Insertion of Ni(I) into Porphyrins at Room Temperature: Preparation of Ni(II)porphyrins, and Ni(II)chlorins and Observation of Hydroporphyrin Intermediates

Article abstract of DOI:10.1021/acs.inorgchem.7b03164

Reduced Nickel porphyrins play an important role as enzymatic cofactors in the global carbon cycle (cofactor F430), and as powerful catalysts in solar-to-fuel-processes such as the hydrogen evolution reaction, and the reduction of CO and CO₂. The preparation of Ni(II)porphyrins requires harsh conditions, and characterization of the reduced species is intricate. We present a very mild, convenient, and high yielding method of inserting Ni into electron rich, and electron deficient porphyrins which at the same time gives access to to Ni(II) phlorins and Ni(II)chlorins and Ni(II)porphyrins.

Full text of DOI:10.1021/acs.inorgchem.7b03164

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Insertion of Ni(I) into Porphyrins at Room Temperature: Preparation
of Ni(II)porphyrins, and Ni(II)chlorins and Observation of
Hydroporphyrin Intermediates
Morten K. Peters† and Rainer Herges*,†
†Otto Diels-Institute of Organic Chemistry, Christian-Albrechts-University Kiel, Otto-Hahn-Platz 4, 24118 Kiel, Germany
S
* Supporting Information
ABSTRACT: Reduced Nickel porphyrins play an important
role as enzymatic cofactors in the global carbon cycle (cofactor
F430), and as powerful catalysts in solar-to-fuel-processes such
as the hydrogen evolution reaction, and the reduction of CO
and CO2. The preparation of Ni(II)porphyrins requires harsh
conditions, and characterization of the reduced species is
intricate. We present a very mild, convenient, and high yielding
method of inserting Ni into electron rich, and electron
deficient porphyrins which at the same time gives access to to
Ni(II) phlorins and Ni(II)chlorins and Ni(II)porphyrins.
(4) the microwave-promoted insertion of metal salts.22
A
INTRODUCTION
■
typical procedure for the preparation of Ni-porphyrins involves
heating of the porphyrin with a large excess of nickel acetate in
DMF (151 °C) to reflux for several hours.23 Metal insertions
usually have to overcome high activation barriers.
Besides the kinetic problem and the problem of bringing the
hydrophobic porphyrins and the water-soluble metal salts
simultaneously in solution, insertion of nickel ions into
porphyrins suffers from the fact that Ni2+ is too small to
perfectly fit into the square planar cavity formed by the four
pyrrole nitrogen atoms. The porphyrin must distort to a
strained, ruffled geometry to adopt favorable Ni−N dis-
tances.24,25
Following an analogous strategy which is used to prepare
Fe(III)porphyrins by introducing Fe(II), and subsequent
oxidation to the Fe(III) complex,26 we explored the possibility
to introduce the larger Ni(0) and oxidize the low valent
intermediates to the Ni(II)porphyrin.
Nickel-hydroporphyrins are powerful catalysts in reduction
processes in nature, and in technologically important reactions.
F430, a nickel containing corphine acts as the coenzyme in the
final step of methane release in archaea by methyl-CoM
reductase, and thus is a key component in the global carbon
cycle.1 Ni-chlorins have been found in marine tunicates,
however, their biochemical role is yet unknown.2 Reduced
Ni-porphyrins are also key intermediates in the reduction of
alkyl halides3,4 and, intriguingly, in the electrochemical
reduction of CO producing H2 and ethylene.5 The hydrogen
evolution reaction (reduction of protons) is another important
direct solar-to-fuel process which has been catalyzed by Ni-
hydroporphyrins. This process has been studied in detail, and
several reduced Ni species were identified.6−9 While the above
processes start from stable Ni(II)porphyrins, and generate the
reduced species electrochemically, we introduce Ni(0) (using
Ni(COD)2) into the free base porphyrins generating Ni-
hydroporphyrins which can be oxidized to Ni(II)porphyrins in
very good yields. This approach is not only a very mild and
convenient synthesis of Ni(II)porphyrins, it also provides
direct, chemical access to reduced Ni-porphyrins, such as the
corresponding phlorin (Ni2+porph-H3−·, 7c) and chlorins
Ni2+porph-H22−, 3b,c). Ni(II)porphyrins have been used as
responsive contrast agents in functional magnetic resonance
imaging (f MRI).10,11
RESULTS AND DISCUSSION
■
We chose Ni(COD)2 as a readily available Ni(0) complex, and
three electronically different porphyrins to investigate the scope
of the approach: 5,10,15,20-tetrakis(4-methoxyphenyl)-
porphyrin (TPPOMe) 1a, as an example for an electron rich
porphyrin, the parent 5,15,10,20-tetraphenylporphyrin (TPP)
1b, and 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin
(TPPF20) 1c, which is a typical example of an electron deficient
porphyrin. Transition metal carbonyl complexes have been
used before to insert metals into porphyrins,27,28 however, in
our hands Ni(CO)4 did not react with 1c. Upon simple mixing
The conventional synthesis of nickel porphyrins requires
harsh conditions. Various methods have been published for the
synthesis of transition metal porphyrins, which can be classified
into several general reaction types:12 (1) reaction of a
porphyrin with a metal salt in an acidic medium (e.g.,
HOAc),13−16 or (2) under basic conditions (e.g., pyridine),16,17
(3) reaction of a porphyrin with a metal salt, or metal complex
in high boiling, polar organic solvents (e.g., DMF)12,18−21 and
Received: December 22, 2017
© XXXX American Chemical Society
A
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of the free base porphyrin with a two- to 4-fold excess of
Ni(COD)2 in toluene at room temperature under a nitrogen
atmosphere, the color immediately changes from red to green
and after stirring for 1−2 h the corresponding Ni-porphyrins
and the Ni-chlorins are isolated (1H NMR and UV−vis spectra
see Figure 1).
The ratio of the latter two compounds depends on the
electronic nature of the porphyrin. Electron rich TPPOMe 1a
forms exclusively the Ni-porphyrin (100% yield), TPP 1b gives
10% Ni-chlorin and 90% porphyrin, and in case of the electron
poor TPPF20, Ni-porphyrin and Ni-chlorin are formed in
approximately equal amounts (51:49%). A larger excess of
Ni(COD)2 favors the formation of the chlorin, however, no
change is observed if more than four equivalents are used.
Chlorins are quite susceptible to oxidation, and can be
quantitatively converted to the corresponding porphyrins
using DDQ (see Table 1).
So, nickel can be inserted into electron-rich as well as
electron-deficient free base porphyrins in a two-step, one-pot
procedure at room temperature in quantitative yields. The
isolated yields in case of the parent tetraphenyl porphyrin 1b
with 91% are somewhat lower because of solubility problems of
Ni-TPP during workup. The formation of Ni-chlorins from the
corresponding free base porphyrins is of synthetic interest as
well. Particularly, electron-deficient chlorins are difficult to
prepare, because catalytic hydrogenation as well as reduction
with in situ generated diimide fail.29 Our method provides a
convenient access to the strongly electron-poor Ni-tetrakis-
(pentafluorophenyl)chlorin 3c, which cannot be prepared by
hydrogenation of the corresponding porphyrin (TPPF20, 1c;
see Scheme 1). Purification of the chlorin 3c by chromatog-
raphy initially turned out to be very difficult, because porphyrin
2c and chlorin 3c exhibit very similar retention times on
standard stationary phases. Separation was achieved on an
amino-functionalized silica gel (see Experimental Section),
taking advantage of the fact that Ni-chlorins exhibit a much
stronger coordination to axial nitrogen ligands as the
corresponding Ni-porphyrins.30
Information about the possible mechanism of our Ni(0)
insertion reaction is provided by studies on the electrochemical
reduction of Ni(II)porphyrins, which should pass through the
same intermediates, albeit in a reverse sequence. Previous
spectroelectrochemical and electron spin resonance (ESR)
Figure 1. 1H NMR of NiTPPF20 2c in CDCl3, at 300 K (left, red) and
the NiTPPF20-chlorin 3c in acetone-d6, at 300 K (right, green) and the
UV−vis spectra at 24 °C in benzene (porphyrin concentration 13.3
μM).
ab c
, ,
Table 1. Conditions and Product Distributions for the Insertion of Nickel into Free Base Porphyrins
yield (%)
entry
free base porphyrin
equiv of Ni(COD)2
equiv of KHMDS
starting material
Ni-porphyrin
Ni-chlorin
Ni-porphyrin after DDQ
1
1a
1a
1a
1b
1b
1b
1c
1c
1c
1c
1c
1c
1a
1b
1c
1a
1b
1c
2
0
0
0
0
0
0
0
0
0
0
0
1
2
2
2
7
7
7
60 1a
40 2a
99 2a
99 2a
87 2b
90 2b
89 2b
42 2c
66 2c
51 2c
51 2c
50 2c
2
4
3
8
4
2
13 1b
d
5
4
10 3b
11 3b
10 3c
27 3c
49 3c
49 3c
50 3c
91 2b
d
6
8
90 2b
7
0.5
1.2
2
48 1c
7 1c
52 2c
8
93 2c
9
100 2c
100 2c
100 2c
10
11
12
13
14
15
16
17
18
4
8
2
100 4c
28 1a
71 1b
4
72 2a
27 2b
34 2c
4
1 2c
2
66 3c
2
100 4a
100 4b
100 4c
2
2
a
b
c
d
Anhydrous toluene was used as a solvent. At room temperature. In all experiments 50 mg of porphyrin was used. Part of the product was lost
through the purification.
B
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a
protonation could either occur at the Ni ion forming a hydride,
at the pyrrole double bond (β position), or at a meso position.
According to Solis et al.6 protonation at the meso carbon atom
interrupting aromatic conjugation, and forming a Ni(II)phlorin
7, is most favorable.
Scheme 1. Metallation of Porphyrins with Ni(COD)2
We therefore propose the following tentative mechanism
(Scheme 2). Ni(COD)2 coordinates in a stepwise fashion to
the porphyrin. Two of the pyrrole nitrogen atoms replace one
of the COD ligands forming a Ni(0) chelate, and subsequent
intramolecular electron transfer and proton shift forms a
Ni(II)phlorin (Ni2+porph-H3− 7).
The phlorin 7 probably is a key intermediate. It would either
eliminate H2 (according to the known hydrogen evolution
reaction) and form the stable Ni(II)porphyrin 2, or it is
protonated forming the stable chlorin 3. The electronic nature
of the porphyrin, obviously, determines whether the hydrogen
evolution reaction, and thus porphyrin 2 formation, or the
protonation, and chlorine 3 formation, is dominant.
a
The yields are isolated yields of 2a−c after DDQ oxidation. The
yields depend on the reaction conditions; see Table 1.
If this mechanism is correct, addition of a base before
metalation should prevent proton transfer and thus the
hydrogen evolution reaction. With 1 equiv of base, the reaction
should stop at the phlorin 7 stage (monoprotonation). After
addition of 1 equiv of potassium hexamethyldisilazane
(KHMDS) to the free base tetrakis(pentafluorophenyl)-
porphyrin (1c) and subsequent addition of 2 equiv of
Ni(COD)2, a very broad band at ∼740 nm in the UV−vis
spectrum is observed, which is typical for phlorins (7c). A
similar spectrum has been observed by Solis et al. upon
studies31−33 and, more recently, experiments combined with
high-level DFT calculations6,23 provide evidence that the one-
electron reduction of Ni(II)TPP 2b and Ni(II)TPPF20 2c
produces a Ni(I) species rather than a Ni(II) anion radical.
The second electron goes to the porphyrin, forming a Ni(I)-
anion radical with one unpaired electron at the Ni+ and one in
the π system of the porphyrin ligand (triplet state). DFT
calculations predict a planar structure for this complex. Electron
transfer is accompanied by proton transfer. Subsequent
Scheme 2. Proposed Mechanism of the Metalation of Free Base Porphyrins 1a−c with Ni(COD)2 and Formation of Ni(II)-
porphyrin 2a−c, and Ni(II)chlorin 3b−c
C
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electrochemical reduction of NiTPPF20 (Ni2+porph2−, 2c).6,34
The UV−vis spectrum of our solution exhibits additional
absorption bands. The absorptions at 526 and 572 nm are due
to NiTPPF20 (Ni2+porph2−, 2c; see Figure 2).
EXPERIMENTAL SECTION
■
General Comments. Procedures were performed in a nitrogen-
filled MBraun glovebox or using standard Schlenk techniques unless
otherwise specified. Toluene was dried over calcium hydride and
stored over molecular sieves in the glovebox. NMR spectra were
measured in deuterated solvents (Deutero). Analytic measurements
were performed by the following instruments: Bruker CABAV 500neo
(1H NMR: 500 MHz, 13C NMR: 125 MHz) and Bruker AV 600 (1H
NMR: 600 MHz, 13C NMR: 150 MHz). The high-resolution (HR)
mass spectra were measured with an APEX 3 FT-ICR with a 7.05 T
magnet by co. Bruker Daltonics. Electron impact (EI) and matrix-
assisted laser desorption/ionization (MALDI) mass spectra were
measured with a Biflex III by co. Bruker. As matrix was used Cl-CCA.
Infrared spectra were measured on a PerkinElmer 1600 Series FT-IR
spectrometer with an A531-G Golden-Gate-Diamond-ATR-unit.
Signals were abbreviated with w, m, and s for weak, medium, and
strong intensities. Broad signals were additionally labeled with br.
UV−Vis spectra were measured on a Lambda 650 or a Lambda 14
spectrometer (PerkinElmer), at 25 °C, in quartz cuvettes of 1 or 10
mm path length. For column chromatography purifications silica gel
(Merck, particle size 0.040−0.063 mm) was used. Rf values were
determined by thin layer chromatography onPolygram Sil G/UV254
(Macherey-Nagel, 0.2 mm particle size). For column chromatography
purifications amino-functionalized silica gel (Sigma-Aldrich, particle
size 75−200 μm) was used. Rf values were determined by TLC-
KPNH-0510-Fl (Biotage).
Figure 2. UV−vis absorption spectra of reduced and deprotonated
porphyrin species recorded in benzene-d6 at 25 °C (100 μM).
Spectrum in black: free base porphyrin 1c treated with 1 equiv of
KHMDS and subsequent addition of 2 equiv of Ni(COD)2. The
spectrum exhibits the broad signature of phlorin 7c (>700 nm) and
the typical Q bands of 2c (526 and 572 nm). Spectrum in red: Free
base porphyrin 1c treated with 7 equiv of KHMDS and 2 equiv
Ni(COD)2. The spectrum is identical to the doubly deprotonated free
base porphyrin 4c.
Synthetic Procedures. 5,10,15,20-Tetra(4-methoxyphenyl) por-
phyrin (TPPOMe) 1a, tetraphenylporphyrin (TPP) 1b, and meso-
tetrakis(pentafluorophenyl)porphyrin (TPPF20) 1c were synthesized
as reported.36−38
Nickel-tetraphenylporphyrin (NiTPP) 2b. Tetraphenylporphyrin
(50.0 mg, 78.0 μmol) and 4 equiv of bis(cycloocta-1,5-diene)nickel
(85.8 mg, 312 μmol) were dissolved in 50 mL of toluene under
nitrogen (glovebox). After stirring for 1 h at room temperature, the
solvent was removed under reduced pressure, and the crude product
was filtered on a short column with dichloromethane. A mixture of the
Ni-chlorin and Ni-porphyrin was obtained. This mixture was dissolved
in dichloromethane (100 mL), and 2,3-dichlor-5,6-dicyano-1,4-
benzoquinone (100 mg, 440 μmol) was added. After it was stirred
for 2 h at room temperature, the solvent was removed under reduced
pressure, and the crude product was purified by column chromatog-
raphy on silica gel (dichloromethane, Rf = 0.82). Violet crystals were
obtained. Yield: 47.8 mg (71.0 μmol, 91%). 1H NMR (500 MHz, 300
Unfortunately, NMR cannot be applied to further character-
ize the radical anions because of severe paramagnetic line
broadening. Upon addition of 2 equiv of base the phlorin band
7c almost disappeared, and no signature of parent Ni2+porph2−
2c is visible. Quenching of the solution with water yields 66%
chlorin 3c and 34% porphyrin 2c. The results support our
mechanism proposed in Scheme 2. A solution of free base
porphyrin 1c containing 7 equiv of base does not react with
Ni(COD)2. Only the deprotonated free base porphyrin is
present (574 nm) in solution (see Supporting Information).35
K, CDCl3): δ = 8.74 (s, 8H), 8.01 (dd, J = 7.8 Hz, 4J = 1.6 Hz, 8H),
3
+
8.72−8.65 (m, 12H) ppm. MS (MALDI): m/z (%) = 670 [M]
.
HRMS (EI): m/z [M]+ calcd. for C44H28N4Ni: 670.166 74; found:
670.16510.
Nickel-5,10,15,20-tetra(4-methoxyphenyl) porphyrin (NiTPPOMe)
2a. 5,10,15,20-(4-Methoxy)tetraphenylporphyrin (50.0 mg, 68.1
μmol) and 4 equiv of bis(cycloocta-1,5-diene)nickel (74.8 mg, 272
μmol) were dissolved in 150 mL of toluene under nitrogen
(glovebox). After it was stirred for 1 h at room temperature, the
solvent was removed under reduced pressure, and the crude product
was purified by column chromatography on silica gel (dichloro-
methane, Rf = 0.76). Violet crystals were obtained. Yield: 53.1 mg
CONCLUSION
■
In conclusion, we describe a very mild (20 °C) and very
efficient method to insert nickel into free base porphyrins using
Ni(COD)2. This method provides isolated yields between 90%
and 100% with electron-rich as well as electron-deficient
porphyrins. Depending on the electronic nature of the
porphyrin increasing amounts of the corresponding Ni-chlorins
are formed, which can be quantitatively oxidized to the
corresponding porphyrins. Electron-deficient TPPF20 2c yields
66% Ni-chlorin, which is not accessible by any conventional
method. The notoriously difficult separation of porphyrin and
chlorin was achieved on an amino-functionalized silica gel,
taking advantage of the very strong coordination of Ni-chlorins
to amino ligands. Particularly interesting is the insertion of
nickel in the presence of base, giving rise to stable solutions of
Ni-hydroporphyrins. Reduced Ni-porphyrins are key inter-
mediates in several technologically interesting processes and
enzyme reactions. Their reactivity can now be investigated in
bulk.
1
(67.2 μmol, 99%). H NMR (500 MHz, 300 K, CDCl3): δ = 8.76 (s,
8H), 7.92 (d, 3J = 8.7 Hz, 8H), 7.21 (d, 3J = 8.7 Hz, 8H), 4.05 (s, 12H)
ppm. MS (MALDI): m/z (%) = 791 [M]+. HRMS (EI): m/z [M]+
calcd. for C48H36N4NiO4: 790.209 00; found: 790.207 43.
Nickel-tetrakis(pentafluorophenyl)porphyrin (NiTPPF20) 2c. Meth-
od 1 (glovebox): Free base 5,10,15,20-tetrakis(pentafluorophenyl)-
porphyrin 1c (50.0 mg, 51.3 μmol) and 2 equiv of bis(cycloocta-1,5-
diene)nickel (Ni(COD)2), (28.2 mg, 102 μmol) were dissolved in 50
mL of toluene under nitrogen (glovebox). After it was stirred for 30
min at room temperature, the solvent was removed under reduced
pressure, and the crude product was filtered over a short column with
dichloromethane to obtain a mixture of Ni-chlorin and Ni-porphyrin.
This mixture was dissolved in dichloromethane (100 mL), and 2,3-
dichloro-5,6-dicyano-1,4-benzoquinone (100 mg, 440 μmol) was
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added. After it was stirred for 2 h at room temperature, the solvent was
removed under reduced pressure, and the crude product was purified
by column chromatography on silica gel (dichloromethane, Rf = 0.89).
Violet crystals were obtained.
ACKNOWLEDGMENTS
■
The authors gratefully acknowledge financial support by the
Deutsche Forschungsgesellschaft within the Sonderforschungs-
bereich 677, “Function by Switching”.
Method 2 (Schlenk line): 5,10,15,20-Tetrakis(pentafluorophenyl)-
porphyrin 1c (50.0 mg, 51.3 μmol) was dissolved in 50 mL of dry
toluene under nitrogen. Then 2 equiv of bis(cycloocta-1,5-diene)nickel
(Ni(COD)2) (28.2 mg, 102 μmol) was added in counter current flow
of nitrogen. After it was stirred for 30 min at room temperature, the
solvent was removed under reduced pressure, and the crude product
was filtered over a short column with dichloromethane to obtain a
mixture of Ni-chlorin and Ni-porphyrin. This mixture was dissolved in
dichloromethane (100 mL), and 2,3-dichlor-5,6-dicyano-1,4-benzo-
quinone (100 mg, 440 μmol) was added. After it was stirred for 2 h at
room temperature, the solvent was removed under reduced pressure,
and the crude product was purified by column chromatography on
silica gel (dichloromethane, Rf = 0.89). Violet crystals were obtained.
REFERENCES
■
(1) Li, Y.; Zamble, D. B. Nickel Homeostasis and Nickel Regulation:
An Overview. Chem. Rev. 2009, 109, 4617−4643.
(2) Sings, H. L.; Bible, K. C.; Rinehart, K. L. Acyl tunichlorins: a new
class of nickel chlorins isolated from the Caribbean tunicate
Trididemnum solidum. Proc. Natl. Acad. Sci. U. S. A. 1996, 93,
10560−10565.
(3) Gosden, C.; Healy, K. P.; Pletcher, D. Reaction of electro-
generated square-planar nickel(I) complexes with alkyl halides. J.
Chem. Soc., Dalton Trans. 1978, 972−976.
(4) Bakac, A.; Espenson, J. H. Mechanistic Investigation of Carbon-
Carbon Bond Formation in the Reduction of Alkyl Halides by
Organonickel Complexes in Aqueous Solution. J. Am. Chem. Soc. 1986,
108, 719−723.
(5) Gong, M.; Cao, Z.; Liu, W.; Nichols, E. M.; Smith, P. T.; Derrick,
J. S.; Liu, Y.-S.; Liu, J.; Wen, X.; Chang, C. J. Supramolecular
Porphyrin Cages Assembled at Molecular−Materials Interfaces for
Electrocatalytic CO Reduction. ACS Cent. Sci. 2017, 3, 1032−1040.
(6) Solis, B. H.; Maher, A. G.; Dogutan, D. K.; Nocera, D. G.;
Hammes-Schiffer, S. Nickel phlorin intermediate formed by proton-
coupled electron transfer in hydrogen evolution mechanism. Proc.
Natl. Acad. Sci. U. S. A. 2016, 113, 485−492.
1
Yield: (52.8 mg, 51.2 μmol, quant). H NMR (500 MHz, 300 K,
CDCl3): δ = 8.79 (s, 8H) ppm. 19F NMR (470 MHz, 300 K, CDCl3,
CFCl3): δ = −136.64 (dd, 3J = 22.8 Hz, 5J = 7.5 Hz, 8F, o-F), −151.31
3
3
5
(t, J = 20.9 Hz, 4F, p-F), −161.20 (td, J = 22.6 Hz, J = 7.5 Hz, 8F,
m-F) ppm. MS (MALDI): m/z (%) = 1030 [M]+. HRMS (EI): m/z
[M]+ calcd. for C44H8F20N4Ni: 1029.978 31; found: 1029.977 14.
Nickel-tetrakis(pentafluorophenyl)chlorin (NiTPCF20 chlorin) 3c.
Method 1 (without KHMDS): Free base porphyrin 1c and Ni(COD)2
were reacted as described in the first part of the synthesis of
(NiTPPF20) 2c (vide supra). The mixture of Ni-chlorin and Ni-
porphyrin was purified by column chromatography on amino-
functionalized silica gel (59791 Supelco) (dichloromethanen/n-
pentane = 1:3, Rf = 0.63). Yield: 25.9 mg (25.1 μmol, 49%).
(7) Whitlock, H. W.; Hanauer, J. R.; Oester, M. Y.; Bower, B. K.
Diimide reduction of porphyrins. J. Am. Chem. Soc. 1969, 91, 7485−
7489.
(8) Stolzenberg, A. M.; Simerly, S. W.; Steffey, B. D.; Haymond, G. S.
The Synthesis, Properties, and Reactivities of Free-Base- and Zn(II)-
N-Methyl Hydroporphyrin Compounds. The Unexpected Selectivity
of the Direct Methylation of Free-Base Hydroporphyrin Compounds.
J. Am. Chem. Soc. 1997, 119, 11843−11854.
Method
2 (with KHMDS): 5, 10, 15, 20-Tetrakis-
(pentafluorophenyl)porphyrin 1c (50.0 mg, 51.3 μmol) and 2 equiv
potassium bis(trimethylsilyl)amide (KHMDS) (20.5 mg, 102 μmol)
were dissolved in 4 mL of benzene-d6 under nitrogen. After 1 min of
stirring at room temperature, 2 equiv bis(cycloocta-1,5-diene)nickel
(28.2 mg, 102 μmol) was added. After 30 min of stirring at room
temperature the mixture of Ni-chlorin and Ni-porphyrin was separated
by column chromatography on an 3-aminopropyl-functionalized silica
gel (59791 Supelco), (dichloromethane/n-pentane = 1:3, Rf = 0.63).
Yield: 34.9 mg (33.9 μmol, 66%).1H NMR (500 MHz, 300 K, acetone-
(9) Nascimento, B. F.; Rocha Gonsalves, A. M.; Pineiro, M. MnO2
instead of quinones as selective oxidant of tetrapyrrolic macrocycles.
Inorg. Chem. Commun. 2010, 13, 395−398.
3
3
d6): δ = 8.70 (d, J = 5.0 Hz, 2H), 8.52 (s, 2H), 8.34 (d, J = 5.0 Hz,
2H), 4.16 (s, 4H) ppm. 19F NMR (470 MHz, 300 K, CDCl3, acetone-
d6): δ = −139.23 (dd, 3J = 23.0 Hz, 5J = 7.7 Hz, 4F, o-F), −139.68 (dd,
3J = 23.0 Hz, 5J = 7.7 Hz, 4F, o-F), −154.90 (t, 3J = 20.5 Hz, 2F, p-F),
−155.15 (t, 3J = 20.5 Hz, 2F, p-F), −162.79 (td, 3J = 22.5 Hz, 5J = 7.7
(10) Venkataramani, S.; Jana, U.; Dommaschk, M.; Sonnichsen, F.
̈
D.; Tuczek, F.; Herges, R. Magnetic Bistability of Molecules in
Homogeneous Solution at Room Temperature. Science 2011, 331,
445−448.
3
5
(11) Dommaschk, M.; Peters, M.; Gutzeit, F.; Schutt, C.; Nather, C.;
̈
̈
Hz, 4F, m-F), −163.36 (td, J = 22.5 Hz, J = 7.7 Hz, 4F, m-F) ppm.
MS (MALDI): m/z (%) = 1032 [M]+. HRMS (EI): m/z [M]+ calcd.
Sonnichsen, F. D.; Tiwari, S.; Riedel, C.; Boretius, S.; Herges, R.
̈
Photoswitchable magnetic resonance imaging contrast by improved
light-driven coordination-induced spin state switch. J. Am. Chem. Soc.
2015, 137, 7552−7555.
(12) Adler, A. D.; Longo, F. R.; Kampas, F.; Kim, J. On the
Preparation of Metalloporphyrins. J. Inorg. Nucl. Chem. 1970, 32,
2443−2445.
̃
for C44H10F20N4Ni: 1031.993 96; found: 1031.989 96. IR: υ = 2921
(m), 2852 (m), 1741 (m), 1632 (w), 1517 (w), 1494 (m), 1466 (w),
1356 (w), 1261 (m), 1074 (w), 1017 (m), 990 (m), 939 (m), 690 (w),
631 (s), 536 (s), 498 (s), 419 (s), 409 (s) cm−1.
ASSOCIATED CONTENT
■
(13) Kingham, D. J.; Brisbin, D. A. Kinetics of metalloporphyrin
formation in glacial acetic acid. Inorg. Chem. 1970, 9, 2034−2037.
(14) Brisbin, D. A.; Balahura, R. J. Kinetic studies of metal-
loporphyrin formation. Part I. Mn(II) with hematoporphyrin. Can. J.
Chem. 1968, 46, 3431−3436.
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b03164.
(15) Choi, E. I.; Fleischer, E. B. Kinetics of the Reaction of Some
Divalent Transition Metal Ions with α, β, γ, δ-Tetra-(4-pyridyl)-
porphine. Inorg. Chem. 1963, 2, 94−97.
Analytical equipment and methods, spectra (PDF)
(16) Rothemund, P.; Menotti, A. R. Porphyrin Studies. The Metal
Complex Salts of α,β,γ,δ-Tetraphenylporphine. J. Am. Chem. Soc. 1948,
70, 1808−1812.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: rherges@oc.uni-kiel.de.
(17) Barnes, J. W.; Dorough, G. D. Exchange and Replacement
Reactions of α,β,γ,δ-Tetraphenyl-metalloporphins. J. Am. Chem. Soc.
1950, 72, 4045−4050.
ORCID
Rainer Herges: 0000-0002-6396-6991
Notes
The authors declare no competing financial interest.
(18) Pasternack, R. F.; Vogel, G. C.; Skowronek, C. A.; Harris, R. K.;
Miller, J. G. Copper (II) incorporation into tetraphenylporphine in
dimethyl sulfoxide. Inorg. Chem. 1981, 20, 3763−3765.
E
DOI: 10.1021/acs.inorgchem.7b03164
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(19) Bain-Ackerman, M. J.; Lavallee, D. K. Kinetics of metal-ion
complexation with n-methyltetraphenylporphyrin. Inorg. Chem. 1979,
18, 3358−3364.
(20) Baum, S. J.; Plane, R. A. Kinetics of the Incorporation of
Magnesium(II) into Porphyrin. J. Am. Chem. Soc. 1966, 88, 910−913.
(21) Bhyrappa, P.; Nethaji, M.; Krishnan, V. Structure of nonplanar
octabromotetraphenyl porphyrin and kinetics of rapid metalation
reactions. Chem. Lett. 1993, 22, 869−872.
(22) Dean, M. L.; Schmink, J. R.; Leadbeater, N. E.; Bruckner, C.
̈
Microwave-promoted insertion of Group 10 metals into free base
porphyrins and chlorins: scope and limitations. Dalton Trans. 2008,
1341−1345.
(23) Han, Y.; Fang, H.; Jing, H.; Sun, H.; Lei, H.; Lai, W.; Cao, R.
Singly versus Doubly Reduced Nickel Porphyrins for Proton
Reduction: Experimental and Theoretical Evidence for a Homolytic
Hydrogen-Evolution Reaction. Angew. Chem., Int. Ed. 2016, 55, 5457−
5462.
(24) Fleischer, E. B. Structure of porphyrins and metalloporphyrins.
Acc. Chem. Res. 1970, 3, 105−112.
(25) Alden, R. G.; Crawford, B. A.; Doolen, R.; Ondrias, M. R.;
Shelnutt, J. A. Ruffling of nickel (II) octaethylporphyrin in solution. J.
Am. Chem. Soc. 1989, 111, 2070−2072.
(26) Buchler, J. W. In Porphyrins and Metalloporphyrins; Smith, K. M.,
Ed.; Elsevier: Amsterdam, Netherlands, 1975; p 157.
(27) Tsutsui, M.; Velapoldi, R. A.; Suzuki, K.; Vohwinkel, F.;
Ichikawa, M.; Koyano, T. Unusual metalloporphyrins. IV. Novel
methods for metal insertion into porphyrins. J. Am. Chem. Soc. 1969,
91, 6262−6266.
(28) Ostfeld, D.; et al. Novel metalloporphyrins. Syntheses and
implications. Acc. Chem. Res. 1974, 7, 52−58.
(29) Peters, M. K.; Thoms, V.; Herges, R. unpublished results.
(30) Dommaschk, M.; Thoms, V.; Schutt, C.; Nather, C.; Puttreddy,
̈
̈
R.; Rissanen, K.; Herges, R. Coordination-Induced Spin-State
Switching with Nickel Chlorin and Nickel Isobacteriochlorin. Inorg.
Chem. 2015, 54, 9390−9392.
́
(31) Lexa, D.; Momenteau, M.; Mispelter, J.; Saveant, J. M. Does
one-electron transfer to nickel (II) porphyrins involve the metal or the
porphyrin ligand? Inorg. Chem. 1989, 28, 30−35.
(32) Kadish, K. M.; van Caemelbecke, E.; Royal, G. Electrochemistry
of Metalloporphyrins in Nonaqueous Media. In The Porphyrin
Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic
Press: San Diego, CA, 2000; Vol. 8, pp 1−114.
(33) Campbell, C. J.; Rusling, J. F.; Bruckner, C. Nickel(II) meso-
̈
Tetraphenyl-Homoporphyrins, -secochlorins, and -chlorophin: Con-
trol of Redox Chemistry by Macrocycle Rigidity. J. Am. Chem. Soc.
2000, 122, 6679−6685.
(34) Fang, Y.; Gorbunova, Y. G.; Chen, P.; Jiang, X.; Manowong, M.;
Sinelshchikova, A. A.; Enakieva, Y. Y.; Martynov, A. G.; Tsivadze, A.
Y.; Bessmertnykh-Lemeune, A.; Stern, C.; Guilard, R.; Kadish, K. M.
Electrochemical and Spectroelectrochemical Studies of Diphosphory-
lated Metalloporphyrins. Generation of a Phlorin Anion Product.
Inorg. Chem. 2015, 54, 3501−3512.
(35) Guo, H.; Jiang, J.; Shi, Y.; Wang, Y.; Wang, Y.; Dong, S.
Sequential Deprotonation of meso-(p-Hydroxyphenyl)porphyrins in
DMF: From Hyperporphyrins to Sodium Porphyrin Complexes. J.
Phys. Chem. B 2006, 110, 587−594.
(36) Maqueira, L.; Iribarren, A.; Valdes, A. C.; De Meloc, C. P.; Dos
Santos, C. G. Preparation and characterization of SDS-stabilized
hydrophobic porphyrinic nanoaggregates in water. J. Porphyrins
Phthalocyanines 2012, 16, 267−272.
(37) Plater, M. J.; Aiken, S.; Bourhill, G. Metallated porphyrins
containing lead (II), copper (II) or zinc (II). Tetrahedron 2002, 58,
2415−2422.
(38) Dommaschk, M.; Gutzeit, F.; Boretius, S.; Haag, R.; Herges, R.
Coordination-Induced Spin-State-Switch (CISSS) in water. Chem.
Commun. 2014, 50, 12476−12478.
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