Synthesis and electronic properties of meso -tetra(3,4,5-trimethoxy)phenyl-porphyrin and -tetrabenzoporphyrin and their phosphorus complexes

Article abstract of DOI:10.1142/S1088424619500871

meso-Tetra(3,4,5-trimethoxy)phenyl-porphyrin and -tetrabenzoporphyrin and their phosphorus complexes were synthesized and their electronic absorption and magnetic circular dichroism (MCD) spectra discussed based on TD-DFT molecular orbital (MO) calculatio

Full text of DOI:10.1142/S1088424619500871

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2019; 23: 1–7
DOI: 10.1142/S1088424619500871
Published at http://www.worldscinet.com/jpp/
Synthesis and electronic properties of meso-tetra(3,4,5-
trimethoxy)phenyl-porphyrin and -tetrabenzoporphyrin
and their phosphorus complexes
Taniyuki Furuyamaa,b*, Yuichi Takahashib, Tomoteru Fukumurab,
Ana C. C. Bacillac and Nagao Kobayashib,c*
a Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-Machi,
Kanazawa 920-1192, Japan
b Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
c Faculty of Textile Science and Technology, Shinshu University, Ueda 386-8567, Japan
Dedicated to Professor Atsuhiro Osuka on the occasion of his 65th birthday.
Received 30 April 2019
Accepted 14 June 2019
ABSTRACT: meso-Tetra(3,4,5-trimethoxy)phenyl-porphyrin and -tetrabenzoporphyrin and their phos-
phorus complexes were synthesized and their electronic absorption and magnetic circular dichroism
(MCD) spectra discussed based on TD-DFT molecular orbital (MO) calculations. Nucleus-independent
chemical shift (NICS) and anisotropy of the induced current density (ACID) calculations were also
carried out for metal-free (and phosphorus) tetrabenzoporphyrins in order to discuss the aromaticity and
flow of electrons in the molecule.
KEYWORDS: porphyrin, tetrabenzoporphyrin, absorption, MCD, phosphorus, ACID, NICS.
compounds are discussed using electronic absorption and
INTRODUCTION
magnetic circular dichroism (MCD) spectra, together
Over the past few years, we have reported phosphorus
with the results of molecular orbital (MO) calculations.
complexes of tetraazaporphyrins (TAPs) having strong
NMR data and the ring current flow of electrons are also
charge-transfer (CT) bands between the Soret and
discussed, based on nucleus-independent chemical shift
Q bands [1], as well as phthalocyanines (Pcs) showing
(NICS) and anisotropy of the current-induced density
Q bands beyond 1000 nm [2, 3]. The phosphorus com-
(ACID) calculations.
plexes of regular porphyrin (Por) and tetrabenzo-
porphyrin (TBP) appear to be important as meso-
nitrogen-removed parent porphyrinoids of TAPs and Pcs,
respectively. Accordingly, we have decided to synthesize
and examine the spectroscopic properties of P(V)Por and
EXPERIMENTAL
Measurments
P(V)TBPs. In order to increase the solubility of the target
compounds, and from the perspective of easy synthesis,
we have designed the synthesis of tetra(3,4,5-trimethoxy)
phenyl-porphyrin and -tetrabenzoporphyrin and their
phosphorus complexes. The electronic structures of these
NMR spectra were obtained on a Bruker AVANCE
500 spectrometer. Chemical shifts are expressed in d
(ppm) values, and coupling constants are expressed
in hertz (Hz). 1H-NMR spectra were referenced to
the residual solvent as an internal standard. 31P-NMR
spectra were referenced to external 85% H3PO4 solution
(0.0 ppm). The following abbreviations are used: s =
singlet, d = doublet, m = multiplet, and brs = broad
singlet. MALDI-TOF mass spectra (MALDI-MS) were
*Correspondence to: Nagao Kobayashi, email: nagaok@
shinshu-u.ac.jp; Taniyuki Furuyama, email: tfuruyama@
se.kanazawa-u.ac.jp.
Copyright © 2019 World Scientific Publishing Company

2
T. FURUYAMA ET AL.
recorded on a Bruker Daltonics solariX spectrometer. Elect-
ronic absorption spectra were recorded on a JASCO
V-570 spectrophotometer. Magnetic circular dichroism
(MCD) spectra were recorded on a JASCO J-725
spectrodichrometer with a magnetic field of up to 1.03 T.
(200 mg) were dissolved in 180 mL CH2Cl2 and the
·
mixture stirred for 5 min. Then, 3 drops of BF3 OEt2
were added to the mixture, and stirred for 12 h, followed
by the addition of p-chloranil (20 mg, 0.09 mmol). After
3 h, the mixture was washed with sat. NaHCO3aq. The
organic layer was dried over MgSO4, and concentrated
in vacuo. The product was purified by silica gel column
chromatography (CHCl3), to give the title compound
Computation
In order to obtain simulated UV-vis absorption
spectra, the Gaussian 09 software package was used
to carry out DFT and TDDFT calculations using the
B3LYP functional with 6-31G(d) basis sets [4]. Nucleus-
independent chemical shift (NICS) [5] calculations
and anisotropy of the current-induced density (ACID)
calculations [6, 7] were performed at the CAM-B3LYP/
6-31G(d) level.
1
(45 mg, 33%) as a purple powder. 500 MHz H-NMR
(CDCl3) d (ppm): 7.52 (m, 8H), 6.54 (m, 8H), 4.23–3.64
(m, 36H), 1.41 (m, 16H).
meso-Tetra(3,4,5-trimethoxyphenyl)-
tetrabenzoporphyrin free-base, H2Ar4TBP
ZnAr4P (45 mg, 0.033 mmol) was dissolved in 5 mL
acetic acid and stirred for 30 min at room temperature.
Then, the solution was neutralized by NaOHaq, and
the resulting precipitation collected by filtration and
washed by water. The resultant purple powder that was
assumed to be the metal-free compound of ZnAr4P
was heated at 200 °C for 10 min under reduced
pressure. Analytically pure H2Ar4TBP (20 mg, 94%)
Synthesis
The synthesis of various metal-free and phosphorus(V)
complexes was carried out according to the procedure
shown in Scheme 1. The key starting compound 1 was
prepared in four steps from commercially available
chemicals by the procedure reported by Ono and Uno
et al. [8, 9]. The specific details of the porphyrin synthesis
are described below. The yield of phosphorus insertion is
not high.
1
was obtained as a green powder. 500 MHz H-NMR
(CDCl3) d(ppm): 7.61 (s, 8H), 7.60–7.20 (12H, br),
4.26 (s, 12H), 3.92 (s, 24H), -1.31 (s, 2H, inner NH).
HRMS-MALDI (m/z) Calcd for C72H62N4O12 [M]+:
1174.4359. Found: 1174.4359. UV-vis (CHCl3/1%
Et3N) lmax nm (e × 10-5): 692 (0.10), 640 (0.38), 592
(0.13), 549 (0.06), 464 (2.87).
Bicyclo[2,2,2]octadiene-fused zinc porphyrin, ZnAr4P
Compound1(58mg,0.40mol)[8,9],3,4,5-trimethoxy-
benzaldehyde (78 mg, 0.40 mmol) and zinc acetate
Ar
Ar
NH
NH
N
N
N
N
N
N
c
b
1
a
Ar
Ar
Zn
Ar
Ar
+
HN
H3CO
H3CO
H3CO
CHO
Ar
Ar
OCH3
Ar =
OCH3
OCH3
H2Ar4TBP
ZnAr4P
+
Cl
Ar
+
Ar
Ar
L
N
N
N
N
N
NH
N
N
c'
d'
Ar
Ar
P
Ar
Ar
P
Ar
Ar
N
N
N
HN
-
ClO4
-
Cl
ClO4
L
Ar
Ar
Ar
OCH3
OCH3
OCH3
L = Cl
P(V)Ar4P
P(V)Ar4TBP
Ar =
H2Ar4P
d
L = OCH3
·
Scheme 1. Synthesis of porphyrins in this study. Reagents and conditions: (a) Zn(OAc)2, BF3 OEt2, CH2Cl2, rt, 12 h, then p-chloranil,
3 h. 33%; (b) AcOH, rt, 30 min, 94%, and then 200°C, 10 min, reduced pressure; (c) POCl3, pyridine, reflux, 3 days, then NaClO4
in CH3CN, rt, 12 h. 25%; (c′) POCl3, pyridine, reflux, 3 days, then NaClO4 in CH3CN, rt, 12 h; (d′) MeOH, rt, 12h, then NaClO4 in
CH3CN, rt, 12 h, 8.5% through (c′) and (d′)
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 2–7

SYNTHESIS AND ELECTRONIC PROPERTIES OF meso-TETRA(3,4,5-TRIMETHOXY)PHENYL-PORPHYRIN
3
meso-Tetrakis(3,4,5-trimethoxyphenyl)-
tetrabenzoporphyrinatophosphorus(V),
P(V)Ar4TBP
stirring the mixture for 12 h at room temperature, the
solvent was removed. Recrystallization from CH2Cl2/
nhexane afforded pure P(V)Ar4P (2.0 mg, 8.5%) as a
purple powder. 500 MHz 1H-NMR (CDCl3) d(ppm): 9.16
(s, 8H), 7.19 (s, 8H), 4.08 (s, 12H), 3.95 (s, 24H), -1.86 (d,
6H, 3JPH = 25.8 Hz). 200 MHz 31P-NMR (CDCl3) d(ppm):
-177. HRMS-MALDI (m/z) Calcd for C58H58N4O14P [M–
ClO4]+: 1065.3682. Found: 1065.3683. UV-vis (CHCl3)
POCl3 (0.2 mL) was added to a solution of H2Ar4TBP
(20 mg, 0.017 mmol) in 2 mL pyridine. After stirring
the mixture for 72 h under reflux, it was concentrated
in vacuo, and the crude P(V)Ar4TBP purified by silica
gel column chromatography (CH2Cl2 : MeOH = 7 : 1
v/v), then alumina column chromatography (CH2Cl2 :
MeOH = 10 : 1). Counter anion exchange was carried
out by dissolving the counter anion mixture of P(V)
Ar4TBP in CH3CN and sodium perchlorate was added to
the solution. After stirring the mixture for 12 h at room
temperature, the solvent was removed. Recrystallization
fromCH2Cl2/nhexaneaffordedpureP(V)Ar4TBP(5.8mg,
l
max nm (e × 10-5): 616 (0.04), 569 (0.08), 451 (0.65).
RESULTS AND DISCUSSION
All NMR and mass data supported the expected
structure of the compounds. The chemical shift values
of the pyrrole hydrogens of H2Ar4P and benzo-
fused H2Ar4TBP appeared at -2.78 and -1.31 ppm,
respectively, indicating that the ring current of the former
is larger compared to the latter. According to chemical-
shift data on the pyrrole nitrogens of tetraazaporphyrin,
phthalocyanine, naphthalocyanine, and anthracocyanine
having the same number of the same substituent at similar
positions, this chemical-shift value is known to shift to
lower field with increasing number of fused benzo-rings
[10], and it was therefore concluded that the ring current
of the tetraazaporphyrin macrocycle decreases in this
order.Accordingly, our present data indicate that a similar
conclusion is induced for regular porphyrins which do
not contain meso-nitrogens. In order to examine whether
the experimental data can be reasonably explained by
quantum chemical calculations, the NICS values for
H2Ar4P and benzo-fused H2Ar4TBP were compared
(Figs 1a and 1b). As can be seen in this figure, the NICS
values in the center of H2Ar4P is negatively larger than
that of H2Ar4TBP, in accordance with the experimental
NMRdata, supportingtheconclusionthatthediamagnetic
ring current is more intense for H2Ar4P without fused
benzenes. In order to further visualise the reason for
this, ACID calculations were performed for H2Ar4TBP
(Fig. 1c). As can be seen, the current flow in the inner
perimeter is clockwise, while that in the peripheral
four benzene rings is also clockwise. Accordingly, it is
inferred that an opposite flow at the border between the
benzene moiety and the inner perimeter reduces the ring
current of the central moiety of H2Ar4TBP, particularly
including the pyrrole b-b line.
1
25%) as a green powder. 500 MHz H-NMR (CDCl3)
d(ppm): 7.75 (m, 8H), 7.58 (m, 8H), 4.19 (s, 12H), 3.80
(s, 24H). 200 MHz 31P-NMR (CDCl3) d(ppm): -176.
HRMS-MALDI (m/z) Calcd for C72H60Cl2N4O12P [M–
ClO4]+: 1273.3317. Found: 1273.3316. UV-vis (CHCl3)
l
max nm (e × 10-5): 715 (0.90), 650 (0.11), 471 (1.34).
meso-Tetra(3,4,5-trimethoxyphenyl) porphyrin
free-base, H2Ar4P
Pyrrole (0.17 mL, 1.6 mmol) and 3,4,5-trimethoxy-
benzaldehyde (490 mg, 1.6 mmol) were dissolved in
250 mL CH2Cl2 and the mixture stirred for 5 min. Then,
·
BF3 OEt2 (3.0 mL, 3 mmol) was added to the mixture, and
it was stirred for 2 h at room temperature, followed by
the addition of p-chloranil (500 mg, 2.0 mmol). After
refluxing for 3 h, the mixture was washed with sat.
NaHCO3aq., then the organic layer dried over MgSO4,
and concentrated in vacuo. The product was purified by
silica gel column chromatography (CH2Cl2 : MeOH =
20: 1), to yield H2Ar4P (61 mg, 16%) as a purple powder
1
after recrystallization from MeOH. 500 MHz H-NMR
(CDCl3) d(ppm): 8.95 (s, 8H), 8.49 (d, 8H, J = 7.0 Hz),
4.18 (s, 12H), 3.97 (s, 24H), -2.78 (s, 2H, inner NH).
HRMS-MALDI (m/z) Calcd for C56H54N4O12 [M]+:
974.3733. Found: 974.3724. UV-vis (CHCl3/1% Et3N)
l
max nm (e × 10-5): 649 (0.04), 591 (0.06), 553 (0.07), 518
(0.17), 424 (3.90).
meso-Tetra(3,4,5-trimethoxyphenyl)
porphyrinatophosphorus(V), P(V)Ar4P
Fig. 2 shows the electronic absorption and MCD
spectra of H2Ar4TBP, P(V)Ar4TBP, H2Ar4P, and
P(V)Ar4P. The shapes of the spectra of H2Ar4TBP and
H2Ar4P are quite similar to those of previously reported
meso-tetraphenylated tetrabenzoporphyrin [11] and
porphyrin [12], respectively, although the positions of
the peaks (and troughs in the case of MCD) are shifted
slightly (a few to 15 nm) to longer wavelengths. Although
the molecular symmetry of H2Ar4TBP and H2Ar4P
changes on metalation from approximate D2h to D4h, the
most significant changes on phosphorus insertion are the
Insertion of phosphorus(V) into H2Ar4P was carried
out as for the above H2Ar4TBP. The resulting crude P(V)
Ar4P containing two axial Cl ligands was dissolved in
MeOH, and the mixture stirred for 12 h, then the solvent
removed. The obtained crude P(V)Ar4P containing two
axial OMe ligands was purified by silica gel column
chromatography (CH2Cl2 : MeOH = 10 : 1 v/v, twice).
Counter anion exchange was carried out by dissolving
the counter anion mixture of P(V)Ar4P in CH3CN and
sodium perchlorate was added to the solution. After
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J. Porphyrins Phthalocyanines 2019; 23: 3–7

4
T. FURUYAMA ET AL.
(a)
(b)
broadening of the Soret band with concomitant decrease
in absorption coefficient, significant red-shift of the Soret
band for P(V)Ar4P, and intensification of the Q band
for P(V)Ar4TBP. The large decrease in the absorption
coefficients at the Soret band by metal insertion has
not been seen for other metal, and is characteristic of
phosphorus insertion. The Q band of P(V)Ar4TBP is
much stronger than that of P(V)Ar4P, experimentally
suggesting that the energy difference between the HOMO
and spectroscopic HOMO–1 in P(V)Ar4TBP is larger
than that of P(V)Ar4P [13–15]. In the MCD spectra of the
phosphorus complexes, dispersion type curves (Faraday
A-term) appeared corresponding to each absorption
peak, suggesting that the excited state is degenerate. The
MCD intensity per unit absorbance in the Q band region
is larger than that in the Soret region, reflecting a large
angular momentum change in the Q band region [16].
From the minus-to-plus sign change in ascending energy,
it is inferred that the DHOMO (energy difference between
the HOMO and spectroscopic HOMO-1) is larger than
the DLUMO (energy difference between the LUMO and
spectroscopic LUMO+1) [14–16].
Ar
Ar
c'
d'
c
d
b
b
NH
N
N
NH
N
c
N
Ar
Ar
Ar
Ar
HN
HN
a
a
d
Ar
Ar
NICS(0) = -14.865
NICS(1) = -12.881
a = -12.669
NICS(0) = -12.906 c = 4.725
NICS(1) = -11.135 c' = 3.071
NICS(-1)= -12.241 d = -11.204
a = -8.428 d' = -10.714
b = 0.357
b = -3.440
c = 3.838
d = 1.595
(c)
In order to enhance the interpretation of the spectra,
molecular orbital calculations have been performed,
and the results are shown in Fig. 3, with some data
summarized in Table 1. From the data appearing in Fig. 3
and Table 1, the following information emerged. (1) The
DHOMO>DLUMO relationship always exists for both
metal-free and phosphorus-inserted species, supporting
a minus-to-plus sign pattern of MCD in ascending
energy [16]. (2) Insertion of the highly positive P(V)
ion stabilizes the frontier orbitals by ca. 3 eV. (3) The
Fig. 1. Computed NICS values (in ppm) for the DFT-optimized
structure of (a) tetraphenylporphyrin and (b) tetraphenyl-
tetrabenzoporphyrin at various positions (3,4,5-trimethoxy
groups were omitted from the structure of H2Ar4P and
H2Ar4TBP for clarity). (c) CalculatedACID plot for H2Ar4TBP
at an isovalue of 0.03.
Fig. 2. Electronic absorption (bottom) and MCD (top) spectra of (a) H2Ar4TBP (gray) and P(V)Ar4TBP (black) and (b) H2Ar4P
(gray) and P(V)Ar4P (black) in CHCl3
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SYNTHESIS AND ELECTRONIC PROPERTIES OF meso-TETRA(3,4,5-TRIMETHOXY)PHENYL-PORPHYRIN
5
Fig. 3. Partial molecular energy diagram and orbitals of phosphorus(V) complexes (left) and metal-free complexes (right), and their
calculated absorption spectra (bottom). Calculations were performed at the B3LYP/6-31G* level. The orbitals 274–279 of P(V)
Ar4P are 3,4,5-trimethoxyphenyl-centered orbitals and therefore a1u type orbital 273 is the spectroscopic HOMO–1 (The HOMO of
P(V)Ar4P is a2u-type orbital 280)
DHOMO of P(V)Ar4TBP was estimated to be larger than
that of P(V)Ar4P, in accordance with the more intense
Q band of the former [13]. (4) As found experimentally,
the calculated positions of both the Q and Soret bands
of P(V)Ar4P appeared at shorter wavelength than those
of P(V)Ar4TBP. (5) The calculated Soret band intensity
of P(V)Ar4P is slightly weaker than that of H2Ar4P;
however, the intensity of P(V)Ar4TBP is much weaker
than that of H2Ar4TBP. Thus, the marked weakening
of the Soret band on going from H2Ar4TBP to P(V)
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6
T. FURUYAMA ET AL.
Table 1. Calculated transition energies, oscillator strengths (f), and compositionsa
Compound
l (nm)
f
Composition (%)
[P(V)Ar4TBP]+
663.4 (Q)
663.2 (Q)
421.5 (B)
0.15
0.15
0.83
H-1→L+1 (11%), H→L (85%)
H-1→L (11%), H→L+1 (85%)
H-9→L (7%), H-9→L+1 (10%), H-8→L+1 (2%), H-7→L (4%),
H-5→L+1 (3%), H-4→L (3%), H-4→L+1 (11%), H-3→L (8%),
H-1→L (11%), H-1→L+1 (20%), H→L (7%), H→L+1 (5%)
421.4 (B)
0.83
H-9→L (9%), H-9→L+1 (8%), H-8→L (3%), H-7→L+1 (4%),
H-5→L (3%), H-4→L (12%), H-4→L+1 (3%), H-3→L+1 (8%),
H-1→L (20%), H-1→L+1 (11%), H→L (5%), H→L+1 (7%)
[P(V)Ar4P]+
605.2 (Q)
604.8 (Q)
381.0 (B)
380.0 (B)
0.05
0.07
0.78
0.82
H-7→L+1 (5%), H-3→L+1 (3%), H-2→L+1 (11%), H→L (70%),
H→L+1 (6%)
H-7→L+1 (4%), H-3→L (4%), H-2→L (12%), H→L (7%), H→L+1
(69%)
H-15→L+1 (3%), H-9→L (33%), H-8→L+1 (9%), H-7→L+1 (25%),
H-6→L (8%), H-3→L+1 (2%), H-2→L+1 (3%), H–>L (5%)
H-9→L+1 (35%), H-8→L (10%), H-7→L (24%), H-6→L+1 (7%),
H-3→L (3%), H-2→L (3%), H→L+1 (5%)
H2Ar4TBP
H2Ar4P
631.2 (Q)
612.3 (Q)
442.1 (B)
428.3 (B)
0.01
0.10
1.37
1.42
H-1→L (45%), H→L+1 (54%)
H-1→L+1 (26%), H→L (74%)
H-11→L (3%), H-1→L (52%), H→L+1 (43%)
H-1→L+1 (72%), H→L (25%)
582.8 (Q)
546.2 (Q)
406.2 (B)
0.03
0.06
0.79
H-1→L (32%), H→L+1 (65%)
H-1→L+1 (34%), H→L (64%)
H-11→L+1 (7%), H-7→L (3%), H-5→L (4%), H-4→L (4%),
H-2→L+1 (8%), H-1→L (45%), H-1→L+1 (3%), H→L+1 (20%)
398.6 (B)
0.93
H-7→L (3%), H-7→L+1 (5%), H-6→L+1 (3%), H-4→L+1 (3%),
H-3→L+1 (4%), H-2→L (3%), H-2→L+1 (5%), H-1→L (3%),
H-1→L+1 (41%), H→L (21%)
a To identify the Q and B band assignments, the Gouterman’s four orbitals were used. When no CT band is expected, the band at
the longest wavelength which has large H→L and/or H→L+1 composition is assigned to the Q band. The B band appears at shorter
wavelength than the Q band and its intensity is (much) higher than that of the Q band. The B band has large contribution of the
H-1→L and/or H-1→L+1 transitions.
Ar4TBP was reproduced by the calculations. However,
there are two aspects that are not compatible with the
experiments. Firstly, (6) the calculated Soret band was
estimated to shift to shorter wavelength, in contrast to
longer wavelength shift by phosphorus insertion, and
secondly, (7) some weak bands were calculated between
the Soret and Q bands of P(V)Ar4P (not shown, these
are CT bands between the central porphyrin core and
the 3,4,5-trimethoxyphenyl groups), although no such
features were observed experimentally.
phosphorus complexes of meso-tetra(3,4,5-trimethoxy-
phenyl)porphyrin and meso-tetra(3,4,5-tri methoxy-
phenyl)tetrabenzoporphyrin. It was found that the
diamagnetic ring current in the normal porphyrin
skeleton is larger than in tetrabenzoporphyrin. This
was supported also by NICS and ACID calculations.
On phosphorus(V) ion insertion, the Soret band
intensity of the two complexes decreased significantly
and shifted to longer wavelength, while the Q band of
tetrabenzoporphyrin intensified significantly. In the MO
calculations, the significant decrease of the Soret band
intensity of benzoporphyrin was reproduced, although
somedecreaseoftheSoretbandonP(V)ioninsertioninto
normal porphyrin (i.e. into H2Ar4P) was also estimated.
The true reason for the decrease of Soret band intensity
CONCLUSIONS
In summary, we have described the synthesis
and spectroscopic characterization of metal-free and
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SYNTHESIS AND ELECTRONIC PROPERTIES OF meso-TETRA(3,4,5-TRIMETHOXY)PHENYL-PORPHYRIN
7
on P(V) ion-insertion was, however, not elucidated, even
7. Geuenich D, Hess K, Köhler F and Herges R. Chem.
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8. Okujima T, Jin G, Hashimoto Y, Yamada H, Uno H
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based on the results of MO calculations. In agreement
with the experimentally observed intensification of the
Q band, the calculated DHOMO increased on going from
H2Ar4TBP to P(V)Ar4TBP. The minus-to-plus MCD
sign in ascending energy seen experimentally indicated
that DLUMO is smaller than DHOMO in both metal-
free and P(V) ion-inserted complexes [16], and this was
reproduced by MO calculations. Since the insertion of
the P(V) ion stabilized the frontier orbitals by ca. 3 eV,
the phosphorus complexes appeared to be more stable
than other transition metal-inserted porphyrins and
benzoporphyrins to oxidation in the air.
12. Rhoda HM,Akhigbe J, Ogikubo J, Sabin JR, Ziegler
CJ, Bruckner C and Nemykin VN. J. Phys. Chem.
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13. Gouterman M. In The Porphyrins, Ed. by Dolphin
D., NewYork: Academic Press. 1978. V. 3. Chap. 1.
14. “Spectroscopic HOMO–1” and “spectroscopic
LUMO+1” are sometimes different from the
calculated HOMO–1 and LUMO+1, respectively.
The most often encountered case is that containing
substituent groups. If the coefficients of molecular
orbitals are larger for substituent groups rather
than along the inner perimeter of the ligand, these
orbitals are often (but not always) eliminated from
the spectroscopic consideration. An example is seen
in Fig. 3 of Ref. 15. The spectroscopic HOMO–1,
HOMO, LUMO, and LUMO+1 are orbitals that can
be derived from a parent hydrocarbon perimeter.
15. Okujima T, Ando C, Agrawal S, Matsumoto H,
Mori S, Ohara K, Hisaki I, Nakae T, Takase M, Uno
H and Kobayashi N. J. Am. Chem. Soc. 2016; 138:
7540–7543.
Acknowledgments
This work was supported by JSPS KAKENHI Grant
Numbers 18K19071 (TF) and 18K05076 (NK). The
authors thank the Ministry of Education, Culture, Sports,
Science and Technology (MEXT), Japan for conducting
mass spectrometry measurements (Dr. Akio Miyazato at
JAIST).
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