aggregates are formed in CDCl3, presumably through
coordination of the diethoxyphosphoryl groups to the metal
centers. Indeed, methanol can replace the axially coordinat-
It was shown, that temperature variations significantly in-
fluence the association process in both solvents. Although
the spectrum of 1Zn in CDCl3 at 303 K is significantly
broadened, an increase of the temperature to 323 K results
in a resolution gain through the suppression of the associa-
tion. In this case all the resonances expected for the mono-
meric 1Zn are observed and the spectrum becomes similar
to the one observed in the CDCl3/[D4]MeOH solutions (see
the Supporting Information, Table S1). The only exception
À
À
is that the resonance pattern of the OCH2 diastereotopic
protons differs from the one of 1Zn in CDCl3/[D4]MeOH.
The temperature decrease to 223 K leads to the formation
of more stable associates. The phosphorus signal is shifted
upfield by dꢀ1 ppm upon cooling of the sample (see the
Supporting Information, Figure S9–S11). The observed
change is in accordance with the formation of associated
species of meso-mono-phosphorylated zinc porphyrins.[60,64]
This small change of the chemical shift is the result of two
opposite factors: the magnetic anisotropy of the p system of
the porphyrin ring induces the upfield shift of the resonance
peak. In contrast, the P=O···Zn coordination leads to a
downfield shift. This data allows to conclude, that the struc-
ture of associate A (Figure 6A) differs from that of dimer B
(Figure 6B), because two phosphorus resonances are expect-
ed in the 31P{1H} NMR spectrum for compound B.
ed P(O)ACHTUNGTRENNUNG(OEt)2 groups in the molecular aggregates favoring
the formation of the monomeric 1Zn form.
The association of 3Zn in CDCl3 is weaker than that of
1Zn and the proton resonances of 3Zn are only slightly
broadened at room temperature (see the Supporting Infor-
mation, Figure S5). Sharp resonances of all aromatic protons
were observed after the addition of only 5 mL (ꢀ1% v/v) of
[D4]MeOH. Under these conditions, the chemical shifts of
all protons are similar to those observed in pure CDCl3.
Variable-temperature NMR (VT-NMR) studies (223–
323 K) of solutions of 1Zn and 3Zn in [D]chloroform and
[D8]toluene provided additional information about the struc-
ture of the aggregates in solution (see the Supporting Infor-
mation, Table S1). Schematic representations of possible
structures of the associates are shown in Figure 6. Besides
the dimeric species, which were obtained in the solid state
(Figure 6A), at least two other supramolecular associates
A gradual temperature decrease of the 1Zn solution from
323 to 223 K results in a significant evolution of the
1H NMR spectrum (Figure 7). Cooling the sample to 253 K
leads to broadening and a shift of all the signals, whereas a
further temperature decrease to 223 K affords a novel com-
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15099

R. Guilard et al.
We intended to finish the assignment of all the protons in
dimer
A by changing the solvent to the less polar
[D8]toluene, which should favor the 1Zn association. Sur-
prisingly, the obtained spectra were more complicated than
the ones obtained in CDCl3. One broad phosphorus signal is
observed at 303 K (see the Supporting Information, Fig-
ure S13). At 323 K this signal was shifted downfield and
became more narrow, proving that the aggregates were still
present in solution (see the Supporting Information, Fig-
ure S14). The temperature decrease down to 223 K resulted
not only in an upfield shift of the signal (see the Supporting
Information, Figure S12), but also in its splitting into two
components with a 1:1.4 intensity ratio showing that two di-
astereomers of dimer A could exist under these conditions.
Although the (Rp,Sp) isomer is relevant to the X-ray data
(Figure 1), the (+/À)-(Rp,Rp) isomer can be derived from
the first one by the inversion of one of the porphyrin mole-
cules (Figure 8). This diastereoisomer possesses only a C2
axis and exists as a pair of enantiomers, the phosphorus res-
onances of which must coincide.
Figure 7. Variable-temperature 1H NMR spectra of 1Zn in CDCl3 at 223
(top), 303 (middle), and 323 K (bottom).
plicated set of resonances. This data are in accordance with
a decreased symmetry of the possible associated species
(Figure 6) compared to the starting Zn porphyrin.
A set of five multiplets in the d=4–7 ppm range was at-
tributed to the protons of the Ph1 substituent, which are
non-equivalent and shielded by the adjacent porphyrin p
system. The chemical shifts of the two doublets at d=4.09
and 6.47 ppm of the ortho protons and the corresponding
triplets at d=5.76 and 6.60 ppm of the meta protons, are sig-
nificantly different and correspond to all the associate forms
given in Figure 6. The resonances of the inner-oriented
ortho and meta protons occupy the most upfield position.
Moreover, the obtained spectrum corresponds rather to
dimer A than to oligomer C. Indeed, two sets of upfield-
shifted resonances of five phenyl protons, namely Ph1 and
Ph3, are expected for oligomer C. The resonance pattern of
the pyrrolic protons is also in agreement with structure A.
Dimer A possesses only an inversion center, which is locat-
ed in the middle of a Zn–Zn line. This determines a paired
equivalence of the protons of two porphyrin molecules
forming the dimer, but also results in the non-equivalence of
all the protons within each particular porphyrin fragment.
The multiplet at dꢀ8.9 ppm corresponds to two pyrrole pro-
tons, whereas two doublets at d=8.72 and 8.63 ppm corre-
spond to one proton each. The pair of correlated signals of
the pyrrole protons, each of them being overlapped with the
resonances of the phenyl protons, are found at d=8.93 and
7.90 ppm by correlation spectroscopy (COSY). These signals
can be attributed to the P4(6) and P4(7) protons, respectively,
because of their significant difference in the chemical shifts
due to the influence of the Ph1 substituent discussed above.
The doublet at d=8.31 ppm can be assigned to the P1
proton, which is directly subjected to the shielding effect of
the porphyrin p system in the dimeric species. Moreover,
this signal is not correlated to any other signal.
Figure 8. Enantiomeric pair of the presumed (+/À)-(Rp,Rp) diaster-
eoisomer of dimer A.
1
The H NMR spectra of 1Zn in [D8]toluene are in agree-
ment with this proposal (Figure 9). The spectrum at 303 K is
broadened and an increase of the temperature to 323 K
does not lead to a complete suppression of the dimerization.
Nevertheless, the observed resonances can be partially as-
signed. Thus, three broad multiplets at d=8.10–8.35, 7.56–
7.68, and 7.53 ppm correspond to the ortho, meta, and para
protons of the meso-phenyl substituents, respectively (based
on their chemical shifts and their integrals ratio of 2:2:1).
Two narrow doublets at d=8.40 and 8.89 ppm are coupled
according to the COSY spectrum and can be assigned to the
b protons of the P4 ring, H7 and H6, respectively. Two broad-
ened signals of the P2 and P3 protons are found in the d=
8.96–9.04 ppm range. A broad signal is observed at d
ꢀ8.63 ppm and can be attributed to the P1 proton, because
this proton is the most influenced by the partial dimeriza-
tion.
The temperature decrease to 223 K slows down the ex-
change processes and a doubled set of narrow multiplets in
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Zinc b-(Dialkoxyphosphoryl)porphyrins
FULL PAPER
cant overlap. Nevertheless, twelve doublets are observed in
the d=9.1–7.6 ppm region, which correlate with twelve trip-
let signals as revealed by the COSY experiment. These pairs
can be attributed to the ortho and meta protons of six
phenyl groups. The remaining protons of the phenyl groups
are observed as a series of overlapped signals in the d=7.2–
7.8 ppm region.
The spectral behavior of porphyrin 3Zn, bearing isoprop-
yl substituents at the phosphoryl groups, is similar to that of
1Zn. Nevertheless, steric hindrance of the bulkier isopropyl
substituents results in a less efficient association and less sig-
nificant shifts of the resonances. Thus, a set of relatively
1
narrow resonances is observed in the H NMR spectrum of
3Zn in CDCl3 at 303 K, testifying that the derivative is pre-
dominantly in a monomeric form. The temperature increase
to 323 K results in the spectrum relevant to the monomer
3Zn (see the Supporting Information, Figures S6 and S7).
The temperature decrease to 223 K results in a broadening
of the signals without a notable shift of the resonances cor-
responding to a low degree of association. The association is
enhanced in toluene (see the Supporting Information, Fig-
ure S8). The temperature decrease in [D8]toluene shifts the
monomer/dimer equilibrium and leads to the formation of
two dimeric diastereomers A in a 1:1.7 ratio. The descrip-
Figure 9. 1H NMR spectra of 1Zn in [D8]toluene at 223 (top), 303
(middle), and 323 K (bottom).
a 1:1.4 ratio is observed within the d=4.0–10.0 ppm spectral
region of the spectrum (Figure 9). The assignment of the
protons is not easy due to the overlap of the signals; howev-
er the assignment of the resonances in this region can be
based on the relative intensities of signals and the COSY
data. Close proximity of the observed subsets and equal
number of observed resonances fit the symmetry of dimeric
diastereoisomers A. The d=4.4–7.0 ppm spectral region is
occupied by sub-sets of resonances, which are attributed to
the protons of the Ph1 substituent, the most upfield signals
are expected for inner-oriented ortho and meta protons. The
set of doublets in the d=9.40–8.30 ppm region was attribut-
ed to the aromatic protons of the porphyrin core. The
broad-band 31P-decoupling experiment allows for the assign-
ment of the P1 protons. Six pairs of doublets corresponding
to two subsets of the P2, P3, and P4 protons are clearly iden-
tified by the COSY experiment. A slight difference of the
chemical shifts (dꢀ0.05–0.1 ppm) is observed within this
series for four pairs of protons. In contrast, the other two
pairs demonstrate the difference between the component
resonances at d=0.47 and 0.81 ppm for the major and
minor species, respectively. These pairs of signals are attrib-
uted to the protons of the P4 fragments as observed for the
monomeric form of the compound at 323 K. The rotation
barrier of the Ph1 substituent should be higher in the case of
the dimer than for the monomeric form. Furthermore, its
perpendicular orientation with respect to the porphyrin
macrocycle is expected according to the presence of five dis-
tinct signals of this moiety in the upfield region. Conse-
quently, the influence of magnetic anisotropy of this aromat-
ic ring onto the H7 proton is presumed to be the same as in
the monomeric form. Other pairs of resonances can be at-
tributed to the P2 and P3 fragments of the two isomeric
dimers. The precise assignment of all resonances of the Ph2,
Ph3, and Ph4 protons is not possible because of their signifi-
1
tion of the H and 31P{1H} NMR spectra is provided in the
Supporting Information.
In conclusion, although a complete assignment of all the
1
signals observed in the H NMR spectra of 1Zn and 3Zn at
low temperatures was not possible due to the signals over-
lap, the obtained data allowed an unambiguous interpreta-
tion of the aggregate structure in solution. The behavior of
1Zn and 3Zn at different temperatures in different solvents
is consistent with the self-aggregation leading to the forma-
tion of dimer A. Two diastereomers exist in solution and
their ratio depends on the nature of the substituents and sol-
vents.
Conclusions
Metal-mediated carbon–phosphorous bond-forming reac-
tions were successfully applied to the synthesis of b-(dia-
lkoxyphosphoryl)porphyrins. An unusual one-pot sequence
involving consecutive reduction and phosphorylation of
H2TPPBr4 provided bis
good yields.
ACHTUNGTRENN(UNG dialkoxy)phosphorylporphyrins in
According to X-ray studies, 1Zn and 3Zn exist as zinc b-
À
phosphorylporphyrinate cofacial dimers formed by two P
O···Zn coordination bonds in the solid state. This self-organ-
ization is also observed in weakly polar solvents. The stabili-
ty of these aggregates in solution is dependent on the nature
of the alkoxy substituents of the dialkoxyphosphoryl group.
Thus, b-phosphorylporphyrins can be viewed as new model
compounds for a weakly coupled chlorophyll pair in photo-
synthesis and molecular precursors for the design of coordi-
nation polymers.
Chem. Eur. J. 2012, 18, 15092 – 15104
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
15101

R. Guilard et al.
AHCTUNGTERG[NNUN 2,12-(Diethoxyphosphoryl)-5,10,15,20-tetraphenyl-porphyrinato]zinc
Experimental Section
(5Zn) and [2,13-(diethoxyphosphoryl)-5,10,15,20-tetraphenyl-porphyrina-
to]zinc (6Zn): A 15 mL round bottom flask equipped with a reflux con-
denser and a magnetic stir bar was charged with the bromoporphyrin
All chemicals used were of analytical grade and were purchased from
Acros and Aldrich Co. unless stated otherwise. Silica gel (0.04–0.063 mm,
230–400 mesh ASTM, Merck) was used for column chromatography. An-
alytical thin-layer chromatography (TLC) was carried out by using
Merck silica gel 60 plates (precoated sheets, 0.2 mm thick, with fluores-
cence indicator F254). [5,10,15,20-Tetraphenyl]porphyrin (H2TPP),[73] [2-
bromo-5,10,15,20-tetraphenyl]porphyrin (H2TPPBr), and[60,64] [2,3,12,13-
tetrabromo-5,10,15,20-tetraphenyl]porphyrin (H2TPPBr4),[62] were pre-
pared and metallated[63] to afford [2-bromo-5,10,15,20-tetraphenylpor-
phyrinato]zinc (ZnTPPBr) and [2,3,12,13-tetrabromo-5,10,15,20-tetra-
phenyl-porphyrinato]zinc (ZnTPPBr4) according to literature procedures.
H2TPPBr4 (100 mg, 0.108 mmol), PdACHTUNGRTENUNG(OAc)2 (24.1 mg, 0.108 mmol), and
PPh3 (86.8 mg, 0.323 mmol). The flask was then evacuated and purged
with N2 three times. Toluene (abs., 9 mL), EtOH (abs., 6 mL), diethyl-
phosphite (165 mL, 1.290 mmol), and triethylamine (225 mL, 1.613 mmol)
were added through a syringe and the resulting mixture was heated to
reflux for 5 days until complete conversion of the bromide. The mixture
was then cooled and concentrated to give a solid, which was purified by
column chromatography on silica gel by using CHCl3 and hexane, fol-
lowed by CHCl3 and MeOH as eluent. The brown fraction (MeOH/
CHCl3, 1:99 (v/v)) was collected and evaporated to give a mixture (1:1)
of 2,12- and 2,13-diethoxyphosphoryl-5,10,15,20-tetraphenylporphyrins
(5H2 and 6H2) (77.1 mg, 81%). The attempts to separate these porphyr-
ins by using column chromatography were unsuccessful. The individual
compounds were obtained as zinc complexes after metallation of the por-
[2-(Diethoxyphosphoryl)-5,10,15,20-tetraphenyporphyrin (1H2): A 15 mL
round bottom flask equipped with a reflux condenser and a magnetic stir
bar was charged with the bromoporphyrin H2TPPBr (25 mg,
0.036 mmol), PdACHTUNGTRENNUNG(OAc)2 (8.1 mg, 0.036 mmol), and PPh3 (28.3 mg,
0.108 mmol). The flask was then evacuated and purged with N2 three
times. Toluene (abs., 3 mL), diethylphosphite (55 mL, 0.432 mmol), and
triethylamine (75 mL, 0.540 mmol) were added through a syringe and the
resulting mixture was heated to reflux for 4 h until complete conversion
of the bromide. Upon cooling the mixture was concentrated to give a
solid, which was purified by column chromatography on silica gel by
using CHCl3 and hexane as eluent. The reddish-purple fraction (CHCl3/
hexane, 80:20 (v/v)) was collected and concentrated to give 1H2 as a
phyrins mixture with ZnACHTNUGTRNEG(UN OAc)2·2H2O by using the procedure described
for ZnTPPBr. Purification by column chromatography on silica gel
(MeOH/CHCl3, 1:99 (v/v)) allowed to isolate 5Zn and 6Zn.
AHCTUNGTERG[NNUN 2,12-(Diethoxyphosphoryl)-5,10,15,20-tetraphenyl-porphyrinato]zinc
(5Zn): 1H NMR (600 MHz, CDCl3/CD3OD, 1:1 (v/v)): d=9.15 (d, J=
8.2 Hz, 2H; b-H), 8.39 (d, J=4.7 Hz, 2H; b-H), 8.15 (d, J=4.7 Hz, 2H;
b-H), 7.84 (m, 4H; o-Ph), 7.81 (m, 4H; o-Ph), 7.42 (m, 8H; m-Ph), 7.30
(t, J=7.7 Hz, 4H; p-Ph), 3.67 (m, 8H; CH2), 0.96 ppm (t, J=7.1 Hz,
12H; CH3); 31P NMR (600 MHz, CDCl3/CD3OD, 1:1 (v/v)): d=
17.5 ppm; MS (MALDI TOF): m/z calcd for (C52H46N4O6P2Zn)+: 950.3;
found: 950 [M]+; IR (powder, micro-ATR): n˜ =1232 cmÀ1 (P=O); UV/
Vis (CHCl3): (loge) lmax =431 (5.03), 504 (sh), 525 (sh), 566 (3.62),
612 nm (3.58).
1
purple solid in 87% (23.5 mg) yield. H NMR (600 MHz, CDCl3/CD3OD,
1:1 (v/v)): d=9.05 (d, J=8.3 Hz, 1H; b-H), 8.51 (d, J=4.4 Hz, 1H; b-H),
8.47 (d, J=4.4 Hz, 1H; b-H), 8.39 (d, J=4.4 Hz, 1H; b-H), 8.26 (m, 3H;
b-H), 7.79 (m, 4H; o-Ph), 7.69 (m, 4H; o-Ph), 7.32 (m, 12H; m-Ph, p-
Ph), 3.60 (m, 4H; CH2), 0.88 (t, J=7.2 Hz, 6H; CH3), À3.00 ppm (s, 2H;
NH); 31P NMR (300 MHz, CDCl3/CD3OD, 1:1 (v/v)): d=16.5 ppm; MS
(MALDI TOF): m/z calcd for (C48H39N4O3P)+: 750.3; found: 751
[M+H]+; IR (powder, micro-ATR): n˜ =1245 cmÀ1 (P=O); UV/Vis
(CHCl3): (loge) lmax =424 (5.34), 489 (sh), 522 (4.02), 559 (3.56), 599
(3.53), 656 nm (3.65).
AHCTUNGTERG[NNUN 2,13-(Diethoxyphosphoryl)-5,10,15,20-tetraphenyl-porphyrinato]zinc
(6Zn): 1H NMR (600 MHz, CDCl3/CD3OD, 1:1 (v/v)): d=9.10 (d, J=
8.2 Hz, 2H; b-H), 8.46 (s, 2H; b-H), 7.96 (s, 2H; b-H), 7.82 (dd, J=7.7,
1.6 Hz, 4H; o-Ph), 7.74 (d, J=7.7 Hz, 4H; o-Ph), 7.33 (m, 12H; m-Ph, p-
Ph), 3.62 (m, 8H; CH2), 0.92 ppm (t, J=7.1 Hz, 12H; CH3); 31P NMR
(600 MHz, CDCl3/CD3OD, 1:1 (v/v)): d=17.5 ppm; MS (MALDI TOF):
m/z calcd for (C52H46N4O6P2Zn)+: 950.3; found: 950 [M]+; IR (powder,
micro-ATR): n˜ =1240 cmÀ1 (P=O); UV/Vis (CHCl3): (loge) lmax =433
(4.85), 500 (sh), 529 (sh), 566 (3.44), 612 nm (3.36).
[2-(Diethoxyphosphoryl)-5,10,15,20-tetraphenyl-porphyrinato]zinc (1Zn):
The same procedure as for ZnTPPBr was applied and yielded the prod-
1
uct in 78% (19,6 mg). H NMR (600 MHz, CDCl3/CD3OD, 1:1 (v/v)): d=
9.16 (d, J=8.2 Hz, 1H; b-H), 8.48 (m, 2H; b-H), 8.45 (m, 2H; b-H), 8.36
(d, J=4.5 Hz, 1H; b-H), 8.13 (d, J=4.5 Hz, 1H; b-H), 7.83 (m, 8H; o-
Ph), 7.40 (m, 12H; m-Ph, p-Ph), 3.66 (m, 4H; CH2), 0.95 ppm (t, J=
7.1 Hz, 6H; CH3); 31P NMR (600 MHz, CDCl3/CD3OD, 1:1 (v/v)): d=
18.2 ppm; MS (MALDI TOF): m/z calcd for (C48H39N4O3P)+: 752;
found: 750.8 [MÀZn+H]+; MS (MALDI TOF): m/z calcd for
(C48H37N4O3PZn)+; 812.2; found: 813 [M+H]+; IR (powder, micro-
ATR): n˜ =1228 cmÀ1 (P=O); UV/Vis (CHCl3): (log e) lmax =429 (5.49),
524 (sh), 562 (4.08), 604 nm (3.77).
[2-(Diisopropoxyphosphoryl)-5,10,15,20-tetraphenyl-porphyrinato]zinc
(3Zn): A 15 mL round bottom flask equipped with a reflux condenser
and a magnetic stir bar was charged with the (bromoporphyrinato)zinc
ZnTPPBr (20 mg, 0.026 mmol), CuI (15 mg, 0.079 mmol), and Cs2CO3
(121 mg, 0.370 mmol). The flask was then evacuated and purged with N2
three times. Toluene (abs., 3 mL), diisopropylphosphite (106 mL,
0.634 mmol), and dimethylethylenediamine (60 mL, 0.555 mmol) were
added through a syringe and the resulting mixture was heated to reflux
for 2 days until complete conversion of the bromide. The mixture was
then cooled and concentrated to give a solid, which was purified by
column chromatography on silica gel by using CH2Cl2 and methanol as
eluent. The purple fraction (CH2Cl2/methanol, 99:1 (v/v)) was collected
and evaporated to give 3Zn as a purple solid in 86% (18.9 mg) yield.
1H NMR (300 MHz, CDCl3/CD3OD, 3:2 (v/v)): d=9.24 (d, J=8.4 Hz,
1H; b-H), 8.59 (m, 2H; b-H), 8.55 (m, 2H; b-H), 8.45 (d, J=4.8 Hz, 1H;
b-H), 8.20 (d, J=4.8 Hz, 1H; b-H), 7.92 (m, 8H; o-Ph), 7.43 (m, 12H; m-
Ph, p-Ph), 4.36 (m, 2H; CH), 1.02 (m, 6H; J=6.2 Hz, CH3), 0.98 ppm
(m, 6H; J=6.2 Hz, CH3); 31P NMR (300 MHz, CDCl3/CD3OD, 3:2 (v/v)):
d=14.9 ppm; HRMS (ESI, positive mode): m/z calcd for
(C50H41N4NaO3PZn)+: 863.21000; found: 863.20792 [M+Na]+; IR
(powder, micro-ATR): n˜ =1230 (sh), 1213 cmÀ1 (P=O); UV/Vis (CHCl3):
(loge) lmax =431 (5.56), 565 (4.18), 607 nm (3.93).
[2-(Dibutoxyphosphoryl)-5,10,15,20-tetraphenyl-porphyrinato]zinc
(2Zn): A 15 mL round bottom flask equipped with a reflux condenser
and a magnetic stir bar was charged with the (bromoporphyrinato)zinc
ZnTPPBr (20 mg, 0.026 mmol), CuI (15.1 mg, 0.079 mmol), and Cs2CO3
(120.5 mg, 0.370 mmol). The flask was then evacuated and purged with
N2 three times. Toluene (abs., 3 mL), dibutylphosphite (124 mL,
0.634 mmol), and dimethylethylenediamine (60 mL, 0.555 mmol) were
added through a syringe and the resulting mixture was heated to reflux
for 12 h until complete conversion of the bromide. The mixture was then
cooled and concentrated to give a solid, which was purified by column
chromatography on silica gel by using CHCl3 and hexane as eluent. The
purple fraction (CHCl3/hexane, 60:40 (v/v)) was collected and evaporated
to give 2Zn as
a
purple solid in 94% (21.4 mg) yield. 1H NMR
(300 MHz, CDCl3/CD3OD, 1:1 (v/v)): d=9.16 (d, J=8.1 Hz, 1H; b-H),
8.48 (m, 4H; b-H), 8.36 (d, J=4.8 Hz, 1H; b-H), 8.13 (d, J=4.8 Hz, 1H;
b-H), 7.84 (m, 8H; o-Ph), 7.35 (m, 12H; m-Ph, p-Ph), 3.60 (m, 4H;
CH2), 1.30 (m, 4H; CH2), 1.03 (m, 4H; CH2), 0.58 ppm (t, J=7.4 Hz,
6H; CH3); 31P NMR (300 MHz, CDCl3/CD3OD, 1:1 (v/v)): d=18.1 ppm;
MS (MALDI TOF): m/z calcd for (C52H45N4O3PZn)+: 868.3; found: 870
[M+2H]+; IR (powder, micro-ATR): n˜ =1220 cmÀ1 (P=O); UV/Vis
(CHCl3):] (loge) lmax =430 (5.60), 527 (sh), 562 (4.18), 605 nm (3.85).
[2-(Dibutoxyphosphoryl)-5,10,15,20-tetraphenyl]porphyrin
(2H2):
A
15 mL round bottom flask equipped with a reflux condenser and a mag-
netic stir bar was charged with the bromoporphyrin H2TPPBr (18.5 mg,
0.026 mmol), PdACHTNUTRGNE(UNG OAc)2 (6 mg, 0.026 mmol), and PPh3 (21 mg,
0.08 mmol). The flask was then evacuated and purged with N2 three
times. Toluene (abs., 3 mL), dibutylphosphite (62 mL, 0.32 mmol), and
15102
www.chemeurj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 15092 – 15104

Zinc b-(Dialkoxyphosphoryl)porphyrins
FULL PAPER
triethylamine (56 mL, 0.4 mmol) were added through a syringe and the
resulting mixture was heated to reflux for 2 days until complete conver-
sion of the bromide. After cooling the mixture was concentrated to give
a solid, which was purified by column chromatography on silica gel by
using CH2Cl2 and methanol as eluent. The reddish-purple fraction
(CH2Cl2/methanol, 99.5:0.5 (v/v)) was collected and concentrated to give
2H2 as a purple solid in 92% (19.8 mg) yield. 1H NMR (300 MHz,
CDCl3/CD3OD, 3:2 (v/v)): d=9.12 (d, J=8.2 Hz, 1H; b-H), 8.65 (m, 2H;
b-H), 8.53 (d, J=5.0 Hz, 1H; b-H), 8.48 (m, 2H; b-H), 8.34 (d, J=
5.0 Hz, 1H; b-H), 7.94 (m, 8H; o-Ph), 7.48 (m, 12H; m-Ph, p-Ph), 3.63
(m, 4H; CH2), 1.34 (m, 4H; CH2), 1.08 (m, 4H; CH2), 0.63 ppm (t, J=
7.3 Hz, 6H; CH3); 31P NMR (300 MHz, CDCl3/CD3OD, 3:2 (v/v)): d=
16.2 ppm; HRMS (ESI, positive mode): m/z calcd for (C52H47N4NaO3P)+:
829.32835; found: 829.32813 [M+Na]+; HRMS (ESI, positive mode): m/z
calcd for (C104H94N8NaO3P)+: 1636.67028; found: 1636.66901 [2M+Na]+;
IR (powder, micro-ATR): n˜ =1250 (P=O), 3330 cmÀ1 (NH); UV/Vis
(CHCl3): (loge) lmax =424 (5.59), 523 (4.26), 558 (3.76), 599 (3.69),
656 nm (3.81).
Acknowledgements
This work was supported by the CNRS, the ARCUS Burgundy-Russia
project (2007–2010), the Russian Foundation for Basic Research (grant
no. 12-03-93110), and was carried out in the frame of the International
Associated French–Russian Laboratory of Macrocycle Systems and Re-
lated Materials (LAMREM) of CNRS. The authors thank Dr. A. N. Mo-
lokanov for helpful discussions concerning this work.
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Spectroscopic measurements: H, 13C, and 31P NMR spectra were record-
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X-ray crystallographic analysis: Single-crystal X-ray diffraction experi-
ments for complexes of 1Zn and 3Zn were carried out on a Bruker
SMART APEX II diffractometer with a CCD area detector (graphite
monochromator, MoKa radiation, l=0.71073 ꢂ, w scans). The single crys-
tals of 1Zn were slightly reflected in q>228. The attempts to grow single
crystals by slow evaporation from methanol/benzene/CHCl3 or methanol/
benzene/heptane at room temperature or 58C were unsuccessful; slow
diffusion of heptanes into methanol/benzene or methanol/benzene/CHCl3
also did not lead to the formation of single crystals. The OEt fragment
(O(2), C(45), C(46)) in 1Zn are disordered. There are disordered mole-
cules of methanol and water with a multiplicity 0.5 in the crystal packing
cell of 3Zn. The semi-empirical method SADABS was applied for the
absorption correction.[74] The structures were solved by direct methods
and refined by the full-matrix least-squares technique against F2 with the
anisotropic displacement parameters for all non-hydrogen atoms. All the
hydrogen atoms were placed geometrically and included in the structure
factors calculation in the riding motion approximation. All the data re-
duction and further calculations were performed by using the SAINT and
SHELXTL-97 program packages.[75,76] CCDC-842626 (1Zn) and CCDC-
842627 (3Zn) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
X-ray
108H86N8O6P2Zn2; monoclinic; crystal size: 0.06ꢃ0.03ꢃ0.02 mm; space
group C2/c; a=36.91(3), b=11.194(10), c=24.70(2) ꢂ; a=90, b=
122.78(2), g=908; V=8578(14) ꢂ3; Z=8(4), calcd =1.382 MgmÀ3
2qmax =136.48; T=173(2) K; m=1.084 mmÀ1
min =0.947; max =0.736;
crystal
structure
data
for
(1Zn)2·2C6H6:
Formula:
C
D
;
;
T
T
35256 measured reflections; 16846 independent reflections (Rint
0.1566); 7463 refined parameters; R=0.0917; wR2 =0.1524.
=
X-ray crystal structure data for (3Zn)2·H2O·CH3COOH: Formula:
104H100N8O12P2Zn2; triclinic; crystal size: 0.14ꢃ0.12ꢃ0.10 mm; space
C
¯
group P1; a=11.552(2), b=13.355(3), c=16.383(3) ꢂ; a=83.292(3), b=
72.131(3), g=79.394(3)8; Z=2(1); Dcalcd
V=2359.6(8) ꢂ3;
1.288 MgmÀ3; 2qmax =136.48; T=173(2) K; m=1.084 mmÀ1; Tmin =0.947;
max =0.736; 35256 measured reflections; 19300 independent reflections
(Rint =0.0859); 8273 refined parameters; R1=0.0717; wR2 =0.1647.
=
T
Chem. Eur. J. 2012, 18, 15092 – 15104
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
15103

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Received: July 23, 2012
Published online: October 5, 2012
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