Glycoporphyrin Catalysts for Efficient C-H Bond Aminations by Organic Azides

Article abstract of DOI:10.1021/acs.organomet.5b00436

We report herein the synthesis of new glycoporphyrin ligands which bear a glucopyranoside derivative on each meso-aryl moiety of the porphyrin skeleton. The saccharide unit is directly conjugated to the porphyrin or a triazole spacer is placed between the carbohydrate and porphyrin ring. The obtained glycoporphyrin ligands were employed to synthesize cobalt(II), ruthenium(II), and iron(III) complexes which were tested as catalysts of C-H bond aminations by organic azides. Two of the synthesized complexes were very efficient in promoting catalytic reactions, and the results achieved indicated that ruthenium and iron complexes show an interesting complementary catalytic activity in several amination reactions. The eco-friendly iron catalyst displayed very good chemical stability in catalyzing the amination reaction for three consecutive runs without losing catalytic activity. (Chemical Equation Presented).

Full text of DOI:10.1021/acs.organomet.5b00436

Article
pubs.acs.org/Organometallics
Glycoporphyrin Catalysts for Efficient C−H Bond Aminations by
Organic Azides
Giorgio Tseberlidis, Paolo Zardi, Alessandro Caselli, Damiano Cancogni, Matteo Fusari, Luigi Lay,*
and Emma Gallo*
Department of Chemistry, University of Milan, Via Golgi 19, 20133 Milan, Italy
S
* Supporting Information
ABSTRACT: We report herein the synthesis of new
glycoporphyrin ligands which bear a glucopyranoside derivative
on each meso-aryl moiety of the porphyrin skeleton. The
saccharide unit is directly conjugated to the porphyrin or a
triazole spacer is placed between the carbohydrate and
porphyrin ring. The obtained glycoporphyrin ligands were
employed to synthesize cobalt(II), ruthenium(II), and iron-
(III) complexes which were tested as catalysts of C−H bond
aminations by organic azides. Two of the synthesized
complexes were very efficient in promoting catalytic reactions,
and the results achieved indicated that ruthenium and iron
complexes show an interesting complementary catalytic activity
in several amination reactions. The eco-friendly iron catalyst displayed very good chemical stability in catalyzing the amination
reaction for three consecutive runs without losing catalytic activity.
as multifunctional molecular scaffolds, since they are available
from the chiral pool in a variety of stereoisomeric forms with
well-defined spatial arrangement of the different hydroxyl
groups. Consistently, the insertion of saccharide functionalities
on the porphyrin periphery can modulate chemical character-
istics of the catalyst while preserving its low toxicity.12,13 In fact,
the presence of glycoside units on the skeleton provides chiral
properties to the ligand and fine-tunes the solubility in water or
organic solvents, depending on the nature of hydroxyl
protecting groups on the carbohydrate fragment. For the
selection of an eco-friendly catalytic metal, it is useful to draw
from natural systems such as cytochrome P-450 chemistry14−17
which contains iron as the active metal center. It should be
noted that inexpensive and durable iron complexes18−25 have
been extensively employed to promote the C−H bond
amination and that, among all the catalysts, iron porphyrins26
display high catalytic efficiency. Recently, Che and coauthors
disclosed that [Fe(F20TPP)Cl (TPP = dianion of tetraphe-
nylporphyrin) is a competent catalyst for the promotion of C−
N bond formation27 by also using organic azides28,29 as
aminating agents. While glycoconjugated porphyrins have been
used in photodynamic therapy (PDT) for active targeting of
membrane receptors,30−33 quite surprisingly there are only a
few examples in the literature describing their use in
catalysis.34−36 In particular, iron glycoporphyrin complexes
have been sparsely used in catalytic reactions34 and have never
been employed to catalyze amination reactions.
INTRODUCTION
■
The activation of C−H bonds represents a “hot” topic due to
the enormous synthetic potential of this class of organic
transformations and the ubiquity of C−H functionalities in
almost every molecular scaffold. Among all kinds of C−H bond
activations, the C−H bond amination allows the conversion of
low -cost products, such as simple hydrocarbons, into high-
added-value nitrogen-containing derivatives which often
present important biological and/or pharmaceutical features.1
The insertion of an aza fragment into an organic skeleton can
be sustainably performed by using organic azides (RN3) as
nitrogen sources, thanks to the atom efficiency and eco-
compatibility of this class of aminating agents.2−5 The
environmental benefits of the azide-based methodology can
be further increased by employing a reaction catalyst which also
presents sustainable features. Among all the catalysts active in
C−H bond aminations, metal porphyrins have a good catalytic
efficiency as well as an acceptable environmental sustain-
ability.6−9 In order to enhance this latter catalyst characteristic,
it is important to introduce favorable functional groups on the
porphyrin skeleton and low-toxicity transition metals in the
porphyrin core.
Among the major classes of biomolecules, carbohydrates are
widely recognized as key mediators of vital cellular recognition
phenomena. The broad structural diversity featured by oligo-
and polysaccharides ensures that these biomolecules play a
fundamental role in many crucial biological events including,
just to mention a few, embryogenesis, inflammatory processes,
pathogens infections, tumor growth and metastasis, and
immune response.10,11 In addition, carbohydrates may serve
Received: May 22, 2015
© XXXX American Chemical Society
A
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Some of us have extensively studied the amination of
benzylic37−41 and allylic42−44 C−H bonds catalyzed by
ruthenium(II) porphyrin complexes, and to expand this part
of the chemistry we studied the activity of ruthenium(II)
glycoporphyrin catalysts obtained by introducing glucoside
units onto the porphyrin skeleton. In addition and for the first
time, we report the catalytic activity of iron(III) glycoporphyrin
catalysts in the amination of activated sp3 C−H bonds and their
activity was compared with that of structurally analogous
ruthenium(II) complexes.
porphyrin51 with NaNO2/NaN3 in TFA, resulting in the ααββ
atropoisomer of meso-tetrakis(2-azidophenyl)porphyrin 8,
which was reacted with Zn(OAc)2·2H2O to yield the desired
compound 9 in 90% yield. The azido substituent displays a
typical IR absorbance at 2121.4 cm−1. In addition, the free
porphyrin 11 was synthesized in two steps by first forming the
glycoporphyrin zinc derivative 10, which was treated with 37%
HCl to afford 11. The monosaccharide units of all synthesized
glycoporphyrins display hydroxyl groups protected as benzyl
ethers in order to increase the solubility of the corresponding
metal complexes in organic solvents and to allow, if needed,
easy deprotection using mild methods, such as hydrogenolysis
on Pd/C, which preserves the chemical structure of the metal
complexes.
RESULTS AND DISCUSSION
■
As reported in Scheme 1, we synthesized the three porphyrin
ligands 3, 7, and 11 by using a minor modification of reported
synthetic procedures.
Porphyrin 3 was employed as a ligand for the corresponding
complexes CoII(3), RuII(3)CO, and FeIII(3)OMe, while
porphyrins 7 and 11 were used to synthesize the complexes
FeIII(7)OMe and FeIII(11)OMe, respectively (Figure 1).
Scheme 1. Synthesis of Glycoporphyrin Ligands 3, 7, and 11
Figure 1. Structures of synthesized glycoporphyrin complexes.
The reaction of glycoporphyrin 3 with CoCl2·6H2O yielded
the complex CoII(3) in 92% yield. The complex was simply
filtered off by the reaction medium and obtained in pure form
without any other purification procedure. Conversely, the
reaction between free ligand 3 and Ru3(CO)12 did not afford
the related metal complex either in decalin or in 1,2,4-
trichlorobenzene. We therefore used a different synthetic
strategy to obtain the complex RuII(3)(CO). We first
synthesized RuII(F20TPP)(CO)52 (TPP2− = dianion of
tetraphenylporphyrin), which was then conjugated with 2,
giving the complex RuII(3)(CO) in 65% yield. Both cobalt and
ruthenium complexes were fully characterized; interestingly,
they were soluble in common organic solvents (CH2Cl2,
CHCl3, AcOEt, THF, Et2O, CH3CN, MeOH, DMF) except for
n-hexane.
Porphyrin 3 was obtained in a good yield by reacting meso-
tetrakis(pentafluorophenyl)porphyrin (1)45 with methyl 2,3,6-
tri-O-benzyl-α-D-glucopyranoside (2).46,47 Porphyrin 1 was
chosen as the starting material to ensure both a regioselective
nucleophilic aromatic substitution reaction on the para
position45,48 and a good catalytic activity of its metal
derivatives. In fact, it has already been reported that electron-
deficient iron porphyrins usually show a better activity in
nitrene transfer reactions involving organic azides.28
The other two ligands 7 and 11 were both synthesized by a
1,3-dipolar cycloaddition “click” reaction49 between the zinc
complex of meso-tetrakis(4-azidophenyl)porphyrin 4 or meso-
tetrakis(2-azidophenyl)porphyrin 9 and the glucoside 5,50
which was prepared by reacting 2 with propargyl bromide in
the presence of sodium hydride. It should be noted that the
synthesis of 7 occurred through the first formation of the zinc
glycoporphyrin 6 which was treated with 37% HCl to give the
free ligand.
The synthesis of the iron complexes FeIII(3)(OMe),
FeIII(7)(OMe), and FeIII(11)(OMe) was performed by
following a procedure recently reported by some of us where
FeBr2 was used as the metal source.53 The initial formation of
an iron(II) glycoporphyrin complex was followed by an
oxidation process in atmospheric oxygen, yielding an iron(III)
species. The workup of the reaction in CH3OH was then
responsible for the presence of the methoxy axial ligand on the
iron center. Analytical data are in accord with the proposed
structures.
The complexes CoII(3), RuII(3)(CO), and FeIII(3)(OMe)
bear the saccharide units on the para position of meso-aryl
groups; therefore, it is reasonable to predict that the presence
of these chiral entities cannot have any influence on the
The synthesis of the zinc porphyrin 9 has never been
reported in the literature; thus we herein describe the reaction
of the ααββ atropoisomer of meso-tetrakis(2-aminophenyl)-
B
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stereoselectivity of the catalytic reaction because they are too
far from the metal center. In addition, the typical low
concentration of the catalyst in the reaction medium does
not allow an intermolecular interaction between the active
metal center and a chiral fragment of a vicinal porphyrin
molecule. On the other hand, the presence of O-benzyl-
protected monosaccharides on the porphyrin skeleton increases
the solubility in organic solvent and paves the way to perform
catalytic reactions in water after deprotection of the sugars’
hydroxyl groups.
In order to better understand this result, we repeated the
model reaction in the presence of the parent Fe(TPP)OMe
complex to investigate a possible inhibition role of saccharide
units. After 24 h the azide was mainly converted into the
corresponding ArNH2 and ArNNAr and the 1H NMR
analysis of the crude revealed the formation of the benzylic
amine 12 only in traces. This result suggested that the poor
catalytic activity of FeIII(7)(OMe) and FeIII(11)(OMe)
complexes is not due to the presence of saccharide/triazole
units but to the electronic behavior of the iron(III) center.
Considering that the catalytic activity of iron(III) porphyrin
complexes has a remarkable ligand dependence,26,56 it is
reasonable to envisage a crucial role of fluorinated electron-
deficient porphyrin ligands to promote amination reactions.
Future efforts will be devoted to synthesizing fluorinated iron
porphyrin complexes with analogous triazole/saccharide frag-
ments to better investigate their catalytic activity. Complex
CoII(3) was active in promoting the test reaction reported in
Table 1, but the modest catalytic efficiency observed (Table 1,
entry 3) did not encourage a deeper investigation of its catalytic
behavior.
Complex FeIII(7)(OMe) also exhibits the saccharide units on
the para positions of meso-aryl groups; however, the triazole
spacer between the carbohydrate and the porphyrin ring and
the absence of fluorine atoms on aryl rings modify the
electronic behavior of the iron metal center. The hydrogen-
bonding capability54,55 of the triazole spacer should also have a
positive effect on catalytic reactions when the saccharide/
triazole units are placed on the ortho positions of meso-aryl
substituents to form porphyrin ligand 11. The resulting
FeIII(11)(OMe) catalyst has one C2 axis within the porphyrin
plane and exhibits an open space on either side for substrate
access and at the same time a steric chiral bulk surrounding the
N core. On the basis of our previous results53 we can suggest
that this molecule displays a preorganized but yet flexible
structure, giving breathing space to move freely.
Conversely, very good results were observed by using
RuII(3)(CO) (Table 1, entry 4) and FeIII(3)(OMe) (Table 1,
entry 5). In both cases the amine 12 was obtained in only 15
min and in very high yields.
As expected, none of the chiral catalysts reported in Table 1
promoted the reaction enantioselectivity and amine 12 was
always obtained in a racemic form.
All complexes discussed above were tested in the catalytic
model reaction between 3,5-bis(trifluoromethyl)phenyl azide
and ethylbenzene, forming benzylic amine 12, and the data
obtained are reported in Table 1.
In order to estimate the role of carbohydrate fragments in the
reaction outcome, the reaction was carried out in the presence
of RuII(F20TPP)(CO) (Table 1, entry 6) and FeIII(F20TPP)-
(OMe)57 (Table 1, entry 7) to form 12 in 68% and 82% yields
in 20 and 45 min, respectively. It is worth noting that the
catalytic results obtained in the presence of FeIII(F20TPP)-
(OMe) indicate an important role of the axial methoxy ligand.
In fact, it was recently reported by Che and coauthors that the
analogous reaction between ethylbenzene and 4-nitrophenyl
azide, catalyzed by FeIII(F20TPP)(Cl), afforded the desired
benzylic amine with a satisfactory yield of 71% but with a very
long reaction time of 36 h.28
Table 1. Synthesis of Benzylic Amine 12 Catalyzed by
a
Glycoporphyrin Complexes
yield (%)
b
c
d
entry
catalyst
t (h)
12
ArNH2
A comparison between the catalytic results obtained by
employing RuII(3)(CO) and FeIII(3)(OMe) and those
achieved with RuII(F20TPP)(CO) and FeIII(F20TPP)(OMe)
indicated a positive role of carbohydrate units in terms both of
yields and reaction times. Thus, we decided to investigate the
reaction scope by testing the activity of the most effective
catalysts, RuII(3)(CO) and FeIII(3)(OMe), in the amination of
various hydrocarbon substrates by different aryl azides. The
results are reported in Table 2. In all cases primary amine and
diazene derived from the decomposition of the employed azide
accounted for the rest of the reaction mass balance.
1
2
3
4
5
6
7
FeIII(7)(OMe)
FeIII(11)(OMe)
CoII(3)
30
25
4
15
10
56
90
92
68
82
70
75
40
RuII(3)(CO)
0.25
0.25
0.33
0.75
FeIII(3)(OMe)
RuII(F20TPP)(CO)
FeIII(F20TPP)(OMe)
20
10
a
Reactions were run under nitrogen in 6.0 mL of refluxing
ethylbenzene with 8.75 × 10−2 mmol of 3,5-bis(trifluoromethyl)-
phenyl azide (ArN3) and 1.75 × 10−3 mmol of the catalyst (2% with
b
respect to the azide). Reactions were run until complete azide
Ethylbenzene was employed to test the activity of the two
selected catalysts toward azides which exhibit different
electronic characteristics for the presence of either EWG or
EDG substituents on the aryl moiety (Table 2, entry 1). Our
previous works39 revealed that ruthenium porphyrin catalysts
are more efficient in activating electron-deficient in comparison
to electron-rich aryl azides, and this trend was confirmed by
comparing the Ru(3)CO-catalyzed reactions of ethylbenzene
with 3,5-bis-(trifluoromethyl)phenyl azide or 4-tert-butylphenyl
azide (product 12 vs 13, Table 2, entry 1).
conversion, which was monitored by IR spectroscopy by following the
c
d
N3 absorbance decrease at 2116 cm−1. Isolated yields. NMR yields
calculated in the crude reaction mixture using 2,4-dinitrotoluene as the
internal standard.
As shown in Table 1, complexes FeIII(7)(OMe) and
FeIII(11)(OMe) show a low catalytic activity after a long
reaction time (Table 1, entries 1 and 2). The azide was
completely consumed, but the principal reaction products,
1
identified by the H NMR analysis of the crude residue, were
ArNH2 (see Table 1) and traces of ArNNAr derived from
The synthesis of compound 12 occurred in comparable
the decomposition of the employed aryl azide.
yields with the catalysts FeIII(3)(OMe) and RuII(3)(CO) (92%
C
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catalyzed synthesis of 12 was repeated for three consecutive
runs by adding an equal amount of 3,5-bis(trifluoromethyl)-
phenyl azide after each complete consumption of the azide
itself. Compound 12 was formed with a total yield of 90%, thus
pointing out that the excellent stability of the iron complex
assured the recyclability of the process.
Table 2. Amines 12−30 Synthesized in the Presence of
a
RuII(3)(CO) and FeIII(3)(OMe)
To better explore the catalytic competence of Fe(3)OMe, we
tested differently substituted aryl azides in the amination of
ethylbenzene to form compounds 14−18 (Table 2, entry 1).
The synthesis of amine 15 deserves particular attention,
because this compound is not efficiently formed in the
presence of ruthenium porphyrins. In addition, the p-(MeO)-
C6H4 (PMP) protecting group on the nitrogen atom can be
easily removed,58,59 yielding the corresponding free amino
derivatives.
Ru(3)CO and Fe(3)OMe catalysts were also active in the
reaction between ethylbenzene and sulfonyl or benzyl azides to
form aminated compounds 19−21. The synthesis of sulfonyl
derivatives 19 and 20 was better promoted by Ru(3)CO in
comparison to the Fe(3)OMe catalyst (Table 2, entry 2). In
contrast, a reverse situation was observed in the synthesis of 21.
In this case only Fe(3)OMe demonstrated a modest catalytic
activity, forming the desired compound in 40% yield (Table 2,
entry 3). The discrepancy in the catalytic activities between the
two complexes was also observed in the amination of methyl
phenylacetate by 3,5-bis(trifluoromethyl)phenyl azide to give
22 (Table 2, entry 4). In fact, while Ru(3)CO complex
promoted the synthesis of 22 in 30 min in 72% yield,
Fe(3)(OMe) was catalytically inert. When the Fe(3)(OMe)-
catalyzed amination of methyl phenylacetate was repeated using
the electron-rich 4-tert-butylphenyl azide, adduct 23 was
obtained in 15% yield, confirming that electron-rich azides
are activated by Fe(3)(OMe) slightly better than electron-poor
azides. The difference in the catalytic activities between
Fe(3)(OMe) and Ru(3)CO complexes was also observed in
the amination of cumene, toluene, and tetrahydronaphthalene,
where the synthesis of 24, 26, and 28 by 3,5-bis-
(trifluoromethyl)phenyl azide was more efficient in the
presence of Ru(3)CO in comparison to Fe(3)(OMe) catalyst
(Table 2, entries 5−7). However, the reaction between 4-tert-
butylphenyl azide and cumene, toluene, or tetrahydronaph-
thalene was catalyzed by Fe(3)(OMe), forming 25, 27, and 29
in fair yields (Table 2, entries 5−7). It should be noted that
these reactions were not carried out in the presence of
Ru(3)CO, owing to the unsatisfactory result achieved in the
Ru(3)CO-catalyzed amination of ethylbenzene by 4-tert-
butylphenyl azide (Table 2, entry 1; product 13).
a
Reactions were run under nitrogen in 6.0 mL of refluxing
hydrocarbon with 8.75 × 10−2 mmol of the azide and 1.75 × 10−3
mmol of the catalyst (2% with respect to the azide). Reactions were
run until complete azide conversion, which was monitored by IR
Finally, the reported catalytic methodology was also tested in
the amination of the C−H allylic bond of cyclohexene, where
Ru(3)CO was more active than Fe(3)(OMe) (Table 2, entry 8;
product 30). The iron catalyst was also ineffective by
employing 4-tert-butylphenyl azide, and the resulting aminated
compound was formed only in traces.
All data reported in Table 2 indicate that in several cases the
use of Ru(3)CO or Fe(3)(OMe) did not afford matching
catalytic results and that, generally speaking, the correct choice
of the glycoporphyrin ruthenium or iron catalyst is crucial in
promoting the reaction of the selected hydrocarbon with an
electron-poor or -rich azide.
b
spectroscopy by following the N3 absorbance decrease (see the
c
d
Supporting Information) Isolated yields. Measured by 1H NMR
spectroscopy with respect to azide using 2,4-dinitrotoluene as the
internal standard.
and 90%, respectively), while the RuII(3)(CO)-catalyzed
amination of ethylbenezene by 4-tert-butylphenyl azide formed
13 in only 30% yield. Remarkably, compound 13 was obtained
in 15 min in 86% yield by using Fe(3)OMe as the catalyst,
suggesting a lower dependence of the iron-based methodology
with respect to the electronic characteristics of the azide.
Considering that the sustainability of a synthetic procedure is
strongly related to the catalyst recyclability, the Fe(3)(OMe)-
CONCLUSION
We reported herein the synthesis of the three glycoporphyrin
ligands 3, 7, and 11, which have been used to synthesize the
■
D
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by TLC up to the point that its spot was no longer observable and
then by IR spectroscopy measuring the N3 characteristic absorbance at
2200−2000 cm−1. The reaction was considered to be finished when
the absorbance of the azide measured was below 0.03 (by using a 0.5
mm thickness cell). The solution was then evaporated to dryness, and
the crude reaction mixture was purified by flash chromatography (see
the Supporting Information for purification procedures).
corresponding cobalt(II), ruthenium(II), and iron(III) deriva-
tives, which were tested as catalysts of C−H bond aminations.
Ruthenium and iron glycoporphyrins demonstrated the best
catalytic efficiency and in several cases a very interesting
complementarity. Considering the increasing attention of the
scientific community in developing sustainable catalytic
procedures, data achieved by using iron glycoporphyrins to
promote hydrocarbon aminations by organic azides deserve
special attention. It is also important to emphasize that the very
good chemical stability of Fe(3)(OMe) allowed the complete
conversion of 3,5-bis(trifluoromethyl)phenyl azide into the
corresponding amine 12 three consecutive times in the same
catalytic reaction. The sustainability of our methodology is
related to (i) the use of organic azides as eco-friendly aminating
agents, (ii) the presence of low-toxiity, cheap, and stable iron
metal as the active center, and (iii) the presence of saccharide
units to modulate the chemical characteristics and the catalytic
performance of the porphyrin ligands.
In this paper we have shown for the first time the catalytic
activity of iron glycoporphyrins in amination reactions.
Ongoing studies in our laboratory are addressed to the
synthesis of water-soluble iron glycoporphyrins by delivering
the hydroxyl groups of saccharide units. The study of the
catalytic activity of these complexes in water could broaden the
scope of amination reactions and further enhance the process
sustainability for the use of the perfect green solvent water as
the reaction medium.
Synthesis of 3. NaH (60%; 180.0 mg, 4.5 mmol) was added under
nitrogen to a toluene (15.0 mL) solution of compounds 145 (110.0
mg, 0.113 mmol) and 246 (314.0 mg, 0.676 mmol). The resulting
solution was refluxed for 24 h until the complete consumption of the
porphyrin 1 was observed by TLC (SiO2, n-hexane/AcOEt 5/5).
Residual NaH was quenched with 1.0 N HCl, and then CHCl3 (40.0
mL) was added to the mixture. The organic phase was extracted with
H2O until pH 7 and then dried over Na2SO4 and filtered. The solvent
was evaporated to dryness under vacuum and the residue purified by
flash chromatography (SiO2, gradient elution from n-hexane/AcOEt
1
7/3 to 5/5) to yield the purple solid 3 (171.0 mg, 55%). H NMR
(300 MHz, CDCl3): δ 8.43 (8H, s, CHβ), 7.50−7.01 (60H, m, CHAr),
5.26 (4H, d, J = 10.9 Hz, CH2), 4.95−4.67 (28H, m, CH2 and CH),
4.44 (4H, m, CH), 4.31 (4H, m, CH), 4.07 (8H, m, CH2), 3.80 (dd, J
= 9.2, 2.3 Hz, CH), 3.54 (12H, s, OCH3), −3.05 (2H, s, NH). 19F
NMR (282 MHz, CDCl3): δ −139.2 (8F, dd, J = 22.7, 7.3 Hz), −156.4
(8F, dd, J = 22.7, 7.3 Hz). 13C NMR (75 MHz, CDCl3): δ 146.5 (C,
J1
= 236.2 Hz), 140.7 (C, J1
= 240.2 Hz), 138.6−137.5 (C),
C−F
C−F
C−F
129.0−127.0 (CHAr), 113.9 (C, t, J2
= 19.4 Hz), 104.2 (C), 98.1
(CHanomeric), 81.2 (CH), 80.7 (CH), 75.6 (CH2), 74.0 (CH2), 73.6
(CH2), 69.6 (CH), 69.3 (CH2), 55.8 (OCH3). UV−vis (CH2Cl2): λmax
(log ε) 416 nm (5.54), 509 nm (4.36), 585 nm (3.90), 656 nm (3.08).
Anal. Calcd for C156H134F16N4O24 (2752.7): C, 68.07; H, 4.91; N,
2.04. Found: C, 68.55; H, 5.05; N, 1.85.
Synthesis of 6. CuSO4·5H2O (36.8 mg, 0.148 mmol) and sodium
ascorbate (29.3 mg, 0.148 mmol) were added to 4.0 mL of a THF/
H2O 1/1 solution of 449 (25.0 mg, 0.03 mmol) and 550 (74.7 mg,
0.148 mmol). The resulting solution was stirred for 3 h at 50 °C until
the complete consumption of 4 was observed by TLC (SiO2, CH2Cl2/
MeOH 98/2), and then the mixture was extracted with CH2Cl2 (3 ×
5.0 mL). The organic phase was washed with H2O (4.0 mL), dried
over Na2SO4, and filtered. The solvent was evaporated to dryness
under vacuum and the residue purified by flash chromatography (SiO2,
gradient elution from CH2Cl2 to CH2Cl2 containing 2% of MeOH) to
yield the purple solid 6 (74.5 mg, 87%). 1H NMR (400 MHz, CDCl3):
δ 9.00 (8H, s, Hβ), 8.34 (8H, d, J = 8.0 Hz, CHortho‑Ph), 7.88 (8H, d, J =
8.0 Hz, CHmeta‑Ph), 7.75 (4H, s, CHtriazole), 7.42−7.17 (60H, m, CHAr),
5.00 (4H, d, J = 11.0 Hz, CH2), 4.87−4.41 (32H, m, CH2 and CH),
3.95 (4H, t, J = 9.0 Hz, CH), 3.72−3.54 (20H, m, CH2 and CH), 3.39
(12H, s, OCH3). 13C NMR (100 MHz, CDCl3): δ 150.3 (C), 146.1
(C), 143.5 (C), 139.0 (C), 138.2 (C), 136.5 (C), 135.6 (CHortho‑Ph),
132.3 (CHβ), 128.6−128.1 (CHAr), 120.7 (CHtriazole), 119.9 (C), 118.7
(CHmeta‑Ph), 98.3 (CHanomeric), 81.9 (CH), 80.1 (CH), 77.8 (CH), 75.7
(CH2), 73.6 (CH2), 70.1 (CH), 68.7 (CH2), 65.9 (CH2), 55.4
(OCH3). UV−vis (CH2Cl2): λmax (log ε) 424 nm (5.36), 453 nm
(3.87), 548 nm (4.16), 587 nm (3.46). Anal. Calcd for
C168H160N16O24Zn (2852.5): C, 70.74; H, 5.65; N, 7.86. Found: C,
70.53; H, 5.80; N, 7.70.
EXPERIMENTAL SECTION
■
General Conditions. All catalytic reactions and some synthetic
procedures (where specified) were carried out under a nitrogen
atmosphere employing standard Schlenk techniques and vacuum-line
manipulations. All solvents were dried by using standard procedures,
unless specified.
Reagents. Organic azides,60 meso-tetrakis(pentafluorophenyl)-
porphyrin (1),45 methyl 2,3,6-tri-O-benzyl-α-D-glucopyranoside
(2),46 [Zn(meso-tetrakis(4-azidophenyl)porphyrin)] (4),49 methyl
2,3,6-tri-O-benzyl-4-O-(prop-2-ynyl)-α-D-glucopyranoside (5),50
[RuII(F20TPP)(CO)] (TPP2− = dianion of tetraphenylporphyrin),52
the ααββ atropoisomer of meso-tetrakis(2-aminophenyl)porphyrin,51
[FeIII(F20TPP)(OMe)],57 and [FeIII(TPP)(OMe)]61 were synthesized
as reported in the literature. All other starting materials were
commercial products and were used as received.
Instruments. NMR spectra were recorded at room temperature
either on a Bruker Avance 300-DRX spectrometer, operating at 300
1
MHz for H, at 75 MHz for 13C, and at 282 MHz for 19F, or on a
1
Bruker Avance 400-DRX spectrometer, operating at 400 MHz for H,
100 MHz for 13C, and 376 MHz for 19F. Chemical shifts (ppm) are
1
reported relative to TMS. The H NMR signals of the compounds
described in the following have been assigned by COSY and NOESY
techniques. Assignments of the resonance in 13C NMR were made by
using the APT pulse sequence and HSQC and HMBC techniques.
Infrared spectra were recorded on a Varian Scimitar FTS 1000
spectrophotometer. UV-vis spectra were recorded on an Agilent 8453E
instrument. MALDI-TOF spectra were acquired either on a Bruker
Daltonics Microflex instrument or on a Bruker Daltonics Autoflex III
TOF/TOF instrument at the CIGA, University of Milan. High-
resolution MS (HR-MS) spectra were obtained on a Bruker Daltonics
ICR-FTMS APEX II instrument at the CIGA, University of Milan.
Microanalysis was performed on a PerkinElmer 2400 CHN Elemental
Analyzer instrument.
General Procedure for Catalytic Reactions. In a typical run, the
catalyst (1.75 × 10−3 mmol) and azide (8.75 × 10−2 mmol) were
added under nitrogen to a hydrocarbon (6.0 mL) which was used as
the reaction solvent. The resulting solution was refluxed using a
preheated oil bath. The consumption of the aryl azide was monitored
Synthesis of 7. HCl (37%; 2.5 mL) was added to a AcOEt (10.0
mL) solution of 6 (52.0 mg, 0.018 mmol). The resulting solution was
stirred for 3 h at room temperature until the complete consumption of
6 was observed by TLC (SiO2, CH2Cl2/MeOH 97/3); then 10.0 mL
of H2O was added, and the organic phase was extracted with H2O until
pH 7. The resulting solution was dried over Na2SO4 and filtered. The
solvent was evaporated to dryness under vacuum to yield the purple
1
solid 7 (49.8 mg, 99%). H NMR (300 MHz, CDCl3): δ 8.95 (8H, s,
CHβ), 8.37 (8H, d, J = 8.3 Hz, CHortho‑Ph), 8.03 (8H, d, J = 8.3 Hz,
CHmeta‑Ph), 7.93 (4H, s, CHtriazole), 7.52−7.23 (60H, m, CHAr), 5.14
(4H, d, J = 11.9 Hz, CH2), 5.08 (4H, d, J = 11.0 Hz, CH2), 4.96−4.80
(12H, m, CH2), 4.75−4.65 (12H, m, CH2 and CHanomeric), 4.60 (4H,
d, J = 12.0 Hz, CH2), 4.06 (4H, t, J = 9.0 Hz, CH), 3.88 (4H, d, J =
10.5 Hz, CH2), 3.84−3.71 (12H, m, CH2 and CH), 3.64 (4H, dd, J =
9.6, 3.5 Hz, CH), 3.42 (12H, s, OCH3), −2.73 (2H, s, NH). 13C NMR
E
DOI: 10.1021/acs.organomet.5b00436
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Organometallics
Article
(75 MHz, CDCl3): δ 146.5 (Ctriazole), 142.4 (C), 139.1 (C), 138.2 (C),
137.00 (C), 135.6 (CHortho‑Ph), 128.9−127.6 (m, CHAr), 120.9
(CHtriazole), 119.1 (C), 119.0 (CHmeta‑Ph), 98.4 (CHanomeric), 82.1
(CH), 80.1 (CH), 77.9 (CH), 75.9 (CH2), 73.7 (CH2), 73.6 (CH2),
70.2 (CH), 68.7 (CH2), 66.3 (CH2), 55.4 (OCH3). UV−vis
(CH2Cl2): λmax (log ε) 421 nm (5.53), 516 nm (4.15), 551 nm
(3.85), 591 nm (3.67), 648 nm (3.65). Anal. Calcd for C168H162N16O24
(2789.2): C, 72.34; H, 5.85; N, 8.03. Found: C, 72.55; H, 6.05; N,
7.82.
m, CH2). 13C NMR (100 MHz, CDCl3): δ 149.9 (C), 149.8 (C),
149.5 (C), 149.5 (C), 144.0 (C), 143.7 (C), 138.7 (C), 138.6 (C),
138.3 (C), 137.6 (C), 137.4 (C), 137.1 (C), 137.0 (C), 136.5 (CH),
135.6 (CHAr), 131.9 (CHβ), 131.8 (CHβ), 131.6 (CHβ), 129.7
(CHAr), 128.6−127.6 (CHAr), 127.5−126.9 (CHAr), 126.5 (CHAr),
125.6 (CHAr), 125.5 (CHAr), 124.3 (CHAr), 124.2 (CHAr), 115.4
(CHAr), 97.9 (CHanomeric), 97.8 (CHanomeric) 81.4 (CH), 79.7 (CH),
77.2 (CH), 75.2 (CH2), 74.9 (CH2), 73.3 (CH2), 73.1 (CH2), 72.7
(CH2), 72.6 (CH2), 69.5 (CH), 69.2 (CH), 68.4 (CH2), 67.9 (CH2),
65.1 (CH2), 64.7 (CH2), 55.0 (OCH3). UV−vis (CH2Cl2): λmax (log
ε) 430 nm (5.49), 555 nm (4.17). Anal. Calcd for C168H160N16O24Zn
(2852.5): C, 70.74; H, 5.65; N, 7.86. Found: C, 70.38; H, 5.91; N,
7.45.
Synthesis of 8. The ααββ atropoisomer of meso-tetrakis(2-
aminophenyl)porphyrin51 (100.0 mg, 0.148 mmol) was dissolved
under nitrogen in TFA (3.0 mL), and the resulting solution was cooled
in ice bath. A solution of NaNO2 (81.7 mg, 1.184 mmol) in H2O (0.5
mL) was added to the mixture with stirring. After 15 min a solution of
NaN3 (115.5 mg, 1.776 mmol) in H2O (0.5 mL) was also added to the
mixture, which was stirred for an additional 1 h. Then, H2O (10.0 mL)
was added and the mixture was extracted with CH2Cl2 (4 × 40.0 mL).
The organic phase was washed with H2O (2 × 50.0 mL), dried over
Na2SO4, and filtered. The solvent was evaporated to dryness under
Synthesis of 11. Complex 10 (69.0 mg, 0.024 mmol) was
dissolved in AcOEt (10 mL), and HCl (37%; 2.5 mL) was added with
stirring. The resulting solution was stirred for 3 h at room temperature
until the complete consumption of 10 was observed by TLC (SiO2,
CH2Cl2/MeOH 97/3); then H2O (10.0 mL) was added, and the
organic phase was extracted with H2O until pH 7, dried over Na2SO4,
and filtered. The solvent was evaporated to dryness under vacuum to
yield the purple solid 11 (66.0 mg, 99%). 1H NMR (400 MHz,
CDCl3): δ 8.70−8.62 (6H, m, CHβ), 8.51 (2H, s, CHβ), 7.99 (2H, d, J
= 7.5 Hz, CHAr), 7.95−7.83 (10H, m, CHAr), 7.82−7.70 (4H, m,
1
vacuum to yield the purple compound 8 (128.0 mg, 90%). H NMR
(400 MHz, CDCl3): δ 8.70 (8H, s, CHβ), 8.10 (4H, d, J = 7.4 Hz,
CHAr), 7.85 (4H, t, J = 8.4 Hz, CHAr), 7.60 (4H, d, J = 8.1 Hz, CHAr),
7.53 (4H, t, J = 7.4 Hz, CHAr), −2.62 (2H, s, NH). 13C NMR (100
MHz, CDCl3): δ 141.7 (C), 135.8 (CHAr), 133.7 (C), 130.2 (CHAr),
123.4 (CHAr), 118.0 (CHAr), 115.6 (C). UV−vis (CH2Cl2): λmax (log
ε) 421 nm (5.20), 454 nm (3.77), 514 nm (3.95), 547 nm (3.38), 592
nm (3.48), IR (ATR): 3312.9 cm−1 (νNHpyr), 2121.4 cm−1 (νN3). Anal.
Calcd for C44H26N16 (778.8): C, 67.86; H, 3.37; N, 28.78. Found: C,
68.05; H, 3.61; N, 28.46.
CHAr), 7.26−7.15 (20H, m, CHAr), 7.05−6.78 (26H, m, CHtriazole
+
CHAr), 6.71 (4H, t, J = 7.5, CHAr), 6.50−6.38 (10H, m, CHAr), 6.34
(4H, t, J = 7.4, CHAr), 4.63−4.53 (6H, m, CH2), 4.48−4.38 (8H, m,
CH2 + CHanomeric), 4.36 (2H, d, J = 3.4 Hz, CHanomeric), 4.05 (4H, m,
CH2), 3.96−3.86 (4H, m, CH2), 3.73 (6H, m, CH2), 3.53 (4H, td, J =
9.3, 3.2 Hz, CH), 3.43−3.33 (6H, m, CH2 + CH), 3.24 (6H, s,
OCH3), 3.22−3.12 (8H, m, CH2 + CH), overlapping with 3.18 (6H, s,
OCH3), 3.10−2.97 (4H, m, CH), 2.97−2.87 (4H, m, CH), 2.64 (2H,
d, J = 9.6 Hz, CH), 2.51 (2H, dd, J = 10.7, 3.8 Hz, CH). 13C NMR
(100 MHz, CDCl3): δ 144.2 (C), 143.9 (C), 138.7 (C), 138.5 (C),
138.3 (C), 138.0 (C), 137.7 (C), 137.0 (CHAr), 136.9 (CHAr), 135.7
(C), 130.11 (CHβ), 130.08 (CHβ), 128.4 (CHAr), 128.2 (CHAr), 128.1
(CHAr), 127.93 (CHAr), 127.87 (CHAr), 127.6 (CHAr), 127.4 (CHAr),
127.03 (CHAr), 127.2 (CHAr), 126.7 (CHAr), 125.8 (CHAr), 125.7
(CHAr), 124.2 (CHAr), 124.0 (CHAr), 115.1 (C), 115.0 (C), 98.0
(CHanomeric), 81.6 (CH), 81.5 (CH), 79.8 (CH), 79.7 (CH), 77.6
(CH), 77.0 (CH), 75.3 (CH2), 75.1 (CH2), 73.3 (CH2), 73.0 (CH2),
72.5 (CH2), 69.8 (CH), 69.6 (CH), 68.5 (CH2), 67.8 (CH2), 65.0
(CH2), 64.6 (CH2), 60.5 (CH2), 55.1 (OCH3). UV−vis (CH2Cl2):
λmax (log ε) 422 nm (5.39), 519 nm (4.21), 552 nm (3.66), 593 nm
(3.72), 650 nm (3.33). Anal. Calcd for C168H162N16O24 (2789.2): C,
72.34; H, 5.85; N, 8.03. Found: C, 72.64; H, 6.13; N, 7.75.
Synthesis of 9. A solution of Zn(AcO)2·2H2O (225.0 mg, 1.026
mmol) in MeOH (1.0 mL) was added to a CH2Cl2 (20.0 mL) solution
of 8 (50.0 mg, 0.064 mmol). The resulting solution was stirred for 3 h
at room temperature until the complete consumption of 8 was
observed by TLC (SiO2, CH2Cl2/n-hexane 7/3); then H2O (15.0 mL)
was added to the solution, and the organic phase was extracted with
H2O (3 × 10.0 mL), dried over Na2SO4, and filtered. The solvent was
evaporated to dryness under vacuum to give the purple compound 9
1
(50.7 mg, 94%). H NMR (400 MHz, CDCl3): δ 8.80 (8H, s, CHβ),
8.10 (4H, d, J = 7.5 Hz, CHAr), 7.85 (4H, t, J = 7.4 Hz, CHAr), 7.64−
7.49 (8H, m, CHAr). 13C NMR (100 MHz, CDCl3): δ 150.3 (C),
141.6 (C), 135.7 (CHAr), 134.4 (C), 131.9 (CHβ) 130.0 (CHAr), 123.4
(CHAr), 117.9 (CHAr), 116.5 (C), 114.2 (C). UV−vis (CH2Cl2): λmax
(log ε) 421 nm (4.91), 467 nm (3.19), 510 nm (3.00), 549 nm (3.78),
585 nm (2.85). IR (ATR): 2121.4 cm−1 (νN3). Anal. Calcd for
C44H26N16Zn (842.1): C, 62.75; H, 2.87; N, 26.61. Found: C, 62.53;
H, 2.44; N, 27.03.
Synthesis of CoII(3). CoCl2·6H2O (24.0 mg, 0.088 mmol) was
added to a DMF (20.0 mL) solution of 3 (54.0 mg, 0.019 mmol)
under nitrogen. The solution was refluxed for 4 h until the complete
consumption of 3 was observed by TLC (SiO2, CH2Cl2/n-hexane 5/
5), H2O (20.0 mL) was added, and the product was extracted with
CH2Cl2 (3 × 20.0 mL). The combined organic phases were washed
with H2O (2 × 10.0 mL) and then dried over Na2SO4 and filtered.
The solvent was evaporated to dryness, and n-hexane (10.0 mL) was
added to the residue. The resulting purple solid was collected by
filtration (49.3 mg, 92%). UV−vis (CH2Cl2): λmax (log ε) 412 nm
(5.18), 510 nm (4.01), 582 nm (3.50), 656 nm (2.91). MS (MALDI)
m/z: 2809.9 [M]+.
Synthesis of 10. Complex 9 (47.0 mg, 0.056 mmol) and
compound 5 (140.5 mg, 0.279 mmol) were dissolved in 7.0 mL of a
THF/H2O 1/1 solution. CuSO4·5H2O (69.5 mg, 0.279 mmol) and
sodium ascorbate (55.2 mg, 0.279 mmol) were added with stirring,
and the resulting solution was stirred for 24 h at room temperature
until the complete consumption of 9 was observed by TLC (SiO2,
CH2Cl2/MeOH 97/3). The mixture was extracted with CH2Cl2 (7.0
mL), and the organic phase was washed with H2O (7.0 mL), dried
over Na2SO4, and filtered. The solvent was evaporated to dryness
under vacuum, and the crude product was purified by flash
chromatography (SiO2, gradient elution from CH2Cl2 to CH2Cl2
containing 3% of MeOH) to yield the purple solid 10 (103.9 mg,
Synthesis of RuII(3)(CO). NaH (60 wt %; 166.4 mg, 4.16 mmol)
was added under nitrogen to a toluene (14.0 mL) solution of
RuII(F20TPP)(CO)52 (115.0 mg, 0.104 mmol) and 246 (290.0 mg,
0.624 mmol). The solution was refluxed for 10 h until the complete
consumption of RuII(F20TPP)(CO) was observed by TLC (SiO2,
CH2Cl2/n-hexane 5/5), and then residual NaH was quenched with 1.0
N HCl. CHCl3 (20.0 mL) was added to the mixture, and the organic
phase was extracted with H2O until pH 7, dried over Na2SO4, and
filtered. The solvent was evaporated to dryness under vacuum, and the
resulting residue was purified by flash chromatography (SiO2, gradient
elution from n-hexane/AcOEt 7/3 to 5/5) to yield the purple solid
RuII(3)(CO) (197.0 mg, 65%). 1H NMR (300 MHz, CDCl3): δ 8.59−
8.31 (8H, br, CHβ), 7.35 (60H, br, CHAr), 5.23 (4H, d, J = 10.7 Hz,
1
65%). H NMR (400 MHz, CDCl3): δ 8.71 (2H, s, CHβ), 8.67 (4H,
m, CHβ), 8.57 (2H, s, CHβ), 8.06 (4H, t, J = 6.8 Hz, CHAr), 7.95−7.73
(10H, m, CHAr), 7.69 (2H, td, J = 7.5, 1.2 Hz, CHAr), 7.26−7.15
(16H, m, CHAr), 7.06−6.98 (10H, m, CHtriazole + CHAr), 6.93−6.86
(8H, m, CHAr), 6.81 (2H, t, J = 7.3 Hz, CHAr), 6.73−6.63 (8H, m,
CHAr), 6.51 (2H, s, CHAr), 6.46 (4H, d, J = 7.3 Hz, CHAr), 6.07−5.91
(8H, m, CHAr), 4.59−4.48 (6H, m, CH2), 4.45−4.31 (10H, m, CH2 +
CHanomeric), 3.98 (2H, d, J = 10.3, CH2), 3.88 (2H, d, J = 11.9, CH2),
3.83−3.67 (8H, m, CH2), 3.50−3.40 (8H, m, CH2 + CH), 3.39−3.27
(4H, m, CH2 + CH), 3.14 (6H, s, OCH3), overlapping with 3.13−3.07
(4H, m, CH), 3.06 (6H, s, OCH3), 3.03−2.93 (4H, m, CH), 2.90−
2.81 (2H, m, CH), 2.80−2.64 (6H, m, CH2 + CH), 2.60−2.42 (4H,
F
DOI: 10.1021/acs.organomet.5b00436
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
CH2), 4.94−4.59 (28H, m, CH2 and CHanomeric), 4.41 (4H, br, CH),
4.27 (4H, br, CH), 4.02 (8H, br, CH2), 3.76 (4H, br, CH), 3.52 (12H,
s, OCH3), −3.20 (2H, s, NH). 13C NMR (75 MHz, CDCl3): δ 146.5
ACKNOWLEDGMENTS
■
We gratefully acknowledge the MIUR-Italy (PRIN 2010−2011:
contract 2010JMAZML_003) for financial support.
(C, J1
= 252.0 Hz), 144.2 (C), 140.7 (C, J1
= 248.0 Hz) 138.7
C−F
C−F
(C), 138.1 (C), 137.9 (C), 132.1 (CHβ, br), 129.1−126.9 (CHAr),
114.21 (C, br), 98.1 (CHanomeric), 81.1 (CH), 80.6 (CH, m), 75.5
(CH2), 73.9 (CH2), 73.6 (CH2), 69.6 (CH), 69.3 (CH2), 60.5 (CH2),
55.7 (OCH3). 19F NMR (282 MHz, CDCl3): δ −138.6 (4F, m),
−140.4 (4F, m), −156.3 to −157.9 (8F, m). IR (ATR): 1954 cm−1
(νCO). UV−vis (CH2Cl2): λmax (log ε) 407 nm (5.29), 525 nm (4.26),
555 nm (3.87), 607 nm (3.69). MS (MALDI) m/z: 2852.7 [M −
CO]+.
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ASSOCIATED CONTENT
■
S
* Supporting Information
Text and figures giving experimental details and NMR spectra
of isolated compounds. The Supporting Information is available
free of charge on the ACS Publications website at DOI:
10.1021/acs.organomet.5b00436.
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AUTHOR INFORMATION
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Corresponding Authors
*E-mail for L.L.: luigi.lay@unimi.it.
*E-mail for E.G.: emma.gallo@unimi.it.
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Notes
The authors declare no competing financial interest.
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