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reductive coupling of 2 was performed. Under these condi-
tions, zinc porphyrins and carboxylic ester moieties in the sub-
strates did not interfere with the reaction. A 1:1 mixture of
[
Ni(cod) ] (7–20 equiv) and 2,2’-bpy (7–20 equiv) was treated
2
with porphyrinatozinc 2 in anhydrous THF or anhydrous DMF
under an argon atmosphere at 508C for 12 h. When ethyl-sub-
stituted 2b was used as the starting material, the coupling re-
0
action proceeded in THF, and seven equivalents of the Ni –bpy
system were enough to consume most of the starting material.
However, in the case of the Mes-substituted complex 2a, the
conditions discussed above were insufficient, and treatment
0
with 20 equivalents of the Ni –bpy system in the more active
[
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solvent DMF gave better results with regard to the reprodu-
cible consumption of starting materials. After the reactions
were completed, the mixture was washed with an aqueous
ammonium solution to remove excess of nickel species, and
the organic layer was extracted with CHCl . The organic layer
3
was analyzed by means of a GPC system fitted with three poly-
styrene-based GPC columns (two TSKgel G2500HHR (exclusion
limit 20000 Da, 7.8 mm inner diameter (I.D.)30 cm) and
a TSKgel G2000HHR (exclusion limit 10000 Da, 7.8 mm I.D.
3
0 cm)) connected in series to a photodiode array detector.
The elution profiles from the GPC column monitored at l=
56 and 566 nm, respectively, are depicted as solid lines in
5
Figure 2. Only porphyrin derivatives can be observed at this
detection frequency. The plain Gaussian curves shown in
Figure 2, which were obtained by deconvolution analysis by
using OriginPro8 software, revealed that more than 10 compo-
nents containing porphyrin oligomers were present in the
crude samples. The ratio of each component varied in each ex-
periment, even under the same conditions, and the represent-
ed profiles are most typical. In the sample analyzed in Fig-
ure 2a and b, the component eluting at 22.5 and 25.6 mL, re-
spectively (shaded areas, assigned as C-3mer, see below), were
obtained as the dominant species. The crude mixture was fur-
ther separated by using a preparative GPC column packed
with polystyrene-based gel (Biorad S-X1 (exclusion limit
Figure 2. Bold lines in a) and b): typical GPC chromatograms of reaction mix-
tures obtained by nickel-mediated coupling of 1a (R=Mes) and 1b
(R=ethyl) (column: TOSOH TSKgel G2500HHR (300 mm (length))2 (exclu-
sion limit, 20000 Da)+TOSOH TSKgel G2000HHR (300 mm (length))1 (ex-
À1
clusion limit, 10000 Da), eluent: pyridine, flow rate: 1.0–1.2 mLmin ), moni-
tored at: a) l=556, and b) 566 nm). EV: elution volume. Plain lines in a) and
b): deconvolution analysis of the chromatograms by Gaussian curve fitting
by means of OriginPro8 software. The shaded peaks indicate C-3mers: a) 1a,
and b) 1b.
1
4000 Da), 3 cm diameter1 m length) with a mixture of tolu-
ene and pyridine (85:15 v/v) as the eluent under atmospheric
pressure. MALDI-TOF MS analysis of the fractions showed mass
fragments that were approximately two to five times larger
than those of starting monomers 2, which suggested that the
reductive coupling reaction produced di- to pentameric por-
phyrin oligomers. Some estimated structures are shown in
Scheme 1. The terminal moieties of acyclic porphyrin oligo-
mers, indicated as X in A-nmer in Scheme 1, were assigned as
H, Cl, or OH, but some unidentified signals were also observed
in the MALDI-TOF MS analyses.
method could be used to isolate the C-3mer 1b, other chro-
matographic techniques involving modified silica gel were sur-
veyed to find a more efficient method. Four analytes, com-
pound 2b and three fractions containing mainly acyclic dimer
(ethyl A-2mer), acyclic trimer (ethyl A-3mer), and cyclic trimer
(ethyl C-3mer), were prepared to compare the elution behavior
in various modified silica-based columns. Eight HPLC columns
(COSMOSILꢁ series), C18-MS-II, Cholester, PYE, pNAP, NPE, PBB-
R, NPE, and CN-MS (4.6 mm I.D.15 cm), supplied by Nacalai
Tesque were tested. The chemical structures of the functional
groups on these columns are shown in Figure 3. Thus, octadec-
yl, cholesterol ether, pyrenylethyl, naphthylethyl, pentabromo-
benzyl ether, nitrophenylethyl, and cyanopropyl moieties were
attached to silica gel (5 mm particle, 120 pore). GPC and
MALDI-TOF MS analyses of the four analytes used herein are
shown in Figures S1–S4 in the Supporting Information. A mix-
ture of toluene and pyridine was used as the eluent. The polar-
ity parameters of the solvents were 2.3 (toluene) and 5.3 (pyri-
The following detailed analysis describes the case of using
ethyl-substituted 2b as a starting material for the coupling re-
action. In the GPC chromatographic separation, compounds
corresponding to the trimer were detected in two fractions,
with the later eluting compound assigned as the target C-
3
mer 1b based on high-resolution MALDI-TOF MS analysis.
However, in addition to the target C-3mer 1b, the fraction con-
tained other mono- and dimeric porphyrin derivatives; thus
further purification was required. Although a recycling GPC
[
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dine); therefore, the combination of these solvents worked
Chem. Eur. J. 2015, 21, 11745 – 11756
11747 ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim