Inorganic Chemistry
Article
non-hydrogen atoms were refined anisotropically. The X-ray data for
compound 5 was collected on a Bruker Kappa CCD diffractometer
equipped with a graphite-monochromated Mo Kα radiation source at
200 K using the θ−2θ scan mode. An empirical absorption correction
by multiscans was applied, and all of the non-hydrogen atoms were
refined with anisotropic displacement factors. The hydrogen atoms
were placed in ideal positions and fixed with relative isotropic
displacement parameters. The solvent molecules that could not be
identified or modeled were found and eventually squeezed using
PLATON. The corresponding loop of the residual electron-voids
(from PLATON) was appended in the corresponding cif file. CCDC
No. 1914824 (for compound 5) contains the supplementary
crystallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
Computational Details. All the calculations were done using the
Gaussian 09 program package. The DFT38 method, with hybrid
functional B3LYP in conjunction with basis set 6-31G(d,p),39 was
used to optimize the structures of the compounds 6 and 8 in ground
(S0) states. With the same hybrid functional and basis set the vertical
excitation energies and oscillator strengths were obtained for the 50
lowest S0 → Sn transitions at the optimized S0-state equilibrium
geometries using TD-DFT method.40−45 All the computations in the
toluene media were performed using the self-consistent reaction field
(SCRF) under the polarizable continuum model (PCM).46,47 The
electronic absorption spectra, including oscillator strengths, were
systematically investigated using TD-DFT with PCM model on the
basis of the S0-optimized structures.
depending on the way it is connected with the rest of the
macrocycle, which affects macrocyclic aromatic character. In
meta-benziporphyrins, the meta-phenylene ring hinders the π-
delocalization of the macrocycle; hence, it is nonaromatic,
whereas in para-benziporphyrins, the p-phenylene ring is
involved in π-conjugation of the macrocycle to some extent,
and the extent of π-conjugation depends on the heteroatom
present in the macrocycle, making the p-benziporphyrins
aromatic in nature. We prepared the two missing core-
modified p-benziporphyrins, namely, selena p-benziporphyrin
and tellura p-benziporphyrin, by condensing benzitripyrrane
with appropriate diols, 2,5-bis(hydroxymethylphenyl) seleno-
phene/2,5-bis(hydroxymethylphenyl) tellorophene in a 1:1
ratio under mild acid-catalyzed conditions followed by
purification to afford pure selena p-benziporphyrin/tellura p-
benziporphyrin in decent yields. To find the effects of change
of modifying macrocyclic core by replacing the pyrrole ring
that is across the p-phenylene ring moiety with other
heterocycles such as thiophene, selenophene, and tellurophene
on structure, spectral and electrochemical properties were
investigated using various spectral and electrochemical
techniques and DFT studies. The crystallographic and DFT
studies clearly indicated that the distortion in the macrocycle
increases as we change the five-membered pyrrole ring with
other five-membered heterocycles, and maximum distortion in
the macrocycle was observed for tellura p-benziporphyrins.
NMR studies revealed that the diatropic ring current decreases
as the distortion in the macrocycle increases. Absorption,
electrochemical, and DFT studies support these observations.
Thus, while p-benziporphyrins exhibit diatropic ring currents,
the diatropic ring current decreases as the size of the core
atoms increases. Furthermore, the tellura p-benziporphyrin
readily forms a stable Pd(II) complex with distorted square-
planar geometry. Further studies on the coordination behavior
of core-modified p-benziporphyrins with various metal salts are
currently under investigation in our laboratory.
General Procedure for Synthesis of p-Benziporphyrins (4−6).
The benzitripyrrane48 8 and the thiophene, selenophene, and
tellurophene diols29−33 10/11/12 were synthesized by the reported
methods. Samples of 1,3-benzene-bis((4-phenyl)methanol 8 (0.50
mmol) and appropriate diol 10/11/12 were dissolved in 200 mL of
dichloromethane, and nitrogen was bubbled through the solution for
15 min. After 15 min, TFA was added to the same solution and
allowed to stir for 1 h under inert atmosphere. DDQ (2.5 mmol) was
added to the solution and stirred in open air for 30 min. The solvent
was removed on a rotary evaporator under vacuum. The crude
compound was purified by basic alumina column chromatography
using petroleum ether/dichloromethane (80/20) as eluent affording
the dark green solid in 4−6% yield.
Synthesis of Compound 5. Compound 5 was synthesized from 8
(194 mg, 0.50 mmol) and 11 (185 mg, 0.50 mmol) by following the
general procedure reported above for compounds 4−6. Yield 6% (20
EXPERIMENTAL SECTION
■
General Experimental. The chemicals such as BF3·OEt2 and
DDQ were used as obtained from Aldrich. All other chemicals used
for the syntheses were reagent grade unless otherwise specified.
Column chromatography was performed on silica gel and basic
alumina. Compounds 2,9 4,22 and 7−12 were synthesized by the
1
mg); H NMR (400 MHz, CDCl3) δ 8.23 (s, 2H), 8.08−7.97 (m,
6H), 7.72−7.57 (m, 10H), 7.52 (d, J = 4.6 Hz, 2H), 7.39 (d, J = 7.8
Hz, 4H), 5.85 (s, 4H), 2.54 (s, 6H). 13C NMR (101 MHz, CDCl3) δ
167.0, 156.2, 152.1, 149.1, 146.9, 140.0, 137.9, 137.5, 137.3, 135.5,
135.5, 133.0, 132.2, 131.2, 130.7, 129.3, 128.7, 128.4, 21.6. HRMS
(electrospray ionization (ESI)): calcd for C48H35N2Se[M + H]+ m/z
719.1965; found m/z 719.1992.
1
reported methods. The H and 13C NMR spectra were recorded in
CDCl3 on Bruker 400 and 500 MHz instruments. The frequencies for
13C nucleus are 100.06 and 125.77 MHz for 400 and 500 MHz
instruments, respectively. Tetramethylsilane [Si(CH3)4] was used as
Synthesis of Compound 6. Compound 6 was synthesized from 8
(194 mg, 0.50 mmol) and 12 (196 mg, 0.50 mmol) by following the
general procedure reported above for compounds 4−6. Yield 4% (15
1
an internal standard for H and 13C NMR. Absorption spectra were
obtained with Shimadzu UV−vis−NIR (NIR = near-infrared)
spectrophotometer. CV studies were performed with BAS electro-
chemical system utilizing the three-electrode configuration consisting
of a glassy carbon (working electrode), platinum wire (auxiliary
electrode), and saturated calomel (reference electrode) electrodes.
The experiments were done in dry dichloromethane using 0.1 M
tetrabutylammonium perchlorate as supporting electrolyte. The HR
mass spectra were recorded with a quadrupole time-of-flight (Q-
TOF) micro mass spectrometer.
1
mg); H NMR (400 MHz, CDCl3) δ 8.05 (s, 2H), 7.88 (dd, J = 7.8,
1.5 Hz, 4H), 7.83 (d, J = 4.7 Hz, 2H), 7.62−7.55 (m, 10H), 7.52 (t, J
= 7.4 Hz, 4H), 7.46 (t, J = 7.3 Hz, 2H), 7.24 (d, J = 4.7 Hz, 2H), 6.51
(s, 4H). 13C NMR (101 MHz, CDCl3) δ 169.6, 167.9, 154.8, s149.1,
146.0, 142.5, 139.8, 135.5, 134.6, 132.6, 132.1, 131.4, 131.0, 130.4,
129.5, 128.9, 128.7, 128.4, 128.1, 127.3, 117.4, 114.2. HRMS (ESI):
calcd for C46H31N2Te[M + H]+ m/z 741.1549; found m/z 741.1541.
Synthesis of Compound 6-Pd(II). Tellura p-benziporphyrin 6 (10
mg, 0.013 mmol) and palladium(II) chloride (9.8 mg, 0.055 mmol) in
acetonitrile/chloroform (10:10 mL) were stirred at room temperature
for 2 h. The solution was washed with water and back extracted with
dichloromethane; the organic layers were combined, and the solvent
was evaporated under reduced pressure. The compound was
recrystallized with CH2Cl2−pet ether to give the 6-Pd(II) (9 mg,
72%) as a dark green solid. 1H NMR (400 MHz, CDCl3) δ 8.19 (d, J
= 7.1 Hz, 1H), 8.10−8.02 (m, 2H), 7.79−7.81 (m, 4H), 7.74−7.51
X-ray Crystal Structure Analysis. Single-crystal X-ray structure
analysis was performed on a Rigaku Saturn 724 diffractometer that
was equipped with a low-temperature attachment. Data were collected
at 293 K using graphite-monochromated Mo Kα radiation (λα
=
0.710 73 Å) by ω-scan technique. The data were reduced by using
Crystal Clear-SM Ex-pert 2.1 b24 software. The structures were
solved by direct methods and refined by least-squares against F
utilizing the software packages SHELXL-97, SIR-92, and WINGX. All
L
Inorg. Chem. XXXX, XXX, XXX−XXX