Meso-Tetraphenylporphyrin-derived oxypyriporphyrin, oxypyrichlorin, and thiomorpholinochlorin, as their Ni(II) complexes

Article abstract of DOI:10.1142/S1088424612500654

trans-Diolchlorin was prepared by nucleophilic addition of methyl-Grignard bromide to meso-tetraphenyl-2,3-dioxoporphyrin, as its free base or Ni(II) complex. The trans-configuration of the vic-diol functionality was shown by single crystal X-ray diffractometry. The nickel complex of the trans-dimethyldiol proved susceptible to Pb(IV) acetate-induced, oxidative diol cleavage, generating a meso-tetraphenylsecochlorin bismethylketone Ni(II) complex, the first example of this chromophore class. Under Br?nsted- basic conditions, this bisketone cyclized via an intramolecular aldol condensation to provide a meso-tetraphenyloxypyriporphyrin. Reduction of this porphyrin analog saturated the double bond in the pyridinone moiety, generating an oxypyrichlorin. Reaction of the meso-tetraphenylsecochlorin bismethylketone Ni(II) complex with Lawesson's reagent induced the formation of a thiomorpholinochlorin substituted with two methylene groups, the first example of any porphyrin analog containing a thiomorpholine moiety.

Full text of DOI:10.1142/S1088424612500654

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2012; 16: 576–588
DOI: 10.1142/S1088424612500654
Published at http://www.worldscinet.com/jpp/
meso‑Tetraphenylporphyrin‑derived oxypyriporphyrin,
oxypyrichlorin, and thiomorpholinochlorin, as their Ni(II)
complexes
Subhadeep Banerjeea, Matthias Zellerb and Christian Brückner*a◊
a Department of Chemistry, University of Connecticut, Unit 3060, Storrs, CT 06269-3060, USA
b Department of Chemistry, Youngstown State University, One University Plaza, Youngstown, OH 44555-3663, USA
Dedicated to Professor Emanuel Vogel in memoriam
Received 10 November 2011
Accepted 8 February 2012
ABSTRACT: trans-Diolchlorin was prepared by nucleophilic addition of methyl-Grignard bromide
to meso-tetraphenyl-2,3-dioxoporphyrin, as its free base or Ni(II) complex. The trans-configuration of
the vic-diol functionality was shown by single crystal X-ray diffractometry. The nickel complex of the
trans-dimethyldiol proved susceptible to Pb(IV) acetate-induced, oxidative diol cleavage, generating a
meso-tetraphenylsecochlorin bismethylketone Ni(II) complex, the first example of this chromophore
class. Under Brønsted-basic conditions, this bisketone cyclized via an intramolecular aldol condensation
to provide a meso-tetraphenyloxypyriporphyrin. Reduction of this porphyrin analog saturated the
double bond in the pyridinone moiety, generating an oxypyrichlorin. Reaction of the meso-tetraphenyl-
secochlorin bismethylketone Ni(II) complex with Lawesson’s reagent induced the formation of a
thiomorpholinochlorin substituted with two methylene groups, the first example of any porphyrin analog
containing a thiomorpholine moiety.
KEYWORDS: tetraphenylporphyrin, diolchlorins, secochlorins, porphyrinoids, thiomorpholines,
oxypyriporphyrins.
For the majority of these applications it is desirable
INTRODUCTION
to tune the photophysical properties of the chromophore.
The physical and chemical properties of tetrapyrrolic
The methodologies that can be employed to modulate
macrocycles in nature are modified by the degree
the electronic properties of synthetic porphyrinoids may
of saturation of the macrocycle, as in chlorins (2,3-
mimic nature [7], but can also go beyond the strategies
dihydroporphyrins), by variation of their conformation
realized in nature. Thus, contracted [8] and expanded [9]
(either through macrocycle-protein interactions or through
porphyrins, i.e. porphyrins containing fewer or more than
variation of the native conformation of the macrocycle),
four pyrroles, and porphyrins containing annulated ring
and by variation of the substituents on the macrocycle
periphery [1]. Synthetic porphyrins, chlorins, and their
systems that expand the porphyrin p-system are known
[10]. Also, porphyrin isomers were reported, such as the
analogs, are of potential utility in a number of applications
porphycenes and corrphycenes firstly described by Vogel
that range from their use as photo-chemotherapeutics [2],
and co-workers [11]. Porphyrin analog containing other
optical labels in biology [3], components in functional
atoms in place of a pyrrole nitrogen (carbaporphyrins,
devices [4], light harvesting dyes [5], or catalysts [6].
thiaporphyrins, selenaporphyrins, etc.) [12] and porphy-
rinoids containing additional heteroatoms in place of
the carbon within the porphyrin framework are also
known [13]. Lastly, porphyrinoids were described in
SPP full member in good standing
which a pyrrolic moiety was expanded by a carbon or
heteroatom. We broadly refer to the latter categories of
*Correspondence to: Christian Brückner, email: c.bruckner@
uconn.edu, fax: +1 860-486-2981, tel: +1 860-486-2743
Copyright © 2012 World Scientific Publishing Company

MESO–TETRAPHENYLPORPHYRIN-DERIVED OXYPYRIPORPHYRIN
577
O
porphyrinoids as pyrrole-modified porphyrins. Examples
include porphyrins containing non-pyrrolic heterocycles
such as azetes [14, 15], oxazoles [16–20], imidazoles
[21, 22], pyrazoles [23], pyrazines [24], or morpholines
[20, 25–28].
Ph
Ph
CO2R
OMe
NH
N
NH
N
N
Ph
Ph
Ph
Ph
N
HN
HN
The bulk of these porphyrinoids are made by total
synthesis, i.e. they are synthesized in one or more steps
from mono-pyrrolic precursors [11, 12, 29]. We, and
others, developed alternative synthetic strategies that
allow the insertion or removal of single atoms into, or
out of, the porphyrinic macrocycle [15, 18–21, 25,
27, 28, 30, 31]. These syntheses sometime provided
complementary routes toward the same chromophore
classes that were pioneered using total syntheses (e.g.
octaalkyloxypyriporphyrins) [30, 32, 33], but frequently
they provided access to chromophores not previously
described [30], particularly when considering meso-
tetraarylporphyrin-derived porphyrinoids [15–17, 19, 20,
22, 28, 31, 34, 35].
1
2
Ph
Ph
O
OEt
Ph
Ph
O
O
O
OEt
Ph
NH
N
N
NH
N
N
Ph
Ph
Ph
HN
HN
3
4
Ph
Ph
The earliest examples of porphyrinoids prepared
by atom insertion or replacement reactions of a
porphyrin were the result of fortuity [16, 17, 32, 36].
For example, Callot and Schaeffer reported a Ni(II)-
induced rearrangement of an N-substituted meso-
tetraphenylporphyrin that resulted in a ring expansion
to form azine-modified porphyrin 1 [36]. These reports
demonstrated the principle possibility of expanding
a porphyrin framework by inserting an atom into a
porphyrin and set the stage for more rational explorations.
For instance, methoxy-substituted oxypyriporphyrin
2 (as a mixture of inseparable regioisomers) was
prepared by Pandey and co-workers by design in the
form of diazomethane addition to meso-tetraphenyl-
2,3-dioxoporphyrin [37]. Crossley and King reported the
expansionofapyrrolicsubunitinaporphyrinbysubjecting
Ni(II) complex, to form octaalkyloxypyriporphyrin
Ni(II) complex 7Ni (Scheme 1) [32]. Oxidative cleavage
of the diol moiety in [octaethylchlorinato]Ni(II) 5Ni
generated secochlorin diketone 6Ni that, however, could
not be isolated but underwent an aldol condensation
to form oxypyriporphyrin 7 under all reactions
conditions tested [32]. The corresponding free base
oxypyriporphyrin 7 was prepared along an analogous
pathway [30]. In contrast to the octaethylporphyrin-
derived secochlorins 6 and 6Ni, tetraaryl-porphyrin-
based secochlorin bisaldehydes 14 and 14Ni could both
be isolated [14, 18, 38].
We see considerable synthetic potential for a hitherto
elusive bisketone secochlorin of type 6 for use in the
preparation of novel pyrrole-modified porphyrins
if it could be prevented from undergoing an aldol
cyclization. Since methylketones are of lesser CH-acidity
than ethylketones, we set out to prepare such a bis-
methylketone secochlorin to answer the question whether
it would be suitable for the formation of pyrrole-modified
porphyrins.
meso-tetraphenyl-2,3-dioxoporphyrin to
a
Baeyer–
Villiger oxidation, thus generating the porphyrin-like
anhydride 3 [16]. Lastly, morpholinochlorins, such as 4,
chlorin-analogs of remarkable conformational flexibility,
were prepared from meso-tetraphenylporphyrin along
rational multi-step routes [20, 25–28, 35].
Bonnett and co-workers firstly described the step-
wise functionalization of octaethylporphyrin, as its
O
O
OH
OH
O
N
N
N
N
N
N
N
N
N
N
N
M
M
M
N
5, M = 2H
5Ni, M = Ni(II)
6, M = 2H
6Ni, M = Ni(II)
7, M = 2H
7Ni, M = Ni(II)
Scheme 1. Synthesis of octaalkyloxypyriporphyrin by oxidation and subsequent aldol condensation of a diolchlorin
Copyright © 2012 World Scientific Publishing Company
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578
S. BANERJEE ET AL.
We will detail here our investigations to this end.
In short, we will describe the synthesis of a meso-
tetraphenylporphyrin-derived bis-methylketone seco-
chlorin and studies with respect to its conversion to
in 78% yield. It possessed, as expected, a chlorin-
like UV-vis spectrum that was very similar to that of
diolchlorin 8 (Fig. 1). An HR-MS (ESI+) confirmed the
uptake of two methyl groups and two hydrogens by the
starting material. The presence of methyl groups and
meso-tetraphenylporphyrin-derived
pyrrole-modified
1
chromophores containing six-membered rings, namely
oxypyri-porphyrin, -chlorins, and an altogether novel
thiomorpholinochlorin. Incidentally, we also report
the assignment of the relative stereochemistry of the
b-substituents of an intermediate trans-diolchlorin by
single crystal X-ray diffraction.
2-fold symmetry of 10 were indicated by its H (1.73
ppm, s, 6H) and 13C NMR (25.7 ppm, s, total 21 signals
corresponding to one half of the molecule plus the
methyl group) spectra. Thus, all spectral and analytical
data point toward the formation of tertiary diolchlorin 10,
the product expected based on the findings of Stark and
Wiehe [44].
Free base diol 10 is susceptible to Ni(II) insertion,
generating 10Ni. However, since this reaction is sluggish
(requiring 48 h at pyridine reflux temperatures in the
presence of a 10-fold excess of Ni(II) acetate), the Ni(II)
diol complex is preferably made by MeMgBr addition to
the Ni(II) dioxo complex 9Ni. This Grignard addition to
RESULTS AND DISCUSSION
Retrosynthetic analysis of
secochlorin
a
bismethylketone
Retrosynthetically, a bismethylketone secochlorin (I)
can be derived by oxidatively cleaving a b,b′-dimethyl-
b,b′-dihydroxychlorin (II), itself the product
of the dihydroxylation of the correspon-
ding b,b′-dimethylporphyrin (III), such as
meso-tetraphenyl-b-octamethylporphyrin
(Scheme 2) [39]. We excluded octame-
thylporphyrin from consideration because
of its relative insolubility under neutral
conditions [40].
An alternative pathway in which the
b-methyl substituents are introduced later in
the synthetic sequence seemed also attractive
(Scheme 2). A diol chlorin V, generated
by dihydroxylation of a tetraarylporphyrin
VI, is oxidized to the corresponding dione
IV [41, 42]. Alternatively, a number of
complementary pathways toward meso-
tetraaryl-2,3-dioxoporphyrins are available
[16, 43]. Dione IV is then subjected to
O
Ar
M
Ar
M
Ar
OH
OH
O
O
O
N
N
N
M
Ar
Ar
Ar
(IV)
(I)
(II)
OH
Ar
OH
Ar
N
M
(V)
Ar
M
Ar
M
N
a
double methyl-Grignard addition,
a
N
reaction recently described by Stark, Wiehe,
and co-workers [44]. They reported the
preparation of meso-tetraaryl-2,3-dialkyl/
aryl-2,3-dihydroxychlorins 10a by addition
of Grignard reagents to meso-tetraaryl-2,3-
dioxoporphyrin 9a (Scheme 3). Cleavage of
the tert-diol functionality in II would gene-
rate the target meso-tetraphenylsecochlorin
dimethylketone.
Ar
Ar
(III)
(VI)
Scheme 2. Retrosynthetic analysis of a secochlorin bisketone (I)
R
O
Ar
Ar
OH
OH
O
R
NH
N
N
NH
N
N
RMgBr
Ar
Ar
Ar
Ar
Synthesis of trans-vic-diolchlorin 10
HN
HN
Reaction of the non-polar dioxochlorin
9 [42], itself prepared by oxidation of
the corresponding cis-diolchlorin 8 [25],
with excess MeMgBr in THF at ambient
temperature results in the consumption of the
starting material (TLC control) within 5 min.
The purple, polar product 10 was isolated
Ar
9a, Ar = 3-MeOPh
Ar
10a, Ar = 3-MeOPh,
R = n-C6H13, 3,5-(CF3)2-Ph, CF3
Scheme 3. The synthesis of 2,3-dimethyl-2,3-dihydrocychlorin 10a as
described by Stark, Wiehe, and co-workers [44]
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MESO–TETRAPHENYLPORPHYRIN-DERIVED OXYPYRIPORPHYRIN
579
the nickel(II) complex 9Ni proceeds as smoothly as for
the free base, and the spectroscopic and analytical results
for the product parallel those found for the free base.
Also, the oxidation of known nickel diolchlorin 8Ni [25]
to form dione 9Ni is unproblematic [42].
Single crystal X-ray structure of trans-vic-diolchlo-
rins 10 and 10Ni
The solid state structure of diol chlorin 10 and its
nickel complex 10Ni were determined by single crystal
X-ray diffractometry (Fig. 2). The structures prove them
to be trans-vic-diols, the diol configuration that might
be expected based on the mechanism of their formation.
This finding implies that the diol chlorins described by
the groups of Stark and Wiehe are also trans-configured
[44]. Interestingly, we were also able to gather chemical
findings suggesting the trans-diol configuration in
10/10Ni (see Fig. 2).
The conformation of the macrocycle of free base
diol deviates only little from the mean plane, with the
largest deviation in the pyrrolidine moiety that is due to
the avoidance of an eclipsed conformation of the cis-
substituents. The dihedral angle between a methyl group
and its neighboring hydroxy groups is 35.4°. This is
significantly larger than the corresponding 17° dihedral
angle between the methoxy groups and the much smaller
Fig. 1. Comparison of the UV-vis spectra (CH2Cl2) of (a) free
base trans-diol 10 with cis-diol chlorin 8; (b) trans-diol nickel
complex 10Ni with cis-diol chlorin nickel complex 8Ni
Fig. 2. X-ray crystal structure of 10 and 10Ni. (A) and (D): Top views, sp2 hydrogen atoms omitted for clarity. (B) and (E): Front
view, along one Npyrrolidine–N and Npyrrolidine–Ni–N axis, respectively; meso-phenyl groups and sp2 hydrogen atoms omitted for clarity.
(C) and (F): Side view along Npyrrole–Npyrrole and Npyrrole–Ni–Npyrrole axis, respectively; meso-phenyl groups and sp2 hydrogen atoms
omitted for clarity. For 10, only one of the two crystallographically independent molecules is shown. The disorder of the diol unit
inherent to both structures (12%) also omitted for clarity
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 579–588

580
S. BANERJEE ET AL.
neighboring hydrogens in meso-tetraphenyl-cis-2,3-
dimethoxychlorin [45].
chlorin nickel complex 10Ni 1.908 Å, a value very close
to that of nickel chlorophin (1.910 Å) [14, 38].
The increased deviation from planarity of 10 compared
to meso-tetraphenyl-cis-2,3-dimethoxychlorin may be
the origin of the slightly bathochromically shifted UV-vis
spectra of 10 (and 10Ni) (Fig. 1), although we cannot
rule out electronic influences. We have previously shown
the UV-vis spectra of chlorins to be particularly sensitive
toward substitution at their benzylic positions [45].
On account of the small ion size of the square planar
d8-ion Ni(II), Ni(II) porphyrin and chlorin complexes are
generally ruffled [46]. This is also observed for 10Ni,
but this does not lead to a significantly larger dihedral
angle between the cis-configured hydroxy and methyl
groups (36.3°) compared to the free base. A comparison
of the solid state conformations of the macrocycles in
terms of the deviation of the C20N4 macrocycle in [meso-
tetraphenylporphyrinato]Ni(II), [meso-tetraphenyl-2,3-
dioxochlorinato]Ni(II) 9Ni, and the Ni(II) chlorinato
complex 10Ni illustrates the influence of the saturation
and concomitant larger conformational flexibility of the
macrocycles. In pure ruffling deformation modes, the
average Ni–N bond distance can be used a measure of
the degree of deformation, with shorter bond distances
indicating larger degrees of ruffling. The average Ni–N
bond distance in the nickel porphyrin is 1.931 Å [47], in
the nickel dioxochlorin 9Ni 1.939 Å [42], and in the diol
Oxidative cleavage of trans-diols 10 and 10Ni
The oxidative cleavage of free base 10 using freshly
recrystallized Pb(OAc)4 only yielded an intractable
mixture of unidentifiable products, paralleling the findings
by Bonnett for the oxidative diol cleavage of free base
octaethyl-cis-diolchlorin [32]. To our initial surprise, the
method we developed to bring about this cleavage in free
base octaethyl-cis-diolchlorin (NaIO4 heterogenized on
silica gel under basic conditions) [18] failed to bring about
any reaction. Considering the selectivity of periodates for
the oxidation diols that can adopt a cis-conformation [48],
however, this finding is a direct chemical indicator for the
trans-configuration of diol 10Ni.
In previous examples in which secochlorins were
prepared by the oxidative cleavage of diolchlorins,
nickel(II) complexation greatly stabilized the seco-
chlorin. This also proved to be the case here. Thus,
treatment of polar green trans-diolchlorin nickel
complex 10Ni with 3 eq of Pb(OAc)4 in THF generated
a non-polar, brown product that could be isolated
in 66% yield (Scheme 4). Its HR-MS indicated the
expected composition of secochlorin bisketone 11Ni.
Its UV-vis spectrum is reminiscent of the characteristic
OH
O
Ph
Ph
Ph
OH
Me
OH
OH
Ph
O
Me
N
N
N
N
N
N
N
N
N
N
N
N
(i)
(ii)
M
M
M
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
8, M = 2H
8Ni, M = Ni(II)
9, M = 2H
9Ni, M = Ni(II)
10, M = 2H
10Ni, M = Ni(II)
(iii)
for 10Ni (iv)
O
O
Ph
Ph
Ph
O
Me
Ph
N
N
N
N
N
N
N
N
N
N
N
N
O
Ph
(vi)
(v)
Ni
Ni
Ni
Ph
Ph
Ph
Ph
Ph
Ph
Ph
13Ni
12Ni
11Ni
Reaction Conditions: (i) DDQ, D.[42] (ii) for M = 2H: 1. MeMgBr, THF, 2. ~2% TFA in CH2Cl2 3. Et3N; for M = Ni(II): 1. MeMgBr,
THF, 2. H2O.[44] (iii) Ni(OAc)2, pyridine, D, 48 h. (iv) Pb(OAc)4, THF, rt (v) DBU, CH2Cl2. (vi) L-selectride, THF, -78° C to rt
Scheme 4. Synthesis and cyclization of secochlorin bisketone 11Ni
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MESO–TETRAPHENYLPORPHYRIN-DERIVED OXYPYRIPORPHYRIN
581
Fig.3.UV-visspectralcomparison(CH2Cl2)ofmeso-tetraphenyl-
secochlorin bisketone 11Ni and meso-tetraphenylsecochlorin
bisaldehyde 14Ni
Fig. 4. Partial 1H NMR spectrum (400 MHz, CDCl3, rt) of 11Ni
and its assignments; * indicates residual CHCl3
compound is an hybrid between the meso-tetraphenyl-
secochlorin bisaldehyde 14 and octaethylsecochlorin
bisketone 6. This compound expands the short list of
secochlorins that have become known and that include
Sessler’s photochemically prepared secochlorin ester
15 [49], Hoffman’s secoporphyrazine 16 [50], and
Chang’s secochlorin 17, the historically first example of
a porphyrinoid with a broken b,b′-bond [51].
spectrum of the corresponding secochlorin bisaldehyde
14Ni (Fig. 3), though it is overall slightly blue-shifted
(lmax = 665 nm) and features only a single broad Soret
band at 453 nm.
1
The H and 13C NMR spectra of 11Ni also supported
the expected secochlorin bisketone structure. The spectra
indicate the presence of a porphyrin of overall two-fold
symmetry with a symmetrically modified b,b′-position
(two doublets and one singlet for the b-protons) (Fig. 4).
A methylketone functionality is indicated by a methyl
group at 1.54 and 25.6 ppm, with a signal at 198.1 ppm
assigned to the carbonyl group. The latter functionality is
also expressed in the IR spectrum of this compound (vC=O
at 1681 cm-1).
Reactivity of secochlorin bismethylketone 11Ni
Formation of oxypyriporphyrin 12Ni. The ability to
isolate 11Ni indicates that it possesses, as hypothesized,
a lower reactivity toward an intramolecular aldol
reaction than secochlorin bisethylketone 6Ni. However,
treatment of 11Ni with DBU rapidly converts it to a new
Compound 11Ni is the first example of a meso-
tetraphenylsecochlorin bisketone. Structurally, this
Me2N
Ar
CONMe2
N
CHO
Me2N
CONMe2
CHO
NH
N
N
N
N
N
N
N
N
M
Ar
Ar
HN
Me2N
NMe2
N
Me2N
NMe2
Ar
14, M = 2H
14Ni, M = Ni(II)
16
O
CO2Me
Ac/HO(CH2)3
CO2Me
NH
N
N
N
N
N
Ni
HN
N
(CH2)3OH/Ac
15
17
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582
S. BANERJEE ET AL.
1
compound in 90% yield that we could, based on its H
and 13C NMR spectra (presence of a ketone functionality
indicated by a peak at 195.1 ppm), composition as per
HR-MS (C46H31N4NiO for [MH+]), and IR (vC=O at
1670 cm-1) identify as the aldol condensation product
oxypyriporphyrin 12Ni (Scheme 4). It is noteworthy
that even in the presence of a strong nucleophile like
hydrazine, meso-tetraphenylsecochlorin bisketone 11Ni
also formed aldol product 12Ni rather than a product
resulting from a nucleophilic addition of hydrazine to the
ketone functionalities. Again, this mirrors findings on the
octaethylporphyrin-based secochlorins [32].
“benzylic position” with respect to the porphyrinoid
p-system, stabilizing the charge, but thereby also
strongly affecting the chromophore (Scheme 5). meso-
Tetra(p-dimethyl-phenyl)porphyrins exhibit similar
hyperporphyrin spectra upon protonation as the cationic
charge is delocalized into the porphyrinic chromophore
and transitions between orbitals associated with the
substituents and the porphyrinic orbitals emerge [52].
Formation of oxypyrichlorin 13Ni. Oxypyriporphyrin
12Ni can be reduced using L-selectride to produce a new
dark green product in 89% yield (Scheme 4). The UV-vis
spectrum of this product is metallochlorin-like, with a Soret
band at 439 nm and a single Q-band at 647 nm (Fig. 6).
Figure 5 shows the UV-vis spectrum of oxypyriporph-
yrin 12Ni. It is, like that of the octaethylporphyrin
derived analog 7Ni, metalloporphyrin-like, though
slightly (~15 nm) red-shifted, with a sharp Soret band
at 453 nm and two nearly equal intensity Q-bands at 581
and 627 nm. Remarkably, addition of acid (2% TFA in
CH2Cl2) to 12Ni results in a dramatic shift of its UV-vis
spectrum (Fig. 5). The two Q-bands of 12Ni seen under
neutral conditions merge to one band that is ~84 nm red-
shifted (lmax = 711 nm). This shift is fully reversible upon
neutralization (with Et3N). Since the inner nitrogens are
protected by the Ni(II) center, we believe that pyridinone
12Ni is protonated at the ketone oxygen and that the
positive charge is stabilized by the resonance structure
shown that places the cationic charge onto the tertiary
carbon within the pyridinone. This carbon is also in a
1
The H and 13C NMR spectra of this product clearly
demonstrated that the reduction of the double bond of the
a,b-unsaturated ketone within the pyridinone moiety had
taken place. Retention of the ketone group was indicated
by a peak at 207.1 ppm, while its IR stretching frequency
shifted from 1670 cm-1 in pyridinone 12Ni to 1701 cm-1
for the new product, indicating the loss of conjugation
[53]. The signal in the alkene region of 12Ni that was
assigned to the single pyridinone hydrogen was replaced
by three signals, at 4.02 ppm (m, 1H), 3.37–3.28 ppm
(dd, 1H), and 3.13 ppm (d, 1H), assigned to a single
benzylic and two a-keto hydrogen atoms. The methyl
group now attached to an sp3-carbon shows a resonance
at 1.27 ppm (d, 3H) compared to the corresponding signal
in 12Ni at 1.54 ppm. Also, the methyl group attached
to the sp3-carbon atom introduces a face differentiation
in 13Ni into an upper and lower hemisphere above and
below the plane of the porphyrin. This rationalizes the
two well separated signals for the diastereotopic a-keto
hydrogen atoms. Thus, the reduction product can be
unambiguously identified as oxypyrichlorin 13Ni.
The intramolecular aldol reaction of free base
octaethylporphyrin-derived secochlorin 6 formed an
intermediate alcohol before it dehydrated to the final
aldol condensation product 7 [30]. This alcohol, the
free base octaalkylporphyrin-based analog to 13Ni, also
possessed a sp3-hybridized morpholine-b-carbons and a
chlorin-like optical spectrum.
Concentrations of acids that protonate 12Ni show no
affect on the chromophore of 13Ni, and even 10-fold
higher TFA concentrations do not effect protonation.
Fig. 5. UV-vis spectrum of pyridinone porphyrin 12Ni in
CH2Cl2 and acidified with 2% TFA
H
H
O
O
Ph
Ph
Me
Ph
Me
N
N
N
N
N
N
N
N
H+
Ni
Ni
12Ni
Ph
Ph
Ph
Et3N
12Ni·H+
Ph
Ph
Scheme 5. Acid-induced resonance forms of protonated pyridinone porphyrin 12Ni
Copyright © 2012 World Scientific Publishing Company
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MESO–TETRAPHENYLPORPHYRIN-DERIVED OXYPYRIPORPHYRIN
583
Fig. 6. UV-vis spectrum (CH2Cl2) of oxypyrichlorin 13Ni and
thiomorpholine 18Ni
This is readily rationalized. The absence of the a,b-
conjugated ketone in 13Ni does not provide an ability to
delocalize a cationic charge resulting from protonation of
the ketone and consequently, chlorin 13Ni cannot be as
readily protonated as 12Ni.
Fig. 7. 1H NMR spectrum (400 MHz, CDCl3, rt) of 18Ni and its
assignments; * indicates residual CHCl3
Formation of thiomorpholinochlorin 18Ni
Lawesson’s reagent converts carbonyl groups in
ketones, esters, amides, lactone and lactams to their
thionated analogs [54, 55]. When we reacted brownish
secochlorin bisketone Ni(II) complex 11Ni with a
several-fold stoichiometric excess of Lawesson’s reagent
in refluxing toluene, the rapid formation of a non-polar
green product is observed. The composition of this
compound was, as determined by HR-MS (ESI+ 100%
CH3CN), C46H30N4NiS, i.e. corresponding to the starting
material that underwent a O-to-S exchange and a loss of
one equivalent of water.
the bisketone to a monothioketone-monoketone (or bis-
thioketone) is followed by a nucleophilic ring-closure
initiated by the enthiol form of the thioketone. This ring-
closure is not unlike that observed during the formation of
the morpholinochlorins [28]. Finally, loss of H2O (or H2S)
establishes the thiomorpholine moiety carrying the two
exocyclic double bonds. Cyclizations of 1,4-bisketones
to thiophenes upon reaction with Lawesson’s reagent are
known [54].
While the thiomorpholine structure for 18Ni
rationalizes most spectroscopic and analytical data,
the non-equivalency of the two o- and m-hydrogens
on the phenyl groups adjacent to the thiomorpholino
moiety require an additional explanation. Nickel(II)
porphyrins are, on account of the small low-spin Ni(II)
ion radius, ruffled. Ni(II) complexes of secochlorins
and morpholinochlorins are, as demonstrated by
multiple examples, particularly ruffled [25, 28]. Thus,
[thiomorpholinochlorinato]Ni(II) complex 18Ni can
reasonably be expected to be also ruffled. This confor-
mational mode orients one methylene groups up and the
other methylene group down relative to the mean plane
of the porphyrin, giving rise to a face differentiation of
the adjacent phenyl groups.
The UV-vis spectrum of this compound is
metallochlorin-like, with some resemblance to the
spectrum of [morpholinochlorinato]Ni(II) [25], though it
is more red-shifted than the latter (lmax = 665 nm) (Fig. 6).
1
Figure 7 shows the H NMR spectrum of compound
1
18Ni. In comparison to the H NMR spectrum of the
starting material 11Ni (Fig. 4), it becomes evident that
the compound is also two-fold symmetric (two doublets
and one singlet assigned to the b-protons characteristic
for two-fold symmetric porphyrins) but that the spectrum
is spread over a wider chemical shift range. Moreover,
one set of phenyl groups — presumably the phenyl
groups adjacent to the pyrrole-modification site — is
differentiated from the other, and its o- and m-protons
are differentiated into two sets each (for the o-protons,
two d at 8.56 and 6.81 ppm, 2H each). No hydrogens
attached to sp3-carbons are detectable. Instead, two
singlets suggestive of the presence of a methylene group
(s 5.31, 2H, and 4.23 ppm, 2H) are observed, suggestive
of the thiomorpholinochlorin structure shown.
Thiaporphyrins, porphyrins in which one or more
nitrogens of the porphyrin are replaced by sulfurs are
well-known [12], as are meso-thienylporphyrins [56].
Also, sulfur-containing ring-expanded tetrapyrrolic
macrocycles were described [57], but as far as we are
aware of, 18Ni is the first porphyrinoid containing a
thiomorpholine moiety, and the first example in which
a sulfur atom was inserted into a preformed porphyrin.
The putative mechanism of formation of 18Ni is
straight forward (Scheme 6). The initial conversion of
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 583–588

584
S. BANERJEE ET AL.
Ph
Ni
Ph
Ni
S
O
N
N
N
N
N
N
N
O
Ph
(i)
Ph
Ph
Ph
N
Ph
Ph
11Ni
18Ni
– H2X
Ph
Ph
Ph
S
SH
S
N
N
N
XH
Ph
O
Ph
X
Ph
Ni
Ni
Ni
Reaction conditions: (i) Lawesson’s reagent, toluene, reflux, 15 min.
Scheme 6. Formation of thiomorpholinochlorins 18Ni
metallochlorin-like. After the starting material was
EXPERIMENTAL
consumed (reaction control by TLC, silica gel-CH2Cl2),
theexcessGrignardreagentwasquenchedwithTFA(~2%
solution in CH2Cl2, 5 mL), followed by neutralization
with Et3N (~3 mL). At this stage, the UV-vis spectrum
of the crude reaction mixture was free base chlorin-like.
The reaction mixture was diluted with CH2Cl2 (20 mL),
taken up in a separatory funnel, and washed with water
(5 × 10 mL). The organic layer was separated, dried
over anhydrous Na2SO4 and concentrated by rotary
evaporation. The crude product was purified over a silica-
gel column (CH2Cl2). The major fraction was collected
and evaporated to dryness to yield a dark blue powder.
Yield 61–78%. Rf (silica-CH2Cl2) = 0.31. 1H NMR (400
MHz, CDCl3, Me4Si): d, ppm 8.56 (d, 3J = 4.8 Hz, 2H),
Materials and instruments
All solvents and reagents (Aldrich, Acros, CIL) were
used as received. Analytical (aluminum backed, silica gel
60, 250 µm thickness) and preparative (20 × 20 cm, glass
backed, silica gel 60, 500 µm thickness) TLC plates, and
the flash column silica gel (premium grade, 60 Å, 32–63
µm) used were provided by Sorbent Technologies, Atlanta,
GA. 1H and 13C NMR spectra were recorded on a Bruker
DRX400 or a Bruker Avance 300 MHz instrument. High
and low resolution mass spectra were provided by the Mass
Spectrometry Facilities at the Department of Chemistry,
University of Connecticut. UV-vis spectra were recorded
on a Cary 50 spectrophotometer, Varian Inc, and IR spectra
on a JASCO FT-IR-410 using an ATR attachment.
Free base meso-tetraphenyl-b,b′-dioxoporphyrin 9,
or its Ni(II) complex 9Ni, were prepared by DDQ
oxidation of the corresponding cis-vic-diolchlorin
8 or 8Ni, respectively [42], which themselves were
prepared by OsO4-mediated dihydroxylation of meso-
tetraphenylporphyrin [25].
3
8.45–8.43 (d, J = 7.6 Hz, 2H, overlapping with s, 2H),
3
8.24 (br s, 2H), 8.06 (d, J = 4.8 Hz, 2H), 7.93 (br s,
2H), 7.79 (t, 3J = 7.6 Hz, 2H), 7.70 (m, 8H), 7.57 (t, 3J =
7.6 Hz, 2H), 7.51 (d, 3J = 7.6 Hz, 2H), 1.73 (s, 6H), -1.40
(br s, 2H). 13C NMR (100 MHz, CDCl3, D1 = 4 s, Me4Si):
d, ppm 162.6, 152.8, 141.7, 140.0, 135.3, 133.8, 133.7,
133.3, 132.4, 128.2, 127.9, 127.7, 127.3, 127.2, 126.7,
124.0, 123.3, 112.2, 88.5, 25.7. UV-vis (CH2Cl2): lmax
,
nm (log e) 370 (sh) 417 (5.14), 519 (4.04), 546 (3.92),
597 (3.62) 651 (4.30). HR-MS (ESI+, 100% CH3CN):
m/z 677.2902 (calcd. for C46H37N4O2 [MH]+ 677.2917).
[meso-tetraphenyl-trans-2,3-dimethyl-2,3-dihydro-
xychlorinato]Ni(II) 10Ni. Prepared as a dark green
crystalline material along the procedure described
for its free base analog 10. Alternatively, Ni(II) can
be inserted according to a procedure described for
[meso-tetraphenyl-cis-2,3-dihydroxychlorinato]Ni(II)
but requiring a ~10-fold stoichiometric excess of Ni(II)
and several days of heating to reflux [25]. Yield 77–86%.
Preparation of compounds
meso-tetraphenyl-trans-2,3-dimethyl-2,3-dihydro-
xychlorin 10. To a solution of meso-tetraphenyl-2,3-
oxoporphyrin 9 (30 mg, 4.60 × 10-5 mol) in dry THF
(6 mL) at ambient temperature was added slowly a
solution of MeMgBr (500 mL of a 3.0 M solution in
Et2O, 1.50 × 10-3 mol), and the mixture was stirred for
5–10 min. The color of the solution turned dark green
and the UV-vis spectrum of the reaction mixture became
Copyright © 2012 World Scientific Publishing Company
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MESO–TETRAPHENYLPORPHYRIN-DERIVED OXYPYRIPORPHYRIN
585
Rf (silica-CH2Cl2) = 0.31. 1H NMR (400 MHz, CDCl3 +
= 4.0 Hz, 1H), 7.88 (br s, 4H), 7.77 (br s, 4H), 7.74 (d,
3J = 4.0 Hz, 1H), 7.68–7.45 (m, 14H), 7.38 (s, 1H), 1.64
(s, 3H). 13C NMR (75 MHz, CDCl3, D1 = 6 s, Me4Si):
d, ppm 195.1, 161.1, 144.6, 143.7, 142.4, 142.3, 140.8,
140.5, 139.8, 139.4, 139.1, 134.5, 133.9, 133.5, 133.2,
133.0, 132.2, 132.1, 131.3, 131.2, 128.2, 128.0, 127.6,
127.3, 127.1, 123.3, 122.6, 116.5, 114.7, 23.6. UV-vis
(CH2Cl2): lmax, nm (log e) 453 (4.97), 581 (3.86) 627
(3.89). UV-vis (CH2Cl2 + 2%TFA): lmax, nm (log e) 456
(4.74), 711 (3.99). HR-MS (ESI+, 100% CH3CN): m/z
713.1889 (calcd. for C46H31N4NiO [MH]+ 713.1851).
[meso-tetraphenyl-3,2a-hydro-3-methyl-2-oxo-2a-
homoporphyrinato]Ni(II) 13Ni. To a solution of [meso-
tetraphenyl-3-methyl-2-oxo-2a-homoporphyrinato]-
Ni(II) 12Ni (8 mg, 1.10 × 10-5 mol) in THF (5 mL) at
-78 °C was added L-selectride (0.4 mL of a 1.0 M
solution in THF) and the reaction mixture was stirred for
1 h and gradually warmed to rt. The color of the solution
turned from yellow-green to olive-green over the course
of the reaction. After the starting material was consumed
(reaction control by TLC, silica gel-CH2Cl2), the excess
reductant was quenched with water (1 mL). The organic
layer was separated, dried over anhydrous Na2SO4, and
concentrated at rt by passing a gentle stream of N2 over
the solution. The product was not stable to evaporation on
the rotary evaporator. The crude product was purified by
preparative TLC (20 × 20 cm, 500 µm silica-CH2Cl2) and
isolated as an olive-green powder. Yield 89%. Rf (silica-
D2O, Me4Si): d, ppm 8.45 (br s, 2H), 8.29 (d, 3J = 4.0 Hz,
3
2H), 8.11 (s, 2H), 8.02 (d, J = 4.0 Hz, 2H), 7.84 (br s,
3
4H), 7.61 (m, 8H), 7.53 (t, J = 8.0 Hz, 2H), 7.40 (br s,
2H), 1.54 (s, 6H) Note: D2O was added to the solvent
to shift the water peak that otherwise would have over-
lapped with the methyl signal. 13C NMR (75 MHz,
CDCl3, D1 = 5 s, Me4Si): d, ppm 152.4, 150.4, 144.8,
143.2, 141.5, 141.2, 136.5, 136.1, 135.6, 132.0, 131.2,
131.1, 130.9, 130.4, 130.2, 127.8, 112.9, 91.1, 27.2.
UV-vis (CH2Cl2): lmax, nm (log e) 418 (5.98), 573 (sh)
620 (5.20); HR-MS (ESI+, 100% CH3CN): m/z 732.2064
(calcd. for C46H34N4NiO2 [M]+ 732.2035).
[meso-tetraphenyl-1,4-diacetyl-chlorophinato]Ni(II) -
11Ni. To a solution of [meso-tetraphenyl-trans-2,3-
dimethyl-2,3-dihydroxychlorinato]Ni(II) 10Ni (55 mg,
7.50 × 10-5 mol) in THF (5 mL) at ambient temperature
was added Pb(OAc)4 (100 mg, 2.25 × 10-4 mol, freshly
recrystallized from glacial acetic acid and dried over
KOH-P2O5 mixture) in portions over 5 min. The reaction
mixture was stirred for a total of 15 min. The color of the
solution turned from dark green to dark brown. After the
starting material was consumed (reaction control by TLC,
silica gel-2:1 CH2Cl2:petroleum ether 30–60), the crude
reaction was filtered through a plug of neutral alumina.
The plug was washed with THF (4 × 5 mL) and the
combined eluates were dried in vacuo. The product was
purified by preparative TLC (20 × 20 cm, 500 µm silica,
eluent-1:1 CH2Cl2/petroleum ether) and isolated as a dark
brown crystalline material. Yield 59–66%. Rf (silica-2:1
1
CH2Cl2) = 0.66. H NMR (300 MHz, CDCl3, Me4Si): d,
ppm 8.27 (d, 3J = 4.8 Hz, 1H), 8.22 (d, 3J = 4.8 Hz, 1H),
1
3
CH2Cl2/petroleum ether) = 0.53. H NMR (400 MHz,
8.17 (d, J = 8.0 Hz, 1H), 8.08 (s, 1H), 7.83 (br s, 3H),
CDCl3 + D2O, Me4Si): d, ppm 8.27 (d, 3J = 4.0 Hz, 2H),
8.10 (s, 2H), 7.98 (d, 3J = 4.0 Hz, 2H), 7.86 (br s, 4H), 7.63
(m, 6H), 7.52 (m, 6H), 1.54 (s, 6H). 13C NMR (75 MHz,
CDCl3, D1 = 6 s, Me4Si): d, ppm 198.2, 148.1, 143.9,
140.7, 140.2, 138.9, 138.4, 133.9, 133.4, 132.3, 130.7,
130.6, 128.2, 128.1, 127.7, 127.3, 114.3, 25.6. UV-vis
(CH2Cl2): lmax, nm (log e) 415 (sh), 453(0.67), 612 (sh),
666 (0.12). HR-MS (ESI+, 100% CH3CN): m/z 731.2004
(calcd. for C46H33N4NiO2 [MH]+ 731.1957).
7.78 (d, 3J = 5.1 Hz, 1H), 7.73 (d, 3J = 5.1 Hz, 1H), 7.62
3
3
(m, 7H), 7.51 (t, J = 8.0 Hz, 1H), 7.45 (t, J = 8.0 Hz,
1H), 7.34 (t, 3J = 8.0 Hz, 1H), 6.90 (d, 3J = 8.0 Hz, 1H),
4.03 (m, 1H), 3.35–3.29 (dd, 2J = 18.6 Hz, 3J = 6.3 Hz,
3
3
1H), 3.15 (d, J = 18.6 Hz, 1H), 1.27 (d, J = 6.9 Hz,
3H). 13C NMR (100 MHz, CDCl3, D1 = 6 s, Me4Si): d,
ppm 207.1, 146.7, 146.1, 146.0, 143.2, 142.1, 140.6,
140.2, 139.5, 139.4, 138.8, 138.7, 135.4, 134.4, 134.3,
133.2, 133.1, 133.0, 131.5, 130.4, 130.1, 129.3, 129.1,
128.2, 128.1, 128.0, 127.8, 127.7, 127.6, 127.4, 126.8,
124.9, 115.2, 110.7, 46.2, 34.2, 17.3. UV-vis (CH2Cl2):
[meso-tetraphenyl-3-methyl-2-oxo-2a-homopor-
phyrinato]Ni(II) 12Ni. To a solution of meso-tetra-
phenyl-1,4-diacetyl-chlorophinato]Ni(II) 11Ni (10 mg,
1.36 × 10-5 mol) in CH2Cl2 (5 mL) was added 1,8-diaza-
bicyclo[5,4,0]undec-7-ene (DBU) (1.0 mL) at ambient
temperature and the reaction mixture was stirred for
5 min. The color of the solution turned from dark brown
to yellowish-green. After the starting material was
consumed (reaction control by TLC, silica gel-CH2Cl2),
the crude reaction was loaded onto a silica gel column and
eluted with 1:1 CH2Cl2/petroleum ether 30–60, followed
by 100% CH2Cl2. The product was, after slow evaporation
of the solvent, isolated as a yellowish-green crystalline
material. Yield 85–90%. Rf (silica-CH2Cl2) = 0.50.
1H NMR (300 MHz, CDCl3, Me4Si): d, ppm 8.40 (d,
l
max, nm (log e) 439 (4.78), 647 (4.03). HR-MS (ESI+,
100% CH3CN): m/z 714.1947 (calcd. for C46H32N4NiO
[M]+ 714.1930).
[meso-tetraphenyl-2,3-dimethylene-2a-thia-2a-
homoporphyrinato]Ni(II) 18Ni. To a solution of [meso-
tetraphenyl-1,4-diacetyl-chlorophinato]Ni(II) 11Ni (21 mg,
3.40 × 10-5 mol) in toluene (7 mL) at rt was added
Lawesson’s reagent (55 mg, 1.36 × 10-4 mol). The
reaction mixture was stirred for 20 min and then
gradually brought to reflux. The color of the solution
turned from dark brown to olive-green over the
course of the reaction. After the starting material was
consumed (reaction control by TLC, silica gel-CH2Cl2),
the reaction was cooled and filtered through a short
plug of silica gel. The solvent was removed by rotary
3
3J = 4.0 Hz, 1H), 8.35 (d, J = 4.0 Hz, 1H), 8.32 (d,
3
3
3J = 4.0 Hz, 1H), 8.31 (d, J = 4.0 Hz, 1H), 7.97 (d, J
Copyright © 2012 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2012; 16: 585–588

586
S. BANERJEE ET AL.
evaporation and the crude product was purified by
preparative TLC (20 × 20 cm, 500 µm silica-CH2Cl2)
and isolated as an olive-green powder. Yield 81%. Rf
(silica-2:1 CH2Cl2/petroleum ether 30–60) = 0.78. 1H
the corresponding b-alkylsecochlorin bisethylketones.
Incidentally, we have also proven the trans-configuration
of the vic-diol functionality of the tetraphenyldiolchl-
orins generated by methyl Grignard addition to the
corresponding diones. Thus, this work is another
example of the plasticity of the “breaking and mending of
porphyrins” approach toward the synthesis of porphyrin
and chlorin analogs. Particularly the functionalities of
the thiomorpholinochlorin appear to be promising for
subsequent functional group manipulations.
3
NMR (400 MHz, CDCl3, Me4Si): d, ppm 8.56 (d, J =
8.0 Hz, 2H), 8.21 (d, 3J = 4.0 Hz, 2H), 8.03 (s, 2H), 7.86
(br s, 4H), 7.69 (d, 3J = 4.0 Hz, 2H), 7.60 (m, 8H), 7.43
(t, 3J = 8.0 Hz, 2H), 7.28 (m, 2H), 6.81 (d, 3J = 8.0 Hz,
2H), 5.31 (s, 2H), 4.23 (s, 2H). 13C NMR (75 MHz,
CDCl3, D1 = 6 s, Me4Si): d, ppm 147.8, 142.7, 142.5,
140.9, 139.5, 138.9, 138.8, 134.4, 133.3, 132.9, 131.9,
130.0, 129.3, 128.1, 127.7, 127.4, 127.2, 126.2, 118.0,
113.1. UV-vis (CH2Cl2): lmax, nm (log e) 442 (4.89),
618 (sh), 665 (4.16). HR-MS (ESI+, 100% CH3CN):
m/z 728.1563 (calcd. for C46H30N4SNi [M]+ 728.1545).
Acknowledgements
This work was supported by the NSF (CHE-0517782,
CMMI-0730826, CMMI-1014926, and CHE-1058846).
The X-ray diffractometer was funded by NSF Grant
0087210, Ohio Board of Regents Grant CAP-491, and
by Youngstown State University.
X-ray diffractometry
Diffraction data for 10 and 10Ni were collected on
a Bruker AXS SMART APEX CCD diffractometer at
100 K using monochromatic Mo Ka radiation with the
omega scan technique. Data were collected, unit cells
determined, and the data integrated and corrected for
absorption and other systematic errors using the Apex2
suite of programs [58]. The structures were solved by
direct methods in the centrosymmetric space group P21/n
and refined by full matrix least squares against F2 with
all reflections using SHELXTL [58]. All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms
were placed in calculated positions and refined as riding.
Compound 10 exhibited two crystallographically
independent but chemically identical molecules. Both
molecules exhibit disorder of their alcohol moieties (in
0.880(4) to 0.120(4) ratios). Major and minor moieties
are created by a non-crystallographic mirror operation
and are enantiomers of each other. Data of 10 were
collected of a non-merohedrally twinned crystal (180
degree rotation around the real/reciprocal axis 1 0 -1), and
refinement of the twinning gave a 0.679(1) to 0.381(1)
ratio of twin moieties. Details of disorder and twinning
are given in the “_exptl_special_details” section of the
crystallographic information file of 10 (see Supporting
information).
Supporting information
A reproduction of the H, 13C NMR and IR spectra
1
of 10, 10Ni, 11Ni, 12Ni, 13Ni, and 18Ni; ORTEP
reproductions and packing diagram of the solid state
structures of 10 and 10Ni are given in the supplementary
material. This material is available free of charge via the
Internet at http://www.worldscinet.com/jpp/jpp.shtml.
Crystallographic data have been deposited at the
Cambridge Crystallographic Data Centre (CCDC)
under numbers CCDC-852843 (10) and 852844 (10Ni).
Copies can be obtained on request, free of charge, via
www.ccdc.cam.ac.uk/data_request/cif or from the
Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: +44 1223-336-033
or email: deposit@ccdc.cam.ac.uk).
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