Full Papers
indicate that the active catalyst for this system is probably
a molecular species.
Semihydrogenation of 1-phenyl-1-propyne with authentic parti-
cle-based precursors and molecular precursors: The appropriate
catalyst precursor (0.008 mmol, 0.4 mol% based on Pd content)
was added to a 2-necked Schlenk that was equipped with a hydro-
gen gas bag and a valve with a septum containing 10 mL of a pre-
viously prepared, degassed stock solution of MeCN with 0.83m 1-
phenyl-1-propyne and 8.3m p-xylene. If required, 0.002 mmol of
the appropriate poison was added as 0.5 mL of a stock solution of
the poison. Then the mixture was placed under a hydrogen atmos-
phere by ten cycles of evacuation and subjecting to hydrogen at-
mosphere. Periodic sampling was performed by taking 0.05 mL of
the mixture, filtering over a plug of silica with 1 mL of DCM which
was analyzed by GC. DLS-measurements were performed by taking
We found that TMTU is a superior poison ligand relative to
the standard poison ligand CS for the copolymerization and
2
the semihydrogenation reaction. We propose, because of its
versatility and coordination properties, to add TMTU to the
range of available poison ligands and use it in future poisoning
studies involving late transition metal (pre)catalysts.
Overall, this study has demonstrated the importance of de-
termining the type of active catalyst. None of the semihydro-
genation reactions appear to be as straightforward as they
were originally presented. Critical evaluation of such systems,
preferably in early stages of research, is essential. Protocols as
the one presented here may facilitate such critical evaluations
as a valuable tool for catalyst development, since it is straight-
forward, reliable and probably applicable to various other
types of catalytic reactions.
1
.5 mL of the solution, which was filtered over a 0.4 mm filter and
transferred to a custom made cuvette that was adapted with
a Schlenk connector that allowed inert handling.
A “hot” filtration test for the semihydrogenation of 1-phenyl-1-
propyne with supported catalyst materials: The normal catalytic
procedure was performed, only after 5 min a sample was taken
and the reaction mixture was filtered over a column of Celite. The
filtrate was transferred to another 2-necked Schlenk and exposed
to hydrogen and the solution was allowed to react further and pe-
riodic samples were taken to determine the activity of the liquid
phase.
Experimental Section
Complex synthesis and catalytic experiments were performed
using Schlenk techniques under dry nitrogen. Solvents were dried
according to standard procedures and distilled prior to use unless
[
110]
stated otherwise.
Maleic anhydride was crystalized from hot
Determination of the Pd leaching from the particle precatalyst
materials in the semihydrogenation of 1-phenyl-1-propyne:
Using ten times the standard amount of Pd on C and five times
the standard volume of stock solution the reaction was run for
twenty-one hours and filtered over Celite. The solution was con-
centrated on a rotatory evaporation device and dried under higher
3
DCM. [Pd(Cl(h -C H )] , triethyl amine, formic acid, potassium tert-
3
5 2
butoxide triphenylphosphine, Pd nano-powder, Pd on carbon
10 wt%), Pd on BaSO4 (10 wt%) and Lindlar’s catalyst (5 wt%)
(
were purchased from Sigma-Aldrich. The BASF Nano-Cat was pur-
chased from Strem chemicals. A Pd-DVTMS [1,3-divinyl-1,1,3,3-tet-
ramethyl-disiloxane palladium(0)] solution was generously provid-
À2
vacuum 310 mbar. The obtained oil was analyzed for Pd con-
[102]
[111]
ed by Umicore. Compounds 5
and 12
were synthesized ac-
tent using ICP-AES.
cording to literature procedures. NMR spectra were recorded by
using Bruker AV 400 MHz, Bruker DRX 300 MHz and Varian Mercury
Transfer semihydrogenation of 1-phenyl-1-propyne using the
proposed in situ generated [Pd IMes(MA)] catalyst: The proce-
0
3
00 MHz spectrometers. HR mass spectrometry was performed by
using a Bruker MicrOTOF-Q machine using ESI. GC analysis were
performed by using a Thermo Scientific Trace GC Ultra equipped
with a R-Rxi 5 ms column (30 m, ID 0.25 mm) and quantified using
the response factor corrected GC-areas in respect to the internal
standard. ICP-AES analyses were performed by using a Mikroanaly-
tisches Laboratorium Kolbe, Mülheim an der Ruhr, Germany. DLS
data were obtained by using an ALV/LSE 5003 light scattering elec-
tronics and multiple Tau digital correlator. Complex synthesis is de-
scribed in the Supporting Information, SI8.
dure was performed according to the procedure as described by
Hauwert et al., with minor adaptations in volumes and instead of
Schlenk glassware a Radleys’ twelve-place reaction station with in-
tegrated heating and cooling setup was used for these experi-
[49]
ments.
In a typical experiment mesityl imidazolium chloride
(12.5 mg, 0.037 mmol) was suspended in 20 mL MeCN and stirred
overnight. KOtBu (18 mg, 0.15 mmol) was added to generate the
free carbene and the mixture was stirred for one hour. [Pd(tBu-
DAB)(MA)] (6) (12.4 mg, 0.033 mmol) was added and the reaction
was stirred for another hour. Subsequently, determining the exact
amounts by post-weighing, 1-phenyl-1-propyne (0.38 g, 3.3 mmol),
p-xylene (0.35 g, 3.3 mmol), NEt3 (1.69 g, 16.7 mmol), and formic
acid (0.77 g, 16.7 mmol) were added in that order. After addition of
the formic acid the reaction was heated to 708C. At this tempera-
ture the appropriate amount of poison was added. Samples for
GC-analysis were taken at regular intervals by taking 0.05 mL of
the reaction mixture, and filtering it over a plug of silica with 1 mL
DCM. DLS samples were prepared by taking 1.5 mL of the reaction
mixture, filtering it over a 0.4 mm filter and transferring it to a spe-
cially designed cuvette that was adapted with a Schlenk connec-
tion. The TOFs for the quantitative poisoning analysis were deter-
mined around 15% conversion.
The copolymerization of CO and styrene: A three-necked, ther-
mostated 75 mL glass reactor equipped with a magnetic stirrer
and connected to a temperature controller was heated to 308C.
After establishment of the reaction temperature 20 mL 2,2,2-tri-
fluoroethanol (TFE), 10 mL of styrene, 0.0127 mmol of the selected
precatalyst and 0.0635 mmol of 1,4-benzoqinone were added, after
which the solution was bubbled through with CO for 10 min. Sub-
sequently, if required, the appropriate amount of poison was
added, followed by addition of the appropriate amount of poison,
if required. The solution was bubbled through with CO for 10 min
and afterwards a previously filled, 4 L balloon was connected to
the reactor. The system was stirred for 24 h, after which the reac-
tion mixture was poured onto methanol (100 mL) and stirred for
1
.5 h at room temperature. The obtained solid was filtered, washed
Transfer semihydrogenation of 1-phenyl-1-propyne using pre-
II
thoroughly with methanol and dried under vacuum until a constant
weight was obtained and analyzed by NMR spectroscopy.
formed or Pd (IMes) precatalysts with PPh additives: A stock so-
3
lution was prepared, adding in their respective order: acetonitrile
ChemCatChem 2015, 7, 2095 – 2107
2105
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Drost, Ruben M.
