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FAREGHI‐ALAMDARI ET AL.
immobilized catalysts is frequently observed, since there are a
number of challenges and obstacles such as leaching of palla-
dium species from the supports, easy agglomeration of palla-
dium particles and low utilization efficiency of palladium.
Thus, it is desirable to develop more efficient and simple het-
erogeneous palladium porphyrin catalysts for Suzuki cou-
pling reactions.[20]
Various strategies should be considered to overcome the
general problems of Suzuki reaction catalysts (like difficult
separation, moisture and air sensitivity, non‐recyclability
and non‐environmentally friendly conditions). Regarding
reaction media, water is not only non‐toxic, inexpensive and
safe,[21] but most Suzuki products are insoluble in water,
and thus this can be a suitable factor for the easy separation
of products from reactants by simple extraction and, more
importantly, separation and recovery of catalyst can be easy.
During our work on carbon–carbon coupling reactions,[22]
the idea of using water as a green solvent encouraged us to
pyrrolic), 8.47 (d, 8H, aromatic), 8.32 (d, 8H, aromatic),
4.14 (s, 12H, OCH3), −2.77 (s, 2H, pyrrolic hydrogens).
FT‐IR (cm−1): 3310 (N─H), 2944 (C─H, sp3), 1722
(C═O), 1604 (C═N), 1275 (C─N). UV–visible (DMF, nm):
419 (Soret band), 519, 554, 598 and 653 (Q bands).
2.2.2
(organocatalyst)
| Synthesis of palladium–porphyrin complex
The [Pd‐TMCPP] organocatalyst was prepared by refluxing
[H2TMCPP] (0.30 g, 0.354 mmol) and PdCl2 (0.135 g,
0.763 mmol) in DMF (100 ml) for 12 h. The purification of
[Pd‐TMCPP] was performed by repeated recrystallization
and precipitation from DMF–H2O solutions. Yield 86.1%
1
(0.29 g). H NMR (400 MHz, DMSO‐d6, δ, ppm): 8.86 (s,
8H, β‐hydrogens pyrrolic), 8.47 (d, 8H, aromatic), 8.32 (d,
8H, aromatic), 4.11 (s, 12H, OCH3). FT‐IR (cm−1): 2944
(C─H, sp3), 1724 (C═O), 1607 (C═N), 1275 (C─N). UV–
visible (DMF, nm): 416 (Soret band), 527 and 562 (Q bands).
design
a
new air‐ and moisture‐stable palladium
organocatalyst, namely meso‐tetrakis[4‐(methoxycarbonyl)
phenyl]porphyrinatopalladium(II), [Pd‐TMCPP], that can be
applied as a heterogeneous and recyclable catalyst in aqueous
media for Suzuki cross‐coupling reaction.
2.3 | Spectroscopic and physical data
4‐Methoxy‐1,1′‐biphenyl (3a). M.p. 87–89 °C. FT‐IR (KBr,
ν, cm−1): 3060, 3055, 2959, 1605, 1485, 1249, 1036. H
1
NMR (400 MHz, CDCl3, δ, ppm): 3.85 (3H, s), 6.98 (2H, d,
J = 8.4 Hz), 7.30 (1H, t, J = 7.2 Hz), 7.42 (2H, t,
J = 7.6 Hz), 7.55 (4H, t, J = 7.6 Hz). Anal. Calcd for
C13H12O (%): C, 84.75; H, 6.57. Found (%): C, 83.56; H, 5.86.
2‐Methoxy‐1,1′‐biphenyl (3b). M.p. oil. FT‐IR (KBr, ν,
cm−1): 3059, 2932, 1597, 1481, 1259, 1028. 1H NMR
(400 MHz, CDCl3, δ, ppm): 3.78 (3H, s), 6.98 (1H, d,
J = 8.8 Hz), 7.02 (1H, t, J = 8.8 Hz), 7.28–7.33 (3H, m),
7.40 (2H, t, J = 7.2 Hz), 7.53 (2H, d, J = 5.2 Hz). Anal.
Calcd for C13H12O (%): C, 84.75; H, 6.57. Found (%): C,
82.95; H, 5.66.
2
| EXPERIMENTAL
2.1 | General methods
All solvents and chemicals were of reagent grade quality and
were purchased commercially and used without further puri-
fication. Fourier transform infrared (FT‐IR) spectra were
recorded with a Nicolet Magna 550 spectrometer. UV–visible
spectra were recorded using a GBC cintra‐6 UV–visible spec-
trophotometer. NMR spectra were recorded with a Bruker
DPX‐400 MHz spectrometer using CDCl3 and DMSO‐d6 as
solvents. Elemental analyses (C, H, N) were conducted using
a Carlo Erba EA 1108 analyser. Melting points were deter-
mined with a Stuart Scientific SMP2 apparatus and are
uncorrected. The amount of Pd leached in the catalytic reac-
tion was determined using a inductively coupled plasma
(ICP) analysis (Perkin‐Elmer instrument).
4‐Phenylphenol (3c). M.p. 156–159 °C. FT‐IR (KBr, ν,
cm−1): 3406, 3036, 1603, 1486. 1H NMR (400 MHz, CDCl3,
δ, ppm): 6.93 (2H, d, J = 8.4 Hz), 7.33 (1H, t, J = 7.2 Hz),
7.44 (2H, t, J = 7.6 Hz), 7.51 (2H, d, J = 8.4 Hz), 7.56 (2H,
t, J = 7.2 Hz), 8.28 (1H, d, J = 6.8 Hz). Anal. Calcd for
C12H10O (%): C, 84.68; H, 5.92. Found (%): C, 83.95; H, 5.66.
1,1′‐Biphenyl (3d). M.p. 68–69 °C. FT‐IR (KBr, ν,
1
cm−1): 3033, 1567, 1477. H NMR (400 MHz, CDCl3, δ,
ppm): 7.33–7.38 (2H, m), 7.45 (4H, t, J = 7.2 Hz), 7.61
(4H, d, J = 8 Hz). Anal. Calcd for C12H10 (%): C, 93.46; H,
6.54. Found (%): C, 92.75; H, 5.86.
2.2 | Palladium organocatalyst preparation
2.2.1
| Synthesis of organic ligand
Meso‐tetrakis[4‐(methoxycarbonyl)phenyl]porphyrin, [H2TM
CPP], was synthesized according to the following proce-
dure.[23] Freshly distilled pyrrole (1.4 ml, 20 mmol) was
added to a mixture of 4‐formylmethylbenzoate (3.42 g,
20 mmol) and nitrobenzene (15 ml). The mixture was
refluxed for 4 h in the presence of propionic acid (70 ml)
and then cooled to room temperature. The purple crystals of
the porphyrin were filtered, washed with distilled water and
4‐Nitro‐1,1′‐biphenyl (3e). M.p. 107–109 °C. FT‐IR
1
(KBr, ν, cm−1): 3098, 1597, 1513, 1476, 1344. H NMR
(400 MHz, CDCl3, δ, ppm): 7.46–7.53 (3H, m), 7.64 (2H,
d, J = 6.8 Hz), 7.75 (2H, d, J = 8.8 Hz), 8.31 (2H, d,
J = 6.8 Hz). Anal. Calcd for C12H9NO2 (%): C, 72.35; H,
4.55; N, 7.03. Found (%): C, 71.18; H, 4.66; N, 6.44.
2‐Hydroxy‐5‐phenylbenzaldehyde (3f). M.p. 96–99 °C.
FT‐IR (KBr, ν, cm−1): 3419, 3043, 2856, 1673, 1603, 1465.
1H NMR (400 MHz, CDCl3, δ, ppm): 6.94 (1H, d,
J = 8.8 Hz), 7.54 (2H, t, J = 7.6 Hz), 7.63 (2H, m), 7.70
1
dried in an oven at 80 °C. Yield 20.4% (0.9 g). H NMR
(400 MHz, DMSO‐d6, δ, ppm): 8.85 (s, 8H, β‐hydrogen