Edge Article
Chemical Science
a xed set of reactants. It helps in reducing catalyst deteriora- on an Agilent 6890-N Gas Chromatograph with an Agilent 5973
tion and increases longevity and product yield.
mass selective detector calibrated with acetophenone.
The set of reactions, catalyst, and rotation sequence will
depend on the synthetic goals of a given laboratory or organi-
zation. Once again, the analogy with agriculture is very
enlightening. When 16 farmers in one region were asked to
provide their favorite crop rotation strategy, they provided 16
different answers, where some crop rotations make frequent
appearances (rye, alfalfa, garlic).14 Just as in chemistry, there is
no perfect rotation sequence, as external parameters must be
considered, including the usefulness of the crop or target
product, and in our case, consideration that one reaction may
play a key role in maintaining catalyst (“soil”) performance.
Therefore, different laboratories may create rotation sequences
that meet their needs, involving some reactions included
mainly for catalyst reactivation, such as the catalyst irradiation
in THF in the case above.
Catalyst synthesis
Palladium nanoparticles (ꢀ2 wt%) supported on TiO2
(Pd@TiO2), were prepared by photodeposition of PdNP onto
TiO2 (P25) and fully characterized as described in our previous
report.8
Sonogashira C–C coupling
Visible light-induced Sonogashira C–C coupling was performed
as described in our previous report.7 In brief, 15 mg of Pd@TiO2
were dispersed in 4 mL of HPLC grade methanol (MeOH) in
a 10 mL clean tube, then 15 mL of iodobenzene (1 eq., 0.13
mmol), 18 mL of phenylacetylene (1.3 eq., 0.16 mmol) and 35 mg
of K2CO3 (2 eq., 0.26 mmol), were added. The reaction mixture
was purged with Ar for 15 min then irradiated with 1 ꢂ 465 nm
LED set up at 1.6 W cmꢁ2 for 5 h (or 7 ꢂ 450 nm LEDs set up at
2.7 W cmꢁ2 for 30 min) under continuous stirring. The solid
catalyst was separated by centrifugation. Quantication was
done by GC-FID using t-butyl benzene as an external standard
(see ESI Table S7†).
Experimental section
Materials
Unless otherwise specied, all chemicals were purchased from
Sigma-Aldrich or Fisher Scientic and used without further
purication. Titanium dioxide (TiO2-P25) was purchased from
Univar Canada. All solvents were of HPLC grade.
Alkene isomerization/hydrogenation
Visible light-induced isomerization (or hydrogenation) of
estragole was performed with slight modications to our
previous report.7 In brief, 15 mg of Pd@TiO2 were dispersed in
4 mL of HPLC grade MeOH in a clean quartz cuvette, then 25 mL
(0.16 mmol) of estragole were added. The reaction mixture was
purged with Ar for 15 min and then irradiated with 7 ꢂ 450 nm
LEDs set up at 2.7 W cmꢁ2 for 5 h under continuous stirring (or
with 1 ꢂ 368 nm LED set up at 0.3 W cmꢁ2 for hydrogenation).
The progress of the reaction was monitored by GC-MS. The
quantication was done by GC-FID using t-butyl benzene as an
external standard (see ESI Table S8†).
Instrumentation
Transmission electron microscopy (TEM) images were collected
on a JEM-2100F FETEM (JEOL) operating at 200 kV. The Pd
content of the catalysts was determined by Inductively Coupled
Plasma Optical Emission Spectrometry (ICP-OES), using Agilent
5110 ICP-OES instrument. Approximately 10 mg portions were
accurately weighed in triplicate and digested with aqua regia.
Solutions were further diluted and measured by ICP-OES. The
Pd 340.458 nm emission line was used for quantication. The
XPS spectra were measured on a Kratos Nova AXIS spectrometer
equipped with an Al X-ray source. The XPS data were collected
using AlKa radiation at 1486.69 eV (150 W, 15 kV), charge
neutralizer and a delay-line detector (DLD) consisting of three
multi-channel plates. Binding energies are referred to the C 1s
peak at 284.8 eV. XPS data was analyzed using CasaXPS so-
ware, Version 2.3.15 and all ttings obtained using a Gaussian
30% Laurentian and a Shirley baseline. UV irradiation used for
catalyst synthesis was performed in a Luzchem photoreactor
equipped with UVA lamps (typically operated with 14 lamps,
corresponding to ꢀ0.029 W cmꢁ2 with ꢀ4% spectral contami-
nation. Light-emitting diodes (centered at 368 and 465 nm,
respectively) of 10 W from LedEngin and Luzchem LED illu-
minator (LEDi) equipped with a head of seven powerful blue
LEDs (centered at 450 nm) with adjustable intensity at focal
point were used as described for the photocatalytic reactions
Ullmann homo-coupling
Light-induced Ullmann homo-coupling of methyl 4-iodo-
benzoate was carried out based on our recent publication:6
20 mg Pd@TiO2 were dispersed in 4 mL of tetrahydrofuran
(THF) in a clean quartz tube, then 26 mg (0.1 mmol, 1 eq.) of
methyl-4 iodobenzoate and 65 mg (0.2 mmol, 2 eq.) of Cs2CO3
were added. The reaction mixture was purged with Ar for 10 min
prior to irradiation. Irradiation sources used: 1 ꢂ 465 nm LED
plus 1 ꢂ 368 nm LED set up at 1.6 and 0.3 W cmꢁ2, respectively;
or 1 ꢂ 368 nm LED set up at 0.3 W cmꢁ2. The progress of the
reaction and the quantication were done by GC-FID using t-
butyl benzene as an external standard (see ESI Table S9†).
Catalyst recyclability
studied. Quantication was carried out in a Perkin Elmer, The catalyst was recovered aer each cycle by centrifugation
Claurus Gas Chromatograph coupled to a Flame Ionization (3500 rpm for 15 min). Once the supernatant was decanted, the
Detector (FID) and a DB-5 column (30 m length, 0.320 mm catalyst was washed three times with ꢀ6 mL fresh methanol.
diameter, 0.25 mm lm) using Ar as a carrier gas and t-Butyl Each time the catalyst was dispersed via sonication and isolated
benzene as external standard. GC-MS analyses were performed through centrifugation. The recovered clean catalyst was
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Chem. Sci.