Unexpected hydroxylamine-induced ring-closure reactions of meso-tetraphenylsecochlorin bisaldehyde

Article abstract of DOI:10.1039/c0ob00920b

Reaction of meso-tetraphenylsecochlorin bisaldehyde with hydroxylamine results in the formation of the known meso-tetraphenyl-2-nitroporphyrin and the novel meso-tetraphenylimidazolophorphyrin. The products are the result of two diverging pathways of the presumed intermediate monooxime monoaldehyde that are unusual and surprising, but fully rationalized. The structures of both products were confirmed by spectroscopic techniques and single crystal X-ray diffractometry. This reaction represents the first reaction in which a pyrrole in a porphyrin was formally replaced by an imidazole moiety. The optical properties of the free base and metalloimidazoloporphyrin under neutral and acidic conditions are discussed. Further, an alternative synthesis of the imidazoloporphyrin Ni(ii) based on meso-tetraphenyl-1-formyl-chlorophin is presented.

Full text of DOI:10.1039/c0ob00920b

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PAPER
Unexpected hydroxylamine-induced ring-closure reactions of
meso-tetraphenylsecochlorin bisaldehyde†
Joshua Akhigbe,a Gretchen Peters,a Matthias Zellerb and Christian Bru¨ckner*a
Received 22nd October 2010, Accepted 13th December 2010
DOI: 10.1039/c0ob00920b
Reaction of meso-tetraphenylsecochlorin bisaldehyde with hydroxylamine results in the formation of
the known meso-tetraphenyl-2-nitroporphyrin and the novel meso-tetraphenylimidazolophorphyrin.
The products are the result of two diverging pathways of the presumed intermediate monooxime
monoaldehyde that are unusual and surprising, but fully rationalized. The structures of both products
were confirmed by spectroscopic techniques and single crystal X-ray diffractometry. This reaction
represents the first reaction in which a pyrrole in a porphyrin was formally replaced by an imidazole
moiety. The optical properties of the free base and metalloimidazoloporphyrin under neutral and acidic
conditions are discussed. Further, an alternative synthesis of the imidazoloporphyrin Ni(II) based on
meso-tetraphenyl-1-formyl-chlorophin is presented.
Introduction
The development of synthetic methodologies toward the synthesis
of chlorins and related oligopyrrolic macrocycles constitutes a
major aspect of current porphyrin research.1 This is because of
the often attractive optical properties of these macrocycles with
respect to their use as UV-vis or fluorescent labels in biological
systems, their phototoxicity, or their promise in artificial light-
harvesting systems. Two principal approaches toward the synthesis
of chlorins and their analogues, such as porphyrinoids containing
a non-pyrrolic building block, can be pursued: total synthesis,2
or the b,b¢-manipulation of a preformed porphyrin.1,3 We, and
others,4–7 pursued the latter approach and developed methods
toward the formal replacement of one (or two) pyrrolic units
of meso-tetraaryl- or b-octaalkylporphyrins by a non-pyrrolic
building block, generating pyrrole-modified porphyrins that are
frequently chlorin-like.8–17
Thus, pyrrole-modified porphyrins containing four- (azete)7,13,16
(1), five- (oxazole)4,10,18–20 (2) and six-membered (morpholine
This is followed by Step B, a diol cleavage reaction to the corre-
(3),8,10,11 pyridinone,5,14 and pyrazine9) heterocycles have become
known. We like to paraphrase our three-step approach as the
‘breaking and mending of porphyrins’ (Scheme 1). In Step A, one
(or two) b,b¢-double bond(s) of a porphyrin are activated, generally
by conversion to the corresponding 2,3-dihydroxychlorin.8,14,15,21
sponding secochlorin (the ‘breaking’ of the porphyrin).13,20,22,23 The
secochlorin bisaldehyde is subsequently reacted under conditions
that lead to the formation of, for instance, a non-pyrrolic building
block (Step C). This ‘mending’ stage of the synthesis may involve
more than one functional group transformation.8–12,14,20
We recently reported a mild synthesis of the long-time elusive
free base secochlorin bisaldehyde 5 by oxidative cleavage of the
corresponding diolchlorin under basic conditions (Scheme 2).20
Secochlorin 5 (and its Ni(II) complex 5Ni)13,22 showed in all the
reactions tested to date the typical reactivity of an aromatic
aldehyde. We therefore surmised that the reaction of hydroxyl-
amine with bisaldehyde 5 would form oxime I that is poised to
undergo an intramolecular ring-closure to form the hemiacetal
II and subsequently lactone III upon spontaneous oxidation.
aDepartment of Chemistry, University of Connecticut, Unit 3060, Storrs, CT,
06269-3060, USA. E-mail: c.bruckner@uconn.edu; Fax: +860-486-2981;
Tel: +860-486-2743
bDepartment of Chemistry, Youngstown State University, One University
Plaza, Youngstown, OH, 44555-3663, USA
† Electronic supplementary information (ESI) available: 1H, 13C NMR
and UV-vis/fluorescence spectra of all novel compounds obtained, select
2D NMR spectra, and experimental details to the crystal structure
determination of 6 and 7, including the cif file. CCDC reference numbers
798353 and 798354. See DOI: 10.1039/c0ob00920b/
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been accomplished. Since only one other porphyrinoid containing
a seven-membered carbacycle, tropiporphyrin 4, synthesized using
total synthesis by the group of Lash, is known,24 we were
intrigued by the idea of synthesizing a porphyrinoid containing
a seven-membered heterocycle using the ‘breaking and mending’
approach. We report here the results of those experiments.
Results and discussion
Reaction of secochlorin bisaldehyde 5 with hydroxylamine
Reaction of medium-polarity (Rf 0.61, silica-CH2Cl2), brownish 5
with a 30-fold stoichiometric excess of hydroxylamine hydrochlo-
ride (H2NOH·HCl) in refluxing pyridine generates, over the course
of 1 h under aerobic conditions, one major non-polar (Rf 0.73,
silica-CH2Cl2), brownish (62% isolated yield) and one minor polar
(Rf 0.25, silica-CH2Cl2), purple product (15% isolated yield). No
reaction was observed under anaerobic conditions. As determined
by HR-MS (ESI+, 100% CH3CN), the major product possessed
the composition C44H30N4O2 (for MH+, expected: 660.2400;
found: 660.2337), fitting the expected oxadiazepinone derivative
Scheme 1 The ‘breaking and mending’ principle of conversion of a
porphyrin in three steps to a pyrrole-modified porphyrin.
Precedent reactions suggest that hemiacetals of type II are readily
susceptible to oxidation.20,23 As a result, the formal replacement of
a pyrrole by a seven-membered oxadiazepinone ring would have
1
III. The H NMR (CDCl3) of this product showed the presence
of a porphyrinoid with no axial symmetry (e.g., six d assigned to
Scheme 2 Planned and observed reactions. Reaction conditions: (i) 30 eq NH2OH·HCl, pyridine, D, 1 h. All compounds in Roman numerals were not
directly observed.
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the b-protons), and a seemingly diagnostic low-field peak (s at
9.06 ppm) we assigned to the imine proton (see ESI†).
The UV-vis spectrum of the compound is a red-shifted distorted
porphyrin-like spectrum (Fig. 1). At first glance, this may strike
one as incongruent with structure III but the spectrum of porpho-
lactone 2, for instance, provides a precedent.4,10 The presence of
the single sp2-b-carbon in 2 causes a porphyrin-like—and not a
chlorin-like—spectrum. In contrast, oxazolochlorins carrying an
sp3-carbon at this position are chlorin-like.19,20,23,25 In transference,
the sp2-imine carbon in III may very well be responsible for its
porphyrin-like spectrum.
Fig. 2 X-ray structure of low polarity product 2-nitroporphyrin 7. A:
side view; B: top view. All hydrogens attached to sp2-carbons removed for
clarity. For details, see ESI.†
Since nitroporphyrin 7 is known, including its crystal structure
(even though the CH3OH solvate of 7 crystallized here was not
known),31 we will not describe this compound (or its known Ni(II)
and novel Pd(II) and Pt(II) complexes formed by metal insertion
into the free base) in any detail (see ESI†). Instead, we will focus
on its mode of formation.
Fig. 1 UV-vis spectrum (CH2Cl2) of the presumed species III, the major,
non-polar reaction product from the reaction of 5 with hydroxylamine.
Using standard methodologies,26 metal insertion of Ni(II),
Pd(II), and Pt(II) into the major product proceeded smoothly,
providing the corresponding complexes with the expected compo-
sitions, spectral data, and metalloporphyrin-like optical properties
(see ESI†).
The finding of a 2-nitroporphyrin 7 as the major product from
the reaction of secochlorin bisaldehyde 5 and hydroxylamine might
appear incongruous at first. However, a sequence of straight
forward reactions rationalize its formation (Scheme 2). Formation
of oxime I is followed by an oxime-to-nitrone (IV) tautomeric
exchange, a known tautomer equilibrium.32 Either this nitrone
oxidizes spontaneously to the corresponding nitro compound VI,
which then undergoes an intramolecular Henry reaction to form 7,
or the nitrone is basic enough to undergo an intramolecular Henry-
type condensation to form nitrone porphyrin V, followed by oxida-
tion to the final product 7.33 Whatever the exact mechanism might
be, the reaction is surprisingly efficient and clean, likely reflecting
the large thermodynamic stability of the final product. Provided
that 2-nitroporphyrins are readily made by direct nitration of
porphyrins using a range of methods,27,28 this new method for the
formation of nitroporphyrins does not constitute a competitive
synthetic pathway.
Irrespective of the supporting evidence for the assignment of
the major product as the desired oxadiazepinone III, a number
of findings ran counter to this: at 156 ppm the most deshielded
peak in the 13C NMR spectrum of the product did not quite fit
the expectation of a carbonyl/lactone carbon shift (see ESI†),
but since the lactone carbonyl is also shifted in porpholactones
(167 ppm for 2),10 this finding in itself was not alarming. The
FT-IR spectrum of the major product (neat, ATR) did not
indicate the presence of a carbonyl group (see ESI†). Moreover,
the collision-induced tandem MS of the major product did not
show any of the expected fragmentation patterns and, instead,
showed a prominent fragmentation suggestive of the loss of NO2.
Lastly, a convincing chemical finding directly contradicted the
oxadiazepinone structure: reaction of the low polarity compound
with NaBH4 quantitatively formed meso-tetraphenylporphyrin
(TPP)!
Identification of the high polarity compound
The identification of the high polarity reaction product held
another surprise. Its UV-vis spectrum in neutral solution is
porphyrin-like but exhibits a very unusual optical shift in
acidic conditions (for a detailed description of the UV-vis
Identification of the low polarity compound
A crystal structure analysis of the major, non-polar product
provided a conclusive resolution of the conflicting evidence
(Fig. 2). It proved to be the known 2-nitro-tetraphenylporphyrin
7!27–29 Incidentally, this product possesses the same composition
(C44H30N4O2) as the targeted oxadiazepinonoporphyrin; the b-
hydrogen adjacent to the nitro group is significantly low-field
shifted and it does, naturally, not contain a carbonyl group.
Moreover, its NaBH4 reduction to generate the corresponding
porphyrin is a known reaction.30
1
spectrum of this compound, vide infra). Its H NMR spectrum
reflects a porphyrin without axial symmetry (e.g., six signals
for six non-equivalent b-protons), containing one unusual s at
10.2 ppm (see ESI†). Its composition, as measured by HR-
MS (ESI+, 100% CH3CN) indicated the composition C43H28N5
for MH+, i.e., the formal replacement of one CH group in
6 by a nitrogen. This provided a tantalizing hint that this
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product might be imidazoloporphyrin 6. Indeed, this structural
assignment could be confirmed by single crystal crystallography
(Fig. 3).
Imidazoloporphyrin
6
is one of the few examples of
b-azaporphyrins and b-azacarbaporphyrins. Examples include
the imidazoloporphyrin 8,36 the triazoloporphyrin 9,37 and the
pyrazole derivative 10.38,39 All the b-alkylderivatives were pre-
pared along 3 + 1-type total syntheses. Among the meso-
arylporphyrinoids, N-confused porphyrin 11 might be the closest
relative to imidazoloporphyrin 6. In essence 11 is the carbapor-
phyrin analogue to 6.
We interpret the occurrence of imidazoloporphyrin 6 as indirect
proof that the target compound, diazepinone III is formed
by the reaction of bisaldehyde 5 with hydroxylamine after all
(Scheme 2). This is because the formation of 6 can be rational-
ized by the extrusion of CO2 from III. Neither the thermally
induced loss of CO2 from (electron-rich) aromatic compounds
nor the decarboxylation of porphyrinoids at this position (cf. the
-
formation of porpholactone 2 by MnO4 -induced oxidation of the
corresponding 2,3-diolchlorin)10 is surprising.
Interestingly, reaction of the Ni(II) complex of secochlorin
bisaldehyde 5 with hydroxylamine under the conditions de-
scribed above generates exclusively the Ni(II) complex of the
2-nitroporphyrin 7, and not a trace of the Ni(II) imidazolopor-
phyrin 6Ni.
Fig. 3 X-Ray structure of high-polarity product imidazoloporphyrin 6.
A: top view; B: side view. All hydrogens attached to sp2-carbons removed
for clarity. For details, see ESI†.
Ni(II) complex of imidazoloporphyrin 6, and alternative synthesis
of 6Ni
Insertion of Ni(II) into free base imidazoloporphyrin 6 proceeds
smoothly under standard conditions,26 producing the complex 6Ni
(Scheme 3). It possesses all the expected spectroscopic properties.
Its optical properties are delineated below.
The crystal structure of 6 is isostructural to the solvent-free
triclinic polymorph of TPP,34 highlighting how the packing of
these molecules is only determined by the overall shape of the
molecule and the meso-substituents. An equivalent observation
was made for the crystal structure of N-confused TPP 11.35
The second nitrogen atom of the imidazole moiety was found
to be nearly randomly distributed between all eight possible
positions, with an occupation between 6.1(3) and 17.1(3)% per
site. Nonetheless, the data obtained did allow for a reliable
determination of the distribution of N atoms vs. CH groups, thus
unambiguously confirming the compound as imidazoloporphyrin
6 by diffractometry (for details, see ESI†).
Scheme 3 Reaction Conditions: (i) 10 eq Ni(OAc)2·4H2O, pyridine, D,
24 h. (ii) 45 eq NH2OH·HCl, pyridine, D, 1 h.
An alternative synthesis for 6Ni is available by reaction of
12Ni with hydroxylamine under the conditions described above
for 5/5Ni, and generates the Ni-complex of imidazoloporphyrin
6Ni in moderate yields (Scheme 3). [meso-Tetraphenyl-1-formyl-
chlorophinato]Ni(II) (12Ni) is available either by means of de-
formylation of secochlorin bisaldehyde 5Ni, or by Vilsmeier–Haak
formylation of the corresponding chlorophin.13,16,22 Evidently, the
intermediate oxime loses water to ring-close in an oxidative
fashion. It thus represents yet another novel, step-wise and rational
way of incorporating a nitrogen into the porphyrin framework.
The difficulty in preparing 12Ni in larger quantities, however,
renders this synthesis of interest only to academics.13,16,22
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This reaction raises the question whether the reaction mech-
anism of the reaction of 5 with hydroxylamine as described in
Scheme 2 proceeds via the seven-membered intermediates shown,
or if a spontaneous (thermal) deformylation of monooxime I takes
place. We cannot be sure but tend to discount the latter option as
we never observed any other spontaneous deformylations of the
secochlorin bisaldehydes, even after prolonged heating in a range
of solvents (including benzonitrile, b.p. 188–191 ◦C).
Optical properties of imidazoloporphyrins 6 and 6Ni
The UV-vis spectrum of 6 in neutral medium is a typical
etio-type porphyrin spectrum and very similar, albeit 3–5 nm
bathochromically shifted, compared to that of the spectrum of
TPP (Fig. 4).40 Likewise, the fluorescence spectrum of 6 (Fig. 5)
and the UV-vis spectrum of its Ni(II) complex, 6Ni, (Fig. 6) are
in shape and position very similar to those of TPP and its Ni(II)
complex, TPPNi.
Fig. 6 UV-vis spectrum of imidazoloporphyrin 6Ni in CH2Cl2 (solid
trace) and CH2Cl2 + 2% TFA (dotted trace).
protonation of the periphery (and the low overall symmetry
of the chromophore).41 The fluorescene yield of TPP is greatly
diminished upon protonation. However, 6 still shows strong
fluorescence under acidic conditions, and the spectrum reflects the
red-shifted absorption spectrum. Whether one or two (or none) of
the inner nitrogens are protonated and what the respective relative
basicities of the inner and outer nitrogen(s) are is a matter of
current study.
TPPNi is inert toward inner nitrogen protonation (at the
conditions of 2% TFA in CH2Cl2). Imidazolo-analogue 6Ni,
however, can be protonated at the outer nitrogen. This causes
a large red-shift of the metallochlorin-like spectrum (Fig. 6) but
because protonation at this position most likely does not change
the conformation of the chromophore, it does not shift the position
of the Soret band (though it reduces its extinction coefficient by
about a third).
Fig. 4 UV-vis spectrum of imidazoloporphyrin 6 in CH2Cl2 (solid trace)
and CH2Cl2 + 2% TFA (dotted trace).
Conclusions
In conclusion, the reaction of secochlorin 5 with hydroxylamine
provides as the major product the known 2-nitroporphyrin 7
and as a minor product the novel imidazoloporphyrin 6, the
latter likely by way of an intermediate oxadiazepinochlorin.
Both products reflect the large driving force in porphyrinoids
to form a planar macrocycle incorporating four (planar) five-
membered heterocycles. The two syntheses of imidazoloporphyrin
6 presented show, for the first time, how a b-CH group in
meso-tetraphenylporphyrin can be replaced in a step-wise and
rational approach by an imine-type nitrogen. We thus again
demonstrated the potential of the ‘porphyrin breaking and
mending’ strategy for the preparation of novel pyrrole-modified
porphyrinoids.
Fig. 5 Fluorescence spectrum of imidazoloporphyrin 6 in CH2Cl2 (solid
trace) and CH2Cl2 + 2% TFA (dotted trace).
We are currently engaged in finding more efficient pathways
for the synthesis of 6, and the study of the acid/base, chemical,
and coordination properties of this unique pyrrole-modified TPP
derivative.
In contrast, optical spectra vastly different from those of TPP
and TPPNi were recorded under acidic conditions. Protonation of
free base 6 resulted in a dramatic bathochromic shift of the UV-
vis and fluorescence spectra (Fig. 4 and 5), whereas only minor
red-shifts are observed for TPP.18 Also, for protonated 6, four
side bands were still discernible, whereas protonated TPP shows
only two side bands. We interpret the differences by protonation
of the nitrogen in the porphyrinic b-position as well as at the
inner nitrogen(s). The shift of the Soret band upon protonation
might indicate the distortion of the porphyrin from planarity
upon protonation of the inner nitrogens whereas the number
of side bands and their red-shift might be an indication of the
Experimental
Materials and instruments
All solvents and reagents (Aldrich, Acros) were used as received.
meso-Tetraphenylsecochlorinato bisaldehyde 5 was freshly pre-
pared by oxidative cleavage (NaIO4/silica) of meso-tetraphenyl-
2,3-dihydroxychlorin as described before, and used immediately.20
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[meso-Tetraphenyl-1-formyl-chlorophinato]Ni(II) (12Ni) was pre-
pared by partial deformylation of the corresponding bisalde-
hyde or, alternatively, by Vilsmeier–Haak formylation of
[meso-tetraphenylchlorophinato]Ni.13,16,22 Analytical (aluminium
backed, silica gel 60, 250 mm thickness), preparative (20 ¥ 20 cm,
glass backed, silica gel 60, 500 or 1000 mm thickness) TLC plates,
[meso-Tetraphenyl-2-aza-porphyrinato]Ni(II) (6Ni) from reaction
of [meso-tetraphenyl-1-formyl-chlorophinato]Ni(II) (12Ni) with
hydroxylamine (Route A)
Monoaldehyde 12Ni (4.5 mg, 6.95 ¥ 10-6 mol) was dissolved
in pyridine (5.0 mL) in a round-bottom flask equipped with a
magnetic stir bar. H2N-OH·HCl (22.0 mg, 3.17 ¥ 10-4 mol) was
added and the mixture was heated to reflux for 14 h. Once the
starting material was consumed (reaction control by TLC), the
reaction mixture was evaporated to dryness by rotary evaporation,
taken up in CH2Cl2 and filtered through a plug of silica gel in a
glass frit (M). The filtrate was washed with water (2 ¥ 10 mL),
dried over anhydrous sodium sulfate, and evaporated to dryness
by rotary evaporation. The resulting solid was separated on a
preparative TLC plate (6 ¥ 20 cm glass-backed, 500 mm silica,
CH2Cl2/25% petroleum ether 30–60). Isolated yield of 6Ni was
56% yield (2.6 mg).
˚
and the flash column silica gel (standard grade, 60 A, 32–63 mm)
1
used were provided by Sorbent Technologies, Atlanta, GA. H
and 13C NMR spectra were recorded on a Bruker DRX400 or
a Varian 500 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, and the fluorescence spectra
on a Cary Eclipse spectrophotometer, both Varian Inc. IR spectra
were acquired on a JASCO FT-IR-410 using an ATR (ZnSe)
unit.
[meso-Tetraphenyl-2-aza-porphyrinato]Ni(II) (6Ni) by insertion of
Ni(II) into free base 6 (Route B)
meso-Tetraphenyl-2-aza-porphyrin 6 and meso-tetraphenyl-2-
nitro-porphyrin 7 by reaction of meso-tetraphenyl-secochlorin-
2,3-bisaldehyde 5 with hydroxylamine
Free base imidazoleporphyrin 6H2 (7.0 mg, 1.14 ¥ 10-5 mol) was
added to a solution of pyridine (10 mL) and Ni(CH3CO2)2·4H2O
(32 mg, 1.4¥ 10-4 mol, ~11 eq) in a round-bottom flask equipped
with a magnetic stir bar and the mixture was heated to reflux for
24 h. When the starting material was consumed (reaction control
by UV-vis and TLC), the mixture was allowed to cool, the solvent
was removed in vacuo and triturated in a minimal amount of
CH2Cl2. The resulting mixture was separated on a preparative
TLC plate (CH2Cl2/25% petroleum ether 30–60). Isolated yield
of 6Ni was 78% (5.9 mg). 6Ni: Rf (silica-CH2Cl2) 0.45; 1H NMR
(400 MHz, CDCl3): d 10.1 (s, 1H), 8.83 (two overlapping d, 3J =
In a round-bottom flask equipped with a magnetic stir bar, crude
bisaldehyde 5 (61 mg, 9.42 ¥ 10-2 mmol; from the reaction of 61 mg
meso-tetraphenyl-2,3-dihydroxychlorin) was dissolved in pyridine
(20 mL). NH2OH·HCl (196 mg, 2.82 mmol, ~30 eq) was added and
the mixture was heated to reflux for 1 h. Once the starting material
was consumed (reaction control by UV-vis and TLC), the reaction
mixture was evaporated to dryness by rotary evaporation. The dry
residue was taken up in CH2Cl2 and filtered through a plug of
silica gel in a glass frit (M), the filtrate washed with water (2 ¥
10 mL), dried over anhyd. Na2SO4, and evaporated to dryness
by rotary evaporation. The resulting mixture was separated on
a preparative TLC plate (silica, CH2Cl2-pet ether 1 : 1). Isolated
yields of 7 were 62% (38 mg), and of 6 15% (8.5 mg). 6: Rf (silica-
3
4.0 Hz, 2H), 8.72–8.70 (m, 4H), 8.09 (dd, J = 8.0, 1.0 Hz, 2H),
8.06 (dd, 3J = 8.0, 1.0 Hz, 2H), 8.02–7.98 (m, 4H), 7.75–7.64 (m,
12H) ppm; 13C NMR (100 MHz, CDCl3): d 158.0, 151.0, 146.1,
145. 1, 144.9, 144.7, 144.2, 143.4, 140.8, 140.0, 139.2, 136.5, 134.5,
134.3, 134.0, 133.9, 133.3, 133.2, 132.9, 132.4, 132.3, 128.5, 128.2,
128.1, 127.9, 127.4, 127.3, 127.2, 120.5, 120.0, 119.4, 119.3 ppm;
UV-vis (CH2Cl2 + drop Et3N) lmax (log e) 416 (5.23), 531 (4.06),
562 (3.75) nm; UV-vis (CH2Cl2 + 2% TFA) lmax (log e) 415 (5.04),
605 (4.22); MS (ESI+, cone voltage = 30 V, 100% CH3CN); HR-MS
(ESI+, 100% CH3CN) m/z calcd for C43H28N5Ni 672.1698, found
672.1598.
1
CH2Cl2) 0.25; H NMR (400 MHz, CDCl3): d 10.2 (s, 1H), 9.10
3
3
(d, J = 4.0 Hz, 1H), 9.06 (d, J = 4.0 Hz, 1H), 8.95–8.92 (m,
2H), 8.74 (s, 2H), 8.29–8.26 (m, 4H), 8.22–8.20 (m, 4H), 7.83–
7.75 (m, 12H) ppm. 13C NMR (100 MHz, CDCl3): d 162.0, 161.3,
156.8, 156.4, 148.2, 141.9, 141.8, 141.1, 140.2, 139.9, 139.7, 139.5,
138.2; 135.3, 135.25, 135.2, 134.8, 134.7, 129.5, 128.8, 128.7, 128.5,
128.4, 128.15, 128.1, 127.9, 127.3, 127.2, 127.0, 120.9, 120.7, 120.5,
120.4 ppm; UV-vis (CHCl2 + drop Et3N): lmax (log e) 420 (5.49),
520 (4.14), 559 (3.83), 600 (3.72), 654 (3.95) nm; UV-vis (CHCl2 +
2% TFA) lmax (log e) 427 (5.18), 541 (3.90), 586 (3.76), 658 (3.92),
717 (4.39) nm; MS (ESI+, 100% CH3CN) m/z calcd for C43H30N5
(for M·H+) 616.2501, found 616.2585. 7: Rf (silica-CH2Cl2) = 0.73;
1H NMR (400 MHz, CDCl3): d 9.06 (s, 1H), 9.02 (d, 3J = 5.2 Hz,
1H), 8.95 (d, 3J = 4.8 Hz, 1H), 8.92–8.90 (m, 2H), 8.74–8.71
[meso-Tetraphenyl-2-nitroporphyrinato]Ni(II) 7Ni by reaction of
5Ni with hydroxylamine
Prepared as described for the free base reaction using bisaldehyde
5Ni. The resulting mixture was separated on a preparative TLC
plate (silica, CH2Cl2-pet ether 2 : 3) and 7Ni was isolated in 38%
yield (12.9 mg). Spectroscopic data for 7Ni are identical to those
reported before (see also ESI†).42
3
(m, 2H), 8.26 (d, J = 8 Hz, 2H), 8.23–8.17 (m, 6H), 7.83–7.70
(m, 12H), -2.60 (s, 2H, exchangeable with D2O) ppm; 13C NMR
(100 MHz, CDCl3): d 156.6, 156.4, 153.1, 146.0, 142.5, 141.6,
141.4141.1, 140.4, 140.2, 139.4, 138.0, 135.06, 135.04, 134.7, 134.6,
131.9, 129.9, 129.5, 128.9, 128.6, 128.4, 128.3, 128.0, 127.1, 126.99,
126.94, 126.90, 123.0, 120.8, 120.6, 120.1 ppm; UV-vis (CHCl2)
Crystal structure determinations
Single crystals of 6 (CH2Cl2/MeOH) and 7 (CH2Cl2/MeOH)
were grown by vapour phase diffusion of a non-solvent into
dilute solutions of the compounds using the solvent combinations
indicated in parentheses (solvent/non-solvent). The crystals were
mounted in inert oil on a glass fibre or Mitegen micromesh mount
l
max (log e) 427 (5.80), 527 (4.68), 5.64 (4.12), 604 (4.11), 664 (4.43)
nm; MS (ESI+, 100% CH3CN) m/z calcd for C44H30N5O2 660.2400
([M·H]+), found 660.2337. The data, included here for comparison,
are commensurate with those reported before.27,29
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Table 1 Crystal dataa
J. Am. Chem. Soc., 2008, 130, 15864–15871; T. Ko¨pke, M. Pink and
J. M. Zaleski, Org. Biomol. Chem., 2006, 4, 4059–4062.
7 T. Ko¨pke, M. Pink and J. M. Zaleski, Chem. Commun., 2006, 4940–
4942.
Compound
6
7·CH3OH
8 C. Bru¨ckner, S. J. Rettig and D. Dolphin, J. Org. Chem., 1998, 63,
Formula
C43H29N5
615.71
C45H33N5O3
691.76
Monoclinic
M/g mol-1
Crystal system
Space group
2094–2098.
9 C. J. Campbell, J. F. Rusling and C. Bru¨ckner, J. Am. Chem. Soc., 2000,
122, 6679–6685.
10 J. R. McCarthy, H. A. Jenkins and C. Bru¨ckner, Org. Lett., 2003, 5,
19–22.
Triclinic
¯
P1(#2)
C2/c
˚
a, b, c/A
6.334 (2), 10.352 (3),
12.149 (4)
94.288 (5), 99.895 (5),
101.107 (5)
765.2 (4)
38.963 (16), 9.070
(4), 25.863 (11)
90.00, 130.953 (5),
90.00
a, b, g (◦)
11 H. W. Daniell and C. Bru¨ckner, Angew. Chem., Int. Ed., 2004, 43,
1688–1691.
3
12 J. R. McCarthy, M. A. Hyland and C. Bru¨ckner, Org. Biomol. Chem.,
2004, 2, 1484–1491; K. K. Lara, C. K. Rinaldo and C. Bru¨ckner,
Tetrahedron, 2005, 61, 2529–2539.
13 C. Bru¨ckner, M. A. Hyland, E. D. Sternberg, J. MacAlpine, S. J. Rettig,
B. O. Patrick and D. Dolphin, Inorg. Chim. Acta, 2005, 358, 2943–
2953.
14 C. Ryppa, D. Niedzwiedzki, N. L. Morozowich, R. Srikanth, M.
Zeller, H. A. Frank and C. Bru¨ckner, Chem.–Eur. J., 2009, 15, 5749–
5762.
˚
V/A
6902 (5)
100(2)
8
16363
7040 (0.089)
7040/0/480
T/K
100(2)
1
7609
3744 (0.059)
3744/0/223
Z
Reflections measured
Unique (Rint
)
Data/restraints/
parameters
Goodness-of-fit on F2
R(F) [I > 2s(I)]
R(F) [all data]
1.092
0.062
1.223
0.1457
0.1625
0.961
0.086
0.1951
0.2202
0.2784
15 S. Banerjee, M. Zeller and C. Bru¨ckner, J. Org. Chem., 2010, 75, 1179–
1187.
wR(F2) [I > 2s(I)]
wR(F2) [all data]
16 S. Banerjee, M. A. Hyland and C. Bru¨ckner, Tetrahedron Lett., 2010,
51, 4505–4508.
17 G. E. Khalil, P. Daddario, K. S. F. Lau, S. Imtiaz, M. King, M.
Gouterman, A. Sidelev, N. Puran, M. Ghandehari and C. Bru¨ckner,
Analyst, 2010, 135, 2125–2131.
a For details, see ESI.
18 C. Bru¨ckner, P. C. D. Foss, J. O. Sullivan, R. Pelto, M. Zeller, R. R.
Birge and G. Crundwell, Phys. Chem. Chem. Phys., 2006, 8, 2402–
2412.
and transferred to the cold gas stream of the diffractometer.
Crystal data are listed in Table 1. For additional information,
see ESI†.
19 J. R. McCarthy, M. J. Perez, C. Bru¨ckner and R. Weissleder, Nano
Lett., 2005, 5, 2552–2556.
20 J. Akhigbe, C. Ryppa, M. Zeller and C. Bru¨ckner, J. Org. Chem., 2009,
74, 4927–4933.
21 L. P. Samankumara, M. Zeller, J. A. Krause and C. Bru¨ckner, Org.
Biomol. Chem., 2010, 8, 1951–1965.
Acknowledgements
22 C. Bru¨ckner, E. D. Sternberg, J. K. MacAlpine, S. J. Rettig and D.
Dolphin, J. Am. Chem. Soc., 1999, 121, 2609–2610.
23 J. R. McCarthy, P. J. Melfi, S. H. Capetta and C. Bru¨ckner, Tetrahedron,
2003, 59, 9137–9146.
24 T. D. Lash and S. T. Chaney, Tetrahedron Lett., 1996, 37, 8825–8828;
K. M. Bergman, G. M. Ferrence and T. D. Lash, J. Org. Chem., 2004,
69, 7888–7897.
This work was supported by the US National Science Foundation
under Grant Numbers CHE-0517782 and CMMI-0730826 (to
CB). GP was supported through NSF-REU grant CHE-0754580.
The diffractometer was funded by NSF grant 0087210, by the
Ohio Board of Regents grant CAP-491, and by YSU.
25 C. Bru¨ckner, J. R. McCarthy, H. W. Daniell, Z. D. Pendon, R. P. Ilagan,
T. M. Francis, L. Ren, R. R. Birge and H. A. Frank, Chem. Phys., 2003,
294, 285–303.
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Org. Biomol. Chem., 2011, 9, 2306–2313 | 2313
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